JP5042134B2 - Diamond thin film - Google Patents

Description

The present invention removes or reduces strain, defects, color, etc. existing in a vapor-phase synthetic diamond thin film formed on a substrate or a free-standing diamond thin film (foil or plate) from which the substrate has been removed, or to an oriented polycrystal or single crystal. And a modified diamond thin film .
As used herein, “diamond thin film” includes “diamond free-standing film” and “processed diamond thin film” unless otherwise specified.

There are various kinds of diamonds, from transparent large single crystals to colored polycrystalline diamonds, and the crystal contains various lattice defects and impurities such as Ni and Si. These diamonds are divided into type I that absorbs light having a wavelength of 3000 angstroms or less with respect to light in the ultraviolet region and type II that transmits light of 2250 angstroms or more. Type II is more pure.
Further, the type I is classified into type Ia (most of natural diamonds) containing 0.1% or more of flaky nitrogen and type Ib in which 500 ppm or more of nitrogen is substituted with carbon. The type II can be divided into a high resistance type IIa and a type IIb indicating a p-type semiconductor.
These diamonds generally have high hardness, low coefficient of thermal expansion, chemical stability (inert), high thermal conductivity, high insulation, high infrared transmittance, high reflectivity, high sound velocity, wide band gap semiconductor characteristics, high-speed carrier It has many desirable physical properties such as color center, negative electron affinity, biocompatibility, and excellent acoustic properties.
Utilizing these characteristics, cutting tools, wear-resistant coating materials, circuit boards, high-frequency devices, heat sinks, various optical components, electronic device components such as semiconductors and radiation sensors, surface acoustic wave filters, speakers, artificial joints, and other living bodies It is being studied for use in functional parts and is a material with many important industrial uses.

As is well known, in the middle of this century, diamond was successfully synthesized at high pressure and has been widely used as an industrial material. In addition, a method for producing a diamond thin film in the gas phase has been developed.
A well-known method for forming a thin film on a substrate is a vapor deposition method (CVD). There are several methods described below for forming a diamond thin film using this CVD method.
For example, a quartz tube opened near a tungsten filament heated to a high temperature (around 2000 ° C.) is disposed, and a diluted mixed gas of hydrocarbon gas such as methane and hydrogen is introduced through this quartz tube to obtain a temperature of 500 ° C. A method of decomposing and depositing diamond from the mixed gas on a substrate heated to ˜1100 ° C., a microwave plasma CVD method using a plasma discharge instead of the tungsten filament method, and an RF (radio frequency) plasma CVD method Further, there are a DC (direct current) arc plasma jet method, and a method in which a flame of oxyacetylene is applied to a substrate at high speed in the atmosphere to decompose and precipitate diamond from a hydrocarbon-containing gas.

In the above method, by dissociating hydrogen into atoms, the graphite formed at the same time is preferentially removed, and diamond is formed using the principle of growing a diamond structure film. The deposition mechanism is extremely complex and is not currently well understood.
In addition, there are not only significant differences in quality, manufacturing operability or manufacturing capability depending on the type of manufacturing method described above, but also the film formation parameters such as temperature, reaction gas composition, gas pressure, reaction gas flow rate, substrate type, substrate The present situation is that it is extremely sensitive to many factors such as temperature and film forming apparatus, and has not yet reached a level that can sufficiently satisfy the problem of producing diamond stably, reproducibly and efficiently.
In particular, the microwave plasma CVD method or the RF (high frequency) plasma CVD method using the plasma discharge has a problem of becoming a complicated and expensive device such as requiring a complicated tuning device for stabilizing the plasma. Further, the growth of diamond was extremely slow compared to the expensive apparatus, and the obtained diamond film had a defect that high density defects and strains were inherent.

Next, the diamond thin film formed on the substrate by the CVD method as described above, many of the manufacturing process causes stress due to tensile strain and compressive strain, and in some cases cracks may occur. The diamond thin film may peel off from the substrate.
The occurrence of such strain is caused by defects in the diamond thin film, grain boundaries and impurities at the grain boundary, as well as differences in thermal expansion characteristics between the substrate or coating substrate on which the diamond thin film is formed or coated and the diamond. Is.
In addition, even if it is attempted to obtain a diamond thin film having the desired characteristics, quality deterioration such as formation of pseudo diamond or diamond-like carbon thin film having low characteristics or graphitization occurs.
These are because, as described above, even if the CVD method is currently one of the few effective means for forming a film-like diamond, the result is not sufficient because the diamond cannot be produced stably and reproducibly. ing.

For this reason, there is an attempt to offset the stress by simultaneously forming a diamond film on both sides of the substrate by the CVD method (JP-A-5-306194).
However, this also does not guarantee that diamonds are formed correctly and evenly on both sides of the substrate (although there is a description of the desire to form a uniform film so that unbalanced internal strain does not occur, in fact, Is not stable) and a strained state still exists in the crystal.
In addition, it is difficult to achieve ideal as long as the heating temperature of the substrate, the gas flow direction for film formation, and the decomposition deposition are not finely controlled so that diamond is formed as evenly as possible on both sides. There is a problem that the design and control methods are complicated.

Further, in order to reduce the inclusions present in the synthetic diamond grains, reduce the residual strain of the diamond lattice and increase the toughness, annealing is performed in an alumina crucible in an atmosphere of hydrogen or a mixed gas of hydrogen and an inert gas. (Japanese Patent Laid-Open No. 7-165494), a proposal of heating to 1600 to 2200 ° C. by irradiating with an electron beam in order to reduce the color of diamond grains (Japanese Patent Publication No. 62-43960) or nitrogen, boron There is also an attempt to recover lattice damage by doping high concentration of arsenic, phosphorus, etc., roughening the diamond crystal surface, and then annealing using a radio frequency (RF) coil (JP-A-6-166594). .
However, either method seems to have a certain effect in reducing distortion, but the amount is small, and in the last proposal, it is not possible to recover a crystal once damaged (damaged) It seems not easy. In any case, it was not an effective means for reducing the residual strain of the diamond lattice.

Recently, CBN (cubic boron nitride), BCN (including boron carbonitride, solid solution of CBN and diamond) or CN (cubic carbon-nitrogen compound) thin film having the same crystal structure as diamond and forming a hard film. However, since these are composed of binary compounds or ternary compounds, they tend to deviate from the stoichiometric composition during film formation (in CBN, the phenomenon in which the element ratio B / N of the bond fluctuates locally in the crystal). There is a tendency for more defects and distortions to occur.
In particular, the CBN film can be used as a high temperature semiconductor film (which may be capable of forming an n-type semiconductor, and in combination with diamond having the characteristics of a p-type semiconductor, suggesting the possibility of an ultrafast carrier transistor). The film is expected to be able to form a hard film that is harder than diamond. However, as described above, many distortions and defects are likely to occur at the stage of film formation. there were.

  The present invention effectively removes or reduces strain, defects, color, etc. present in a thin film such as vapor-phase diamond formed on a substrate, a thin film (foil or plate) such as free-standing diamond from which the substrate is removed, or orientation. It is an object of the present invention to provide a thin film of diamond or the like modified into a crystalline polycrystal or a single crystal stably and with good reproducibility, and a modification method therefor and a thin film formation method of diamond or the like.

The present invention
1 Diamond thin film having a surface modified by microwave irradiation , having a film thickness region modified by 0.1 μm or more along the film thickness direction of the diamond thin film, and evaluated by Raman spectroscopy Diamond thin film 2 characterized in that the half width of the spectrum is constant and the half width is 85% or less of the maximum half width of the remaining thickness of the film. 2. The diamond thin film according to 1 above, which is a crystal, an oriented polycrystal, or a single crystal.
3. The diamond thin film according to 1 or 2 above, wherein at least a part of the modified portion of the diamond thin film is made into a semiconductor, and further on the modified portion of the diamond thin film. The diamond thin film according to any one of 1 to 3 above, wherein a single crystal film is formed, characterized in that at least a part of the diamond thin film is coated with a metal, ceramics, conductor or insulator. The diamond thin film according to any one of 1 to 4 above

The present invention removes or reduces strain, defects, color, etc. present in a thin film such as vapor phase diamond formed on a substrate or a free-standing diamond thin film (foil or plate) from which the substrate has been removed, or is oriented polycrystal or single crystal. A thin film such as diamond that can be transformed into a crystal, a modification method, and a thin film formation method. Compared with a conventional electron beam or high-frequency heating annealing in a crucible, the present invention is a strain or texture modification. The range and performance of the film can be greatly improved, and a thin film such as diamond can be modified stably and reproducibly. In addition, a thin film such as diamond can be modified at a low cost without requiring a complicated apparatus or a control method.
In addition, by adjusting the temperature, time, intensity, frequency, atmosphere, etc. of microwave irradiation, the thickness of the modified layer of the irradiated object can be adjusted, or the thickness can be modified to a certain depth. The reforming operation that can be performed is flexible, and there is no restriction on the order of the steps of the reforming operation. In other words, simultaneously with the modification, a new high quality or highly oriented polycrystalline film or single crystal film is formed on the surface to be modified, or the damaged surface is irradiated with microwaves on the surface damaged by a laser or the like. It can be said that the surface of a thin film such as diamond is made into a semiconductor simultaneously with the modification. Thus, it has the characteristic that operativity is very excellent.

For example, carbon bonds such as SP bonds and sP ² bonds, which are bonding modes other than the diamond component, are formed in a diamond thin film produced by a vapor phase method. The more such non-diamond components, the more defects are formed in the formed diamond film, which often degrades the crystallinity of the film, and diamond grains with different orientations grow in the film. Due to this, a significant strain is induced in the vicinity of the grain boundary.
The presence of this non-diamond component and the presence of strain near the grain boundary are considered to be one of the causes that hinder the heteroepitaxial growth of diamond.
As a method for investigating such defects in diamond, Raman spectroscopy is said to be the most effective analytical method for identifying and quantifying non-diamond components contained in diamond thin films and examining the crystallinity of diamond itself. (Toray Research Center THE TRC NEWS No. 35 (Apr. 1991) 16-21 “Evaluation of diamond (like) film by Raman spectroscopy”)

In the present invention, the half-value width (half-value width) (cm ⁻¹ ) of the Raman parameter is adopted as one of evaluation methods for evaluating the amount of strain in a thin film such as diamond, that is, the degree of crystallinity. That is, the half-value width of good natural diamond or the like was compared with the half-value width of the thin film such as diamond obtained in the present invention, and the characteristics were examined.
As this half-value width approaches that of natural diamond, lattice defects, contamination with impurities or non-uniform distortion are eliminated, and the crystallinity of natural diamond approaches. At the same time, a cathode luminescence emission (CL) image was used as a method for evaluating defects in thin films such as diamond.

In the present invention, a thin film such as diamond is irradiated with a microwave of 1 GHz to 500 GHz and heated to modify the thin film such as diamond as described above.
Here, if the frequency of the microwave irradiated for heating is less than 1 GHz, it is insufficient for heating the diamond thin film, and the change in the half width of the diamond spectrum evaluated by Raman spectroscopy is also observed before and after irradiation. There wasn't. On the other hand, if it exceeds 500 GHz, the microwave hardly penetrates into the diamond thin film and has no modification effect. Therefore, it is necessary to use microwaves in the above range.
The atmosphere is a vacuum that can prevent graphitization of diamond or the like, an inert gas, a reducing gas, or a mixed gas thereof.
Directly or part of the gas is turned into plasma by microwave irradiation, and the irradiated object such as diamond is heated.
As described above, it is known that a diamond thin film can be formed by utilizing microwaves for plasma generation. However, the microwave itself is irradiated to diamond or the like directly or in combination with plasma to generate a heating or thin film. No effort has been made.
From such a point, it is impossible to imagine from the above that a microwave of 1 GHz to 500 GHz is effective for reforming to reduce defects and distortion existing in a thin film such as diamond.
Further, as described above, means for reforming means such as annealing in an electron beam or a crucible have been proposed, but this does not effectively reduce defects present in a thin film such as diamond.
As described above, the present invention, which has the effect of modifying a thin film of diamond or the like containing defects and strains formed by the gas phase into a more excellent one, has novelty and remarkable effects.

  Examples of the present invention will be described below in comparison with comparative examples. The embodiment of the present invention is merely an example and can be variously changed. Therefore, the scope of the present invention is not limited to the following examples, and includes various modifications within the scope not departing from the gist of the present invention. Further, examples and comparative examples of diamond thin films are shown unless otherwise specified, but the present invention can be equally applied to CBN, BCN, or CN thin films.

(Example 1 and comparative example)
In this embodiment, a diamond thin film is placed in a microwave irradiation apparatus, and microwaves of 1 GHz to 500 GHz are irradiated and heated. FIG. 1 is a schematic explanatory diagram of the apparatus.
A container made of alumina fiber (Al2O3 fiberboard) is placed in the center of the apparatus, and a diamond free-standing film (sample) is placed therein. Microwaves are arranged so that the diamond solid body is irradiated at an angle of 45 °.
A temperature measuring device (Thermal Video System) is placed in the alumina container at a position perpendicular to the microwave incident direction, and the temperature of the diamond surface is constantly measured. FIG. 2 shows an enlarged explanatory diagram of sample arrangement, microwave irradiation direction, and temperature measurement. Nitrogen gas at 1 atm was passed through the apparatus (in a N2 gas stream). In this embodiment, 6
A pulse microwave of 0 GHz (Pulse wide 5.5 msec, Repetition frequency 5 Hz) was used, but a continuous wave can also be used.

In this embodiment, a diamond free-standing film synthesized by vapor deposition is used, but a diamond thin film formed on a substrate may be used.
For example, a diamond free-standing film is formed on a Mo substrate by the above-described DC (direct current) arc plasma CVD method using plasma discharge, and the formed diamond film is peeled off from the substrate by heating (stripping using the difference in temperature expansion). Alternatively, it is dissolved and removed by chemical means to form a diamond free-standing film. Two films of 500 μm thus obtained (self-supporting films) were laminated and used as a sample.
The diamond free-standing film may be formed by other known microwave plasma CVD method, RF (radio frequency) plasma CVD method, or oxygen acetylene flame method.
As an embodiment of the present invention, a large number of diamond free-standing film samples were prepared, and the diamond free-standing film sample was irradiated from a 45 ° angle using the 60 GHz pulsed microwave, and 800 ° C., 1300 ° C., It heated at 1500 degreeC, 1800 degreeC, 2200 degreeC, and 2500 degreeC, respectively (each is heating attainment temperature).
As a comparative example, a natural good diamond and a sample of the diamond free-standing film that were not irradiated with microwaves were prepared. The above results are shown below.

(Test 1)
First, comparison is made using a cathode luminescence emission (CL) image.
FIG. 3 shows the same sample subjected to vapor deposition of diamond. FIG. 3 shows an embodiment of the present invention, in which the final growth surface is heated to 1500 ° C. (attainment temperature) using the above-mentioned 60 GHz pulsed microwave. Shows a cathode luminescence image (× 20) of the surface removed by a thickness of ˜50 μm.
FIG. 4 shows, as a comparative example, a cathodoluminescence image of a surface processed by removing a thickness of ˜50 μm from the final growth surface as it is simply subjected to diamond vapor phase growth, that is, an unirradiated sample (× 30).
As is clear from the comparison of the cathode luminescence images, the CL emission in the example of the present invention shown in FIG. 3 is much higher than that in the unprocessed comparative example not irradiated with the microwave shown in FIG. It can be seen that it has increased. That is, it can be seen that it has CL emission similar to natural good diamond.
This is presumed to be due to a decrease in defects and strains distributed in the diamond vapor phase growth surface and its thickness direction. In any case, it can be seen that heating by microwave irradiation is effective in modifying the diamond vapor phase growth film.

(Test 2)
Next, the diamond free-standing film sample was irradiated from a 45 ° angle using natural diamond, 60 GHz pulsed microwave, and 800 ° C, 1300 ° C, 1500 ° C, 1800 ° C, 2200 ° C, 2500 ° C. The half-value width (cm ⁻¹ ) of the Raman parameter of the sample of the diamond thin film according to the embodiment of the present invention heated to the above and the sample of the vapor growth diamond not irradiated with microwaves are compared. FIG. 5 shows the half-value width (cm ⁻¹ ) of the Raman parameter of natural diamond.
In the figure, there are six half-value widths from light yellow (111) face to brown (100) face as natural diamond, but they are in the range of about 3.5 to 4.5 cm ⁻¹ .
FIG. 6 shows an example of the present invention in which microwaves are irradiated and heated to the above temperatures, and a comparative example of the half-value width (cm ⁻¹ ) of the Raman parameters that are not irradiated with microwaves. The left end is a comparative example not irradiated with microwaves, and has a half width of about 8 to 10 cm ⁻¹ .
On the other hand, in the examples of the present invention, those which were irradiated with microwaves and heated to 1300 ° C. had a half width of about 7 to 7.5 cm ^{−1 and} were further irradiated with microwaves to 1500 ° C. The one that has been heated to 5 to 6 cm ^{−1 has} a half width of 4 to 5 cm ⁻¹ by irradiation and heating to a high temperature of 2200 ° C. to 2500 ° C. Thus, it was confirmed that it has a value that approximates the half-value width of natural diamond. This result agrees well with the result of the cathode luminescence image.

The heating up to 800 ° C. shown in FIG. 6 shows a tendency to be slightly larger than the comparative example in which microwaves are not irradiated. However, it was observed that the microwave was satisfactorily absorbed from around 500 ° C.
It is presumed that the half-value width apparently showed a tendency to increase at a stage in the middle of strain recovery, but the clear reason is unknown. However, it can be considered that the reforming effect exists from around 500 ° C.
After that, the half-value width decreased rapidly with increasing heating temperature. This shows that microwave irradiation is extremely effective for modifying distortions and defects in diamond crystals.
In the examples, a 60 GHz microwave was used, but a modification effect was confirmed with a microwave of 1 GHz or more. Although the microwave frequency was increased and irradiation exceeding 500 GHz was carried out, at such a high frequency, the microwave hardly penetrated into the diamond film, and the modification effect could not be confirmed. Therefore, it can be seen that microwaves of 1 GHz to 500 GHz are effective for the reforming effect.
Moreover, although the heating temperature by microwave irradiation is based on the property of a diamond thin film, it was confirmed that there exists a modification effect in the range of 500 ° C to 3000 ° C.

(Example 2)
A diamond free-standing film having a thickness of 500 μm having a polycrystalline part and an oriented polycrystalline part having a thickness of 100 μm and flattened irregularities on the final growth surface was prepared, and a microwave of 60 GHz was applied to this free-standing film on the side of the final growth surface And heated by irradiation. The reforming atmosphere is in an Ar stream and the heating temperature is 800 ° C.
Tables 1 and 2 show the relationship between the irradiation conditions and the ultimate temperature (the transition of the diamond thin film heating temperature) in which the microwave irradiation heating is repeated twice with the microwave output constant.
It can be seen that when the diamond thin film heated to 800 ° C. by the first microwave irradiation is further subjected to the second microwave irradiation under the same conditions, the ultimate temperature decreases (from Table 1 to Table 2). In addition, the fall of the ultimate temperature by irradiation beyond this is hardly seen.

(Test 3)
The refractive index of the microwave-irradiated surface of the diamond thin film obtained above was measured, and the thickness of this surface was sequentially reduced by machining, and the refractive index in the depth direction from the microwave-irradiated surface was measured. By measuring the refractive index in the depth direction, it can be confirmed that a region where the refractive index is constant from the microwave irradiation surface along the film thickness direction is generated, and at the same time, microwaves of the free-standing film are generated. It was confirmed that the film had a higher refractive index than the non-irradiated side, that is, the opposite surface.
The refractive index characteristic has a relationship of [dielectric constant = (refractive index) ^1/2 ] with the dielectric constant. As a result of comparing this dielectric loss characteristic with a diamond thin film having the same structure not irradiated with microwaves, it was confirmed that the microwave irradiated thin film of the present invention had a reduction in high-frequency dielectric loss exceeding 10%.
In terms of the refractive index, when the refractive index of the microwave irradiation modified portion is 0.1% or more higher than the minimum refractive index of the non-modified portion, the effect of reducing the high-frequency dielectric loss increases, and is particularly effective. It is.
A test was conducted to determine whether or not normal heating was effective regardless of microwaves. Although the results of heating up to 1600 ° C. stepwise showed no effect.
Thus, it was confirmed that heating at 500 ° C. or higher by microwave irradiation is extremely effective for reducing the high-frequency dielectric loss.

(Example 3)
Next, one or more kinds of gases selected from carbon, nitrogen or boron source supply gas or gas containing semiconducting elements in the reforming atmosphere are simultaneously heated by irradiating a thin film such as diamond with microwaves of 1 GHz to 500 GHz. An example of forming a polycrystalline thin film such as diamond, an oriented polycrystalline thin film, a single crystalline thin film, or a semiconductor thin film thereof on the object to be modified at the same time as the modification will be described.
In the gas phase synthesis process of the diamond film, the generation of the diamond component and the generation of the non-diamond component are unavoidable together with the generation of the diamond component as described above. It has been found that the etching action of atomic hydrogen produced by dissociating and activating (hydrocarbon-based) gas is effective.
For this reason, in the current technology, while trying to improve the quality of polycrystalline diamond thin films, the carbon concentration in the carbon source gas is reduced, the thin film formation rate is lowered, and the etching effect of non-diamond components by atomic hydrogen Is trying to increase.
However, since this etching action induces the generation of various lattice defects in the diamond thin film, a large amount of tensile strain and compressive strain accumulate in the generated diamond film.
For this reason, conventional polycrystalline diamond films with high crystallinity with reduced strain in the films, highly oriented polycrystalline films, and single crystal films that are indispensable for producing wide band gap semiconductors instead of silicon It was not realized.

In this embodiment, a polycrystalline diamond thin film with a substrate having a thickness of 10 μm and formed by a microwave CVD method was used.
This diamond thin film with a substrate is inserted into a microwave irradiation apparatus in the same manner as in Example 1, and the diamond thin film is irradiated with microwaves and heated, and at the same time, a carbon source gas is introduced into the modified atmosphere, A diamond thin film was formed. And the structure of the obtained thin film was evaluated by Raman spectroscopy.
As a result, a modified oriented polycrystalline film in which the half-value width of the diamond spectrum evaluated by Raman spectroscopy is 85% or less of the maximum half-value width value of the remaining film thickness, and further by selecting a micro frequency, A diamond thin film having a single crystal structure on the upper portion was obtained. This structure could be confirmed similarly by SEM and X-ray diffraction.
As described above, it has been found that the polycrystalline diamond film having a high crystallinity with less distortion in the film that could not be realized conventionally, the same polycrystalline film having a high orientation and a single crystal film can be easily manufactured by the present invention.
In particular, a diamond thin film having a single crystal structure is useful as a wide band gap semiconductor material or a high thermal conductive heat sink.

Example 4
Next, an example of manufacturing a diamond electronic device in which a part of the modified portion has semiconductor characteristics will be described.
Similarly to Example 3 above, a diamond thin film with a substrate is inserted into a microwave irradiation apparatus, and the diamond thin film is irradiated with heat and heated, and at the same time, a gas containing a carbon source gas and B as semiconductor elements in a modified atmosphere Then, a p-type diamond polycrystalline thin film, an oriented diamond thin film, and a single crystal film were formed on the diamond thin film.
It was confirmed that the characteristics of the obtained semiconductor thin film were drastically improved by the modification effect of microwave irradiation. In addition, although the example of the diamond thin film formed in the board | substrate was shown above, the same result was obtained also with the self-supporting film | membrane.

(Example 5)
Next, an example of using a diamond thin film as a heat sink will be described.
It is indispensable to fix the parts to be cooled on the diamond thin film to improve heat dissipation, to ensure electrical contact of the parts to be cooled, and to form a metallized layer etc. on the diamond thin film in order to ensure device function. .
In this example, a 0.5 μm thick metallized layer of Ti, Pt, and Au was formed by sputtering on the diamond thin film modified by irradiating microwaves to the diamond thin film as described above. The diamond thin film used in this case has a modified portion in which the half width of the diamond spectrum evaluated by Raman spectroscopy of 0.1 μm or more is 85% or less of the maximum half width value of the remaining thickness of the film. Yes.
On the other hand, for comparison, a metallized layer was similarly formed on a diamond thin film having no modified portion, and these heat dissipation properties were compared.
As a result, although depending on the thickness of the diamond and the thickness of the modified portion, the modified metallized diamond heat sink has improved thermal conductivity and improved heat dissipation by at least 20%. Thus, the modification of diamond by microwave irradiation heating can improve the performance as a device provided with a metallized layer.
In the above description, the heat sink has been described. However, the improvement of the characteristics was confirmed also in the diamond thin film formed with the insulating film such as the outer ceramic film, the ceramic conductive film and the like.

(Example 6)
Generally, a diamond thin film is used as a smooth surface by removing irregularities on the final growth surface by processing. Such smoothing is performed while adhering to the substrate, and the processing specifications required for the smoothed surface are improving year by year. For example, the surface roughness is several nm, and the flatness is required to be 20 nm or less for the surface acoustic wave filter.
As a substrate for forming a diamond thin film, Si single crystal, Mo, W, Pt, SiC, SiO 2, AlN, or the like is used, but these have an extremely large thermal expansion coefficient compared to diamond and are at the diamond film forming temperature. When the substrate temperature is cooled from a high temperature of 800 to 1000 ° C., it is inevitable that a large strain (compression strain on the film forming side and tensile strain on the substrate side) is applied to the diamond.
In addition, as described above, since many crystal defects and strains are introduced even during diamond film formation, distortion of the shape is inevitable in flat processing of the diamond thin film. This is particularly problematic when it is necessary to produce a special three-dimensional free-standing film.

From the above, in this example, when the diamond thin film with a substrate having a diameter (φ) of 2 inches was precisely planarized, the diamond thin film surface was irradiated with microwaves of 1 GHz or more and modified before the processing. The value obtained by evaluating the crystallinity of the modified portion at this time by the Raman spectral half width was 85% or less of the value of the maximum half width of the non-modified portion.
Next, the diamond thin film was smoothed with a diamond grindstone. The flatness after processing was 10 nm or less, and excellent flatness was achieved. At the same time, the fracture resistance of diamond thin films has been greatly improved.
Further, the final growth surface of the thin film was planarized, and a 300 μm-thick diamond free-standing film from which the substrate was removed was used, and the final growth surface side of diamond was irradiated with microwaves of 1 GHz or more with the microwave irradiation surface.
The diamond thin film after removing the substrate is often slightly deformed into a concave shape because the compressive strain from the substrate is released, but by performing appropriate microwave irradiation heating, the deformation of the concave shape is reduced. A self-supporting film that was repaired and extremely flat and improved in strength could be obtained.

As shown in the above embodiment, the crystal growth surface on the substrate can be irradiated with microwaves for modification, and the self-solid structure can also irradiate the initial growth surface after removing the substrate. As a result, the film such as diamond can be modified in the same manner as the crystal growth surface.
In addition, by adjusting the temperature, time, intensity, frequency, atmosphere, etc. of microwave irradiation, the thickness of the modified layer of the irradiated object can be adjusted, or the thickness can be modified to a certain depth. it can.
There is no particular limitation on the thickness of the film that can modify the film of diamond or the like, which is an object to be irradiated.
As described above, the modification by microwave irradiation of the present invention is applied directly to the surface of the final growth such as grinding or polishing for cutting or device fabrication directly on the vapor phase growth surface of vapor phase synthetic diamond or the like. Can be done.
Further, in the above description, for ease of understanding, the examples and comparative examples have been described with a focus on diamond thin films. However, the present invention is equally applicable to CBN, BCN, or CN thin films, and the effects thereof are the same. Was confirmed.
In addition, simultaneously with the above modification, when a diamond thin film or the like is to be made into a semiconductor, a reactive gas containing a semiconducting element is introduced into an atmosphere gas alone or together with a carbon supply source gas, and at least a part of the diamond is introduced. It can be made semiconductor.
Furthermore, simultaneously with the above modification, a high-quality or highly-oriented polycrystalline film or a single crystal film can be formed on a thin film such as diamond that is the surface to be modified.

Specify the direction of microwave irradiation or make multiple reflections to irradiate only a specific area of the irradiated object, or evenly irradiate it to freely change the distortion and modification area of the diamond, and some areas Alternatively, the entire area can be modified. The present invention includes all of these. It is possible to impart a shape to the diamond film by controlling and modifying the distribution and amount of residual strain.
In particular, the film formed on the substrate not only reduces the strain by microwave irradiation and increases the strength of the film itself such as diamond, but also improves the consistency of the surface with the substrate by reducing the strain of the film itself, for example. The adhesion strength of can also be increased.
Furthermore, the microwave irradiation of the present invention can be applied to an oriented film with improved polycrystalline or oriented film quality, or diamond having a single-layered superior film characteristic, for example, a YAG laser for device fabrication, etc. The damaged surface can be recovered by microwave irradiation to form a thin film such as diamond that is almost the same as the other portions.

The present invention removes or reduces strain, defects, color, etc. present in a thin film such as vapor phase diamond formed on a substrate or a free-standing diamond thin film (foil or plate) from which the substrate has been removed, or is oriented polycrystal or single crystal. A thin film such as diamond that can be transformed into a crystal, a modification method, and a thin film formation method. Compared with a conventional electron beam or high-frequency heating annealing in a crucible, the present invention is a strain or texture modification. The range and performance of the film can be greatly improved, and a thin film such as diamond can be modified stably and reproducibly. In addition, a thin film such as diamond can be modified at a low cost without requiring a complicated apparatus or a control method.
In addition, by adjusting the temperature, time, intensity, frequency, atmosphere, etc. of microwave irradiation, the thickness of the modified layer of the irradiated object can be adjusted, or the thickness can be modified to a certain depth. The reforming operation that can be performed is flexible, and there is no restriction on the order of the steps of the reforming operation. In other words, simultaneously with the modification, a new high quality or highly oriented polycrystalline film or single crystal film is formed on the surface to be modified, or the damaged surface is irradiated with microwaves on the surface damaged by a laser or the like. It can be said that the surface of a thin film such as diamond is made into a semiconductor simultaneously with the modification. Thus, it has the characteristic that operativity is very excellent.
Diamonds and the like modified according to the present invention can remove or reduce deterioration factors such as strain and defects, and have high hardness, low friction sliding property, low thermal expansion coefficient, high temperature and chemical stability (inert ), High thermal conductivity, high insulation, high infrared transmittance, high reflectivity, high sound speed, wide band gap semiconductor characteristics, high-speed carrier, color center, negative electron affinity, biocompatibility, excellent acoustic characteristics, etc. The desirable characteristics of the material are further improved, the stability of the characteristics and the fracture reliability are remarkably improved, and can be applied to a wide range of uses such as diamond as described above.

It is a schematic explanatory drawing of the apparatus which arrange | positions thin films, such as a diamond, in a microwave irradiation apparatus, and irradiates and heats a microwave of 1 GHz-500 GHz. It is explanatory drawing which shows the arrangement | positioning of the sample in a microwave irradiation apparatus, the irradiation direction of a microwave, and temperature measurement. It is a cathode luminescence image of the surface near the surface which heated diamond to 1500 ° C using the microwave of 60 GHz in the example of the present invention. It is a cathode luminescence image of a surface near a diamond vapor phase growth surface, that is, a sample not irradiated with microwaves. This is the half-value width (cm ⁻¹ ) of the Raman parameter of natural diamond. The graph shows a comparative example of the half-value width of the Raman parameter of the example at each temperature heated by irradiation with the microwave of the present invention and the same half-value width without irradiation of the microwave.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Microwave irradiation direction 2 Temperature measuring device 3 Alumina fiber board 4 Sample 5 Argon gas introduction hole 6 Leak hole

Claims (5)

A diamond thin film having a surface modified by microwave irradiation , having a film thickness region modified by 0.1 μm or more along the film thickness direction of the diamond thin film, and evaluated by Raman spectroscopy The diamond thin film is characterized in that the half width is constant and the half width is 85% or less of the maximum half width of the remaining thickness of the film.   The diamond thin film according to claim 1, wherein at least a part of the modified portion in the diamond thin film is polycrystalline, oriented polycrystalline, or single crystal.   The diamond thin film according to claim 1 or 2, wherein at least a part of the modified portion of the diamond thin film is made into a semiconductor.   The diamond thin film according to any one of claims 1 to 3, wherein the polycrystal, the oriented polycrystal, or the single crystal film is further formed on the modified portion of the diamond thin film.   The diamond thin film according to any one of claims 1 to 4, wherein at least a part of the diamond thin film is coated with metal, ceramics, a conductor, or an insulator.