JPH02177531A - Mask for x-ray exposure - Google Patents

Abstract

PURPOSE:To manufacture the title mask for X-ray exposure with sufficient endurance X-ray irradiation by a method wherein an amorphous thin film or a crystalline thin film comprising a compound film of an amorphous thin film and a crystalline thin film is used as an X-ray transmissive thin film comprising a pattern transfer region. CONSTITUTION:A thermal oxide film is formed on the surface of an Si substrate 11 in surface direction of 100; parts of the thermal oxide film are selectively made into diffusion windows; a BN disc is used as a diffusion source to diffuse boron in N2 atmosphere; boron diffused regions 12 and no-boron diffused regions are formed on tie surface of the Si substrate 11. The boron diffused region 12 in the central part of the Si substrate 11 is used as a pattern transfer region 13 while the no-boron diffused regions in the peripheral parts of the regions 13 are used as alignment regions 14. Such an X-ray mask is provided with high elastic modulus and excellent X-ray transmission. Furthermore, even if the pattern transfer region 13 is irradiated with SOR light for a long time, the boron diffused regions 12 are not subjected to any damage by irradiation and the misalignment of patterns.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to an X-ray exposure mask.

(Prior Art) In recent years, X-ray lithography, which uses X-rays with a shorter wavelength than light, has been attracting attention as a way to overcome the limitations of pattern miniaturization by light exposure. In this X-ray lithography, unlike an exposure method using light, there is currently no technology for reducing and transferring a predetermined pattern. Therefore, an X-ray exposure mask that selectively transmits X-rays is placed between the X-ray source and the object to be exposed, and a transferred pattern is created on the surface of the object by irradiating a bundle of X-rays through this mask. A 1:1 equal-size transfer method is adopted.

In this same-size transfer method, the dimensional accuracy and positional accuracy of the pattern of the X-ray exposure mask directly becomes the device accuracy, so the pattern of the X-ray exposure mask has a dimension of about one-tenth of the minimum line width of the device. Accuracy and positional accuracy are required. Furthermore, since SOR light (synchrotron radiation) is the preferred X-ray source, the X-ray exposure mask must have a structure that will not be damaged by powerful X-rays.

Furthermore, as device line widths start from 0.5- and move toward 0.11 in the next generation, the aspect ratio of the pattern cross section of the X-ray exposure mask increases, which increases various manufacturing difficulties. I'll come. As described above, in the practical application of the X-ray exposure method, the most important key is the development of the structure and manufacturing method of the X-ray exposure mask.

An X-ray exposure mask generally has the following structure. That is, a thin film (
On this X-ray transparent thin film, a mask pattern (
It has a structure in which an X-ray absorber pattern) is formed. The mask support is provided to support the X-ray transparent thin film because it is extremely thin and mechanically weak.

Conventionally, such an X-ray exposure mask has been used, for example, as shown in Fig. 3 (
Produced by the methods shown in a) to (f) (J
, Vac, Sci, Technol, , 21.4 (
1982), p. 1017).

First, as shown in FIG. 3(a), an internal stress of 5 to 15 dyn/cm is applied to the Si substrate 31 by the LPCVD method.
A second SiN film 32 is formed. Further, a thin SiN film 33 is also formed on the back surface of the Si substrate 31. The SEN film 32
is used as an X-ray transparent thin film. In addition, the X-ray transparent thin film has strong X! It is required that the self-supporting film has high resistance to I irradiation and also has tensile stress. At present, BN is used as the material.

Si, SiC, Ti, etc. have been reported.

Next, as shown in FIG. 3(b), 5iN1 on the back side
! After selectively removing the central part of 133, the Si on the surface side
A W film 54 is formed as a line absorber on the N film 3 film. X
The radiation absorber is required to have a large X-ray absorption coefficient at the exposure wavelength, low internal stress, and easy microfabrication. At present, Au is the material for this purpose.
5Ta, WlWN, etc. have been reported. For the internal stress of the X-ray absorber, 1 x 10' dyn/c
Since it is essential that the stress is as low as o 2,
Line absorbers are generally deposited by sputtering with controlled internal stress.

Next, as shown in FIG. 3(c), SiO□ with an internal stress of 1:1 is deposited on the W film 34 by sputtering.
Membrane 35 membrane type 5. Furthermore, after applying a resist 3B for electron beam drawing on the SiO□ film 35, pattern drawing is performed by electron beam drawing to form a desired pattern on the resist 3B. Here, a multilayer structure such as a high-sensitivity resist/intermediate layer/W film is used as the resist because the resist pattern is used as a mask and the cross-sectional aspect ratio is large and the wall surface is perpendicular to the substrate. This is because it is required to form a line absorber pattern.

Next, as shown in FIG. 3(d), the SiO film 35 is selectively etched by dry etching using the resist 3B as a mask. Thereafter, as shown in FIG. 3(e), the W film 34 is selectively etched to form a resist 3B and a SiO□ film 35 film type 5.

That is, the pattern of the W film 34 is formed by etching using the pattern of the 5i02 film 35 as an intermediate mask. The etching method adopted here requires that an appropriate etching selection ratio with the mask material be obtained, that the pattern conversion difference (difference in line width between the etched material and the mask material) is small, and that the wall surface of the etched material is vertical. The following conditions are required: no deposits or residues are formed, and etching stability and reproducibility are good.

Finally, as shown in FIG. 3(f'), the Si substrate 31 is etched using a wet etching method such as KOH using the SiC film 33 on the back surface as a mask.

An X-ray exposure mask is manufactured in the manner described above.

As mentioned above, the characteristics of the material constituting the X-ray transparent thin film include excellent resistance to X-ray irradiation. In recent years, the quality of the X-ray transparent thin film has changed due to intense X-ray irradiation, resulting in a decrease in visible light transmittance and changes in the internal stress of the X-ray transparent thin film. This is because the problem of distortion has become clear.

Regarding such radiation damage, there has been a report regarding an X-ray exposure mask using BNsSiNsSiC as an X-ray transparent thin film. For BN, irradiation with an SOR equivalent to approximately 1500 exposures at a dose equivalent to a resist sensitivity of 100 sJ/am2 reduced the visible light transmittance by as much as 30%, and the pattern distortion decreased to 1-. reach (W, A, Johnson et
al,,Proc,or t,he 19875PI
E, 773-03). Regarding SiC, a positional distortion of about 0.14 occurs due to SOR irradiation equivalent to 1200 exposures on a PMMA resist (Sol
id 5tate Lecnol, 22°No, 5.6
8 (1982)), P.M.
SOR equivalent to 20,000 exposures for MA resist
Due to the irradiation, a positional distortion of about 0.054 occurs (
M, Horl et al, 1st Mlcropro
cessConferencc, p, 7g, July 7
1988 JAPAN).

On the other hand, polycrystalline Si as an X-ray transparent thin film
(K, Iguchl et al, lst Mlcro
process Conre-renee, p. 80.
July/198g JAPAN), Crystalline 5i, B
In an X-ray exposure mask using Si formed by the crystalline S11 epitaxial method in which X! It has been reported that even when irradiated with I, no radiation damage occurs to an X-ray transparent thin film.

These reports show that it is necessary to select a thin film having a structure with excellent crystallinity as an X-ray transparent thin film that satisfies X-ray irradiation resistance.

In addition, the X-ray transparent thin film must have excellent mechanical strength and visible light transmittance for alignment purposes. As mentioned above, crystalline Si or crystalline Si in which B is diffused has excellent X-ray irradiation resistance, and its elastic modulus is higher than that of SiN or B N (1.4 to 1.5
x 10” Pa), and it is also a promising material because it has a very wide range of uses. However, Si has a low visible light transmittance (for example, Si with a film thickness of about 1 μM has a wavelength of 683 ns). Transmittance to laser light is 20
35%), it is difficult to perform alignment using optical systems currently in practical use.

In order to solve this problem, for example, Fig. 4(a) or (
An X-ray exposure mask with the structure shown in b) has been proposed (
For example, R.E., Acosta et al., 5PIE
con-rerence, vol, 448. p, 11
4 (1983)).

The X-ray exposure mask shown in FIG.
A thin Si film 42 is formed by diffusing M442.
An X-ray absorber pattern 43 is formed in the center of the SL thin film 42, and a portion of the periphery of the SL thin film 42 is selectively removed to form a diffraction grating pattern 44 having a stencil structure. The region where the X-ray absorber pattern 43 is formed functions as a pattern transfer region 45, and the region where the diffraction grating pattern 44 is formed functions as an alignment region 4B.

The X-ray exposure mask shown in FIG.
A Si thin film 42 is formed in which the Si thin film 42 is diffused, and an X-ray absorber pattern 43 is formed in the center of the Si thin film 42.
A portion of the peripheral portion of the Si thin film 42 is selectively thinned to increase visible light transmittance, and a diffraction grating pattern 44 is formed thereon. The region where the X-ray absorber pattern 43 is formed functions as a pattern transfer region 45, and the region where the diffraction grating pattern 44 is formed functions as an alignment region 46.

However, in the X-ray exposure mask shown in FIG. 4(a) or (b), the alignment area 4B has a partially stencil structure or a very thin film structure, so The drawback was that it lacked mechanical strength and was impractical.

(Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned problems. X has sufficient resistance to lI irradiation and is easy to optically align without compromising mechanical strength.
The purpose of the present invention is to provide a mask for line exposure.

[Structure of the Invention] (Means for Solving the Problems) The X-ray exposure mask of the present invention includes an X-ray transparent thin film and an
A pattern transfer area consisting of an X-ray absorber pattern formed on a radiation-transparent thin film, a laser light-transparent thin film provided around the pattern transfer area, and a diffraction pattern formed on the laser light-transparent thin film. In the X-ray exposure mask having an alignment area consisting of a lattice pattern, the X-ray transparent thin film is made of a crystalline thin film, and the laser beam transparent thin film is an amorphous thin film or an amorphous thin film and a crystalline thin film. It is characterized by consisting of a composite membrane with.

In the present invention, the crystalline thin film constituting the X-ray transparent thin film is desirably a thin film with a single crystal or polycrystalline structure containing at least silicon.

In the present invention, the amorphous thin film constituting the laser-transmissive thin film is preferably a silicon compound, boron nitride, or a thin film obtained by introducing impurity atoms into a silicon compound or boron nitride.

(Function) According to the present invention, since a crystalline thin film is used as the X-ray transparent thin film constituting the pattern transfer area, irradiation damage does not occur even when exposed to X-rays for X#s exposure times of 106 shots or more. do not have. Therefore, internal stress changes in the X-ray transparent thin film due to X-ray irradiation and positional distortion of the pattern due to internal stress changes do not occur, making it possible to transfer fine patterns with high precision over a long period of time. . In addition, any material can be used as the X-ray transparent thin film as long as it satisfies the characteristics of excellent X-ray irradiation resistance and high X-ray transmittance. Since it is possible to ignore the characteristic that it has excellent efficiency, the range of selection of thin film materials is expanded.

On the other hand, since an amorphous thin film or a composite film of an amorphous thin film and a crystalline thin film is used as the laser light-transmissive thin film constituting the alignment region, visible light transmittance of nearly 90% can be obtained. , alignment accuracy can be significantly improved.

In addition, conventionally, when using a thin film material with high visible light transmittance as a thin film constituting an X-ray mask in order to improve alignment accuracy, it is required to have high elastic modulus and excellent resistance to X-ray irradiation. However, any thin film can be used as a laser light transmitting thin film as long as these characteristics can be ignored, the film has excellent visible light transmittance, and has a predetermined internal stress.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIGS. 1(a) to 1(a) are cross-sectional views showing a method for manufacturing an X-ray mask according to an embodiment of the present invention in order of steps.

First, as shown in FIG. 1(a), a thermal oxide film (not shown) is formed on the surface of a 3-inch Si substrate 11 with a plane orientation of (100), and a part of the film is selectively opened to serve as a diffusion window. Using a BN disk as a diffusion source, boron is diffused at 1100°C in an N2 atmosphere to form a boron diffusion region 1 on the surface of the Si substrate 11.
2 and a region in which boron is not diffused was formed. Si substrate 1
1 The boron diffusion region 12 at the center is the pattern transfer region 13
As shown in FIG. 1, the peripheral region where boron is not diffused is used as the alignment region 14. The boron diffusion length in the boron diffusion region 12 is about 21 cm, and the boron concentration is 5 x 1019 cm-'. Next, the Si substrate 11 was oxidized at 800° C. in an 02 atmosphere. As a result,
A silicided boron oxide film layer was formed on the boron diffusion layer 12. Thereafter, the thermal oxide film used as the diffusion window was removed using an HF solution.

Next, as shown in FIG. 1(b), by LPCVD method, SiCII 2 H2/N H3 was added as a reaction gas.
An amorphous SiN x film 15 having a thickness of 2 Hm was formed at 850° C. using the following method. The tensile stress of this SiNw film 15 is approximately 3 x 10' dyn/cm2.

Next, as shown in FIG. 1(e), a resist is applied on the SiN and H2S, a resist pattern is formed by photolithography, and a CF film is etched by reactive ion etching.
The SiN film 15 was selectively etched using 4/H2 gas to open a part of the SiN film 15.

Next, as shown in FIG. 1(d), a W film 1B with a thickness of 0.5- was formed by sputtering a W target using Ar as a sputtering gas at a gas pressure of 3 mTorr and a power of 3 kW. Formed. The internal stress of this WM16 is 1 x 10' d
yn/an-'. Next, WII! After applying a resist (CMS: chloromethylated polystyrene) 17 with a film thickness of 0.7 to 1G, baking treatment was performed.

Subsequently, as shown in FIG. 1(e), the resist 17 is exposed by electron beam lithography using a variable shaped beam under the conditions of an acceleration energy of 50 keV and a dose of 150 pc/am2, and the resist 17 is exposed on the pattern transfer area 13. A resist pattern having a line and space of 0.2 to 0.51 and a diffraction grating pattern with a line width of IIIM was formed on the alignment region 14. Next, using the resist pattern as a mask, SF6+O was etched by reactive ion etching using an ECR type plasma etching device.
Using a mixed gas of □, Wllite is anisotropically etched under the conditions of microwave power of 450 W and gas pressure of 3 mTorr, and a 0.2 to 0.5
fi line and space pattern 18, forming a 1-line width diffraction grating pattern 19 on the alignment region 14;
The resist pattern was peeled off.

Finally, as shown in FIG. 1 (1'), the S i
Using the Nx film 15 as a mask, Si on the back side of the pattern transfer region 13 and alignment region 14 is
The substrate 11 was back etched. At this time, the boron diffusion region 12 is not etched by the KOH solution, but the etching progresses easily in the region where boron is not diffused.

In the above manner, 0.2 to 0
．． A pattern transfer region 13 in which a 5-line-and-space pattern 18 is formed, and an alignment region 1 in which a 1-line width diffraction grating pattern 19 is formed on the SiNx film 15.
An XtI mask with 4 was fabricated.

In such an X-ray mask, the X-ray transparent thin film constituting the pattern transfer region 13 is made of a crystalline St thin film in which boron is diffused (boron diffused region 12), so it has a high elastic modulus and is X-ray transparent. Excellent.

Furthermore, even when the pattern transfer region 13 is irradiated with SOR light at an absorption dose of 500 MJ/cm3 for a long time, no damage to the boron diffusion region 12 due to the irradiation or positional distortion of the pattern is observed, and the X-ray irradiation resistance is It was confirmed that it is excellent. Furthermore, as a result of transferring a pattern to a resist coated on a substrate to be exposed through an X-ray mask using SOR light, lines and spaces of 0.2 to 0.5- were formed on the resist.

On the other hand, in the alignment region 14, the visible light transmittance is i1N
As a result, the transmittance for laser light with a wavelength of 833 ns was 90%. On the other hand, in the boron diffusion region 12, the transmittance for laser light having a wavelength of 833 ns was about 30%. A significant improvement in transmittance was thus confirmed.

Furthermore, we heterodyne measured the relative positional deviation between the X-ray mask and the exposed substrate using a commercially available He-Ne transverse Zeeman laser, and evaluated the alignment accuracy between the two.
It was confirmed that positioning i control was possible with an accuracy of 0.02 μs.

Embodiment 2 FIGS. 2(a) to 2(f) are cross-sectional views showing a method for manufacturing an X-ray mask according to another embodiment of the present invention in order of steps. In addition,
In FIG. 2, the same parts as the first factor are given the same reference numerals to simplify the explanation.

First, as shown in FIG. 2(a), BN was used as a diffusion source over the entire surface of the 3-inch Si substrate 11 with a plane orientation (10G).
Boron was diffused at 1100° C. in an N2 atmosphere using a disk to form a boron diffusion region 12.

The boron diffusion length in the boron diffusion region 12 is approximately 1
The boron concentration in one direction of μ11 depth is 5 x 10'c
111-'. Next, the Si substrate 11 was oxidized at 800° C. in an 02 atmosphere. As a result, a silicided boron oxide film layer was formed on the boron diffusion layer 12.

Next, as shown in FIG. 2(b), a part of the periphery of the boron diffusion region 12 was selectively etched by a normal photolithography process to form a thin boron diffusion region 21. The thickness of this thin boron diffusion region 21 is approximately 0.2
− is. The boron diffusion region 12 at the center of the Si substrate 11 is used as the pattern transfer region 13, and a part of the thin boron diffusion region 21 at the periphery thereof is used as the alignment region 14.

Next, as shown in FIG. 2(c), S i Cj? 2 H2/NH
3 to a film thickness of 1.3 at 850°C. A film 15 of amorphous SiN was formed. The tensile stress of this SiN m film 15 is about 3×10′ dyn/as 2.

Next, as shown in FIG. 2(d), the SiNw film 1
Resist is applied to the entire surface of 5, and CF is used as a reactive gas.
By plasma etching using 4/H2, the SiNm film 15 on the boron diffusion region 12 is etched back, and the surface of the boron diffusion region I2 and the surface of the SiN film 15 on the thin boron diffusion region 21 around it are flattened. It became. Furthermore,
A part of the SiNw film 15 on the back side was selectively etched to open a part of the SiNm film 15.

Next, in the same manner as in FIGS. 1(d) and (e), as shown in FIG. 2(e), a film with a thickness of 0 is formed by sputtering.
．． 5-WG was formed, a resist with a film thickness of 0.7 H was applied on the WM, and the pattern was transferred by electron beam lithography using a variable shaped beam and reactive ion etching using an ECR type plasma etching device. Area 1
A line and space pattern 1g of 0.2 to 0.5 tn was formed on 3, and a diffraction grating pattern 19 of 11 line width was formed on alignment region 14, and the resist pattern was peeled off.

Finally, as shown in Figure 2 ( ), the SiN on the back side
Using the x film 15 as a mask, Si2 on the back side of the pattern transfer area 13 and alignment area 14 is removed using a KOH solution.
& Board 11 was back etched. As above,
A pattern transfer region 13 in which a 0.2 to 0.5 line and space pattern 1B is formed on the boron diffusion region 12, a thin boron diffusion region 21, and the SiN* film 1.
An X-ray mask having an alignment region 14 in which a 1-linewidth diffraction grating pattern 19 was formed on a composite film of No. 5 was manufactured.

In such an X-ray mask, the X-ray transparent thin film constituting the pattern transfer region 13 is made of a crystalline Si thin film in which boron is diffused (boron diffused region 12), so it has a high elastic modulus and is X-ray transparent. , excellent resistance to X-ray irradiation. Then, using SOR light, the pattern was transferred to a resist coated on a substrate to be exposed through an X-ray mask, and as a result, lines and spaces of 0.2 to 0.5- were formed on the resist.

On the other hand, the thin boron diffusion region 21 constituting the alignment region 14 has a film thickness of 0.2. Since it is thin, visible light is not extremely attenuated, and since the amorphous SiNm film 15 acts as an antireflection film, the visible light transmittance is high. When we actually measured the visible light transmittance in alignment area 4, we found that the transmittance for laser light with a wavelength of 633n was 9.
It was 0%. Furthermore, since the alignment region 14 has a composite film structure of the thin boron diffusion region 21 and SiN, 1i15, it has sufficient mechanical strength.

Here, the X-ray mask of Example 1 and the X! 11
Comparing the mechanical strengths of the masks, it is possible that Example 1 is slightly inferior in mechanical strength. However, since the alignment area is smaller than the pattern transfer area, it is considered that there is no problem with mechanical strength. In fact, for the X-ray mask of Example 1, when a 4-×4-cross pattern is formed at 4 mm intervals in a 24×24 us' pattern transfer area, the amount of positional deviation between the pattern drawn on the resist and the W film pattern is was 80 nm at 3σ, and a highly accurate pattern could be formed. This indicates that the X-ray mask of Example 1 has small plane distortion, and is considered to have excellent mechanical strength.

Note that the present invention is not limited to the embodiments described above.

For example, in the above embodiment, the Si substrate with boron diffused is
Although it is used as a radiation-transparent thin film, any material with excellent crystallinity such as an epitaxial layer containing boron or polycrystalline silicon may be used.

Further, in the above embodiment, an amorphous SiN film formed by LPCVD was used as the laser light transmitting thin film constituting the alignment region, but the present invention is not limited to this, and an amorphous thin film such as boron nitride or other silicon compounds may be used. Any material can be used as long as it has good visible light transmittance.

Further, although the LPCVD method is used as a method for forming the thin film, it is also possible to use a plasma CVD method, a sputtering method, a photo-CVD method, or the like.

Further, in the above embodiment, a W pattern is formed on the SL substrate, but an Au film or a Ta film formed by a plating method may also be used.

In addition, although the W pattern is formed before back-etching the St substrate, the back-etched Si
W may be formed on the ring.

Further, conditions such as film thickness of each part can be changed as appropriate according to specifications. In addition, various modifications can be made without departing from the gist of the present invention.

[Brief explanation of the drawing]

FIGS. 1(a) to 1(a) are cross-sectional views showing the method for manufacturing an X-ray mask according to Example 1 of the present invention in the order of steps, and FIG. 2(a)
-() are cross-sectional views showing the method for manufacturing an X-ray mask in the order of steps in Example 2 of the present invention, and FIGS. 3(a) to (r) are cross-sectional views showing the method for manufacturing the conventional figure,'
! Figures B4 (a) and (b) are cross-sectional views of conventional X-ray masks, respectively. 11... Silicon substrate, 12... Boron diffusion region,
13... Pattern transfer area, 14... Alignment area, 15... SiN * film, 1B... W film, 17.
...Resist, 18...Line and space pattern, 19...Diffraction grating pattern, 21...Thin boron diffusion region. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 4

Claims (3)

[Claims] (1) a pattern transfer area consisting of an X-ray transparent thin film and an X-ray absorber pattern formed on the X-ray transparent thin film;
In the X-ray exposure mask, the X-ray exposure mask has a laser light-transmissive thin film provided at the periphery of the pattern transfer region and an alignment region formed of a diffraction grating pattern formed on the laser light-transmissive thin film. 1. An X-ray exposure mask characterized in that the transparent thin film is a crystalline thin film, and the laser light-transmissive thin film is an amorphous thin film or a composite film of an amorphous thin film and a crystalline thin film. (2) The X-ray exposure mask according to claim (1), wherein the crystalline thin film constituting the X-ray transparent thin film is a thin film having a single-crystalline or polycrystalline structure containing at least silicon. (3) X according to claim (1), characterized in that the amorphous thin film constituting the laser light transmitting thin film is a thin film made of a silicon compound, boron nitride, or a silicon compound or boron nitride into which impurity atoms are introduced. Mask for line exposure.