JPS6313339B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a surface protective film on a semiconductor, and more particularly to a method for forming a surface protective film on a semiconductor using a chemical vapor deposition method and a high frequency sputtering method.

Traditional chemical vapor deposition
According to deposition (hereinafter abbreviated as CVD method),
It utilizes the thermal decomposition reaction of a reactive gas. For example, silicon oxide film is formed by thermal decomposition of SiH ₄ (monosilane) gas and O ₂ (oxygen) gas at 400°C to 600°C, and silicon oxide film is formed by thermal decomposition of SiH ₄ (monosilane) gas and O 2 (oxygen) gas at 600°C to 800°C.
It is formed by the thermal decomposition of gas and NH ₃ (ammonia) gas. When forming a protective film at such a high temperature, if the material to be deposited is a heat-sensitive material, such as a - group compound semiconductor, thermal deterioration of the semiconductor surface, that is, thermal decomposition damage to the semiconductor surface layer cannot be avoided. For example, gallium arsenide or indium phosphide, which are representative - group compound semiconductors, have a
From ℃ to 400℃, the constituent elements arsenic or phosphorus evaporate significantly.

Therefore, it is desirable to form a protective film at a low temperature that does not cause thermal deterioration of the semiconductor surface, and for this purpose, protective film formation is usually performed by a plasma CVD method using high-frequency discharge or a high-frequency sputtering method. The plasma CVD method uses high-frequency discharge to accelerate the decomposition reaction of reactive gases.
The high-frequency sputtering method is a method of depositing a reaction product on an object to be evaporated, and the high-frequency sputtering method is a method in which ions generated by electric discharge collide with a target, and the ejected target particles are deposited on the object to be evaporated.

According to the above two methods, it is possible to form a protective film on the semiconductor at low temperature, but the residual gas in the vacuum, the reaction gas, or the hydrogen contained in the target can easily destroy the protective film. It gets taken inside. For example, when forming a silicon nitride film using plasma CVD, hydrogen is mixed into the silicon nitride film due to undecomposed reaction gases SiH ₄ and NH ₃ . In addition, when forming a silicon oxide film using the high frequency sputtering method, silanol groups (Si-OH groups) contained in the SiO ₂ target are
is mixed into the formed film in large quantities. Therefore, compared to high-temperature CVD methods, films containing hydrogen (1) are hygroscopic, (2) are difficult to obtain dense films, and (3) have weak chemical resistance, such as NH ₄ : A silicon nitride film formed by plasma CVD has a disadvantage that the etching rate is 100 to 1000 times faster than that of a solution of HF=6:1. Therefore, when a pattern is drawn by opening a part of the insulating film using the conventional exposure technique using a photosensitive agent, a clear pattern cannot be formed due to so-called side etching.

In order to eliminate the above drawbacks, after forming a protective film at a low temperature, heat treatment is performed at a high temperature of 500°C to 900°C in an inert gas atmosphere such as Ar (argon) or _N2 to remove hydrogen from the film. This has traditionally been done. However, high-temperature heat treatment cannot (1) prevent thermal deterioration of the exposed portion of the semiconductor surface where the protective film is not formed; (2)
Since the temperature of the semiconductor also rises, the difference in the coefficient of thermal expansion between the protective film and the semiconductor, that is, the coefficient of thermal expansion of the semiconductor is generally larger, may cause the protective film and the semiconductor to bend or crack. It has disadvantages such as peeling.

An object of the present invention is to provide a method for forming a surface protective film for a semiconductor, which aims to eliminate the above-mentioned drawbacks.

The present invention is a process of forming an insulating film on a semiconductor surface at a low temperature by a plasma CVD method or a high-frequency sputtering method, and then irradiating at least a portion of the surface of the insulating film with charged particles or laser light to heat the irradiated portion. This is a method in which the area other than the irradiated area is removed by etching to form a patterned surface protective film only on the irradiated area.

According to the present invention, the surface of the insulating film formed on the semiconductor surface is selectively irradiated with charged particles or laser light, so that the heat generated by charged particle irradiation or laser light irradiation is mainly absorbed in the insulating film. Absorbed. Therefore, since mainly the insulating film portion is heated, (1) thermal deterioration of the exposed portion of the semiconductor surface can be prevented, and (2) the effect of temperature increase on the semiconductor due to electron beam irradiation heating is lower than that of conventional methods. The heat treatment is smaller than that in the case of heat treatment in an inert gas atmosphere, so there is no curvature or cracking of the formed film and semiconductor due to differences in thermal expansion coefficients, or peeling of the formed film. (3) Incorporation into the insulating film (4) Through selective densification, exposure technology using conventional photosensitizers can be eliminated by increasing temperature and forming a dense protective film that does not absorb moisture. without using
It has the advantage that a patterned insulator film can be formed directly.

EXAMPLES Hereinafter, with reference to the drawings, experimental results that are the premise of the present invention and examples of the present invention will be shown in order, but it will be easily understood that the present invention is not limited to these.

As a first experiment which is a premise of the present invention, a silicon nitride film was formed on the surface of a gallium arsenide compound semiconductor. The silicon nitride film was formed by the plasma CVD method, and the rate of reaction gas was 5 c.c./min.
Flow rate of SiH ₄ and 10 c.c. per minute. Flow rate of NH ₃ and 70 c.c. per minute.
Flow N ₂ , set the substrate temperature to 300℃, and set the pressure to 1.0Torr.
The discharge power was set to 100W. The silicon nitride film formed had a thickness of 1470 Å and a refractive index of 1.83.
FIG. 1a shows a cross-sectional view of a silicon nitride film 11 formed on a gallium arsenide semiconductor 12 under the above conditions, and the coefficient of thermal expansion of the silicon nitride film 11 is higher than that of the gallium arsenide semiconductor 12. Because of its small size, when the silicon nitride film 11 is returned to room temperature from the film forming temperature of 300° C., it receives compressive stress and bends slightly as shown in the figure. The sample shown in Figure 1a was prepared at a temperature of 600°C in an _N2 atmosphere according to the conventional method.
When heat treated for 30 minutes, the silicon nitride film 11 tends to become denser due to the release of hydrogen contained in the silicon nitride film 11 and shrinks, and the gallium arsenide semiconductor 12 thermally expands. Cracks and peeling of the silicon nitride film 11 occurred. According to the invention, the sample of FIG.
When the entire surface of the silicon nitride film 11 was irradiated with an electron beam with a radiation current of 3×10 ^-7 amperes accelerated to 5KV in a vacuum of 10 ^-9 Torr for 3 minutes, cracks and cracks were observed as shown in Figure 1b. Not only does the silicon nitride film 11 not peel off, but the peeling of the silicon nitride film 11 is approximately 3.
The compressive stress of ×10 ¹⁰ dynes/cm ² was reduced to approximately 0.6 × 10 ⁹ dynes/cm ² and the curvature became less noticeable. This is because the silicon nitride film 11 is mainly heated by the electron beam irradiation, hydrogen contained in the silicon nitride film 11 is released, and the silicon nitride film 11 is later densified. This is the result of contraction and stress relaxation. Infrared absorption spectroscopy shows that the hydrogen contained in the silicon nitride film 11 was released by the electron beam irradiation, and the Si-H group was approximately 1/20
This was confirmed by a decrease in In addition, the thickness of the silicon nitride film after electron beam irradiation decreased to 1430 Å,
The refractive index increased to 1.98, and the etching rate for a solution of NH ₄ F:HF = 6:1, which was about 3500 Å per minute before electron beam irradiation, increased to about 150 Å per minute, and the etching rate for the silicon nitride film increased from about 3500 Å per minute before electron beam irradiation. 11 has become more dense.

As a second experiment which is the premise of the present invention, a silicon oxide film was formed on the surface of an indium phosphide semiconductor by high frequency sputtering. The silicon oxide film was formed in an Ar atmosphere of 0.1 Torr, at a substrate temperature of 250°C.
The discharge power was 200W. The silicon oxide film formed had a thickness of 1260 Å and a refractive index of 1.46. The state in which the silicon oxide film is formed on the indium phosphide is exactly the same as in the case of Fig. 1a, and is indicated by 1 in the figure.
Consider replacing 1 with a silicon oxide film and 12 with indium phosphide. According to the present invention, when the entire surface of the silicon oxide film was irradiated with an electron beam under the same conditions as in the first embodiment, similar to the first embodiment, as shown in FIG. Curvature has been reduced. Infrared absorption spectroscopy revealed that the silanol group (Si-
(OH group) was reduced to approximately 1/10 by electron beam irradiation. In addition, the etching rate for a solution of NH ₄ F:HF = 6:1 is approximately
While it was 3000 Å, it decreased to about 900 Å per minute after electron beam irradiation, indicating that the silicon oxide film 11 had become dense.

As an example of the present invention, an example will be shown in which the protective film forming method according to the present invention is applied to a diffusion mask. FIG. 2 shows a conventional process for manufacturing a diffusion mask. First, a protective film 22 such as a silicon nitride film or a silicon oxide film is formed on the entire surface of the semiconductor 21 using a conventional method (FIG. 2a).
A photosensitive agent 23 is applied on top of the photosensitive material 2 (FIG. 2b). Then, the protective film where the light is diffused is removed by ultraviolet exposure technology, and a diffusion mask made of the protective film is formed (FIG. 2c). FIG. 3 shows an example of a diffusion mask manufactured using the protective film forming method according to the present invention. First, plasma is placed on the semiconductor 31.
After forming the silicon nitride film 32 by the CVD method (FIG. 3a), the silicon nitride film 32' other than the portion to be diffused was irradiated with an electron beam (FIG. 3b). As described in the first embodiment, the silicon nitride film 32' in the electron beam irradiation area is denser than the silicon nitride film 32'' that has not been irradiated with the electron beam.After electron beam irradiation, _NH4F ：HF＝
When the silicon nitride film was etched with a 6:1 solution, the silicon nitride film 32'' that had not been irradiated with the electron beam was selectively etched more than 10 times faster than the silicon nitride film 32' in the electron beam irradiated area. A diffusion mask was formed as shown in _FIG . The silicon nitride film 32'' other than the above portion is preferentially removed. This has the advantage that the diffusion mask can be formed by directly writing the protective film with an electron beam without introducing conventional ultraviolet exposure technology.

As described above, in the method for forming a protective film for a semiconductor according to the present invention, when a protective film is formed at a low temperature using plasma CVD or high frequency sputtering, hydrogen contained in the protective film is transferred to charged particles. Alternatively, it can be separated by laser beam irradiation, and problems such as bending and cracking of the protective film and semiconductor, peeling of the protective film, etc. can be removed, and the protective film can be made denser. This method has various advantages in that the etching rate can be selectively determined between the beam irradiated portion and the non-irradiated portion.

[Brief explanation of the drawing]

FIG. 1 shows a cross section of a protective film formed on a semiconductor, with (a) showing the state before electron beam irradiation, and (b) showing the state after electron beam irradiation. In FIG. 1, 11 is a protective film and 12 is a semiconductor. FIG. 2 shows a method of manufacturing a diffusion mask using a conventional method, in which 21 is a semiconductor, 22 is a protective film,
23 is a photosensitizer. FIG. 3 shows a method of manufacturing a diffusion mask according to the present invention, in which 31 is a semiconductor, 32 is a protective film, 32' is an electron beam irradiation part,
32'' is a protective film on a portion not irradiated with an electron beam.

Claims (1)

[Claims] 1 After forming an insulating film on a semiconductor surface by a plasma CVD method or a high-frequency sputtering method, at least a portion of the surface of the insulating film is selectively irradiated with a focused charged particle beam or a laser beam. A semiconductor surface characterized in that an insulating film is selectively formed on the semiconductor surface only in the irradiated part by heating the part and preferentially removing the insulating film other than the irradiated part by etching. How to form a protective film.