JPH01267513A - Imaging lens - Google Patents

Abstract

PURPOSE:To obtain a high resolution on a short wavelength side by consisting the imaging lens of lenses constituted, successively from an object side, of 1st, 2nd and 3rd lens groups having positive, negative and positive refracting powers and determining the focal lengths of the respective lens groups and the entire system so as to satisfy specific conditions. CONSTITUTION:The entire part of this lens is constituted, successively from the object side, of the 1st, 2nd, and 3rd lens groups having the positive, negative and positive refracting powers. The 1st lens group is constituted of 2 pieces of the positive lens and the 2nd lens group is constituted of 2 pieces of the negative lenses and the 3rd lens group is constituted to include 3 pieces of the positive lenses. A meniscus lens, the convex face of which is directed to the image side, is used for a piece on the object side among these positive lenses and a meniscus lens, the convex face of which is directed to the object side, is used for a piece on the image side. The focal lengths of the respective lens groups and the entire system, designated as fI, fII, iIII, (f), are so determined as to satisfy the condition 0.4<¦fI/f¦<1.2; 0.05<¦fII/f¦<0.4, fII<0; 0.2<fII/f¦0.6. The resolving power in a UV region is thereby enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to lead drawing or dot drawing of a reduced projection image on, for example, a high-resolution film or resist to produce a liquid crystal pattern and a thermal head of a printer.

The present invention relates to a short wavelength imaging lens used in a reduction projection device for manufacturing encoders, LSI reticles, and the like.

[Prior Art and Problems to be Solved by the Invention] The imaging lens of this type of reduction projection apparatus is required to have extremely high resolving power in order to print a high-density pattern onto an object.

In general, the resolving power of an imaging lens improves as the wavelength used becomes shorter, so in this type of projection device, the H-line (4
A light source such as an ultra-high pressure mercury lamp that generates light such as 0.05 nm) or i-line (365 nm) is used. In addition,
Since these devices use sensitive materials such as high-resolution films and resists that are sensitive to short wavelengths, a short wavelength light source is also advantageous in improving drawing speed.

Furthermore, in order to obtain high resolution, it is necessary to suppress each aberration of the imaging lens to a value close to the theoretical limit. In particular, with the imaging lens of a stepper, the wafer such as an LSI is stepped relative to each other and exposed by dividing it into multiple shots, so it is necessary to prevent pattern deviation for each shot, so it is necessary to completely correct distortion aberration. There is a need to.

In general optical systems, in order to correct chromatic aberration, spherical aberration, coma aberration, etc., a glass material with a large dispersion and a glass material with a small dispersion, or a glass material with a large refractive index and a glass material with a small refractive index are combined. In optical systems with a positive lens, a glass material with a relatively high refractive index is often used to suppress the Petzval sum that occurs there. Keeping the Petzval sum small is important not only to reduce field curvature but also to reduce other problems. This is because it is often advantageous in terms of correcting various aberrations.

However, optical systems for short wavelengths require glass materials that are difficult to cause fluorescence emission and solarization due to ultraviolet absorption, and glass materials that have high transmittance in the ultraviolet region, so there is little flexibility in the glass materials that can be used. Since the refractive index is low, it is difficult to correct aberrations by increasing the refractive index of the positive lens in a double series.

Therefore, in conventional projection devices, the light beam from the light source is limited to a narrow spectrum width where chromatic aberration can be almost ignored through a wavelength selection filter, thereby reducing the design constraints for correcting chromatic aberration among the above-mentioned aberrations. , and other aberrations are often corrected strictly.

However, the narrower the spectral width of the projection light beam, the greater the energy loss, so it is desirable to make the spectral width as wide as possible from the perspective of improving drawing speed.

The present invention has been made in view of the above-mentioned problems, and aims to provide an imaging lens that has high resolution and is achromatized over a wider spectral width than before on the short wavelength side, particularly near the i-line.

[Means for Solving the Problems] The design features of the imaging lens according to the present invention for achieving the above object include a first lens, a first lens, and a second lens having positive, negative, and positive refractive powers in order from the object side. 2. Consisting of the third lens group, the first
The lens group is composed of two sets of positive lenses, the second lens group is composed of two negative lenses, and the third lens group is composed of three positive lenses, and among these positive lenses, one on the object side is When a meniscus lens has a convex surface facing the image side, and one lens on the image side has a convex surface facing the object side, and the focal length of each lens group and the entire system is fl+fl+fm+f, 0.4<lff/fl< 1.2...■
0.05<lfl/f+<0.4, f,<o
... ■0.2 < lf, /fK0.6 ... The condition of ■ is satisfied.

In a three-group lens system that has positive refractive power as a whole, a configuration in which the first group on the object side is positive, the second group is negative, and the third group is positive is most effective in terms of correcting various aberrations. configuration 1
It is one.

In addition, in order to keep the Petzval sum small and correct the field curvature well with this imaging lens, as mentioned above, there are a limited number of glass materials that can be used, and the refractive index of those glass materials is small. It is desirable to increase the number of lens components by suppressing the refractive power of each lens.

Therefore, in the imaging lens of the present invention, by configuring the third lens group having a relatively large positive refractive power from three or more positive lenses having a relatively small refractive power, the spherical surface generated on each surface is Various aberrations such as aberration and coma are reduced as much as possible.

Further, a meniscus lens having a concave surface facing a diverging light beam and a meniscus lens having a convex surface facing a converging light beam are arranged at the closest to the object side and the closest to the image side of the third lens group, respectively. These meniscus lenses not only have the function of suppressing the occurrence of spherical aberration, but also have a structure that is useful in setting the refractive power to a small value by adopting a meniscus shape and keeping the Petzval sum small.

The focal length of the second lens group is the same as that of the first lens group. In order to correct various aberrations such as undercorrected spherical aberration, coma aberration, and field curvature that occur in the third positive lens in a well-balanced manner, it is necessary that the value be within the range of formula (2). If the upper limit is exceeded, the negative refractive power of the second lens is too weak to correct the various aberrations mentioned above, and conversely, if it is below the lower limit, the negative refractive power becomes too strong and higher-order aberrations are overcorrected. As a result, it becomes difficult to maintain good imaging performance.

It is preferable that the focal lengths of the first and third lens groups be within the ranges of formulas 1 and 0, respectively, in relation to formula 2.

If the upper limits are exceeded, the refractive power of the positive lens becomes too weak, making it difficult to correct spherical aberrations, comatic aberrations, etc. Below the lower limits, the refractive power of the positive lens becomes too large, and the Petzval sum generated by the positive lens becomes jf by the second lens group
J cannot be completely eliminated, making it difficult to correct the image WJ curvature.

Furthermore, in order to satisfactorily correct axial chromatic aberration and lateral chromatic aberration, it is desirable that the following conditional expression be satisfied.

When the refractive index for the wavelength λ is nλ, nssm-
Dispersion value V of the object side lens of the second lens group defined by nssm
°1 and the dispersion value V'mt of the image side lens of the second lens group
and the dispersion value V°□1 of the positive lens of the first and third lenses, "m+<75...■-1"at<95...■-2"+w*>100... (2) The distance d between the first and second lens groups should be set to a value that satisfies the condition of -3, and the distance d between the first and second lens groups should be 0.05<Idt, /f+<0.4...■.

Equation (2) attempts to limit the distance between the first lens group and the second lens group in relation to the focal length, and when it falls below the lower limit, the first lens group approaches the second lens group and the second lens group approaches the second lens group. Since the height of the light rays incident on the lens group increases, the negative refractive power of the second lens group becomes too weak, the Petzval sum increases, and it becomes difficult to correct the curvature of field. If the upper limit is exceeded, on the other hand, the height of the light rays incident on the second lens group will be low, making it difficult to correct chromatic aberration of magnification related to off-axis light, and the negative refraction of the second lens group The force increases too much and high-order aberrations occur, making it impossible to obtain good imaging performance.

The formula shows the range of dispersion defined using the refractive index at the wavelength near the i-line, and if these are within the specified range, axial and lateral chromatic aberrations near the i-line can be suppressed. Can be corrected.

For the positive lens, a glass material with low internal absorption such as Fk5 or fused silica is suitable as a low dispersion material.
The negative lens of the lens group is made of high dispersion material and is made of i such as Lf and F.
It is preferable to use a glass material that has relatively good transmittance near the line.

[Example] In Table 1 showing numerical examples of the present invention on pages 14 and 15, R is the radius of curvature of the lens surface shown in order from the object side, and D is the distance # between each surface along the optical axis. (lens thickness and air spacing), n is the refractive index at the d-line (wavelength 588 nm), yd is the Atsube number, ni is the refractive index at the i-line, Fmo
, is the F number, and f is the focal length.

The relationship between each numerical example and the conditional expressions (1) to (2) of the present invention described above is as shown in the table below.

Numerical Example Conditional Expression (1) (2) (3) % Expression % FIGS. 1, 3, and 5 are lens sectional views corresponding to each numerical example. These imaging lenses are, in order from the object side on the left side in the figure, a lens group I consisting of two positive lenses, and a second lens group I consisting of two negative lenses. , is constructed by arranging a third lens group III consisting of four positive lenses.

In the first and second numerical implementation, 2.4, 5, 6 from the object side.
The eighth lens is a meniscus lens, which is arranged so that its convex surface faces a converging light beam and the concave surface faces a diverging light beam. Further, each of these internal pressure lenses has a small refractive power, and is advantageous in correcting spherical aberration and keeping the Petzval sum low.

FIG. 2, FIG. 4, and FIG. 6 are aberration diagrams of each numerical example. In the leftmost diagram, the spherical aberration SA is shown by a solid line, and the sine condition SC is shown by a broken line. Also, for axial chromatic aberration and lateral chromatic aberration, 365, 350, 380, 345, 38
Five data of 5nffl are shown. Astigmatism is shown in the sagittal direction S by a solid line and in the meridional direction H by a broken line.

In both cases, aberrations are well corrected.

In the third numerical example, one of the positive lenses in the lens group I is a bonded lens in order to highly correct chromatic aberration.

[Effects] As explained above, according to the present invention, it is possible to provide an imaging lens with few aberrations and high resolution in the ultraviolet region.

Furthermore, by satisfying predetermined conditions, it is possible to achromatize over a relatively wide range, widening the spectral width of the usable luminous flux, increasing energy efficiency, and shortening the time required for exposure compared to conventional methods.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an imaging lens according to a first numerical example of the present invention, and FIG. 2 is an aberration diagram thereof. FIG. 3 is a sectional view of the imaging lens according to the second numerical example, and FIG. 4 is an aberration diagram thereof. FIG. 5 is a sectional view of an imaging lens according to the third numerical example, and FIG. 6 is an aberration diagram thereof. I, II, [11... 1st, 2nd, 3rd lens group procedural correction document (method) August 1988 IK date 1988 Patent Application No. 96302 2, title of invention Imaging lens 3, Relationship of the person making the amendment with outside the prefecture Patent applicant address 2-36-9 Maeno-cho, Itabashi-ku, Tokyo Name (0
52) Asahi Optical Industry Co., Ltd. Rei 4, Agent address: 4F Kazutaka Dai 4 Building, 1-13-12 Kakigara-cho, Nihonbashi, Chuo-ku, Tokyo 6, Subject of amendment: Specification 7, Contents of amendment (1) Specification No. Delete pages 14 and 15. (2) On page 10, line 4 of the specification, “Page 14 and
"on page 5" should be corrected to "J" below "r". (3) The 1st to 3rd numerical examples attached in the attached sheet are listed in the 10th specification.
Insert after the last line of the page. Third numerical example

Claims (3)

[Claims] (1) The first lens has positive, negative, and positive refractive powers in order from the object side.
, second and third lens groups, and the first lens group is composed of two lens groups.
The second lens group consists of two negative lenses, and the third lens group includes three positive lenses, with one of the positive lenses on the object side having a convex surface facing the image side. Meniscus lens, the one on the image side is a meniscus lens with a convex surface facing the object side, and when the focal lengths of each lens group and the entire system are f_I, f_II, f_III, and f, respectively, 0.4<|f_ I/f|<1.2 0.05<|f_II/f|<0.4, f_II<00.2
An imaging lens characterized by satisfying the following condition: <|f_III/f|<0.6. (2) When the refractive index for wavelength λ is n_λ, ν
'=(n_3_8_5-1)/{(n_3_5_■-n
_3_■_■)}, the dispersion value ν'_II_1 of the object-side lens of the second lens group, the dispersion value ν'_II_2 of the image-side lens of the second lens group, and The imaging system according to claim 1, wherein the dispersion value ν'_ I _III_+ of the positive lens of the three lens groups satisfies the following conditions: ν'_II_1<75 ν'_II_2<95 ν'_ I _III_+>100. lens. (3) Imaging according to claim 1, wherein the distance d_ I _II between the first and second lens groups satisfies the following condition: 0.05<|d_ I _II/f|<0.4. lens.