CN111235633A - A method for preparing self-supporting silicon carbide wafers by CVD on the surface of silicon melt - Google Patents

Abstract

A method for preparing self-supporting silicon carbide wafers on the surface of silicon melt by CVD, comprising: preparing a silicon film on a patterned substrate; raising the temperature in a growth furnace to melt the silicon film to form a silicon melt; keeping the temperature unchanged , pass hydrocarbon gas into the growth furnace, and form a silicon carbide seed crystal layer suspended on the surface of the silicon melt after a period of time; pass hydrocarbon gas and silicon hydride gas into the growth furnace, in the silicon carbide seed crystal layer Homoepitaxial growth on the layer to form a silicon carbide self-supporting layer; after cooling the pattern substrate containing the silicon carbide self-supporting layer, the silicon film is removed to obtain a peeled silicon carbide self-supporting layer, which is ground, polished and shaped. That is, the silicon carbide wafer is obtained. The method avoids the disadvantages of the traditional method, and has the advantages of simplicity, practicability, and easy popularization; the invention can use a low-cost sapphire substrate, and the substrate can be reused, thereby further reducing the cost.

Description

A method for preparing self-supporting silicon carbide wafers by CVD on the surface of silicon melt

technical field

The invention belongs to the field of silicon carbide semiconductor materials, in particular to a method for preparing self-supporting silicon carbide wafers on the surface of silicon melt by CVD.

Background technique

Silicon carbide semiconductor material (4H-SiC) is a new third-generation semiconductor material, which has a very important application in the field of high-power power electronics. Among them, homoepitaxial growth of silicon carbide thick films on silicon carbide substrates is a key step to realize silicon carbide power devices. The current preparation scheme has two shortcomings: one is that a silicon carbide substrate is required, which increases the difficulty of making silicon carbide power devices because the substrate is extremely difficult to prepare; the other is that the substrate needs to be thinned so that greatly reduces the device resistance. The above shortcomings not only increase the cost of device fabrication but also cause waste of raw materials.

SUMMARY OF THE INVENTION

In view of this, one of the main purposes of the present invention is to provide a method for preparing self-supporting silicon carbide wafers on the surface of silicon melt by CVD, in order to at least partially solve at least one of the above technical problems.

In order to achieve the above object, as an aspect of the present invention, a method for preparing a self-supporting silicon carbide wafer by CVD on a silicon melt surface is provided, comprising:

(1) prepare a silicon film on a pattern substrate;

(2) raising the temperature in the growth furnace to melt the silicon film to form a silicon melt;

(3) keeping the temperature constant, feeding hydrocarbon gas into the growth furnace, and forming a silicon carbide seed crystal layer suspended in the silicon melt surface layer after a period of time;

(4) feeding hydrocarbon gas and silicon hydride gas into the growth furnace, and homoepitaxially growing on the silicon carbide seed crystal layer formed in step (3) to form a silicon carbide self-supporting layer;

(5) cooling the patterned substrate containing the silicon carbide self-supporting layer obtained in step (4) and removing the silicon film to obtain a peeled silicon carbide self-supporting layer, which is ground, polished and shaped to obtain the carbide silicon wafer.

Based on the above technical solutions, the method for preparing self-supporting silicon carbide wafers by CVD on the silicon melt surface of the present invention has at least one of the following advantages over the prior art:

1. This method avoids the disadvantages of traditional methods, and has the advantages of simplicity and ease of implementation, and easy promotion;

2. In the present invention, it is no longer necessary to use expensive and rare silicon carbide substrates, but low-cost sapphire substrates can be used, so that they only bear the role of support, and silicon melt is used as a transformation bed to feed the growth of silicon and carbon. After a certain amount of time, a self-supporting silicon carbide thick film material with a certain thickness can be grown, and then the thick film can be carbonized by wet etching the residual silicon layer. The silicon layer is peeled off to form a starting material for making silicon carbide power devices. In addition, the aforementioned substrate can also be reused, further reducing the cost.

Description of drawings

1 is a schematic diagram of the stepped surface and cross-sectional shape of a graphic substrate in an embodiment of the present invention;

2 is a schematic diagram of the shape of the surface corrugation of the graphic substrate and its distribution in the embodiment of the present invention;

3 is a schematic diagram of the whole process of preparing a silicon carbide epitaxial thick film in an embodiment of the present invention;

FIG. 4 is a schematic diagram of a process of melting a silicon film and growing silicon carbide in an embodiment of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

The invention discloses a method for preparing a self-supporting silicon carbide wafer on the surface of silicon melt by CVD, comprising:

(1) prepare a silicon film on a pattern substrate;

(2) raising the temperature in the growth furnace to melt the silicon film to form a silicon melt;

(3) keeping the temperature constant, feeding hydrocarbon gas into the growth furnace, and forming a silicon carbide seed crystal layer suspended in the silicon melt surface layer after a period of time;

(4) feeding hydrocarbon gas and silicon hydride gas into the growth furnace, and homoepitaxially growing on the silicon carbide seed crystal layer formed in step (3) to form a silicon carbide self-supporting layer;

(5) cooling the patterned substrate containing the silicon carbide self-supporting layer obtained in step (4) and removing the silicon film to obtain a peeled silicon carbide self-supporting layer, which is ground, polished and shaped to obtain the carbide silicon wafer.

In some embodiments of the present invention, the temperature is increased to 1500 to 1800 degrees Celsius in the step of increasing the temperature in step (2).

In some embodiments of the present invention, the silicon melt in step (2) is a silicon melt with steps or corrugations on the surface.

In some embodiments of the present invention, the growth time of the silicon carbide seed layer in step (3) is 1 to 2 hours.

In some embodiments of the present invention, the pressure in the growth furnace in step (3) is 600 to 760 Torr.

In some embodiments of the present invention, the molar mass ratio of silicon element and carbon element in the hydrocarbon gas and the silicon hydride gas in the step (4) is 1:(0.8 to 1.5);

In some embodiments of the present invention, the growth time of the silicon carbide layer in step (4) is 3 to 8 hours.

In some embodiments of the present invention, the hydrocarbon gas in step (4) includes propane, and the silicon hydride gas includes silane.

In some embodiments of the present invention, the pattern on the pattern substrate described in step (1) includes steps;

In some embodiments of the present invention, the shape of the steps includes micro-nano steps, continuous corrugated steps or discontinuous corrugated steps;

In some embodiments of the present invention, the steps are formed due to substrate inclination or by pattern etching.

In some embodiments of the present invention, the thickness of the silicon film in step (1) is 200 to 1000 nanometers.

In some embodiments of the present invention, the method for removing the silicon film in step (5) includes wet etching;

In some embodiments of the present invention, the wet etching specifically includes:

Putting the prepared silicon carbide film pattern substrate into an alkaline solution, keeping the temperature at 80 to 100 degrees Celsius, and after 2 to 4 hours, the silicon film is removed;

In some embodiments of the present invention, the alkali solution includes an aqueous KOH solution, and the concentration of the aqueous KOH solution is 40 wt % to 60 wt %.

In an exemplary embodiment, the method for preparing a self-supporting silicon carbide wafer of the present invention includes the following steps:

Step 1, take a graphic substrate as a supporting substrate;

Step 2: Prepare a silicon film on the pattern substrate by sputtering or electron beam evaporation. The thickness of the silicon film is 200 nanometers to 1 micrometer, and then the temperature is raised in the growth furnace to 1500-1800 degrees Celsius to melt it to form a melt , this liquid phase is used as the parent phase and fluidized bed for the subsequent growth of silicon carbide; at high temperature, the surface of silicon melt is affected by the pattern substrate, and has fine steps or fine ripples, and silicon molecules at the steps of the pattern substrate are more likely to move to the surface The movement causes fine steps or corrugations to be formed on the melt surface correspondingly, which increases the surface area of the silicon melt, and the tips of the steps or corrugations and the adjacent facets are more likely to contact the carbon source.

Step 3: Pour the hydrocarbon gas containing carbon element into the growth furnace, and at a high temperature of 1500-1800 degrees Celsius, the carbon element is dissolved in the near-surface layer of the silicon melt, and combined with the silicon element to form a suspension of silicon carbide seed grains with a certain density After 1 to 2 hours, the seed grains grow and fuse with each other to form a silicon carbide seed layer with a thickness of 100 nanometers to 300 nanometers, which is suspended on the surface of the silicon melt and becomes the capping layer of the silicon melt; control The silicon vapor pressure and the growth furnace pressure are balanced, so as to control the seed crystal to be suspended on the surface of the silicon melt, so that it will not sink, and will not be stirred and split by the silicon molecules in the melt. After a certain period of time, the seed grains grow and merge with the adjacent seed grains, forming a silicon carbide seed crystal film on the molten silicon surface.

Step 4. Simultaneously feed the hydrocarbon gas containing carbon element and the simple silicon-hydrogen compound gas containing silicon element into the growth furnace, and perform homoepitaxial growth with the silicon carbide seed crystal layer as the substrate at high temperature for 3-8 After an hour, the thickness of the homoepitaxial layer is 50-200 microns to form a silicon carbide self-supporting thick film material; wherein, the molar mass ratio of carbon element and silicon element in the hydrocarbon gas and the silicon hydride gas is 1: (0.8-1.5);

Step 5. After the growth furnace is cooled to room temperature, take out the pattern substrate with the silicon carbide self-supporting thick film material, and then use wet etching to remove the residual silicon film, so that the self-supporting thick film material falls off the surface of the pattern substrate by itself, and the The silicon carbide is peeled off from the supporting material;

In step 6, the obtained silicon carbide self-supporting material is subjected to double-sided grinding and polishing and circumferential shaping treatment, so that both sides are flat and bright, that is, the silicon carbide wafer is prepared.

The technical solutions of the present invention will be further described below through specific embodiments and accompanying drawings. It should be noted that the following specific embodiments are only for illustration, and the protection scope of the present invention is not limited thereto.

The chemicals and raw materials used in the following examples are either commercially available or self-made by known preparation methods.

In the preparation method of the silicon carbide epitaxial film of this embodiment, a nano-patterned substrate is used, the material is sapphire or 4H-SiC, the surface crystal orientation is (0001) or (000-1), and the difference is <11-20 >Or other directions such as the <1100> direction have a certain angle to form a substrate inclination angle, such as 0 degrees, 4 degrees, 8 degrees, etc., to form micro-nano strip-like steps, as shown in Figure 1, with a specific angle to the reference edge Or an angle, such as 0 degrees, 30 degrees, 45 degrees, 90 degrees, etc., which is 0 degrees in Figure 1. The surface steps can also be in other shapes, as shown in Figure 2, which are continuous corrugated or intermittent corrugations, with specific angles or angles between the corrugations and the reference edge, such as 0 degrees, 30 degrees, 45 degrees , 90 degrees, etc. The step height is 50 nanometers to 1 micrometer, and the mesa width is 100 nanometers to 2 micrometers, as shown in Figure 1. The micro-nano steps on the surface can be formed due to the inclination of the substrate, or can be formed by pattern etching.

A thin layer of silicon film is prepared on the surface of the pattern substrate by electron beam or magnetron sputtering. The silicon film thickness is 200 nanometers to 1 micrometer. As shown in step 2 in Figure 3.

The silicon film is melted in a silicon carbide epitaxial growth furnace. As shown in step 1 in Figure 4. The furnace temperature is raised to about 1500-1800 degrees Celsius to melt the silicon film and make it have a certain vapor pressure.

The surface of the silicon melt is affected by the pattern substrate and has similarities, and also has fine steps, or forms fine ripples, because at high temperature, the silicon molecules at the steps of the substrate are more likely to move to the surface, so that the corresponding parts of the melt surface form fine steps or The corrugation increases the surface area of the silicon melt, and the steps or corrugated tips and adjacent facets are easy to contact with the carbon source, and the compound reaction generates seed crystals, thereby forming a high-density seed crystal region, suspended on the surface of the silicon melt, Under certain conditions, the seed crystals grow and merge with each other to form a capping layer, that is, an ultra-thin seed crystal film layer, which also has fine surface steps, which is beneficial to the subsequent chemical vapor deposition using the step flow growth mode for co-sustained epitaxial silicon carbide growth.

At this time, a carrier gas hydrogen atmosphere is introduced, the flow rate is 1 slm-30 slm, and the pressure of the growth chamber is 600-760 Torr. At this time, the reaction source gas of carbon (ie, hydrocarbon gas), such as propane, is introduced into the carrier gas hydrogen atmosphere, keeping the pressure of the growth chamber unchanged, the flow rate of propane is 100sccm-500sccm, and the carbon source is dissolved in the silicon melt. High-density silicon carbide seed grains are formed on the surface, which can be used as seed crystals to grow silicon carbide. After 1-2 hours, the seed grains grow and merge with the adjacent seed grains, forming silicon carbide seed crystals on the surface of the molten silicon film. Ultra thin film. As shown in Figure 4, step 2.

At this time, a silicon source (ie, silicon hydride compound gas), such as silane, is introduced to make the molar mass ratio of carbon and silicon to be 1: (0.8-1.5), and homoepitaxial growth is carried out. After 3-8 hours, the silicon carbide film grows to 50 The reaction source gas of silicon and carbon can be turned off at -200 microns, and the temperature is lowered to room temperature in a hydrogen atmosphere to end the growth, as shown in the third step in Figure 4.

Take out the substrate with the grown silicon carbide film, and carefully remove the residual silicon layer by wet etching, as shown in step 5 in FIG. 3 . The substrate on which the silicon carbide film is grown is placed in a KOH aqueous solution with a mass percentage of 40%-60%, and the temperature is kept at about 80-100 degrees Celsius. After 2-4 hours, the silicon carbide film and the substrate can be separated. The residual silicon film is removed by etching, thereby peeling off the grown silicon carbide film from the pattern substrate to form a self-supporting silicon carbide thick film material.

The self-supporting silicon carbide thick film material is flattened on both sides by the method of grinding and polishing, the burr on the surface of the silicon carbide material is removed and the surface roughness is reduced to less than 1 nanometer, and then the self-supporting silicon carbide thick film material is shaped. , the preparation of the self-supporting silicon carbide wafer can be completed, as shown in the sixth step in FIG. 3 .

The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above-mentioned specific embodiments are only specific embodiments of the present invention, and are not intended to limit the present invention. Within the spirit and principle of the present invention, any modifications, equivalent replacements, improvements, etc. made should be included within the protection scope of the present invention.

Claims (10)

1. A method for preparing a self-supporting silicon carbide wafer by CVD on a silicon melt surface, comprising: (1) prepare a silicon film on a pattern substrate; (2) raising the temperature in the growth furnace to melt the silicon film to form a silicon melt; (3) keeping the temperature unchanged, feeding the hydrocarbon gas into the growth furnace, and forming a silicon carbide seed crystal layer suspended in the silicon melt surface layer after a period of time; (4) feeding hydrocarbon gas and silicon hydride gas into the growth furnace, and homoepitaxially growing on the silicon carbide seed crystal layer formed in step (3) to form a silicon carbide self-supporting layer; (5) cooling the patterned substrate containing the silicon carbide self-supporting layer obtained in step (4) and removing the silicon film to obtain a peeled silicon carbide self-supporting layer, which is ground, polished and shaped to obtain the carbide silicon wafer. 2. The method according to claim 1, wherein In the step of raising the temperature in step (2), the temperature is raised to 1500 to 1800 degrees Celsius. 3. The method according to claim 1, wherein In step (2), the silicon melt is a silicon melt with steps or corrugations on the surface. 4. The method of claim 1, wherein In step (4), the hydrocarbon gas includes propane, and the silicon hydride gas includes silane. 5. The method of claim 1, wherein The graphic on the graphic substrate described in step (1) includes steps; The shape of the steps includes micro-nano steps, continuous corrugated steps or discontinuous corrugated steps. 6. The method of claim 5, wherein The steps are formed due to substrate inclination or by pattern etching. 7. The method of claim 1, wherein, In step (1), the thickness of the silicon film is 200 to 1000 nanometers. 8. The method of claim 1, wherein: The method for removing the silicon film in step (5) includes wet etching. 9. The method of claim 8, wherein: The wet etching specifically includes: The patterned substrate on which the silicon carbide film has been prepared is placed in an alkaline solution, and the temperature is kept at 80 to 100 degrees Celsius. After 2 to 4 hours, the silicon film is removed. 10. The method of claim 9, wherein: The alkali solution includes KOH aqueous solution, and the concentration of the KOH aqueous solution is 40wt% to 60wt%.

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