JPS62259426A - Formation of thin film - Google Patents

Abstract

PURPOSE:To prevent a reactive product thin film from forming on an ultraviolet light transmission window without coating oil or the like by applying a bias voltage of a discharge starting voltage or lower to a first electrode and a second electrode provided on the window or near the window or ultraviolet light source. CONSTITUTION:A power source 11 is so provided as to apply a bias voltage to between a first electrode 4 and a second electrode 2 provided on an ultraviolet light transmission window or near the window or ultraviolet light source. Ion species or active species slightly charged in which reactive product contained in reaction gas becomes solid is separated from the window 5 or near the light source 6 by a bias voltage applied to between the electrodes 4 and 2. Thus, an optical CVD method can be applied to a wide semiconductor device to simply obtain a semiconductor device having preferably boundary characteristic without damage on a base of the feature of the optical CVD method.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Application of the Invention The present invention relates to a method for producing a thin film of a photochemical vapor phase reaction product on a substrate.

(b) Prior art In recent years, photochemical vapor phase reaction (hereinafter referred to as photoCV
D method) is attracting attention.

The conventional apparatus used for thin film production using this photoCVD method places a film forming substrate in a reaction vessel having a window for transmitting ultraviolet light, and introduces a thin film production gas under reduced pressure.
Ultraviolet light introduced through the ultraviolet light transmission window causes a photochemical vapor phase reaction in the reaction vessel, and a thin film of the reaction product is deposited on the substrate. The ultraviolet light transmission window is made of a material that easily transmits ultraviolet light, such as quartz glass, lithium fluoride, and magnesium fluoride.

In addition, in order to increase the production rate of thin films, mercury sensitization method is used, in which mercury is added together with the gas for forming thin films in the reaction vessel, and in order to make it possible to form thin films over a large area, the pressure in the ultraviolet light source chamber is reduced. In addition, efforts have been made to make the ultraviolet light transmitting window thicker.

By the way, in this photo-CVD method, ultraviolet light is introduced into the reaction vessel through an ultraviolet light transmission window, so a thin film is formed not only on the film forming substrate but also on the transmission window, so it is not sufficient immediately after the introduction of ultraviolet light. A large amount of ultraviolet light is irradiated onto the substrate through the window, but as a thin film is formed on the transmission window, the amount of ultraviolet light transmitted decreases, and eventually a thin film is formed on the substrate. The problem was that it would no longer be possible.

In addition, as a solution to this problem, it has been proposed to coat the reaction vessel side of the transmission window with oil, but oil components are incorporated into the film formed during the photochemical vapor phase reaction and deteriorate the film quality. There was a problem.

(c) Purpose of the invention The present invention solves these problems.

That is, this is a method of forming a thin film on the ultraviolet light transmitting window by photo-CVD without forming a reaction product thin film without applying oil or the like.

(D) Structure of the Invention The present invention provides a method for forming a thin film on a substrate by decomposing and activating a gas for forming a thin film using ultraviolet light. A bias voltage equal to or lower than the discharge starting voltage at the pressure in the reaction chamber during the photochemical vapor phase reaction is applied to the first electrode located at the first electrode and the second electrode provided at a distance opposite to the first electrode. However, it is a thin film formation method characterized by forming a thin film on a substrate by photochemical vapor phase reaction. In other words, ionic species or slightly charged active species that cause the reaction product contained in the reaction gas to become solid,
The feature is that by applying a bias voltage between the first electrode and the second electrode, the ultraviolet light can be moved away from the ultraviolet light transmitting window or near the ultraviolet light source.

Naturally, this bias voltage is a value lower than the discharge start voltage at the pressure inside the reaction vessel during the photochemical vapor phase reaction.

The first electrode and the second electrode are made of aluminum, molybdenum, tungsten, stainless steel, platinum, copper, chromium, silver, magnesium, or nickel.

The electrode is preferably made of zinc, cobalt, iron, indium, a metal selected depending on the reactive gas used, or an alloy thereof, and has an aperture ratio of 90% or more.

Examples are shown below.

Example 1゜ FIG. 1 shows an outline of the apparatus used in the present invention.

A second electrode (2) provided in the reaction vessel (1) serves both as a heater for heating the substrate and as a substrate support.

A low-pressure mercury lamp (6) is used as the ultraviolet light source, and the ultraviolet light source chamber α is under reduced pressure and adjacent to the reaction chamber through a quartz glass plate (5) as an ultraviolet light transmitting window.

The first electrode (4) on the ultraviolet light transmitting window is made of nickel,
The entire surface of the window was thinly coated and then patterned in a lattice shape so that the line width was 50 μm and the aperture ratio was 90%. The size of the cough window was 3QQmm x 300n and the thickness was about 3mm. Moreover, between the first electrode (4) and the second electrode (2),
An application power source 00 is provided so that a bias voltage can be applied.

Using this apparatus, an attempt was made to fabricate a silicon nitride thin film by the photo-CVD method. The conditions are shown below.

Gas flow rate S iz Hb 10 SCCMN
H3500SCCM Nz 500 SCCC C window pressure 400Pa Substrate temperature 300°C At this time, the distance between the first electrode (4) and the second electrode (2) is approximately 5
At zero, the bias voltage is set to negative polarity on the first electrode (4) side so that, for example, ionized St does not approach the window side.
It was set to 0.30.60V. The relationship between the thickness of the thin film and the reaction time at that time is shown in FIG. The curve @ is the result at 0 hours, which is about 1000 people with a reaction time of 60 minutes, and there is a tendency for a thick film to form beyond that time. This is an ultraviolet light transmitting window (
This shows that a film was also formed in 5), so that an amount of ultraviolet light sufficient to fully decompose the reaction gas did not pass through.

On the other hand, the bias voltage of the present invention is 30■ (curve α31),
60V (curve Q4)), the film formation rate tends to slow down over time, but compared to curve α2, it is clearly faster (it is also possible to form a thick film, and it is possible to reach the critical film formation rate). If the thickness is also curve αa, ○■ (curve (2))
The number has reached 3,000, which is about three times the number compared to the previous year.

Furthermore, after these films are formed, if a voltage higher than the discharge starting voltage is applied between the first and second electrodes and an etching gas is introduced into the reaction chamber, there is an advantage that the inside of the reaction chamber can be cleaned using the same equipment configuration. be.

Example 2 Next, using the same apparatus as in Example 1, an amorphous silicon film was manufactured.

The other experimental conditions were exactly the same as in Example 1 except that 20 SCCM of He-based 10% 5izHb was flowed as the thin film forming gas. In this example, the bias voltage is OV and 25
I went with V. The results are shown in FIG. In the case of OV, the film thickness stopped increasing completely about 10 minutes after the start of the reaction as shown by curve α, but when a bias voltage of 25V was applied between the first and second electrodes as in the present invention, As shown by curve αQ, the film thickness continues to increase even after 10 minutes, reaching approximately 1 in 60 minutes.
It has reached 000 people.

Note that the present invention is not limited only to the examples.

Further, in Example 1.2, the second electrode also serves as a substrate support, but the structure is not particularly limited to this.

Furthermore, although the ultraviolet light transmitting window was provided in this example, a structure in which the ultraviolet light source is directly placed in the reaction chamber may also be used.

(E) Effect By employing the configuration of the present invention, the film formation speed and critical film thickness are improved by about three times compared to the conventional photo-CVD method.

This has made it possible to apply the photo-CVD method to wide semiconductor devices, and it has become possible to easily obtain semiconductor devices with good interfacial properties without damaging the underlying layer, which is a feature of the photo-CVD method.

In addition, since no oil or the like is applied on the ultraviolet light transmitting window unlike the conventional method, impurities are not mixed into the formed thin film and a good film quality can be obtained.

Furthermore, when a voltage higher than the discharge starting voltage is applied between the first electrode and the second electrode and etching is used as the reaction gas, there is an advantage that the reaction chamber can be etched with the same equipment configuration.

[Brief explanation of drawings]

FIG. 1 shows the apparatus of the invention. FIGS. 2 and 3 show the relationship between the thickness of the thin film obtained by the present invention and the reaction time. 1... Reaction chamber 2... Second electrode (substrate support) 4... First electrode 5... Ultraviolet light transmission window 6... Ultraviolet light source

Claims (1)

[Claims] In a method of forming a thin film on a substrate by decomposing and activating a gas for forming a thin film using ultraviolet light, a first electrode provided on or near an ultraviolet light transmitting window or near an ultraviolet light source is used. While applying a bias voltage lower than the discharge start voltage at the reaction chamber pressure during the photochemical vapor phase reaction between the second electrode and the second electrode provided at a distance from the first electrode, the photochemical vapor phase reaction is applied to the substrate. A thin film forming method characterized by forming a thin film on.