JP3026648B2 - 1x projection lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to an equal-magnification projection lens that projects an AB pattern, a printed circuit board pattern, and the like onto a workpiece coated with a photoconductor at an equal magnification and exposes the same.

[0002]

2. Description of the Related Art A conventional exposure apparatus generally uses a high-pressure mercury lamp as a light source, and projects a pattern on a work only with light having a wavelength near an h-line. On the other hand, there is a demand to increase the light energy to shorten the exposure time and improve the throughput.

[0003] Generally, the sensitivity of a photoreceptor applied to a work reaches a peak near 360 nm to about 440 nm. Therefore, in order to effectively use the energy of a light source to increase the energy of light, only the h-line is used. Instead, it is desirable to use light of a wide range of wavelengths, including shorter wavelengths.

[0004] Since the transmittance of a glass material having a shorter wavelength becomes lower as the refractive index becomes higher, when the glass material is used including a short wavelength as described above, the lens is made of only a glass material having a low refractive index. There must be.

On the other hand, as a 1: 1 projection lens, positive, positive,
Conventionally, a target lens having six negative, negative, positive, and positive lenses has been used. In the case of 1 × projection, the objective lens does not generate coma aberration, chromatic aberration of magnification, and distortion, and thus is advantageous over other types of lenses.

[0006]

However, when a lens is composed of only a glass material having a low refractive index, it is difficult to correct spherical aberration and astigmatism using the conventional six-lens structure.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and is a unit-magnification projection lens in which aberration has been well corrected in a wide wavelength range including light having a wavelength shorter than the h-line. The purpose is to provide.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, a unity magnification lens according to the present invention has a biconvex positive first lens.
A lens, a positive meniscus second lens, a positive meniscus third lens, a negative meniscus fourth lens, a negative meniscus fifth lens, a positive meniscus sixth lens,
The seventh lens having a positive meniscus and the eighth lens having a biconvex positive shape are symmetrically arranged. The refractive index of each of the positive lenses is np, the dispersion value of each of the negative lenses is νm, and the focal length of the first lens is Where f1, the focal length of the fourth lens is f4, and the focal length of the entire system is f, the refractive index np of each positive lens satisfies the condition of np <1.70 (1) , and the dispersion value of each negative lens where νm satisfies the condition νm <35 ... (2) , and 0.5 <f1 / f <0.85 ... (3) 0.1 <| f4 / f | <0.25 ... (4) where νm = (nh-1 ) / (ni-ng) nh: Refractive index for h-line ni: Refractive index for i-line ng: Refractive index for g-line

[0009]

Embodiments of the present invention will be described below.

As shown in FIG. 1, the projection lens of the embodiment has a biconvex positive first and eighth lens, a positive and negative meniscus second and seventh lenses, and a positive meniscus third and sixth lens. And the fourth and fifth lenses of the negative meniscus. With the eight-sheet configuration, spherical aberration and astigmatism can be satisfactorily corrected even if only a low refractive index glass material is used.

In the lens of the embodiment, the refractive index of the positive lens is np, the dispersion value of the negative lens is νm, the focal length of the first lens is f1, the focal length of the fourth lens is f4, and the focal length of the whole system is Is f, and the conditions of (1) to (4) are satisfied.

Np <1.70 (1) νm <35 (2) 0.5 <f1 / f <0.85 (3) 01 <│f4 / f│ <025 (4) where νm = (Nh-1) / (ni-ng) nh: refractive index for h line ni: refractive index for i line ng: refractive index for g line

Equation (1) defines the refractive index of the positive lens. When the refractive index is 1.70 or more, the transmittance for i-line decreases, and the exposure energy decreases.

Equation (2) defines the dispersion of the negative lens. Since only the third and fourth lenses are negative lenses, they must have the function of correcting axial chromatic aberration generated by the other six positive lenses. If the expression (2) is not satisfied, the curvature of each lens becomes excessively large to correct the axial chromatic aberration, so that the spherical aberration cannot be corrected. Therefore, the correction of the axial chromatic aberration and the correction of other aberrations are compatible. Becomes difficult.

Equation (3) defines the focal lengths of the first lens and the eighth lens, and is a necessary condition for ensuring telecentricity and long back focus.

In this type of projection optical system, telecentricity is required so that a drawn pattern is not displaced or distorted even when the drawing surface has irregularities or the like, and a jig for confirming focus is inserted. For this purpose, it is desirable that the working distance, that is, the back focus is long.

When f1 / f is 0.5 or less, the curvature of field becomes excessively large, deteriorating the imaging performance and losing telecentricity. When the ratio is 0.85 or more, the ratio of the back focus to the focal length becomes small, and when the required back focus is secured, the distance between the object and the image becomes long and the device becomes large.

Equation (4) defines the focal length of the fourth lens and the fifth lens, and is a condition for favorably correcting spherical aberration, curvature of field, and astigmatism. │f4 / f
Is less than 0.1, the negative power of the fourth and fifth lenses becomes excessive, the spherical aberration becomes excessive, and it becomes difficult to correct astigmatism. If the value is 0.25 or more, the negative power becomes excessively small, so that the Petzval sum becomes large positively, and the field curvature becomes large and under becomes, so that good imaging performance cannot be obtained.

Next, specific numerical examples will be shown.

[0020]

First Embodiment FIG. 1 shows a first embodiment of the present invention. The specific numerical configuration is shown in Table 1. FIG.
Shows various aberrations due to this configuration. In the table, f is the focal length, FNo. Is the F number, r is the radius of curvature, d is the surface spacing, nh is the refractive index for the h line, ν is the refractive index for the i line, ni, and ng is the refractive index for the g line, and ν = (nh−1) / ( ni-ng).

[0021]

[Table 1]

[0022]

Embodiment 2 FIG. 3 shows Embodiment 2 of the present invention. The specific numerical configuration is shown in Table 2. FIG.
Shows various aberrations due to this configuration.

[0023]

[Table 2]

[0024]

Third Embodiment FIG. 5 shows a third embodiment of the present invention. Table 3 shows a specific numerical configuration. FIG.
Shows various aberrations due to this configuration.

[0025]

[Table 3]

[0026]

As described above, according to the present invention, it is possible to provide a lens whose aberration has been well corrected for light of a wide range of wavelengths including a wavelength shorter than the h-line. Accordingly, the exposure time can be shortened by effectively utilizing the energy of the light source, and the throughput can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a first embodiment.

FIG. 2 is a diagram illustrating various aberrations of the first embodiment.

FIG. 3 is a sectional view of a lens according to a second embodiment.

FIG. 4 is a diagram illustrating various aberrations of the second embodiment.

FIG. 5 is a sectional view of a lens according to a third embodiment.

FIG. 6 is a diagram illustrating various aberrations of the third embodiment.

Claims (1)

(57) [Claims] 1. A biconvex positive first lens, a positive meniscus second lens, a positive meniscus third lens, a negative meniscus fourth lens, a negative meniscus fifth lens, and a positive meniscus. The sixth lens, a positive meniscus seventh lens, and a biconvex positive eighth lens are symmetrically configured.
The refractive index of each positive lens is np, and the dispersion value of each negative lens is ν
m, the focal length of the first lens is f1, the focal length of the fourth lens is f4, and the focal length of the entire system is f .
The refractive index np satisfies the condition of np <1.70 (1) , the dispersion value νm of each negative lens satisfies the condition of νm <35 (2) , and 0.5 <f1 / f <0.85. (3) 0.1 <| f4 / f | <0.25… (4) where νm = (nh-1) / (ni-ng) nh: refractive index for h line ni: refractive index for i line ng: for g line A 1: 1 projection lens characterized by satisfying the condition of refractive index.