JP2000331927A - Projection optical system and projection aligner using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly precisely image-form a pattern by correcting birefringence having an optical element included in a projection optical system, SOLUTION: In this projection optical system, a projection optical system PL having plural lens elements 1, 2, and 3 is provided with a birefringence correcting member made of one-axial crystal having a main axis in an optical axial direction and/or materials having distortion distribution equivalent to the one-axial crystal. Thus, birefringence generated by the plural lens elements 1, 2, and 3 can be canceled by the birefringence correcting member.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a semiconductor device, CC
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 particularly relates to a step-and-repeat method (stepper) or a step-and-scan method (scanner). In the projection exposure apparatus of (1), the effect of the birefringence of the optical element (glass material) constituting the projection optical system is corrected, so that the projection exposure apparatus is suitable for obtaining a high-resolution pattern.

[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). A so-called stepper is widely used as an apparatus capable of forming such a fine pattern with high accuracy. In a stepper, a pattern on a reticle is illuminated with short-wavelength light in the ultraviolet region, and a fine circuit pattern is formed on a semiconductor wafer such as silicon through a projection optical system by reduction projection. I have.

At this time, various severe conditions are imposed on a projection optical system in order to transfer a pattern on a reticle with high accuracy. The pattern size that can be resolved by the projection optical system is inversely proportional to NA (numerical aperture).
A design is required to make A larger. 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. Furthermore, since the birefringence of the glass material also has a significant effect on the imaging characteristics, it is known that its size needs to be suppressed to about 2 nm / cm.

However, it is very difficult to control such high-precision birefringence uniformly over the entire surface of a glass material for a projection optical system having a diameter of up to 300 mm. 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 description here will focus 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 the quartz glass, birefringence which is considered to be caused by residual stress due to impurities, heat history and the like is experimentally observed. In the production of high quality quartz glass for lithography, the direct method (Di
Rect method), VAD (vapor ax)
ial deposition method, sol gel (sol)
-Gel) method, plasma burner (plasma bu)
(rner) method or the like is used, but it is difficult to suppress the contamination of impurities to a negligible level with the current technology in any method. Also, when cooling the quartz glass formed in a high temperature state, the stress generated due to the difference in cooling between the surface and the center, that is, the stress due to heat history can be reduced to some extent by heat treatment such as annealing, In principle, it is difficult to make it completely zero.

A process for manufacturing a lens element used in a projection optical system for lithography will be described with reference to FIG. First, a quartz glass ingot 100 is formed in a rotationally symmetric shape, and is cut to a required thickness to obtain a disk-shaped member 101. Ingot 1
00 is always symmetrical with respect to the central axis 100a, so that 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 lens element 102 is made by performing cutting and polishing on the member 101. Here, the distortion that appears when impurities are mixed in the ingot 100 will be described.

FIG. 18 shows a cut surface of the ingot 100, and it is assumed that the impurity concentration in the surrounding hatch 103 is high. The 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. When the coefficient of thermal expansion increases due to the inclusion of impurities, the part naturally shrinks in the cooling process. For this reason, those that have no stress in the heated state tend to shrink more in the peripheral part by lowering the temperature. If attention is paid to the central portion of the glass material through which the light beam passes, compression as shown by an arrow in FIG. 18 is received from the peripheral portion, and internal stress is generated. Internal stress causes birefringence.

[0010] The second reason is that the quartz glass is changed over time when used in a stepper. When quartz glass is irradiated with light from a short wavelength light source such as a KrF or ArF laser, compaction is achieved.
Is known to occur. Although a detailed description of the generation process is omitted, the observed phenomenon is that the refractive index of the portion through which the light flux has passed increases and the volume shrinks.

In FIG. 19, when a laser beam is applied to a hatched region 111 on a disk-shaped glass material 110, 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 flux passes, FIG.
A tensile force as indicated by an arrow is received from the peripheral portion, and an internal stress is generated. The 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.

As described above, the glass material of the projection optical system for the stepper is often provided with the central axis 120 as shown in FIG.
A distortion symmetric with respect to a remains, and as a result, birefringence occurs. In FIG. 21, reference numeral 120 denotes a glass material used in the projection optical system, and the line segment denoted by 121 or the like indicates the direction of the fast axis due to birefringence, and its length corresponds to the magnitude of birefringence. Although the birefringence is zero at the center 120a,
The figure shows that the birefringence increases as it goes to the periphery.

The effect that appears when an optical system is made of a glass material as shown in FIG. 21 will be described with reference to FIG. Here, a projection optical system is represented by three lens elements 130 to 132. The object point O and the image point I have a conjugate relationship, and a completely aberration-free image can be realized if the influence of birefringence is ignored. Here, it is assumed that each of the three lens elements 130 to 132 has birefringence as shown in FIG. The effect of birefringence will be described by considering three rays, that is, a ray 133 on the optical axis and rays 134 and 135 passing through the periphery of the lens.

For each of the three light beams, the polarization state in the object space is considered by decomposing into components 139 to 141 inside the paper of components 136 to 138 perpendicular to the paper. Before the incidence on the lens, it is assumed that the wavefronts corresponding to the polarization components 136 and 139, the polarization components 137 and 140, and the polarization components 138 and 141 have the same phase. Next, the polarization state after transmission through the lens is represented by components 142 to 144 perpendicular to the paper surface and components 145 to 147 inside the paper surface. First, since the ray 133 passes through the center of each lens element, it is not affected by birefringence.
The wavefronts corresponding to polarization components 142 and 145 remain coincident. However, since the light beams 134 and 135 pass through the periphery of the lens element, the influence of birefringence appears. Here, since the polarization components 140 and 141 before incidence coincide with the fast axis direction, the wavefronts of the polarization components 146 and 147 advance after the polarization components 143 and 144 after passing through the lens element, respectively.

Here, two polarization components 144 and 147 are used.
(Or the deviation Φ of the wavefront between the polarization components 143 and 146)
Can be expressed as a function of θ as shown in FIG. 23, where θ is the angle between the light ray and the optical axis. Although the details of the function form naturally depend on the design data of the projection lens and the birefringence characteristics of the glass material, basically, the influence as a quadratic function of θ appears most strongly.

FIG. 22 shows the effect within one section of the projection lens. However, as far as the object point on the optical axis is considered, the actual effect appears symmetrically with respect to the optical axis. Will be represented. A more detailed description of the effect on the wavefront caused by birefringence can be found in the paper Y.Y. Unno, “Distorte
d wave front produced by
a high-resolution project
ion optical system having
rotation all symmetric
birefringence, "Appled Opt
ics, Vol. 37, no. 31, 1998, pp7
241-7247.

[0017]

Although it is practically difficult to completely suppress the birefringence generated by a glass material to zero, the demand for birefringence in a projection optical system for a stepper is becoming increasingly severe. . FIG. 22 indicates that the shape of the wavefront of the imaging light differs depending on the polarization direction, and the imaging characteristics are deteriorated as compared with the case where the influence of birefringence is not considered.

Further, in order to realize a projection optical system having higher performance, the number of lens elements constituting the projection optical system tends to increase, and the total thickness of the glass material increases. Therefore, the amount of birefringence per unit length is set to the above value (2n
(m / cm), the total amount of birefringence is not negligible. Furthermore, the increasingly shorter wavelengths for the exposure light source also serve to increase the effect 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 beam (wavelength 193 nm). For example, 10
If the birefringence is 0 nm, the wavefront aberration corresponding to 100/365 = 0.27 wavelength is obtained for an i-line having a wavelength of 365 nm, but 100/193 = for an ArF laser light source having a wavelength of 193 nm. It can be seen that the effect on the imaging characteristics increases as the wavelength becomes shorter, even if the birefringence of the same magnitude is assumed, which corresponds to the wavefront aberration of 0.52 wavelength. For optical glass materials having birefringence symmetrical about the center, use glass materials having different birefringence amounts for each lens element,
JP-A-8-1070 discloses that by optimizing the combination, the adverse effect on optical characteristics can be reduced to some extent.
No. 6, but in such a way of thinking,
It is no longer possible to meet the demand for higher precision of the projection optical system. For this reason, it is necessary to cancel the birefringence itself of the glass material by some means.

The present invention provides a projection optical system, a projection exposure apparatus, and a device using the exposure apparatus, which can satisfactorily correct the birefringence of the projection optical system and / or the birefringence generated during the projection exposure process. The purpose of the present invention is to provide a manufacturing method.

[0021]

According to a first aspect of the present invention, there is provided a projection optical system having one or a plurality of lens elements, wherein the projection optical system comprises a uniaxial crystal having a principal axis in an optical axis direction. And / or at least one birefringence correcting member made of a material having a strain distribution equivalent to that of the uniaxial crystal, wherein the birefringence correcting member has one of the lens elements. Alternatively, it is characterized in that it is determined so as to cancel birefringence occurring in a plurality.

A projection optical system according to a second aspect of the present invention is a projection optical system having one or a plurality of lens elements, wherein the projection optical system includes at least one birefringence correction member. The characteristic is characterized in that it is determined to cancel birefringence occurring in one or more of said lens elements.

A projection optical system according to a third aspect of the present invention is a projection optical system having a plurality of lens elements, wherein the projection optical system has a variable birefringence member.

According to a fourth aspect of the present invention, in the first or second aspect of the invention, the projection optical system has a telecentric configuration on the image side, and has a first birefringence correction member as an element closest to the image. A second birefringence correction member is provided near the stop position of the projection optical system.

According to a fifth aspect of the present invention, in the first aspect of the present invention, the birefringence correction member is a parallel plate, and the thickness and birefringence characteristics of the plurality of lens elements are different. It is characterized in that it is determined to cancel the birefringence that occurs in.

According to a sixth aspect of the present invention, in the fifth aspect of the invention, the material of the birefringence correction member is a single crystal of MgF ₂ , and the correction member is integrated with a substrate having no birefringence. It is characterized by being provided.

According to a seventh aspect of the present invention, in the fifth aspect of the present invention, a stress adjusting means for adjusting a birefringence correction amount is provided in a peripheral portion of the birefringence correction member.

According to an eighth aspect of the present invention, in the fifth aspect of the present invention, the material of the birefringence correction member is a single crystal of MgF _2, a single crystal of CaF ₂ , or fused quartz, and a stress adjusting means is provided around the periphery thereof. It is characterized by having.

The projection exposure apparatus according to the ninth aspect of the present invention is the first aspect of the invention.
The invention according to any one of the above-described embodiments, is characterized in that the pattern on the first object plane is projected on the second object plane using the projection optical system.

According to a tenth aspect of the present invention, there is provided a device manufacturing method including the steps of exposing a wafer with a reticle device pattern using the projection exposure apparatus of the ninth aspect, and developing the exposed wafer. It is characterized by.

[0031]

FIG. 1 is a sectional view of a main part of a projection optical system according to a first embodiment of 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 3. .

The lens elements 1 to 3 are formed by cutting and polishing quartz glass (fused quartz). Reference numeral 4 denotes a birefringence correction member. 5 is a reticle, 6
Is a wafer. The pattern on the reticle 5 is reduced and projected onto the wafer 6 by the projection optical system PL by the step-and-repeat method or the step-and-scan method.

In the projection optical system PL of this embodiment, the birefringence correcting member 4 composed of a uniaxial crystal having a principal axis in the optical axis direction in a part of the lens element or an optical member having a strain distribution equivalent to the uniaxial crystal is provided. The thickness, surface shape, and birefringence characteristics of the birefringence correction member 4 are determined so as to cancel birefringence generated by another lens element.

Here, the fused quartz constituting the lens elements 1 to 3 is, as described with reference to FIG.
Has birefringence, which is distributed radially around the optical axis 120a (PLa). In FIG. 1, three light beams 7, 8, and 9 emitted from one point of the reticle 5 are used to explain the effect of birefringence. In particular, the polarization components of the light ray 7 before entering the lens element 1 are 10 and 1
Then, the polarization component after the lens element 3 is emitted is specified by 12 and 13. Further, the polarization component after emission from the correction member 4 is designated by 14 and 15. Here, the polarized lights 10, 12, and 14 represent polarized light components in a direction parallel to the paper surface, and the polarized light lights 11, 13, and 15 represent polarized light components in a direction perpendicular to the paper surface.

As shown in FIG. 1, before entering the lens element 1, the polarization components 10 and 11 have equal wavefronts. However, the transmission of the light through the three lens elements 1, 2, 3 causes a shift in the wavefront between the polarization components 12 and 13. The oscillation direction of the electric field of the polarization component 12 in the lens elements 1 to 3 coincides with the fast axis direction described with reference to FIG. 20, so that the polarization component 12 has a relatively more wavefront than the polarization component 13. Then, when the image reaches the image plane (wafer plane) 6 in this state, the imaging characteristics deteriorate. Therefore, in the present embodiment, the birefringence correcting member 4 provided at the position closest to the image plane of the projection lens PL causes the polarization component 1
The wavefront shift generated between 2 and 13 is corrected and converted into two polarization components 14 and 15 having the same wavefront, and the wafer surface 6 is corrected.
Is incident.

Here, the optical operation of the correction member 4 will be described with reference to FIGS. The correcting member 4 is a parallel flat plate having a thickness d made of a uniaxial optical crystal, and is used such that its crystal axis (in this case, the main axis and the optical axis) coincides with the direction of the optical axis PLa of the projection lens. . Magnesium fluoride (MgF ₂ ) or the like can be used as a uniaxial crystal having high transmittance in the ultraviolet region and excellent physical durability. Further, it is assumed that the light ray 20 is perpendicularly incident on the correction member 4 and the light ray 21 is incident on the correction member 4 at an angle θ.

First, for the light ray 20, the polarization components before incidence are represented by 22 and 23.
Numeral 23 is incident on the correction member 4 as an ordinary ray (the electric field oscillation direction is perpendicular to the main axis). Therefore, no shift in the wavefront appears between the polarized light components 24 and 25 after transmission.

On the other hand, the polarization component before the incidence of the light beam 21 is changed to 26.
And 27, the polarization component 27 passes through the correction member 4 as an ordinary ray, while the polarization component 26 transmits through the correction member 4 as an extraordinary ray. Since the refractive index of the material of the correction member 4 is different between the ordinary ray and the extraordinary ray, the polarization components 28 and 29 are different.
As shown by, a wavefront shift Ψ (θ) occurs between the two polarization components 28 and 29.

[0039] For example MgF ₂ is positive crystal, the refractive index n _e of the extraordinary ray to be greater than the refractive index n _o of the ordinary ray, the wave front of the polarization component 28 compares the wavefront polarization component 29 relatively You will be late. FIG. 3 is a refractive index ellipsoid showing the refractive index of the uniaxial crystal in the xz plane. The refractive index of a ray forming an angle θ ′ with the main axis is represented by a point A for an ordinary ray and for an extraordinary ray Is given by the point B. Theta as the refractive index of the extraordinary ray 'values at = 90 ° and n _e, the general angle theta' for the p (e '). FIG.
It can be clearly understood from FIG. 3 that the refractive index for the extraordinary ray changes depending on the direction e ′ of the ray inside the crystal. here

[0040]

[Outside 1] Can lead to a relationship. Neglecting the geometrical optical beam separation due to birefringence, the incident angle θ and the direction θ ′ in the crystal are Snell's law sin θ = nsin θ ′, where n =
(N _o + n _e ) / 2, and the wavefront deviation Ψ (θ) is

[0041]

[Outside 2] It can be expressed as. FIG. 4 shows this as a function of the angle θ.

From these results, it can be seen that the use of the uniaxial crystal changes the amount of wavefront shift between polarization components generated by birefringence according to the incident angle of a light beam. If a positive uniaxial crystal as shown in FIG. 2 is used, the wavefront of the polarized light component 26 parallel to the paper surface can be delayed with respect to the perpendicular polarized light component 27. Therefore, the shift of the wavefront generated between the polarization components 12 and 13 in FIG.
Correction can be performed as represented by the polarization components 14 and 15. Although the description so far has been made for the light ray 7, the same description can be made for the light ray 9.

Since the ray 8 is not affected by the birefringence at all in the lens elements 1 to 3 and the correction member 4, it is always guided from the object plane 5 to the image plane 6 in an ideal state. If the influence of birefringence generated in the lens elements 1 to 3 is represented by Φ (θ) in FIG. 22, the birefringence correction amount of the birefringence correction member 4 shown in FIG.
(Θ) can be set so as to satisfy the relationship of Φ (θ) −Ψ (θ) = 0.

In the present embodiment, for the reasons explained above,
The correction member 4 corrects the effect of the birefringence of the glass material so that the projection lens can exhibit its original imaging characteristics.

This is caused by the influence of the glass material for the projection lens PL.
To cancel birefringence, the wavefront generated by the correction member 4 must be
It is necessary to control the amount. For that, abnormal
The difference n between the refractive index of the ray and the ordinary ray_e -N_o Value or thickness
What is necessary is just to change d. However, the correction member 4 is, for example, M
gF_Two , The refractive index difference n_e -N _o 
Is determined automatically, so only the thickness parameter d is
Parameters.

Hereafter, the determination of the plate thickness d will be described on the assumption that MgF ₂ is used for the correction member 4. HANDBOOK OF OPTICS II S
second Edition (ISBN 0-07-0)
47974-7) Chapter 33 (33.64)
According to the data described on page 4), the dependence of the refractive index on the wavelength of MgF ₂ is as follows for the ordinary ray and the extraordinary ray.

[0047]

[Outside 3] Is given by However, the unit of the wavelength λ is μm. When using an ArF excimer laser as a light source, by substituting λ = 0.193μm, ordinary refractive index n ₀ = 1.427670, extraordinary refractive index n _e = 1.4
41134. By substituting these values into [Equation 2] through the above [Equation 1],

[0048]

[Outside 4] Is obtained. Considering the case where the image-side numerical aperture is NA = 0.7, the maximum value of the angle θ is approximately 4 from sin θ = 0.7.
5 °. When d = 1 mm and the change of Ψ (θ) is calculated in the range of 0 < θ < 45 °, the relationship shown in FIG. 5A is obtained. By setting the thickness of the correction member 4 to 1 mm, a light beam (7 and 9 in FIG. 1) transmitted through the periphery of the projection lens and incident on the image plane at an angle of 45 ° has a size of 0.003.
Wavefront shift correction by birefringence of 7 mm can be performed. Here, it is clear from the above equation that the thickness d and the birefringence correction amount Ψ (θ) have a proportional relationship.

In the projection lens, a correction unit
Wavefront shift due to birefringence generated in glass materials other than material 4 is qualitative
Before being expressed by the function Φ (θ) in FIG.
As described above, the specific value is the ray in FIG.
The birefringence of the glass material at the position where 7, 9 is transmitted is 2 nm / c.
m, the total length of light rays 7, 9 passing through the glass material is 50
cm, the wavefront shift amount between the polarization components 12 and 13 is 10
It is about 0 nm. Assuming that the thickness of the correction member 4 is 1 mm
Wavefront deviation correction by 0.0037mm birefringence is possible.
Therefore, to correct the wavefront deviation of 100 nm,
The thickness d of the positive member 4 is about 27 μm. Such thin
It is not possible to hold the member alone in the projection lens.
Therefore, in this embodiment, as shown in FIG.
d MgF _Two Is provided on a transparent substrate. Ingredient
Physically, fused quartz, CaF_Two Does not show birefringence such as
MgF on the substrate_Two Deposition of the desired configuration
It becomes possible now. Excluding the effect of birefringence,
There is no effect of the change in the thickness d of the leader on the aberration of the optical system.
The birefringence that actually occurred in the projection optical system
The thickness d of the correction member 4 is determined based on the size of the fold.
It becomes possible.

In addition to adjusting the thickness of the correction member d, Mg
The ordinary ray refractive index n ₀ = 1.42 that the F ₂ crystal originally has
7670 varied by mechanical means the difference between the extraordinary refractive index n _e = 1.441134 and it is also possible to adjust the correction amount of birefringence. FIG. 6 shows a configuration in which a stress adjusting unit 30 is provided around the correction member 4. Although MgF ₂ is a positive one wheel crystals, by applying a uniform force in an inward direction from the periphery of the circular flat plate, the difference in refractive index n _e -n ₀
Can be reduced. According to that method, while maintaining the plate thickness d constant, the difference between the refractive index n _e -n ₀
The ability to correct birefringence can be made variable by changing the magnitude of. The stress adjusting means 30 is a metal belt fixed to the periphery of the correction member 4, and has a function of uniformly applying a force inward to the periphery of the correction member 4 by the screw 31.

By applying the method described above, for example, it is possible to give a birefringent property equivalent to that of a uniaxial crystal to a glass material such as CaF ₂ or fused quartz which originally does not exhibit birefringence. The correction capability of the birefringence generated by the other lens elements of the projection lens can be continuously varied over a wide range.

In the present embodiment, the description has been made on the assumption that the lens element constituting the projection lens has a fast axis distribution which spreads radially in the optical axis direction (FIG. 21). Are concentrically distributed, the signs of the birefringence to be corrected are reversed, and it is necessary to use a negative uniaxial crystal for the correction member 4. However, there is no negative uniaxial crystal having a high transmittance in the ultraviolet region and satisfying conditions such as physical strength. Therefore, according to the method described with reference to FIG. 5, a negative uniaxial crystal is formed by applying a uniform inward force to the periphery of the flat plate using a glass material that does not normally exhibit birefringence, such as fused quartz or CaF _2. The same operation as is realized.

Although the correcting member 4 has been described as a parallel plate in the above description, the surface of the correcting member 4 has a spherical surface for fine birefringence correction that cannot be canceled only by adjusting the refractive index. Alternatively, it may be processed into an aspherical shape and used.

FIG. 7 is a schematic view of a main part of a second embodiment of the present invention. This embodiment is an improvement of Embodiment 1 of FIG. The second embodiment differs from the first embodiment in FIG. 1 in that, in addition to the correction member 4 provided between the final surface on the image side and the wafer surface, the second birefringence correction The difference is that a member 42 is provided.

In the first embodiment, the description has been made on the assumption that the object point and the image point exist on the optical axis of the photographing lens PL. In a projection exposure apparatus, a projection optical system having a telecentric configuration on the image side is often used. In this projection optical system, as shown in FIG. 8, the principal rays 50 and 51 at each image height are perpendicularly incident on the parallel flat plate 4 irrespective of the image height, and the spread of the surrounding rays also depends on the image height. It does not change. Therefore, basically, the birefringence for the off-axis object point as well as the on-axis object point is corrected by the method described in the first embodiment.

However, in FIG. 7, the influence of birefringence on the three rays 44, 45, and 46 going from the object point P1 not existing on the optical axis 43 to the image point P2 is as follows. And the impact on First, since the principal ray 45 does not always pass on the optical axis 43 of the projection lens PL having zero birefringence, a wavefront shift occurs due to a difference in polarization direction. Also, the light ray 44
Passes through the periphery of the lens where the value of birefringence is larger than that of the light ray 46, so that the influence of birefringence also appears as a result. Therefore, considering only the effects of the lens elements 1, 2, and 3, the polarization components 44P and 44P in the direction parallel to the paper surface.
5P, 46P and polarization components 44S, 45 in the direction perpendicular to the paper surface.
The shift Ψ (θ) of the wavefront appearing between S and 46S is as shown in FIG. The birefringence that can be corrected by the correcting member 4 is basically limited to zero for the principal ray of θ = 0 and the distribution shape is symmetrical on the left and right. Cannot perform sufficient correction.

Therefore, in the present embodiment, the distribution of the wavefront deviation Δ (θ) shown in FIG. 9 with respect to the light beam from the off-axis object point P1 is shown in FIG. 10 by the second birefringence correction member 42. ′
(Θ) form. Here, the second correction member 42
Is a uniaxial optical crystal arranged such that the crystal axis (equal to the main axis and the optical axis in this case) is oriented in the optical axis direction, similarly to the correction member 4, or a glass material having properties equivalent to the uniaxial crystal. Since the three light beams 44, 45, and 46 are incident on the correction member 42 at substantially the same angle, the distribution of the wavefront shift Ψ (θ) shown in FIG. 9 is uniformly reduced by the shift amount Δ. . Here, the magnitude of the deviation amount Δ is
As described in the first embodiment, the correction member 4 can be adjusted by adjusting the thickness of the correction member 42 or the size of the birefringence of the correction member 42.

The magnitude of the birefringence to be corrected by the correction member 42 actually changes according to the distance h of the object point P1 from the optical axis 43. When the value of the distance h changes, the object point P
Since the angle at which the light beam emitted from 1 enters the correction member 42 changes, the correction amount of the birefringence by the correction member 42 also changes automatically. Therefore, it is possible to configure the optical system so that the optimum correction is realized at all object heights. The luminous flux emitted from the object point on the optical axis 43 is incident on the correction member 42 almost perpendicularly.
In 2, the correction amount of the birefringence becomes zero, and in that case, the influence of the birefringence is corrected only by the correction member 4.

As described above, by using the correction member (first correction member) 4 and the correction member (second correction member) 42 in combination, the influence of birefringence generated on the off-axis object point can be reduced. Correction can be performed with high accuracy. However, for the off-axis object point, as shown in FIG. 10, the asymmetry of the distribution around the principal ray is not completely corrected even by the correction member 42.

Therefore, as shown in FIG.
Are used for portions where the light rays 44, 45, and 46 are converged light fluxes. If the angles at which the light rays 44, 45, and 46 enter the correction member 42 are represented by α1, α2, and α3, respectively, the relationship α1>α2> α3 holds.
The birefringence correction amount can be designed so as to be the largest for the light ray 44 and the smallest for the light ray 46.

As a result, the distribution Ψ (θ) shown in FIG.
As shown in FIG. 11 as a distribution Ψ ″ (θ), it is possible to convert the distribution into a distribution that is almost completely symmetrical around the principal ray. However, high-precision correction similar to the on-axis object point is possible.
The birefringence may be corrected by using two or more correction members as correction members.

Next, FIG. 13 is a schematic view of a main part of a third embodiment in which the projection optical system of the present invention is mounted on a stepper. FIG.
In the figure, 60 is a reticle on which a circuit pattern is drawn, 61 is a projection optical system according to the present invention, and 62 is a wafer to which the circuit pattern is transferred. The illumination light flux 63 from the illumination system 67 illuminates an illumination area 64 on the reticle 60, and the circuit pattern drawn in the area 64 changes the projection optical system 6.
1 is reduced and transferred to an exposure area 65 on the wafer 62. In the stepper, 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. The projection optical system 61 includes the birefringence correction member according to the present invention, and is capable of correcting the influence of the birefringence of the glass material and realizing a highly accurate image.

Next, FIG. 14 is a schematic view of a main part of a fourth embodiment in which the projection optical system of the present invention is mounted on a step-and-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 to which the circuit pattern is transferred. The illumination light beam 73 from the illumination system 67 illuminates the illumination area 74 on the reticle 70, and the circuit pattern drawn in the area 74 is reduced and transferred to the exposure area 75 on the wafer 72 via the projection optical system 71. Is done. The step & scan 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 synchronously scanned to reduce and transfer the entire circuit pattern on the reticle 70. . The projection optical system 71 includes the birefringence correction member according to the present invention, and can realize high-precision imaging by correcting the influence of birefringence of the glass material.

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

FIG. 15 shows a manufacturing flow of 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.

On the other hand, in step 3 (wafer manufacturing), 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. 16 shows a detailed flow of the above 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. Step 14 (ion implantation) implants ions into the wafer. Step 15
In (resist processing), a photosensitive agent is applied to the wafer. In step 16 (exposure), the circuit pattern on the mask is printed onto the wafer by exposure using the above-described exposure apparatus.

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 removal), the resist which 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 the present embodiment, it is possible to easily manufacture a highly integrated semiconductor device which has been conventionally difficult to manufacture.

[0075]

According to the present invention, the birefringence correcting member can favorably correct the birefringence of the projection optical system.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a main part of a projection optical system according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a polarization state change in transmission of a birefringence correction member according to the present invention.

FIG. 3 is an explanatory diagram of a birefringent ellipsoid in a positive uniaxial crystal glass material.

FIG. 4 is an explanatory diagram of a relationship between an incident angle with respect to a birefringence correction member and a birefringence correction ability.

5A is an explanatory diagram showing a specific example of a birefringence correction amount, and FIG. 5B is a diagram showing a configuration in which a birefringence correction member is provided integrally on a transparent substrate.

FIG. 6 is an explanatory diagram of a birefringence correction capability adjusting means in the birefringence correction member.

FIG. 7 is a schematic diagram of a main part of a projection optical system according to a second embodiment of the present invention.

FIG. 8 is an explanatory diagram of a light ray distribution with respect to an off-axis object point.

FIG. 9 is an explanatory diagram of the influence of birefringence on an off-axis object point.

FIG. 10 is an explanatory diagram of an effect of the second birefringence correction member.

FIG. 11 is an explanatory diagram of an incident angle of a light beam when the second birefringence correction member is used in a convergent light beam.

FIG. 12 is a diagram illustrating an effect of a second birefringence correction member.

FIG. 13 is a schematic diagram of a main part of a third embodiment of a stepper to which the projection optical system of the present invention is applied.

FIG. 14 is a schematic diagram of a main part of a scanner according to a fourth embodiment to which the projection optical system of the present invention is applied.

FIG. 15 is a flowchart of a device manufacturing method according to the present invention.

FIG. 16 is a flowchart of the wafer process of FIG.

FIG. 17 is an explanatory diagram of a manufacturing process of a glass material.

FIG. 18 is an explanatory diagram of occurrence of internal stress distribution caused by a glass material manufacturing process.

FIG. 19 is an explanatory diagram of occurrence of compaction.

FIG. 20 is an explanatory diagram of occurrence of internal stress distribution caused by compaction.

FIG. 21 is an explanatory diagram of birefringence generated symmetrically with respect to the optical axis.

FIG. 22 is an explanatory diagram of the influence of birefringence on the polarization state of a light beam.

FIG. 23 is an explanatory diagram of the relationship between the angle of a light beam and the magnitude of the influence of birefringence.

[Explanation of symbols]

 1, 2, 3 lens element 4, 42 birefringence correction member 5 first object (reticle) 6 second object (wafer) 7, 8, 9 light beam PL projection optical system 30 stress adjusting means 31 screw

Claims (10)

[Claims] 1. A projection optical system having one or a plurality of lens elements, wherein the projection optical system includes at least one birefringence correction member made of a uniaxial crystal having a main axis in an optical axis direction and / or the uniaxial crystal. And at least one birefringence correction member made of a material having a strain distribution equivalent to that of the lens element. The characteristics of the birefringence correction member are determined so as to cancel birefringence generated in one or more of the lens elements. A projection optical system, characterized in that: 2. A projection optical system having one or a plurality of lens elements, wherein the projection optical system includes at least one birefringence correction member, and the characteristic of the birefringence correction member is:
A projection optical system, which is determined so as to cancel birefringence generated in one or a plurality of the lens elements. 3. A projection optical system having a plurality of lens elements, wherein the projection optical system has a variable birefringence member. 4. The projection optical system has a configuration in which the image side is telecentric, has a first birefringence correction member as an element closest to the image side, and has a second birefringence near the stop position of the projection optical system. 3. The projection optical system according to claim 1, further comprising a correction member. 5. The apparatus according to claim 1, wherein the member is a parallel flat plate, and a thickness and a birefringent characteristic thereof are determined so as to cancel birefringence generated in the plurality of lens elements. 5. The projection optical system according to any one of 1 to 4. The material of claim 6 wherein said member is a single crystal of MgF _2, MgF ₂ is projected according to claim 5, characterized in that is provided integrally with the substrate on the substrate having no birefringence Optical system. 7. The projection optical system according to claim 5, further comprising a stress adjusting means for adjusting a birefringence correction amount in a peripheral portion of said member. 8. The projection according to claim 5, wherein the material of the member is a single crystal of MgF _2, a single crystal of CaF ₂ , or a fused quartz, and a stress adjusting means is provided in a peripheral portion thereof. Optical system. 9. The method according to claim 1, wherein
A projection exposure apparatus, characterized in that a pattern on a first object plane is projected onto a second object plane using the projection optical system described in the paragraph. 10. A device manufacturing method, comprising: means for exposing a wafer with a reticle device pattern using the projection exposure apparatus according to claim 9; and developing the exposed wafer.