JPH06120152A - Manufacture of hydrogen-doped amorphous semiconductor film - Google Patents

Abstract

PURPOSE:To reduce the optical deterioration of an amorphous semiconductor film by causing at least one of inactive atom having a predetermined kinetic energy, hydrogen atom and the constituent atom of the amorphous semiconductor film to collide with the surface of the amorphus semiconductor film simultaneously with or before hydrogen annealing. CONSTITUTION:A p-layer of a-SiC:H is formed; thereafter, Ar plasma treatment is performed as sputtering process; and hydrogen annealing by hydrogen plasma treatment is performed. Subsequently, an i-layer of a-Si:H is formed; thereafter, the Ar plasma treatment is performed as sputtering process; hydrogen annealing by the hydrogen plasma treatment is performed; and then an n-layer of muc-Si:H is formed. Further, Ar of RF power 20-700W and H2 of RF power 20-800W are preferred. Thus, the Ar plasma treatment and H2 plasma treatment of a film surface are successively performed after film formation so that unstable hydrogen in the film is reduced.

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 a hydrogen-doped amorphous semiconductor film. The hydrogen-doped amorphous semiconductor film of the present invention is used in amorphous solar cells and the like.

[0002]

2. Description of the Related Art Amorphous Si solar cells have the advantage of being able to form large-area solar cells with thin films, but on the other hand, defects such as dangling bonds in amorphous Si films when used under outdoor sunlight. Increase and the output decreases over time (photodegradation). It is considered that this is due to an increase in the amount of Si—H ₂ bonds in the amorphous Si film, especially in the i layer thereof.

Therefore, Japanese Patent Laid-Open No. 260662/1990 discloses that the hydrogen concentration of the base layer adjacent to the substrate side of the intrinsic (i) layer is suppressed to 10% or less so that the base layer becomes an i-layer effective for photoelectric conversion. That is, the auto-doping of hydrogen is suppressed to suppress the increase in the amount of Si—H ₂ bonds in the i layer.

[0004]

However, although the above-mentioned publication suppresses the auto-doping of hydrogen from the base layer to the i-layer, it is not a solution to the basic problem of reducing excess hydrogen formed in the i-layer itself. I won't. The present invention has been made in view of the above problems, and an object thereof is to reduce the amount of hydrogen existing at an unstable position in an amorphous semiconductor film to reduce its photodegradation.

[0005]

A method of manufacturing a hydrogen-doped amorphous semiconductor film according to the present invention comprises a deposition step of decomposing a source gas to deposit an amorphous semiconductor film doped with hydrogen atoms on a substrate, and a deposition step. A hydrogen annealing step of exposing the formed amorphous semiconductor film to a hydrogen plasma atmosphere to reduce dangling bonds in the surface portion of the amorphous semiconductor film, the hydrogen annealing step comprising: At the same time or before that, at least one of an inert atom having a predetermined kinetic energy, a hydrogen atom, and a constituent atom of the amorphous semiconductor film is made to collide with the surface of the amorphous semiconductor film to cause unstable hydrogen in the amorphous semiconductor film. It is characterized in that a sputtering process for reducing the concentration is provided.

If the kinetic energy of the atom hitting the film is small,
Since the unstable hydrogen in the film cannot be moved by the required distance, the minimum energy level required is naturally present, but it is possible to impart this required energy to the atom hitting the film by means such as plasmaization or electric field acceleration. it can.

[0007]

In the amorphous semiconductor film deposited in the deposition process, not only hydrogen bonds effective for reducing dangling bonds of amorphous semiconductor atoms but also Si-H ₂ bonds at relatively unstable positions in the film are formed. In such a state, excess hydrogen is taken in, and this excess hydrogen increases dangling bonds and the like due to light irradiation, reduces photoelectric conversion efficiency, and reduces conductivity.

According to the present invention, the surface of the amorphous semiconductor film is hit with at least one of an inert atom having a predetermined kinetic energy, a hydrogen atom, and a constituent atom of the amorphous semiconductor film, so that the effective hydrogen bond is smaller than the above-mentioned effective hydrogen bond. Hydrogen that binds to an adjacent atom in the film by the binding energy (that is, exists in a relatively unstable position in the film) is knocked out of the film or relocated to the position of an unbonded hand.

[0009]

As described above, in the method for producing a hydrogen-doped amorphous semiconductor film of the present invention, an inert atom having a predetermined kinetic energy, a hydrogen atom, and an amorphous semiconductor are provided at the same time as or before the hydrogen annealing step. Since it has a sputtering process in which at least one of the constituent atoms of the film collides with the surface of the amorphous semiconductor film, hydrogen at an unstable position in the amorphous semiconductor film is knocked out of the film or is bonded to hydrogen. Move it to the position of the unbonded hands, which reduces photodegradation.

In the above sputtering process, effective hydrogen atoms at the bonding positions of the constituent atoms of the amorphous semiconductor film with the dangling bonds on the surface of the amorphous semiconductor film are also repelled and the dangling bonds also increase. The hands are recombined with hydrogen atoms by a hydrogen annealing process performed at the same time as or after the sputtering process.

[0011]

EXAMPLE 1 An example of the present invention is amorphous Si.
The manufacturing process applied to a solar cell is shown in FIG. 1, and the produced amorphous Si solar cell is shown in cross section in FIG. Basic Step First, a glass substrate 101 formed by patterning a transparent conductive film 102 made of SnO2 is placed in a vacuum container, and silane (SiH4) and phosphine (PH) are placed therein.
4), diborane (B2H6), methane (CH4), hydrogen (H2) or the like is caused to flow at a low pressure, high frequency is applied while adjusting each flow rate, and the gas is decomposed by glow discharge, and then is placed on the glass substrate 101. A hydrogen-doped amorphous Si (a-Si: H) film 103 having a three-layer structure of p, i, and n is deposited. After that, the electrode 104 made of, for example, aluminum is formed on the amorphous S.
It is formed by patterning on the i film 103 by a mask vapor deposition method or a photolithography method. Next, using the electrode 104 as a mask, dry etching is performed using CF ₄ to divide the amorphous Si film 103 into a predetermined number of island-shaped regions. Next, the serial connection electrode 105 is formed by a mask vapor deposition method, the island regions are connected in series, and then the protective layer 10 made of epoxy resin is formed.
After coating 7, the lead wire 106 is attached to complete the solar cell.

Since the feature of this embodiment lies in the step of forming the amorphous Si film 103, the film forming step will be described below. FIG. 1 shows a process flow, and Table 1 shows process parameters of each process. The degree of vacuum inside the container is 0.2-2.
It was set to 0 torr.

[0013]

[Table 1]

First, an a-SiC: H p layer (film thickness of about 8 n
m) is formed (step a), and then a plasma treatment step of Ar (argon) is performed as a sputtering step.
After that, a hydrogen annealing step is performed by hydrogen plasma treatment (step c), and then an a-Si: H i layer (having a film thickness of about 40) is formed.
0 nm) is formed (step b), then a plasma treatment step of Ar (argon) is performed as a sputtering step, and then a hydrogen annealing step is performed by hydrogen plasma treatment (step c), and then μc-Si: An n layer (film thickness: about 15 nm) of H (μc means microcrystal) was formed (step d).

That is, in this embodiment, after the film formation, the film surface is sequentially subjected to Ar plasma treatment and H2 plasma treatment, thereby reducing unstable hydrogen in the film and reducing dangling bonds on the film surface. . The Ar plasma treatment and the hydrogen plasma treatment were carried out after the p layer was formed and then the i layer was formed every 20 nm. A photo-acceleration test was performed in which each sample produced under the same conditions except that the Ar plasma treatment and the hydrogen plasma treatment were changed in time was irradiated with light energy of -200 mW / cm ² for 100 hours. The results are shown in Table 2. Samples 1 to 5 are conventional samples that do not undergo Ar plasma treatment. From Table 2,
It was found that the output change, that is, the decrease rate of the output current, was significantly reduced by the Ar plasma treatment and the hydrogen plasma treatment.

[0016]

[Table 2]

Furthermore, the hydrogen content (at%) in the i-layer of some samples was measured by a secondary ion mass spectrometer (SIMS).
The results of measurements made in step 1 are also shown. From this result, it is estimated that the output reduction is reduced as the hydrogen content in the i-layer is reduced. FIG. 5 shows the output deterioration amount when the Ar plasma processing time and the hydrogen plasma processing time are variously changed. From this figure, Ar plasma treatment time is 35 seconds to 75 seconds,
It is understood that the hydrogen plasma treatment time is preferably 40 seconds to 80 seconds.

The processing time varies depending on the flow rate and the degree of vacuum. Also, both plasma treatments may overlap. FIG. 3 shows R in Ar plasma processing.
The results of examining the output reduction are shown for a number of samples prepared under the conditions of Table 1 except that the F power and Ar gas flow rate were changed. Specifically, in FIG. 3, the aptitude region is a region that satisfies the following conditions. Ar gas flow rate 5
500 sccm, RF power 20-700 W, and chamber pressure 0.5-5 torr are suitable conditions.

FIG. 4 is a graph showing the results of examining the decrease in output of many samples prepared under the conditions of Table 1 except that the RF power and the H2 gas flow rate in the H2 plasma treatment were changed. To be more specific, the aptitude region in FIG. 4 is a region that satisfies the following conditions. H ₂ gas flow rate 5-700
Sccm, RF power of 20 to 800 W, and chamber pressure of 0.01 to 10 torr are preferable conditions.

Incidentally, the plasma generation condition is determined by the Ar gas flow rate and the RF power. From the above experiment,
It was also found that when the Ar flow rate exceeds 500 sccm, the conductivity of the amorphous Si film decreases, so that the Ar plasma processing condition is not appropriate. It was also found that the conductivity of the amorphous Si film was lowered even when the RF power was high. Furthermore, similar experimental results were obtained for hydrogen plasma treatment.

The results of analyzing the meaning of the Ar plasma treatment will be described below. Amorphous Si solar cells are manufactured by decomposing SiH4 under reduced pressure by hydrogen glow discharge to form an amorphous Si PIN diode. Since hydrogen is taken into the amorphous Si film more than necessary in this process, when the amorphous Si is irradiated with light, electrons and holes excited by light energy are recombined at recombination centers. . At this time, hydrogen bound in an unstable state or excessively incorporated into the film moves due to local breakdown of the electrically neutral condition, creating a new trap level. As a result, the electric resistance of the amorphous Si film increases. As a result, the conversion efficiency of the amorphous Si solar cell decreases as the light irradiation time increases.

It is known that hydrogen in the amorphous Si film can be reduced by forming the film at a high temperature of 300 ° C. or higher, and the photodegradation of the solar cell formed by the high temperature film formation can be reduced. Has also been investigated. However, the energy conversion efficiency of the solar cell manufactured by this method is lower than that of a conventional solar cell formed at a film forming temperature of 200 ° C to 350 ° C. That is, hydrogen in the amorphous Si has a function of bonding to dangling bonds which are recombination centers of the amorphous Si and reducing the recombination centers. Therefore, if the hydrogen doping amount is extremely reduced, the recombination centers of the amorphous Si will rather increase, the conductivity will decrease, and the photoelectric conversion efficiency will decrease.

Therefore, if hydrogen is introduced into the amorphous Si without excess or deficiency, the unstable level of hydrogen is small, so that the rate of increase of recombination centers can be suppressed even when irradiated with light, and photodegradation is small. It should be possible. In this embodiment, after a-Si: H is formed as a hydrogen-doped amorphous semiconductor film, the surface of the film is hit with an inert atom to weakly bond hydrogen, hydrogen taken in an unstable position during film formation. In A plasma
The r radical is removed by applying it to the film surface. After that, unbonded hands on the film surface are reacted with hydrogen radicals to cover a-Si with hydrogen without excess or deficiency.

As a result, an a-Si: H film, an a-SiC: H film or the like having good conductivity and photoelectric conversion efficiency can be obtained. Note that the gas used to remove excess hydrogen on the surface of the film is not limited to Ar, and the same action can be obtained as long as it is an inert atom having a necessary kinetic energy, a hydrogen atom, or a constituent atom of the amorphous semiconductor film. To be (Embodiment 2) Another embodiment will be described.

A solar cell in which two layers of pin solar cells were laminated was prepared by the same process as in Example 1. The p layer of the lower solar cell is a boron-doped a-SiC film with a thickness of 8 nm,
The i-layer is an i-layer amorphous Si having a film thickness of 100 nm using Ar plasma treatment and hydrogen plasma treatment, and the n-layer is a microcrystalline Si film having a film thickness of 15 nm doped with phosphorus. The upper layer solar cell has an a
-SiC, the i-layer is an i-layer amorphous Si having a thickness of 400 nm using Ar plasma treatment and hydrogen plasma treatment, and the n-layer is a microcrystalline Si film having a thickness of 15 nm doped with phosphorus.
A test sample was prepared by using a film obtained by stacking the above two layers, connecting a predetermined number of them in series with the same structure as in FIG. 2 and coating a protective layer.

This test sample was converted into light energy-200
Irradiation with mW / cm ² was performed for 100 hours, and the change in output was examined. As a result, the rate of change was 4%. From this, it was found that the laminated solar cell of this example had extremely excellent light deterioration resistance.

[Brief description of drawings]

FIG. 1 is a film forming process diagram showing a manufacturing process of a solar cell to which the present invention is applied.

FIG. 2 is a cross-sectional view of the solar cell manufactured in the process of FIG.

FIG. 3 is a diagram showing a possible region and an appropriate region of Ar plasma processing.

FIG. 4 is a diagram showing a feasible region and an appropriate region for hydrogen plasma processing.

FIG. 5 is a diagram showing an output deterioration amount when the Ar plasma processing time and the hydrogen plasma processing time are variously changed.

Claims (1)

[Claims] 1. A deposition step of decomposing a source gas to deposit a hydrogen atom-doped amorphous semiconductor film on a substrate, and exposing the deposited amorphous semiconductor film to a hydrogen plasma atmosphere to form a surface of the amorphous semiconductor film. In the method for producing a hydrogen-doped amorphous semiconductor film, which comprises a hydrogen annealing step of reducing dangling bonds of a portion, at the same time as or before the hydrogen annealing step, an inert atom having a predetermined kinetic energy, a hydrogen atom, A hydrogen-doped amorphous semiconductor, comprising a sputtering step of colliding at least one of constituent atoms of the amorphous semiconductor film with a surface of the amorphous semiconductor film to reduce an unstable hydrogen concentration in the amorphous semiconductor film. Membrane manufacturing method.