JPH07333829A - Optical element and its production - Google Patents

Abstract

PURPOSE:To realize a process for producing optical element capable of realizing a reflection type optical element of high resolution prevented from degrading the contrast of X-ray reflection, facilitating correction of pattern defects in stages for producing the optical element having X-ray absorber patterns and improving the yield. CONSTITUTION:This optical element is formed by disposing an intermedite film 3 which is formed out of a material having a low etching rate to the etching of an X-ray absorber 4 and is used as a protective film of multilayered film 2 between the X-ray absorber 4 and the multilayered film 2 on a substrate 1. Pattern formation is executed without impairing the reflectivity of X-ray reflection parts by etching the X-ray absorber 4 without exposing the multilayered film surface to an etching atmosphere at the time of forming a mask 4' by patterning by X-ray absorber 4. As a result, the reflection surface having the uniform reflectivity is provided in a wide range region on the mask and the mask defects are decreased since the correction by a convergent ion beam is facilitated. The mask for X-ray exposure with which the improvement in the yield is possible in the lithography stage in semiconductor element production is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element for reflecting X-rays or extreme ultraviolet rays and a method for manufacturing the same, and more particularly to an X-ray reflection type mask, a diffraction grating, a reflection type Fresnel lens and the like used in a projection exposure apparatus. The present invention relates to a suitable optical element and a method for manufacturing the same.

[0002]

2. Description of the Related Art A projection exposure apparatus for transferring a circuit pattern of a semiconductor element or the like drawn on a mask onto a wafer is required to have high resolution in order to transfer a fine pattern. Generally, the larger the numerical aperture (NA) of the projection optical system or the shorter the exposure wavelength, the higher the resolution.
However, a large NA causes a decrease in the depth of focus during pattern transfer, and therefore its size is practically limited.

On the other hand, in the X-ray region or in the extreme ultraviolet region having a wavelength close to this, the refractive index of the substance is extremely close to 1, so that it is difficult to use a transmission type lens and it is necessary to use a reflection type optical system. In recent years, there have been two reflective films with different refractive indices.
Since a multilayer mirror in which a large number of thin films of different kinds of substances are alternately laminated has been put into practical use and X-rays can be directly incident and reflected, a study has been made to improve resolution by using X-rays as a light source of a projection exposure apparatus. It is being actively conducted.

FIG. 2 is a cross-sectional view of an essential part showing two types of structural examples conventionally proposed as a reflective mask. FIG. 1A shows an example thereof, in which a multi-layer film 2 in which a large number of substances mainly containing heavy elements and a large number of substances mainly containing light elements are alternately laminated is provided on a substrate 1 with a predetermined mask. This structure is manufactured by a process of transferring a pattern by lithography, that is, a process of partially removing it by etching using a resist or the like as a mask.

FIG. 1B shows another example, in which a multi-layered film 2 in which a large number of substances containing a heavy element and a large number of light elements are alternately laminated is formed on a substrate 1. Further, a step of forming an X-ray absorber layer on the multilayer film and patterning it by selectively etching it to form a pattern 4'of the X-ray absorber, that is, using a resist or the like as a mask. This structure is manufactured by a process of partially removing the X-ray absorber by etching.

An example of a reflection type mask for X-ray exposure used in such an X-ray projection exposure apparatus is disclosed in Japanese Laid-Open Patent Publication No. 64-4021.

[0007]

FIG. 2 of the above-mentioned prior art.
In the case of manufacturing the structure shown in (a), the surface of the multilayer film 2 which is a portion that reflects X-rays is protected by a resist mask or the like when forming a mask pattern by lithography, and can be processed without being damaged by ion irradiation or the like. Therefore, a pattern with high reflectance can be formed. However, when the pattern multilayer film to be left as a mask is defective, it is extremely difficult to correct only the defective portion as a reflecting surface.
The reason is that the multilayer film 2 is formed by alternately laminating thin films of two kinds of substances having different refractive indexes, and the film forming structure is complicated.

On the other hand, in the case of manufacturing the structure shown in FIG. 2 (b) of the prior art described above, it is not possible to carry out etching at a constant rate at all locations within the region where the X-ray absorber is selectively removed by etching. Have difficulty. Therefore, the portion of the multilayer film 2 exposed by the rapid progress of the etching of the X-ray absorber is continuously exposed to the etching atmosphere until the etching of the portion where the other etching is slow is completed, and the layer of the multilayer film 2 is exposed. It suffers damage such as a decrease in the number and surface roughness.

Further, when the defect of the X-ray absorber pattern portion 4'generated in the manufacturing process is to be repaired, the excess X-ray absorber is removed by etching with the focused ion beam. At this time, the multilayer film 2 is used. Similarly, the number of layers is reduced, the surface is roughened, and the structure is damaged by the mutual diffusion of the multilayer film. The damaged multilayer film 2 has a problem that the reflectance with respect to X-rays is lowered, so that the contrast with the X-rays reflected by the X-ray absorber pattern portion 4'is lowered.

Therefore, an object of the present invention is to eliminate the structural problem shown in FIG. 2 (b) of the prior art, and the first object is a multilayer film having a high reflectance in a wide range. A second object is to provide an optical element having an X-ray absorber pattern, that is, a high-resolution reflective optical element that prevents a reduction in contrast. A second object is to provide a high reflectance in a wide range. Provided is an improved method for manufacturing an optical element having a high yield, by which a defect of a reflection portion or a pattern defect can be easily repaired in a manufacturing process of an optical element having an X-ray absorber pattern on a multilayer film. Especially.

[0011]

In order to achieve the above first object, the optical element of the present invention has an X-layer structure in which thin films of at least two kinds of substances having different refractive indexes are alternately laminated on a substrate. An intermediate film for protecting the multilayer film is arranged on the multilayer film for reflecting rays, and a pattern of the X-ray absorber is arranged on the intermediate film.

The intermediate film for protecting the multilayer film is made of X-ray in an atmosphere in which the X-ray absorber is selectively etched.
It is preferable that the material has an etching rate lower than the etching rate of the linear absorber. Further, in order to minimize the attenuation of X-ray intensity when passing through the intermediate film, it is preferable that the product of the X-ray absorption coefficient of the material used for the intermediate film and the film thickness of the intermediate film is small. Moreover, it is preferable that the film thickness of the intermediate film be an integral multiple of the cycle length of the multilayer film, whereby the X-rays reflected on the surface of the intermediate film and the X-rays reflected by the multilayer film are in phase with each other, and the reflectance is improved. Will be improved.

A preferred material for use as the intermediate film is
C, Cr, Al, Ni, Al ₂ O ₃ , SiO ₂ , Si
_{It is 3} N ₄ , SiC or BN, and may be a composite composition film of two or more of these. Further, the film structure is preferably a single layer, but a multilayer film structure may be used if necessary.

The thickness of the intermediate film is preferably as thin as possible in consideration of not attenuating the intensity of X-rays incident on the multilayer film as much as possible, preferably 1 to 100 nm, and more practically 5 to 20 nm. Is more preferable. A film thickness of 1 nm is the limit that can be formed by the current technology, and it is difficult to achieve a film thickness less than that.
This is because if it exceeds 00 nm, the absorption of X-rays remarkably increases. X-ray transmittance of the interlayer film is at least 80%
I want For that purpose, it is necessary to reduce the thickness in this way.

As the X-ray absorber, for example, W, Ta, P
Heavy metals such as t, Au, and Ge can be used, the absorptivity of X-rays is high, and the etching rate at the time of pattern formation by lithography is faster than that of the intermediate film.

A typical example of application of the optical element of the present invention is X for fine processing by lithography.
It is a reflective mask for line exposure and is effective for manufacturing electronic devices such as LSI and liquid crystal display devices.
The present invention can also be applied to optical elements such as reflective Fresnel lenses, and similarly high-performance elements can be realized with high yield.

In order to achieve the second object,
The method for producing an optical element of the present invention comprises the steps of alternately laminating thin films of at least two kinds of substances having different refractive indexes on a substrate to form a multilayer film reflecting X-rays or extreme ultraviolet rays,
It comprises a step of forming an intermediate film as a protective layer of the multilayer film and a step of forming an X-ray or extreme ultraviolet absorber pattern on the intermediate film.

This intermediate film is preferably made of a material having an etching rate lower than that of the X-ray absorber in the atmosphere for etching the X-ray absorber, as in the case of the optical element. Moreover,
In order to reduce the attenuation of X-ray intensity when passing through the intermediate film, it is preferable that the product of the X-ray absorption coefficient of the material used for the intermediate film and the film thickness of the intermediate film is small.

Specifically, the step of forming the intermediate film is performed by using C, Cr, Al, Ni, Al ₂ O ₃ , SiO ₂ ,
The step of forming a thin film containing at least one substance selected from the group consisting of Si ₃ N ₄ , SiC and BN, and forming the absorber pattern is performed by W, Ta,
By comprising a step of forming at least one metal thin film selected from the group consisting of Pt, Au and Ge, and a step of patterning the metal thin film by lithography through a predetermined mask pattern. is there.

In the step of forming the intermediate film, the thickness of the thin film to be formed is 1 to 100 nm, more preferably 5 to 100 nm.
The thickness is 20 nm, which is a step of forming a film having a film thickness that is substantially an integral multiple of the cycle length of the multilayer film.

As the method for forming the multilayer film, the X-ray absorber and the intermediate film, magnetron sputtering is preferable, but in addition, ion beam sputtering, electron beam evaporation, CVD, resistance heating evaporation, etc. Well-known film forming methods can also be used.

As a method of forming a resist mask pattern for patterning the X-ray absorber, a focused ion beam, optical exposure with a mercury lamp or an excimer laser may be used in addition to electron beam drawing.

In order to pattern the X-ray absorber using a resist mask, various dry etching pattern forming methods are effective. For example, reactive ion etching using plasma, especially low temperature dry etching is used. preferable.

[0024]

By providing the intermediate film as the protective film for the multilayer film, the multilayer film is not exposed to the etching atmosphere when the pattern forming of the X-ray absorber and the etching for the correction are performed. A surface having a high X-ray reflectance can be obtained in a wide range without any damage due to a decrease in the number of layers of the multilayer film, surface roughness, mutual diffusion, or the like.

As described above, the intermediate film has a function of protecting the surface of the multilayer film from being damaged by the processing beam and the reaction gas when the X-ray absorber pattern is formed and / or the pattern is modified. There is. Therefore, in order to exert its function, the absorption loss of X-rays should be minimized to ensure sufficient resistance to etching when the X-ray absorber is patterned, that is, the X-ray absorber. The difference in etching rate between the intermediate film and the intermediate film is large, and the intermediate film remains after the X-ray absorber is removed by etching even when the pattern formation is completely completed. Is acting as.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. <Embodiment 1> FIG. 1 is a process chart showing a method of manufacturing a reflective mask according to an embodiment of the present invention. As shown in FIG. 3A, the substrate 1 is made of Si having a thickness of 5 mm, and is surface-polished in advance to have a surface roughness of rms (root mean square) value of 0.3 nm. A multilayer film 2, an intermediate film 3, and an X-ray absorber 4 were sequentially stacked and laminated on this substrate by using a magnetron sputtering device. The multilayer film 2 was formed by alternately laminating a Mo thin film having a thickness of 2.5 nm and a Si thin film having a thickness of 4.2 nm in 50 layers each. At this time, the reflectance of the multilayer film 2 with respect to X-rays having a wavelength of 13 nm and an incident angle of 5 ° was 60%. The intermediate film 3 is formed by stacking Al with a thickness of 10 nm, and the X-ray absorber 4 is formed with W by 100 nm
Laminated. Then, an electron beam resist P is formed on the X-ray absorber 4.
MMA was applied to a thickness of 1.0 μm, and electron beam exposure and development were performed to form a predetermined resist mask pattern 5 for manufacturing an LSI.

Then, as shown in FIG. 2B, the exposed portion of the X-ray absorber (W) 4 was removed by reactive ion etching to form a pattern 4 '. SF ₆ is used as the etching reaction gas, and the gas pressure is 0.05 to 15
When performed in the range of Pa, the etching rate of W is 20 times or more the etching rate of the intermediate film (Al) 3,
Even when the same time as the time required to etch W having a thickness of 0 nm is further added, the multilayer film 2 can be protected by Al having a thickness of 5 nm or more. Even after etching the X-ray absorber 4 over the entire surface of the substrate, the multilayer film 2 was not exposed. The resist pattern 5 could be easily removed by immersion in an organic solvent such as acetone or oxygen plasma etching, and a reflective mask having the structure shown in FIG. 1 (b) was obtained.

The transmittance of X-rays having a wavelength of 13 nm is 95% for the intermediate film (Al) 3 having a thickness of 10 nm, and the X-ray reflectance at the reflecting surface for X-rays having an incident angle of 5 ° is It showed 54%. Furthermore, when the film thickness of the intermediate film (Al) 3 is made to coincide with the period length of 6.7 nm of the multilayer film 2, the X-ray reflectance at the reflecting surface with respect to the X-ray with an incident angle of 5 ° is It showed 58%.

In the above steps, the yield when patterning the X-ray absorber and forming a mask was about 70% as in the conventional case. Can be easily corrected, and can be used as a completely normal product, resulting in a yield of 10
It was possible to achieve 0%.

That is, in the defect correcting method for the reflective mask having the structure of this embodiment, the focused ion beam using W (CO) ₆ is used for the defective portion of W constituting the pattern 4'of the X-ray absorber. W was locally formed by the soft assist deposition to fill the defective portion. On the other hand, when W was removed incompletely by focused ion beam etching with Ga ions, the reflection portion (W pattern 4 ') was removed.
The X-ray reflectance of the surface of the multilayer film 2 which was not covered with the above) was 50%.

Using this reflective mask in a projection exposure apparatus,
The X-ray from the X-ray source was reflected, and a predetermined pattern was projected on the X-ray resist on the semiconductor substrate, which was applied to the manufacture of a semiconductor device. As a result, a fine pattern of 0.1 μm could be formed on the semiconductor substrate corresponding to the entire surface of the mask. As a result, the yield in the lithographic process for manufacturing semiconductor devices has been significantly improved.

In the above embodiment, Al is used as the intermediate film 3.
Other than C, Cr, Ni, Al ₂ O ₃ , SiO
₂ , Si ₃ N ₄ , SiC, and BN, which have a single composition and a composite composition of two or more kinds, and which are necessary films which are clarified from the etching rate ratios with the X-ray absorber 4 respectively. Similar results were obtained by stacking thicknesses. As a result of a more detailed experimental study of these compositions forming the intermediate film 3, a large difference in etching rate from the X-ray absorber 4 and a high etching resistance, a small X-ray absorption loss, and a film formation Taking into account characteristics such as ease of use, and if you have a strong ranking,
It can be classified into two groups. A group [C, SiO ₂ , Si ₃ N ₄ , SiC]> B group [Cr, BN]> C group [Al, Ni, Al
₂ O ₃ ].

Although W was used as the X-ray absorber 4, other materials such as Ta, Pt, Au, and Ge could be used.

As the method for forming the multilayer film 2, the X-ray absorber 4 and the intermediate film 3, the magnetron sputtering method was used.
Other well-known film forming methods are also used for this, such as ion beam sputtering, electron beam evaporation, and CVD.
Method, resistance heating vapor deposition method or the like can be used.

Further, as a method for forming the resist pattern 5, in addition to electron beam drawing, a focused ion beam, optical exposure using a mercury lamp or an excimer laser may be used.

<Embodiment 2> In the same manner as in Embodiment 1, except that the pattern 4'of the X-ray absorber shown in FIG. 1 is used as a repeating pattern of lines and spaces of a predetermined width. , A diffraction grating was manufactured. Also in this case, the same effect as in Example 1 was obtained.

<Embodiment 3> In the same manner as in Embodiment 1, except that the pattern 4'of the X-ray absorber shown in FIG. 1 is replaced by a pattern of concentric circles having a predetermined width and a space. Then, a reflective Fresnel lens was manufactured by forming a pattern that becomes finer toward the outer periphery. Also in this case, the same effect as in Example 1 was obtained.

[0038]

As described above in detail, according to the present invention, the intended purpose can be achieved. That is, in the reflection type mask which is one of the optical elements of the present invention, when the pattern of the X-ray absorber is formed or modified on the multilayer film that reflects X-rays, the pattern is formed on the multilayer film. By providing an intermediate film that protects the X-rays, the X-ray reflection part made of a multilayer film is not damaged, so that the occurrence of defects that reduce the reflectance can be reduced, and the defects of the pattern that is projected and exposed can also be reduced. Therefore, the yield in the lithographic process for manufacturing semiconductor devices is improved. The same applies to other diffraction gratings and reflection type Fresnel lenses, which are effective for pattern formation or correction of the X-ray absorber, and the yield is significantly improved.

[Brief description of drawings]

FIG. 1 is a process drawing showing a method of manufacturing a reflective mask that is an embodiment of the present invention.

FIG. 2 is a diagram showing a structure of a conventional reflective mask.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Multilayer film, 3 ... Intermediate film, 4 ... X-ray absorber, 4 '... Patterned X-ray absorber, 5 ... Resist pattern.

Front page continued (72) Inventor Hiroaki Oizumi 1-280 Higashi Koikekubo, Kokubunji, Tokyo Inside Hitachi Central Research Laboratory (72) Inventor Hiromasa Yamanashi 1-280 Higashi Koikeku, Tokyo Kokubunji City Hitachi Ltd. Central In the laboratory (72) Inventor Takashi Matsuzaka 1-280, Higashi Koigokubo, Kokubunji, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd.

Claims (11)

[Claims] 1. A multilayer film which reflects X-rays or extreme ultraviolet rays in which thin films of at least two kinds of substances having different refractive indexes are alternately laminated on a substrate, and a multilayer film arranged on the multilayer film. An optical element comprising an intermediate film to be protected, and an X-ray or extreme ultraviolet absorber pattern provided on the intermediate film. 2. The optical element according to claim 1, wherein the intermediate film is made of a material having an etching rate slower than an etching rate of the absorber when the absorber is processed into a predetermined pattern. 3. The film thickness of the intermediate film is constituted by a film thickness which is substantially an integral multiple of the cycle length of the multilayer film.
Alternatively, the optical element described in 2. 4. The optical element according to claim 1, wherein the intermediate film has a film thickness of 5 to 20 nm. 5. The intermediate film is formed of C, Cr, Al, Ni, A.
1 ₂ O ₃ , SiO ₂ , Si ₃ N ₄ , SiC and BN, and at least one substance selected from the group consisting of W, Ta, Pt, Au and Ge. The optical element according to any one of claims 1 to 4, comprising at least one metal thin film selected. 6. A reflective mask comprising the optical element according to claim 1. 7. A diffraction grating composed of the optical element according to claim 1. 8. A reflective Fresnel lens comprising the optical element according to claim 1. 9. A step of forming a multilayer film that reflects X-rays or extreme ultraviolet rays by alternately laminating thin films of at least two kinds of substances having different refractive indexes on a substrate, and an intermediate film as a protective layer of the multilayer film. And a step of forming an X-ray or extreme ultraviolet absorber pattern on the intermediate film. 10. The step of forming the intermediate film is carried out by C, C
r, Al, Ni, Al ₂ O ₃ , SiO ₂ , Si ₃ N ₄ , Si
The steps of forming a thin film containing at least one substance selected from the group consisting of C and BN and forming the absorber pattern are W, Ta, Pt, Au and G.
10. The method comprising the steps of forming at least one kind of metal thin film selected from the group consisting of e, and patterning the metal thin film by lithography through a predetermined mask pattern. Of manufacturing optical element of. 11. In the step of forming the intermediate film, the thickness of the thin film to be formed is set to 5 to 20 nm, and the film is formed to have a film thickness that is substantially an integral multiple of the cycle length of the multilayer film. The method for manufacturing an optical element according to claim 9 or 10, which comprises the step of: