阅读说明：本技术 金刚石晶体的研磨方法和金刚石晶体 (Method for grinding diamond crystal and diamond crystal ) 是由 金圣祐 藤居大毅 大山幸希 小山浩司 于 2019-03-14 设计创作，主要内容包括：实现能够从主面上去除包含位错的加工变质部的金刚石晶体的研磨方法和从主面上去除了该加工变质部的金刚石晶体。准备主面的面取向为(100)的金刚石晶体,接着,在对金刚石晶体的主面实施机械研磨时,将金刚石晶体与旋转的研磨轮的接触部位处的研磨轮的旋转方向上的切线方向设为相对于金刚石晶体的<110>方向为±10°以内,对金刚石晶体的主面实施机械研磨。通过该机械研磨,使加工变质部与金刚石晶体的面取向(111)方向平行地、进而贯通地出现在金刚石晶体的主面上。接着,对金刚石晶体的主面实施CMP,去除与面取向(111)方向平行地出现的加工变质部,从而从主面上去除加工变质部。(A polishing method for a diamond crystal capable of removing a processed modified part including dislocations from a main surface, and a diamond crystal from which the processed modified part has been removed from the main surface are provided. A diamond crystal having a main surface with a plane orientation of (100) is prepared, and then, when the main surface of the diamond crystal is mechanically polished, the main surface of the diamond crystal is mechanically polished while setting a tangential direction in a rotational direction of a polishing wheel at a contact portion between the diamond crystal and the rotating polishing wheel to within + -10 DEG with respect to a <110> direction of the diamond crystal. By this mechanical polishing, the processing-modified part appears on the main surface of the diamond crystal in parallel to the plane orientation (111) direction of the diamond crystal, and further penetrates the main surface. Next, CMP is performed on the main surface of the diamond crystal to remove the processing-altered part appearing parallel to the plane orientation (111) direction, thereby removing the processing-altered part from the main surface.)

1. A method for grinding diamond crystals, characterized in that,

preparing a diamond crystal having a main surface with a plane orientation of (100),

then, when the main surface of the diamond crystal is mechanically polished by using a polishing wheel, the main surface of the diamond crystal is mechanically polished so that the processing modified part appears on the main surface of the diamond crystal in parallel to the plane orientation (111) direction of the diamond crystal and penetrates the main surface of the diamond crystal, with the tangential direction of the polishing wheel in the rotational direction at the contact part between the diamond crystal and the rotating polishing wheel being within ± 10 ° with respect to the <110> direction of the diamond crystal,

next, CMP is performed on the main surface of the diamond crystal to remove the processing-altered part appearing parallel to the plane orientation (111) direction, thereby removing the processing-altered part from the main surface.

2. The method of polishing diamond crystals according to claim 1, wherein the CMP is performed so that the surface roughness Rq of the main surface is 5nm or less.

3. A diamond crystal characterized in that the plane orientation of the main surface is (100), that the crystal does not contain a process-altered part parallel to the plane orientation (111) direction, and that the process-altered part parallel to the plane orientation (111) direction does not appear on the main surface.

4. A diamond crystal according to claim 3, wherein the surface roughness Rq of the main surface is 5nm or less.

Technical Field

The present invention relates to a method for grinding diamond crystals and diamond crystals.

Background

Diamond crystals are expected as the ultimate semiconductor material. The reason for this is that diamond crystals have many excellent characteristics, such as high thermal conductivity, high electron mobility and hole mobility, high breakdown field strength, low dielectric loss, and a wide band gap, which are incomparable with semiconductor materials. The band gap is about 5.5eV, and has an extremely high value in the conventional semiconductor material. In particular, in recent years, ultraviolet light emitting elements, field effect transistors, heat dissipating plates, and the like, which make full use of a wide band gap, and which have excellent high-frequency characteristics, have been developed.

Patent document 1 discloses an example of such a diamond crystal.

Disclosure of Invention

Problems to be solved by the invention

In the case where diamond crystals are used for semiconductor applications, a mode in which a semiconductor layer is formed on a main surface of diamond crystals may be considered. Therefore, in order to control the surface roughness on the main surface to a value within a value required in the market, it is necessary to perform polishing on the main surface.

Therefore, the present applicant formed a diamond crystal by heteroepitaxial growth on the surface of the base substrate, and further performed mechanical polishing of the main surface (plane orientation (100)) of the grown diamond crystal, and measured the same by a synchrotron X-ray topography method. A morphology photograph of a side surface of a diamond crystal based on the synchrotron X-ray morphology is shown in fig. 10.

As shown in fig. 10, it was confirmed that a processed modified portion 6 including dislocations was formed through the main surface of the diamond crystal at the main surface of the diamond crystal subjected to mechanical polishing and at a thickness portion in the vicinity thereof.

When a diamond crystal is used for semiconductor applications, it is not preferable that a process modified portion including dislocations is formed so as to penetrate through the main surface because dislocations and defects are also formed in the semiconductor layer in succession to the process modified portion when the semiconductor layer is formed on the main surface of the diamond crystal. Therefore, it is required that the main surface of diamond crystal at the market stage is free from a processed and altered part including dislocations.

Therefore, the present applicant introduced Chemical mechanical polishing (hereinafter referred to as "CMP") and observed the state of the main surface, and confirmed that the processing-denatured portion appearing on the main surface could not be completely removed only by performing CMP.

The present invention has been made in view of the above problems, and an object thereof is to provide a method for polishing a diamond crystal capable of removing a processed modified portion including dislocations from a main surface, and a diamond crystal from which the processed modified portion has been removed from the main surface.

Means for solving the problems

The above problems are solved by the following invention. That is, the method for polishing diamond crystals according to the present invention is characterized by preparing diamond crystals having a main surface with a plane orientation of (100), then, when mechanical polishing is performed on the main surface of the diamond crystals using a polishing wheel, setting a tangential direction in a rotational direction of the polishing wheel at a contact portion between the diamond crystals and the rotating polishing wheel to be within ± 10 ° with respect to a <110> direction of the diamond crystals, performing mechanical polishing on the main surface of the diamond crystals so that a processing modified portion appears on the main surface of the diamond crystals in parallel to the plane orientation (111) direction of the diamond crystals and penetrating the main surface, then, performing CMP on the main surface of the diamond crystals to remove the processing modified portion appearing in parallel to the plane orientation (111) direction, thereby removing the processing modified portion from the main surface.

Further, the diamond crystal of the present invention is characterized in that the plane orientation of the main surface is (100), and the diamond crystal does not include a process-modified portion parallel to the plane orientation (111) direction, and the process-modified portion parallel to the plane orientation (111) direction does not appear on the main surface.

Effects of the invention

According to the polishing method of diamond crystals of the present invention, the mechanical polishing is intended to cause the processing-modified portion to appear on the main surface of the diamond crystals so as to run parallel to the plane orientation (111) direction of the diamond crystals and to penetrate therethrough. The machining-denatured portion temporarily appears in a concentrated manner in parallel to the plane orientation (111) direction of the diamond crystal, and thus the machining-denatured portion of the diamond crystal can be completely removed by CMP after mechanical polishing. In this way, a polishing method of a diamond crystal capable of removing a processed modified portion including dislocations from a main surface and a diamond crystal from which the processed modified portion has been removed from the main surface can be realized.

Drawings

Fig. 1 is an explanatory view showing diamond crystals for carrying out the polishing method according to the present invention.

Fig. 2 is an explanatory view schematically showing a rotation direction of the grinding wheel in the grinding method according to the present invention, a tangential direction at a contact portion of the diamond crystal and the grinding wheel in fig. 1, and a <110> direction of the diamond crystal.

Fig. 3 is a plan view of the grinding wheel shown in fig. 2 viewed from the grinding wheel side in the direction of rotation, the contact portion between the diamond crystals and the grinding wheel, the tangential direction, and the <110> direction of the diamond crystals.

Fig. 4 is a plan view showing a modification of fig. 3.

Fig. 5 is a plan view showing another modification of fig. 3.

Fig. 6 is an explanatory view showing a processing-altered part that appears parallel to the (111) direction of the diamond crystal and penetrates the main surface after mechanical polishing in the polishing method according to the present invention.

Fig. 7 is an explanatory view schematically showing a diamond crystal after removing the processing-denatured portion shown in fig. 6 by CMP.

Fig. 8 is a photograph of the profile of the side surface of a diamond crystal obtained by subjecting the diamond crystal according to the embodiment of the present invention to mechanical grinding and measuring by a synchrotron X-ray topography method.

Fig. 9 is a topographical photograph of the side surface of a diamond crystal subjected to CMP and measured by synchrotron X-ray topography for a diamond crystal according to an example of the present invention.

Fig. 10 is a photograph of the profile of the side of a diamond crystal obtained by subjecting the diamond crystal to mechanical grinding and measuring by synchrotron X-ray topography.

Detailed Description

A first feature of the present embodiment is a method for polishing diamond crystals, comprising the steps of preparing diamond crystals having a main surface with a plane orientation of (100), mechanically polishing the main surface of the diamond crystals by setting a tangential direction of the diamond crystals in a rotational direction of a polishing wheel at a contact portion between the diamond crystals and the rotating polishing wheel to within ± 10 ° with respect to a <110> direction of the diamond crystals, and causing a processing-modified portion to appear on the main surface of the diamond crystals so as to penetrate the main surface of the diamond crystals in parallel with the plane orientation (111) direction of the diamond crystals, and performing CMP on the main surface of the diamond crystals to remove the processing-modified portion appearing in parallel with the plane orientation (111) direction, thereby removing the processing-modified portion from the main surface.

A second feature of the present embodiment is a diamond crystal having a main surface with a plane orientation of (100), which does not include a process-altered portion parallel to the plane orientation (111) direction, and which does not have a process-altered portion parallel to the plane orientation (111) direction on the main surface.

According to this method and structure, the mechanical polishing is performed so that the processing-modified portion is present on the main surface of the diamond crystal so as to penetrate therethrough in parallel to the plane orientation (111) direction of the diamond crystal. By temporarily concentrating the processing-modified portions in parallel with the plane orientation (111) direction of the diamond crystals, the processing-modified portions of the diamond crystals can be completely removed by CMP after mechanical polishing. In this way, a polishing method of a diamond crystal capable of removing a processed modified portion including dislocations from the main surface and a diamond crystal from which the processed modified portion has been removed from the main surface can be realized. Further, within ± 10 °, ± 0 ° is included.

A third feature of the present embodiment is a polishing method for diamond crystals, in which CMP is performed so that the surface roughness Rq of the main surface is 5nm or less. Further, a diamond crystal is characterized in that the surface roughness Rq of the main surface is 5nm or less.

According to this method and configuration, since a diamond crystal in which the surface roughness Rq of the main surface is suppressed to 5nm or less can be obtained, a diamond crystal which can be used as a base crystal for growth of a semiconductor layer can be realized.

A method of polishing diamond crystals and diamond crystals according to an embodiment of the present invention will be described below with reference to fig. 1 to 7. First, as shown in fig. 1, a diamond crystal 1 is prepared which is a bulk body and in which the plane orientation of the main surface 2 is (100) and the <110> direction is the direction indicated by the arrow 5 in fig. 1. The diamond crystal 1 may be either single crystal or polycrystalline. In addition, although fig. 1 illustrates a diamond crystal having a quadrangular main surface 2 as an example of the appearance of the diamond crystal 1, the appearance is not limited to a quadrangle, and may have any shape.

The thickness of the diamond crystal 1 is preferably a thickness having a strength enough not to cause a trouble during processing, and more specifically, is preferably 0.3mm or more. Further, since the diamond crystal is an extremely hard material, the upper limit of the thickness is preferably 3.0mm or less in consideration of easiness of cleaving after formation of an element or a device.

The method of growing the diamond crystal 1 may be any method as long as it is a hetero-epitaxial growth method or a homoepitaxial growth method based on a vapor phase growth method such as a Chemical Vapor Deposition (CVD) method, and a diamond crystal having a main surface with a plane orientation of (100) may be prepared from the grown diamond crystal.

Next, as shown in fig. 2, the main surface 2 of the diamond crystal 1 is mechanically polished using a polishing wheel (polishing wheel) 3. Commercially available grinding wheels 3 and grinding materials can be used.

When the main surface 2 of the diamond crystal 1 is mechanically ground using the grinding wheel 3, fig. 2 shows two places (4a and 4b) representing the contact portion between the diamond crystal 1 and the rotating grinding wheel 3. In fig. 2 and 3, the rotation direction of the grinding wheel 3 is indicated by an arrow 3 a. In the present application and embodiment, the tangential directions 4a1 and 4b1 in the rotational direction 3a at the contact points 4a and 4b are set to be within ± 10 ° with respect to the <110> direction of the diamond crystal 1 (the direction of the arrow 5 in fig. 1 to 3). Further, within ± 10 °, ± 0 ° is included. In fig. 2 and 3, the manner in which the tangential directions 4a1 and 4b1 form an angle θ of ± 0 ° (i.e., parallel to each other) with the <110> direction 5 of the diamond crystal 1 is illustrated. Therefore, the drawing symbol θ is not shown in fig. 3.

The present applicant has verified that by mechanically polishing the main surface 2 of the diamond crystal 1 with the tangential directions 4a1 and 4b1 set within ± 10 ° with respect to the <110> direction 5, the processing modified part 1a is concentrated on the main surface 2 parallel to and penetrating the plane orientation (111) direction of the diamond crystal 1 as shown in fig. 6. In fig. 6, only one processing-modified portion 1a is shown with priority for easy observation, but it was confirmed by the applicant's verification that a plurality of processing-modified portions 1a are present in a direction parallel to the plane orientation (111) direction, aligned and concentrated, and penetrating through the main surface 2.

More specifically, the polishing wheel 3 is moved while being in contact with the main surface 2 so as to continuously form contact portions in which the angle θ formed by the tangential directions 4a1 and 4b1 and the <110> direction 5 is ± 10 °. Specifically, the polishing wheel 3 is moved while being in contact with the entire surface of the main surface 2, and the polishing wheel 3 is moved while being in contact with the entire surface of the main surface 2 so that the angle θ is within ± 10 ° at least once at a contact portion with the polishing wheel 3 over the entire surface of the main surface 2.

In the original state, if the machining-altered part 1a is present on the main surface 2 after mechanical polishing so as to penetrate therethrough, the diamond crystal 1 is determined to be a defective product. However, in the present application and the present embodiment, it was found that the process-altered part including the above-described part 1a can be completely removed by CMP described later. Therefore, it is necessary to make the processing-modified part 1a appear at a stage of the mechanical polishing.

The detailed principle of the occurrence of the processing-modified portion 1a parallel to the plane orientation (111) direction is not clear, but the applicant presumes as a hypothesis that the plane orientation in which the processing-modified portion is relatively likely to occur by some kind of processing is the (111) direction and the direction parallel to the (111) direction. It is considered that the processing-denatured portion 1a is concentrated in parallel to the (111) direction by moving the grinding wheel 3 in contact with the main surface 2 by controlling the angle θ within ± 10 ° as described above with the plane orientation of the main surface 2 being (100). Further, since the processing modified portion 1a appears by mechanical polishing, it is estimated that the processing modified portion 1a contains dislocations.

As a result of the verification by the applicant, therefore, the following conclusions are drawn: the conditions for causing the processing-denatured portion 1a to appear on the main surface 2 so as to run parallel to the plane orientation (111) direction of the diamond crystal 1 and penetrate therethrough are that the plane orientation of the main surface 2 is (100) and the tangential directions 4a1 and 4b1 are within ± 10 ° with respect to the <110> direction 5 of the diamond crystal 1.

As shown in fig. 4 or 5, in the contact portion where the angle θ is deviated from ± 10 ° and does not enter within ± 10 ° at a time, the process modified portion including the dislocation is not intensively parallel to the plane orientation (111) direction, and the surface roughness is not flat at an atomic level. As a result, even when CMP described later is performed, the processing-altered part cannot be removed quickly. Further, it is considered that a new process-altered part is formed from CMP, and as a result, it was confirmed that the process-altered part on the main surface 2 could not be completely removed. Fig. 4 or 5 shows, as an example, a mode in which a contact portion having an angle θ of ± 45 ° is formed with reference to the <110> direction 5.

Next, CMP is performed on the main surface 2 of the mechanically polished diamond crystal 1 to remove the processing-altered part 1 a. The CMP is performed until a time when the processing modified part 1a can be removed from the main surface 2. Fig. 7 illustrates the diamond crystal 1 after the removal of the processing-altered part by CMP.

As the polishing material used in CMP, commercially available products can be used, and for example, zinc oxide, chromium oxide, cerium oxide, titanium oxide, iron oxide, silicon dioxide, and the like can be used. Further, a commercially available polishing pad may be used.

The detailed principle of the removal of the modified portion 1a by CMP is not clear. However, the applicant presumes that the process-altered part 1a is removed quickly before a new process-altered part by CMP is formed, and therefore, the process-altered part including the main surface 2 of the part 1a can be completely removed by CMP. As described above, when it is estimated that the (111) direction and the direction parallel to the (111) direction of the diamond crystal 1 are plane orientations in which the process-altered part is relatively likely to appear by some kind of processing, it is estimated that the process-altered part 1a is also likely to be subjected to alteration by CMP, and it is estimated that the process-altered part 1a is rapidly removed before a new process-altered part by CMP is formed.

As described above, according to the method for polishing diamond crystals 1 and the diamond crystals 1 according to the present invention and the present embodiment, the processing modified portion 1a is caused to appear on the main surface 2 so as to penetrate through the diamond crystals 1 in parallel to the plane orientation (111) direction of the diamond crystals 1 by the mechanical polishing. By temporarily concentrating the processing-modified portions 1a in parallel with the plane orientation (111) direction of the diamond crystal 1, the processing-modified portions including 1a can be completely removed by CMP after mechanical polishing. Thus, the polishing method of the diamond crystal 1 capable of removing the process modified portion 1a including the dislocation from the main surface 2 can be realized. Further, it is also possible to realize the diamond crystal 1 in which the plane orientation of the main surface 2 is (100) and the process modified portion 1a parallel to the plane orientation (111) direction is not included, and the process modified portion 1a is removed from the main surface 2 without appearing. The presence or absence of the processing-modified part 1a can be measured by, for example, a synchrotron X-ray topography method.

Further, when the diamond crystal 1 produced by the polishing method according to the present invention is used for semiconductor applications, the processing-altered part 1a does not appear on the main surface 2, and therefore, introduction of dislocations and defects into the semiconductor layer formed on the main surface 2 is prevented. Therefore, the diamond crystal 1 capable of improving the characteristics of the semiconductor layer can also be provided.

The surface roughness Rq of the main surface 2 is controlled to 5nm or less by performing CMP. The measurement of Rq can be performed by a surface roughness measuring instrument. Therefore, a diamond crystal in which the surface roughness Rq of the main surface is controlled to 5nm or less can be obtained, and thus a diamond crystal which can be used as a base crystal for growth of a semiconductor layer can be realized.

Examples of the present invention will be described below, but the present invention is not limited to the following examples.