Optical projection system

Abstract: A first lens, a second lens, and a third lens are arranged successively in a direction of travel of a ray. The first lens has a predetermined negative refracting power. The second lens has a predetermined negative refracting power. The third lens has a predetermined positive refracting power. A group of fourth lenses follows the third lens in the direction of travel of the ray and has a predetermined positive refracting power. At least one of surfaces of the first, second, third, and fourth lenses is aspherical. The following conditions (1), (2), and (3) are satisfied: (1) 4f < f3 < 20f (2) 0.65 < (f4/d34) < 1.40 (3) 10f < R5 where the character "f" denotes a focal length of the optical projection system, the character "f3" denotes a focal length of the third lens, the character "f4" denotes a focal length of the fourth lens group, the character "d34" denotes a distance between a rear principal point of the third lens and a front principal point of the fourth lens group, and the character "R5" denotes a radius of curvature of a front surface of the third lens.

Description: BACKGROUND OF THE INVENTION This invention generally relates to an optical projection system, and specifically relates to an optical projection system for photolithography used in producing integrated circuits, large-scale integrated circuits, or other semiconductor devices. During the fabrication of semiconductor devices such as integrated circuits, photolithography transfers an image from a photographic mask to a resultant pattern on a semiconductor wafer. Such photolithography generally includes a light exposure process in which a semiconductor wafer is exposed to light having information of a mask pattern. Optical projection systems are used to perform the light exposure process. In general, transferred mask patterns are very fine so that optical projection systems are required to have a high resolution. The high resolution necessitates a large numerical aperture of the optical projection system and also an essentially null aberration of the optical projection system in the light exposure field. In addition, since a plurality of light exposure steps are sequentially performed to transfer different mask patterns onto a semiconductor wafer in an overlappling manner to complete a composite mask pattern, the optical projection system is required to have a very small distortion. Japanese published examined patent application 57-12966 discloses an optical projection system using a g-line and i-line light source. This prior-art optical projection system generally requires a large number of thick lenses. Japanese published unexamined patent application 60-28613 discloses an optical projection system using an excimer laser as a light source. This prior-art optical projection system generally requires a large number of lenses. Furthermore, in this prior-art optical projection system, when an ArF excimer laser is used, the laser light is absorbed by lenses of the system at a high rate. SUMMARY OF THE INVENTION It is an object of this invention to provide an excellent optical projection system for photolithography as defined in claims 1 and 4. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view of an optical projection system according to a first embodiment of this invention. Fig. 2(a) is a diagram showing the spherical aberration in the optical projection system of Fig. 1. Fig. 2(b) is a diagram showing the astigmatism in the optical projection system of Fig. 1. Fig. 2(c) is a diagram showing the distortion in the optical projection system of Fig. 1. Fig. 3(a) is a diagram showing the meridional transverse aberration in the optical projection system of Fig. 1 which occurs under conditions where an image height is 10.60 mm. Fig. 3(b) is a diagram showing the sagittal transverse aberration of the optical projection system of Fig. 1 which occurs under conditions where the image height is 10.60 mm. Fig. 3(c) is a diagram showing the meridional transverse aberration in the optical projection system of Fig. 1 which occurs under conditions where the image height is 0 mm. Fig. 3(d) is a diagram showing the sagittal transverse aberration of the optical projection system of Fig. 1 which occurs under conditions where the image height is 0 mm. Fig. 4 is a sectional view of an optical projection system according to a second embodiment of this invention. Fig. 5(a) is a diagram showing the spherical aberration in the optical projection system of Fig. 4. Fig. 5(b) is a diagram showing the astigmatism in the optical projection system of Fig. 4. Fig. 5(c) is a diagram showing the distortion in the optical projection system of Fig. 4. Fig. 6(a) is a diagram showing the meridional transverse aberration in the optical projection system of Fig. 4 which occurs under conditions where an image height is 10.60 mm. Fig. 6(b) is a diagram showing the sagittal transverse aberration of the optical projection system of Fig. 4 which occurs under conditions where the image height is 10.60 mm. Fig. 6(c) is a diagram showing the meridional transverse aberration in the optical projection system of Fig. 4 which occurs under conditions where the image height is 0 mm. Fig. 6(d) is a diagram showing the sagittal transverse aberration of the optical projection system of Fig. 4 which occurs under conditions where the image height is 0 mm. Fig. 7 is a diagram showing the relationship between the modulation transfer function and the spatial frequency in the optical projection system of Fig. 4. Fig. 8 is a sectional view of an optical projection system according to a third embodiment of this invention. Fig. 9(a) is a diagram showing the spherical aberration in the optical projection system of Fig. 8. Fig. 9(b) is a diagram showing the astigmatism in the optical projection system of Fig. 8. Fig. 9(c) is a diagram showing the distortion in the optical projection system of Fig. 8. Fig. 10(a) is a diagram showing the meridional transverse aberration in the optical projection system of Fig. 8 which occurs under conditions where an image height is 10.60 mm. Fig. 10(b) is a diagram showing the sagittal transverse aberration of the optical projection system of Fig. 8 which occurs under conditions where the image height is 10.60 mm. Fig. 10(c) is a diagram showing the meridional transverse aberration in the optical projection system of Fig. 8 which occurs under conditions where the image height is 0 mm. Fig. 10(d) is a diagram showing the sagittal transverse aberration of the optical projection system of Fig. 8 which occurs under conditions where the image height is 0 mm. Fig. 11 is a sectional view of an optical projection system according to a fourth embodiment of this invention. Fig. 12(a) is a diagram showing the spherical aberration in the optical projection system of Fig. 11. Fig. 12(b) is a diagram showing the astigmatism in the optical projection system of Fig. 11. Fig. 12(c) is a diagram showing the distortion in the optical projection system of Fig. 11. Fig. 13(a) is a diagram showing the meridional transverse aberration in the optical projection system of Fig. 11 which occurs under conditions where an image height is 10.60 mm. Fig. 13(b) is a diagram showing the sagittal transverse aberration of the optical projection system of Fig. 11 which occurs under conditions where the image height is 10.60 mm. Fig. 13(c) is a diagram showing the meridional transverse aberration in the optical projection system of Fig. 11 which occurs under conditions where the image height is 0 mm. Fig. 13(d) is a diagram showing the sagittal transverse aberration of the optical projection system of Fig. 11 which occurs under conditions where the image height is 0 mm. Fig. 14 is a sectional view of an optical projection system according to a fifth embodiment of this invention. Fig. 15(a) is a diagram showing the spherical aberration in the optical projection system of Fig. 14. Fig. 15(b) is a diagram showing the astigmatism in the optical projection system of Fig. 14. Fig. 15(c) is a diagram showing the distortion in the optical projection system of Fig. 14. Fig. 16(a) is a diagram showing the meridional transverse aberration in the optical projection system of Fig. 14 which occurs under conditions where an image height is 10.60 mm. Fig. 16(b) is a diagram showing the sagittal transverse aberration of the optical projection system of Fig. 14 which occurs under conditions where the image height is 10.60 mm. Fig. 16(c) is a diagram showing the meridional transverse aberration in the optical projection system of Fig. 14 which occurs under conditions where the image height is 0 mm. Fig. 16(d) is a diagram showing the sagittal transverse aberration of the optical projection system of Fig. 14 which occurs under conditions where the image height is 0 mm. DESCRIPTION OF THE FIRST PREFERRED EMBODIMENT With reference to Fig. 1, an optical projection system according to a first embodiment of this invention includes a first lens 1, a second lens 2 following the first lens 1, and a third lens 3 following the second lens 2. A group 4 of fourth lenses 4a, 4b, and 4c succeeds the third lens 3. The lens 4a of the group 4 immediately follows the third lens 3. In the group 4, the lens 4a precedes the lens 4b, and the lens 4c follows the lens 4b. Incident rays sequentially pass through the first lens 1, the second lens 2, the third lens 3, and the fourth lens group 4. These lenses 1-4c are supported by known devices (not shown) in such a manner that they have a common optical axis. The first lens 1 has a negative refracting power. The second lens 2 has a negative refracting power. The third lens 3 has a positive refracting power. The fourth lenses 4a-4c have positive refracting powers. The fourth lens group 4 has a positive refracting power. It is preferable that at least one of surfaces of the lenses 1-4c is aspherical. It is preferable that the following conditions (1), (2), and (3) are satisfied: (1) 4f < f3 < 20f (2) 0.65 < (f4/d34) < 1.40 (3) 10f < R5 where the character "f" denotes a focal length of the optical projection system, the character "f3" denotes a focal length of the third lens 3, the character "f4" denotes a focal length of the fourth lens group 4, the character "d34" denotes a distance between a rear principal point of the third lens 3 and a front principal point of the fourth lens group 4, and the character "R5" denotes a radius of curvature of a front surface of the third lens 3. Various characters will be introduced to specify the characteristics of the lenses 1-4c and the relationships among the lenses 1-4c. The radii of curvature of the front surface and the rear surface of the first lens 1 are denoted by the characters R1 and R2 respectively. The radii of curvature of the front surface and the rear surface of the second lens 2 are denoted by the characters R3 and R4 respectively. The radii of curvature of the front surface and the rear surface of the third lens 3 are denoted by the characters R5 and R6 respectively. The radii of curvature of the front surface and the rear surface of the lens 4a are denoted by the characters R7 and R8 respectively. The radii of curvature of the front surface and the rear surface of the lens 4b are denoted by the characters R9 and R10 respectively. The radii of curvature of the front surface and the rear surface of the lens 4c are denoted by the characters R11 and R12 respectively. The thickness of the first lens 1 is denoted by the character d1. The thickness of the second lens 2 is denoted by the character d3. The thickness of the third lens 3 is denoted by the character d5. The thickness of the lens 4a is denoted by the character d7. The thickness of the lens 4b is denoted by the character d9. The thickness of the lens 4c is denoted by the character d11. It should be noted that the lens thicknesses d1, d3, d5, d7, d9, and d11 are measured along the optical axis. The distance between the rear surface of the first lens 1 and the front surface of the second lens 2 is denoted by the character d2. The distance between the rear surface of the second lens 2 and the front surface of the third lens 3 is denoted by the character d4. The distance between the rear surface of the third lens 3 and the front surface of the lens 4a is denoted by the character d6. The distance between the rear surface of the lens 4a and the front surface of the lens 4b is denoted by the character d8. The distance between the rear surface of the lens 4b and the front surface of the lens 4c is denoted by the character d10. It should be noted that these distances d2, d4, d6, d8, and d10 are measured along the optical axis. The refractive indexes of glass material of the lenses 1, 2, 3, 4a, 4b, and 4c are denoted by the characters n1, n2, n3, n4, n5, and n6 respectively. These refractive indexes n1-n6 are determined with respect to light having a wavelength of 193 nm. In one example of the optical projection system of this embodiment, the lenses 1, 2, 3, 4a, 4b, and 4c are designed so that the previously-mentioned lens parameters have the following values. R1 = -573.75000 d1 = 200.00 n1 = 1.560769 R2 = 591.4613 d2 = 813.129 R3 = -329.1979* d3 = 90.687 n2 = 1.560769 R4 = -666.4207 d4 = 555.124 R5 = 2262.686* d5 = 140.741 n3 = 1.560769 R6 = -1193.422 d6 = 57.632 R7 = 856.7510 d7 = 153.836 n4 = 1.560769 R8 = -7183.481 d8 = 333.031 R9 = 754.1443 d9 = 129.443 n5 = 1.560769 R10 = -5310.126 d10 = 125.81 R11 = 347.1155 d11 = 149.823 n6 = 1.560769 R12 = 538.1785* where the character "*" denotes that the related surface is aspherical, and the radii R1-R12 and the thicknesses and the distances d1-d11 are represented in unit of mm. The aspherical surfaces (R3, R5, and R12) of the lenses 2, 3, and 4c are designed as follows. In general, the characteristics of an aspherical surface are defined in the following known equation. Z(h) = [(h²/R)/{1 + √ 1 - (1 + K)h²/R² }] + Ah⁴ + Bh⁶ + Ch⁸ + Dh¹⁰ (1) where the character Z(h) denotes a sag quantity; the character "h" denotes a distance from the optical axis; the character R denotes a radius of curvature; the character K denotes a conic coefficient; and the characters A, B, C, and D denote aspherical surface coefficients. In respect of the aspherical surface (R3) of the lens 2, the coefficients K and A-D are chosen as follows. R3: K = -0.03608 A = 2.014E-10 B = -2.302E-15 C = 4.023E-20 D = 2.721E-24 where the character E denotes an exponential, and "E-N" means that the value which precedes "E-N" is multiplied by 10 -N . In respect of the aspherical surface (R5) of the lens 3, the coefficients K and A-D are chosen as follows. R5: K = 5.661 A = -8.343E-10 B = 2.499E-16 C = 2.187E-21 D = -3.910E-23 In respect of the aspherical surface (R12) of the lens 4c, the coefficients K and A-D are chosen as follows. R12: K = 1.810 A = 1.213E-9 B = -2.094E-14 C = 4.809E-18 D = -9.969E-23 The previously-mentioned example of the optical projection system has the following characteristics. Under conditions where light having a wavelength λ of 193 nm is used and an image height Y is 10.60 mm: the focal length "f" of the optical projection system is 100 mm; the numerical aperture N.A. of the optical projection system is 0.45; the magnification of the optical projection system is 1/5; the focal length f3 of the third lens 3 is 1382.40 mm; and the ratio "f4/d34" between the focal length f4 of the fourth lens group 4 and the distance d34 between the rear principal point of the third lens 3 and the front principal point of the fourth lens group 4 is 1.129. Fig. 2(a), Fig. 2(b), and Fig. 2(c) show the spherical aberration, the astigmatism, and the distortion of the previously-mentioned example of the optical projection system respectively. Fig. 3(a) and Fig. 3(b) show the meridional transverse aberration and the sagittal transverse aberration of the previously-mentioned example of the optical projection system respectively under conditions where the image height Y is 10.60 mm. Fig. 3(c) and Fig. 3(d) show the meridional transverse aberration and the sagittal transverse aberration of the previously-mentioned example of the optical projection system respectively under conditions where the image height Y is 0 mm. The first lens 1 and the second lens 2 function to perform a correction which moves Petzval's sum to a value near zero. The third lens 3 and the fourth lens group 4 are designed to form a dioptric Schmidt optical system which corrects the coma and the spherical aberration of the optical projection system. These corrective arrangements and the provision of at least one aspherical lens surface ensure that the optical projection system can be essentially free from aberrations and can be composed of a small number of lenses. In addition, the optical projection system absorbs light at a lower rate than that in the prior art systems. DESCRIPTION OF THE SECOND PREFERRED EMBODIMENT Fig. 4 shows a second embodiment of this invention which is similar to the embodiment of Figs. 1-3 except for the following design changes. The embodiment of Fig. 4 additionally includes a fifth lens 5 which succeeds a fourth lens group 4. The fifth lens 5 has a common optical axis with lenses 1-3 and the fourth lens group 4. The fifth lens 5 has a negative refracting power. The radii of curvature of the front surface and the rear surface of the fifth lens 5 are denoted by the characters R13 and R14. The distance between the rear surface of a lens 4c and the front surface of the fifth lens 5 which is measured along the optical axis is denoted by the character d12. The thickness of the fifth lens 5 which is measured along the optical axis is denoted by the character d13. With respect to light having a wavelength of 193 nm, the refractive index of glass material of the fifth lens 5 is denoted by the character n7. In one example of the optical projection system of this embodiment, the lenses 1, 2, 3, 4a, 4b, 4c, and 5 are designed so that their lens parameters have the following values. R1 = 361.1966* d1 = 17.861 n1 = 1.560769 R2 = 149.2153 d2 = 429.297 R3 = -2254.465* d3 = 16.824 n2 = 1.560769 R4 = 489.8852 d4 = 247.598 R5 = 2993.532* d5 = 52.384 n3 = 1.560769 R6 = -564.7170 d6 = 21.052 R7 = 1029.028 d7 = 64.766 n4 = 1.560769 R8 = -632.4123 d8 = 283.667 R9 = 280.7900 d9 = 48.378 n5 = 1.560769 R10 = 920.3827 d10 = 46.114 R11 = 174.9364 d11 = 45.734 n6 = 1.560769 R12 = 348.2636* d12 = 124.315 R13 = -254.2200* d13 = 16.855 n7 = 1.560769 R14 = -2140.726 where the character "*" denotes that the related surface is aspherical, and the radii R1-R14 and the thicknesses and the distances d1-d14 are represented in unit of mm. The aspherical surfaces (R1, R3, R5, R12, and R13) of the lenses 1, 2, 3, 4c, and 5 are designed as follows. As described previously, the characteristics of an aspherical surface are defined in the equation (1). In respect of the aspherical surface (R1) of the lens 1, the coefficients K and A-D are chosen as follows. R1: K = -5.946 A = 4.194E-8 B = 2.179E-13 C = -1.844E-16 D = 3.136E-20 where the character E denotes an exponential, and "E-N" means that the value which precedes "E-N" is multiplied by 10 -N . In respect of the aspherical surface (R3) of the lens 2, the coefficients K and A-D are chosen as follows. R3: K = -369.862 A = -1.603E-8 B = 2.167E-13 C = -4.502E-18 D = 2.483E-22 In respect of the aspherical surface (R5) of the lens 3, the coefficients K and A-D are chosen as follows. R5: K = 29.473 A = -1.310E-9 B = -7.525E-15 C = 2.489E-20 D = -2.782E-25 In respect of the aspherical surface (R12) of the lens 4c, the coefficients K and A-D are chosen as follows. R12: K = 0.0327 A = -1.065E-9 B = -1.233E-13 C = 8.755E-19 D = 1.161E-23 In respect of the aspherical surface (R13) of the lens 5, the coefficients K and A-D are chosen as follows. R13: K = -62.855 A = -7.389E-7 B = 2.930E-10 C = -2.209E-14 D = -6.476E-17 Under conditions where light having a wavelength λ of 193 nm is used and an image height Y is 10.60 mm: the focal length "f" of the optical projection system is 100 mm; the numerical aperture N.A. of the optical projection system is 0.45; the magnification of the optical projection system is 1/5; the focal length f3 of the third lens 3 is 851.722 mm; and the ratio "f4/d34" between the focal length f4 of the fourth lens group 4 and the distance d34 between the rear principal point of the third lens 3 and the front principal point of the fourth lens group 4 is 0.882. Fig. 5(a), Fig. 5(b), and Fig. 5(c) show the spherical aberration, the astigmatism, and the distortion of the optical projection system respectively. Fig. 6(a) and Fig. 6(b) show the meridional transverse aberration and the sagittal transverse aberration of the optical projection system respectively under conditions where the image height Y is 10.60 mm. Fig. 6(c) and Fig. 6(d) show the meridional transverse aberration and the sagittal transverse aberration of the optical projection system respectively under conditions where the image height Y is 0 mm. Fig. 7 shows the relationship between the modulation transfer function (MTF) and the spatial frequency of the projection optical system under conditions where the image height Y is 10.60 mm and the image height Y is 0 mm. DESCRIPTION OF THE THIRD PREFERRED EMBODIMENT Fig. 8 shows a third embodiment of this invention which is similar to the embodiment of Figs. 4-7 except for the following design changes. In the embodiment of Fig. 8, lenses 1, 2, 3, 4a, 4b, 4c, and 5 are designed so that their lens parameters have the following values. R1 = 505.350* d1 = 3.000 n1 = 1.560769 R2 = 165.000 d2 = 521.550 R3 = -2176.430* d3 = 3.0000 n2 = 1.560769 R4 = 479.6000 d4 = 247.377 R5 = 2477.590* d5 = 50.0000 n3 = 1.560769 R6 = -526.1900 d6 = 11.522 R7 = 1345.960 d7 = 50.000 n4 = 1.560769 R8 = -613.4500 d8 = 356.208 R9 = 294.2700 d9 = 30.000 n5 = 1.560769 R10 = 1232.070 d10 = 30.020 R11 = 193.4100 d11 = 22.000 n6 = 1.560769 R12 = 352.1500* d12 = 161.144 R13 = -160.7380* d13 = 3.0000 n7 = 1.560769 R14 = -301.6440 where the character "*" denotes that the related surface is aspherical, and the radii R1-R14 and the thicknesses and the distances d1-d14 are represented in unit of mm. The aspherical surfaces (R1, R3, R5, R12, and R13) of the lenses 1, 2, 3, 4c, and 5 are designed as follows. As described previously, the characteristics of an aspherical surface are defined in the equation (1). In respect of the aspherical surface (R1) of the lens 1, the coefficients K and A-D are chosen as follows. R1: K = -0.302 A = 2.593E-8 B = 3.952E-13 C = -2.140E-16 D = 3.756E-20 where the character E denotes an exponential, and "E-N" means that the value which precedes "E-N" is multiplied by 10 -N . In respect of the aspherical surface (R3) of the lens 2, the coefficients K and A-D are chosen as follows. R3: K = -184.400 A = -1.541E-8 B = 7.278E-14 C = -2.926E-19 D = 6.444E-23 In respect of the aspherical surface (R5) of the lens 3, the coefficients K and A-D are chosen as follows. R5: K = 41.240 A = -1.168E-9 B = -6.467E-15 C = 2.090E-20 D = -1.210E-25 In respect of the aspherical surface (R12) of the lens 4c, the coefficients K and A-D are chosen as follows. R12: K = 0.0290 A = -1.084E-9 B = -3.270E-14 C = -3.170E-19 D = 2.105E-24 In respect of the aspherical surface (R13) of the lens 5, the coefficients K and A-D are chosen as follows. R13: K = -16.008 A = -5.892E-7 B = 2.437E-10 C = -2.210E-14 D = -6.476E-17 Under conditions where light having a wavelength λ of 193 nm is used and an image height Y is 10.60 mm: the focal length "f" of the optical projection system is 100 mm; the numerical aperture N.A. of the optical projection system is 0.45; the magnification of the optical projection system is 1/5; the focal length f3 of the third lens 3 is 778.620 mm; and the ratio "f4/d34" between the focal length f4 of the fourth lens group 4 and the distance d34 between the rear principal point of the third lens 3 and the front principal point of the fourth lens group 4 is 0.867. Fig. 9(a), Fig. 9(b), and Fig. 9(c) show the spherical aberration, the astigmatism, and the distortion of the optical projection system respectively. Fig. 10(a) and Fig. 10(b) show the meridional transverse aberration and the sagittal transverse aberration of the optical projection system respectively under conditions where the image height Y is 10.60 mm. Fig. 10(c) and Fig. 10(d) show the meridional transverse aberration and the sagittal transverse aberration of the optical projection system respectively under conditions where the image height Y is 0 mm. DESCRIPTION OF THE FOURTH PREFERRED EMBODIMENT Fig. 11 shows a fourth embodiment of this invention which is similar to the embodiment of Figs. 4-7 except for the following design changes. In the embodiment of Fig. 11, lenses 1, 2, 3, 4a, 4b, 4c, and 5 are designed so that their lens parameters have the following values. R1 = 4480.716* d1 = 57.718 n1 = 1.560769 R2 = 454.077 d2 = 386.334 R3 = -4709.995* d3 = 22.256 n2 = 1.560769 R4 = 1649.148 d4 = 296.127 R5 = 2547.206* d5 = 26.707 n3 = 1.560769 R6 = -661.2696 d6 = 180.065 R7 = 590.0694 d7 = 53.909 n4 = 1.560769 R8 = -1050.142 d8 = 16.682 R9 = 273.9922 d9 = 39.849 n5 = 1.560769 R10 = 892.8735 d10 = 4.125 R11 = 128.7190 d11 = 53.888 n6 = 1.560769 R12 = 232.1479* d12 = 113.451 R13 = -190.5371* d13 = 13.384 n7 = 1.560769 R14 = 429.5090 where the character "*" denotes that the related surface is aspherical, and the radii R1-R14 and the thicknesses and the distances d1-d14 are represented in unit of mm. The aspherical surfaces (R1, R3, R5, R12, and R13) of the lenses 1, 2, 3, 4c, and 5 are designed as follows. As described previously, the characteristics of an aspherical surface are defined in the equation (1). In respect of the aspherical surface (R1) of the lens 1, the coefficients K and A-D are chosen as follows. R1: K = -109.360 A = 1.387E-8 B = -1.549E-12 C = 8.326E-17 D = -1.882E-20 where the character E denotes an exponential, and "E-N" means that the value which precedes "E-N" is multiplied by 10 -N . In respect of the aspherical surface (R3) of the lens 2, the coefficients K and A-D are chosen as follows. R3: K = -3933.68 A = -2.565E-8 B = 3.056E-13 C = -7.972E-18 D = 3.337E-22 In respect of the aspherical surface (R5) of the lens 3, the coefficients K and A-D are chosen as follows. R5: K = 3.993 A = -1.415E-9 B = -5.250E-14 C = -5.048E-19 D = -1.293E-23 In respect of the aspherical surface (R12) of the lens 4c, the coefficients K and A-D are chosen as follows. R12: K = -0.00887 A = -1.399E-9 B = -3.901E-13 C = -2.368E-19 D = 1.441E-22 In respect of the aspherical surface (R13) of the lens 5, the coefficients K and A-D are chosen as follows. R13: K = 5.798 A = -8.440E-7 B = 5.184E-10 C = -2.209E-14 D = -6.476E-17 Under conditions where light having a wavelength λ of 193 nm is used and an image height Y is 10.60 mm: the focal length "f" of the optical projection system is 100 mm; the numerical aperture N.A. of the optical projection system is 0.45; the magnification of the optical projection system is 1/5; the focal length f3 of the third lens 3 is 905.876 mm; and the ratio "f4/d34" between the focal length f4 of the fourth lens group 4 and the distance d34 between the rear principal point of the third lens 3 and the front principal point of the fourth lens group 4 is 0.907. Fig. 12(a), Fig. 12(b), and Fig. 12(c) show the spherical aberration, the astigmatism, and the distortion of the optical projection system respectively. Fig. 13(a) and Fig. 13(b) show the meridional transverse aberration and the sagittal transverse aberration of the optical projection system respectively under conditions where the image height Y is 10.60 mm. Fig. 13(c) and Fig. 13(d) show the meridional transverse aberration and the sagittal transverse aberration of the optical projection system respectively under conditions where the image height Y is 0 mm. DESCRIPTION OF THE FIFTH PREFERRED EMBODIMENT Fig. 14 shows a fifth embodiment of this invention which is similar to the embodiment of Figs. 4-7 except for the following design changes. In the embodiment of Fig. 14, lenses 1, 2, 3, 4a, 4b, 4c, and 5 are designed so that their lens parameters have the following values. R1 = -647.0977 d1 = 200.00 n1 = 1.560769 R2 = 545.1320 d2 = 821.1736 R3 = -333.2931* d3 = 86.586 n2 = 1.560769 R4 = -715.0375 d4 = 549.439 R5 = 2243.695* d5 = 143.590 n3 = 1.560769 R6 = -1201.589 d6 = 66.666 R7 = 855.2784 d7 = 149.058 n4 = 1.560769 R8 = -7031.113 d8 = 330.014 R9 = 758.2768 d9 = 120.777 n5 = 1.560769 R10 = -5024.299 d10 = 126.382 R11 = 352.3274 d11 = 152.195 n6 = 1.560769 R12 = 547.6737* d12 = 58.639 R13 = 389366.05* d13 = 0.0004 n7 = 1.560769 R14 = 80504.838 where the character "*" denotes that the related surface is aspherical, and the radii R1-R14 and the thicknesses and the distances d1-d14 are represented in unit of mm. The aspherical surfaces (R3, R5, R12, and R13) of the lenses 2, 3, 4c, and 5 are designed as follows. As described previously, the characteristics of an aspherical surface are defined in the equation (1). In respect of the aspherical surface (R3) of the lens 2, the coefficients K and A-D are chosen as follows. R3: K = -0.05174 A = 2.681E-10 B = -8.178E-16 C = 5.872E-20 D = 2.065E-24 where the character E denotes an exponential, and "E-N" means that the value which precedes "E-N" is multiplied by 10 -N . In respect of the aspherical surface (R5) of the lens 3, the coefficients K and A-D are chosen as follows. R5: K = 5.8542 A = -8.318E-10 B = 2.365E-16 C = -2.343E-21 D = -2.984E-27 In respect of the aspherical surface (R12) of the lens 4c, the coefficients K and A-D are chosen as follows. R12: K = 1.6202 A = 1.038E-9 B = -1.150E-14 C = 3.064E-18 D = 9.213E-23 In respect of the aspherical surface (R13) of the lens 5, the coefficients K and A-D are chosen as follows. R13: K = 0.0000 A = -1.434E-10 B = -1.001E-10 C = 2.288E-17 D = -2.529E-30 Under conditions where light having a wavelength λ of 193 nm is used and an image height Y is 10.60 mm: the focal length "f" of the optical projection system is 100 mm; the numerical aperture N.A. of the optical projection system is 0.45; the magnification of the optical projection system is 1/5; the focal length f3 of the third lens 3 is 1416.653 mm; and the ratio "f4/d34" between the focal length f4 of the fourth lens group 4 and the distance d34 between the rear principal point of the third lens 3 and the front principal point of the fourth lens group 4 is 1.125. Fig. 15(a), Fig. 15(b), and Fig. 15(c) show the spherical aberration, the astigmatism, and the distortion of the optical projection system respectively. Fig. 16(a) and Fig. 16(b) show the meridional transverse aberration and the sagittal transverse aberration of the optical projection system respectively under conditions where the image height Y is 10.60 mm. Fig. 16(c) and Fig. 16(d) show the meridional transverse aberration and the sagittal transverse aberration of the optical projection system respectively under conditions where the image height Y is 0 mm.

Claims: An optical projection system for photolithography comprising: a first lens (1), a second lens (2), and a third lens (3) arranged successively in a direction of travel of a ray, the first lens (1) having a predetermined negative refracting power, the second lens (2) having a predetermined negative refracting power, the third lens (3) having a predetermined positive refracting power; a group of fourth lenses (4) which follows the third lens (3) in the direction of travel of the ray and which has a predetermined positive refracting power; wherein at least one of the surfaces of the first (1), second (2), third (3), and fourth lenses (4a, 4b, 4c) is aspherical, and wherein the following conditions (1), (2), and (3) are satisfied: (1) 4f < f3 < 20f (2) 0.65 < (f4/d34) < 1.40 (3) 10f < R5 where the character "f" denotes a focal length of the optical projection system, the character "f3" denotes a focal length of the third lens (3), the character "f4" denotes a focal length of the fourth lens group (4), the character "d34" denotes a distance between a rear principal point of the third lens (3) and a front principal point of the fourth lens group (4), and the character "R5" denotes a radius of curvature of a front surface of the third lens (3). The optical projection system of claim 1 wherein the front surface of the third lens (3) is aspherical. The optical projection system of claim 1 wherein each of the fourth lenses (4a, 4b, 4c) has a predetermined positive refracting power. An optical projection system for photolithography comprising: a first lens (1), a second lens (2), and a third lens (3) arranged successively in a direction of travel of a ray, the first lens (1) having a predetermined negative refracting power, the second lens (2) having a predetermined negative refracting power, the third lens (3) having a predetermined positive refracting power; a group of fourth lenses (4) which follows the third lens (3) in the direction of travel of the ray and which has a predetermined positive refracting power; a fifth lens (5) following the fourth lens group (4) in the direction of travel of the ray and having a predetermined negative refracting power; wherein at least one of the surfaces of the first (1), second (2), third (3), fourth lenses (4a, 4b, 4c), and fifth lenses (5) is aspherical, and wherein the following conditions (1), (2), and (3) are satisfied: (1) 4f < f3 < 20f (2) 0.65 < (f4/d34) < 1.40 (3) 10f < R5 where the character "f" denotes a focal length of the optical projection system, the character "f3" denotes a focal length of the third lens (3), the character "f4" denotes a focal length of the fourth lens group (4), the character "d34" denotes a distance between a rear principal point of the third lens (3) and a front principal point of the fourth lens group (4), and the character "R5" denotes a radius of curvature of a front surface of the third lens. The optical projection system of claim 4 wherein the front surface of the third lens (3) is aspherical. The optical projection system of claim 4 wherein each of the fourth lenses (4a, 4b, 4c) has a predetermined positive refracting power.

Inventors: ARAKI NOBUHIRO, KAWATA KOICHI, KOGA KEISUKE, NOMURA NOBORU, SATO TAKEO, ARAKI, NOBUHIRO, KAWATA, KOICHI, KOGA, KEISUKE, NOMURA, NOBORU, SATO, TAKEO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1989
Main classification: G02B13
IPC codes: G02B13