JPH02213481A - Thin film forming device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] Regarding a thin film forming apparatus used for forming amorphous silicon-based thin films, etc., it is possible to use a wide variety of material gases, and to form high-quality thin films at high speed under low pressure. The purpose is to efficiently form a discharge electrode for high-frequency discharge, which has a space sandwiched between two walls that face each other through a predetermined distance, to conduct the material gas introduced into the vacuum container. Thin film formation in which a thin film is formed on the surface of a substrate placed in the vacuum container by decomposing and activating it as a plasma using hollow cathode plasma and high frequency plasma generated as a potential, and using the active species generated thereby. In the device,
A conductor that is grounded or to which a positive voltage is applied is provided near the opening of the space on the base side.

[Industrial application field]

The present invention relates to a thin film forming apparatus used for forming amorphous silicon-based thin films and the like.

Amorphous silicon (a
-5i), a-5i alloy thin films, 5t(h, 5fNx+S) used for insulator thin films of electronic devices
Thin films such as iC, 1, etc., thin films of boron and carbon used for coating films on the walls of nuclear fusion reactors, and high-temperature semiconductor materials such as diamond and boron nitride (BN).

Thin films such as boron carbide (BtC), boron, silicon carbide (SiC), and boron phosphite (BP), WSi thin films used in electronic devices, and thin films such as TiN and hC used for coating cutting tools are generally produced using plasma. It is formed by CVD method.

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]

A conventional thin film forming apparatus of this type is shown in FIG.

This device is a high-frequency
Hollow cathode plasma CVD equipment, below RF-HC
It is abbreviated as a plasma CVD device.

In the figure, 1 is a vacuum vessel, 2 is a discharge electrode, 3 is a ground electrode, and 4
is a high frequency (RF) power supply, 5 is a matching box 1.6
7 is a material gas introduction part, 7 is an exhaust pipe, 8 is an insulator, 9 is a vacuum seal such as an O-ring, and 10 is an active species generated by decomposition and activation by plasma. The discharge electrode 2 is provided with a hollow cathode discharge space 12 formed between two wall surfaces 11a and llb facing each other with a predetermined distance therebetween, and a connection surface 11c connecting these wall surfaces 112.11b above. A gas outlet 13 is formed in the.

14 is an opening on the lower side of the space 12. 15 is an introduced gas diffusion chamber for temporarily diffusing the material gas introduced from the material gas introduction part 6; 16 is a grounding shield that prevents plasma from forming in unnecessary parts surrounding the discharge electrode 21; This is to prevent this from occurring.

The base 100 is set on the ground electrode 3 facing the discharge electrode 2, and film formation on the base 100 is performed in the following procedure.

When forming a film, the substrate 100 is heated to a predetermined temperature by a heater (not shown), a material gas is introduced into the vacuum container l from the material gas introduction part 6, and a desired RF Power is supplied to the discharge electrode 2. The introduced material gas enters the sulfur diffusion chamber 5, where it is diffused and blown out from the gas outlet 13 into the space 12.

Then, the material gas is efficiently decomposed and activated by the high-density hollow cathode plasma generated here, and the generated active species 10 are blown onto the substrate 100 to form a film. Further, the material gas that is not decomposed by the hollow cathode plasma is decomposed and activated by the RF plasma, and the active species generated thereby are also used to form a film.

This RF-HC plasma CVD apparatus can form a thin film at high speed even under a low pressure of several tens of mTorr, where polymolecular powder is difficult to generate. Therefore, there is no need to clean the multi-molecular powder, and there is no defect caused by the multi-molecular powder.
High material gas usage efficiency.

The principle of plasma generation in this RF-HC plasma CVD apparatus will be explained in detail as follows.

In the RF-HC plasma CVD apparatus, the discharge electrode 2 is kept at a negative potential most of the time due to self-bias during plasma generation. Hollow cathode discharge is performed by wall surfaces 11a and llb provided at an appropriate interval on the negative potential discharge electrode 2.
It is generated using a plasma bulk with a positive potential. In other words, an electric field created near the discharge electrode causes cations to collide with the surface of the discharge electrode to emit secondary electrons, and the electric field accelerates these electrons to a speed necessary for gas decomposition. These accelerated electrons create a space in which the material gas is most efficiently decomposed. When the spacing between the opposing wall surfaces 11a and llb is selected so that the spaces with high decomposition efficiency formed with respect to the opposing wall surfaces become one, a hollow cathode plasma that is a high-density plasma is formed. . It is also conceivable that the decomposition efficiency may be improved by causing electrons to reciprocate between the opposing wall surfaces due to the electric field created by the negative potential of the opposing wall surfaces. Therefore, in the RF-HC plasma CVD method, the electric field formed near the discharge electrode, that is, the spatial potential gradient, is very important. It is known that this spatial potential gradient depends on the plasma density (electron density) between the discharge electrode and the ground electrode, and when the plasma density is low, the spatial potential gradient (electric field) becomes small.

Therefore, in order to generate strong hollow cathode plasma in the narrow space 12 formed by the wall surfaces 113.11b provided on the discharge electrode, the space potential gradient must be increased. That is, the RF plasma generated between the discharge electrode and the ground electrode must have a certain degree of high density.

[Problem to be solved by the invention]

However, depending on the type of gas, pressure, or device configuration, the plasma between the discharge electrode and the ground electrode may have a low density.

Therefore, in conventional RF-HC plasma CVD equipment, depending on the type of gas, pressure, and equipment configuration, a sufficient electric field (potential gradient) cannot be obtained near the discharge electrode, resulting in unstable hollow cathode plasma and sometimes became very small.

Furthermore, the RF plasma generated at the same time had a reduced plasma density due to a decrease in the supply of electrons from the hollow cathode plasma.

As a result, depending on the type of gas, pressure, and device configuration, there have been problems such as slow formation of thin films, poor utilization efficiency of material gas, and large variations in film formation speed and film properties.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thin film forming apparatus that can use a wide variety of gases, and can form high-quality thin films at high speed and with efficient use of material gases under low pressure.

[Means to solve the problem]

FIG. 1 is a diagram explaining the principle of the present invention, and in the figure, 21 is a conductor. This figure illustrates an example in which the present invention is applied to the thin film forming apparatus shown in FIG. 4, and the same members as in FIG. 4 are given the same reference numerals.

The conductor 21 is provided near the opening 14 on the base 100 side of the space 12, and is grounded or applied with a positive voltage (V≧0).

[For production]

Film formation by this apparatus is performed by the same procedure as explained in connection with FIG. Because of this, the plasma density between the discharge electrode 2 and the ground electrode 3 is small, and the spatial potential gradient near the discharge electrode 2 is small, as shown in Figure 2 (ta).
Also under the conditions of the device configuration, it is possible to increase the spatial potential gradient near the opposing wall surfaces 11a and 11b that generate hollow cathode plasma. Therefore, even under conditions where the plasma density between the discharge electrode 2 and the ground electrode 3 is small (which is likely to occur), a large potential gradient due to the provision of the conductor 21 causes secondary electron emission due to ion bombardment from the opposing wall surfaces 11a and llb. , which enables the acceleration of secondary electrons and the reciprocating movement of electrons between the wall surfaces 11a and 11b.As a result, the plasma density improves and the space charge density decreases, further increasing the space potential gradient as shown in Figure 2 ( As shown in bl, it becomes possible to form thin films at high speed using devices with more configurations at lower pressure.At the same time, electrons from the hollow cathode plasma The RF plasma between the ground electrode 2 and the ground electrode 3 also has a high density.

〔Example〕

The invention will now be described in detail with reference to FIG.

FIG. 3 is a schematic explanatory diagram of the structure of the thin film forming apparatus of this example (FIG. 3(a) is a cross-sectional view, and FIG. 3(b) is a longitudinal sectional view). The provided discharge electrode 32 is a cylindrical ground electrode arranged concentrically with the discharge electrode 31 .

Note that the same members as in FIG. 1 are given the same reference numerals.

In this embodiment, a base 10 fixed to a cylindrical ground electrode 32 is used.
The ground electrode 32 is connected to the fixing member 33. And fixed member 33! is held between. These fixing members 33. ．． 33g has the same diameter and the same material (aluminum) as the ground electrode 32 so that the plasma is distributed uniformly throughout the entire axial direction of the ground electrode 32. Furthermore, the fixing member 33. A motor (not shown) is connected to the ground electrode 32 so that the ground electrode 32 can be rotated so that the thickness and quality of the thin film deposited on the substrate 100 during film formation are uniform in the circumferential direction.

The discharge electrode 31 includes four spaces 12 formed by opposing wall surfaces 112.11b. This space 12 for generating hollow cathode plasma has a width of 8 m and a depth of 30 m.
m, and the length was 400M.

A ground shield 34 is provided on the upper and lower surfaces of the discharge electrode 31, and the distance between the discharge electrode 31 and the side wall of the vacuum vessel 1 is maintained at 2 to 3 ml, thereby preventing plasma generation in these parts. are doing. Further, the discharge electrode 31 is connected to a ground shield 34 by an insulator 8. It is insulated from the vacuum container 1. Further, the surface of the ground electrode 32 of the discharge electrode 31 is partially covered with a shield plate 35, and the discharge area is adjusted so that the self-bias voltage of the discharge electrode 31 is negative.

The conductor 21, which is a feature of the present invention, is provided on an extension of the wall surface 11b near the opening 14 of the four hollow cathode discharge generation spaces 12.

The procedure for forming a thin film using this apparatus is as follows.

First, the base 100 is fixed to the ground electrode 32 with a stainless steel mask 36, and the ground electrode 32 is rotated by a motor. On the other hand, the inside of the vacuum container 1 is evacuated from the exhaust pipe 7 to 10-' Torr or less by fully opening the exhaust valve 37 using a rotary pump and a wide-area turbo molecular pump (not shown). Next, the base 100 is heated to a predetermined temperature by the heater 38 placed inside the ground electrode 32. At this time, heating is performed in a gas atmosphere or processing gas plasma depending on the purpose. When the temperature of the substrate 100 becomes constant at the target value, the atmospheric gas and plasma processing gas are evacuated, and then the material gas introduction section is heated. 6, a material gas is introduced into the vacuum container 1 while controlling its flow rate. The material gas enters the -tan diffusion chamber 15 from the material gas introduction part 6, and is diffused here to form 4
Almost equal amounts of gas are blown into the space 12 from the gas blow-off ports 13 provided in the two hollow cathode discharge generation spaces. Here, the opening/closing state of the exhaust valve 37 is adjusted to set the pressure inside the vacuum container 1 to a desired level.

Following this, the RF power source 4 is turned on and a predetermined amount of power is supplied to the discharge electrode 31 to generate plasma. At this time, the matching box 5 with a built-in blocking capacitor adjusts the variable capacitor in advance so that the reflected waves are small when plasma is generated, and the matching box 5 adjusts the variable capacitor in advance so that the reflected waves are small when plasma is generated. If the waves increase, each is readjusted to maintain the desired value. After starting thin film formation in this way,
After the time required to form a thin film with the desired thickness has elapsed, the output of the RF power source 4 is lowered and turned off, and the heating power source (not shown) of the heater 38 is turned off.
The exhaust valve 37 is fully opened to stop the material gas. After the material gas in the vacuum container 1 has been completely exhausted and the temperature of the substrate 100 has cooled to 50° C. or lower, N2 gas is poured into the vacuum container 1 until it reaches atmospheric pressure, the vacuum container 1 is opened, and the substrate 100 is removed. Take out.

During this film formation, in the present invention, a conductor 2 is placed near the opening 14.
1, as described above in connection with FIG. This effect can be formed with high gas utilization efficiency, and this effect will be explained next. That is, 5 it of material gas
H1 (disila 7) Color a-5t: H<hydrogenated amorphous silicon) When forming a film using an apparatus with a conventional structure (the apparatus in which the conductor 21 is removed from the apparatus shown in FIG. 3), hollow cathode plasma and RF plasma are used. The following effects can be obtained by applying the present invention (providing the conductor 21) to an apparatus configuration in which the density is low and the film formation rate is slow.

In the conventional RF-HC plasma CVD equipment, the discharge electrode 3
1 and the ground electrode 32 is 17 mm, the flow rate of the material gas 5iJi is 100 sccm, the pressure is 50 mTorr,
When a-5i:H was deposited under the condition of RF power of 800 W, the film formation rate was extremely slow at 2.6 μm/h. On the other hand, by providing the conductor 21 as shown in FIG. 3, the film forming rate was more than doubled to 5.4 μm/h. In addition, when observing the plasma state during the formation of these two films, it was found that when the conductor 21 was not provided, the opposing wall surface 11
The light emitted from the hollow cathode plasma generated in the space 12 between a and Ilb and the hollow cathode plasma generated between the discharge electrode 31 and the ground electrode 32 exhibited flickering or wavering temporal changes. On the other hand, conductor 2
1, the luminescence of the hollow cathode plasma was strong and stable, and the luminescence of the RF plasma also became stronger as it was closer to the hollow cathode plasma. It is known that the intensity of light emitted from plasma is closely related to plasma density, and the higher the plasma density, the stronger the light emission intensity. Therefore, by providing the conductor 21, the emission intensity can be increased.
It is clear that the density of the hollow cathode plasma was able to be improved since the film formation rate was improved.

In addition, by providing the conductor 21, an electric field of 5 kV/cy
a, The light-dark resistance ratio of a-5t measured under the condition of incandescent light bulb light intensity 1 mJ/cmz is 4.9X10' to 9.3X
I was able to improve it by 10'. This is because when the conductor 21 was not provided, the material gas was not sufficiently excited because the plasma density was low and the electrons were not sufficiently accelerated by the electric field formed near the surface of the discharge electrode 31. it is conceivable that.

In the above explanation, an example has been described in which a cylindrical ground electrode is used and a flat base is attached to it to form a film.
Instead, the film is formed while being held between fixed members. In this case, the substrate plays the role of the ground electrode.

Furthermore, in the above explanation, an example was described in which film formation is performed without rotating the ground electrode 32 (or cylindrical conductor base), but more uniform film formation is possible if the ground electrode 32 (or cylindrical conductor base) is moved up and down in addition to rotation. It is.

〔Effect of the invention〕

As described above, according to the present invention, by providing a conductor near the opening of the hollow cathode discharge space, stable and high-density hollow cathode discharge can be more easily obtained. As a result, restrictions on material gases, pressures, and equipment configurations that can be used in RF-HS plasma CVD equipment can be relaxed.
This greatly contributes to improving productivity and reducing costs during thin film formation.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the principle of the present invention, Fig. 2 (al, (b) is an explanatory diagram of the effect of the present invention, and Fig. 3 (al, (b) is an outline of the structure of a thin film forming apparatus according to an embodiment of the present invention. 4 is a schematic explanatory diagram of the structure of a conventional thin film forming apparatus, in which 1 is a vacuum vessel, 2.31 is a discharge electrode, 10 is an active species, 11a and llb are wall surfaces, 12 is a space, 14 21 is a conductor, and 100 is a base.

Claims (1)

[Claims] A discharge for high-frequency discharge having a space (12) sandwiched between two wall surfaces (11a) and (11b) facing each other at a predetermined distance, through which gas introduced into a vacuum container (1) is directed. electrode(
2) was decomposed and activated in a plasma state by a hollow cathode plasma and high frequency plasma generated at a negative potential, and the activated species (10) thus generated were utilized and placed in the vacuum container (1). In a thin film forming apparatus for forming a thin film on the surface of a base (100), an opening (1) of the space (12) on the base (100) side is provided.
4) A thin film forming apparatus characterized in that a conductor (21) which is grounded or to which a positive voltage is applied is provided near the device.