JPH04299575A - Forming method of polycrystalline semiconductor layer and manufacture of photovoltaic device using the same - Google Patents

Abstract

PURPOSE:To easily form a polycrystalline semiconductor layer at a low temperature, and obtain a method for forming fine unevenness for texture effect on the polycrystalline semiconductor layer. CONSTITUTION:After an amorphous semiconductor layer 2 is formed on a substrate 1, said layer is irradiated with a light 15 via a photo mask 10. In the state that a temperature distribution is formed on the surface, the semiconductor layer 2 is heat-treated and crystallized, thereby forming a polycrystalline semiconductor layer on the surface of which unevenness is formed.

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 polycrystalline semiconductor layer suitable for use as a solar cell, an optical sensor, etc., and a method for manufacturing a photovoltaic device using this polycrystalline semiconductor layer.

0002

[Prior Art] Generally, a photovoltaic device includes a transparent electrode and three amorphous semiconductor layers of p-type, i (intrinsic) type, and n-type conductivity on a transparent substrate such as glass. and a back electrode are laminated in this order.

Although such photovoltaic devices have the advantage of being inexpensive, they have the problem of lower photoelectric conversion efficiency than photovoltaic devices using crystalline silicon.

Furthermore, although photovoltaic devices using an amorphous semiconductor layer have photosensitivity in the range of 300 to 800 nm, there is now a demand for photovoltaic devices that are sensitive to longer wavelengths. It's here.

For this reason, photovoltaic devices using crystalline polycrystalline silicon are attracting attention. Polycrystalline silicon has a mobility that is about one to two orders of magnitude higher than that of amorphous silicon, and is thermally stable and highly reliable. Moreover, the photosensitivity is wide, ranging from 300 to 1100 nm.

On the other hand, in a photovoltaic device using an amorphous semiconductor layer, one method for improving photoelectric conversion efficiency is to provide fine irregularities to scatter and reflect light incident on the optical semiconductor layer. Some materials have a so-called texture effect that reduces loss and increases the optical path length in the optical semiconductor layer to increase light absorption efficiency.

[0007]

[Problems to be Solved by the Invention] Conventionally, SILSO polycrystalline silicon substrates and cast polycrystalline silicon substrates have been used for polycrystalline silicon, but these substrates have been exposed to high temperatures exceeding 1000°C during the substrate formation process. This required complicated and difficult steps, such as a heat treatment process.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for easily forming a polycrystalline semiconductor layer such as polycrystalline silicon at a low temperature, and also for forming fine irregularities in the polycrystalline semiconductor layer for a texture effect. Take it as a challenge.

[0009]

[Means for Solving the Problems] A method for forming a polycrystalline semiconductor layer according to the present invention includes forming an amorphous semiconductor layer on a substrate, and then selectively irradiating the semiconductor layer with light while The method is characterized in that the semiconductor layer is crystallized by performing heat treatment with a temperature distribution provided, thereby forming a polycrystalline semiconductor layer having an uneven surface.

The method for manufacturing a photovoltaic device according to the present invention includes a step of forming an amorphous semiconductor layer of one conductivity type on a substrate, and selectively irradiating this semiconductor layer with light to create a temperature distribution on the surface. a step of crystallizing the semiconductor layer by performing heat treatment in a state in which a polycrystalline semiconductor layer of one conductivity type is formed with unevenness formed on the surface; The method is characterized by comprising a step of forming a semiconductor layer.

[0011]

[Operation] On the surface of a semiconductor, a temperature difference occurs between a portion that is irradiated with light and a portion that is not irradiated with light. Depending on this temperature distribution, a polycrystalline semiconductor layer with fine irregularities on the surface can be formed.

0012

[Example] First, according to FIGS. 1 to 3, the first embodiment of the present invention will be described.
An example will be described.

1 to 3 show a method for forming a polycrystalline semiconductor and a method for manufacturing a photovoltaic device according to the present invention.
2 is an enlarged sectional view of the main part after the heat treatment, and FIG. 3 is a sectional view of the photovoltaic device.

In this example, titanium (Ti
) as an n-type impurity on a metal substrate 1 consisting of
) is doped with n-type amorphous silicon layer 2 having a thickness of 10 μm.

The above-mentioned n-type amorphous silicon layer 2 is formed on the substrate 1 by, for example, a radio frequency (RF) glow discharge method. The film forming conditions at this time were silane gas (SiH4) 1
0 sccm, phosphine (PH3) diluted with 0.1% hydrogen (H2) 1 sccm, substrate temperature 500°C, pressure 0
．． The temperature was 12 Torr, the RF power was 20 W, and the deposition rate was 3 Å/sec.

Subsequently, as shown in FIG. 1, the substrate 1 is placed in a vacuum container on a mounting table 20 having a built-in heater 21. Then, a quartz photomask 10 having light transmitting portions 11 and light shielding portions 12 alternately provided is placed on the n-type amorphous silicon layer 2 . The width of the light transmitting portion 11 and the light shielding portion 12 in this embodiment is approximately 3 μm.

Thereafter, the inside of the vacuum container is evacuated to maintain a vacuum state, and visible light or ultraviolet light 1 is applied from above the photomask 10.
5 and heat-treated at a temperature of 600° C. for 10 hours.

By irradiating this visible light or ultraviolet light 15,
In the vicinity of the surface of the n-type amorphous silicon layer 2, the temperature of the portion irradiated with light from the light-transmitting portion 11 of the photomask 10 rises to 620° C., and the temperature of the portion that is not irradiated with light due to the light-shielding portion 12 increases. The temperature is about 600°C.

Further, the temperature of the n-type amorphous silicon layer 2 near the substrate 1 is influenced by the substrate 1, so that there is almost no difference in temperature between the light irradiated part and the non-light irradiated part.

By this heat treatment, the amorphous silicon layer is crystallized to form a polycrystalline silicon layer through so-called solid phase growth. As a result of this solid phase growth, the surface of the n-type polycrystalline silicon layer 2a is formed with irregularities corresponding to the period of the temperature distribution. That is, as shown in FIG.
The unevenness is formed at a period of about m. The height of the unevenness at this time is about 2 μm.

After that, on the n-type polycrystalline silicon layer 2a,
Film thickness 10 doped with boron (B) as p-type impurity
A p-type amorphous silicon layer 3 of 0 Å is formed.

The above-described p-type amorphous silicon layer 3 is formed on the substrate 1 by, for example, a radio frequency (RF) glow discharge method. The film forming conditions at this time were silane gas (SiH4) 5
sccm, diborane (B) diluted with 1% hydrogen (H2)
2H6) 25sccm, substrate temperature 120℃, pressure 0.2
Torr, RF power 6W.

Then, as shown in FIG. 3, a transparent electrode 4 made of ITO or the like is provided on the p-type amorphous silicon layer 3 by sputtering or the like to obtain a photovoltaic device.

Now, when we measured the photosensitivity of the photovoltaic device using thin film polycrystalline silicon shown in FIG.
Both the long wavelength sensitivity of 0 nm or more and the short wavelength sensitivity of 500 nm or less were improved.

Next, a second embodiment of the present invention will be described with reference to FIGS. 4 to 6.

4 to 6 show a method for forming a polycrystalline semiconductor and a method for manufacturing a photovoltaic device according to a second embodiment of the present invention, FIG. 4 is a cross-sectional view showing a state in which heat treatment is performed, and FIG.
6 shows an enlarged sectional view of the main part after heat treatment, and FIG. 6 shows a sectional view of the photovoltaic device.

In this embodiment, a p-type amorphous silicon layer 6 doped with boron (B) as a p-type impurity and having a thickness of 4000 Å is formed on an n-type polycrystalline silicon substrate 5.

The above-mentioned p-type amorphous silicon layer 6 is formed by, for example, a radio frequency (RF) glow discharge method. The film forming conditions at this time were 10 sccm of silane gas (SiH4).
, diborane (B2H6) diluted with 1% hydrogen (H2)
5 sccm, H230 sccm, substrate temperature 350° C., pressure 0.07 Torr, and RF power 30 W.

Subsequently, as shown in FIG. 4, the n-type polycrystalline silicon substrate 5 is placed on a mounting table 20 containing a heater 21 in a vacuum container. Then, as described above, a quartz photomask 10 having light transmitting portions 11 and light shielding portions 12 alternately provided is placed on the p-type amorphous silicon layer 6. The width of the light transmitting portion 11 and the light shielding portion 12 in this embodiment is approximately 0.
It is about 5 μm.

Thereafter, the inside of the vacuum container is evacuated to maintain a vacuum state, visible light or ultraviolet light is irradiated from above the photomask 10, and heat treatment is performed at a temperature of 650° C. for 10 hours.

By irradiating this visible light or ultraviolet light, in the vicinity of the surface of the p-type amorphous silicon layer 6, the temperature rises to 670° C. in the irradiated portion, and the light is not irradiated. The temperature of the portion is approximately 650°C.

In addition, p near the n-type polycrystalline silicon substrate 5
Due to the influence of the substrate 1, there is almost no temperature difference in the temperature of the mold amorphous silicon layer 6 between the light irradiated area and the non-light irradiated area.

As a result of the solid-phase growth caused by this heat treatment, the surface of the p-type polycrystalline silicon layer 6a has irregularities corresponding to the period of the temperature distribution. That is, as shown in FIG. 5, in this example, unevenness is formed at a period of about 1 μm. The height of the unevenness at this time is about 2000 Å.

Thereafter, as shown in FIG. 6, aluminum (Al) is formed on the p-type polycrystalline silicon layer 6a by vapor deposition or the like, and this Al is patterned to form a comb-shaped electrode 7, which is used for light emission. Obtain an electromotive force device.

Now, when we measured the photosensitivity of the photovoltaic device using thin film polycrystalline silicon shown in FIG.
Both the long wavelength sensitivity of 0 nm or more and the short wavelength sensitivity of 500 nm or less were improved.

[Effects of the Invention] As explained above, according to the present invention, a temperature difference occurs between the light irradiated part and the non-light irradiated part on the semiconductor surface, and the surface temperature changes according to this temperature distribution. A polycrystalline semiconductor layer having fine irregularities can be formed. Therefore, when this polycrystalline semiconductor layer is used in a photovoltaic device, the photoelectric conversion efficiency is improved due to the so-called texture effect.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention and showing a state in which heat treatment is performed.

FIG. 2 is an enlarged cross-sectional view of the main part after heat treatment, showing the first embodiment of the present invention.

FIG. 3 is a sectional view of a photovoltaic device, showing a first embodiment of the present invention.

FIG. 4 is a sectional view showing a second embodiment of the present invention and showing a state in which heat treatment is performed.

FIG. 5 is an enlarged sectional view of the main part after heat treatment, showing a second embodiment of the present invention.

FIG. 6 shows a second embodiment of the invention and is a sectional view of a photovoltaic device.

[Explanation of symbols] 1 Board 2 N-type amorphous silicon 2a N-type polycrystalline silicon 3 P-type amorphous silicon 4 Transparent electrode 10 Photomask 5 N-type polycrystalline silicon substrate 6 p-type amorphous silicon 6a p-type polycrystalline silicon 7 Comb-shaped electrode

Claims (2)

[Claims] 1. After forming an amorphous semiconductor layer on a substrate, heat treatment is performed while selectively irradiating the semiconductor layer with light and creating a temperature distribution on the surface to form the semiconductor layer. A method for forming a polycrystalline semiconductor layer, which comprises crystallizing and forming a polycrystalline semiconductor layer having an uneven surface. 2. A step of forming an amorphous semiconductor layer of one conductivity type on a substrate, selectively irradiating the semiconductor layer with light and performing heat treatment with a temperature distribution on the surface, A step of crystallizing the semiconductor layer to form a polycrystalline semiconductor layer of one conductivity type with unevenness formed on the surface, and a step of forming a semiconductor layer of another conductivity type on the polycrystalline semiconductor layer of one conductivity type. Method of manufacturing a photovoltaic device.