JP2004253751A - Method of cvd epitaxial growth - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of homoepitaxial growth capable of reducing the dispersion in the film-thickness distribution even in a case where the temperature differs between the circumferential area and the center of the susceptor, when a cold-wall method is used. <P>SOLUTION: In the method of homoepitaxial growth of silicon carbide (SiC) using a cold-wall CVD technique, the growth is carried out at a crystal-growth rate of 2 μm/hour or higher. The divergence from the average of the grown crystal thickness is within the range of -10% to +10% at every portion of the growth plane. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for epitaxially growing silicon carbide using a vapor-phase chemical vapor deposition (CVD) method, and more particularly, to a CVD epitaxial growth method capable of reducing a variation in a grown film thickness even when a cold wall method is used. About the method.
[0002]
[Prior art]
With the remarkable improvement in performance of power semiconductor devices 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 controllers, etc. is desired, the 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 higher efficiency, higher voltage, and higher capacity of the device.
[0003]
Silicon carbide (SiC) has better breakdown field strength and thermal conductivity than silicon single crystal and relatively high electron mobility, so it can improve performance compared to Si-based semiconductor devices. Is expected as a semiconductor material. In addition, SiC is thermally and chemically stable, has excellent radiation resistance, and has a large number of polytypes, some of which are capable of emitting light in the visible region. It is a material that has received a great deal of attention in that it also has
[0004]
Since the thermal diffusion of impurities is difficult for SiC and the ion implantation technique is not sufficiently established, vapor phase doping in which a dopant is added during epitaxial growth is effective as a carrier concentration control method. As a technique of such a vapor phase doping, a 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, and the like, and can be used for a large substrate.
[0005]
Step control epitaxy is a technique for intentionally introducing an off angle of several degrees to the surface of a SiC substrate to increase the atomic step density on the surface of the substrate, and performing crystal growth by a step flow based on lateral growth of steps. . Such a technique is preferable in that a single crystal of the same polytype as the substrate grows in SiC having a large number of polytypes, since information on the period of the atomic arrangement is given from the steps. Further, it is preferable in that the temperature during the growth can be lowered as compared with the growth of the SiC single crystal by the conventional CVD method, and the quality sufficient for application to the device can be obtained.
[0006]
Non-Patent Document 1 below discloses a technique in which SiC is homoepitaxially grown on a SiC substrate surface having a predetermined off angle inclined from a (0001) plane by a cold wall method using step control epitaxy. ing. FIG. 4 is a schematic diagram of a CVD crystal growth apparatus used in the above-mentioned 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 a flow rate of a gas supplied from the cylinder 1, and a gas controlled by the mass flow controller 2. It includes a crystal growth furnace 3 that is sent out to perform a CVD crystal growth reaction, and an exhaust gas cleaning system 4.
[0007]
The crystal growth furnace 3 is of a cold wall type in which the wall 5 is cooled by flowing water in the direction of arrow X, and a substrate 7 is set on a susceptor 6 in the crystal growth furnace 3. The wall 5 is provided with a heating device 8. Further, a hydrogen gas purifier 9 is attached to a cylinder containing hydrogen gas in the cylinder 1, and the hydrogen gas supplied by the hydrogen gas purifier 9 is to be purified.
[0008]
In the CVD crystal growth apparatus, the gas supplied from the cylinder 1 is sent to the crystal growth furnace 3 at a controlled flow rate by the mass flow controller 2, and the CVD epitaxial growth is performed in the crystal growth furnace 3. The gas that has passed through the crystal growth furnace 3 is discharged through the exhaust gas cleaning system 4 in the direction of arrow Y.
[0009]
[Non-patent document 1]
Phys. stat. sol. (B) p. 202, 247 (1997)
[0010]
[Problems to be solved by the invention]
However, in the CVD crystal growth apparatus described in 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 decreases at the periphery, so that the center and the end of the substrate 7 are Causes a temperature difference, and as a result, a variation in the thickness of the grown film causes a height difference. Therefore, when used as a semiconductor device, it may cause variations in characteristics.
[0011]
The present invention has been made in order to solve the above-mentioned problems of the prior art, and reduces the variation in the film thickness distribution even when there is a difference in the temperature around the susceptor when using the cold wall method in the CVD epitaxial growth method. To provide a method capable of performing 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 provides a CVD epitaxial growth method in which a silicon carbide (SiC) is homoepitaxially grown by a cold wall method using CVD, wherein the crystal growth rate is 2 μm / hour or more.
[0013]
According to the present invention, even when there is a temperature drop around the susceptor, which can occur in the CVD epitaxial growth method using the cold wall method, the variation in the film thickness can be reduced.
[0014]
Preferably, the deviation of the crystal growth film thickness from the average is in the range of −10% to + 10% in any region of the growth surface. Thereby, a favorable semiconductor material can be obtained.
[0015]
Preferably, on a 6H-SiC substrate surface having an off angle within a range of 3 ° to 5 ° from a (0001) plane to a (11-20) plane, or from a (0001) plane to a (11-20) plane. On a 4H-SiC substrate surface having an off angle in the range of 7 ° to 9 °, a crystal is grown at a substrate temperature in the range of 1400 ° C to 1800 ° C. Thereby, epitaxial growth by step control can be promoted.
[0016]
Preferably, a nitrogen gas is used as a dopant, and the concentration of the nitrogen gas is set 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. Perform growth. Further, crystal growth is performed by using diborane gas as a dopant and setting 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 reaction furnace. Is preferred. As a result, variations in the impurity concentration of the crystal growth film can be reduced.
[0017]
Preferably, the ratio of carbon atoms to silicon atoms present in the source gas is in the range of 1 to 6. As a result, variations in film thickness can be reduced, and the impurity concentration can be made uniform.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention provides a method for homoepitaxially growing silicon carbide by a cold wall method using CVD (gas phase chemical vapor deposition), wherein the method comprises growing the crystal at a crystal growth rate of 2 μm / hour or more. To provide. If it is less than 2 μm / hour, near the center of the substrate, the grown species move by the crown motion to a degree that cannot be ignored compared to the growth rate, and the substrate edge becomes thick. This causes a problem that the film thickness varies.
[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, such as mass conversion obtained from the mass difference before and after crystal growth, the length of a specific crystal defect, the epitaxial growth layer An optical method utilizing an interference phenomenon between light reflected at the outermost surface and light reflected at the interface between the epitaxial growth layer and the substrate can be used. In the optical method, the light at the interface between the epitaxial growth layer and the substrate generates a phase difference with respect to the light reflected on the surface of the epitaxial growth layer according to the wavelength and the film thickness, and thus is determined by measuring the intensity of the reflected light. be able to. Further, as a destructive method, there is a method of breaking down the formed epitaxial growth layer and performing SIMS analysis.
[0020]
In the present invention, by setting the crystal growth rate to 2 μm / hour or more, the deviation of the crystal growth film thickness from the average in any region of the growth surface is −10% to + 10%. %, And the difference in height of the grown film thickness can be reduced.
[0021]
Here, the deviation of the grown film thickness from the average 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 the mass difference before and after crystal growth, and the film thickness at each location on the substrate can be measured using SIMS, CV, FTIR, or the like.
[0022]
ADVANTAGE OF THE INVENTION The CVD epitaxial growth method of this invention can solve the defect regarding the film thickness when crystal-growing by the cold wall method. When performing the CVD epitaxial growth using the cold wall method, the ambient temperature of the susceptor is lower than the central temperature of the substrate, and the temperature of the substrate installed on the susceptor is also lower than the central temperature of the substrate. ing. Due to such a difference in the temperature distribution on the substrate, a large difference in the level of the thickness of the crystal grown also occurs.
[0023]
It is considered that this difference in the film thickness is due to the crown motion of the crystal growth species. That is, it is considered that if there is a difference in temperature on the substrate, the grown species moves from a high temperature portion to a low temperature portion by crown motion. Therefore, the slower the growth rate of the film thickness, the longer the time during which the grown species can perform the crown motion, and the greater the difference in film thickness.
[0024]
The present inventors have found that by setting the crystal growth rate to 2 μm / hour or more, the time during which crown movement is possible can be suppressed, and the height difference in the formed film thickness can be reduced. That is, in the method described in Non-Patent Document 1, the formed film has a deviation in the range of -90% to + 14% from the average of the grown film thickness. Is used, the deviation from the average of the grown 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, the crystal growth rate increases in proportion to the flow rate of SiH ₄ as shown in FIG. 5, but saturates at a flow rate of SiH ₄ that is equal to or higher than a certain value, so that the crystal growth rate becomes constant. . Here, 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. (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 within a range of 3 ° to 5 ° from the (0001) plane to the (11-20) plane direction 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 ° from the (0001) plane to the (11-20) plane.
[0027]
This is because the use of the substrate enables homoepitaxial growth by a step flow. Since the crystal is grown by the step flow, information on the period of the atomic arrangement from the step is given, so that the same polytype single crystal as the substrate grows. Therefore, SiC having a large number of polytypes is preferable in that crystal growth of the same type 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 above-described substrate, and is not limited to the range of the off-angle as long as crystal growth by a step flow is possible. In the present invention, the crystal growth is not limited to the crystal growth by the step flow, and the crystal growth by twinning may be performed using a just substrate that does not introduce an off-angle.
[0028]
In the present invention, when nitrogen gas is used as a dopant in order to reduce variation in the dopant concentration of the formed epitaxially grown film, the concentration of the nitrogen gas is set to 1 × 10 ⁻⁷ per unit volume of the crystal growth reactor. It is preferable to carry out crystal growth within the range of mol / cm ³ to 1 × 10 ⁻¹² mol / cm ³ . If the concentration is less than 1 × 10 ⁻¹² mol / cm ³ , the controllability is lost because it is almost the same as the background nitrogen concentration. If it exceeds 1 × 10 ⁻⁷ , a large amount of nitrogen is contained in the crystal. This is because the crystallinity is reduced by being incorporated. Preferably, the crystal is grown within the range of 10 ⁻⁸ to 10 ⁻¹¹ mol / cm ³ , more preferably within the range of 10 ⁻⁹ to 10 ⁻¹⁰ mol / cm ³ .
[0029]
Further, in the present invention, when diborane gas is used as a 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 perform crystal growth inside. If the concentration is less than 1 × 10 ⁻¹⁶ mol / cm ³ , the controllability is lost because it is almost the same as the background boron concentration, and if it exceeds 1 × 10 ⁻¹¹ , a large amount of boron is incorporated. This is because crystallinity is reduced. Preferably, it is in the range of 1 × 10 ⁻¹¹ mol / cm ³ to 1 × 10 ⁻¹⁴ mol / cm ³ , and more preferably, 1 × 10 ⁻¹¹ mol / cm ³ to 1 × 10 ⁻¹² mol / cm ^3. It is preferable that the crystal grows within the range.
[0030]
In the present invention, the variation in the impurity concentration in the formed crystal can be confirmed by measuring a plurality of locations in the crystal growth plane by CV or SIMS.
[0031]
In the present invention, the ratio of carbon atoms to silicon atoms (C / Si) present in the source gas is preferably in the range of 1 to 6. When C / Si is less than 1, the crystal growth rate is undesirably reduced. Further, when C / Si exceeds 6, it is not preferable because crystallinity is reduced. More preferably, C / Si is 2-4.
[0032]
Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.
[0033]
【Example】
(Example 1)
The procedure for performing the CVD epitaxial growth of the present invention will be described below. First, before growing, the susceptor was baked in a hydrogen gas atmosphere at a temperature of 1500 ° C. for 10 minutes. Here, the hydrogen gas used in this embodiment 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, which is manufactured by a sublimation method, is set on a susceptor, and the susceptor is put into a growth furnace together with a susceptor holder. Evacuation was performed.
[0034]
Thereafter, the evacuation was stopped, and hydrogen gas was introduced to bring the pressure to atmospheric pressure. FIG. 1 shows the relationship between the temperature profile and the gas introduction amount at this time. 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 flowed at that temperature for 10 minutes. Examples of the flow rates of the hydrogen gas and the hydrogen chloride gas are 1 mL / min and 0.03 mL / min, respectively.
[0035]
After 10 minutes, the temperature was raised to 1500 ° C., the hydrogen chloride gas was stopped, and epitaxial growth was started. The source gases used in 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. . Further, hydrogen gas was flowed at a flow rate of 3 slm. At this time, the crystal growth rate was 3 μm / hour.
[0036]
(Example 2)
In Example 1, in order to perform n-type doping, nitrogen gas (0.5% in hydrogen) as a doping material was further supplied 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 . At this time, the crystal growth rate was 3 μm / hour. SIMS measurements at a plurality of locations within the crystal growth plane showed that there was almost no variation in the 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 set to 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 . At this time, the crystal growth rate was 2.5 μm / hour. SIMS measurements at a plurality of locations within the crystal growth plane showed that there was almost no variation in the impurity concentration.
[0038]
FIG. 2 shows the results of analyzing the film thickness distribution of the epitaxial film grown on the SiC substrate in the above Examples 1 to 3 using SIMS. The deviation from the average of the thickness of the grown film on the surface is in the range of −10% to + 10% in any region of the substrate surface, which indicates that the surface has good surface morphology.
[0039]
(Comparative Example 1)
Epitaxial growth was performed using the same procedure as in Example 1 except that the flow rate of SiH ₄ was 15 sccm and the flow rate of C ₃ H ₈ was 10 sccm. 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 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 . At this time, the crystal growth rate was 1.2 μm / hour.
[0042]
FIG. 3 shows the results of analyzing the thickness distribution of the obtained epitaxial films in Comparative Examples 1 to 3 using SIMS. The deviation from the average of the thickness of the grown film on the surface is wide in the range of -90% to + 14%, and the variation of the film thickness is large.
[0043]
The embodiments and examples disclosed this time are to be considered in all respects as illustrative and not restrictive. 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 grown film thickness from the average can be in the range of -10% to + 10%, and the morphology of the surface can be improved. can do. Also, the variation in the impurity concentration in the formed crystal film thickness is good.
[Brief description of the drawings]
FIG. 1 is a graph showing a relationship between a temperature profile and a gas introduction amount during epitaxial growth.
FIG. 2 is a schematic view showing the result of analyzing the surface of a grown film thickness formed by using the CVD epitaxial growth method of the present invention by using SIMS.
FIG. 3 is a schematic diagram showing a result of analyzing, by using SIMS, a surface of a growth film thickness formed by using a conventional CVD epitaxial growth method.
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 a relationship between a crystal growth rate and a 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 wall, 6 susceptor, 7 substrate, 8 heating device, 9 hydrogen gas purifier.

Claims (7)

A method for growing SiC homoepitaxially by a cold wall method using CVD, wherein the crystal is grown at a crystal growth rate of 2 μm / hour or more. 2. The CVD epitaxial growth method according to claim 1, wherein the deviation of the crystal growth film thickness from the average is in the range of -10% to + 10% in any region of the growth surface. Crystal growth at a substrate temperature in the range of 1400 ° C. to 1800 ° C. on a 6H—SiC substrate surface having an off angle in the range of 3 ° to 5 ° from the (0001) plane to the (11-20) plane. The CVD epitaxial growth method according to claim 1, wherein: Crystal growth at a substrate temperature in a range of 1400 ° C. to 1800 ° C. on a 4H—SiC substrate surface having an off angle in a range of 7 ° to 9 ° from a (0001) plane to a (11-20) plane. The CVD epitaxial growth method according to claim 1, wherein: Crystal growth is performed by using nitrogen gas as a dopant and setting the concentration of the nitrogen gas 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 any one of claims 1 to 4, wherein: Using a diborane gas as a dopant, and performing the crystal growth 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. The CVD epitaxial growth method according to claim 1, wherein: The CVD epitaxial growth method according to any one of claims 1 to 6, wherein the ratio of carbon atoms to silicon atoms present in the source gas is in the range of 1 to 6.

Images