JPS60140310A - Projecting lens - Google Patents

Abstract

PURPOSE:To correct satisfactorily an aberration by constituting the first - the third lens groups of a refractive power of positive, negative and positive in order from an object side, of plural lenses of a single glass material, and satisfying a specified condition between focal distances of each leans group. CONSTITUTION:The first - the third lens groups I , II and III having a refractive power of positive, negative and positive in order from an object are constituted. Each lens group I -III is constituted of plural lenses by using a single glass material, for instance, a molten quartz. When focal distances of each lens group I -III are denoted as f1, f2 and f3, respectively, a condition of 0.8<=¦f1/ f2¦<=3.8, and 1.1<=¦f1/f3¦<=4 is satisfied. In this way, it becomes unnecessary to take a chromatic aberration into consideration, and a lens having a high performance is constituted against a narrow light emitting spectrum.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a projection lens used when manufacturing integrated circuits such as ICs and LSIs using a projection exposure apparatus.
The present invention relates to a projection lens that is effective when printing an integrated circuit pattern onto a silicon wafer or the like using a light source that emits an emission spectrum close to a short-wavelength bright line in the range of nm to 400 nm.

Conventionally, projection lenses for printing patterns of integrated circuits such as ICs and LSIs on entire silicon wafers using a projection exposure apparatus t'z have been required to have extremely high resolution.

In general, the shorter the wavelength used, the better the resolution of the image projected by the projection lens, so a light source that emits as short a wavelength as possible has been used. For example, at present, light with a wavelength of 436 nm or 365 nm from a mercury lamp is often used in projection exposure apparatuses. In order to obtain a high resolving power, a projection lens is required to have an optical system that can completely correct aberrations and have a resolving power close to the theoretical limit value. In particular, in order to print a pattern, aberrations are corrected so that the resolving power is not limited to only one corner of the screen, but extends over the entire screen to the theoretical limit. For example, in the manufacture of integrated circuits, the process of printing integrated circuit patterns is performed multiple times, so a projection lens is used in which distortions among various optical sorptions are almost completely corrected.

The wavelength of the mercury lamp used in projection exposure equipment is 365 n.
When using light with a small wavelength width centered around a single line of Fraunhofer sand, four to five types of glass materials with good transmittance on the short wavelength side are used to eliminate chromatic aberration. Also, for these glass materials, errors between values such as refractive index 1 dispersion used in design values and actual values, and variations in various values within the same glass material, are Lenses, TV lenses.

The requirements are more than one order of magnitude stricter than other general optical systems such as .

This is because various aberrations such as chromatic aberration must be corrected in units of a fraction of a wavelength by utilizing the slight difference in refractive index and dispersion of the glass material that constitutes the projection lens.

Further, as a projection lens, it is preferable to use an optical system as bright as possible, but the transmittance of glass materials on the short wavelength side is low, and since a large number of lenses are used, it is generally difficult to obtain high transmittance.

For example, a projection lens targeting wavelength 436 nm and wavelength 3
In a projection lens targeted at 65 nm, the transmittance of the latter is about % to 1 of the transmittance of the former.

For this reason, in a projection exposure apparatus f intended for short wavelengths, a reflection system is used, or a projection lens using a ridge glass having good transmittance on the short wavelength side is used.

The present invention is characterized by providing a high-performance projection lens for a projection exposure apparatus using a light source having a relatively narrow emission spectrum distribution within a wavelength range of about 15 Qnm to 400 nm. The object of the present invention is to provide a projection lens that exhibits a unique effect when the wavelength width is narrowed by means such as injection and locking using an excimer laser as the main emission spectrum.

The main features of the projection lens for achieving the object of the present invention are, in order from the object side, positive, negative, and positive refractive powers Ml;
The third lens group is composed of three lens groups, and the gL second . The third lens group is composed of a plurality of lenses each made of a single glass material, and the first lens group is composed of a plurality of lenses each made of a single glass material. second and third
When the focal lengths of the lens groups are f, , f, , f, respectively, 08 ≦ l fl/f2 1 ≦ 3.8...
... (1) 11 ≦ l fI/ f* l ≦
4. The following condition (2) must be satisfied.

The reason why it was constructed from a single glass material was because the wavelength range used was light with a very narrow emission spectrum of an excimer laser, so there was no need to consider chromatic aberration. Preferably, multiple glass materials are used to correct chromatic aberration.

All of the embodiments of the projection lens of the present invention, which will be described later, are made of a single glass material of only fused silica, and the wavelength used is 248.
Mainly 5 nm. However, if it is a material that transmits light with a wavelength of 248.5 nm, it does not need to be fused silica, for example, C.
aF, , MgP, etc. may also be used.

The projection lens of the present invention has three lens groups, and is a reduction system in which the second lens group with negative refractive power is located in the center of the lens, and the first and third lens groups with positive refractive power are arranged on both sides of the second lens group. By setting the above-mentioned conditional expression (11, f2+), good aberration correction is achieved.

The condition (11, <21 is based on properly setting the refractive power of each lens group, which is one of the basics of lens performance)
If the lower limit value is exceeded in order to properly correct the N-curvature, the Petzval sum will become large and the image plane will be under-corrected, and if the upper limit value is exceeded, the field curvature will be over-corrected and it is difficult to properly correct aberrations over the entire screen. It becomes difficult.

Furthermore, in order to achieve better aberration correction in the present invention, the lens group is composed of two lens groups I, I, having negative and positive refractive powers in order from the object side, and the lens group At least one of each of a double-convex lens (21) having convex surfaces and a lens Ill having a positive refractive power is composed of M lenses, and the focal length of the lens group (2) is set to f12.
The second lens group is configured to have a meniscus-shaped lens with negative refractive power with convex surfaces facing the object side and the image side, and the focal length of the second lens group is f2. It is to be completely satisfied.

The lens L2 F:): The supplementary magnification of the projection lens is
, 17, it is preferable to use a meniscus-shaped lens with a convex surface facing the object 11111, and when the reduction magnification is about 1/7 to 1/12, it is preferable to use a biconvex lens to properly correct aberrations.

In order to maintain good imaging performance as a projection lens over the entire screen, in addition to the Kr/i and field curvature conditions, coma aberration is compensated for almost zero over the entire screen, iE L, and in addition, spherical aberration and axial aberration. The outer halo aberration must be corrected.

For this purpose, in an optical system that satisfies the conditions m and f21, it is preferable to construct the second lens group with meniscus-shaped lenses with negative refractive power, with convex surfaces facing the object side and the image plane side, respectively. ), in the projection lens of the present invention, spherical aberration is mainly corrected by appropriately setting the radius of curvature of the lens surface of the second lens group. At this time, the coma retraction is corrected at the same time as the spherical retraction, and for this purpose, it is preferable that the second lens group is composed of at least two meniscus-shaped lenses VC having negative )ffA refracting power. One is to have a lens shape with a convex surface facing the object side, and the other is to have a lens shape with a convex surface facing the image plane. The entire lens system consists of three lens groups: positive, negative, and positive, with the second lens group and the first lens group. This is to provide an effect of correcting insufficient correction of spherical aberration occurring in the third lens group. By further arranging at least two meniscus-shaped lenses with refractive power in the second lens group as described above, comatic aberration can be corrected, that is, the beam portion above and the beam portion below the off-axis principal ray. is balanced with. In other words, the lower beam part is formed by a meniscus lens placed on the object side with its convex surface facing the object side, and the upper beam part is formed by a negative meniscus lens placed on the image side with its convex surface facing the image plane. The aberration f of the off-axis light beam can be corrected in a well-balanced manner, and the off-axis coma yield can be well corrected. Moreover, since the principal ray of the off-axis beam passes near the optical axis of the second lens group, the configuration (shape) of the second lens group itself does not have much influence on distortion and astigmatism, and the refractive system is divided into three parts. By keeping the system to condition (output (2)), the second lens group can effectively correct spherical aberration and coma aberration. In particular, coma aberration can be corrected by appropriately arranging the negative meniscus lens described above. Furthermore, in order to satisfactorily correct off-axis meridional and sagittal haloes, it is preferable to satisfy condition (3). If the combined refractive power of the meniscus lens group is too strong compared to the refractive power of the second lens group, which is the second partial system, the biconvex lens and positive lens of the lens group will cause spherical convergence, and when coma aberration is corrected. , high-order halo aberration occurs in the lens group, and it is difficult to correct it over the entire screen, especially when using a single glass material. If all aberrations are corrected, surface aberrations will occur, making it difficult to achieve good correction.

Therefore, it is particularly preferable for a lens system made of a single glass material to satisfy conditions (1) and (2) and to be within the range of condition (X(). +31
゜ (6), +71, (8), +91 all satisfy condition (3) 1-1 Example 1, 4+, +11
indicates that the value is close to that limit. Condition flj,
t2+, (3) was a condition to satisfy the imaging performance (resolution, contrast ratio) required for a projection lens for printing integrated circuits, but it is also an important performance condition required for a projection lens. There is distortion.

Since the printing process is performed many times when manufacturing ICs and LSIs, alignment must be performed at each step, and in order to achieve accurate alignment for each exposure device, distortion of the projection lens must be minimized. must be kept in check.

This is especially true for reduction projection lens systems that use a single steel material to reduce distortion to almost zero.

It is composed of three lens groups with negative and lE refractive powers, and the lens group is further composed of two lenses if, , I, with refractive powers of IIM K @ and IE from the object side, and the lens group I, , I, the focal length of each fII + fl2
+When the focal length of the four lens groups is fl, the condition is iS! In the projection lens of the present invention, especially when used as a $11f small system, it is preferable to configure the lens group to have one tail.

There are two lens groups I, , I with negative and positive refractive powers.

In the second lens, distortion is mainly corrected using lens group ■1.

In particular, it is preferable that lens group (1) be composed of at least two meniscus-shaped lenses with negative refractive power and convex surfaces facing the object side, in order to fully correct distortion.

If the lens is composed of three or more lenses, the sharing of refractive power will be reduced, and the effects of other cooling effects will be reduced, which is preferable.

In addition, by making lens ① have a positive refractive power and configuring it with at least two lenses with one sample positive refractive power, the position through which the off-axis principal light image passes is near the optical axis, so that φ curvature aberration, In addition to correcting astigmatism, off-axis coma and halo are well corrected.

If the upper limit of conditional expression (4) or the lower limit of conditional expression (5) is exceeded, a large amount of negative distortion will occur, which is undesirable. If it exceeds this, positive distortion will occur and other aberrations will also increase, which is undesirable.

Next, numerical values of numerical examples 1 to 10 of the present invention are shown. In the numerical examples, Ri is the radius of curvature of the first lens from the object side, DI is the thickness and air gap of the 14th lens from the object side, and Ni is the radius of curvature of the first lens from the object side. It is the refractive index of glass.

The glass material 5IO2 is fused silica and has a refractive index of 1.521130 at a wavelength of 248.5 nm.

Numerical implementation lJ1 to 5 are magnification %, NA = 0.3, screen size 14 x 14 mm, numerical examples 6 to 10 are magnification station, N
A=0.35. Screen size l OXI O Figures 1 and 2
The figures show cross-sectional views of lenses of Numerical Example 1 and Numerical Example 6 of the present invention, respectively.

In addition, the aberration diagrams of numerical examples 1 to 10 are shown in Figs. 3 to 12, respectively.
As shown in the figure.

In Numerical Example 1, as shown in FIG. 3, aberrations are well corrected. Numerical implementation i+11 (2+ is condition (1).

(2) In the case of taking one shift near the lower limit value, the aberration curve is compared with Example (I) as shown in Fig. 4 under the condition f.
i1. f2) approaches the upper limit value, the refractive power of the lens group with negative refractive power becomes weaker, and therefore Petzval
The sum is exactly the same as the conditional expression fi1. If f2+ノ'F limit is exceeded, 1J! The surface curvature becomes uneven and dark, making it difficult to satisfy the conditions of uniform resolution over the entire screen, which is an important requirement for a projection lens.

Condition tl), as an example of the lower limit value side of +21, the implementation column (1
Figure 5 shows the aberration curve of Example (3), which satisfies conditions m and +21, and shows Example (3) as an example that is close to the middle. Curvature is good.

Example (4) corrects the difference in the spherical surface 11 of Example (2) by 1-
This is an fc drawing.

Example (6) is a reduction system with a specification of magnification I≦, and the performance is good by satisfying conditions (1) and f2) as shown in Figure 8 of the aberration curve.
7) is an example near the one-h limit of condition m, (21), as shown in the aberration curve in FIG.
By hitting the +21 beam directly, the refractive power of the second lens group becomes weaker.
The sum becomes small and the image plane/four tracks are over-corrected, approaching the limit of the requirement iL for a projection lens, which is to have uniform high resolution over the entire screen.

Condition i11. Example +6+ as the upper limit of +21,
The f/l was compared, and Example 18) was found as an intermediate value.

The aberration curve at this time is shown in FIG. Condition (1),
(2) was added by 71 points, and the image ml curvature was well corrected.

Example (9) is an example in which the spherical aberration of Example (8) is slightly overcorrected. Implementation column 5 is based on the above condition (
It is close to the upper limit value of condition (4) and the lower limit value of condition (5), and is 90〈distortion aberration is negative (insufficient compensation 1E) as shown in Fig. 7.
This approaches the limit value, and Example 1O is close to the lower limit value of condition (4) and the upper limit value of condition (5), and the Φ curvature aberration becomes iE+ overcorrected and approaches the limit value.

As shown in Fig. 41 and Fig. 2 of the projection lens of the present invention, the lens group is divided into two lens groups L+■, and the lens purchase for each lens group is specified by L/C. In addition, the 8142 lens group has a lens with additional refractive power in the middle & aperture L, and the spherical aperture is fully corrected as shown in the actual example in Figures 1 and 2. However, if the correction of spherical aberration is shared by the meniscus-like lens of full negative refractive power in the second lens group, there is no need to use it.

In addition, in the projection lens of the present invention, each of the three lens groups has a meniscus-like lens with a convex ml facing toward the image plane side from the object side to jlo, a biconvex lens, and a positive refractive power with a convex surface facing the object side. It is preferable to configure the lens with two meniscus-shaped lenses (1) for a total of four lenses. This is effective in achieving good aberration correction over the entire screen, but it is constructed with four or more lenses, for example, a biconvex lens is divided into two, making a total of five lenses (or seven lenses may also be used).

Furthermore, although the embodiment of this book is made of a single glass material, it goes without saying that it may be made of a large number of different types of glass. However, it is convenient to configure it with a single glass, and it also reduces the K cost, so it is preferable.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 show the lens of Numerical Example 1.6 of the present invention;
The analytical surface views and FIGS. 3 to 12 are the li! of the present invention, respectively. FIG. 2 is a diagram of i-value dust examples 1 to 1O. In the figure, T, [, use is Taniya No. 1. Second. The third lens group is a Y-positive image, M is a meridional image plane, and S is a sagittal image plane. 0 Applicant: Canon Co., Ltd.

Claims (4)

[Claims] (1) Ml with positive, negative, and positive refractive powers in order from the object side,
It is composed of three lens groups: a second and a third lens group; Second. The third lens group is composed of a plurality of lenses each made of a single glass material, and the first lens group is composed of a plurality of lenses each made of a single glass material. The focal lengths of the second and third lens groups are respectively f, , f2 . f
A projection lens satisfying the following conditions: 0.8≦l fl/fl +≦3.8 1.1≦l ft/f, +≦4. (2) The GL lens group consists of two lens groups I, , I with negative and positive refractive powers in order from the object side, and the lens #It is a biconvex lens T11 with both lens surfaces convex and a positive refractive power. The lens group (2) has at least one lens (2), respectively. The focal length of f17. The second lens group is configured to have a meniscus-shaped lens with a negative refractive power with convex surfaces facing the object side and the image plane side, and the condition is satisfied when the focal length of the second lens group is ft. The projection lens according to claim 1, characterized in that 'f: is satisfied. (3) The projection lens according to claim 2, wherein the lens I22 is a meniscus lens with a convex surface facing the object side. (4) The lens group consists of two lens groups I, , I having negative and positive refractive powers in order from the object side, and the lens #
Let the focal lengths of I, , I, respectively be fII + fI2
2. The projection lens according to claim 1, wherein the projection lens satisfies a patent condition in which the focal length of the first lens group is characterized.