JP4419409B2 - CVD epitaxial growth method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of epitaxially growing silicon carbide using vapor phase chemical vapor deposition (CVD), and more particularly, CVD epitaxial growth that can reduce fluctuations in growth film thickness even when a cold wall method is used. Regarding the method.
[0002]
[Prior art]
With the remarkable performance improvement of power semiconductor elements in recent years, the application range of power electronics technology has been greatly expanded. In the power field where development of DC power transmission systems, frequency converters, high-speed power control devices, etc. is desired, power conversion capacity using power electronics technology is expected to increase more and more, and power semiconductors that can be the heart of power electronics There is a demand for further higher efficiency, higher voltage, and larger capacity of the device.
[0003]
Silicon carbide (SiC) has superior dielectric breakdown field strength and thermal conductivity compared to silicon single crystal, and has relatively large electron mobility, so performance can be improved compared to Si-based semiconductor devices. It is expected as a semiconductor material. In addition, SiC is thermally and chemically stable, has excellent radiation resistance, and there are a number of polytypes, some of which enable light emission in the visible region. It is a material that has received much attention in that
[0004]
SiC is difficult to thermally diffuse impurities, and the ion implantation technique is not sufficiently established. Therefore, as a carrier concentration control method, vapor phase doping in which a dopant is added during epitaxial growth is effective. As such a vapor phase doping method, vapor phase chemical vapor deposition (CVD) is generally used. The CVD method is useful in that it can control the impurity concentration, the pn junction interface, etc., and can be used for a large substrate.
[0005]
Step-controlled epitaxy is a technology that intentionally introduces an off-angle of several degrees into the SiC substrate surface to increase the atomic step density on the substrate surface, and performs crystal growth by step flow by lateral growth of the steps. . Such a technique is preferable in that a single crystal of the same polytype as that of the substrate grows in SiC having a large number of polytypes because information on the period of atomic arrangement is given from the step. Further, it is preferable in that the temperature at the time of growth can be lowered as compared with the growth of a SiC single crystal by a conventional CVD method, and a quality sufficient for application to a device can be obtained.
[0006]
The following Non-Patent Document 1 discloses a technique in which SiC is homoepitaxially grown by a cold wall method on a SiC substrate surface having a predetermined off angle inclined from the (0001) plane by using step control epitaxy. ing. FIG. 4 is a schematic view of a CVD crystal growth apparatus used in Non-Patent Document 1. In FIG. 4, the CVD crystal growth apparatus includes a cylinder 1 containing a source gas and a dopant gas, a mass flow controller 2 for controlling the flow rate of the gas supplied from the cylinder 1, and a gas controlled by the mass flow controller 2 By being sent out, a crystal growth furnace 3 for performing a CVD crystal growth reaction and an exhaust gas cleaning system 4 are included.
[0007]
The crystal growth furnace 3 is a cold wall system in which the wall 5 is cooled by flowing water in the direction of arrow X, and a substrate 7 is installed on a susceptor 6 in the crystal growth furnace 3. The wall 5 is attached with a heating device 8. Moreover, the hydrogen gas refiner 9 is attached to the cylinder containing hydrogen gas in the cylinder 1, and the hydrogen gas supplied by the hydrogen gas refiner 9 is purified.
[0008]
In the CVD crystal growth apparatus, the gas supplied from the cylinder 1 is sent to the crystal growth furnace 3 with the flow rate controlled by the mass flow controller 2, and CVD epitaxial growth is performed in the crystal growth furnace 3. The gas that has passed through the crystal growth furnace 3 is released in the direction of arrow Y through the exhaust gas cleaning system 4.
[0009]
[Non-Patent Document 1]
Phys.stat.sol. (B) 202, 247 (1997)
[0010]
[Problems to be solved by the invention]
However, in the CVD crystal growth apparatus of Non-Patent Document 1, in the cold wall method in which the wall 5 of the film forming chamber is cooled, the temperature of the susceptor 6 is decreased in the surroundings. As a result, a temperature difference occurs, and as a result, a difference in height occurs in the variation of the growth film thickness. Therefore, it may cause variation in characteristics when used as a semiconductor device.
[0011]
The present invention has been made to solve the above-described problems of the prior art, and in the CVD epitaxial growth method, even when there is a difference in the temperature around the susceptor when the cold wall method is used, variation in film thickness distribution is reduced. It is an object of the present invention to provide a method capable of homoepitaxial growth. The present invention also provides a method for reducing variations in impurity concentration distribution in a homoepitaxially grown film.
[0012]
[Means for Solving the Problems]
The present invention employs a CVD method on a 4H-SiC substrate surface having an off angle in the range of 7 ° to 9 ° from the (0001) plane to the (11-20) plane direction by a cold wall method. In the method of homoepitaxially growing , the crystal growth rate at a substrate temperature within a range of 1400 ° C. to 1800 ° C. in a ratio of carbon atoms to silicon atoms (C / Si) existing in a source gas within a range of 2 to 4 wherein the growing at 2 [mu] m / hr or more, to provide a CVD epitaxial growth method.
[0013]
According to the present invention, even when there is a temperature drop around the susceptor, which can occur in a CVD epitaxial growth method using a cold wall method, variations in film thickness can be reduced.
[0014]
Preferably, the deviation from the average of the crystal growth film thickness is within a range of −10% to + 10% in any region of the growth surface. Thereby, a good semiconductor material can be obtained.
[0016]
Preferably, nitrogen gas is used as a dopant, and the concentration of the nitrogen gas is within a range of 1 × 10 ⁻⁷ mol / cm ³ to 1 × 10 ⁻¹² mol / cm ³ per unit volume of the crystal growth reactor. Growing up. Further, diborane gas is used as a dopant, and crystal growth is performed with the concentration of the diborane gas within a range of 1 × 10 ⁻¹¹ mol / cm ³ to 1 × 10 ⁻¹⁶ mol / cm ³ per unit volume of the crystal growth reactor. It is preferable. Thereby, the variation in the impurity concentration of the crystal growth film can be reduced.
[0017]
In the present invention, by setting the ratio of carbon atoms to silicon atoms (Si / C) in the source gas in the range of 2 to 4 , the variation in film thickness can be reduced, and the impurity concentration can be made uniform. it can.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a CVD epitaxial growth method characterized in that a silicon carbide is homoepitaxially grown by a cold wall method using CVD (vapor phase chemical vapor deposition), and the crystal growth rate is grown at 2 μm / hour or more. It is to provide. If it is less than 2 μm / hour, the growth species move by the crown motion near the center of the substrate and cannot be ignored as compared with the growth rate, and the substrate edge becomes thick. This is because there arises a problem that the film thickness varies due to this.
[0019]
In the present invention, in order to determine the crystal growth rate, as a non-destructive method that does not destroy the formed crystal film, the mass conversion obtained from the mass difference before and after crystal growth, the length of a specific crystal defect, and the epitaxial growth layer An optical method using an interference phenomenon between the light reflected on the outermost surface and the light reflected on the interface between the epitaxial growth layer and the substrate can be used. In this optical method, the light at the interface between the epitaxial growth layer and the substrate produces a phase difference with respect to the light reflected on the surface of the epitaxial growth layer according to the wavelength and film thickness, and thus is obtained by measuring the intensity of the reflected light. be able to. In addition, as a destructive method, there is a method of performing SIMS analysis by destroying the formed epitaxial growth layer.
[0020]
In the present invention, by setting the crystal growth rate to 2 μm / hour or more, the crystal growth film thickness varies from −10% to + 10% from the average of the crystal growth film thickness in any region of the growth surface. %, And the height difference in the grown film thickness can be reduced.
[0021]
Here, the deviation from the average of the grown film thickness can be determined by comparing the average value of the film thickness with the film thickness at each location on the substrate. The average value of the film thickness can be obtained from a mass difference before and after crystal growth, and the film thickness at each location on the substrate can be measured using SIMS, C-V, FTIR, or the like.
[0022]
The CVD epitaxial growth method of the present invention can solve the problems related to the film thickness when crystals are grown by the cold wall method. When CVD epitaxial growth is performed using the cold wall method, the susceptor ambient temperature decreases compared to the substrate center temperature, and the temperature of the substrate placed on the susceptor also decreases compared to the substrate center temperature. ing. Due to the difference in temperature distribution on the substrate, a large difference in height also occurs in the film thickness variation of the crystal growth.
[0023]
This difference in film thickness is considered to be due to the crown motion of the crystal growth seed. That is, it is considered that when there is a difference in temperature on the substrate, the growth species move from the high temperature portion to the low temperature portion by the crown motion. Therefore, the slower the growth rate of the film thickness, the longer the time during which the growth species can perform the crown movement, and the greater the difference in film thickness.
[0024]
The present inventors have found that the difference in height of the formed film thickness can be reduced by suppressing the time during which crown movement is possible by setting the crystal growth rate to 2 μm / hour or more. That is, in the method described in Non-Patent Document 1, the formed film thickness has shifted from the average of the grown film thickness in the range of −90% to + 14%. Is used, the deviation from the average growth film thickness can be reduced to -10% to + 10%.
[0025]
In general, there is a correlation between the crystal growth rate and the flow rate of the source gas. In the present invention, as shown in FIG. 5, the crystal growth rate increases in proportion to the flow rate of SiH ₄ , but the crystal growth rate becomes constant when saturated at a flow rate of SiH ₄ above a certain level. . FIG. 5 is a graph showing the relationship between the crystal growth rate and the SiH ₄ flow rate at a crystal growth temperature of 1500 ° C. in the present invention (Silicon Carbide and Related Materials 2001, item 184).
[0026]
In the present invention, it is preferable to use a 6H—SiC substrate surface having an off angle in the range of 3 ° to 5 ° in the (11-20) plane direction from the (0001) plane of the SiC substrate. Further, it is preferable to use a 4H—SiC substrate surface having an off angle in the range of 7 ° to 9 ° in the (11-20) plane direction from the (0001) plane.
[0027]
This is because homoepitaxial growth by step flow is possible by using the substrate. By growing the crystal by the step flow, information on the period of atomic arrangement from the step is given, so that a single crystal of the same polytype as the substrate grows. Therefore, SiC having a large number of polytypes is preferable in that the same type of crystal growth as that of the substrate is performed. Further, it is preferable in that the temperature during growth can be lowered as compared with the case where no off-angle is introduced. However, the present invention is not limited to the substrate, and is not limited to the range of the off angle as long as crystal growth by a step flow is possible. Further, in the present invention, the crystal growth is not limited to the crystal growth by the step flow, and the crystal growth by the twin crystal may be performed using the just substrate that does not introduce the off angle.
[0028]
In the present invention, when nitrogen gas is used as the dopant in order to reduce the variation in the dopant concentration of the formed epitaxial growth film, the concentration of the nitrogen gas is set to 1 × 10 ⁻⁷ per unit volume of the crystal growth reactor. Crystal growth is preferably performed within a range of mol / cm ³ to 1 × 10 ⁻¹² mol / cm ³ . This is because if it is less than 1 × 10 ⁻¹² mol / cm ³ , controllability is lost because it is comparable to the background nitrogen concentration, and if it exceeds 1 × 10 ⁻⁷ , a large amount of nitrogen is contained in the crystal. It is because it is taken in and crystallinity falls. Crystal growth is preferably performed within a range of 10 ⁻⁸ to 10 ⁻¹¹ mol / cm ³ , and more preferably within a range of 10 ⁻⁹ to 10 ⁻¹⁰ mol / cm ³ .
[0029]
In the present invention, when diborane gas is used as the dopant, the concentration of the diborane gas is in the range of 1 × 10 ⁻¹¹ mol / cm ³ to 1 × 10 ⁻¹⁶ mol / cm ³ per unit volume of the crystal growth reactor. It is preferable to carry out crystal growth inside. This is because if it is less than 1 × 10 ⁻¹⁶ mol / cm ³ , controllability is lost because it is comparable to the background boron concentration, and if it exceeds 1 × 10 ⁻¹¹ , a large amount of boron is taken in. This is because crystallinity is lowered. Preferably, it is in the range of 1 × 10 ⁻¹¹ mol / cm ³ to 1 × 10 ⁻¹⁴ mol / cm ³ , more preferably 1 × 10 ⁻¹¹ mol / cm ³ to 1 × 10 ⁻¹² mol / cm ^3. It is preferable that the crystal grow within this range.
[0030]
In the present invention, the variation in impurity concentration in the formed crystal can be confirmed by measuring a plurality of locations in the crystal growth surface by CV or SIMS.
[0031]
Moreover, in this invention, it is preferable that ratio (C / Si) of the carbon atom with respect to the silicon atom which exists in source gas exists in the range of 1-6. When C / Si is less than 1, the crystal growth rate decreases, which is not preferable. Moreover, when C / Si exceeds 6, it is not preferable because crystallinity is lowered. More preferably, C / Si is 2-4.
[0032]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.
[0033]
【Example】
Example 1
The procedure for performing the CVD epitaxial growth of the present invention will be described below. First, before the growth, baking was performed by heating the susceptor for 10 minutes at a temperature of 1500 ° C. in a hydrogen gas atmosphere. Here, the hydrogen gas used in this example is hydrogen gas purified through a hydrogen purifier using a silver palladium alloy film. Next, a 4H—SiC wafer having an off angle of 8 ° from the (0001) plane to the (11-20) plane direction, which was prepared by a sublimation method, was set on the susceptor, and the susceptor was placed in a growth furnace together with the susceptor holder. Evacuation was performed.
[0034]
Thereafter, the exhaust was stopped and hydrogen gas was introduced to bring it to atmospheric pressure. The relationship between the temperature profile and the gas introduction amount at this time is shown in FIG. In FIG. 1, the horizontal axis is time, and the vertical axis is temperature. In this example, after reaching 1300 ° C. in hydrogen gas, hydrogen chloride gas was allowed to flow at that temperature for 10 minutes. Examples of the flow rates of hydrogen gas and hydrogen chloride gas are 1 mL / min and 0.03 mL / min, respectively.
[0035]
After 10 minutes, the temperature was raised to 1500 ° C., hydrogen chloride gas was stopped, and epitaxial growth was started. The source gases used for the epitaxial growth were SiH ₄ (1.0% H ₂ dilution) and C ₃ H ₈ (1.0% H ₂ dilution), and the flow rates of the source gases were 50 sccm and 33 sccm, respectively. . Moreover, hydrogen gas was flowed at a flow rate of 3 slm. The crystal growth rate at this time was 3 μm / hour.
[0036]
(Example 2)
In Example 1 above, in order to perform n-type doping, nitrogen gas (0.5% in hydrogen) as a doping material was further flowed at a flow rate of 6 sccm. At this time, the concentration of nitrogen gas per unit volume in the crystal growth furnace was 4.3 × 10 ⁻¹⁰ mol / cm ³ . The crystal growth rate at this time was 3 μm / hour. When a plurality of locations in the crystal growth plane were measured by SIMS, there was almost no variation in impurity concentration.
[0037]
(Example 3)
In Example 1, in order to perform p-type doping, diborane gas (5 ppm in hydrogen) as a doping material was further added at a flow rate of 40 sccm. In Example 3, the flow rate of C ₃ H ₈ was 66 sccm. At this time, the concentration of diborane gas per unit volume in the crystal growth furnace was 2.8 × 10 ⁻¹² mol / cm ³ . The crystal growth rate at this time was 2.5 μm / hour. When a plurality of locations in the crystal growth plane were measured by SIMS, there was almost no variation in impurity concentration.
[0038]
In the said Examples 1-3, the result of having analyzed the film thickness distribution of the epitaxial film crystal-grown on the SiC substrate using SIMS is shown in FIG. The deviation from the average of the growth film thickness on the surface is in the range of −10% to + 10% in any region of the substrate surface, which indicates that the surface morphology is good.
[0039]
(Comparative Example 1)
Except that the flow rate of SiH ₄ was set to 15 sccm and the flow rate of C ₃ H ₈ was changed to 10 sccm, epitaxial growth was performed using the same procedure as in Example 1 above. The crystal growth rate at this time was 1.2 μm / hour.
[0040]
(Comparative Example 2)
CVD epitaxial growth was performed using the same procedure as in Example 2 except that nitrogen gas (100 ppm in hydrogen) was used and the flow rate of the nitrogen gas was set to 100 sccm. At this time, the concentration of nitrogen gas per unit volume in the crystal growth furnace was 1.4 × 10 ⁻¹⁰ mol / cm ³ . The crystal growth rate at this time was 1.2 μm / hour.
[0041]
(Comparative Example 3)
CVD epitaxial growth was performed using the same procedure as in Example 3 except that diborane gas (5 ppm in hydrogen) was used and the flow rate of the nitrogen gas was 100 sccm. At this time, the concentration of diborane gas per unit volume in the crystal growth furnace was 7.1 × 10 ⁻¹² mol / cm ³ . The crystal growth rate at this time was 1.2 μm / hour.
[0042]
FIG. 3 shows the result of analyzing the film thickness distribution of the obtained epitaxial films in SIMS 1 to 3 using SIMS. The deviation from the average of the growth film thickness on the surface is in a wide range of −90% to + 14%, and the film thickness variation is large.
[0043]
It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
[0044]
【The invention's effect】
According to the CVD epitaxial growth method of the present invention, even when the cold wall method is used, the deviation of the growth film thickness from the average can be within the range of −10% to + 10%, and the surface morphology is improved. can do. Also, the variation in impurity concentration in the formed crystal film thickness is good.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between a temperature profile and the amount of gas introduced during epitaxial growth.
FIG. 2 is a schematic view showing the result of analyzing the surface of the grown film thickness formed using the CVD epitaxial growth method of the present invention using SIMS.
FIG. 3 is a schematic view showing the result of analyzing the surface of the grown film thickness formed using a conventional CVD epitaxial growth method using SIMS.
FIG. 4 is a schematic view of an apparatus for performing CVD epitaxial growth using a cold wall method.
FIG. 5 is a graph showing the relationship between the crystal growth rate and the SiH ₄ flow rate at a crystal growth temperature of 1500 ° C.
[Explanation of symbols]
1 cylinder, 2 mass flow controller, 3 crystal growth furnace, 4 exhaust gas cleaning system, 5 walls, 6 susceptor, 7 substrate, 8 heating device, 9 hydrogen gas purifier.

Claims (3)

Using CVD, in a cold wall type, (0001) Oite on 4H-SiC substrate surface having off-angles in the range from plane (11-20) plane direction of 7 ° to 9 °, SiC homo In the epitaxial growth method, the ratio of carbon atoms to silicon atoms in the source gas (C / Si) is in the range of 2 to 4, and the crystal growth rate is 2 μm / at a temperature in the range of 1400 ° C. to 1800 ° C. grown over time, deviations from the average of the crystal growth film thickness, the device fabrication region, characterized in der Rukoto the range of -10% ~ + 10%, CVD epitaxial growth method. Nitrogen gas is used as a dopant, and the concentration of the nitrogen gas is within a range of 1 × 10 ⁻⁷ mol / cm ³ to 1 × 10 ⁻¹² mol / cm ³ per unit volume of the crystal growth reactor. The CVD epitaxial growth method according to claim 1 , wherein: Using diborane gas as a dopant, the concentration of the diborane gas is within a range of 1 × 10 ⁻¹¹ mol / cm ³ to 1 × 10 ⁻¹⁶ mol / cm ³ per unit volume of the crystal growth reactor. The CVD epitaxial growth method according to claim 1, wherein the CVD epitaxial growth method is characterized.

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