JPH0198216A - Formation of amorphous thin-film - Google Patents

Abstract

PURPOSE:To form an excellent thin-film stably at a fixed film formation rate at all times regardless of the lapse of time by measuring the intensity of light in a vacuum chamber, controlling an output from a light source on the basis of the measured value and keeping the intensity of light constant with time. CONSTITUTION:The inside of a vacuum chamber 1 in which a substrate 2 is arranged horizontally is decompressed through an exhaust valve 5. A raw material gas to which mercury is doped is fed from a raw-material gas supply nozzle 4 while the substrate 2 is heated by a heater 3. The upper section of the surface of the substrate 2 in the vaccum chamber 1 is irradiated vertically with light through a window 7 composed of synthetic quartz glass, etc., from a light source 6 such as a low pressure mercury lamp installed outside the vacuum chamber 1. An output from the light source 6 is controlled by a light-source output control section 10 on the basis of the measured value of the intensity of light in the vacuum chamber 1 by employing a light-intensity measuring instrument 8 such as photoelectric tube mounted into the vacuum chamber 1 at that time. The intensity of light in the vacuum chamber 1 is kept constant at all times. The film formation rate of an amorphous thin-film on the substrate 2 is held constant all the time, thus also preventing the change of the quality of the film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for forming an amorphous thin film of amorphous silicon, amorphous germanium, etc. on a substrate by a photo 0'VD method.

[Conventional technology]

Amorphous S1 (hereinafter abbreviated as a-3i), amorphous Ge
(hereinafter abbreviated as a-Ge), amorphous 5iGe' (hereinafter abbreviated as a-3iGe), etc. have excellent photoelectric properties, so they can be used in solar cells, electrophotographic photoreceptors, optical sensors, etc.
It is used in a wide range of fields such as thin film transistors.

Methods for manufacturing amorphous thin films such as a-9i include ion blating method, sputtering method, vacuum evaporation method, and O
V D (C!chemical Vaper Deposit
tion) method, etc., but silanes such as SiH (S1H
) to 4 n
a-S generated by decomposition by 2n+2 glow discharge
Based on i! Plasma CVD methods are commonly used to deposit on.

However, recent research has shown that amorphous thin films such as the a-3i thin film manufactured by plasma CVD are photosensitive due to damage to the film due to plasma and the introduction of impurities into the film from the inner wall of the chamber due to hydrogen atoms. It has become clear that there are limits to the improvement of characteristics.

Therefore, recently, a photo-CVD method that does not have the above-mentioned problems has been adopted. This method uses light energy to excite the raw material gas, generate radicals, and deposit a
This method involves depositing an amorphous thin film such as a Si thin film, and there are two methods: a direct excitation method and a mercury-sensitized excitation method. The direct excitation method is a method in which the source gas is directly excited by irradiating the source gas with extremely strong light such as an excimer laser, but it cannot be said to be a technically established method yet. On the other hand, in the mercury sensitized excitation method, a raw material gas is doped with a trace amount of mercury vapor, the mercury is excited by irradiation from a light source, and the generated mercury radicals react with the raw material gas to form amorphous materials such as a-3i thin films. It is a method of depositing thin films onto a substrate, and is increasingly being used.

Conventionally, the photo-CVD method using mercury sensitization has been carried out using an apparatus as shown in FIG. That is, vacuum chamber 1
The substrate 2 is placed horizontally in the vacuum chamber 1, the pressure inside the vacuum chamber 1 is reduced through the exhaust valve 5, and while the substrate 2 is heated by the heater 3, for example, silanes or their halides, or A gas doped with mercury is supplied to a raw material gas such as silicon halide. A light source 6 such as a low-pressure mercury lamp is provided outside the vacuum chamber 1, and irradiates light vertically onto the surface of the substrate 2 through a window 7 provided in the vacuum chamber 1 made of synthetic quartz glass or the like that easily transmits ultraviolet rays. This causes a photochemical reaction between mercury and the raw material gas.

However, in this optical OVD method, it was inevitable that a thin film would also adhere to the surface of the window 7 on the vacuum chamber 1 side through which light enters. For this reason, there was a drawback that the light intensity within the vacuum chamber 1 gradually decreased as the film forming time progressed, and the film forming rate gradually decreased. Furthermore, as shown in FIG. 5 by taking the Ge composition ratio in the a-8iGe thin film as an example, the composition of the amorphous thin film formed on the substrate 2 changes as the light intensity changes, so that certain characteristics cannot be maintained. It was difficult to stably form an amorphous thin film.

Regarding the method of preventing thin film adhesion to the windows of optical OVD equipment, please refer to "Survey Report on New Electronic Materials ■, Photoexcitation Process Technology Research Report 1" by the Japan Electronic Industry Promotion Association, March 1986, Vol. Although detailed explanations are given on pages 35 to 38, none of the methods could be said to be sufficient.

[Problem that the invention seeks to solve]

In view of such conventional circumstances, the present invention provides a method for stably forming an amorphous thin film with excellent characteristics at a constant film formation rate regardless of the passage of time, using the optical OVD method. That is.

[Means for solving problems]

The present invention is a method of forming an amorphous thin film on a substrate by optical OVD method, in which the light intensity in a vacuum chamber is measured,
The method is characterized in that the light intensity within the vacuum chamber is kept constant over time by controlling the output of the light source based on this measured value.

The method of the present invention will be explained in detail with reference to FIG. 1, which shows a specific example of a manufacturing apparatus.

As in the normal case, the substrate 2 is placed horizontally in the vacuum chamber 1, the pressure inside the vacuum chamber 1 is reduced through the exhaust valve 5, and while the substrate 2 is heated with the heater 3, mercury is supplied from the raw material gas supply nozzle 4. A raw material gas doped with is supplied. Light is vertically irradiated onto the surface of the substrate 2 inside the vacuum chamber 1 from a light source 6 such as a low-pressure mercury lamp provided outside the vacuum chamber 1 through a window 7 made of synthetic quartz glass or the like.

At this time, the light intensity inside the vacuum chamber 1 is measured using a normal light intensity measuring device 8 such as a phototube installed inside the vacuum chamber 1, and the light source output control section adjusts the output of the light source 6 based on this measurement value. 10 to keep the light intensity inside the vacuum chamber 1 constant.

If the light intensity measuring device 8 is always fixed within the light irradiation area, a thin film will adhere to its surface and accurate photometry will not be possible. It is preferable to take it in and out of the irradiation area. Even by such intermittent measurement of light intensity, it is possible to maintain the light intensity within the vacuum chamber 1 constant.

In addition, even when carrying out the method of the present invention, perfluorination, which has a low vapor pressure and transmits ultraviolet rays, is applied to the surface of one vacuum chamber of the window 7, as already known as a means for preventing thin film adhesion to the window 7. It is effective to apply a thin layer of polyethyl (trade name: 7 Onpurin Oil).

[Effect]

In the method of the present invention, when a thin film adheres to the window 7 through which light enters and the light intensity inside the vacuum chamber 1 decreases, the light intensity measuring device 8 detects this and the light source output control section 10 controls the light source 6.
, the light intensity inside the vacuum chamber 1 is always constant regardless of the elapse of the film forming time.

Therefore, the deposition rate of the amorphous thin film on the substrate 2 is always constant, and changes in the film quality of the amorphous thin film that depend on changes in light intensity can also be prevented.

〔Example〕

Using the apparatus shown in FIG. 1, a thin film of a-SiG was formed on a substrate by a mercury-sensitized OVD method under the following conditions.

Light source: Low pressure mercury lamp (185mm, 254n
m) Raw material gas: SiH50sccm+GeH105c
an pressure: 0.30 torr mercury temperature =
600 Substrate temperature: 200 C Incidentally, the surface of the window 7 on the vacuum chamber 1 side was coated with Fonpurine oil.

In this case, as a first embodiment, the light intensity measuring device 8 is intermittently rotated into and out of the light irradiation area by the rotary motor 9, and the light intensity is measured every 3 minutes, and the light intensity inside the vacuum chamber 1 is measured. The a-3iGe thin film is applied to the substrate 2 by controlling the light source output control unit 10 so that IQ mJ/fi1m2.
formed on top.

In addition, as Example 2, the light intensity was measured while the light intensity measuring device 8 was always fixed within the light irradiation area, and the light intensity was also 1.
Control the light source output control unit 10 so that the distance is 0m.
-3iGe thin film was formed on substrate 2. In Examples 1 and 2, a low-pressure mercury lamp of 254 liters was used to measure the light intensity.
A resonance line of mm was used.

Furthermore, as a comparative example, vacuum chamber 1 was
An a-3iGe thin film was formed on the substrate 2 with the initial light intensity set at 10 mW and without controlling the light source output.

FIG. 3 shows the relationship between the film thickness and film-forming time of each a-3iGe thin film formed. In the comparative example, as the film deposition time progresses, the nitrogen 7 becomes cloudy due to the adhesion of the film, so the light intensity decreases and the film formation rate gradually decreases, whereas in Example 1 of the present invention, the film formation rate is always constant. It turns out that there is something. In addition, in Example 2, the film formation rate increased as the film formation time progressed, but this was because the film gradually adhered to the fixed light intensity measuring device, and the light intensity was measured accordingly. It is.

In addition, for the a-8iGe thin films obtained in Example 1 and Comparative Example, the Ge composition ratio profile in the film thickness direction was determined by E S
CA (E/ectron 5pectroscope
y for Chemi-aal Analysis)
The results are shown in FIG.

In the comparative example, as the film formation time progresses (the closer it gets to the surface)
In contrast to the decrease in the Ge content, in Example 1, a nearly constant Ge composition ratio was obtained in the film thickness direction, resulting in a homogeneous a-3i film.
It can be seen that a Ge thin film was formed.

It should be noted that the method of the present invention can be applied to the formation of amorphous thin films other than the a-3iGe thin films shown in the examples, and as long as it is a photo-CVD method, not only the mercury sensitization method but also the direct excitation method may be used. Needless to say.

〔Effect of the invention〕

According to the present invention, the light intensity within the vacuum chamber 1 can be kept constant regardless of the elapse of the film formation time, so that an excellent amorphous film with constant film quality can be obtained at a constant film formation rate over time. A thin film can be stably formed on a substrate.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing a specific example of an apparatus for carrying out the method of the present invention, and FIG. 2 is a schematic sectional view of a conventional apparatus. Figure 3 shows a-3iG for the example and comparative example.
This is a graph showing the relationship between the film thickness and film formation time of the e thin film, and Fig. 4 is the same (a-8i) graph showing the Ge composition ratio in the film thickness direction of the thin film. It is a graph showing the relationship between the strength and the Ge composition ratio of the a-3iGe thin film. 1. Vacuum chamber 2. Substrate 3. Heater 4
・・Raw material gas supply nozzle 6・・Light source 7・・Window 8・・
Light intensity measuring device 9...Rotating motor 1o...Light source output control section Fig. 2 Fig. 3 Film forming time (minutes)

Claims (2)

[Claims] (1) In a method of forming an amorphous thin film on a substrate using the photoCVD method, the light intensity in the vacuum chamber is measured and the output of the light source is controlled based on this measurement value. A method for forming an amorphous thin film characterized by keeping the strength constant over time. (2) The amorphous thin film according to claim (1), wherein the light intensity is intermittently measured by moving a light intensity measuring device into and out of the light irradiation area in a vacuum chamber. How to form.