JPH0697025A - Formation of stencil mask - Google Patents

Abstract

PURPOSE:To easily form a stencil mask wherein its mechanical strength is especially excellent, its thermal stability is high, it does not dislocate a beam due to the charging-up of electrons, it is accurate, it is thin and its productivity is high regarding a reduction-transfer electron-beam lithographic technique using the stencil mask. CONSTITUTION:An inorganic film 12 is deposited on a semiconductor silicon substrate 11, and a resist pattern 13 is formed on the inorganic film 12. The inorganic film 12 is etched by using the resist pattern 13 as a mask. A metal tungsten film 14 is deposited selectively on the semiconductor silicon substrate 11 by using the pattern of the inorganic film 12 as a mask. In addition, the inorganic film 11 is removed, and the silicon substrate is dissolved and removed. Thereby, it is possible to easily form a stencil mask which uses the metal tungsten film 14 as a mask material, whose mechanical strength is excellent and whose thermal stability is high.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam lithography technique for microfabrication of semiconductor devices, and more particularly to a stencil mask forming method in reduction transfer type electron beam lithography using a stencil mask. is there.

[0002]

2. Description of the Related Art The electron beam lithography technique is used as a tool for advanced development of LSI because it does not require the use of a reticle and can form a fine pattern. Conventionally, a widely used electron beam drawing method is a method of sequentially drawing patterns one by one with a Gaussian beam or a variable shaped beam using a field emission type or thermionic electron gun,
It is called the so-called one-stroke writing method. That is, a method capable of drawing an arbitrary figure on the resist by focusing the electron beam generated from the electron gun into a narrow beam spot on the resist surface by the focusing lens and further controlling the position of the beam spot by the deflection system. Is.
This method has the merit that distortion and aberration inside the deflection field can be electrically corrected and the accuracy can be increased depending on the control technique, and many developments have been made and put to practical use. However, on the other hand, in this method, since the spot diameter of the electron beam is about 0.1 to 2 μm, the size of the drawing pattern becomes small, and the number of spots to be drawn becomes enormous. Since there is a limit to the spot movement speed due to the limit of the operating frequency, the time required for drawing becomes very long, and the throughput is lowered.

Therefore, in order to solve these drawbacks, a reduction transfer method has recently been adopted in which all patterns of an LSI chip are not drawn like a single stroke, but partial patterns are transferred using a mask. Figured out. That is, this is a method in which the repeated area of the LSI pattern is decomposed into partial patterns of small areas, this pattern is formed into a stencil mask, and the pattern is sequentially transferred using this mask. However, this method is expected to have a very high throughput, but it is very difficult to form the stencil mask to be used. For example, an example of a stencil mask forming method currently considered is shown in FIG.

An acceleration voltage of 50K is applied to the semiconductor silicon substrate 11.
Boron ions 42 are implanted with V and a dose amount of 1 × 10 ²⁰ cm ⁻² to form an ion implantation layer 41 (FIG. 4).
(A)). An epi layer 43 of silicon is formed thereon, and a nitride film is deposited as a protective film 44 on the epi layer and on the back surface of the silicon substrate (FIG. 4B). After that, the silicon oxide film on the back surface of the semiconductor silicon substrate is selectively removed using lithography technology and dry etching technology, and the back surface of the semiconductor silicon substrate is masked with the silicon oxide film to a boron injection layer with an ethylenediamine / pyrocatechol solution. Etching is performed to remove the protective film (FIG. 4C).
A resist pattern 45 is formed on the epi layer using an electron beam lithography technique (FIG. 4D). Using the resist pattern 45 as a mask, the epi layer and the ion implantation layer are etched to form a mask pattern (FIG. 4E).

The stencil mask used in electron beam reduction transfer lithography can be formed by the above method. However, with this method, a protective film must be deposited, and since it is necessary to form a mask that blocks the electron beam only by the ion-implanted layer and epi layer of silicon, the mask film thickness is several tens of μm or more. Next to
Etching is not easy either.

[0006]

As described above, in the stencil mask used in electron beam reduction transfer lithography, if only a silicon material is used, the film thickness is required to be several tens of μm or more. (FIG. 3) shows the range of electrons in silicon with respect to the acceleration voltage of the electron beam. Usually, the accelerating voltage used in electron beam lithography is 20 to 50 KV, so that when a silicon material is used as a mask, a film thickness of about 20 μm is required. It is very difficult to etch silicon with a film thickness of several tens of μm or more, and many steps such as ion implantation, epitaxial technology, lithography, and etching are required, which makes the process of stencil mask creation complicated. There are drawbacks. Further, silicon itself is fragile and fragile, and undoped silicon has a poor electron conductivity, and there is a problem that the beam is displaced due to charge-up caused by irradiation with an electron beam. That is, it is desired that the stencil mask has a film thickness as thin as possible, has mechanical strength, has good electronic conductivity, and has good dimensional stability and thermal stability due to temperature change.

Therefore, it is conceivable to deposit a metal on the surface of the silicon mask to prevent charge-up and reduce the film thickness. (Fig. 3), like silicon,
The range of electrons for gold is also shown. Since gold cannot be etched, it can only be deposited on the mask surface, and is very difficult to handle as an impurity in the silicon semiconductor process. Furthermore, when the mask is irradiated with the electron beam, heat is generated,
The mask deforms, but the coefficient of thermal expansion at this time is 2.5 × 10 ^-6 / deg for silicon and 14.2 × 10 for gold.
^-6 / deg, and the thermal conductivity of silicon is 1.7 cm.de
Since g and gold are 3.1 cm.deg, it is considered that the mask is distorted by depositing gold on the surface of the silicon mask. In order to solve these problems, the present inventors have completed a method of forming a stencil mask for electron beam reduction transfer lithography.

[0008]

The stencil mask forming method of the present invention comprises the steps of depositing an inorganic film on the surface of a semiconductor silicon substrate, forming a resist pattern on the inorganic film using a lithography technique, and Using the pattern as a mask, transferring the pattern by etching the inorganic film, and exposing the semiconductor silicon substrate,
A method comprising: selectively depositing metallic tungsten on the semiconductor silicon substrate; and, after removing the inorganic film, selectively removing a silicon portion of the semiconductor silicon substrate from a back surface. It is a thing. And, desirably, a method is provided in which the inorganic film deposited on the semiconductor silicon substrate is a silicon oxide film, and the metal tungsten deposited on the semiconductor silicon substrate has a thickness of 3 μm or more.

Furthermore, according to the present invention, a step of depositing an inorganic film on the surface of a semiconductor silicon substrate, a resist pattern is formed on the inorganic film by a lithography technique, and the inorganic pattern is formed using the resist pattern as a mask. A step of etching a film and the semiconductor silicon substrate to transfer a pattern, a step of selectively depositing metal tungsten on the semiconductor silicon substrate, and a step of removing the inorganic film and then removing the silicon portion of the semiconductor silicon substrate from the back surface. And a step of selectively removing it from the above. And, desirably, a method is provided in which the inorganic film deposited on the semiconductor silicon substrate is a silicon oxide film, and the metal tungsten deposited on the semiconductor silicon substrate has a thickness of 3 μm or more.

That is, the atomic masses of gold and tungsten are close to each other, and as shown in (FIG. 3), the range of electrons in tungsten is about the same as in the case of gold. Tungsten is deposited on the silicon surface for thinning. This tungsten has a thermal expansion coefficient of 4.5 × 10 ^{−6 /} deg and a thermal conductivity of 1.7, respectively.
cm.deg, which is very close to that of silicon. Further, it has high electronic conductivity and excellent mechanical strength, and can be used in the silicon semiconductor process.

[0011]

According to the present invention, the stencil mask forming process described above makes it possible to easily form a stencil mask for electron beam reduction transfer lithography which has a small film thickness and does not cause beam distortion due to charge-up.
In particular, by using a silicon material and tungsten that have values close to each other in thermal expansion coefficient and thermal conductivity, thermal strain does not occur, and there is no need to deposit gold. You can That is, by using tungsten-silicon, the mechanical strength is excellent, and the dimensional stability due to temperature change,
It is possible to form a stencil mask having good thermal stability. Therefore, by using the present invention, it is possible to effectively form a thin stencil mask that is accurate and has excellent thermal stability.

[0012]

First, the outline of the present invention will be described. INDUSTRIAL APPLICABILITY The present invention makes it possible to form a thin and highly practical stencil mask free from thermal strain by using metallic tungsten. Since the atomic masses of silicon, tungsten, and gold are 28, 184, and 197, respectively, the range of electrons is the longest in silicon, and tungsten and gold have almost the same range. In addition, since silicon and tungsten have values close to each other in thermal conductivity and thermal expansion coefficient,
It is not distorted by the heat of the electron beam.
Furthermore, since tungsten can be used in a semiconductor silicon process and can be selectively deposited on a substrate, it can be easily and accurately patterned as a stencil mask for electron beam reduction transfer lithography.

A stencil mask forming method according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a process sectional view of a stencil mask forming method according to an embodiment of the present invention. A silicon oxide film having a thickness of 5 μm was deposited as an inorganic film 12 on the semiconductor silicon substrate 11, and a resist pattern 13 was formed on the inorganic film by using a lithography technique. Using this resist pattern as a mask, the inorganic film was etched to obtain a pattern having an accurate and vertical cross-sectional shape (FIG. 1A). After removing this resist pattern,
Using the pattern of the inorganic film as a mask, metal tungsten 14 was selectively deposited on the semiconductor silicon substrate 11 to a thickness of 5 μm (FIG. 1B). Further, the silicon oxide film which is an inorganic film was removed (FIG. 1C). Then, this substrate is dipped in an ethylenediamine / pyrocatechol solution to dissolve and remove only the silicon region 11 to use the metal tungsten film 14 as it is as a mask material, which has excellent mechanical strength and high thermal stability. It was possible to form a stencil mask without distortion due to (Fig. 1
(D)).

As described above, according to the present embodiment, by using metallic tungsten as a mask material as it is, the stencil mask forming process can be greatly simplified, and even when the electron beam acceleration voltage is 50 keV. ,
It is possible to form a practical stencil mask for electron beam reduction transfer lithography capable of blocking electrons. Although the silicon oxide film is used as the inorganic film here, a silicon nitride film may be used.

A second embodiment of the present invention will be described below with reference to the drawings. (FIG. 2) is a process sectional view of a stencil mask forming method according to the second embodiment of the present invention. A silicon oxide film having a thickness of 2 μm is deposited as an inorganic film 21 on a semiconductor silicon substrate 11, and a resist pattern 2 is formed on the inorganic film 21 by a lithography technique.
Formed 2. With this resist pattern as a mask,
The inorganic film was etched, and further, the silicon substrate was etched by about 3 μm to obtain a pattern having an accurate vertical cross-sectional shape (FIG. 2A). After removing this resist pattern, metal tungsten 2 is selectively formed on the semiconductor silicon substrate 11 using the pattern of the inorganic film as a mask.
3 was deposited to a thickness of 5 μm (FIG. 2 (b)). Further, the silicon oxide film which is an inorganic film was removed (FIG. 2C).
Then, this substrate is dipped in an ethylenediamine / pyrocatechol solution to dissolve and remove only the silicon region 11 to use the metal tungsten film 23 as a mask material as it is, which has excellent mechanical strength and high thermal stability.
It was possible to form a stencil mask that was not strained by heat (Fig. 2 (d)).

As described above, according to the present embodiment, by using metallic tungsten as a mask material as it is, the stencil mask forming process can be greatly simplified, and there is no distortion due to heat, and the thin film is sufficient. It is possible to form an accurate and practical stencil mask for electron beam reduction transfer lithography that can block electrons and does not cause beam deviation due to charge-up.
Although the silicon oxide film is used as the inorganic film here, a silicon nitride film may be used.

[0018]

As described above, according to the present invention,
By selectively depositing tungsten on the semiconductor silicon substrate and using this metallic tungsten as it is, beam deviation due to charge-up of electrons, which has excellent mechanical strength, high thermal stability, and no thermal distortion, occurs. It is possible to easily form a stencil mask that is accurate, thin, and highly practical. Further, since tungsten has a heavy atomic mass and the range of electrons is 5 μm or less, a thin film having a mask film thickness of 5 μm or less can sufficiently shield electrons, and is effective as a stencil mask for electron beam reduction transfer lithography. And can greatly contribute to the manufacture of ultra-high density integrated circuits.

[Brief description of drawings]

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

FIG. 2 is a process sectional view of a stencil mask forming method according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a range of electrons with respect to an acceleration voltage of an electron beam.

FIG. 4 is a process sectional view of a conventional stencil mask forming method.

[Explanation of symbols]

 11 Semiconductor Silicon Substrate 12 Inorganic Film 13 Resist Pattern 14 Tungsten

[Procedure amendment]

[Submission date] October 22, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction content]

[0018]

As described above, according to the present invention,
By selectively depositing tungsten on the semiconductor silicon substrate and using this metallic tungsten as it is, beam deviation due to charge-up of electrons, which has excellent mechanical strength, high thermal stability, and no thermal distortion, occurs. It is possible to easily form a stencil mask that is accurate, thin, and highly practical. Further, since tungsten has a heavy atomic mass and the range of electrons is 5 μm or less, a thin film having a mask film thickness of 5 μm or less can sufficiently shield electrons, and is effective as a stencil mask for electron beam reduction transfer lithography. It can act and make a great contribution to the manufacture of ultra-high density integrated circuits.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

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

FIG. 2 is a process sectional view of a stencil mask forming method according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a range of electrons with respect to an acceleration voltage of an electron beam.

FIG. 4 is a process sectional view of a conventional stencil mask forming method.

[Explanation of reference numerals] 11 semiconductor silicon substrate 12 inorganic film 13 resist pattern 14 tungsten

Claims (4)

[Claims] 1. A step of depositing an inorganic film on a surface of a semiconductor silicon substrate, a resist pattern is formed on the inorganic film by using a lithography technique, and the inorganic film is etched by using the resist pattern as a mask to form a pattern. Transferring, exposing the semiconductor silicon substrate,
And a step of selectively depositing metallic tungsten on the semiconductor silicon substrate, and a step of selectively removing the silicon portion of the semiconductor silicon substrate from the back surface after removing the inorganic film. Method for forming stencil mask. 2. A step of depositing an inorganic film on a surface of a semiconductor silicon substrate, a resist pattern is formed on the inorganic film by using a lithography technique, and the inorganic film and the semiconductor silicon substrate are masked with the resist pattern. A step of etching and transferring a pattern, a step of selectively depositing metal tungsten on the semiconductor silicon substrate, and a step of selectively removing the silicon portion of the semiconductor silicon substrate from the back surface after removing the inorganic film. A method for forming a stencil mask, comprising: 3. The stencil mask forming method according to claim 1, wherein the inorganic film deposited on the semiconductor silicon substrate is a silicon oxide film. 4. The stencil mask forming method according to claim 1, wherein the metal tungsten deposited on the semiconductor silicon substrate has a thickness of 3 μm or more.