JPH05343335A - Formation of silicon nitride film - Google Patents

Abstract

PURPOSE:To form a good-quality silicon nitride thin-film on a silicon substrate surface by a low-pressure CVD method. CONSTITUTION:The atmosphere of a silicon substrate 2a for a period, during which the temperature rises from a low-temperature region to a high- temperature region necessary for deposit formation, is substituted by ammonia gas. Thus, a thermal nitride film 15 grows on the surface of the silicon substrate 2a. After that, ammonia gas and dichlorosilane gas are supplied as raw material gas so that a silicon nitride thin-film 13 is formed on the surface of the thermal nitride film 15. In this manner, a silicon oxide film is not formed in a temperature-rise process and a uniform and good-quality silicon nitride thin-film can be obtained.

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 silicon nitride thin film as a capacitor on the surface of a semiconductor substrate such as a silicon substrate by a low pressure CVD method.

[0002]

2. Description of the Related Art FIG. 3 is a partial cross-sectional view of a semiconductor manufacturing apparatus for forming a silicon nitride thin film on the surface of a semiconductor substrate by a low pressure CVD method. In the figure, 1 is a cylindrical reaction chamber, 2 is a silicon substrate as a semiconductor substrate to be processed, and is supported by a susceptor 3. Four
Is a gas supply unit for supplying gas such as silane gas, nitrogen gas, dichlorosilane gas, and ammonia gas while controlling the flow rate.
Is in communication with. A vacuum pump 6 communicates with the reaction chamber 1 through an exhaust pipe 7 and can exhaust gas and air in the reaction chamber 1. Reference numeral 8 is a heater for heating the reaction chamber 1, 9 is a manifold for supporting the reaction chamber 1, and a pipe 5 and an exhaust pipe 7 penetrate through and are supported by the housing 10. Reference numeral 11 is a lid on which the susceptor 3 is placed, and the elevator 1
It is configured to be able to move up and down by 2.

Next, a method of forming a silicon nitride film on the surface of a silicon substrate using this semiconductor manufacturing apparatus will be described. First, the silicon substrate 2 is washed with a hydrofluoric acid solution,
The silicon oxide film on the surface of the silicon substrate 2 is removed. After that, the silicon substrate 2 is washed with water, and then, for example, nitrogen gas is blown to dry the silicon substrate 2 to obtain a clean silicon substrate.

On the other hand, the inside of the reaction chamber 1 is kept at, for example, 300 ° C., and in this state, the lid 11 is lifted by the elevator 12.
And the silicon substrate is placed on the susceptor 3. Next, the elevator 12 is operated to raise the lid 11, the susceptor 3 is introduced into the reaction chamber 1, the lid 11 is closed, and then the vacuum pump 6 is used to discharge the air inside the reaction chamber 1.
Next, nitrogen gas is supplied from the gas supply unit 4 to replace the inside of the reaction chamber 1 with nitrogen gas, and then the inside of the reaction chamber 1 is maintained at a predetermined pressure, for example, 0.2 Torr. From this state, the current of the heater 8 is increased to raise the temperature inside the reaction chamber 1 to a predetermined temperature necessary for deposit formation, for example, 700 ° C. The reason why nitrogen gas is used here is that it is easy to handle and the risk is low.

When the temperature is raised to 700 ° C., the temperature is kept constant thereafter, and ammonia gas and dichlorosilane gas, which are raw material gases, are introduced into the reaction chamber 1 from the gas supply unit 4. When a silicon nitride thin film having a predetermined thickness is formed on the surface of the silicon substrate by these source gases, the inside of the reaction chamber 1 is replaced with nitrogen gas again. Then, the inside of the reaction chamber 1 is returned to atmospheric pressure with nitrogen gas, the lid 11 is lowered, and the silicon substrate is taken out.

[0006]

Since the conventional method of forming a silicon nitride thin film has been performed by the above-described method, the method shown in FIG.
As shown in FIG. 4, the silicon oxide film 14 is formed on the surface of the clean silicon substrate 2a (FIG. 4A) during the temperature rising process in the nitrogen gas atmosphere (FIG. 4B). This is because oxygen and water vapor remaining inside the reaction chamber 1 oxidize the surface of the silicon substrate 2a. Therefore, the intended silicon nitride thin film 13 is formed with the silicon oxide film 14 interposed between the silicon nitride thin film 13 and the silicon substrate 2a (FIG. 4C). As a result, the expected high-quality silicon nitride thin film cannot be obtained. For example, when this silicon nitride thin film is used as a capacitance insulating film of (D) RAM or the like, the silicon oxide film 14 having a small dielectric constant is interposed, and a desired capacitance cannot be obtained.

The present invention has been made to solve the above problems, and an object thereof is to form a high-quality silicon nitride thin film by a low pressure CVD method.

[0008]

According to the method of forming a silicon nitride film of the present invention, the semiconductor surface is placed in an atmosphere containing ammonia gas which is a raw material gas for deposition formation, and the deposition is performed from a low temperature region. The temperature is raised to a high temperature range necessary for formation.

[0009]

In the forming method according to the present invention, since the temperature raising process is performed in the ammonia gas atmosphere, the silicon oxide film is not formed on the surface of the silicon substrate, and the thermal nitride film is formed by the ammonia gas.

[0010]

EXAMPLES Example 1. Hereinafter, a method for forming a silicon nitride thin film according to a first embodiment of the present invention will be described with reference to FIGS. First, as in the conventional case, the silicon substrate 2 is washed with a hydrofluoric acid solution to remove the silicon oxide film on the surface of the silicon substrate 2. Then, the silicon substrate 2 is washed with water, and then, for example, nitrogen gas is sprayed to dry the silicon substrate 2 to obtain a clean silicon substrate 2a (FIG. 1A). Next, this silicon substrate 2a is placed on the susceptor 3 and introduced into the reaction chamber 1 kept at 300 ° C. (FIG. 2T1), and after closing the lid 11, the air inside the reaction chamber 1 is exhausted using the vacuum pump 6. (Fig. 2T2).

Next, the gas supply unit 4 supplies ammonia gas, which is a raw material gas in the subsequent step, to replace the inside of the reaction chamber 1 with the ammonia gas, and then the inside of the reaction chamber 1 is brought to a predetermined pressure, for example, 0.2 Torr. keep. From this state, the temperature inside the reaction chamber 1 is raised to a predetermined temperature required for deposit formation, for example, 700 ° C. During this time, the ammonia gas in the reaction chamber 1 causes the thermal nitride film 15 to grow on the surface of the silicon substrate 2a as shown in FIG. 1B (FIG. 2T3).

When the temperature inside the reaction chamber 1 becomes uniform, ammonia gas and dichlorosilane gas, which are raw material gases, are introduced from the gas supply unit 4. With these source gases,
As shown in FIG. 1C, the silicon nitride thin film 13 grows on the surface of the thermal nitride film 15 formed by the above ammonia gas (FIG. 2T4). Then, the inside of the reaction chamber 1 is returned to atmospheric pressure with nitrogen gas (FIG. 2T5), and the lid 11 is lowered to take out the silicon substrate 2 (FIG. 2T6).

As described above, in this embodiment, since a homogeneous silicon nitride thin film is formed without interposing the silicon oxide film 14, when used as a capacitance insulating film of (D) RAM or the like, a desired capacitance is obtained. A good quality insulating film having a value can be obtained.

Example 2. In the above embodiment, the raw material gases are ammonia gas (NH ₃ ) and dichlorosilane gas (Si
The case where H ₂ Cl ₂ ) is used has been described, but the present invention can be similarly applied to the case where ammonia gas and silane gas (SiH ₄ ) are used, and the same effect can be obtained. Further, although the case where only the ammonia gas is used as the atmosphere of the temperature raising process has been described, a mixed gas atmosphere in which this ammonia gas is mixed with an inert gas such as nitrogen or argon may be used. Further, in the above-mentioned embodiment, the case where the temperature is set to 300 ° C. as the low temperature region before the temperature is raised, but different temperatures may be set in the range of 350 ° C. or less. Further, the temperature in the high temperature region during deposition is not limited to 700 ° C. Further, the object on which the silicon nitride thin film is formed is not limited to the surface of the silicon substrate, and may be the surface of the polycrystalline film undoped or doped.

[0015]

As described above, according to the present invention, since the atmosphere containing the ammonia gas as the raw material gas is used during the temperature rising from the low temperature region to the high temperature region required for the deposition formation, the silicon oxide film does not intervene. A good quality silicon nitride film can be formed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a silicon substrate for explaining a method for forming a silicon nitride thin film according to a first embodiment of the present invention.

FIG. 2 is a diagram showing each step of the forming method of FIG. 1 together with the temperature inside the furnace.

FIG. 3 is a partial cross-sectional view showing the configuration of a semiconductor manufacturing apparatus for forming a thin film by a low pressure CVD method.

FIG. 4 is a cross-sectional view of a silicon substrate for explaining a conventional forming method.

[Explanation of symbols]

 2, 2a Silicon substrate 13 Silicon nitride thin film 15 Thermal nitride film

Claims (1)

[Claims] 1. A method for depositing and forming a silicon nitride film on a semiconductor surface by a low pressure CVD method, wherein the semiconductor surface is placed in an atmosphere containing an ammonia gas which is a raw material gas for forming the deposit and is in a low temperature range. To a high temperature region necessary for the above-mentioned deposition formation, the method for forming a silicon nitride film.