CN203474963U - Chemical vapor deposition equipment for producing silicon carbide epitaxial wafer - Google Patents

Abstract

The utility model provides equipment for improving the uniformity of a silicon carbide epitaxial wafer. According to the chemical vapor deposition equipment, the silicon carbide epitaxial wafer with the uniform thickness can grow. An arc-shaped airflow stopping ring is mounted below airflow of a reaction cavity and then a silicon carbide substrate is arranged on a supporting platform; the reaction cavity is heated to a temperature needed by epitaxy and reaction gas and carrier gas are introduced; finally, a silicon carbide epitaxial layer is formed on the silicon carbide substrate. According to the equipment provided by the utility model, the thickness of the prepared silicon carbide epitaxial wafer is uniform and the device is simple; the most feasible and cheapest method for improving traditional equipment is provided; excessive cost input is not needed and the equipment is good for industrial production.

Description

A chemical vapor deposition equipment for producing silicon carbide epitaxial wafers

【Technical field】

The utility model belongs to the field of chemical vapor deposition, and in particular relates to a chemical vapor deposition equipment for producing silicon carbide epitaxial wafers. the

【Background technique】

Silicon carbide (SiC) is the third-generation wide-bandgap semiconductor material. It has the characteristics of wide bandgap, high critical breakdown electric field, high thermal conductivity, and high carrier saturation drift velocity. It is especially suitable for high-temperature, high-voltage, and high-power power electronics. Semiconductor devices such as semiconductors are of great significance to the development of industries such as hybrid electric vehicles, electric vehicles, solar inverters, and smart grids. the

The production of silicon carbide materials, whether it is crystal growth or epitaxial growth, is not easy, and growing high-quality epitaxial wafers is a challenge to the process. The reaction chamber, the cleanliness of the reaction chamber and other process parameters (temperature, pressure, reaction gas flow rate, etc.) will affect the quality of the silicon carbide epitaxial layer (surface defects, doping, etc.) concentration, concentration uniformity, epitaxial layer thickness, thickness uniformity, etc.). Among them, the thickness uniformity of the epitaxial wafer and the thickness of the epitaxial layer will directly affect the performance of the final device, so the thickness uniformity and the thickness of the epitaxial wafer are regarded as important indicators of the quality of the epitaxial wafer. The parameters that affect the thickness uniformity and the thickness of the epitaxial wafer in epitaxial growth include: the structure of the reaction chamber, the temperature distribution in the reaction chamber, the size of the air flow in the reaction chamber, and the distribution of gas concentrations in various parts of the reaction chamber wait. In the traditional horizontal vapor deposition equipment shown in Figure 1, during the epitaxial growth, due to the "depletion" phenomenon when the reaction gas source passes through the reaction chamber during the reaction process, that is, when the reaction gas flows parallel to the substrate, the The concentration in the inflow direction of the airflow is higher, and the concentration in the outflow direction of the airflow is smaller due to the "consumption" phenomenon, so the epitaxial layer on the substrate surface near the inflow direction of the airflow will be thicker and the epitaxial layer in the outflow direction of the airflow will be thinner. This non-uniformity has a great impact on device fabrication, especially for thicker epitaxial layers. the

The patent number is ZL98812328.2, and the utility model name is a patent for growing a very uniform silicon carbide epitaxial layer. An improved chemical vapor deposition method is disclosed. The reactor is heated until the silicon carbide raw material gas forms an epitaxial layer on the substrate in the reactor. Layer temperature, let the raw material gas and carrier gas flow through the heated reactor to form a silicon carbide epitaxial layer on the substrate, while the carrier gas includes a mixture of hydrogen and a second gas, where the thermal conductivity of the second gas is lower than that of hydrogen The thermal conductivity makes the consumption of the raw material gas through the reactor lower than that of using a single hydrogen as the carrier gas, but its operation process is complicated, and an additional gas source is added, which increases the manufacturing cost. In recent years, silicon carbide epitaxy technology has been very mature in low-voltage devices, but there are still many shortcomings in silicon carbide thick epitaxy technology in high-voltage devices, such as the difficulty of achieving thicker silicon carbide epitaxial layers due to uniformity and surface defects; The growth rate is too low, making the thick silicon carbide epiwafers required to grow high-voltage devices prohibitively expensive. the

【Content of utility model】

In order to obtain silicon carbide epitaxial wafers with good uniformity, the utility model provides a chemical vapor deposition equipment for growing silicon carbide epitaxial wafers. By improving the structure of the chamber, an arc-shaped air flow blocking ring is added to the reaction chamber. The body is heated to the temperature required for epitaxial growth, and then the reaction gas and carrier gas are introduced, and the silicon carbide epitaxial layer is finally formed on the silicon carbide substrate. The added gas flow blocking ring can relatively increase the concentration of the reaction gas in the gas flow outflow area to make up for the problem of small thickness caused by the "consumption" phenomenon, so as to achieve the purpose of uniform silicon carbide epitaxial growth thickness. the

A chemical vapor deposition equipment for producing silicon carbide epitaxial wafers according to the utility model, the equipment cavity is sequentially composed of a graphite support table, a graphite soft felt layer, a quartz wall layer and a heating induction coil from the inside to the outside, and the equipment cavity also includes a Fix the arc-shaped air flow blocking ring on the graphite support platform. the

In the equipment of the present utility model, the shape of the barrier ring is arc-shaped, and the width of the arc-shaped barrier ring is 0.8 to 1.2 cm (as shown in Figure 8). The shape of the silicon carbide substrate used in the utility model is circular, and the The radius of the arc-shaped barrier ring is 1-1.5 cm larger than the radius of the substrate wafer, and the arc of the barrier ring is 90-180 degrees. the

In the equipment of the present utility model, the barrier ring is a graphite barrier ring, so that the barrier ring has good stability at 1500°C to 1700°C, and no deformation or softening phenomenon occurs, which ensures the stability of the gas concentration in the barrier ring area and prevents the When the ring is made of high-purity graphite, the influence of impurities on the epitaxial growth of silicon carbide can be reduced. the

In the equipment of the present utility model, the blocking ring contacts the support platform, and is directly reinforced on the graphite support platform through graphite screws. The setting height of the blocking ring is 0.3-0.7 cm, and the resistance to the air flow is balanced, and no eddy current is generated, which ensures the smoothness of the air flow. Stablize. the

The equipment of the utility model is used in the production of epitaxial wafers, especially silicon carbide epitaxial wafers. the

In the equipment of the present utility model, the surface of the barrier ring is coated with silicon carbide or tantalum carbide coating to prevent impurities in the graphite from diffusing into the reaction chamber. the

The equipment provided by the utility model solves the problem of uneven thickness of the silicon carbide epitaxial layer airflow inflow direction and outflow direction, improves the reaction chamber of silicon carbide epitaxial growth, and installs an airflow blocking ring in the airflow outflow direction in the chamber, through blocking The role of the ring is to increase the concentration of the reaction gas in the area of the outflow direction of the gas flow, so as to make up for the problem of small thickness caused by the "consumption" phenomenon. the

Compared with the prior art, the utility model overcomes the problems of thicker thickness above the airflow and smaller thickness below the airflow caused by the "depletion" phenomenon in the airflow direction of the traditional reaction source. Through the function of the barrier ring, the concentration of the gas source under the gas flow is increased, so that the thickness below the gas flow is close to the thickness above. Due to the reduction of the thickness difference between the upper and lower parts, the uniformity becomes smaller, and the thickness of the silicon carbide epitaxial layer becomes more accurate. Uniformity, the thickness uniformity of the epitaxial sheet produced as a whole is reduced from 1.9-2.5% to 1-1.4%. The utility model has another advantage: it is economical, simple and does not cause excessive cost investment in use. the

The traditional chemical vapor deposition (Chemical Vapor Deposition, referred to as CVD) method, silicon carbide epitaxy generally adopts this method. The general process is: first put the silicon carbide substrate into the reaction chamber, and then pass an inert gas into the reaction chamber (usually H ₂ gas), and maintain a certain pressure in the chamber, and then heat the reaction chamber, usually to above 1500°C, and then feed the reaction gas source (for example: SiH ₄ as silicon source, C ₂ H ₄ as Carbon source, _H2 is generally the carrier gas), under this condition, a silicon carbide film will be deposited on the silicon carbide substrate, that is, the epitaxial layer, and finally cooled. As shown in Figure 2, the reaction chamber described in the utility model is cylindrical, from the inside to the outside, followed by: a graphite support platform 4, used to support the silicon carbide substrate 5, which can prevent the graphite soft felt layer 3 from being exposed to high temperature. The lower decomposition will pollute the cavity. The graphite support table 4 is surrounded by graphite soft felt layer 3, which is used as an insulation layer and induction coil 1 to maintain the temperature conditions required for the epitaxial growth of silicon carbide in the reaction chamber. The graphite soft felt layer 3 The outside is the quartz wall layer 2, which is used as the wall of the reaction chamber. The outside of the quartz wall layer 2 is a circle of induction coils 1 to provide heat for the reaction chamber. The left side is the air inlet 7, and the right side is the gas outlet 6. The left end comes in, passes through the high temperature area and deposits a silicon carbide film on the heated silicon carbide substrate, that is, the epitaxial layer, and then the exhaust gas is discharged from the right end. During the experiment, first clean up the reaction chamber under normal pressure, then put the silicon carbide substrate 5, place the barrier ring 8, vacuumize, and fill the chamber with hydrogen to maintain the pressure in the chamber at a low pressure state (20 ～60Torr), generally 40Torr, start heating, heat to 1500℃～1550℃ for 5～20 minutes, pass in hydrogen (2～20slm) and ethane for in-situ etching to clean the particles or damage on the surface, and pass in ethane The purpose of alkane is mainly to suppress excessive etching and the formation of silicon droplets during etching, and then continue to heat to 1600-1700 °C, and then feed the reaction gas source silicon source SiH4 (2-50 sccm) and carbon source C2H4 ( 2 to 50 sccm) and dopants for epitaxial growth, and when the growth reaches the target thickness, the reaction source and power supply can be cut off to start cooling. Using a Fourier transform infrared spectrometer (FTIR), test the thickness of the test points along the airflow direction to determine the uniformity of the epitaxial wafer in the airflow direction. The test results are shown in Table 1.

Table 1 Experimental results of epitaxial wafer thickness uniformity

point 1 2 3 4 5 6 7 8 9 10 Uniformity mean standard deviation Tradition 7.86 7.81 7.8 7.75 7.74 7.68 7.65 7.57 7.5 7.41 2.95% 7.677 0.145 Example 1 7.87 7.86 7.84 7.81 7.79 7.76 7.71 7.7 7.69 7.69 1.16% 7.772 0.072 Example 2 7.88 7.87 7.84 7.82 7.78 7.75 7.69 7.67 7.66 7.66 1.42% 7.762 0.088

【Description of drawings】

The utility model is further described below in conjunction with accompanying drawing and example,

Figure 1 is a schematic diagram of the growth of silicon carbide epitaxial wafers by the traditional horizontal chemical vapor deposition method;

Fig. 2 is the schematic diagram of the silicon carbide epitaxial wafer grown by the horizontal chemical vapor deposition method of the utility model;

Figure 3 is a top view of the utility model (the arc of the barrier ring is 180°);

Fig. 4 is the top view of the utility model (the blocking ring is 90°);

Figure 5 schematic diagram of test points;

Fig. 6 implements the result figure of one;

Fig. 7 implements the result figure of two;

Figure 8 is a schematic diagram of the barrier ring width;

Among them: 1-heating induction coil, 2-quartz wall layer, 3-graphite soft felt layer, 4-graphite support platform, 5-silicon carbide substrate, 6-airflow outlet, 7-airflow inlet, 8-blocking ring. the

【Detailed ways】

Example 1

As shown in Figure 3, the arc of the barrier ring is 180 degrees, the width is 0.9 cm, and the height is 0.4 cm. Through the above process, the growth of the epitaxial wafer is completed. In the corresponding airflow direction of the silicon carbide substrate, 10 points were measured at intervals, point 1 corresponds to the airflow above, and point 10 corresponds to the airflow below, and the measurement results are shown in Figure 5. The thickness of the silicon carbide epitaxial wafer obtained in Example 1 From 2.13% to 0.97%. the

Example 2

As shown in FIG. 4, when the radian of the barrier ring is 90 degrees, the width is 1.0 cm, and the height is 0.5 cm, the growth of the epitaxial wafer is completed through the above process flow. On the corresponding air flow direction of the silicon carbide substrate, 10 points were measured at intervals, point 1 corresponds to the air flow above, and point 10 corresponds to the air flow below, and the measurement results are shown in Figure 6. The thickness of the silicon carbide epitaxial wafer obtained in Example 2 Uniformity decreased from 2.13% to 1.19%. the

Example 3

The width of the graphite barrier ring is 0.8 cm, the height is 0.3 cm, the radius is 1 cm larger than the width of the substrate wafer, and the thickness uniformity of the epitaxial wafer obtained when the arc is 100 degrees is reduced from 2.16% to 1.21%. the

Example 4

The width of the graphite barrier ring is 1.0 cm, the height is 0.5 cm, the radius is 1.2 cm larger than the width of the substrate wafer, and the thickness uniformity of the epitaxial wafer obtained when the arc is 110 degrees is reduced from 1.99% to 1.20%. the

Example 5

The thickness uniformity of the epitaxial wafer produced when the silicon carbide-coated graphite barrier ring is 1.2cm wide, 0.7cm high, and the radius is 1.5cm larger than the width of the substrate wafer is reduced from 2.16% to 1.21% when the arc is 150 degrees . the

Claims (4)

1. the chemical vapor depsotition equipment for the production of silicon carbide epitaxy sheet, equipment cavity is followed successively by graphite brace table, graphite soft felt layer, quartzy parietal layer and heat induced coil from inside to outside, and described equipment cavity also comprises that is fixed on an arc air-flow catch ring on graphite brace table.

2. equipment as claimed in claim 1, is characterized in that the wide 0.8～1.2cm of described arc catch ring, the large 1～1.5cm of radius of radius ratio substrate wafer, and arranging is highly 0.3～0.7cm.

3. equipment as claimed in claim 1, the radian that it is characterized in that described catch ring is 90～180 degree.

4. equipment as claimed in claim 1, is characterized in that described catch ring is fixed on brace table by graphite screw.

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