JPS60200965A - Manufacture of thin film of amorphous silicon carbide - Google Patents

Abstract

PURPOSE:To obtain a homogeneous film free from defects by subjecting hydrogensilanes coexisting with methyl hydrogensilanes to photolysis. CONSTITUTION:Methyl hydrogensilanes represented by a general formula (CH3)1SibHc (where b=1-3, a+c=2b+2, 2b+1>=a, a>=1, 2b+1>=c, and c>=1) are prepd. The methyl hydrogensilanes and hydrogensilanes are fed to the surface of a substrate with a carrier gas, and they are subjected to photolysis or mercury sensitized photolysis.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an amorphous silicon carbide thin film, particularly an amorphous silicon carbide thin film with little damage to a substrate.

Amorphous silicon carbide (hereinafter abbreviated as a-8iO)
As for this, this is a high optical hand cap (Eopt
), its application to solar cell window frame materials, light-emitting elements, electrophotographic photoreceptors, etc. is being considered, and the manufacturing method is based on hydrogenated silane, alkylsilane, or halogenated silane and hydrocarbon. Method of plasma OVD of compounds (JP-A-57-27914, JP-A-5
7-22112, JP-A-57-104276, JP-A-57-455365, JP-A-57-200215), methods of thermally decomposing these gases and mixed gases (JP-A-57-116200) No., JP-A-57-118
082), the ion blating method (see Japanese Patent Laid-Open No. 55-18678), and the sputtering method (see Japanese Patent Laid-Open No. 56-40284).

However, in the plasma OVD method, it is difficult to obtain a high-quality film because high-energy particles such as ions generated by plasma discharge collide with the produced film, and reaction decomposition products adhere to the reactor wall. Therefore, there is a limit to the repeated use of the reactor, and there is a disadvantage in that it is necessary to clean the deposits in order to obtain a homogeneous product.Also, since SiH4 or Si2H6, which is highly flammable, is used as the starting material, it is difficult to handle. (There was a problem in that strict precautions were required and the cost was high.On the other hand, when using halogenated silane as a raw material gas, there was a problem in the treatment of hydrochloric acid and chlorine that were produced as by-products during plasma decomposition. It also had the disadvantage of slow speed.Also, since the pyrolysis method requires high temperatures, the film tends to crack due to the difference in thermal expansion between the substrate and the film, and the adhesive strength is poor. It is easy to form clusters of each element (furthermore, it is difficult to obtain a homogeneous and high-quality film, and the coating speed is slow. Also, since the same gas as the plasma OVD method is used as the starting material, the plasma OVD method is different from the plasma OVD method. It has been recognized that the same disadvantages exist and that ion blating and sputtering methods also suffer from the same drawbacks as pyrolysis methods due to the high temperatures required.

The present invention is characterized by overcoming such disadvantages by supplying a-8iO thinly and subjecting it to photodecomposition or mercury-sensitized photodecomposition.

That is, the present inventors investigated various methods for producing a-8iO thin films that do not generate ions and do not require high temperatures, and found that although the photodecomposition reaction is slow when using methylhydrodiene silane alone, it can be When irradiated with light together with hydrogen silanes consisting of methylhydrogen silanes, hydrogen silane radicals activated by hydrogen abstraction decompose these methylhydrogen silanes to form a-
The present invention was completed by confirming that 8iO can be easily obtained and that a homogeneous film without any defects can be obtained since an a-8iO thin film can be formed only by a radical reaction.

The hydrogen silanes used as starting materials in the method of the present invention are represented by SiH4,8i□H6 or 5i3H, which is converted into amorphous silicon (hereinafter abbreviated as a-8i) through a photodecomposition reaction. ), it is necessary to use methylhydrodienesilanes, which serve as a C2 carbon source, in order to convert this a-8i to a-8iO.

The methylhydrogensilanes are methylhydrogensilane compounds or methylhydrogenpolysilane compounds represented by the general formula % 0≧1),
This includes 0H3SiH3, (OH3)2SiH2゜(O
Ha )381H1(OHa5iH2)21((O
H3)2 SiH)21H2H I (OH3s1a2)・510H31((OH3)25i
H)2・5i(OH3)2゜(OH3)2Si・8i0
H3,0H3Si・:8. Examples include LH3 (1H) (However, among these, those with three or more methyl groups bonded to the silicon atom have a slower reaction rate than those with two or less methyl groups, so the silicon atom It is preferable that 2 or less methyl groups are attached to the methylhydrogensilane.The photodecomposition rate of this methylhydrodiene silane alone is slow, but
Since the photodecomposition reaction is promoted when any hydrogen silane such as SiH4, Si2H6 or 5i3H87'j is present, the addition of this hydrogen silane is an essential requirement. a-8iO obtained by the method of the present invention
The properties of the thin film vary depending on the amount of methylhydrodiene silane added, and if this is 10 mol% or less, a-8i
Carbon theft in O is reduced, and if it is 90% or more, the amount of carbon becomes large (and becomes high resistance, making it impractical).
It is often set at 5 to 80 mol%, and according to this, an a-8i0 thin film having a high optical bend gap of 2.U to 2.5 eV, which is required as a window frame material for solar cells, can be easily obtained. be able to. In addition, both the hydrogen silanes and methylhydrodiene silanes are in gaseous form and are placed in the reaction chamber in equal amounts, but they are flowed along with the carrier gas to dilute the concentration as necessary. . The carrier gas may be an inert gas such as hydrogen, helium, or argon, or a mixed gas thereof.

In addition, a-8iO obtained by photolysis of these gases
The thin film may be made n-type or p-type by adding doping such as PH, B2H6, etc. to this starting material gas.

On the other hand, the light source for photodegrading methylhydrogensilanes may be any source that can irradiate high-energy light (photons), such as a high-pressure mercury lamp,
Examples include low-pressure mercury lamps, and the wavelength of low-pressure mercury lamps (1,849A).

In 2.537A), S1□H6 reacts, but no reaction occurs with SiH4, so when using SiH4, it is best to use mercury sensitization, and in this case, a trace amount of mercury is added to the reaction system. When the mercury is excited by light irradiation and collides with the gas molecules, it imparts energy to the gas molecules, causing the gas to decompose and achieve the desired purpose.

The following method of the present invention will be explained based on the accompanying drawings. FIG. 1 shows the method for producing an a-8iO thin film by the photolysis method of the present invention.In this reactor 1, a substrate 3 is placed on a base 2 for immediate heating; A vacuum state of about 1 to 5 torr is maintained by suction from the suction port 4 by a vacuum pump.

This reactor is also provided with a lid plate 5 made of quartz glass or the like on its upper part, and a mercury lamp 6 is passed through the quartz glass.
The methylhydrogensilane introduction lower and the hydrogensilane introduction port 8 are illuminated with light from the
When the raw material gas is introduced from the carrier gas, it is decomposed by the light energy emitted from the mercury lamp, and the resulting a-8i 0 is deposited on the substrate 3 in the form of a thin film. be done. Furthermore, Fig. 2 shows a method in which this is carried out by a mercury sensitization method, in which case the hydrogen silanes are introduced via a mercury storage tank 9 maintained at 20 to 70°C. It is designed to cause mercury vapor to follow.

The method of the present invention involves photolyzing hydrogen silanes in the coexistence of methylhydrodiene silanes to produce a-8i
The hydrogen silanes and methylhydrogen silanes are irradiated with light from a mercury lamp, etc., and when exposed to light from a mercury lamp, etc. ) Since this reaction is a radical reaction, the a7sio thin film obtained in this way does not reach high temperatures, is not damaged by ion bombardment, and adheres to the substrate with sufficient adhesive strength, and is of good quality. In addition to having the advantage of being homogeneous and highly conductive, this a'-8iO thin film can be made into n-type or p-type by doping, and cells made from it can have high It has the advantage of exhibiting photoelectric conversion efficiency.

Next, examples of the method of the present invention will be given.

Example 1 Using the photolysis apparatus shown in Fig. 1, two
After placing a CII+ square glass substrate (Corning 7059; trade name manufactured by Corning Glass Co., USA), the pressure inside the reactor was reduced, and SiH gas 200C,C diluted to 10% by volume with helium scum was added to the reactor for 7 minutes. and methyl 6 silane (C) 1si1+3) gas 5C, C, 7 minutes (C1
(3Sij (3/5i2t (6 + He = 0.025 flow rate ratio)) was supplied to maintain the pressure at 5 Torr.The glass substrate was then heated to 200°C, and a low pressure mercury lamp (wavelength 1
．． When the light from 849'A) was irradiated for 60 minutes, an a-9iC thin film with a thickness of 500'A was formed on this substrate.

Next, the optical forbidden band width (Eopt) of this a-SiC thin film is
) was measured to be 2.08 eV, but the flow rate ratio of 0H3SiH3/Si2H6+)le in the above was set to 0.
．． Eopt is 2.2 when set to 05, 0.1, 0.5
0, 2.28, and 2.34 eV, and it was found that this Eopt can be freely controlled by the gas flow rate ratio.

In addition, in the above, the Eopt of the thin film obtained using only Si2H6 gas obtained by diluting this reaction gas to 10% by volume with helium without adding CH35IH3 was 1.72 eV.
Therefore, it was confirmed that when CH35lH3 gas is added, Eopt increases in proportion to the amount of addition, and that a-5iC is generated by its photodecomposition.

Example 2 In the method of Example 1, the flow rate ratio of S121 (6 gas) and CH35iI (3 gas) diluted to 10% by volume with helium gas was set to 0.05, and 1 volume 2 of hydrogen gas was used.
A-8iC with a thickness of 500'A was prepared in the same manner as in Example 1 except that BH gas diluted to 1x, 3%, 5X4 was added.
When a thin film was made, the obtained a-3iC thin film was of P type and its Eopt was 2. It was OeV.

Next, the dark conductivity and AMI of this a-3iC thin film.

When the photoconductivity was measured under 10 w/Cl112 light irradiation, the results shown in MAi in FIG. 3 were obtained. Also, for comparison, CH35IH3-8i2H6,
Using CH35iH-3iH as a raw material gas and B2H64 as a doping agent, P was deposited to a thickness of 5,000A using a plasma CvD method using a substrate heater temperature of 350°C, pressure of 1 Torr, plasma output of 4W, and high-frequency power of a frequency of 13.5f1MHz.
A type a-SiC thin film was made (Eopt=2.0eV),
When the photoconductivity and dark conductivity were measured, line 2 (for CH35iH3-Si2H6) and line 3 (for CH35iH3-Si2H6) in Fig. 3 were measured.
CH3S+H3'S+H4) was obtained, and it was confirmed from these results that an a-9iC thin film with higher conductivity (higher resistance value) could be obtained by photolysis method than by plasma CvD method. Therefore, if this is used as a window frame material for solar cells, it is expected that the open circuit voltage will increase and the photoelectric conversion efficiency will be significantly improved.

Example 3 Using the mercury-sensitized photolysis apparatus shown in Fig. 2, the same glass substrate as in Example 1 was placed on the heating base, and the reactor was heated to
After reducing the pressure to Torr, 5i2)16 gas diluted to 10 volumes with helium gas 200C0C1/min,
Dimethylsilane [(OH) SiH] Gas 5G-32
2C, 7 minutes (flow rate ratio 0.025) and 0.05, 0.2, 1, 2.
B2H6 gas diluted to 1 volume 2 with 5X amount of hydrogen gas was added. At this time, the SiH gas was passed through a mercury storage tank maintained at a temperature of 50°C, and then the glass substrate was heated to 250°C.
Then, a low-pressure mercury lamp (2,537A
) was irradiated for 60 minutes, a P-type a-5ic thin film with a thickness of approximately 1,000λ was formed on this substrate, and the photoconductivity and dark conductivity of this film were measured, as shown in Figure 4. The results shown in were obtained.

Example of statement ILI:H3)2S as raw material waste in Example 3 above
iH,.

A p-type a- When a 3iC thin film was made and its photoconductivity and dark conductivity were measured, the results shown in Figure 4 were obtained, and in this case also a P-type a-9iG@ film was obtained, but pffa-5lG It was found that 6 (c H3) 2 S I H2 requires a smaller amount of OH to obtain a thin film.

Example 4 Using the photolysis device shown in Figure 1, S1
H6 gas was mixed with a carrier gas, and an n-type S1 layer was deposited on an aluminum plate under the conditions shown in /%1 in Table 1 according to the method of Example 1, and then under the conditions of A2 in Table 1. Below, a 1-type S1 layer was deposited on top of this n-type S1 layer, and then the temperature of the mercury bath was set to 50°C in the mercury-sensitized photolysis apparatus shown in FIG. After depositing a p-type SiO layer or a p-type S1 layer on this 1-type S1 layer under the same conditions, a 5no2.ITO layer was deposited on this, and a glass plate was laminated to form an aluminum/n1p (
a-8i + a-310) / Sn o2a I
When a cell made of T 2 O/glass was made and the conversion efficiency of this cell was measured, the results shown below and in FIG. 5 were obtained.

(P layer formation conditions) Experiment/f63 (5th prisoner curve) Source gas Si□H,+(OH3)2SiH2Voc=0
．． 831 (vl, l5c=13.38(mA/<1'f
i).

FF=0.609, EFF=6.77 (%)
Experiment Δ64 (Figure 5 IB curve) Raw material gas S1□H6+c2H2 Voc=0.800tvJ, l5c=12.37(mA
/cm).

F”F O,634,EFF=6.28(%) Experimental rot 5
(Curve in Figure 5) Raw material gas Sl. H6 Voc=0.799tvl, l5c=11.10(mA
/m).

FF=0.610. EFF=5.41 (%) Therefore, from this, the conversion efficiency of the cell depends on the type of raw material gas: Si2H6+ (OH3)2 BIH2> 5i2H
It was confirmed that the order was s+ 02H2>Si2H6.

Table 1

[Brief explanation of the drawing]

Fig. 1 is a schematic vertical cross-sectional view of the photolysis device used in the method of the present invention, Fig. 2 is a schematic longitudinal cross-sectional view of the mercury-sensitized photolysis device used in the method of the present invention, and Fig. 3 is a schematic longitudinal cross-sectional view of the photolysis device used in the method of the present invention. Obtained a-3i
C-n'! The photoconductivity curve of IIA, FIG. 4 shows the a-3iG photoconductivity curve, dark conductivity curve, and optical forbidden band IIJ (Eopt) curve obtained in Example 3 and Comparative Example 1, and FIG. 3 shows a conversion efficiency curve of the cell obtained in Example 4. l...Reactor 2.Fist/Heating base 3...Substrate 4...Suction port 5...Lid cover 6...Mercury lamp 7.8-...Reaction gas inlet 8. ...Mercury storage tank patent applicant Shin-Etsu Chemical Co., Ltd. Figure 1 Figure 2-82H6/ [S i (CH3)H3÷Si2H6
or SiH4] (%) Fig. 4 82H6/ (Si2H6÷5i(CH3)2H2)
(%Fig. 5 □Kamari (V))

Claims (1)

[Scope of Claims] 1. A method for producing an amorphous silicon carbide thin film, which comprises supplying hydrogen silanes and methylhydrodiene silanes together with a carrier gas onto a substrate and subjecting them to photodecomposition or mercury-sensitized photodecomposition. 2. Claim 1 in which the methylhydrodiene silane is represented by the general formula %c, c≧1)
A method for producing an amorphous silicon carbide thin film as described in 2.