JP2009209028A - Process of manufacturing diamond polycrystal substrate and diamond polycrystal substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diamond polycrystal substrate which has a high quality and a large area and is obtained by gas phase synthesis without requiring a continuous operation and to provide its manufacturing process. <P>SOLUTION: The diamond polycrystal substrate is obtained by making available a film-forming seed substrate different from diamond, forming diamond polycrystals with a thickness of less than 500 μm by a gas phase synthesis method from the seed substrate, separating the diamond polycrystals from the seed substrate to obtain a diamond polycrystal self-supporting substrate, further growing diamond polycrystals on the diamond polycrystal self-supporting substrate to obtain a diamond polycrystal substrate with a thickness of not less than 500 μm and polishing both sides of the substrate. The diamond polycrystal substrate obtained has a transmittance of light with a wavelength of 400 nm of not less than 35%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a polycrystalline diamond substrate and a polycrystalline diamond substrate, and in particular, has a large area applicable to optical parts such as windows for ultraviolet to infrared light, microwaves, and high frequencies, and mirrors and lenses thereof. The present invention relates to a method for producing a high-quality diamond polycrystalline substrate and a diamond polycrystalline substrate.

  Diamond is transparent in a wide wavelength range from X-rays, ultraviolet to infrared light, and even in the microwave region, and its thermal conductivity at room temperature is the highest among existing materials. Furthermore, since the dielectric loss of microwaves is small, and the hardness and Young's modulus are high and are not easily distorted, it is particularly promising as a transmission window for infrared lasers and microwaves with a large thermal load. As an artificial diamond applied to such an optical use, a large-area, thick diamond polycrystalline substrate obtained by a vapor phase synthesis method is required. However, a diamond polycrystalline substrate having a thickness of 500 μm or more obtained under normal gas phase synthesis conditions is brown or black as a whole and is not suitable for use as an optical component due to absorption loss and dielectric loss. On the other hand, for example, by a method exemplified in Patent Document 1, a high-quality and thick diamond polycrystalline substrate that is transparent from the ultraviolet region to the infrared region and further into the microwave region can be obtained.

Patent Document 1 shows an example in which diamond is synthesized on a molybdenum substrate for 30 days continuously. This is because continuous synthesis is inevitably required to obtain a 500 μm thick plate because the substrate and diamond are separated by thermal stress during cooling. If the synthesis is terminated in the middle without using an appropriate technique, there is a problem that the substrate and diamond cannot be separated cleanly and decomposed. That is, the long-term continuous operation as in Patent Document 1 is not suitable for industrial mass production, and there are problems such as deterioration in yield and increase in production cost.
JP-A-10-067596

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a high-quality and large-area diamond polycrystalline substrate obtained by a gas phase synthesis method that does not require continuous operation and a method for producing the same.

In order to solve the above problems, the present invention has the following aspects.
(1) A method for producing a polycrystalline diamond substrate by a vapor phase synthesis method, comprising preparing a seed substrate for film formation different from diamond and depositing a polycrystalline diamond having a thickness of less than 500 μm by a vapor phase synthesis method, A diamond polycrystal and a seed substrate are separated to form a diamond polycrystal self-supporting plate. Further, a diamond polycrystal is further grown on the diamond polycrystal self-supporting plate by a vapor phase synthesis method to obtain a diamond polycrystal substrate having a thickness of 500 μm or more. A method for producing a diamond polycrystalline substrate, comprising:

  (2) The polycrystalline diamond substrate according to (1), wherein the seed substrate for film formation is one selected from silicon, silicon nitride, aluminum nitride, silicon carbide, molybdenum and tungsten Manufacturing method.

  (3) The method for producing a polycrystalline diamond substrate according to (2), wherein silicon oxide is deposited on the surface of the seed substrate for deposition before the deposition of diamond.

  (4) The diamond according to (2) above, wherein at least one kind of metal different from the seed substrate is formed on the surface of the seed substrate for film formation before the film formation of diamond. A method for producing a polycrystalline substrate.

  (5) The diamond polycrystal according to any one of (1) to (4), wherein the diamond polycrystal formed on the seed substrate for film formation has a thickness of 150 μm or more and 350 μm or less. A method for manufacturing a substrate.

  (6) Performing one or more of reactive ion etching, ECR plasma etching, and microwave plasma etching on the surface of the diamond polycrystalline free-standing substrate on the diamond growth side, and then further growing the polycrystalline diamond. The method for producing a polycrystalline diamond substrate according to any one of (1) to (5), which is characterized in that

  (7) After performing one or more of reactive ion etching, ECR plasma etching, and microwave plasma etching on the surface of the diamond polycrystal free-standing substrate where the seed substrate for film formation exists, The method for producing a diamond polycrystalline substrate according to any one of (1) to (6), wherein the growth is further performed.

  (8) The method for producing a polycrystalline diamond substrate according to any one of (1) to (7), wherein the step of additionally growing the polycrystalline diamond is repeated twice or more.

  (9) A diamond polycrystalline substrate having a thickness of 500 μm or more manufactured by a vapor phase synthesis method, and having a light transmittance of 35% or more after polishing both surfaces of the diamond substrate, the diamond substrate There are no black spots with a diameter of 50 μm or more, and when the cross section or side surface of the diamond substrate is observed with an optical microscope or an electron microscope, a layer in which a plurality of vapor phase synthesis is repeated is observed. A diamond polycrystalline substrate.

  (10) The diamond polycrystalline substrate according to (9), wherein a thickness of the diamond polycrystalline substrate is 1 mm or more.

  (11) The diamond polycrystalline substrate according to (9) or (10) above, wherein the diamond polycrystalline substrate has a light transmittance of 50% or more at a wavelength of 400 nm.

  (12) The diamond polycrystalline substrate according to any one of (9) to (11) above, wherein no black spots having a diameter of 10 μm or more are present in the diamond polycrystalline substrate.

  By using the method for manufacturing a polycrystalline diamond substrate of the present invention, a large-area, high-quality diamond multi-layer that can be applied to optical parts such as windows for ultraviolet to infrared light, microwaves, and high frequencies, mirrors, and lenses thereof. A crystal substrate can be obtained without continuous synthesis for a long time.

  In order to solve the problem of Patent Document 1, the inventors first conducted an experiment in which diamond was intermittently grown on a silicon substrate. The synthesis conditions other than the silicon substrate were conditions similar to those of Patent Document 1, and a total of four additional synthesis was performed for a total of 30 days. After synthesis, the silicon substrate was etched away with hydrofluoric acid to obtain a diamond polycrystalline free-standing substrate. . As a result of mechanically polishing both surfaces of the diamond polycrystalline free-standing substrate, a number of black spots 2 as illustrated in FIG. 1 were observed inside the diamond substrate by microscopic observation, although it was partially transparent. It was. Next, as a comparison, an experiment was conducted in which diamond polycrystals were continuously grown on a silicon substrate under the same gas conditions by a microwave plasma CVD method. After 30 days of continuous synthesis, the same processing was performed and the inside of the substrate was observed. As a result, many black spots similar to those during intermittent synthesis were observed.

  When the black spots are observed in detail, there are minute cracks having a diameter of about 10 to 500 μm in the crystal grain boundaries and crystal grains of the polycrystalline diamond, and light is absorbed in the cracked areas to form black spots. I understood it. Moreover, in the example of the intermittent growth implemented previously, the dust etc. which were embedded in the boundary surface of additional growth existed, and it turned out that these are also black spots. The present inventors considered that the minute cracks were caused by the accumulation of stress inside the polycrystalline diamond, and came to recall the present invention.

  That is, in the present invention, a seed substrate for film formation different from diamond is prepared, a diamond polycrystal having a thickness of less than 500 μm is formed by a vapor phase synthesis method, and then the diamond polycrystal and the seed substrate are separated to form a self-supporting diamond polycrystal. A diamond polycrystal substrate having a thickness of 500 μm or more is obtained by further growing a diamond polycrystal on the diamond polycrystal free-standing plate by vapor phase synthesis. The stress inside the polycrystalline diamond is inevitably generated when cooling from the temperature during synthesis (about 900 ° C.) to room temperature, mainly due to the difference in thermal expansion coefficient between the diamond and the seed substrate. When this internal stress exceeds the elastic limit of diamond, black spots appear as microcracks along with plastic deformation. As a result of detailed investigations on the diamond polycrystal plate thickness, black spot generation rate, and size, the present inventors have found that if the growth plate thickness is less than 500 μm, black spots do not occur or even if they occur, optical components As a result, we found out that it was at a level where there was no practical problem. The black spots referred to in the present invention are a general term for minute cracks in the substrate, dust at the growth interface, etc. Same thing.

  The thickness of the diamond polycrystalline layer before separating the seed substrate may be less than 500 μm, but preferably 150 μm or more and 350 μm or less. Thereby, there are few micro cracks, the handling after seed substrate isolation | separation is easy, and the follow-up growth of a diamond polycrystal becomes easy. This diamond polycrystalline layer of less than 500 μm may be continuously grown once or intermittently several times later. If the surface layer is obtained intermittently by additional growth, it is better to etch the surface layer by reactive ion etching, ECR plasma etching, or microwave plasma etching before additional growth. As a gas phase synthesis method for obtaining a polycrystalline diamond, any of known techniques such as a hot filament method, a direct current plasma method, an arc jet method, etc. can be used, but preferably a large area with high quality and continuous operation stability. The microwave plasma method is preferable because of its excellent resistance.

  The seed substrate for film formation is preferably selected from silicon, silicon nitride, aluminum nitride, silicon carbide, molybdenum and tungsten. By using these materials for the seed substrate, it is possible to grow a diamond polycrystalline layer having moderate adhesiveness with diamond and low internal stress. In consideration of the peeling resistance of the polycrystalline diamond and the generation of diamond nuclei at the initial stage of growth, it is desirable that one or more types of silicon oxide or different metals are formed on the surface before the diamond growth.

  Thereafter, when separating the polycrystalline diamond substrate grown on the seed substrate, known methods such as electrolytic etching, acid etching, grinding, laser processing, and dry etching can be used as a method for selectively removing the seed substrate. . The diamond polycrystalline substrate after separating the seed substrate can be further grown to a desired thickness by vapor phase synthesis. The surface on which the additional growth is performed can be performed on either the upper or lower surface of the diamond polycrystalline substrate. At this time, since the diamond is not restrained by the seed substrate, there is essentially no thermal stress, and therefore no microcracking occurs. As a result, even when the diamond polycrystalline substrate is thickened to a thickness at which black spots are generated in the conventional technique, the black spots are not generated in the technique of the present invention, or even if they are generated, there is no practical problem in optical parts. As an example, the size of black spots is less than 50 μm in diameter, more preferably less than 10 μm. The size of the black spot having a diameter of 50 μm means that the black spot is present within a circle having a diameter of 50 μm assuming that the center of the black spot is the center of the circle.

  Black spots cause not only minute cracks, but also surface dust during additional growth. In order to eliminate this influence, it is better to perform reactive ion etching, ECR plasma etching, or microwave plasma etching on the surface (surface) of the diamond polycrystalline free-standing plate on the diamond growth side before additional growth. The etching thickness on the surface side is desirably 10 nm or more and 5 μm or less. Etching with such a thickness enables not only the influence of dust but also the removal of the surface-modified layer before the additional growth, thereby reducing internal stress during diamond growth. Furthermore, it is desirable to perform the above-described etching also on the surface (back surface) where the seed substrate for film formation exists. The etching thickness on the back side is desirably 1 μm or more and 100 μm or less. Since the nucleation variation of diamond depending on the seed substrate is generated on the back surface side, the initial growth layer has variations. Since this variation may cause internal stress at the time of further growth, the generation of black spots can be suppressed by performing etching with the thickness in advance.

  There is no problem even if the additional growth is repeated twice or more to the desired thickness. As a result, the growth can be stopped and restarted at an arbitrary time, and there are few restrictions on the growth time as in the prior art, and the productivity is improved. Even when repeated two or more times, it is desirable to perform the etching before each additional growth. It is desirable to synthesize diamond polycrystals with the same synthesizer before and after seed substrate separation, but they may be additionally grown with another synthesizer. As for the surface of the additional growth, it is preferable to perform additional growth as it is on the surface grown from the original seed substrate, but it is also possible to perform additional growth on the opposite surface (the surface on the seed substrate side).

  The diamond polycrystalline substrate thus obtained can then be used as an optical plate by mechanically polishing both sides, or can be used as a mirror or a lens after being subjected to dry etching or laser processing. In that case, the light transmittance at a wavelength of 400 nm after double-side polishing is 35% or more, preferably 50% or more. The diamond polycrystalline substrate obtained by this method can easily determine the presence or absence of additional growth by observing the growth side surface or cross section. For example, after a polycrystalline substrate is cleaved with a laser or the like and the cross section is polished, etching is performed with microwave plasma in a hydrogen atmosphere. When this surface is observed with an optical microscope or an electron microscope, it can be determined by clearly showing the additional growth boundary surface 3 as illustrated in FIG.

  The diamond polycrystalline substrate of the present invention will be described more specifically based on examples.

  First, a polycrystalline silicon substrate having a diameter of 50 mm and a thickness of 3 mm was prepared as a seed substrate for diamond growth. The surface of the silicon substrate has been lapped, and the surface was scratched with # 800 diamond abrasive grains. Next, a silicon substrate was placed in a known microwave plasma CVD apparatus. Then, a polycrystalline diamond was grown on this seed substrate by a microwave plasma synthesis method. Table 1 shows the growth conditions.

  By this growth, a substrate in which the diamond polycrystal 5 was grown on the silicon seed substrate 4 as schematically shown in FIG. 3 was obtained. The thickness of the gas phase synthetic diamond polycrystalline layer was 210 μm. Next, the growth surface was mechanically mirror-polished and the silicon substrate was removed by etching with hydrofluoric acid (FIG. 4). The obtained polycrystalline diamond free-standing substrate 6 was visually transparent, and as a result of observing the inside with an optical microscope, no black spots with a diameter of 10 μm or more were observed.

  Next, this diamond polycrystalline free-standing substrate 6 was placed in the same microwave plasma CVD apparatus as the first growth, and diamond polycrystalline was further grown under the same conditions as in Table 1. However, in order to eliminate temperature changes due to warpage of the diamond substrate, the thermal resistance of the holding table on which the diamond substrate is placed was changed to control the substrate surface temperature to be the same as that when growing on the silicon substrate. . The additional growth time was 350 hours. As a result, a diamond polycrystalline free-standing substrate having a total thickness of 550 μm was obtained (FIG. 5). Then, both sides of this polycrystalline substrate were mechanically polished, and the inside was evaluated as a double-sided mirror-surface free-standing substrate having a thickness of 510 μm (FIG. 6). As a result, no black spots with a diameter of 10 μm or more were observed. The light transmittance at a wavelength of 400 nm was 60%, showing good characteristics that could be used as an optical component for ultraviolet to infrared.

(Comparative Example 1)
In this comparative example, the seed substrate used, the growth conditions, and the like were the same as those in Example 1, and diamond polycrystals were continuously grown with a synthesis time of 550 hours. The thickness of the polycrystalline diamond after the growth was 560 μm. After the growth surface was polished, the silicon substrate was removed by acid etching, and the substrate surface was mechanically polished. As a result, many black spots having a diameter of 50 μm or more as shown in FIG. It was transparent except for the black spots, but due to the influence of black spots, the average light transmittance of the entire substrate at a wavelength of 400 nm was 30%, which was insufficient for use as an optical component.

  In this embodiment, a tungsten substrate having a diameter of 30 mm and a thickness of 5 mm is prepared as a seed substrate for forming a polycrystalline diamond film. First, silicon oxide is deposited on the surface of the tungsten substrate to a thickness of 500 nm by a known magnetron sputtering apparatus. did. A polycrystalline diamond was grown on this seed substrate using the same diamond synthesizer as in Example 1. The growth conditions are as shown in Table 2.

After the growth, the diamond polycrystalline substrate was separated at the interface between the silicon oxide film and the tungsten substrate when the substrate was cooled. The diamond remained integral when separated. Thereafter, the silicon oxide film was removed by etching with hydrofluoric acid, and the plate thickness was evaluated as a diamond polycrystalline free-standing substrate. Subsequently, this free-standing substrate surface was placed in a diamond synthesizer, and diamond polycrystals were additionally grown under the same conditions as in Table 2. However, the growth was stopped every 100 hours, once taken out and evaluated, and this was repeated seven times. It should be noted that the surface was etched under an etching condition in a hydrogen / oxygen atmosphere in which CH ₄ was removed from the conditions shown in Table 2 for 1 hour before each growth. As a result, a diamond polycrystalline free-standing substrate having a total plate thickness of 1050 μm was obtained. When both surfaces were mechanically polished and evaluated, the plate thickness was 1000 μm, black spots having a diameter of 50 μm or more did not exist inside the substrate, and most were transparent. Further, the light transmittance at a wavelength of 400 nm was 42%, which was a value that could be used as an optical component. After cutting this substrate with a laser, the cross section was polished, and further subjected to microwave plasma treatment in a hydrogen atmosphere, and the cross section was evaluated with a scanning electron microscope. It was confirmed that it was a growth substrate.

  In the present embodiment, an example will be described in which various seed substrates are prepared and the synthesis time of growth on the seed substrate and growth after the freestanding substrate are changed. The seed substrate size is 50 mm in diameter and 3 mm in thickness. The synthesizing apparatus was the same as in Examples 1 and 2, and the synthesis conditions were the same as in Example 1. When performing the post-growth, the same surface etching in a hydrogen / oxygen atmosphere as in Example 2 was performed before the synthesis. The respective evaluation results are shown in Table 3. In Table 3, “silicon nitride + Mo 200 nm film formation” refers to a film of Mo formed on a silicon nitride substrate by sputtering to a thickness of 200 nm.

  As shown in Table 3, the black spots and 400 nm transmittance of the obtained diamond polycrystalline substrate vary depending on the seed substrate, the growth repetition time, and the plate thickness. Can be selected according to the intended use.

  In this example, a polished polycrystalline silicon carbide substrate having a diameter of 25 mm and a thickness of 2 mm was prepared as a diamond growth seed substrate. The surface of this polycrystalline silicon carbide substrate was scratched with No. 500 diamond powder, and then polycrystalline diamond was grown under the same diamond growth conditions as in Table 2.

  After the growth, the silicon carbide substrate portion was ground and removed, and the plate thickness was evaluated as a diamond polycrystalline free-standing substrate. As a result, it was 400 μm. The surface (back surface) from which this seed substrate was removed was etched using a commercially available reactive ion etching apparatus. The etching time was adjusted so that the etching gas was oxygen and the etching thickness on the back surface was 50 μm. After the etching, it was placed in a diamond synthesizer so that the back side was an additional growth surface, and diamond polycrystal was additionally grown under the same conditions as in Table 2. However, the growth was stopped every 200 hours, once taken out and evaluated, and this was repeated four times. Before each additional growth, the surface on the additional growth side was etched by 1 μm by the reactive ion etching. As a result, a diamond polycrystalline free-standing substrate having a total plate thickness of 1100 μm was obtained. When both surfaces were mechanically polished and evaluated, the plate thickness was 1050 μm, black spots having a diameter of 10 μm or more did not exist inside the substrate, and the entire surface was transparent. The light transmittance at a wavelength of 400 nm was 62%, and it showed good characteristics that can be used as an optical component for a wide wavelength from ultraviolet to infrared light.

  As described above, if the method for producing a polycrystalline diamond substrate of the present invention is used, a large area that can be applied to optical parts such as windows for ultraviolet to infrared light, microwaves, and high frequencies, and mirrors and lenses thereof. And a high-quality diamond polycrystalline substrate can be obtained without the need for continuous synthesis.

It is the schematic diagram of the black spot seen from the diamond polycrystal free-standing substrate main surface. It is the scanning electron micrograph of the cross section of the diamond polycrystal self-supporting substrate which performed additional growth. It is a side view when a diamond polycrystalline substrate is grown on a silicon substrate. FIG. 3 is a side view of a self-supporting substrate separated from a silicon substrate after polishing the surface of the polycrystalline diamond layer. It is a side view after further growing a diamond polycrystal on a diamond polycrystal. It is a side view after polishing both surfaces of a diamond polycrystalline freestanding substrate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Black spotted diamond polycrystalline substrate 2 Black spot 3 Diamond polycrystal additional growth interface 4 Silicon substrate 5 Diamond polycrystal layer 6 Diamond polycrystal substrate 7 Diamond polycrystal additional growth layer

Claims (12)

  A method for producing a polycrystalline diamond substrate by vapor phase synthesis, comprising preparing a seed substrate for film formation different from diamond, forming a polycrystalline diamond having a thickness of less than 500 μm by vapor phase synthesis, and then producing the polycrystalline diamond And separating the seed substrate into a diamond polycrystalline free-standing plate, and further growing the polycrystalline diamond on the diamond polycrystalline free-standing plate by vapor phase synthesis to obtain a diamond polycrystalline substrate having a thickness of 500 μm or more. A method for producing a polycrystalline diamond substrate, comprising:   2. The method for manufacturing a polycrystalline diamond substrate according to claim 1, wherein the seed substrate for film formation is one selected from silicon, silicon nitride, aluminum nitride, silicon carbide, molybdenum and tungsten.   3. The method for producing a polycrystalline diamond substrate according to claim 2, wherein a silicon oxide film is formed on the surface of the seed substrate for film formation before the diamond film is formed.   3. The method for producing a diamond polycrystalline substrate according to claim 2, wherein at least one kind of metal different from the seed substrate is formed on the surface of the seed substrate for film formation before the diamond is formed. Method.   5. The method for producing a diamond polycrystalline substrate according to claim 1, wherein a thickness of the diamond polycrystalline film formed on the seed substrate for film formation is 150 μm or more and 350 μm or less. .   The diamond polycrystal free-standing substrate is subjected to one or more of reactive ion etching, ECR plasma etching, and microwave plasma etching on the surface of the diamond growth side of the diamond polycrystal free-standing substrate, and diamond polycrystal is additionally grown. The method for producing a diamond polycrystalline substrate according to any one of claims 1 to 5.   One or more of reactive ion etching, ECR plasma etching, and microwave plasma etching are performed on the surface of the diamond polycrystal free-standing substrate where the seed substrate for film formation exists, and then the diamond polycrystal is additionally grown. The method for producing a polycrystalline diamond substrate according to claim 1, wherein the method is characterized in that:   The method for producing a polycrystalline diamond substrate according to any one of claims 1 to 7, wherein the step of additionally growing the polycrystalline diamond is repeated two or more times.   A diamond polycrystalline substrate having a plate thickness of 500 μm or more manufactured by a vapor phase synthesis method, and having a light transmittance of 35% or more at a wavelength of 400 nm after polishing both surfaces of the diamond substrate, There are no black spots with a diameter of 50 μm or more, and when the cross-section or side surface of the diamond substrate is observed with an optical microscope or an electron microscope, a layer obtained by repeating a plurality of vapor phase synthesis is recognized, Diamond polycrystalline substrate.   The diamond polycrystalline substrate according to claim 9, wherein the diamond polycrystalline substrate has a thickness of 1 mm or more.   The diamond polycrystalline substrate according to claim 9 or 10, wherein the diamond polycrystalline substrate has a light transmittance of 50% or more at a wavelength of 400 nm.   The diamond polycrystalline substrate according to any one of claims 9 to 11, characterized in that no black spots having a diameter of 10 µm or more are present in the diamond polycrystalline substrate.

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