JPH0119467B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to cases in which a metal or ceramic coating is formed on the surface of a three-dimensional shaped base material such as a tool, a mold, or a mechanical part to improve functionality. This paper relates to a method for forming highly adhesive thin films by plasma CVD applied to.

[Prior Art] Conventionally, a chemical vapor deposition method (hereinafter abbreviated as CVD method) has been put to practical use in order to form ceramic thin films on tools, molds, machine parts, and the like. In this method, a base material is placed in a furnace heated to a high temperature, and a raw material gas is fed for a required period of time to cause a chemical reaction to proceed between the base material and the base material to form a thin film. This method is called a "thermal CVD method" because the formation of the film layer depends on thermal energy.

In recent years, physical vapor deposition methods (hereinafter abbreviated as PVD methods) such as ion plating have been developed.
It has become possible to form thin films at lower temperatures.

In addition, a plasma CVD method has been developed that allows ceramic thin films to be coated on substrates with complex shapes at low temperatures, resulting in amorphous silicon films for making solar cells,
It has mainly been used in the semiconductor field, such as interlayer insulating films, but several applications have been reported for tools, molds, and machine parts.

[Problems to be Solved by the Invention] Incidentally, in the thermal CVD method, the temperature of the base material must be raised to a high temperature of about 1000° C., and the accompanying thermal damage to the base material cannot be avoided.

Although the PVD method can be processed at low temperatures of around 500°C, it is not possible to uniformly form a film on substrates with complex shapes.

The plasma CVD method is said to be able to coat substrates with complex shapes with ceramic thin films at low temperatures, and several cases have been reported in which it has been applied to tools, molds, and machine parts, but it is difficult to withstand high loads. At present, it has not been possible to obtain sufficient adhesion between the film and the base material. Furthermore, there are problems with the uniformity of the formed film, the amount of impurities in the film, etc., and the method has not reached the level of practical use.

The reason for the decrease in adhesion of ceramic thin films is that the surface of the base material differs from the original composition of the base material.In other words, there is a layer such as an oxide layer on the surface of the base material, and it is difficult to apply the thin ceramic layer on top of it. This is to form. In the past, this kind of recognition was lacking.

Further, the problem of impurities is due to the following reasons. In the conventional plasma CVD method, a plasma discharge field is formed using a discharge sustaining gas such as hydrogen gas, and then a reactive gas is introduced into the plasma discharge field to start film formation. With this method, when a plasma discharge field is formed using a discharge sustaining gas, impurity atoms attached to the plasma generation electrode, plasma generation coil, or wall of the vacuum chamber will fly out into the reduced pressure space due to the sputtering phenomenon caused by the plasma impact. This is because it adheres to the surface of the base material.

Therefore, the present invention uses the plasma CVD method to
The purpose of this method is to uniformly form a metal and/or ceramic thin film with low impurity concentration and high adhesion on a complex-shaped base material at a temperature that does not cause thermal damage to the base material.

[Means for Solving the Problems] The present invention provides two independent main and sub discharge mechanisms for cleaning the substrate and forming a film in a reduced pressure space, and first, the sub discharge mechanism cleans the substrate. After the required time has elapsed, raw material gas is introduced immediately, and after the pressure in the reduced pressure space has reached the set operating pressure and stabilized, plasma discharge is started instantly. This is a method for forming a highly adhesive thin film using a plasma CVD method, which is characterized in that a negative potential is generated in the plasma to form a highly adhesive metal and/or ceramic thin film.

The plasma discharge is generated by applying a DC voltage, high frequency, or low frequency to a base material placed in a reduced pressure space. In this case, the pressure in the space is relatively low, about 10 ^-2 to ^{10 -5} Torr, and if a plasma discharge field is formed in such a way that the base material receives the strongest ion bombardment, oxides on the surface of the base material will be removed. It is possible to remove impurity layers such as. In addition, plasma CVD
Under the pressure conditions used in processing, the mean free path of atoms and molecules is smaller than the geometry of the substrate, so if the plasma discharge is too strong, some parts of the complex-shaped substrate may be damaged by discharge cleaning. Spattered impurity atoms and molecules may be re-adsorbed onto the surface of the base material and become firmly bonded to the base material. Therefore, a relatively low pressure as described above is preferable.

However, when discharge cleaning is stopped, the surface of the substrate is immediately exposed to the oxygen molecules remaining in the vacuum container.
It is instantly covered with impurity molecules such as water vapor molecules. The plasma CVD method has a processing pressure of 0.1 to several
Torr range, so at the start of film formation, the pressure during discharge cleaning or the ultimate pressure of background exhaust after discharge cleaning (10 ^-5 ~
The pressure inside the vacuum vessel must be increased from 10 ^-8 Torr) to the processing pressure. Since this takes several minutes to several tens of minutes, the surface of the substrate will be covered with oxygen molecules, water vapor molecules, etc. within this time.

Therefore, in the present invention, plasma CVD is performed using pressure during discharge cleaning or background pressure.
When increasing the pressure in the reduced pressure vessel to the processing pressure, a weak discharge field is created around the substrate, and cleaning continues until the start of film formation. After the gas pressure reaches the set operating pressure and becomes stable, film formation occurs instantly. A plasma discharge field is created to form a ceramic thin film on the surface of the substrate. After the pressure within the reduced-pressure container reaches the pressure of the film-forming conditions, a weak plasma discharge that meets the pressure of the film-forming conditions may be continued for several seconds to several minutes until the film-forming starts.

As an embodiment of the present invention, the negative potential generated at the start of discharge is applied to the substrate as it is until the film thickness reaches several hundred to several thousand angstroms at the initial stage of film formation.
Thereafter, the potential of the substrate is brought to the earth potential or discharge field potential several times for several seconds over several minutes. As a result, a film having a stable composition with high adhesion and a low impurity concentration is formed.

As mentioned above, when a reaction gas is introduced into a vacuum vessel and film formation is started after forming a plasma discharge field with hydrogen gas or the like as in the past, impurities spattered from the electrodes, coils, walls of the vacuum vessel, etc. , the surface of the substrate becomes contaminated. In the present invention, a reactive gas is introduced into a reduced pressure container without forming a plasma discharge field for film formation, and the discharge cleaning is continued until the reactive gas composition and processing capacity reach target values. In this case, since the discharge field is weak, cleaning of the base material occurs with priority over film formation.

When the reaction gas composition and pressure in the vacuum container reach the target values, power is instantly applied to the plasma generation electrode or plasma generation coil to generate plasma, which instantly stabilizes and generates a clean substrate. It was discovered that a film with a stable composition was formed on the surface of the material. In addition, the weak plasma discharge field that had been formed around the base material disappears without any effect on the plasma discharge field that was formed for film formation, leaving the base material in a state with a negative potential. It will be placed in a plasma discharge field that was created for film formation. For this reason, the base material is subjected to weak ion bombardment before film formation, and since a negative potential is applied at the start of film formation and during subsequent film growth, the base material is subjected to strong ion bombardment due to a strong plasma discharge field. A strong film with good adhesion and few impurities can be formed on the surface. Although adhesion can be improved by applying a negative potential to the substrate only during film formation, even stronger adhesion can be obtained by combining this with discharge cleaning.

In addition, by arbitrarily changing the potential of the base material at the same time as the start of film formation or after a predetermined period of time,
Films with various crystal structures can be created.

Additionally, when using the plasma CVD method to process substrates with complex shapes such as drills and other sharp edges, localized arc discharge occurs at the edges, reducing the performance of the formed film. There are many losses. However, in the case of the present invention, although the potential of the base material varies depending on the film quality, in general, if the potential of the base material is brought to earth potential or the potential of the discharge field several times a minute or more within a few seconds, arc discharge can occur without changing the film quality. discovered that it can be prevented.

In addition, at the initial stage of film formation, when the film thickness is from several hundred to several thousand Å, arc discharge does not occur even if a continuous potential is applied to the substrate, and stronger adhesion is achieved by applying a continuous potential. was found to be obtained.

[Example] Example 1 Figures 1a and 1b show the basic structure of a capacitively coupled plasma CVD apparatus suitable for carrying out the present invention. This device consists of a vacuum container 2 that forms a vacuum space 1 inside.
An upper electrode 3 is disposed substantially horizontally at an upper stage within the reduced pressure container 2. A lower electrode 4 is disposed at a lower position in the reduced pressure container 2 facing the upper electrode 3. This lower electrode 4 is normally kept at earth potential. Further, a gas blowing nozzle 5 is provided between the upper electrode 3 and the lower electrode 4.
to be placed. This nozzle 5 may be comb-shaped, ring-shaped, or mesh-shaped. Furthermore, a substrate holder 7 is arranged between the nozzle 5 and the lower electrode 4,
The base material 6 is fixed to this base material holder 7. The base material holder 7 can also rotate around its axis while fixing the base material 6 thereon. An electric heater 8 is disposed below the lower electrode 4 for heating the base material 6, and a heater 9 is disposed on the side surface of the vacuum container 2. This heater 9 may be an electric heater or a halogen lamp heater.

The substrate holder 7 also serves as a potential applying electrode that also serves as a plasma generation electrode during discharge cleaning of the substrate 6. A cleaning discharge power source 10 is connected to the substrate holder 7, and cleaning plasma is generated around the substrate 6. A discharge field 11 is formed. The plasma discharge power source may be a DC power source, an AC power source, a high frequency power source, or a low frequency power source. Alternatively, it may be an alternating power supply with an arbitrary waveform. In addition, in order to strengthen and stabilize the cleaning plasma discharge field 11, a power source 1 is connected to the gas nozzle 5 and the lower electrode 4.
2 and 13, voltage can be applied, and auxiliary electrodes and thermionic emitting filaments can be used together.

During film formation, the substrate holder 7 is left connected to the power source 10, or the switch 1 is turned off.
By the switching operation in step 6, the power source 17 is connected, and an arbitrary waveform potential is applied to the base material 6. The cleaning discharge power source 10 and the power source 17 may be a common power source.

The upper electrode 3 is a plasma discharge field 18 during film formation.
This upper electrode 3 is connected to a discharge power source 19 during film formation. The discharge power source 19 used during film formation may be a DC power source, a high frequency power source, or a low frequency power source.

The gas supply system can mix the gases from the reaction gas supply system 20 and the liquid raw material gas supply system 21 and then flow the mixed gases into the reduced pressure container 2 by operating the valve 22 . Further, until the vaporizer 23 is stabilized, the reaction gas containing the liquid raw material can be allowed to flow through the exhaust path 25 to the vacuum pump 26 by operating the valve 24. During this period, plasma discharge field forming gas is supplied to the reduced pressure container 2 from the supply path 27 in order to stabilize the pressure in the reduced pressure container 2 at the pressure during film formation or to continue cleaning the substrate 6. It can be supplied internally.

An exhaust path 29 including a large displacement vacuum pump 28 and an exhaust path 31 including a vacuum pump 30 during film formation are connected to the lower end of the reduced pressure container 2.
In the figure, 32 and 33 are valves, and 34 is a dark space.

Next, the method of the present invention will be explained along with the operation of the above device. First, the inside of the decompression container 2 is evacuated to a pressure of about 10 ^-5 to 10 ^-8 Torr by the vacuum pump 28, and the substrate 6 set in the substrate holder 7 is heated to a predetermined temperature by the heaters 8 and 9. . Thereafter, an inert gas such as Ar gas, a gas having a chemical etching effect such as hydrogen, or a mixture of both gases is introduced into the decompression vessel 2 from the supply path 27, while the large displacement vacuum pump 28 is being introduced. Continue exhausting through the exhaust route 29. When the pressure inside the vacuum container 2 stabilizes at the desired pressure of about 10 ^-3 to ^{10 -4} Torr, a voltage for generating cleaning plasma is applied to the substrate holder 7, and the substrate 6 is heated.
A glow discharge field 11 is formed around the base material to perform discharge cleaning of the base material. If necessary, a voltage is applied to the nozzle 5 and the lower electrode 4, or an auxiliary electrode or a thermionic emission filament is activated to stabilize the plasma. By this discharge cleaning, an impurity layer formed in the atmosphere on the surface of the base material 6 can be removed. After continuing the discharge cleaning for several minutes to several minutes, the exhaust route is switched from the exhaust route 29 to the exhaust route 31 including the vacuum pump 30 used during film formation by operating the valves 32 and 33, A discharge field maintenance gas or a cleaning gas during film formation is introduced into the reduced pressure container 2 through the supply path 27, and the pressure inside the reduced pressure container 2 is increased to the pressure during film formation. During this time, the voltage applied to the substrate holder 7 is
As the internal pressure rises, it is lowered to form a weak discharge field around the base material 6. This discharge cleaning can prevent impurity molecules from adhering to the surface of the base material 6 within the reduced pressure vessel 2. Furthermore, even if the gas introduction is temporarily stopped before increasing the pressure inside the decompression vessel 2, and the pressure inside the decompression vessel 2 is lowered to 10 ^-6 to 10 ^-8 Torr through the route of the exhaust path 29 including the vacuum pump 28, good. While performing the above operations, carrier gas is introduced into the vaporizer 23 containing the liquid raw material, and the exhaust path 25 including the vacuum pump 26 is
A mixed reaction gas is flowed according to the gas composition and flow rate conditions used for film formation.

The pressure inside the reduced pressure container 2 is stabilized at the pressure during film formation,
After the vaporizer 23 stabilizes, the valve 22,
By simultaneous operations 32 and 33, the mixed reaction gas is flowed into the vacuum container 2, and the discharge field maintenance gas or cleaning gas during film formation, which had been flowing into the vacuum container 2 up to this point, is flowed into the exhaust path 25 including the vacuum pump 26. This operation may be performed using a single valve that can switch in multiple directions at once. By the above operation, the mixed reaction gas can be introduced into the vacuum container 2 without changing the pressure inside the vacuum container 2, so during this time, the substrate can be continuously subjected to stable and weak discharge cleaning. can. After that, a predetermined power is applied to the upper electrode 3 by the power source 19, and the discharge field 1 for film formation is instantaneously applied to the upper electrode 3.
form 8. The plasma discharge field 18 stabilizes instantaneously, and due to the voltage previously applied to the base material for discharge cleaning, a dark space 34 is formed around the base material in the plasma discharge field 18, and the base material This means that a negative potential is applied to
This results in a continuous ion bombardment effect during film formation.

In this way, a high-quality film with excellent adhesion and few impurities can be formed on a clean base material.

In addition, at the same time as the start of film formation or after a predetermined period of time, the power supply 10 is switched from the power supply 10 to the power supply 1 by switching the switch 16.
7 or by changing the voltage applied to the base material 6 using the power source 10 as is.
Various film qualities can be obtained.

Example 2 In order to carry out the plasma CVD method of the present invention, a width
We manufactured a cubic stainless steel vacuum vessel measuring 600mm, depth 600mm, and height 600mm. The upper electrode has a diameter
The size of the lower electrode was 200 mm, and the lower electrode had a square shape with one side of 300 mm. The distance between the upper and lower electrodes is 100
It was set to mm. As shown in Figure 2, the nozzle is a 6 mm diameter tube with a closed end, with gas outlets 0.6 mm in diameter drilled at a 20 mm pitch on the side, and a total of 6 nozzles arranged approximately horizontally, alternating from the left and right. It was arranged so that it faced the lower electrode side.

Using _TiCl4 as liquid raw material and plasma discharge using _N2 gas, Ar gas and _H2 gas as reaction gas, using Ar gas and _H2 gas as cleaning gas, TiN
A film was formed.

After heat-treating an SKH51 plate measuring 40 mm long, 40 mm wide, and 5 mm thick, it was mirror-polished, degreased, fixed to a substrate holder in a vacuum vessel, and the vacuum vessel was evacuated to 10 ^-6 Torr, and Ar gas was evacuated to 50C. Continue evacuation while introducing into the vacuum vessel at a flow rate of .c./min to maintain the pressure inside the vacuum vessel at 2×10 ^-3 Torr. After that, apply a DC voltage of -1kV to the substrate holder and + to the lower electrode and nozzle.
When a DC voltage of 500V was applied, a stable Ar plasma glow discharge was generated around the base material.
The impurity layer formed on the surface of the substrate in the atmosphere was completely removed in several tens of minutes. After that, once the vacuum container is
After exhausting to 10 ^-6 Torr, the lower electrode and nozzle are set to earth potential, the exhaust route is switched to the exhaust route used during film formation, H ₂ gas is introduced, and the pressure is reduced to 0.3 Torr, which is the pressure during film formation. At the same time as increasing the internal pressure, the DC voltage applied to the substrate holder was lowered to -300V. During this time, a weak H ₂ plasma glow discharge is generated around the base material, and the base material continues to be discharge-cleaned.
When the pressure inside the vacuum vessel stabilized at a predetermined pressure, 13.56MHz, 2.0KW high frequency power was applied to the upper electrode, which had been matched in advance, and a stable plasma discharge field was instantly formed, causing a drop in the surface of the substrate. TiN film started to be deposited. A dark space is created around the base material, and the potential of the base material is -
It became 150V. Film formation was continued in this state for about 100 minutes. As a result, a 3.5 μm golden yellow TiN film was formed on the SKH51 substrate. Furthermore, the surface of the TiN film mirrored the surface roughness of the base material.
When we evaluated the adhesion of the formed TiN film using a scratch test, we found that a high critical load of 40N was obtained, and when we observed the destruction of the film, we found that the TiN film itself was destroyed while the film adhered to the base material. It turned out that it was.

For comparison with this result, a 3.5 μm TiN film was mirror-polished with a potential of -200 V applied to the substrate without plasma discharge cleaning.
When formed on an SKH51 base material and subjected to a scratch test, the critical load was 25N. Also
When observing the destruction of the TiN film, it was observed that the TiN film was separated from the base material interface and the base material surface was exposed. Furthermore, when the potential applied to the substrate after plasma discharge cleaning is set to the earth potential, the critical load is 30N, and TiN
The film had peeled off from the base material interface.

Example 3 A high-speed steel drill with a drill diameter of 6 mm was coated with a TiN film to a thickness of approximately 2 μm in the same manner as in Example 2, and a cutting test was performed. The number of holes that can be drilled with the drill is four times that of a drill without one. Furthermore, when we measured the film thickness on the margin and rake face of the drill coated with TiN film, we found that a uniform TiN film was formed over the entire length with a thickness range of ±20%. In the case of this example, even though the film was formed while the drill was fixed without rotating, a good film thickness distribution was obtained, and the film was formed uniformly on a substrate with a complex shape. It has been demonstrated that this is possible. Furthermore, as shown in Fig. 3, the drill with a TiN film formed without electrical discharge cleaning was only able to drill 1.5 times as many holes as the drill with no coating.

Example 4 The concentration of impurities taken into the film near the interface with the base material was investigated with and without applying a bias to the base material during film formation. The same mirror-polished SKH51 plate used in Example 2 was used as the base material, and after plasma discharge cleaning, -
The impurity concentration near the interface between the TiN film formed by applying a potential of 200 V and the base material after plasma discharge cleaning was performed using the earth potential was investigated using Auger electron spectroscopy. As a result, as shown in Figure 5, in the case of the earth potential, an abnormally large amount of oxygen is taken in near the interface, but when a potential of -200V is applied to the base material as shown in Figure 4, oxygen is taken in in an abnormally large amount near the interface. It was found that the oxygen concentration of In this way, it has been demonstrated that it is important not only to perform electrical discharge cleaning of the substrate, but also to apply a potential to the substrate during film formation.

As shown in Examples 2, 3, and 4, the plasma discharge cleaning of the substrate before film formation and the application of potential to the substrate during film formation are very effective in improving the adhesion between the film and the substrate. It has been proven that

Note that the plasma CVD method according to the present invention includes:
Of course, the present invention is not limited to the above embodiments; for example, the base material holder and the lower electrode may be made the same, the base material is fixed to the lower electrode, and the lower electrode may be used as a potential applying power source that also serves as a cleaning plasma discharge power source. . Further, instead of the nozzle, a system may be used in which the reaction gas is supplied in a shower form from the upper electrode.
It was also demonstrated that a film with excellent adhesion can be created by temporarily stopping the discharge after plasma discharge cleaning of the substrate and performing discharge cleaning for several tens of seconds to several minutes before film formation.

Alternatively, a pump system having a stable pumping speed over a wide range of pressures may be used, and the pumping may be carried out in one route.

In addition, the arrangement direction of each electrode does not matter whether it is upward or downward.
It may be reversed, or it may be of a horizontally opposed type.

[Effects of the Invention] According to the present invention, ceramic coatings can be formed on tools, molds, machine parts, etc. with uniformity and high adhesion with low impurity concentration by plasma CVD method, resulting in high functionality. can be done.

[Brief explanation of drawings]

Figures 1a and b are schematic diagrams of the capacitively coupled plasma CVD apparatus used in the present invention, Figure 2 is a perspective view of the gas blowing nozzle, Figure 3 is a graph showing the cutting test results of the drill, and Figure 4. is a graph showing the results of Auger electron spectroscopy when a bias potential of -200V is applied, and FIG. 5 is a graph showing the results of Auger electron spectroscopy when earth potential is applied. DESCRIPTION OF SYMBOLS 1... Decompression space, 2... Decompression container, 3... Upper electrode, 4... Lower electrode, 5... Gas blowing nozzle, 6... Base material, 7... Base material holder, 8... Electric heater , 9... Heater, 10... Cleaning discharge power supply, 11... Cleaning plasma discharge field, 12... Power supply, 13... Power supply, 16... Switch, 17... Power supply, 18... Plasma discharge field, 19... ...discharge power supply, 20 ... reaction gas supply system, 21 ... liquid raw material gas supply system, 22 ... valve, 23 ... vaporizer, 24 ... valve, 2
5... Exhaust route, 26... Vacuum pump, 27...
Supply route, 28... Vacuum pump, 29... Exhaust route, 30... Vacuum pump, 31... Exhaust route, 3
2...Valve, 33...Valve, 34...Dark Space.

Claims (1)

[Claims] 1. In a reduced pressure space, two independent main and sub-discharge mechanisms are prepared for cleaning the substrate and forming a film, and first the sub-discharge mechanism starts cleaning the substrate, and after the required time has elapsed. By quickly introducing the raw material gas and after the pressure in the depressurized space reaches the set operating pressure and stabilizes, the main plasma discharge is immediately started, thereby creating a negative potential on the substrate at the same time as film formation begins. , a highly adhesive thin film formation method using a plasma CVD method, which is characterized by forming a highly adhesive metal and ceramic thin film. 2 At the initial stage of film formation, until the film thickness reaches several hundred to several thousand Å,
The negative potential generated at the start of the discharge is applied to the base material as it is, and then the potential of the base material is changed to the earth potential or the potential of the discharge field several times for several seconds every few minutes. plasma
Highly adhesive thin film formation method using CVD method.