JPS58114725A - Vapor deposition method - Google Patents

Abstract

PURPOSE:To prevent the influence of residual oxygen effectively and to deposit evaporated amorphous Si films having good quality on a substrate in the stage of heating and evaporating a evaporating source and depositing the same on the substrate in a vacuum vessel by setting the oxygen pressure in the vessel at values approximately lower than specific values in the presence of a reducing gas. CONSTITUTION:For example, Si evaporated from an evaporating source 2 in a vacuum of the order of 10<-4>Torr is deposited as amorphous Si (a-Si) on a substrate 1. At this same instant, an inert gas from an introducing pipe 6 is sucked onto the substrate 1 of negative potential to bind H in the a-Si so that dangling bonds are embedded with the H. If the oxygen pressure is set at about <=10<-5> Torr in the presence of gaseous hydrogen in this case, the dark conductivity of the a-Si film is increased and the ratio to the rate of change in photoconductivity when irradiated with light is made >=3 digits.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vapor deposition method, and in particular to a vapor deposition method for amorphous silicon (
Hereinafter, it will be abbreviated as a-gi. ) is related to a vacuum evaporation method.

Conventionally, attempts have been made to deposit silicon on the surface of a single-crystal silicon wafer in vacuum to form an epitaxial growth film of silicon. However, the normal degree of vacuum (
It is known that at temperatures of 1 G"-' to 10-' Torr), the resulting silicon film becomes a crystalline film containing a large amount of oxygen.

This oxygen enters from the outside due to a design flaw in the vacuum equipment or a leak after the evaporation operation (operation in which gas is passed through the Pel Jar to return it to atmospheric pressure), but a non-negligible amount (normally 10" Torr). Therefore, during deposition, silicon atoms tend to react with oxygen gas in the space inside the Pelger while reaching the substrate to be deposited from the storage boat. After the film has been deposited, its surface is very active, and oxygen flying at high speed collides with it, producing silicon oxide.This oxidation reaction on the film surface occurs because the substrate is generally heated. It occurs more intensely.

Therefore, in order to prevent the influence of oxygen, it is necessary to draw a very high vacuum inside the Pelger, but this is extremely difficult as described above. Therefore, recently, MBE (Molecu
The inside of the device is heated to ~1O-10Tor using a precise vacuum evaporation technology called lar B@am Epitaxy.
Attempts have been made to evaporate silicon under extremely high vacuum conditions, and some success is being achieved. However, the operating conditions must be set very strictly, and there are future issues with the controllability of various parameters.

On the other hand, the use of a-8i as solar cells and electrophotographic photoreceptors has been studied in recent years. This a-8i is deposited on the substrate by, for example, a vacuum evaporation method, but at this time, the a-8i
In order to fill the dangling bonds inside with hydrogen atoms and improve its photosensitive characteristics, active hydrogen gas is supplied, and a-8
In order to control the electrical conductivity of t, dopants such as phosphorus and aluminum may be evaporated and doped into a-8t.

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In addition, the problem of the influence of oxygen basically exists in the same way as above.

As a result of intensive study of the problems caused by oxygen in silicon vapor deposition, the inventors have finally found a solution to the problem. The background to this will be explained below.

In the above-mentioned a-8t vapor deposition method, the vapor deposition is performed by setting the vacuum level not so high by using a diffusion pump or the like to pull the inside of the Pelger equipped with a discharge tube for activating hydrogen gas. Even if this is done, the hydrogen pressure inside the Pelger (including activated hydrogen gas) will be I x 10 = Tor
If r@degree, oxygen gas pressure (residual gas) is 10=To
Even if the rr@ degree is high, almost no oxygen is detected in the deposited film in the analysis results such as infrared absorption spectrum after film formation.
The film quality was also found to be good. In addition, even if there is even more oxygen as a residual gas at 10 = 11 degrees, if the above hydrogen pressure is IO-' Torr, almost no oxygen will be detected in the film, and the film quality will deteriorate. was also found to be good. In these cases, it depends on the relationship between oxygen pressure and hydrogen pressure, the degree of activation or ionization of hydrogen, the voltage applied to the substrate, the amount of active or ionized hydrogen that is directly emitted to the substrate, and the amount of active or ionized hydrogen that collides with the substrate. In general, it has been confirmed that the greater the degree of hydrogen activity or ionization, the higher the substrate voltage, and the more effectively the discharge tube is directed toward the substrate, the greater the effect of preventing the effects of oxygen mentioned above. Ta.

Therefore, since an ultra-high vacuum device is used, the degree of vacuum inside the Pel jar is not so high (usually around 10-' Torr) in a vapor deposition device that uses a normal diffusion pump (or rotary pump). It was discovered for the first time by the present inventors that a high-quality a-8i film can be formed by effectively preventing the influence of residual oxygen.

This brings great advantages in terms of productivity and cost, and is of great practical significance. Moreover, the above MB
At the same time, it was confirmed that the harmful effects of hydrocarbons, which have been a problem with E, were not detected.

The present inventor has devised the present invention based on this recognition. That is, in the vapor deposition method according to the present invention, when heating and vaporizing an evaporation source such as silicon, the oxygen pressure in the vacuum chamber is reduced to 10 - 'It is characterized by being less than Torr.

Therefore, in the vapor deposition method according to the present invention, by actively making a reducing gas exist, even if the inside of the vacuum chamber is not made to be in a high vacuum as described above and the oxygen pressure is increased to approximately 1 O-1 Torr, the influence of the oxygen can be avoided. can be virtually eliminated. This is fundamentally different from conventional vacuum evaporation methods, which aim to reduce oxygen pressure as much as possible.
It offers significant advantages in terms of productivity, operability, and cost, and is also revolutionary in that it can be operated under normal vacuum conditions and provides high-quality deposited films at a high yield.

The above remarkable effects brought about by the vapor deposition method according to the present invention are as follows:
It is thought to be based on the following phenomena.

First of all, the main reason why oxygen enters a deposited film such as silicon is the collision of oxygen atoms with the deposition surface, but this phenomenon decreases as the partial pressure of a reducing gas such as hydrogen increases. it is conceivable that. However, the range of oxygen (
This is because the mean freedom 1i) is reduced, and the number of collisions of oxygen with the deposition surface is reduced.

Next, it is thought that this is because, due to the action of the above-mentioned reducing gas, even if the vapor deposition surface is oxidized with oxygen, it is reduced again, and oxidation is effectively prevented.

This effect becomes even greater when the reducing gas is activated or ionized. When activated or ionized hydrogen is used as a reducing gas, it is possible that when this hydrogen collides with oxygen in space, it becomes a stable compound H,0 (this can be confirmed with a mass spectrometer). .

The action of oxygen can be effectively blocked by the action of the reducing gas described above, but generally when the reducing gas pressure is lowered, the oxygen pressure is also lowered and it is necessary to significantly reduce the amount of oxygen in the vacuum chamber. Usually reducing gas, especially hydrogen gas pressure is 10-7
~10-”Torr is best, and 10-s~10-
' Torr is preferable.

In addition, the reducing gas is activated or
, it is effective to ionize it into one ion and send it into a vacuum chamber. In this case, supplying active or ionized hydrogen can prevent the above-mentioned action of oxygen and fill the dangling bonds in the deposited silicon with hydrogen atoms.
A L film can be formed. It is desirable to suppress oxygen to an undetectable amount within the discharge tube. In other words, if oxygen is present in the discharge area due to a leak in the vacuum chamber or insufficient purity of raw hydrogen, this oxygen will be activated by the discharge,
This is because activated oxygen very easily reacts with silicon, making it impossible to form a high-quality a-8i film.

The substrate for vapor deposition is usually maintained at a temperature of room temperature to 500° C. to facilitate deposition of the vapor deposition material.

In addition, the base has a DC voltage of θ to -6KV or 0 to 6KV.
An alternating current voltage of
It is desirable to aspirate and promote vapor deposition.

In addition, it is preferable to evaporate at a rate of 2 to 50X/see of the evaporated substance rays from the evaporation source.For this purpose, a film thickness gauge is placed in the vacuum chamber, and the temperature of the heater etc. is controlled based on the detected value. It is better. A dopant evaporation source may be provided in parallel with the evaporation source, or an introduction pipe for dopant supply gas may be provided in the vacuum chamber. By incorporating this dopant into a deposited film, for example a silicon film, its conductivity or valence electrons can be controlled.

Hereinafter, the present invention will be explained in more detail based on the embodiments shown in FIGS. 1 and 2.

FIG. 1 shows an example of a vacuum deposition apparatus that can be used to carry out the method of the invention. This apparatus includes a vacuum chamber (ie, a Pelger) 3 containing a substrate 1 to be evaporated and a silicon evaporation source 2. The substrate 1 is heated to, for example, 350 to 450° C. by a heater 4, while a DC bias voltage of 0 to −6 KV is applied by a DC power source 5.

In the figure, 6 is an introduction tube for introducing active hydrogen and/or hydrogen ions, 7 is a discharge tube provided in the introduction tube 6 to activate or ionize hydrogen gas 9, and 8 is an exhaust tube. and connected to a vacuum pump (not shown).

By using this device, for example 10-4'l'
At the same time, silicon evaporated from the evaporation source 2 is deposited as a-8i on the substrate 1 under a vacuum of the order of orr,
Hydrogen atoms are bonded to the deposited a-8t by suctioning the active gas from the introduction tube 6 onto the substrate 1 at a negative potential, so that the above-mentioned dangling bonds are filled with hydrogen atoms. The obtained hydrogen-containing a-8i has sufficient dark resistance and photosensitivity, and has a uniform film quality with little variation.

Using this vacuum evaporation apparatus, an a-8i film was formed under the following conditions.

Condition I Condition ■ Hydrogen pressure 10-' Torr 10-' To
rr Substrate voltage -4KV -4KV Substrate temperature
350℃ 350℃ deposition rate lO or/se
a 10/sea As a result, as follows, condition I,
A-81 films (hydrogen-containing) having different film properties depending on If were obtained.

conditions! Condition ■ (Ω-aIm) ” According to this result, when the hydrogen pressure is 10-' Torr, the oxygen pressure is set to 1O-6 Torr as in the method of the present invention.
If it is set below (ulO'Torr in the above), σD can be made thicker and the ratio to ΔσP can be made to be three orders of magnitude or more. Although this ratio usually needs to be one order of magnitude or more, the results are sufficiently satisfactory. On the other hand, if the oxygen pressure is IF' T
When orr is 9, the amount of oxygen is too large, and σD and σD
/ΔσP both deteriorate, resulting in a film that cannot be put to practical use.

(dashed line), when the oxygen pressure is changed
(Characteristics of the film obtained when It can be seen that the dangling bonds of a-81 decrease and σD decreases, and Δσpa tends not to increase.Therefore, depending on the oxygen partial pressure, there is a peak or a sufficient value of σD. However, there is a region where a sufficient ratio with 8σP can be obtained.
If the oxygen pressure is set to approximately 10-' Torr or less when r, the ratio to ΔσP can be maintained by one order of magnitude or more while maintaining σD high, which is an appropriate condition. Also, increase the hydrogen pressure to 10-
When the oxygen pressure is lowered to 10 Torr, the change curve for 10-' Torr tends to shift somewhat to the left in the drawing, but in this case, if the oxygen pressure is set to 10=Torr or less, both σD1ΔσP are sufficient. be able to.

Therefore, from this result, the practical hydrogen pressure range (10'
~10-' Torr), the sensory pressure is set to 10-' T
It is understood that the oxygen pressure can be increased to about 1.0 orr, and that if this oxygen pressure is selected depending on the hydrogen pressure, a satisfactory condition can be achieved.

In addition, in the above device, since the hydrogen gas discharge tube 7 is placed outside the Pel jar 3, there is much less contamination than when it is placed inside the Pel jar 3, and the heat inside the Pel jar during operation is reduced. The electrodes and constituent materials of the discharge tube will not be damaged by water or gas.

Therefore, the degree of freedom in selecting the material of the discharge tube is increased, and the structure and arrangement thereof can be arbitrarily determined. Also,
The structure of the cooling water pipe (not shown) inside the discharge tube is easy to design, its cooling efficiency is good, and the discharge tube itself can be easily replaced outside the Pelger. However, it goes without saying that the discharge tube may be provided within the Pelger in terms of feeding the active gas.

Although the present invention has been illustrated above, the above-mentioned example can be further modified based on the technical idea of the present invention.

[Brief explanation of the drawing]

The drawings illustrate the present invention, and FIG. 1 is a schematic cross-sectional view of an example of a vacuum evaporation apparatus, and FIG. 2 is a graph showing changes in film characteristics depending on oxygen pressure as a function of hydrogen pressure. In addition, in the symbols used in the drawings, 1...
・・・・・・・・・・・・・・・Board 2・・・・・・・・・
・・・・・・・・・・Silicon 6・・・・・・・・・・
......Hydrogen introduction pipe 7...
・・・・・・It is a discharge tube. Agent Patent Attorney Hiroshi Kakiita

Claims (1)

[Claims] 1. When heating and evaporating an evaporation source in a vacuum chamber and depositing it on a substrate, the oxygen pressure in the vacuum chamber is approximately reduced with a reducing gas present in the vacuum chamber. 10-'Torr
A vapor deposition method characterized by the following: 2. The method according to claim 1, in which the oxygen gas pressure is also lowered as the reducing gas pressure is lowered. 3. The method described in claim 1 or claim 2, characterized in that hydrogen gas is present in the vacuum chamber at a pressure of 10-' to 1 G-'' Torr. 4. The hydrogen gas pressure is set to 10-1 to 1 G-'' Torr. ' Torr, the method described in claim 3. 5. Any one of claims 1 to 4, in which the reducing gas is activated or ionized by a discharge tube. 6. The method described in claim 5, in which the discharge tube is placed outside the vacuum chamber. 7. The method described in claim 5, in which the oxygen in the discharge tube is suppressed to an undetectable minute amount. 8. The method described in any one of claims 1 to 7, wherein the substrate is maintained at a temperature of room temperature to 500°C. 9. Direct current voltage of 0 to -6KV or F1.0 to the base.
Claims 1-- characterized by an AC voltage of 6KV.
The method described in any one of Section 8. 10. The evaporation rate of the vapor deposition material from the evaporation source is 2 to 50λ/
s@a, the method according to any one of claims 1 to 9. 11. The method according to any one of claims 1 to 10, which uses silicon as an evaporation source and features amorphous silicon on the substrate.