JP2018030750A - Crystal substrate with Ni thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate for growing a single crystal diamond capable of absorbing warpage and growing a gas phase for a long time without performing etching or laser processing. By forming a Ni film having a thickness of 0.1 to 1.0 μm on a single crystal diamond, a substrate for growing a single crystal diamond capable of forming a random micropattern by heating can be obtained. By annealing the substrate in a hydrogen atmosphere, random microneedles according to the pattern are formed, and the needle length is extended by the Ni layer under the needle, while the vapor phase of the thick-film single crystal diamond substrate by lateral crystal growth. It will be possible to grow. [Selection diagram] Fig. 2

Description

  The present invention relates to a crystal substrate used for vapor phase growth of a thick single crystal diamond substrate.

  Currently, in vapor phase growth of a single crystal diamond substrate, a method of forming a thin film on which diamond is vapor-phase grown and vapor-depositing a diamond thick film on the thin film is disclosed in WO2015 / 190427 (hereinafter referred to as Patent Document 1). It has been published as after application. In Patent Document 1, vapor phase growth of a single crystal diamond using a columnar diamond is performed, and the stress generated due to the difference in thermal expansion between the base substrate and the diamond layer to be grown is warped by the columnar diamond. This makes it possible to perform vapor phase growth over a period of several tens of hours and form a thick film.

  As a specific method for forming the columnar diamond, there are methods described in Japanese Patent Application Laid-Open No. 03-045594 (hereinafter described as Patent Document 2) and Patent 4794625 (hereinafter described as Patent Document 3). In Patent Document 3, diamond formation in a specific range is enabled by photolithography and reactive ion etching, respectively. In addition, Patent Document 3 describes that the effect of smooth etching other than the portion where the columnar diamond is formed is also provided, and that the columnar diamond can be formed by ion beam etching or the like.

WO2015 / 190427 Japanese Patent Laid-Open No. 03-045594 Patent 4792625

  On the other hand, the method described in Patent Document 2 has a problem that a high-aspect ratio columnar diamond cannot be formed because the carbon film is formed on the metal film used for masking. Yes. The method described in Patent Document 3 uses etching, laser processing, or the like when forming the columnar diamond, and an apparatus for forming the columnar diamond must be prepared separately from the diamond vapor phase growth apparatus such as an exposure apparatus and a laser light source. Don't be.

In order to solve the above-mentioned problems, the invention described in the present application aims to provide a substrate for growing a single crystal diamond capable of reducing the warp and vapor-phase growth for a long time without performing etching or laser processing using the exposure apparatus. It is said.

  For the above purpose, the invention described in the present application is characterized in that a Ni film having a thickness of 0.1 to 1.0 μm is formed on a single crystal diamond layer. More specifically, a Ni film having a thickness of 0.1 to 1.0 μm on the surface of a flat single crystal diamond having a thickness capable of forming random microneedles having the same effect as the columnar diamond. The technical feature is to laminate the layers.

The invention described in the second aspect of the present invention is characterized in that a substrate other than the diamond substrate is used as the base substrate of the diamond layer.

  According to the technical features described above, the invention described in the present application can provide a crystal substrate for single crystal diamond vapor phase growth capable of absorbing stress without using the exposure apparatus and the laser light source. In other words, the crystal substrate according to the present invention can form a patchy random micropattern by aggregating the Ni thin film by heating the Ni thin film formed with a film thickness within a specific range on the single crystal diamond layer. It has become. More specifically, by forming a Ni thin film with a film thickness of 0.1 to 1.0 μm, a random micro pattern density decrease caused by aggregation when the film thickness becomes less than 0.1 μm, and 1.0 μm A crystal substrate for single crystal diamond vapor phase growth capable of preventing the formation of random microneedles caused by increasing the density of the pattern when the pattern is exceeded and capable of lateral epitaxial growth from the needle can be obtained. In addition, since the said pattern is comprised in the state which does not have orientation, the diamond under the said Ni is heat-processed by annealing in hydrogen atmosphere, and a needle-like random microneedle is formed. Along with this, the single crystal diamond is vapor-phase grown on the needle, the needle absorbs the stress, and the same effect as the columnar diamond can be obtained. In the single crystal diamond substrate according to the present invention, the needle is formed only by heat treatment. For this reason, in the vapor phase growth on the needle, after forming the needle to a certain length, the vapor phase growth is performed by mixing hydrogen in the vapor phase growth atmosphere and performing the vapor phase growth. It is possible to perform the formation in parallel.

  In the invention described in the present application, the density of the needles can be adjusted by the thickness of the Ni film to be laminated and the film formation temperature. This is because the aggregation of the stacked Ni changes due to the difference in the film thickness, so that the vapor phase growth is performed at an optimum density according to the area and film thickness of the thick single crystal diamond to be vapor phase grown, and the It is possible to improve the quality of crystals grown by optimizing the density. That is, the random microneedles formed from the substrate according to the present invention form a single crystal diamond substrate while being bonded to each other by lateral epitaxial growth starting from the needle tip. For this reason, by optimizing the density of the needle, the distance between the needles can be adjusted to a value suitable for the bonding, and the generation of a single crystal diamond can be performed while suppressing the generation of crystal defects during the bonding. .

  In addition to the above effects, it is possible to improve the mass productivity of the single crystal diamond substrate by using the invention described in the second aspect of the present invention. More specifically, as the single crystal diamond for forming the Ni film, by using a single crystal diamond that is vapor-phase grown on the base substrate, it is possible to select a thickness and shape that can be easily handled for the base substrate, and the base substrate By increasing the diameter, a single crystal diamond necessary for forming the needle can be provided in a large area. In the present invention, during the vapor phase growth of the thick film single crystal diamond substrate, the needle length is extended by mixing hydrogen into the vapor phase growth atmosphere, the stress that can be absorbed by the needle is increased, and the stress The effect of reducing warpage due to absorption can be stably imparted during the vapor phase growth. Therefore, by using the present invention, the problem of reduction in needle length due to growth of the columnar diamond base, which has occurred during vapor phase growth of single crystal diamond using a conventional columnar diamond, is solved. It is possible to start vapor phase growth at the needle tip even from a short state and to shorten the overall growth time.

As described above, by using the invention described in the claims of the present application, it is possible to reduce the warp accompanying the absorption of the stress and to grow the vapor phase for a long time without performing etching or laser processing using an exposure apparatus. A substrate for growing a single crystal diamond can be provided.

The perspective view of the single-crystal diamond board | substrate used in the best embodiment of this invention The diamond substrate shown in FIG. 1 and a vapor phase growth method of a thick single crystal diamond substrate using the diamond substrate

  The best embodiment in the present invention will be described below with reference to FIGS. In addition, about the symbol and component number in a figure, the common symbol or number is provided to what functions as the same component.

  FIG. 1 shows a perspective view of a single crystal diamond substrate used in this embodiment, and FIG. 2 shows a vapor phase growth method of a thick single crystal diamond substrate using the substrate. In addition, about the growth apparatuses, such as a growth stage, a chamber, and a target, description in a figure is abbreviate | omitted.

  As shown in FIG. 1, in this embodiment, an iridium (Ir) single crystal film 2 is formed as a pretreatment on a base substrate 1 made of MgO single crystal, and a diamond layer 3 is grown on the Ir film. Thereafter, a Ni film 4 having a thickness of 0.5 μm is formed. Further, as can be seen from FIGS. 2A to 2H, in this embodiment, the Ir film is first formed on the base substrate made of MgO single crystal (see b in the figure), and then CVD method or the like is used. A single crystal diamond layer is vapor-phase grown (see c in the figure), and the Ni film is formed on the diamond layer (see d in the figure).

  By providing the technical feature, the single crystal diamond substrate described in the present embodiment can agglomerate the Ni film 4 by heating the substrate to form a patchy random micropattern 5. (See e in the figure). Since the pattern is formed in a state having no orientation, the diamond layer 3 under the Ni is thermally processed by annealing in a hydrogen atmosphere to form the needle-like random microneedles 7 (FIG. (See middle f). Thereby, by using the single crystal diamond substrate described in the present embodiment, the needle is formed only by processing using heat, and the lateral crystal growth on the needle reduces warpage and improves crystal quality. A thick single crystal diamond substrate having an effect can be formed.

Detailed description will be given below. For the base substrate 1 for forming the first diamond layer, MgO single crystal is used in this embodiment, but other materials include aluminum oxide (α-Al ₂ O ₃ : sapphire), Si, quartz, platinum, Examples thereof include iridium and strontium titanate (SrTiO ₃ ). Of these, the MgO single crystal substrate and the aluminum oxide (sapphire) single crystal substrate are extremely stable thermally and have a diameter of up to 8 inches (about 203.2 mm). For the reason that it is possible, it is preferable as a substrate for a diamond layer used when forming a base substrate.

  Further, when the diamond layer 3 is directly laminated on the base substrate 1, at least one surface is mirror-polished. This is because the diamond layer is grown on the mirror-polished surface side in the diamond layer growth step. The mirror polishing may be performed so that at least one side is smooth enough to grow a diamond layer. As a guideline, the surface roughness Ra is preferably 10 nm or less. This is because when Ra exceeds 10 nm, the quality of the diamond layer to be grown deteriorates. It is assumed that there is no crack on the one side. Further, Ra can be measured with a surface roughness measuring machine. As the substrate, a substrate whose both surfaces are mirror-polished may be used as necessary. In this case, any one surface can be arbitrarily used as a growth surface of the diamond layer.

  In the case where an MgO single crystal substrate is used as the base substrate for directly forming the diamond layer, it is preferable to use the (001) plane as the growth surface of the diamond layer, but planes other than (001) can also be used. Further, the shape in the plane direction of the substrate for the diamond layer is not particularly limited, and may be, for example, a circular shape or a square shape. When the substrate is circular, it is preferably 2 inches (about 50.8 mm) or more in diameter from the viewpoint of enlargement, more preferably 3 inches (about 76.2 mm) or more, and 6 inches. More preferably (about 152.4 mm). The upper limit of the diameter of the substrate is not particularly limited, but is preferably 8 inches or less from a practical viewpoint. In the present application, in consideration of the dimensional tolerance of the substrate, the range of 49.8 mm to 50.8 mm, which is obtained by subtracting 1.0 mm, which is 2% of 50.8 mm, is defined as 2 inches.

While the size of the base substrate is defined in a circular shape, the size is preferably 50 mm × 50 mm or more, and more preferably 75 mm × 75 mm or more from the viewpoint of increasing the size when the substrate is square. Further, the upper limit of the dimension is preferably 200 mm × 200 mm or less from a practical viewpoint. Thus, the substrate surface for the diamond layer has an area of at least 20 cm2. Furthermore, it is more preferable to have an area up to 1297 cm ² from the viewpoint of increasing the size.

  Further, the thickness of the base substrate is preferably 3.0 mm or less, more preferably 1.5 mm or less, and still more preferably 1.0 mm or less. Although the lower limit of thickness is not specifically limited, It is preferable that it is 0.05 mm or more from a viewpoint of ensuring rigidity, and it is more preferable that it is 0.4 mm or more. In addition, when the planar shape is circular and the diameter is 50 mm or more and 150 mm or less, the thickness is preferably 0.3 mm or more, and when the diameter exceeds 150 mm, the thickness is preferably 0.6 mm or more.

  After the base substrate 1 is prepared and the Ir film 2 is formed as a pretreatment, a diamond layer 3 made of a diamond single crystal is grown and formed on one side. The growth method of the diamond layer 3 is not particularly limited, and a known method can be used. Specific examples of the growth method include a vapor phase growth method such as a pulsed laser deposition (PLD) method and a chemical vapor deposition (CVD) method.

  Here, before the diamond layer 3 is grown, the base substrate is thermally cleaned, and then the diamond layer is grown. In the PLD method, a target containing graphite, amorphous carbon, or diamond is subjected to laser sputtering in a gas atmosphere substantially consisting of oxygen to disperse carbon from the target, and a diamond layer is formed on one surface of the base substrate. Grow. The furnace pressure is preferably 1.33 × 10 −4 Pa to 133.32 Pa, the substrate temperature is 300 ° C. to 1000 ° C., and the target-substrate distance is preferably 10 mm to 100 mm.

  When the CVD method is used, a diamond layer substrate is placed in a CVD growth furnace, and a CVD diamond single crystal is grown on one surface of the substrate. As a growth method, a direct current plasma method, a hot filament method, a combustion flame method, an arc jet method, or the like can be used, but a microwave plasma method is preferable in order to obtain high-quality diamond with little contamination.

  In the epitaxial growth of the diamond layer by the microwave plasma CVD, a gas containing hydrogen and carbon is used as a source gas. Methane is introduced into the growth furnace as a gas containing hydrogen and carbon at a methane / hydrogen gas flow rate ratio of 0.001% to 30%. The pressure inside the furnace is maintained at about 1.3 × 103 Pa to 1.3 × 105 Pa, and plasma is generated by applying microwaves with a frequency of 2.45 GHz (± 50 MHz) or 915 MHz (± 50 MHz) to a power of 100 W to 60 kW. . CVD diamond is grown by depositing active species on one side of the substrate maintained at a temperature of 700 ° C. to 1300 ° C. by heating with the plasma. The thickness of the diamond layer is set so as to be equal to the length of the random microneedles to be formed, and it is preferable to grow with a thickness of 30 μm or more and 500 μm or less.

  Next, a Ni film 4 is formed on the formed diamond layer 3 (see d in FIG. 2). The formation may be performed in an arbitrary thickness in the range of 0.1 μm to 1.0 μm using sputtering or the like. In this embodiment, the Ni film 4 having a film thickness of 0.5 μm is formed on the diamond layer 3 by setting the sputtering time to several hours. As a result, the single crystal diamond substrate described in the present embodiment was able to agglomerate the Ni thin film by heating the substrate to form the patchy random micropattern 5 (see e in FIG. 2).

  The random micropattern 5 described in the present embodiment obtained by the above-described effect is a state in which the stacked Ni film 4 is aggregated and re-formed in a non-uniform state having no orientation and has no orientation. It consists of Therefore, by annealing the pattern 5 in a hydrogen atmosphere, the diamond under Ni can be thermally processed to form needle-like random microneedles 7 (see f in FIG. 2). Here, the density of the needle 7 can be adjusted by changing the thickness of the Ni film 4. This is due to the fact that the Ni film of the micropattern 5 re-formed by the annealing does not have orientation, and Ni aggregation changes depending on the thickness of the stacked Ni film 4. That is, the pattern of the Ni film formed by conventional photolithography, etc., in principle, imparts orientation to the formed Ni. Therefore, when the thermal processing by annealing is applied after removing the resist, Along with this, thermal processing proceeds vertically, and a columnar diamond single crystal is formed. Therefore, when changing the density of the columnar diamond conventionally used, it is necessary to change the density of the pattern to be formed. On the other hand, in the random micropattern 5 described in the present embodiment, the density of the needles 7 can be adjusted by the film thickness of the Ni film 4 formed first. Thus, by using the single crystal diamond substrate described in the present embodiment, the needle is formed and the lateral crystal growth on the needle is performed only by processing using heat without removing the substrate from the growth furnace by removing the resist or the like. Thus, it is possible to form a thick single crystal diamond substrate having the effects of reducing warpage due to temperature change and improving crystal quality.

  The diamond layer 3 is formed by heteroepitaxial growth on the surface of the base substrate or the surface of the Ir layer. For this reason, while many crystal defects are formed in the formed diamond layer, it is also possible to thin out the defects by forming a plurality of microneedles.

  After the needle formation, a thick single crystal diamond substrate layer 8 is grown on the tip of the needle to form a thick single crystal diamond substrate (see g in FIG. 2). In this embodiment, by growing a diamond single crystal from the tip of each needle, the growth of the diamond single crystal can be progressed uniformly from any needle. More specifically, it is possible to start lateral crystal growth of a diamond single crystal grown from each needle at the same timing by performing vapor phase growth with the needle directions aligned. In addition, by using hydrogen and methane in the atmosphere during vapor phase growth, the formation of needle 7 by hydrogen and Ni layer 6 and the vapor phase growth of thick film substrate layer 8 by methane can be performed simultaneously. Compared with the case where vapor phase growth is performed later, the temperature change that occurs between needle formation and vapor phase growth can be suppressed, and the effect of reducing warpage caused by the temperature change can also be imparted.

  Here, in this embodiment, a single crystal diamond substrate layer is produced by laterally growing diamond single crystals from each needle. The substrate layer can change the number of needles that can be formed in accordance with the diameter of the substrate, and can increase the number of needles as the diameter increases. Therefore, a 2-inch diamond substrate layer can be produced from a 2-inch base substrate, and an 8-inch diamond substrate layer can be produced from an 8-inch base substrate.

  After the formation of the diamond substrate layer, the diamond layer under Ni is processed to an Ir layer leaving the needle portion, and the diamond substrate layer is separated (see h in FIG. 2). Here, regarding the separation at the bottom of the needle portion, in this embodiment, when the thick film single crystal diamond substrate layer is grown, the stress B caused by the warp generated in the base substrate and the thick film single crystal diamond substrate layer is applied to the needle portion. When it is absorbed and processed up to the Ir layer, the diamond layer that connects the needles disappears, and the stress is released by separation between the needles, thereby separating the thick single crystal diamond substrate 9 from the underlying substrate. Yes. (See g and h in Fig. 2)

  The warping is caused by a difference in thermal expansion coefficient and lattice constant between the substrates. That is, the base substrate made of MgO single crystal has a thermal expansion coefficient and a lattice constant larger than that of the thick single crystal diamond substrate layer made of diamond single crystal. Therefore, during cooling after the substrate layer growth, a tensile stress B is generated in the direction shown in FIG. 2G from the center to the end on the thick single crystal diamond substrate layer side. This stress is generated due to the stress generated by the lattice constant difference between the base substrate and the thick single crystal diamond substrate layer and / or the difference in thermal expansion coefficient between the base substrate and the thick single crystal diamond substrate layer, As a result of the stress, a large warp is generated in the diamond substrate layer, the diamond layer substrate, and the entire needle so that the diamond substrate layer side has a convex shape as shown in FIG.

  With respect to the occurrence of the warp, as shown in FIG. 2G, in this embodiment, the Ni layer 7 is left, and the diamond layer under Ni is continuously processed by mixing hydrogen in the growth atmosphere, so that a thick single crystal diamond is obtained. The vapor phase growth of the substrate layer 8 and the formation of the needle 6 are performed in parallel. For this reason, the stress generated by the vapor phase growth of the substrate layer 8 can be absorbed for a long time by continuing to extend the needle length, and the stress is absorbed during the vapor phase growth. When the permissible amount was exceeded, the needle portion 6 was broken, and the thick single crystal diamond substrate layer could be protected.

  In addition to the method for producing the thick single crystal diamond substrate layer 8, details regarding the separation of the substrate layer will be described below. In the present embodiment, the stress generated by the lattice constant difference between the base substrate and the thick single crystal diamond substrate layer and / or the stress generated by the difference in thermal expansion coefficient is absorbed by the extension of the needle length, and below the Ni. The stress is released by processing the entire diamond layer, and the substrate layer can be separated without using a separate apparatus, tool, or process after the growth of the thick single crystal diamond substrate layer ( (See h in FIG. 2). For this reason, the method described in this embodiment makes it possible to simplify the manufacturing process of the thick film single crystal diamond substrate and facilitate the separation process. The needle is formed in a direction perpendicular to the diamond layer and the (001) plane of the diamond single crystal forming each needle so that the stress exceeds the allowable amount of the needle. The breakage of the needle 6 (generated at g in FIG. 2) can proceed smoothly. In addition, the thickness of the diamond layer 3 used in the present embodiment is set to be the length of the needle 6 to be formed, and it is preferable that the diamond layer 3 grows with a thickness of 30 μm to 500 μm. In addition, the needle 6 may be formed while leaving a uniform diamond layer in a partial thickness of the bottom.

  Regarding the shape of the needle 6, the aspect ratio consisting of the bottom surface and the height of the needle 6 used in the present embodiment is set to such a value that each needle does not fill up during the growth of the diamond substrate layer, and specifically 5 or more is desirable. . Moreover, although the cross-sectional shape of the needle may be square or circular, the needle 6 needs to be quickly destroyed when the stress exceeds an allowable amount. Therefore, since the cross-sectional shape of the needle is circular (ie, the needle is conical), the stress is applied evenly in the circumferential direction, so that the destruction of each needle when the allowable amount is exceeded is uniform. I can do it. Therefore, it is desirable that the cross-sectional shape of the needle is circular from the viewpoint of preventing cracks, tears or cracks in the diamond substrate layer 8 due to non-uniform fracture.

As described above, by using the substrate described in the embodiment of the present application, a single crystal diamond growth substrate capable of absorbing warpage and vapor-phase growth for a long time without performing etching or laser processing is provided. I was able to.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Ir film 3 Diamond layer 4 Ni film 5 Random micro pattern 6 Random microneedle 7 Ni layer 8 Thick film single crystal diamond substrate layer 9 Thick film single crystal diamond substrate B Stress

Claims (2)

A crystal substrate in which a Ni film having a thickness of 0.1 to 1.0 μm is formed on a single crystal diamond layer.
  The substrate according to claim 1, wherein a substrate other than a diamond substrate is used as a base substrate serving as a base for the crystal substrate.

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