JP2016119428A - Diamond etching method, diamond crystal defect detection method and crystal growth method of diamond crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an art of etching a diamond more easily.SOLUTION: A diamond etching method comprises the steps of: preparing an etchant composed of a base compound composed of alkali metal halide and an alkali metal hydroxide-containing additive; and melting the prepared etchant and soaking the diamond in the molten etchant. By doing this, the diamond is etched.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a technique for etching diamond.

  Diamond has high strength and good thermal conductivity, and has attracted attention as a substrate for electronic devices. However, in order to use as a substrate for an electronic device, it is necessary to remove a damaged layer in which the surface is flat at the atomic level and crystal defects and the like are introduced by processing.

  In general, examples of processing methods that can flatten a diamond surface include skiff polishing, laser processing, ion beam processing, plasma sputtering, thermal chemical polishing, and chemical mechanical polishing. However, these processing methods have many technical problems such as long processing time, high processing cost, or high level of proficiency in processing technology, and a flat surface from which processing damage on the surface has been removed. It is not always easy to manufacture a diamond substrate having

Thus, attempts have been made to improve the crystallinity of the diamond surface by removing the damaged layer by etching. For example, in Non-Patent Document 1, a sample, potassium hydroxide (KOH) and sodium peroxide (Na ₂ O ₂ ) in a ratio of 4: 1 are placed in a stainless steel crucible, and then heated at 730 ° C. After that, it is reported that KOH and Na ₂ O ₂ are washed with water, and this improves the crystallinity of the surface. However, since the washed water becomes strongly alkaline, it is necessary to pay attention to the waste liquid treatment. Furthermore, Na ₂ O ₂ is an oxidizable solid with extremely high reactivity, and its handling is not always easy.

In Non-Patent Document 2, diamond is treated at 1100 ° C. for 3 minutes in an atmosphere in which oxygen (O ₂ ) flows at 745 μmol / s and hydrogen (H ₂ ) flows at 1378 μmol / s, so that silicon nitride (SiN) It has been reported that a quadrangular prism pit with a flat bottom surface can be formed in the region where the pattern is formed. However, in this method, the ratio of O ₂ and H ₂ is close to the stoichiometric ratio, and it is necessary to pay a high level of attention in order to prevent the atmosphere in the heating furnace and the ignition of the exhaust. Thus, it is not easy to flatten the surface of diamond by etching.

  In addition, the request | requirement of planarization of a diamond surface is not necessarily restricted to manufacture of the diamond substrate for electronic devices. For example, in the case of diamond for jewelry, in order to increase the commercial value, it is required to increase the reflectance of light on the surface so that the entire diamond shines better. Even in this case, in order to increase the reflectance of light on the surface, it is expected to smooth the polished surface and suppress scattering.

  Furthermore, in order to use diamond as a substrate for an electronic device, it is required to reduce crystal defects in the manufactured substrate. In order to reduce crystal defects, it is necessary to evaluate the occurrence of crystal defects in the substrate. Crystal defects in diamond can be detected by CL imaging for observing the intensity distribution of light emission (cathode luminescence: CL) generated by electron beam irradiation using a scanning electron microscope, or a high-intensity X-ray light source such as synchrotron radiation. It can be detected by the X-ray topography used. However, both methods require expensive equipment, and it is difficult to carry out the occurrence of crystal defects simply and at low cost.

Therefore, it has been proposed to generate an etch pit at the position of the crystal defect by etching and observe the generated etch pit. In order to generate such etch pits, Non-Patent Document 3 proposes etching with a molten solution of potassium nitrate (KNO ₃ ) at 525 ° C., and Non-Patent Document 4 proposes etching from 600 ° C. to 900 ° C. Etching with a KNO ₃ melt or sodium nitrate (NaNO ₃ ) melt has been proposed. However, in these non-patent documents, although detection of dislocations on the {111} plane has been reported, dislocation detection on the (001) plane suitable for evaluation of crystal defects of a substrate for electronic devices has not been detected. Not.

JA Maj, AT Macrander, GJ Waldschmidt, SF Krasnicki, Y. Zhong, R. Khachatryan, YS Chu, R. Erck, and J. Woodford, Adv. X-ray Anal., Vol. 48 (2005), p. 176 -182 C.D.McGray, R.A.Allen, M. Cangemi, J. Geist, Rectangular scale-similar etch pits in monocrystalline diamond., Diamond and Related Materials, Vol. 20 (2011), p. 1363-1365 A. R. Patel, Physica, Vol. 28 (1962), p. 44-51 A. F. Khokhryakov, Y. N. Palyanov, Journal of Crystal Growth, Vol. 293 (2006), p. 469-474

  As described above, etching for flattening the surface of diamond is not always easy, and an etching method for generating etch pits suitable for evaluating crystal defects of a substrate for an electronic device has not yet been established.

  The present invention has been made to solve the above-described conventional problems, and an object of the present invention is to provide a technique for etching diamond more easily.

  In order to achieve at least a part of the above object, the present invention can be realized as the following forms or application examples.

[Application Example 1]
A method for etching diamond, comprising preparing an etchant comprising a main agent comprising an alkali metal halide and an additive comprising an alkali metal hydroxide, and immersing the diamond in the molten etchant, A method for etching diamond, wherein the diamond is etched. According to this application example, it is possible to perform etching for flattening the surface of diamond, and it is possible to generate etch pits suitable for evaluating crystal defects of the substrate for electronic devices.

[Application Example 2]
The diamond etching method according to application example 1, wherein the alkali metal hydroxide contained in the additive has a weight ratio of 0.5% to 20% with respect to the main agent. According to this application example, etching can be performed at a sufficiently high etching rate, and the waste liquid can be more easily processed.

[Application Example 3]
3. The diamond etching method according to application example 1 or 2, wherein the additive further includes a transition metal. According to this application example, etching can be performed at a sufficiently high etching rate even at a lower etching temperature.

[Application Example 4]
The diamond etching method according to Application Example 3, wherein the transition metal contained in the additive has a weight ratio of 0.005% to 1% with respect to the main agent. According to this application example, the etching rate can be sufficiently increased and the etching amount can be adjusted more appropriately.

[Application Example 5]
The diamond etching method according to Application Example 3 or 4, wherein the additive includes, as the transition metal, iron (Fe), chromium (Cr), cobalt (Co), molybdenum (Mo), nickel (Ni) and A method for etching diamond, comprising at least one transition metal selected from the group consisting of copper (Cu). According to this application example, etching can be performed at a higher etching rate.

[Application Example 6]
A method for detecting a crystal defect of diamond, comprising: a step of etching diamond by the etching method according to any one of Application Examples 1 to 5; and a step of observing etch pits generated by the etching. Defect detection method. According to this application example, since it is possible to detect crystal defects by observing etch pits suitable for evaluating crystal defects of electronic device substrates, it is easy to manufacture higher-quality electronic device substrates. It becomes.

[Application Example 7]
A crystal growth method for growing a diamond crystal on a diamond seed crystal, the etching step of etching the surface of the seed crystal by the etching method according to any one of Application Examples 1 to 5, and the etching was performed. And a crystal growth step of growing a diamond crystal on the surface of the seed crystal. According to this application example, crystal growth can be performed on a seed crystal having a good surface crystallinity, so that a diamond crystal with fewer crystal defects can be grown.

[Application Example 8]
The crystal growth method according to Application Example 7, further comprising: a surface of the seed crystal on which the etching is performed by chemical mechanical polishing or thermal chemical polishing after the etching step and before the crystal growth step. A crystal growth method for flattening. According to this application example, formation of a damaged layer by processing can be suppressed, and the surface on which crystal growth is performed can be made flat, so that a diamond crystal with fewer crystal defects can be grown.

  Note that the present invention can be realized in various modes. For example, diamond etching method, diamond substrate manufacturing method using the etching method and diamond crystal growth method, diamond substrate manufactured by the manufacturing method, diamond crystal grown by the growth method, and diamond crystal defect detection It can be realized in a manner such as a method.

Process drawing which shows the board | substrate manufacturing process in 1st Embodiment. Explanatory drawing which shows the specific example of the etching process in a board | substrate manufacturing process. A surface morphology observation image on the seed crystal side of the diamond substrate before etching. Surface morphology observation image on the seed crystal side of the diamond substrate after etching. Surface morphology observation image on the growth edge side of the diamond substrate after etching. The surface form observation image by the optical microscope of the area | region which measured the surface roughness. The surface form observation image by the optical microscope of the growth edge side of the diamond substrate after the process in a comparative example. The surface form observation image of the diamond substrate etched with the etching agent containing Fe.

Embodiments of the present invention will be described in the following order based on examples.
A. First embodiment:
A1. Diamond substrate manufacturing process:
A2. Etching process:
A3. Example of the first embodiment:
B. Second embodiment:
B1. Etching agent:
B2. Example of the second embodiment:
C. Other application forms:

A. First embodiment:
A1. Diamond substrate manufacturing process:
FIG. 1 is a process diagram showing a diamond substrate manufacturing process (hereinafter also simply referred to as “substrate manufacturing process”) in the first embodiment. FIGS. 1A to 1E show the form of a workpiece in each process such as a diamond substrate. In FIGS. 1C to 1E, the broken line indicates the form of the work before execution of each process (that is, after execution of the previous process), and the solid line indicates the form of the work after execution of each process. Show.

  In the substrate manufacturing process of the first embodiment, first, as shown in FIG. 1A, a mosaic diamond substrate MDS (hereinafter also referred to as “mosaic substrate”) is prepared. Specifically, a diamond seed crystal SDB having an area smaller than that of the mosaic substrate MDS is prepared. A plurality of seed crystal substrates SDS is obtained by slicing the diamond seed crystal SDB. Next, the obtained seed crystal substrates SDS are arranged without gaps, and a single crystal diamond layer (bonded diamond layer) BDL for bonding the seed crystal substrate SDS is crystal-grown on the arranged seed crystal substrates SDS. Thereby, the seed crystal substrate SDS is bonded, and the mosaic substrate MDS is obtained.

  Next, as shown in FIG. 1B, a single crystal diamond 91 is grown on the surface of the seed crystal substrate SDS opposite to the bonded diamond layer BDL. By separating the single crystal diamond 91 from the mosaic substrate MDS, a diamond substrate (growth substrate) 91 is obtained. FIG. 1C shows a state where the single crystal diamond 91 is thus separated from the mosaic substrate MDS. Note that the creation of the mosaic substrate MDS and the separation of the growth substrate 91 from the mosaic substrate MDS can be performed using, for example, a technique disclosed in Japanese Patent Application Laid-Open No. 2010-150069.

  As shown in FIG. 1C, on the surface of the growth substrate 91 on the seed crystal substrate SDS side (seed crystal side) 91a, a mark (boundary mark) PSB at the boundary portion of the single crystal substrate SDS is generated. This boundary mark PSB is generated due to a gap between adjacent single crystal substrates SDS. Further, when a non-diamond layer is formed by ion implantation or the like for separating the growth substrate 91, the non-diamond layer remains in the vicinity of the surface of the seed crystal side 91a of the growth substrate 91. On the other hand, unevenness occurs on the surface of the growth substrate 91 on the crystal growth end side (growth end side) 91b of the diamond due to bunching or the like generated during crystal growth.

  Therefore, in the first embodiment, both surfaces of the growth substrate 91 are skiff-polished, so that the boundary mark PSB generated on the surface of the seed crystal side 91a, the non-diamond layer remaining in the vicinity of the surface, and the surface of the growth end side 91b The unevenness of the is removed. As a result, as shown in FIG. 1C, a diamond substrate (polishing substrate) 92 from which relatively large irregularities, non-diamond layers and the like are removed is obtained. Note that the skiff polishing is performed by applying a paste containing diamond abrasive grains to a disk-shaped iron polishing disk and pressing the surface of the growth substrate 91 while rotating the polishing disk.

  In the skiff polishing, the surface roughness of the polishing substrate 92 can be sufficiently reduced by using sufficiently fine diamond abrasive grains. However, since both the substrate and the abrasive grains are diamond, a scratch SCR is generated on the surface of the polishing substrate 92 as shown in FIG. In the Skyf polishing, the growth substrate 91 is pressed against the polishing disk with a high surface pressure, so that crystal defects and the like are introduced, and a damaged layer DMG having a thickness of several μm to several tens of μm is formed on the surface of the polishing substrate 92. Occur. The scratch scratch SCR and the damage layer DMG are generated on both surfaces of the polishing substrate 92. In FIG. 1D, however, the scratch scratch SCR and the damage layer DMG generated on one surface of the polishing substrate 92 are illustrated for convenience of illustration. It is shown.

  In the first embodiment, the surface of the polishing substrate 92 is etched in order to remove the scratch SCR and the damage layer DMG generated on the surface of the polishing substrate 92 in this way. By this etching, a diamond substrate (etching substrate) 93 from which scratch scratch SCR and damaged layer DMG have been removed is obtained. A specific method of etching will be described later.

  In the etching substrate 93, the scratch SCR and the damage layer DMG present in the polishing substrate 92 are removed, but the surface roughness is not necessarily sufficiently small. Therefore, in the first embodiment, finish polishing is performed on the etching substrate 93 in order to make the surface flatter (FIG. 1E). In FIG. 1E as well, only the unevenness generated on one surface of the etching substrate 93 is shown for convenience of illustration. By this finish polishing, a diamond substrate 94 from which the irregularities on the surface of the etching substrate 93 are removed is obtained. Finish polishing is, for example, thermochemical polishing in which a diamond substrate is pressed against a heated metal plate such as iron, and polishing is performed using a chemical reaction between a metal such as iron and diamond, or an abrasive containing an oxidizing chemical. It can be performed by various methods such as chemical mechanical polishing in which polishing is performed.

  As described above, in the first embodiment, the scratch SCR and the damage layer DMG can be removed by etching. Therefore, it is possible to remove the processing damage applied to the diamond substrate and more easily manufacture a diamond substrate having a flat surface. In the example of FIG. 1, skiff polishing is performed before etching and finish polishing is performed after etching. However, at least one of skiff polishing and finish polishing may be omitted. In the first embodiment, the scratch SCR and the damage layer DMG are removed by etching. However, in general, the etching can remove the surface portion of the diamond without applying stress. In addition, it is possible to remove surface damage formed in various processes for manufacturing a substrate (crystal).

A2. Etching process:
FIG. 2 is an explanatory diagram illustrating a specific example of an etching process in the substrate manufacturing process of the first embodiment. In the first embodiment, etching is performed by immersing the polishing substrate 92 in an etching agent heated and melted in an air atmosphere using the muffle furnace 20. As an etching agent, a material obtained by adding an appropriate amount of potassium hydroxide (KOH) as an additive to potassium chloride (KCl) as a main agent can be used.

The etching is first arranged in a furnace 24 of a muffle furnace 20 surrounded by a heater 22 and is made of a material having corrosion resistance against an etching agent such as nickel (Ni), platinum (Pt), alumina (Al ₂ O ₃ ). A solid etching agent and a polishing substrate 92 are placed in the crucible 30 (FIG. 2A). Next, the heater 22 of the muffle furnace 20 is energized to raise the temperature in the furnace 24. When the temperature in the furnace 24 (temperature in the furnace) exceeds the melting point of the etching agent, the solid etching agent charged in the crucible 30 is melted as shown in FIG. The polishing substrate 92 is immersed therein. Note that the melting point of the etching agent is lower than the melting point (776 ° C.) of KCl which is the main agent.

  Even after the etching agent is melted, the temperature rise is continued until the furnace temperature reaches a predetermined etching temperature (described later). After the furnace temperature reaches the etching temperature, the surface of the polishing substrate 92 is etched by holding the furnace temperature at the etching temperature for a predetermined holding time (for example, 5 hours), and the etching substrate 93 is obtained. The holding time is appropriately changed based on the etching rate of the diamond substrate by the etching agent, the depth of the scratch SCR (FIG. 1D), and the thickness of the damaged layer DMG.

  After the holding time has elapsed, the temperature in the furnace 24 is lowered. When the temperature in the furnace falls below the melting point of the etching agent due to the temperature drop, the molten etching agent in the crucible 30 is solidified and the etching substrate 93 is embedded in the solid etching agent as shown in FIG. It becomes. After the furnace temperature reaches approximately room temperature, the solid etching agent and the etching substrate 93 are put into water. Thereby, the solid etching agent covering the etching substrate 93 is dissolved, and the etching substrate 93 is taken out as shown in FIG.

  The amount of KOH added to the etching agent can be appropriately set as long as the ratio of KOH weight to KCl weight (KOH weight ratio) is 0.5% or more. However, when the KOH weight ratio is lowered, the effect of adding KOH is attenuated. Therefore, the KOH weight ratio is preferably 1.0% or more. On the other hand, when the KOH weight ratio increases, the amount of KOH evaporated from the surface of the molten etchant increases, which may corrode etching apparatuses such as the crucible 30 and the muffle furnace 20. Further, since the etching substrate 93 is taken out, the water charged with the solid etching agent and the etching substrate 93 becomes strongly alkaline, and the environmental burden during waste liquid treatment increases. Therefore, the KOH weight ratio is preferably 20% or less. Furthermore, when the KOH weight ratio increases, the etching rate increases, and the flatness of the etching substrate 93 may decrease. Therefore, the KOH weight ratio is more preferably 5% or less.

  The etching temperature can be appropriately set within a range from the melting point (776 ° C.) of KCl which is the main agent of the etching agent to 1300 ° C. However, when the etching temperature is lowered, the etching rate may rapidly decrease. Therefore, the etching temperature is preferably 900 ° C. or higher. On the other hand, when the etching temperature approaches the boiling point (1327 ° C.) of the additive KOH, the amount of evaporation of KOH increases rapidly. Therefore, the etching temperature is preferably 1200 ° C. or lower.

  In the example of FIG. 2, the solid etching agent and the polishing substrate 92 are charged in advance in the crucible 30, and the crucible 30 is heated by the muffle furnace 20, but the etching method is limited to this. Not. For example, an etching agent may be melted in advance, and the polishing substrate may be immersed in the molten etching agent.

  In the first embodiment, KCl is used as the main agent of the etching agent, but various alkali metal halogens such as sodium chloride (NaCl), potassium fluoride (KF), and sodium fluoride (NaF) are used instead of KCl. A compound (alkali halide) can also be used. In addition, a mixture of a plurality of alkali metal halides can be used as the main agent. However, it is preferable to use at least one of KCl and NaCl as the main agent because it is easier to obtain. Further, as an additive for the etching agent, other alkali metal hydroxides such as sodium hydroxide (NaOH) and lithium hydroxide (LiOH) can be used instead of KOH, and a plurality of alkali metal hydroxides can be used. It is also possible to mix and use.

A3. Example of the first embodiment:
[Example]
In the example of the first embodiment, the diamond substrate separated from the mosaic substrate after crystal growth on the mosaic substrate (mosaic substrate MDS in FIG. 1) to confirm that etching is possible according to the first embodiment. (Growth substrate 91 in FIG. 1) was prepared. The surface morphology of the prepared diamond substrate was observed with an optical microscope, and the weight and thickness were measured.

Next, the diamond substrate was etched. Specifically, first, an crucible made of alumina (Al ₂ O ₃ ) was charged with an etching agent having a KOH weight ratio of 1.6% and the diamond substrate, and then the crucible. Was placed in a muffle furnace, and the muffle furnace was heated. After the furnace temperature reached the etching temperature of 1100 ° C., the furnace temperature was maintained at 1100 ° C. for a holding time of 5 hours. After the elapse of the holding time, the temperature was lowered, and after the furnace temperature reached approximately room temperature, the crucible was taken out of the muffle furnace. The entire crucible taken out and the etching agent and the etched diamond substrate were poured into water to dissolve the etching agent to obtain an etched diamond substrate.

  Next, the diamond substrate after etching thus obtained was evaluated. Specifically, the surface morphology of the diamond substrate on the seed crystal side and the growth end side (seed crystal side 91a and growth end side 91b in FIG. 1) was observed using an optical microscope. Further, the surface roughness on the growth end side was measured. Furthermore, in order to calculate the etching rate, the weight and thickness of the diamond substrate were measured as before the etching. The etching rate on one side calculated from the change in the thickness of the diamond substrate before and after etching was 1.9 μm / h. Moreover, the weight of the diamond substrate decreased by 16.6% by the etching.

  FIG. 3 is a surface morphology observation image on the seed crystal side of the diamond substrate before etching. 3A is an observation image of the entire substrate, and FIG. 3B is an enlarged image of a region (left square region) indicated by a left square in FIG. 3A. ) Is an enlarged image of the area (right square area) indicated by the right square in FIG. As shown in FIGS. 3A to 3C, many surface damages due to the crystal manufacturing process were observed on the surface of the diamond substrate before the etching. In FIG. 3A, the portion indicated by the arrow is the boundary mark PSB (FIG. 1), and the lines in the [100] direction and [010] direction that divide the entire other substrate are observed images of the entire substrate. This is an artifact (false image) that appeared when

  FIG. 4 is a surface morphology observation image on the seed crystal side of the diamond substrate after etching. 4A is an observation image of the entire substrate, and FIG. 4B and FIG. 4C are enlarged images of the left square region and the right square region shown by squares in FIG. 4A, respectively. It is. As shown in FIGS. 4A to 4C, many surface damages existing before etching (FIG. 3) were removed by etching. On the other hand, a large number of black dots located at the lower right of the right square region are etch pits appearing at the positions of crystal defects.

  FIG. 5 is a surface morphology observation image on the growth end side of the diamond substrate after etching. FIG. 5A is an observation image of the entire substrate, and FIG. 5B is an enlarged image of a square region indicated by a square in FIG. This square region is located on the boundary mark PSB (FIG. 1) indicated by the arrow. As can be seen from FIG. 5A, the etched surface is a substantially flat surface. On the other hand, defects generated on the boundary mark PSB (FIG. 1) appeared as etch pits. As shown in FIG. 5B, the etch pit that appears at the position of the crystal defect has an inverted pyramid shape. When the shape of such an inverted pyramid-shaped etch pit has changed to an asymmetric shape, the progress direction of dislocation can be grasped based on the change of the shape. Further, when the apex of the inverted pyramid shape disappears, it can be determined that the crystal defect is a dislocation introduced by processing.

  FIG. 6 is an image observed by an optical microscope of the surface morphology of the region where the surface roughness was measured. The surface roughness was measured along the broken line in FIG. The surface roughness Ra was 0.087 μm, and flatness at the atomic level was not obtained, but it was found that the polishing amount in the finish polishing can be sufficiently reduced.

[Comparative example]
As a comparative example, a diamond substrate was prepared in the same manner as in the example, and etching of the diamond substrate was attempted. In the comparative example, the KOH weight ratio of the etching agent was 0.4%, and the holding time during etching was 0.5 hour. Other points are the same as in the embodiment.

  FIG. 7 is a surface morphology observation image by an optical microscope on the growth end side of the diamond substrate after the treatment in the comparative example. As shown in FIG. 7, in the comparative example, linear irregularities extending obliquely generated by bunching were observed. This is equivalent to what appeared as the surface form before the treatment, and it is considered that the etching hardly progressed by setting the KOH weight ratio of the etching agent to 0.4%. The weight and thickness of the diamond substrate hardly changed before and after etching.

  Thus, it was found that the diamond substrate can be etched by melting the etching agent obtained by adding KOH to KCl and immersing the diamond substrate in the molten etching agent. Further, it has been found that this etching can sufficiently flatten the surface of the diamond substrate and can detect defects such as dislocations by generating etch pits.

B. Second embodiment:
B1. Etching agent:
The second embodiment is different from the first embodiment in that the etching agent used in the etching process is different. Since other points are the same as those of the first embodiment, the description thereof is omitted here. Specifically, the second embodiment is different from the first embodiment in which only KOH is added as an additive in that iron (Fe) is added in addition to KOH as an additive.

  In the second embodiment, by adding Fe to the etching agent in addition to KOH, the etching rate can be made faster than in the first embodiment in which no Fe is added. In addition, it is also possible to add other transition metals that can take a plurality of oxidation numbers alone or in combination with a plurality of transition metals containing Fe instead of Fe. However, among the transition metals, the group consisting of Fe, chromium (Cr), cobalt (Co), molybdenum (Mo), nickel (Ni), and copper (Cu), in that the etching rate can be further increased. Preferably, at least one transition metal selected from is added.

  The amount of KOH added to the etching agent is determined in the same manner as in the first embodiment. The ratio of Fe weight to KCl weight (Fe weight ratio) can be appropriately set in the range of 0.002% to 1%. However, when the Fe weight ratio is small, the effect of adding Fe decreases. Therefore, the Fe weight ratio is preferably 0.005% or more, and more preferably 0.01% or more. Further, when the Fe weight ratio is increased, the etching rate rapidly increases, and it becomes difficult to adjust the etching amount. Therefore, the Fe weight ratio is preferably 0.5% or less.

  Also in the second embodiment, as in the first embodiment, various alkali metal halides or a mixture of a plurality of alkali metal halides can be used as a main agent instead of KCl. Further, various alkali metal hydroxides or a mixture of a plurality of alkali metal hydroxides can be used instead of KOH contained in the additive.

B2. Example of the second embodiment:
[Example 1]
The first example (Example 1) of the second embodiment is the same as that of the first embodiment except for the diamond substrate to be prepared, the etching method and conditions, etc., except that the etching agent is different. It is. Therefore, here, the used etching agent and the etching result with the etching agent will be described, and the description of the same parts as those of the example of the first embodiment will be omitted.

  In Example 1, the KOH weight ratio was set to 1.6%, which is the same as that of the first embodiment, and the etching agent was prepared with Fe weight ratios of 0.1% and 0.25%. Then, the prepared etching agent and the diamond substrate were placed in a crucible and etched.

  As a result, in all the samples, the diamond substrate completely disappeared after etching for 5 hours. From this, it was found that the etching rate can be set to 20 μm / h or more by setting the addition amount of Fe to 0.1% or more by weight ratio of Fe.

[Example 2]
In the second example (Example 2) of the second embodiment, the KOH weight ratio is 1.6%, which is the same as in Example 1, the Fe weight ratio is 0.02%, and the etching temperature is 900 ° C. did. In addition, the holding time during etching was 10 minutes. The other points are the same as those in the first embodiment.

  FIG. 8 is a surface morphology observation image of a diamond substrate etched with an etching agent containing Fe. 8A is a surface morphology observation image on the seed crystal side after etching, and FIG. 8B is a surface morphology observation image on the growth end side after etching. As shown in FIG. 8, it is possible to perform etching for flattening the surface of the diamond substrate and to generate etch pits corresponding to crystal defects by using an etching agent to which Fe is added. I understood that. In addition, this etching reduced the weight of the diamond substrate by about 1%. Therefore, by adding Fe to the etching agent as in the second embodiment, the etching rate can be sufficiently increased even at an etching temperature lower than that of the first embodiment in which Fe is not added (900 ° C. in Example 2). It turns out that it can be fast.

C. Other application forms:
In each of the above embodiments, the scratch scratch SCR (FIG. 1), the damage layer DMG, and the like are removed by immersing and etching the diamond substrate in a molten etching agent. Can also be used.

C1. Application form 1:
As described above, etch pits are generated in the diamond substrate by the etching of the above embodiments. Therefore, the crystal defects of the diamond substrate can be detected by applying the etching method of each of the above embodiments to generate etch pits and observing the generated etch pits. In this case, the etching temperature is preferably 1000 to 1100 ° C. in order to generate etch pits more reliably. On the other hand, in order to suppress the generation of etch pits and make the etched surface more flat, the etching temperature is preferably 900 ° C. or lower.

C2. Application form 2:
In each of the above embodiments, etching is used to process the single crystal diamond substrate 91 crystal-grown on the mosaic substrate MDS (FIG. 1). However, the mosaic substrate MDS is configured by the etching method of each of the above embodiments. It is also possible to etch the surface of the seed crystal substrate SDS or the surface of another seed crystal and grow single crystal diamond on the surface. Even in this case, it is preferable to perform finish polishing after the etching.

C3. Application form 3:
Moreover, in each said embodiment, although the etching method of said each embodiment is used in order to etch a diamond substrate, the object of an etching is not limited to a diamond substrate. For example, the jewelry diamond may be etched to remove scratches during polishing and smooth the surface. When the surface is smoothed in this way, the reflectance of light on the surface increases, and the jewelery diamond shines better.

20 ... Muffle furnace 22 ... Heater 24 ... Inside the furnace 30 ... Crucible 91 ... Growth substrate 92 ... Polishing substrate 93 ... Etching substrate 94 ... Diamond substrate BDL ... Bonded diamond layer DMG ... Damaged layer MDS ... Mosaic substrate PSB ... Border mark SCR ... Scratch Scratches SDB ... Diamond seed crystal SDS ... Seed crystal substrate

Claims (8)

A diamond etching method comprising:
Preparing an etching agent comprising a main agent comprising an alkali metal halide and an additive comprising an alkali metal hydroxide;
Etching the diamond by immersing the diamond in the molten etchant;
Diamond etching method.   The diamond etching method according to claim 1, wherein the alkali metal hydroxide contained in the additive has a weight ratio of 0.5% to 20% with respect to the main agent. The diamond etching method according to claim 1 or 2,
The additive further includes a transition metal,
Diamond etching method.   The diamond etching method according to claim 3, wherein the transition metal contained in the additive has a weight ratio of 0.005% to 1% with respect to the main agent. The diamond etching method according to claim 3 or 4,
The additive is at least one selected from the group consisting of iron (Fe), chromium (Cr), cobalt (Co), molybdenum (Mo), nickel (Ni) and copper (Cu) as the transition metal. Contains transition metals,
Diamond etching method. A method for detecting crystal defects in diamond,
Etching diamond by the etching method according to any one of claims 1 to 5;
Observing etch pits generated by the etching;
including,
A method for detecting crystal defects in diamond. A crystal growth method for growing a diamond crystal on a diamond seed crystal,
An etching step of etching the surface of the seed crystal by the etching method according to any one of claims 1 to 5;
A crystal growth step for growing a diamond crystal on the surface of the etched seed crystal;
including,
Crystal growth method. The crystal growth method according to claim 7, further comprising:
After the etching step and before the crystal growth step, the surface of the seed crystal subjected to the etching is flattened by chemical mechanical polishing or thermal chemical polishing.
Crystal growth method.