JP2706546B2 - Coating method for inner peripheral cylindrical body - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for coating an inner peripheral cylindrical body by a sputtering method, and is particularly suitable for coating an inner surface or an end surface of a relatively small diameter cylindrical body. It relates to a coating method.

[Conventional technology]

A coating apparatus using a sputtering method is known, and an example thereof is a DC bipolar sputtering apparatus. The basic structure thereof is, for example, shown in FIG. 19, in which a negative potential metal electrode (cathode) 2 is provided in a grounded depressurized closed vessel 1 under a discharge gas atmosphere introduced by a discharge gas introduction device 3. The material 4 to be coated set on the anode is coated.
According to this conventional apparatus, the temperature of the cathode rises because the cathode is violently beaten by cations. If the cathode is left as it is, the cathode melts and must be constantly cooled with cooling water. The above-mentioned conventional apparatus has a coating speed that is nearly an order of magnitude slower than that of an apparatus using a vacuum evaporation method, is extremely inefficient, and is not economical at all. In order to improve this, the frequency of collision with gas molecules by confining electrons near the electrode or performing spiral motion without applying a magnetic field inside the depressurized closed container and causing electrons emitted from the cathode to go straight, Increasingly, a large number of ions have been generated, the sputtering has been performed intensely, and an apparatus by a magnetron sputtering method in which the coating speed has been increased has been adopted. As a method for realizing higher-speed film formation, an ECR sputtering method capable of generating high-density plasma by utilizing electron cyclotron resonance has been developed.

However, this ECR sputtering method is not without its drawbacks, and the waveguide (cavity) normally used has a cutoff wavelength uniquely determined by the frequency of the microwave, so the diameter (inner diameter) of the cylindrical body to be coated In the case where is a tube, a cylinder, or the like having a small diameter smaller than the cutoff wavelength, the coating could not be applied to the inner surface thereof.

[Problems to be solved by the invention]

The present invention has been made in view of the fact that it was difficult to coat a narrow place with the conventional sputtering method as described above, and therefore, the coating of the inner peripheral surface cylindrical body which can easily coat the inner surface even with a small-diameter coating target material. It is an object to provide a method.

[Means for solving the problem]

The present invention achieves the intended object by focusing on using a coaxial mode without a cutoff wavelength in order to solve the above-mentioned problem, and a method for coating an inner peripheral cylindrical body of the present invention includes the steps of: An inner peripheral cylindrical body and a central electrode (target) provided coaxially inside the inner peripheral cylindrical body, reducing the pressure in the vacuum apparatus and supplying a discharge gas,
Applying a magnetic field to the inside of the inner peripheral surface cylindrical body and irradiating microwaves to generate electron cyclotron resonance plasma, generating the sputtering by setting the center electrode to a negative potential with respect to the inner peripheral surface cylindrical body, The inner peripheral surface of the cylindrical body is coated.

(Operation)

A coaxial waveguide in which an inner peripheral cylindrical body is installed in a discharge gas such as an argon gas under reduced pressure, and a target center electrode (hereinafter referred to as a target) is provided on an axis of the inner peripheral cylindrical body. Is formed, and a microwave is applied to the coaxial waveguide and a magnetic field corresponding to the frequency of the microwave is applied to generate an electron cyclotron resonance plasma. When the target is set to a negative potential and the inner peripheral cylindrical body is grounded, positive ions in the plasma collide with the target, atoms and molecules are sputtered from the target, and these atoms and molecules are formed on the inner surface of the inner peripheral cylindrical body. A coating is formed. When coating the inner surface of an insulator such as ceramics, a film is formed on the inner surface of the insulator by installing a cylindrical insulator inside the inner peripheral cylindrical body.

When the target is insulated from the surroundings in a DC manner, the target floats in the plasma, and this potential is determined by the plasma. Plasma electrons and positive ions come into the target, but no current can flow because the target is cut off from the external circuit. That is, positive ions and electrons of the amount of each I _i = en _i v _i flowing into the _{target, I e = en e v e} , (n i, v i is the density and velocity of the ion, n _e, v _e is the electron Density and velocity), then I _i
= I _e , but usually n _i = n _e , v _i ≪Ve, so I
_i «I _e, and this result target placed in the plasma trying to meet the I _i = I _e become negative potential (self-bias effect). With this effect, a negative potential can be obtained without applying a negative potential to the target from the outside.

Each magnetic field line in the plasma can have a potential independently. Everywhere on one magnetic field line, the potential is the same. This is because if there is a potential difference between the same lines of magnetic force, electrons move and cancel the potential. Therefore, a circular and annular split electrode concentric with the coaxial body is provided on the end face of the coaxial body formed by the inner peripheral cylindrical body and the target, and by controlling this potential, the potential of each magnetic field line can be controlled. Sputtering can be controlled. When the target and the split electrode are formed of the same material, the split electrode also becomes a target, and sputtering occurs, and a coating can be formed on the end surface of the inner circumferential body facing the split electrode.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1A is an overall configuration diagram of an apparatus for implementing the present embodiment. The apparatus includes a film forming unit 10 for forming a film on the inner surface of a pipe 11 to be coated, and a coaxial converter for converting microwaves to the film forming unit 10 from a waveguide mode to a coaxial mode.
20, a microwave waveguide 30 for propagating microwaves to the coaxial converter 20, a film-forming unit 10 and a coaxial converter 20, and a sealed tube 40 forming a vacuum space. A magnetic field coil 50 for generating a magnetic field, and the microwave waveguide 30;
Microwave generator that irradiates microwaves to the microwave, a vacuum pump that evacuates the sealed tube 40, and a sealed tube 40
And a discharge gas introducing device for introducing a discharge gas into the inside. The vacuum pump and the discharge gas introduction device are not shown. The sealed tube 40 is provided with a probe mounting seat 42 for mounting a probe 42 ′ for measuring the internal electron temperature, electron density, ion saturation current, etc., a penetration seat 43 for penetrating the microwave waveguide 30, and a connection portion for a vacuum pump. The main body 41 and the lid 41 ′ are provided with a connection portion 45 for connecting the discharge gas introduction device to the main body 41, and a magnetic field coil is provided at the center of the main body 41 of the sealed tube 40.
50 are wound in several rows. FIG. 1 (b) shows a closed tube 40.
3 shows an example of the distribution of the magnetic flux density B in the axial direction of FIG.

FIG. 2 (a) is a longitudinal sectional view of the film forming unit 10 and the coaxial converter 20, and the film forming unit 10 has a small-diameter pipe 11 to be coated on which an inner surface, an end surface, or an outer surface is formed. When,
An electrode, that is, a target 12 is provided on the central axis of the pipe 11. Reference numeral 16 denotes a flange 16 for attaching the pipe 11 to the coaxial converter 20.

The coaxial converter 20 includes a microwave waveguide 30 extending to an axial center inside the sealed tube 40 by the through seat 43 of the sealed tube 40.
A box 21 for attaching a pipe of the film forming unit 10 to a coaxial path unit 22 attached to one side surface of the box 21, and a microwave waveguide 30. With a flange 24, the flange 23 is a pipe
Fix the flange 16 on the 11 side to support the pipe 11 horizontally,
The flange 24 fixes the microwave waveguide 30.

The target 12 is the center conductor of the coaxial path section 22 of the coaxial converter 20
Fix to 25. FIG. 2 (b) is a cross-sectional view taken along the line AA of FIG. 2 (a) in the direction of the arrow.

FIG. 3 shows a microwave waveguide 30, which has the same cross-sectional shape as the box 21 and is connected at one end to the flange 24. Penetrating part 31 connected with penetrating flange 32 and penetrating seat 43
And a flange 33 made of a fluororesin (trade name: Teflon), which is interposed as a packing between the flanges 32 and allows microwaves to pass therethrough but prevents the invasion of air into the sealed tube 40, and three metal rods
A stub tuner 35 that adjusts the amount of insertion of the microwave 34 to supply microwave power to the plasma to the maximum, and a microwave generation (not shown) that is generated when the plasma generated in the film forming unit 10 is irradiated with the microwave. It comprises an isolator 36 for preventing return to the device, and a relay 37 between the isolator 36 and the microwave generator.

FIG. 4 (b) schematically shows the structure of the stub tuner 35, which is formed by arranging three metal rods 34 upright in a waveguide. The phase and amplitude of the wave r reflected back from the load and the wave r 'reflected by the metal bar 34 by changing the depth of the three metal bars 34, that is, the amount of protrusion into the microwave waveguide 30 are changed. Is adjusted so that the reflected waves r and r 'interfere with each other to be in a non-reflective state as shown in FIG. 4 (a), so that all the microwave power is absorbed by the load. .

5 (a), 5 (b) and 5 (c) show three types of microwave guided modes. FIG. 5 (a) shows a high-frequency electric field generated by a microwave passing through a waveguide having a rectangular cross section. FIG. 5 (b) shows a waveguide mode, and FIG. 5 (b) shows a circular mode showing a high-frequency electric field by a microwave passing through a waveguide having a circular cross section.
Represents a coaxial mode indicating a high-frequency electric field by a microwave passing through the coaxial waveguide.

In this device, the microwave generated by the microwave generator is transmitted in a waveguide mode (FIG. 5 (a)) with good transmission efficiency, and after passing through the microwave waveguide 30, it is provided in the pressure reducing tube 40. The signal is converted into a coaxial mode (FIG. 5 (c)) by the coaxial converter 20. This conversion method will be described with reference to FIG.

The microwave passing through the microwave waveguide 30 generates a standing wave as shown in FIG. 6 in the rectangular cross-section 21 of the coaxial converter 20 shown in FIG. A standing wave of a microwave is a wave that does not travel spatially, and a traveling wave of the same frequency whose traveling directions are opposite to each other is generated by overlapping the traveling wave, where the traveling wave is reflected at a boundary, Coaxial converter 20
Since the conductor 25 is installed at the so-called antinode where the electric field of the standing wave becomes maximum, the microwave is converted from the rectangular mode to the coaxial mode as it is.

Next, a method of forming a coating on the inner surface and the end surface of the pipe 11 will be described.

The inside of the sealed tube 40 is depressurized by operating the vacuum pump, and discharge gas is injected from the discharge gas introduction device. When an electric current is passed through the magnetic field coil 50 and the microwave is irradiated from the microwave generator to the microwave waveguide 30, an ECR plasma is generated in the pipe 11. Next, a negative potential is applied to the target 12, and the pipe 11 is set to the ground potential. This causes a sputtering method in which ions in the ECR plasma collide with the target 12 having a negative potential and release atoms or molecules of the target 12, and the released atoms and molecules form a coating on the inner surface of the pipe 11. .

Next, processing conditions and results of the first embodiment will be described. The processing conditions are shown below.

Discharge gas: N ₂ + Ar (flow rate ratio N _2: 10 to 30%) Gas pressure: 10 ^-3 to 10 ^-4 torr center electrode (target): external diameter × Material = 8 mm × T _i (99.99
9%) Pipe (substrate): outer diameter x inner diameter x material = 19 mm x 17 mm x steel Magnetic flux density: 875 Gauss Microwave generator: Magnetron, 900 W x 2.45 GHz, used as a power supply, half-wave rectified 60 Hz alternating current.

The magnetic flux density B is determined as follows. Assuming that the cyclotron frequency of the electrons in the ECR plasma is fc, the microwave frequency is f and the ECR condition is given by f = fc. Also, since there is a relationship of fc = 2.8 * B [GHz] (B is KGauss), if f = 2.45 GHz, B = fc / 2.8 = 2.45 / 2.8 =
0.875KGauss = 875Gauss.

Next, a processing state and a result will be described with reference to FIGS.

FIGS. 7 to 12 show the state of the ECR plasma, and the measurement of the plasma parameters adopted the deep needle method using a flat plate Langmuir probe.

Fig. 7 (a) shows the time evolution of the reflected wave Pr of the microwave,
(B) shows the time evolution of the ion saturation current Jis. Since the power supply of the magnetron uses half-wave rectification of 60 Hz, microwaves are generated for 8 msec out of about 16 msec in one cycle. On the vertical axis, (a) is watts (W) and (b) is amps (A). (A) and (b), an ion saturation current is generated with a delay of about 1.8 msec after microwave application. This is probably because the microwave power has a threshold for ECR plasma generation.

FIG. 8 is a diagram showing the dependence of the ion saturation current Jis of FIG. 7 on the magnetic field and the pressure in the discharge region, which was performed to confirm that it was an ECR discharge. As described above, the resonance magnetic density B corresponding to the microwave frequency f = 2.45 GHz is 875 Gauss. 8 represents the upper limit magnetic flux density of the discharge region,
The point Δ represents the lower limit of the magnetic flux density. As a result, since plasma is generated near the resonance magnetic flux density of 875 Gauss, it can be seen that ECR plasma is generated in the pipe 11.
Normally, when the pressure increases, the ECR discharge shifts to the microwave discharge, and plasma is generated in a wide range of the magnetic field.However, in this embodiment, even when the pressure increases, the discharge region is localized near the resonance magnetic field. I have. Since the ECR plasma is generated in a very narrow area, electrons accelerated by the microwave have a high probability of recombination on the inner wall of the pipe 11 without colliding with neutral particles. Is difficult to occur, and only an ECR discharge with extremely high ionization efficiency occurs. 9 to 11 show the distribution of plasma parameters in the radial direction of the pipe 11, and FIG. 9 shows the electron density ne.
, Fig. 10 shows the distribution of electron temperature Te, and Fig. 11 shows the space potential.
The distribution of Vs is shown. The pressure is p = 2 × 10 ⁻⁴ torr. 9 to 11, the vertical line at r = 4 mm indicates the outer diameter of the target 12, and the vertical line at r = 8.5mm indicates the inner diameter of the pipe 11. The electron density ne has a hill-type distribution as shown in FIG. 9, and has a peak value of 8 × 10 ¹⁰ cm ^−3.
Density. The electron temperature Te is almost constant in a space of r = 4 to 7 mm as shown in FIG.
It is a high value. This indicates that the electrons were sufficiently heated by the ECR. The space potential Vs is also uniformly distributed in the radial direction, and a high value Vs = 50 V is obtained. Ions enter the target 12 placed in the plasma with an energy of approximately Vs. Therefore, as Vs is larger, ions of higher energy are incident on the target, and the ions of higher energy cause more intense sputtering, and the speed of forming a film on the inner surface of the pipe 11 increases. No.
FIG. 12 is a diagram showing the time evolution of the radial distribution of the ion saturation current Jis, and shows the plasma formation process. Plasma starts to be generated from a place where the electric field strength is strong near the target 12 (t = 1.8 msec), and then rapidly rises to reach a steady state (t = 2.0 msec). In the magnetron used in this embodiment, a half-wave rectified 60 Hz alternating current was used as a power source, so that about half of one cycle of about 16 msec was used.
Microwaves are generated only for 8 msec, so ECR plasma is generated only for the corresponding time.However, by using a DC power supply, microwaves can be continuously oscillated, thus doubling the film forming speed. be able to.

The following is a summary of the plasma parameters.

Electron density ne = 10 ¹⁰ -10 ¹² cm ^-3 Electron temperature Te = 10 eV-100 eV Space potential Vs = several eV-several V This will be compared with data by other sputtering methods.

Ne = 10 ⁸ -10 ¹⁰ cm ⁻³ Te = ≦ 10 eV Vs = several eV−several tens eV In the case of the DC or high frequency glow discharge sputtering method, ne = 10 ⁹ -10 ¹² cm ^{− 3} Te ≦ 10 eV Vs = several eV to tens of eV Although the magnetron sputtering method is known as a high-speed film forming method, the plasma density of the present embodiment is:
The density is equal to or higher than the plasma density by this magnetron sputtering method. Moreover, since the discharge gas pressure is 1/10 or less of the magnetron sputtering method, it can be said that it is more advantageous than the magnetron sputtering method.

 An example of film formation according to the present embodiment will be described below.

Type of film: TiN film Properties of film Hardness: 1200 to 2000 kg / mm ² (Vickers hardness Hv) Specific wear amount: 10 ^-7 to 10 ^-8 / mm ² kgf (film thickness 5 μm) This will be described with reference to FIGS.
FIG. 13 and FIG. 14 show a film forming unit 10 when the second embodiment is carried out.
The target 12 is a floating electrode, and divided electrodes 14 and 15 are provided at the ends of the pipe 11 and the target 12, and a disk-shaped divided electrode 14 is provided at a portion corresponding to the target 12 to provide a variable negative electrode. An electric potential is applied, and an annular divided electrode 15 is provided at a plasma space formed between the pipe 11 and the target 12, that is, at an end of the coaxial waveguide 11 'to apply a variable electric potential. The target 12 is disposed on the center axis of the pipe 11,
The floating electrode is insulated and supported by the heat-resistant insulator 13.
In FIG. 13, the thickness of the insulator 13 between the targets 12, 12 is about 1 mm. The other conditions are the same as those in the first embodiment.

Next, the operation of the split electrode, which is a feature of the second embodiment, will be mainly described.

As shown in FIG. 13, when a magnetic flux B is applied to a coaxial waveguide 11 'composed of a pipe 11 and a target 12 and microwaves are applied, ECR plasma is generated. Electrons in the plasma move around the lines of magnetic force as shown in FIG.
This operation will be described with reference to FIG. In the figure, the electrons in the magnetic flux B move around the lines of magnetic force indicated by horizontal lines. The potential in the plasma is determined by the difference between ions and electrons, but electrons having a smaller mass are easier to move than ions, so the potential is almost determined by electrons. For this reason, in a strong magnetic field, almost each magnetic line of force can have an electric potential independently, and the electric potential becomes almost the same anywhere on one magnetic line of force. Point P ₄ of the same magnetic force line Given the potential Vd in this order point Q ₄ also point Q ₄
And the same potential Vd. Thus, it is possible to control the potential of the P ₁ to P ₇ of S ₂ side by applying a respective electric potential distribution of Q ₁ to Q ₇ of the S ₁ side. It is possible to control the potential of the floating electrode R by the the R and floating electrode for controlling the potential of the point Q _5. Using this, the potential of the target 12 is
The potential of the plasma can be controlled by controlling the potential of the split electrode 15. Thereby, the forming speed and the thickness of the coating film formed on the inner surface of the pipe 11 can be easily controlled. The potential of the plasma can be finely controlled by further dividing the divided electrode 15 into a number of annular electrodes. The split electrodes 14 and 15 also serve to reflect microwaves as shown in FIG. 16, prevent the microwaves from leaking from the end of the coaxial waveguide 11 ', and reduce the plasma density in the coaxial waveguide 11'. To be dense. The same Al as the target 12 is applied to the split electrodes 14 and 15
Alternatively, when a target material such as Ti is used, the sputtered particles also act on the end face of the pipe 11 to enable coating of the end face.

 Next, a third embodiment will be described with reference to FIGS.

In the third embodiment, the material to be coated is an insulator, and ceramics is used as the insulator. FIG. 17 shows a pipe 11 on the inner surface of the pipe 11 in FIG.
A cylindrical ceramic 17 having an outer diameter slightly smaller than the inner diameter of 11 is provided, and the other parts are the same as the second embodiment.

As is apparent from this embodiment, not only metal but also semiconductor and insulator can be used as the material to be coated.
In the first to third embodiments, the outer shape of the material to be coated or the pipe 11 containing the material to be coated is cylindrical, but only the inner surface is cylindrical and the coaxial waveguide 11 'is formed together with the target 12. For example, the outer shape does not need to be cylindrical, and may be, for example, a polygonal prism.

〔The invention's effect〕

The present invention uses a coaxial mode having no cutoff wavelength to generate ECR plasma in a small-diameter cylindrical body or a tubular body and form a coating film on the inner surface of the small-diameter tube or the like by sputtering. However, it is possible to produce a dense film quickly and inexpensively.

BRIEF DESCRIPTION OF THE DRAWINGS The drawings explain the device for carrying out the present invention and the contents of the invention. FIG. 1 (a) is a schematic configuration diagram of the device, and FIG. 1 (b) is FIG. 1 (a). Graph showing the magnetic field arrangement formed inside the decompression tube shown in the corresponding to the decompression tube,
FIG. 2A is a schematic sectional view showing a film forming unit and a coaxial converter;
FIG. 2 (b) is a cross-sectional view taken along the line AA of FIG. 2 (a) in the direction of the arrow, FIG. 3 is a front view showing the microwave waveguide together with the coaxial converter, and FIG. 4 (a). ) Is a schematic diagram in which a reflected wave of a microwave is generated, FIG. 4B is a schematic diagram of a stub tuner for adjusting the phase and amplitude of the reflected wave to the opposite phase to the amplitude of the microwave, and FIGS. 5B is a schematic diagram showing a coaxial mode, FIG. 6C is a schematic diagram showing a coaxial conversion, and FIG. 7A is a reflected wave of a microwave. Diagram showing the time evolution of the 7th
FIG. (B) is a diagram showing the time evolution of the ion saturation current, FIG. 8 is a diagram showing the magnetic field and the pressure dependence of the discharge region, FIG. 9 is a diagram showing the radial distribution of the electron density, and FIG. FIG. 11 shows the radial distribution of the electron temperature, FIG. 11 shows the radial distribution of the space potential, FIG. 12 shows the time evolution of the radial distribution of the ion saturation current, and FIG. 13 shows the inner circumference. In the plasma generated on the inner surface of the cylindrical body, an explanatory diagram showing the state in which the target constitutes a floating electrode and the direction of the magnetic field lines, and FIG. 14 corresponds to the inner cylindrical body and the divided electrode for the center electrode Explanatory diagram shown
FIG. 15 is an explanatory view showing the relationship between magnetic field lines and electrons in the plasma generated in the inner peripheral surface cylindrical body, FIG. 16 is a view showing the action of the floating electrode and the split electrode, and FIG. 17 is a view of the cylindrical insulator. Explanatory drawing when coating the inner surface and the end surface, FIG. 18 is FIG.
FIG. 19 is a schematic view showing an example of a conventional apparatus. 10 Film forming section 11 Inner peripheral cylindrical body (pipe) 12 Center electrode (target) 14, 15 Split electrode 20 Coaxial converter 30 Microwave waveguide 40 Hermetic type Decompression tube 50: Magnetic field coil

Claims (1)

(57) [Claims] An inner peripheral cylindrical body and a central electrode provided coaxially inside the inner peripheral cylindrical body are provided in a vacuum device, and the inside of the vacuum device is decompressed to discharge gas. Supply, applying a magnetic field to the inside of the inner peripheral surface cylindrical body and irradiating a microwave to generate electron cyclotron resonance plasma, and performing sputtering by setting the center electrode to a negative potential with respect to the inner peripheral surface cylindrical body. A method for coating an inner peripheral cylindrical body, comprising generating and coating an inner surface of the inner peripheral cylindrical body.