JPH0273979A - Formation of thin film - Google Patents

Abstract

PURPOSE:To form a thin film excellent in film characteristics by a CVD method at the atmospheric pressure by providing a high resistor to an electrode and specifying both the distance between a base plate and the electrode and flow rate of gas to be supplied and also coating the high resistor of the electrode with the element constituting the thin film. CONSTITUTION:A high resistor 4 having >=10<11>OMEGAcm resistivity is provided on at least one of the opposed faces of the counter electrodes 2, 3 in a film formation chamber 1. The distance between a base plate 5 and the electrode 2(3) or between the base plate 5 and the high resistor 4 is regulated to 10-0.1mm. The surface of the electrode 2 or the high resistor 4 is coated with at least one of the elements constituting a thin film. A gaseous mixture of gas for forming the film and He is supplied to a discharge space so that Q/S value obtained by dividing flow rate Q of gas with volume S of the discharge space is regulated to 1-10<2>sec<-1>. High-frequency voltage is impressed to the counter electrodes 2, 3 to cause glow discharge close to the atmospheric pressure and the thin film is formed on the base plate 5. Thereby the impurities in the a-Si thin film can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Technical Field The present invention relates to the production of amorphous silicon (a-5l:an+) by a plasma CVD method under pressure near atmospheric pressure.

The present invention relates to a method for forming thin films such as phous 5lllcon).

For example, amorphous silicon a-S, which normally contains several at% to several tens of at% (atomic percent) of H in its film.
L films are seen as promising materials for low-cost solar cells. Other uses include image sensors, optical sensors, thin film transistors, and photosensitive materials for copying machines. Single crystal S
It has the advantage that it is cheaper than 1 and that it is easier to obtain one with a large area.

As such thin film forming methods, thermal CVD method, plasma C
The VD method and the like are known.

Since the thermal CVD method requires heating the substrate, it can only be used with heat-resistant materials.

On the other hand, the plasma CVD method can form a thin film at a lower temperature than the thermal CVD method.

Therefore, thin films can be formed on low-cost glass substrates, polymer films, etc. with poor heat resistance, and they are widely used.

In the plasma CVD method, excitation energy is provided not in the form of heat but in the form of the kinetic energy of electrons and ions in the plasma, and the chemical energy of neutral radicals. Therefore, the temperature of the substrate can be lowered than in thermal CVD.

- As an example, amorphous silicon a-5l is 5pe
A thin film forming method using glow discharge was invented by AR.
Since it was possible to incorporate an appropriate amount of H into the film and reduce the defect density in the film, it became possible to produce films that could withstand device applications such as solar cells and sensors.

W, E, 5pear, P, G, Recomber: 5o
lldComn+un,,17. pH9 This is a parallel plate type electrode with 100klHz N13.56Mfl
An AC voltage of z is applied to cause glow discharge in a mixed gas such as 5IH4/H2 or 5IH4-SiF4/H2 at a low pressure of 0.1 to 2 Torr.

Of course, dopants may also be added. This is P■
This is done by mixing gases such as a/H2 and BJ8/H2.

(a) Prior Art Since the invention of 5pear, a-Sl manufacturing equipment has been improved many times, but basically it performs glow discharge at low pressure.

Glow discharge does not occur unless the pressure is as low as 0.1-10 Torr. When the pressure is higher than this, the discharge shifts to a localized arc discharge, making it impossible to form a film on a substrate with poor heat resistance or to form a film uniformly over a large area. So such pressure is chosen.

Therefore, the container required an expensive vacuum chamber and had to be equipped with a vacuum pump.

In particular, in the case of photoelectric conversion materials such as solar cells using a-Sl, it is strongly required from a cost standpoint that a large area thin film can be formed all at once.

However, in the plasma CVD method, glow discharge is maintained to keep plasma stable. Glow discharge occurs in vacuum (0,1
~10 Torr).

Films can only be formed in a vacuum, so if you want to make a large-area film, you have to make the entire vacuum container larger.

A high-output vacuum pump is also required.

In this case, the equipment becomes extremely expensive.

(1) Atmospheric pressure plasma CVD method In order to put thin films such as A-5L into practical use, cost reduction is an important factor, but conventional plasma CVD under reduced pressure
Method D had a major problem: high equipment costs.

However, recently, plasma CVD under atmospheric pressure
An invention was made that made law possible.

For example, there is JP-A-83-50478 (S, published on March 3, 1983).

The present inventors, ii. Japanese Patent Application No. 83-199647
Application) 1ii Japanese Patent Application No. 1983-199848 (S, l1f
3.8. IO application) iv Japanese Patent Application No. 83-199649 (
S, filed on August 10, 1983).

FIG. 2 shows a slightly modified version of the one indicated by iv.

Inside the film forming chamber 1, electrodes 2.3 facing each other are provided. One end is grounded and is called a ground electrode 3. The other electrode is referred to as the non-grounded electrode 2.

A high resistance element 4 is placed on the electrode 2. Further, a sample substrate 5 is placed on the electrode 3. Here, the electrode 2 and the high resistance body 4 also serve as a gas supply port to the discharge space, and the high resistance body 4 is a porous plate.

The purpose of inserting the high-resistance element 4 here is to ensure that the glow discharge does not occur locally but widely over the entire electrode plate, and a high-resistance element is inserted between the electrode 3 and the sample substrate 5. You can.

In addition, the high resistance element 4 is a porous plate and the gas supply port is
This is to effectively perform gas replacement at the center of the plasma and to obtain uniform film formation. Here, the distance g between the sample substrate 5 and the high resistance element 4 is set to be 10 mm to 0.1 mm.

A high frequency power source 7 is connected to the non-grounded electrode 2 .

This can use, for example, a 13.58 MHz RF oscillator and an amplifier.

A mixed gas obtained by diluting a large amount of raw material gas with Be gas is introduced from the gas inlet 6, supplied to the discharge space via the electrode 2 and the high-resistance element 4, and is discharged outside the film forming chamber 1 from the gas outlet 9. be done. Furthermore, with respect to the volume S of the discharge space, the flow rate Q of the mixed gas is such that Q/S is 15ec-" ~ l02sec-'
Make it so that

Problems that Cken's invention aims to solve Thin film formation using the plasma CVD method under atmospheric pressure is an extremely promising method for reducing costs, but when considering application to devices, the film properties are poor and doesn't amount to anything. For example, a-Sl films are increasingly being applied to solar cells, image sensors, optical sensors, thin film transistors, electrophotographic photoreceptors, etc.; It is desirable that the sensitivity (ratio of photoelectric conductivity to dark electrical conductivity (σd): Δσah/σd) is high, and that the defect density (N, ) in the film, which has a large effect on device characteristics, is low. .

A thin film, such as an a-Sl film, produced by the conventional atmospheric pressure plasma CVD method has values of Δσ2ゎ, Δσ2t, and /σ6 that are equivalent to a-Slli produced by the low-pressure plasma CVD method. However, Ns is I x 1018spl
n/cc, which is higher than that of the a-5L film formed by low-pressure plasma CVD and used in devices such as solar cells (Ns < 5 x 1015 spln/cc), which poses a problem when applied to devices. Ta.

In order to solve this problem, the inventors developed a-5llll! using the conventional atmospheric pressure plasma CVD method. Various studies were conducted on the causes of high Ha.

As a result, the constituent elements of the electrode or high-resistance material are sputtered from the electrode or high-resistance material that faces the film-forming substrate through the plasma by the high-density plasma at near atmospheric pressure, and a large amount of the constituent elements of the electrode or high-resistance material are sputtered into the a-Sl film. The present invention was based on the discovery that this substance is incorporated as an impurity.

(J) Purpose The purpose of the present invention is to provide a method for forming a thin film with good film properties that can be used for device applications in a thin film forming method using plasma CVD under atmospheric pressure, which is promising for cost reduction. It is something to do.

(1) Structure of the Invention and Means for Solving Problems The present invention provides an electrode that faces a sample substrate via plasma, or an electrode that faces the sample substrate via plasma, in order to prevent impurity contamination due to plasma sputtering. As the high-resistance material, a material containing at least one element among the constituent elements of the thin film to be formed is used.

Or, among the constituent elements of the thin film to be deposited on the surface of the electrode or high-resistance body facing the sample substrate,
Coating or pasting a material consisting of at least one element.

As the material facing the sample substrate, it is preferable to use the same material as the thin film to be formed or the main constituent material of the thin film to be formed.

FIG. 1 shows a thin film 10 to be formed on the opposite surface of a high resistance element 4 facing a sample substrate 5, as an example of the present invention.
An example of coating is shown below.

The structure is the same as that shown in FIG. 2, except that the surface facing the sample substrate is coated with a film-forming material.

Inside the film forming chamber 1, electrodes 2.3 facing each other are provided. One end is grounded and is called the other electrode 3. The other electrode is referred to as the non-grounded electrode 2.

A high resistance element 4 is placed on the electrode 2. Further, a sample substrate 5 is placed on the electrode 3. Here, the electrode 2 and the high resistance body 4 also serve as a gas supply port to the discharge space, and the high resistance body 4 is a porous plate.

Here, the reason for inserting the high resistance element 4 is to ensure that the glow discharge does not occur locally but widely over the entire electrode plate.If the sample substrate 5 is conductive, the electrode 3 and the sample substrate It is preferable to insert a high-resistance element between the lines 5 and 5.

In addition, the high resistance element 4 is a porous plate and the gas supply port is
This is to effectively perform gas replacement at the center of the plasma and to obtain uniform film formation.

Here, the distance g between the sample substrate 5 and the high resistance element 4 is 10V+
+ ~0.1mm.

A high frequency power source 7 is connected to the non-grounded electrode 2 .

This can use, for example, a 13.58 MHz RF oscillator and an amplifier.

A mixed gas obtained by diluting a large amount of raw material gas with He gas is introduced from the gas inlet 6, supplied to the discharge space via the electrode 2 and the high-resistance element 4, and then exhausted from the film forming chamber 1 through the gas outlet 9. be done. In addition, with respect to the volume S of the discharge space, the flow rate Q of the mixed gas is Q/S of 15 sec-' to 102 sec-'
Make it so that

(ii) Function As shown in FIG. In the case of forming a-C, a film of a-C or graphite is formed respectively.
Even if plasma sputtering occurs, the sputtered elements are
It is a constituent element of the target thin film, can prevent impurities from entering the film, reduce the defect density in the film, and form a thin film that is promising for device applications.

Furthermore, when forming a p-type a-5L doped with B or an n-type a-S+ film doped with P, the material facing the sample substrate should be a non-doped SIN film that does not contain a doping element! You may also use E. When forming an a-SlGe film, asIGe is used as the material facing the sample substrate.
film, or crystalline 5IGe material, a-5t film (which may or may not contain hydrogen), crystalline Sl, a-Ge film (
(It may or may not contain hydrogen) or may be a crystalline Ge material. This is because the elements mixed into the film formed from the material facing the sample substrate are constituent elements of the formed film. ), the first
A-5L films were formed under the conditions shown in the table, and the film properties were compared. Note that 5IO3 is used as the high-resistance element 4, and the surface coating material 10 of the high-resistance element is an a-5F film (thickness 5
gm).

RF power RF frequency Electrode area High resistance element, distance between boards Base plate Film forming time 00W 13.5f film MHz 10caX l0cm 3n+m quartz glass 0mln The properties of the obtained film are shown in Table 2.

Table 2 Film properties Invention Eg (eV) 1.78 Δσah (S/Cm) 7 X 10-5σd (S/
Cm) 8 X 10-'N5 (spln/cc)
8 X 10'' Comparative Example ■, 89 Xl0-5 5 X 10-'.

I This is the value calculated by

Δσpb is a value measured using a light source of AMl, 51001 mW/cm".

Ns is the value of unpaired electron pairs (dangling bonds and one of defects in the film) in the film determined by electron spin resonance (ESR).

The oxygen impurity concentration is a value determined by secondary ion mass spectrometry (SIMS).

In the present invention, O from the SIO□ used as the high resistance element 4 is
It can be seen that there is no plasma sputtering, the amount of oxygen in the film is reduced, Ns is reduced, and Δσph is also improved.

(1) Effects According to the present invention, impurities in thin films such as A-5L films can be reduced by using the atmospheric pressure plasma CVD method, which is expected to reduce equipment costs. , it is possible to form thin films with good film properties that are promising for device applications such as thin film transistors and electrophotographic photoreceptors.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an apparatus used in the thin film forming method of the present invention. FIG. 2 is a schematic sectional view of an apparatus used in the thin film forming method disclosed in Japanese Patent Application No. 83-199649 filed by the present inventor. 1゜2゜3゜4゜5゜6゜7゜8゜9゜10゜, film formation chamber non-grounded electrode grounded electrode porous plate high resistance sample substrate gas inlet high frequency power supply heater gas outlet purpose of film formation Thin film inventor Yui Shito Tomikawa 1) Junhiko

Claims (1)

[Claims] A high-resistance element with a resistivity of 10^1^1 Ωcm or more is installed on at least one of the opposing surfaces of two electrodes facing each other, and on the electrode or the high-resistance element facing this high-resistance element,
A sample substrate is installed, and the distance between the sample substrate and the electrode facing the sample substrate, or the distance between the sample substrate and the high resistance element facing the sample substrate, is set to 10 mm or less, 0.1 mm. With the above, the mixed gas consisting of the film forming gas and He is adjusted so that the value Q/S obtained by dividing the gas flow rate Q by the volume S of the discharge space is 1 to 10^2 sec^-^1.
A high-frequency voltage is supplied to the discharge space on the sample substrate and applied to the counter electrode under pressure close to atmospheric pressure to generate a voltage between the sample substrate and the electrode facing the sample substrate, or between the sample substrate and the electrode facing the sample substrate. In the method of forming a thin film on a sample substrate by causing a glow discharge between the electrode and the high-resistance object, the electrode facing the sample substrate on which the thin film is to be formed or the electrode facing the sample substrate on which the thin film is to be formed is used. The surface of the high-resistance material is coated with a material consisting of at least one of the constituent elements of the thin film to be formed, or
The electrode facing the sample substrate on which the thin film is to be formed or the high resistance element facing the sample substrate on which the thin film is to be formed is made of a material consisting of at least one element among the constituent elements of the thin film to be formed. A thin film formation method characterized by: