JPH0551754A - Formation of thin film by plasma cvd method - Google Patents

Abstract

PURPOSE:To form various high-quality thin films such as an insulating thin film, protective film and amorphous silicon thin film on a substrate at a high rate and low cost by using plasma CVD. CONSTITUTION:A substrate 5 to be treated is held by a holder 4 in a reaction furnace 1. A permanent magnet 9 is set on the rear side of each substrate 5. The substrate 5 is heated by a heater 6, the reaction furnace is closed, a gaseous reactant is uniformly supplied on the surface of the substrate 5, a high-frequency voltage is impressed between the holder 4 grounded through a high-frequency oscillator 7 and an electrode 3, hence the cycloidal movement of electrons is caused close to the substrate surface by the magnetic field of the magnet and a high-frequency electric field, a high-density and high-efficiency plasma discharge is generated only on the effective thin film forming region, and a high-quality thin film is formed on the substrate surface at a high rate. Besides, a film is not formed on the unwanted site, the device is repaired less frequently, the consumption of energy and gaseous reactants is reduced, and a thin film is formed with this simple device at a low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing various kinds of high quality thin films such as insulating thin films on a substrate by plasma CVD at high speed.

[0002]

2. Description of the Related Art As a method for forming a thin film, a vacuum deposition method,
P represented by ion plating and sputtering method
VD (Physical Vapor Deposition)
ion) method, CVD (Chemical Vapor Deposi) that thermally decomposes a reaction gas to form a thin film
ionization method, a plasma CVD method in which the reaction gas is decomposed by plasma discharge, and the like, and these methods are properly used according to the application of the thin film.

Of these, the plasma CVD method capable of forming a film at a low temperature includes SiN and SiO ₂ used for semiconductor devices.
Insulating thin film and protective film such as Amorphous S for solar cells
In recent years, it has been widely used as a method for forming an i thin film. For example, J. Electrochem. So
c. : ELECTROCHEMICAL SCIENC
E AND TECHNOLOGY Magazine Vol126, N
o6, John R. et al., pages 930-934. Halla
han and the like are SiO produced by the parallel plate plasma CVD method.
₂ Describes the formation of thin films.

This conventional plasma CVD method will be outlined below with reference to FIG. Grounded holder 4 in reactor 1
Then, the substrate 5 to be treated is held and heated to a predetermined temperature by the heater 6. Next, the reaction furnace 1 is closed and a reaction gas is supplied into the reaction furnace 1 from the gas supply system 2. As the reaction gas, for example, silane gas (SiH ₄ ) and nitric oxide gas (N ₂ O) are used at the time of forming a silicon oxide thin film, and these are passed through the flow rate control units 2a and 2b and the flow rate is adjusted and sent. .. Then, these gases mixed in the gas supply system are made to flow uniformly from the shower electrode 3 provided in the lower part of the reaction furnace 1 toward the surface of the base material. On the other hand, a high frequency oscillator 7 applies a high frequency voltage between the electrode 3 and the grounded holder 4. As a result, the supplied mixed gas is brought into a plasma state and a reaction of the gas occurs to form a silicon oxide thin film on the base material.

The film quality and the film forming rate of the silicon oxide thin film produced by this method depend on the temperature of the substrate to be heated, the reaction gas pressure, the flow rate of the reaction gas, the flow rate ratio, and the like.

[0006]

In the above-mentioned conventional plasma CVD method, when the film formation speed is increased, the following problems such as deterioration of film quality occur.

That is, as an effective method for increasing the film formation rate, a method of increasing the flow rate of the reaction gas and increasing the gas pressure is usually adopted. However, if the film formation rate is increased by such a method, the quality of the obtained thin film is not so good because, for example, in the case of an insulating film, there arises a problem that the withstand voltage is lowered. Also, when the gas flow rate and gas pressure are increased,
Many unreacted species of silane gas are formed, a large amount of dust is generated in the reaction furnace, and the resulting film tends to have many pinholes. Further, the large amount of dust generated causes the vacuum exhaust system (8 in FIG. 4) to be clogged and the maintenance frequency of the apparatus to be increased, resulting in a high film forming cost.

[0008]

In order to solve the above problems and enable high-quality thin films to be formed at high speed, the present invention uses a holder that is grounded in a reaction furnace for a substrate to be processed. After holding and heating and sealing the reaction furnace, the reaction gas is evenly distributed on the surface of the substrate to be treated, and a high-frequency electric field is applied between the holder gas and the electrodes in the furnace to form a plasma state. In the plasma CVD method for producing a thin film on the surface of the substrate to be treated, a permanent magnet is installed on the back side of the substrate to be treated, and the magnetic field of the magnet is generated on the surface portion of the substrate to be treated. A high frequency electric field is applied.

[0009]

In general, it is known that the deposition rate and film quality of a thin film in the plasma CVD method greatly depend on the excitation efficiency of the reaction gas. That is, when a plasma discharge with high excitation efficiency is generated, the film formation rate is increased and the film quality is also improved. However, simply increasing the reaction gas pressure or the gas flow rate increases the number of excited species in the reaction gas and increases the film formation rate, but as described above, it causes problems such as deterioration of film quality and increased maintenance of the apparatus. ..

Therefore, the inventor has noticed that the electrons perform a cycloidal motion in the electric field and the magnetic field, which has an effect of improving the reaction gas excitation efficiency during plasma discharge.
Then, as a method for forming a high-quality thin film at a high speed without increasing the film forming cost, a permanent magnet is installed on the back side of the substrate to be processed, and the cycloidal movement of electrons by the magnetic field and the high frequency electric field of the magnet is used as the substrate. The above-mentioned method of the present invention, which is generated only in the vicinity of the surface and causes a highly efficient plasma discharge in the relevant portion, has been conceived.

A number of thin film forming methods using the ECR (electron cyclotron resonance) -plasma CVD method generally known as a magnetic field combined plasma CVD method have been reported. However, in these magnetic field combined methods, a large electromagnet is used to apply a magnetic field to the entire plasma reaction region, so that the apparatus becomes large-scale. Further, the effective thin film formation region is extremely small when viewed from the entire plasma reaction region, and the utilization efficiency of energy and reaction gas is poor. Furthermore, since a highly efficient plasma discharge occurs in the entire reaction area, a thin film is formed at high speed not only on the substrate to be treated but also on unnecessary parts such as the reaction furnace wall, resulting in peeling of the deposited film on the reaction furnace wall. Since flakes are generated and pinholes are easily generated on the substrate to be processed, the frequency of device repairs for preventing this is also increased, which causes a significant increase in film formation cost.

The method of the present invention has also solved such problems. That is, in the method of the present invention, a permanent magnet is installed on the back side of the substrate to be treated to generate a high-density, high-efficiency plasma discharge due to the cycloidal motion of electrons only near the surface of the substrate to be treated. Less wasted reaction gas. Further, since high-speed film formation occurs only in the effective thin film formation region, the amount of film formed on a portion other than the substrate surface is smaller than the amount of film formed on the substrate, and the maintenance frequency of the apparatus can be reduced. Furthermore, since a permanent magnet is additionally provided on the back side of the substrate, the conventional simple plasma C
The VD device can be used as it is without increasing the size of the device or increasing the equipment cost. Therefore, the film forming cost is significantly reduced as compared with the plasma CVD method using the magnetic field combined type proposed so far.

Examples will be described below, but the method of the present invention and the thin film formed by this method are not limited to the examples.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 outlines the method of the present invention.
The only difference from the conventional method of FIG. 4 is that the permanent magnet 9 is installed on the back side of the substrate 5 to be processed, and the apparatus used can be the conventional apparatus. Here, the same parallel plate type plasma CVD apparatus as in FIG. 4 is taken as an example.

As shown in FIG. 2, the permanent magnets 9 may be attached to the back surface of the holder 4 so as to correspond to the respective substrates 5 to be treated, or embedded in the holder 4 as shown in FIG. For example, it may be directly attached to the back surface of the substrate 5 to be processed.

A SiO ₂ film was formed on a 20 mm square copper alloy substrate (substrate to be treated) by the method of the present invention using a permanent magnet using the parallel plate type plasma CVD apparatus of FIG. For comparison, a film forming experiment was also conducted in the same apparatus by a conventional method in which a permanent magnet was not installed on the back surface of the substrate.

The common conditions in this experiment are shown below.

Substrate used (base material): Cu alloy (Ni3.
2, Si0.7, Zn 0.3 wt%) ・ Reaction gas: SiH ₄ + N ₂ O ・ Reaction gas flow rate: SiH ₄ 100 sccm, N ₂ O
600sccm-Reaction gas pressure: 1 Torr-Substrate temperature: 250 ° C-Substrate-electrode distance: 30mm-Applied high frequency: Frequency = 13.56MHz, Output = 500W-Holder area: 400 x 400mm-Electrode area: 500 x 500mm Film time: 1 hour The permanent magnet 9 used in the method of the present invention is a SmCo magnet having a diameter of 20 mm and a thickness of 5 mm, which is provided on the back side of the copper alloy substrate which is the base material to be processed for each substrate. I installed them one by one. 10mm from the surface of the copper alloy substrate surface side at this time
The magnetic flux density at the distant position was about 1000 Gauss as measured by a Gauss meter.

Table 1 shows the film thickness of the SiO ₂ film obtained after film formation for 1 hour according to the present invention and the conventional method, the film formation speed, and the dielectric breakdown voltage value examined for film characteristic evaluation.

[0020]

[Table 1]

As can be seen from the table, in the method of the present invention,
Even if the conditions of the reaction gas flow rate, the reaction gas pressure, etc. are the same as those of the conventional method, the film formation rate is doubled, and the dielectric breakdown voltage is the same as that of the conventional method in spite of the speeding up of the film formation. Equivalent values were obtained, demonstrating that the method of the present invention enables high-speed deposition of high-quality thin films.

[0022]

As described above, according to the method of the present invention, the gas flow rate and the gas pressure are increased to increase the film formation rate by a simple method of installing a permanent magnet on the back side of the substrate to be treated. In this case, a high-quality thin film can be formed at high speed without causing problems (deterioration of film quality, generation of dust, troubles caused by dust), which is useful for improving the productivity of products using the thin film.

Further, the apparatus to be used may be a simple type conventionally used, and further, since the thin film is formed efficiently only in the effective thin film forming region, it is not necessary to form the film on unnecessary portions such as the reactor wall. The number of films is small, and the frequency of device repairs for avoiding the generation of flakes due to the thin film generated in unnecessary portions can be reduced. In addition, the amount of energy and the amount of reaction gas that are wasted in film formation at unnecessary portions are reduced, which reduces the film formation cost.

The method of the present invention can be effectively utilized for forming various thin films using various plasma CVD apparatuses other than the parallel plate type plasma CVD apparatus.

[Brief description of drawings]

FIG. 1 is a diagram showing a specific example of the method of the present invention.

FIG. 2 is a diagram showing an example of a permanent magnet setting method.

FIG. 3 is a diagram showing another example of a permanent magnet setting method.

FIG. 4 is a diagram showing a conventional thin film forming method using a parallel plate plasma CVD apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reactor 2 Gas supply system 2a, 2b Flow rate controller 3 Shower-like electrode 4 Holder 5 Processed substrate 6 Heater 7 High frequency oscillator 8 Vacuum exhaust system 9 Permanent magnet

Claims (1)

[Claims] 1. A substrate to be treated is held by a grounded holder in a reaction furnace, and after heating and sealing the reaction furnace, a reaction gas is uniformly distributed on the surface of the substrate to be treated. In a plasma CVD method in which a high-frequency electric field is applied between the holder and an electrode in a furnace to generate a thin film on the surface of the substrate to be processed, a permanent magnet is installed on the back side of the substrate to be processed. Then, the magnetic field of this magnet is generated on the surface portion of the substrate to be treated to apply the high-frequency electric field, and a method for producing a thin film by the plasma CVD method is characterized.