JPH0351089B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a silicon semiconductor obtained by doping indium at the same time when a silicon tetrafluoride-containing raw material gas is decomposed under glow discharge to produce a silicon semiconductor on a substrate. The present invention relates to compensated intrinsic (hereinafter referred to as i-type) silicon semiconductors, p-type silicon semiconductors, and methods of manufacturing these semiconductors.

Silicon semiconductors have been well known for quite some time, but in recent years, amorphous silicon semiconductors have been found to be used in solar cell elements, electrophotographic photoreceptors, optical sensors, thin film transistors, and various other applications. Development and research are also active. As an amorphous silicon semiconductor, the dark electric conductivity is 1× depending on the type of element doped with it.
N-type and p-type semiconductors with a resistance of about 10 ^-9 Ω ^-1 cm ^-1 or higher are well known, but in addition to these, the development of i-type amorphous silicon semiconductors, which are particularly used in the production of solar cells, is underway. It is progressing.

An i-type amorphous silicon semiconductor has a dark electrical conductivity of about 1×10 ^-10 to ^{10 -12} Ω ^-1 cm ^-1 , and a weak n-type amorphous silicon semiconductor usually has a valence of 3. It is made by doping a metal, for example boron. At that time, p-type amorphous silicon semiconductors are also produced by increasing the amount of boron doped.

Since amorphous silicon semiconductors are often used in the form of thin films, they are generally produced by a method of decomposing silicon-containing raw material gas and chemical vapor deposition on a substrate (hereinafter referred to as CVD method).
However, the properties, performance, etc. of the amorphous silicon semiconductors obtained vary depending on the type of gas used as the silicon-containing raw material and the manufacturing method, and there are various proposals regarding amorphous silicon semiconductors and their manufacturing methods. Both are still insufficient. Relatively preferable materials are those obtained from silane-based gases such as silane and disilane by plasma CVD.
The amorphous silicon semiconductor obtained by this method is of weak n-type and contains a small amount of hydrogen atoms bonded to silicon atoms. This hydrogen atom acts as a dangling bond terminator.
terminator).

The amorphous silicon semiconductor obtained from the silane gas by plasma CVD can be easily doped with boron, for example, by mixing borane with the silane gas and performing the above method. I-type and p-type semiconductors can be easily obtained depending on the doping amount. However, the amorphous silicon semiconductor obtained from the above-mentioned silane gas by the plasma CVD method may not have sufficient semiconductor properties such as photovoltaic power and UV deterioration resistance for some applications, such as solar cells. , its improvement is desired.

Plasma CVD similar to the above from chlorosilane
Although an amorphous silicon semiconductor can be obtained by this method, it also does not have sufficient semiconductor properties. On the other hand, silicon tetrafluoride is difficult to form a vapor deposited film using plasma CVD, but silicon tetrafluoride-containing gas, such as a mixed gas of silicon tetrafluoride and silane, can be used for CVD under glow discharge.
The amorphous semiconductor obtained by this method is also a weak n-type semiconductor containing fluorine atoms and hydrogen atoms as dangling bond terminators, and is preferable because it has better semiconductor properties than those made from the above-mentioned silane-based or chlorosilane gas. be. However, even if an amorphous silicon semiconductor is produced by a plasma CVD method by mixing diborane, boron fluoride, etc. with a silicon tetrafluoride-containing gas, boron is not effectively doped, and a high-quality i-type or p-type semiconductor cannot be obtained. do not have.

The present inventors came up with the idea of doping an element other than boron into an amorphous silicon semiconductor obtained by plasma CVD from a silicon tetrafluoride-containing gas,
We focused on indium as a doping element, but learned that indium hydride does not yet exist.As a result of detailed research, we used metallic indium as the cathode electrode of the glow discharge described above, and created a mixed gas of silicon tetrafluoride and silane gas. CVD under glow discharge using argon gas mixed with
When this process is performed, argon gas acts to cause sputtering of metallic indium, and indium is doped into the silicon semiconductor. First, an i-type semiconductor is obtained, and when the amount of doping is further increased, a p-type semiconductor is obtained. I discovered that.

The object of the present invention is to provide a novel silicon semiconductor with excellent semiconductor properties, ultraviolet deterioration resistance, etc., especially its i.
An object of the present invention is to provide a method for manufacturing semiconductors of type and p-type.

In the method for manufacturing a silicon semiconductor of the present invention, a raw material gas containing silicon tetrafluoride and a sputtering gas are supplied into a reaction chamber in which a cathode made of metal indium and a substrate electrode are placed opposite each other, and in the presence of both gases, the cathode and substrate electrode are placed opposite each other. It is characterized by causing glow discharge between the electrode and the electrode.

The silicon tetrafluoride-containing raw material gas used in the production method of the present invention is a mixture of silicon tetrafluoride gas and other gases, and the other gases include hydrogen, monosilane (SiH ₄ ), disilane (Si ₂ H ₆ ), silane-based gases such as higher-order silane (SinH ₂ n ₊₂ ), or mixtures thereof. These raw material gases are those that do not contain impurity components. The raw material gas used in the production method of the present invention always contains silicon tetrafluoride, so that the silicon semiconductor produced is
It contains a trace amount of fluorine atoms bonded to silicon atoms as a dangling bond terminator, giving it excellent semiconductor properties. Although there are no restrictions on the composition of the raw material gas, a mixed gas of silane and silicon tetrafluoride containing about 40 to 60% by volume of silicon tetrafluoride is preferred. The sputtering gas used in the production method of the present invention has the effect of knocking out the metallic indium of the cathode electrode as particles in a form suitable for doping when glow discharge is caused in the above-mentioned raw material gas, and usually performs the preferable doping. In order to achieve this, it is necessary to decompose the raw material gas by glow discharge and at the same time cause sputtering to occur in metallic indium, and the reaction chamber in which the glow discharge is caused must be designed so that the raw material gas and the sputtering gas coexist. Both gases are supplied. Examples of sputtering gases include argon, neon, and the like. When glow discharge occurs, the ratio of the coexisting sputtering gas to the raw material gas affects the amount of indium doped in the silicon semiconductor that is produced; if the above ratio is small, the amount of doping is small, and therefore the semiconductor that is produced is i-type. Therefore, when the above ratio is large, the amount of doping becomes large, and therefore the generated semiconductor becomes p-type. Normally, in order to obtain preferred i-type and p-type semiconductors, the ratio of the sputtering gas to the raw material gas is preferably about 2 to 20 in terms of volume ratio for argon, for example.

As mentioned above, it has been conventional to obtain an amorphous silicon semiconductor from a silane-based gas or a mixture of silane-based gas and diborane gas by the plasma CVD method, and the equipment used for this method is already known.
This device usually includes a reaction chamber that is equipped with an inlet for raw material gas and an outlet for decomposed gas, and can be shut off from outside air.
A cathode for causing glow discharge in the chamber, a substrate for depositing silicon at a position facing the cathode, or a substrate electrode for mounting and fixing the substrate, and a device for heating the substrate. It is equipped with a device for applying a direct current or high frequency high electric field between electrodes, a vacuum pump to reduce the pressure inside the reaction chamber, and elements for connecting, operating, and normal operation of these devices and elements. . An apparatus for carrying out the method of the invention can be easily obtained by slightly modifying the conventional apparatus described above. That is, it can be obtained by replacing the conventional cathode electrode with one made of metal indium and, if necessary, providing a sputtering gas inlet in the reaction chamber. Metallic indium with a purity of about 99.99% is sufficient for use as an electrode. Therefore, the feature of the novel silicon semiconductor manufacturing method of the present invention is that the silicon tetrafluoride-containing raw material gas and the sputtering gas are supplied to a reaction chamber in which a cathode made of metal indium and a substrate electrode are placed opposite each other. The purpose is to cause a glow discharge between the cathode and the substrate electrode in the presence of the cathode.

In the manufacturing method of the present invention, the metal indium of the cathode not only acts as an electrode when glow discharge is performed in the presence of a silicon tetrafluoride-containing raw material gas and a sputtering gas, but also acts as an electrode for the silicon produced by decomposition. The mixture acts to release indium from the electrode in a form that can be doped into the deposited silicon. Therefore, as a certain discharge continues, a silicon layer uniformly doped with indium is formed on the substrate. The substrate used in the manufacturing method of the present invention may be any ordinary substrate, and examples of the material include glass, stainless steel, and heat-resistant plastic. The temperature of the substrate is usually 400°C or less, preferably about 200 to 350°C. The reaction chamber used in the manufacturing method of the present invention may also be of a conventional type, and its material may be stainless steel, quartz glass, or other material that does not cause contamination to the produced semiconductor. When the substrate is an electrical insulator, glow discharge is performed by making the base plate on which it is placed an electrical conductor. The electric field applied for glow discharge is usually on the order of several hundred volts to a thousand volts, and the power source may be either direct current or high frequency alternating current. Typically, a glow discharge is approximately
It is carried out under a pressure based on a feed gas of 10 to 100 mTorr. Continue the glow discharge,
In order to continuously increase the thickness of the deposited silicon layer, the raw material gas and the sputtering gas are continuously supplied into the reaction chamber, and the mixture of decomposed gas and undecomposed feed gas produced by glow discharge is continuously supplied. The reaction chamber is then evacuated from the reaction chamber, during which time a steady state is maintained. Even if metallic indium is used for the cathode, in glow discharge in the presence of only source gas, indium is not doped into the deposited silicon semiconductor, and neither i-type nor p-type semiconductors can be obtained. In the presence of sputtering gas, the amount of indium doped is determined by the applied electric field for glow discharge, in addition to the sputtering gas concentration as described above.
Since it is affected by the gas pressure supplied in the reaction chamber, the substrate temperature, etc., it can be adjusted by appropriately combining these conditions.

Thus, according to the manufacturing method of the present invention, an i-type or p-type silicon semiconductor can be produced on a substrate by adjusting the amount of indium doped. about
Thin films are obtained at speeds of 50 to 1200 Å/min. The semiconductor obtained by the manufacturing method of the present invention can be determined by measuring dark electrical conductivity without the need for chemical analysis.
It is possible to directly determine whether the semiconductor is i-type or p-type, which corresponds to the amount of indium doped. Also, n
Whether the material belongs to type or p-type can be determined by measuring thermoelectromotive force using a conventional method. The semiconductor obtained by the manufacturing method of the present invention can be either amorphous or microcrystalline depending on the manufacturing conditions,
Both are useful. In addition, the obtained silicon semiconductor usually contains fluorine atoms and hydrogen atoms bonded to silicon atoms as dangling bond terminators, and the amount thereof is preferably 0.2 to 2 atomic percent fluorine and 5 to 20 atomic percent hydrogen. . Although the silicon semiconductor of the present invention contains fluorine atoms bonded to silicon atoms as dangling bond terminators, it is doped with indium and exhibits excellent performance.

Examples will be described below following comparative examples, but the technical scope of the present invention is not limited thereto.

Comparative Example 1 A Corning 7059 glass plate was placed on a stainless steel base in a stainless steel reaction chamber that had a raw material gas inlet, an argon gas inlet, and a cracked gas exhaust port, and was equipped with a cathode electrode made of metallic indium. The reaction chamber was evacuated using a high-performance vacuum pump and heated to a substrate temperature of 300°C. Next, while supplying monosilane gas from the raw material gas inlet at a rate of 0.5 ml/min (converted to standard conditions) and silicon tetrafluoride gas at a rate of 0.5 ml/min,
Adjust the opening of the decomposed gas exhaust valve connected to the vacuum pump, apply an electric field of 600 volts, output 54 watts,
The reaction chamber was heated to 20 mTorr (30 mTorr) while performing a high-frequency glow discharge at a frequency of 13.56 MHz.
A silicon thin film was formed on the substrate by maintaining the temperature for 1 minute.

Next, aluminum was deposited on the silicon thin film by vacuum evaporation to form a gap-type aluminum electrode, and the dark electrical conductivity of the silicon thin film was measured using a Kesley electrometer and found to be 1.50×10 ^-9 It was Ω ^-1・cm ^-1 . Furthermore, when the thermoelectromotive force of the thin film was measured using the electrometer, positive power was generated on the heating electrode side, indicating that it was a weak n-type semiconductor.

Comparative Example 2 A silicon thin film was formed in the same manner as in Comparative Example 1 above, except that argon gas was further supplied as a sputtering gas into the reaction chamber at a rate of 1 ml/min in terms of standard conditions. When the conductivity was measured, it was found to be 3.6×10 ⁻⁹ Ω ⁻¹ ·cm ⁻¹ , and the thermoelectromotive force measurement results also showed that it was a weak n-type semiconductor film.

Example 1 The same procedure as in Comparative Example 2 was carried out except that the argon gas supply amount was changed to 6 ml/min in terms of standard conditions.
A silicon thin film was formed, and its dark electrical conductivity was measured to be 3.3×10 ⁻¹² Ω ⁻¹ ·cm ⁻¹ , confirming that an i-type semiconductor was obtained.

Example 2 A silicon thin film was formed in the same manner as in Comparative Example 2 except that the argon gas supply rate was changed to 10 ml/min in standard conditions, and its dark electrical conductivity was measured to be 6.6×10 ^-11 Ω. ^-1 ·cm ^-1 , indicating that this thin film was also an i-type semiconductor.

Example 3 A silicon thin film was formed in the same manner as in Comparative Example 2, except that the argon gas supply rate was changed to 15 ml/min in standard conditions, and its dark electrical conductivity was measured to be 3.5 × 10 ^-9 Ω. ^-1 ·cm ^-1 , and the thermoelectromotive force measurement results confirmed that this film was a p-type semiconductor.

The results of Comparative Example 2 and Examples 1 to 3 above show that as the supply ratio of argon gas to the raw material gas increases, the weak n-type semiconductor changes to an i-type semiconductor and then to a p-type semiconductor.

The novel semiconductor of the present invention has excellent semiconductor characteristics and UV deterioration resistance because it contains fluorine atoms bonded to silicon atoms as dangling bond terminators derived from its raw material gas, and when used, it has excellent performance. A solar cell can be obtained.

Solar cells are p-type, i-type, and n-type with a thickness of about 1μ.
is obtained by bonding semiconductor films in that order. Therefore, by the method of the present invention, it is possible to first form a p-type semiconductor film on a substrate, and then to form an i-type semiconductor thereon simply by changing the manufacturing conditions, and to form p-type and i-type semiconductors. A bonded semiconductor film is obtained. Further, by applying a plasma CVD method using an n-type semiconductor generation raw material gas, for example, a gas in which phosphine is mixed with the raw material gas, an n-type semiconductor film can be generated, and p-type, i-type and A device in which n-type semiconductor films are bonded in that order, that is, a solar cell can be easily obtained.

Claims (1)

[Claims] 1 A raw material gas containing silicon tetrafluoride and a sputtering gas are supplied into a reaction chamber in which a cathode made of metallic indium and a substrate electrode are placed opposite each other, and a glow discharge is generated between the cathode and the substrate electrode in the presence of both gases. 1. A method for producing a silicon semiconductor doped with indium and containing fluorine atoms bonded to silicon atoms.