JPS5835927B2 - Manufacturing method of amorphous silicon - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing amorphous silicon used in solar cells, electrophotographic photoreceptors, and the like.

In recent years, amorphous silicon obtained by vapor phase growth has attracted attention because it is extremely useful in solar cells and other applications.

As a conventional method for manufacturing amorphous silicon, for example, Japanese Patent Application No. 54-89440 (
For example, a vapor deposition method based on a direct current ion brating method as disclosed in Japanese Patent Application Laid-Open No. 56-13776) can be mentioned.

This method has a silicon evaporation source and a substrate in a vacuum chamber, and evaporates silicon from the evaporation source and activates the silicon vapor by irradiating the vapor with thermionic electrons emitted from a tungsten heater, for example. ionize the
By causing the generated silicon ions to collide with the substrate to which a negative DC voltage has been applied, amorphous silicon is formed on the surface of the substrate.

Note that at this time, hydrogen gas or the like can be added to make the silicon film contain hydrogen gas or the like.

However, in such a DC ion blating method, tungsten evaporates from a tungsten heater for emitting thermoelectrons, and becomes mixed into the formed amorphous silicon as an undesirable impurity, and also causes the formation of silicon ions. In order to perform this constantly, the evaporation rate from the silicon evaporation source cannot be kept below a certain level, and therefore it may not be possible to form amorphous silicon with the desired performance.

Amorphous silicon formed by the method described above has many so-called dangling bonds due to its amorphous, irregular atomic arrangement structure.

This dangling bond is a state in which electrons that should form a bond do not form a bond and remain as they are, or a state in which a covalent bond remains broken, and as a result, the effects of silicon as a semiconductor material, such as photoelectric phenomena, are not sufficiently achieved. There are drawbacks that cannot be exploited.

A method is also known in which a portion of silane (SiH+) gas is decomposed by glow discharge to form amorphous silicon using silicon ions, and at the same time, active hydrogen atoms generated are introduced into the amorphous silicon to seal the dangling bonds. However, in this method, it is impossible to arbitrarily change the ratio of hydrogen atoms to silicon, and therefore it is difficult to obtain amorphous silicon having desired characteristics.

In view of the above-mentioned circumstances, the present invention provides a method for easily manufacturing amorphous silicon in which the dangling bonds are sealed, and therefore has excellent performance as a semiconductor material, and also has desired properties and functions. The purpose is to

An embodiment of the present invention will be described below with reference to the drawings.

In the present invention, as shown in FIG. For example, 10-6 to 1O-2T
The ionized hydrogen obtained by discharging hydrogen gas in the hydrogen discharge tube 4 is transferred to the silicon evaporator disposed inside the Pel jar 1 through a conduit 5 extending into the Pel jar 1, for example. In this state, the silicon evaporation source 6 is heated to evaporate the silicon, and the ionization electrode 7 located near the silicon evaporation source 6 is powered by a direct current power source 8. By applying the voltage, the silicon vapor is activated to ionize, and the high frequency voltage causes a glow discharge in the Pel jar 1 to ionize the silicon vapor and hydrogen. The installed substrate 9 is heated in advance by the heater 10 and a negative voltage is applied to the substrate 9 by the DC power supply 11, thereby forming amorphous silicon on the surface of the substrate 9.

12 is a shutter.

In the above, in order to heat the silicon evaporation source 6, any heating means such as resistance heating, electron gun heating, induction heating, etc. can be used, and the voltage applied to the ionization electrode 7 is usually +50V to 200V. The heating temperature of the substrate 9 can be any value from room temperature to about 500°C, but is generally set within the range of 100 to 300°C. The voltage is usually set within the range of 0 to -3V.

FIG. 2 shows the hydrogen discharge tube 4 in detail.

This hydrogen discharge tube 4 includes a glass hydrogen supply tube 13 through which hydrogen gas flows, and a discharge electrode 1 provided inside this hydrogen supply tube 13.
4.15 and a cooling jacket tube 16 provided on the outer periphery of the hydrogen supply tube 13 in the discharge region between these discharge electrodes 14.15, and the hydrogen gas pressure in the discharge region is 1.
A voltage from the power supply 17 causes a discharge to occur between the discharge electrodes 14 and 15 while the temperature is maintained below O-2 Torr, and as a result, a portion of the hydrogen gas is ionized to produce ionized hydrogen, which is not ionized. The hydrogen gas is introduced together with hydrogen gas through a conduit 5 that is continuous with the hydrogen supply pipe 13.

Cooling water is then allowed to flow through the cooling jacket pipe 16.
Overheating is prevented.

Note that the distance between the discharge electrodes 14 and 15 is usually 10 to 15, and the applied voltage is 500 to 5 oov.

Furthermore, even if a voltage is applied with a polarity opposite to that shown in FIG. 2, the purpose will be sufficiently achieved.

Furthermore, in order to discharge hydrogen gas, a high frequency power source can be used instead of a DC power source, and in this case, an improvement in discharge efficiency is expected. Since it is sufficient to provide a high-frequency coil on the outer periphery of the discharge electrodes 14 and 15, it is possible to avoid introduction of the electrode material of the discharge electrodes 14 and 15 as impurities.

The hydrogen gas supplied to the hydrogen discharge tube 4 may be obtained from a hydrogen gas cylinder as is, but it is necessary to avoid undesirable impurities from being mixed into the amorphous silicon formed on the substrate 9. Therefore, it is preferable to supply high-purity hydrogen gas to the hydrogen discharge tube 4.

Although various methods are known for obtaining high-purity hydrogen gas, it is convenient to use a hydrogen purifier as shown in FIG. 3, for example.

This hydrogen purifier consists of an inner tube 21 made of palladium, an outer tube 22 surrounding the inner tube 21, and a heater 23 that heats the inner tube 21. Heater 2 while letting gas flow through
When the inner tube 21 is heated by 3, the hydrogen gas flows through the inner tube 2.
As a result, high-purity hydrogen gas is obtained from a discharge tube 24 made of a glass tube connected to the inner tube 21.

Since the present invention is as described above, silicon evaporated from the silicon evaporation source 6 and introduced ionized hydrogen or with the help of electrons and ultraviolet light are activated by the ionization electrode 7 and become easily ionized, and ionized by glow discharge. The silicon ions generated as a result are heated to a substrate 9.
The amorphous silicon is deflected by the negative voltage and hits the substrate 9, loses charge and adheres to the substrate 9, forming amorphous silicon.

In the space where the silicon is activated or further ionized, ionized hydrogen from the hydrogen discharge tube 4 exists, or ionized hydrogen generated by ionizing hydrogen gas introduced with ionized hydrogen by glow discharge. Because of the existence of these ionized hydrogens, these ionized hydrogens collide with the silicon ions onto the substrate 9, and as a result, the amorphous silicon formed on the surface of the substrate 9 has its dangling bonds blocked by hydrogen atoms. .

According to the present invention, since the ionized hydrogen generated by the hydrogen discharge tube 4 is introduced into the vicinity of the silicon evaporation source 6, in combination with the action of the ionization electrode 7, the silicon vapor is activated and easily ionized. As a result, a discharge can be easily generated and the state of the discharge can be made stable.

Furthermore, in the hydrogen discharge tube 4, a considerable amount of ultraviolet rays that have an ionizing effect on silicon are emitted by discharging hydrogen gas, and the silicon vapor is irradiated with ionized hydrogen, so that the ionization of silicon is further promoted by this ultraviolet ray. I can do it.

Further, in the present invention, as described above, hydrogen gas is also ionized by the glow discharge inside the Pelger 1, so the ionized hydrogen generated as a result is introduced into the amorphous silicon together with the ionized hydrogen generated in the hydrogen discharge tube 4. , Therefore, high hydrogen gas usage efficiency can be obtained, and
The amount of ionized hydrogen introduced through the conduit 5 and the amount of hydrogen gas introduced together with it can be controlled by, for example, changing the amount of hydrogen gas supplied to the hydrogen discharge tube 4, the discharge voltage in the hydrogen discharge tube 4, etc. Therefore, it is possible to control the hydrogen introduction rate in the amorphous silicon formed on the substrate 9, and it is possible to obtain amorphous silicon having desired performance.

Ionized hydrogen loses its ionized state when it collides with metal, but the hydrogen supply tube 13 and the conduit 5 following it in the hydrogen discharge tube 4 are made of glass, and the ionized hydrogen is directly brought into the vicinity of the silicon evaporation source 6. By supplying the hydrogen, the generated ionized hydrogen can be used without losing its activity, and as a result, the Pel jar 1 can be made of metal, for example.

This is because when ionized hydrogen is transferred through a glass tube, the initial ionized hydrogen adheres to the inner surface of the tube, but subsequent ionized hydrogen is prevented from adhering to the inner surface of the tube by the already attached ionized hydrogen. This is because it can be transported over a sufficiently long distance.

Further, in the present invention, a doping agent evaporation source is provided in the Pelger 1, and phosphorus, arsenic, boron, antimony, etc. are evaporated simultaneously with the evaporation of silicon in the silicon evaporation source 6, so that these are contained as impurities, and therefore n Amorphous silicon can be produced as a type or p-type semiconductor.

As the doping agent, it is also possible to use compounds such as phosphine, arsine, diborane, etc. In this case, it is sufficient to simply allow these gases to exist in the Pelger 1.

Further, in the present invention, since undesirable impurity vapor is not generated unlike the direct current ion blating method which uses a tungsten heater for generating thermionic electrons, amorphous silicon having the desired components can be obtained.

In addition, since a large amount of ionized hydrogen and electrons, or even ultraviolet light, which is effective in glow-discharging the silicon vapor from the silicon evaporation source 6 using the ionization electrode I, is supplied, the minimum required evaporation rate of the silicon evaporation source 6 is can be significantly relaxed, and therefore amorphous silicon with desired performance can be obtained by arbitrarily controlling the evaporation rate.

Furthermore, as shown in FIG. 1, by providing a butterfly valve 2 and other pressure control mechanisms in the exhaust path 3 for exhausting the inside of the Pel Jar 1, the hydrogen pressure including ionized hydrogen in the Pel Jar 1 can be kept below 10" Torr. can be controlled to any size, and from this point of view as well, the hydrogen introduction rate can be controlled to obtain amorphous silicon with desired performance.

It is preferable to use the butterfly valve 2 as the air pressure control mechanism because the air pressure can be easily controlled over a wide range of 10-6 to 10-2 Torr.

Furthermore, in addition to the above structure, a second hydrogen discharge tube is installed on the substrate 9.
By providing it near the surface, it becomes possible to further dramatically increase the amount of hydrogen in the formed film, and as a result, the amount of silicon evaporated, that is, the manufacturing speed can be improved.

In this case as well, the second hydrogen discharge tube may have the structure shown in FIG. 2, and a sufficient effect can be obtained even if the power source is connected to the polarity opposite to that shown in FIG.

As described above, according to the method of the present invention, the dangling bonds are blocked by hydrogen atoms by an extremely simple method, and therefore, it has excellent performance as a semiconductor material, and also includes conditions that can be arbitrarily and accurately controlled. Amorphous silicon having desired performance can be easily produced.

[Brief explanation of the drawing]

FIG. 1 is a configuration explanatory diagram showing an example of the apparatus used in the method for manufacturing amorphous silicon of the present invention, FIG. 2 is an explanatory cross-sectional view of a hydrogen discharge tube, and FIG. 3 is an explanatory cross-sectional view showing an example of a hydrogen purifier. It is a diagram. 1...Pelger, 2...Butterfly valve, 3.
... Exhaust path, 4... Hydrogen discharge tube, 5... Conduit, 6.
...Silicon evaporation source, 7...Ionization electrode, 8,11
...DC power supply, 9...board, 10...heater
12...Shutter 13...Hydrogen supply pipe, 14.1
5... Discharge electrode, 16... Cooling mantle, 17...
・Power supply, 21... Inner tube, 22... Outer tube, 23...
Heater 24...Discharge pipe.

Claims (1)

[Claims] 1. Ionized hydrogen generated by electric discharge is introduced into the vicinity of a silicon evaporation source disposed in a vacuum chamber, and silicon is evaporated from the silicon evaporation source in an atmosphere where this ionized hydrogen exists. At least this silicon vapor is caused to glow discharge by the action of an ionizing electrode and the aid of a hydrogen discharge tube, and a negative DC voltage is applied to the substrate disposed in the vacuum chamber, thereby introducing hydrogen atoms onto the surface of the substrate. 1. A method for producing amorphous silicon, characterized by forming amorphous silicon. 2. Claims characterized in that the doping agent is evaporated from a doping agent evaporation source disposed in the vacuum chamber at the same time as the silicon is evaporated, thereby forming amorphous silicon containing the doping agent. 1st
A method for producing amorphous silicon as described in . 3. Claim 1, characterized in that the inside of the vacuum chamber is maintained at a controlled vacuum level of 1 O-2 Torr or less.
The method for producing amorphous silicon according to item 1 or 2.