JPH0562917A - Manufacture of amorphous silicon thin film - Google Patents

Abstract

PURPOSE:To stably maintain plasma by a method wherein the atom like hydrogen, to be fed to a film-forming region, is grown by bringing hydrogen molecules to come in contact with heated metal surface, and the feeding condition of the atom like hydrogen is independently controlled separating from the film- deposition condition. CONSTITUTION:A substrate A is attached to an electrode 101, a film-forming chamber 117 is depressed, and the substrate A is heated up. H2 gas and Ar gas are fed to the film-forming chamber 117, and the pressure of the chamber is adjusted. On the other hand, a nozzle 118 is heated up, the H2 gas, entering into the film-forming chamber passing through the nozzle 118 together with Ar gas, is thermo-dissociated and formed into atomic hydrogen. Besides, RF is applied to an electrode 102, and plasma is generated between the electrodes 101 and 102. SiH4 gas is allowed to flow into the film-forming chamber 117, and an a-Si film is formed by plasma. At this time, the SiH4 gas is fed intermittently by switching a valve 116, and an a-Si film-forming process and an atom like hydrogen feeding process are repeated alternately. Accordingly, the feeding of atom-like hydrogen can be controlled independent of film formation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses amorphous silicon and its compound as a semiconductor thin film used for solar cells, photoelectric conversion devices such as line sensors and area sensors, TFTs of liquid crystal displays, and electrophotographic photoreceptors. The present invention relates to a method for manufacturing an amorphous silicon thin film deposited on a substrate.

[0002]

2. Description of the Related Art Amorphous silicon (hereinafter referred to as "a-S
abbreviated as “i”) and a compound thereof are not only advantageous in that they can be formed at low temperatures, but also have a large light absorption in visible light,
It is widely used for solar cells that require a large area, line sensors, area sensors, photoelectric conversion devices such as electrophotographic photoreceptors, and TFTs for liquid crystal displays.

As a method of forming the a-Si semiconductor thin film, an RF plasma CVD method (so-called GD method) using SiH ₄ , Si ₂ H ₆ as a film forming gas, a microwave plasma CVD method, and hydrogen have been used so far. Si type in the presence of gas
A reactive sputtering method or the like has been used which is carried out in Ar plasma by Get. Note that the experimental, In addition to this, an optical CVD method, there are reports on ECRCVD method, a vacuum deposition method of Si in the presence of atomic hydrogen, Si ₂ H
There is also an example of film formation by a thermal CVD method such as ₆ .

Almost all of the a-Si films obtained by these methods are so-called hydrogenated a-Si containing 10% or more of hydrogen, and have characteristics as an electronic material that can be used in an a-Si semiconductor device. have. Such a-S
The most popular method for producing i is the plasma CVD method described below.
iH ₄ or Si ₂ H ₆ gas is used. Then, if necessary, it is diluted with hydrogen gas to generate plasma at a high frequency of 13.56 MH _Z or 2.54 GH _Z , thereby decomposing the film forming gas and producing reactive active species. Then, the a-Si film is deposited on the substrate. Then, if a doping gas such as PH, BH, or BF is mixed in the film forming gas, an n-type or p-type a-Si semiconductor device can be manufactured. In the case of a-Si, unlike single crystal Si, it is possible to form a film on a low-temperature substrate or a glass substrate, and it is easy to increase the area, and the light absorption is stronger than that of crystalline silicon, and the characteristics are higher. However, it is widely used in a field different from crystalline silicon because it is isotropic, has no directionality, and has no crystal grain boundaries such as polycrystal.

Further, in the above-mentioned plasma CVD method, it is possible to make a material containing a microcrystalline phase in an amorphous phase,
Therefore, if necessary, select the proportion of the microcrystalline layer,
A semiconductor device that can be used in various fields has been provided.

As a recent new movement, in the a-Si film forming method, many proposals have been made to improve the quality of the a-Si film by irradiation with hydrogen plasma. For example, Japanese Patent Fair 2-
That is the method disclosed in Japanese Patent No. 27824 or Japanese Patent Laid-Open No. 2-197117. However, these methods have problems that high temperature is required and that a-Si is easily crystallized.

[0007] As an idea different from these, the Journal of
Non-Crystalline Solids 114, 145 (198)
9) and new material 21st century forum material association forum comprehensive symposia proceedings (199.2.4) or the spring meeting of the Japan Society of Applied Physics (1990) proceedings. In these methods, an a-Si layer is deposited thick enough to form an a-Si network and H-atoms can be easily diffused, and then hydrogen plasma irradiation is repeated. I have to step on it. As a result, it is possible to obtain a high quality product while suppressing the crystallization of a-Si.

[0008]

However, in these methods, since high frequency plasma such as RF or microwave is used to generate atomic hydrogen, the high frequency plasma used for the deposition of the a-Si layer and the above-mentioned atoms are used. It is necessary to interact with the high-frequency plasma for generating hydrogen gas and to control the above-mentioned two types of plasma independently,
Not only is it difficult to control, but it is also difficult to optimize the process. That is, for example, if RF plasma is used for film formation of the a-Si layer and microwave plasma is used for atomic hydrogen generation, basically, these two types of plasma are stored in one vacuum chamber. Must coexist stably and efficiently. However, it is difficult for both of them to individually select the optimum discharge pressure. Further, in order to input the microwave into the vacuum, an input window made of quartz glass or other material that absorbs a small amount of microwaves is required, but SiH ₄ is diffused back toward the input window, and the SiH ₄ is injected into the window. There is also a problem that the a-Si is deposited and the microwave input strength is lowered.

[0009]

In order to solve the above problems, the present invention uses a-Si to generate atomic hydrogen in a vacuum.
It is intended to provide a realistic method for producing an amorphous silicon thin film, which uses any means that does not hinder the stable generation of the plasma that forms the layer.

[0010]

That is, in the present invention, a film deposition step of depositing an a-Si layer on a substrate and a step of supplying atomic hydrogen to a film formation region are alternately repeated, In the method for producing an amorphous silicon thin film to be formed, the atomic hydrogen is generated by bringing hydrogen molecules into contact with the heated metal surface.

[0011]

Therefore, when the deposition of the a-Si layer / the supply of atomic hydrogen is alternately repeated to deposit the film, only the plasma control for depositing the a-Si layer is always performed in vacuum. Therefore, the plasma can be supplied stably and efficiently.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Next, FIG.
It will be described with reference to FIGS. The procedure for depositing an a-Si film in the present invention is, as an example thereof, as shown in FIG.
During a predetermined time period t _D, after deposition of the a-Si layer, that only atomic hydrogen supply another predetermined time t _A with respect to a-Si layer in this deposition, repeating a set of steps Is. For example, let v _{D be} the deposition rate during t _D :
The deposition film thickness L after repeating each step n times and the deposition time t _T required for this are as follows when simply calculated.

L = v _D · t _D · n (1) t _T = (T _D + t _A ) n (2) Therefore, the average deposition rate V _D is V _D = L / t _T = {t _D / (t _D + t _A )} · v _D ··· (3) In actual film formation, do L and V _D match the values obtained by the above formula? , Which is slightly smaller than that.

Note that t _D , v _D , and t _{A at} each step are
The present invention is not limited to the simplest example described above, and for example, t _D , v _D , and t _A may change at each step, and v _D is not a constant value but a function of time. May be.

In the manufacturing method of the present invention, the surface of the deposited film is irradiated with atomic hydrogen during t _A. It is not always clear what is happening during this time. However, it is considered that atomic hydrogen diffuses into the deposited layer to some extent, which promotes extraction of excess atomic hydrogen and rearrangement (structural relaxation) of the Si network. In practice, the thickness of the layer of a-Si is deposited between t _D l (=
v _D · t _D ) needs to be about 2 atomic layers or more, for example, 10 Å or more.

If the newly deposited layer is only about one atomic layer, the amorphous structure cannot be stably maintained, and the a-Si film is crystallized infinitely by irradiation of atomic hydrogen. It becomes extremely difficult to control the degree. The possible cause is that the following processes are being implemented. That is, a- formed by irradiation of atomic hydrogen one step before
The layer of atomic hydrogen on the surface of the Si layer promotes the diffusion of the surface of Si atoms deposited on the surface in the next step, and further, since Si can hardly form a three-dimensional network in this step, In the next irradiation with atomic hydrogen, the a-Si network (two-dimensional) cannot be maintained and the crystallization occurs.

As described above, in forming the a-Si film, in order to prevent the excessive rearrangement of the Si network due to the irradiation of atomic hydrogen, and to realize the structural relaxation in the state of good controllability. It is necessary to deposit more than 10Å.
The a-Si layer deposited during t _D is partially μc
-Si may be contained, but if the thickness of the body stacking during t _D is 10 Å or more, it is considered that the structure containing μc-Si is relaxed while the structure is preserved. Uncontrollable excessive crystallization can be prevented. In other words, after the a-Si film is deposited to a thickness of 10 Å or more, uncontrolled crystallization does not occur even if the atomic hydrogen is sufficiently supplied, and microcrystals are contained to a desired degree. The structure can be relaxed while maintaining the amorphous structure.

On the other hand, if the thickness of the a-Si layer in each step is 100 Å or more, the structural relaxation does not proceed no matter how much atomic hydrogen is supplied. The degree of such structural relaxation can be confirmed by the reduction of the hydrogen concentration in the a-Si film and the reduction of the peak full width at half maximum of Raman spectrum at 480 cm ^-1 . Therefore, a− that accumulates during t _D
The thickness of the Si layer needs to be 100 Å or less, preferably 50 Å or less. If t _A is sufficiently long, for example, about 60 sec, the hydrogen concentration in the a-Si film can be reduced to 5% or less without increasing the spin density so much. Such a-S
The i film has an advantage that the effect of photodegradation on the electric conductivity does not appear, the mobility of holes is increased, and the device characteristics are improved.
Further, especially when the substrate temperature is lowered, the deterioration of the characteristics is small, so that a low-cost substrate such as a plastic substrate can be used.

The method of supplying atomic hydrogen in the production method of the present invention is a simple method of bringing hydrogen molecules into contact with a heated metal surface. In this case, an advantageous metal material is tungsten (W) or palladium (Pb). Further, it is effective that the heating temperature is 1000 ° C. or higher. For example, in the case of W, at a temperature of 1500 to 2000 ° C., almost all of H ₂ is dissociated into H ⁺ (atomic hydrogen). Various methods are possible for bringing hydrogen molecules into contact with the metal surface. The simplest method is to blow out hydrogen gas from a thin nozzle 118 made of burning tungsten as shown in FIGS. Here, the inside of the vacuum chamber-117 is set to 5
It is practically easy to blow out hydrogen molecules from the nozzle 118 while keeping it at about 0 mTorr, and when passing through the nozzle 118, the hydrogen molecules are thermally dissociated into atomic hydrogen, and Is oriented.

As shown in FIG. 3, in order to supply atomic hydrogen, a tungsten wire 302 is installed in the nozzle 301, and this is connected to a power source 304 via a lead wire 303. The wire may be burnt. Also, if you want to supply atomic hydrogen to a large area substrate,
As shown in FIG. 4, a nozzle 401 having a flat mouth may be used. Here, a winding 403 is arranged at the outlet of the nozzle 401, which is connected to a power source 404 via a lead wire.
It is connected to the. As a heater for producing atomic hydrogen, instead of the winding 403 as shown in FIG. 4, a plate 501 as shown in FIG. 5 is piled up via a spacer 502. You may use the thing. Here again, a power source 505 is connected to the plate 501 at a location of the interconnection 503 via a lead wire. In this case, the contact area of hydrogen gas increases, and the atomic hydrogen production efficiency increases. Further, since heated Pb or its alloy has a strong effect of permeating hydrogen, it is also possible to exude hydrogen from the heating element 603 composed of Pb as shown in FIG. 6, without forming a nozzle. is there. In this case, the heating element 6
03 is located inside the nozzle 601, and is heated by a heater 602 surrounding the nozzle 601.

Thus, to supply atomic hydrogen,
If the above method is performed, plasma is not used, so that the supply conditions of atomic hydrogen can be controlled independently of the film formation conditions of the a-Si film. Here, since the control parameters are only the nozzle temperature and the flow rate of hydrogen gas, it is possible to control very easily. Further, the pressure inside the film forming chamber 117 (vacuum chamber) can be independently controlled in a wide range independently of the hydrogen gas flow rate by using a conductance adjusting valve of the exhaust system. Therefore, the discharge conditions of the film forming process can be optimized independently.

In the atomic hydrogen supply step between the repeated film forming steps, the supply of the film forming gas such as SiH ₄ is stopped, but only the above atomic hydrogen supply is continued. Here, if the pressure in the film forming chamber is maintained at about 50 mTorr by the conductance adjusting valve, it is easy to maintain the plasma stably even when the film forming gas is stopped. Note that Ar or the like may be mixed with the deposition gas in order to stabilize the plasma. If necessary, in the atomic hydrogen supplying step, plasma may be turned off and only atomic hydrogen may be supplied from the nozzle.

The shape of the nozzle of the above embodiment is shown in FIG.
As shown in FIG. 7, a double cylinder having a water jacket 706 on the periphery is formed, and the heating element 702 is located at a portion 705 having a large inner diameter, and the heating element 702 is connected to the nozzle 701 via a spacer 703.
If they are arranged in parallel with each other in the direction of the gas flow inside, it is possible to prevent the film forming gas from back diffusing into the heating portion (heating element) inside the nozzle 701 against the flow of hydrogen gas inside the nozzle 701. It is possible to prevent decomposition of the film-forming gas in a portion and accompanying deposition of Si on the surface of the heated metal, and extremely stable film formation of a-Si on the substrate. In addition,
By providing the water jacket 706, it is possible to prevent the outside of the nozzle from being contaminated by the thermal decomposition of the film-forming gas such as SiH ₄ .

An overall apparatus for realizing such a manufacturing method is schematically shown in FIG. Here, the high frequency electrodes 101, 1
A hydrogen supply nozzle 118 is installed in a normal RF plasma CVD apparatus having 02. Then, gas supply systems 120, 121, 12 such as H ₂ and Ar are supplied to this nozzle.
It is arranged so that gas can be supplied from 2 or the like. In the figure, reference numerals 120, 130, 140 and 150 are various gas supply valves, 121, 131, 141 and 151 are flow rate controllers, 122, 132 and 142.
And 152 are gas supply sources. The nozzle 118
Is made of tungsten, and current is applied to it from 1500 to 200
Heat to 0 ° C. Of course, the nozzle material is T
It is possible to use high melting point materials such as a, Pd, and Mo. Then, hydrogen molecules (hydrogen gas) are dissociated into atomic hydrogen when passing through the nozzle. Figure 2
Shows the cross section of the nozzle. Here, reference numeral 201 is a tungsten pipe forming a main part of the nozzle, 204 is a conducting wire, and 205 is an AC power source. Reference numeral 202 denotes a ceramic pipe for insulating pipes, and the pipe 201 is connected to the SU via the ceramic pipe 202.
It is connected to the S gas pipe 203.

Further, the film forming gas supply systems 160, 161, 1
62 and the like can supply the film forming gas to the vacuum chamber 117 through the switching valves 116 through the pipes 112 and 113. In the figure, reference numerals 160 and 1
70, 180, 190 and 210 are valves for supplying various gases, 161, 171, 181, 191 and 211.
Is a flow controller, 162, 172, 182, 192
And 212 are gas supply sources. Then, the switching valve 116 can switch the gas to the exhaust line 114 and the exhaust trap 115.

The film forming chamber (vacuum chamber) 117 is
Heater-1 for heating the substrate A inside the high frequency electrode 101
03 is provided, and the substrate is heated by heat transfer. In the figure, reference numeral 104 is a lead wire for the heater 103, 105 is a ground lead, 106 is a matching box for plasma control, 107 is a high frequency power supply,
Reference numeral 08 is an exhaust duct, and 109 is a vacuum pump.

A specific example of carrying out the a-Si film manufacturing method of the present invention using the apparatus having such a structure will be described below. First, the substrate A is attached to the electrode 101, the pressure inside the film forming chamber 117 is reduced to the level of 10 ⁻⁷ Torr, and then the heater-1 is used.
03 is energized to heat the substrate A to 280 ° C. Then H
₂ gas is supplied from the gas supply systems 120, 121 and 122 and Ar gas is supplied from the gas supply systems 130, 131 and 132 to the film forming chamber 117, and the pressure in the chamber is adjusted to 50 mTorr. On the other hand, in the nozzle 118, this nozzle is set to 1800
The mixture is heated to 0 ° C., and the H ₂ gas flowing through the Ar gas and flowing into the film forming chamber is thermally dissociated into atomic hydrogen or the like. Furthermore, the electrode 102 by applying a RF of 13.56MH _Z,
A plasma is generated between the electrodes 101 and 102. At this time, the matching box 106 works to keep the plasma stable. Then, the gas supply systems 160, 161,
Starting to flow SiH ₄ gas from 162. Initially, the gas is directed to the exhaust line 114, but when the gas flow becomes stable, the switching valve 116 is activated to introduce the gas into the film forming chamber 117 and use the plasma that has already been generated. Enter the film forming process. In this case, as shown in FIG. 8, by switching the valve 116, the supply of SiH ₄ gas is interrupted, and the step of forming the a-Si film and the step of supplying atomic hydrogen are alternately repeated. And, for example, the above aS
An a-Si layer is deposited to a thickness of 20Å for each film forming step of the i film. The atomic hydrogen supply process during this period is continued for, for example, 60 seconds. The pressure in the film forming chamber when SiH ₄ was flown was 0.1 Torr.

The a-Si semiconductor thin film (thickness 5000 Å) manufactured in this way is, according to the actual test results,
The hydrogen concentration in the film is about 6 at%. This numerical result was about half of the normal case where continuous film formation was performed without supplying atomic hydrogen from the nozzle. Further, the deterioration of the deterioration characteristics due to the conventional photocurrent irradiation is small in the present invention, which is about 1/5 of that in the case of continuous film formation.

Next, using a nozzle as shown in FIG.
A case of manufacturing an a-Si film by the above-mentioned apparatus will be described. Each step is almost the same as the above-mentioned embodiment, except that the heating temperature of the substrate A by the heater is set to 340 ° C. and the pressure in the film forming chamber 117 is adjusted to 50 mTorr. Here again, the high-frequency electrode 102 has 13.
Applying an RF of 56MH _Z is, SiH the film forming chamber 117
_No glow discharge occurs between the electrodes while the gas is not flowing. Atomic hydrogen is supplied to the surface of the substrate A from the nozzle 118. When the SiH ₄ gas is introduced into the film forming chamber 117 by the switching operation of the valve 116 and the internal pressure reaches 40 mTorr, glow discharge occurs and an a-Si film is deposited on the surface of the substrate A. When the supply of SiH ₄ gas is stopped after the film deposition for 20 seconds, the film forming chamber 117
The internal pressure drops and the glow discharge stops. In this state, the supply of atomic hydrogen from the nozzle 118 is continued for 60 seconds. By repeating this, the deposition of the a-Si film having the required thickness is achieved.

For example, 5 μm deposited in this way
The a-Si film has a hydrogen concentration of about 4 at%, and has a hole drift mobility of about one digit higher than that of the a-Si film formed by the ordinary GD method, and exhibits good characteristics.

[0031]

As shown in the above embodiments, by using the method for producing an a-Si film of the present invention, there are problems in the conventional production method, for example, film crystal accompanied by atomic hydrogen plasma irradiation. Stability and stability due to coexistence of high-frequency plasma,
It is possible to avoid the difficulty of controllability, to control the supply condition of atomic hydrogen independently of the film deposition condition, to independently control, and to maintain stable plasma. As a result, the photoelectric characteristics and photodegradation characteristics of the film were significantly improved, and a good a-Si semiconductor thin film could be produced.

[Brief description of drawings]

FIG. 1 is a schematic view of an example of a film forming apparatus for carrying out the present invention.

FIG. 2 is a schematic view of a main part showing a means for supplying atomic hydrogen in the present invention.

FIG. 3 is a schematic view of a main part showing a means for supplying atomic hydrogen in the present invention.

FIG. 4 is a schematic view of a main part showing a means for supplying atomic hydrogen in the present invention.

FIG. 5 is a schematic view of a main part showing a means for supplying atomic hydrogen in the present invention.

FIG. 6 is a schematic view of a main part showing a means for supplying atomic hydrogen in the present invention.

FIG. 7 is a schematic view of an essential part showing a means for supplying atomic hydrogen in the present invention.

FIG. 8 is a time chart of film formation in the present invention.

[Explanation of symbols]

 101, 102 high frequency electrode 103 heater 106 matching box 116 switching valve 117 film forming chamber (vacuum chamber) 118 nozzle 302 tungsten wire 403 winding 501 plate

Claims (1)

[Claims] 1. A method of manufacturing an amorphous silicon thin film, wherein a film deposition step of depositing an a-Si layer on a substrate and a step of supplying atomic hydrogen to a film formation region are alternately repeated to form a film. The method for producing an amorphous silicon thin film, wherein the atomic hydrogen is generated by bringing hydrogen molecules into contact with a heated metal surface.