JP2004319909A - Mask for electron beam exposure and its forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that since an electron beam shielding film, an antistatic film and a supporting film of a mask for electron beam exposure are composed of discrete materials, material cost is increased and an intricate processing system is required. <P>SOLUTION: The mask for electron beam exposure has a diamond film functioning as the supporting film and the electron beam shielding film wherein the diamond film is covered with a silicon carbide thin film functioning as the antistatic film. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electron beam exposure mask used for transferring a pattern by an electron beam and a method for manufacturing the same.
[0002]
[Prior art]
Recently, in the field of semiconductor integrated circuits and the like, a higher degree of integration is required, and with this trend, fine processing technology tends to further advance. For this reason, the fine processing by the photolithography technique, which has been widely adopted in the past, is approaching its limit in relation to the wavelength of light. Under such circumstances, an exposure technique using an electron beam or an X-ray has attracted attention. Since an electron beam exposure mask required for electron beam exposure can be easily prepared as compared with an X-ray exposure mask, electron beam exposure technology has attracted much attention.
[0003]
This type, as a mask for electron beam exposure used in electron beam exposure technology, by irradiating the mask with an electron beam, the electron beam transmitted through the mask onto a substrate such as a semiconductor wafer coated with a resist, There is an electron transmission type mask that exposes a resist with an electron beam.
[0004]
On the other hand, an electron beam exposure mask to be irradiated with an electron beam is required to have high mechanical strength and high thermal conductivity. Further, it is preferable that the aspect ratio, which is the ratio between the opening dimension and the opening height (that is, the depth) of the pattern formed on the mask, is as small as possible. This means that the mask is desirably formed of a material having sufficient mechanical strength even if the thickness is reduced.
[0005]
Japanese Patent Application Laid-Open No. 2002-217094 (Patent Document 1) discloses an electron beam transmission type mask including a mask portion having a pattern to be transferred and a support frame supporting the mask portion. The disclosed mask is premised on application to a system using an electron beam accelerated by an acceleration voltage of about 10 KV as an exposure light source (paragraph 0003).
[0006]
Specifically, the electron beam transmission type mask is formed using a silicon wafer, and the mask portion is formed at the center of the silicon wafer. In this case, the support frame is formed by a silicon wafer left around the mask portion. The mask portion has a configuration in which a silicon nitride film, a diamond film formed on the silicon nitride film, and a tantalum film provided on the diamond film are sequentially stacked. Here, the tantalum film functions as an electron beam shielding film for shielding the electron beam for exposure.
[0007]
Further, the electron beam transmission type mask disclosed in Patent Document 1 is provided with an antistatic film formed of platinum palladium on the electron beam incident side of the diamond film, and the mask is exposed to the electron beam for exposure by the antistatic film. Prevents charging. It also describes that tungsten or chromium is used instead of the tantalum film forming the electron beam shielding film, and that a platinum palladium film forming an antistatic film is used as the electron beam shielding film.
[0008]
Furthermore, when the diamond film is exposed, a film having a high optical reflectivity such as a metal is formed in order to prevent the contrast of the pattern of the mask portion from being lowered due to its high optical transmittance. (Patent Document 1, paragraph 0022).
[0009]
On the other hand, as this type of electron beam exposure technique, it has been proposed to perform exposure using an electron beam of low energy (for example, an electron beam accelerated by an acceleration voltage of about 2 KV), and this technique is based on Low Energy Electron. Known as beam Proximity Projection Lithography (LEEPL). In this technique, a low-energy electron beam is irradiated onto a mask for electron beam exposure which is arranged very close to a semiconductor substrate to be exposed (for example, a position 50 μm away from the substrate). A pattern formed on an electron beam exposure mask is transferred onto a semiconductor substrate. For this reason, the pattern formed on the mask is exposed at the same magnification on the semiconductor substrate.
[0010]
[Patent Document 1]
JP, 2002-217094, A
[Problems to be solved by the invention]
In the electron beam transmission type mask disclosed in Patent Document 1, since the electron beam irradiated on the mask has high energy, an atomic number such as tantalum, tungsten, or chromium is used to shield the electron beam. A large substance was used, and further, an antistatic film such as platinum had to be used. As a result, in addition to the diamond film, the electron beam transmission type mask disclosed in Patent Document 1 needs to be provided with an electron beam shielding film such as tantalum and an antistatic film such as platinum, and the configuration is complicated. Not only was it very expensive and poorly feasible.
[0012]
As described above, to shield an electron beam, a substance having a large atomic number is used. However, according to experiments and studies by the present inventors, a low-energy electron beam necessarily has a large atomic number. It turned out that there was no need to use the substance. For example, it has been found that an electron beam accelerated by an acceleration voltage of 2 kV can sufficiently shield even a low-density substance such as Poly-methyl methacrylate (PMMA).
[0013]
An object of the present invention is to provide a mask suitable for exposure using a low energy electron beam based on the above fact.
[0014]
Another object of the present invention is to provide the above-mentioned mask having high transparency, high thermal conductivity, high durability, and excellent workability.
[0015]
Still another object of the present invention is to provide a mask for electron beam exposure which has a simple structure and can prevent charging.
[0016]
It is another object of the present invention to provide a method for manufacturing an electron beam exposure mask suitable for exposure with a low energy electron beam.
[0017]
[Means for Solving the Problems]
According to one embodiment of the present invention, there is provided an electron beam exposure mask including a mask portion having a diamond film and a silicon carbide thin film formed on the surface of the diamond film.
[0018]
Further, the mask portion is surrounded by a support portion (that is, a support), and the support is formed of silicon. In this case, it is desirable that the silicon is shifted from the (100) plane. This is because in the (100) plane of silicon, its open face is perpendicular to the diamond film, and as a result, it is easily broken. In other words, it is desirable that the silicon is shifted from the (100) plane so that the open face of the silicon is not perpendicular to the diamond film.
[0019]
In the above-mentioned mask, the diamond film has a thickness of 0.1 μm or more, and functions as an electron shielding film, a heat conductive film, and a mask portion supporting film, while the silicon carbide thin film functions as an antistatic film. I do. Such an electron beam exposure mask is preferably used for exposure with an electron beam of 1 to 4 keV.
[0020]
Next, according to another aspect of the present invention, there is provided a method of manufacturing a mask for electron beam exposure, comprising a step of forming a diamond film and a step of forming silicon carbide on the surface of the diamond film. can get. In this case, the diamond film is preferably formed on a silicon substrate having a substantially (100) surface.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
With reference to FIGS. 1 to 5, a method for manufacturing an electron beam exposure mask according to an embodiment of the present invention will be described in the order of steps. First, as shown in FIG. 1, a silicon wafer 10 having a surface shifted from the (100) surface is prepared. Specifically, it is desirable that the silicon wafer has a surface that is deviated from the (100) plane by ± 5 ° or more. By using such a silicon wafer, a mask that is hard to be broken by electron beam irradiation is manufactured. can do.
[0022]
Subsequently, a diamond film 101 having a thickness of 0.1 to 1 μm (preferably 0.1 to 0.5 μm) is formed on the main surface of the silicon wafer 100 by, for example, a plasma CVD method using microwaves. Is done. The method for forming the diamond film 101 is, for example, entitled "Synthesis of High-Quality Diamond by Plasma CVD" in the Journal of the Society of Plasma and Nuclear Fusion, Vol. 76, No. 9, pp. 833-841 (September 2000). Since the method described in the paper can be used, it will not be described in detail here.
[0023]
Since the diamond film can be grown in a vapor phase at a growth rate of 1 μm / hour, the diamond film 101 having the above thickness can be easily formed by performing the vapor phase growth for about 30 minutes. The diamond film 101 thus obtained has a higher hardness (Young's modulus) and a higher thermal conductivity than other materials, and has a higher transmittance in a wide wavelength range from infrared to ultraviolet. Since it is shown, it is ideal as a mask material, but since it is an insulator, it is necessary to add antistatic means.
[0024]
According to experiments performed by the present inventors, the diamond film 101 exhibiting transparency over a wide wavelength range exhibits a high electron beam shielding effect against electron beams accelerated at an acceleration voltage of about 1 to 4 kV. There was found. Actually, when an electron beam accelerated by an acceleration voltage of 2 kV is vertically injected into the diamond film 101 having a thickness of 0.15 μm, the electron beam does not enter the diamond film 101 in a depth direction of 0.10 μm or more. It turns out. From this, it was found that the diamond film 101 having a thickness of 0.1 μm or more serves as a shielding film for shielding low energy electron beams.
[0025]
Next, as shown in FIG. 2, a silicon carbide thin film 102 is formed on the diamond film 101 in a thickness of 10 atomic layers or more. The silicon carbide thin film 102 has a lower resistance than the diamond film 101 and exhibits conductivity as compared with the diamond film 101. Actually, the silicon carbide thin film 102 has a specific resistance of 20 μΩ · cm or less. Therefore, in the present invention, by utilizing this property, the silicon carbide thin film 102 is used as an antistatic layer. As described above, when the silicon carbide thin film 102 is formed on the surface of the diamond film 101, the transparency is lower than the transparency of the diamond film 101 itself. Was very thin, and the reduction in transparency was practically negligible in the subsequent steps.
[0026]
Here, a method for forming silicon carbide thin film 102 shown in FIG. 2 will be specifically described.
[0027]
A silicon film having a thickness of 5 to 10 nm is formed on the surface of the diamond film 101 by sputtering, and then the silicon film is irradiated with an electron beam to convert the silicon film on the surface of the diamond film 101 into a silicon carbide thin film 102. Could be changed.
[0028]
Further, as another method for forming the silicon carbide thin film 102, a gas containing silicon, for example, a gas such as siloxane or silane is adsorbed on the diamond film 101, and then an electron beam is applied thereto. Silicon carbide thin film 102 was formed.
[0029]
As described above, after the silicon carbide thin film 102 is formed, as shown in FIG. 3, on the surface (rear surface) opposite to the surface of the silicon wafer 100 on which the diamond film 101 is formed, tantalum, titanium tantalum, or And a reinforcing film 103 formed of a metal such as titanium. In this case, the reinforcing film 103 is formed by sputtering, CVD, or the like. Further, the reinforcing film 103 may be formed of a film other than a metal, for example, a silicon carbide thin film, a titanium silicon film, or the like.
[0030]
Subsequently, as shown in FIG. 4, after selectively removing the reinforcing film 103 formed on the back surface of the silicon wafer 100, the diamond film 101 is exposed from the back surface of the silicon wafer 100 using the reinforcing film 103 as a mask. To form a membrane-shaped mask portion. In this case, the etching of the silicon wafer 100 may be, for example, wet etching using a KOH solution or dry etching.
[0031]
Next, as shown in FIG. 5, the diamond film 101 and the silicon carbide thin film 102 are selectively removed by RIE (reactive ion etching) using oxygen gas, and the diamond film 101 and the silicon carbide thin film 102 are patterned. . The etching of the diamond film 101 and the silicon carbide thin film 102 is performed with a patterned resist or the like disposed on the silicon carbide thin film 102.
[0032]
Since the diamond film 101 and the silicon carbide thin film 102 constituting the mask portion are substantially transparent, alignment and the like are easy. Therefore, patterning by RIE can be performed with high accuracy. Thus, the diamond mask 200 including the patterned mask portion and the support portion (support) surrounding the mask portion is obtained. In the figure, two support members are provided with the mask portion interposed therebetween. However, actually, these support members are provided so as to surround a large number of mask portion regions of the substrate in a lattice shape.
[0033]
In this configuration, the diamond film 101 itself has a portion that mechanically supports itself and the silicon carbide thin film 102, and the surface of the silicon wafer 100 that directly or indirectly contacts the diamond film 101 is shifted from (100). It can be seen that the material has a rough surface.
[0034]
FIG. 6 shows a use state of the diamond mask 200 according to the present invention. As shown in the figure, the diamond mask 200 is arranged on the semiconductor wafer 201 at a very small interval of about 50 μm. As is clear from this, the illustrated diamond mask 200 is an equal-size mask.
[0035]
In the illustrated state, an electron beam accelerated at an acceleration voltage of about 2 kV is irradiated from the upper side of the figure. A part of the electron beam is irradiated onto the semiconductor wafer 201 through an opening formed by patterning the diamond film 101 and the silicon carbide thin film 102, while the other part of the electron beam is shielded by the diamond film 101. As described above, the diamond film 101 is heated by the irradiation of the electron beam, but since the diamond film 101 itself has a high thermal conductivity, the heat is efficiently dispersed.
[0036]
On the other hand, since the diamond film 101 is covered with the conductive silicon carbide thin film 102, even when the diamond film 101 is irradiated with an electron beam, charged particles such as secondary electrons due to the irradiation of the electron beam are carbonized. Discharge is performed through the silicon thin film 102. As a result, the electron beam passing through the opening formed in the diamond film 101 is irradiated onto the semiconductor wafer 201 without being affected by the charging of the diamond film 101. In the above-described embodiment, the case where silicon having a plane shifted from the (100) plane is used. However, when cracking does not pose a problem, silicon having the (100) plane may be used. .
[0037]
【The invention's effect】
According to the present invention, the diamond film 101 has high transparency, high thermal conductivity, and high mechanical strength. Therefore, the diamond film 101 has high durability and can minimize heating accompanying electron beam irradiation. Thus, a mask which is less likely to be deformed can be obtained. Further, since the diamond film 101 is covered with the conductive silicon carbide thin film 102, it is possible to prevent the electrification by irradiation with an electron beam, and thus a mask optimal for electron beam exposure can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating one step in manufacturing an electron beam exposure mask according to the present invention.
FIG. 2 is a cross-sectional view illustrating a step that follows the step of FIG.
FIG. 3 is a cross-sectional view illustrating a step performed after the step of FIG.
FIG. 4 is a cross-sectional view illustrating a step that follows the step of FIG.
FIG. 5 is a cross-sectional view illustrating an electron beam exposure mask obtained in the above manufacturing process.
FIG. 6 is a diagram showing a use state of the electron beam exposure mask according to the present invention.
[Explanation of symbols]
REFERENCE SIGNS LIST 100 silicon wafer 101 diamond film 102 silicon carbide thin film 103 reinforcing film 200 electron beam exposure mask 201 semiconductor wafer

Claims (19)

An electron beam exposure mask, comprising: a mask portion having a diamond film and a silicon carbide thin film formed on the surface of the diamond film. 2. The electron beam exposure mask according to claim 1, wherein the diamond film and the silicon carbide thin film are patterned. The diamond film according to claim 1, wherein the diamond film has a part which itself and the silicon carbide thin film are mechanically supported, and at least a part of the other part is supported by a support. A mask for electron beam exposure, wherein the support contains silicon. 4. The method according to claim 3, wherein a surface of the silicon directly or indirectly in contact with the diamond film has a surface deviated from a (100) plane, and the deviation is such that the open surface is not perpendicular to the diamond film. A mask for electron beam exposure characterized by the following. 5. The method according to claim 1, wherein the diamond film functions as an electron beam shielding film, a heat conductive film, and a mask portion supporting film, and the silicon carbide thin film functions as an antistatic film. Electron beam exposure mask. The electron beam exposure mask according to any one of claims 1 to 5, wherein the diamond film has a thickness of 0.1 µm or more. 7. The electron beam exposure mask according to claim 6, wherein the electron beam exposure mask is used for exposure with an electron beam of 1 to 4 keV. 4. The electron beam exposure mask according to claim 3, wherein the support includes a reinforcing film provided on a back surface of the silicon. 9. The electron beam exposure mask according to claim 8, wherein the reinforcing film is selected from Ta, TaN, Ti, and SiC. 5. The electron beam exposure mask according to claim 4, wherein the deviation is at least ± 5 °. A method for manufacturing a mask for electron beam exposure, comprising: a step of forming a diamond film; and a step of forming silicon carbide on a surface of the diamond film. The method for manufacturing an electron beam exposure mask according to claim 11, further comprising a step of preparing a silicon substrate having a surface shifted from (100), wherein the diamond film is formed on the surface. 13. The method according to claim 11, wherein forming the silicon carbide thin film includes forming a silicon film on the diamond film, and irradiating the silicon film with an electron beam to form the silicon carbide. A method for manufacturing an electron beam exposure mask. 14. The method according to claim 13, wherein the step of forming the silicon film is a step of forming a film on the surface of the diamond film by sputtering. 14. The method for manufacturing an electron beam exposure mask according to claim 13, wherein a silicon film having a thickness of 3 to 10 nm is provided in the step of forming the silicon film. 13. The method according to claim 11, wherein the step of forming the silicon carbide thin film includes exposing the diamond film to a gas atmosphere containing silicon, causing the silicon film to adsorb silicon, and irradiating the silicon with an electron beam. Producing a silicon carbide thin film. 17. The mask part according to claim 11, wherein the silicon substrate is removed from a back surface opposite to a surface on which the diamond film is formed, and one or more mask portions are formed by the diamond film and the silicon carbide thin film. A method for producing an electron beam exposure mask, characterized by leaving a pattern. 18. The method according to claim 17, further comprising a step of patterning the diamond film and the silicon carbide thin film in the mask portion. 6. A method for manufacturing a semiconductor device, comprising: arranging the mask for electron beam exposure according to claim 1 in close proximity to a semiconductor substrate, and irradiating the semiconductor substrate with an electron beam through the mask. Method.

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