JPH071752B2 - Method for manufacturing semiconductor device - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor device.

[Prior Art] As materials for semiconductor devices such as solar cells including an amorphous semiconductor layer, a-Si: H, a-SiC: H, a-SiGe: H, a-SiN: H, a-Si:
F: H, a-Ge: H, and the like, and microcrystalline semiconductors thereof are used. These depositions are RF or DC plasma CVD
It is usually done using a device.

In the conventional method, all amorphous semiconductor layers are deposited at a film forming temperature of about 220 ° C. or higher using this type of apparatus.

[Problems to be Solved by the Invention] When a semiconductor layer is formed on a transparent conductive film by such a method, electrons in plasma and ions or radicals which are decomposition products of a semiconductor forming gas are deposited on the substrate surface. Because of direct collision, ITO, In ₂ O ₃ , ITO / SnO ₂ , Cd _x Sn Oy (X = 0.5 to 2,
The transparent conductive film formed of Y = 2 to 4), Ir _z O _1-z (z = 0.33 to 0.5) or the like is partially or wholly reduced and metallized. This phenomenon occurs even at the film forming temperature of 220 ° C. even in the process of depositing the intrinsic layer after depositing the first impurity-doped layer.
Before and after or more than this, electrons, ions, radicals, etc. are transferred to the substrate through the gaps in the first impurity-doped layer (the first doped layer is generally thin and is easily formed into islands and has a gap between islands). It occurs because it collides with a surface.

The metal generated in this way diffuses not only into the deposited first impurity-doped layer but also into the intrinsic layer, and acts as a kind of dopant or cancels out electrons and holes generated in the intrinsic layer. Since it becomes a bonding center, the interface between the semiconductor / transparent conductive film and the interface between the first impurity-doped layer / intrinsic layer are significantly deteriorated.

This diffusion progresses not only during the deposition of the first impurity-doped layer but also during the intrinsic layer deposition, but during the intrinsic layer deposition, the diffusion of the dopant atoms of the first impurity-doped layer also proceeds.

Further, when the metallization occurs, the conductivity and the transparency of the transparent conductive film itself are also lowered, so that the characteristics of the semiconductor device, particularly the photoelectric conversion characteristics are significantly lowered.

The present invention is intended to reduce the problems caused by the alteration of the transparent conductive film that occurs when the amorphous semiconductor is deposited on the transparent conductive film as described above, and further, to reduce the problem between the first impurity-doped layer and the intrinsic layer. The effect of the recombination center is reduced by strengthening the built-in electric field of.

[Means for Solving Problems] In the present invention, an amorphous semiconductor is provided on a transparent conductive film as a first impurity-doped layer (hereinafter, referred to as a first doped layer), an intrinsic layer, and a conductivity opposite to that of the first doped layer. Type second impurity-doped layer (hereinafter referred to as the second doped layer), a semiconductor layer from a portion in contact with the first doped layer that is deposited as a part of the intrinsic layer to a portion having a thickness of 80 Å when deposited in this order. The present invention relates to a method for manufacturing a semiconductor device, wherein the maximum film forming temperature during deposition is 10 to 180 ° C., which is 20 to 250 ° C. lower than the maximum film forming temperature of the intrinsic layer to be formed thereafter.

[Examples] The transparent conductive film used in the present invention is a transparent conductive film having a thickness of about 0.01 to 1.0 μm that is generally used for manufacturing a semiconductor device. There is no limit.

Specific examples of the transparent conductive film include ITO, ITO / SnO ₂ , In
₂ O ₃ , SnO ₂ , Cd _x Sn Oy (X = 0.5 to 2, Y = 2 to 4), I
Examples include r _z O _1-z (z = 0.33 to 0.5) and CdO.
It is not limited to these.

All of these conductive films are easily reduced by a reducing plasma containing hydrogen atoms, and the reduction is remarkable at a high temperature as in a general chemical reaction.

Examples of the first doped layer deposited on the transparent conductive film in the present invention include a-Si: H, a-SiC: H, a-Ge: H, and a-Si: F:
P-type or n-type ones such as H and μc-Si: H are generally used, but not limited to these.

The intrinsic layer and the second doped layer formed after the first doped layer is deposited are particularly limited as long as they are the second doped layer having a conductivity type opposite to that of the normally used intrinsic layer and the first doped layer. Not a thing.

Specific examples of such an intrinsic layer include a-Si: H, a-Si: F,
Second doped layer, such as undoped ones such as a-Si: F: H, a-SiGe: H, a-SiSn: H, a-SiN: H, or those doped with a small amount of B or P As a specific example of, when the first doped layer is p-type, n-type μc-Si: H, a-SiC: H, aS
If the first doped layer is n-type, such as i: H and a-SiN: H, p
Examples include a-Si: H, μc-Si: H, and a-SiC: H.

In the present invention, the maximum film formation temperature at the time of deposition of the semiconductor layer from the part in contact with the first doped layer that is deposited as a part of the intrinsic layer to the part with a thickness of 80 Å is The film is formed at a temperature of 10 to 180 ° C, which is 20 to 250 ° C lower than the maximum film forming temperature.

As used herein, the maximum film formation temperature means the semiconductor layer of a portion of the semiconductor layer from the portion in contact with the first doped layer deposited as a part of the intrinsic layer to the portion having a thickness of 80Å. The temperature of the surface on which the highest semiconductor layer is deposited during deposition, and in the part of the intrinsic layer that is subsequently formed, the highest temperature of the surface on which the semiconductor layer is deposited during film formation Say.

Usually, reduction of the transparent conductive film occurs remarkably when the first doped layer is formed, especially when the film forming temperature is about 220 ° C. or higher, but the thickness of the first doped layer is
It is generally as thin as about 80 to 300Å, and in some cases the layer is formed into islands and gaps occur between the islands.
Even when the intrinsic layer is formed under the above-mentioned conditions, it is reduced by the reducing plasma containing hydrogen atoms through the first doped layer. During the intrinsic layer deposition, diffusion of dopant atoms in the first doped layer also progresses.

However, from the part in contact with the first doped layer deposited as a part of the intrinsic layer to the part with a thickness of 80Å, if necessary,
The maximum film formation temperature during deposition of the semiconductor layer up to a thickness of 80 to 2000Å is 20 to 250 ° C lower than the maximum film formation temperature of the intrinsic layer to be formed thereafter, preferably 10 to 180 ° C. When the film is formed at the maximum film formation temperature, the film formation temperature is low, so that the transparent conductive film is less likely to be reduced even when contacted with a reducing plasma containing hydrogen atoms, and is reduced during the deposition of the first doped layer. It is also possible to prevent the generated metal and the diffusion of the dopant in the first doped layer. Therefore, the amount of metal produced is reduced and the diffusion is also reduced, and the deterioration of semiconductor characteristics such as the generation of recombination centers and the decrease of doping efficiency due to the contamination of the semiconductor layer by the metal is remarkably improved.

Furthermore, the maximum film forming temperature of the first doped layer is 10 to 180 ° C, and the semiconductor layer is deposited from the portion in contact with the first doped layer to the portion with a thickness of 80 Å, if necessary, to the portion with a thickness of 80 to 2000 Å. By setting the temperature equal to or lower than the maximum film forming temperature at that time, the effect that the transparent conductive film is less likely to be reduced can be more remarkable. In addition, when the film is formed by such a method, 80 Å from the first doped layer and the part in contact with the first doped layer
Thickness of the semiconductor layer up to the thickness of 80 to 2000Å, and the intrinsic layer to be deposited after that, from the low deposition temperature to the high deposition temperature. Since the p-layer having a small internal stress and the intrinsic layer having a large internal stress are smoothly connected to each other, it is possible to form a film by raising Defects such as dangling bonds due to mechanical stress at the interfaces of the semiconductor layer / intrinsic layer that is subsequently deposited up to the thickness of 80 Å, if necessary, up to the thickness of 80 to 2000 Å Occurrence can be reduced. Further, from the first doped layer / portion in contact with the first doped layer, 80
The forbidden band width of the semiconductor layer up to the thickness of Å, if necessary, up to the thickness of 80 to 2000 Å / semiconductor layers to be subsequently formed, changes smoothly from wide to narrow Therefore, the internal electric field at the interface can be uniformly increased as compared with the conventional first doped layer / intrinsic layer interface. The internal electric field can be further increased by using a material having a wide band gap such as a-SiC: H for the first doped layer. Furthermore, when the first doped layer is a μc-Si: H layer,
The effect is that a smooth interface between μc: Si: H and intrinsic can be obtained.

A semiconductor layer (intrinsic layer formed at a low maximum film formation temperature) is formed from a portion in contact with the first doped layer to a portion having a thickness of 80Å, and if necessary, a portion having a thickness of 80 to 2000Å In this case, it is preferable that the plasma condition is, for example, a pressure in the range of 0.2 to 2.5 Torr, and a pressure at or near the maximum at which the glow discharge can be maintained, and the RF power is in the range (5 to 20 mW / cm ² ), which is preferably 10 to 1 ° C., which is 20 to 250 ° C. lower than the maximum film formation temperature of the subsequently formed intrinsic layer.
_{Photoconductivity} σ _ph of 10 ^-5 (Ωcm) even at the maximum film forming temperature of 80 ° C
^-1 or more, optical bandgap E _opt 1.8eV
It can be a degree. Further, the influence of plasma on the transparent conductive film can be reduced.

However, since the electrical properties of the intrinsic layer formed at this low maximum film forming temperature may be inferior to those of the intrinsic layer formed at the high maximum film forming temperature, the entire intrinsic layer may have a low maximum film forming temperature. It is not preferable to make it at the film temperature, and in practice it is possible to reduce the influence of plasma when making a normal intrinsic layer,
The intrinsic layer may be deposited at a low maximum film forming temperature by a thickness that can prevent alteration of the transparent conductive film and diffusion of the dopant in the first doped layer. That is, depending on the film formation conditions of the intrinsic layer having a low maximum film formation temperature, a part of the intrinsic layer is contacted from the part in contact with the first doped layer to the part having a thickness of 80 Å, if necessary, to the part having a thickness of 80 to 2000 Å. The effect of the present invention can be obtained by depositing.

Of course, the thickness of the intrinsic layer deposited at a low maximum deposition temperature is
For example, if it becomes as large as 500Å, 1000Å, or even 2000Å, the effect of preventing reduction of the transparent conductive film or diffusion of metal becomes great, but a too large value is not preferable for the above reasons. The preferred thickness of the intrinsic layer deposited at low maximum deposition temperature is 150-400Å, the most preferred thickness is 200-300Å.

The film formation temperature of the intrinsic layer formed at a low maximum film formation temperature does not have to be constant, and may be gradually changed. The point is that, from the maximum film formation temperature of the semiconductor layer to be formed thereafter, at least from the portion in contact with the first doped layer to the portion having a thickness of 80 Å,
If necessary, film deposition up to 80-2000Å thickness is 20-250
It may be carried out at a maximum film forming temperature which is lower by 50 ° C., preferably 50 to 200 ° C.

In order to avoid the influence of plasma on the transparent conductive film during the deposition of the intrinsic layer formed at a low maximum film forming temperature, it is preferable to deposit at the maximum film forming temperature of 10 to 180 ° C.

As an apparatus for carrying out the method of the present invention, a normal capacitive coupling type RF parallel plate type CVD apparatus, an inductive coupling type RFCVD apparatus,
Examples of the DC parallel plate type CVD device include, but are not limited to. In particular, a remarkable effect is seen in the parallel plate type CVD apparatus.

Next, the method of the present invention will be described based on examples.

Example 1 and Comparative Example 1 A 4000 Å-thick SnO ₂ electrode was formed on a glass plate by a spray method, and this was used as a substrate.

On the substrate, the substrate temperature is 30 ° C, the CVD pressure is 1.5 Torr, and SiH ₄ / CH.
_The RF power density is 10 mW / c with the flow rate ratio of ₄ is 2/3 and the net flow rate of B ₂ H ₆ is 1% with respect to the total flow rate of SiH ₄ + CH _4.
After depositing 100 Å p-type a-SiC: H layer at m ² , the deposition temperature is 10
200 Å of i-type a-Si: H layer (intrinsic layer formed at low maximum film forming temperature) was deposited at 0 ° C (constant) and CVD pressure of 1 Torr using SiH ₄ gas with RF power density of 10 mW / cm ² . . Then the film formation temperature 190
℃ (constant), CVD pressure 1.0 Torr, SiH ₄ gas, 10mW / c
An i-type a-Si: H layer was deposited at 6000Å in m ² . Further film formation temperature
180 ° C. (constant), PH ₃ 1 flow rate% relative to SiH ₄ in CVD pressure 2 Torr, introducing as H ₂ is 30 flow rate doubled, RF power density 70
n-type μc-Si: H layer was deposited 300 Å at mW / cm ²
l was deposited by a vacuum vapor deposition method to 1000 L to prepare a solar cell having an area of 1 cm ² .

The characteristics of the obtained solar cell were measured using AM-1, 100mW / cm ² solar simulator, J _SC 15.2mA, V _OC 0.
It was 9V, FF 61.0%, and η 8.4%. Moreover, the result of having measured the current-voltage characteristic of the obtained solar cell is shown in FIG.

As a comparative sample, a solar cell was prepared in the same manner as in Example 1 except that the i-type a-Si: H layer formed at the film formation temperature of 100 ° C. (constant) was not deposited, and the characteristics of the solar cell were measured. Then,
It was J _SC 15.0mA, V _OC 0.78V, FF 59.5%, and η 6.96%. Moreover, the result of having measured the current-voltage characteristic of the obtained solar cell is shown in FIG.

The film-forming temperature was measured by mounting an ultrafine chromel-alomer thermocouple on the surface of the substrate on which the semiconductor layer was deposited, which was confirmed not to be affected by plasma electrolysis.

[Effects of the Invention] When a semiconductor device is manufactured by the method of the present invention, V _OC , F
A semiconductor device having significantly improved F and η can be obtained.

[Brief description of drawings]

FIG. 1 is a graph showing current-voltage characteristics of a semiconductor device (solar cell) manufactured by the method of the present invention and the conventional method.

Claims (3)

[Claims] 1. When depositing an amorphous semiconductor on a transparent conductive film in the order of a first impurity-doped layer, an intrinsic layer, and a second impurity-doped layer of a conductivity type opposite to that of the first impurity-doped layer, The maximum deposition temperature of the semiconductor layer from the portion in contact with the first impurity-doped layer that is deposited as a part to the portion with a thickness of 80 Å is 20 times higher than the maximum deposition temperature of the intrinsic layer to be deposited thereafter. A method for manufacturing a semiconductor device, characterized in that the film is formed at 10 to 180 ° C. lower by 250 ° C. 2. The maximum film formation temperature of the first impurity-doped layer is 10 to 10.
80 ° C from the portion in contact with the first impurity-doped layer to 80 ° C
The manufacturing method according to claim 1, which is equal to or lower than the maximum film formation temperature of the intrinsic layer up to the thickness of Å. 3. The first impurity-doped layer is an a-SiC: H layer or μc
-The manufacturing method according to claim 1, which is a Si: H layer.