JPS59161811A - Formation of semiconductor thin film - Google Patents

Abstract

PURPOSE:To obtain a semiconductor thin film of wide optical forbidden band width by a method wherein disilane or mixture gas of disilane and biluting gas is prepared as raw material and a discharge energy of less than 5.5 KJ per unit mass of disilane is applied to the raw material to form the semiconductor thin film. CONSTITUTION:Disilane or mixture gas of disilane and diluting gas is prepared as raw material and the raw material is decomposed by a glow discharge and an amorphous silicon thin film is formed on a substrate. The glow discharge energy of less than 5.5 KJ per unit mass of disilane is applied. H2, He, Ne, Ar and the like is used as above diluting gas. Moreover, P type or N type semiconductive additive may be added to the disilane or the mixture gas of disilane and diluting gas and a compound of III-group elements such as B2H6 is used as the P type additive and a compound of V-group elements such as PH3 and AsH3 is used as the N type additive. The semiconductor thin film obtained with above method has a wide optical forbidden band width and can be utilized as a window material of an amorphous silicon photoelectric conversion element.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a semiconductor thin film made of amorphous silicon, and particularly to a method for forming the thin film having a wide optical forbidden band.

Amorphous silicon (hereinafter abbreviated as A-8I) thin films have been extensively studied recently, and are being used in solar cells, photosensitive drums, scanning circuits for image reading devices, drive circuits for image display devices, and the like.

Therefore, when such an a-3i thin film is used as a window material for a solar cell, that is, a thin film with low incident light loss, it is desirable that the optical forbidden band (hereinafter referred to as Eopt) of the silicon thin film be as large as possible.

Because light with energy greater than Eopt is
This is because it is cut by the a-3i layer before reaching the photoactive layer and is not used effectively.

With conventional technology, it was difficult to form such a window material using only silicon raw materials, so amorphous silicon carbide (hereinafter referred to as a-3iCx), which is silicon with carbon and nitrogen introduced therein, and amorphous silicon nitride were used. (hereinafter a-8IN
y) was studied, and boron-doped pla-5
iCx is partially put into practical use as a window material for heterojunctions.

However, (i) a-3iCx and a-3iNy are inherently difficult to conduct electricity, and when these are used as window materials, problems arise due to low electrical conductivity. In a-3iCx and a-3iNy, E'opt increases when the amount of C and N is increased and the values of X and y are increased, but the electrical conductivity decreases significantly, so the values of X and y are often changed. It was not possible to increase Eopt by increasing Eopt. For example, p-type a-3iC
For x, EOpt is 1.9 to 2. It is said that it is best to use OeV in terms of balance with electrical conductivity, but the electrical conductivity at this time is still low at about 10-78-Cm-1, making it difficult to use in photoelectric conversion elements such as solar cells. In this case, the window material acts as a resistance component, which is disadvantageous to improving efficiency. (
ii) Furthermore, a carbon source must be used as a raw material for a-3iCx formation. As a result, carbon is deposited inside the glow discharge chamber, and a new problem arises in that the deposited carbon must be removed. As mentioned above, the conductivity is a-
Since it is greatly influenced by the value of X in 3iCx, the composition and control of the silicon raw material and carbon raw material must be strictly controlled, making the process complicated.

The present invention has been made in view of these points, and its object is to provide a method for forming a semiconductor thin film suitable as a window coating material only from silicon raw materials.

As a result of intensive studies from the above viewpoint, the present inventors found that a silicon thin film formed by glow discharge decomposition using disilane gas has an increased EOpt (Japanese Patent Application No. 134709/1982), and also found that the discharge conditions As a result of further investigation, surprisingly, Eop exceeding 1.9eV
The present invention was completed by discovering discharge conditions under which an a-3i film having t can be obtained.

Furthermore, even in an a-3i:H film doped with a substance that provides p-type or n-type conductivity, its Eop
t exceeds 1.8 e V, and the conductivity of these p-type or η-type a-3i:H is approximately 10"
Since it is larger than S-em', it has suitable properties as a window material. That is, in the present invention, a mixed gas of disilane or synlane and a diluent gas is used as a raw material, a substance imparting p-type or n-type conductivity is further added as needed, and the mixture is decomposed by claw discharge to form a substrate. A method for forming a semiconductor thin film, characterized in that the thin film is formed by applying glow discharge energy of 5.5 KJ or less per unit of disilane.

It provides:

Hereinafter, the constituent elements of the present invention will be divided in detail.

In the present invention, Synlan means M formula S+nH2+1→
In the polysilane compound composed of 2, n=2. Of course, it is preferable that it be highly pure, but it does not matter that it contains higher-order substances such as trisilane, tetrasilane, etc. (n = 3.4 in the general formula), which behave in the same way as disilane in glow discharge. do not have.

Disilane can be produced by a physical synthesis method in which monosilane is partially converted into disilane through silent discharge, but from the point of view of industrially producing solar cells, it is possible to synthesize disilane using a chemical method that allows stable quality products to be obtained in large quantities. It is more preferable to use a conventional synthetic method (for example, a method such as reducing hexachlorodine oran).

In the present invention, the p-type conductivity-imparting substance used as necessary is, for example, a group II element compound such as 82 H6 (diborane), and the n-type conductivity imparting substance (1-conducting substance is
For example, it is a group V element compound such as PH3 (phosphine) or AsH3 (arsine).

The ratio of these substances to disilane is 1
The amount is 0.1 to 5 parts by volume per 00 parts by volume.

H2, He5N is used as a diluent gas to dilute disilane etc.
e, Ar, etc. are used. The total amount of diluent gas used for disilane is 4 parts to 2 parts by volume per 1 part by volume of disilane.
o capacity parts, preferably 1 o capacity parts or more.

Further, for a p-type to n-type conductivity imparting substance, 10 to 1000 parts by volume of diluent gas is used per 1 part by volume of the substance.

In the present invention, a-3i:
Preferably, H is formed. Although the electrical characteristics are improved by using this gas, it is thought that it has the role of reducing the influence of polymolecular impurities and mitigating damage to the film caused by plasma. The dilution ratio is not particularly limited, but as mentioned above, it is convenient for production to be in the range of 5 to 2° vol., and the above-mentioned effects are greatly exhibited.

In the present invention, as described above, a thin film is formed by applying glow discharge energy of 5.5 KJ or less per unit mass of disilane, and the glow discharge energy per unit mass of disilane is calculated using the following formula.

For example, a raw material gas consisting of disilane (S12 H6) diluted to 1Qvo1% with helium (He) 0.5β/
The energy when adding glow discharge power of IOW to minutes is calculated as follows.

Average molecular weight of raw material gas - (62,2184x 0.1
14.0026x O,9) = 9.824 (g
r)S]2 Weight fraction of H6 - (62,2184X 0
．． 1) /9.824=0.633 Substituting this into the above equation (1) gives the energy per unit mass of disilane - Now, if 103J is expressed as KJ, the energy is 1.7
It can be expressed as K J/g S +2 Hs.

There is no particular restriction on the lower limit of the above glow discharge energy. In short, any material that can form a stable glow discharge state may be used. This value also changes depending on the conditions of the glow discharge equipment and the raw material gas used. As a preferable specific example, in the case of Ginran alone or a raw material gas diluted with a diluent gas such as He or Ar (argon), 0
．． 5KJ/g-3i2 H6 or higher, H2 (hydrogen)
In the case of dilution, it is slightly larger at 1.5 KJ/g-3i. H6
That's all.

In the present invention, it is preferable to increase the flow rate of the raw material gas when forming a-5i. In the above energy calculation formula, the flow rate is in the denominator, and the larger the flow rate, the greater the glow discharge power that can be applied. There is an advantage that the rate of formation of a-3i increases as the flow rate increases.

In addition, other desirable results can also be obtained, such as reducing the variation in conductivity of p- or n-type a-3i:H and increasing the photosensitivity of l-type a-3i. The preferred range of flow rate varies depending on the shape, capacity, material, etc. of the glow discharge equipment, so it is difficult to specify the range unequivocally, but when forming Type 1 A-31, IOA/sec, preferably 20 people/ A feed gas flow rate that maintains a formation rate in excess of sec is desirable.

Further, in the present invention, it is preferable to increase the pressure for forming the a-3i film in the range of 1 to 10 Torr.

Light sensitivity is improved by increasing the pressure. The detailed reason for this is unknown, but as the pressure increases, the mean free path of the plasma becomes smaller, and the plasma directly
It is thought that the 5i film may become ineffective in damaging the 5i film.

In the present invention, the temperature when forming a-3i is 4
Maintained below 50°C. Preferably 100℃~400℃
It is ℃.

When the glow discharge energies are made equal, Eopt becomes larger at lower temperatures, but a-3i:H film formation does not proceed effectively at temperatures lower than 100t:.

Specifically, the film peels off and yellow amorphous silicon powder is generated, making it impossible to achieve the object of the present invention.

Further, at temperatures exceeding 400° C., although it is possible to form an amorphous silicon film, electrical properties such as photosensitivity deteriorate.

Next, embodiments of the present invention will be described. A substrate on which a semiconductor thin film is to be formed is placed in a reaction chamber capable of glow discharge. Heat and maintain at a temperature of 100 to 400°C under reduced pressure. Next, raw material gas is introduced, and glow discharge energy of 5 KJ or less per unit mass of disilane is applied to increase the pressure to 1 to 10 To.
An a-3i film containing hydrogen may be formed using rr.

The semiconductor thin film obtained in the present invention has a wide optical forbidden band [
1], window polishing materials for amorphous/recon photoelectric conversion elements including 1-4, A-3i solar cells, hack contact materials, and elements disposed on the light incident side of Kundem junction elements. In addition to being suitable for use as a silicon material, it can also be usefully used in various devices using amorphous silicon.

EXAMPLES The present invention will be explained in more detail with reference to Examples below.

Examples 1 to 11 Capacitively coupled high frequency plasma CV D (C1+
chemical vapor deposition)
A 7059 glass substrate manufactured by Corning was installed in the substrate installation section of the apparatus. 1O-7 Torr by oil diffusion pump
The substrate was heated to a temperature of 300° C. (thin film formation temperature) while being evacuated.

Jinlan diluted with He (dilution ratio S1□ H6/He
= 1/9), and a semiconductor thin film was formed under the discharge conditions shown in Table 1. In the same way, H to diluted PH3 or B2 H6 (dilution ratio PH3/H2=
1/99, B2 H6/H2=1/99) was added to the disilane to form a p-type or p-type semiconductor thin film. The flow rates of disilane PH, B2 H6 in Table 1 indicate the total flow rate including the diluent gas.

The time for forming the thin film, that is, the glow discharge time, was determined so that the thickness of the thin film was approximately 5000 mm. This time] type,
This differs between p-type and p-type silicon layers, and the average times required are 7 minutes and 40 seconds, 14 minutes and 40 seconds, and 13 minutes and 40 seconds, respectively.

After measuring the light absorption coefficient α of the thin film with a spectrophotometer, Eopt is calculated as (αhν)″ for the energy of incident light (hν).
was plotted, and the straight line portion was extrapolated to obtain the value of the intercept with the hv axis. The conductivity was measured by forming electrodes at intervals of 200 μm, applying a voltage between the electrodes, and measuring the current. The results, including the relationship between glow discharge energy and Eopt, are shown in Table 1.

The electrical conductivity in Table 1 above is the value when no light is irradiated.

For type 1 thin films, the photoconductivity under MI irradiation is approximately 1
07~10''s-cm'.

As shown in Table 1, B2 H6 was added at 4% to disilane.
Even in the doped Example 11, the Eopt C1.
76 eV, which is 0.1 compared to 1.64 eV of p-type amorphous silicon for comparison below.
It has a wide Eopt of 2 eV.

(In addition, in the example for comparison, only the discharge power was increased to 50W under the same conditions as Example 9 above, and it was 13.2KJ/g-312
A p-type silicon thin film is formed using H6 discharge energy. ) Examples 12 to 14 Table 2 shows the results obtained under the same conditions as in Example 6, except for the thin film formation temperature, which was changed as shown in Table 2.

Examples 15 to 17 Table 3 shows the results obtained under the same conditions as in Example 9, with only the thin film formation temperature being changed as shown in Table 3.

51

Claims (2)

[Claims] (1) In a method of forming a semiconductor thin film on a substrate by decomposing a mixed gas of ginrane or disilane and a diluent gas as a raw material by glow discharge, the above-mentioned disilane unit mass light is applied with glow discharge energy of 5.5 KJ or less. A method for forming a semiconductor thin film, the method comprising forming a thin film. (2) The method according to claim 1, wherein an n-type or n-type conductivity imparting substance is further added to the mixed gas of ginrane or disilane and the diluent gas.