TWI771781B - A kind of positive axis silicon carbide single crystal growth method - Google Patents

Abstract

The present invention provides a method for growing a positive-axis silicon carbide single crystal. The steps include: (A) screening a silicon carbide material source, and retaining the silicon carbide material source with a size greater than 1 cm and a density of ≧ 3 g/cm ³ ; (B) Fill the screened silicon carbide source into the bottom of a graphite crucible; (C) place a positive-axis silicon carbide on the top of the graphite crucible as a seed; (D) place the silicon carbide source and the The graphite crucible of the seed crystal is placed in an induction high temperature furnace for physical vapor transport; (E) performing a silicon carbide crystal growth process; and (F) obtaining a silicon carbide single crystal.

Description

A kind of positive axis silicon carbide single crystal growth method

The present invention relates to a method for growing a positive-axis silicon carbide single crystal, in particular to a method for growing a positive-axis silicon carbide single crystal by adjusting the size of a silicon carbide material source.

With the development of science and technology, high power density, small components and high frequency have become indispensable conditions. Among many ceramic materials, silicon carbide substrates have excellent characteristics that were not achieved by silicon substrates in the past, and high frequency has gradually become one of the indicators. Therefore, silicon carbide wafers play a very important role, and the development of silicon seems to have Reaching the limit, the growth of component performance is limited by the material itself, so it is necessary to actively develop new materials to replace the materials currently used in the industry to break through this bottleneck. The excellent conditions of silicon carbide can solve the specifications that current silicon cannot achieve, such as the energy gap value is three times higher than that of traditional silicon substrates, the collapse electric field is ten times higher, and the saturation electron drift rate is higher than two times. Silicon carbide crystal growth usually uses off-axis seed crystals to provide surface growth steps, thereby controlling crystal quality and reducing defect density. With the recent rise of the 5G communication market, the substrates used in high-frequency components are mainly positive-axis substrates. In the past, off-axis crystals were mostly processed into positive-axis crystals. However, this method will reduce the utilization rate of the crystal and greatly increase it. the cost of the positive-axis substrate.

At present, off-axis seeds are mostly used in the preparation of silicon carbide crystals. There are two main reasons, namely, reducing the defect density and maintaining the crystal form.

Reducing defect density: The preparation of large-scale and low-defect density silicon carbide crystals has always been the focus of research. According to previous research experience, the seeds grown along the c-axis direction tend to extend defects, including micropipes (Micropipes, MPs), dislocations (Micropipes, MPs). threading dislocations, TDs), stacking faults (SFs), large angle grain boundaries (Large Angle Grain Boundary, LAGDs). The seed crystals with an off-angle of 8 degrees in the early stage were gradually adjusted to the seed crystals with an off-angle of 4 degrees. However, the off-angle of the seed crystal is beneficial to the growth of the silicon carbide crystal, but if the latter is used as a positive-axis substrate, its utilization rate will be greatly reduced. CREE Corporation of the United States has been devoted to the research on the growth of silicon carbide crystals, and disclosed a method of using off-axis seeds to reduce defect density in its patent application USA20060075958A. Another patent, USA20060032434A, discloses a seed crystal fixture, so that the angle between the seed crystal growth surface and the horizontal direction is in the range of 0°<a≦20°. However, the thermal field of the PVT method has a significant difference in the axial direction. Using a fixture to make the seed crystal deviated will cause the temperature field around the crystal to be more inconsistent and difficult to control.

Crystal form maintenance: The purpose is to stabilize the growth crystal form through the surface step mode. As shown in the first figure, when the atoms are adsorbed to the crystal surface, due to the principle of energy balance, the atoms will migrate to A step or kink to stabilize its energy, and atoms will bond at this location as far as the distance allows. This surface step growth mode is called Kossel, also known as lateral growth. (Lateral growth).

To sum up, the particle size of the current silicon carbide growth crystal source generally falls between 300 and 800 μm. In the early stage of growth, due to the small particle size, the specific surface area of the raw material with this particle size is large, resulting in C/Si The vapor is generated in large quantities and cannot be controlled, so that the surface of the positive-axis seed crystal cannot control the accumulation mode, resulting in the uncontrollable crystal form and the formation of polycrystals. Therefore, the applicant of this case has developed a positive-axis silicon carbide single crystal growth method through painstaking research, which is effective. The uncontrollable factors of C/Si vapor in the early stage of crystal growth are reduced, the reaction conditions on the growth surface are favorable for the growth of the target crystal form, and finally silicon carbide single crystal crystals are obtained.

In view of the above-mentioned shortcomings of the known technology, the main purpose of the present invention is to provide a method for growing a positive-axis silicon carbide single crystal, which can control the silicon carbide material for the positive-axis seed crystal by means of physical vapor transport (PVT). The size of the source, the control of the vapor concentration and evaporation rate of the source, can effectively reduce the defect density of the crystal and maintain the crystal form, solve the limitation that the growth of silicon carbide crystal requires off-axis silicon carbide as a crystal seed, and reduce the cost of preparing the positive-axis substrate.

In order to achieve the above object, according to a solution proposed by the present invention, a method for growing a positive-axis silicon carbide single crystal is provided. The steps include: (A) screening a silicon carbide material source, and retaining a silicon carbide material source with a size greater than 1 cm; ( B) Fill the screened silicon carbide source into the bottom of the graphite crucible; (C) Place the positive-axis silicon carbide on the top of the graphite crucible as a seed crystal; (D) Put the silicon carbide source and the seed crystal into the stone The ink crucible is placed in an induction high temperature furnace for physical vapor transport; (E) performing a silicon carbide crystal growth process; and (F) obtaining a silicon carbide single crystal.

Preferably, the shape of the silicon carbide material source is a polygonal plate shape above a triangle, a circle, a ring, a column or a cone.

Preferably, any dimension of the silicon carbide source is >1 cm.

Preferably, the density of the silicon carbide source is ≧3 g/cm ³ .

Preferably, the purity of the silicon carbide source is ≧99.99%.

Preferably, the nitrogen concentration of the silicon carbide source is ≦1E16cm ⁻³ .

Preferably, the boron concentration of the silicon carbide source is ≦1E16cm ⁻³ .

Preferably, the phosphorus concentration of the silicon carbide source is ≦1E16cm ⁻³ .

Preferably, the aluminum concentration of the silicon carbide source is ≦1E16cm ⁻³ .

Preferably, any dimension of the silicon carbide source is 1.5-2 cm.

The above summary, the following detailed description and the accompanying drawings are all for the purpose of further illustrating the manner, means and effect adopted by the present invention to achieve the predetermined object. The other objects and advantages of the present invention will be explained in the following descriptions and drawings.

1: High temperature furnace

2: Insulation material

3: Crucible

4: Seed

5: Silicon carbide source

6: Nucleus

7: Air source

S1-S6: Steps

The first figure is a schematic diagram of the lateral growth mechanism of the crystal.

The second figure is a schematic diagram of the formation mechanism of the two-dimensional nuclei of the present invention.

The third figure is a schematic diagram of the silicon carbide growing graphite crucible of the present invention.

The fourth figure is the crystal diagram of the 4H silicon carbide single crystal of the present invention.

Fig. 5 is a flow chart of a method for growing a positive-axis silicon carbide single crystal according to the present invention.

The following describes the implementation of the present invention with specific examples, and those skilled in the art can easily understand the advantages and effects of the present invention from the contents disclosed in this specification.

Please refer to the second figure is a schematic diagram of the formation mechanism of the two-dimensional nuclei of the present invention, and the third figure is a schematic diagram of the silicon carbide growth graphite crucible of the present invention. The present invention provides a method for growing a positive-axis silicon carbide single crystal. When preparing a silicon carbide single crystal by a physical vapor transport (PVT) method, generally at high temperature, a silicon carbide material source 5 is used to sublime the silicon carbide. method. The crucible 3 containing the seed crystal 4 and the silicon carbide source 5 is decompressed and heated to a temperature of about 2000-2400° C. in an atmosphere of inert gas, and the silicon carbide source 5 is sublimated by decompression and heating, and controlled The gas source 7 reaches the surface of the seed crystal 4 for crystal growth, and the seed crystal 4 can be a 4-inch or 6-inch positive-axis silicon carbide single crystal.

In more detail, please refer to FIG. 5, which is a flow chart of a method for growing a positive-axis silicon carbide single crystal according to the present invention. The steps include: step S1, screening the silicon carbide material source 5, and retaining the silicon carbide material with a size larger than 1 cm Source 5. In step S2 , the screened silicon carbide material source 5 is filled into the bottom of the graphite crucible 3 . In step S3 , the positive-axis silicon carbide is placed on the top of the graphite crucible 3 as the seed crystal 4 . step S4, placing the graphite crucible 3 containing the silicon carbide material source 5 and the seed crystal 4 in the induction high-temperature furnace 1 for the physical vapor transport method. In step S5, a silicon carbide crystal growth process is performed, and in step S6, a silicon carbide single crystal is obtained.

In this embodiment, the silicon carbide crystal growth process uses physical vapor transport (PVT), the growth temperature is about 2000~2400°C, the pressure is 0.1~50torr, and the growth rate generally falls within 100~200μm /hr, the material and growth time are quite expensive and long. Therefore, it is very important to improve the yield and reduce the cost. It is necessary to reduce the defect density of the crystal prepared by the positive-axis seed crystal to improve the availability of the crystal. The present invention controls the concentration and evaporation rate of the silicon carbide source 5 by regulating the size of the silicon carbide source 5, so that the reaction conditions on the growth surface are favorable for the growth of the target crystal form, and finally a silicon carbide single crystal is obtained.

It is mentioned in the prior art that the general particle size of the current silicon carbide growth crystal source is about 300~800 μm. In the early stage of growth, the particle size of the raw material is small, so the specific surface area is large, resulting in C/ A large amount of Si vapor is produced and cannot be controlled, so that the surface of the positive-axis seed crystal cannot control the accumulation mode, resulting in the uncontrollable crystal form and the formation of polycrystalline. Therefore, in the present invention, by adjusting the size of the silicon carbide material source 5, the size of any dimension of the silicon carbide material source 5 is selected to be >1 cm, preferably, the size of any dimension of the silicon carbide material source 5 is 1.5-2 cm, which effectively reduces the C/Si The uncontrollable factors of the vapor in the early stage of crystal growth, and then with the appropriate growth temperature and thermal field distribution, make silicon carbide nucleate in the center of the seed crystal 4 to become a two-dimensional nucleation seed 6 (as shown in the second figure) in the early stage of growth. Nucleus 6 will be formed with different growth temperatures to form specific The crystal form (4H or 6H), once the crystal form is confirmed, the atoms will start to stack according to the nuclear seed, and then a single crystal silicon carbide crystal will be obtained.

In this embodiment, any dimension of the silicon carbide material source 5 is more than 1 cm, and the shape can be irregular shapes such as polygonal plates above triangles, circles, rings, columns or cones, and the purity is ≧99.99% . In addition, since the material and growth time of the silicon carbide crystal growth process are expensive and long, in this embodiment, the density of the silicon carbide material source 5 is selected to be ≧3 g/cm ³ , so that under the same growth time, the Larger silicon carbide single crystals can be obtained.

In this embodiment, the selected silicon carbide source has a nitrogen concentration of ≦1E16cm ^-3 , a boron concentration of ≦1E16cm ^-3 , a phosphorus concentration of ≦1E16cm ^-3 , and an aluminum concentration of ≦1E16cm ^-3 . These four items are common. Elements that affect the electrical properties of silicon carbide. With the increase in the use of high-frequency components in recent years, the demand for semi-insulating silicon carbide wafers has also increased rapidly. Therefore, reducing the element concentration is to avoid doping (Doping) Silicon carbide crystals conduct electricity. Finally, by adjusting the concentration of the silicon carbide material source 5 and matching the appropriate growth temperature and thermal field distribution, the silicon carbide nucleates in the center of the seed crystal 4 in the early stage of growth, rather than concentrated on the edge of the seed crystal 4 .

Please refer to Fig. 3. In this embodiment, a silicon carbide material source 5 with a size larger than 1 cm is used. The silicon carbide material source 5 is washed with deionized water, dried, and placed in the bottom of the graphite crucible 3 where silicon carbide is to be grown. The silicon carbide wafer with the positive axis is used as the seed crystal 4, and is fixed on the top of the graphite crucible 3. Finally, the graphite crucible 3 is put into the heat insulating material 2, and the assembly of the graphite crucible 3 for silicon carbide single crystal growth is completed. will stone The ink crucible 3 is placed in the induction high temperature furnace 1, and the silicon carbide crystal growth process is carried out. crystals (as shown in Figure 4).

To sum up, the present invention is a method for controlling the growth of a single crystal of silicon carbide by using positive-axis silicon carbide as the seed crystal 4 . By regulating the size of the silicon carbide material source 5 , the gas source of the silicon carbide material source 5 is further controlled. The evaporation rate and growth surface concentration of 7 are favorable for the growth of silicon carbide of a specific crystal type, and a uniform silicon carbide single crystal is obtained. To improve the growth of silicon carbide, off-axis seed crystals are required, resulting in a decrease in crystal utilization rate and a high process cost. In addition to the reduction of growth costs, due to the factor of off-axis seed growth, the grown crystal does not need to be oriented from off-axis to positive axis, which reduces the number of crystal processing items, improves the utilization rate and reduces the effect of complicated processing steps.

In addition, in order to solve the requirement of positive-axis wafers, it is known that the off-axis crystal is oriented and turned to the positive axis for wafer slicing, resulting in a large amount of residual loss and directional processing. The utilization rate of silicon carbide single crystal preparation and the reduction of additional directional processing steps are directly used for wafer slicing, grinding and polishing with the prepared crystal, which greatly reduces off-axis loss and the complexity of the slicing process, that is, the effect of reducing the cost of the silicon carbide process. .

The above-mentioned embodiments are merely illustrative to illustrate the features and effects of the present invention, and are not intended to limit the scope of the substantial technical content of the present invention. Anyone who is familiar with this art can, without violating the spirit and scope of creation, The examples are modified and changed. Therefore, the protection scope of the present invention should be as listed in the patent application scope described later.

S1-S6: Steps

Claims (9)

A method for growing a positive-axis silicon carbide single crystal, the steps comprising: (A) screening a silicon carbide material source, and retaining the silicon carbide material source with a size greater than 1 cm; (B) filling the screened silicon carbide material source into a The bottom of the graphite crucible; (C) a positive axis silicon carbide is placed on the top of the graphite crucible as a seed; (D) the graphite crucible containing the silicon carbide source and the seed is placed in a physical gas phase The transmission method is used in an induction high temperature furnace, wherein the density of the silicon carbide source is ≧3g/cm ³ ; (E) performing a silicon carbide crystal growth process; and (F) obtaining a positive-axis silicon carbide single crystal. The method for growing an ortho-axis silicon carbide single crystal as described in item 1 of the claimed scope, wherein the shape of the silicon carbide source is a polygonal plate shape above a triangle, a circle, a ring, a column or a cone. The method for growing a positive-axis silicon carbide single crystal as described in item 1 of the claimed scope, wherein any dimension of the silicon carbide source is >1 cm. The method for growing a positive-axis silicon carbide single crystal as described in item 1 of the claimed scope, wherein the purity of the silicon carbide source is ≧99.99%. The method for growing a positive-axis silicon carbide single crystal as described in item 1 of the claimed scope, wherein the nitrogen concentration of the silicon carbide source is ≦1E16cm ⁻³ . The method for growing a positive-axis silicon carbide single crystal as described in item 1 of the claimed scope, wherein the boron concentration of the silicon carbide source is ≦1E16cm ⁻³ . The method for growing a positive-axis silicon carbide single crystal as described in item 1 of the claimed scope, wherein the phosphorus concentration of the silicon carbide source is ≦1E16cm ⁻³ . The method for growing a positive-axis silicon carbide single crystal as described in item 1 of the claimed scope, wherein the aluminum concentration of the silicon carbide source is ≦1E16cm ⁻³ . The method for growing a positive-axis silicon carbide single crystal as described in item 1 of the claimed scope, wherein any dimension of the silicon carbide source is 1.5-2 cm.

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