JPH0590128A - Aligner - Google Patents

Abstract

PURPOSE:To obtain an aligner capable of obtaining a high contrast image of a fine pattern. CONSTITUTION:An illumination optical system 4 is preferably constituted as ring belt illumination wherein the central part of a light source is shielded, and transparently illuminates a photo mask 1 in which a pattern is formed, with exposure light having a specified wavelength. A projection optical system 2 is installed below the photo mask 1. On the pupil surface of the projection optical system 2, a polarization member 5 is arranged, which transmits only the light whose electric vector oscillates in the direction parallel to the sides of the pattern of the photo mask 1. Diffracted light generated by transparently illuminating the photo mask 1 is collected by the projection optical system 2, and converted into a TE polarization light wherein oscillation direction of the electric vector is uniform, by the polarization member 5, thereby forming a pattern image on an image surface 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus used for transferring an image of a circuit pattern formed on a photomask onto a wafer surface in a lithography process for manufacturing a semiconductor device.

[0002]

2. Description of the Related Art An exposure apparatus generally used in a lithography process for manufacturing a semiconductor device has a structure as shown in FIG. In the figure, a photomask 21
Are held horizontally so as to be orthogonal to the optical axis of the illumination optical system 24, and are transmitted and illuminated by exposure light having a predetermined wavelength emitted from the illumination optical system 24. The photomask 21, which has been widely used conventionally, has a structure in which a light-shielding pattern made of a metal such as chrome is formed on a transparent substrate, and when it is transmitted and illuminated, diffracted light corresponding to the pattern shape is generated. .. These diffracted lights are again collected on the image plane 23 by the projection optical system 22, whereby the pattern image of the photomask 21 is transferred onto the wafer surface held so as to match the image plane 23. At this time, since the projection optical system of the conventional exposure apparatus does not include a polarizing member, the light collected on the image plane 23 has no polarization characteristics, that is, TE polarized light (described later) and TM polarized light (described later). ) Is in the average state.

[0003]

By the way, the conventional exposure apparatus as described above has a problem that it cannot cope with the miniaturization of circuit patterns accompanying the high integration of semiconductor elements. Development of a technique capable of forming a contrast image is required. Under these circumstances, as a method of increasing the contrast of a pattern image, in recent years, projection exposure is performed by using a phase shift mask provided with a phase shift unit that changes the phase of transmitted light at a specific location of a light transmitting unit of a photomask. Various shift methods have been proposed.
For example, Japanese Patent Publication No. 62-50811 discloses a technique relating to a spatial frequency modulation type phase shift mask.
The phase shift method forms a pattern image by using information on the phase of light in addition to information on the amplitude of light, and uses a photomask consisting only of a light transmitting portion (bare surface portion of the substrate) and a light shielding portion. A certain degree of improvement in the imaging performance has been realized as compared with the method.

However, this phase shift method also has its own limit, and satisfactory high-contrast images have not been obtained for fine patterns. The present invention has been made in view of the above point, and by utilizing the third information other than the amplitude and phase of light, it is possible to realize high-resolution and high-contrast imaging performance, and the optical lithography technique It is an object of the present invention to provide an exposure apparatus capable of developing new developments of.

[0005]

An exposure apparatus of the present invention comprises a projection optical system for projecting a pattern on a photomask, and in order to achieve the above-mentioned object, the projection optical system has a substantially pupil plane. A polarizing member that transmits light whose electric vector oscillates in a direction parallel to the side of the pattern is arranged.

The polarizing member preferably used in the present invention is
Specifically, only the light whose electric vector oscillates in the tangential direction of the circle centered on the optical axis of the projection optical system is transmitted.

[0007]

The operation of the present invention will be described with reference to FIG. Figure 2
3 schematically shows the state of diffracted light in the vicinity of the image plane 23 of the exposure apparatus described in FIG. First, as shown in FIG.
This is a state called TE (transverse electric) polarized light, in which the vibration direction of the electric vector is light perpendicular to the incident surface (inner surface of the paper). On the other hand, FIG. 2B shows TM (transverse m
This is a state called polarized light, and the vibration direction of the magnetic vector is perpendicular to the incident surface, that is, the vibration direction of the electric vector is on the incident inner surface. In the conventional device in which the projection optical system does not include a polarizing member, the TE polarized light shown in FIG. 2A and the T polarized light shown in FIG.
Although an image is formed by light in an average state of M-polarized light, a photochemical reaction of a photosensitive material such as a photoresist proceeds by the action of an electric field of light which is an electromagnetic wave. It becomes a problem.

As can be seen by comparing FIGS. 2 (a) and 2 (b), in the case of TE polarization, the vibration directions of the electric vectors of the 0th order, ± 1st order ... They are aligned in the vertical direction, and the interference effect of diffracted light is maximized,
The image has high contrast. In the case of TM-polarized light, the vibration direction of the electric vector of diffracted light of different orders is shifted by an amount corresponding to the angle formed by the traveling directions of the diffracted lights, and the interference effect between the diffracted lights decreases, and It works to reduce the contrast.

In the present invention, since a polarizing member that transmits only the light whose electric vector oscillates in the direction parallel to the side of the pattern formed on the photomask is arranged at approximately the pupil position of the projection optical system, The non-polarized diffracted light generated by the photomask is a plane (incident surface) that forms the diffraction angle.
It is converted into TE polarized light having a vibrating plane orthogonal to, and an image with high contrast is obtained.

The arrangement direction of the actual circuit pattern formed on the photomask is various, and an isolated pattern such as a hole pattern is also included in addition to the line-and-space pattern repeated at a constant cycle. As the polarizing member used in (3), it is preferable to use a polarizing member that transmits only the light whose electric vector oscillates in the tangential direction of the circle centered on the optical axis of the projection optical system. If such a polarizing member is used, only light whose electric vector oscillates in the direction parallel to the sides of the pattern will always pass through the polarizing member, regardless of the orientation of the pattern.

Next, in order to make the explanation easier to understand, the photomask 21 is provided with a line-and-space pattern (a pattern in which light-shielding portions and light-transmitting portions are alternately repeated with the same width) extending in the direction perpendicular to the paper surface. Consider that the pattern image is formed by the 0th-order diffracted light and the ± 1st-order diffracted lights of the diffracted light from the photomask 21. In this case, the amplitude of the 0th-order diffracted light is 1/2, and the amplitude of the ± 1st-order diffracted light is 1 / π.

As shown in FIG. 2, x (horizontal direction of paper), y (vertical direction of paper), z (vertical direction of paper) coordinate axes are set, and the direction cosine of the 0th-order diffracted light is (0, 0, 1). ), ±
Letting the direction cosine of the first-order diffracted light be (± α, 0, γ), the wave motion (vector amount) of the _0th-order diffracted light and the ± first-order diffracted light is ψ ₀ , ψ
Assuming ± ₁ , the wave motion of each diffracted light in case of TE polarization is
It is represented by. In the formula, k is a constant (= 2π / λ).

[0013]

[Equation 1]

Waves ψ _{0 of} the 0th order diffracted light and ± 1st order diffracted light,
The wave field Ψ _TE that combines ψ ± ₁ is given by Equation 4, and the intensity distribution I
_TE (x, z) = | Ψ | ² is given by Equation 5.

[0015]

[Equation 2]

On the other hand, the waves of each diffracted light in the case of TM polarized light are represented by equations 6-8.

[0017]

[Equation 3]

Waves of the _{0th order} diffracted light and the ± 1st order diffracted light ψ ₀ ,
The wave field Ψ _TM obtained by combining ψ ± ₁ is given by Equation 9, and the intensity distribution I _TM (x, z) = | Ψ | ² is given by Equation 10.

[0019]

[Equation 4]

Now, consider the log slope value as an image evaluation index. The log slope value is a differential value when the logarithm of the intensity I at the boundary of light and dark in geometrical optics is taken, that is, a value of ∂log I / ∂x. The larger this value is, the higher the contrast of the image. From equations 5 and 10, the log slope values for TE polarized light and TM polarized light can be calculated. Assuming that the best focus plane is considered for the sake of simplicity, if Z = 0 is calculated, the log slope value LS _{TE for TE} polarized light is given by Equation 11, and the log slope value LS _{TM for} TM polarized light is given by Equation 12 Becomes The log slope value in the non-polarized state is the average state of TE polarized light and TM polarized light.

[0021]

[Equation 5]

Considering the term multiplied by 4λ / α in the equation 12, since the numerator is smaller than 1 and the denominator is larger than 1, it is understood that the value of the equation 12 is smaller than the value of the equation 11 as a whole. To be done. This means that imaging with TE polarized light is T
It shows that it has a higher log slope value than the image with M polarization. Further, since α corresponds to the diffraction angle, the superiority of the TE polarized light increases as the fine pattern has a larger diffraction angle.

Further, since the non-polarized state is the average state of TE polarized light and TM polarized light, the image formation by TE polarized light is naturally
It has a higher log slope value than an image formed by non-polarized light and achieves a so-called high-contrast image. Moreover, since the polarization and phase of light are independent information,
A phase shift mask can be used in the exposure apparatus of the present invention, and it is possible to further improve the imaging performance by appropriately combining the three pieces of information on the amplitude, phase and polarization of light.

[0024]

1 is a schematic diagram showing the structure of an exposure apparatus according to an embodiment of the present invention. In the figure, an illumination optical system 4 uses an ultrahigh pressure mercury lamp, an excimer laser, or the like as a light source, and emits exposure light having a wavelength that can sensitize a photoresist used in a lithography process.

The photomask 1 is held in a horizontal plane so as to be orthogonal to the optical axis of the illumination optical system 4. The shape of the pattern formed on the photomask 1 is not particularly limited, but here, in order to make the description concrete,
A so-called line-and-space pattern in which light-transmitting portions and light-shielding portions such as chrome are alternately repeated is formed,
The pattern is assumed to extend in the direction perpendicular to the paper surface.

Below the photomask 1, a projection optical system 2 is provided.
Are arranged, and the position in the optical axis direction is adjusted so that the focus on the light source (illumination optical system 4) side of the projection optical system 2 and the pattern forming surface of the photomask 1 substantially coincide with each other. As shown in FIG. 1B, the pupil plane of the projection optical system 2 (not necessarily at the exact pupil position) is centered on the optical axis of the projection optical system 2 (center of the pupil). A polarizing member 5 is arranged in the tangential direction of the concentric circles to transmit only the light whose electric vector oscillates.

A wafer stage (not shown) on which a wafer (not shown) is placed is provided below the projection optical system 2 so that the image plane 3 of the projection optical system 2 and the wafer surface coincide with each other. In addition, the position on the optical axis is adjusted. The wafer stage is also movable in a horizontal plane, and the relative position between the wafer and the photomask 1 is adjusted using an alignment means (not shown) before exposure.

In the exposure apparatus having the above-described structure, when the photomask 1 is transmitted and illuminated by the exposure light from the illumination optical system 4, as shown in FIG.
Then, diffracted light that spreads in the left-right direction (pattern arrangement direction) within the paper surface is generated. At this stage, the diffracted light is in a state in which the TE polarized light and the TM polarized light are averaged, and there is no bias in the vibration direction.

Next, the diffracted light enters the projection optical system 2,
It reaches the polarizing member 5 arranged on the pupil plane. Here, the 0th-order diffracted light of the diffracted light from the photomask 1 does not depend on the formation position of the pattern (whether the pattern is at the central portion or at the end of the illumination area), and is the center of the pupil of the projection optical system 2. (Polarizing member 5
Each of the ± 1st-order, ± 2nd-order, ...
The light beam is incident on a position distant by a predetermined distance in the radial direction (pattern arrangement direction) from the center of the pupil. When the arrangement direction of the pattern is the horizontal direction of the paper surface as in this embodiment, the incident position of the diffracted light of each order on the polarization member 5 is a circle centered on the optical axis of the projection optical system 2 (see FIG. 1). (See (b)) are arranged at a predetermined interval on the diameter across the right and left of the drawing. Polarizing member 5
As described above, since only the light whose electric vector oscillates in the tangential direction of the circle centered on the optical axis of the projection optical system 2 is transmitted, the diffracted light of each order is shown in FIG.
Only the component in which the electric vector oscillates in the vertical direction of (b) is transmitted through the polarizing member 5.

At this time, since the polarization state of the transmitted light becomes unstable at the center of the polarizing member 5 as shown in FIG. 1B, the incident position of the 0th order diffracted light is deviated from the center of the polarizing member 5. It is desirable to let This can be easily realized by shielding the central part of the light source of the illumination optical system 4 to provide annular illumination. That is, with the annular illumination, the photomask 1 is illuminated from a direction slightly tilted from the vertical direction (optical axis direction), and the 0th-order diffracted light of the polarization member 5 is proportional to the tilt. Since the light is incident at a position displaced from the center in the radial direction (at this time, the positions of the diffracted lights of the first and higher orders are also displaced outward in the radial direction in order), it is possible to prevent light having different vibration directions from passing through the polarizing member 5. it can.

Returning to FIG. 1A, in the exposure light transmitted through the polarization member 5 of the projection optical system 2, the vibration direction of the electric vector is aligned with the direction perpendicular to the paper surface (direction parallel to the side of the pattern).
It becomes E-polarized light and forms an image of the line-and-space pattern of the photomask 1 on the image plane 3. Thereby, the image plane 3
The pattern image is transferred to a predetermined position of the wafer held by the.

In the present embodiment, as described above, an image is formed only by light whose vibration directions are uniform, so that the interference effect of diffracted light is increased and a high-contrast image is transferred onto the wafer surface. Further, as the pattern pitch becomes smaller, the diffraction angle of the diffracted light of the first order or more becomes larger.
When an image is formed with light in a non-polarized state (TE polarized light + TM polarized light), the contrast of the image decreases as the deviation of the TM polarized light in the vibration direction increases. When the image is formed only by itself, the vibration direction of the electric vector does not change even if the diffraction angle changes, so that high contrast is maintained. That is, by using the exposure apparatus having the structure as shown in FIG. 1, it is possible to obtain a high-contrast image even if the pattern pitch becomes very small.
The finer the pattern, the clearer the advantage over the conventional exposure apparatus.

In the above description, for the sake of explanation, the pattern of the photomask 1 is arranged in the left-right direction on the paper surface. However, even if the arrangement direction is another direction, a high-contrast image can be similarly obtained. Needless to say, the exposure apparatus of this embodiment can handle patterns of any shape. That is, if the arrangement direction of the pattern changes, the direction in which the diffracted light spreads changes correspondingly, and the alignment direction of the incident position of the diffracted light of each order on the pupil plane of the projection optical system 2 also changes (for example, the arrangement direction of the pattern). Is in the vertical direction of the paper surface of FIG. 1B, the incident position of the diffracted light of each order is aligned on the diameter across the concentric circles of the FIG. 1B in the vertical direction of the paper surface). Is for transmitting only light having an oscillating surface in the tangential direction of the concentric circles in FIG. 1B, no matter which direction the pattern is arranged, the electric power is always parallel to the sides of the pattern. Only the light whose vector oscillates will pass through the polarizing member 5.

On the contrary, when the arrangement direction of the pattern is limited to one direction, the polarizing member 5 (FIG. 1) in which the vibration direction of the transmitted light changes depending on the position in the circumferential direction.
Even if (b)) is not used, it suffices to use a polarizing member that transmits only light that oscillates in the same direction (direction parallel to the side of the pattern) regardless of the incident position. Next, as an example, with the exposure wavelength λ = 365 nm, from Equations 11 to 12, each polarization state (T
The result of obtaining the log slope value of the pattern image at the best focus obtained with E-polarized light, TM-polarized light, and the average of TE-polarized light and TM-polarized light is shown. From the results shown in Table 1, it is clear that the superiority of the present invention is exerted in the case of a fine pattern. For example, the exposure apparatus of the present invention is very useful for manufacturing a semiconductor element having a high degree of integration such as 64M DRAM. It is understood to be effective.

[0035]

[Table 1]

In the above description, for the sake of simplicity, the case where a photomask pattern-formed only with a light-shielding film was used was explained, but the exposure apparatus of the present invention is used in combination with a phase shift mask. You can also do it. Regarding the phase shift mask, in addition to the spatial frequency modulation method in which a phase shift member is added to one of the adjacent light transmitting portions via the light shielding portion (for example, the method described in Japanese Patent Publication No. 62-50811), the thickness is different. Multi-stage method with phase member,
There are various types such as an auxiliary pattern method in which an auxiliary pattern made of a phase shift member is provided on the peripheral portion of the light shielding pattern, an edge enhancement method in which a phase shift member is provided at the boundary between the light shielding portion and the light transmitting portion, and a chromeless method in which a pattern is formed only by the phase shift member Although a method has been proposed, the present invention can be combined with any type of phase shift mask.

In the above description, the case where the transmission type photo smak is used has been described, but the present invention uses the reflection type photomask in which the reflection member (reflection film) is provided on the transparent substrate. It is also applicable in some cases. In a reflective mask, an image is formed by epi-illuminating a photomask and collecting the reflected light from the reflective film with an imaging optical system.The light transmitting part is the dark part of the image and the reflective part is the bright part of the image. As will be dealt with, by providing a polarizing member on the pupil plane of the imaging optical system that transmits light whose electric vector oscillates in a direction parallel to the sides of the pattern, the image of It is possible to increase the contrast.

[0038]

As described above, in the exposure apparatus of the present invention, a polarizing member that transmits only the light whose electric vector oscillates in the direction parallel to the side of the pattern to be transferred is provided on the pupil plane of the projection optical system. Therefore, an image is formed by light in which the vibration directions of the electric vectors are aligned in the same direction, the interference between the diffracted lights increases, and an image with high contrast can be obtained.

Further, according to the present invention, even if the circuit pattern is miniaturized and the diffraction angle of the light from the photomask is increased, a high contrast can be maintained. Therefore, the finer pattern is superior to the conventional exposure apparatus. To be demonstrated. Furthermore, the exposure apparatus of the present invention can form an image by utilizing the three pieces of information of the amplitude, phase and polarization of light in combination with a phase shift mask developed in recent years, which will lead to a new development of lithography technology. It is very useful for making efforts.

[Brief description of drawings]

1A is a configuration diagram showing a structure of an exposure apparatus according to an embodiment of the present invention, and FIG. 1B is a schematic plan view of a polarizing member used in the embodiment of the present invention.

FIGS. 2A and 2B are conceptual diagrams showing a state of image formation by TE and TM polarized light, respectively.

FIG. 3 is a configuration diagram showing a configuration of a conventional exposure apparatus.

[Explanation of symbols for main parts]

 1 Photomask 2 Projection optical system 3 Image plane 4 Illumination optical system 5 Polarizing member

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[Procedure amendment]

[Submission date] September 9, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0003

[Correction method] Change

[Correction content]

[0003]

By the way, the conventional exposure apparatus as described above has a problem that it cannot cope with the miniaturization of circuit patterns accompanying the high integration of semiconductor elements. Development of a technique capable of forming a contrast image is required. Under such circumstances, as a method of increasing the contrast of the pattern image, for example,
Japanese Laid-Open Patent Publication No. 62-50811 specifies a light transmitting portion of a photomask.
The phase shift part that changes the phase of the transmitted light is provided at
Phase shift mask for projection exposure using a phase shift mask
G method is disclosed. Such a phase shift method forms a pattern image by using the information on the phase of light in addition to the information on the amplitude of light, and for example, a photo image is composed of a light transmitting part (bare surface part of the substrate) and a light shielding part. A certain degree of improvement in the imaging performance has been realized as compared with the method using a mask.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0033

[Correction method] Change

[Correction content]

In the above description, for the sake of explanation, the pattern of the photomask 1 is arranged in the left-right direction on the paper surface. However, even if the arrangement direction is another direction, a high-contrast image can be similarly obtained. Needless to say, the exposure apparatus of this embodiment can handle patterns of any shape. That is, if the arrangement direction of the pattern changes, the direction in which the diffracted light spreads changes correspondingly, and the alignment direction of the incident positions of the diffracted light of each order on the pupil plane of the projection optical system 2 also changes (for example, the arrangement direction of the pattern changes). In the vertical direction on the paper surface of FIG. 1B, the incident position of the diffracted light of each order is as shown in FIG.
(B) The concentric circles are aligned on the diameter across the vertical direction on the paper surface), but the polarizing member 5 in the present embodiment transmits only light having an oscillating surface in the tangential direction of the concentric circles of FIG. 1 (b). Therefore, no matter how the patterns are arranged, only the light whose electric vector oscillates in the direction parallel to the sides of the pattern is transmitted through the polarizing member 5.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0036

[Correction method] Change

[Correction content]

In the above description, for the sake of simplicity, the case where a photomask pattern-formed only with a light-shielding film was used was explained, but the exposure apparatus of the present invention is used in combination with a phase shift mask. You can also do it. Regarding the phase shift mask, the space around which the phase shift member is added to one of the light transmitting parts adjacent to each other through the light shielding part.
In addition to the wave number modulation method, a multi-step method in which phase members having different thicknesses are provided, an auxiliary pattern method in which an auxiliary pattern made of a phase shift mask member is provided at the peripheral portion of the light shielding pattern, and a phase shift member is provided at the boundary between the light shielding portion and the light transmitting portion. Various methods have been proposed, such as an edge enhancement method to be provided and a chromeless method in which a pattern is formed only with a phase shift member, but the present invention can be combined with any type of phase shift mask.

Claims (2)

[Claims] 1. An exposure apparatus having a projection optical system for projecting a pattern on a photomask, wherein light whose electric vector oscillates in a direction parallel to a side of the pattern on a substantially pupil plane of the projection optical system. An exposure apparatus, in which a polarizing member that transmits light is arranged. 2. The polarizing member transmits only light whose electric vector oscillates in a tangential direction of a circle centered on the optical axis of the projection optical system. Exposure equipment.