JPH02159380A - Thin film forming device - Google Patents

Abstract

PURPOSE:To form a good-quality thin film on a base body at high velocity by providing a magnetic field forming means in the space formed with the opposite wall surfaces of a discharge electrode and making plasma density large in the case of performing hollow cathode discharge in the above-mentioned space. CONSTITUTION:A gaseous material is introduced into the diffusion chamber 25 of a vacuum vessel 1 through an introduction part 5. One part of this gaseous material is introduced into the space 22 which is formed by the two opposite wall surfaces 23a, 23b of a discharge electrode 21, decomposed and activated as a plasma state by hollow cathode discharge. A thin film is formed on the surface of a base body 100 by utilizing the produced activated species 30. At this time, a magnetic field forming means 32 is constituted by arranging the permanent magnets 341, 342 to the outside near to the opening part 33 of the space 22 so that the opening part 33 side is made the same pole. Plasma density is made large by trapping plasma in the space 22. Thereby stable and high- density hollow cathode discharge plasma is generated even at such low pressure that polymolecular powder is not generated for the many kinds of gaseous materials and a good-quality thin film is formed at high velocity.

Description

[Detailed description of the invention] [Summary] Regarding a hollow cathode discharge type thin film forming apparatus used for forming amorphous silicon thin films, etc., it can be used for many types of material gases under low pressure without generating polymolecular powder. The purpose of this technology is to generate stable, high-density hollow cathode discharge plasma to form high-quality thin films at high speed. The vacuum vessel is decomposed and activated as a plasma by a hollow cathode discharge generated using a discharge electrode having a space sandwiched between two opposing wall surfaces. In an apparatus for forming a thin film on the surface of a substrate disposed within the space, the apparatus is configured to include a magnetic field forming means for confining hollow cathode plasma in the space and increasing plasma density.

[Industrial application field]

The present invention relates to a hollow cathode discharge type thin film forming apparatus used for forming amorphous silicon thin films and the like.

Amorphous silicon (a-3i)-based thin films and carbon-based thin films used for photoconductors and surface protection films for solar cells, reading sensor arrays, photosensitive drums, etc., insulator thin films for electronic devices, and coating films for nuclear fusion reactor walls. Boron thin films and carbon films used in
), thin films of boron, silicon carbide (S i C), boron phosphite (BP), etc., WSi thin films used in electronic devices, TiN and TiC thin films used as coating films for cutting tools, etc. are generally formed by the plasma CVD method. be done.

In recent years, as the effectiveness of these thin films has been confirmed and their practical use progresses, a thin film forming apparatus that can improve productivity and reduce costs has been desired.

[Conventional technology]

Conventionally, many plasma CVD apparatuses are used to form thin films, which decompose the material gas into a plasma state through collisions between the material gas and electrons, and form a thin film on a substrate using the active species generated thereby. It is used. In this plasma CVD apparatus, the pressure in the space where plasma is generated is high, and polymolecular powder is sometimes formed due to repeated reactions between active species or between active species and material gas.

This polymolecular powder adheres to the thin film growth surface, vacuum vessel, and discharge electrode, causing defects in the formed thin film.

Further, the generation of powder requires cleaning of the vacuum container and the like, and also causes trouble in opening and closing the valve attached to the vacuum container, causing a decrease in thin film productivity.

In order to prevent the generation of this multimolecular powder, it is necessary to lower the pressure in the vacuum container, especially in the space where activation or decomposition is not active, and to reduce the frequency of collisions between active species or between active species and material gas. However, when the pressure inside the vacuum container is lowered, the density of both the material gas and the electrons decreases, so the frequency of mutual collisions decreases, and the generation of active species is significantly reduced, conversely, the proportion of the material gas that is not decomposed increases. Become. Therefore, the thin film deposition rate becomes slow and the material gas utilization efficiency decreases, resulting in problems such as poor thin film productivity and high costs.

Therefore, the use of a high-density plasma generation method has been proposed in order to increase the frequency of collisions between material gas and electrons even at low pressures where polymolecular powder is not generated. This method includes
There are microwave discharge method and hollow cathode discharge method.

First of all, in the microwave discharge method, the plasma density is 1
By using a magnetic field of the order of 0"cm-' and as high as 1
It has the advantage of being able to maintain stable discharge even at low pressures of 0-'torr. As described above, a microwave plasma CVD apparatus that uses a magnetic field can form a thin film at a high speed and has high material gas utilization efficiency even at low pressures where no polymolecular powder is generated.

Therefore, depending on the type of thin film, it is an extremely excellent thin film forming apparatus. On the other hand, microwaves tend to locally generate high-density plasma, making it difficult to uniformly form a thin film over an arbitrary large area. Furthermore, depending on the type of thin film to be formed, there has been a problem in that the properties of the obtained thin film are very poor due to plasma damage or the like.

On the other hand, the hollow cathode discharge method has the advantage that the plasma density can be increased by about two orders of magnitude compared to high frequency discharge, and a thin film can be formed relatively easily over any large area. This method is an object to which the present invention is applied, and FIG. 4 is a perspective view showing an outline of the structure of a conventional thin film forming apparatus that implements this method.

This device is based on the patent application filed in 1986, already proposed by the applicant.
No. 109195 (filed on May 6, 1988), in the figure, 1 is a vacuum vessel, 2 is a discharge electrode, 3 is a ground electrode, 4 is a discharge space between these electrodes, 5 is a material gas inlet, 6 is an exhaust port, 11 is a high frequency (RF) power source,
12 is a blocking capacitor. The discharge electrode 2 is provided with a concave space 8 for hollow cathode discharge sandwiched between two wall surfaces 7a and 7b facing each other at a predetermined distance, and the space 8 has a plurality of gas outlet ports 9 and a gas reservoir 0.
It communicates with the material gas introduction section 5 via. gas reservoir 10
is for temporarily diffusing the material gas that has flowed in from the material gas introduction section 5 so that the flow rate of the material gas blown out into the space 8 from each gas outlet 9 is constant. 3a is a heater provided on the ground electrode 3, and 100 is a substrate for film formation set on the ground electrode 3. In an apparatus using this hollow cathode discharge, the material gas is efficiently decomposed by the high-density plasma generated near the material gas inlet before it diffuses into the discharge space 4, so film formation can be performed even at low pressure. The speed is fast and the efficiency of material gas utilization can be increased. Although FIG. 4 shows an apparatus using RF hollow cathode discharge, a DC hollow cathode discharge apparatus in which an anode is provided between the base 100 and the discharge electrode 2 may also be used.

[Problem to be solved by the invention]

However, in the case of this hollow cathode discharge method, as the pressure is lowered, the frequency of collisions between material gas and electrons decreases, and the probability of ionization due to collisions decreases, so depending on the type of material gas, plasma may In some cases, the plasma became unstable and the plasma density decreased significantly, making it impossible to maintain the plasma. In other words, when the pressure is set low enough to prevent the generation of polymolecular powder, depending on the type of material gas, it may not be possible to maintain a stable, high-density plasma due to hollow cathode discharge, resulting in large variations in the formed thin film or Problems have arisen in that the film speed becomes slow and the types of material gases that can be used are limited.

The present invention is capable of forming high-quality thin films at high speed by generating stable, high-density hollow cathode discharge plasma for many types of material gases even under low pressure where no polymolecular powder is generated. The purpose is to provide a device.

[Means to solve the problem]

FIG. 1 is a diagram explaining the principle of the present invention. In the figure, 21 is a discharge electrode, and 22 is a space provided in the discharge electrode 21 for hollow cathode discharge. Note that the same reference numerals are used for members similar to those in the conventional art.

The space 22 is formed between two wall surfaces 23a and 23b that face each other at a predetermined distance within the discharge electrode 21, and a gas outlet 24 is formed on a connecting surface 23c that connects these wall surfaces 23a and 23b above. has been done.

In the present invention, a magnetic field forming means 32 is provided in the space 22 to confine the hollow cathode plasma and increase the plasma density. In the case of this figure, the magnetic field forming means 32
shows an example in which permanent magnets 341.34□ are arranged outside near the opening 33 of the space 22. The permanent magnets 34342 are arranged so that the opening 33 side has the same magnetic pole.

Reference numeral 25 denotes an introduced gas diffusion chamber, which is used to diffuse the material gas introduced from the material gas introduction part;
Reference numeral 6 denotes a ground shield, which is used to prevent plasma from being generated in unnecessary areas surrounding the discharge electrode 21.

Further, 27 is a matching box containing a blocking capacitor, 28 is an insulator, 29 is a vacuum seal such as an O-ring, and 30 is an active species generated by decomposition and activation by plasma.

[For production]

At least a portion of the material gas introduced into the vacuum vessel 1 from the material gas introduction section 5 is guided into the space 22, where hollow cathode discharge is performed. This hollow cathode discharge is
Electrons generated by gas ionization and secondary electrons released from the discharge electrode by ion bombardment were applied to the discharge electrode 21 (
A high-density plasma is generated and maintained by causing reciprocating motion between the opposing wall surfaces 23a and 23b using a negative potential (or produced by a self-bias). By the way, in the present invention, the magnetic field forming means 32 is provided as described above, and the permanent magnet 34I.

Using the Lorentz force generated by 34□, space 22
The electrons 31 in the hollow cathode plasma trying to exit through the opening 33 from the wall surface 23a.

It is confined within the space 22 between 23b. Therefore, space 2
The electron density of the hollow cathode plasma in the magnetic field forming means 3 becomes thicker as the rate of decrease decreases.
2 simultaneously produces a magnetron discharge effect and can further improve plasma density.

As a result, it is possible to increase the probability of collision between electrons and gas even for gases with a small ionization coefficient, so it is stable against more types of gases even under low pressure where polymolecular powder does not occur. This makes it possible to generate and maintain high-density hollow cathode discharge.

The thin film is formed on the surface of the substrate 100 by using the active species 30 generated by decomposing and activating the material gas by the hollow cathode discharge generated as described above.

〔Example〕

The present invention will now be described in detail with reference to FIGS. 2 and 3.

Figure 2 is a schematic explanatory diagram of the structure of the thin film forming apparatus (Figure 2 (a)
is a cross-sectional view, and FIG. 2(b) is a vertical cross-sectional view). This figure shows a configuration that enables thin film formation on a substrate fixed to a cylindrical ground electrode (or a cylindrical conductor base). type ground electrode. Note that the same members as in FIG. 1 are given the same reference numerals.

The discharge electrode 41 is arranged concentrically at an interval of 20 squares outside the ground electrode 42 having a diameter of 80 cm, and has four hollow cathode discharge spaces 22.

The space 22 has a wall surface 23a made of 5US304 board with a thickness of 1.
, 23b, and outside near the opening 33 of the space 22, there are permanent magnets 34., 23b, as described above. ．． 34□
A magnetic field forming means 32 is provided. Wall surface 23
The distance between the walls 23a and 23b is 8, and the strength of the magnetic field by the magnetic field forming means 32 is 6 on the surface of the walls 23a and 23b.
30 Gauss.

Further, the discharge electrode 41 is made of 5US304, and the parts other than the discharge surface are covered with a grounding shield 43 of 5US304. Further, as shown in FIG. 2(a), the ground shield 43 is partially disposed on the ground electrode 42 side of the discharge electrode 41, and serves also to set the self-bias of the discharge electrode 41 to a negative potential.

The ground electrode 42 is arranged in the longitudinal direction (vertical direction in FIG. 2(b)).
the same diameter, so that the plasma is uniform throughout.
Fixing member 44 made of the same material (aluminum). and a fixing member 442 are provided and held between the fixing members 44. and 442, and the fixing member 44. It is rotated during film formation by being driven by a motor (not shown) connected to the motor.

Next, the normal operating procedure of this device will be explained.

When forming a film, the base lot is first fixed in a notch provided in the ground electrode 42 using a stainless steel mask 45, and the ground electrode 42 is rotated.

Next, the inside of the vacuum container (1) is evacuated from the exhaust port 6 to 10-'torr or less by using a rotary pump and a wide-area turbo molecular pump (not shown) with the exhaust valve 46 fully open. Subsequently, the base 101 is heated to a predetermined temperature by the heater 47 placed inside the ground electrode 42. Base 1
After the temperature of 01 becomes constant at a predetermined temperature, the material gas whose flow rate is set to a predetermined value by a flow rate regulator (not shown) is introduced into the vacuum container 1 from the material gas inlet 5, and the exhaust valve 4
The pressure inside the vacuum container 1 is set to a desired value by adjusting the opening/closing state in step 6. At this time, the material gas is supplied to the material gas introduction section 5
The gas enters the gas diffusion chamber 48 and diffuses there, and is blown out into the space 22 from each gas outlet 24 in approximately equal amounts.

In this state, the RF power source II is turned on to provide a predetermined power, and then the matching box 27 is used to reduce reflected waves and generate plasma.

At this time, if conditions such as pressure change from the set values due to plasma generation, each is readjusted to maintain the desired conditions.

After starting thin film formation in this way, after the time required to form a thin film with a desired thickness has elapsed, the output of the RF power source 11 is lowered, the RFt source 11 and the heater 47 heating power source are turned off, and the exhaust valve 46 is closed. Open fully and stop the material gas. After the material gas in the vacuum container 1 has been completely exhausted and the temperature of the ground electrode 42 has cooled to 50°C or less, N2 gas is poured into the vacuum container 1 until it reaches atmospheric pressure, and the vacuum container 1 is opened to remove the substrate. Take out 101.

A desired thin film is formed on the surface of the base 101 by the above-mentioned operating procedure, but in this example, the thin film attempts to exit from the space 22 through the opening 33 by utilizing the Lorentz force generated by the permanent magnets 341°34□. The electrons 31 in the hollow cathode plasma are confined within the space 22 as shown in FIG. 3(b). That is, in this example, 1. Magnetic field forming means 3
Compared to the case of FIG. 3(a) where no space 22 is provided,
The electron density of the hollow cathode plasma inside becomes larger.

In addition, the magnetic field forming means 32 simultaneously produces a magnetron discharge effect and can further improve the plasma density. As a result, it is possible to increase the probability of collision between electrons and gas even for gases with a small ionization coefficient, and it is stable and high-density for more types of gases even under low pressure where polymolecular powder is not generated. It becomes possible to generate and maintain a hollow cathode discharge. Next, experimental results regarding this effect will be explained.

The experiment was conducted for the case of forming a film of hydrogenated amorphous silicon (a-Si:H), and the opening 33 and the connecting surface 23c were
The distance (length of the space 22) was set to 30 lines. Other spatial structures and dimensions of each electrode.

The arrangement is as described above. The material gas is disilane (disilane), which can provide stable hollow cathode discharge when the space 23 is not sloped so as to become narrower on the opening 33 side.
Two types of gas were used: SizH6) and 5ttH, in which stable discharge could not be obtained, mixed with an equal amount of helium (He).

a-3i:H thin film has a flow rate of St, Hh of 101005
e, the pressure inside the vacuum vessel 1 is set so that no Si□H7 powder is generated 5
It was formed at 0 mtorr and RF power of 800W. Material gas: 5izH6, mixed gas (S12H6: H
Table 1 below shows the results of examining the film formation rate when e=1:1) with and without the magnetic field forming means 32.

Table 1: Film Formation Rate First, when 5izJ (6) was used as the material gas, light emission due to hollow cathode plasma was observed between the opposing wall surfaces 23a and 23b regardless of the magnetic field.However,
When a magnetic field was formed, a brighter hollow cathode plasma was generated, and at the same time, bright plasma was observed on the discharge surface of the discharge electrode 41 near where the magnetic field forming means 32 was provided. This is considered to be because high-density hollow cathode plasma and magnetron plasma were obtained at the same time. The film formation speed was approximately doubled by providing a magnetic field. The light-dark resistance ratio of the a-3i:H film formed was as follows: electric field 5KV/cm, light intensity of incandescent lamp 100mJ/
As a result of measurement under cnl conditions, the film quality was as large as 1.1×10', and no significant deterioration in film quality was observed as in the microwave plasma CVD method.

Next % S f ZH6100sccm and He 10
When a mixed gas of 0 sccm is used as the material gas, unless the magnetic field forming means 32 is provided, no light emission due to plasma will be seen between the wall surfaces 23a and 23b (hollow cathode discharge will not occur), and the cylindrical portion of the discharge electrode 41 Only weak light emission was observed between the ground electrode 42 and the cylindrical ground electrode 42. On the other hand, when the magnetic field generating means 32 was provided, strong light emission was observed between the wall surfaces 23a and 23b and on the discharge surface of the discharge electrode 41 near where the magnetic field generating means 32 was installed. By providing a magnetic field, the film formation rate could be increased by about 3.6 times. The film formed a-3i:H
The light-dark resistance ratio of a without a magnetic field was measured under the conditions of an electric field of 5 kV/am and an incandescent lamp light intensity of 100 mJ/c+d.
5.6X10' for -3i:H, a-3i:H with magnetic field
It was 9.6X10'.

Therefore, S i ZH6100sccm and He100sccn, which could not be used because the film formation speed was very slow in film formation using hollow cathode plasma at low pressure.
Even a positive mixed gas can be used by providing the magnetic field forming means 32.

In the above explanation, an example is described in which a permanent magnet is used as the magnetic field forming means, but the same effect can be obtained even if an electromagnet is used as the magnetic field forming means.

〔Effect of the invention〕

As described above, according to the present invention, even under low pressure where no polymolecular powder is generated, for many types of material gases,
Stable, high-density hollow cathode discharge plasma can be generated to form high-quality thin films at high speed, which greatly contributes to improving thin film productivity and reducing costs.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the principle of the present invention, Fig. 2 (a) and (b) are explanatory diagrams of a general structure of a thin film forming apparatus according to an embodiment of the present invention, and Fig. 3 (a) and (b) are illustrations of the invention. Fig. 4 is an explanatory diagram of the structure of a conventional thin film forming apparatus, in which 1 is a vacuum vessel, 21.41 is a discharge electrode, 22 is a space, and 23a and 23b are 30 is an active species, 32 is a magnetic field forming means, and (1) 00 is a substrate.

Claims (1)

[Claims] At least a portion of the material gas introduced into the vacuum container (1) is transferred to two wall surfaces (23a) facing each other with a predetermined distance therebetween.
, (23b) is decomposed and activated as a plasma by a hollow cathode discharge generated using a discharge electrode (21) having a space (22) sandwiched therebetween, and the activated species (30) generated thereby are utilized. Then, the vacuum container (
1) A thin film forming apparatus for forming a thin film on the surface of a substrate (100) disposed in the space (22), comprising a magnetic field forming means (32) for confining hollow cathode plasma in the space (22) and increasing plasma density.
) is provided.