JPH1154411A - Projection optical system and projection aligner using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To excellently correct the birefringence of an optical element incorporated in a projection optical system and, to transfer patterns with high accuracy, by incorporating a means which corrects the birefringence of the optical element in the optical system. SOLUTION: A birefringence correcting member 8 is incorporated in an optical system so as to cancel phase variation. Since a material equivalent to the optical glass used for lens elements 1-5 must be used for the member 8, and birefringence having a prescribed distribution must be caused through the optical glass, such a phenomenon as the structural birefringence is utilized. Namely, the phase difference between a polarized component in the direction parallel to the grooves of a diffraction grating and the polarized component in the direction perpendicular to the groove can be set at an arbitrary value, by using a fine diffraction grating indicating the structural birefringence and appropriately selecting the duty ratio of the grating and the depths of the grooves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a semiconductor device, CC
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection optical system for manufacturing a device such as a liquid crystal device, a projection exposure apparatus using the same, and a method for manufacturing a device using the same, and in particular, a projection exposure apparatus of a step-and-repeat method or a step-and-scan method. The present invention is suitable for a projection exposure apparatus that obtains a high-resolution pattern by correcting the influence of birefringence of an optical element (glass material) constituting a projection optical system in a (stepper).

[0002]

2. Description of the Related Art Recently, high integration of semiconductor elements such as DRAMs and CPUs has been remarkable, and a circuit pattern having a size of 0.25 μm or less is required for the most advanced elements (devices). As an apparatus capable of forming such a fine pattern with high accuracy, a so-called stepper is widely used. In a stepper, a fine circuit pattern is formed on a reticle by illuminating a pattern on the reticle with short-wavelength light in the ultraviolet region and reducing and projecting it on a semiconductor wafer such as silicon via a projection optical system. ing.

At this time, in order to transfer a pattern on a reticle with high accuracy, various severe conditions are imposed on a projection optical system. Since the pattern size that the projection optical system can resolve is inversely proportional to NA (numerical aperture),
A design for further increasing the NA is required. Further, it is necessary that the aberration is highly corrected in the entire region corresponding to the area of the semiconductor chip.

[0004] Such a design is realized using a high-speed computer and dedicated design software. When manufacturing the projection optical system, one piece of the projection optical system
Of course, it is necessary to process the lenses with high precision according to the design values, but it is also necessary to pay close attention to the glass material used. Since the refractive index of the glass material is deeply related to the imaging characteristics of the projection optical system, its uniformity is very strictly controlled and is usually suppressed to the order of 10 ^-6 or less. Further, it is known that the birefringence of the glass material also has a significant effect on the image forming characteristics, so that its size needs to be suppressed to about 2 nm / cm.

However, in a glass material for a projection optical system having a diameter of up to 200 mm, it is very difficult to control such a highly accurate birefringence uniformly over the entire surface. This usually causes some birefringence.

The first reason is attributable to the manufacturing process of the glass material. At present, quartz glass is widely used as a glass material for a lens element for light in the ultraviolet region, and therefore, the following description will be focused on quartz glass. Unlike optical crystals and the like, quartz glass used as a glass material has no directionality in its structure, and therefore does not generate birefringence in an ideal state.

However, in quartz glass, birefringence, which is considered to be caused by residual stress due to impurities, thermal history, and the like, is experimentally observed. In the production of high quality quartz glass for lithography, the direct method (Di-
rectMethod), VAD (vapor axial deposition) method,
Sol-gel method, plasma burner (plasmabur)
ner) method, etc., but it is difficult to suppress the contamination of impurities to a negligible level with the current technology in any method.

Further, when the quartz glass formed in a high temperature state is cooled, the stress generated by the difference in cooling between the surface and the center, that is, the stress due to the heat history, is alleviated to some extent by heat treatment such as annealing. Although it can be done, it is difficult in principle to make it completely zero.

Next, a process of manufacturing a lens element used in a projection optical system at the time of lithography will be described with reference to FIG. First, quartz glass ingot 100
Are formed in a rotationally symmetric shape, and are cut to a required thickness to obtain a disk-shaped member 101. Since the production of the ingot 100 is always performed symmetrically with respect to the central axis 100a, the distribution of impurities remaining in the member 101 and the distribution of stress due to thermal history naturally appear symmetrically with respect to the central axis 101a. Finally, the member 101 is cut and polished to form the lens element 102.

Here, the distortion that appears when impurities are mixed in the ingot 100 will be described. FIG. 25 shows a cut surface of the ingot 100, and it is assumed that the impurity concentration is high in the peripheral hatch portion 103. Ingot 100 is heated during the annealing process. When heat is applied, the internal stress becomes almost completely zero. By slowly cooling from that state, a material having zero internal stress is produced ideally even at room temperature. However, when impurities are mixed, the coefficient of thermal expansion of the material changes. If the coefficient of thermal expansion is increased by the inclusion of impurities, the part naturally contracts more in the cooling process.

[0011] For this reason, what has no stress in the heated state tends to shrink more in the peripheral portion by lowering the temperature. Focusing on the central part of the glass material through which the light flux passes,
Compression shown by an arrow in FIG. 25 is received from the peripheral portion, and internal stress is generated. Internal stress causes birefringence.

The second reason is that the quartz glass is changed over time when used in a stepper. It is known that when a quartz glass is irradiated with light from a short wavelength light source such as a KrF or ArF laser, a phenomenon called compaction occurs. Although a detailed description of the generation process is omitted, the observed phenomenon is that the refractive index of the portion where the light flux has passed increases and the volume shrinks.

In FIG. 26, for a disc-shaped glass material 110,
When the laser beam is applied to the shaded region 111, the volume of that portion tends to shrink. Of course, the peripheral portion not irradiated with the laser beam is not affected by the compaction. Therefore, as a whole, the central portion tries to contract and the peripheral portion tries to prevent the contraction.

Therefore, in the equilibrium state, if attention is paid to the central portion of the glass material through which the light beam passes, a pulling force shown by an arrow in FIG. 27 is received from the peripheral portion, and internal stress is generated. . Internal stress causes birefringence. The above phenomenon also occurs in the projection optical system of the stepper. Since the occurrence of compaction is particularly remarkable with respect to the ArF laser light, it is feared that it will become a serious problem in practical use of a projection exposure apparatus using the ArF laser light as a light source in the future.

[0015]

As described above,
It is practically difficult to completely suppress the birefringence generated in the glass material to zero. On the other hand, the requirements for birefringence in projection optical systems for steppers are becoming more and more severe.
In order to realize a higher performance projection optical system, the number of lens elements constituting the projection optical system tends to increase, and the total thickness of the glass material increases. Therefore, even if the amount of birefringence per unit length is suppressed to the above-mentioned value (about 2 nm / cm), the total amount of birefringence is not negligible. Further, the fact that the wavelength for the exposure light source is becoming shorter and shorter also works in the direction of increasing the influence of birefringence.

Specifically, i used in a projection exposure apparatus
A comparison is made between a linear light source (wavelength 365 nm) and an ArF laser light source (wavelength 193 nm). For example, 100
If the birefringence of nm is present, this corresponds to a wavefront aberration of 100/365 = 0.27 for an i-line with a wavelength of 365 nm, but is 100 for an ArF laser light source with a wavelength of 193 nm.
/ 193 = 0.52 Equivalent to the wavefront aberration for the wavelength, and it can be seen that the influence on the imaging characteristics increases as the wavelength becomes shorter, even if the birefringence of the same magnitude is assumed.

With respect to the optical glass material having birefringence symmetrical with respect to the center, it is possible to reduce the adverse effect on the optical characteristics to some extent by using a glass material having a different birefringence amount for each lens element and optimizing the combination. Although disclosed in Japanese Unexamined Patent Publication No. Hei 8-107060, it is no longer possible to meet the demand for higher precision of the projection optical system with such a concept. For this reason, it is necessary to cancel the birefringence itself of the glass material by some means.

According to the present invention, by providing a birefringence correcting member for correcting an appropriately set birefringence in the projection optical system, the birefringence of the projection optical system and the birefringence generated in the process of performing projection exposure are provided. It is an object of the present invention to provide a projection optical system capable of satisfactorily correcting refraction and transferring a pattern with high precision, a projection exposure apparatus using the same, and a method for manufacturing a device using the same.

[0019]

According to the present invention, there is provided a projection optical system comprising:
(1-1) In a projection optical system that projects a pattern of a first object onto a second object, the projection optical system has a birefringence correction unit that corrects birefringence of an optical element included therein. It is characterized by:

In particular, (1-1-1) the birefringence correction means is composed of one or more optical members having a predetermined structural birefringence.

(1-1-2) The one or more optical members have a distribution obtained by adding a distribution of structural birefringence generated thereby cancels birefringence generated from an optical element constituting the projection optical system. It is set as follows.

(1-1-3) The one or more optical members generate a structural birefringence by using a diffraction grating having a period shorter than the wavelength used.

(1-1-4) The diffraction grating is provided on a surface of an optical element included in the projection optical system.

(1-1-5) The birefringence correction means comprises one or a plurality of optical members having a predetermined stress distribution.

(1-1-6) The one or more optical members are:
A distribution obtained by adding a distribution of stress generated thereby is set so as to cancel birefringence generated from an optical element constituting the projection optical system. And so on.

According to the projection exposure apparatus of the present invention, (2-1) a pattern on the first object plane illuminated by the light beam from the illumination system
The projection optical system according to 1) is characterized in that the projection exposure is performed on the second object plane.

(2-2) The pattern on the first object plane is illuminated with the light beam from the slit opening to form the pattern on the first object plane.
-1) a speed ratio of the first object and the movable stage on the second object surface mounted on the movable stage by the projection optical system in the short direction of the slit opening corresponding to the projection magnification of the projection optical system; The projection exposure is performed while scanning in synchronization with.

The method for manufacturing a device according to the present invention includes the step of (3-1) printing a device pattern on a substrate using the projection exposure apparatus of the constitution (2-1) or (2-2). And

[0029]

FIG. 1 is a sectional view of a main part of a projection optical system according to the present invention. This embodiment is applicable to a step-and-repeat method or a step-and-scan method. In the figure, PL denotes a projection optical system, which is usually constituted by several tens of optical elements whose aberrations have been corrected with high precision, but is simplified and represented by lens elements 1 to 5. .

Here, the lens elements 1 to 5 are formed by cutting and polishing quartz glass. Details of a configuration in which the projection optical system PL is actually mounted on a stepper will be described later. 6 is a reticle, and 7 is a wafer. The pattern on the reticle 6 is reduced and projected onto the wafer 7 by the projection optical system PL by the step-and-repeat method or the step-and-scan method.

In the drawing, reference numeral 8 denotes a birefringence correcting member according to the present invention, and the details of its operation will be described later.

As described above, it is difficult to completely suppress the occurrence of distortion symmetrical with respect to the central axis in the manufacturing process of the quartz glass used as the material of the lens elements 1 to 5. Alternatively, when used together with a short-wavelength light source such as an ArF laser, distortion occurs due to volume shrinkage due to compaction. Therefore, the effect when such distortion occurs in the glass material will be described. First, the stress generated by the distortion will be described with reference to FIG.

In FIG. 2, reference numeral 10 denotes a disk cut out from an ingot of quartz glass with a predetermined thickness h, which is a glass material before being processed into a lens element. Reference numeral 11 denotes the center axis of the disk 10. Also, x as in 12,
Define the y and z coordinate axes. In this case, since the stress in the direction (z-direction) along the central axis 11 can be ignored, the radial stress σ _{r at} the point P represented by the polar coordinates (r, θ) in the xy plane as shown in FIG. Attention is paid only to the stress σ _θ in the circumferential direction. Considering the balance of the force in the radial direction with respect to the minute region 13 indicated by oblique lines near the point P, -σ _r · rdθ
_{+ (Σ r + dσ r)} (r + dr) dθ-σ θ dθ · d
A relationship of r = 0 is obtained, and a small amount of a higher order is omitted to summarize the result. σ _θ −σ _r = r (dσ _r / dr) ‥‥ (1)
Is obtained.

Since the strain remaining in the glass material 10 changes in the radial direction, the derivative of the stress σ _{r with} the radius r is not generally zero. Therefore, the right side of the equation (1) has a finite non-zero value when r ≠ 0 (other than on the center axis), which means that the stress σ _{r in the} radial direction _r and the circumferential direction other than on the center axis 11 This means that the stress σ _θ has different values.

At this time, the effect observed optically is shown in FIG.
This will be described with reference to FIG. As shown in FIG. 4, the point P (r,
It is assumed that a light beam linearly polarized in the y direction at a wavelength λ enters the position θ). Here, the polarization direction of the linearly polarized light is indicated by an arrow 14. When the incident light is transmitted through the disk 10, a different refractive index is sensed for the polarization component 15 in the radial direction and the polarization component 16 in the circumferential direction. As a result, as shown in FIG. 5, after transmitting through the disk 10, a phase difference Φ occurs between the two polarization components, and the polarization state of the light beam is converted from linearly polarized light to elliptically polarized light. Here, the phase difference Φ is calculated by using the stresses σ _r and σ _θ as follows: Φ (r) = (2π / λ) C · h ｛σ _θ (r) −σ _r
(R)｝ It is expressed as (2).

C is called a photoelastic constant and is a value specific to a substance. When the light beam passes through the disk-shaped glass material 10 in this way,
The polarization state changes. The effect of each glass material is of course insignificant, but after passing through several tens of elements, it has an insignificant adverse effect on the imaging characteristics of the projection optical system. In an actual projection optical system,
Considering the influence of equation (2) for each element, it is known that the total amount of phase change due to birefringence in the entire projection optical system is as shown in FIG.

Here, the horizontal axis is the radius r of the lens element.
Is represented by a pupil coordinate ρ of the optical system. The pupil coordinates will be described with reference to FIG. 17 and 18 are lens elements in the figure. Focusing on the light beam 19 passing through the lens elements 17, 18, the radius r ₁ measured from the center axis (optical axis) 20 in the lens element 17 and the position from the center axis 20 in the lens element 18 are specified to specify the position. A plurality of parameters such as the measured radius r ₂ are required, which is inconvenient.

Therefore, by focusing on the pupil position 21 of the entire optical system and designating the light beam 19 with the height pupil coordinate ρ through which the light beam 19 passes, the characteristics of the optical system can be represented by one parameter. Will be. Therefore, assuming that the position of the light beam transmitted through the optical system is defined using ρ as the pupil coordinates, the maximum value is ρ
_Assume that it is ₀ .

The results shown in FIG. 6 are measured experimentally by means of a phase modulation method or the like using an actually assembled optical system. However, if accuracy is sacrificed to some extent, it is also possible to calculate by simulation. The phase modulation method is described in detail in Echihiro Mochida: Optical Technology Contact vol. 27. No. 3 (1989). For this reason, although the description here is omitted, the sensitivity is extremely high, and the value of the refractive index difference Δn due to birefringence is 1
It has the advantage that the measurement can be performed with an accuracy of ^{0-8 and} the ^fast axis and the slow axis can be determined simultaneously.

When the fast axis and the slow axis are known, the sign of Φ (ρ) in FIG. 6 can be directly determined. In any case, what is meant in FIG. 6 is the center of the optical system (ρ = 0)
The amount of phase change due to birefringence is zero for a light beam that passes through, but the amount of phase change due to birefringence reaches π / 4 for a light beam that passes through the periphery (ρ = ρ ₀ ). That is.

Although the detailed description of the effect on the imaging characteristics using the theoretical formula is omitted, as a phenomenon, astigmatism having a magnitude of about λ / 4 appears in the optical system. The aberration allowed in the projection optical system for the stepper is λ
/ 100, and large aberrations as described above cannot be tolerated.

In the present invention, the phase change as shown in FIG. 6 is canceled by using the birefringence correcting member 8 in the optical system in FIG.
It is clear that a member having a birefringence having the opposite sign to the optical axis symmetry can be used to cancel the birefringence generated symmetrically to the optical axis. However, the magnitude of the amount of birefringence must be about the same as the amount of birefringence generated in the entire projection optical system PL.

Here, a specific configuration of the birefringence correction member 8 will be described. As a material of the birefringence correction member,
Due to the requirement that the lens must be transparent to exposure light and have sufficient durability,
5 must be equivalent to the optical glass used. In order to generate a birefringence having a predetermined distribution for such an optical glass, a phenomenon called structural birefringence is used here.

First, structural birefringence will be described with reference to FIG. In the figure, reference numeral 25 denotes a phase type diffraction grating formed on the surface of the optical glass. As shown in the enlarged view on the right side, the diffraction grating 25 has a period: b, a depth: d, and a width of a portion of the optical glass forming the fine grating is a. Here, the duty ratio t is used for further discussion.
Is defined as t = a / b. Reference numeral 26 denotes an incident light beam (wavelength: λ) incident on the diffraction grating 25,
Reference numeral 27 denotes an emitted light beam emitted from the diffraction grating.

Reference numeral 28 denotes a polarization component 29 of the incident light beam 26 in a direction parallel to the groove of the diffraction grating 25.
Represents the polarization component in the direction perpendicular to the groove. Similarly, reference numeral 30 denotes a polarization component of the emitted light 27 in a direction parallel to the groove of the diffraction grating 25, and reference numeral 31 denotes a polarization component of a direction perpendicular to the groove of the diffraction grating 25.

Here, the period b of the diffraction grating 25 is required to be "b is equal to or smaller than λ" in order to prevent diffracted light other than the zero-order light from being emitted as the emitted light 27.

In FIG. 8, the incident light 26 has a polarization component.
There was no phase difference between 28 and 29.
The transmission of 25 indicates that a phase difference Ψ is generated between the polarization components 30 and 31. Therefore, the incident light 26
Is linearly polarized light, the emitted light 27 can be understood to be converted to elliptically polarized light. Such a phenomenon is called structural birefringence and has been known for a long time in the field of optics.

For example, “M. Born and E. Wolf: Princi
ples of Optics, 1st ed. (Pergamon Press, New Yor
k., 1959) pp.705-708, Aoyama et al .: "Birefringent Elements Using Fine Diffraction Gratings and Their Applications", Optics Vol. 21, No. 5, p.
p.269-274 (1992) "and other detailed explanations. Hereinafter, those contents will be summarized and described.

First, a fine diffraction grating 25 as shown in FIG.
Has a different refractive index depending on the polarization direction of the incident light flux 26. Refractive index n _II where polarization of the incident light 26 is parallel to the grooves of the diffraction grating 25, polarization of the incident light 26 is represented by the following respective vertical n _⊥ the grooves of the diffraction grating 25.

[0050]

(Equation 1) Here, t is the duty ratio defined above, n ₁ is the refractive index of the member constituting the diffraction grating 25, and n ₂ is the refractive index of the medium on which the light beam enters. n ₁ = 1.6, n ₂ =
FIG. 9 shows the result of calculating the dependence of n _II and n に 対_する on t as 1.0. When the depth of the groove of the diffraction grating 25 is d, the phase difference 現 れ る appearing between the polarization component parallel to the groove of the diffraction grating 25 and the polarization component perpendicular to the groove of the diffraction grating is

[0051]

(Equation 2) Given by

From the equations (3) to (5), the duty ratio t
It can be seen that the phase difference Ψ can be set to an arbitrary value by appropriately selecting the groove depth d.

Next, assuming that the birefringence correcting member 8 is inserted into the pupil position 21 of the projection optical system PL shown in FIG. 7, a specific configuration will be described. FIG. 10 is used for the description.

FIG. 10 shows that, in the projection optical system shown in FIG.
5 is for explaining the relation of the phase difference between the polarization component in the radial direction and the polarization component in the circumferential direction when transmitting through the birefringence correction member 5 and the birefringence correction member 8. Assuming that birefringence symmetrical with respect to the optical axis in a glass material, a phase difference occurs between a radially polarized light component and a circumferentially polarized light component of incident light, which will be described with reference to FIGS. 4 and 5. As you did.

In FIG. 10, reference numerals 41 to 44 denote polarization components in the radial direction, and reference numerals 45 to 48 denote polarization components in the circumferential direction. The phase difference between the two is naturally zero before the light beam 40 enters the lens element 1.

At this time, the projection optical system as a whole has a birefringence generated in each of the lens elements 1 to 5,
Assume that a phase difference Φ (ρ) shown in FIG. 6 occurs as a function of the pupil radius coordinate ρ. Further, Φ (ρ) is changed to Φ (ρ) = Φ ₁
Decompose according to (ρ) + Φ ₂ (ρ) and phase difference Φ ₁ (ρ)
Is a phase difference generated by the lens elements 1 to 3, and a phase difference Φ ₂ (ρ) is a phase difference generated by the lens elements 4 to 5.

In the birefringence correction member 8, it is assumed that a phase difference Ψ (ρ) between the polarization components in the radial direction and the circumferential direction occurs as a function of the pupil coordinate ρ. Then, in the light beam immediately before entering the birefringence correction member 8, the phase difference between the radial and circumferential polarization components is given by Φ ₁ (ρ), and the light beam immediately after passing through the birefringence correction member 8 is given. The phase difference is Φ ₁ (ρ) +
Ψ (ρ), and the phase difference after passing through the lens elements 4 and 5 is Φ ₁ (ρ) + Φ ₂ (ρ) + Ψ (ρ) = Φ (ρ)
+ Ψ (ρ) ‥‥ (6).

The essence of the present invention is to insert a birefringent member capable of giving a phase difference function Ψ (ρ) such that the equation (6) becomes zero in the optical path.

When considered in conjunction with FIG. 6, it is clear that the phase difference function Ψ (ρ) where equation (6) is zero is as shown in FIG. That is, the phase difference Φ (ρ) has the opposite sign and the same absolute value.

As described above, by using the fine diffraction grating 25 exhibiting structural birefringence and appropriately selecting the duty ratio t and the groove depth d, the direction parallel to the grooves of the diffraction grating can be obtained. And the phase difference between the polarized light component in the direction perpendicular to the groove of the diffraction grating and the polarized light component can be set to an arbitrary value.

Therefore, a fine diffraction grating is formed on the surface of the birefringence correction member 8 so as to be symmetric with respect to the optical axis. In this case, a configuration in which the diffraction grating 25 is arranged concentrically with respect to the optical axis as shown in FIG.
As shown in (1), a configuration in which the diffraction grating 25 is arranged radially with respect to the optical axis is possible.

The period of the fine diffraction grating required to cause structural birefringence only requires the condition that the wavelength is equal to or less than the wavelength λ as described above. become. Therefore, it is desirable that the period of the diffraction grating falls within the range of λ / 3 to λ. Therefore, in the configuration in which the diffraction gratings are arranged radially with respect to the optical axis, the radial direction is divided into a plurality of regions as shown in FIG. 13 so that the period inside each region falls within the above range.

The difference in function between the structures shown in FIGS. 12 and 13 is explained as follows. In FIG. 12, the light beam incident on the point P between the radial polarization component 50 and the circumferential polarization component 51 is transmitted through the member 8 so that the phase of the radial polarization component 50 is The phase of the polarization component 51 in the direction can be relatively delayed. On the other hand, if the same is considered in the structure of FIG. 13, the phase of the polarization component 53 in the circumferential direction can be advanced relatively to the phase of the polarization component 52 in the radial direction. That is, both can be used properly depending on the sign of birefringence generated in the projection optical system. Here, in order to generate the phase difference Ψ (ρ) shown in FIG. 11, the structure shown in FIG. 13 may be applied.

The amount of phase correction must be changed in the radial direction. For that purpose, the duty ratio of the fine diffraction grating or the depth of the groove may be changed in the radial direction. However, since it is extremely difficult to continuously change the duty ratio in manufacturing, a configuration in which the depth of the groove is changed will be described with reference to FIG. The amount of phase correction is zero on the optical axis of the optical system as is clear from FIG. Therefore, as shown in FIG. 14, the depth of the groove of the fine diffraction grating may be zero near the central axis and deeper toward the periphery.

The position where the birefringence correcting member 8 is inserted is preferably near the pupil position of the projection optical system.
It is not necessarily limited to that. Further, in the present embodiment, the description has been given using a parallel plate as the birefringence correction member, but the shape is not limited to the parallel plate, and the shape of the convex surface or the concave surface like a normal lens element is used. You may have it.

FIG. 15A shows an example in which a fine diffraction grating is formed on the convex surface concentrically with respect to the central axis.
(B) is an example in which a fine diffraction grating is formed on a convex surface radially with respect to a central axis. Furthermore, in the present embodiment, the case has been described where the birefringence correction member is formed of one optical element, but a plurality of members may share the correction amount of birefringence.

At this time, it is possible to correct a larger birefringence or a birefringence having a more complicated distribution, which is generated in the projection optical system.

FIG. 16 is a schematic view of a main part of a second embodiment in which the projection optical system of the present invention is mounted on a stepper. In the figure
Reference numeral 60 denotes a reticle on which a circuit pattern is drawn, 61 denotes a projection optical system according to the present invention, and 62 denotes a wafer to which the circuit pattern is transferred. The illumination light flux 63 from the illumination system 67 is a reticle
The illumination area 64 on the area 60 is illuminated, and the circuit pattern drawn on the area 64 is reduced and transferred to the exposure area 65 on the wafer 62 via the projection optical system 61. For steppers,
After the pattern on the reticle 60 is collectively reduced and transferred onto the wafer 62, the wafer 62 is repeatedly stepped by a predetermined amount and exposed again.

In the figure, reference numeral 66 denotes a birefringence correction member, which is detachable and replaceable so that the correction amount can be adjusted according to the birefringence amount of the projection optical system 61. It is characteristic.

FIG. 17 shows the projection optical system according to the present invention in a step &
FIG. 13 is a schematic diagram of a main part of a third embodiment mounted on a scan type exposure apparatus. In the figure, 70 is a reticle on which a circuit pattern is drawn, 71 is a projection optical system, and 72 is a wafer on which the circuit pattern is transferred. Illumination beam 73 from illumination system 67
Illuminates an illumination area 74 on the reticle 70, and the circuit pattern drawn in the area 74 is transmitted through the projection optical system 71,
The image is reduced and transferred to an exposure area 75 on the wafer 72. Step &
The scanning type exposure apparatus differs from the conventional stepper in the following points.

In the stepper, the pattern on the reticle 70 is collectively reduced and transferred onto the wafer 72.
In the step-and-scan type exposure apparatus, the circuit pattern is illuminated by the slit-shaped illumination area 74, and the reticle 70 and the wafer 72 are scanned in synchronization with each other.
The entire upper circuit pattern is reduced and transferred.

When the coordinate system is represented by 76, the scan direction 77 of the reticle 70 is the negative direction of the x-axis, and the scan direction of the wafer 72 is
78 is the positive direction of the x-axis. In the figure, reference numeral 79 denotes a birefringence correction member, which is characterized in that it can be removed and replaced like a stepper.

In the step & scan type exposure apparatus, since the illumination area 74 has a slit shape, the influence of compaction when illuminating with, for example, ArF laser light does not appear symmetrically with respect to the optical axis.

Next, the light transmission area of the lens element in the projection optical system 71 will be described with reference to FIG. In the figure, reference numeral 80 denotes a representative lens element, which is represented in the xy plane (81 is a coordinate axis).

Here, corresponding to the shape of the illumination area 74 shown in FIG. 17, also in the lens element 80, the area through which the light beam passes has a shape elongated in the y-axis direction as shown by oblique lines 82. Therefore, distortion due to compaction also occurs according to the shape. The resulting birefringence of the optical system is, of course, asymmetric with respect to the optical axis.

When expressed using the same pupil coordinates as those used in FIG. 6, the amount of phase change due to birefringence is as shown in FIG. That is, they have different distributions in the x-axis direction and the y-axis direction. In order to correct such a distribution of birefringence, it is possible to cope by making the distribution of the groove depth described in FIG. 14 different in the x-axis direction and the y-axis direction.

Next, Embodiment 2 of the birefringent member according to the present invention
Will be described. In the first embodiment shown in FIGS. 1 to 8, as a specific configuration of the birefringence correction member 8, the material of the birefringence correction member must be transparent to exposure light and have sufficient durability. From the request, use the same as the optical glass used for the lens elements 1 to 5,
The case where a phenomenon called structural birefringence was used to generate birefringence was shown.

On the other hand, as described above, in the present embodiment, as compared with the first embodiment, the distortion remains during the production of the optical glass, and the birefringence appears due to the influence as described above. The optical glass is positively strained to generate desired birefringence. This is the only difference from the first embodiment, and the other configuration and its usage are basically the same.

In order to leave distortion in the optical glass,
This is achieved by precisely controlling the temperature during the annealing process. Generally speaking, annealing is performed to remove distortion remaining in the optical glass. However, in producing the birefringence correction member according to the present invention, the process of annealing is used to generate residual distortion.

The annealing process will be described with reference to FIG. In the figure, reference numeral 130 denotes an optical member serving as a source of the birefringence correction member 8. The optical member 130 has a disk shape, and a position on the member is designated by a distance r from the central axis 131.

FIG. 20A shows a state before heating in the annealing process, and FIG. 20B shows a state in which heat is uniformly applied to the entire optical member 130. In this state, there is almost no stress distribution inside the optical member 130, but a large stress distribution can be generated in the cooling process shown in FIGS. 20C and 20D. In FIG. 20C, a large residual stress is generated inside the optical member 130 after the optical member 130 has returned to room temperature by blowing gas near the center and rapidly cooling. FIG. 20E shows the stress distribution.

The stress σ _{r in the} radial direction r and the stress σ in the circumferential direction
_{Although θ} is shown as a function of the radius r, they coincide at the center, and it can be seen that the difference between the two increases as the radius r increases. When an object having such a stress difference is inserted into the optical path, a phase difference calculated from Expression (2) occurs.

Here, the stress distribution generated in the optical member is as follows.
The adjustment is made so as to cancel the phase difference due to the birefringence of the entire projection optical system shown in FIG. For that purpose, it is necessary to strictly control the temperature of the gas to be blown, the position to be blown, and the temperature after the gas is blown. For these, optimum conditions can be found by repeating experiments. As an example, as shown in FIG. 20 (D), a gas is blown to the peripheral portion to be rapidly cooled to obtain a stress distribution as shown in FIG. 20 (F).

As a method for generating a residual stress in the birefringence correcting member 8, the same effect can be realized by changing the impurity concentration in the optical member 130 in the radial direction instead of controlling the temperature distribution in the annealing process. It is possible.
Further, it is of course possible to impart a desired internal stress distribution to the disk-shaped glass material or the lens element by applying a mechanical pressure from the outside.

In the step-and-scan type exposure apparatus shown in FIG. 17, birefringence asymmetric with respect to the optical axis occurs in the projection optical system. A method of correcting asymmetric birefringence by using the birefringence correction plate of the present embodiment in such an exposure apparatus will be described with reference to FIG.

Here, as in the case described with reference to FIG.
The birefringence of the correction member is adjusted by controlling the temperature distribution during annealing. In FIG.
Indicates a state where heat is uniformly applied to the whole in the annealing process, and 164 indicates a state after cooling with different temperature distributions in the x direction and the y direction. In this state, the residual strain in the member has different distributions in the x direction and the y direction. By inserting such a member into the projection optical system, the birefringence generated asymmetrically with respect to the optical axis of the optical system. It compensates for the effects of gender.

Next, an embodiment of a method of manufacturing a semiconductor device using the above-described projection exposure apparatus will be described.

FIG. 22 shows a flow of manufacturing a semiconductor device (a semiconductor chip such as an IC or an LSI, or a liquid crystal panel or a CCD).

In step 1 (circuit design), the circuit of the semiconductor device is designed. Step 2 is a process for making a mask on the basis of the circuit pattern design.

In step 3 (wafer manufacture), a wafer is manufactured using a material such as silicon. Step 4
The (wafer process) is called a pre-process, and an actual circuit is formed on the wafer by lithography using the prepared mask and wafer.

The next step 5 (assembly) is called a post-process, and is a process of forming a semiconductor chip using the wafer produced in step 4, and includes an assembly process (dicing and bonding) and a packaging process (chip encapsulation). And the like.

In step 6 (inspection), inspections such as an operation confirmation test and a durability test of the semiconductor device manufactured in step 5 are performed. Through these steps, a semiconductor device is completed and shipped (step 7).

FIG. 23 shows a detailed flow of the wafer process. Step 11 (oxidation) oxidizes the wafer's surface. Step 12 (CVD) forms an insulating film on the wafer surface.

In step 13 (electrode formation), electrodes are formed on the wafer by vapor deposition. In step 14 (ion implantation), ions are implanted into the wafer. Step 15
In (resist processing), a photosensitive agent is applied to the wafer. Step 16 (exposure) uses the above-described exposure apparatus to print and expose the circuit pattern of the mask onto the wafer.

In step 17 (development), the exposed wafer is developed. In step 18 (etching), portions other than the developed resist are removed. In step 19 (resist stripping), the resist that has become unnecessary after the etching is removed. By repeating these steps, multiple circuit patterns are formed on the wafer.

By using the manufacturing method of this embodiment, it is possible to easily manufacture a highly integrated semiconductor device which has conventionally been difficult to manufacture.

[0097]

As described above, according to the present invention, by providing a birefringence correction member for correcting an appropriately set birefringence in a projection optical system, the birefringence and projection exposure of the projection optical system are provided. Optical system capable of favorably correcting the birefringence generated in the process of performing the above and transferring a pattern with high precision, a projection exposure apparatus using the same, and a method for manufacturing a device using the same. .

In particular, according to the present invention, even when the glass material constituting the projection optical system has birefringence, it is possible to correct the effect and transfer a pattern with high accuracy. In addition, effects such as the effect of distortion due to compaction generated by the glass material absorbing ArF laser light or the like can be corrected.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a cross section of a projection optical system according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining the effect of residual distortion of an optical element.

FIG. 3 is a diagram for explaining the effect of residual distortion of an optical element.

FIG. 4 is a diagram for explaining the influence of birefringence of an optical element.

FIG. 5 is a diagram for explaining the influence of birefringence of an optical element.

FIG. 6 is a view for explaining a phase difference generated by the birefringence of the glass material according to the present invention.

FIG. 7 is a diagram for explaining pupil coordinates of an optical system;

FIG. 8 is a view for explaining structural birefringence of Embodiment 1 of the birefringence correction means according to the present invention.

FIG. 9 is a view for explaining a difference in a refractive index depending on the direction of polarized light.

FIG. 10 is a diagram for explaining a phase change due to birefringence according to the present invention.

FIG. 11 is a distribution of a phase change amount generated by a birefringence correction member.

FIG. 12 is an explanatory diagram of a birefringence correction member using structural birefringence according to the present invention.

FIG. 13 is an explanatory diagram of a birefringence correction member using structural birefringence according to the present invention.

FIG. 14 is a view for explaining the depth distribution of the fine diffraction grating according to the present invention.

FIG. 15 shows a fine diffraction grating formed on a convex surface according to the present invention.

FIG. 16 is a schematic view of a main part of a stepper according to a second embodiment of the present invention.

FIG. 17 is a schematic diagram of a main part of a step & scan type projection exposure apparatus according to a third embodiment of the present invention.

FIG. 18 is a diagram for explaining an asymmetric distortion distribution generated in the step & scan type projection exposure apparatus according to the third embodiment of the present invention.

FIG. 19 is a diagram illustrating an asymmetric distortion distribution generated in the step & scan type exposure apparatus according to the third embodiment of the present invention.

FIG. 20 is a schematic diagram of a main part of a birefringence correction unit according to a second embodiment of the present invention.

FIG. 21 is an explanatory diagram of a birefringence correcting unit according to a second embodiment of the present invention.

FIG. 22 is a flowchart of a device manufacturing method according to the present invention.

FIG. 23 is a flowchart of a device manufacturing method of the present invention.

FIG. 24 is a view for explaining a manufacturing process of the lens element.

FIG. 25 is a diagram for describing internal strain generated by the influence of impurities.

FIG. 26 is a diagram for explaining occurrence of compaction.

FIG. 27 is a diagram for describing internal distortion caused by the influence of compaction.

[Explanation of symbols]

 1 to 5 optical element 6 first object (reticle) 7 second object (wafer) 8, 164 birefringence correction means 10 quartz glass 11 central axis 25 diffraction grating 130 optical member PL projection optical system

Claims (10)

[Claims] 1. A projection optical system for projecting a pattern of a first object onto a second object, wherein the projection optical system has a birefringence correction unit for correcting birefringence of an optical element included therein. A projection optical system, characterized in that: 2. The projection optical system according to claim 1, wherein said birefringence correction means comprises one or a plurality of optical members having predetermined structural birefringence. 3. The one or more optical members are configured such that a distribution obtained by adding a distribution of structural birefringence generated thereby cancels birefringence generated from optical elements constituting the projection optical system. 3. The projection optical system according to claim 2, wherein: 4. The projection optical system according to claim 2, wherein the one or more optical members generate a structural birefringence using a diffraction grating having a period smaller than a wavelength used. . 5. The projection optical system according to claim 4, wherein said diffraction grating is provided on a surface of an optical element included in said projection optical system. 6. The projection optical system according to claim 1, wherein said birefringence correction means comprises one or a plurality of optical members having a predetermined stress distribution. 7. The one or more optical members are set such that a distribution obtained by applying a stress distribution generated by the one or more optical members cancels a birefringence generated from an optical element constituting the projection optical system. The projection optical system according to claim 6, wherein: 8. A projection optical system according to claim 1, wherein a pattern on the first object plane illuminated with a light beam from the illumination system is projected and exposed on the second object plane. Characteristic projection exposure apparatus. 9. A pattern on the first object surface is illuminated with a light beam from the slit opening, and the pattern on the first object surface is mounted on the movable stage by the projection optical system according to claim 1. Projecting and exposing while scanning the first object and the movable stage in the short direction of the slit opening at a speed ratio corresponding to the projection magnification of the projection optical system on the second object surface. A projection exposure apparatus. 10. A device manufacturing method comprising printing a device pattern on a substrate using the projection exposure apparatus according to claim 1. Description: