USRE37846E1

Movatterモバイル変換

Info

Publication number: USRE37846E1
Application number: US09/709,518
Authority: US
Inventors: Hitoshi Matsuzawa; Misako Kobayashi; Kazumasa Endo; Yutaka Suenaga
Original assignee: Nikon Corp
Current assignee: Nikon Corp
Priority date: 1995-01-06
Filing date: 2000-11-13
Publication date: 2002-09-17
Anticipated expiration: 2015-08-18
Also published as: DE69526568T2; EP0721150A2; EP1162508A2; EP0721150B1; DE69526568D1; US5835285A; EP1162508A3; JPH08190047A; KR960029823A; EP0721150A3; JP3454390B2; KR100387149B1

Abstract

The present invention relates to an exposure apparatus using a projection optical system to realize a small size and the bitelecentricity as securing a wide exposure area and a large numerical aperture and to realize extremely good correction for aberrations, particularly for distortion. The projection optical system comprises a first lens group G₁with a positive refracting power, a second lens group G₂with a negative refracting power, a third lens group G₃with a positive refracting power, a fourth lens group G₄with a negative refracting power, a fifth lens group G₅with a positive refracting power, and a sixth lens group G₆with a positive refracting power in order from the side of the first object R, wherein the second lens group G₂comprises a front lens L_2Fwith a negative refracting power, a rear lens L_2Rof a negative meniscus shape, and an intermediate lens group G_2Mdisposed between the front lens and the rear lens, and wherein the intermediate lens group G_2Mhas a first lens L_M1with a positive refracting power, a second lens L_M2with a negative refracting power, and a third lens L_M3with a negative refracting power in order from the side of the first object R. The system is arranged to satisfy within suitable ranges of focal lengths for the first to sixth lens groups G₁-G₆, based on the above arrangement.

Description

This is a continuation of application Ser. No. 08/516,903, filed Aug. 18, 1995, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exposure apparatus having a projection optical system for projecting a pattern of a first object onto a photosensitive substrate etc. as a second object, and more particularly to a projection optical system suitably applicable to projection exposure of a pattern for semiconductor or liquid crystal formed on a reticle (mask) as the first object onto the substrate (semiconductor wafer, plate, etc.) as the second object.

2. Related Background Art

As the patterns of integrated circuits become finer and finer, the resolving power required for the exposure apparatus used in printing of wafer also becomes higher and higher. In addition to the improvement in resolving power, the projection optical systems of the exposure apparatus are required to decrease image stress. In order to get ready for the finer tendency of transfer patterns, light sources for exposure have recently been changing from those emitting the light of exposure wavelength of the g-line (436 nm) to those emitting the light of exposure wavelength of the i-line (365 nm) that are mainly used at present. Further, a trend is to use light sources emitting shorter wavelengths, for example the excimer laser (KrF:248 nm, ArF:193 nm).

Here, the image stress includes those due to bowing etc. of the printed wafer on the image side of projection optical system and those due to bowing etc. of the reticle with circuit pattern etc. written therein, on the object side of projection optical system, as well as distortion caused by the projection optical system.

With a recent further progress of fineness tendency of transfer patterns, demands to decrease the image stress are also becoming harder.

Then, in order to decrease effects of the wafer bowing on the image stress, the conventional technology has employed the so-called image-side telecentric optical system that located the exit pupil position at a farther point on the image side of projection optical system.

On the other hand, the image stress due to the bowing of reticle can also be reduced by employing a so-called object-side telecentric optical system that locates the entrance pupil position of projection optical system at a farther point from the object plane, and there are suggestions to locate the entrance pupil position of projection optical system at a relatively far position from the object plane as described. Examples of those suggestions are described for example in Japanese Laid-open Patent Applications No. 63-118115 and No. 5-173065 and U.S. Pat. No. 5,260,832.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a high-performance projection optical system which can achieve the bitelecentricity in a compact design as securing a wide exposure area and a large numerical aperture and which can be well corrected for aberrations, particularly which can be very well corrected for distortion. The projection optical system can be applied to an exposure apparatus.

To achieve the above object, an exposure apparatus according to the present invention comprises at least a wafer stage allowing a photosensitive substrate to be held on a main surface thereof, an illumination optical system for emitting exposure light of a predetermined wavelength and transferring a predetermined pattern of a mask (reticle) onto the substrate, a projection optical system provided between a first surface on which the mask as a first object is disposed and a second surface on which a surface of the substrate as a second object is corresponded, for projecting an image of the pattern of the mask onto the substrate. The illumination optical system includes as alignment optical system for adjusting a relative positions between the mask and the wafer, and the mask is disposed on a reticle stage which is movable in parallel with respect to the main surface of the wafer stage. The projection optical system has a space permitting an aperture stop to be set therein. The photosensitive substrate comprises a wafer such as a silicon wafer or a glass plate, etc., and a photosensitive material such as a photoresist or the like coating a surface of the wafer. In particular, as shown in FIG. 1, the projection optical system includes a first lens group (G₁) with a positive refracting power, a second lens group (G₂) with a negative refracting power, a third lens group (G₃) with a positive refracting power, a fourth lens group (G₄) with a negative refracting power, a fifth lens group (G₅) with a positive refracting power, and a sixth lens group (G₆) with a positive refracting power in order from the side of the first object (for example, a mask).

The second lens group (G₂) comprises a front lens (L_2F) with a negative refracting power disposed as closest to the first object and shaded with a concave surface to the second object, a rear lens (L_2R) of a negative meniscus shape disposed as closest to the substrate and shaped with a concave surface to the mask, and an intermediate lens group (G_2M) disposed between the front lens (L_2F) and the rear lens (L_2R). In particular, the intermediate lens group (G_2M) has a first lens (L_M1) with a positive refracting power, a second lens (L_M2) with a negative refracting power, and a third lens (L_M3) with a negative refracting power in order from the side of the first object.

Further, the projection optical system according to the present invention is arranged to satisfy the following conditions (1) to (6) when f₁is a focal length of the first lens group (G₁), f₂is a focal length of the second lens group (G₂), f₃is a focal length of the third lens group (G₃), f₄is a focal length of the fourth lens group (G₄), f₅is a focal length of the fifth lens group (G₅), f₆is a focal length of the sixth lens group (G₆), and L is a distance from the first object to the second object:

The projection optical system is so arranged as to have at least the first lens group (G₁) with positive refracting power, the second lens group (G₂) with negative refracting power, the third lens group (G₃) with positive refracting power, the fourth lens group (G₄) with negative refracting power, the fifth lens group (G₅) with positive refracting power, and the sixth lens group (G₆) with positive refracting power in the named order from the first object side.

First, the first lens group (G₁) with positive refracting power contributes mainly to a correction of distortion while maintaining telecentricity, and specifically, the first lens group (G₁) is arranged to generate a positive distortion to correct in a good balance negative distortions caused by the plurality of lens groups located on the second object side after the first lens group (G₁). The second lens group (G₂) with negative refracting power and the fourth lens group (G₄) with negative refracting power contribute mainly to a correction of Petzval sum to make the image plane flat. The two lens groups of the second lens group (G₂) with negative refracting power and the third lens group (G₃) with positive refracting power form an inverse telescopic system to contribute to guarantee of back focus (a distance from an optical surface such as a lens surface closest to the second object in the projection optical system to the second object) in the projection optical system. The fifth lens group (G₅) with positive refracting power and the sixth lens group (G₆) similarly with positive refracting power contribute mainly to suppressing generation of distortion and suppressing generation particularly of spherical aberration as much as possible in order to fully support high NA structure on the second object side.

Based on the above arrangement, the front lens (L_2F) with the negative refracting power disposed as closest to the first object in the second lens group (G₂) and shaped with the concave surface to the second object contributes to correction for curvature of field and coma, and the rear lens (L_2R) of the negative meniscus shape disposed as closest to the second object in the second lens group (G₂) and shaped with the concave surface to the first object contributes mainly to correction for coma. The rear lens (L_2R) also contributes to correction for curvature of field. Further, in the intermediate lens group (G_2M) disposed between the front lens (L_2F) and the rear lens (L_2R), the first lens (L_M1) with the positive refracting power contributes to correction for negative distortion generated by the second lens (L_M2) and third lens (L_M3) of the negative refracting powers greatly contributing to correction for curvature of field.

Condition (1) defines an optimum ratio between the focal length f₁of the first lens group (G₁) with the positive refracting power and the distance (object-to-image distance) L from the first object (reticle etc.) to the second object (wafer etc.). This condition (1) is mainly for well-balanced correction for distortion.

Above the upper limit of condition (1), large negative distortion will appear. In order to achieve a compact design as securing a reduction magnification and a wide exposure area and to achieve good correction for distortion, the upper limit of condition (1) is preferably set to 0.14, as f₁/L<0.14. In order to suppress appearance of spherical aberration of pupil, the lower limit of condition (1) is preferably set to 0.02, as 0.02<f₁/L.

Condition (2) defines an optimum ratio between the focal length f₂of the second lens group (G₂) with the negative refracting power and the distance (object-to-image distance) L from the first object (reticle etc.) to the second object (wafer etc.). This condition (2) is a condition for achieving a compact design as securing a wide exposure region and achieving good correction for Petzval sum.

Here, below the lower limit of condition (2), it becomes difficult to achieve the compact design as securing the wide exposure region and positive Petzval sum will appear, thus not preferred. In order to achieve further compact design or superior correction for Petzval sum, the lower limit of condition (2) is preferably set to −0.032, as −0.032<f₂/L. In order to suppress appearance of negative distortion, the upper limit of condition (2) is preferably set to −0.005, as f₂/L<−0.005.

Condition (3) defines an optimum ratio between the focal length f₃of the third lens group (G₃) with the positive refracting power and the distance (object-to-image distance) L from the first object (reticle etc.) to the second object (wafer etc.). Here, below the lower limit of condition (3), the refractive power of the second lens group (G₂) or the fourth lens group (G₄) becomes too strong, resulting in giving rise to negative distortion and coma in the second lens group (G₂) or giving rise to coma in the fourth lens group (G₄). On the other hand, above the upper limit of condition (3), the refractive power of the second lens group (G₂) or the fourth lens group (G₄) becomes too weak, failing to well correct Petzval sum.

Condition (4) defines an optimum ratio between the focal length f₄of the fourth lens group (G₄) with the negative refracting power and the distance (object-to-image distance) L from the first object (reticle etc.) to the second object (wafer etc.).

Here, above the upper limit of condition (4), coma will appear, thus not preferred. Further, in order to suppress appearance of coma, the upper limit of condition (4) is preferably set to −0.047, as f₄/L<−0.047.

In order to well correct spherical aberration, the lower limit of condition (4) is preferably set to −0.098, as −0.098<f₄/L.

Condition (5) defines an optimum ratio between the focal length f₅of the fifth lens group (G₅) with the positive refracting power and the distance (object-to-image distance) L from the first object (reticle etc.) to the second object (wafer etc.). This condition (5) is for achieving well-balanced correction for spherical aberration, distortion, and Petzval sum as maintaining a large numerical aperture. Below the lower limit of this condition (5), the refracting power of the fifth lens group (G₅) becomes too strong, resulting in giving rise to great negative spherical aberration in addition to negative distortion in the fifth lens group (G₅). Above the upper limit of this condition (5), the refracting power of the fifth lens group (G₅) becomes too weak, which inevitably weakens the refracting power of the fourth lens group (G₄) with the negative refracting power. As a consequence, Petzval sum will not be well corrected.

Condition (6) defines an optimum ratio between the focal length f₆of the sixth lens group (G₆) with the positive refracting power and the distance (object-to-image distance) L from the first object (reticle etc.) to the second object (wafer etc.). This condition (6) is for suppressing appearance of higher-order spherical aberration and negative distortion as maintaining a large numerical aperture. Below the lower limit of this condition (6), the sixth lens group (G₆) itself gives rise to great negative distortion; above the upper limit of this condition (6), higher-order spherical aberration will appear.

On the basis of the above composition it is preferred that when I is an axial distance from the first object to a first-object-side focal point F of the entire projection optical system and L is the distance from the first object to the second object, the following condition be satisfied:

1.0<I/L. (7)

The condition (7) defines an optimum ratio between the axial distance I from the first object to the first-object-side focal point F of the entire projection optical system and the distance (object-image distance) L from the first object (reticle etc.) to the second object (wafer etc.). Here, the first-object-side focal point F of the entire projection optical system means an intersecting point of outgoing light from the projection optical system with the optical axis after collimated light beams are let to enter the projection optical system on the second object side in the paraxial region with respect to the optical axis of the projection optical system and when the light beams in the paraxial region are outgoing from the projection optical system.

Below the lower limit of this condition (7) the first-object-side telecentricity of the projection optical system will become considerably destroyed, so that changes of magnification and distortion due to an axial deviation of the first object will become large. As a result, it becomes difficult to faithfully project an image of the first object at a desired magnification onto the second object. In order to fully suppress the changes of magnification and distortion due to the axial deviation of the first object, the lower limit of the above condition (7) is preferably set to 1.7, i.e., 1.7<I/L. Further, in order to correct a spherical aberration and a distortion of the pupil both in a good balance while maintaining the compact design of the projection optical system, the upper limit of the above condition (7) is preferably set to 6.8, i.e., I/L<6.8.

It is also preferred that the fourth lens group (G₄) have a front lens group disposed as closest to the first object and a rear lens group disposed as closest to the second object, that an intermediate lens group having a first negative lens (L₄₃) and a second negative lens (L₄₄) in order from the side of the first object be disposed between the front lens group in the fourth lens group (G₄) and the rear lens group in the fourth lens group (G₄), that the front lens group have two negative meniscus lenses (L₄₁, L₄₂) each shaped with a concave surface to the second object, that the rear lens group has a negative lens (L₄₆) with a concave surface to the first object, and that when f_4Ais a focal length of the first negative lens (L₄₃) in the fourth lens group (G₄) and f_4Bis a focal length of the second negative lens (L₄₄) in the fourth lens group (G₄), the following condition be satisfied:

0.05<f_4A/f_4B<20. (8)

Below the lower limit of condition (8), the refractive power of the first negative lens (L₄₃) becomes strong relative to the refractive power of the second negative lens (L₄₄), so that the first negative lens (L₄₃) will give rise to higher-order spherical aberration and higher-order coma. In order to suppress appearance of the higher-order spherical aberration and higher-order coma, the lower limit of the above condition (8) is preferably set to 0.1, as 0.1<f_4A/f_4B. On the other hand, above the upper limit of condition (8), the refracting power of the second negative lens (L₄₄) becomes strong relative to the refracting power of the first negative lens (L₄₃), so that the second negative lens (L₄₄) will give rise to higher-order spherical aberration and higher-order coma. In order to further suppress appearance of higher-order spherical aberration and higher-order coma, the upper limit of the above condition (8) is preferably set to 10, as f_4A/f_4B<10.

It is also preferred that when r_2Ffis a radius of curvature of a first-object-side surface of the front lens (L₂F) and r_2Fris a radius of curvature of a second-object-side surface of the front lens (L_2F), the front lens (L_2F) in the second lens group (G₂) satisfy the following condition:

1.00≦(r_2Ff−r_2Fr)/(r_2Ff+r_2Fr)<5.0. (9)

Below the lower limit of this condition (9), sufficient correction for spherical aberration of pupil becomes impossible, thus not preferred. On the other hand, above the upper limit of this condition (9), coma will appear, thus not preferred.

It is also preferred that the fourth lens group (G₄) have a front lens group having a negative lens (L₄₁) disposed as closest to the first object and shaped with a concave surface to the second object, and a rear lens group having a negative lens (L₄₆) disposed as closest to the second object and shaped with a concave surface to the first object, that an intermediate lens group having at least a negative lens (L₄₄) and a positive lens (L₄₅) with a convex surface adjacent to a concave surface of the negative lens (L₄₄) be disposed between the front lens group in the fourth lens group (G₄) and the rear lens group in the fourth lens group (G₄), and that when r_4Nis a radius of curvature of the concave surface of the negative lens (L₄₄) in the intermediate lens group and r_4Pis a radius of curvature of the convex surface of the positive lens (L₄₅) in the intermediate lens group, the following condition be satisfied:

−0.9<(r_4N−r_4P)/(r_4N+r_4P)<0.9, (10)

provided that when L is the distance from the first object to the second object, the concave surface of the negative lens (L₄₄) in the intermediate lens group or the convex surface of the positive lens (L₄₅) in the intermediate lens group satisfies at least one of the following conditions:

|r_4N/L|<2.0 (11)

|r_4P/L|<2.0. (12)

Conditions (10) to (12) define an optimum configuration of a gas lens formed by the concave surface of the negative lens (L₄₄) in the intermediate lens group and the convex surface of the positive lens (L₄₅) in the intermediate lens group. When condition (11) or (12) is satisfied, this gas lens can correct higher-order spherical aberration. For further correction of higher-order spherical aberration, the upper limits of condition (11) and condition (12) are preferably set to 0.8, as |r_4N/L|<0.8 and |r_4P/L|<0.8. Here, above the upper limit or below the lower limit of condition (10), coma will appear, thus not preferred. If neither condition (11) nor condition (12) is satisfied, correction for higher-order spherical aberration is impossible even if condition (10) is satisfied, thus not preferred.

It is also preferred that when f₂₂is a focal length of the second lens (L_M2) with the negative refracting power in the second lens group (G₂) and f₂₃is a focal length of the third lens (L_M3) with the negative refracting power in the second lens group (G₂), the following condition be satisfied:

0.1<f₂₂/f₂₃<10. (13)

Below the lower limit of the condition (13) the refracting power of the second negative lens (L_M2) becomes strong relative to the refracting power of the third negative lens (L_M3), so that the second negative lens (L_M2) generates a large coma and a large negative distortion. In order to correct the negative distortion in a better balance, the lower limit of the above condition (13) is preferably set to 0.7, i.e., 0.7<f₂₂/f₂₃. Above the upper limit of this condition (13) the refracting power of the third negative lens (L_M3) becomes strong relative to the refracting power of the second negative lens (L_M2), so that the third negative lens generates a large coma and a large negative distortion. In order to correct the negative distortion in a better balance while well correcting the coma, the upper limit of the above condition (13) is preferably set to 1.5, i.e., f₂₄/f₂₃<1.5.

It is also preferred that the fifth lens group (G₅) have a negative meniscus lens (for example, L₅₄), and a positive lens (for example, L₅₃) disposed as adjacent to a concave surface of the negative meniscus lens and having a convex surface opposed to the concave surface of the negative meniscus lens and that when r_5nis a radius of curvature of the concave surface of the negative meniscus lens in the fifth lens group (G₅) and r_5Pis a radius of curvature of the convex surface, opposed to the concave surface of the negative meniscus lens, of the positive lens disposed as adjacent to the concave surface of the negative meniscus lens in the fifth lens group (G₅), the following condition be satisfied:

0<(r_5P−r_5n)/(r_5P+r_5n)<1. (14)

In this case, it is preferred that the negative meniscus lens (for example, L₅₄) and the positive lens (L₅₃) adjacent to the concave surface of the negative meniscus lens be disposed between at least one positive lens (for example, L₅₂) in the fifth lens group G₅and at least one positive lens (for example, L₅₅) in the fifth lens group (G₅).

In this case, in order to suppress the negative distortion without generating the higher-order spherical aberrations in the lens (L₆₁) located closest to the first object in the sixth lens group (G₆), it is desirable that the lens surface closest to the first object have a shape with a convex surface to the first object and that the following condition be satisfied when a radius of curvature on the second object side, of the negative lens (L₅₈) placed as closest to the second object in the fifth lens group (G₅) is r_5Rand a radius of curvature on the first object side, of the lens (L₆₁) placed as closest to the first object in the sixth lens group (G₆) is r_6F.

−0.90<(r_5R−r_6F)/(r_5R+r_6F)<−0.001 (15)

This condition (15) defines an optimum shape of a gas lens formed between the fifth lens group (G₅) and the sixth lens group (G₆). Below the lower limit of this condition (15) a curvature of the second-object-side concave surface of the negative lens (L₅₈) located closest to the second object in the fifth lens group (G₅) becomes too strong, thereby generating higher-order comas. Above the upper limit of this condition (15) refracting power of the gas lens itself formed between the fifth lens group (G₅) and the sixth lens group (G₆) becomes weak, so that a quantity of the positive distortion generated by this gas lens becomes small, which makes it difficult to well correct a negative distortion generated by the positive lens in the fifth lens group (G₅). In order to fully suppress the generation of higher-order comas, the lower limit of the above condition (15) is preferably set to −0.30, i.e., −0.30<(r_5R−r_6F)/(r_5R+r_6F).

Also, it is further preferable that the following condition be satisfied when a lens group separation between the fifth lens group (G₅) and the sixth lens group (G₆) is d₅₆and the distance from the first object to the second object is L.

d₅₆/L<0.017 (16)

Above the upper limit of this condition (16), the lens group separation between the fifth lens group (G₅) and the sixth lens group (G₆) becomes too large, so that a quantity of the positive distortion generated becomes small. As a result, it becomes difficult to correct the negative distortion generated by the positive lens in the fifth lens group (G₅) in a good balance.

Also, it is more preferable that the following condition be satisfied when a radius of curvature of the lens surface closest to the first object in the sixth lens group (G₆) is r_6Fand an axial distance from the lens surface closest to the first object in the sixth lens group (G₆) to the second object is d₆.

0.50<d₆/r_6F<1.50 (17)

Below the lower limit of this condition (17), the positive refracting power of the lens surface closest to the first object in the sixth lens group (G₆) becomes too strong, so that a large negative distortion and a large coma are generated. Above the upper limit of this condition (17), the positive refracting power of the lens surface closest to the first object in the sixth lens group (G₆) becomes too weak, thus generating a large coma. In order to further suppress the generation of coma, the lower limit of the condition (17) is preferably set to 0.84, i.e., 0.84<d₆/r₆F.

Also, it is to be more desired that said fifth lens group (G₅) have a negative lens (L₅₈) placed as closest to the second object and having a concave surface opposed to the second object and that the following condition be satisfied when a radius of curvature on the first object side in the negative lens (L₅₈) closest to the second object in said fifth lens group (G₅) is r_5Fand a radius of curvature on the second object side in the negative lens (L₅₈) closest to the second object in said fifth lens group (G₅) is r_5R:

0.30<(r_5F−r_5R)/(r_5F+r_5R)<1.28. (18)

Below the lower limit of this condition (18), it becomes difficult to correct both the Petzval sum and the coma; above the upper limit of this condition (18), large higher-order comas appear, which is not preferable. In order to further prevent the generation of higher-order comas, the upper limit of the condition (18) is preferably set to 0.93, i.e., (r_5F−r_5R)/(r_5F+r_5R)<0.93.

It is more desired that when f₂₁is a focal length of the first lens (L_M1) with the positive refracting power in the intermediate lens group (G_2M) in the second lens group (G₂) and L is the distance from the first object to the second object, the following condition be satisfied:

0.230<f₂₁/L<0.40. (19)

Below the lower limit of condition (19), positive distortion will appear; above the upper limit of condition (19), negative distortion will appear, either of which is thus not preferred. Further, in order to further correct the negative distortion, the second-object-side lens surface of the first lens (L_M1) is preferably formed in a lens configuration shaped with a convex surface facing the second object.

It is also preferred that when f_2Fis a focal length of the front lens (L_2F) with the negative refracting power disposed as closest to the first object in the second lens group (G₂) and shaped with the concave surface to the second object and f_2Ris a focal length of the rear lens (L_2R) with the negative refracting power disposed as closest to the second object in the second lens group (G₂) and shaped with the concave surface to the first object, the following condition be satisfied:

0≦f_2F/f_2R<18. (20)

Also, the front lens (L_2F) and the rear lens (L_2R) in the second lens group (G₂) preferably satisfy the following condition when the focal length of the front lens (L_2F) placed as closest to the first object in the second lens group (G₂) and having the negative refracting power with a concave surface to the second object is f_2Fand the focal length of the rear lens (L_2R) placed as closest to the second object in the second lens group (G₂) and having the negative refracting power with a concave surface to the second object is f_2R.

0≦f_2F/f_2R<18 (20)

The condition (20) defines an optimum ratio between the focal length f_2Rof the rear lens (L_2R) in the second lens group (G₂) and the focal length f_2Fof the front lens (L_2F) in the second lens group (G₂). Below the lower limit and above the upper limit of this condition (20), a balance is destroyed for refracting power of the first lens group (G₁) or the third lens group (G₃), which makes it difficult to correct the distortion well or to correct the Petzval sum and the astigmatism simultaneously well.

In order to further well correct Petzval sum, the intermediate lens group (G_2M) in the second lens group (G₂) preferably has a negative refracting power.

For the above lens groups to achieve satisfactory aberration correction functions, specifically, they are desired to be constructed in the following arrangements.

First, for the fist lens group (G₁) to have a function to suppress appearance of higher-order distortion and appearance of spherical aberration of pupil, the first lens group (G₁) preferably has at least two positive lenses; for the third lens group (G₃) to have a function to suppress degradation of spherical aberration and Petzval sum, the third lens group (G₃) preferably has at least three positive lenses; further, for the fourth lens group (G₄) to have a function to suppress appearance of coma as correcting Petzval sum, the fourth lens group (G₄) preferably has at least three negative lenses. For the fifth lens group (G₅) to have a function to suppress appearance of negative distortion and spherical aberration, the fifth lens group (G₅) preferably has at least five positive lenses; further, for the fifth lens group (G₅) to have a function to correct negative distortion and Petzval sum, the fifth lens group (G₅) preferably has at least one negative lens. For the sixth lens group (G₆) to effect focus on the second object so as not to give rise to large spherical aberration, the sixth lens group (G₆) preferably has at least one positive lens.

For further compact design, the intermediate lens group in the second lens group desirably comprises only two negative lenses.

For the sixth lens group (G₆) to have a function to further suppress appearance of negative distortion, the sixth lens group (G₆) is preferably arranged to comprise three or less lenses including at least one lens surface satisfying the following condition (21).

1/|ΦL|<20 (21)

where

Φ: a refractive power of the lens surface; and

L: the distance (object-to-image distance) from the first object to the second object.

The refractive power of lens surface, stated here, is given by the following equation where r is a radius of curvature of the lens surface, n₁a refractive index of a medium on the first object side of the lens surface, and n₂a refractive index of a medium on the second object side of the lens surface.

Φ=(n₂−n₁)/r

Here, if there are four or more lenses having the lens surface satisfying this condition (21), the number of lens surfaces with some curvature, located near the second object, becomes increased, which generates the distortion, thus not preferable.

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art form this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing to show parameters defined in embodiments of the present invention.

FIG. 2 is a drawing to show schematic structure of an exposure apparatus to which the projection optical system according to the present invention is applied.

FIG. 3 is a lens arrangement drawing of the projection optical system in the first embodiment according to the present invention.

FIG. 4 is a lens arrangement drawing of the projection optical system in the second embodiment according to the present invention.

FIG. 5 is a lens arrangement drawing of the projection optical system in the third embodiment according to the present invention.

FIG. 6 is a lens arrangement drawing of the projection optical system in the fourth embodiment according to the present invention.

FIGS. 7-10 are aberration diagrams to show aberrations in the projection optical system of the first embodiment.

FIGS. 11-14 are aberration diagrams to show aberrations in the projection optical system of the second embodiment.

FIGS. 15-18 are aberration diagrams to show aberrations in the projection optical system of the third embodiment.

FIGS. 19-22 are aberration diagrams to show aberrations in the projection optical system of the fourth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Various embodiments of the projection optical system according to the present invention will be described with reference to the drawings. In the examples, the present invention is applied to the projection optical system in the projection exposure apparatus for projecting an image of patterns of reticle onto a wafer coated with a photoresist. FIG. 2 shows a basic structure of the exposure apparatus according to the present invention. As shown in FIG. 2, an exposure apparatus of the present invention comprises at least awafer stage3 allowing a photosensitive substrate W to be held on a main surface3a thereof, an illumination optical system1 for emitting exposure light of a predetermined wavelength and transferring a predetermined pattern of a mask (reticle R) onto the substrate W, alight source100 for supplying an exposure light to the illumination optical system1, a projectionoptical system5 provided between a first surface P1 (object plane) on which the mask R is disposed and a second surface P2 (image plane) to which a surface of the substrate W is corresponded, for projecting an image of the pattern of the mask R onto the substrate W. The illumination optical system1 includes an alignment optical system110 for adjusting a relative positions between the mask R and the wafer W, and the mask R is disposed on areticle stage2 which is movable in parallel with respect to the main surface of thewafer stage3. Areticle exchange system200 conveys and changes a reticle (mask R) to be set on thereticle stage2. Thereticle exchange system200 includes a stage driver for moving thereticle stage2 in parallel with respect to the main surface3a of thewafer stage3. The projectionoptical system5 has a space permitting anaperture stop6 to be set therein. The sensitive substrate W comprises awafer8 such as a silicon wafer or a glass plate, etc., and aphotosensitive material7 such as a photoresist or the like coating a surface of thewafer8. Thewafer stage3 is moved in parallel with respect to a object plane P1 by astage control system300. Further, since amain control section400 such as a computer system controls thelight source100, thereticle exchange system200, thestage control system300 or the like, the exposure apparatus can perform a harmonious action as a whole.

The techniques relating to an exposure apparatus of the present invention are described, for example, in U.S. patent applications Ser. Nos. 255,927, 260,398, 299,305, U.S. Pat. Nos. 4,497,015, 4,666,273, 5,194,893, 5,253,110, 5,333,035, 5,365,051, 5,379,091, or the like. The reference of U.S. patent application Ser. No. 255,927 teaches an illumination optical system (using a laser source) applied to a scan type exposure apparatus. The reference of U.S. patent application Ser. No. 260,398 teaches an illumination optical system (using a lamp source) applied to a scan type exposure apparatus. The reference of U.S. patent application Ser. No. 299,305 teaches an alignment optical system applied to a scan type exposure apparatus. The reference of U.S. Pat. No. 4,497,015 teaches an illumination optical system (using a lamp source) applied to a scan type exposure apparatus. The reference of U.S. Pat. No. 4,666,273 teaches a step-and repeat type exposure apparatus capable of using the projection optical system of the present invention. The reference of U.S. Pat. No. 5,194,893 teaches an illumination optical system, an illumination region, mask-side and reticle-side interferometers, a focusing optical system, alignment optical system, or the like. The reference of U.S. Pat. No. 5,253,110 teaches an illumination optical system (using a laser source) applied to a step-and-repeat type exposure apparatus. The '110 reference can be applied to a scan type exposure apparatus. The reference of U.S. Pat. No. 5,333,035 teaches an application of an illumination optical system applied to an exposure apparatus. The reference of U.S. Pat. No. 5,365,051 teaches a auto-focusing system applied to an exposure apparatus. The reference of U.S. Pat. No. 5,379,091 teaches an illumination optical system (using a laser source) applied to a scan type exposure apparatus.

As described above, a reticle R (first object) as a projection mask with specific circuit patterns formed therein is disposed on the object plane (P1) of the projection optical system1 and a wafer W (second object) as a substrate on the image plane (P2) of the projection optical system1. Here, the reticle R is held on areticle stage2 and the wafer W on awafer stage3 arranged as movable on a two-dimensional basis. Disposed above the reticle R is an illumination optical system1 for uniformly illuminating the reticle R.

In the above arrangement, light supplied from thelight source100 through the illumination optical system1 illuminates the reticle R to form an image at the pupil position of the projection optical system1 (the position of aperture stop6). Namely, the illumination optical system1 uniformly illuminates the reticle R under Köhler illumination. Then the pattern image of reticle R illuminated under Köhler illumination is projected (or transferred) onto the wafer W.

The present embodiment shows an example of which thelight source100 is a mercury lamp for supplying the i-line (365 nm). The structure of the projection optical system in each embodiment will be described by reference to FIG. 3 to FIG.6. FIG. 3 to FIG. 6 are lens structural drawings of the projection optical systems1 in the first to fourth embodiments, respectively, according to the present invention.

As shown in FIG. 3 to FIG. 6, the projection optical system1 in each embodiment has a first lens group G₁with a positive refractive power, a second lens group G₂with a negative refractive power, a third lens group G₃with a positive refractive power, a fourth lens group G₄with a negative refractive power, a fifth lens group G₅with a positive refractive power, and a sixth lens unit G₆with a positive refractive power in order from the side of reticle R as a first object, is arranged as substantially telecentric on the object side (reticle R side) and on the image side (wafer W side), and has a reduction magnification.

In the projection optical system1 in each of the embodiments shown in FIG. 3 to FIG. 6, an object-to-image distance (a distance along the optical axis from the object plane to the image plane, or a distance along the optical axis from the reticle R to wafer W) L is 1100, an image-side numerical aperture NA is 0.57, a projection magnification β is ⅕, and a diameter of an exposure area on the wafer W is 31.2. The object-to-image distance L and the diameter of the exposure area are expressed in a same unit, and the unit corresponds to a unit of r and d shown in the following tables 1, 3, 5 and 7.

First described is a specific lens arrangement of the first embodiment shown in FIG.3. The first lens group G₁has a negative meniscus lens L₁₁shaped with a concave surface to the image, a positive lens (positive lens of a biconvex shape) L₁₂shaped with a convex surface to the object, and two positive lenses (positive lenses of biconvex shapes) L₁₃, L₁₄each shaped with a strong-curvature surface to the object in order from the object side.

Further, the second lens group G₂has a negative lens (negative lens of a biconcave shape: front lens) L_2Fdisposed as closest to the object and shaped with a concave surface to the image, a negative meniscus lens (rear lens) L_2Rdisposed as closest to the image and shaped with a concave surface to the object, and an intermediate lens group G_2Mwith a negative refractive power disposed between these negative lens L_2Fand negative lens L_2R. This intermediate lens group G_2Mhas a positive lens (positive lens of a biconvex shape: first lens) L_M1shaped with a strong-curvature surface to the image, a negative lens (negative lens of a biconcave shape: second lens) L_M2shaped with a strong-curvature surface to the image, and a negative lens (negative lens of a biconcave shape: third lens) L_M3shaped with a strong-curvature surface to the object in order from the object side.

The third lens group G₃has two positive lenses (positive meniscus lenses) L₃₁, L₃₂each shaped with a strong-curvature surface to the image, a positive lens L₃₃of a biconvex shape, a positive lens (positive lens of a biconvex shape) L₃₄shaped with a strong-curvature surface to the object, and a positive lens (positive meniscus lens) L₃₅shaped with a strong-curvature surface to the object in order from the object side.

The fourth lens group G₄has two negative meniscus lenses (front lens group) L₄₁, L₄₂each shaped with a concave surface to the image, a negative lens (negative meniscus lens: first negative lens) L₄₃shaped with a concave surface to the object, a negative lens (second negative lens: negative lens with a concave surface to the image) L₄₄of a biconcave shape, a positive lens (positive meniscus lens: positive lens having a convex surface adjacent to the concave surface of the negative lens L₄₄) L₄₅shaped with a convex surface to the object, and a negative lens (negative lens of a biconcave shape: rear lens group) L₄₆shaped with a concave surface to the object in order from the object side.

The fifth lens group G₅has two positive lenses (positive lenses of biconvex shapes) L₅₁, L₅₂each shaped with a convex surface to the image, a positive lens L₅₃of a biconvex shape, a negative meniscus lens L₅₄shaped with a concave surface to the object, a positive lens L₅₅shaped with a stronger-curvature surface to the object, two positive lenses (positive meniscus lenses) L₅₆, L₅₇each shaped with a stronger-curvature surface to the object, and a negative meniscus lens L₅₈shaped with a concave surface to the image in order from the object side.

Further, the sixth lens group G₆is composed of a positive lens (positive lens of a biconvex shape) L₆₁shaped with a stronger-curvature surface to the object, and a negative lens (negative lens of a biconcave shape) L₆₂with a concave surface to the object in order from the object side.

In the present embodiment, anaperture stop6 is disposed between the positive meniscus lens L₄₅with the convex surface to the object and the negative lens L₄₆of the biconcave shape, that is, between the intermediate lens group in the fourth lens group G₄and the rear lens group in the fourth lens group G₄.

In the first lens group G₁in the present embodiment, the concave surface of the negative meniscus lens L₁₁with the concave surface to the image and the object-side lens surface of the positive biconvex lens L₁₂have nearly equal curvatures and are arranged as relatively close to each other, and these two lens surfaces correct higher-order distortion.

Since the first lens L_M1with the positive refractive power in the second lens group G_2Mis constructed in the biconvex shape with the convex surface to the image and also with the other convex surface to the object, it can suppress appearance of spherical aberration of pupil.

Since the fourth lens group G₄is so arranged that the negative meniscus lens L₄₁with the concave surface to the image is disposed on the object side of the negative lens (negative biconcave lens) L₄₄and that the negative lens L₄₆with the concave surface to the object is disposed on the image side of the negative lens (negative biconcave lens) L₄₄, it can correct Petzval sum as suppressing appearance of coma.

Since in the first embodiment theaperture stop6 is placed between the image-side concave surface of the negative meniscus lens L₄₁and the object-side concave surface of the negative lens L₄₆in the fourth lens group G₄, the lens group of from the third lend group G₃to the sixth lens group G₆can be arranged around theaperture stop6 with a more or less reduction magnification and without destroying the symmetry too much, thus enabling to suppress asymmetric aberration, particularly coma and distortion. Since the positive lens L₅₃in the fifth lens group G₅has a convex surface opposed to the negative meniscus lens L₅₄and the other lens surface on the opposite side to the negative meniscus lens L₅₄is also a convex surface, higher-order spherical aberration can be prevented from appearing with an increase of numerical aperture.

The specific lens arrangement of the second embodiment shown in FIG. 4 is similar to that of the first embodiment as shown in FIG.3 and described above. The third lens group G₃in the second embodiment is different from that in the first embodiment in that the third lens group G₃is composed of two positive lenses (positive meniscus lenses) L₃₁, L₃₂each shaped with a strong-curvature surface to the image, a positive lens L₃₃of a biconvex shape, a positive lens (positive lens of a biconvex shape) L₃₄shaped with a strong-curvature surface to the object, and a positive lens (positive lens of a biconvex shape) L₃₅shaped with a strong-curvature surface to the object in order from the object side.

In the second embodiment, the fourth lens group G₄is different from that in the first embodiment in that the fourth lens group G₄is composed of two negative meniscus lenses (front lens group) L₄₁, L₄₂each shaped with a concave surface to the image, a negative lens (negative lens of a biconcave shape: first negative lens) L₄₃shaped with a concave surface to the object, a negative lens (second negative lens: negative lens with a concave surface to the image) L₄₄of a biconcave shape, a positive lens (positive meniscus lens: positive lens having a convex surface adjacent to the concave surface of the negative lens L₄₄) L₄₅shaped with a convex surface to the object, and a negative lens (negative lens of a biconcave shape: rear lens group) L₄₆shaped with a stronger concave surface to the object in order from the object side, but the function thereof is the same as that in the first embodiment as described above.

Further, the first and second lens groups G₁, G₂and the fifth and sixth lens groups G₅, G₆in the second embodiment achieve the same functions as those in the first embodiment as described above.

The specific lens arrangement of the third embodiment shown in FIG. 5 is similar to that of the first embodiment shown in FIG.3 and described previously. The first lens group G₁of the present embodiment is different from that of the first embodiment in that the first lens group G₁is composed of a negative meniscus lens L₁₁shaped with a concave surface to the image, a positive lens (positive lens of a biconvex shape) L₁₂shaped with a convex surface to the object, a positive lens (positive lens of a plano-convex shape) L₁₃shaped with a strong-curvature surface to the object, and a positive lens (positive lens of a biconvex shape) L₁₄shaped with a strong-curvature surface to the object in order from the object side, but the function thereof is the same as that in the first embodiment as described previously.

The second to sixth lens groups G₂-G₆in the third embodiment achieve the same functions as those in the first embodiment as described previously.

The specific lens arrangement of the fourth embodiment of FIG. 6 is similar to that of the first embodiment shown in FIG.3 and described previously. The fourth lens group G₄in the present embodiment is different from that of the first embodiment in that the fourth lens group G₄is composed of two negative meniscus lenses (front lens group) L₄₁, L₄₂each with a concave surface to the image, a negative lens (negative lens of a biconcave shape: first negative lens) L₄₃shaped with a concave surface to the object, a negative lens (second negative lens: negative lens with a concave surface to the image) L₄₄of a biconcave shape, a positive lens (positive meniscus lens: a positive lens having a convex surface adjacent to the concave surface of the negative lens L₄₄) L₄₅shaped with a convex surface to the object, and a negative lens (negative lens of a biconcave shape: rear lens group) L₄₆shaped with a concave surface to the object in order from the object side, but the function thereof is the same as that in the first embodiment as described previously.

Further, in the fourth embodiment, the sixth lens group G₆is different from that of the first embodiment in that the sixth lens group G₆is composed of a positive lens (positive lens of a biconvex shape) L₆₁shaped with a stronger-curvature surface to the object and a negative lens (negative meniscus lens) L₆₂shaped with a concave surface to the object in order from the object side.

The first to third lens groups G₁to G₃and the fifth lens group G₅in the present embodiment achieve the same functions as those in the first embodiment described previously.

Table 1 to Table 8 to follow list values of specifications and correspondent values to the conditions for the respective embodiments in the present invention.

TABLE 1

First Embodiment
dO = 94.97557
β = ⅕
NA = 0.57
Bf = 22.68864
L = 1100

	r	d	n

1	758.59372	18.01962	1.66638
2	273.07409	8.00000
3	407.25600	34.43806	1.53627
4	−305.98082	0.50000
5	200.00000	36.31512	1.53627
6	−950.89920	0.50000
7	251.35670	36.00000	1.53627
8	−1111.20100	5.00000
9	−3000.00000	13.00000	1.66638
10	103.53326	19.34714
11	583.43731	21.86239	1.53627
12	−202.73262	3.71513
13	−389.07550	13.00000	1.53627
14	118.39346	25.82991
15	−119.29984	13.00000	1.53627
16	228.68065	35.35939
17	−118.78231	15.61439	1.53627
18	−2000.00000	15.00000
19	−534.21970	30.58806	1.53627
20	−172.96367	0.50000
21	−3045.95900	30.55054	1.53627
22	−252.31005	0.50000
23	787.95642	31.33960	1.53627
24	−470.11486	0.50000
25	429.05519	31.10739	1.53627
26	−1033.56100	0.50000
27	276.54228	29.82671	1.53627
28	3383.80700	0.50000
29	200.56082	25.00000	1.53627
30	149.82206	51.17799
31	191.38232	25.00000	1.53627
32	122.34204	25.15581
33	−276.65501	13.00000	1.66638
34	−597.90043	9.14516
35	−190.18194	13.00000	1.66638
36	360.79756	3.75310
37	434.45763	13.00000	1.53627
38	643.56408	31.17056
39	−951.39487	20.00000	1.66638
40	360.75541	3.46004
41	395.41239	33.29191	1.53627
42	−229.24043	0.50000
43	405.02177	21.76952	1.53627
44	−1456.27300	0.50000
45	334.62149	34.87065	1.53627
46	−316.02886	8.19653
47	−226.66975	20.00000	1.66638
48	−421.19119	0.50000
49	245.00959	27.62592	1.53627
50	−6478.64400	0.50000
51	118.64887	24.82664	1.53627
52	182.84804	0.50000
53	106.94354	29.80517	1.53627
54	305.86346	2.86446
55	330.12685	13.00000	1.66638
56	65.69252	7.67289
57	76.63392	29.80077	1.53627
58	−405.45793	2.41289
59	−314.04117	20.42250	1.53627
60	1180.34006	(Bf)

TABLE 2

Correspondent Values to the Conditions for First
Embodiment

	(1) f1/L = 0.129
	(2) f2/L = −0.0299
	(3) f3/L = 0.106
	(4) f4/L = −0.0697
	(5) f5/L = 0.0804
	(6) f6/L = 0.143
	(7) I/L = 2.02
	(8) f4A/f4B = 4.24
	(9) (r2Ff − r2Fr)/(r2Ff + r2Fr) = 1.07
	(10) (r4N − r4P)/(r4N + r4PY) = −0.0926
	(11) \|r4N/L\| = 0.328
	(12) \|r4P/L\| = 0.395
	(13) f22/f23 = 1.16
	(14) (r5p − r5n)/(r5p + r5n) = 0.165
	(15) (r5R − r6F)/(r5R + r6F) = −0.0769
	(16) d56/L = 0.00698
	(17) d6/r6F = 0.983
	(18) (r5F − r5R)/(r5F + r5R) = 0.668
	(19) f21/L = 0.258
	(20) f2F/f2R = 0.635

TABLE 3

Second Embodiment
dO = 98.09086
β = ⅕
NA = 0.57
Bf = 22.68864
L = 1100

	r	d	n

1	715.79825	18.01962	1.66638
2	257.11993	8.00000
3	402.81202	34.43806	1.53627
4	−298.91362	0.50000
5	200.00000	36.31512	1.53627
6	−811.20841	0.50000
7	202.30081	36.00000	1.53627
8	−912.77876	−0.24598
9	−3000.00000	13.00000	1.66638
10	100.16757	19.34714
11	515.50992	21.86239	1.53627
12	−211.08983	3.71513
13	−334.85048	13.00000	1.53627
14	119.28367	24.34073
15	−124.53825	13.00000	1.53627
16	196.56654	35.64064
17	−122.83913	15.61439	1.53627
18	−2000.00000	15.00000
19	−319.01403	30.58806	1.53627
20	−192.95790	0.50000
21	−1320.53000	30.55054	1.53627
22	−229.09627	0.50000
23	1670.41600	31.33960	1.53627
24	−355.67749	0.50000
25	505.94351	31.10739	1.53627
26	−669.94239	0.50000
27	272.78755	29.82671	1.53627
28	−11188.96200	0.50000
29	205.32433	25.00000	1.53627
30	156.91075	68.35861
31	170.81860	25.00000	1.53627
32	119.41166	25.17539
33	−221.51521	13.00000	1.66638
34	3749.27900	7.91441
35	−299.53056	13.00000	1.66638
36	360.79756	3.75310
37	434.45763	13.00000	1.53627
38	643.56408	18.53967
39	−6417.33300	20.00000	1.66638
40	300.16308	3.46004
41	329.77719	33.29191	1.53627
42	−264.12523	0.50000
43	804.85248	21.76952	1.53627
44	−784.29788	0.50000
45	273.73159	34.87065	1.53627
46	−325.58814	8.19653
47	−214.52517	20.00000	1.66638
48	−405.91293	0.50000
49	396.09997	27.62592	1.53627
50	−579.80514	0.50000
51	115.71351	24.82664	1.53627
52	255.34580	0.50000
53	104.86226	29.80517	1.53627
54	211.50003	2.86446
55	312.25500	13.00000	1.66638
56	66.11566	7.67289
57	76.78058	29.80077	1.53627
58	−437.18968	2.41289
59	−324.32040	20.42250	1.53627
60	2434.44700	(Bf)

TABLE 4

Correspondent Values to the Conditions for Second
Embodiment

	(1) f1/L = 0.119
	(2) f2/L = −0.0292
	(3) f3/L = 0.111
	(4) f4/L = −0.0715
	(5) f5/L = 0.0806
	(6) f6/L = 0.140
	(7) I/L = 2.02
	(8) f4A/f4B = 1.29
	(9) (r2Ff − r2Fr)/(r2Ff + r2Fr) = 1.07
	(10) (r4N − r4P)/(r4N + r4P) = −0.0926
	(11) \|r4N/L\| = 0.328
	(12) \|r4P/L\| = 0.395
	(13) f22/f23 = 1.16
	(14) (r5p − r5n)/(rsp + r5n) = 0.206
	(15) (r5R − r6F)/(r5R + r6F) = −0.0114
	(16) d56/L = 0.00698
	(17) d6/r6F = 0.981
	(18) (r5F − r5R)/(r5F + r5R) = 0.673
	(19) f21/L = 0.257
	(20) f2F/f2R = 0.593

TABLE 5

Third Embodiment
dO = 105.97406
β = ⅕
NA = 0.57
Bf = 21.09296
L = 1100

	r	d	n

1	835.93450	19.00074	1.61298
2	349.00002	6.60188
3	493.73823	30.01023	1.61536
4	−364.99999	1.12825
5	189.67357	32.71424	1.61536
6	∞	1.25667
7	219.68925	26.27974	1.61536
8	−2935.50000	2.86486
9	−1456.03000	15.60000	1.61298
10	98.87901	25.83515
11	572.77742	19.48735	1.48734
12	−245.99492	3.28431
13	−517.01308	16.35209	1.61536
14	118.78195	22.95916
15	−151.83256	12.94478	1.61536
16	196.86505	33.74710
17	−129.25780	12.89677	1.61536
18	−491.95895	13.46314
19	−246.12435	22.58245	1.61536
20	−166.51997	0.39125
21	−1477.30500	28.55306	1.61536
22	−216.04701	0.72991
23	425.36937	33.51075	1.61536
24	−524.95999	0.96043
25	438.35798	25.74084	1.48734
26	−1678.66000	0.33363
27	292.51673	23.69782	1.48734
28	1518.72000	0.83738
29	218.42396	26.38775	1.48734
30	148.35403	33.09868
31	203.95726	27.76454	1.61536
32	133.43801	30.67100
33	−211.86216	13.01538	1.61298
34	−1024.57000	15.53690
35	−160.75584	13.15020	1.61298
36	270.91502	0.55149
37	250.92650	15.66663	1.48734
38	702.02996	23.07586
39	−827.25951	15.36200	1.61298
40	2298.00000	0.73901
41	2301.62000	27.62162	1.48734
42	−223.08205	0.51051
43	488.67440	34.23933	1.48734
44	−319.00802	0.49298
45	500.98379	34.15684	1.61536
46	−369.12909	9.55181
47	−242.59289	18.84686	1.61298
48	−613.52998	0.50392
49	347.10206	30.00332	1.61536
50	−1728.40000	0.49017
51	180.81644	30.27184	1.48734
52	728.32004	0.48766
53	119.02258	38.20547	1.48734
54	609.84003	3.61782
55	1650.31000	19.05217	1.61298
56	77.86795	17.17240
57	81.07073	30.61882	1.48734
58	−335.26499	2.16189
59	−316.96290	26.15191	1.61536
60	−848.55009	(Bf)

TABLE 6

Correspondent Values to the Conditions for Third
Embodiment

	(1) f1/L = 0.117
	(2) f2/L = −0.0288
	(3) f3/L = 0.106
	(4) f4/L = −0.0762
	(5) f5/L = 0.0868
	(6) f6/L = 0.147
	(7) I/L = 2.87
	(8) f4A/f4B = 2.69
	(9) (r2Ff − r2Fr)/(r2Ff + r2Fr) = 1.15
	(10) (r4N − r4P)/(r4N + r4P) = 0.0383
	(11) \|r4N/L\| = 0.246
	(12) \|r4P/L\| = 0.228
	(13) f22/f23 = 1.13
	(14) (r5p − r5n)/(r5p + r5n) = 0.207
	(15) (r5R − r6F)/(r5R + r6F) = −0.0202
	(16) d56/L = 0.00156
	(17) d6/r6F = 0.987
	(18) (r5F − r5R)/(r5F + r5R) = 0.910
	(19) f21/L = 0.324
	(20) f2F/f2R = 0.521

TABLE 7

Fourth Embodiment
dO = 83.70761
β = ⅕
NA = 0.57
Bf = 21.09296
L = 1100

	r	d	n

1	1185.70800	19.00074	1.61298
2	477.18400	6.60188
3	1060.88800	30.01023	1.61536
4	−338.64042	1.12825
5	200.00000	32.71424	1.61536
6	−2276.77900	1.25667
7	248.82758	26.27974	1.61536
8	−1078.61200	3.19741
9	−726.49629	15.60000	1.61298
10	110.53957	25.83515
11	2000.00000	19.48735	1.48734
12	−236.03800	3.28431
13	−3000.00000	16.35209	1.61536
14	109.86653	32.21675
15	−153.78948	12.94478	1.61536
16	226.94451	35.22505
17	−132.31662	12.89677	1.61536
18	−830.43817	15.00000
19	−330.52996	22.58245	1.61536
20	−184.59786	0.39125
21	−1874.03800	28.55306	1.61536
22	−221.73570	0.72991
23	558.10318	33.51075	1.61536
24	−552.83568	0.96043
25	478.84376	25.74084	1.48734
26	−906.26315	0.33363
27	287.03514	23.69782	1.48734
28	2359.17900	0.83738
29	201.46068	26.38775	1.48734
30	155.19710	46.91024
31	198.66962	27.76454	1.61536
32	122.40099	26.77778
33	−220.19752	13.01538	1.61298
34	3835.74700	12.87579
35	−180.57897	13.15020	1.61298
36	270.91501	0.55149
37	250.92650	15.66663	1.48734
38	702.02997	25.47244
39	−1387.52600	15.36200	1.61298
40	404.60733	0.73901
41	437.56885	27.62162	1.48734
42	−242.82524	0.51051
43	476.89455	34.23933	1.48734
44	−364.55546	0.49298
45	500.11721	34.15684	1.61536
46	−381.64661	9.55181
47	−243.22857	18.84686	1.61298
48	−378.77918	0.50392
49	355.95061	30.00332	1.61536
50	6474.81200	0.49017
51	171.50098	30.27184	1.48734
52	722.00626	0.48766
53	113.44841	38.20547	1.48734
54	442.83450	3.61782
55	730.67537	19.05217	1.61298
56	73.59136	17.17240
57	78.92998	30.61882	1.48734
58	−315.11137	2.16189
59	−286.11801	26.15191	1.61536
60	−878.71576	(Bf)

TABLE 8

Correspondent Values to the Conditions for Fourth
Embodiment

	(1) f1/L = 0.119
	(2) f2/L = −0.0278
	(3) f3/L = 0.106
	(4) f4/L = −0.0675
	(5) f5/L = 0.0805
	(6) f6/L = 0.146
	(7) I/L = 2.29
	(8) f4A/f4B = 1.94
	(9) (r2Ff − r2Fr)/(r2Ff + r2Fr) = 1.36
	(10) (r4N − r4P)/(r4N + r4P) = 0.0383
	(11) \|r4N/L\| = 0.246
	(12) \|r4P/L\| = 0.228
	(13) f22/f23 = 1.17
	(14) (r5p − r5n)/(r5p + r5n) = 0.222
	(15) (r5R − r6F)/(r5R + r6F) = −0.0350
	(16) d56/L = 0.00156
	(17) d6/r6F = 1.01
	(18) (r5F − r5R)/(r5F + r5R) = 0.817
	(19) f21/L = 0.395
	(20) f2F/f2R = 0.603

Letting L be the distance (object-to-image distance) from the object plane P1 (reticle plane) to the image plane P2 (wafer plane) and Φ be a refractive power of lens surface in the sixth lens group G₆, in the first embodiment as described previously, 1/|ΦL|=0.130 for the object-side lens surface of the positive lens L₆₁and 1/|ΦL|=0.532 for the object-side lens surface of the negative lens L₆₂, thus satisfying the condition (21). In the second embodiment, 1/|ΦL|=0.130 for the object-side lens surface of the positive lens L₆₁and 1/|ΦL|=0.550 for the object-side lens surface of the negative lens L₆₂, thus satisfying the condition (21). In the third embodiment, 1/|ΦL|=0.151 for the object-side lens surface of the positive lens L₆₁and 1/|ΦL|=0.468 for the object-side lens surface of the negative lens L₆₂, thus satisfying the condition (21). In the fourth embodiment, 1/|ΦL|=0.147 for the object-side lens surface of the positive lens L₆₁and 1/|ΦL|=0.423 for the object-side lens surface of the negative lens L₆₂, thus satisfying the condition (21).

As described above, the sixth lens group G₆in each embodiment is composed of three or less lenses including the lens surfaces satisfying the condition (21).

It is understood from the above values of specifications for the respective embodiments that the projection optical systems according to the embodiments achieved satisfactory telecentricity on the object side (reticle R side) and on the image side (wafer W side) as securing the large numerical apertures and wide exposure areas.

FIG. 7 to FIG. 22 are respectively aberration diagrams to show aberrations in the first to fourth embodiments. Each of FIGS. 7,11,15, and19 shows a spherical aberration of each embodiment. Each of FIGS. 8,12,16, and20 shows an astigmatism of each embodiment. Each of FIGS. 9,13,17, and21 shows a distortion of each embodiment. Each of FIGS. 10,14,18, and22 shows a coma of each embodiment.

Here, in each aberration diagram, NA represents the numerical aperture of the projection optical system1, and Y the image height, and in each astigmatism diagram, the dashed line represents the meridional image surface and the solid line the sagittal image surface.

It is understood from comparison of the aberation diagrams that the aberrations are corrected in a good balance in each embodiment even with a wide exposure area (image height) and a large numerical aperture, particularly, distortion is extremely well corrected up to nearly zero throughout the entire image, thus achieving the projection optical system with high resolving power in a wide exposure area.

The above-described embodiments showed the examples using the mercury lamp as a light source for supplying the exposure light of the i-line (365 nm), but it is needless to mention that the invention is not limited to the examples; for example, the invention may employ light sources including a mercury lamp supplying the exposure light of the g-line (435 nm), and extreme ultraviolet light sources such as excimer lasers supplying light of 193 nm or 248 nm.

In the above each embodiment the lenses constituting the projection optical system are not cemented to each other, which can avoid a problem of a change of cemented surfaces with time. Although in the above each embodiment the lenses constituting the projection optical system are made of a plurality of optic materials, they may be made of a single glass material, for example quartz (SiO₂) if the wavelength region of the light source is not a wide band.

As described above, the projection optical system according to the present invention can achieve the bitelecentricity in a compact design as securing a wide exposure area and a large numerical aperture, and the invention can achieve the projection optical system with high resolving power corrected in a good balance for aberrations, particularly extremely well corrected for distortion.

From the invention thus described, it will be obvious that the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. The basic Japanese Application No. 872/1995 filed on Jan. 6, 1995 is hereby incorporated by reference.