JP3306963B2 - Stencil mask forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a stencil mask used in electron beam lithography, and more particularly to an electron block exposure technique expected to be used as lithography in the sub-micron and sub-half-micron regions in the manufacture of semiconductor devices. A stencil mask forming method.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional method of forming a stencil mask. In the conventional method, first, after a boron diffusion layer 31 is formed on a silicon substrate 30, an epitaxial layer 32 of silicon is formed thereon.
(A)). Next, after a protective film made of a nitride film or an oxide film is formed, the back surface of the substrate is etched to a boron diffusion layer 31 with an alkaline solution to peel off the protective film (FIG. 3).
(B)).

Thereafter, a resist pattern 33 is formed on the epitaxial layer 32 (FIG. 3C). Next, etching is performed by RIE so as to penetrate the substrate, and the resist layer is removed to form a mask pattern (FIG. 3).
(D)).

Japanese Patent Application Laid-Open No. 4-240719 discloses a process obtained by simplifying the above-mentioned conventional method. In this process, as shown in FIG. 4, after a photosensitive glass 42 is applied on a silicon substrate 41, ultraviolet rays are applied to form a pattern (FIG. 4A). Next, using a mask 43 formed by depositing a silicon oxide film on the back surface of the silicon substrate and selectively removing the silicon oxide film, the silicon substrate 4 is removed.
1 is dissolved and removed (FIG. 4 (b)). Thereafter, a metal film 44 is deposited on the photosensitive glass 42 to form a mask (FIG. 4).
(C)).

[0005]

In the above-described method, since the formation of the pattern and the etching of the substrate are performed, there is a limit in reducing the width of the mask pattern. Further, it is desired that the stencil mask has a thickness, that is, a stencil mask having a pattern with a high aspect ratio.

[0006] The above-described RIE etching and patterning of photosensitive glass are both expected as methods capable of fine processing with a high aspect ratio. But RI
E etching is good for stencil masks 20
If a mask is formed by patterning a member having a thickness of μm or more, the cross-sectional shape may be disturbed. In principle, the thickness of the photosensitive glass is also limited to about 20 μm in principle, and when the thickness is further increased, the obtained aspect ratio decreases.

[0007] The disorder in the cross-sectional shape is, for example, as shown in FIG. 5. If the side etch advances and the body becomes thin (FIG. 5 A), the etching hardly progresses and the body becomes thick. (FIG. 5B).

Therefore, in the conventional method, when a thick mask pattern is to be formed, the cross-sectional shape is likely to be disturbed, and when the pattern width is to be narrowed, a mask pattern having a high aspect ratio must be formed. Becomes difficult. As described above, in the conventional method, there are considerable restrictions on the formation of the mask pattern in both the thickness and the pattern width.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method capable of forming a stencil mask which is thicker than before and is structurally strong in order to solve the problems of the conventional method.

A further object of the present invention is to provide a method for forming a stencil mask having a smaller pattern width than a conventional one at a predetermined thickness.

[0011]

A stencil mask forming method according to the present invention comprises the steps of forming a resist pattern using lithography for exposing X-rays, and using the formed resist pattern as a mold in accordance with the shape of the stencil mask. Forming a structure made of a conductive material.

In the present invention, for example, a resist layer made of a photosensitive material for X-rays (photoresist) is first formed on a substrate. For the substrate, silicon or the like on the surface of which titanium is sputter-deposited can be used. As the X-ray photosensitive material, for example, polymethyl methacrylate (PMMA), a copolymer of polymethyl methacrylate and methacrylic acid and the like are preferably used. The thickness of the formed resist layer is 20 μm to 500 μm, preferably 20 μm to 10 μm.
It can be 0 μm.

Next, the resist layer is exposed to X-rays using a mask having a pattern of an absorbing material made of a heavy metal such as tungsten. Synchrotron radiation (S
OR) X-rays can be preferably used. SOR X-rays are particularly suitable for deep lithography because they have high intensity, sharp directivity, and excellent transparency.

When SOR X-rays are used, if X-rays having a wavelength of 2 to 3 ° are mainly used, exposure can be performed on a thick resist having a thickness of up to 500 μm. In addition, the use of SOR X-rays enables exposure of a thick resist with sub-μm accuracy.

The exposed X-ray photosensitive material is developed with a developing solution such as methyl isobutyl ketone to form a resist pattern. The resulting resist pattern has a thickness of 2
0 μm or more, preferably 50 μm to 500 μm, line &
The space can be 3 μm, preferably 1 μm to 10 μm.

According to lithography using X-rays, it is possible to form a highly accurate and sharp pattern having a high aspect ratio on a resist material. In particular,
By using SOR X-rays, 50 μm to 500 μm
A pattern having a thickness of μm and a sharp shape of about 3 μm of line & space can be formed.

In the present invention, a stencil mask is formed by using a high aspect ratio resist pattern formed as described above as a mold instead of using it as a mask. Since the resist pattern is used as a mold, the structure can be formed according to the resist pattern mold without having to etch the substrate into a predetermined shape.

In this step, for example, when the substrate on which the resist pattern is formed has conductivity, a conductive material such as metal can be deposited in the mold of the resist pattern by plating. Next, by separating or removing the resist pattern and the substrate, a structure made of a deposit according to the type of the resist pattern can be obtained as a stencil mask.

In order to easily separate the deposit from the substrate, a film which can be selectively removed with a predetermined acid or alkali or the like is formed on the substrate in advance, a resist layer is formed, and a hardly soluble material is plated. It may be used as a material.

A structure made of a conductive material such as a metal according to a resist pattern type has a shape corresponding to a desired stencil mask. However, as described above, this structure can be used as it is for a stencil mask. Alternatively, it may be used in a mold for mass-producing stencil masks.

When the above structure is used for a mold, an inversion mold can be formed from the mold by a plastic mold or the like, and a stencil mask made of a conductive material such as metal can be formed from the inversion mold. By forming the inverted type, the stencil mask can be easily duplicated, and more practical mass production can be realized.

In order to form a structure by charging a conductive material such as a metal into an inversion mold, for example, electroless plating, electrolytic plating or the like can be used. The conductive material deposited in the inversion mold by plating or the like is removed in excess from the surface by polishing or the like, and has a shape usable as a stencil mask. Next, the inverted mold is removed or separated, and a stencil mask having a desired shape is obtained.

In order to deposit a conductive material in the above-described resist pattern type or the reverse type, a plating technique is preferably used. In addition, various gas phase processes and liquid phase processes can be used.

The conductive material charged into the mold includes:
Nickel, gold, copper, or the like can be used.

[0025]

According to the present invention, if a resist material is subjected to deep lithography by X-rays, a pattern having a width of several μm can be formed on a thick resist of several tens μm. The formed resist pattern has high accuracy,
It has a sharp cross-sectional shape that stands vertically from the substrate.

If such a resist pattern is used as a mold, an ideal structure having a pattern with a thickness of several tens of μm and a width of several μm, and having a cross-sectional shape that stands vertically along the resist pattern can be obtained. Can be formed. Such a structure can be formed by depositing a conductive material such as a metal in the mold of the resist pattern as described above, and has a shape corresponding to the shape of the stencil mask. As described above, such a structure can be used as it is as a stencil mask, and also used as a mold for forming a stencil mask.

[0027]

Embodiment 1 Referring to FIG. 1A, first, a mask 10 for X-ray lithography is formed. Tungsten or the like is used for the absorber 1 of the mask, and SiN or the like is used for the membrane 2. The absorber pattern corresponds to the desired stencil mask hole pattern.

Referring to FIG. 1B, a silicon substrate 3 is prepared, and titanium is coated on the substrate by sputtering to form a titanium film 4. Then, FIG.
As shown in (c), a resist layer made of an X-ray photosensitive material containing polymethyl methacrylate as a main component is formed on the titanium film 4 to a thickness of 50 μm to 100 μm.

Next, referring to FIG. 1D, using the mask 10 described above, X-rays 8 of synchrotron radiation are exposed. By development, a resist pattern 5 'as shown in FIG. 1E is formed. The resulting resist pattern 5 '
Has a wall that is steep perpendicular to the substrate and has a sharp shape.

Referring to FIG. 1F, nickel plating is performed on the substrate, and nickel
Is deposited with a predetermined thickness of 50 μm to 100 μm. Referring to FIG. 1 (g), the resist pattern is dissolved with a stripping solution. Referring to FIG. 1 (h), the nickel film is separated from the substrate by dissolving the titanium film by wet etching using hydrofluoric acid to obtain a stencil mask 6 'made of nickel.

Embodiment 2 The steps shown in FIGS. 1 (a) to 1 (g) are performed in the same manner as in Embodiment 1 to obtain a state in which a nickel structure is formed on a substrate.

Referring to FIG. 2A, a plastic mold 11 is formed on the nickel structure 6 formed on the silicon substrate 3 by plastic molding. FIG.
Referring to (b), the obtained plastic mold 11 is subjected to electroless nickel plating and electrolytic nickel plating to form a nickel structure 12.

Referring to FIG. 2C, the nickel protruding from the plastic mold 11 is removed by polishing. Referring to FIG. 2D, the plastic mold is separated or melted to obtain a nickel stencil mask 16 shaped along the plastic mold. The resulting stencil mask is
Like the first embodiment, the wall has a wall that is vertically steep and has a sharp shape.

According to this process, mass production of a stencil mask becomes possible by repeating the process after forming the plastic mold.

[0035]

As described above, according to the present invention,
If necessary, a mechanically strong stencil mask having a thickness of several tens of μm or more can be obtained. According to the present invention, the pattern size of the stencil mask is set to several μm.
Can be reduced to When a stencil mask having a finer pattern is used, the reduction ratio of the electron optical system in electron beam lithography can be reduced, and the depth of focus can be increased. Furthermore, it is also possible to perform a fine block exposure without changing the reduction ratio.

According to the present invention, a metal stencil mask can be easily formed, and it is not necessary to consider charge-up and the like. In addition, according to the present invention, a stencil mask can be formed by a process that is greatly simplified as compared with the conventional method as described above. The process of the present invention does not require steps such as boron doping and thermal diffusion in the prior art.
The stencil mask can be formed by a simpler process without the need for a process such as gold deposition, as compared with the technology disclosed in US Pat.

Further, the stencil mask formed according to the present invention has a vertical cross section,
This is to realize drawing by an electron beam faithfully to a mask pattern. As described above, the present invention contributes greatly to the development of the electron beam block exposure technology by providing a more useful stencil mask.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a process in a stencil mask forming method according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing steps in a stencil mask forming method according to a second embodiment of the present invention.

FIG. 3 is a cross-sectional view showing an example of a conventional stencil mask forming method.

FIG. 4 is a sectional view showing another example of a conventional stencil mask forming method.

FIG. 5 is a cross-sectional view showing disorder of a cross-sectional shape formed by a conventional stencil mask forming method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Absorber 2 Membrane 3 Silicon substrate 4 Titanium film 5 Resist layer 5 'Resist pattern 6 Nickel 6' Stencil mask 10 Mask 11 Plastic mold 12 Nickel structure 16 Stencil mask

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/027 G03F 1/16

Claims (3)

(57) [Claims] 1. A group using lithography to expose the X-ray
Forming a step of forming a thick 20μm or more resist pattern on the plate, a structure made of a conductive material corresponding to the shape of the stencil mask the resist pattern as a mold without etching, the resist pattern and Separating or removing the substrate
And a step of, characterized by the structure as a stencil mask, a stencil mask formation process. 2. A group using lithography to expose the X-ray
Forming a step of forming a thick 20μm or more resist pattern on the plate, a structure made of a conductive material corresponding to the shape of the stencil mask the resist pattern as a mold without etching, the resist pattern and Separating or removing the substrate
Step and a step of forming an inverted type the structure as a mold, characterized in that it comprises a step of forming a stencil mask made of a conductive material from said inverting, stencil mask formation method of. 3. The X-ray according to claim 1, wherein the X-ray is an X-ray having a wavelength of 2 ° to 3 ° due to synchrotron radiation.
Or the stencil mask forming method according to 2.