JP3238929B2 - Method of forming amorphous silicon carbide film and photovoltaic device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming an amorphous silicon carbide film and a photovoltaic device.

[0002]

2. Description of the Related Art A photovoltaic device using an amorphous semiconductor, in particular, an amorphous silicon, has already been put to practical use for a consumer such as a calculator.

[0003] Such a photovoltaic device is usually provided with a pin
The p-type layer, which has a junction and is provided on the light incident side so that a large amount of light is incident on the i-type layer which is a photoactive layer, is made of amorphous silicon carbide having a wide band gap (hereinafter referred to as a -SiC) film. For example, see U.S. Pat. No. 4,385,199.

[0004]

However, the conventional a
Even in the -SiC film, it could not be said that light was sufficiently transmitted.

In order to extend the life of a photovoltaic device,
reducing the hydrogen concentration in the i-type layer,
Therefore, the i-type layer is formed at a high temperature.

However, when the p-type layer is formed before the i-type layer is formed at a high temperature, the conventional a-SiC film as the p-type layer has poor heat resistance and the formation of the i-type layer. Sometimes this layer was adversely affected. Similarly, when the n-type layer is formed prior to the formation of the i-type layer, i-type layer is similarly formed.
When forming the mold layer, this layer is adversely affected.

[0007]

According to the present invention, there is provided a method for forming an amorphous silicon carbide film in a reaction chamber in which a plasma discharge generated by high-frequency power applied to a discharge electrode is confined in a specific region by a magnetic field. Disposing a film-forming substrate at a position distant from the plasma discharge region, introducing a silicon compound gas and a carbon compound gas larger than this gas amount into the reaction chamber, and decomposing by a plasma discharge; Forming an amorphous silicon carbide film on the substrate by the applied gas;
Wherein the magnetic field intensity is adjusted so that an average of two or more silicon atoms are bonded to one carbon atom in the amorphous silicon carbide film during the formation of the amorphous silicon carbide film. I do.

Further, in the method of forming an amorphous silicon carbide film according to the present invention, after forming the amorphous silicon carbide film on the substrate, a p-type impurity is added to the amorphous silicon carbide film. It is characterized by the following.

Further, in the photovoltaic device of the present invention, the above-mentioned amorphous silicon carbide film in which two or more silicon atoms are bonded on average to one carbon atom is formed on the light receiving surface electrode by a p-type. It is characterized by being provided as a layer.

Further, in the photovoltaic device according to the present invention, the n-type layer formed on the conductive surface of the substrate has an amorphous structure in which two or more silicon atoms are bonded on average to one carbon atom. It is characterized by being made of a silicon carbide film.

[0011]

According to the method of the present invention, since the ratio of direct bonding between silicon atoms and hydrogen atoms is small, an a-SiC film having low light absorption and excellent heat resistance can be formed.

Further, in a photovoltaic device using such an a-SiC film, light collection efficiency is excellent and a high output can be obtained.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides a method of forming an a-SiC film having low light absorption and excellent heat resistance, and a photovoltaic device using the film.

FIG. 1 shows an RF glow discharge device for forming an a-SiC film of the present invention.

In this apparatus, a pair of discharge electrodes 2 and 3 are provided opposite to each other in a reaction chamber 1 which is brought into a low pressure state and into which a raw material gas is introduced. RF is being applied. On one electrode 2,
A substrate 4 for film formation is provided, and an electromagnet 5 for confining plasma formed by the discharge electrodes 2 and 3 is provided near the other electrode 3. This electromagnet 5
Can freely change the current flowing therethrough, the so-called magnetic field current (Img), thereby adjusting the magnetic field strength.

The a-SiC film of the present invention is formed using this apparatus. Table 1 shows conditions for forming one a-SiC film. The table also shows conditions for forming a conventional a-SiC film by a normal plasma CVD method.

[0017]

[Table 1]

FIG. 2 shows the a-Si film formed under these conditions.
4 shows the light absorption characteristics of the C film.

Referring to FIG. 1, the method according to the present invention comprises:
The case where the magnetic field currents of the electromagnets 5 are 0 A, 1 A and 2 A, respectively, and those of the conventional method are indicated by broken lines.

As apparent from FIG. 1, the a-SiC film formed according to the present invention has a small absorption coefficient for light of any wavelength.

FIGS. 3 and 4 show the XPS (X-ray photoelectron spectroscopy) spectral characteristics of the a-SiC film formed by the method of the present invention and the conventional method (solid lines are those according to the method of the present invention).
3 shows an infrared absorption characteristic of an a-SiC film formed according to the present invention.

In view of these characteristics, the a-SiC film formed by the method of the present invention has a higher ratio of carbon atoms and silicon atoms bonded directly than the a-SiC film formed by the conventional method. There are many. In addition, it can be seen that in the a-SiC film formed according to the present invention, the ratio of direct bonding between carbon atoms and hydrogen atoms and between silicon atoms and hydrogen atoms is small.

That is, a-S formed by the method of the present invention
In the iC film, the number of silicon atoms bonded to carbon atoms is equal to or larger than the number of hydrogen atoms bonded to carbon atoms. More specifically, since two or more silicon atoms are bonded on average to one carbon atom in the film, an a-SiC film having a small light absorption coefficient is obtained as described above.

Further, the aS formed by the method of the present invention
The iC film is an a-SiC film having excellent heat resistance because the ratio of bonding between silicon atoms and hydrogen atoms is small.

Incidentally, the a formed by the method of the present invention.
-When a SiC film is used as a p-type layer of a photovoltaic device,
It is necessary to dope the p-type impurity into the a-SiC film.

Usually, a p-type impurity is doped using a p-type impurity compound gas such as B ₂ H ₆ at the time of film formation. However, the present inventors have found that the a-SiC film After the formation, it has been found that it is preferable to dope the p-type impurity in the a-SiC film.

That is, after the a-SiC film is formed by the above-described method, this film is treated in a plasma discharge containing a B ₂ H ₆ gas, so that boron is contained in the a-SiC film as a p-type impurity. (B) is doped.

FIG. 5 (A) shows that a-SiC
Plasma treatment time and a-S when B is doped in the film
The relationship with the dark conductivity of the iC film is shown. FIG. 2B shows the S ₂ of B ₂ H ₆ when the a-SiC film is doped with B by using B ₂ H ₆ gas at the time of formation in the a-SiC film.
shows the relationship between the ratio and the dark conductivity for iH _4.

The a-SiC shown in FIGS.
The films were both formed to a thickness of 200 ° under the conditions shown in Table 1, and the conditions for the plasma treatment with B ₂ H ₆ gas are as shown in Table 2 below.

[0030]

[Table 2]

As apparent from FIGS. 5A and 5B, when forming a p-type a-SiC film, a-SiC
By doping B as a p-type impurity in the film after forming the film, the dark conductivity of the a-SiC film can be greatly improved as compared with the case where B is doped simultaneously with the film formation. .

FIG. 6 shows an embodiment of the photovoltaic device of the present invention using the above-mentioned a-SiC film. The photovoltaic device is made of a transparent substrate such as ITO or SnO ₂ formed on a transparent substrate 10 such as glass. The carbon atom 1 formed on the electrode film 11 by the method of the present invention.
P-type a-SiC film 1 made of amorphous silicon carbide in which two or more silicon atoms are bonded on average
2. Film thickness of about 2000 at 350 ° C using plasma CVD
The i-type a-Si film 13, the n-type a-Si film 14, and the back electrode film 15 formed in Å are formed in this order.

According to this example, the p-type a-
Since the SiC film 12 is doped with B after the film is formed, the concentration of B is high on the i-type a-Si film 14 side and low on the transparent electrode film 11 side, so that the p-type a-SiC film 13 and the transparent electrode The ohmic characteristics with the film 11 deteriorate.

FIG. 7 shows another embodiment of the photovoltaic device of the present invention which solves this problem.
A conventional method, namely, between the p-type a-SiC film 12 and
A second p-type a-SiC film 16 doped with B at a uniform concentration by doping a p-type impurity simultaneously with the film formation is inserted. The thickness of the second p-type a-SiC film 16 is preferably 30 ° or less.

According to this structure, the transparent electrode film 11 and the p-type
-The ohmic characteristics between the SiC film 12 and the second p-type a-
This is improved by the SiC film 16.

According to the photovoltaic device having these structures, the p-type a-SiC film 12 on the light incident side has a small light absorption coefficient and a large dark conductivity, and as shown in FIG. Light collection efficiency is improved compared to the conventional photovoltaic device shown by the broken line,
Further, it is possible to reduce the electric loss in the p-type a-SiC film 12 at the time of taking out the optical carrier generated in the i-type a-Si film 13, thereby forming a photovoltaic device having excellent output characteristics. be able to.

Incidentally, the above-described photovoltaic device uses the a-SiC film of the present invention by forming the p-type a-S
Although it is a form used as the iC film 12, the present invention
An a-SiC film in which two or more silicon atoms are bonded on average to one carbon atom in the film is a photovoltaic device in which an n-type layer is formed first on a substrate by utilizing its heat resistance. It is also suitable for use as an n-type layer of the device.

FIG. 9 is a sectional view showing an embodiment of this type of photovoltaic device. A transparent electrode film 23 such as SnO 2, an n-type a-Si film 24 having a thickness of 10 to 50 °, and a feature of the present invention are provided on the surface of a transparent substrate 21 such as glass having a metal film 22 for back reflection applied to the back surface. An n-type a-SiC film 25 having a film thickness of 50 to 200 ° is formed at a temperature of 300 ° C. using a plasma CVD method,
I-type a with a hydrogen content of 10% or less and a film thickness of 4000 to 8000 mm
-Si film 26, p-type a-Si film 27 having a thickness of 100 to 200 ° and I
The transparent electrode film 28 of TO or the like is formed in this order.

The n-type a-SiC film 25 is formed using the RF glow discharge device shown in FIG. Table 3 shows this n-type a-
One forming condition of the SiC film 25 is shown.

[0040]

[Table 3]

The n-type a-SiC formed under these conditions
Like the p-type a-SiC film of the present invention, the film 25 also includes many bonds between silicon atoms and carbon atoms (Si-C bonds),
Since it is excellent in heat resistance, even if the i-type a-Si film 26 is formed at a high temperature after the formation of the n-type a-SiC film 25,
There is no adverse effect on the i-type a-Si film 26.

Since the conditions for forming the n-type a-SiC film 25 are extremely extreme as shown in Table 3, the n-type a-SiC film 25 is formed directly on the transparent electrode film 23. In this case, the transparent electrode film 23 is damaged, and further, the constituent elements of the transparent electrode film 23 are mixed as impurities into the n-type a-SiC film 25 to deteriorate the characteristics of the film. In order to prevent this, in this embodiment, an n-type a-Si film 24 is formed on the transparent electrode film 23 before the formation of the n-type a-SiC film 25.

FIG. 10 shows the dependence of the conversion efficiency of the photovoltaic device on the temperature at which the i-type a-Si film 26 is formed.
The n-type a-SiC film 25 of this photovoltaic device has a hydrogen content of 8% and a ratio of Si atoms bonded to C atoms of 20%. FIG. 1 also shows a conventional photovoltaic device using an n-type a-Si film similar to an n-type a-Si film 24 formed by an ordinary method instead of the n-type a-SiC film 25. The dependency is also indicated by a broken line.

As can be seen from the figure, the conventional photovoltaic device has i
It can be seen that while the conversion efficiency decreases as the formation temperature of the mold layer increases, the photoelectric conversion efficiency of the photovoltaic device of the present invention is hardly affected by the formation temperature of the i-type a-Si film 26.

By the way, the photoelectric conversion efficiency of the photovoltaic device shown in FIG. 9 is determined by the number of S atoms bonded to C atoms in n-type a-SiC 25.
It is affected by the ratio of i atoms. FIG. 11 shows n-type a-Si
The relationship between the ratio of Si atoms bonded to C atoms in the C film 25 and the photoelectric conversion efficiency is shown.

As can be seen from the figure, when the ratio of Si atoms bonded to C atoms is 20 to 50%, very excellent photoelectric conversion efficiency can be obtained.

FIG. 12 shows the relationship between the amount of hydrogen in the n-type a-SiC film 25 and the photoelectric conversion efficiency.

According to this figure, it is understood that the photoelectric conversion efficiency of the photovoltaic device is affected by the amount of hydrogen in the n-type a-SiC film 25. To improve the photoelectric conversion efficiency, the amount of hydrogen must be reduced. It is preferable that the content be 10% or less.

[0049]

According to the manufacturing method of the present invention, an a-SiC film having low light absorption and excellent heat resistance can be formed.

According to the method of the present invention, when the amorphous silicon carbide film is a p-type layer, p-type impurities are doped after the formation of the amorphous silicon carbide film. Can be improved.

Further, since the photovoltaic device of the present invention has the above-described structure in which the p-type amorphous silicon carbide film is provided on the light incident side, the light collection efficiency is improved and the device has excellent characteristics. .

Further, in the photovoltaic device of the present invention, the n-type layer formed prior to the formation of the i-type layer is made of the amorphous silicon carbide film of the present invention having excellent heat resistance.
Has excellent properties.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an RF glow discharge device for forming an a-SiC film by the method of the present invention.

FIG. 2 shows aS formed by the method of the present invention and the conventional method.
It is a characteristic view showing the light absorption characteristic of iC film.

FIG. 3 shows a-S formed by the method of the present invention and the conventional method.
FIG. 4 is a characteristic diagram showing XPS spectrum characteristics of an iC film.

FIG. 4 is a characteristic diagram showing infrared absorption characteristics of an a-SiC film formed by the method of the present invention.

FIG. 5A is a characteristic diagram showing a relationship between a plasma treatment time and a dark conductivity of an a-SiC film when B is doped into an a-SiC film according to the method of the present invention; Is a
A-SiC using a B ₂ H ₆ gas during the formation of the SiC film
FIG. 4 is a characteristic diagram showing a relationship between a ratio of B ₂ H ₆ gas to SiH ₄ gas and dark conductivity when B is doped in a film.

FIG. 6 is a schematic sectional view showing one embodiment of the photovoltaic device of the present invention.

FIG. 7 is a schematic sectional view showing another embodiment of the photovoltaic device of the present invention.

FIG. 8 is a characteristic diagram showing light collection efficiency of the photovoltaic device of the present invention and the conventional example.

FIG. 9 is a sectional view showing still another embodiment of the photovoltaic device of the present invention.

FIG. 10 shows conversion efficiency i in the photovoltaic device of the present invention.
FIG. 4 is a characteristic diagram showing the temperature dependence of forming a type a-Si film.

FIG. 11 is a characteristic diagram showing the relationship between the ratio of Si atoms bonded to C atoms in the n-type a-SiC film of the photovoltaic device and the photoelectric conversion efficiency.

FIG. 12 is a characteristic diagram showing the relationship between the amount of hydrogen in the n-type a-SiC film of the photovoltaic device of the present invention and the photoelectric conversion efficiency.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-64-81276 (JP, A) JP-A-58-56415 (JP, A) JP-A-61-183974 (JP, A) 253282 (JP, A) JP-A-2-119126 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 31/04-31/078

Claims (8)

(57) [Claims] 1. A step of disposing a film-forming substrate at a position distant from the plasma discharge region in a reaction chamber in which a plasma discharge generated by high-frequency power applied between discharge electrodes is confined in a specific region by a magnetic field. Introducing a silicon compound gas and a carbon compound gas larger than the gas amount into the reaction chamber, and decomposing by a plasma discharge, and forming an amorphous silicon carbide film on the substrate by the decomposed gas. And adjusting the magnetic field intensity such that an average of two or more silicon atoms are bonded to one carbon atom in the amorphous silicon carbide film during the formation of the amorphous silicon carbide film. A method for forming an amorphous silicon carbide film. 2. The amorphous silicon carbide film according to claim 1, wherein after the amorphous silicon carbide film is formed on the substrate, a p-type impurity is added to the amorphous silicon carbide film. A method for forming a carbide film. 3. A photovoltaic device comprising, as a p-type layer, an amorphous silicon carbide film having an average of two or more silicon atoms bonded to one carbon atom on a light receiving surface electrode. . 4. The p-type layer according to claim 1, wherein the
4. The photovoltaic device according to claim 3, wherein a p-type impurity is added after forming an amorphous silicon carbide film in which two or more silicon atoms are bonded on average. 5. An amorphous silicon carbide film to which a p-type impurity is added at a uniform concentration is provided between the light-receiving surface electrode and the p-type layer.
A photovoltaic device as described. 6. A photovoltaic device having at least an n-type layer and an i-type layer formed in this order on a conductive surface of a substrate, wherein the n-type layer has an average of two per one carbon atom. A photovoltaic device comprising an amorphous silicon carbide film in which the above silicon atoms are bonded. 7. The photovoltaic device according to claim 6, wherein in the amorphous silicon carbide film, 20 to 50% of silicon atoms in the film are bonded to carbon atoms. 8. The amorphous silicon carbide film according to claim 6, wherein the amount of hydrogen in the film is 10% or less.
A photovoltaic device as described.