JP4547493B2 - Method for producing diamond single crystal and diamond single crystal - Google Patents

Description

  The present invention relates to a method for producing a diamond single crystal and a diamond single crystal.

Diamond is a material with high hardness, high thermal conductivity, and high chemical stability. In addition to traditionally used for jewelry, it uses mechanical properties such as tools and grindstones, heat sinks for semiconductor lasers, and SAW devices. It is used for electronic materials. Diamond is a wide-gap semiconductor, and research and development for use as an electronic material or an electrode material for water electrolysis have been actively conducted in recent years.

  As a method for producing an industrial diamond single crystal, a high-temperature and high-pressure synthesis method is mainly employed. However, in this method, a large press machine is required to produce a large diamond single crystal, and therefore the synthetic single crystal diamond remains at a maximum size of about 1 cm.

  In recent years, as a method for producing a diamond single crystal, research and development have been actively conducted on crystal growth methods by vapor phase synthesis methods such as a microwave CVD method, a filament CVD method, a direct current discharge method, an arc jet method, and a flame method. In this method, there is no restriction on the apparatus as in the high-temperature and high-pressure method, so that it is expected to be used as a method for synthesizing a larger diamond single crystal.

  However, the vapor phase synthesis method has a problem that particles called abnormal nuclei are likely to be generated on the growth surface during growth, and subsequent crystal growth does not proceed smoothly.

For example, in the current vapor phase synthesis method of a diamond single crystal, diamond is often epitaxially grown on a diamond substrate polished on the (100) plane as a seed crystal. However, in this method, as shown in the schematic cross-sectional view of FIG. 1, abnormal nuclei having mainly the (111) plane are likely to be generated on the (100) plane, which is the growth surface, and once the abnormal nuclei are generated. In this case, there is a problem that the epitaxial growth thereon cannot be continued. In addition, when vapor phase growth on the (100) plane, adding a small amount of nitrogen to the source gas is known to suppress the generation of abnormal nuclei, enable growth for a long time and synthesize a large single crystal, This method has the disadvantage that nitrogen is incorporated into the diamond crystal and the yellowish to blackish brown color is exhibited depending on the amount of incorporation, resulting in an increase in crystal defects.

Further, when growing on the (111) plane of a diamond single crystal, crystal defects called twins are likely to occur. For this reason, this method is used only for high-concentration doping of impurity elements for the purpose of semiconductor manufacturing, taking advantage of the property of easily incorporating impurity elements such as phosphorus and nitrogen into diamond crystals. is there.

In the case where the (110) plane of a dummond single crystal is used as a seed crystal, there are many reports that a very rough surface is formed when epitaxial growth is performed on the (110) plane. For example, the following Non-Patent Document 1 describes a case where a filament method is used to epitaxially grow a thickness of 5.1 μm on a diamond (110) surface at 850 ° C., a hydrogen flow rate of 179 sccm, a methane flow rate of 0.3 sccm, and an acetylene flow rate of 0.15 sccm. The growth surface is described as a rough surface having a hill-like structure with a height of 50 to 250 nm and a width of 100 to 800 nm.

Non-Patent Document 2 listed below shows that the growth surface is about 5 μm thick when epitaxially grown on a diamond (110) surface using a filament method at 850 ° C., a hydrogen flow rate of 165 sccm, a methane flow rate of 0.30 sccm, and an acetylene flow rate of 0.15 sccm. Has been reported to have a coarse structure on the 100 nm scale.

Non-Patent Document 3 below shows that when flame growth is used, epitaxial growth is performed on a diamond (110) surface at 900 ± 100 ° C., oxygen gas 1.3 or 1.5 SLM, thicknesses of 20, 40, and 150 μm under conditions of unknown acetylene flow rate. The growth surface is described as being fairly rough.

Non-Patent Document 4 listed below uses a microwave CVD method to form a temperature of 830 on a diamond (110) surface.
Described as grain growth and rough growth when grown epitaxially for 2 hours at ℃ / methane flow rate ratio of 2%, 4%, 6% or 8% and pressure of 40 Torr (= 5.3kPa) Has been.

Non-Patent Document 5 listed below uses a microwave CVD method on a diamond (110) surface at 650 ° C., 99
It is described that the growth surface is rough when epitaxial growth is performed under the conditions of% hydrogen, 0.7% methane, 0.3% oxygen, and a pressure of 30 Torr (= 4.0 kPa).

As described above, it is considered that the conventionally known method for growing diamond on the (110) plane cannot be used as a method for producing a large single crystal diamond because a rough growth surface is formed.
LF Sutcu, et al .: J. Appl. Phys. 71 (1992) 5930-5940 CJ Chu, et al .: J. Appl. Phys. 70 (1991) 1695-1705 G. Janssen, et al .: J. Cryst.Growth 104 (1990) 752-757 H. Shiomi, et al .: Jpn. J. Appl. Phys. 29 (1990) 34-40 JF DeNatale, et al .: J. Appl. Phys. 69 (1991) 6456-6460

  The present invention has been made in view of the above-described conventional state of the art, and its main object is a method of growing a diamond single crystal by a vapor phase synthesis method, having a regular growth surface, and having an impurity content. It is an object of the present invention to provide a novel diamond single crystal production method that can produce a high-quality diamond single crystal with a very small amount by a relatively simple method and can be effectively used as a synthesis method for a large diamond single crystal.

The present inventor has intensively studied to achieve the above-described object. As a result, when a diamond single crystal is grown by the microwave CVD method, a constant surface is formed on the (110) plane of the diamond seed crystal by controlling the raw material gas flow ratio, pressure and growth temperature to specific conditions. It has been found that epitaxial growth can be continued while maintaining the shape, and growth without occurrence of abnormal nuclei can be performed at high speed, and the present invention has been completed here.

That is, the present invention provides the following method for producing single crystal diamond and single crystal diamond.
1. A method of growing a diamond single crystal by a microwave CVD method, wherein a raw material gas flow rate ratio is 0.2 to 20 for methane and less than 0.12 for nitrogen with respect to hydrogen 100, and a pressure in the CVD chamber is 13 to 33 kPa. A method for producing a diamond single crystal, comprising growing a crystal at a growth temperature of 950 ° C. to 1250 ° C. on a (110) substrate of the diamond single crystal.
2. A diamond single crystal having a growth surface having a surface roughness parallel to the (110) plane of the diamond single crystal and having a maximum height of 1 to 10 μm.
3. Item 3. The diamond single crystal according to Item 2, wherein the growth surface is a plane parallel to the (110) plane composed of facets composed of fine (111) plane and (100) plane.
4). Item 4. The diamond single crystal according to Item 2 or 3, which has a growth stripe based on the shape of the growth surface of the diamond single crystal.
5). Item 5. The single crystal diamond according to Item 4, wherein the growth stripe is a stripe pattern parallel to the (110) plane having a roughness with a maximum height of 1 to 10 μm.
6). Item 6. The single crystal diamond according to any one of Items 2 to 5 obtained by the method according to Item 1.

  Hereinafter, the manufacturing method of the single crystal diamond of this invention is demonstrated concretely.

Diamond Single Crystal Manufacturing Method (i) Seed Crystal In the manufacturing method of the present invention, a diamond single crystal substrate polished on the (110) plane is used as a seed crystal. The diamond seed crystal only needs to have a polished (110) plane used as a growth plane, and the size, shape, and the like can be appropriately selected according to the plasma CVD apparatus and substrate support used.

(Ii) Manufacturing conditions In the present invention, a diamond single crystal is grown by a microwave CVD method. At this time, hydrogen and methane are supplied as reaction gases, and the flow rate ratio is 0.2 with respect to 100 hydrogen. The flow rate of nitrogen is less than 0.12, preferably less than 0.1, with respect to hydrogen 100, in the range of about ˜20, preferably about 4-10.

  Furthermore, the pressure in the CVD chamber is about 13 kPa to 33 kPa, preferably about 20 kPa to 26 kPa, and the temperature of the growth surface is about 950 to 1250 ° C., preferably about 950 to 1050 ° C.

  Other conditions may be the same as the conditions for diamond growth by a known microwave CVD method. For example, a microwave having a frequency permitted for industrial and scientific use such as 2.45 GHz and 915 MHz is usually used as the microwave. The microwave power is not particularly limited, and may be about 0.5 to 5 kW, for example.

By adopting the above conditions and growing a diamond single crystal by a microwave CVD method, it has been fixed on a (110) surface that has been conventionally avoided as a growth surface because it becomes a rough growth surface. It is possible to maintain the epitaxial growth while maintaining the surface shape. In particular, the production conditions of the present invention are characterized in that the growth temperature is as high as 950 ° C. to 1250 ° C., the growth pressure is as high as about 13 kPa to 33 kPa, and the mixing amount of nitrogen gas is extremely small.

Diamond Single Crystal The diamond single crystal obtained by the method of the present invention has a growth plane that is macroscopically parallel to the (110) plane, which is a seed crystal (diamond substrate) plane, as shown in the schematic cross-sectional view of FIG. However, microscopically, this growth surface is not completely parallel to the (110) plane of the seed crystal, but is a growth surface having a large surface roughness. In this case, the growth surface usually has a surface roughness (JIS B 0601) with a maximum height (Ry) of about 1 to 10 μm.

FIG. 3 shows a laser micrograph of the surface shape of the growth surface of the diamond single crystal obtained in Example 1 described later. FIG. 3 is an enlarged view of the (110) growth surface. In this case, the growth surface has a surface roughness with a maximum height of about 3.5 μm. As shown in FIG. 3, this growth surface is composed of an inclined (111) surface and (100) surface, which causes the roughness of the growth surface. The polyhedral shape consisting of minute (111) and (100) planes on the (110) growth plane observed here is called a facet, which is a characteristic growth in the method for producing a diamond single crystal of the present invention. The form of the surface.

FIG. 4 is a plan view schematically showing a facet composed of minute (111) and (100) planes of this growth surface. The (111) plane and (100) plane, which are facets observed on the growth plane, are the original (111) plane of the crystal, as shown in the AA ′ sectional view and the BB ′ sectional view of FIG. It is tilted up to about 5 ° from the (100) plane. In the AA ′ and BB ′ sectional views, the wavy line indicates the original inclination of the crystal, and the angle shown in parentheses in the drawing is the original (111) plane of the crystal, ( 100) The angle formed by the surface.

On the growth surface in this form, growth starts from the ridgeline formed on the growth surface as the intersection of two adjacent (111) facets and two adjacent (100) facets. It is thought that growth progresses by the step flow. Thus, it is considered that when crystal growth is performed on a growth surface slightly inclined from the (100) crystal plane, step flow growth occurs and crystal growth with few defects occurs. For this reason, according to the method of the present invention for crystal growth on the (110) plane, nitrogen atoms are added to suppress the generation of abnormal nuclei as in the conventional single crystal growth on the (100) plane. In addition, the generation of abnormal nuclei can be suppressed and the epitaxial growth can be continued. For this reason, according to the method of the present invention, it is possible to produce a diamond single crystal with high purity and few defects, with no nitrogen mixed into the crystal.

If a large amount of nitrogen is present in the reaction gas, the growth of the (111) facet surface that easily takes in the nitrogen element is extremely suppressed, and the epitaxial growth on the (110) surface cannot be sustained. For this reason, it is an important requirement for crystal growth on the (110) plane in the method of the present invention to avoid as much as possible the incorporation of an impurity element that inhibits the growth of the (111) facet.

  In the method of the present invention, since the crystal growth is performed in a state where the amount of nitrogen is very small, the growth rate on the (110) plane is higher than that on the (100) plane under the same growth conditions. The speed is about twice as high, which is advantageous from the viewpoint of productivity.

  Next, characteristics of the form of the growth stripes of the diamond single crystal obtained by the method of the present invention will be described.

In general, when a diamond single crystal is grown by a vapor phase growth method, growth stripes are observed in parallel with the growth surface in the grown diamond. This growth stripe reflects the difference in color and density that reflects subtle changes in the amount of impurities incorporated during growth, the difference in transition density observed with X-ray topography, and the crystal strain distribution observed with an interference microscope. (See: Ichiro Sunagawa, “Crystal (Growth, Shape, Completeness)” Kyoritsu Shuppan (2003) p.108-114).

  Such growth stripes are observed as stripe patterns parallel to the (100) plane in the conventional vapor phase growth on the (100) plane when the grown single crystal diamond is cut perpendicular to the growth plane.

  On the other hand, high-temperature and high-pressure synthesis methods generally use bulky seed crystals with (100) and (111) planes, and grow while forming growth planes parallel to the (100) and (111) planes. Therefore, growth stripes parallel to the (100) plane and the (111) plane are generated. Therefore, when a diamond crystal grown by the high-temperature and high-pressure synthesis method is cut and processed, growth fringes parallel to the (100) plane or the (111) plane are observed.

In contrast, in the method of the present invention, as described above, growth fringes reflecting the rough growth surface formed by the (111) and (100) facets are observed microscopically, and macroscopically (100 ) And growth stripes parallel to the (111) plane are not observed in principle, and growth stripes parallel to the (110) plane reflecting the growth surface shape are formed. That is, according to the method of the present invention, the maximum height formed by the (111) facet and the (100) facet has a roughness of about 1 to 10 μm, and the growth stripes parallel to the (110) plane as a whole. A diamond single crystal having the following is obtained. The single crystal diamond obtained by the method of the present invention has such characteristic growth stripes.

  Naturally produced diamond single crystals have a lower crystallinity than artificial synthetic diamonds and have many defects such as inclusions, so they are clearly distinguished from synthetic diamonds.

  According to the method for producing a diamond single crystal of the present invention, a high-quality diamond single crystal having a regular growth surface and containing very little impurities can be produced by a relatively simple method utilizing a vapor phase method. Can do.

  By growing a diamond single crystal sufficiently thick by the method of the present invention, and then cutting and polishing, a diamond crystal having an arbitrary crystal plane can be produced. Therefore, the method for producing a diamond single crystal of the present invention is a very useful method for synthesizing a large diamond single crystal useful for various applications.

  Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1
Using a substantially square-shaped single crystal diamond substrate with a thickness of 0.5 mm and a side of about 5.7 mm polished and cleaned on the (110) surface as a seed crystal, this was set in a commercially available microwave plasma CVD apparatus, and hydrogen gas was CVD It was introduced into the chamber and plasma was generated by applying microwave power. Microwave power of about 1200 W so that the substrate temperature is 1000 ° C at a hydrogen gas flow rate of 500 sccm and a pressure of 24 kPa.
And held for 10 minutes. This step is to clean the surface by exposing the diamond substrate to hydrogen plasma and to stabilize conditions such as the temperature in the CVD chamber.

Next, 20 sccm of methane gas was introduced into the CVD chamber, and the microwave power was adjusted so that the temperature of the diamond substrate was maintained at 1000 ° C. After introducing methane gas, crystal growth was performed by holding for 60 minutes, and then the growth was terminated by stopping methane gas. Thereafter, the microwave power and the hydrogen gas flow rate were gradually reduced to 0, and the CVD chamber was evacuated and then leaked with nitrogen to remove the sample.

  For the same sample, change the growth time only and repeat the above process five times. Each time, observe and measure the growth surface of the material using a differential interference microscope and a laser microscope, and grow the thickness using a micrometer. The weight increase was measured with an electronic balance.

The growth thickness measured using a micrometer almost coincided with the value obtained from the weight increase assuming the single crystal density of diamond in consideration of the substrate area. The five growth times are 60 minutes, 180 minutes, 270 minutes, 270 minutes, and 390 minutes, respectively, and the growth thicknesses at that time are 0.020 mm, 0.044 mm, and 0.063 mm.
0.079mm and 0.089mm, and the total growth was 0.295mm.

  FIG. 5 is a differential interference micrograph showing the surface state of the obtained diamond single crystal. As is apparent from FIG. 5, it can be confirmed that defects such as abnormal nuclei are not generated on the growth surface.

FIG. 3 is a laser micrograph in which the growth surface is enlarged. From this, it can be confirmed that the growth surface is composed of (111) facets and (100) facets. The surface shape of this growth surface was substantially the same for each growth time.

  As a result of the surface shape measurement by the laser microscope, the angle between these surfaces is as shown in FIG. 4, and it can be seen that these facets are close to the (111) plane and the (100) plane.

  FIGS. 6B and 6C are drawings showing cross-sectional shapes (roughness curves) of cut surfaces along the straight lines 1 and 2 in the laser micrograph of the growth surface shown in FIG. 6A, respectively. It can be seen from FIG. 6 that the growth surface is a surface having a maximum surface roughness of about 3.5 μm.

The diamond single crystal obtained by the method of the present invention maintains such a surface shape and continues to grow. Therefore, a large diamond single crystal can be obtained using the (110) plane as a crystal growth surface.

Comparative Example 1
The (110) substrate was used under the same conditions as in Example 1 except that the gas flow rate introduced into the CVD chamber during diamond growth was a hydrogen gas flow rate of 500 sccm, a methane gas flow rate of 60 sccm, and a nitrogen gas flow rate of 0.6 sccm. Diamonds were grown for 60 minutes on top.

As a result, 0.176 mm thick polycrystalline diamond grew and no epitaxial growth occurred. From this, it can be seen that when nitrogen gas is added to the source gas and crystal growth is performed on the (110) plane, epitaxial growth cannot be performed while maintaining the growth surface.

Comparative Example 2
As a seed crystal, a diamond single crystal of 3 mm × 3 mm × thickness 0.5 mm polished and washed on the (100) plane was used, and in the same process as in Example 1, a hydrogen gas flow rate of 500 sccm, a methane gas flow rate of 20 sccm, and a nitrogen gas flow rate of 0 sccm Under the conditions, diamond was grown on a (100) substrate for 270 minutes. As a result, a single crystal diamond having a thickness of 0.067 mm was grown.

FIG. 7 is a differential interference micrograph showing the surface state of the obtained diamond single crystal. As is apparent from FIG. 7, when the (100) plane is used as the growth plane, it can be seen that a large number of abnormal nuclei are generated if the reaction gas does not contain nitrogen gas.

FIG. 3 is a cross-sectional view schematically showing a diamond crystal grown on a (100) plane containing abnormal nuclei. It is sectional drawing which shows typically the diamond single crystal obtained by this invention method. 2 is a laser micrograph of the growth surface of the diamond single crystal obtained in Example 1. FIG. 2 is a plan view schematically showing facets composed of a (111) plane and a (100) plane of a growth surface of a diamond single crystal obtained in Example 1. FIG. 2 is a differential interference micrograph showing the surface state of the diamond single crystal obtained in Example 1. FIG. FIG. 6A is a laser micrograph of the growth surface, and FIGS. 6B and 6C are drawings showing the cross-sectional shapes of the cut surface along the straight line 1 and the straight line 2 in FIG. 4 is a differential interference micrograph showing the surface state of the diamond single crystal obtained in Comparative Example 2.

Claims (1)

A method of growing a diamond single crystal by a microwave CVD method, wherein a raw material gas flow rate ratio is 0.2 to 20 for methane and less than 0.12 for nitrogen with respect to hydrogen 100, and a pressure in the CVD chamber is 13 to 33 kPa. A method for producing a diamond single crystal, comprising growing a crystal at a growth temperature of 950 ° C. to 1250 ° C. on a (110) substrate of the diamond single crystal.