JPH05283322A - Mask for exposure to x-ray - Google Patents

Abstract

PURPOSE:To provide a mask for exposure to X-rays, which provides a contrast high enough even with the film of an X-ray absorbent thin, excels in thermal characteristics and does not have any problem with the formation of a very fine pattern. CONSTITUTION:An X-ray absorbent pattern 1 is formed on a mask substrate and constituted by alternately laminating a material 10 having a property of a low refractive index against X-rays and a material 11 having a property of a high refractive index where the thickness of the material 10 and the material 11 are set to strengthen the reflected waves of X-rays with each other on the respective boundaries.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray exposure mask used in an X-ray lithography apparatus which exposes X-rays as a light source.

[0002]

2. Description of the Related Art Conventionally, an X-ray exposure mask as shown in FIG. 3 has been proposed. (Nobufumi Atsuta: "Present and Future of Synchrotron Radiation", Synchrotron Radiation Vol.2 No.1
(May 989)

The X-ray exposure mask comprises an X-ray absorber pattern 1a, a support film 2a, and a support frame 3. The X-ray absorber pattern 1a has a low X-ray transparency and a small coefficient of thermal expansion, and thus is made of gold (A).
u), tantalum (Ta), tungsten (W), etc. are used.

In the wavelength range (0.4 to 1.5 nm) used for synchrotron radiation lithography, an effective refracting optical system cannot be obtained and the X-ray mask is fragile. In general, a proximity exposure method in which the mask pattern is held at a constant interval and the mask pattern is transferred to the wafer at the same magnification is used.

However, in equal-magnification transfer, since the accuracy of the mask directly affects the transfer pattern on the wafer, the requirement for the mask, that is, the contrast (ratio of X-ray transmittance between the support film portion and the absorber portion) is It is large, and the dimensional accuracy and position accuracy of the pattern are high.

In the above-mentioned conventional example, a film thickness of 0.5 to 1 .mu.
Although the X-ray absorber pattern 1a made of Au, Ta, W or the like having a thickness of about m is provided, the film thickness of the absorber pattern 1a must be increased in order to increase the contrast. However, as a result, there arises a problem that it is difficult to form a fine pattern.

[0007]

Therefore, an X-ray exposure mask as shown in FIG. 4 has been devised. (Patent Fair 3-18
21 publication)

This mask has an X-ray absorber pattern 1b.
Has a multilayer structure in which a substance 4 having a large X-ray permeability and a substance 5 having a large X-ray absorbing property are alternately superposed,
It has a function as an X-ray mirror.

That is, the amplitude of the standing wave 7 of the incident X-ray 6 is reduced to reduce the transparency of the absorber pattern 1b. Therefore, even if the film thickness of the absorber pattern 1b is made smaller than that described above with reference to FIG. 3, improvement in contrast can be expected.

Here, carbon (C) is used as the X-ray transparent substance 4, and rhenium tungsten (ReW), tungsten (W), and gold palladium (AuPd) are used as the X-ray absorbing substance 5.

However, the material used for the multilayer structure as the X-ray absorber pattern 1b disclosed herein is
It was obtained from the viewpoint of the substance 4 having a large X-ray transparency and the substance 5 having a large X-ray absorption coefficient, and it cannot be said that the substance is configured to maximize the function of the X-ray mirror.

When the above X-ray absorber pattern 1b becomes an X-ray mirror having a high reflection characteristic and its material is examined, not only the contrast as an exposure mask is improved but also a multilayer structure is obtained. It can be expected that the number of laminated layers can be reduced and the film thickness of the absorber pattern can be reduced, which facilitates formation of a fine pattern.

Further, in this technique, the substance 5 having a large X-ray absorption coefficient is selected, but it is not a preferable selection in view of the thermal expansion of the absorber pattern. The X-rays absorbed by the substance store heat and allow expansion to occur. The accuracy of the transfer pattern from the mask to the wafer will be adversely affected, and consideration for the heat effect will be lacking.

The present invention has been made under such circumstances, and an object of the present invention is to reduce the film thickness of the X-ray absorber pattern to form a sufficiently high contrast and to obtain a thermal characteristic. Another object of the present invention is to provide an X-ray exposure mask which is excellent and has no hindrance in forming a fine pattern.

[0015]

To achieve the above object, a first invention is an X-ray exposure mask comprising an X-ray absorber pattern formed on a mask substrate, wherein the X-ray absorber pattern is A material having a low refractive index property and a material having a high refractive index property are alternately laminated to the X-ray used, and the thickness of the material having the low refractive index property and the material having the high refractive index property Is a mask for X-ray exposure, which is set so that reflected waves of X-rays are mutually strengthened at the boundaries of each other.

In a second aspect of the present invention, the substance having a low refractive index is osmium (Os), iridium (Ir), rhenium (Re), platinum (Pt), gold (Au), tungsten (W), Either ruthenium (Ru) or rhodium (Rh) is selected, and the substance having the high refractive index property is lithium (Li), magnesium (Mg), calcium (Ca), strontium (Sr), or silica. Elementary (S
2. The mask for X-ray exposure according to claim 1, wherein any one of i), aluminum (Al), boron (B), carbon (C), or a compound containing these substances is selected. Is.

[0017]

In any of the inventions, even as an X-ray absorber having a thin film thickness, it has excellent thermal characteristics and high contrast.
A fine pattern can be formed.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 1, an X-ray exposure mask is constructed.

The X-ray absorber pattern 1 is formed on the support film 12. The X-ray absorber pattern 1 has a multi-layered film structure and comprises two kinds of substances having different refractive indices, that is, a substance 10 having a low refractive index and a substance 11 having a high refractive index.
The films are alternately laminated on the support film 12. And
The film thicknesses d1, d2, ... Dm of the respective layers 10, 11 of the multilayer film are provided so as to obtain a multiple interference effect in which reflected lights at the boundaries of the respective layers are mutually strengthened.

By the way, the refractive index of various substances with respect to X-rays differs depending on the substance and also depends on the wavelength of X-rays. Therefore, it is necessary to select a substance having a low refractive index and a high refractive index in consideration of the wavelength of the X-ray used.

In synchrotron radiation lithography using such a transmission type X-ray mask, X-rays in the wavelength region of 0.4 to 1.5 nm are mainly used. Therefore, in this wavelength region, osmium (Os) and iridium (Ir) are used. ), Rhenium (R
e), platinum (Pt), gold (Au), tungsten (W), ruthenium (Ru), rhodium (Rh), etc. are applied as the substance 10 having a low refractive index.

Further, lithium (Li), magnesium (Mg), calcium (Ca), strontium (S
r), silicon (Si), aluminum (Al), boron (B), carbon (C), etc. are applied as the substance 11 having a high refractive index property. Actually, in selecting the optimum one from these substances, the refractive index η can be obtained by using the following equation. η = 1-σ = 1-N · e ² ・ Λ ² / 2π · m · C ² -(1) However, N: 1 cm ³ Number of electrons per electron, e: electron charge,
m: electron mass, λ: wavelength, C: speed of light

As an example calculated using the above formula (1), Table 1 shows the refractive indexes of various substances with respect to MgKα rays having a wavelength of 0.989 nm. The substances of interest are solids at room temperature and are not radioactive or toxic. From Table 1 below, the properties of low refractive index and high refractive index 10, 11
You can select a substance that has.

[0024]

[Table 1]

FIG. 2 schematically shows the operation of this X-ray exposure mask. The support film 12 on which the X-ray absorber pattern 1 is formed is supported by the support frame 13, and these constitute the mask substrate 20.

Since the X-ray absorber pattern 1 has a multilayer film structure of the low refractive index material 10 and the high refractive index material 11, it functions as a mirror for reflecting the incident X-rays 14. Moreover,
The film thicknesses of the respective layers 10 and 11 of the multilayer film are designed so as to produce a multiple interference effect in which the reflected lights at the boundaries mutually reinforce each other, so that the X-ray reflectance at the portion where the absorber pattern 1 is formed is large, The reflected X-ray light 15 is generated.

The multilayer film 10 of the X-ray absorber pattern 1,
The reflected X-ray light 15 reflected by 11 and the multilayer film 1
Since X-rays 16 other than the X-rays absorbed in 0 and 11 are transmitted through the absorber pattern 1 and the support film 12, if the X-ray reflectance of the absorber pattern 1 is increased, X The line transmittance can be reduced.

Therefore, if the X-ray reflectance in the portion where the absorber pattern 1 is formed is increased, the X-ray transmittance here can be made extremely small. On the contrary, in the portion where the absorber pattern 1 is not formed, the X-ray transmittance can be reduced. The transmittance of is increased. Next, a method of manufacturing the X-ray exposure mask thus configured will be described.

First, on the X-ray transparent support film 12,
While controlling the film thickness, a substance 10 having a low refractive index property and a substance 11 having a high refractive index property are alternately formed to form a multilayer film.

Although there are various film forming methods, most of the preferred substances to be used as the absorber pattern 1 of the X-ray exposure mask of the present invention are those having a high melting point. The beam sputtering method, the electron beam evaporation method, etc. are suitable.

Further, by setting the sputtering conditions and the vapor deposition conditions so that the film forming rate is constant, and measuring the resonance frequency change of the crystal unit, the polarization state change of the laser light, the change in the X-ray reflection intensity, etc. It is necessary to control the film thickness with high accuracy by monitoring the film thickness of the stacked layers during film formation. After forming the multilayer film, a fine pattern is drawn on the multilayer film by using an electron beam, a focus ion beam or the like. In this way, the X-ray absorber pattern 1 having the multilayer film structure is formed.
It is possible to form an X-ray exposure mask having

By using the above X-ray exposure mask, the difference in X-ray transmittance between the portion where the absorber pattern 1 is formed and the portion where the absorber pattern 1 is not formed can be increased. That is, since the mask contrast can be increased, a fine resist pattern having a steep edge profile can be obtained.

Further, it is possible to improve the dimensional accuracy of the pattern of the resist which is the transfer medium, and further to improve the throughput by giving a margin to the exposure and development conditions of the resist.

Since the absorber pattern 1 has a function as an X-ray mirror, the X-ray transmittance here becomes small,
Absorber pattern 1 compared to that previously described in FIG.
Can be thinned.

If the thickness of the absorber pattern 1 can be reduced, it becomes easy to form a fine absorber pattern by reactive ion etching or sputter etching. Further, by reducing the film thickness and reducing the ratio of the X-rays that reflect the X-rays as much as possible and are absorbed there, the heat storage by the X-rays can be reduced. That is, when the absorber pattern 1 expands due to heat, it adversely affects the accuracy of the resist pattern, so the effect of reducing heat storage is also important.

On the other hand, the X-ray exposure mask of the present invention is superior in function as an X-ray mirror to the one described above with reference to FIG. 4 because it can efficiently reflect X-rays on the absorber pattern 1. ..

FIG. 5 shows a tungsten (W) / carbon (C) multilayer film which has been described as a preferable multilayer material combination for the X-ray absorber pattern described in FIG.
FIG. 3 shows a comparison of X-ray reflection characteristics of rhenium (Re) / boron (B) multilayer films, which are listed as preferable material combinations in the present invention.

The X-ray reflectance is obtained by theoretical calculation, the X-ray incident angle is 0 ° at normal incidence, and the film thickness of one pair of Re and B and the film thickness of one pair of W and C are equal to each other. 0.59
It was 4 nm.

From the figure, the Re / B multilayer film has a W / C
It can be seen that a reflectance higher than that of the multilayer film can be obtained. Therefore, the absorber pattern 1 in the present invention can be said to be an X-ray mirror having a high reflectance as compared with the one shown in FIG. Excellent in reducing accumulation.

The reflection profile shown in the figure shows the characteristic of a narrow band mirror that a high reflectance is obtained only in an extremely narrow wavelength range. However, in synchrotron radiation lithography, X-rays in the 0.4-1.5 nm wavelength region
Since the line is effective, the transmittance in the absorber pattern increases in the wavelength region where high reflectance cannot be obtained.

Therefore, if the film thickness of each layer 10 and 11 is designed so that a high reflectance can be obtained even in a wide wavelength range, a wide band as an X-ray mirror can be achieved and the above problems can be eliminated. ..

In the above embodiment, lithium (Li), magnesium (Mg), calcium (Ca), strontium (S) are used as the substance having a high refractive index.
r), silicon (Si), aluminum (Al), boron (B), and carbon (C) have been described as being selected, but the present invention is not limited to this, and compounds containing these substances. For example, boron nitride (BN), silicon dioxide (SiO ₂ ), boron carbide (B ₄ C) and the like can be expected to have stability of the multilayer film structure.

Further, the X-ray exposure mask of the present invention is
It goes without saying that even if the entire mask or only the absorber pattern portion is covered with the protective film, a sufficient effect can be obtained. In addition, various modifications can be made within the scope of the present invention.

[0044]

As described above, according to the present invention, the X-ray absorber pattern formed on the mask substrate is used for X-ray absorption.
A substance having a low refractive index property and a substance having a high refractive index property with respect to a line are alternately laminated, and the thicknesses of the substance having the low refractive index property and the material having the high refractive index property are Since the reflection waves of X-rays are set to strengthen each other at the boundaries of each other, even if the film thickness of the X-ray absorber pattern is thin, the contrast is sufficiently high and the thermal characteristics are excellent, and fine patterns can be formed. There is an effect that can be formed.

[Brief description of drawings]

FIG. 1 is a sectional view showing an absorber pattern structure of an X-ray exposure mask, showing an embodiment of the present invention.

FIG. 2 is a diagram schematically showing the action of an X-ray exposure mask of the same embodiment.

FIG. 3 is a cross-sectional view of an X-ray exposure mask showing a conventional example of the present invention.

FIG. 4 is a cross-sectional view of an X-ray exposure mask showing still another conventional example.

FIG. 5 is an X-ray reflectance comparison characteristic diagram of a conventional absorber multilayer film structure and an absorber multilayer film structure of one embodiment of the present invention.

[Explanation of symbols]

20 ... Mask substrate, 1 ... X-ray absorber pattern, 10 ... Low refractive index material, 11 ... High refractive index material.

Claims (2)

[Claims] 1. An X-ray exposure mask comprising an X-ray absorber pattern formed on a mask substrate, wherein the X-ray absorber pattern comprises a substance having a low refractive index with respect to X-rays used. The materials having a high refractive index and the materials having a high refractive index are laminated alternately, and the thicknesses of the material having a low refractive index and the material having a high refractive index are such that the reflected waves of X-rays are mutually strengthened at their boundaries. An X-ray exposure mask, which is set to match. 2. The substance having a low refractive index is osmium (Os), iridium (Ir), rhenium (R).
e), platinum (Pt), gold (Au), tungsten (W), ruthenium (Ru), and rhodium (Rh), the substance having the high refractive index is lithium (Li ), Magnesium (Mg), calcium (Ca), strontium (Sr), silicon (S
2. The mask for X-ray exposure according to claim 1, wherein any one of i), aluminum (Al), boron (B), carbon (C), or a compound containing these substances is selected. ..