JP2016020288A - Forming method for single crystal silicon semiconductor thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To grow an MSE epitaxial film made to have an N concentration lower than 1E+16 (atoms/cc) by using a polycrystalline SiC substrate as a raw material.SOLUTION: In the invention, there is used as a material a polycrystalline SiC substrate at or higher than 7E+15 (atoms/cc) and at or lower than 1E + 16 (atoms/cc), which is manufactured to have a stable N concentration. Said polycrystalline SiC is used as a material to set the Si molten liquid layer thickness at 25 to 200 μm, and a growth temperature between 1600 to 1850°C. Under said condition, an MSE epitaxial film is grown to have an N concentration lower than 1E + 16 (atoms/cc).SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for epitaxially growing single crystal silicon carbide (SiC).

  As the performance of Si semiconductors reaches its limit, SiC semiconductors are attracting attention. However, since the reduction of dislocation defects that become device killer in the substrate is insufficient, the yield is lowered, and this is a big problem in spreading SiC semiconductors.

  As a method for reducing dislocation defects in device killer, the MSE method (Metastable Solvent Epitaxy) shown in Patent Document 1 has been attracting attention.

  By using the MSE method, dislocations that are said to be device killer can be converted into other types of dislocation defects with less harm.

  When impurities such as nitrogen and boron are doped into a SiC semiconductor, they become electron carriers and hole carriers, which greatly affects the electrical characteristics. In order to use a SiC semiconductor as an electronic device, it is important to be able to control the doping amount of impurities that affect the electrical characteristics as described above.

  In the MSE method, as shown in Patent Document 1, the process environment is placed in a vacuum, the inside of the crucible is filled with Si vapor up to the saturated vapor pressure, and a pressure difference from the process environment is provided, so that the process environment enters the crucible. It is possible to suppress the outside air from being mixed. By reducing the contact with the outside air, it is possible to suppress contamination of impurities such as nitrogen in the outside air.

  Furthermore, as shown in FIG. 3 of Patent Document 2, the nitrogen atom concentration (hereinafter referred to as N concentration) of the single crystal SiC epitaxial film (hereinafter referred to as MSE epifilm) grown by the MSE method is set to the N concentration of the raw material. Since the proportional relationship is shown, the N concentration of the MSE epi film can be controlled by controlling the N concentration of the raw material. In the MSE epi film, impurities that can be carriers other than nitrogen are currently 5% or less, and if the nitrogen concentration can be controlled, any carrier density can be controlled with good reproducibility.

JP 2008-230946 A PCT / JP2012 / 050389

  As shown in Patent Document 2, with respect to the doping amount control of impurity nitrogen in the MSE epi film, the conventional MSE method has controlled the N concentration entering the MSE epi film by controlling the N concentration of the raw material. However, when an MSE epitaxial film having an N concentration of 1E + 17 (atoms / cc) or less is grown, there are the following problems.

  When MSE growth is performed using a polycrystalline SiC substrate having an N concentration of 1E + 17 (atoms / cc) or less as a raw material, the N concentration of the grown MSE epitaxial film is almost higher than the N concentration of the raw material. there were.

  As shown in Patent Document 2, it is difficult to stably manufacture a material having an N concentration of 7E + 15 (atoms / cc) or less with good reproducibility.

  When the growth temperature is set to 1800 ° C. at which the film thickness of the MSE epi film is relatively stable and thick, and MSE growth is performed using a material having an N concentration of 7E + 15 (atoms / cc), the MSE epi film The N concentration became 1E + 16 (atoms / cc) or more. As a result, it is difficult to grow an MSE epi film having an N concentration lower than 1E + 16 (atoms / cc).

When it is desired to use the MSE epi film for a device having a withstand voltage of 600 V, the carrier density is controlled to 1E + 16 (cm ⁻³ ), and when it is desired to be used for a device with a withstand voltage of 1200 V, the carrier density is set to 5E + 15 (cm ^−3). ) Must be controlled, and reproducible and uniformly doped. For this purpose, an MSE epi film having an N concentration of 1E + 16 (atoms / cc) or less cannot be stably grown without intentionally introducing nitrogen into the raw material. Cannot be used for.

  An object of the present invention is to grow an MSE epi film of 1E + 16 (atoms / cc) or less that can be used for a device having an N concentration of 600 V or higher.

  The inventor found that the purity of the MSE epifilm produced by the MSE method has a correlation with the growth temperature, and that the difference in the N concentration between the source substrate and the MSE epifilm is reduced.

  FIG. 3 shows a state of epitaxial film growth by the MSE method, wherein 1 is a polycrystalline SiC raw material substrate, 2 is a Si solution in a state where the Si substrate is melted at a high temperature, 3 is an MSE epitaxial film grown by MSE, 4 is a SiC single crystal substrate, and 5 is a nitrogen impurity contained in the raw material substrate 1. As shown in Patent Document 2, the nitrogen impurity 5 taken into the MSE epi film 3 can be controlled only by the N concentration of the raw material substrate 1. This is because the nitrogen impurity 5 of the raw material substrate 1 is dissolved by MSE growth and taken into the MSE epifilm 3 through the Si melt 2. For this reason, it has been expected that the N concentration of the MSE epifilm 3 cannot be reduced unless the N concentration of the raw material substrate 1 is reduced.

  However, as a result of experiments, it has been found that the amount of nitrogen impurities 5 incorporated into the MSE epifilm 3 changes as the growth temperature is changed.

  The nitrogen impurity 5 diffusing from the raw material rises with an increase in the amount of dissolution of the raw material substrate 1 due to the temperature rise. However, the incorporation of nitrogen impurities 5 into the MSE epifilm 3 decreases due to the increase in the C / Si ratio with increasing temperature. As a result of the balance between increase and decrease, it is presumed that there is a growth temperature at which the N concentration of the MSE epifilm 3 becomes a minimum value.

  Based on the above, it is considered that the growth temperature needs to be optimized in order to make the MSE epitaxial film highly pure.

  By optimizing the growth temperature of the MSE epi film according to the present invention, even if a raw material having an N concentration of 7E + 15 (atoms / cc) or more and 1E + 16 (atoms / cc) or less is used, 1E + 16 (atoms / cc) or less. The MSE epitaxial film can be stably grown and can be used for a device having a breakdown voltage of 600 V or higher.

FIG. 1 is a sectional view showing a member configuration for MSE growth according to an embodiment of the present invention. FIG. 2 is a correlation diagram showing the MSE growth temperature, the MSE epi film, and the N concentration of the raw material according to the embodiment of the present invention. FIG. 3 is a cross-sectional view showing that N impurities are mixed into the MSE epi film by the conventional MSE method.

  Hereinafter, an embodiment of an MSE epifilm according to the present invention will be described with reference to the drawings.

  As shown in FIG. 1, a carbon spacer 7 is disposed on a SiC susceptor 6. Then, the polycrystalline SiC raw material substrate 1 is disposed on the carbon spacer 7, and the SiC melt layer SiC spacer 8 is further disposed thereon. In this order, the Si substrate 9, the SiC single crystal substrate 4, and the carbon spacer 7. The SiC heavy stone 10 was disposed. This arrangement is the same as the conventional MSE method.

  As an experimental condition, the N concentration of the polycrystalline SiC raw material substrate 1 was measured before the experiment. The SiC melt layer SiC spacer 8 was manufactured with a thickness of 40 μm so that the thickness of the Si melt layer was 40 μm. Further, the pressure for MSE growth was 70000 Pa, and the diameter of the SiC single crystal substrate 4 was 3 inches.

  The spacer 8 is preferably manufactured to a thickness of 40 μm so that the thickness of the Si melt layer is 40 μm. For example, the thickness of the Si melt layer is in the range of 25 to 200 μm. Moreover, you may manufacture in the range of thickness 25-200 micrometers.

  The MS concentration of the MSE epi film was measured by changing the MSE growth temperature from 1600 to 1900 ° C. under the member arrangement of FIG. 1 and the above experimental conditions.

  FIG. 2 assumes that the MSE growth temperature and the MSE epi film and the N concentration of the MSE epi film grown at around 1700 ° C. will take the minimum values. Furthermore, when the experimental results at 1650 ° C. and 1750 ° C. are compared, the results at 1650 ° C. show the N concentration of the MSE epi film and the N concentration of the raw material compared to 1750 ° C. From this figure, it can be seen that at 1700 ° C., the N concentration of the MSE epi film decreases. Since the degree decreased compared with the N concentration of the SiC raw material substrate 1 before the experiment, the minimum value is estimated to be between 1650 ° C. and 1700 ° C.

From the results of this experiment, it was found that the N concentration of the MSE epi film can be made lower than the N concentration of the SiC source substrate by optimizing the MSE growth temperature.

DESCRIPTION OF SYMBOLS 1 Polycrystalline SiC raw material substrate 2 Si solution 3 MSE epi film 4 SiC single crystal substrate 5 Nitrogen impurity 6 SiC susceptor 7 Carbon spacer 8 SiC spacer for Si melt layer 9 Si substrate 10 SiC weight

Claims (4)

  In the single crystal silicon carbide epitaxial growth, the MSE method is characterized in that the nitrogen impurity mixed in the MSE epi film is reduced in concentration by optimizing the growth temperature.   In single crystal silicon carbide epitaxial growth, when the thickness of the Si melt layer is 25 to 200 μm, the growth temperature is optimized between 1600 and 1850 ° C., so that nitrogen impurities mixed in the MSE epi film can be reduced to 1E + 16 (atoms / cc The MSE method is characterized in that the concentration is lower than that in (1).   In single crystal silicon carbide epitaxial growth, an epitaxial film manufactured based on an MSE method characterized in that a nitrogen impurity mixed in the MSE epi film is reduced in concentration by optimizing the growth temperature.   In single crystal silicon carbide epitaxial growth, when the thickness of the Si melt layer is 25 to 200 μm, the growth temperature is optimized between 1600 and 1850 ° C., so that nitrogen impurities mixed in the MSE epi film can be reduced to 1E + 16 (atoms / cc An epitaxial film manufactured on the basis of the MSE method, characterized in that the concentration is lower than that of (1).

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