JPH05200271A - Method for growing iib type diamond single crystal - Google Patents

Abstract

PURPOSE:To obtain a large single crystal wherein boron is uniformly distributed throughout IIb type diamond grown on a seed crystal, in a method for growing a diamond single crystal by a temp. difference method, by using IIb type diamond wherein boron is contained in a crystal as an isolated substitution type impurity as a carbon source. CONSTITUTION:A carbon source 1 is arranged to a high temp. part and a seed crystal 3 of diamond is arranged to a low temp. part and a solvent 2 is arranged between the carbon source 1 and the seed crystal 3 to be held at temp. melting the solvent 2 or higher under pressure thermally stabilizing diamond or more to grow a new diamond crystal on the seed crystal 3. At this time, IIb type diamond wherein boron is contained in a crystal as an isolated substitution type impurity is used as the carbon source to grow a IIb type diamond crystal uniform in boron concn. distribution on the seed crystal 3 so as to become at least larger than IIb type diamond used as the carbon source. As a result, a large diamond single crystal excellent in semiconductor characteristics can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing a large IIb type diamond single crystal having semiconductor characteristics used for thermistors and transistors.

[0002]

2. Description of the Related Art Diamond has a larger band gap than conventional semiconductor materials such as Si and GaAs.
Further, since the thermal conductivity is high, a semiconductor device and a semiconductor substrate having a wide operating temperature range and excellent heat dissipation characteristics can be expected. It is known that by adding boron (B) at the time of diamond synthesis, it is possible to synthesize a blue-colored diamond crystal called IIb type that exhibits p-type semiconductor characteristics. For example, Japanese Examined Patent Publication No. 38-9552 discloses that when a non-diamond carbonaceous material is converted to diamond by using a catalyst under high temperature and high pressure, boron or boron carbide,
Excellent conductivity by adding boron oxide, boron nitride, nickel boride, lithium borohydride, etc.
Disclosed is the manufacture of type IIb diamond. In addition, The Journal of Physical Chemistry, Vol.75, N
o.12, (1971) 1838 shows a 1-ct class IIb diamond grown by adding a trace amount of boron to a solvent by a temperature difference method.

[0003]

However, the IIb type diamond crystal obtained by the conventional synthesis method cannot be actually used as a semiconductor material. The main reason for this is that the distribution of boron in the crystal is quite uneven,
This is because the electrical characteristics greatly differ depending on the place and direction of the crystal. The reason why the distribution of boron is non-uniform is not well understood, but as a phenomenon, during diamond crystal growth,
It is known that the amount of boron taken into the crystal varies greatly depending on the growth surface. For example, boron is easily incorporated into the (111) plane of diamond,
Boron is hardly incorporated into the growth planes such as the (0) plane, the (110) plane, and the (113) plane. Further, depending on the synthesis conditions, there may be a case where a considerable concentration is observed in the boron concentration distribution within the same growth plane. Further, in normal diamond synthesis, a trace amount of nitrogen in a solvent is taken in by substitution during crystal growth, and a yellowish crystal called Ib type (in this case, the nitrogen donor level is deep, Is not shown)
However, the distribution of nitrogen is also quite uneven within the crystal. When boron is added in such a state that nitrogen is taken into the crystal during crystal growth, the concentration distribution of boron in the crystal becomes more non-uniform, and boron coexists with nitrogen. Being electrically neutralized, the semiconductor properties of diamond crystals become more unstable and non-uniform. The non-uniformity of the boron concentration distribution as described above becomes more remarkable as the size of the crystal becomes larger, and is more susceptible to the subtle changes in the synthesis temperature conditions. An object of the present invention is to solve the above problems and to provide a method for growing a IIb type diamond single crystal having a uniform distribution of boron in the crystal and excellent semiconductor characteristics.

[0004]

According to the present invention, a carbon source is placed in a high temperature portion and a diamond seed crystal is placed in a low temperature portion, and a solvent is placed between the carbon source and the seed crystal, and the solvent is dissolved. In the method of growing a new diamond crystal on the seed crystal by holding the diamond at a temperature equal to or higher than the temperature at which the diamond is thermally stable or at a pressure equal to or higher than the pressure, boron is contained in the crystal as an isolated substitution impurity as the carbon source With IIb type diamond,
On the seed crystal, a IIb type diamond crystal is grown, which is larger than the IIb type diamond used as the carbon source and has a uniform boron concentration distribution inside the crystal. In addition, when diamond is grown on the seed crystal under the above-mentioned diamond growing conditions, the amount of nitrogen and the carbon source II
It is particularly preferable to grow the b-type diamond in a state where boron other than boron in the crystal is not taken into the crystal. Figure 1
Is a schematic explanatory view showing an example of a sample chamber configuration of the present invention,
1 is a IIb type diamond containing a carbon source and containing boron as an isolated substitution type impurity, 2 is a solvent, 3 is a diamond seed crystal, 4 is an insulator, 5 is a graphite heater, and 6 is a pressure medium.

[0005]

The inventors of the present invention tried to add boron in a state where nitrogen was completely removed, because the distribution and electrical characteristics of boron become uneven if nitrogen remains in the crystal even a little. The various addition methods were investigated to find an effective method for uniformly adding boron into the crystal. As a result, in the diamond growth by the temperature difference method, IIb containing boron as an isolated substitution impurity as a carbon source.
It has been found that a large IIb type diamond single crystal in which boron is uniformly distributed can be stably obtained by adopting a method in which only boron in the diamond is added as a dopant to the grown crystal using a type diamond. When diamond, which is an isolated substitution type and has boron in the crystal lattice, is used as the carbon source, the boron element does not completely separate from the adjacent carbon element in the diamond crystal even if it dissolves in the solvent, Diamond that diffuses in the solvent together with the carbon element in the state (Note: each carbon element and boron element microscopically retains the structure of the starting diamond even if it dissolves in the solvent to become a liquid) It is considered that they are incorporated into the crystal, and therefore, it is considered that the boron is uniformly incorporated into the grown crystal without aggregating or causing unevenness on the growth surface. It has been confirmed that the IIb type diamond crystal thus grown has a substantially stable semiconductor characteristic compared to the conventional one, with almost no difference in the boron concentration due to the difference in the growth surface or the growth temperature condition even with a 1-carat large crystal. Then, the present invention has been completed.

As the boron-containing IIb type diamond used as a carbon source in the present invention, boron is added to a carbon source or a catalyst (solvent) in a usual high-pressure high-temperature synthesis method, or vapor phase synthesis such as CVD. In the method, by using a gas containing boron as a raw material, IIb type diamond powder or granules or polycrystals obtained by doping a predetermined amount of boron into a crystal are molded and processed into a predetermined shape, Alternatively, any form such as a powder obtained by crushing granular or polycrystalline IIb type diamond powder by embossing or sintered at high temperature and high pressure can be used. However, it is necessary that all the boron is contained in the diamond crystal as an isolated substitution type impurity, and it is not preferable to contain boron impurities in other forms. The content of boron in diamond used as a carbon source in the present invention is preferably 1 ppm or more. If it is less than 1 ppm, it will be difficult to obtain a diamond having desired semiconductor characteristics.
There is no upper limit to the boron content as long as it does not aggregate in the crystal. In general, diamond having a boron content of more than 1000 ppm is not preferable because boron is likely to partially aggregate. Further, the content of boron impurities other than the isolated substitution type carbon source diamond is specifically 1 pp.
It is preferably m or less.

In the present invention, in order to realize a state where boron other than boron in the carbon source IIb type diamond is not taken into the crystal when the diamond is grown on the seed crystal under the diamond growing condition. As described above, in addition to the condition that there is substantially no boron impurity other than boron as an isolated substitutional impurity in type IIb diamond as a carbon source, the solvent contains almost no boron as an impurity. Is necessary, and the content of the impurity boron in the solvent is preferably 1 ppm or less. When the solvent contains more than 1 ppm of boron, the boron is taken into the growing diamond crystal, and the unevenness of the boron distribution in the grown diamond crystal is noticeable, and the electrical characteristics are improved. It becomes different depending on the case and direction of crystals, and cannot be used as a semiconductor material. As the solvent of the present invention, any of the metals that are often used as a catalyst or solvent for ordinary diamond synthesis, such as Fe, Co, Ni, Mn, Cr, etc., or alloys of these metals can be used.

Further, in order to realize a state in which nitrogen is not taken into the grown crystal when diamond is grown on the seed crystal under the diamond growing condition, the solvent and the carbon source do not contain nitrogen impurities. Using, the diamond sample is grown in a state where the entire sample chamber is vacuum degassed and nitrogen gas in the sample chamber is sufficiently removed, or a necessary amount of nitrogen getter is added to the solvent. As a nitrogen getter,
For example, all metals that have high reactivity with nitrogen, such as Al, Ti, Zr, Hr, V, Nb and Ta, or alloys consisting of two or more of these elements, that do not inhibit diamond crystal growth Can be used. When these nitrogen getters are used, it is necessary to add a sufficient amount such that nitrogen hardly remains in the grown diamond crystal. According to the experiments conducted by the present inventors, the amount of the nitrogen getter added is generally 1 to 5% by weight based on the solvent.
With the above-described structure, an appropriate temperature gradient is provided between the carbon source (1) portion and the seed crystal (3) portion in FIG. 1 so that the carbon source side has a high temperature, and at a temperature equal to or higher than the melting point of the solvent, Under high pressure and high temperature conditions where diamond is in a thermally stable region,
By holding for a long time, it is possible to grow a IIb type diamond single crystal having a large size of 1 carat or more and having a uniform distribution of boron.

[0009]

【Example】

Example 1 As a carbon source, IIb type diamond powder having a particle size of about 20 μm and containing about 5 ppm of boron (B) as an isolated substitution type impurity was pressed and shaped into a diameter of 20 mm and a thickness of 5 mm. A high-purity Fe-40Co alloy (weight ratio of Fe: Co = 60: 40, diameter: 20 mm, thickness: 10 mm) was used as a solvent metal, and 1.0% by weight of Al and Ti were added thereto as a nitrogen getter. The content of B in the solvent metal was 0.1 ppm or less (detection limit) as a result of chemical analysis (ICP emission spectroscopic analysis) and was hardly contained. Three diamond crystals with a diameter of about 500 μm were used as seed crystals. Then, in the sample chamber configuration shown in FIG. 1, the carbon source and the seed crystal part were set in a heater so that there was a temperature difference of about 30 ° C., and a pressure of 5.5 Pa and a temperature of 1300 were used by using an ultrahigh pressure generator. The diamond was grown by holding at 70 ° C. for 70 hours. As a result, a good blue-tinted IIb type diamond single crystal of 0.7 to 0.9 carat was obtained. When these crystals were slice-cut at the center with a laser and then polished, and the crystal cross section was observed, almost no shade of blue was observed. In addition, B in various places in the crystal
As a result of analyzing the content by SIMS (secondary ion mass spectrometry), almost no difference in B content depending on the location was observed,
The B content was 1.3 ppm at any of the locations. The resistivity measured by the four-point probe method was 220 Ω · cm, and almost no difference due to location or direction was observed.

Example 2 About 25 pp of B as an isolated substitution type impurity as a carbon source
Diamond was grown in the same manner as in Example 1 except that IIb type diamond powder containing m was used. As a result, a good blue IIb type diamond single crystal of 0.7 to 0.9 carat was obtained. In the observation of the crystal cross section, almost no shade of blue was seen. In addition, B in various places in the crystal
As a result of analyzing the content by SIMS, almost no difference in B content depending on the location was observed, and B content was B at any location.
The content was 7 ppm. The resistivity measured by the four-point probe method was 80 Ω · cm, and almost no difference due to location or direction was recognized.

Example 3 As a carbon source, B as an isolated substitution type impurity of about 200 p
Diamond was grown in the same manner as in Example 1 except that IIb type diamond powder containing pm was used. As a result, a 0.7 to 0.9 carat deep blue good quality IIb type diamond single crystal was obtained. In the observation of the crystal cross section, almost no shade of blue was seen. Moreover, as a result of analyzing the B content at various points in the crystal by SIMS, almost no difference in the B content depending on the location was observed, and the B content was 48 ppm at any location. The resistivity measured by the four-point probe method was 20 Ω · cm, and almost no difference due to location or direction was observed.

Comparative Example 1 Diamond was grown in the same manner as in Example 1 except that diamond powder containing almost no B (content less than 0.1 ppm [below detection limit]) was used as a carbon source. As a result, colorless and transparent diamond crystals (type IIa) of about 0.8 carat were obtained. The nitrogen concentration of the obtained diamond crystal was measured by ESR and found to be 0.1 p
It was pm or less. Almost no B was detected by SIMS analysis. It had little electrical conductivity and was an insulator.

Comparative Example 2 0.1% by weight of diamond powder containing almost no B as a carbon source (content 0.1 ppm or less [below detection limit])
Example 1 except that the boron powder of Example 1 was used.
Diamonds were grown in the same manner as in. As a result, a blue IIb type diamond single crystal of about 0.7 to 0.9 carat was obtained, but when the cross section of the crystal was observed, a difference in blue concentration was observed depending on the growth surface. That is, although the (111) growth surface was slightly shaded, one surface was blue, while the (100) growth surface was nearly colorless. As a result of analyzing the B content in each place by SIMS,
In the (111) growth plane, 0.9-1.5 ppm, (10
0) The growth surface was about 0.1 ppm, which was greatly different depending on the growth surface, and the variation was large even within the same growth surface. The resistivity measured by the four-point probe method is also 200 to 10,000 Ω.
cm and the location of the crystal greatly differed.

Comparative Example 3 Diamond was grown in the same manner as in Example 1 except that a solvent metal containing B of 5 ppm was used. As a result, a thin bluish IIb type diamond single crystal of about 0.7 to 0.9 carat was obtained. When the cross section of the crystal was observed, a difference in blue concentration was observed depending on the growth surface. That is, although the (111) growth surface was slightly shaded, it was pale blue on one side,
0) It was almost colorless with the growth surface. As a result of analyzing the B content in each place by SIMS, 0.2 to 0.3 ppm was detected on the (111) growth surface, and B was not detected on the (100) growth surface. In addition, the variation in B concentration was large even in the (111) growth plane. An attempt was made to measure the resistivity by the four-point probe method, but there was a large difference depending on the location of the crystal, and in some cases no electrical conductivity was observed.

[0015]

As described above, according to the present invention,
A large IIb type diamond crystal in which boron is uniformly dispersed can be obtained. The synthetic diamond according to the present invention can be used as a semiconductor material such as a thermistor or a transistor.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram of a sample chamber configuration for growing a diamond single crystal, which is one specific example of the present invention.

[Explanation of symbols]

 1 carbon source 2 solvent metal 3 seed crystal 4 insulator 5 graphite heater 6 pressure medium

Claims (2)

[Claims] 1. A carbon source is placed in a high temperature part and a seed crystal of diamond is placed in a low temperature part, and a solvent is placed between the carbon source and the seed crystal, and the temperature is higher than the temperature at which the solvent is dissolved, and the diamond or the thermal In a method of maintaining a pressure equal to or higher than a stable pressure to grow a new diamond crystal on the seed crystal, boron is contained as an isolated substitution type impurity in the crystal in the crystal II
The method as described above, wherein b-type diamond is used to grow, on said seed crystal, a IIb-type diamond crystal having at least a larger concentration distribution of boron inside the crystal than the IIb-type diamond used as the carbon source. 2. When the diamond is grown on the seed crystal under the diamond growing conditions, it is grown in a state in which nitrogen and boron other than boron in the carbon source IIb type diamond are not taken into the crystal. The method according to claim 1, characterized in that