JPH07235532A - Formation of protective film for semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a surface protective film, which can be formed on a semiconductor substrate by a spin coating method and is superior in film quantity, by a method wherein a liquid obtainable by dissolving a polysilane polymer is applied to a semiconductor device, is baked at a specified temperature and the protective film containing silicon carbide as its main component is formed. CONSTITUTION:Processing, such as heating, polymerization, extraction, evaporation and dissolution, of polysilane is performed to prepare a solution obtainable by dissolving polysilane polymer of even molecular weights, this solution is applied to a semiconductor device and thereafter, is baked at a temperature of 400 deg.C or higher and 500 deg.C or lower in an oxygen-containing atmosphere and a silicon carbide-containing protective film is formed. By changing the mixture ratio of oxygen to nitrogen at the time of the firing, the compositional ratio of a silicon carbide film, a silicon nitride film and a silicon oxide film is controlled and the optimum protective film can be obtained. Thereby, as this spin coating method is superior in mass productivity compared to a conventional CVD method and the simplification of a process is contrived, reduction in the coast of the protective film can be contrived.

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 protective film for protecting a semiconductor device from contamination and the like, and more particularly to a method for forming a protective film for a semiconductor device containing silicon carbide.

[0002]

2. Description of the Related Art Conventionally, in order to protect a semiconductor device from contamination such as moisture and alkali metal ions in the atmosphere or stress applied from the outside, after forming an electrode film or a wiring film of a metal such as an aluminum film on a semiconductor substrate, As a final protective film formed on the surface, plasma CVD or low pressure CVD
Generally, a silicon oxide film, a silicon nitride film, or a laminated structure thereof is formed by a CVD method such as. Since the quality of such a final protective film has a great influence on the long-term reliability of the semiconductor device, the following points should be noted.

1. To secure film quality (denseness, stability, mechanical strength, etc.). 2. Good wiring step coverage. 3. It can be formed at a low temperature (generally, the wiring material is a low-melting metal represented by aluminum or the like, so that the formation at a low temperature of about 400 ° C. or lower is required). With respect to the conventional CVD method as mentioned above, the conditions that substantially satisfy the above-mentioned items 1 to 3 are established at present.

However, the conventional CVD method has the following disadvantages in terms of production technology. That is, 4, since ignitable gases such as silane and toxic gases such as phosphine and diborane are used, safety measures are indispensable. 5. The yield is likely to decrease due to the generation of particles.

6. It takes time to form a film and productivity is low. There is a problem that the CVD method itself has. In particular, regarding item 6, there is a large problem in filling the trench as shown in FIG. In some cases, the problem of insufficient step coverage in the above item 2 may be caused again. The trench filling process will be described with reference to FIG. A so-called SO in which a silicon layer 4 is laminated on a silicon substrate 2 via an oxide film 3
Using the I substrate 1, a trench 5 is formed in the silicon layer 4 of the I substrate 1 by using a normal photoetching technique [FIG.
(A)]. Subsequently, an oxide film 6 is deposited on the inner surface and the upper surface of the trench [(b) of the same figure]. Next, polycrystalline silicon 7 is filled in the trench by low pressure CVD. At this time, polycrystalline silicon 7 is also deposited on the oxide film 6 [FIG. The polycrystalline silicon 7 on the oxide film 6 is etched by plasma etching [(d) in the figure]. The trenches for element isolation are filled in the above steps. After that, although not shown in the figure, the oxide film 6 on the silicon layer 4 is partially removed to form an element on the exposed surface layer of the silicon layer 4. In the prior art, it is general to fill the polycrystalline silicon by the CVD method according to the process shown in FIG. 3, but it takes a considerable amount of deposition time to fill the trench evenly, which is a problem. It becomes more serious when the groove width is wide and deep.

As a method for solving the above-mentioned problems 4 to 6, there is a method of forming a surface protective film on a semiconductor substrate by a spin coating method represented by a photoresist. Conventionally,
Polyimide and spin-on glass are known as examples of the surface protective film formed by such a coating method. Spin-on glass is a method in which water glass is spin-coated and baked to form a silicon oxide film.

[0007]

However, these polyimide and spin-on-glass films formed by the coating method are difficult in terms of the film quality of the above item 1 contrary to silicon nitride and silicon oxide formed by the CVD method, There is a history of the past that the CVD method as described in the technology has been changed to the mainstream method. For example, polyimide has problems in adhesiveness and film hardness, and is prone to problems such as peeling. Further, the spin-on glass has insufficient moisture resistance and ion permeability resistance. Many of the drawbacks of these conventional coating methods are:
It is in the material used.

That is, an object of the present invention is to find a method for forming a surface protective film having excellent film quality, which can be applied to a semiconductor substrate by a spin coating method, thereby forming a protective film for a semiconductor device having excellent reliability characteristics. To provide.

[0009]

In order to solve the above problems, the inventor of the present application sought to find a new material. Although there is no example of using a silicon carbide film as a protective film for a semiconductor device,
It has a high hardness, a large thermal conductivity coefficient, and a thermal expansion coefficient close to that of silicon and has physical properties suitable as a protective film. Therefore, a film containing silicon carbide as a main component was selected as a protective film for the semiconductor device. Silicon carbide also has an advantage that a liquid organic silicon compound containing carbon atoms as a raw material can be obtained relatively easily.

As a method of forming the protective film, a liquid in which a polysilane polymer is dissolved is applied onto the semiconductor device and baked. A polysilane polymer having a methyl group, for example, polydimethylsilylene is suitable. Firing is performed in an atmosphere containing oxygen (hereinafter referred to as O ₂ ). In particular, firing is preferably performed in a mixed gas atmosphere of O ₂ and nitrogen (hereinafter referred to as N ₂ ).

[0011]

[Function] When a liquid having a polysilane polymer dissolved therein, such as polydimethylsilylene, is applied to a semiconductor device and baked, carbon atoms and silicon atoms in the compound react with each other to form a silicon carbide film on the surface of the semiconductor device. A saliva film is formed. In particular, by adding O ₂ to the firing atmosphere, the methyl group of the polysilane polymer is oxidized and the polymerization reaction is further promoted, and the firing temperature is increased to a temperature higher than 1000 ° C., which is conventionally required to obtain silicon carbide. The temperature can be reduced, and it can be formed at a practical protective film forming temperature of about 400 ° C.

The composition of the film containing silicon carbide can be changed by changing the mixing ratio of O ₂ and N ₂ in the mixed gas atmosphere of O ₂ and N ₂ at the time of baking and adjusting the baking temperature. A protective film having an appropriate film quality can be obtained.

[0013]

EXAMPLES Examples will be described below. First, we start with the synthesis of cyclic polysilane. Dimethyldichlorosilane is tetrahydrofuran (TH
F) In a solvent, it becomes dodecamethylcyclohexasilane according to the following chemical reaction formula (1).

[0014]

[Chemical 1]

The obtained dodecamethylcyclohexasilane was placed in a high pressure vessel filled with argon (hereinafter referred to as Ar) gas.
When heated to 400 ° C. for 8 hours, a ring-opening reaction represented by the following chemical reaction formula (2) and a subsequent polymerization reaction are caused to generate polysilane polymers [a] and [b].

[0016]

[Chemical 2]

When the produced polysilane polymer [a] is dissolved in diethyl ether, the low molecular weight polymer component (n) of [a] (n)
Component is extremely small) evaporates with diethyl ether, leaving only the polymer component. When this residue is dissolved in a mixed solution of normal hexane and acetone, the high molecular polymer component is dissolved in normal hexane and the low molecular weight polymer component is dissolved and separated in acetone. Thus, a high molecular weight polymer component [B] having a uniform distribution can be obtained.

The synthesized high molecular polymer component [b] was the above polysilane polymer [a] in which n = 25 was most of the high molecular polymer component dissolved in normal hexane. The synthetic method reported by Yajima et al. Was adopted as the method for preparing the above-mentioned polymer component (Yajima et al .: Chem. Lett., (1975) 931). Polymer component dissolved in this normal hexane [B]
Was dropped on a semiconductor device and spin-coated at 500 rpm to form a high molecular weight polymer component [b] layer having a uniform thickness on the semiconductor device. Then, this wafer is heated to 100 ° C.
It was baked in a clean oven for about 1 hour and dried.
In this process, normal hexane, which is a solvent, evaporates to form a polymer layer.

[0019] Thereafter, the semiconductor device 400 ° C., O ₂
By firing for 3 hours in an electric furnace in a mixed atmosphere of 10% N ₂ and O ₂ , an amorphous thin film (film thickness of about 1 μm) made of silicon carbide and silicon nitride was obtained. When the obtained membrane was tested for moisture resistance and ion permeation resistance, it showed extremely excellent moisture resistance and ion permeation resistance.

Conventionally, synthesis of silicon carbide has been attempted in vacuum or in an inert gas atmosphere, but at low temperature (400 ° C. or lower).
In this case, since it becomes powdery, it needs to be baked at 400 ° C or higher, and higher temperature (1000 ° C or higher) is necessary to make an amorphous or polycrystalline thin film. The temperature of the film was too high to be applied. That is, the upper limit of the baking temperature for forming the protective film on the semiconductor substrate is determined from the viewpoint of melting and preventing oxidation of the aluminum wiring film provided on the semiconductor substrate. That is, it was found that it is absolutely necessary to be below the melting point of aluminum (660 ° C.), and from the viewpoint of preventing oxidation, it should be below 500 ° C. By firing in an oxidizing atmosphere, the methyl groups of the high molecular weight polymer can be oxidized and the polymerization reaction can be further promoted, enabling the formation of a surface protective film that meets the intended purpose. It was

FIG. 1 is a sectional view showing the results of a step coverage test conducted under the condition of O ₂ / (N ₂ + O ₂ ) of 0.3. The protective film 10 makes the angle of the silicon substrate 8 100.
It can be seen that the step 9 having a degree and a height of 3 μm is covered. FIG. 2 shows the results of analysis of the produced amorphous thin film when it was fired at various gas flow rate ratios [O ₂ / (N ₂ + O ₂ )] of N ₂ and O _2, and it was included in the thin film. The number of carbon atoms C, oxygen atoms O, and nitrogen atoms N is represented with silicon atom Si as one. O ₂ /
When (N ₂ + O ₂ ) was less than 0.1, it became powdery and the thin film aimed at by the present invention could not be obtained.
When it was 1 or more, a good thin film was obtained.

When O ₂ / (N ₂ + O ₂ ) is in the range of 0.1 to 0.2, a large amount of carbon shown by a solid line and a large amount of nitrogen shown by a dotted line are large. Therefore, a mixture mainly containing silicon carbide and silicon nitride is contained. It can be seen that a film was obtained. Membranes in this range showed particularly good resistance to ion permeation. Also O ₂ / (N ₂ +
When O ₂ ) is 0.6 or more, the thin solid line contains the most oxygen and the thick solid line contains carbon, and the dotted line nitrogen is very small, so a film containing silicon oxide and silicon carbide was obtained. I know that it was done. The film obtained in this range had good adhesion.

The intermediate O ₂ / (N ₂ + O ₂ ) is 0.3.
It can be seen that a mixed film of silicon carbide, silicon nitride, and silicon oxide was obtained because carbon, oxygen, and nitrogen were all contained in the range of 0.5 to 0.5 although the amount of nitrogen shown by the dotted line was slightly small. All the thin films formed under the condition that O ₂ / (N ₂ + O ₂ ) was 0.1 or more covered step 9 shown in FIG. 2 sufficiently.

Further, when the thin film made of silicon carbide, silicon nitride, or silicon oxide of the above-mentioned embodiment was used in place of polycrystalline silicon in the step of filling the trench shown in FIG. 3, a trench having a groove width of 10 μm and a depth of 30 μm was formed. It was also possible to embed by coating and baking. Further, according to the following chemical reaction formula (3), a polymer obtained by heating non-cyclic polydimethylsilylene in Ar at 450 ° C. is dissolved in a solvent and applied to a semiconductor substrate, followed by baking. However, a similar protective film containing silicon carbide was obtained.

[0025]

[Chemical 3]

[0026]

EFFECT OF THE INVENTION By dissolving a polysilane polymer in a solvent and applying it to a semiconductor substrate and baking it, the above-mentioned 1
A protective film containing silicon carbide that satisfies the items 1 to 6 can be obtained. According to the present invention, the above-mentioned drawbacks of the conventional CVD method are eliminated, the mass productivity is superior to the conventional CVD method, and the process can be simplified, so that the cost can be reduced. Further, as described in the examples, films having various compositions can be arbitrarily obtained only by changing the gas flow rate ratio O ₂ / (N ₂ + O ₂ ) at the time of firing, so that the optimum film can be selected according to the application. There is also an advantage.

[Brief description of drawings]

FIG. 1 is a sectional view showing a result of evaluation of step coverage of an example of a protective film according to a forming method of the present invention.

FIG. 2 is a diagram showing the relationship between the gas flow rate ratio O ₂ / (N ₂ + O ₂ ) during firing and the composition of a film formed during the execution of the forming method of the present invention.

FIG. 3 is a cross-sectional view showing a trench filling step for dielectric isolation using a conventional SOI substrate in the order of (a) to (d).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 SOI substrate 2 Substrate 3 Oxide film 4 Silicon layer 5 Trench 6 Oxide film 7 Polycrystalline silicon 8 Silicon substrate 9 Step 10 Protective film

Claims (6)

[Claims] 1. Protection of a semiconductor device, characterized in that a liquid containing a polysilane polymer is applied to the semiconductor device and is baked at a temperature of 400 ° C. to 500 ° C. to form a film containing silicon carbide as a main component. Method of forming a film. 2. The method for forming a protective film for a semiconductor device according to claim 1, wherein the polysilane polymer has a methyl group. 3. The method for forming a protective film for a semiconductor device according to claim 2, wherein the polysilane polymer is polydimethylsilylene. 4. The method for forming a protective film for a semiconductor device according to claim 1, wherein the firing is performed in an atmosphere containing oxygen. 5. The method for forming a protective film for a semiconductor device according to claim 4, wherein the baking is performed in a mixed gas atmosphere of nitrogen and oxygen. 6. The semiconductor device according to claim 5, wherein the firing is performed in an atmosphere of a mixed gas in which the flow rate ratio of oxygen gas in the mixed gas of nitrogen and oxygen is 0.1 or more. Method of forming protective film.