JP2002141292A - Method of manufacturing silicon thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of silicon thin film whose optical characteristics and electronic characteristics are improved. SOLUTION: In a film-forming method of silicon thin film, the silicon thin film is formed on the surface of an insulating substrate by plasma CVD method. Self-heating and an external temperature are given to the substrate, and the function for the film quality of the silicon thin film deposited on the surface of the insulating substrate is controlled, so that alternating potential, such as sawtooth wave, is applied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a plasma CVD.
The present invention relates to a method for producing a silicon-based thin film by a method, wherein a silicon-based insulating thin film that does not break down even with a high electric field strength is applied to a substrate while applying a potential of an alternating frequency of a low-frequency sawtooth wave to a substrate. The present invention also relates to a method for controlling the minority carrier lifetime of a non-doped silicon-based thin film.
The present invention relates to a method for producing a non-doped silicon-based thin film capable of controlling the length of minority carrier lifetime by applying an alternating potential to the surface of an insulating substrate for depositing the silicon-based thin film when growing the silicon-based thin film by the VD method. .

[0002]

2. Description of the Related Art A conventional method for manufacturing an amorphous silicon thin film will be described with reference to FIG. FIG. 2 shows a film forming method using a typical comb-shaped electrode type plasma generating apparatus. In a container (not shown), a plurality of sets of electrode plates including a cathode 1 and an anode 2 are arranged in parallel. A high frequency power of 100 KHz to 13.5 MHz is supplied from a high frequency power supply 3 between the electrodes. A reaction gas such as SiH ₄ is ejected toward the cathode 1 and the anode 2. On the other hand, the substrate 4 is arranged at a position on a plane perpendicular to the parallel electrodes. This substrate 4 is supplied with a DC potential 5 by an electric switch 8 or is
Can be arbitrarily switched. The substrate 4 is held at a position away from the plasma 7, and the amorphous silicon thin film deposited on the substrate 4 is reduced in damage due to the strong ion bombardment peculiar to the plasma having a high electron temperature. By applying a DC potential 5 from the outside, not only the defect density in the film is reduced, but also a high-speed film formation of 3Å / sec is possible. This is a manufacturing method that is expected to improve the performance and reduce the cost of an electronic device using a non-doped high-quality amorphous silicon thin film.

[0003]

However, in the conventional film forming method, the electric conductivity is uniquely determined, it is difficult to freely control those characteristics, and the allowable range in designing a precise electronic element is narrow. There was a problem. In particular, there is a serious disadvantage that the allowable range is narrow in designing an insulating thin film that does not break down even at a high electric field strength. Also, among such physical properties, there has been almost no method capable of controlling the length of the minority carrier lifetime when producing a non-doped silicon-based thin film. Therefore, there is almost no means for realizing an electronic element capable of controlling a rise time or a fall time due to accumulation or recombination of electrons depending on the length of the minority carrier lifetime during film formation, except for doping impurities. Therefore, when manufacturing an electronic element intended to operate at a high frequency, there are disadvantages that the manufacturing cost is limited and the degree of freedom in design is narrow.

An object of the present invention is to provide a method for producing a silicon-based thin film in which the life of minority carriers can be controlled to be short or long while being non-doped. Another object of the present invention is to provide a method for producing a silicon-based thin film which has excellent insulation properties and does not break down even at a high electric field strength and has improved electronic properties.

[0005]

In order to achieve the above object, a method for forming a silicon-based thin film according to the present invention comprises a plasma CVD method.
In the method of forming a silicon-based thin film on the surface of an insulating substrate by the method D, self-heating and applying an external temperature to the substrate, and controlling the film quality of the silicon-based thin film deposited on the surface of the insulating substrate, an arbitrary frequency , An arbitrary potential, and an alternating potential having an arbitrary wave height can be applied. Preferably, the peak value is ± 100 to 500 V, and the frequency is 0.1 to 55 Hz.
Can be used.

Here, it is preferable that the substrate is arranged at a position capable of performing both self-heating by plasma and forced external heating of the substrate during film formation. The substrate is placed at an end of a comb-shaped electrode for generating plasma. It is preferable to install at a position at least 10 mm away from the part. Alternating potential may be applied via a conductive thin film formed on the back surface of the substrate, and the conductive thin film may be a metal plate, sputter, laser ablation, electron beam evaporation, ion implantation, conductive paint, plating, conductive polymer. Alternatively, it may be formed by metal evaporation or the like.

In addition, when it is necessary to shift to another manufacturing process after the formation of the silicon-based thin film, or for the purpose of securing an aesthetic appearance, the conductive film may be removed by etching or the like. . Further, the surface layer of the substrate may be formed by depositing a silicon nitride thin film.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic view of a plasma CVD apparatus, in which the container of the apparatus is not shown. First, the conductive film 44 on the back
A substrate 44 to which A has been applied is prepared. Here, the substrate is a base for the purpose of depositing a silicon-based thin film, and is a polymer such as glass, vinyl, or plastic, or an inorganic oxide such as a paint, an insulating semiconductor, or a sintered product. It has thermal insulation. Further, a conductive liquid or solid substance may be present in the base. After cleaning the substrate 44 with an organic solvent, the substrate is placed on a susceptor in a plasma CVD apparatus so that the surface of the substrate faces plasma, although not shown. The susceptor is a stainless steel guide,
It is fixed via a Teflon (registered trademark) base. First, a monosilane gas and a nitrogen gas were introduced into the plasma CVD apparatus while the conductive film 44A was grounded, and the cathode 11 and the anode 22 were introduced.
To the plasma 77
Is generated, a silicon nitride thin film is deposited on the substrate surface from silicon radicals and atomic nitrogen in the plasma, and a silicon nitride thin film is formed on the substrate. Next, monosilane SiH ₄ gas and hydrogen H ₂ gas are introduced while applying an alternating potential to the conductive thin film on the back surface of the substrate, and silicon is deposited from silicon radicals and atomic hydrogen in the plasma. It is formed on a nitride thin film.

At this time, the susceptor has no means for heating or cooling, and the temperature of the substrate rises due to self-heating by plasma and radiation of the external heater 99. In the present invention, the substrate is placed at a position distant from the discharge electrode, and its temperature can be maintained at any temperature between 120 and 250 ° C. Since an alternating potential is applied to the metal plate or the conductive polymer plate covered with the silicon nitride thin film to be formed, the potential on the substrate surface changes uniformly over the entire substrate. There, silicon radicals and hydrogen atoms from the plasma fly, but on the surface of the silicon nitride thin film, film formation is limited by the polarity and magnitude of the electrostatic potential of the substrate. Here, by limiting the flow ratio, the pressure, and the like of the monosilane gas and the hydrogen gas, an amorphous silicon-based thin film having a constant deposition rate can be obtained on the silicon nitride thin film.

It is important that the alternating potential applied to the substrate is higher than the self-voltage during generation of plasma and that the film is formed while keeping the frequency constant. In particular, making the waveform of the alternating potential into a sawtooth waveform gradually increases the electrostatic potential on the surface of the silicon nitride thin film. Alternatively, the electrostatic potential is gradually reduced. Therefore, it is possible to freely change the binding energy between the silicon already implanted and the silicon radical to be implanted. Therefore, it is important for controlling the deposition direction of the silicon-based thin film. Therefore, the application of the alternating potential is an important means for controlling the length of the minority carrier lifetime of the silicon-based thin film. Here, the silicon-based material is composed of an aggregate of a raw material gas mainly composed of silicon atoms.

The conductive film on the back surface of the substrate for applying an alternating potential to the substrate is provided with a sputtering, laser ablation, electron beam evaporation, ion implantation, It is preferably formed by conductive paint, plating, conductive polymer or metal deposition.

[0012]

An embodiment of the present invention will be described below. First,
A 50 mm square, 0.5 mm thick parallel plate stainless steel is degreased with an organic solvent, and then mounted on the CVD apparatus for film formation shown in FIG. Specifically, on the susceptor electrically floating from the device housing, the substrate surface is parallel to a plane connecting the sides of one or more pairs of comb-shaped electrodes constituting a discharge electrode for plasma generation. The distance is 10 mm. A sawtooth potential having an arbitrary frequency and an arbitrary peak value can be applied to the stainless steel plate. The system was evacuated to a high vacuum so that there was no residual gas molecules such as oxygen, carbides, moisture, dust from the air, and various ions in the system, and then pure nitrogen gas was introduced into the system at 100 sccm. Internal pressure is 0.8 Torr.
After that, the high frequency power of 13.56MHz
Charged to a discharge electrode at cm ² to generate nitrogen plasma. At this time, the potential of the substrate is the same as that of the housing. Next, purity 10
0% monosilane gas is flowed into the apparatus at 20 sccm to deposit a silicon nitride thin film. The vacuum degree during deposition is 0.9 Torr., 30 m
After passing in., stop the flow of monosilane and nitrogen,
Keep under vacuum. Through these deposition processes, the substrate temperature is 20
0-250 ° C.

Subsequent to the deposition of the silicon nitride thin film, a silicon-based thin film is deposited as follows. First, pure hydrogen gas was introduced into the apparatus at 30 sccm, and after the pressure in the apparatus became about 0.8 Torr, high frequency power of 13.56 MHz was applied at 0.1 w / cm.
^{In step 2,} it is charged into a discharge electrode to generate hydrogen plasma. Immediately thereafter, the frequency and peak value 200 shown in FIG. 3 or FIG.
v, while applying a sawtooth potential of negative or positive polarity,
0% monosilane gas flows into the apparatus at 10 sccm to deposit a silicon-based thin film. The degree of vacuum during the deposition is 0.9 Torr. Under these mixed gas flow rate and gas pressure conditions, the deposition rate of amorphous silicon is 2-3Å / sec. Deposition time 60
After the passage of min., stop the flow of monosilane and hydrogen,
Keep under vacuum. Through these deposition processes, the substrate temperature is 20
0-250 ° C. The range of the frequency change of the sawtooth is 0.9 Hz at the maximum on the negative polarity side and 0 at the positive polarity side including the housing ground.
9 Hz.

The electrical properties of the silicon nitride thin film and the silicon-based thin film thus formed were evaluated by the following measurements. FIG. 5 shows a composite diagram of a sample structure for measuring electric withstand voltage in a dark state and a measurement circuit diagram. First, as a sample, a silicon nitride thin film 44C and a silicon-based thin film 10 were deposited on a stainless steel plate 44B.
Then, nickel is deposited thereon at about 100 ° C. One probe 12 stands on the nickel electrode 11B. On the other hand,
Another probe 13 is set up on the stainless steel plate 44B. And
A DC potential is applied from the DC power supply 15 between the two probes. The potential is gradually increased, and the DC voltage V at which the current of the DC ammeter 14 starts to flow rapidly is recorded. The combined thickness t of the silicon nitride thin film 44C and the silicon-based thin film 10 is separately measured. In this embodiment, the silicon nitride thin film 44
C and the silicon-based thin film 10 have the same thickness (for example, 2 μm). Then, the insulation withstand voltage per unit thickness V /
t can be calculated. In the measurement of this example, V / t = 500 MV / cm. This value is an excellent value which is about one order of magnitude higher than the withstand voltage of 10 MV / cm of a silicon oxide film obtained by thermally oxidizing single crystal silicon. Even if the polarity of the above voltage is inverted, V /
There is no change at t = 500MV / cm. Thus, the composite thin film of the silicon nitride thin film 44C and the silicon-based thin film 10 according to the present embodiment can realize excellent electrical characteristics. Although monosilane SiH ₄ was used as a source gas in this embodiment, disilane Si ₂ H ₆ is better to be used in order to obtain a higher film forming speed.

FIG. 6 shows the dependence of the electric conductivity σ _{d in} the dark state on the frequency of the sawtooth wave applied to the substrate. There is no peculiar tendency regarding the sawtooth frequency. σ _d itself is for observing the transport characteristics of majority carriers, and is similar to ordinary electric conductivity.
However, it is generally said that σ _d = 10 ⁻¹¹ Ω− ¹ · cm ^{−1 in} the case of high-quality non-doped amorphous silicon. On the other hand, the present embodiment extends to the order of 10 ^-7 to 10 ^-4 Ω ^-1 cm ^-1 , and σ _d =
It approaches the value of the order of 10 ^-3 Ω ^-1 · cm ^-1 . As described above, this embodiment can realize an intermediate state of electron conduction between high-quality amorphous silicon and microcrystalline silicon.

FIG. 7 illustrates the dependence of the sawtooth frequency on the minority carrier lifetime substrate formed of the silicon-based thin film. When the sawtooth frequency is 0.5 Hz on the negative polarity side and 0.3 Hz on the positive polarity side, the minority carrier lifetime is about 4 to 5 times the average value compared to other sawtooth frequencies, even if the standard deviation is taken into account. There is a feature that it is short. Thus, depending on the choice of the sawtooth frequency, without intentionally doping impurities,
The life of the minority carrier can be shortened.

[0017]

As described above, according to the present invention,
Using a conventional comb-shaped electrode structure plasma CVD device,
A silicon-based insulating thin film can be realized by placing the insulating substrate at a distance slightly away from the electrode and using a film forming method in which a low-frequency alternating potential is applied to the conductive thin film applied to the back surface of the insulating substrate. . Therefore, a synthetic insulating thin film of a silicon-based and silicon nitride film having an excellent withstand voltage of about 500 MV / cm can be realized. In addition, since this synthetic insulating film can be continuously formed using the same reaction furnace, it is a method for manufacturing a high-performance electronic element at low cost. In addition, a conductive state intermediate between high-quality amorphous silicon and microcrystalline silicon can be realized. Furthermore, the present invention provides a manufacturing method capable of selectively controlling the life of minority carriers in a non-doped silicon-based thin film. According to this technique, the rise time or the fall time related to the accumulation or recombination of minority carriers can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic view of a CVD apparatus for describing an embodiment of the present invention.

FIG. 2 is a view showing a conventional method for manufacturing an amorphous silicon thin film.

FIG. 3 is a diagram illustrating a sawtooth potential as an example of an alternating potential applied to a conductive thin film on the back surface of a substrate.

FIG. 4 is a diagram showing a sawtooth potential as another example of the alternating potential applied to the conductive thin film on the back surface of the substrate.

FIG. 5 is a composite diagram of a sample structure and a measurement circuit diagram for measuring electric withstand voltage in a dark state.

FIG. 6 is a diagram showing the dependence of the electrical conductivity in the dark state on the frequency of the sawtooth wave applied to the substrate.

FIG. 7 is a diagram showing the dependence of the sawtooth wave frequency on a minority carrier lifetime substrate formed of a silicon-based thin film.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Silicon-based thin film 11 Cathode 11B Nickel electrode 12, 13 Probe 14 DC ammeter 15 DC power supply 22 Anode 33 High frequency power supply 44 Substrate 44A Conductive film 44B Stainless steel plate 44C Silicon nitride thin film 55 Saw wave generator 66 Housing ground 77 Plasma 88 Electric switch 99 External heater

Claims (8)

[Claims] 1. A method for forming a silicon-based thin film on a surface of an insulating substrate by a plasma CVD method, the method comprising: applying self-heating and an external temperature to the insulating substrate; and applying an alternating potential to the insulating substrate. A method for producing a silicon-based thin film, comprising depositing a silicon-based thin film on a surface. 2. A method of forming a silicon-based thin film on a surface of an insulating substrate by a plasma CVD method, wherein the insulating substrate is subjected to self-heating and an external temperature, and a sawtooth potential is applied to the insulating substrate. A method for producing a silicon-based thin film, comprising depositing a silicon-based thin film on a surface. 3. The method for producing a silicon-based thin film according to claim 2, wherein the peak value of the sawtooth potential can be selected to be negative or positive. 4. The method for producing a silicon-based thin film according to claim 2, wherein the negative or positive polarity of the peak value of the sawtooth potential is sequentially reduced to zero. 5. The substrate according to claim 2, wherein the substrate is disposed at a position where damage from plasma is avoided from an end of a comb-shaped or rod-shaped electrode for generating plasma, or a parallel plate electrode. 5. The method for producing a silicon-based thin film according to any one of 4. 6. The insulating thin film according to claim 2, wherein a dielectric breakdown electric field in a film pressure direction can be at least 500 MV / cm by continuously depositing the insulation and the silicon-based thin film. Manufacturing method. 7. The method according to claim 2, wherein the conductive thin film is formed by sputtering, laser ablation, electron beam evaporation, ion implantation, conductive paint, plating, conductive polymer or metal evaporation. 5. The method for producing a silicon-based thin film according to any one of 4. 8. The method for producing a silicon-based thin film according to claim 5, wherein the metal thin film is removed by means such as etching after forming the silicon-based thin film.