JP2678214B2 - Large diamond synthesis method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for synthesizing a single crystal of a large diamond having a side length of 8 mm or more using a temperature difference method.

(Prior Art) Synthesis of diamond by the temperature difference method is performed by GE (US)
P-4,034,066) was first completed. After that, mass production technology has been advanced, as shown in, for example, Japanese Patent Laid-Open Nos. 59-152214 and 60-210512, and it is currently marketed as a processed product such as a heat sink ultra-precision bite.

4 FIG. 1 is an explanatory view of an example of a diamond synthesizing method by the temperature difference method. As shown in the drawing, the carbon source (11), the solvent (12), the seed crystal (13),
A seed crystal dissolution preventive (14) is placed and heated by a heater (15), and the temperature difference ΔT generated between the carbon source (11) and the seed crystal (13) causes the seed crystal (13) to grow epitaxially on a single surface. This is a method of growing crystals.

(Problems to be Solved) According to the conventional diamond synthesizing method described above, 2
When the crystal size is larger than carat, the solvent is rapidly entrained and a good single crystal cannot be obtained. Further, since it gradually grows from a small seed crystal, it takes 2 weeks or more to synthesize a 2-carat rough stone, which is expensive in terms of cost and is not suitable for practical use. In this case, a large seed crystal (3 mm or more)
Although synthesizing a large single crystal is effective in shortening the crystal growth period, there is a problem in that a single crystal of high quality cannot be obtained because it becomes an aggregated crystal.

Therefore, the maximum single crystal that can be synthesized is 2 carats (diameter
6 mm) and could not be used for applications such as CO ₂ laser window materials, infrared window materials, medical scalpels, and IC bonders that require a size of 8 mm or more.

(Means for Solving the Problems) The present invention solves the above-mentioned problems and provides a method for synthesizing a large diamond that grows a good quality single crystal from a large seed crystal, the characteristic of which is a diameter of 3 mm or more. The (100) face of the seed crystal is used as the growth face, and the growth face is kept at a stable pressure of diamond and at 20-60% from the eutectic point of the solvent and carbon.
In a high temperature atmosphere, the entire surface is once dissolved and then crystal is grown, and the solvent on the side that comes into contact with the carbon source during synthesis has a convex shape composed of a flat surface or a curved surface. To grow under the predominant pressure and temperature conditions.

(Operation) As described above, the diameter is changed by the conventional synthesizing method shown in FIG.
There were two problems when trying to synthesize a large single crystal of 8 mm or more.

(A) The growth time is extremely long and requires 2 weeks or more.

(B) From a size of 6 to 7 mm (2 carats) or more, the metal solvent is rapidly entrained, and a good single crystal cannot be obtained.

In order to solve the above problem (a), it is effective to use a large seed crystal. This is because the growth rate is proportional to the surface area of the crystal, and the initial growth rate with a small surface area is extremely slow. For example, when a seed crystal with a diameter of 1 mm is used, it takes 1 week for the single crystal to reach 3 mm, 10 days for reaching 6 mm, and 2 weeks for reaching 8 mm. Therefore, if a seed crystal of 3 mm or more is used from the beginning, the growth time will be 1/2.
It is reduced below.

However, in the conventional method, when a seed crystal having a diameter of 3 mm or more is used and a large single crystal is suddenly grown, a plurality of small single crystals grow on the seed crystal. For this reason, only aggregated crystals having a plurality of growth base points and involving many solvent inclusions could be synthesized. The cause of this is that the solvent (12) and seed crystal (13) were
A seed crystal dissolution preventing layer (14) is interposed between the two layers until the carbon concentration of the solvent (12) becomes supersaturated.
The point is that 4) did not disappear and the dissolution of the seed crystal (13) was prevented.

That is, when a large seed crystal is used, the dissolution prevention layer is wide, so that the dissolution prevention layer disappears unevenly, and the solvent and the seed crystal contact at some portions. Then, since crystal growth occurs from each of the portions, only aggregate crystals can be obtained.

Crystal growth occurs immediately because the solvent contacts the seed crystal in a supersaturated state. For this reason, steps, defects, and dusts are contained on the seed crystal, and as a result, entrainment of the solvent easily occurs.

The present inventors have found that the following method is effective in order to solve the above problems.

That is, by once dissolving the surface of the seed crystal, steps, defects, dust, etc. on the seed crystal are eliminated, and a clean growth surface is obtained. Further, it is a method of uniformly growing crystals from the entire surface of the dissolved seed crystal by gradually increasing the carbon concentration such as unsaturated → saturated → supersaturated.

And, as means for carrying out the above method, the following 2
It was found that the above method is effective.

One of them is that the dissolution preventing layer is not used and carbon having a saturation concentration or less is contained in the solvent in advance, and at the same time as the solvent is dissolved, the surface of the seed crystal is dissolved and the carbon source (see FIG.
This is a method of gradually increasing the carbon concentration by utilizing the diffusion of carbon from (see) and growing a single crystal.

In this case, it was found that the concentration of carbon contained in the solvent in advance was extremely important, the upper limit was 95% by weight of the saturated concentration under the conditions for crystal growth, and the lower limit was 30% by weight. At a concentration higher than the upper limit, dissolution of the seed crystal surface does not substantially occur. On the other hand, if the concentration is lower than the lower limit, the problem that the seed crystal is completely dissolved and disappeared occurs. Further, it has been found that the preferable concentration for stable crystal growth is in the range of 50 to 90% by weight.

The second method is to use a dissolution control layer instead of the dissolution prevention layer. As the dissolution control layer, Pd, Pt, Rb, Ir,
5 for metals consisting of one or more elements in Ru and Os
A metal layer with ~ 30 wt% Ni or Co was used. The former metal is a refractory metal and is suitable for the purpose of the present invention in that it does not form a carbide. The high melting point metal is necessary because it does not dissolve below the temperature at which the solvent dissolves. Further, when the dissolution adjusting layer forms carbides, carbides may be generated on the surface of the seed crystal and nucleation may occur, which is not suitable for the purpose of the present invention.

The former metal alone does not dissolve until the carbon in the solvent becomes supersaturated, and thus has the same drawbacks as the conventional method. Therefore, in the present invention, by adding one or two elements of Ni and Co to the former metal, the dissolution control layer is uniformly dissolved before the carbon in the solvent becomes supersaturated, and the above-mentioned object is achieved. Found to achieve. At the same time, the concentration of Ni and Co is 5 to
It has also been found that it is preferably in the range of 30% by weight.
If it is smaller than the value, aggregate crystals grow, and if it is larger, the seed crystal melts. Also Ni, Co
Instead of, Fe also has a similar effect, but may form carbides under synthetic conditions.

Next, means in the present invention for solving the above-mentioned problem (b) will be described.

According to the conventional synthesis method shown in FIG. 1, the following problems occur with the growth of the single crystal, so that it is difficult to obtain a good quality single crystal of 2 carats or more and containing no metal solvent.

That is, since the temperature of the growth surface shifts to a high temperature as the crystal grows, the growth surface changes from a low-order surface to a high-order surface. When the growth surface changes, the inclusion of the metal solvent is likely to occur.

In the solvent shape of the conventional method, the carbon concentration on the crystal surface is not uniform, the distribution of supersaturation occurs, and there are a portion that easily grows and a portion that does not easily grow. The metal solvent is easy to be taken into the part where it is difficult to grow.

The present inventors have found that the following two methods are effective for solving the above problems.

The first is a temperature of 20 to 60 ° C higher than the eutectic point of the solvent and carbon so that the seed crystal plane is the (100) plane and the maximum growth plane is the (100) plane and is perpendicular to the carbon diffusion direction. The crystal is grown within the range.

FIG. 2 shows the difference in the growth surface depending on the pressure and temperature conditions for single crystal synthesis. As shown in the figure, when the growth is started from the pressure and temperature conditions on the seed crystal, that is, from the points A and B, the growth surface gradually shifts to the high temperature side and becomes points A ′ and B ′. The growth surface of the former is (100) surface → (111) surface, and that of the latter is (111) surface →
It shifts to the (110) plane, and the inclusion of the solvent easily occurs.
Therefore, it is effective to lower the synthesis temperature according to the crystal growth so that the maximum growth plane is always the (100) plane.

Secondly, in order to make the carbon concentration on the crystal growth surface uniform, a solvent in which the central portion is 20 to 200% higher than the outer peripheral portion or a portion of the high temperature side is spherical is used.

In the conventional synthesis method, the solvent (12) having the shape shown in FIG. 1 was used. Therefore, as shown in FIG. 3, the carbon concentration (the isoconcentration lines indicate the same concentration portion) is low in the central portion (A) and high in the outer peripheral portion (B).
For this reason, when the crystal is grown with the (100) plane as the seed crystal plane, the degree of supersaturation in the central portion (A) is lower than that in the outer peripheral portion (B), and the growth rate becomes slower. ) Has a drawback that the solvent is likely to be involved. The larger the crystal, the larger the difference in concentration between the central portion (A) and the outer peripheral portion (B), resulting in an even greater difference in the growth rate. Therefore, it is considered that the entrainment of the metal solvent occurs rapidly when the thickness is 2 carats (diameter 6 to 7 mm) or more.

To eliminate such drawbacks the present invention, as shown in FIG. 4, the solvent central solvent height (A) compared to (H _0), the solvent height of the outer peripheral portion (B) (H ₁₎ A solvent having a small value was used.

Note that FIG. 3 and FIG. 4 are carbon concentration distributions calculated by the finite element method. Since it is axisymmetric, only the right half cross-sectional view is shown.

As can be seen from FIG. 4, according to the present invention, the difference in concentration between the central portion (A) and the outer peripheral portion (B) is almost eliminated, and the single crystal synthesized by this method is large even with a diameter of 8 mm or more. However, the inclusion of impurities did not occur.

The effect of the present invention is that the above-mentioned solvent height ratio H ₀ / H ₁ is 1.2.
It was found that the effect was exhibited between ~ 3. If it is 1.2 or less, the above effect is not obtained, and if it is 3 or more, the central portion (A) is high and the outer peripheral portion (B) is low.

In addition to the shape shown in FIG. 4, the same effect can be obtained by using a spherical surface in the portion where the solvent and the carbon source are in contact with each other. Further, the same effect was obtained when it was formed by a part of spherical surface or a curved surface. In this case, the important factor is H ₀ during crystal growth.
/ H ₁ ratio, not the shape when set before composition.

As a most effective use of the present invention, the following improvements have been made possible to synthesize a large single crystal having a cross section of the same shape as the solvent and having a diameter of 8 mm or more.

The diagonal length of the seed crystal is 1/4 or more of the solvent diameter.

The shape of the solvent on the seed crystal side is a truncated cone, and the seed crystal is arranged on the circular surface of the truncated cone having a smaller area. Further, the angle between the conical surface and the circular surface is within 5 ° to 45 °.

The solvent which carried out the above is shown in FIG. Seed crystal (5
By making the diagonal length (R ₀ ) of 4) 1/4 or more of the solvent diameter (R ₁ ), the amount of metal solvent involved before the crystal diameter reaches R ₁ was reduced. Even if it was synthesized in the temperature range of 20 to 60 ° C higher than the eutectic point of carbon and solvent (11
3) etc. Higher surface may grow occasionally. This is because the growth and disappearance of the surface facilitates the inclusion of the metal solvent. Therefore, R ₀ / R ₁ in FIG.
Above / 4, the probability of higher order planes reaching R ₁ was reduced.

The angle of the conical surface also reduces the entrainment of the metallic solvent until the single crystal diagonal length (R ₀ ) reaches the solvent diameter (R ₁ ). In particular, it is effective for involving a large amount of solvent near R ₀ R ₁ .

Example 1 As shown in FIG. 6, using the solvent of the present invention, 5.
Under the pressure temperature condition of 6GPa and 1340 ° C., the amount of carbon added in the solvent was added to carry out single crystal synthesis.

Fe-50Ni was used as the solvent metal, and the eutectic temperature with carbon was 13
It was 00 ° C. A seed crystal in which one side of the (100) plane had a length of 3 mm was grown so that the (100) plane was always dominantly grown. The time required for the synthesis was 140 hours.

 The results are shown in Table 1.

(Example 2) By using the solvent control layer in the present invention as shown in FIG. 7, the diamond stable region in which the (100) plane is dominant and the Co content of the dissolution control layer (Pd-Co alloy) are changed, Single crystal synthesis was performed. The solvent used was Fe-70Ni, and the eutectic temperature of the solvent and carbon was 1250 ° C.

The synthesis temperature was 1280 ° C, and the synthesis pressure was 5.6 GPa. The time required for the synthesis was 98 hours.

 The results are shown in Table 2.

As shown in Table 2, when the amount of Co added is 5 to 30% by weight, 1
Good results were obtained with a side length of 8 mm or more.

Similar crystals were also obtained by adding one or more elements of Pt, Ph, Ir, Ru, Os and Co, Ni, Co-Ni alloy instead of Pd.

Example 3 Using a solvent according to the present invention as shown in FIG. 6, the ratio of the central height (H ₀ ) to the outer peripheral height (H ₁ ) of the solvent was changed to show the influence on the synthesized single crystal. investigated.

 The results are shown in Table 3.

The solvent used was Fe-50Ni, and the solvent contained 90% by weight of saturated concentration of carbon in advance.
The growth conditions were 5.5 GPa, pressure and temperature of 1330 ° C., and the growth was performed for 98 hours.

Example 4 Using a solvent according to the present invention as shown in FIG. 5, the influence was investigated by changing the ratio of the solvent outer diameter (R ₁ ) and the diagonal length (R ₀ ) of the seed crystal.

Fe-50Ni was used as the solvent, and 90% by weight of the saturated concentration of carbon was previously contained in the solvent. Synthesis condition is 5.6G
It was grown at Pa and 1340 ° C. for 144 hours.

The results are as shown in Table 4. The single crystals synthesized in Experiment Nos. 32 to 34 had the same shape as the cross section of the solvent.

Example 5 Using the solvent of the present invention as shown in FIG. 6, 5.
The single crystal was synthesized under the pressure of 6 GPa by changing the temperature condition from 1280 to 1380 ℃.

Fe-50Ni was used as the solvent, and the carbon saturation concentration was adjusted to 80
The thing containing the weight% (addition weight 4.4 weight%) was used. As the seed crystal, a (100) plane having a side length of 3 mm was used.
The time required for the synthesis was 98 hours.

 The results are shown in Table 5.

(Effects of the Invention) As described above, according to the synthesis method of the present invention, by dissolving a seed crystal once, it becomes possible to grow a good quality single crystal from a large seed crystal, and the growth time is significantly shortened. It became possible to do.

Further, by using a seed crystal plane of (100) plane, by synthesizing at a temperature condition 20 to 60 ° C. higher than the eutectic point of the solvent and the carbon source, by using a solvent in which the central portion is higher than the outer peripheral portion,
Realizes high quality single crystal synthesis with a diameter of 8 mm or more.

Therefore, CO ₂ laser window material, infrared window material, medical scalpel, I
It is extremely effective for applications such as C bonders.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an example of a conventional diamond synthesis method by a temperature difference method. FIG. 2 is a growth pressure temperature region diagram of each surface of diamond. FIG. 3 and FIG. 4 are carbon concentration diagrams of the conventional method and the method of the present invention calculated by the finite element method. 5, 6 and 7 are all explanatory views of the synthesis method of the present invention.

Claims (4)

(57) [Claims] 1. A method for synthesizing diamond using a temperature difference method, wherein a (100) face of a seed crystal having a diameter of 3 mm or more is used as a growth face, the growth face is under a stable pressure of diamond, and a solvent and carbon are used. Solvent which has a convex shape in which the solvent shape on the side in contact with the carbon source during synthesis is flat or curved after the entire surface is once dissolved in an atmosphere at a temperature 20 to 60 ° C. higher than the eutectic point of And use (10
A method for synthesizing large diamond, characterized in that 0) planes are grown under the predominant pressure and temperature conditions. 2. A large diamond according to claim 1, wherein a solvent containing carbon in an amount of 50 to 90% by weight of the saturated carbon concentration under the growth conditions is used to dissolve the seed crystal plane. Synthesis method. 3. The central portion of the solvent having a convex shape is closer to the outer peripheral portion.
The method for synthesizing a large diamond according to claim (1), which is 20 to 200% thick or has a spherical shape in a contact portion with a carbon source. 4. A seed crystal having a diagonal line of 1/4 or more of the solvent diameter is used as the seed crystal, and the seed crystal is arranged on the smaller circular surface of the solvent having a truncated cone on the side of the seed crystal. The method for synthesizing a large diamond according to claim (1), wherein the diamond cross-sectional shape and the solvent cross-sectional shape are made the same by using a solvent having an angle between a plane and the circular surface of 5 to 45 °.