JPH02219218A - Formation of thin film - Google Patents

Abstract

PURPOSE:To enable a thin film to be formed with a uniform thickness by providing an auxiliary magnetic field creating means between anode and cathode and fluctuating a plasma by means of a auxiliary electric or magnetic field created thereby. CONSTITUTION:Voltages of opposite polarities are applied to auxiliary electrodes 6a and 6b, respectively, by an auxiliary power supply 7 constituting an auxiliary field creating means together with the auxiliary electrodes 6a and 6b arranged on the opposite sides between a cathode 1 and an anode 2, while the polarities of the voltages are reversed periodically. Thereby, an auxiliary electric field is produced between the auxiliary electrodes 6a and 6b in direction perpendicular to a high-frequency field, the direction of the auxiliary field being reversed periodically. A plasma between the cathode and anode 1 and 2 is fluctuated by this auxiliary field. Accordingly, a period of time for which a high density region of the plasma is in contact with a substrate 3 is made uniform and, therefore, ununiformity in distance between the substrate 3 and the plasma is eliminated. Accordingly to this method, a thin film having a uniform thickness can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for forming thin films such as amorphous semiconductor thin films and insulator thin films used in solar cells, thin film transistors, and the like.

[Conventional technology]

Generally, amorphous semiconductor thin films such as a-Si and siN are used.
.

The plasma CVD method using parallel plate RF glow discharge is well known as a method for forming insulator thin films such as Si02, but it has problems in terms of film formation speed, so for example, Japanese Patent Laid-Open No. 197875/1983 Public bulletin (HOIL)
31104), it has been considered to improve the film forming rate by using a so-called magnetron discharge method in which a magnetic field is used in combination with an RF glow discharge method.

By the way, thin film formation using this magnetron discharge method is
This is carried out using an apparatus as shown in FIG. 10, and this apparatus is constructed as follows.

That is, in FIG. 10, (1) and (2) are flat/plate-shaped cathode electrodes and anode electrodes (hereinafter simply referred to as cathodes (1) ), anode (2)), (3) a thin film forming substrate attached to the anode (2), (4)
is a high frequency power supply, and one output terminal is an anode (2)
and the other output terminal is the cathode (1).
It is connected to the.

(5a) and (5b) are annular magnets and cylindrical magnets, which are provided below the cathode (1), and both magnets (5a)
.

The plasma of the reactant gas is confined between the cathode (1) and the anode (2) by the magnetic field formed in (5b).

Then, the high frequency voltage from the power supply (4) is applied to the cathode (1).
The reaction gas applied between the anodes (2) and supplied into the reaction chamber is turned into plasma by glow discharge, and the plasmanized reaction gas components are deposited on the substrate (3), forming a thin film on the substrate (3). is formed.

At this time, since the plasma can be confined by the magnetic fields formed by the magnets (5a) and (5b), the density of the plasma can be increased, and the film formation rate can be improved compared to the conventional RF glow discharge method.

[Problem to be solved by the invention]

In the conventional case, since the plasma is confined by the magnetic field as shown by the arrow in Fig. 10, two lumps of plasma are generated in the cross section, and the trapped plasma and the substrate (3)
There is a problem that the distance between the substrate (3) is not uniform, and the thickness of the thin film formed on the substrate (3) is not uniform.

The present invention has been made with the above points in mind, and an object of the present invention is to make it possible to make the thickness of the formed thin film uniform.

[Means to solve the problem]

In order to achieve the above object, a flat cathode electrode and an anode electrode are arranged in parallel, a thin film forming substrate is attached to the anode electrode, and a high frequency electric field is formed between the two electrodes. A thin film that generates a plasma of a reactive gas, confines the plasma between the two electrodes by a magnetic field formed by a magnet provided outside the cathode electrode, and forms a thin film of the reactive gas component turned into plasma on the substrate. In the forming method of the present invention, a forming means for forming an auxiliary electric field or an auxiliary magnetic field is provided between the two electrodes, and the plasma is oscillated by the auxiliary electric field or the auxiliary magnetic field.

[Effect]

In the above configuration, since the plasma confined between the two electrodes is oscillated by the auxiliary electric field or auxiliary magnetic field produced by the forming means, the time during which the high-density region of the plasma is in contact with the substrate is made uniform, and the interaction between the substrate and the plasma is made uniform. This eliminates the non-uniformity of the distance between the two, and the thickness of the formed thin film can be made uniform.

〔Example〕

Examples will be described with reference to FIGS. 1 to 9.

(Example 1) Example 1 will be described with reference to FIGS. 1 to 4.

In FIG. 1 showing the outline of the forming apparatus, the same symbols as in FIG. 10 indicate the same or equivalent ones, and (6a), (
6b) is a flat plate-shaped auxiliary electrode, which is disposed on both sides between the cathode (1) and the anode (2), and is connected to an auxiliary power source (7) that constitutes a forming means together with both auxiliary electrodes (6a) and (6b). ), voltages of mutually opposite polarity are periodically applied to both the auxiliary electrodes (6a) and (6b).
An auxiliary electric field is formed between the two auxiliary electrodes (6a) and (6b) in a direction perpendicular to the high-frequency electric field and whose direction is periodically reversed.

The plasma between the anodes (2) is oscillated.

By oscillating the plasma confined by the static magnetic field of the magnets (5a) and (5b) in this way, the time in which the plasma is in contact with the substrate (3) in the high-density region is equalized, so that the plasma ( The non-uniformity in the distance between the substrate (3) and the plasma is eliminated, and the thickness of the thin film formed on the substrate (3) can be made uniform.

By the way, in order to find the optimal conditions for the AC voltage and its frequency to be applied to the auxiliary electrodes (6a) and (6b), we investigated the relationship between the voltage and frequency, and the variation in film thickness. As shown in Figure 3, if the film thickness variation is 5% or less, good uniformity is considered, then from Figure 2, the optimal conditions for the AC voltage applied to the auxiliary electrodes (6a) and (6b) are 50V to 500V. It can be seen from FIG. 3 that the optimum frequency condition is 0-5 Hz to 500 KHz.

At this time, if the applied voltage is less than 50V, the plasma will not oscillate sufficiently, so the non-uniformity of the film thickness will not be eliminated.If the applied voltage is more than 500V, the auxiliary electrodes (6a), (6
Since abnormal discharge occurs between b) and the cathode (1), the anode (2), or the reaction chamber, variations in film thickness become large.

On the other hand, if the frequency is 0.5 Hz or less, the plasma oscillation is still insufficient, and if the frequency is 500 KHz or more, the plasma follows and becomes unable to oscillate.

Therefore, both auxiliary electrodes (6a), (
6b), frequency 0.5Hz ~ 500KHz "'Q
, 50V to 500V (7) AC voltage may be applied.

Next, a thin film of a-Si was formed by applying a voltage with a waveform as shown in FIG. 4(a) and Φ) to the auxiliary electrodes (6a) and (6b), respectively, and a -8
A comparison of the film thickness distribution with the thin film of i was made as shown in Figure 5, where the solid line indicates the case where there is an auxiliary electric field due to the forming means, and the broken line indicates the case with the conventional method. From the results shown in the figure, the variation in film thickness of the thin film by the conventional method is approximately ±20%, whereas the variation in film thickness due to the fluctuation of the plasma due to the auxiliary electric field is approximately ±2.5%.
It can be seen that a thin film with extremely high uniformity can be obtained.

The horizontal axis in Fig. 5 represents the distance from one end of the cathode (υ), and the thin film forming conditions common to the conventional method are a substrate temperature of 200 C and an RF power of 100 W.
, pressure Oa ITorr, SiH4 gas flow rate 2°S
CCM, maximum magnetic field strength of magnets (5a), (5b) 15
It is 0 Gauss.

In this way, according to the first embodiment, both the auxiliary electrodes (6a) and (6b) are connected to the auxiliary power source (7) at two frequencies of 0 and 5Hz.
~500KHz, 50V~500V (7) Apply AC voltage to the cathode (1).

Since an auxiliary electric field is formed between the anodes (2) and the plasma is oscillated by this auxiliary electric field, it is possible to eliminate unevenness in the distance between the substrate (3) and the plasma. A thin film with uniform thickness can be formed.

(Example 2 and Example 3) Next, regarding Example 2 and Example 3, FIGS.
This will be explained with reference to the figures.

As Example 2, the auxiliary electrodes (6a) and (6b
), a mesh electrode (8a) as shown in FIG.

(8b) may be provided, and as a third embodiment, the auxiliary electrodes (10a) and (10b) may each be configured by a plurality of small electrode bodies (9) as shown in FIG. In either case, the same effect as in Example 1 can be obtained,
The shape of the auxiliary electrode may be selected as appropriate.

(Example 4) Example 4 will be described with reference to FIGS. 8 and 9.

In FIG. 8, the same symbols as in FIG. 1 indicate the same or equivalent ones, and (Lla) and (llb) are the cathode (
Two first electromagnets (12a) and (12b) of opposite polarity are installed on the left side between the cathode (1) and the anode (2). The first electromagnets (Lla), (llb) and the second electromagnets (12a), (12b) are alternately energized by a power supply not shown, which are two second electromagnets with opposite polarities. A first electromagnet (Ll) is placed between the cathode (1) and anode (2).
a), an auxiliary magnetic field by (1lb) and a second electromagnet (1lb)
2a) and (12b) are formed alternately.

At this time, in FIG. 8, the width of the auxiliary magnetic field in the direction perpendicular to the paper surface is at least at the cathode (1) and the anode (2).
The width of each electromagnet (lla), (l
lb), (12a), and (12b) are set in advance.

Then, as shown in FIG. 8, the first electromagnet (1la)
, (itb) is energized to form an auxiliary magnetic field Ba as shown in the figure, the plasma confined by the main magnetic field Bm of the magnets (5a) and (5b) is energized by the auxiliary magnetic field B.
Attracted by a, the plasma moves to the left.

Next, when the second electromagnets (12a) and (12b) are energized and a similar auxiliary magnetic field Bb is formed, the plasma is attracted to the auxiliary magnetic field Bb, and the plasma moves to the right.
These repetitions cause the plasma to oscillate in the left and right directions.

As a result, as in Example 1, non-uniformity in the distance between the substrate (3) and the plasma can be eliminated, and the thickness of the thin film on the substrate (3) can be made uniform.

By the way, the first and second electromagnets (1la), (1lb
), (12a), and (12b), we investigated the relationship between magnetic field strength and film thickness variation, and found that the relationship between magnetic field strength and film thickness variation is as shown in Figure 9. Assuming that the uniformity is good up to 5%, the optimum condition for the magnetic field strength of the auxiliary magnetic field is 5° Gauss from Fig. 9.
It turns out that this is all.

On the other hand, we also investigated the relationship between the switching frequency and film thickness variations of the first electromagnets (lla), (llb) and the second electromagnets (12a), (12b), and the results were similar to those shown in Fig. 8 above. So, 0.5Hz ~ 500KHz
The frequency was found to be appropriate.

In addition, multiple electromagnetic elements are connected to the cathode (υ) and the anode (
The electromagnets (lla), (llb), (12a), and (12b) may be formed by arranging the electromagnets at predetermined intervals over the same width as 2).

Furthermore, it goes without saying that the configuration of the forming means is not limited to those of the embodiments described above.

〔Effect of the invention〕

Since the present invention is configured as described above, it produces the effects described below.

Since the plasma confined between the cathode and anode electrodes is oscillated by the auxiliary direct rise or auxiliary magnetic field provided by the forming means, unevenness in the distance between the substrate and the plasma is eliminated, resulting in a more uniform film thickness than before. A thin film can be formed.

[Brief explanation of the drawing]

1 to 9 show examples of the thin film forming method of the present invention, FIGS. 1 to 5 show Example 1, FIG. 1 is a schematic diagram, and FIGS. 2 and 3 are auxiliary diagrams. Relationship diagram between the voltage applied to the electrode, each of its frequencies, and the variation in film thickness, 4th
r (a) and (b) are waveform diagrams of the voltage applied to the auxiliary electrode, Figure 5 is a diagram showing the film thickness distribution of the thin film on the substrate, and Figure 6 is a diagram showing the thickness distribution of the thin film on the substrate.
7 and 7 are schematic diagrams of Examples 2 and 3, respectively.
9 and 9 are a schematic diagram of the forming apparatus of Example 4 and a diagram of the relationship between magnetic field strength and film thickness variation, and FIG. 10 is a schematic diagram of a conventional example. (1) - Cathode electrode, (2) Anode electrode, (3) Thin film forming substrate, (5a), (5
b) - magnets, (6a), (6b). (10a), (10b) - auxiliary electrode, (7)... auxiliary power supply, (8a), (8b)... mesh electrode, (t
ta), (ttb)...first electromagnet, (12a),
(12b) - Second electromagnet.

Claims (1)

[Claims] 1. A flat cathode electrode and an anode electrode are arranged in parallel, a thin film forming substrate is attached to the anode electrode, a high frequency electric field is formed between the two electrodes, and a plasma of a reactive gas is generated by the high frequency electric field, In the thin film forming method, the plasma is confined between the two electrodes by a forming magnetic field of a magnet provided outside the cathode electrode, and a thin film made of the reactant gas component turned into plasma is formed on the substrate. A method for forming a thin film, characterized in that a forming means for forming an auxiliary electric field or an auxiliary magnetic field is provided, and the plasma is oscillated by the auxiliary electric field or the auxiliary magnetic field.