JP2748781B2 - Method of forming silicon film - Google Patents

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 film on a substrate by a plasma CVD method using high-frequency discharge.

[0002]

FIG. 3 is a schematic view showing an example of a conventional plasma CVD apparatus. The electrode 6 and the holder / electrode 8 are accommodated in a vacuum vessel 4 evacuated by a vacuum evacuation device (not shown). The holder / electrode 8 is grounded, and the substrate 2 on which a film is to be formed is placed thereon. The substrate 2 is heated by, for example, a heater 10.

A high-frequency power is supplied between a pair of electrodes 6 and 8 from a high-frequency power supply 14 via a matching box 12. This high frequency power is conventionally a continuous sine wave,
Its frequency is usually 13.56 MHz.

In a vacuum vessel 4, a source gas 16 for film formation is provided.
Is introduced. The source gas 16 is conventionally a mixed gas of silane gas (SiH ₄ ) and hydrogen (H ₂ ) gas.

In such an apparatus, the above-described raw material gas 16 is introduced into the vacuum vessel 4 to make the inside of the vacuum vessel 4 about several hundred mTorr, for example, and a high-frequency power source 14 When power is supplied, a high-frequency discharge is generated between the electrodes 6 and 8 and the source gas 16 is turned into plasma (18 indicates the plasma), whereby a silicon film is formed on the surface of the substrate 2.

By the way, in such a plasma 18,
Radicals (active species) contributing to the formation of a high-quality silicon film and radicals unnecessary for film formation and causing particles are mixed, but in the above-described conventional method, unnecessary radicals are used. There is no means to suppress the occurrence of
There is a problem that generation of particles cannot be suppressed.

To solve this problem, the same applicant has developed a film forming method using high-frequency power with double modulation. The apparatus shown in FIG. 1 implements this film forming method. Here, instead of the conventional high-frequency power supply 14, a high-frequency signal generator 20 capable of generating an arbitrary signal waveform and a high-frequency signal from the high-frequency signal generator 20 are generated. A high frequency power supply 14a composed of a high frequency power amplifier 22 for power amplification is used. As a result, as shown in FIG. 2, the first modulation for intermittently changing the original high-frequency signal with a period T and the second modulation for intermittently changing the period with a period shorter than the first modulation are performed. (That is, double modulated) is supplied to the electrode 6 described above.

By using such high frequency power with double modulation, it becomes possible to control the electron temperature which greatly contributes to the generation and extinction of radicals in the plasma 18, thereby enabling the formation of a high quality film. Priority generation of contributing radicals and suppression of unnecessary radicals are possible,
Generation of particles can be suppressed.

The high-frequency signal that is the source of the high-frequency power is
For example, it is a 13.56 MHz sine wave signal as in the conventional example, but is not limited thereto.

The frequency (1 / T) of the first modulation of the high-frequency power is preferably selected from the range of 400 Hz to 1 KHz, since the lifetime of radicals is generally on the order of msec. In view of the electron temperature transition curve and the like, the interval of the second modulation is such that the ON period t ₁ is 0.5 μm.
The off period t _{2 is set} to 3 within the range of
It is preferable to select within the range of μsec to 100 μsec.

[0011]

According to the film forming method using the high frequency power subjected to the double modulation, it is possible to suppress the generation of particles, but the film forming speed of the silicon film is low (however, compared with the prior art, the film forming speed is low). It has been found that there is still room for improvement in this respect.

Therefore, the present invention further improves the film forming method using the high frequency power obtained by applying the double modulation as described above,
A main object of the present invention is to provide a film forming method that enables high-speed film formation while suppressing generation of particles.

[0013]

Means for Achieving the Object To achieve the above object, a method of forming a silicon film according to the present invention uses a mixed gas of a silane gas and an inert gas as a raw material gas, and uses the above-described electrode as a raw material. relative becomes a high-frequency signal, and the source
A first modulation for intermittently transmitting a high-frequency signal , and the first modulation
The During the ON period first the source at a period shorter than the modulation
A high-frequency power that is subjected to a second modulation for further intermittently transmitting a high-frequency signal is supplied.

[0014]

The low deposition rate of the silicon film in the conventional deposition method and the deposition method using the high frequency power with the above-mentioned double modulation was examined by various studies. A mixed gas is used, and S
It has been found that one of the causes is that the amorphous silicon layer formed on the substrate is etched by H ₂ radicals formed in the iH ₄ + H ₂ plasma.

On the other hand, when a mixed gas of silane gas and inert gas is used as a raw material gas as in the present invention,
Since the H ₂ radicals in the plasma are significantly reduced, the effect of etching the amorphous silicon layer due to the H ₂ radicals is suppressed, and the deposition rate is improved. That is, high-speed film formation becomes possible.

Also in the case of the present invention, since the high frequency power subjected to the double modulation as described above is used, it is possible to suppress the generation of particles and to form a dense and high quality film.

[0017]

EXAMPLE A silicon film was formed on a substrate 2 under the following conditions using the apparatus shown in FIG. 1 and high-frequency power subjected to double modulation as shown in FIG.

Source gas 16: SiH ₄ + He substrate 2: 100 mm square glass substrate Size of electrodes 6, 8: 300 mm square Distance between substrate and electrode 6: 50 mm Original high frequency frequency: 13.56 MHz First modulation Frequency: 1 KHz Second modulation interval: ON period t ₁ = 10 μsec OFF period t ₂ = 10 μsec Gas flow rate: SiH ₄ 30 ccm He 250 ccm Gas pressure in vacuum vessel at the time of film formation: 0.1 Torr Substrate temperature: 250 ° C. High frequency output: 200W

As a result, a silicon film is formed on the substrate 2 by about 50
A film could be formed at a film formation rate of nm / min. By the way, under the same conditions, the film formation rate of the above-described method using the double modulation method using the SiH ₄ + H ₂ gas is about 25 nm / m.
In this example, the film formation rate was twice as high in this example.

In the case of the above embodiment, the density of particles having a diameter of 0.3 μm or more on the surface of the substrate 2 is 30 particles / 100 mm square, and a double modulation method is used by using the above-mentioned SiH ₄ + H ₂ gas. The same degree of particle suppression effect as that of the method was obtained.

Further, in the case of the above embodiment, there is no mixing of He into the silicon film, and the optical band gap of the silicon film is as large as 1.8 to 1.9 eV (the ideal value is 1.9 eV). It was confirmed that the characteristics were also good.

In addition, in the case of the above-described embodiment, since the inert gas He is used instead of the explosive gas H ₂ , the effect of increasing the safety can be obtained.

As the inert gas mixed with the silane gas, an inert gas other than He such as Ne may be used. Even in such a case, the etching of the amorphous silicon layer by H ₂ radicals is performed similarly to the case of He. Since the effect can be suppressed, the deposition rate can be increased.

[0024]

As described above, according to the present invention, the use of a mixed gas of a silane gas and an inert gas as a source gas greatly reduces H ₂ radicals in the plasma. The etching effect is suppressed, and high-speed film formation becomes possible.

Moreover, by using the high-frequency power subjected to the double modulation as described above, it is possible to suppress radicals unnecessary for film formation and to suppress generation of particles.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a plasma CVD apparatus used in an embodiment.

FIG. 2 is a schematic diagram illustrating an example of a waveform of a high frequency power subjected to double modulation.

FIG. 3 is a schematic view showing an example of a conventional plasma CVD apparatus.

[Explanation of symbols]

 2 Substrate 6 Electrode 8 Holder / Electrode 14a High frequency power supply 16 Source gas 18 Plasma

Claims (2)

(57) [Claims] 1. A method for forming a silicon film on a substrate by a plasma CVD method in which plasma is generated by high-frequency discharge between electrodes, wherein a mixed gas of a silane gas and an inert gas is used as a source gas, and A first modulation for intermittently interposing the original high-frequency signal with respect to the original high-frequency signal is performed during an ON period of the first modulation.
The original high-frequency signal with a shorter period than the first modulation
And supplying a high-frequency power with a second modulation that further interrupts the process. 2. The method according to claim 1, wherein the frequency of the first modulation is 400 Hz or more.
2. The method for forming a silicon film according to claim 1, wherein the ON period of the second modulation is within a range of 0.5 to 100 [mu] sec, and the OFF period is within a range of 3 to 100 [mu] sec.