JPH0812316A - Sputtering film formation of silicon base thin film - Google Patents

Abstract

PURPOSE:To enable to reduce impurities, form a large area thin film, form a film at high speed, and to form a thin film that has high adhesion strength and is dense. CONSTITUTION:In this sputtering film forming method of a silicon base thin film, silicon having specific resistance of >=500OMEGA.cm is used as a target material 8, and while DC bias is applied to the target 8, plasma 4 formed inside a film forming chamber is made to have the shape of a sheet located almost in parallel to the surface of the target 8 to form a silicon base thin film on the surface of a substrate 10 arranged in the film forming chamber. In this method, since the use of harmful and explosive gas, such as gaseous SiH4 is not required as in the conventional method and a material easy to handle such as Si, Ar, O2 and N2 is able to be used for film formation, safety measure can be reduced and cost-cutting in mass production process is attained. Since gaseous H2 is used at low concentration and is, mixed with gaseous Ar, it is easy to handle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon-based thin film for a liquid crystal display (LCD), especially a TFT (Thin Film).
The present invention relates to a sputtering method for forming a silicon-based thin film capable of forming a silicon-based thin film for m transistor formation at high speed.

[0002]

2. Description of the Related Art For example, in the field of image display, functional thin films used for liquid crystal display devices (LCDs) are required to satisfy the following four items. However,
The purpose in LCD is shown in <>.

(1) Reduction of impurities taken into the film.
Realization of impurities of 1 ppm or less. <High integration and high sensitivity of display element> (2) Establishment of large area thin film formation method. <Enlargement of display screen> (3) Establishment of high-speed film forming method. <Lower cost of display screen> (4) Establishment of thin film forming method having high adhesion strength and dense film structure. <Improvement of Durability of Display Screen> Conventionally, a silicon-based thin film is often used as the functional thin film. This silicon-based thin film is formed by, for example, the following three types of film forming methods.

(A) Plasma CVD method: When one or several kinds of a certain gas (a substance having a boiling point below room temperature) is placed in a container and heated to a high temperature, a reaction occurs depending on the kind of the gas, and a substance having a low vapor pressure is generated. To generate. This is vapor growth (Ch
It is a process of thin film growth called abbreviated as emical vapor deposition (CVD), and a film forming method utilizing this growth method is a CVD method. Further, a plasma CVD method is a method that enables formation of a thin film even at low temperature by converting the above gas into plasma by using an apparatus in which a CVD apparatus is combined with an apparatus for discharging.

In the plasma CVD method, when a silicon-based thin film is formed, for example, SiH ₄ is used as a gas.
Methods using gas are known. Compared with other film forming methods,
Although a large area thin film can be formed at low temperature, it has the following disadvantages.

(A) Since the SiH ₄ gas contains two or more orders of magnitude more impurities than the sputtering target, the amount of impurities in the film is large.

(B) The film formation speed is about 10 nm / min, but a higher speed is desired in terms of mass productivity.

Since (c) SiH ₄ gas is toxic and explosive, safety measures are indispensable and cause a high cost.

(B) Vacuum evaporation method: Vacuum evaporation is a process of heating and evaporating a substance to be formed into a thin film in a vacuum and adhering it to a certain surface to grow a thin film. This growth method is used. The formed film forming method is a vacuum evaporation method.

In the vacuum deposition method, when a silicon-based thin film is formed, for example, a method of using high-purity Si as a substance for heating and evaporating is known. Since it is possible to form a film in an ultrahigh vacuum of 2 to 3 orders of magnitude as compared with other film forming methods, the amount of impurities taken into the film is small and a high-purity thin film can be formed, but on the other hand, it has the following disadvantages.

(A) It is difficult to simultaneously increase the thin film formation rate and form a thin film having a large area and a good film thickness distribution.

(B) Structural defects (for example, dangling bonds which are dangling bonds of Si atoms) are likely to occur in the film. Further, since it is difficult to form a compound, this structural defect cannot be repaired.

(C) Since the substance is attached by the energy of heating and evaporation, the adhesion strength of the film is weak and it is difficult to form a dense film.

(C) Sputtering method: Sputtering refers to high-energy particles (mostly positive ions accelerated by an electric field on the surface of a solid, and generating this positive ion is called "discharge"). This is a phenomenon in which atoms and molecules on the surface of the solid are exchanged with momentum of high-energy particles to be ejected from the surface when they collide, and this phenomenon is used to form a thin film on the substrate. Is the sputtering method.

In the sputtering method, a high voltage is applied to a base material (generally called a "target") for forming the above-mentioned solid, that is, a thin film, and Ar gas is used as a gas for causing discharge, for example. Energetic particles collide with the target. Direct current (D
Two types are used: C) and alternating current (RF). here,
When a DC (RF) power source is used, the film forming method is DC (R
F) It will be called a sputtering method.

The sputtering method has a higher adhesion strength than other film forming methods and can form a thin film having a dense film structure.
In particular, the DC sputtering method enables higher speed film formation than the RF sputtering method, but has the following disadvantages.

(A) An insulator target, that is, a high-purity Si target having a high specific resistance, cannot be sputtered because the target surface is charged up.

(B) To reduce structural defects in the film (for example, dangling bonds which are dangling bonds of Si atoms),
A reactive gas such as pure hydrogen (H ₂ ) is added to pure argon (Ar).
When used as a mixture with, the formation rate of the film is significantly reduced (for example, 1/100% compared to the case where no reactive gas is used).
Deposition rate of 2 to 1/4).

(C) Since foreign matter is likely to be formed discontinuously on the target surface, abnormal discharge is likely to occur on the target surface.

Further, since the RF sputtering method can sputter an insulator target as compared with the DC sputtering method, it is possible to reduce impurities taken into the film by using a high-purity Si target. It has the following disadvantages.

(D) Even when Ar gas is used as the gas for causing the discharge, the film forming rate is reduced to about 1/2 of that of the DC sputtering method.

(E) To reduce structural defects in the film (for example, dangling bonds which are dangling bonds of Si atoms),
A reactive gas such as pure hydrogen (H ₂ ) is added to pure argon (Ar).
When it is used as a mixture, the film formation rate is further significantly reduced (for example, the film formation rate is 1/2 to 1/4 as compared with the RF sputtering method using no reactive gas, Compared with the DC sputtering method that does not use a reactive gas,
It will be reduced to 1/8).

As described above, each film forming method has advantages and disadvantages, and there is still a film forming method capable of satisfying all the four requirements for the functional thin film that can be used in the liquid crystal display (LCD). Therefore, the establishment was desired.

[0024]

DISCLOSURE OF THE INVENTION The present invention can solve the following four items required for a functional thin film that can be used in the above-mentioned liquid crystal display device (LCD). It is an object of the present invention to provide a sputtering film forming method.

(1) Reduction of impurities taken in the film.
Realization of impurities of 1 ppm or less.

(2) Establishment of a large area thin film forming method with high target utilization efficiency.

(3) Establishment of high-speed film forming method.

(4) Establishment of a thin film forming method having high adhesion strength and a dense film structure.

[0029]

According to the method for forming a thin film of a silicon-based thin film of the present invention, in the method for forming a thin film of a silicon-based thin film by sputtering, silicon (Si) having a specific resistance of 500 Ω · cm or more is used as a target material. ,
While applying a DC bias to the silicon target,
The plasma formed inside the film forming chamber is formed into a sheet shape that is positioned substantially parallel to the surface of the silicon target, and a silicon-based thin film is formed on the surface of the substrate arranged inside the film forming chamber. To do.

Further, the sputtering method for forming a silicon-based thin film of the present invention is characterized in that the width of the silicon target is made smaller than the width of the plasma forming a sheet shape.

Further, in the method for forming a silicon-based thin film by sputtering according to the present invention, at least one reaction of hydrogen (H ₂ ) gas, oxygen (O ₂ ) gas and nitrogen (N ₂ ) gas is carried out in the film forming chamber. Characteristic gas is introduced to form a silicon-based thin film containing at least one of hydrogen, oxygen, and nitrogen.

[0032]

The operation of the present invention will be described together with the findings obtained in making the present invention.

Problems in forming a functional thin film usable for the above-mentioned liquid crystal display (LCD), that is,
(1) Reduction of impurities taken into the film. Impurity 1pp
realization of m or less, (2) establishment of a large area thin film formation method with high target utilization efficiency, (3) establishment of high speed film formation method,
(4) Among the establishment of a thin film forming method having high adhesion strength and a dense film structure, a solution to (2) to (4) is proposed in Japanese Patent Laid-Open No. 2-104663.

In this publication, the arc discharge plasma flow is deformed into a sheet by a magnetic field, and the ions in the sheet plasma are accelerated to a target kept at a negative potential with respect to the sheet plasma to perform sputtering. , A method for forming a coating film on a substrate arranged to face the target with a sheet plasma interposed therebetween, and an apparatus therefor.

This sheet plasma sputtering method is
The following problems, which have occurred due to the drawback of the conventional DC sputtering method, that is, "the target itself also serves as the discharge cathode for plasma generation", are solved.

A) A high discharge voltage is required, and the film formation rate is slow because it is limited to glow discharge. B) The gas pressure during film formation is higher than that in arc discharge (for example, 3 × in the case of argon gas). 10 ^-3 Torr ~ ³ x 10
^-2 Torr), c) It is difficult to achieve both large area thin film formation and high target utilization efficiency.

As a result, the sheet plasma sputtering method has the following four problems caused by the drawback of the conventional DC sputtering method, that is, "the target itself also serves as the discharge cathode for plasma generation". , (A)
It is difficult to achieve both large-area thin film formation and high target utilization efficiency, (b) a material having a high specific resistance cannot be used as a target material, (c) a high gas pressure during film formation reduces the film formation rate, (D) Abnormal discharge is likely to occur,
Among them, the problems of (a) and (c) could be solved.

However, in the examples of the above publications, it is reported only when a conductive target material is used, and a target material having a high specific resistance has not been studied. According to the general idea of the sputtering method, no matter how much the DC bias is applied to the target having a high specific resistance, a stable sputtering phenomenon does not occur, and much faster film formation cannot be expected.

Therefore, the present inventor has made a fundamental review of the above-described high-efficiency sheet plasma sputtering method. As a result, even if the target material has a high specific resistance, for example, high-purity silicon (Si),
By optimizing the distance between the sheet plasma and the target, the thickness of the sheet plasma, and the sheet plasma current value in addition to the DC bias application to the target,
It has been found that stable sputtering is possible.

Further investigation of this situation revealed that the formation rate of the silicon-based thin film was proportional to the sheet plasma current value even when a Si target having a high specific resistance, which could not be conventionally sputtered, was used. It is considered that the reason is that in the above-described high-efficiency sheet plasma sputtering method, the applied current to the target also increases as the sheet plasma current increases, without depending on whether the specific resistance of the target is high or low.

By utilizing this phenomenon, it was found that the problem (b) in the above-mentioned sputtering method, that is, the problem that "the insulator target cannot be used" can be solved. That is, film formation using a high-purity Si target with high specific resistance has become possible. This thing is
This means that there is a possibility that the problem (1) in forming the functional thin film used in the liquid crystal display (LCD) described above, that is, “reduction of impurities taken into the film” can be realized. .

When a target having a high specific resistance is used, abnormal discharge may occur on the target surface.
The inventor further investigated this situation, and when the width of the target was made smaller than the width of the sheet plasma,
It was found that the occurrence of abnormal discharge can be suppressed almost completely. That is, it has been found that the problem (d) in the above-mentioned sputtering method, that is, the problem that "abnormal discharge easily occurs" can be solved by setting the ratio of the width of the Si target to the width of the sheet plasma to be less than 1. As a result, a large amount of power can be stably applied to the target, and a process with high mass productivity can be constructed.

The inventor also tried to form a silicon-based thin film by introducing a reactive gas into the film forming chamber in order to reduce structural defects in the film. As a result, it was found that even when a reactive gas is used to form a silicon-based thin film containing at least one of hydrogen, oxygen, and nitrogen, the same action as that when the reactive gas is not used is obtained. It was Therefore, it is possible to efficiently reduce the structural defects in the film under the stable discharge condition without being affected by the impurities contained in the target material, and further improve the electrical characteristics. it can.

Further, in the present invention, it is not necessary to use toxic and explosive SiH ₄ gas as in the conventional CVD method, and raw materials that are easy to handle, namely Si, Ar,
Since it is possible to form a film with O ₂ , N _2, etc., it is possible to reduce safety measures and reduce the cost of the mass production process. Also, H
_{The 2} gas is easy to handle because it is used in a low concentration by mixing with Ar gas.

As described above, the high-efficiency sheet plasma sputtering method is used, and by appropriately controlling the sheet plasma current value and the ratio of the sheet plasma width to the target width, a high specific resistance and high purity can be obtained. Stable D for silicon (Si) targets
C sputtering is now possible.

Therefore, according to the sputtering film forming method for a silicon-based thin film of the present application, the above-mentioned liquid crystal display device (LC
Problems in forming the functional thin film used in D), that is, (1) reduction of impurities taken into the film, (2)
There are four issues: establishment of a thin film formation method with high target utilization efficiency and large area, (3) establishment of high-speed film formation method, (4) establishment of a thin film formation method having high adhesion strength and a dense film structure. That's all solved.

The Si target material has a specific resistance of 5
A material of 00 Ω · cm or more is used. In the case of conventional DC sputtering using a DC power source with a high film formation rate, if high-purity Si (500 Ω · cm or more) with high specific resistance is used as the target, a large voltage drop occurs in the target section and the target itself generates plasma. Since it also serves as an electrode for plasma, plasma is not generated or becomes extremely weak even if generated. As a result, film formation cannot be performed because sputtering does not occur, or even if film formation is possible, the film formation rate is extremely slow. As a solution to this problem, in general, high-purity Si is doped with an appropriate amount of phosphorus (P) or boron (B) to obtain a specific resistance of 1
Low-purity Si, which is suppressed to about 0 ⁻¹ to 10 ⁻² Ω · cm, is used as a target. Therefore, phosphorus (P) and boron (B), which are also used to control the electrical characteristics of the thin film, are
It is not good because it is present in an indefinite amount in the film.

On the other hand, in the case of RF sputtering using an RF power source, high-purity Si having a high specific resistance can be used, but since the film formation rate is reduced to about half that in the case of DC sputtering, mass production is possible. Not good for On the other hand, in the present invention, by using the sheet plasma type sputtering film forming apparatus described below under appropriate film forming conditions, sputtering can be continued even when the DC power source is applied to the target, and therefore high purity is achieved. The Si target material is now available.

Examples of the gas material include high-purity argon (Ar), hydrogen (H ₂ ), oxygen (O ₂ ), nitrogen (N
₂ ) and mixed gases thereof are preferred. Film formation is possible using SiH ₄ gas, but it is not good because it is toxic and explosive. In addition, when a silicon-based thin film containing at least one of hydrogen, oxygen, and nitrogen is formed by using Ar gas and a reactive gas, among bonds of Si atoms in the silicon-based thin film, a bond that cannot be bonded, that is, The bonding of these hydrogen, oxygen, and nitrogen to the dangling bond is more preferable because it can reduce structural defects in the film as compared with a silicon-based thin film formed using only Ar gas.

Since a Si film formed by using only Ar gas generally has many structural defects in the film and is amorphous, amorphous Si, that is, amorphous silicon (hereinafter referred to as "a- Si)). In addition, as described above, the a-Si thin film obtained by doping hydrogen, oxygen, nitrogen, etc. in the film is hydrogenated amorphous silicon (hereinafter, referred to as “a-Si: H”), amorphous silicon oxide (hereinafter, referred to as “a-Si: H”). It is referred to as "a-Si: O") and amorphous silicon nitride (hereinafter referred to as "a-Si: N").

As the film forming apparatus, for example, the sheet plasma type sputtering film forming apparatus shown in FIG.
The same device as that of Japanese Patent No. 04663) may be used. Less than,
The film forming method of the present invention will be described with reference to FIG.

FIG. 3 is a view seen from the thickness direction of the sheet plasma, and the sheet plasma has a width in the direction perpendicular to the paper surface. In FIG. 3, 1 is a pressure gradient type plasma gun, 2 is an arc discharge columnar plasma flow along a magnetic field, and 3 is a pair of rectangular permanent magnets that transform the columnar plasma flow into a sheet plasma flow. 4 is a sheet-shaped plasma flow. Reference numeral 5 denotes an arc discharge anode, which forms a discharge with the plasma gun. Reference numeral 6 denotes an air-core coil for drawing plasma, which forms a magnetic field 7 in the direction of the anode 5 from the plasma gun 1 and guides the sheet-shaped plasma flow 4 to the anode 5 in a stable manner. Reference numeral 8 denotes a sputtering Si target (shown by the thickness, which has a large width in a direction perpendicular to the drawing) on which an ion stream is incident from the sheet plasma surface, and 9 denotes a target 8 and a sheet plasma 4. A DC power supply 10 for applying a negative bias voltage indicates a substrate on which a thin film is formed on the surface by sputtering particles. Reference numeral 11 denotes a DC power source that applies a negative voltage to the cathode of the plasma gun 1.
The cathode is used for arc discharge between the cathode and the anode 5 to turn the Ar gas taken in through the gas inlet 12 into plasma. Reference numeral 13 is a gas introduction port for taking in gases (H ₂ , O ₂ , N ₂ ) for reactive sputtering.

The gas pressure in the film forming chamber, that is, the gas pressure in the space sandwiched between the target 8 and the substrate 10 is 1 × 10 ⁻⁴ to prevent the gas due to the back pressure from mixing into the Si thin film.
It is preferably 1 × 10 ⁻³ Torr. This gas pressure range does not depend on the type or flow rate of gas.

The temperature of the substrate 10 is selected depending on the desired electrical characteristics and adhesion to the Si thin film, but in the usual case, it is preferably 200 to 350 ° C, and 250 to 300 ° C.
Is more preferable.

The crystal form of the thin film may be crystalline or amorphous. However, when a silicon-based thin film is used as a functional thin film for liquid crystal, amorphous S in which structural defects in the film, that is, dangling bonds are reduced.
i, that is, amorphous silicon (a-Si) is often used.

The thin film applied device formed by the method of the present invention is, for example, a TFT (Thin Film Transistor) used in a liquid crystal display (LCD) or various sensors,
There are thin films for photoelectric conversion used in solar cells and photoconductors, and protective films in various devices.

[0057]

【Example】

(Embodiment 1) FIG. 1 is a diagram showing the relationship between the specific resistance of the Si target used in forming the Si thin film of the present invention and the impurity concentration in the formed Si thin film (marked with a circle in the figure). ). The result of the impurity concentration in the Si thin film formed by the conventional DC magnetron type sputtering film-forming apparatus shown in FIG. 1 (marked with ● in the figure) is shown for the case where a target capable of discharging is used. Specific resistance is 1 × 10 ^-3 Ω
・ Cm and 1 × 10 ⁻⁴ Ω · cm.

FIG. 2 is a diagram (marked with a circle in the figure) showing the thin film forming rate when the Si thin film of the present invention is formed.
A target having a specific resistance of 1000 Ω · cm was used.

The film forming apparatus used in FIGS. 1 and 2 is the sheet plasma type sputtering film forming apparatus shown in FIG. The impurity concentration in the Si thin film is represented by the sum of the phosphorus (P) concentration and the boron (B) concentration taken into the Si thin film.

The film forming procedure of this example will be described below with reference to FIG.

The target 8 has a specific resistance ρ of 5 × 1.
Various Si targets in the range of 0 ^{3 to} 5 × 10 ⁻⁶ Ω · cm were used (however, when confirming the thin film formation rate, a Si target with a specific resistance ρ of 1000 Ω · cm was used).
The size of the target 8 is as follows: thickness D = 5 mm (vertical direction of paper), width W = 100 mm (vertical to paper), length L
= 350 mm (left-right direction on paper). Also, the base 1
As 0, a glass substrate for liquid crystal (AN glass) manufactured by Asahi Glass was placed. The size of the substrate 10 has a thickness D = 1.1 m
m (vertical direction of paper surface), width W = 100 mm (vertical direction to paper surface), length L = 200 mm (horizontal direction of paper surface).

First, the inside of the vacuum chamber of the sputtering film forming apparatus is decompressed to 10 ⁻⁷ Torr or less by a vacuum exhaust device (not shown), and then Ar gas is introduced into the pressure gradient plasma gun 1 from the gas inlet 12. It is. The Ar gas flow rate at that time was fixed at 30 sccm.

Next, by applying a negative voltage E to the cathode of the plasma gun 1 using the DC power supply 11, the arc discharge columnar plasma flow 1 was generated between the anode 5 and the plasma gun. Here, the cathode voltage E of the plasma gun 1 is variable in the range of 10 to 500 Volt.

Further, the arc discharge columnar plasma flow 1 was transformed into a sheet plasma flow by using a pair of rectangular permanent magnets 3. This sheet-shaped plasma flow has a thickness D
= 15 mm (vertical direction of paper), width W = 100 mm
(Perpendicular to the paper surface). At this time, the distance from the thickness lower end of the sheet-shaped plasma flow to the surface of the target 8 is
The distance from the upper end of the thickness to the surface of the substrate 10 was 45 mm.

As the conditions for forming the Si thin film, the gas pressure near the substrate 10 was 1 mTorr, the temperature of the substrate 10 was 270 ° C., and the film forming time was 3 minutes. FIG. 1 shows the results of examining the impurity concentration (sum of phosphorus (P) concentration and boron (B) concentration incorporated in the Si thin film) in the produced Si thin film. This impurity concentration measurement is performed by Auger electron spectroscopy (Au
ger electron spectroscopy, AES). The thin film formation rate in FIG. 2 was obtained from the measured film thickness.
Furthermore, when the film structure of the Si thin film produced in this example was examined by an X-ray diffraction method, the diffraction peak was broad in all the samples. From this, it was judged that all the produced Si thin films had an amorphous crystal structure, that is, an amorphous structure. Therefore, hereinafter, the Si thin film will be referred to as an a-Si (amorphous-Si) thin film.

In this example, in order to reduce the impurity concentration in the a-Si thin film by an order of magnitude (1 ppm or less) compared with the conventional example (marked with ● in the figure), the resistivity of the Si target was set to 500.
It has been found that it is necessary to set Ω · cm or more (see FIG. 1). Therefore, it was determined that when an a-Si thin film was formed using a Si target that satisfied this condition, the amount of impurities taken into the film could be significantly reduced. In addition, a in this example
It was also separately found that the -Si thin film has higher-grade electrical characteristics than ever before.

Further, in this example, when the distance between the sheet plasma and the target, the thickness of the sheet plasma, the sheet plasma current i, etc. are optimized in addition to the DC bias application to the target, the bias current I of the target 8 is
It has been found that high-speed sputtering is possible because of a sufficiently large value. Then, this bias current I
It was also confirmed that was substantially proportional to the above plasma current i. The plasma current i was changed by increasing or decreasing the negative voltage applied to the cathode of the plasma gun 1.

FIG. 2 is a diagram showing the measurement results.
The horizontal axis of FIG. 2, that is, the sputtering power is the bias voltage applied to the target 8 (fixed at 500 V).
And the above-mentioned bias current I. From FIG. 2, it was found that the sheet plasma type sputtering film forming apparatus of this example can form an a-Si thin film at a sufficient film forming rate.

On the other hand, in the conventional DC magnetron type sputtering film forming apparatus, stable discharge could not be maintained, and film formation could not be performed on a Si target having a high specific resistance of 1000 Ω · cm.

Therefore, in this example, a high-purity a-Si thin film, which could not be formed by the conventional film-forming method, can be produced at high speed, so that a high-quality a-Si thin film can be produced at low cost. Can be provided.

Example 2 In this example, the width of the Si target was increased or decreased with respect to the width of the sheet plasma, and the number of occurrences of abnormal discharge observed near the surface of the Si target during film formation was measured. FIG. 4 is a diagram showing the measurement results. At this time, the resistivity of the Si target is 1000 Ω.
fixed to cm.

The other points were the same as in Example 1.

In this example, the ratio of the width of the Si target to the width of the sheet plasma is set to less than 1, that is, the width of the Si target is made smaller than the width of the sheet plasma, the number of abnormal discharges is set to 2 times / It turns out that it is necessary to be less than a minute. By constructing a mass production line to satisfy this condition, it has become possible to provide a method for forming a silicon-based thin film with high yield.

(Example 3) In this example, instead of the sheet-shaped plasma flow of Example 1 formed only of Ar gas, the sheet-shaped plasma flow is changed to Ar gas and a reactive gas (hydrogen, oxygen). , At least one gas of nitrogen). At this time, the resistivity of the Si target is 1000
The ratio of the width of the Si target to the width of the sheet plasma was fixed at 0.8, respectively, at Ω · cm. The other points were the same as in Example 1.

FIG. 5 is a diagram showing the thin film formation rate of this example. Symbols in the figure indicate ⊚ = a-Si: H film,
□ mark = a-Si: O film, Δ mark = a-Si: N film.
The a-Si thin film formation rate at this time is the same as that of the conventional example (● in the figure.
It was found that the amount was 5 times or more that of (H ₂ ) mark, ● (O ₂ ) mark, ● (N ₂ ) mark).

The measurement results of the impurity concentration in the a-Si thin film of this example showed the same tendency as in Example 1. That is, it has been found that the specific resistance of the Si target needs to be 500 Ω · cm or more in order to reduce the impurity concentration in the a-Si thin film by one order of magnitude (1 ppm or less) as compared with the prior art.

Further, even when the a-Si thin film of this example was formed, the occurrence of abnormal discharge observed near the surface of the Si target could be prevented by using the Si target having the specific resistance in the above range.

It was confirmed that the above results are the same when the produced Si thin film is crystalline, for example, when it is a SiO _x film or a SiN _x film.

Therefore, in this example, a silicon-based thin film (a-Si thin film, SiO _x film,
It has been found that even when a SiN _x film or the like) is formed, the amount of impurities taken into the film can be significantly reduced and high-speed formation is possible. As a result, in the case of an a-Si thin film, a high-speed processing for reducing structural defects in the film, that is, dangling bonds, can be realized, and a device using the a-Si thin film described above can be manufactured at low cost. Can be provided. In addition, Ar gas and reactive gas (hydrogen, oxygen,
Even when using at least one gas of nitrogen)
Since the problem of occurrence of abnormal discharge can be solved, it is possible to provide a stable film forming method.

In the present invention, unlike the conventional CVD method, it is not necessary to use toxic and explosive SiH ₄ gas, and the raw materials that are easy to handle, namely Si, Ar and O.
_Since it is possible to form a film with ₂ , N _2, etc., the cost required for various safety measures can be reduced, and the cost of the mass production process can be reduced. Further, since the H ₂ gas is mixed with Ar gas and used at a low concentration, the handling becomes easy.

[0081]

According to the present invention, it is possible to obtain a sputtering film forming method for a silicon-based main thin film, which enables high-speed formation of a high-purity silicon-based thin film.

Further, the number of abnormal discharges that occur during the formation of a silicon-based thin film can be significantly reduced, and a sputtering film-forming method for a silicon-based thin film with a high yield can be obtained. Further, structural defects in the film can be reduced. Also, Ar
Even when a silicon-based thin film is formed using a gas and a reactive gas, the number of abnormal discharges can be significantly reduced. Therefore,
It is possible to obtain a sputtering method for forming a silicon-based thin film that can use a safe gas and can construct a low-cost process.

[Brief description of drawings]

FIG. 1 S used in forming an a-Si thin film of the present invention
It is a diagram which shows the relationship between the specific resistance of i target and the impurity concentration in the formed a-Si thin film.

FIG. 2 is a diagram showing a thin film formation rate when only Ar gas is used in forming an a-Si thin film of the present invention.

FIG. 3 is a sheet plasma type sputtering film forming apparatus used when forming an a-Si thin film of the present invention.

FIG. 4 is a diagram showing the relationship between the ratio of the width of the Si target to the width of the sheet plasma and the number of abnormal discharges observed during film formation.

FIG. 5 is a diagram showing a thin film formation rate when Ar gas and a reactive gas are used in forming an a-Si thin film of the present invention.

[Explanation of symbols]

 1: Pressure gradient type plasma gun 2: Arc discharge cylindrical plasma flow 3: Pair of rectangular permanent magnets 4: Sheet-shaped plasma flow 5: Anode 6: Air core coil for plasma extraction 7: Coil magnetic field 8: Si target 9 : Sputtering power supply 10: Substrate 11: Plasma generation power supply 12: Ar gas inlet 13: Reactive gas inlet

Claims (5)

[Claims] 1. A sputtering method for forming a silicon-based thin film, wherein silicon (Si) having a specific resistance of 500 Ω · cm or more is used as a target material, and a DC bias is applied to the silicon target while the inside of the film forming chamber is being applied. Of the silicon-based thin film, characterized in that the plasma formed on the substrate is formed into a sheet shape that is positioned substantially parallel to the surface of the silicon target, and the silicon-based thin film is formed on the surface of the substrate placed in the film formation chamber. Sputtering method. 2. The method of sputtering film formation of a silicon-based thin film according to claim 1, wherein the width of the silicon target is smaller than the width of the plasma having a sheet shape. 3. The method for sputtering film formation of a silicon-based thin film according to claim 1, wherein hydrogen (H ₂ ) gas is introduced into the film formation chamber to form a silicon hydride film. 4. The method for sputtering film formation of a silicon-based thin film according to claim 1, wherein oxygen (O ₂ ) gas is introduced into the film formation chamber to form a silicon oxide film. 5. The method for sputtering film formation of a silicon-based thin film according to claim 1, wherein a nitrogen (N ₂ ) gas is introduced into the film formation chamber to form a silicon nitride film.