JP2007085899A - X-ray absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an absorber pattern for extra-fine and high-accuracy X-ray optical elements. <P>SOLUTION: At least a portion of the components of X-ray absorber is set to be a Ta compound;, and tantalum oxide or tantalum nitride is available as the Ta compound. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an absorber used for an X-ray optical element such as a diffraction grating of an X-ray microscope or a micro X-ray measuring instrument, a Fresnel zone plate, or a mask for X-ray lithography.

  A diffraction grating or Fresnel zone plate used as an X-ray lens or filter, or a mask for X-ray lithography usually has an absorber pattern made of a material that absorbs X-rays on a substrate that transmits X-rays well. It has the formed structure (for example, refer nonpatent literature 1-nonpatent literature 6). Here, it is the absorber pattern that is important for determining the performance as the X-ray optical element. When the wavelength of the X-ray is long and the absorption by the substrate is large, the substrate is eliminated and only the through-hole pattern of the absorber is used. An X-ray optical element may be configured.

  The size and shape of the absorber pattern vary depending on the wavelength of the target X-ray and the function of the element. 3A is a plan view of the X-ray diffraction grating, FIG. 3B is a cross-sectional view of the X-ray diffraction grating of FIG. 3A, and FIG. 4A is a plane of the X-ray Fresnel zone plate. FIG. 4B is a cross-sectional view of the X-ray Fresnel zone plate of FIG. 3 and 4, 10 and 20 are substrates, 11 and 21 are absorber patterns, and 12 and 22 are Si supports.

  As shown in FIGS. 3A and 3B, the X-ray diffraction grating has an absorber pattern 11 that is a set of linear patterns having a constant width, and the X-ray Fresnel zone plate is shown in FIG. 4 (A) and 4 (B), it has a concentric pattern, and has an absorber pattern 21 in which the line width gradually decreases as the radius increases. In the case of a mask for X-ray lithography, it has a complicated absorber pattern such as a semiconductor integrated circuit. The performance of the X-ray optical element depends on how accurately these absorber patterns are formed.

Conventionally, SiN having a thickness of 0.2 to 2 μm has been used as a material for a substrate that transmits X-rays well, Ni, Au, or Ta has been used as a material for an absorber, and a Si plate has been used as a material for supporting the substrate. . SiN has features such as high X-ray transmittance, chemical stability, uniform and smooth composition, and high strength, and is widely used as a thin film substrate material.
On the other hand, materials used for the absorber material are different depending on the wavelength of the target X-ray and the manufacturing technology. Ni can be easily patterned by a plating method and absorbs X-rays in a relatively long wavelength region as compared with other materials as shown in FIG. 5, so it is used as an absorber for long-wavelength X-rays. I came. Au is also used as a general-purpose absorber material because it can be patterned by a plating method and has a large absorption coefficient for X-rays in a wide wavelength region.

  In recent years, dry etching techniques have been used that have fewer defects than plating methods and enable stable pattern formation. Since Ni and Au are materials that cannot be dry-etched, Ta absorbers have emerged as materials that have an X-ray absorption coefficient equivalent to these materials and can be dry-etched. Ta absorbers are chemically stable and can form fine patterns, and are currently used for diffraction gratings and Fresnel zone plates including fine patterns of 50 nm class.

  6 (A) to 6 (D) are cross-sectional views showing a manufacturing process of an X-ray Fresnel zone plate using a Ta absorber. First, as for thin film deposition, as shown in FIG. 6A, an SiN film 31 is deposited on the Si plate 30 to a predetermined thickness, and then a Ta film 32 is deposited. LP-CVD is usually used for depositing the SiN film 31, and the Ta film 32 is formed by sputtering. Next, using an electron beam drawing apparatus, a resist pattern 33 is formed as shown in FIG. Then, the Ta film 32 is dry-etched using the resist pattern 33 as a mask (FIG. 6C). Finally, as shown in FIG. 6D, the SiN film 31 on the back surface is partially removed, the Si plate 30 is back-etched with an alkaline solution, and the manufacture of the Fresnel zone plate is completed.

In the example of FIG. 6, the Ta film is etched with a resist pattern mask. However, a hard mask material such as SiO ₂ is formed between the Ta film and the resist pattern, and the hard mask material is used with the resist pattern as a mask. In some cases, the Ta film is etched using a hard mask after etching. In some cases, after the thin film is formed, back etching is performed to form a thin film region including only the Ta film and the SiN film, and then a resistor pattern is formed and the Ta film is etched.

Takeshi Namioka et al., “X-ray imaging optics”, Baifukan, first edition, p. 96-99, 1999 A.Ozawa et al., "APPLICATION OF X-RAY MASK FABRICATION TECHNOLOGIES TO HIGH RESOLUTION, LARGE DIAMETER Ta FRESNEL ZONE PLATES", Microelectronic Engineering, Vol.35, p.525-529, 1997 Yoshio Suzuki et al., “Performance Test of Fresnel Zone Plate with 50 nm Outermost Zone Width in Hard X-ray Region”, Japanese Journal of Applied Physics, Vol.44, No.4A, p.1994-1998, 2005 Y. Kagoshima et al., “Scanning hard X-ray microscope with tantalum phase zone Plate at the Hyogo-BL (BL24XU) of SPring-8”, Nuclear Instruments and Methods in Physics Research, Section A 467-468, p.872. -876, 2001 Z. Chen et al., “Design and fabrication of Fresnel zone Plates with large numbers of zones”, 1997 American Vacuum Society, vol.15, No.5, p.2522-2527, 1997 D. hambach et al., “High aperture diffractive x-ray and extrme ultraviolet optical elements for microscopy and lithography applications”, 1999 American Vacuum Society, vol. 17, No. 6, p. 3212-3216, 1999

  As the performance of optical instruments such as an X-ray microscope progresses, demands on the shape and quality of the absorber pattern of the Fresnel zone plate and the diffraction grating have become strict. Specifically, an absorber pattern having a width of 30 nm or less, an absorber pattern having a height of 10 nm or less, or an absorber pattern having an aspect ratio (ratio of height to width) of 10 or more is required. Yes. In order to realize such a requirement, it is necessary to increase the accuracy of etching of the Ta film in the step of FIG.

In general, reactive ion etching is used for etching Ta, and a chlorine-based gas such as Cl ₂ is used as a gas. In this system, Ta and Cl are reacted to form TaCl ₃ , and etching proceeds by removing TaCl ₃ by exhaust. However, since TaCl ₃ has a low vapor pressure at room temperature, it is necessary to raise the temperature to the range of 50 ° C. to 100 ° C. to increase the volatilization rate. On the other hand, Ta and Cl react very easily, so when the temperature is raised, even electrically neutral Cl active species that do not have directionality react, and so-called undercut occurs in which etching proceeds in the direction of the pattern side surface. Occurs. For this reason, when it becomes a fine pattern, control of a pattern shape becomes difficult.

  Further, when the pattern becomes fine, active species having no directivity collide with the side surface of the pattern and it is difficult to reach the bottom of the pattern, resulting in a phenomenon that the etching rate rapidly decreases. This phenomenon is called a microloading effect. In the etching of Ta, since the influence of neutral active species is large, the microloading effect is large. The etching rate of a 50 nm wide pattern is about 1/3 of the etching rate of a 1 μm wide pattern, and a 30 nm wide pattern is obtained. Then, the etching rate is about 1/7 of the pattern having a width of 1 μm.

  For this reason, in a Fresnel zone plate in which a pattern with a width of 30 nm and a pattern with a width of 1 μm or more are mixed, the time for completing the etching varies greatly depending on the pattern width. growing. In addition, in order to etch a pattern with a width of 30 nm, the thickness of the resist as an etching mask is required to be seven times or more. However, if the resist is thick, it becomes difficult to form a fine pattern. It is impossible to form As a matter of course, both the etching depth control and the pattern dimension control become very difficult as the pattern becomes finer.

Furthermore, Ta has a smaller crystal grain in the film deposited at room temperature and can form fine patterns. When the film is formed at a temperature of 250 ° C. or higher, the crystal grains become large, so that the pattern side wall becomes rough and the processing accuracy is lowered. Since Ta formed at room temperature has a crystal grain of 50 nm or less, even if a pattern with a width of about 50 nm is formed, it is not affected by the crystal grain. It is known to change greatly. This phenomenon is thought to be due to the fact that the side surface of the pattern generated by etching of Ta is oxidized by the atmosphere, and this Ta oxide has a compressive stress. Accordingly, since a severe stress change occurs in a region where narrow patterns are densely packed, the thin film substrate is deformed in such a region, resulting in wrinkles and pattern displacement. For a Fresnel zone plate or a diffraction grating, such pattern deformation is fatal and cannot be used as an element.
As described above, the Ta absorber has several problems in processing characteristics and has a problem that it is not suitable as a material for an extremely fine and highly accurate X-ray optical element.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to realize an extremely fine and highly accurate absorber pattern for an X-ray optical element.

The X-ray absorber of the present invention is characterized in that at least a part of the constituent material is a Ta compound.
In one configuration example of the X-ray absorber according to the present invention, the Ta compound is Ta oxide or Ta nitride.
Moreover, one structural example of the absorber for X-rays of this invention is formed in the predetermined | prescribed pattern according to the wavelength of the object X-ray, or the function as an X-ray optical element.

  According to the present invention, as a new absorber material for X-ray diffraction gratings and Fresnel zone plates frequently used in X-ray microscopes and the like, at least a part of the constituent material is made of a Ta compound, so that conventional Cl Etching can be performed relatively easily by reactive ion etching using F-based gas instead of system gas, and a stable etching shape can be obtained. In addition, when a Ta compound is used, the microloading effect hardly occurs. For example, in a Fresnel zone plate in which different pattern widths are mixed, the etching completion time does not vary greatly depending on the pattern width, resulting in damage to the substrate. Can be suppressed. In addition, since it is not necessary to change the thickness of the resist for etching the absorber according to the pattern width, it is easy to form a fine pattern. Further, when the Ta compound is used, the side surface of the pattern generated by etching is not further oxidized by the air, so that the stress of the film does not change in the processing step, and as a result, the pattern is not deformed. In this way, according to the present invention, the X-ray absorber can be processed with a high accuracy up to a fine pattern of 30 nm or less, so that a high-performance X-ray optical element can be realized.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present embodiment provides a new X-ray absorber material having excellent processing characteristics. A specific new absorber material is a Ta compound such as TaN or Ta ₂ O ₅ . As shown in FIG. 1, X-ray absorption coefficient of TaN is about 95% Ta, X-ray absorption coefficient of Ta ₂ O ₅ is about 1/2 of Ta, and Ni in the short wavelength region, even Ta ₂ O ₅ It exceeds the absorption coefficient. Therefore, these materials are materials that can be sufficiently used as Fresnel zone plates and diffraction gratings. In these Ta compounds, since Ta is chemically bonded to other elements, even if a new surface appears on the side surface of the pattern after etching, it is not further oxidized. For this reason, the stress of the film is stable and does not change in the processing step.

This embodiment has been conceived since it has been found that Ta compounds can be etched relatively easily by reactive ion etching using an F-based gas. TaN and Ta ₂ O ₅ have a low etching rate with a Cl-based gas. However, etching is relatively easy with a mixed gas of SF ₆ , NF ₃ , CH ₄ and Ar. In addition, since the Ta compound does not easily react with neutral radicals like the silicon oxide film, the etching shape is also stable. Further, there is almost no microloading effect, and a 30 nm wide pattern and a 1 μm wide pattern are etched at the same rate. Further, since it is not polycrystalline like Ta, it is not affected by crystal grains. The manufacturing process has the advantage that it can be used as it is by simply replacing the Ta film with a TaN film or Ta ₂ O ₅ film in the process of FIG.

The X-ray absorption characteristics and processing characteristics as described above are general characteristics of Ta compounds including not only TaN and Ta ₂ O ₅ but also TaS ₂ and TaC. This embodiment covers all Ta compounds. Is.
The present embodiment relates to an absorbent material and is not limited to any manufacturing process. For example, in the process of FIG. 6, a hard mask material is formed on the Ta compound absorber, the hard mask material is etched using the resist pattern as a mask, and the Ta compound is etched using the hard mask after etching. Is also applicable.

Further, although reactive ion etching is described as an example of the Ta compound etching method, it is not limited to reactive ion etching, and dry etching such as inductively coupled etching (ICP) or ECR etching is used. You can also. Furthermore, a mixed gas of SF ₆ , NF ₃ , CH ₄ and Ar is taken up as an etching gas, but other etching gases such as CF ₄ , C ₂ F ₆ , C ₃ F ₆ , C ₄ F ₈ , C ₄ F ₁₀ or can also be used a mixture of these gases.
Further, the conventional Ta and the Ta compound of the present embodiment can be used in two layers.

  As described above, according to the Ta compound of the present embodiment, a fine absorber pattern having a width of 30 nm or less can be formed, and as a result, a Fresnel zone plate that can be used for a high-resolution X-ray microscope can be manufactured. . Further, when applied to the production of an X-ray diffraction grating, a highly accurate absorber pattern can be formed, and a high-performance diffraction grating can be realized.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the present embodiment, a specific example of the first embodiment will be described. The manufacturing process of the Fresnel zone plate described below corresponds to the Ta film replaced with the Ta ₂ O ₅ film in FIG.
In the present embodiment, a SiN film is formed to a thickness of 0.3 μm by LP-CVD using SiH ₂ Cl ₂ and NH ₃ on a Si wafer having a diameter of 4 inches, and a Ta ₂ O ₅ film is formed on the SiN film. Was formed to a thickness of 0.2 μm by ECR sputtering in an O ₂ atmosphere.

Subsequently, ZEP520, which is a positive electron beam resist made by Nippon Zeon Co., is applied to the Ta ₂ O ₅ film to a thickness of 0.1 μm, baked at 190 ° C. for 30 minutes, and then Fresnel zone using an electron beam exposure apparatus. A pattern of plates was formed. The pattern at this time had a diameter of 520 μm, a first zone width of 2.3 μm, and an outermost peripheral width of 30 nm.

Next, the Ta ₂ O ₅ film was etched by reactive ion etching using this resist pattern as a mask. Here, a mixed gas of SF ₆ , NF ₃ , CH ₄ and Ar is used as an etching gas, the flow rate of SF ₆ gas is 10 sccm, the flow rate of NF ₃ gas is ₃ sccm, the flow rate of CH ₄ gas is 1 sccm, and the flow rate of Ar gas. Was 4 sccm. At this time, the etching rate ratio between the resist and the Ta ₂ O ₅ film was 1: 3. The microloading effect was hardly observed, and the etching of the pattern with a width of 30 nm was completed with 30% overetching of the time required for etching in the pattern with a width of 1 μm. The etching rate ratio between the Ta ₂ O ₅ film and the SiN film was 3: 1, and the SiN film was hardly damaged.

Next, the SiN film on the back surface was etched by reactive ion etching with C ₂ F ₆ gas to open a window, and the Si wafer was etched using a 30% KOH solution to form a 1 mm square SiN substrate.
As a result, a good Ta ₂ O ₅ pattern Fresnel zone plate could be formed. It was confirmed that this Fresnel zone plate performs a sufficient function as an X-ray lens.

[Third Embodiment]
In the first and second embodiments, a Ta compound is used as the X-ray absorber material. However, a material obtained by mixing a Ta compound and a W compound may be used, or a mixture of Ta compound and Hf compound may be used. The material may be used, a two-layer structure of Ta compound and W compound may be used, or a two-layer structure of Ta compound and Hf compound may be used. The material combined with the Ta compound is preferably a material having a relatively large X-ray absorption coefficient and capable of dry etching.

Further, a two-layer structure of a Ta compound and Ta may be used as the X-ray absorber material. By combining with thin Ta, the X-ray absorption coefficient can be made larger than when only Ta compound is used, and the problem of Ta etching can be reduced. Further, since Ta ₂ O ₅ has a low etching rate, a Ta ₂ O ₅ film can be used as an etching mask for the Ta film. In this case, it is not possible to remove the Ta ₂ O ₅ film after etching the Ta film, a two-layer structure of the Ta ₂ O ₅ film and the Ta film.

  Further, as the X-ray absorber material, a two-layer structure of a Ta material and a substrate material such as SiN may be used. For long-wavelength X-rays, the SiN substrate is removed to reduce the attenuation at the substrate so that only the Ta compound pattern is removed. Form. That is, where there is no Ta compound line, SiN is removed by etching and an opening that penetrates to the back surface is formed. FIG. 2A shows a plan view of the X-ray diffraction grating in this case, and FIG. 2B shows a cross-sectional view of the X-ray diffraction grating. At this time, the absorber pattern 11 made of the Ta compound is supported by the Ta compound remaining in the vertical direction in FIG. SiN 10 remaining under the absorber pattern 11 can be regarded as an absorber rather than a substrate. 2A and 2B, the mechanical strength can be increased as compared with a single layer structure of a Ta compound.

  The present invention can be applied to an X-ray optical element.

It is a figure which shows the X-ray absorption coefficient of the absorber material for X-rays concerning the 1st Embodiment of this invention. It is the top view and sectional drawing of the diffraction grating for X-rays in the 3rd Embodiment of this invention. It is the top view and sectional drawing of the diffraction grating for X-rays. It is the top view and sectional drawing of a Fresnel zone plate for X-rays. It is a figure which shows the X-ray absorption coefficient of the absorber material for conventional X-rays. It is sectional drawing which shows the manufacturing process of the Fresnel zone plate for X-rays using Ta absorber.

Explanation of symbols

10, 20 ... Substrate, 11, 21 ... Absorber pattern, 12, 22 ... Si support.

Claims (3)

In an X-ray absorber made of a material that absorbs X-rays,
An X-ray absorber, wherein at least a part of the constituent material is a Ta compound. The X-ray absorber according to claim 1,
The X-ray absorber, wherein the Ta compound is Ta oxide or Ta nitride. The X-ray absorber according to claim 1,
An X-ray absorber characterized by being formed in a predetermined pattern according to the wavelength of the X-ray to be processed and the function as an X-ray optical element.

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