JPH0820596B2 - Projection lens - Google Patents

Description

TECHNICAL FIELD The present invention relates to a projection lens used for printing a desired fine pattern on a photoresist-coated light-sensitive material in the field of photolithography, and more particularly to a projection lens. The present invention relates to a projection lens suitable for printing with near-ultraviolet light.

<< Prior Art >> Examples of this type of projection lens include an ultra-precision projection lens conventionally used in an ultra-precision reduction printing apparatus called, for example, a stepper, and a plate-making enlargement lens used for reduction.

<< Problems to be Solved by the Invention >> The above-mentioned conventional ultra-precision projection lens is one in which various aberrations are corrected with high accuracy only in the near-ultraviolet region, for example, g-line in order to obtain high resolution, and therefore There are such difficulties.

I. Although the photosensitive wavelength range of the photoresist extends from the near-ultraviolet region to the ultraviolet region, since only the g-line is considered in the above conventional example, only the g-line bright line can be used among the g-line, h-line and i-line. Therefore, the energy that contributes to the exposure is small, the time required for the exposure is long, and the printing efficiency is unavoidably reduced.

B. The effective screen size is small.

On the other hand, the conventional plate-making enlargement lens is a plate-making lens in consideration of the visible light region, so that the effective screen size is large and various aberrations in the visible light region are corrected with high accuracy. There are such difficulties.

C. It has low transmittance in the near-ultraviolet region and low resolution.

The present invention has been made in view of such circumstances, and an object of the present invention is to solve the above-mentioned problems (1) to (3).

<< Means for Solving the Problems >> The present invention is configured as follows to solve the above problems.

That is, the first lens group and the second lens group are arranged in order from the object side, and the first lens group is a positive meniscus lens with a convex surface facing the object side and a positive meniscus lens with a convex surface facing the object side. The second lens group includes, in order, a negative lens, a positive meniscus lens having a convex surface directed toward the image side, and a positive lens having a convex surface having a smaller radius of curvature directed toward the image surface side. And the internal transmittance (thickness 10 mm) of the glass material for the i-line is T _i , the refractive indices for the g-line, h-line, and i-line are n _g , n _h , and n _i , respectively, and the dispersion value is ν _{When h} = (n _h -1) / (n _i -n _g ), each lens has T _i > 90%, positive lens is 1.60 <n _h <1.70 45 <ν _h <52, negative lens is 1.55 <N _h <1.65 28 <ν _h <36 made of a glass material, and the second and third lenses from the object side are cemented together.
When the focal lengths of the _second , _third , _fourth , and _fifth lenses from the object side are f ₂ , f ₃ , f ₄ , and f ₅ , respectively, the conditional expression −1.5 <(f ₂ / f ₃ ) <− 1.2 −2.4 It is characterized by satisfying <(f ₅ / f ₄ ) <-1.8.

That is, in the present invention, the first lens group and the second lens group have a Gaussian type lens configuration, and the positive lens and the negative lens constituting each lens group have g-line, h-line,
Considering the near-ultraviolet region of the i-line, it is made of a glass material having an internal transmittance for the i-line (when the thickness is 10 mm) of 90% or more.

<< Operation >> In the present invention, the first lens group and the second lens group have a Gauss type lens configuration, and a large aperture ratio and a large angle of view can be obtained.

That is, as shown in FIG. 1, the central concave surface r ₆
・ At r ₇ , the ray height is low, so the power of these surfaces can be increased, resulting in a smaller Petzval sum and a larger angle of view. At the same time, these concave surfaces may cause sagittal and coma aberrations, but this point is corrected as follows.

That is, in order to correct various aberrations such as coma and curvature, it is generally desirable that the refractive index of the glass material forming the positive lens is as high as possible, but a high transmittance is secured also for the i-line. The glass material used for is limited, and it is not possible to use a glass material having a very high bending rate. Therefore,
A glass material suitable for the above conditions will be selected. In this case, a composite system of the second lens L ₂ and the third lens L ₃ and a composite system of the fourth lens L ₄ and the fifth lens L ₅ are selected. Is a meniscus lens or equivalent thereto, and a combined system of the second lens L ₂ and the third lens L ₃ , and the fourth lens L ₄ and the fifth lens
Sagittal coma and astigmatism are corrected by reducing the power of the combined system with L ₅ . Note that the range of the dispersion value ν _h of the glass material and the intention to reduce the power are limited, so that the values of (f ₂ / f ₃ ) and (f ₅ / f ₄ ) are limited to −1.5 <(f ₂ / f ₃ ) <-1.2 -2.4 <(f ₅ / f ₄ ) <-1.8 is added.

As a result, when using a mercury lamp, the g-line (435.83n), which is the main bright line within the photosensitive wavelength range of the photoresist, is used.
m), h line (404.66 nm), i line (365.01 nm), transmittance, chromatic aberration, etc. are improved. With the above configuration, the projection lens has a large effective screen size, high resolution, and overall transmittance is improved.

<< Examples >> Hereinafter, examples of the projection lens according to the present invention will be described with reference to a lens data table (Tables 1 to 4), an arrangement diagram of the lenses, and diagrams showing various aberrations (FIGS. 1 to 9) To illustrate.

In each lens data table, f is the focal length of the entire system, Y is the image height (screen size), F is the effective F number, m is the reference magnification, and
Ti represents the internal transmittance (thickness: 10 mm) of each glass material for the i-line, and r, d, n, and ν _h correspond to the symbols in FIG. 1, respectively, the radius of curvature and the center thickness of the lens (surface Distance), refractive index, and dispersion value. Also, n _g , n _h , and n _i are the g line,
Refractive indexes for h-line and i-line, ν _h are dispersion values defined by the following equation.

ν _h = (n _h −1) / (n _i −n _g ) In all the following Examples 1 to 4, the reference magnification m is − (1/2), the effective F number is 5.6, and the maximum image is High Y
It is set to be 31.5.

Moreover, in all of Examples 1 to 4, the second lens is used.
An example of a six-element structure in which L ₂ and the third lens L ₃ are cemented and arranged is illustrated. The second lens L ₂ , the third lens L ₃ , and the fourth lens
The focal lengths of L ₄ and the fifth lens L ₅ are f ₂ , f ₃ , f ₄ , and f _{5, respectively.}
Then, it is configured to satisfy −1.5 <(f ₂ / f ₃ ) <− 1.2 −2.4 <(f ₅ / f ₄ ) <− 1.8.

On the other hand, FIG. 3, FIG. 5, FIG. 7, and FIG. 9 showing lens characteristics correspond to Examples 1 to 4, respectively, and three types showing spherical aberration, astigmatism, and distortion. Graphs A, B, and C are included. In the graph of spherical aberration A, the horizontal axis represents the aberration amount and the vertical axis represents the F number, and the spherical aberration curves g, h, and g for the g line, h line, and i line, respectively.
i is shown. In the graph B showing astigmatism, S shows a sagittal image plane, M shows a meridional image plane, and similarly to the graph C showing distortion surface aberration, it shows the aberration about the h line. If annotation is added in advance to the graph showing distortion, these graphs (Fig. 3, Fig. 3,
(FIGS. 5, 7, and 9) show that the distortion is substantially zero over all image heights for all four examples.

Example 1 Table 1 shows the lens data of this example, FIG. 2 is a diagram showing the arrangement of lenses, and FIG. 3 is an aberration diagram.

In this embodiment, the first lens group G ₁ is composed of a positive meniscus lens L ₁ having a convex surface directed toward the object side, a positive meniscus lens L _2, and a negative meniscus lens L _3, and the second lens group G ₂ is composed of a negative meniscus lens L ₄ whose convex surface faces the image plane side in order, a positive meniscus lens L _5, and a double-sided convex lens L _6, and are arranged in a combination of convex-concave / concave-convex. The second lens L ₂ and the third lens L ₃ are cemented and arranged.

In this _{embodiment, (f 2 / f 3)} = - 1.44, (f 5 / f 4) = -
It is 2.00.

With this configuration, various aberrations at the reference magnification are satisfactorily corrected.

Example 2 Table 2 shows the lens data of this example, FIG. 4 is a diagram showing the arrangement of lenses, and FIG. 5 is an aberration diagram. This example is
The first lens group G ₁ is made up of a positive meniscus lens L ₁ having a convex surface directed toward the object side, a positive meniscus lens L _2, and a negative meniscus lens L _3, and the second lens group G ₂ is sequentially imaged. The negative meniscus lens L ₄ having a convex surface facing the surface side, the positive meniscus lens L _5, and the double-sided convex lens L ₆ are arranged and configured in a convex-concave-concave-convex combination. The second lens L ₂ and the third lens L ₃ are cemented and arranged.

In this _{embodiment, (f 2 / f 3)} = - 1.36, (f 5 / f 4) = -
It is 1.86.

With this configuration, various aberrations at the reference magnification are satisfactorily corrected.

Example 3 Table 3 shows the lens data of this example, FIG. 6 is a diagram showing the arrangement of lenses, and FIG. 7 is an aberration diagram. This example is
The first lens group G ₁ is made up of a positive meniscus lens L ₁ having a convex surface directed toward the object side, a positive meniscus lens L _2, and a negative meniscus lens L _3, and the second lens group G ₂ is sequentially imaged. The negative meniscus lens L ₄ having a convex surface facing the surface side, the positive meniscus lens L _5, and the double-sided convex lens L ₆ are arranged and configured in a convex-concave-concave-convex combination. The second lens L ₂ and the third lens L ₃ are cemented and arranged.

In this _{embodiment, (f 2 / f 3)} = - 1.22, (f 5 / f 4) = -
It is 2.32.

With this configuration, various aberrations at the reference magnification are satisfactorily corrected.

Example 4 Lens data of this example are shown in Table 4, a lens arrangement diagram is shown in FIG. 8, and an aberration diagram is shown in FIG. This example is
The first lens group G ₁ is made up of a positive meniscus lens L ₁ having a convex surface directed toward the object side, a positive meniscus lens L _2, and a negative meniscus lens L _3, and the second lens group G ₂ is sequentially imaged. The negative meniscus lens L ₄ having a convex surface facing the surface side, the positive meniscus lens L _5, and the double-sided convex lens L ₆ are arranged and configured in a convex-concave-concave-convex combination. The second lens L ₂ and the third lens L ₃ are cemented and arranged.

In this _{embodiment, (f 2 / f 3)} = - 1.36, (f 5 / f 4) = -
It is 1.88.

With this configuration, various aberrations at the reference magnification are satisfactorily corrected.

<< Effects of the Invention >> As is apparent from the above description, since the projection lens according to the present invention is configured as described above, the following effects are achieved.

I. The positive lens and the negative lens forming each lens group are g
It is formed of a glass material in consideration of the near-ultraviolet region including the X-ray, the H-line and the i-line, and the light transmittance in the photosensitive wavelength region of the photoresist is significantly improved, whereby the printing time can be shortened.

B. You can increase the effective screen size.

C. Various aberrations are significantly improved, and the image quality can be improved.

[Brief description of drawings]

FIG. 1 is a layout diagram showing the specifications of the lens, and FIGS.
FIG. 6, FIG. 8 and FIG.
FIG. 3 is a view showing the arrangement of lenses according to Embodiment 4;
FIG. 7 and FIG. 9 are aberration diagrams of lenses corresponding to Examples 1 to 4, respectively. G ₁ ...... First lens group, L ₁ ...... First lens, L ₂ ...... Second lens, L ₃ ...... Third lens, G ₂ ...... Second lens group, L ₄ ......
4th lens, L ₅ ... 5th lens, L ₆ ... 6th lens,
n _g , n _h , n _i ... Refractive index for g-line, h-line and i-line, ν _h ... Dispersion value, T _i ... Transmittance for i-line, respectively.

Claims (1)

[Claims] 1. A first lens group and a second lens group are arranged in order from the object side. The first lens group has a positive meniscus lens having a convex surface directed toward the object side and a positive meniscus lens having a convex surface directed toward the object side. The second lens group includes a negative lens, a positive meniscus lens having a convex surface directed toward the image surface side, and a convex surface having a smaller radius of curvature directed toward the image surface side. It consists of a positive lens and the internal transmittance (thickness 10 mm) for the i-line of the glass material is T _i
The refractive indices for g-line, h-line, and i-line are n _g , n _h , and
Let n _i and the dispersion value be ν _h = (n _h -1) / (n _i −n _g ), each lens has T _i > 90%, and positive lens has 1.60 <n _h <1.70 45 <ν _h <52 The negative lens is made of a glass material satisfying 1.55 <n _h <1.65 28 <ν _h <36, and the second and third lenses from the object side are cemented together to form 2, 3 and 4, respectively. When the focal lengths of the fourth and fifth lenses are f ₂ , f ₃ , f ₄ , and f ₅ , conditional expression −1.5 <(f ₂ / f ₃ ) <− 1.2 −2.4 <(f ₅ / f ₄ ) A projection lens that satisfies <-1.8.