KR20090124111A - Process for growing single crystal diamond - Google Patents

Abstract

PURPOSE: A process for growing single crystal diamond is provided to minimize the temperature difference between diamonds and minimize the temperature change by the plasma contact. CONSTITUTION: The pit(23) having the intaglio pattern corresponding to the mold substrate(21) to the crystalline morphology of the diamond seed(24) is formed. In the diamond seed, the growth is included in the pit of the mold substrate. The quick freeze part(22) controls the temperature of the mold substrate. The mold whole of the substrate is relatively uniformly contacted with the plasma(20). The intaglio pattern of the pit formed in the mold the inverted pyramid or the cubic shape. The diamond seed has the octahedron shape.

Description

Diamond single crystal growth method {PROCESS FOR GROWING SINGLE CRYSTAL DIAMOND}

The present invention relates to a method for growing diamond single crystals, and more particularly, to a vapor phase synthesis method for growing diamond single crystals for jewelry.

Diamond is divided into natural diamond existing in nature and synthetic diamond artificially synthesized. Synthetic diamond is further divided into diamond synthesized by high temperature and high pressure synthesis and diamond produced by meteorological chemical synthesis.

The high temperature and high pressure synthesis method is a method in which a diamond forms a thermodynamically stable state of 1000 ° C. or more and tens of thousands of air pressure or more and is converted into graphite by using a transition metal such as Co as a catalyst. It is mainly used to synthesize diamond powder and also to grow single crystal diamond. However, the growth conditions for growing single crystal diamond are difficult and mass synthesis is difficult due to the limitation of the size of the synthesis chamber.

Vapor chemical synthesis is carried out using microwave, direct current power source or hot filament, mainly using microwave plasma to decompose the mixed gas of hydrogen and methane to synthesize diamond. However, the growth of single crystal diamond tends to increase the temperature of the diamond due to the heating of the plasma. The growth of the diamond during growth causes a change in the growth pattern of the diamond and the occurrence of defects. very important. In addition, in order to grow a large number of single crystal diamonds, temperature uniformity in the horizontal direction of the substrate on which the diamond is placed is required, but there is a problem that mass production is difficult due to difficulty in securing the horizontal uniformity of the plasma. Therefore, in order to grow a large number of diamond single crystals by using a gas phase synthesis method, solutions to problems such as securing temperature uniformity and growth crystal plane control for crystal defect control during growth are required.

Currently, the method of growing diamond single crystal for jewelry is mainly using microwave vapor chemical vapor deposition. Generally, 1mm diameter natural diamond or high temperature and high pressure synthetic diamond is used as a seed of growth to grow on a substrate. do.

In order to maintain the growth rate at several tens of mu m / h or more to make the synthetic cost of diamond economical, a high temperature plasma region having a synthesis pressure of about 100 torr is utilized. In this case, however, temperature heating of the diamond single crystal by plasma becomes very severe, and in particular, the portion of the substrate protruding in the plasma direction is subjected to very severe heating by direct contact with the plasma. Therefore, when the diamond seed is grown, the diamond grows in the plasma direction, and thus the temperature of the growing diamond single crystal becomes higher. This increase in temperature has a direct impact on the growth behavior of the diamond, causing crystal defects. Therefore, there is a need for a method capable of minimizing temperature change due to plasma contact during diamond growth.

In order to solve this problem, in order to maintain a constant temperature of the diamond seed as proposed in US Pat. No. 68,580,78, a separate jig is made to cool the seed and the temperature is measured in real time. Another method is to keep the temperature of the diamond constant by changing the contact distance. However, when growing multiple diamond seeds at the same time, this method requires a method for controlling several jig separately, and it is difficult to realize the temperature measurement device and controller of each diamond. Thus, there is a need for a new method of temperature maintenance for simultaneously growing large quantities of diamond seeds for commercial production.

In addition, when the diamond seed is grown, various growth surfaces such as (100), (111), (112), and (113) appear as diamonds due to the characteristics of crystal growth. Therefore, in order to grow excellent crystalline single crystal diamond, there is a need for a method capable of growing only to a specific crystal plane such as (100) crystal plane. In the case of diamond, it can be grown in the form of a cube or an octahedron by changing the growth temperature or the concentration of gas used. In general, natural diamonds used in jewelry have an octahedral shape, because the shape is similar to the final shape of processed gemstones. Therefore, it is advantageous to grow in the shape of an octahedron in order to minimize the amount of processing during the processing of jewelry. However, as described above, the (111) growth surface in the gas phase growth is problematic because of the high occurrence of defects. Therefore, the grown diamond shape needs a method capable of (100) plane growth while maintaining the octahedron.

1 is a schematic diagram of a diamond vapor phase synthesis method according to the conventional method. The rounded portion shows the plasma 10 of the mixed gas of hydrogen-methane. The single crystal diamonds 14 are placed and grown in the metal cooling unit 12 that is cooled under water. The plasma 10 is in direct contact with the diamond 14 and a temperature rise of the diamond 14 occurs due to the energy of the plasma 10. As the diamond 14 grows, the top of the diamond gets closer to the plasma 10 and thus the temperature rise is more severe. In addition, since the degree of contact between the diamond 14 and the plasma 10 is different, the degree of temperature rise is also different, which makes it very difficult to maintain a constant temperature of the diamond. For this reason, the diamond temperature measurement must be made for each diamond, and the temperature control is also required for each diamond independently, which makes the installation of this very complicated.

The present invention solves the problems as described above, to minimize the temperature change between the diamond to grow and minimize the temperature variation during the diamond growth, and to minimize the growth defects while maintaining the desired growth pattern of diamond To provide a method.

In order to achieve the above technical problem, the present invention provides a diamond seed and the step of providing a mold substrate having at least one pit having an intaglio pattern corresponding to the crystal shape of the diamond seed and a thermal conductivity of 1 W / cmK or more After positioning in the pit of the mold substrate provides a diamond single crystal growth method comprising the step of growing into a diamond single crystal by vapor phase chemical vapor deposition in the pit.

According to a preferred embodiment of the present invention, the method may further include providing a metal cooling unit under the mold substrate for controlling the temperature of the mold substrate.

Further, in the method of the present invention, the mold may be made of a material selected from the group consisting of a high melting point metal, a ceramic material, a high thermal conductive material, and a single crystal material.

In the process of the present invention, it is preferred that the reactor gas used in the gas phase chemical vapor deposition method is a mixture of hydrogen and methane, and the content of methane is in the range of 0.5 to 10% (v / v).

According to a preferred embodiment of the present invention, the reactor may further comprise 50% (v / v) of oxygen relative to methane.

In the method of the present invention, the intaglio pattern of the pit formed in the mold is preferably inverted pyramid or cube shape.

In the method of the present invention, it is preferable that the diamond seed has an octahedral shape, and the intaglio pattern of the pit formed on the mold substrate is an inverse pyramid shape that enables growth to the (100) plane as an inverse paramide shape.

In the method of the present invention, the pits formed on the mold substrate may be formed by electrical discharge machining, mechanical indentation process, or chemically anisotropic corrosion process.

In the process of the present invention, the vapor phase chemical vapor deposition can be carried out by microwave, direct current power supply or hot filament.

According to the method of the present invention, there is a problem of temperature change due to contact with plasma generated during diamond single crystal growth, a problem of maintaining a constant temperature between diamonds that occurs when a plurality of diamond single crystals are grown simultaneously, and a growth pattern and growth surface of diamond. Independent control problems, diamond growth defects caused by the surface defects of the diamond seed problem is solved. Therefore, the effect is that the mass production of jewelry diamonds can be made very easy.

The present invention provides a mold substrate having a good thermal conductivity in which at least one pit having an intaglio pattern corresponding to the crystal shape of the diamond seed is formed to prevent direct contact between the diamond seed and the plasma. It provides a diamond single crystal growth method comprising the step of growing in a diamond single crystal by the vapor phase chemical vapor deposition while maintaining the temperature of the diamond seed in the pit by positioning the inside to block direct contact between the plasma and the diamond during growth. Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

2 is a schematic diagram of a diamond single crystal growth method according to an embodiment of the present invention. The mold substrate 21 has at least one pit 23 having an intaglio pattern corresponding to the crystal shape of the diamond seed, and the diamond seed 24 is located within the pit 23 of the mold substrate 21. In the state, the single crystal is grown by the plasma 20. Preferably, a metal cooler 22 for controlling the temperature of the mold substrate 21 is provided below the mold substrate.

According to the method of the present invention, the entire mold substrate 21 is brought into contact with the plasma 20 relatively uniformly, and a large area of contact with the metal cooling part 22 occurs, so that the temperature can be kept relatively stable. In addition, it is easy to transfer the temperature in the horizontal direction through the substrate 21 to help maintain a uniform temperature.

In addition, since the diamond single crystal grows in the pit 23 of the mold substrate 21, direct contact between the diamond seed or the single crystal 24 and the plasma 20 may be minimized. The temperature of the diamond single crystal 24 is maintained similar to the temperature of the substrate 21. Therefore, the measurement of temperature is also solved by measuring the temperature of the substrate 21, and one temperature measurement and temperature control system is sufficient.

The growth pattern of the diamond single crystal is shown in FIG. Diamond single crystals generally consist of a combination of (100) and (111) crystal planes, including (100) plane cubes (a) and (111) plane cubes (b), and (100) and There is a dodecahedron (c) consisting of a combination of (111) planes. When the diamond grows, the growth plane becomes the (100) and (111) planes, and the shape of the single crystal is determined by the relative growth speed of these growth planes.

4A and 4B are examples of a mold substrate used for diamond single crystal growth according to the present invention. Pits 43 having negative patterns on the upper surface 41 of the substrate are produced. The intaglio pattern is determined by the shape of the diamond seed. For example, if the diamond seed is an octahedron (Fig. 3 (b)) and the growth condition is a growth condition in the <100> direction, the intaglio is a square horn or a pyramid. 5 illustrates a state in which the octahedral diamond seed 55 is placed in the pit 53 formed on the mold substrate 51 of FIGS. 4A and 4B. Although not shown, when the seed is a cube seed (Fig. 3 (a)) and the growth direction is <100>, the intaglio is formed in a cube shape, and when the <111> direction is the growth direction, the corner of the cube is formed. Use a crushed intaglio in the form of a triangular pyramid as the vertex.

In a preferred embodiment of the present invention, for the growth of gemstone diamond, generally use an octahedral diamond seed and use a plate-shaped mold substrate that can be uniformly arranged in a certain direction. On one side of the substrate, a mold is made by digging an inverted pyramidal square pyramid that cuts an octahedron in half. The square pyramidal intaglio molds are arranged on the substrate at regular intervals, and the octahedral diamond seeds are arranged in the intaglio. The diamond seeds thus arranged are arranged so that the (100) directions are perpendicular to the substrate and the (100) directions of each diamond seed are arranged parallel to each other in a direction parallel to the direction of the substrate.

On the other hand, when the diamond seed of the cube is used, the mold of the substrate is processed in the form of a square pillar, and in this case as well, the (100) direction of the seed is arranged perpendicular to the substrate. The depth of the mold should be deeper than the size of the seed and will generally be dug to a depth similar to the final size of the diamond to be grown.

The fabrication of pits having such intaglio patterns can be performed using various methods such as electric discharge machining, mechanical indentation, and chemical corrosion, depending on the material of the substrate.

In addition, the material of the substrate that can be used is all substrates that can be used for the gas phase synthesis of diamond, for example, high melting point metal substrates such as Mo, W, Cu, ceramic substrates such as SiC, Si substrates, etc., thermal conductivity of 1 W / It is preferable to use cmK or more, more preferably 1 W / cmK or more and 4 W / cmK or less (for example, about 4 W / cmK for copper).

In the case of electric discharge machining, Mo, W substrate, etc. can be used, and the embossed corners, triangular horns, square pillars, etc. are dug on the discharge electrode, and the desired intaglio is produced on the substrate through the electric discharge machining using the electrode. In the case of metals such as Cu, the intaglio can be easily produced by mechanical indentation. The shape of the indentation can be determined by changing the shape of the indentation.

In the case of Si, on the other hand, it is fragile and cannot be applied to the indentation method. However, when a Si single crystal substrate is used, an intaglio of a desired shape can be produced by anisotropic chemical vapor deposition. For example, a case of making a negative mold of a square pyramid to be used for a seed of an octahedron is as follows. On the surface of the (100) Si substrate, a SiO ₂ film having a thickness of several hundred nm to be used as a mask film during chemical corrosion is formed by a thermal oxidation method, and a square array pattern is formed by a general photolithographic method (ref). At this time, the length of one square can be adjusted between 1 mm and 3 mm depending on the size of the final growth diamond desired, but is not limited thereto. The SiO ₂ portion of the square portion is corroded to expose Si. In addition, when Si is etched with an anisotropic corrosion solution of Si such as a (CH ₃ ) ₄ NOH-KOH solution, a pyramidal indent is formed on the Si substrate.

The material of the substrate can be selected according to the required conditions such as temperature uniformity required for growth conditions, diamond nucleation on the substrate, separation from the substrate after diamond growth, and the like. When thermal conductivity in the direction parallel to the substrate is important, it is advantageous to use the Cu substrate having the largest thermal conductivity, and Mo or W substrate is advantageous to solve the problem of adhesion between the diamond and the substrate during growth. The problem of nucleation of new diamond in the substrate during the growth of diamond has the advantage of Si or Cu substrate. Therefore, the choice of substrate material may vary depending on the desired purpose such as the number of diamonds to be grown at one time, the crystallinity of the desired diamond, and the growth rate of the diamond.

The use of the mold substrate according to the present invention makes it possible to solve two problems in terms of temperature control. First, it minimizes the contact between the diamond and the plasma during the growth of the diamond. Since the growth surface of the diamond does not come into contact with the plasma until it reaches the top of the substrate mold, the local temperature rise due to contact with the plasma can be minimized. Second, since the heat transfer in the lateral direction through the substrate can be minimized the temperature variation between each diamond. Therefore, in the case of growing a plurality of diamonds it is possible to maintain a constant temperature between each growing diamond can easily control the growth rate and the formation of defects. Thus, growing multiple diamond seeds at the same time eliminates the need to measure and control the temperature of each diamond, providing the possibility of mass production.

In addition, the use of such a mold-type substrate is possible because the shape of the grown diamond is the same as the intaglio shape of the mold, it is possible to change the growth pattern of the diamond irrespective of the growth surface of the diamond, and also to change the growth surface, growth rate and bonding control Do. In the case of using an inverted mold having an inverted pyramid square pyramid structure, the grown diamond has the engraved shape as it is, so that it is manufactured in the form of a pyramid square pyramid regardless of the growth type. At this time, depending on the type of growth surface, the final shape can be adjusted between the octahedron (when grown to (111) plane) or the square pyramid (when grown to (100) plane). When the diamond is made in the form of a square pyramid, it is closer to the final shape of the processed gemstone, thereby reducing the cost of processing. In addition, the basic shape of the grown diamond can be selected independently of the growth surface because the mold is determined by the shape. This is very advantageous for controlling the growth bonding of diamond, providing a way to minimize crystal defects.

Another advantage is that the growth defects of the diamond caused by the surface defects of the diamond seeds can be minimized. In general, the diamond seed used for diamond single crystal growth is used for a variety of reasons, such as the processing of natural diamond or high-temperature, high-pressure synthetic diamond into a square or the like. The diamond seed is machined by mechanical methods such as lapping or polishing, and there are surface defects due to machining. Therefore, the removal of such surface defects is necessary before the diamond grows, and has a great influence on the crystallinity of the diamond. However, if the mold substrate is used, since the diamond grown in nature is used as it is, all problems caused by surface defects can be solved.

Hereinafter, the embodiment of the present invention will be described in more detail, but the present invention is not limited thereto.

<Example 1>

As a mold substrate as shown in FIGS. 4A and 4B, a circular single crystal Si intaglio having a thickness of 5 mm and a diameter of 50 mm was used, and the base length of the square pyramid intaglio was 2.5 mm. Negative pits were arranged 5 x 5 on the substrate and the spacing between the negative pits was 2 mm. Place an octahedral diamond seed with a size of about 200 μm in the intaglio pit, use an Astex vapor phase synthesizer (microwave output 5 KW), draw a vacuum to 10 ^-5 torr, pressurize hydrogen Was raised to 10 torr and then the plasma was excited. While increasing the pressure, the plasma output was increased to bring the hydrogen plasma into contact with the substrate. The final pressure was 100 torr and the plasma output was 4 KW. In order to remove impurities that may be present on the substrate surface and the diamond seed surface, a treatment was performed for 10 minutes in a hydrogen plasma state. At this time, the temperature of the Si substrate was measured at 950 ℃ by an optical temperature measuring system. Methane was then introduced to bring the concentration of gas to 3% (v / v). It was grown for 500 hours under these conditions. After 400 hours of growth, the diamond grew to the top of the substrate and the diamond temperature was similar to the temperature of the substrate. On the other hand, the temperature of the diamond located in the center of the substrate was measured to be about 20 ^o C higher than the diamond located outside. This is considered to be due to the thermal conductivity of the Si substrate not being large compared to that of the metal.

After the growth was over, the Si was removed by corrosion and the diamond was collected. The diamond showed a pyramid-shaped transparent shape, about 3 mm high. The shape and transparency between the diamonds were similar to each other indistinguishable from the naked eye. As a result of observing the growth surface of the diamond by SEM, there was no difference in growth pattern even though the temperature difference between the center and the outer diamond was about 20 ^o C. The growth surface of the diamond was very flat, and no visible defects such as twins were found.

<Example 2>

To reduce the temperature difference between the diamonds, diamonds were grown under the same conditions by forming the same pits on the Cu substrate as in Example 1. After 400 hours of growth, the temperature difference between the diamond at the center of the substrate and the outer diamond at the top of the peak decreases below 5 ^o C. From this, it can be used as a substrate with high thermal conductivity to make the temperature between the growing diamond more constant. And it was found.

<Example 3>

Substrate conditions, diamond seed surface treatment conditions and other growth conditions were the same as in Example 1 except that the growth rate of methane was increased to 5% (v / v) to increase diamond growth rate. After 200 hours of growth, the thickness of the grown diamonds was about 2.5 mm, and the growth rate was about doubled. However, the diamond color was light brown and the transparency was also reduced. On the other hand, the growth surface of the diamond, unlike Example 1 was found that twins were formed, it was also found that the formation of small diamond crystals between the intaglio pits. Therefore, it can be seen that there is a need to optimize the gas composition to suppress the formation of crystal defects in diamond and to increase the growth rate.

<Example 4>

Oxygen was added to the hydrogen-methane mixture gas to increase the growth rate of diamond and minimize the formation of twins. The concentration of methane was fixed at 5% (v / v) and oxygen was added up to 1% (v / v). Other growth conditions were the same. The diamond grown after 200 hours was about 1.8 mm thick. The growth rate decreased by about 10% with the addition of oxygen. On the other hand, the transparency of the diamond was very good as in Example 1, it was found that the occurrence of twins on the diamond growth surface is significantly reduced. Therefore, it was found that oxygen was very effective in increasing the crystallinity of diamond without significantly decreasing the growth rate.

1 is a schematic diagram illustrating a diamond single crystal growth method according to the prior art.

Figure 2 is a schematic diagram showing a diamond single crystal growth method according to an embodiment of the present invention.

3 is a perspective view showing the detective of various diamond single crystals.

4A and 4B are a plan view and a cross-sectional view of a mold substrate according to an embodiment of the present invention.

5 is a cross-sectional view showing a diamond seed placed in a pit of a mold substrate according to an exemplary embodiment of the present invention.

Claims (10)

Providing a mold substrate having at least one pit having a negative pattern corresponding to the crystal shape of the diamond seed and having a thermal conductivity of at least 1 W / cmK and positioning the diamond seed within the pit of the mold substrate and then within the pit. A diamond single crystal growth method comprising the step of growing into diamond single crystals by vapor chemical vapor deposition. The method of claim 1, And providing a metal cooling portion under the mold substrate to control the temperature of the mold substrate. The method of claim 1, And wherein the mold is made of a material selected from the group consisting of high melting point metals, ceramic materials, high thermal conductivity materials, and single crystal materials. The method of claim 1, The reactor gas used in the chemical vapor deposition method is a mixture of hydrogen and methane. The method of claim 4, wherein The content of methane is characterized by a range of 0.5 to 10% (v / v). The method of claim 4, wherein And wherein the reactor further comprises 50% (v / v) oxygen relative to methane. The method of claim 1, The intaglio pattern of the pit formed in the mold is inverted pyramid or cube shape. The method of claim 1, The diamond seed has an octahedral shape, and the intaglio pattern of the pit formed on the mold substrate is an inverse pyramid shape which enables growth to the (100) plane as an inverse pamide shape. The method of claim 1, Wherein the pits formed on the mold substrate are formed by electrical discharge machining, mechanical indentation, or chemically anisotropic corrosion. The method of claim 1, The vapor phase chemical vapor deposition method is characterized in that carried out by microwave, direct current power source or hot filament.

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