JPH06163362A - Projection exposure device - Google Patents

Abstract

PURPOSE:To enlarge focus depth without damaging transfer fidelity even to a plurality of isolated patterns in relative proximity by setting a coherence factor of illumination light to a reticle at a specified value more. CONSTITUTION:A coherent reduction member for reducing coherence between an imaging light LFa which is distributed inside a circular region FA arranged in a Fourier transform surface FTP inside an imaging optical path between a reticle R and a wafer or in proximity thereto and an optical axis of a projection lens PL on the Fourier transform surface or on a surface proximity thereto is its center, and an imaging light LFb which is distributed in a region FB in an outside thereof is provided. Furthermore, an illumination optical system whose coherence factor of illumination light to the reticle R (ratio between the number of illumination flux numerical aperture and the numerical aperture on the reticle R side of the projection lens PL) is 0.5 or more is used. Thereby, it is possible to increase focus depth during projection exposure of an isolated pattern such as a contact hole.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection type exposure apparatus used for forming fine patterns in semiconductor integrated circuits, liquid crystal displays and the like.

[0002]

2. Description of the Related Art A projection optical system used in a projection type exposure apparatus of this type is incorporated in the apparatus by ultra-precision processing of glass materials and precise assembly and adjustment. Currently, in the semiconductor manufacturing process, a reticle (mask) is irradiated with i-line (wavelength 365 nm) of a mercury lamp as illumination light, and transmitted light of a circuit pattern on the reticle is projected onto a photosensitive substrate (wafer, etc.) through a projection optical system. Mainly used is a stepper that forms an image. An excimer stepper using an excimer laser (KrF laser having a wavelength of 248 nm) as illumination light is also used for evaluation or research. When the projection optical system for the excimer stepper is composed of only a refracting lens, usable glass materials are limited to quartz and fluorite.

Generally, in order to faithfully transfer a fine reticle pattern onto a photosensitive substrate by exposure using a projection optical system, the resolution and depth of focus (DOF: depth of focus) of the projection optical system are important factors. Has become.
Among the projection optical systems currently in practical use, those for the i-line having a numerical aperture (NA) of about 0.6 have been obtained. When the wavelengths of the illumination light used are the same, increasing the numerical aperture of the projection optical system improves the resolution accordingly. However, the depth of focus (DOF) decreases with increasing numerical aperture NA. The depth of focus is defined by DOF = ± λ / NA ² where λ is the wavelength of the illumination light.

FIG. 1 schematically shows an image forming optical path of a conventional projection optical system. The projection optical system is a lens system G of the front group.
A lens system GB of the rear group. This type of projection optical system is generally one in which both the reticle R side and the wafer W side are telecentric, or one in which only the wafer W side is telecentric. Now, in FIG. 1, three arbitrary points A, B, and C are assumed on the pattern surface of the reticle R (the object surface of the projection optical system). Rays L ₁ , L ₂ , L ₃ , La, L traveling from point A in various directions
a ', of the La ", light L ₁ occurs at an angle that can not enter the lens system GA of the projection optical system. Moreover, of the light incident on the lens system GA of the front group, ray L _2, L ₃
Is a pupil e located on the Fourier transform plane FTP in the projection optical system.
cannot pass p. And the other rays La, L
a ′ and La ″ pass through the pupil ep, enter the lens system GB of the rear group, and converge at the point A ′ on the surface of the wafer W (pupil surface of the projection optical system). Among the light rays generated from A, the light rays that have passed through the pupil ep of the projection optical system (a circular area centered on the optical axis AX) contribute to forming a point image at the point A ′. A ray La that passes through the center point CC (position of the optical axis AX) of the pupil ep among the rays directed to the point A ′ is called a principal ray, and this principal ray La is, in the case of a telecentric projection optical system on both sides, the object plane side, It is parallel to the optical axis AX in each space on the image plane side.

The same applies to the light rays generated from the other points B and C on the reticle R, and only the light rays passing through the pupil ep contribute to the formation of the point images B'and C '. Similarly, the light rays Lb and Lc that travel from the points B and C in parallel with the optical axis AX and enter the lens system GA are both chief rays passing through the center point CC of the pupil ep. In this way, the pupil ep has a Fourier transform and an inverse Fourier transform with respect to the pattern surface of the reticle R and the surface of the wafer W, and the light rays that contribute to image formation among the light rays from the pattern on the reticle are All the pupils ep will overlap and pass.

The numerical aperture of such a projection optical system is generally expressed as a value on the wafer side. In FIG. 1, among the rays that contribute to the formation of the point image A ′, the angles θw formed by the rays La ′ and La ″ passing through the outermost part in the pupil ep with the principal ray La on the wafer W are the projection optical system. Corresponding to the numerical aperture NA _W on the wafer (image plane) side, and is represented by NAw = sin θw Therefore, the angle θr formed by the light rays La ′ and La ″ with the principal ray La on the reticle R side is ) Side numerical aperture NAr, which is represented by NAr = sin θr. Further, when the image forming magnification of the projection optical system is 1 / M (M = 5 in the case of 1/5 reduction), there is a relationship of M · NAr = NAw.

In order to increase the resolution, the numerical aperture NAw (NAr) must be increased. In other words, this means increasing the diameter of the pupil ep and further increasing the effective diameters of the lens systems GA and GB. It is nothing but making it bigger.
However, since the depth of focus DOF decreases in inverse proportion to the square of the numerical aperture NAw, even if a projection optical system with a high numerical aperture can be manufactured, the required depth of focus cannot be obtained. , Becomes a big obstacle in practical use.

When the wavelength of the illumination light is 365 nm of the i-line and the numerical aperture NAw is 0.6, the depth of focus DOF becomes about 1 μm (± 0.5 μm) in width, and one shot on the wafer W is obtained. In a region (20 mm square to 30 mm square), unevenness or curvature of the surface causes DOF or more in a portion having a DOF or more. Also on the stepper system, focusing for each shot area of the wafer W,
Since it becomes necessary to perform leveling and the like with extremely high accuracy, the load on the mechanical system, the electrical system, and the software (measurement resolution, servo control accuracy, setting time, etc.) will increase.

Therefore, the applicant of the present invention has solved such problems of the projection optical system, and has a high resolution and a large focus without using a phase shift reticle disclosed in Japanese Patent Publication No. 62-50811. A new projection exposure technique capable of obtaining both depth and depth is disclosed in JP-A-4-101.
It was proposed in Japanese Patent Laid-Open No. 148, Japanese Patent Laid-Open No. 4-225358 and the like. This exposure technique increases the apparent resolving power and the depth of focus by controlling the reticle illumination method to a special shape while maintaining the existing projection optical system.
HRINC (S uper H igh R esoluti
on by I llumi N ation C ontro
l) We call it the law. The SHRINC method irradiates the reticle with two illumination lights (or four illumination lights) symmetrically inclined in the pitch direction of the line and space pattern (L & S pattern) on the reticle R, and is generated from the L & S pattern. The 0th-order diffracted light component and one of the ± 1st-order diffracted light components are passed symmetrically with respect to the center point CC in the pupil ep of the projection optical system, and two-beam interference (interference between one 1st-order diffracted light and the 0th-order diffracted light) occurs. The principle is utilized to generate a projected image (interference fringe) of an L & S pattern.

According to the image formation utilizing the two-beam interference as described above, the occurrence of the wavefront aberration at the time of defocusing can be suppressed more than in the case of the conventional method (normal vertical illumination), so that the depth of focus apparently becomes large. Of. However, in the SHRINC method, the desired effect can be obtained when the pattern formed on the reticle R has a periodic structure like an L & S pattern (lattice). Can't get the effect.
In general, in the case of an isolated minute pattern, the diffracted light from there occurs as almost uniform Franforfer diffraction with respect to the diffraction angle, and is clearly divided into 0th-order diffracted light and high-order diffracted light in the pupil ep of the projection optical system. It is distributed almost uniformly without being separated.

Therefore, as an exposure method for increasing the apparent depth of focus for an isolated pattern such as a contact hole, the exposure for one shot area of the wafer W is divided into a plurality of times, and the wafer W is subjected to the optical axis between the exposures. A method of moving a certain amount in a certain direction has been proposed, for example, in Japanese Patent Laid-Open No. 63-42122. This exposure method is FLEX ( F ocu
s L attitude enhancement EX
This is called the "posure) method, and a sufficient depth of focus expansion effect can be obtained for isolated patterns such as contact holes. However, since the FLEX method requires multiple exposure of a slightly defocused contact hole image, the sharpness of the resist image obtained after development is inevitably reduced. The problem of deterioration of sharpness (profile deterioration) is to use a resist with a high gamma value,
Multi-layer resist is used, or CEL (Contr
It can be compensated by using ast Enhancement Layer).

As an attempt to increase the depth of focus when projecting a contact hole pattern without moving the wafer W in the optical axis direction during the exposure operation as in the FLEX method, 1
991 Spring Applied Physics Society Proceedings 29a-ZC-8,
The Super-FLEX method announced in 9 is also known. This Super FLEX method uses the pupil e of the projection optical system.
A transparent phase plate is provided on p, and the phase plate has such a characteristic that the complex amplitude transmittance given to the image-forming light sequentially changes from the optical axis AX toward the periphery. By doing so, the image formed by the projection optical system maintains sharpness with a constant width (wider than before) around the best focus surface (the surface conjugate with the reticle R) in the optical axis direction. , The depth of focus increases.

[0013]

Among the various conventional techniques described above, the FLEX method and the Super FLEX method can obtain a sufficient depth of focus increasing effect for an isolated contact hole pattern. However, it has been found that in the case of a plurality of contact hole patterns that are close to each other to some extent, both methods cause an unnecessary film slip in the photoresist between the holes, which makes it practically difficult to use.

Further, in the FLEX method, even for an isolated contact hole pattern, the sharpness of the image (synthesized optical image obtained by multiple exposure) is inevitably deteriorated. There is also the problem that the degree decreases. Further, it is difficult to apply the scanning exposure type exposure apparatus by the FLEX method of the type in which the wafer is continuously moved or vibrated in the optical axis direction during the exposure work, and the exposure is divided into the first exposure and the second exposure. In the system in which the wafer is moved in the optical axis direction by a certain amount during the non-exposure period between each exposure operation, there is a problem that the throughput is significantly reduced and the throughput is significantly reduced.

Therefore, the present invention has an object to obtain a projection exposure apparatus having an increased depth of focus when projecting and exposing isolated patterns such as contact holes, and particularly for a plurality of isolated patterns which are relatively close to each other. An object of the present invention is to provide a device that can obtain a depth of focus expansion effect without deteriorating transfer fidelity.

[0016]

In order to solve the above problems, in the present invention, an illuminating means (1 to 1) for irradiating a mask (reticle R) on which a fine pattern is formed with illuminating light for exposure.
4) and a projection optical system (PL) for injecting light generated from the pattern of the mask and projecting an image of the pattern onto the sensitive substrate (wafer W) by imaging, the mask and the sensitive substrate. A circular area (FA) which is arranged on the Fourier transform plane (FTP) in the image forming optical path between or and the plane near the Fourier transform plane or on the plane near the Fourier transform plane and whose center is the optical axis of the projection optical system. A coherence reducing member (CCM) for reducing coherence between the image forming light (LFa) distributed inside and the image forming light (LFb) distributed in the area (FB) outside thereof is provided, and the mask is further provided. An illumination optical system in which the coherence factor (σ value: the ratio of the numerical aperture of the illumination light beam to the numerical aperture on the mask side of the projection optical system) of the illumination light is set to about 0.5 or more is used.

Further, a projection optical system provided with a coherence reducing member (CCM) is used, and a ring-shaped light source image is formed on the light source image plane conjugate with the Fourier transform plane of the projection optical system generated in the illumination means. Forming means (82) is provided, or, like the SHRINC method, means (83, 84) for forming a plurality of light source images separated from each other on the light source image plane is provided.

[0018]

In the present invention, a coherence reducing member is provided on a surface (hereinafter referred to as a pupil surface) in the projection optical system which has an optical Fourier transform relationship with the reticle pattern surface, or a surface in the vicinity thereof. A part of the image-forming light distributed in a circular or annular shape on the pupil plane and an image-forming light distributed in the other part are set not to interfere with each other. As a result, the exposure light beam (imaging light) that has been transmitted and diffracted in the reticle pattern, particularly through the contact hole pattern, is spatially divided into two light beams that do not interfere with each other in the pupil plane and reach the exposure target such as a wafer. To do. Even on the wafer, the two light beams do not interfere with each other (are incoherent), so that an intensity combined image of the images (contact hole images) produced by the respective light beams can be obtained. In the conventional exposure method, when the light beams that have passed through the minute contact hole pattern on the reticle and are diffracted reach the wafer surface through the projection optical system, they are all combined amplitude-wise (coherent addition) and the reticle pattern image (optical image ) Was formed. Conventional Super-FLE
Also in the X method, since the imaging light distributed on the pupil plane is only partially phase-shifted, it is still coherent addition.

Assuming that the pupil plane of the projection optical system has no phase shift plate or the like, in best focus (focused state), the optical path length from any one point on the reticle to the corresponding image point on the wafer. Are the same regardless of which optical path in the projection optical system passes (Fermat's principle), so amplitude synthesis on the wafer results in light synthesis without phase difference,
All act in the direction of increasing the strength of the contact hole pattern.

However, when the wafer is defocused, the above optical path length becomes different depending on the optical line in the projection optical system. As a result, the above-mentioned amplitude composition is the optical path difference (phase difference).
The addition of the light having the above value causes a canceling effect in a part, and weakens the central strength of the contact hole pattern.
If the incident angle of an arbitrary ray incident on one image point on the wafer is θ and the optical path length of the ray (chief ray) incident vertically on the wafer is a reference (= 0), the optical path difference generated at this time is It is expressed as approximately 1/2 (ΔF · sin ² θ). Here, ΔF represents the defocus amount. Since the maximum value of sin θ is the numerical aperture NAw on the wafer side of the projection optical system, when all the light that has passed through the pupil ep among the diffracted light from the minute hole pattern is amplitude-combined on the wafer as in the conventional case, the maximum value is obtained. Will result in an optical path difference of 1/2 (ΔF · NAw ² ). At this time, assuming that an optical path difference of λ / 4 is allowed as the depth of focus, the following relationship holds.

1/2 (ΔF · NAw ² ) = λ / 4 When this equation is put together again, ΔF = λ / (2NAw ² ), which is in agreement with the generally-known depth of focus. For example, i-line (wavelength 0.3
65 μm), numerical aperture NAw = 0.50
Assuming that, the depth of focus ± ΔF / 2 is ± 0.73 μm, which is a value with almost no margin for a process step difference of 1 μm on the wafer.

On the other hand, in the present invention, as shown in FIG. 2, a coherence reducing member CCM is provided on the pupil plane (FTP) of the projection optical system. At this time, an imaging light beam (the principal ray is LLp) diffracted by the isolated pattern Pr formed on the pattern surface of the reticle R
Enters the front lens group GA of the projection optical system PL and then reaches the Fourier transform plane FTP. And the Fourier transform plane F
In TP, the circular transparent portion F at the center in the pupil plane ep
The light fluxes transmitted through A and the annular transmission portion FB are controlled (converted) to a state where they do not interfere with each other. Therefore, on the wafer W, the light flux LFa transmitted through the circular transmissive portion FA of the coherence reducing member CCM and the light flux LFb transmitted through the peripheral transmissive portion FB do not interfere with each other. As a result, the luminous flux LFa from the circular transmitting portion FA and the luminous flux LF from the peripheral portion FB are formed.
b independently interfere with each other by themselves to form an image (intensity distribution) Pr ′ of a hole pattern. That is, an image obtained by the interference of only the light beam LFa and an image produced by the interference of only the light beam LFb is simply added in terms of intensity, and an isolated contact hole or the like obtained by the present invention is obtained. It becomes a pattern image Pr '.

The illumination light ILB for the reticle R may have a constant numerical aperture sin ψ / 2 as in the conventional case. However, the numerical aperture NAr on the reticle side of the projection optical system PL is set to the condition NAr> sin ψ / 2. Therefore, the principle of image formation in the present invention will be described with reference to FIG. FIG. 3 shows a structure of the coherence reducing member CCM and a state of an image-forming light flux that forms an image Pr ′ of the contact hole,
3 schematically shows each relationship with the optical path difference ΔZ of each light flux at the time of defocusing.

A light beam LFa passing through the central portion as shown in FIG.
In amplitude combination within, since the light flux LFa includes the angle range from the vertically incident light (the principal ray LLp) to the incident angle θ ₁ ,
The maximum value ΔZ ₁ of the optical path difference when the defocus amount is ΔF is ΔZ ₁ = 1/2 (ΔF · sin ² θ ₁ ). The horizontal axis of the graph at the bottom of FIG. 3 represents the sine of the incident angle.
Let nθ ₁ = NA ₁ . On the other hand, in amplitude combination in the light flux LFb passing through the peripheral portion as shown in FIG. 3B, since the light flux LFb has an incident angle range from the incident angle θ ₁ to the numerical aperture NAw (sin θw), the defocus amount is ΔF. The maximum optical path length difference ΔZ _{2 at that time} is ΔZ ₂ = 1/2 (ΔF) (NAw ² −sin ² θ ₁ ).

Since the first light beam LFa and the second light beam LFb do not interfere with each other, the deterioration of the image Pr ' ₁ due to the interference of only the light beam LFa and the deterioration of the image Pr' ₂ due to the interference of only the light beam LFb occur. This is caused only by the optical path length differences ΔZ ₁ and ΔZ ₂ in the light flux. For example, when sin θ ₁ is set so that sin ² θ ₁ = 1/2 (NAw ² ), that is, when the radius of the first transmission part FA is set so as to substantially satisfy the relationship of ² sin ² θ ₁ = NAw ^2. , The maximum optical path difference ΔZ due to the first light flux LFa
₁ and the maximum optical path difference ΔZ ₂ due to the second light flux LFb are as follows.

ΔZ ₁ = 1/2 (ΔF · sin ² θ ₁ ) =
1/4 (ΔF · NAw ² ) ΔZ ₂ = 1/2 (ΔF) (NAw ² −sin ² θ ₁ ) = 1/4
(ΔF · NAw ² ) Thus, the two incoherent light beams LFa and L
Each of the Fbs has substantially the same maximum optical path difference, 1/4 (ΔF · NAw ² ), when defocused by ΔF, and this value is half that in the conventional case. In other words, even if the defocus amount (2ΔF) is twice as large as the conventional one, the same maximum optical path length difference as in the case of the defocus amount ΔF in the conventional projection method will suffice, resulting in the isolated pattern Pr.
The depth of focus at the time of imaging is increased about twice. The pupil plane ep of the projection optical system PL, a method of exchanging a plurality of light beams do not interfere with imaging light beam from each other, thereafter SFINCS (S patial F ilter for
It will be referred to as INC oherent S tream) method.

As described above, the depth of focus of the image of the contact hole pattern is increased by the SFINCS method, which is due to the coherence reducing member arranged on the pupil plane in the projection optical system. However, the function of the coherence reducing member is only to reduce coherence inside one light beam which is transmitted through one minute transmission region (contact hole pattern) on the reticle and diffracted, and for example, on the reticle. There is no action of reducing the coherence between the light beams that have respectively passed through the two adjacent contact holes. Therefore, as is conventionally known, when the coherence of the illumination light on the reticle (spatial coherence) is high, that is, when the incident angle range of the illumination light flux is narrow, the images are connected (proximity effect) between adjacent patterns. Will occur.

In an actual reticle pattern, a plurality of contact hole patterns are often arranged close to each other. Therefore, simply using the SFINCS method,
Sufficient resolution (separation ability) cannot be exhibited for such close hole patterns. Therefore, in the present invention, by setting the σ value (ratio of the numerical aperture of the illumination light beam (corresponding to the incident angle range) and the numerical aperture on the reticle side of the projection optical system) to a relatively large value, for example, 0.5 or more, The spatial coherency of the illumination light on the reticle is reduced so that the proximity effect does not occur easily. That is, the illumination light that passes through one contact hole pattern and the illumination light that passes through the contact hole pattern adjacent thereto can be made in a state where they do not interfere with each other. Alternatively, the illumination optical system may be a ring-shaped illumination system or a so-called modified light source (the above-mentioned SHRINC method) so that coherences (coherence) of transmitted light of adjacent contact holes have opposite signs. It is also possible to cause amplitude cancellation of the images and darken the middle of both contact hole patterns to further enhance the separation ability.

[0029]

FIG. 4 shows the overall construction of a projection exposure apparatus according to an embodiment of the present invention. In FIG. 4, the high-intensity light emitted from the mercury lamp 1 is converged on the second focal point by the elliptical mirror 2 and then becomes divergent light and enters the collimator lens 4. A rotary shutter 3 is arranged at the position of the second focal point, and controls passage and blocking of illumination light. The illumination light converted into a substantially parallel light flux by the collimator lens 4 is
It is incident on the interference filter 5, where only the desired spectrum required for exposure, eg, the i-line, is extracted. The illumination light (i-line) emitted from the interference filter 5 passes through the polarization control member 6 for aligning the polarization direction, and then enters the fly-eye lens 7 as an optical integrator.
The polarization control member 6 may be omitted depending on the configuration of the coherence reducing member CCM in the projection optical system PL and the nature of the light source, which will be described later.

The illumination light (substantially parallel luminous flux) incident on the fly-eye lens 7 is divided by a plurality of lens elements of the fly-eye lens 7, and a secondary light source image (mercury) is provided on each exit side of each lens element. An image of the light emitting point of the lamp 1) is formed. Therefore, the same number of point light source images as the number of lens elements are distributed on the exit side of the fly-eye lens 7 to form a surface light source image. A variable diaphragm 8 for adjusting the size of the surface light source image is provided on the exit side of the fly-eye lens 7. Illumination light (divergent light) that has passed through the diaphragm 8 is reflected by a mirror 9 and enters a condenser lens system 10, and then illuminates the rectangular opening of the reticle blind 11 with a uniform illuminance distribution. In FIG. 4, of the plurality of secondary light source images (point light sources) formed on the exit side of the fly-eye lens 7, the optical axis A
Only illumination light from one secondary light source image located on X is representatively shown. Moreover, by the condenser lens system 10,
The exit side of the fly-eye lens 7 (the surface on which the secondary light source image is formed) is a Fourier transform surface for the rectangular aperture surface of the reticle blind 11. Therefore, fly eye lens 7
From each of the plurality of secondary light source images of the condenser lens system 1
The respective illumination lights that have entered 0 are superimposed on the reticle blind 11 as parallel light beams having slightly different incident angles.

The illumination light passing through the rectangular opening of the reticle blind 11 enters the condenser lens 14 via the lens system 12 and the mirror 13, and the light emitted from the condenser lens 14 reaches the reticle R as the illumination light ILB. Here, the rectangular opening surface of the reticle blind 11 and the pattern surface of the reticle R are arranged conjugate with each other by a composite system of the lens system 12 and the condenser lens 14,
The image of the rectangular opening of the reticle blind 11 is the reticle R
The image is formed so as to include a rectangular pattern formation region formed in the pattern surface of the. As shown in FIG. 4, the illumination light ILB from one secondary light source image located on the optical axis AX of the secondary light source image of the fly-eye lens 7 has an inclination with respect to the optical axis AX on the reticle R. There is no parallel light flux, but
This is because the reticle side of the projection optical system PL is telecentric. Of course, on the exit side of the fly-eye lens 7, a large number of secondary light source images (off-axis point light sources) that are displaced from the optical axis AX are formed, but the illumination light from them is all on the reticle R. Then, it becomes a parallel light beam inclined with respect to the optical axis AX and is superimposed in the pattern formation region. still,
The pattern surface of the reticle R and the exit side surface (light source image surface) of the fly-eye lens 7 are the condenser lens system 10 and the lens system 1.
Of course, it goes without saying that the composite system of the condenser lens 14 has an optical relationship of Fourier transform. Also, the incident angle range ψ of the illumination light ILB on the reticle R is
(See FIG. 2) changes depending on the aperture diameter of the diaphragm 8.
The incident angle range ψ also becomes smaller when the aperture area is made smaller and the area of the surface light source is made smaller. Therefore, diaphragm 8
Will adjust the spatial coherency of the illuminating light. As a factor representing the degree of spatial coherency, the ratio (σ value) of the sine of the maximum incident angle ψ / 2 of the illumination light ILB and the numerical aperture NAr of the projection optical system PL on the reticle side.
Is used. This σ value is usually σ = sin (ψ /
2) / NAr, and most of the steppers currently in operation are used in the range of σ = 0.5 to 0.7.
In the present embodiment, σ ≧ 0.7 is set in view of the characteristics of the resist currently used normally and the practical viewpoint.

A predetermined reticle pattern is formed on the pattern surface of the reticle R by a chrome layer. Here, the chrome layer is vapor-deposited on the entire surface, and a minute rectangular opening (transparent without a chrome layer is formed therein). It is assumed that there are a plurality of contact hole patterns formed in part).
The contact hole pattern may be designed to have a size of 0.5 μm square (or diameter) or less when projected onto the wafer W, and the projection magnification of the projection optical system PL may be 1
The size on the reticle R is determined in consideration of / M. Further, since the dimension between adjacent contact hole patterns is usually considerably larger than the dimension of the opening of one contact hole pattern, it exists as an isolated minute pattern. That is, the two adjacent contact hole patterns are often separated to the extent that the light (diffracted and scattered light) generated from each of them does not strongly influence each other like a diffraction grating. However, as will be described later in detail, there is also a reticle in which contact hole patterns are formed in close proximity to each other.

In FIG. 4, the reticle R is held on the reticle stage RST, and the optical image (light intensity distribution) of the contact hole pattern of the reticle R is imaged on the photoresist layer on the surface of the wafer W via the projection optical system PL. To be done.
Here, the optical path from the reticle R to the wafer W in FIG. 4 is shown only by the chief ray of the imaging light flux. And the projection optical system P
The Fourier transform plane FTP in L is provided with the coherence reducing member CCM described in FIGS. 2 and 3 above. The coherence reducing member CCM has a diameter that covers the maximum diameter of the pupil ep, and can be moved out of the optical path or into the optical path by the slider mechanism 20. If the stepper is used exclusively for exposing the contact hole pattern, the coherence reducing member CCM may be fixed in the projection optical system PL. However, when performing exposure work in a lithography process by a plurality of steppers, in consideration of the most efficient operation of each stepper, it is hesitant to assign one specific stepper to the exposure dedicated to the contact hole pattern. Therefore, the coherence reducing member CCM is the projection optical system PL.
It is desirable that the stepper be provided so that it can be inserted into and removed from the pupil ep so that the stepper can be used even when exposing a reticle pattern other than the contact hole pattern. Depending on the projection optical system, its pupil position (Fourier transform plane FT
A circular aperture stop for changing the effective pupil diameter may be provided in P). In this case, the aperture stop and the coherence reducing member CCM are arranged as close as possible without mechanical interference.

The wafer W moves two-dimensionally (hereinafter referred to as XY movement) in a plane perpendicular to the optical axis AX, and
The wafer is held on a wafer stage WST that is slightly moved (hereinafter, referred to as Z movement) in a direction parallel to the optical axis AX. The XY movement and the Z movement of the wafer stage WST are performed by the stage drive unit 22, the XY movement is controlled according to the coordinate measurement value by the laser interferometer 23, and the Z movement is set to the detection value of the focus sensor 24 for autofocus. It is controlled based on. Stage drive unit 2
2. The slider mechanism 20 and the like operate according to a command from the main control unit 25. This main control unit 25 further sends a command to the shutter drive unit 26, and the shutter 3
In addition to controlling the opening and closing of the aperture, a command is sent to the aperture control unit 27 to control the size of each aperture of the diaphragm 8 or the reticle blind 11. Further, the main control unit 25 can input the reticle name read by a bar code reader 28 provided in the reticle transport path to the reticle stage RST. Therefore, the main control unit 2
5 is a slider mechanism 20 according to the input reticle name.
And the operation of the aperture drive unit 27 are comprehensively controlled to automatically adjust the size of each aperture of the diaphragm 8 and the reticle blind 11 and the necessity / non-necessity of the interference reducing member CCM according to the reticle. be able to.

Here, the structure of a part of the projection optical system PL in FIG. 4 will be described with reference to FIG. FIG. 5 shows a partial cross section of the projection optical system PL, which is made entirely of a refractive glass material. The lowermost lens GA ₁ of the front lens group GA and the uppermost lens GB ₁ of the rear lens system GB are shown. The Fourier transform plane FTP exists in the space between and. Although the projection optical system PL holds a plurality of lenses by a lens barrel, the coherence reducing member CC
An opening is provided in a part of the lens barrel for inserting and removing M. In addition, a cover 20B that does not directly expose the coherence reducing member CCM and the slider mechanism 20 in whole or in part is extended from the opening of the lens barrel. This cover 20
B prevents minute dust floating in the outside air from entering the pupil space of the projection optical system PL. The slider mechanism 20 has
An actuator 20A such as a rotary motor, a pen cylinder, and a solenoid is connected. Further, a channel Af communicating with the pupil space is provided in a part of the lens barrel, and clean air whose temperature is controlled is supplied to the pupil space through the pipe 29, so that a part of the exposure light of the coherence reducing member CCM is supplied. The temperature rise due to absorption and the temperature rise of the entire pupil space are suppressed. In addition, the clean air forcibly supplied to the pupil space,
By forcibly discharging it through the slider mechanism 20 and the actuator 20A, it is possible to prevent dust generated in the slider mechanism 20 and the like from entering the pupil space.

FIG. 6 shows a first embodiment of the interference reducing member.
In this embodiment, an image is formed to reduce coherence.
The polarization state of light is controlled. Polarized like this
Is a polarization state control member
Called PCM. FIG. 6A shows the polarization state control member PC.
A sectional view of M and FIG. 6B are plan views. As shown in FIG.
As described above, the radius r of the circular transmission part FA₁Is the pupil ep
Effective maximum radius r of ₂Against 2r₁ ²= R₂ ² Is set to, but in reality
Good. As is clear from this equation, the surface of the circular transmission part FA
Product πr₁ ²Is the effective pupil aperture area πr₂ ²About half
It has become.

Now, the light source (mercury lamp 1) in FIG. 4 is light of random polarization state (light is a combination of light of various polarization states, and the polarization state changes with time).
To occur. In the first embodiment of the present invention, since the linear polarization plate is used as the polarization state control member PCM of FIG. 6, the polarization control member 6 in FIG. 4 is omitted. In that case,
The polarization state of the light flux passing through the contact hole pattern on the reticle and reaching the polarization state control member PCM is also random. The polarization state control member PCM shown in FIG.
A circular transmission part FA having a radius r ₁ from C is configured by a polarizing plate that transmits only linearly polarized light in a specific direction, and a ring-shaped peripheral transmission part FB coaxial with the center point CC is orthogonal to the circular transmission part FA. It is composed of a polarizing plate that transmits only linearly polarized light in the direction. Therefore, as shown in FIG. 6C, the polarization state of the image-forming light flux after passing through the polarization state control member PCM of FIG. Plane (polarization plane), and becomes a plane of polarization from the upper left to the lower right in the peripheral transmission part FB, becomes linearly polarized light having polarization directions orthogonal to each other, and does not interfere with each other (LF
a, LFb). Both the central and peripheral light fluxes that do not interfere with each other reach the wafer W, and each of them amplitude-combines only with itself, and separately images (intensity distribution) P
The principle of increasing the depth of focus of the composite image (composite intensity distribution) by creating r ₁ 'and Pr ₂ ' is as described in the section of action.

Alternatively, the polarization state control member P shown in FIG.
A quarter-wave plate is provided on the exit side (wafer side) of the CM, and the first linearly polarized light transmitted through the central transmission part FA and the second linearly polarized light transmitted through the peripheral transmission part FB orthogonal to the first linear polarization. Orthogonal polarized light may be converted into circularly polarized light having mutually opposite rotations. As described above, circularly polarized lights having opposite rotations do not interfere with each other and are suitable for the present invention.

In the above first embodiment, the projection optical system PL
Since the polarization state control member PCM in the inside is composed of a polarizing plate, half of the original amount of light to be transmitted through the projection optical system PL is absorbed by the polarizing plate as the polarization state control member PCM. . This also means a decrease in exposure power, but heat (energy of the absorbed exposure light) accumulates in the projection optical system, which poses a problem in terms of the stability of the optical system and the glass material.

An embodiment for solving this heat problem (exposure power loss) will be described as a second embodiment with reference to FIG. In this embodiment, the polarization characteristic of the illumination light ILB becomes important. Therefore, a polarizing plate is used as the polarization control member 6 in FIG. Alternatively, if the light source is a laser or the like and linearly polarized light from the beginning, this polarizing plate may not be used. If the polarization characteristics of the illumination light ILB to the reticle R are aligned by using the polarization control member 6 as described above, the light is transmitted through the contact hole pattern and diffracted to reach the polarization state control member PCM in the projection optical system PL. The image-forming light flux is also in a state of being aligned with a specific linearly polarized light.

Therefore, when the illumination light ILB is linearly polarized, a half-wave plate is used as the polarization state control member PCM as shown in FIG. 7 (A). FIG. 7A shows the polarization state of light immediately before entering the polarization state control member PCM, and here, it is assumed that the polarization state is linear polarization having a vibration plane of an electric field in the vertical direction. Figure 7 (B) shows the plane structure of the polarized state control member PCM, circular transmitting portion FA ₁ in the center of the radius r ₁ is constituted by a half-wave plate, annular transmitting portion FA ₂ near the transmitting portion FA It is a normal transparent plate (eg, quartz) having a thickness (optical thickness) almost equal to ₁ (1/2 wavelength plate). The polarization state of the light immediately after passing through the polarization state control member PCM of FIG. 7 is converted from the partial polarization state of the circular transmission part FA ₁ into the linear polarization in the left-right direction as shown in FIG. The polarization state does not change at all in the band-shaped transmission portion FA ₂ . Therefore, similarly to the first embodiment, it is possible to obtain a polarization state in which the central portion and the peripheral portion of the image-forming light beam do not interfere with each other. Here, the axial direction (in-plane rotation) of the half-wave plate serving as the transmissive portion FA ₁ is set to the axial direction that converts the direction of the incident linearly polarized light into the direction orthogonal thereto. Axial direction of wave plate and illumination light IL
In order to optimize the polarization direction of B, the polarization state control member PCM and the polarization control member 6 may be in-plane relatively adjustable in the rotation direction.

Further, as a modification, the central transmitting portion FA ₁
And the surrounding annular transmission part FA ₂ are both ¼ wavelength plates,
In addition, the axial directions of both (the direction in which the refractive index is high in the plane of the flat plate) may be orthogonal to each other. At this time, the transmitted lights of both the transmission parts FA ₁ and FA ₂ are circularly polarized lights having mutually opposite rotations, and also do not interfere with each other. At this time, the axial direction of the both and the polarization direction of the linearly polarized illumination light are 4
Adjust so that it deviates by 5 °.

Alternatively, the illumination light ILB itself may be used as circularly polarized light for the wavelength plates having the above two configurations.
In this case, when the half-wave plate is used as the polarization state control member PCM, the lights passing through the central transmission part FA ₁ and the peripheral transmission part FA ₂ are circularly polarized in mutually opposite directions, and thus polarized light is polarized. When a quarter wavelength plate is used as the state control member PCM, the linearly polarized lights are orthogonal to each other. To make the illumination light ILB itself circularly polarized, a quarter wavelength plate, a Fresnel rhomboid, or the like may be provided closer to the reticle than the polarizing plate 6 in the illumination system.

When the incident light flux (illumination light ILB) is circularly polarized light as described above, it is not necessary to rotate and adjust the axial directions of the half-wave plate and the quarter-wave plate according to the polarization characteristics of the illumination light. It is convenient. The polarization state control member P as described above
The use of CM is extremely convenient in that the problem of absorption of exposure energy as in the first embodiment described above is eliminated and heat accumulation in the projection optical system PL is suppressed. However, this time, the light amount loss (more than half) accompanying the alignment of the illumination light ILB into one polarization state in the illumination optical system remains a problem. Therefore, an example of an illumination system in which the light amount loss of the illumination light is reduced will be described as a third embodiment with reference to FIG. The system of FIG. 8 is provided instead of the polarization control member 6 of FIG. First, in FIG. 8A, the incident light beam is split and combined by the two polarization beam splitters 6C and 6D. That is, the P-polarized light component (polarized light in the vertical direction) is transmitted through the first polarization beam splitter 6C, and the second polarization beam splitter 6D is also transmitted and goes straight. On the other hand, the S-polarized light (polarized light in the direction perpendicular to the paper surface) component split by the beam splitter 6C is reflected by the mirror 6E,
The beams are combined by the beam splitter 6D via 6F and proceed coaxially with the P-polarized component. At this time, the mirrors 6E, 6
The optical path of F gives an optical path difference of 2 × d ₁ to P-polarized light and S-polarized light. Therefore, the temporal coherence length ΔLc of the incident light beam
Is shorter than 2d ₁ , the P-polarized component and the S-polarized component after combining are incoherent (non-coherent) in terms of time, in addition to having complementary polarization directions. Illumination light having these two polarization components is used, and the polarization state control member P
When the CM shown in FIG. 7 is used, as shown in FIG.
After entering the polarization state control member PCM, the P polarization component (for example, the white arrow direction) and the S polarization component (for example, the black arrow direction) respectively pass through the polarization state control member PCM as shown in FIG. 9C. Then, there are four light beams that do not interfere with each other. That is, the original polarization direction is rotated by 90 ° in the circular transmission part FA ₁ (1/2 wavelength plate). The four light beams have different polarization directions, and even if the transmission parts FA ₁ and FB ₁ have the same polarization direction, they do not interfere with each other because they are temporally incoherent. That is, the S-polarized component that has passed through the transmissive portion FA ₁ is converted into a P-polarized component and has the same polarization direction as the P-polarized component that has transmitted through the transmissive portion FB ₁ , but the two lights are temporally incoherent. So do not interfere. If Figure 8
When the illumination light from the polarization control member configured as in (A) is not used, the P-polarized light and the S-polarized light in FIG. 9 remain coherent in time, and therefore, after passing through the polarization state control member PCM. If the respective light fluxes have the same polarization direction, they will interfere with each other, and the effect of the present invention will be weakened. FIG. 8 (A)
Since the system shown in (1) can make a large difference in optical path length between the two polarization components to be combined, it is suitable for a light source having a relatively long temporal coherence length, for example, a laser light source with a narrow band.

When linearly polarized light is used as the laser light source, the effect of the present invention can be obtained without using the polarization control means having the structure shown in FIG. 8A. However,
When a polarization control means as shown in FIG. 8A is used for a linearly polarized laser light source, the illumination light can be made into two light fluxes that are temporally incoherent. There is an effect that interference fringes (irregularity of illuminance) can be reduced. In this case,
The polarization direction of the linearly polarized light incident on the beam splitter 6C at the first stage in (A) is intermediate between the P polarization direction and the S polarization direction as shown in FIG. The polarization direction LPL is preferably 45 ° from both.

By the way, when the light source is a light source having a comparatively large spectral width such as a mercury lamp, its temporal coherence length is short. Therefore, a simple member as shown in FIG. It can be used as the control member 6. This member is a transparent parallel plate 6G made of quartz or the like with a polarizing reflection film 6H attached to the surface thereof, and a total reflection film 6J made of metal or the like on the back surface thereof so that the collimated light flux from the mercury lamp is reflected at a predetermined angle. Is located in. At this time, of the randomly polarized incident light from the mercury lamp, the S-polarized component (direction perpendicular to the paper surface) is reflected by the surface film 6H, and the P-polarized component is transmitted through the surface film 6H and the parallel plate 6G. The S-polarized light component and the P-polarized light component reflected by the film 6J on the back surface are given an optical path difference that is approximately twice the thickness (optical thickness) of the substantially parallel plate 6G.

For example, in the case of i-line from a mercury lamp, the center wavelength λ is 365 nm and the wavelength width Δλ is about 5 nm.
A commonly used formula for coherent length, ΔLc = λ ² / Δ
From λ, the coherent length ΔLc is about 26 μm.
Therefore, a sufficiently thin parallel plate 6G (for example, about 1 mm thick)
Even in this case, it is possible to provide a sufficient optical path length difference to eliminate the temporal coherence.

Of course, even in the above-mentioned embodiment, instead of making the illumination light ILB into two linearly polarized light beams which are orthogonal to each other and are temporally incoherent light beams, they are circularly polarized lights having mutually opposite rotations and temporally. Even with two incoherent light fluxes, a good effect can be obtained as in the above-described embodiment, and there is no light quantity loss. To make the illumination light ILB or the light flux before reaching the polarization state control member PCM circularly polarized,
Similarly, a quarter wavelength plate or the like may be provided in the optical path from the system shown in FIGS. 8A and 8B to the polarization state control member PCM.

In the above, an embodiment using a polarizing plate utilizing a polarization characteristic, a quarter wavelength plate or a half wavelength plate as the coherence reducing member provided on the pupil plane of the projection optical system has been described. As the property reducing member, a member using the above-mentioned temporal coherency may be used. That is, a member that gives an optical path difference equal to or longer than the coherent length of the light between the imaging light passing through the central portion and the peripheral portion of the pupil plane may be used.

For example, it has the same structure as the polarization state control member PCM shown in FIGS.
When A and the peripheral transmissive portion FB are made of normal glass or quartz having a slightly different thickness, the temporal coherency between the light flux transmitted through the central transmissive portion FA and the light flux transmitted through the peripheral transmissive portion FB is It can almost disappear. For example, the coherent length ΔLc of the i-line is about 26 as described above.
Therefore, assuming that the refractive index n of the glass used is 1.5, (n-1) t ≧ 26 μm, where t is the difference between the thicknesses of the two (FA, FB), and t ≧ 52μ
It is sufficient if there is a difference in thickness of m. Alternatively, both transmissive portions (FA, FB) may have the same thickness and have different refraction indexes of both materials (use different materials) to give an optical path length difference of coherent length or more. As described above, the effects of the present invention can be similarly obtained even if the coherence of the light flux in the pupil plane is reduced by the polarization action or the coherence is reduced by the optical path length difference.

Although the respective embodiments of the coherence reducing member provided on the pupil plane of the projection optical system have been described above, the incident angle range (σ value etc.) of the illumination light beam ILB to the reticle will be described next. FIG. 10 (A) is 0.3 in terms of the size on the wafer.
The transparent patterns PA and PB, which are contact hole patterns of square μm, are similarly formed on the wafer in a reduced size of 0.
FIG. 11 is a partial cross-sectional view of two contact hole pattern reticles R1 that are arranged side by side by 66 μm apart. FIG. 10 (B),
(C) and (D) show that when the pattern of the reticle R1 is projected by the projection optical system PL for the i-line having the wafer side numerical aperture NAw of 0.57, the σ value is 0.4,
FIG. 6 shows simulation results of a coherence function (complex coherence) on a reticle when illuminated by a 0.6 and 0.8 illumination system. The coherence function is generally obtained by Fourier transforming the light source shape seen from the object (here, reticle) according to the Fansitter-Zernike theorem. In this type of projection exposure apparatus (stepper), the light source shape is generally a circle equivalent to the aperture shape of a circular diaphragm (for example, diaphragm 8 in FIG. 4) arranged on the exit surface of the fly-eye lens 7. The Fourier transform of the circle is the well-known Bessel function of the first kind, and the radius of the circle that is the light source shape is defined by σ · NAr, so the coherence function is 2 · J ₁ (2πxNArσ / λ) / (2πxNArσ /
λ). Here, x corresponds to a distance from a reference point defined at an arbitrary position on the reticle.

The reference of the coherence function in the case of FIG. 10 is the center position of the left contact hole pattern PA. In the coherence function C4 in the case of σ = 0.4 shown in FIG. 10B, the value of the coherence function at the position of the contact hole PB on the right side is also +. Therefore, the luminous flux transmitted through the reference left contact hole pattern PA and the right contact hole pattern PB
The luminous flux that has passed through has an interfering property that strengthens each other in terms of amplitude.
As a result, both hole patterns PA that should originally be dark areas,
A part of the light quantity of both hole images reaches the part on the wafer corresponding to the middle light shield part PM of PB by diffraction, and these interfere with each other to strengthen each other, so that the middle light shield part PM.
Can't be dark enough.

FIG. 11A shows such an illumination condition (σ
= 0.4), the intensity distribution of the optical image (simulation value) of the hole pattern formed when the coherence reducing portion CCM is provided on the pupil plane ep is shown. In the figure, Eth represents the amount of light (exposure amount) necessary for the positive resist to be completely dissolved after development, and Ec represents the amount of light (film slip strength) at which the positive resist begins to dissolve. The vertical magnifications of the optical image (intensity distribution) shown in the figure are aligned so that the slice width at the level where the light amount is Eth is 0.3 μm, which is the designed value.

When σ = 0.4, the light intensity between the two hole images becomes larger than the film slip intensity Ec as shown by the distribution I4 shown in FIG. It is impossible to obtain a good pattern which is completely separated due to slipping. The coherence reducing member CCM arranged on the pupil plane ep is the center transmission part FA or FA.
₁ radius is 1 / √ of pupil radius (equivalent to NAw = 0.57)
2 and the inner radius of the peripheral transparent portion (annular zone) FB (or FB ₁ ) is equal to the radius of the central transparent portion FA (or FA ₁ ),
The outer radius is assumed to be equal to the pupil radius. Further, as described above, the same result can be obtained regardless of whether the material of the coherence reducing member uses the polarization effect or the optical path length difference equal to or longer than the coherent length.

FIG. 10C shows the coherence function C6 when the σ value is set to 0.6 under the same conditions as in FIG. 10B.
Indicates. At this time, the contact hole pattern P on the right side
At the position of B, the value of the coherence function is almost 0, and therefore, the light beams that have passed through both hole patterns hardly interfere with each other. As a result, the light fluxes that circulate from the two hole images to the portion on the wafer corresponding to the intermediate light-shielding portion PM do not strengthen each other, so the separation between the two holes is better than when σ = 0.4. .

FIG. 11B shows a simulation result of the intensity distribution I6 of the optical image in this case. According to the simulation result, the amount of light in the middle portion is slightly larger than the film slip strength Ec, and it is expected that a slight film slip occurs in the resist pattern. However, if this amount is
The problem would be solved by using resists with improved performance over the current ones. Even under the condition of σ = 0.6 in FIG. 11B, the coherence reducing member arranged on the pupil plane is the same as that in the case of σ = 0.4.

FIG. 10D shows the coherence function C8 when the σ value is 0.8. At this time, the value of the coherence function of the illumination light reaching the contact hole pattern PB on the right side has the opposite sign (reverse polarity) to the value of the coherence function of the illumination light reaching the contact hole pattern PA on the left side (that is, the opposite phase). Of light), and therefore
The wraparound lights from both hole patterns PA and PB cancel each other out, and the intermediate light-shielding portion PM can be sufficiently darkened.

FIG. 11C shows the intensity distribution I ₈ of the optical image (simulation value) at σ = 0.8. Conditions other than the σ value are the same as those in FIGS. 11A and 11B. σ =
At 0.8, the intensity distribution I ₈ of the optical image is below the film slip strength Ec at the intermediate portion, and the resist patterns of both hole patterns are completely separated. In the above description, the amount of light Ec at which the film slip of the positive resist starts is set to half of Eth, but this is the capability of the current positive resist, and if the capability of the positive resist is improved in the future, the film slip strength Ec will be closer to Eth. . In this case, both hole patterns can be completely separated even if about σ = 0.6 as described above. If the distance between the two hole patterns is more than the above condition of 0.66 μm, for example, about 0.8 μm, σ =
Even at 0.6, both hole patterns are well separated. This is not only due to the increased distance between the two hole patterns, but also 0.8 μm under the condition of σ = 0.6.
The fact that the coherence function C6 at the distant position (hole pattern PB) is negative also greatly contributes. From the above, depending on the characteristics (improvement) of the resist, considering the current distance between hole patterns (about 1 μm),
It is desirable to perform projection exposure with a σ value of approximately 0.5 or more.

As described above, in order to make the values of the coherence function in both the adjacent contact holes have opposite signs, one method is to use illumination light having a large σ value as described above. The ring illumination method and the SHRINC method can be used to obtain further effects. 12
Is an embodiment for realizing these illumination methods in the apparatus shown in FIG. 4, and FIG. 12 (A) shows another form near the fly-eye lens 7 in FIG. Fly eye lens 7
A plurality of turret-type convertible diaphragms 80, 81-are provided in the vicinity of the exit side surface of the turret, and the turret 800 is rotatable by a drive system 800a. The replacement rotary drive system 800a operates according to a command from the main control unit 25 via the drive unit 27a. The command at this time is, for example, based on the information from the bar code on the reticle as described above, or is input by the operator. FIG. 12B shows the shape of each diaphragm attached to the turret. In FIG. 12 (B), 81 represents a conventional illumination system diaphragm having a circular aperture, 82 represents an annular illumination diaphragm having a ring-shaped aperture, and 83 and 84 represent a so-called modified light source of the SHRINC method. Represents each aperture.
Since the respective diaphragms 81, 82, 83, 84 are arranged close to the exit side of the fly-eye lens 7, they are almost conjugate with the pupil ep (Fourier transform plane) of the projection lens PL. Figure 1
3 shows the coherence function of the illumination light on the reticle pattern when the annular illumination method and the SHRINC method are applied to the present invention. Here, FIG. 18A is a partial cross-sectional view of the reticle R1 which is the same as FIG. 10A. The simulation conditions here are those shown in Fig. 1 except for the illumination system.
This is the same as the condition of 0. Now, in FIG. 13B, σ = 0.
The central part of the illumination light flux (secondary light source image) under the condition of 7 is
The simulation result of the coherence function in the case of the annular illumination in which only about 2/3 of the maximum radius is shielded is shown. Again, the coherence function can be obtained by Fourier transforming the light source shape. For example, in the case of ring illumination, if the ring ratio (here, 2/3) is ξ and the outermost diameter of the ring light source image is σ, the coherence function is The function (complex coherence) is ρ = 2π
xNArσ / λ and use the Bessel function of the 1st kind

[0060]

[Equation 1]

It becomes Again, x is the distance to any point relative to the reference point. In addition, FIG.
SH which forms four light source images each having about 0.25 as the σ value of each aperture centered on four points that are optimum when a hole pattern exists at a pitch of 0.66 μm in the direction
It represents a coherence function in the RINC method. The four light source images of the SHRINC method are adjusted (rotational direction) with respect to the two contact hole patterns PA and PB arranged on the reticle. In addition, SHRI
The optimum light source image position in the NC method is disclosed in JP-A-4-225.
As described in detail in Japanese Patent Publication No. 514, etc., it is determined according to the periodicity (pitch) of the pattern on the reticle.
Further, as shown in FIG. 12B, two types of diaphragms 83 and 84 to which the SHRINC method is applied are prepared, but either one is used. Now, with these illumination systems, the value of the coherence function in the contact hole pattern PB on the right side can be made largely negative with respect to the hole pattern PA on the left side. So these annular lighting systems,
Or, if the SHRINC system is used, the above-mentioned circular diaphragm 81
Since the canceling effect of light is stronger in the middle portion between the two hole images than in the case of σ = 0.8 using
The amount of light at M becomes even lower and the two hole images become better separated. FIG. 14 shows simulation results of the intensity distributions IA and IS of the optical image in this case, FIG. 14A shows the case of the annular illumination method under the above conditions, and FIG. 14B shows the SHRINC method under the above conditions. Shows the case. As can be seen from these simulations, the middle part of the two hole pattern images is sufficiently dark in any illumination method. Also in this case, the coherence reducing member on the pupil plane is the same as when σ = 0.4, 0.6, and 0.8 described above.

Next, the increase of the depth of focus according to the present invention will be described based on the simulation result. Figure 15
(A) is for the SFINCS method using an interference reducing member,
= 0.8, an intensity distribution at the best focus position when an illumination system (a circular aperture stop 81 selected so that σ = 0.8) is added is shown in FIGS. 15 (B) and 15 (C). The intensity distributions at the defocus position of 1 μm and the defocus position of 2 μm are shown, respectively, and these distributions are simulation results of the optical image of the hole pattern. The conditions (NA, wavelength, pattern shape) here are the same as those in FIGS. Note that FIG. 15A is the same as FIG. 11C, but is shown here again for easy comparison with the defocused state. As is clear from the simulation of FIG. 15, the image intensity between the two hole pattern images is suppressed to be smaller than the film slip intensity Ec even at the defocus position of 2 μm.

Now, FIGS. 16A, 16B and 16C show the SFINCS method using the coherence reducing member shown in FIG.
The same annular illumination system as used in the simulation of (A) (an annular aperture 82 that shields the center of the secondary light source image of a size corresponding to σ = 0.8 by a radius of 2/3) is added. The simulation result of the intensity distribution of the hole pattern image obtained when the
It is each intensity distribution in a defocus position of μm and a defocus position of 2 μm.

FIGS. 17A, 17B and 17C show FIG.
The result of simulating the intensity distribution of the hole pattern image when the SHRINC method used in (B) is combined with the SFINCS method is shown. For comparison, FIG. 19 shows a simulation result of the intensity distribution of an optical image by a normal (conventional) imaging method. In the normal method, there is no pupil plane coherence reducing member, and the σ value is set to 0.6. Other conditions (N.
A. , Wavelength, pattern shape)
The conditions are the same as in the INCS method. Compared with the normal imaging method (FIG. 19), the SFINCS method according to the present invention (FIG. 1)
5,16,17) clearly shows an increase in the depth of focus,
2 μm when the SFINCS method according to the present invention is used for the intensity distribution at the 1 μm defocus position of the normal method
The intensity distribution at the defocus position maintains almost the same image quality (contrast). That is, the depth of focus is about 2
It has been doubled. FIG. 18 shows an image intensity distribution obtained by a modified example of the present invention. The σ value of the illumination system is set to 0.8 by using the circular aperture stop 81, but the coherence reducing member provided on the pupil plane is the same as that described above. Make the structure a little different from the one. Specifically, the vicinity of the center of the coherence reducing member as shown in FIG. 6B is a circular light-shielding portion centered on the optical axis CC. At this time, the radius of the light shielding portion was set to 0.31 × NAw with respect to the effective radius of the pupil (that is, numerical aperture = NAw). Further, the radius of the central transmitting portion FA (same as the inner radius of the peripheral transmitting portion FB) is set to 0.74 × NAw. It is needless to say that the method of reducing the coherence used here may be either a method utilizing a polarization effect or a method utilizing an optical path length difference. As is clear from the simulation result of FIG. 18, even when the same illumination system of σ = 0.8 is used, the dark portion between the two hole images is sufficiently darker in FIG. 18 than in the example in FIG. It can be seen that the separation ability is improved.

FIG. 20 shows, for comparison, a simulation result of the intensity distribution of the hole pattern image when the FLEX method is combined with the normal illumination method. FLE here
The X method is a method of performing multiple exposure by moving the wafer to each of three focus positions, and the movement positions (focus positions) of the wafer in the Z direction are −1 μm, 0 μm, and +1 respectively.
μm. Further, in this FLEX method, two contact hole patterns P are formed at the best focus position.
The optimum conditions are such that the resist images of A and PB are separated (the strength at the intermediate light-shielding portion PM is equal to or less than the film slip strength Ec), and the depth of focus can be increased. As can be seen from this simulation result, 2 μ obtained by the conventional FLEX method
m intensity distribution at defocused position (Fig. 20 (C))
When compared with the intensity distribution at a 2 μm defocused position obtained by the SFINCS method of the present invention (FIGS. 14 to 18), the hole pattern image obtained by the present invention has a higher peak intensity and a higher quality image. You can see. still,
If the conditions of the FLEX method simulated in FIG. 20 are changed to make the difference between the focus positions more than that, or to make the focus positions four points or more and perform multiple exposure, as shown in FIG. 20C. The image intensity distribution at the 2 μm defocus position is improved, but in the intensity distribution at the best focus position of FIG. 20A, the intensity of the intermediate portion of the two hole pattern images exceeds the film slip intensity Ec, Film slippage will occur in the resist pattern.

FIG. 21 shows a conventional Super for comparison.
9 shows a result of simulation by the FLEX method. 21 (A), (B), and (C) show a filter having a numerical aperture NAw of 0.57 and a complex amplitude transmittance of −0.3 in a portion within a radius of 0.548 NAw from the pupil center point. The intensity distribution I ₁₃ at the best focus position, the intensity distribution I ₁₄ at the defocus position of 1 μm, and the intensity distribution I ₁₅ at the defocus position of 2 μm, which are obtained when the image is provided in FIG. In the Super FLEX method, the central intensity at the best focus position is high and the profile is sharp as shown in FIG. 21, but the decrease in central intensity due to the defocus amount occurs abruptly from a certain amount. However, the effect of expanding the depth of focus is approximately the same as the effect of the present invention shown in FIGS. However, Super F
According to the LEX method, the area around the original image (center intensity) is shown in FIG.
Sub-peaks (ringing) as shown in (A) occur.

In order to prevent such ringing, FIGS. 22A, 22B and 22C use a filter having a weaker action than the pupil filter of the Super FLEX method used as the simulation model in FIG. The simulation result in the case is shown. In this case, the numerical aperture NAw of the projection optical system is 0.57, and the radius of the pupil center is 0.447 NA.
A filter with a complex amplitude transmittance of -0.3 in the portion corresponding to w is used. 22A to 22C show the intensity distribution I ₁₆ at the best focus position, the intensity distribution I ₁₇ at the defocus position of 1 μm, and the intensity distribution I ₁₈ at the defocus position of 2 μm. Although the ringing is weaker than in the case of 21, the effect of increasing the depth of focus is also reduced at the same time.

In the simulations of FIGS. 21 and 22, the center-to-center distance between the two hole patterns PA and PB is determined under the condition that the peak of ringing due to one hole pattern overlaps with the center intensity part of the other hole pattern. Therefore, the effect of ringing does not appear between the two hole pattern images. On the contrary, the distance between the centers of the two hole patterns PA and PB is the same as the previous condition (0.6 on the wafer).
6 μm) means that the influence of ringing appears.

FIG. 23 is a simulation result of the intensity distribution at the best focus position of two contact hole images arranged with the center-to-center distance of 0.96 μm (converted on the wafer). The image intensity distribution I ₂₃ according to the SFINCS method (invention) under the conditions shown in FIG. 18 is 2 as in 323 (A).
The space between two hole images is sufficiently dark, and a good resist pattern can be formed. However, S under the conditions shown in FIG.
In the upper FLEX method (1), ringing due to each of the two hole patterns is synthesized (added) as in the intensity distribution I ₂₄ of FIG. 23B, and a bright subpeak (film is formed in the middle of the two hole images). The verifying strength Ec or more) occurs, and the resist in this part is film-verified. Therefore, a good resist image cannot be obtained. On the other hand, when two hole patterns with a center-to-center distance of 0.96 μm are projected by the Super FLEX method (2) under the conditions shown in FIG. 22, the image intensity distribution I ₂₅ becomes as shown in FIG. 23 (C). . In this way, Supe is relatively weak
In the case of the r FLEX method (2), a good resist image can be obtained because the ringing is small and the film is free from the film. However, under this condition, as described with reference to FIG. 22, it is not possible to obtain a sufficient depth of focus expansion effect as compared with the SFINCS method of the present invention.

FIG. 24 shows contact hole patterns PA ₁ , PA ₂ , PA ₃ , PA used in a memory cell portion in a DRAM as an example of a plurality of adjacent contact holes.
₄ shows an example of a two-dimensional array of ₄ . When the Super FLEX method is used for such a hole pattern group, ringing (sub-peak) occurs around each hole.
Ra, Rb, Rc, Rd occur, and the region R where they overlap
At o, the peak intensities of the four ringings will overlap. In such a case, in the case of only two hole patterns (two ringings overlap each other), the film VERY did not occur.
Even in the X method (2), the size of the sub-peak is as shown in FIG.
About twice as much as the state shown in (C), and again the film-verification strength E
Since it is c or more, good pattern transfer cannot be performed. That is, an image of a hole (ghost image) that originally does not exist on the reticle is formed at the position of the region Ro on the wafer.

On the other hand, SFINCS according to the present invention
In the case of the method, as shown in FIG. 23 (A), since the light intensity distribution in the middle of the two hole patterns is equal to or less than 1/2 of the film-verification intensity Ec, the addition is performed in the region Ro shown in FIG. Even if the strength is further doubled from the state of FIG. The connection of images at the time of projecting a plurality of close contact hole patterns as shown in the above simulation results mainly passes through the central circular area FA (or FA ₁ ) in the pupil plane ep of the projection lens PL. It occurs due to the image light flux. By the way, an imaging light flux L passing only through the central circular area FA (or FA ₁ ).
If the size (radius) D ₁ of the image Pr ₁ ′ of one contact hole pattern formed by Fa is as small as the exposure wavelength λ, the numerical aperture NA ₁ corresponding to the radius r ₁ of the circular area FA. It is known from the optical theory that it is given by the following relation based on.

D ₁ ≈0.61 (λ / NA ₁ ) Here, NA ₁ is the numerical aperture on the wafer side corresponding to the radius r ₁ and is determined as shown in FIG. In this case, even if the hole pattern PA or PB on the reticle is square, the image Pr ₁ ′ formed on the wafer has a substantially circular shape. Therefore, in order to increase the degree of separation between the two close hole pattern images, the magnification of the projection lens PL is 1 /
Considering M, the distance on the reticle is 0.61 · M · (λ /
It is important that the spatially incoherent state, that is, the coherence function of one of the two positions is approximately zero or negative between the illumination lights that reach the two positions separated by NA ₁ ). Is. This means that the numerical aperture NAi (sin of the illumination light beam ILB reaching the reticle is
ψ / 2) is the central circle area FA (or FA ₁ ) in the pupil ep.
Numerical aperture NA ₁ / on the reticle side of the imaging light flux LFa that passes through
It is nothing more than M. This is because, based on the above-mentioned expression of the coherence function, the distance on the wafer where the coherence function becomes 0 is approximately 0.61λ / NA ₁ similarly to the above.

[0073] Here, when the numerical aperture NA ₁ / M of the reticle side of the imaging optical flux LFa and NAr _1, the case using the conventional circular aperture stop 81 NAi> as NAr ₁ can not be realized , Annular illumination system (annular aperture 8 in FIG.
2) should be adopted. In this case, when the numerical aperture corresponding to the radius of the central circular light-shielding portion of the annular stop 82 is NAs (value on the reticle), k = NAi / NAr ≦ 1 and approximately

[0074]

[Equation 2]

A circular light-shielding portion at the center so as to satisfy the relationship of
It has been found that it is sufficient to determine the radius of. like this
In relation, the distance on the reticle is 0.61 · M · (λ /
NA ₁) Illumination light reaching each of two positions separated by
A state in which the comrades are incoherent, that is, their two positions
The coherence function at one position relative to the other
It can be zero or negative. In addition, annular lighting system
Use of NAi / NAr₁Limited to the case of ≦ 1
Not NAi / NAr₁Even if ≧ 1, naturally
A ring-shaped illumination system can be adopted.

FIG. 25 schematically shows the appearance of the exit side surface of the fly-eye lens 7 which is imaged in the pupil plane ep of the projection lens PL. In FIG. 25A, an image on the exit surface side of the fly-eye lens 7, that is, an image on the exit surface side of the fly-eye lens 7 is enclosed within a circle CN _{1 having} a size of about 80% (0.8r ₂ ) with respect to the effective maximum radius r ₂ of the pupil ep. A secondary light source image is formed. In this case, the circle CN ₁ represents a σ value of 0.8. In addition, FIG. 25 (A)
A circle CN having a radius r ₁ is a center circular transmission area FA (or FA ₁ ) of the coherence reducing member CCM and an annular transmission area FB.
(Or FB ₁₎ represents the boundary between.

Here, assuming that the relationship of 2r ₁ ² ≈r ₂ ² is set, the radius r ₁ corresponds to 0.707 in σ value. As described above, a good result is obtained particularly in the image formation of a plurality of contact hole patterns that are close to each other in the illumination condition of σ = 0.8. As a result, the secondary light source image ( This is because the size of the exit surface of the fly-eye lens 7 is larger than the boundary circle CN (corresponding to σ = 0.707). This is completely equivalent to the above-mentioned condition, NAi / NAr ₁ > 1.

On the other hand, in FIG. 25 (B), the area of the secondary light source image in the pupil plane ep is relatively small, and within the circle CN ₂ (radius 0.5r ₂ ) of σ = 0.5. To fly eye lens 7
The case where an image of the exit surface of is formed. As a matter of course, the circle CN ₂ is smaller than the boundary circle CN, and the above condition k
= NAi / NAr ₁ ≦ 1. At this time k =
0.5 / 0.707 ≈ 0.71 and the numerical aperture NAs of the central circular light-shielding part when switching to annular illumination is

[0079]

[Equation 3]

Since NAr ₁ corresponds to 0.707 in σ value, NAs corresponds to approximately 0.38 in σ value. A circle CN ₃ in FIG. 25B shows the arrangement of the central light shielding portion on the pupil plane ep, and the size of the light shielding portion on the exit surface of the fly-eye lens 7 is specified from this. Figure 25
In the case of (B), the size of the secondary light source image corresponds to a σ value of 0.5, and the size of the central light-shielding portion of the annular illumination diaphragm 82 corresponds to a σ value of 0.38. The radius of the central light-shielding portion with respect to the radius of the secondary light source image on the exit surface of the eye lens 7 is
It is set to about 0.38 / 0.5≈0.76.

The formula for determining the size (numerical aperture NAs) of the central light-shielding portion of the ring-shaped diaphragm 82 is applied under the condition of 0.62≤k≤1, but the lower limit of k Value 0.6
2 is determined on the condition that the radius of the required light-shielding portion becomes equal to the radius of the secondary light source image when the annular aperture is provided on the secondary light source image. For example, with the boundary circle CN of the coherence reducing member CCM (σ value 0.707) being left unchanged, σ =
Consider the case of a lighting condition of 0.42. At this time k =
0.42 / 0.707 ≈ 0.594, and the ring zone diaphragm 8
The numerical aperture NAs of the central light-shielding portion of 2 is required to be 0.45 or more in σ value. However, since the size of the original secondary light source image is only 0.42 in the σ value, the value is unsuitable. This is the size of the original secondary light source image (σ = 0.4
2) on the reticle is 0.61 · M · λ / NA ₁ (= 0.
61.λ / NAr ₁ ) two contact hole patterns that are well separated and cannot be projected and imaged.
It means that the spatial coherency has become higher. That is, it means that the illumination condition of σ = 0.42 is originally unsuitable for projection by the SFINCS method of a plurality of contact hole patterns that are close to each other on the reticle by about 0.61λ / NAr ₁ .

When the distance between the plurality of contact hole pattern images to be transferred onto the wafer is set to about dimension D ₁ (0.61 · M · λ / NA ₁ on the reticle), the pitch of 4 (or 2) with optimized placement
If the SHRINC method using the secondary light source image (four apertures in the diaphragms 83 and 84) is adopted, two positions having a pitch of M · D _{1 to} 2M · D ₁ on the reticle, The coherence function at one position relative to the other can be near zero or negative (inverse sign). Here, when the interval is D ₁ , 4 by the SHRINC method
Optimal's coherence function to the interval D ₁ arrangement of light source images is negative, coherence function arrangement of the four light source image and it is the best to the distance 2 × D ₁ by SHRINC method becomes zero.

FIG. 26 shows the arrangement of the image 83 'of the diaphragm 83 on the pupil plane ep of the projection lens PL, and the light-shielding portions extending in the x-direction and the y-direction intersect at the center CC to form a cross shape. At this time, each width in the x and y directions of the cross-shaped light-shielding portion is
The fly-eye lens 7 is set so as to match the boundary lines of the plurality of prismatic elements. Furthermore, the fly-eye lens 7 that appears in each of the four openings of the cross-shaped light-shielding portion
It is desirable to make the number of elements in the same as much as possible.

Now, in FIG. 26, the fly-eye lens 7
The exit end surface of is divided into four by the four openings of the diaphragm 83, and the center of gravity points PG _{1 to} PG ₄ on the light amount of each of the divided sets of fly-eye lenses are indicated by black circles. The x direction from the center CC of the light amount centroids PG _{1 to} PG ₄ , y
The eccentricity amounts Px and Py in the respective directions correspond to the pitches MD _{1 to} 2MD ₁ of the pattern on the reticle.

SHR means that the positions of the centers of gravity PG _{1 to} PG ₄ correspond to the pattern pitches MD _{1 to} 2MD _1.
The principle of the INC method will be explained as shown in FIG. That is, when the periodic pattern with the pitches MD _{1 to} 2MD ₁ is present on the reticle R, the illumination light beam LB generated from the light quantity center of gravity of one set of four divided fly-eye lenses.
P is incident on the reticle R with an inclination with respect to the principal ray (broken line) perpendicular to the reticle R. Then, the 0th-order ray from the reticle pattern passes on the point PG ₁ in the pupil ep in the projection lens PL (front group lens GA, rear group lens GB). This point P
G ₁ is the light amount center of gravity point PG ₁ in FIG.

On the other hand, one 1st-order diffracted ray from the reticle pattern advances symmetrically with the 0th-order ray with respect to the principal ray (broken line), and passes through a point symmetrical with the point PG ₁ with respect to the center CC on the pupil plane ep. To do. In the case of a pattern having a pitch in the x direction, the first-order diffracted ray passes through the position of the light amount centroid PG ₂ in the pupil ep in FIG. 26, and in the case of a pattern having a pitch in the y-direction, the first-order diffracted ray is In FIG. 26, the light quantity passes through the center of gravity PG ₄ .

That is, so that such a state can be obtained.
The inclination of the illumination light beam LBP according to the pattern pitch, in other words
Center of light intensity of each set of 4 divided fly-eye lenses
The eccentricity amounts Px and Py of the points are determined. Transfer on wafer
At least two contact hole pattern images
Interval is D₁~ 2D₂If the exposure wavelength is i-line (λ =
0.365 μm), the numerical aperture of the circular transparent area FA on the wafer side
NA₁Is 0.707 NAw, the wafer side aperture of the projection lens
If the number NAw is 0.57, the interval D₁Is D₁=
0.61λ / NA₁About 0.55 μm (on reticle
Is 2.76 μm). Also, the distance D on the wafer ₁
Optimum lighting with the SHRINC method
Incident angle θ of ray LBP (FIG. 27) on the reticle_kIs s
in2θ_k= Λ / MD₁Is determined by. From this formula, M
・ Sin θ_k≒ λ / 2D₁Is 0 due to the illumination ray LBP
It has the same value as the numerical aperture NAk of the next ray on the wafer side. Yo
Therefore, the following equation holds.

NAk = λ / 2D ₁ = λ / 2 (0.61λ
/ NA ₁ ) = NA ₁ /1.22 Therefore, the position of the light amount gravity center point corresponding to the interval D _{1 to} 2D ₁ is NAk to NAk / 2 as the numerical aperture on the wafer side.
It will be good if it exists in. In other words, the circle (radius Px√2) corresponding to between NA ₁ /1.22~NA ₁ /2.44 against the yen CN numerical aperture NA ₁ when the the Px = Py as shown in FIG. 26 above The center of gravity points PG _{1 to} PG ₄ are arranged at.

Although the respective embodiments of the present invention and the operation thereof have been described above, when the illumination light ILB to the reticle R is given a specific polarization direction, it is judged whether the polarization direction is suitable or not, or A means for photoelectrically detecting a part of the light flux passing through the projection optical system may be provided on the wafer stage WST in order to judge whether the polarization state of the image-forming light flux after passing through the state control member PCM is good or bad. Further, when using a reticle having a line and space, the coherence reducing member CCM may be moved out of the projection optical system PL, and a part of the illumination system may be exchanged so as to be suitable for the SHRINC method. When the contact reduction pattern CCM is used during projection exposure of the contact hole pattern and the modified illumination system such as the SHRINC method or the annular illumination light source is used together, the reticle to be exposed is changed from the contact hole to the line and space. In this case, only the coherence reducing member CCM needs to be withdrawn.

Further, the interference reducing member CCM shown in each of the embodiments of the present invention is composed of a circular or ring-shaped transparent portion, but this is not limited to a literal shape. For example, the circular transparent portion may be transformed into a polygon including a rectangle, and the annular transparent portion may be transformed into a shape surrounding the polygon in a ring shape. Furthermore, the interference reduction member CCM
In the above, the central circular transmission portion is surrounded by a maximum of two annular transmission portions, but the annular transmission portion may be divided into more parts.

In this case, of the circular transmission portion and each of the n-weighted ring-shaped transmission portions, at least one set of mutually-interfering portions (having the same polarization state) has a phase difference of π with respect to each other. Thus, a phase shifter may be provided. Furthermore, the coherence reducing member CCM may use any one or more regions of the circular or annular region that divides the effective pupil area into n + 1 equal parts as the light shielding portion.

Further, in each of the embodiments of the present invention, the projection lens constituted by the refractive elements is used as the projection optical system.
In addition, the present invention can be applied in the same manner to any of a projection optical system including all reflective elements or a projection optical system in which a reflective element and a refractive element are combined.
In particular, a broadband light from a xenon mercury lamp, or a reflection method using a plurality of bright lines from a mercury lamp as illumination light,
Alternatively, in the catadioptric projection exposure apparatus, since the temporal coherence length ΔLc of the exposure light is short (about several μm), it is convenient to use a coherence reducing member that utilizes the difference in optical path length. Although not illustrated as a simulation in each of the above embodiments, if the SFINCS method and the FLEX method according to the present invention are combined, even if the amount of moving the wafer in the optical axis direction by the Z stage is small, it is sufficient. The effect of expanding the depth of focus will be obtained. In other words, this means that a synergistic effect can be obtained between the focal depth extension by the SFINCS method and the focal depth extension by the FLEX method (or continuous movement of the wafer during exposure).

In each of the embodiments of the present invention, the coherence reducing member CCM (polarization state controlling member PCM) is arranged on the Fourier transform plane FTP of the projection optical system PL. Depending on the structure of the elements and the combination state, they can be arranged slightly off the Fourier transform plane FTP. For example, in the case of the projection lens having the configuration as shown in FIG. 5, the position of the air gap in the vicinity of the lens is about two to three lenses above the lowermost lens GA _{1 of} the front lens group GA (reticle side). The coherence reducing member CCM may be provided. In short, when the hole pattern is projected, if the position has a luminous flux distribution substantially equal to the distribution of the imaging luminous flux in the pupil ep of the Fourier transform plane FTP, the coherence reducing member CCM
May be provided anywhere. Therefore, the near-pupil surface in the present invention means an arbitrary position within the range in which the light flux distribution on the Fourier transform surface is preserved to some extent.

[0094]

As described above, according to the present invention, the depth of focus during projection exposure of an isolated pattern such as a contact hole is set to F
It can be expanded to the same extent as the LEX method or the Super FLEX method, and it does not move or vibrate the photosensitive substrate in the optical axis direction unlike the FLEX method.
Further, there is an advantage that it is not necessary to prepare a spatial filter having a complex function of complex amplitude transmittance as in the Super FLEX method. In particular, in the present invention, the ringing itself, which is likely to occur due to spatial filtering on the pupil plane (Fourier transform plane) of the projection optical system, is suppressed sufficiently small, so that a plurality of contact hole patterns are arranged relatively close to each other. Even if it is
It is possible to obtain a great effect that the adverse effect (occurrence of a ghost image) caused by the superposition of the ringing sub-peak portions unlike the FLEX method is eliminated. Also the conventional FLEX
Even if the photosensitive substrate is not moved in the direction of the optical axis as in the method, the effective depth of focus is enlarged by about 2 times or more, so that the mask and the photosensitive substrate are moved relative to each other in a plane perpendicular to the optical axis. It can be applied as it is to a projection exposure system of a scanning exposure system (step and scan system).

[Brief description of drawings]

FIG. 1 is a diagram illustrating a conventional projection exposure method.

FIG. 2 is a diagram showing a principle configuration for carrying out the projection exposure method of the present invention.

FIG. 3 is a diagram illustrating the principle of increasing the depth of focus by the exposure method of the present invention.

FIG. 4 is a diagram showing an overall configuration of a projection exposure apparatus suitable for implementing the present invention.

FIG. 5 is a partial cross-sectional view showing a partial structure of the projection optical system.

FIG. 6 is a diagram showing a configuration of a polarization state control member PCM according to the first embodiment of the present invention.

FIG. 7 is a diagram showing a configuration of a polarization state control member PCM according to a second embodiment of the present invention.

FIG. 8 is a diagram showing a configuration of a polarization control means according to a third embodiment for making the polarization characteristics of illumination light different from each other and at the same time making them incoherent.

9 is a diagram illustrating polarization characteristics when the polarization state control member PCM of FIG. 7 and the polarization state control means of FIG. 8 are combined.

FIG. 10 is a graph showing a result of simulating a change in coherence function with respect to two contact hole patterns on a reticle, which are close to each other, depending on a σ value of illumination light.

FIG. 11 is a graph showing a result of simulating an image intensity distribution when two hole patterns are projected by a normal exposure method with different σ values.

FIG. 12 is a diagram showing a conversion diaphragm mechanism for switching the shape of a light source image inside the illumination system.

FIG. 13 is a graph showing a result of simulating a coherence function for two contact hole patterns that are close to each other on a reticle by an annular illumination method and a SHRINC method.

FIG. 14 is a graph showing the results of simulating the image intensity distributions of two hole patterns using the SFINCS method for the annular illumination method and the SHRINCS method, respectively.

FIG. 15 is a graph simulating a change in intensity distribution associated with defocus of a contact hole pattern image when the SFINCS method is applied with σ = 0.8.

FIG. 16 is a graph simulating how the intensity distribution changes with defocus of the contact hole pattern image when the SFINCS method is applied in the annular illumination method.

FIG. 17 is a graph simulating a change in intensity distribution associated with defocusing of a contact hole pattern image when the SFINCS method is applied to the SHRINC method.

FIG. 18 is a graph simulating a change in intensity distribution due to defocus of a contact hole pattern image when σ = 0.8 and the SFINCS method in which the central portion of the coherence reducing member is shielded from light is applied.

FIG. 19 is a graph simulating a change in intensity distribution associated with defocusing of a contact hole pattern image when a conventional normal exposure method (circular light source image) of σ = 0.6 is applied.

FIG. 20 is a graph simulating a change in image intensity distribution due to defocus when two hole patterns are projected by the conventional FLEX method.

FIG. 21: Two hole patterns are replaced by a conventional Super
The graph which simulated the change of the image intensity distribution accompanying a defocus when it projects by FLEX method (1).

FIG. 22 shows two hole patterns in the conventional Super
The graph which simulated the change of the image intensity distribution accompanying a defocus when it projects by FLEX method (2).

FIG. 23 shows the distance between two hole patterns that are close to each other.
The graph which simulated the image intensity distribution at the time of best focus obtained by various exposure methods when it made it different from the case of 2.

FIG. 24 is a diagram showing a relationship between two-dimensionally distributed contact hole patterns and ringing generation positions.

FIG. 25 is a diagram showing a positional relationship between an exit surface shape of a fly-eye lens of an illumination system and a pupil plane in a projection lens.

FIG. 26 is a diagram showing the positional relationship between the fly-eye lens of the illumination system and the diaphragm used in the SHRINC method, as viewed in the pupil plane of the projection lens.

FIG. 27 is a ray diagram illustrating the principle of the SHRINC method.

[Explanation of symbols]

 1 light source 7 fly eye lens 8 illumination system diaphragm 14 condenser lens R reticle W wafer PL projection lens CCM interference reduction member PCM polarization state control member

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location G03F 9/02 H 9122-2H

Claims (5)

[Claims] 1. A illuminating means for irradiating a mask on which a fine pattern is formed with an illuminating light for exposure with a predetermined numerical aperture, and the light generated from the pattern of the mask is incident.
In a projection exposure apparatus including a projection optical system for image-projecting the image of the pattern on a sensitive substrate, a coherence factor determined by a ratio of a numerical aperture of the illumination light by the illumination unit and a numerical aperture of the projection optical system. (Σ value) is set to 0.5 or more, and it is arranged on the Fourier transform plane in the image forming optical path between the mask and the sensitive substrate, or in the vicinity thereof, and on the Fourier transform plane,
Or, in a circular area of a predetermined radius centered on the optical axis of the projection optical system on the surface in the vicinity thereof, or in a ring-shaped area of a predetermined width centered on the optical axis, and the distribution distributed in other areas. A projection exposure apparatus comprising a coherence reducing element for reducing coherence between image lights. 2. An illumination means for irradiating a mask on which a fine pattern is formed with illumination light for exposure, and the light generated from the pattern of the mask is incident to form an image of the pattern on a sensitive substrate. In a projection exposure apparatus provided with a projection optical system for projecting an image, the Fourier transform plane in the image forming optical path between the mask and the sensitive substrate, or a plane in the vicinity thereof, is arranged on the Fourier transform plane, or Imaging light distributed in a circular area having a predetermined radius centered on the optical axis of the projection optical system on a near surface, or in an annular area having a predetermined width centered on the optical axis, and in other areas. A coherence reducing element for reducing coherence between the light source image plane and the light source image plane in a substantially conjugate relationship with the Fourier transform plane of the projection optical system. Includes means to make the shape like a ring A projection optical device characterized by the above. 3. An illumination means for irradiating a mask on which a fine pattern is formed with an illumination light for exposure, and light generated from the pattern of the mask is incident to form an image of the pattern on a sensitive substrate. In a projection exposure apparatus provided with a projection optical system for projecting an image, the Fourier transform plane in the image forming optical path between the mask and the sensitive substrate, or a plane in the vicinity thereof, is arranged on the Fourier transform plane, or Imaging light distributed in a circular area having a predetermined radius centered on the optical axis of the projection optical system on a near surface, or in an annular area having a predetermined width centered on the optical axis, and in other areas. And a illuminating means having a light source image plane having a substantially conjugate relationship with a Fourier transform plane of the projection optical system, and the light source image planes are spaced apart from each other. A means for forming multiple light source images A projection optical device comprising: 4. A stage for moving the sensitive substrate and the projection optical system in the direction of the optical axis, and the stage is moved by a predetermined amount during projection exposure of the pattern of the mask onto the sensitive substrate, or The device according to any one of claims 1, 2 and 3, further comprising a driving member for vibrating. 5. An illumination means for irradiating a mask on which at least two fine hole patterns are formed at predetermined intervals with an illuminating light for exposure, and the light generated from the hole pattern of the mask is incident on the mask. In a projection exposure apparatus comprising a projection optical system for image-projecting an image of the hole pattern onto a sensitive substrate, a Fourier transform surface in an image forming optical path between the mask and the sensitive substrate, or a surface in the vicinity thereof. Between the imaging light distributed on the Fourier transform surface or on a surface in the vicinity thereof and distributed in a circular area having a predetermined radius centered on the optical axis of the projection optical system and an area outside the circular area. , Or on the Fourier transform surface, or on the surface in the vicinity thereof, the coherence between the imaging light distributed in each of the ring-shaped area of a predetermined width centered on the optical axis and the other area An interference reducing member for reducing the above; The illumination so that the value of the coherence function of the illumination light on the pattern surface of the mask is substantially zero or opposite in polarity to the position of one of the two hole patterns separated by the predetermined distance from the other position. A projection exposure apparatus comprising: a setting member for setting an incident angle range of light on a mask.