JPH04123424A - Film formation of silicon-based thin film - Google Patents

Abstract

PURPOSE:To uniformize film quality over the whole film thickness and to prevent defects such as pin holes and weak spots by starting RF discharge after only the dilute gas of the material gas and the dilute gas is introduced into a chamber to adjust the substrate temperature and the in-chamber pressure and by introducing the material gas into the chamber. CONSTITUTION:Only the dilute gas is introduced into the chamber to adjust the substrate temperature and the in-chamber pressure; then, RF discharge is started, and the material gas is introduced into the chamber. Before RF discharge is started, substance deposited on a substrate by thermolysis does not exist in the chamber; therefore, there is no conventional possibility that the thermolysis substance of the material gas is deposited on the substrate before RF discharge is started. Introducing the material gas into the chamber after RF discharge is started allows a silicon-based thin film formed by plasma CVD to grow uniformly without defects such as pin holes and weak spots over the whole area from the beginning of film formation.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is applicable to StN (silicon nitride) film, 510 (silicon oxide) film, a-Si:H (hydrogenated amorphous silicon) film, n''-a - Silicon-based thin films such as Si (amorphous silicon with added impurities) are heated using plasma C
The present invention relates to a method for forming a silicon-based thin film using a VD method.

[Conventional technology]

For example, a thin film transistor includes a gate electrode, a gate insulating film, an n-type semiconductor film, and an n-type semiconductor film on a substrate made of glass or the like.
It is manufactured by laminating a type semiconductor film and source and drain electrodes, and generally the gate insulating film is made of SiN.
film or Si film is used, and the n-type semiconductor film is a-
A 3l:H film is used, and an n”-a-S film is used as an n-type semiconductor film.
i membrane is used.

These SiN films, Si films, a-8t:H films, n''-a
Most silicon-based thin films such as -8t films are formed on substrates by plasma CVD. In this plasma CVD method, source gas and diluent gas are introduced into a chamber, the substrate is heated to a predetermined film forming temperature, and the pressure inside the chamber (gas pressure) is maintained at a predetermined pressure.The source gas is then heated by RF discharge. This is a method of depositing a silicon-based thin film on a substrate by using diluent gas in a plasma state.
The film is formed using SiH4 (silane) as the main raw material gas, NH3 (ammonia) as the auxiliary raw material gas, and N2 (nitrogen) as the diluent gas.
The film was formed using 20 (laughing gas) as an auxiliary raw material gas and N2 (nitrogen) as a diluent gas. In addition, the a-St:H film is formed using SiH4 as a raw material gas and N2 (hydrogen) as a diluent gas, and the n''-a-8t film is formed using SiH4 as a main raw material gas and PH3 (phosphine) as an auxiliary raw material gas. The film was formed using N2 (hydrogen) as a diluent gas.

The formation of a silicon-based thin film by this plasma CVD method is as follows:
Conventionally, this is done as follows.

FIG. 6 is a timing diagram of gas introduction and RF discharge when forming a SiN film. To form this SiN film, first, SiH, which is the main raw material gas, and an auxiliary raw material gas are placed in the chamber. All gases, NH, gas, and N2 gas, which is a diluent gas, are introduced at the same time, and then the temperature of the substrate and the pressure in the chamber (gas pressure) are adjusted to the predetermined film forming temperature and pressure. In this method, RF discharge is started after the substrate temperature and chamber pressure have stabilized. Note that the time required for adjusting and stabilizing the substrate temperature and chamber pressure varies depending on the film forming apparatus and the size of the substrate, and may take about 15 minutes. It has started at that point.

In addition, the gas introduction into the chamber and the RF discharge are continued during the film formation time determined according to the thickness of the SiN film to be formed, and when the film formation time has elapsed, the RF discharge is first stopped. After a few seconds, the introduction of all gases was stopped.

Note that although the formation of the SiN film has been described here, the formation of the SiN film is
Conventionally, when forming other silicon-based thin films such as iO film, a-5i:H film, and n''-a-81 film, all gases are introduced into the chamber at the same time, and the substrate temperature and the inside of the chamber are controlled. This is done by starting RF discharge after the pressure has stabilized.

[Problem to be solved by the invention]

However, the quality of the silicon-based thin film formed by the above-mentioned conventional film-forming method is not uniform over the entire film thickness, and the film quality of the lower layer portion is different from that of the other portion. Note that the thickness of this lower layer with different film quality is extremely small, and if the silicon-based thin film is formed relatively thick, it will not have much effect on the properties of the silicon-based thin film, but if the silicon-based thin film is formed thin. When it is formed into a film, it has a great influence on the properties of the silicon-based thin film.

Moreover, the silicon-based thin film formed by the conventional film-forming method has defects such as pinholes and weak spots scattered therein, and therefore the characteristics of the silicon-based thin film are unstable. It should be noted that defects such as pinholes and weak spots described above cause a decrease in dielectric breakdown voltage in SiN films and SiO films, deteriorate semiconductor characteristics in a-Si:H films, and deteriorate n''-a- The conductive properties of the 8i film deteriorated.

The present invention was made in view of the above-mentioned circumstances, and its purpose is to provide stable silicon with uniform film quality throughout the film thickness and free from defects such as pinholes and weak spots. An object of the present invention is to provide a method for forming a silicon-based thin film, which can obtain a silicon-based thin film.

[Means to solve the problem]

In a method for forming a silicon-based thin film on a substrate by plasma CVD, the present invention first introduces only the dilution gas into a chamber out of the source gas and the dilution gas, adjusts the substrate temperature and the chamber pressure, and then Start the RF discharge,
This method is characterized in that the source gas is then introduced into the chamber.

[For production]

That is, the present invention was made based on the clarification of the causes of nonuniform film quality and defects such as pinholes and weak spots that occur in silicon-based thin films formed by conventional film forming methods. It is something.

The factors that cause the film quality of silicon-based thin films formed by conventional film-forming methods to become non-uniform and the causes of defects such as pinholes and weak spots are considered to be as follows.

In conventional film deposition methods, all gases are first introduced into the chamber at the same time, and RF discharge is started after the substrate temperature and chamber pressure have stabilized. During the time until the start, that is, the time during which the substrate temperature and chamber pressure are adjusted, the raw material gas, which is an active gas, undergoes thermal decomposition and adheres to the substrate. When the pyrolyzed substances of the raw material gas adhere to the substrate before the start of RF discharge, the plasma CVD deposited film that is formed by starting the RF discharge after this will be coated with the deposited layer of the pyrolyzed substances. deposit on top. Figure 6 shows the change in thickness of the deposited film over time when a silicon-based thin film is deposited using the conventional film deposition method. Substances (e.g. S
In forming an iN film, it is an adhesion layer of St (St, etc.) in the main source gas. For this reason, silicon-based thin films formed by conventional film-forming methods have a film quality of the lower layer that is produced by plasma CVD.
It is a thermal decomposition substance of raw material gas that is not caused by film formation, and therefore the film quality in the film thickness direction is non-uniform.

Moreover, in the conventional film-forming method, the thermal decomposition substances of the raw material gas deposited before the start of RF discharge are in a scattered state (a state similar to the adhering state of water droplets when water is sprayed on a flat plate surface).
As a result, the degree of growth of the plasma CVD deposited film that is subsequently deposited becomes non-uniform, and defects such as pinholes and weak spots occur in the deposited silicon-based thin film. The characteristics of this silicon-based thin film become unstable.

Therefore, in the present invention, first, only the dilution gas is introduced into the chamber to adjust the substrate temperature and the chamber internal pressure, and then, after starting RF discharge, the source gas is introduced into the chamber. When a silicon-based thin film is formed by the film forming method of the present invention, the thickness change of the deposited film over time is shown in FIG. According to the present invention, before the start of RF discharge, there is no substance in the chamber that thermally decomposes and adheres to the substrate, so unlike the conventional film forming method, before the start of RF discharge, the source gas is removed. Since thermal decomposition substances do not adhere to the substrate, and the raw material gas is introduced into the chamber after starting RF discharge, silicon-based thin films formed by plasma CVD can be deposited from the initial stage of film formation. It grows uniformly over the entire area without producing defects such as pinholes or weak spots.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

(First Example) First, an example in which the present invention is applied to the formation of a SiN film will be described. FIG. 1 is a timing chart of gas introduction and RF discharge when forming a SiN film, and the SiN film is formed as follows.

First, only N2 gas, which is a diluent gas, is introduced into the chamber, and then the temperature of the substrate and the pressure inside the chamber (gas pressure) are adjusted.
and are adjusted to a predetermined film-forming temperature and pressure. After the substrate temperature and chamber pressure have stabilized, first RF
After starting the discharge and stabilizing the discharge state, SiH4 gas, which is the main raw material gas, and NH gas, which is the auxiliary raw material gas, are introduced into the chamber. When the RF discharge is started in this way and all the gases (St H4, NHi, N2) necessary for forming the SiN film are introduced into the chamber,
At this point, the formation of the SiN film by the plasma CVD method is started.

The time required for adjusting and stabilizing the substrate temperature and chamber pressure varies depending on the film forming apparatus and the size of the substrate, but approximately 15 minutes is required, and the time required for RF discharge to reach a stable state is several minutes. Since it is sufficient to allow for 10 seconds, RF discharge can be started 15 minutes after the introduction of N2, and introduction of SiH gas and NH gas can be started within 1 minute after the start of RF discharge. . In addition, the above 5
The introduction of the in4 gas and the NH gas may be started at the same time, but in order to reduce the fluctuation in the chamber pressure due to the introduction of these raw material gases, the introduction of the 5IH4 gas and the NH gas may be started at different times as shown in the figure. It is desirable to introduce the gas, and in this way, it is possible to easily correct pressure fluctuations caused by the introduction of the gas. However, 5iHn gas and NH,
The time difference between the introduction of the gas and the gas is determined by the time required to control the pressure in the chamber at a constant level, and in this example, one minute or less is sufficient. In addition, when introducing 5IH4 gas and NH gas at different times in this way, it is best to introduce NH gas, which is an auxiliary raw material gas, first, and introduce 5fH4 gas, which is a main raw material gas, last. desirable.

In addition, the gas introduction into the chamber and the RF discharge are performed continuously during the film formation time determined according to the thickness of the SiN film to be formed, and when the film formation time has elapsed, the RF discharge is first stopped. After a few seconds, stop introducing all gases.

In this example, first, only N2 gas, which is a diluent gas, is introduced into the chamber to adjust the substrate temperature and chamber pressure, and then, after starting RF discharge, SiH4 gas, which is the main raw material gas, is introduced into the chamber. Since the auxiliary raw material gas, NH, is introduced into the chamber, the thickness of the deposited film changes over time as shown in FIG. 5.

Since the N2 gas introduced into the chamber before the start of RF discharge does not contain substances that thermally decompose and adhere to the substrate, it is necessary to Thermal decomposition substances do not adhere to the substrate, and therefore the quality of the deposited SiN film becomes uniform throughout the film thickness. In addition, since RF discharge is started with only N2 gas introduced into the chamber, S
There is also the effect that the N2 gas plasma cleans the surface (iN film deposition surface, film surface, plate surface or surface of an electrode formed on the substrate surface), and therefore the SiN film is deposited on a clean surface. The quality of the film is uniform even at the interface with the deposition surface.

In addition, since SiH4 gas and NH3 gas are introduced into the chamber after starting RF discharge, the SiN film formed by the plasma CVD method has problems such as pinholes and weak spots throughout the film from the initial stage of film formation. Since the SiN film grows uniformly without any defects, the dielectric breakdown voltage of the formed SiN film is also sufficient.

Moreover, in the conventional film-forming method, all the gases are introduced into the chamber before the start of RF discharge, so during the unstable discharge state immediately after the start of RF discharge, SiN is scattered on the substrate. However, in the above embodiment, after the RF discharge is started and the discharge state is stabilized, SiH4, which is the source gas, is deposited. Since gas, NH, and gas are introduced into the chamber, the SI
N is not deposited on the substrate in a scattered state, and therefore defects such as pinholes and weak spots can be more reliably prevented from occurring.

(Second Example) Next, an example in which the present invention is applied to the formation of a SiO film will be described. FIG. 2 is a timing diagram of gas introduction and RF discharge when forming an S10 film, and the S10 film is formed as follows.

First, only N2 gas, which is a diluent gas, is introduced into the chamber, and then the substrate temperature and chamber internal pressure are adjusted. After the substrate temperature and chamber pressure stabilize,
First, RF discharge is started, and after the discharge state is stabilized, 5IH4 gas, which is the main raw material gas, and N2, which is the auxiliary raw material gas, are
is introduced into the chamber, and Si is deposited by plasma CVD method.
Start forming the O film. In addition, also in this example,
Introduction of SiH4 gas and N20 gas may be started at the same time, but if SiH4 gas and N20 gas are introduced at different times as shown in the figure, pressure fluctuations due to gas introduction can be reduced and correction thereof can be made easier. can be done. In this case, it is desirable to introduce the N20 gas, which is the auxiliary raw material gas, first, and to introduce the SiH4 gas, which is the main raw material gas, last. Further, the RF discharge and gas introduction are stopped in the same manner as in the first embodiment described above after the film forming time has elapsed.

In this example as well, first, only N2 gas, which is a diluent gas, is introduced into the chamber to adjust the substrate temperature and chamber pressure, and then, after starting RF discharge, SiH4 gas, which is a raw material gas, and N2 gas are introduced into the chamber. Since gas is introduced into the chamber, the thickness of the deposited film changes over time as shown in FIG. It is possible to form a Si film that is uniform over the entire region and has sufficient dielectric breakdown voltage.

(Third Example) Next, an example in which the present invention is applied to the formation of an a-3t:H film will be described. FIG. 3 is a timing diagram of gas introduction and RF discharge when forming an a-5t:H film.
The 5t:H film is formed as follows.

First, only H2 gas, which is a diluent gas, is introduced into the chamber, and then the substrate temperature and chamber internal pressure are adjusted. After the substrate temperature and chamber pressure stabilize,
First, RF discharge is started, and after the discharge state becomes stable, SiH4 gas, which is a raw material gas, is introduced into the chamber, and the formation of an a-8t:H film by plasma CVD is started.

Note that stopping the RF discharge and stopping the gas introduction after the film-forming time has elapsed is the same as in the first embodiment.

In this example as well, first, only H2 gas, which is a diluent gas, is introduced into the chamber to adjust the substrate temperature and chamber pressure, and then, after starting RF discharge, SiH4 gas, which is a raw material gas, is introduced into the chamber. Since the deposited film is introduced within the interior, the thickness of the deposited film changes over time as shown in FIG.

Since the H2 gas introduced into the chamber before the start of RF discharge does not contain substances that thermally decompose and adhere to the substrate, H2 gas is introduced before the start of RF discharge. Since thermal decomposition substances do not adhere to the substrate during the process, and SiH4 gas is introduced into the chamber after starting RF discharge, the SiN film formed by the plasma CVD method is It grows uniformly over the entire area without producing defects such as pinholes or weak spots. Therefore, the a film formed by this film forming method is
The -5i:H film has uniform film quality over its entire thickness and stable semiconductor properties. In this embodiment, the same effects as in the first embodiment can be obtained, such as the effect of cleaning the film-forming surface using H2 gas plasma.

(Fourth Example) Next, an example in which the present invention is applied to the formation of an n"-a-5t film will be described. FIG. This is a timing diagram of gas introduction and RF discharge, and the formation of this n''-a-Si film is performed as follows.

First, only H2 gas, which is a diluent gas, is introduced into the chamber, and then the substrate temperature and chamber internal pressure are adjusted. After the substrate temperature and chamber pressure stabilize,
First, RF discharge is started, and after the discharge state is stabilized, 5tH4 gas, which is the main raw material gas, and PH, which is the auxiliary raw material gas,
Gas is introduced into the chamber and the formation of an n''-a-Si film by plasma CVD is started.Also in this example, the introduction of 5tH4 gas and PH3 gas may be started at the same time. By introducing the SiH4 gas and the PH3 gas at different times as shown in the figure, it is possible to reduce pressure fluctuations due to gas introduction and to easily correct them.

In this case, it is desirable to introduce the PH3 gas, which is the sub-source gas, first, and the SiH4 gas, which is the main source gas, last. Further, the RF discharge and gas introduction are stopped in the same manner as in the first embodiment described above after the film forming time has elapsed.

In this example as well, first, only H2 gas, which is a diluent gas, is introduced into the chamber to adjust the substrate temperature and chamber pressure, and then, after starting RF discharge, SiH4 gas, which is a raw material gas, and PH gas are introduced into the chamber. .

Because gas is introduced into the chamber, the thickness of the deposited film changes over time as shown in Figure 4.
Therefore, it is possible to form an n''''-a-8i film having uniform film quality over the entire film thickness and stable conductive properties.

Note that the present invention is applicable to SiN film, S10 film, a-3i:
It goes without saying that the present invention is applicable not only to H films and n''-a-Si films but also to the formation of other silicon-based thin films by plasma CVD.

〔Effect of the invention〕

According to the present invention, of the source gas and diluent gas, only the dilute gas is first introduced into the chamber, and after adjusting the substrate temperature and chamber pressure, RF discharge is started, and then the source gas is introduced into the chamber. Because of this introduction, it is possible to obtain a silicon-based thin film with stable properties, which is uniform over the entire film thickness, and is free from defects such as pinholes and weak spots.

[Brief explanation of the drawing]

Fig. 1 is a timing diagram of gas introduction and RF discharge showing an example in which the present invention is applied to the formation of a SiN film, and Fig. 2 is a timing diagram of gas introduction and RF discharge showing an example in which the present invention is applied to the formation of an SiO film. R
The timing diagram of F discharge, FIG. 3 shows the present invention in a-St:H
Fig. 4 is a timing diagram of gas introduction and RF discharge showing an example in which the present invention is applied to film formation. 5 is a timing chart showing the change in thickness of a deposited film over time when a silicon-based thin film is formed using the film-forming method of the present invention, and FIG. A diagram showing changes in the thickness of a deposited film over time when a thin film is deposited. Figure 7 is a timing diagram of gas introduction and RF discharge when depositing an S1N film, showing a conventional film deposition method. It is.

Claims (1)

[Claims] In a method of forming a silicon-based thin film on a substrate using plasma CVD, only the diluent gas is first introduced into the chamber out of the source gas and diluent gas, and after adjusting the substrate temperature and chamber pressure, RF discharge is started. A method for forming a silicon-based thin film, characterized in that a source gas is introduced into a chamber.