JPH07128592A - Reduction stepping lens - Google Patents

Abstract

PURPOSE:To provide the reduction stepping lens which is improved in transmittance and is provided with high resolution by reducing the total thickness of the glass material of a lens system. CONSTITUTION:This reduction stepping lens is composed of total three groups; a first group I having a negative refracting power, a second group II having a positive refracting power and a third group III having a positive refracting power and is constituted to satisfy the conditions 3<¦f1/f¦<5, 10<f2/f<25 when the focal lengths of the first group I, the second group II and the entire system are respectively defined as f1 f2 and f. The respective groups have at least one face of aspherical faces. The respective aspherical faces are preferably aspherical faces of a shape to weaken the refracting power near the optical axis nearer the peripheral edges from the optical axis of the lenses. The respective lenses are preferably composed of the glass material having a refractive index of 3<=1.6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reduction projection lens mounted in an apparatus for manufacturing integrated circuits such as ICs and LSIs, and particularly to a circuit pattern from a mask on which a circuit pattern is drawn by a reduction projection exposure method. The present invention relates to a reduction projection lens used when transferring a film onto a silicon wafer.

[0002]

2. Description of the Related Art Generally, the resolving power of a projected image by a projection lens is proportional to its numerical aperture and inversely proportional to the wavelength used. In recent years, as circuit patterns have become highly integrated, lenses with good resolving power have been required, and as the numerical aperture increases, the resolving power improves in proportion to it, but the depth of focus becomes shallower. , The focus will need to be very accurate. Further, the silicon wafer on which the circuit pattern is transferred is required to have a very strict flatness, which is not suitable for practical use. Therefore, in recent years, rather than increasing the numerical aperture, the wavelength used has been shortened to increase the resolution while maintaining the depth of focus.

Currently, from 436 nm by mercury lamp to 3
Light of 65 nm has come to be used, but in recent years,
JP-A-60-140310 and 193n using a KrF excimer laser having an emission spectrum of 248 nm.
There is a proposal such as Japanese Patent Laid-Open No. 1-315709 which uses an ArF excimer laser having an emission spectrum of m.

[0004]

By the way, when the wavelength used for projection exposure is 250 nm or less, the glass material is made of SiO ₂ from the viewpoint that the transmittance of the usable glass material is less likely to decrease.
Or, it is limited to CaF ₂ . Moreover, considering workability and the like, there is no glass material that can use only SiO ₂ , and further, at a wavelength of 200 nm or less, the transmittance is low even if this SiO ₂ is used. A conventional reduction projection lens that uses an excimer laser as the light source and uses SiO ₂ has a large number of lenses and a large total thickness of the glass material, so the transmittance is low. Therefore, the magnification fluctuation and the best focus fluctuation due to the exposure light heat absorption of the lens However, there are problems such as low throughput due to insufficient exposure.

The present invention has been made in view of such circumstances, and an object thereof is to provide a high-resolution reduction projection lens capable of improving the transmittance by reducing the total thickness of the glass material of the lens system. Is to provide.

[0006]

In order to achieve the above object, the reduction projection lens of the present invention comprises, in order from the object side, a first lens group having a negative refractive power and a second lens group having a positive refractive power. It is composed of a total of three groups including a lens group and a third lens group having a positive refractive power, and the focal lengths of the first lens group, the second lens group, and the entire system are f ₁ , f ₂ , and f, respectively. When this is done, the following conditions are satisfied.

3 <| f ₁ / f | <5 (1) 10 <f ₂ / f <25 (2) In this case, each group has at least one aspherical surface, The aspherical surface is preferably an aspherical surface having a shape that weakens the refractive power in the vicinity of the optical axis from the lens optical axis toward the periphery. Further, it is desirable that each lens is made of a glass material having a refractive index of 1.6 or less.

[0008]

The reason why the above configuration is adopted and the operation thereof will be described in detail below. As a reduction projection lens, the field curvature must be almost completely corrected in order to secure high resolution and a wide exposure area. In order to correct the field curvature, the Petzval sum should be suppressed to a small value.
It is necessary to arrange a large number of lenses having negative refracting power at appropriate positions. Therefore, the reduction projection lens is inevitably increased in the number of lenses.

On the other hand, in order to increase the transmittance of the reduction projection lens, it is necessary to reduce the total thickness of the glass material. For that purpose, it is necessary to reduce the thickness of each lens and reduce the number of lenses. is necessary. That is, it is difficult to simultaneously satisfy the condition of ensuring high resolution and the condition of reducing the total thickness of the glass material.

In order to effectively reduce the Petzval sum with a small number of lenses, the reduction projection lens of the present invention has a large refractive power due to the negative refractive power of the first lens unit disposed near the object plane and having a low ray height. A negative Petzval value is generated, and the positive Petzval sum is reduced by the positive refracting power of the second lens group and the third lens group, which are arranged at positions where the ray height on the image plane side is high thereafter. . With this configuration, the Petzval sum can be reduced with a small number of lenses.

The conditional expressions for | f ₁ / f | and f ₂ / f limit the refracting power of each lens group, and are constituent requirements necessary for achieving a high resolution projection lens. .
In this case, if | f ₁ / f | is 5 or more, the refracting power of the first lens group becomes too small, and the overall Patzval sum cannot be suppressed small. If it is 3 or less, the negative refracting power is negative. Becomes larger, the curvature of the surface of the first lens group becomes tighter, and the generation of various aberrations becomes larger. Also, f ₂ / f
Is more than 25, it is impossible to form a light beam with a small number of lenses having a positive refractive power, and if less than 10, the positive refractive power becomes large and negative spherical aberration occurs. Grows larger.

Further, the front focal position of the third lens group is f
_{When 3F} and the distance from f _3F with respect to the rear principal point of the second lens unit as d _S , it is desirable that the following conditions be satisfied.

−0.1 <d _S / f ₂ <0.2 (3) The sign of the expression (3) is f _3F from the rear principal point of the second lens group.
When is on the image side, it is positive, and when it is on the object side, it is negative. In the reduction projection lens as in the present invention, the exit side telecentric is generally used in order to suppress the fluctuation of the image magnification due to the defocus of the image surface or the poor flatness of the image surface. In the case of the present invention, f _3F corresponds to the pupil position. That is, the above conditions define the relationship between the second lens group and the pupil position. -0.1> d _S / f
_{When the value} becomes 2, inner coma aberration is generated in the second lens group, synergizes with inner coma aberration generated in the first lens group, and it becomes difficult to correct coma aberration in the third lens group. On the other hand, d _S / f ₂ > 0.2
Then, the outer coma aberration is excessively generated, and the aspherical surface of the third lens group has a function of correcting the spherical aberration and producing the outer coma aberration as described later. In addition, the outer coma aberration of the second and third lens groups increases, and the outer coma aberration remains as a whole.

Separately, the reduction projection lens of this construction is
It is desirable to have at least one aspherical surface in each group. This is to correct various aberrations that cannot be corrected by the above-described configuration with a small number of lenses. The aspherical surface of the first lens group is used to correct the positive distortion aberration generated here. The aspherical surface of the second lens group is used to correct negative spherical aberration due to the small number of constituent lens elements. The aspherical surface of the third lens group is used for correcting the inner coma aberration generated in the first lens group and for correcting the spherical aberration generated in the main lens group itself. Furthermore, it is preferable that these aspherical surfaces are aspherical surfaces having a shape in which the refractive power in the vicinity of the optical axis is weakened from the lens optical axis toward the periphery.

Separately, the reduction projection lens of this structure is
It is preferable to use a glass material having a refractive index of 1.6 or less. This is because it is not necessary to consider the chromatic aberration of the lens when using light with a very narrow spectral width such as an excimer laser, and it is necessary to use a glass material having a refractive index of 1.6 or more for correcting chromatic aberration. Because there is no.

[0016]

EXAMPLES Examples 1 to 1 of the reduction projection lens of the present invention will be described below.
4 will be described. 1 to 4 show Embodiments 1 to 1, respectively.
4 shows a lens cross-sectional view of No. 4, but in any embodiment,
Magnification is 1/5, numerical aperture is 0.45, object-image distance is 100
The exposure area is 0 mm, the exposure area is 10 × 10 mm, and the glass material is made of SiO ₂ . The lens data of these examples will be described later.

First, a first embodiment of the present invention will be described. In FIG. 1, the first group I is one negative meniscus lens with a convex surface facing the object side, and the second group II is a biconvex lens 1.
The third lens group III consists of two positive meniscus lenses with the concave surface facing the image side and a positive power meniscus lens with the concave surface facing the image side. It consists of three meniscus lenses.

In Example 1 and Example 2 described below, one powerless meniscus lens having a concave surface facing the image side is arranged particularly near the image plane of the third lens group III. In this case, it is more preferable to use an aspherical surface on at least one of the surfaces in order to correct higher-order coma. Further, when the focal length of this powerless meniscus lens is f ₃₃ , it is preferable that the following condition is satisfied. When 2000 (mm) <| f ₃₃ | (4) | f ₃₃ | is 2000 mm or less, low-order coma aberration occurs in the spherical component.

Next, a second embodiment of the present invention will be described. In FIG. 2, the first group I is composed of one negative meniscus lens having a convex surface facing the object side, the second group II is composed of one positive meniscus lens having a convex surface facing the object side, and the third group III is composed of both lenses. It consists of one convex lens, one positive meniscus lens with a concave surface facing the image side, and one powerless meniscus lens with a concave surface facing the image side, for a total of three lenses. The powerless meniscus lens having the concave surface facing the image side of the third lens group III has the same operation as that of the first embodiment.

Next, the third embodiment of the present invention will be described with reference to FIG.
In the first group I, one negative meniscus lens having a convex surface facing the object side is used, the second group II is one positive meniscus lens having a convex surface facing the object side, and the third group III is a biconvex lens 1 And one positive meniscus lens with a concave surface facing the image side.

In the fourth embodiment of the present invention, in FIG. 4, the first group I is one negative meniscus lens having a convex surface facing the object side, and the second group II is a positive meniscus lens having a convex surface facing the object side. From one meniscus lens, the third group III consists of one biconvex lens and one positive meniscus lens with the concave surface facing the image side.

The lens data of each embodiment are shown below.
In the lens data, R ₁ , R ₂ , ... Are the radius of curvature of each lens surface, d ₁ , d ₂ ... Are the intervals between the lens surfaces,
n ₁ , n ₂ , ... Are the refractive indices of each lens at 193 nm, and the aspherical shape is expressed by the following equation, where x is the optical axis direction and y is the direction orthogonal to the optical axis. It ^{x = (y 2 / r)} / [1+ {1- (y 2 / r 2)}
^1/2 ] + Ay ⁴ + By ⁶ + Cy ⁸ + Dy ¹⁰ where r is a paraxial radius of curvature, and A, B, C, and D are fourth-order, sixth-order, eighth-order, and tenth-order aspherical coefficients, respectively.

Example 1 R ₁ = 149.072 d ₁ = 4 n ₁ = 1.56 R ₂ = 53.071 (aspherical surface) d ₂ = 580.412 R ₃ = 685.808 d ₃ = 1.808 n ₂ = 1.56 R ₄ = -855.88 d ₄ = _{0.08 R 5 = 332.732 d 5 =} 10.304 n 3 = 1.56 R 6 = 970.134 ( _{aspherical) d 6 = 196.429 R 7 =} 236.31 d 7 = 10.938 n 4 = 1.56 R 8 = 1175.523 d 8 = 0.714 R 9 = 87.26 d _{9 = 42.891 n 5 = 1.56 R} 10 = 194.005 d 10 = 53.429 R 11 = 68.841 ( _{aspherical) d 11 = 13.136 n 6 =} 1.56 R 12 = 59.862 aspheric coefficient the second surface A = -0.105 × 10 ^-5 B = -0.126 × 10 ^-9 C = -0.242 × 10 ^-13 D = -0.176 × 10 ^-16 6th surface A = 0.986 × 10 ^-8 B = 0.485 × 10 ^-13 C = 0.116 × 10 ^-17 D = 0.44 × 10 ^-22 11th surface A = -0.745 × 10 ^-6 B = -0.359 × 10 ^-9 C = -0.115 × 10 ^-12 D = -0.595 × 10 ^-17
.

Example 2 R ₁ = 1736.215 d ₁ = 5.866 n ₁ = 1.56 R ₂ = 68.889 (aspherical surface) d ₂ = 543.701 R ₃ = 263.312 d ₃ = 1.11.509 n ₂ = 1.56 R ₄ = 819.653 (aspherical surface) _{d 4 = 165.728 R 5 = 220.315} d 5 = 22.409 n 3 = 1.56 R 6 = -1415.823 d 6 = 49.904 R 7 = 106.825 d 7 = 37.488 n 4 = 1.56 R 8 = 254.313 d 8 = 46.233 R 9 = 96.597 ( _{aspherical) d 9 = 6.904 n 5 =} 1.56 R 10 = 103.38 second surface A = -0.639 × 10 ^-6 aspherical coefficient ^{B = -0.155 × 10 -10 C =} -0.103 × 10 -13 D = 0.563 × 10 ^-18 4th surface A = 0.223 × 10 ^-7 B = 0.151 × 10 ^-12 C = 0.241 × 10 ^-17 D = 0.209 × 10 ^-21 9th surface A = -0.277 × 10 ^-6 B = -0.522 × 10 ^-10 C = -0.497 x 10 ^-14 D = 0.69 x 10 ^-18
.

Example 3 R ₁ = 6336.701 d ₁ = 4 n ₁ = 1.56 R ₂ = 65.016 (aspherical surface) d ₂ = 561.539 R ₃ = 261.005 d ₃ = 15.817 n ₂ = 1.56 R ₄ = ∞ (aspherical surface) _{d 4 = 176.959 R 5 = 232.483} d 5 = 20.768 n 3 = 1.56 R 6 = -632.184 d 6 = 40.867 R 7 = 126.144 d 7 = 28.872 n 4 = 1.56 R 8 = 413.522 ( aspherical surface) aspherical coefficients second Surface A = -0.779 × 10 ^-6 B = -0.179 × 10 ^-10 C = -0.182 × 10 ^-13 D = 0.307 × 10 ^-17 4th surface A = 0.268 × 10 ^-7 B = 0.792 × 10 ^-13 C = 0.250 x 10 ^-17 D = 0.155 x 10 ^-21 8th surface A = 0.438 x 10 ^-7 B = 0.215 x 10 ^-12 C = 0.424 x 10 ^-16 D = 0.645 x 10 ^-20
.

Example 4 R ₁ = 7761.76 d ₁ = 4 n ₁ = 1.56 R ₂ = 65.426 (aspherical surface) d ₂ = 566.358 R ₃ = 260.181 d ₃ = 14.689 n ₂ = 1.56 R ₄ = 3358.89 (aspherical surface) _{d 4 = 167.605 R 5 = 217.213} d 5 = 21.986 n 3 = 1.56 R 6 = -768.035 ( _{aspherical) d 6 = 44.28 R 7 =} 137.413 d 7 = 26.994 n 4 = 1.56 R 8 = 634.5 ( aspherical) non Spherical coefficient 2nd surface A = -0.777 × 10 ^-6 B = -0.144 × 10 ^-10 C = -0.182 × 10 ^-13 D = 0.307 × 10 ^-17 4th surface A = 0.275 × 10 ^-7 B = 0.13 × 10 ^-12 C = 0.417 x 10 ^-17 D = 0.175 x 10 ^-21 6th surface A = 0.523 x 10 ^-9 B = -0.25 x 10 ^-12 C = 0.951 x 10 ^-17 D = -0.425 x 10 ^-22 Eighth surface A = 0.484 x 10 ^-7 B = 0.678 x 10 ^-12 C = 0.114 x 10 ^-16 D = 0.534 x 10 ^-20
.

Next, FIGS. 5 to 5 are aberration diagrams showing spherical aberration, astigmatism, distortion, and lateral aberration in the above-mentioned Examples 1 to 4, respectively.
It shows in FIG. In the figure, Y is the image height ratio, M is the meridional image plane, and S is the sagittal image plane. The values of the conditional expressions (1) to (3) of each example are shown in the following table.

[0028]

As described above, according to the present invention,
It is possible to obtain a high-resolution reduction projection lens having a thin total thickness of the glass material of the lens system and good transmittance.

[Brief description of drawings]

FIG. 1 is a lens sectional view of a reduction projection lens according to a first embodiment of the present invention.

FIG. 2 is a lens cross-sectional view of Example 2.

FIG. 3 is a lens cross-sectional view of Example 3.

FIG. 4 is a lens cross-sectional view of Example 4.

FIG. 5 is an aberration diagram showing spherical aberration, astigmatism, distortion, and lateral aberration of Example 1.

FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, distortion, and lateral aberration of Example 2.

FIG. 7 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and lateral aberration of Example 3.

FIG. 8 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and lateral aberration of Example 4.

[Explanation of symbols]

 I ... 1st lens group II ... 2nd lens group III ... 3rd lens group

Claims (3)

[Claims] 1. A first lens element having a negative refractive power in order from the object side.
The first lens group is composed of a lens group, a second lens group having a positive refractive power, and a third lens group having a positive refractive power.
A reduction projection lens characterized by satisfying the following conditions when the focal lengths of the lens group, the second lens group, and the entire system are f ₁ , f ₂ , and f, respectively. 3 <| f ₁ / f | <5 (1) 10 <f ₂ / f <25 (2) 2. Each group has at least one aspherical surface,
2. The reduction projection lens according to claim 1, wherein each aspherical surface is an aspherical surface having a shape in which the refractive power near the optical axis is weakened toward the periphery from the optical axis of the lens. 3. The reduction projection lens according to claim 1, wherein each lens is made of a glass material having a refractive index of 1.6 or less.