JP3938424B2 - Diamond thin film production equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the technical field of a plasma CVD apparatus, and more particularly to the technical field of a plasma CVD apparatus that can form a large-area diamond thin film using microwaves.
[0002]
[Prior art]
Diamond is a semiconductor material with the same crystal structure as silicon, and has a wide band gap, high heat resistance, and high hardness. Therefore, diamond has recently been used as a high-frequency power device, short-wavelength optical device, and wear-resistant coating material. Attention has been paid.
However, in order to use diamond for a semiconductor device, high-pressure synthetic diamond is expensive and impractical.
[0003]
Therefore, techniques that can produce a high-quality diamond thin film at low cost have been studied, and a microwave plasma CVD method, a hot filament CVD method, a DC discharge method, a combustion flame method, and the like have been proposed.
[0004]
Among them, the microwave plasma CVD method is regarded as promising because it can form a high-quality diamond thin film. The code | symbol 101 of FIG. 3 is the elements on larger scale of the diamond thin-film manufacturing apparatus of a prior art which manufactures a diamond thin film by the microwave plasma CVD method.
[0005]
The diamond thin film manufacturing apparatus 101 includes a waveguide 111 and a quartz tube 115. The waveguide 111 has a rectangular cross section, and the quartz tube 115 penetrates the waveguide 111 vertically. It is erected in.
[0006]
When a substrate to be deposited is inserted into the quartz tube 115, a source gas containing carbon atoms is introduced into the quartz tube 115, a microwave generator (not shown) is operated, and microwaves are emitted into the waveguide 111. The microwave is irradiated to the quartz tube 115, and plasma 117 is generated in the quartz tube 115.
When the carbon atoms in the plasma reach the substrate surface and the crystal grows, a diamond thin film is formed.
[0007]
However, since the microwave has a short wavelength, the cutoff density, which is the upper limit of the plasma density that can be propagated, is 7 × 10 ¹⁰ cm ³ , and cannot propagate through the plasma at a density higher than the cutoff density.
[0008]
Therefore, the microwave cannot penetrate into the high-density plasma, so that the plasma density does not increase. There is also a problem that only a small-area diamond thin film can be formed on the substrate surface. For example, when a microwave with a frequency of 2.45 GHz is used, since the wavelength is as short as about 12 cm, only a diamond thin film with a diameter of about 1 cm can be formed.
[0009]
In order to spread the plasma, the diamond thin film manufacturing apparatus 102 shown in FIG. 4 has been proposed.
The diamond thin film manufacturing apparatus 102 includes an electromagnetic horn 122 in addition to the waveguide 121 and the quartz tube 125, and one end of the electromagnetic horn 122 has the same shape and size as the cross-sectional shape of the waveguide 121. The other end is formed in an opening that is several times larger.
[0010]
One end of the electromagnetic horn 122 is connected to the waveguide 121, and the other end side is provided with a quartz tube 125. A substrate to be deposited is previously placed in the quartz tube 125, and a source gas is introduced. At the same time, when a microwave generator (not shown) is operated and the microwave is introduced into the waveguide 121, the microwave is diverged in the electromagnetic horn 122 and irradiated from the opening end toward the quartz tube 125.
[0011]
In this diamond thin film manufacturing apparatus 102, microwaves are irradiated to a large area in a quartz tube 125 having a large diameter or a stainless steel vacuum chamber, so that a relatively large plasma 127 can be generated. The limit is about cm, and the growth rate is slow.
[0012]
On the other hand, there is known an electron cyclotron resonance diamond thin film manufacturing apparatus that generates a high-density plasma by resonantly exciting the plasma with a strong magnetic field (875 G or more). There are disadvantages such as need.
[0013]
When the diamond thin film is used for a flat display, a heat sink for a semiconductor integrated circuit board, a membrane for an X-ray exposure mask, or a wear-resistant coating material, using the characteristics, at least a diameter of 10 cm or more, Practically, it is necessary to form a diamond thin film having a side of about 20 cm to 50 cm. Therefore, none of the above-mentioned prior art devices are suitable for practical use.
[0014]
[Problems to be solved by the invention]
The present invention was created to solve the above-mentioned disadvantages of the prior art, and an object thereof is to provide a technique capable of forming a diamond thin film having a large area at high speed.
[0015]
[Means for Solving the Problems]
In order to solve the above problems, the invention according to claim 1 is a diamond having a vacuum chamber, a gas introduction tube, and a waveguide, a substrate disposed in the vacuum chamber, and a carbon atom in the composition formula. A thin film source gas is introduced into the vacuum chamber by the gas introduction tube, microwaves are radiated into the waveguide, the source gas is excited to generate plasma, and the substance in the plasma is converted into the substrate. A diamond thin film manufacturing apparatus for forming a thin film on the substrate surface by reaching the surface, wherein a slot is provided on a side surface of the waveguide so that the microwave leaks from the slot into the vacuum chamber. A variable voltage power source configured and capable of applying a negative voltage to the substrate is provided .
[0016]
According to a second aspect of the present invention, in the diamond thin film manufacturing apparatus according to the first aspect, a dielectric window is hermetically fixed to the surface of the waveguide where the slot is provided.
[0017]
Invention of Claim 3 is a diamond thin-film manufacturing apparatus of any one of Claim 1 thru | or 2, Comprising: The front-end | tip part of the said gas introduction pipe is arrange | positioned in the said dielectric material window vicinity, The said front-end | tip part The source gas supplied from is flowed in a direction parallel to the surface of the dielectric window.
[0018]
A fourth aspect of the present invention is the diamond thin film manufacturing apparatus according to any one of the first to third aspects, wherein the variable voltage power source is configured to apply a positive voltage to the substrate. It is characterized by.
[0019]
A fifth aspect of the present invention is the diamond thin film manufacturing apparatus according to any one of the first to fourth aspects, wherein a potential is provided at a position between the waveguide and the substrate in the vacuum chamber. A controllable electrode is provided.
[0020]
A sixth aspect of the present invention is the diamond thin film manufacturing apparatus according to any one of the first to fifth aspects, wherein the vacuum chamber is provided with a temperature measuring window through which the back surface of the substrate can be observed. It is characterized by.
[0021]
A seventh aspect of the present invention is the diamond thin film manufacturing apparatus according to any one of the first to sixth aspects, wherein the waveguide has a temperature measuring hole through which the film formation surface of the substrate can be observed. It is provided.
[0022]
The invention according to claim 8 is the diamond thin film manufacturing apparatus according to any one of claims 1 to 7, wherein the vacuum chamber is provided with at least two measurement windows, and one of the measurement windows is provided. Is configured to be able to irradiate measurement light onto the film formation surface of the substrate at an incident angle of 50 ° or more and less than 90 °, and the other measurement window allows reflected light returned by the film formation surface to pass therethrough. It was configured as described above.
[0023]
The present invention is configured as described above, a substrate is placed in a vacuum chamber, a raw material gas for a thin film is introduced from a gas introduction tube, a microwave is emitted into the waveguide, and the raw material gas is excited to generate plasma. When a substance in plasma is caused to reach the substrate surface, a thin film can be formed.
[0024]
In this diamond thin film manufacturing apparatus, a slot is provided on the side surface of the waveguide, and microwaves are leaked from the slot into the vacuum chamber, so that plasma can be generated in the vicinity of the waveguide. Thus, when the plasma surface is extremely excited, the inside of the plasma becomes higher than the cutoff density by diffusion.
[0025]
If the dielectric window is airtightly fixed on the surface of the waveguide where the slot is provided, the inside of the vacuum chamber and the inside of the waveguide are separated in an airtight manner, so that impurities can enter the vacuum chamber. In addition, the inside of the vacuum chamber can be maintained in a high vacuum state.
[0026]
In addition, if the tip of the gas introduction tube is arranged in the vicinity of the dielectric window so that the source gas flows in a direction parallel to the dielectric window, impurities separated from the dielectric window are carried by the source gas. Since it is left and removed by evacuation, the purity of the formed thin film is improved.
[0027]
In addition, a variable voltage power source is configured so that a voltage of a desired magnitude can be applied between the substrate disposed in the vacuum chamber and the vacuum chamber, and the diamond thin film is applied to the vacuum chamber while keeping the substrate at a negative potential. When formed, the diamond nucleus generation density increases, and the crystal orientation grows while matching.
[0028]
Conversely, when the substrate is set to a positive potential with respect to the vacuum chamber, the dielectric window is carbonized, and impurities are not mixed when a diamond thin film is subsequently formed on the substrate. When the window material is mixed as an impurity, such a positive potential treatment can be performed.
[0029]
Furthermore, if a potential controllable electrode is provided at a position between the plasma and the substrate in the vacuum chamber, the position of the plasma can be moved, so that the distance between the dielectric window and the plasma is increased, and the dielectric The window can be prevented from being etched.
[0030]
In the diamond thin film manufacturing apparatus described above, a high-purity thin film can be formed at a high speed on the film formation surface of the substrate, and when a temperature measurement window capable of observing the back surface of the substrate is provided in the vacuum chamber, Since the substrate temperature during thin film formation can be monitored, the film thickness controllability of the thin film is improved.
In this case, a temperature measuring hole through which the film formation surface of the substrate can be observed may be provided in the waveguide.
[0031]
Further, at least two measurement windows are provided in the vacuum chamber, and measurement light is irradiated from one measurement window to the film formation surface of the substrate at an incident angle of 50 ° or more and less than 90 °, and the other measurement window is passed through. If the configuration is such that the reflected light can be emitted outside the vacuum chamber, the state of the thin film during film formation can be observed.
[0032]
In the case where the slot is formed in a narrow groove shape and at least two slots are provided, the microwaves leaking from the slots into the vacuum chamber are strengthened and the generated plasma density is increased.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 2 (a) and FIG. 1 corresponding to the cross-sectional view taken along the line AA in FIG. 2 (a), reference numeral 1 is the diamond thin film manufacturing apparatus of the present invention, and a vacuum whose bottom side is open. It has a tank 20 and a waveguide 4 arranged on the bottom side of the vacuum tank 20.
[0034]
The vacuum chamber 20 and the waveguide 4 are airtightly fixed to each other, and one slot (thin groove-like through hole) 6 is provided on the side surface 35 of the waveguide 4 on the vacuum chamber 20 side. Yes. The slot 6 is formed with a width of about 10 mm and a length of about 6 cm. The dielectric window 5 is hermetically fixed to the upper portion of the slot 6, and the inside of the vacuum chamber 20 is hermetically sealed from the inside of the waveguide 4. It is separated.
[0035]
On the other hand, a substrate holder 30 on which a substrate can be placed is provided on the ceiling side of the vacuum chamber 20. When a diamond thin film is formed by the diamond thin film manufacturing apparatus 1, first, a vacuum atmosphere in the vacuum chamber 20. The substrate made of a silicon wafer treated with diamond powder having a particle size of 1 μm or less is placed on the substrate holder 30 while maintaining the above.
[0036]
Reference numeral 31 in FIG. 1 indicates the substrate in this state, and the film formation surface 32 of the substrate 31 is directed to the waveguide 4 side in the lower position. The film formation surface 32 and the dielectric window 5 are They are arranged opposite to each other in parallel.
[0037]
Next, while the vacuum chamber 20 is evacuated, the substrate 31 is heated by a heating mechanism (not shown) to raise the temperature.
[0038]
A portion of the vacuum chamber 20 on the back surface of the substrate 31 is provided with a temperature measuring window 22 made of a hole and a quartz material hermetically sealing the hole. When the temperature of the substrate 31 is raised, 31 The infrared light emitted from the back surface is passed through the temperature measuring window 22, the infrared light passed by the infrared thermometer 38 disposed in the vicinity of the temperature measuring window 22 is received, and the temperature is raised while measuring the temperature. I let you.
[0039]
The diamond thin film manufacturing apparatus 1 includes a gas introduction system (not shown) and a gas introduction pipe 9 connected to the gas introduction system, and an end of the gas introduction pipe is provided from the ceiling side of the vacuum chamber 20 to the inside. It is inserted vertically.
[0040]
The distal end portion 10 of the gas introduction tube 9 is bent in the horizontal direction in the vicinity of the dielectric window 5, and when the substrate 31 is stabilized at 850 ° C., the hydrogen diluted methane gas (methane 1% -hydrogen 99%) from the distal end portion 10. Or a mixed gas having a dilution ratio of methane 3% -hydrogen 97%).
[0041]
Due to the release of the hydrogen diluted methane gas, the inside of the vacuum chamber 20 is 20 Torr to 30 Torr.
After stabilizing at the Torr pressure, a microwave was introduced into the waveguide 4, and the microwave was leaked into the vacuum chamber 20 through the slot 6 and the dielectric window 5.
[0042]
The slot 6 of the waveguide 4 has its longitudinal direction perpendicular to the microwave traveling direction 24, and the source gas is excited by the leaked microwave, and the slot 6 is located near the dielectric window 5. Plasma 3 having an elliptical shape with a minor axis in the direction and an area of 20 to 30 cm ² was generated.
[0043]
In this diamond thin film manufacturing apparatus 1, a 2.45 GHz microwave (wavelength 12 cm) is used, and the plasma wave is directed from the rear side of FIG. It is supposed to progress along.
[0044]
As described above, the slot 6 of the waveguide 4 has a length in the longitudinal direction of 6 cm and is ½ of the wavelength of the microwave. The longitudinal direction of the slot 6 corresponds to the microwave traveling direction 24. Are oriented vertically.
[0045]
According to such a configuration, the microwave leaked from the slot 6 into the vacuum chamber 20 forms a standing wave in the slot 6 and generates a high-density plasma 3 near the dielectric window 5.
[0046]
In general, microwaves are reflected on a plasma surface with a density higher than the cut-off density (7 × 10 ¹⁰ cm ^{−3 with} respect to a frequency of 2.45 GHz) and cannot enter the plasma. The plasma that can be generated has an upper limit of the cutoff density.
[0047]
However, in this diamond thin film manufacturing apparatus 1, the microwave extremely excites the surface portion of the plasma 3 in the vacuum chamber 20 near the dielectric window 5, so that the plasma 3 in that portion diffuses toward the substrate 31, As a result, the inside of the generated plasma 3 has a higher density than the cutoff density, and the film formation rate can be improved.
[0048]
However, when such a high-density plasma 3 approaches the dielectric window 5, the dielectric window 5 is etched by the plasma 3, and when released, it becomes an impurity and may be mixed into the diamond thin film.
[0049]
In the diamond thin film manufacturing apparatus 1, two variable voltage power sources 26 and 28 are provided outside the vacuum chamber 20, and the vacuum chamber 20 is positioned between the dielectric window 5 and the substrate holder 30. A net-like electrode 15 is provided.
[0050]
The electrode 15 is connected to the electrode of one variable voltage power supply 26 so that it can be placed at a desired potential with respect to the waveguide 4. Further, the substrate 31 disposed in the vacuum chamber 20 is connected to the other variable voltage power supply 28 and is configured to be placed at a desired potential with respect to the vacuum chamber 20.
[0051]
Since the plasma 3 generated in the vicinity of the dielectric window 5 is located between the dielectric window 5 and the electrode 15, if the potential of the electrode 15 is controlled by one variable voltage power supply 26, the plasma 3 and the dielectric window The distance between 5 can be changed. Therefore, the distance between the plasma 3 and the dielectric window 5 can be appropriately separated so that the dielectric window 5 is not etched by the plasma 3.
[0052]
Further, as described above, the distal end portion 10 of the gas introduction tube 9 is bent in the horizontal direction, and the source gas 11 discharged from the distal end portion 10 flows in a direction parallel to the surface of the dielectric window 5. It has become. Therefore, even when the material constituting the dielectric window 5 is liberated, the material is carried away by the flow of the source gas 11 and removed by evacuation, so that it is mixed into the diamond thin film being formed as an impurity. There is nothing.
[0053]
In the diamond thin film manufacturing apparatus 1, two measurement windows 21 ₁ and 21 ₂ are provided on the side wall of the vacuum chamber 20, and a light irradiation device (not shown) is disposed in the vicinity of _one measurement window 21 ₁ . . In addition, a light receiving device is disposed in the vicinity of the other measurement window 21 ₂ .
[0054]
The substrate 31 is placed at a negative potential with respect to the vacuum chamber 20 by the variable voltage power supply 28, the microwave power is set to 800 W, and the temperature of the substrate 31 is set to 800 by observing the temperature of the substrate 31 from the temperature measuring window 22 as described above. A thin film was formed while maintaining the temperature.
[0055]
When the thin film is grown, the measurement light 27 ₁ in a certain polarization state passes through _one measurement window 21 ₁ and is incident on the film 31 on the substrate 31 during the formation of the thin film at an incident angle of 50 ° or more and less than 90 °. irradiating the 32, is reflected by the film forming surface 32, the polarization state reflected light 27 ₂ changes, and passed through the other of the measuring window 21 _2, received by the light receiving device arranged outside the vacuum chamber 20, ellipsometry Measurements were made.
[0056]
After film formation, the substrate was taken out and subjected to Raman spectroscopic analysis. As a result, a beak was observed at 1332 cm ⁻¹ , and it was confirmed that a diamond thin film containing no impurities had grown on the film formation surface 32. It was. The growth rate was 0.2 to 0.3 μm per hour. The crystal orientation matching of the diamond thin film formed on the substrate 31 was high.
[0057]
When the number of slots was increased to 2, the microwave power was 2 kW, the substrate temperature was 850 °, and the reaction was performed for 60 minutes, a diamond thin film was formed in a 15 cm diameter region on the substrate surface.
Thus, according to the plasma wave CVD apparatus 1 of the present invention, a high-quality diamond thin film can be formed at a high deposition rate.
[0058]
By the way, the waveguide 4 is provided with a minute temperature measuring hole 23 on the surface opposite to the surface on which the slot 6 is formed as compared with the slot 6. Therefore, when performing temperature control of the substrate 31 during thin film formation, an infrared thermometer in which infrared light radiated from the film forming surface 32 side of the substrate 31 and passed through the temperature measuring hole 23 is disposed in the vicinity of the temperature measuring hole 23. The light may be received by 29 and temperature measurement may be performed.
[0059]
When the diamond thin film was grown by changing the temperature of the substrate 31, the relationship between the substrate temperature and the growth rate was the same as that obtained by a conventional diamond thin film manufacturing apparatus. Since the temperature measurement of the board | substrate 31 was performed using the temperature measurement window 22 or the temperature measurement hole 23, it has confirmed that the temperature measurement result was exact.
[0060]
Further, the diamond thin film manufacturing apparatus 1 using a source gas in which hydrogen gas is added to methane gas, a source gas in which hydrogen gas and oxygen gas are added to methane gas, or a source gas in which hydrogen gas and argon gas are added to methane gas is used. As a result of plasma generation and formation of a thin film, it was confirmed by Raman spectroscopic analysis and electron microscope observation that the thin film was a diamond thin film.
[0061]
The case where one or two slots are provided on the side surface 35 of the waveguide has been described above. However, as shown in FIG. 2B, three or more slots 6 ′ are formed in a “C” shape. You may arrange. In this case, if the length L of each slot and the center-to-center distance W are set to ½ of the in-tube wavelength of the microwave, the intensity of the microwave leaked into the vacuum chamber 20 can be increased.
[0062]
【The invention's effect】
The formation speed of the thin film is high, and a thin film containing no impurities can be formed.
Good controllability of substrate temperature.
In particular, a high-quality diamond thin film having a large area can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a diamond thin film manufacturing apparatus according to the present invention (cross-sectional view taken along line AA in FIG. 2).
FIG. 2A is a diagram for explaining the slot shape and arrangement of the diamond thin film manufacturing apparatus.
(b): Diagram showing another example of slot arrangement [FIG. 3] Example of a conventional diamond thin film manufacturing apparatus [FIG. 4] Other example of a conventional diamond thin film manufacturing apparatus [Explanation of Symbols]
DESCRIPTION OF SYMBOLS 1 ... Diamond thin film manufacturing apparatus 3 ... Plasma 4 ... Waveguide 5 ... Dielectric window 6, 6 '... Slot 9 ... Gas introduction pipe 10 ... Tip part of gas introduction pipe 11 ... Source gas 15 ... Electrode 20 ... Vacuum chamber 21 ₁ , 21 ₂ ... Measurement window 22 ... Temperature measurement window 23 ... Temperature measurement hole 27 ₁ ... Measurement light 27 ₂ ... Reflected light 28 ... Variable voltage power supply 31 ... Substrate 32 ... Film-forming surface 35 ... Waveguide side surface

Claims (8)

A vacuum chamber, a gas introduction tube, and a waveguide;
A substrate is placed in the vacuum chamber, a diamond thin film gas having carbon atoms in the composition formula is introduced into the vacuum chamber by the gas introduction tube, microwaves are radiated into the waveguide, The source gas is excited to generate plasma,
A diamond thin film manufacturing apparatus for causing a substance in the plasma to reach the substrate surface and forming a thin film on the substrate surface,
A slot is provided on a side surface of the waveguide,
The microwave is configured to leak from the slot into the vacuum chamber ,
An apparatus for producing a diamond thin film, comprising: a variable voltage power source capable of applying a negative voltage to the substrate . 2. The diamond thin film manufacturing apparatus according to claim 1, wherein a dielectric window is hermetically fixed to a surface of the waveguide where the slot is provided. The tip of the gas introduction pipe is disposed in the vicinity of the dielectric window,
3. The diamond thin film production according to claim 1, wherein the source gas supplied from the tip is configured to flow in a direction parallel to a surface of the dielectric window. 4. apparatus. The variable voltage power source is configured to be able to apply a positive voltage to the substrate,
The diamond thin film manufacturing apparatus according to any one of claims 1 to 3, wherein the dielectric window is carbonized. 5. The diamond thin film production according to claim 1, wherein a potential controllable electrode is provided at a position between the waveguide and the substrate in the vacuum chamber. apparatus. The diamond thin film manufacturing apparatus according to any one of claims 1 to 5, wherein the vacuum chamber is provided with a temperature measuring window through which the back surface of the substrate can be observed. The diamond thin film manufacturing apparatus according to claim 1, wherein the waveguide is provided with a temperature measuring hole through which a film formation surface of the substrate can be observed. The vacuum chamber is provided with at least two measurement windows,
One measurement window is configured to be able to irradiate measurement light at an incident angle of 50 ° or more and less than 90 ° to the film formation surface of the substrate,
8. The diamond thin film manufacturing apparatus according to claim 1, wherein the other measurement window is configured to allow the reflected light returned from the film-forming surface to pass therethrough. 9.

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