JPS61283112A - Forming method for amorphous semiconductor film - Google Patents

Abstract

PURPOSE:To reduce the production of powder and to enable the accumulation of a uniform film even in a large area by executing in gas pressure which is specific for ion average free step in a vessel in the width of a sheath when radical-forming a raw gas to accumulate it on a substrate. CONSTITUTION:Gas containing hydrogen as exciting gas is supplied from an exciting gas supply port 13 to an ion source. Magnets 15 are disposed on the back and side surfaces of a plasma source 14 to form a cusp magnetic field 15a. An AC voltage is applied between a filament 16 and anode (wall) 17 to discharge, thereby generating a plasma. The plasma passes through a porous grid 18 to a reaction chamber 20 in which raw gas is supplied in advance from a raw gas inlet 19 to move by a dispersed magnetic field by an external magnetic field 21 to contact with raw gas (SiH4) to form a radical. Since a negative bias is applied to a substrate 22 in the chamber, cation in the plasma is accelerated to the substrate 22. A sheath of width SiS formed between the substrate 22 and the plasma is accumulated under the gas pressure of SiS<lambda with respect to the average free stroke lambda of the ion.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for forming an amorphous semiconductor film containing a compensating element, such as silicon or germanium, which reduces the density of localized states.

Conventional technology For forming amorphous semiconductor films such as amorphous silicon and amorphous germanium for solar cells, electrophotographic photoreceptors, etc., the plasma CVD method, which can form thin films at relatively low temperatures, is most commonly used. has been done. For example, when forming an amorphous silicon film, this method uses 5iH4 (silane gas) or a mixed gas of S I H4 and H2 as a raw material gas, and sets the substrate temperature to 200 to 350°C and the gas pressure to 0.
．． In this method, high frequency power is applied between an electrode and a substrate facing each other under control at 1 to 1 Torr to generate plasma, decompose silane gas, and form a film on the substrate.

In this case, the deposition rate is slow at about 3 μm/h and about 20 μm/h.
When manufacturing an electrophotographic photoreceptor that requires a diameter of μm or more, 6
It requires more time and is difficult to mass produce quickly. Also,
When high-frequency power is increased to increase the deposition rate, a large amount of powdered silicon is generated in the raw material gas due to a gas phase reaction, which clogs the exhaust system of the manufacturing equipment, posing a major problem in mass production.

Electron cyclotron resonance (EC) was proposed as a means to solve the problems of the plasma CVD equipment mentioned above.
This is a plasma CVD apparatus using R). (Unexamined Japanese Patent Publication No. 56
(Japanese Patent Laid-Open No. 59-169187) FIG. 2 shows the basic configuration of this device. 1 is a plasma generation chamber, 2 is a film formation chamber, and a waveguide 3 from a magnetron power source is connected to the plasma generation chamber 1 through a waveguide window 4, and a magnetic coil 5 is installed around the outer circumference of the waveguide 3. It is. Further, the outer periphery of the film forming chamber 2 is cooled by a water-cooled vibro. A plasma excitation gas is introduced into the plasma generation chamber 1 from the first gas introduction lower, plasma is excited in the plasma generation chamber 1 by microwaves, and electron cyclotron resonance is generated in the plasma by applying a magnetic field. Then, the plasma is guided by a diffused magnetic field from the inlet 8 to the substrate 1o on the substrate holder 9 disposed in the film forming chamber 2. A raw material gas is introduced into the film forming chamber 2 through the second gas introduction ports 11 and 11A and brought into contact with plasma to decompose the raw material gas 12 and deposit a film.

However, it has become possible to sustain the discharge, and the energy used for film formation is given by the energy of the ions incident on the substrate 1o, and the collision of ions on the film surface turns the film into honey, which increases the substrate temperature. A high-quality film can be obtained even when the temperature is set at room temperature. It has been shown that this method can form a high-quality insulating layer such as SIN-Si02 or Si for semiconductor processing at a low temperature. This is thought to be due to the fact that only the very surface is raised to a high temperature by ion energy and the 5i-H bond is terminated.

Problems to be Solved by the Invention Although the CVD method using ECR1 as described above can deposit a film at low temperature and at high speed, it is not suitable for forming a uniform film over a large area because it uses microwaves and a magnetic field. Furthermore, the generation of silicon powder, which was a drawback of the CVD method, is still unknown.

Furthermore, it is unknown whether an amorphous semiconductor film containing hydrogen, which is a monovalent compensating element, and which reduces the localized density of states upon ion injection can be formed.

An object of the present invention is to realize a method for depositing an amorphous semiconductor film that generates a small amount of powder and can deposit a uniform film even over a large area.

In addition, we will use a monovalent element such as hydrogen as an excitation gas to realize a full film deposition method that can form an amorphous semiconductor film containing hydrogen, which is a monovalent compensating element that reduces the localized density of states upon ion incidence. The purpose is to

Means for Solving the Problems The pressure inside the container in which the substrate to be deposited is placed is reduced, and gasified molecules, which are the raw materials for the deposited film, are introduced into the container and the amorphous molecules deposited on the substrate are introduced into the container. A method for forming a film, the method comprising pre-exciting a gas using electrical discharge, bringing the excited gas containing ions into contact with the raw material gas introduced into the container, converting the raw material gas into radicals, and depositing the excited gas on the substrate. The width of the sheath (hereinafter referred to as 5ill) formed between the substrate and the plasma containing the ions and radicals is equal to the mean free path (λ) of the ions in the container. The test is carried out at a gas pressure such that 5ill<λ.

A pre-excited gas, excited and ionized by the working electrical discharge, is introduced into the container in which the substrate is placed.

At this time, the ions attract electrons and come into contact with the raw material gas, producing a large amount of radicals. These radicals diffuse to the substrate surface, react with the film material on the substrate, and are deposited.

In addition, the ions have a relatively short lifetime and lose energy before adhering to the substrate due to collisions with neutral molecules present in the sheath where no plasma exists. Therefore, even if a large amount of ions are generated, the amount reaching the substrate is extremely small, which is considered to be the reason for slowing down the deposition rate. At this time, a large amount of gas phase reaction is induced due to collisions between ions and radicals in the gas phase, and a polymer of the semiconductor material is generated, which causes powder to adhere to the inside of the reaction container. Based on this idea, by controlling the gas pressure to reduce the width of the sheath, it was possible to significantly improve the deposition rate and to significantly reduce the generation of powder in the reaction vessel. Furthermore, by using a gas containing hydrogen as the excitation gas, it was possible to form a semiconductor film in which the density of localized states could be reduced.

Example Embodiments of the present invention will be described below with reference to the drawings.

[Example 1] FIG. 1 shows an ion source used in the present invention. A gas containing hydrogen as an excitation gas is introduced into the ion source through an excitation gas inlet 13. Magnets 1r are arranged on the back and side surfaces of the plasma source 14 to create a cusp magnetic field 16a. The maximum magnetic field strength is approximately 2.3 KG, 1 KG inside the plasma source 14, and 20 KG inside the plasma source 14.
It is G. Plasma consists of filament 16 and anode (wall) 1
An alternating current voltage of 120 V to 260 V is applied between the 7 and 7, and a large amount of discharge occurs. Since the electron confinement time becomes longer due to the cusp magnetic field 15a, stable discharge is achieved even at 10 to 10 Torr. The plasma generated in this way flows through the porous grid 1
8, the raw material gas (SiH4) is guided by the diffusion magnetic field of the external magnetic field 21, and moves to the reaction chamber 20 into which the raw material gas has been previously introduced from the raw material gas inlet 19.
It comes into contact with and becomes radical.

Since a negative bias of 2 oV is applied between the reaction chamber and the substrate 22, positive ions in the plasma are accelerated toward the substrate 22. At this time, the pressure in the reaction chamber 20 is 5×10
It is evacuated and controlled by a pump 23 to ~5X10 Torr. Further, the distance from the porous grid 18 to the substrate 22t is set to about 16 CI11. Since the ionization rate of the plasma is several inches, the mean free path of the ions introduced at this time is
From the equation of i r -Child, the ion saturation current (I
) is proportional to 1-f/2. For example, the negative bias voltage (Vf) is proportional to v5/l. At 5 x 10-' Torr. =30mA/
'crl.

When vi=-20v, the ion sheath width is 0.2+llff
It is about 1. However, at 5X10 Torr, the saturation current of ions is low. = 1 mA/CIl, the ion sheath width is about 1M. The dark conductivity and photoconductivity (646n) of the amorphous silicon film deposited on the substrate in this state are
The hydrogen content was determined from the infrared absorbance using m light at 1.4 μW/Ci. The substrate is heated from room temperature to 3 by the heater 24.
Although controlled up to 60°C, there is little dependence on substrate temperature.

It was also confirmed that the deposition rate at this time was extremely fast at 2 o 11 m/h.

FIG. 3 shows the results of dark conductivity and photoconductivity. a1a in the figure
, 31b contains SiH4 as source gas and excitation gas, respectively.
and H2, and the flow rate of each is 67%, and 32a and 32b have a flow rate ratio of 34%. 31b and 32b show dark conductivity, and 31a and 32a show photoconductivity. At around 5×10 Torr, where the width of the ion sheath is equal to the mean free path of the ions, the photoconductivity is equal to the dark conductivity, resulting in a film of poor quality for a semiconductor material with no photosensitivity. Also, in Fig. 4, 5 x 10-'
This shows that the amount of hydrogen contained in the amorphous silicon film can be controlled by the ratio of the flow rates of source gas and excitation gas at Torr. 41 shows the case where the excitation gas is hydrogen f: 100%, and 42 shows the case where the excitation gas is He/H2=O-24, each being 40 to 14 atm%.

It was found that it was possible to control up to 20 to 5 atm%.

In addition, under such deposition conditions, the amount of silicon powder generated in the deposition container is clearly different from that of normal plasma CVD, and even if the film is deposited to a thickness of 20 μm or more, which is required for electrophotographic photoreceptors, the amount of silicon powder generated in the deposition container is extremely small. Since the occurrence of body damage is extremely small, the time required for equipment maintenance is no longer needed, and productivity is significantly improved.

In addition, although SiH4 was used as the raw material gas, other 5tF
4,5ick4,5t2H6,5t2F6,5tH2F
In addition to silicon-based gases such as 2°SiHF and 5IHC13, GeH4, GeF4. GaN2F2. Go2F
6. GeH3F.

It is also possible to form an amorphous germanium, amorphous silicon, or germanium semiconductor film using a germanium-based gas such as G e HF s.

[Example 2] Next, a case will be described in which B2H6 is added as a doping gas into the deposition container using the apparatus shown in FIG.

In Figure 6, 5 x 10-' Torr, SiH
4/ The dark conductivity 61b and the photoconductivity 51a were measured in the same manner as in FIG. 3 by changing the amount of B2H6 at 34 N2.

On the other hand, 52b, 52a for 5 x 10"-2 Torr
As shown in Figure 2, the sensitivity is low and the amount of silicon powder generated increases significantly.

Although a mixed gas of H gas, H, and He was used as the excitation gas, similar results can be obtained by using a mixture of H gas and a rare gas such as Ar, No, or Xe.

In addition to B, other doping materials include P and As.

It is clear that any material that can be gasified, such as Ga, is suitable.

Effects of the Invention As described above, according to the present invention, an amorphous semiconductor film could be deposited at an extremely high deposition rate and with almost no powder generated in the reaction vessel. Furthermore, an amorphous semiconductor film in which valence electrons can be controlled can be easily obtained by using a monovalent element that reduces the localized state density as an excitation gas in the semiconductor film.

As a result, functional devices using amorphous semiconductor films, such as electrophotographic photoreceptors and solar cells, can be manufactured more cheaply and easily than with conventional CVD methods.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a deposition apparatus used in an embodiment of the present invention, FIG. 2 is a sectional view showing an example of a conventional ECR plasma CVD apparatus, and FIG. 3 is a sectional view showing an example of a conventional ECR plasma CVD apparatus. Graph showing the dark conductivity and photoconductivity of a quality semiconductor film, Figure 4 shows the measurement of the hydrogen concentration in the film 13...Gas inlet, 14
...Plasma source, 16...Magnet,
16...Filament, 17...Anode, 18...Porous grid, 19...Source gas inlet, 2o...Reaction chamber, 21...
...External magnetic field, 22...Substrate. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 3
Figure 4 StH? / N2 s, the quantity ratio ('/-) Peng 8 ward miq 憾

Claims (3)

[Claims] (1) A method for forming an amorphous semiconductor film in which the pressure inside a container in which a substrate to be deposited is placed is reduced, gasified molecules, which are raw materials for the deposited film, are introduced into the container and deposited on the substrate. pre-exciting an excited gas using an electrical discharge in a space adjacent to the container, bringing the excited gas containing ions into contact with the raw material gas introduced into the container, and The width of the sheath (denoted as Si_S) formed between the substrate and the plasma containing the ions and radicals is determined by the mean free path (Si_S) of the ions in the container. λ), S
A method for forming an amorphous semiconductor film, characterized in that deposition is performed at a gas pressure such that i_S<λ. (2) An amorphous semiconductor film according to claim 1, wherein an amorphous silicon film containing hydrogen is deposited by using a gas containing silicon as a raw material gas and using a gas containing hydrogen as an excitation gas. Formation method. (3) Reduce the pressure inside the container where the substrate is placed to 5 x 10^-^
3. The method for forming an amorphous semiconductor film according to claim 2, characterized in that the number is 2 or less.