JP2017100911A - Method for manufacturing epitaxial silicon carbide single crystal wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an epitaxial SiC single crystal wafer including a high quality SiC single crystal thin film excellent in in-plane uniformity of doping density on a SiC single crystal substrate.SOLUTION: The method for manufacturing an epitaxial SiC single crystal wafer comprises: passing a silicon and carbon based material gas having 1.0 or more and 2.0 or less of an atomic number ratio of carbon to silicon (a C/Si ratio), a doping gas and a carrier gas on a SiC single crystal substrate in an epitaxial growth furnace to epitaxially grow SiC at a growth temperature of 1550°C or more and 1700°C or less by a thermal CVD method. The Sic is epitaxially grown by controlling growth conditions of the epitaxial growth so that the product of a growth furnace internal pressure P(kPa) during the epitaxial growth and a growth rate R(μm/hr.) of the obtained epitaxial layer is 45 or more and 100 or less.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for manufacturing an epitaxial silicon carbide single crystal wafer.

  Silicon carbide (hereinafter referred to as SiC) is attracting attention as an environmentally resistant semiconductor material because it is excellent in heat resistance and mechanical strength and is physically and chemically stable. In recent years, there has been an increasing demand for epitaxial SiC single crystal wafers as substrates for high frequency, high voltage electronic devices.

  When manufacturing power devices, high-frequency devices, etc. using an epitaxial SiC single crystal wafer (hereinafter sometimes referred to simply as a SiC wafer), a thermal CVD method (thermochemical vapor deposition method) is usually performed on a SiC single crystal substrate. It is common to epitaxially grow a SiC thin film using a method called) or to implant a dopant directly by ion implantation, but in the latter case, annealing at a high temperature is required after implantation. Thin film formation by epitaxial growth is frequently used.

  When a device is formed on an epitaxial SiC single crystal film (hereinafter sometimes referred to simply as “epitaxial film”), in order to stably manufacture the device as designed, the thickness and doping density of the epitaxial film, In-plane uniformity of the doping density becomes important. In particular, in recent years, SiC wafers have become larger in diameter, and the area of devices has also increased. In order to improve device yield, the uniformity of the doping density within the wafer surface has become more important. Specifically, the in-plane uniformity of the doping density of epitaxial films on 4-inch wafers, which is the current mainstream, needs to be stably 5-10% in terms of standard deviation / average value (σ / mean). is there.

  However, since the doping density is determined in a complicated manner, such as the ratio of the number of carbon atoms to the number of silicon atoms (C / Si ratio) in the material gas for growing the epitaxial film, the growth temperature, the growth pressure, etc. It is difficult to make mean the above value stably. Further, in recent years, since the demand for thick epitaxial films has increased, high-speed epitaxial growth has been carried out by increasing the flow rates of silicon-based and carbon-based material gases and reducing the pressure in the growth furnace (for example, non-patented). It is more difficult to achieve high doping density in-plane uniformity under high-speed growth. In addition, in the case of a thick epitaxial film, the doping density is generally required to be low because it is applied to a high breakdown voltage device, etc., and the wafer in-plane uniformity can be maintained by eliminating the segregation of the doping density. Technological development to improve in-plane uniformity has become an even more important issue.

Applied Physics Express 1 (2008) 015001

  This SiC wafer is expected to be applied to devices in the future, but the in-plane uniformity of the doping density of the epitaxial film is stable with σ / mean, including high-speed epitaxial growth and general growth rates. It is difficult for the conventional technology to make it to be ˜10%, and there are problems such as deterioration in device characteristics and reduction in yield due to the necessity of using SiC wafers with poor in-plane uniformity.

  The present invention has been made in view of such a situation, and provides a stable manufacturing method of an SiC wafer having a high-quality epitaxial film excellent in wafer in-plane uniformity of doping density.

  The inventors of the present invention provided a high-quality epitaxial film excellent in uniformity in the wafer surface of the doping density by adjusting the product of the growth furnace pressure and the growth rate to be within a certain range during epitaxial growth. It was discovered that a SiC wafer could be obtained.

That is, the present invention
(1) On a silicon carbide single crystal substrate in an epitaxial growth furnace, a silicon-based and carbon-based material gas having a carbon to silicon atomic ratio (C / Si ratio) of 1.0 or more and 2.0 or less, a doping gas, In a method of manufacturing an epitaxial silicon carbide single crystal wafer by flowing a carrier gas and epitaxially growing silicon carbide by a thermal CVD method at a growth temperature of not less than 1550 ° C. and not more than 1700 ° C. Carbonization is carried out by adjusting the product of the furnace pressure P (kPa) and the growth rate R (μm / hr.) Of the obtained epitaxial layer to be in the range of 45 to 100 (45 ≦ P × R ≦ 100). An epitaxial silicon carbide single crystal wafer manufacturing method characterized by epitaxially growing silicon;
(2) The method for producing an epitaxial silicon carbide single crystal wafer according to (1), wherein the growth rate R of the epitaxial layer is controlled by adjusting a flow rate of a material gas,
(3) The method for producing an epitaxial silicon carbide wafer according to (1) or (2), wherein the off angle of the silicon carbide single crystal substrate is 4 ° or less,
(4) The method for producing an epitaxial silicon carbide wafer according to any one of (1) to (3), wherein a diameter of the silicon carbide single crystal substrate is 4 inches (100 mm) or more,
It is.

  According to the present invention, in a SiC wafer in which an epitaxial film is formed on a SiC single crystal substrate, a high-quality SiC wafer excellent in in-plane uniformity of a doping density SiC wafer is provided, including the case of high-speed epitaxial growth. Is possible.

  Further, since the manufacturing method of the present invention is a CVD method, an epitaxial film having a simple apparatus configuration, excellent controllability, high reproducibility and stability can be obtained.

  Furthermore, since the device using the SiC wafer obtained in the present invention is formed on a high-quality epitaxial film having excellent in-plane uniformity of doping density, its characteristics and yield are improved.

FIG. 1 is a diagram showing a typical growth sequence when performing conventional epitaxial growth. FIG. 2 is a diagram showing a growth sequence when epitaxial growth is performed according to an example of the present invention. FIG. 3 shows the in-plane values of P × R and the doping density of the epitaxial film when the pressure in the growth furnace during epitaxial growth is P (kPa) and the growth rate of the epitaxial layer is R (μm / hr.). It is a figure of an example which shows the relationship of uniformity. FIG. 4 is a diagram showing measurement points used when evaluating in-plane uniformity of doping density in a 4-inch substrate.

  The present invention adjusts the wafer surface having a doping density by adjusting the product of the growth furnace pressure and the growth rate within a certain range when epitaxially growing a SiC thin film on a SiC single crystal substrate by thermal CVD. It has been found that a SiC wafer having a high quality epitaxial film with excellent internal uniformity can be obtained. Usually, when the growth rate of epitaxial growth is desired to be increased, the concentration of the material gas is increased. However, nucleation in the gas phase is likely to occur, and the quality of the epitaxial film is deteriorated. That is, the time when the pressure in the growth furnace is lowered is when the SiC thin film is grown at high speed. Here, the inventors performed epitaxial growth at a normal growth rate without changing the concentration of the material gas even when the pressure in the growth furnace was experimentally lowered. The in-plane distribution of the doping density between the epitaxial film grown in this way and the high-growth epitaxial film in which the concentration of the material gas was increased by lowering the growth pressure was compared and evaluated. As a result, it was found that the product of the growth furnace pressure and the growth rate is related to the in-plane uniformity of the doping density, as shown below. The growth rate is calculated by measuring the growth time and the epitaxial film thickness after growth, and is proportional to the concentration (flow rate) of the material gas until the nucleation occurs (that is, nucleation occurs). Si droplets are generated, and the raw material Si is consumed there, and the growth rate decreases because it does not contribute to growth).

Hereinafter, the present invention will be specifically described.
First, epitaxial growth on a SiC single crystal substrate will be described. The apparatus preferably used for epitaxial growth in the present invention is a horizontal CVD apparatus. The CVD method has a simple apparatus configuration and can control growth by gas on / off, and is therefore a growth method with excellent controllability and reproducibility of the epitaxial film.

FIG. 1 shows an example of a typical growth sequence when performing conventional epitaxial film growth, together with the gas introduction timing. First, a SiC single crystal substrate is set in a growth furnace, the inside of the growth furnace is evacuated, and hydrogen gas is introduced to adjust the pressure to 5 to 20 kPa. Then, increase the hydrogen gas flow rate and growth furnace temperature while keeping the pressure constant, reach the epitaxial growth temperature of 1550-1700 ° C, then etch the surface of the SiC single crystal substrate in 100-200L of hydrogen gas per minute (About 10 minutes) After the etching is completed, SiH ₄ and C ₃ H _{8 as} material gases and N ₂ as a doping gas are introduced to start epitaxial growth. The SiH ₄ flow rate is 100 to 150 cm ^{3 /} min, and the C ₃ H ₈ flow rate is 50 to 70 cm ^{3 /} min (the ratio of the number of C atoms to the number of Si atoms in the material gas (C / Si ratio) is about 1 to 2) ), The epitaxial growth rate is ~ 10 μm per hour. The flow rate of N ₂ is determined by the required doping density, but is generally 10 to 50 cm ³ per minute, and the value of the doping density is 1E15 cm ^{−3 to} 1E16 cm ⁻³ . Epitaxial growth is performed for a certain period of time, and when a desired film thickness is obtained, the introduction of SiH ₄ and C ₃ H ₈ is stopped, and the temperature is lowered with only hydrogen gas flowing. After the temperature has dropped to room temperature, the introduction of hydrogen gas is stopped, the growth chamber is evacuated, an inert gas is introduced into the growth chamber, the growth chamber is returned to atmospheric pressure, and the epitaxial SiC wafer is taken out.

Next, an example of the growth sequence in the present invention will be described with reference to FIG. The process until the SiC single crystal substrate is set and the surface of the SiC single crystal substrate is etched is the same as in FIG. After etching is completed, the growth furnace pressure is adjusted to P (kPa) (FIG. 2 shows the case where the pressure is lowered), and the flow rate of SiH ₄ and C ₃ H ₈ which are material gases is the epitaxial layer The growth rate is adjusted to R (μm / hr.), And the following formula (1)
45 ≦ P × R ≦ 100 (1)
To satisfy the relationship. As shown in FIG. 2, the flow rate adjustment of SiH ₄ and C ₃ H ₈ (N ₂ if necessary) is performed, for example, while these gases are discharged to the vent line without flowing into the growth reactor. . After the adjustment is completed, material gas and N ₂ are introduced into the growth furnace to start epitaxial growth. The subsequent procedure is the same as in FIG.

In adjusting the growth conditions so as to satisfy the above formula (1), the growth furnace pressure P is adjusted in the range of 5 kPa to 20 kPa, which is employed in general epitaxial growth as shown in FIG. In addition, the growth rate R is preferably adjusted in the range of 5 μm / hr. To 20 μm / hr. In the example of FIG. 2, the pressure in the growth furnace is decreased after the etching is completed, and the flow rate of the material gas supplied to the SiC single crystal substrate is decreased. Of course, the pressure P is increased or maintained as it is, Increase or maintain the flow rate of the material gas (in the example of FIG. 2, it is better to adjust the flow rate of SiH ₄ and C ₃ H ₈ within the above range) so that the formula (1) is satisfied. You can also. In controlling the growth rate R, the growth temperature may be adjusted. As for the silicon-based material gas and the carbon-based material gas, for example, other hydrocarbon gas is used as the carbon-based material gas, or other silane-based gas is used as the silicon-based material gas. be able to. Similarly, other known gases can be used for the doping gas and the carrier gas.

  FIG. 3 shows the relationship between the in-plane uniformity of the doping density expressed in σ / mean with respect to P × R during epitaxial growth. As can be seen from FIG. 3, as P × R increases, σ / mean decreases, that is, in-plane uniformity improves. This is considered as follows. The in-plane uniformity of the doping density was evaluated as in the examples described later.

When the carrier gas flow rate is constant, if the growth pressure is small, the gas flow rate in the growth furnace increases, so the time during which the material gas and N ₂ stay on the SiC single crystal substrate is shortened. The doping to the epitaxial film is performed by replacing the nitrogen atom generated by the decomposition of N ₂ with the C position of SiC, but this requires a certain amount of time, and the time spent on the SiC single crystal substrate If the length becomes shorter, the reaction necessary for the replacement is not sufficiently performed, and the exhaust is performed. As a result, it is considered that doping in the SiC wafer surface becomes non-uniform.

  If the flow rate of the material gas is increased and the growth rate is increased at this time, the number of Si and C atoms that react with the nitrogen atoms increases, so even if the time for the nitrogen atoms to remain on the SiC single crystal substrate is short, the substitution reaction is sure. To improve the uniformity. On the other hand, when the growth pressure increases, the gas flow rate decreases, and there is sufficient time for the substitution reaction, but the movement of nitrogen atoms that reach the surface of the SiC single crystal substrate and the nitrogen atoms that move on the surface becomes slow. When the growth rate is increased by increasing the flow rate of the material gas in that state, the portion where SiC that does not contain nitrogen atoms grows before the nitrogen atoms reach the substitution site, and the uniformity of the doping density deteriorates. Conceivable. That is, in order to obtain in-plane uniformity with good doping density, it is necessary to increase the growth rate when the gas flow rate is high (low growth pressure), and to decrease the growth rate when the gas flow rate is low (high growth pressure). It has been found that σ / mean is 10% or less when the above relational expression (1) is satisfied, which leads to the present invention.

  From FIG. 3, it can be seen that if P × R is 45 (kPa · μm / hr.) Or more, the doping density σ / mean can be stably reduced to 10% or less, but it is difficult to confirm the upper limit experimentally. It is. This is because if P or R is increased, the growth becomes unstable and a mirror-like epitaxial film cannot be obtained, but considering the maximum values of R and P that are generally used at present, P × R is considered to be substantially 100 (kPa · μm / hr.) Or less. As described above, the preferable range of the growth furnace pressure P is 6 kPa to 12 kPa, and the growth rate R is 7 μm / hr. To 14 μm / hr. In addition, if the C / Si ratio in the material gas when growing the epitaxial layer is too small, the residual impurity density increases, so that the uniformity of the doping density within the wafer surface is degraded. On the other hand, if the C / Si ratio is too large, killer defects occur frequently, which adversely affects both the device characteristics and the in-wafer uniformity of the doping density. Therefore, the C / Si ratio is 1.0 or more and 2.0 or less, more preferably 1.2 or more and 1.8 or less. Furthermore, if the growth temperature when the epitaxial layer is grown is too low, killer defects increase, and if it is too high, the epitaxial layer surface roughness that adversely affects the uniformity of the doping density in the wafer surface occurs. It is 1580 ° C. or higher and more preferably 1580 ° C. or lower. Note that the tendency shown in FIG. 3 hardly changes within the range of the C / Si ratio and the growth temperature.

  The present invention is intended to stably obtain in-plane uniformity with a good doping density for an epitaxial film in a SiC wafer. As can be seen from the above description, a SiC single atom of nitrogen atoms contributing to doping can be obtained. One point is to set the growth rate while controlling the movement on the crystal substrate with a parameter called growth pressure (gas flow rate). Therefore, in the present invention, the wider the area where the gas movement is to be controlled, the more effective the operation becomes, and the SiC single crystal substrate has a diameter of 4 inches (100 mm) or more. It is suitable for a large-diameter SiC single crystal substrate such as a so-called 150 mm diameter substrate or 200 mm diameter substrate that has been reported. Further, when the step density on the surface of the SiC single crystal substrate decreases, the gas adsorbed on the surface needs to move over a long distance on the substrate to react, so that the effectiveness of the present invention is similarly enhanced. In other words, the smaller the off-angle of the SiC single crystal substrate, which is the angle tilted in the <11-20> direction with respect to the (0001) plane, the greater the effect. However, if the off angle is too small, the growth itself becomes difficult, so the off angle of the SiC single crystal substrate should be 0.5 ° or more, and the upper limit is the current mainstream of SiC single crystal substrates. ° or less is preferred.

  Devices suitably formed on the SiC wafer thus manufactured can be used for, for example, Schottky barrier diodes, PIN diodes, MOS diodes, MOS transistors, etc., and particularly preferably used for power control. It is a device.

  EXAMPLES Hereinafter, although this invention is demonstrated based on an Example, this invention is not restrict | limited to these contents.

(Example 1)
SiC with a 4H type polytype, which was sliced from a SiC single crystal ingot for 4 inch (100mm) wafers to a thickness of about 400μm, then subjected to roughing, normal polishing with diamond abrasive grains, and chemical mechanical polishing (CMP). Epitaxial growth was performed on the Si surface of the single crystal substrate. The off-angle of the SiC single crystal substrate (angle tilted in the <11-20> direction with respect to the (0001) plane) is 4 °. As a growth procedure, the SiC single crystal substrate was set in an epitaxial growth furnace, the inside of the growth furnace was evacuated, and the pressure was adjusted to 7.3 kPa while introducing hydrogen gas. After that, increase the hydrogen gas flow rate and growth furnace temperature while keeping the pressure constant, and finally etch the SiC single crystal substrate in hydrogen gas for 10 minutes in hydrogen gas at 150L / min and temperature of 1635 ° C. It was. After etching, the temperature and pressure of the growth furnace remain unchanged at 1635 ° C and 7.3 kPa, the SiH ₄ flow rate is 140 cm ^{3 /} min, the C ₃ H ₈ flow rate is 63 cm ^{3 /} min, and the doping N ₂ flow rate is 13 cm ^{3 /} min. The growth was started (C / Si ratio was 1.35), and the epitaxial layer was grown to a thickness of 10 μm. The growth rate was 10.9 (μm / hr.), And P × R was 79.3 (kPa · μm / hr.). After the growth, the introduction of SiH ₄ , C ₃ H ₈ and N ₂ was stopped, and the temperature was lowered with only hydrogen gas flowing. After the temperature has dropped to room temperature, stop introducing hydrogen gas, evacuate the growth chamber, introduce inert gas into the growth chamber, return the growth chamber to atmospheric pressure, and then remove the resulting SiC wafer. It was.

  The in-plane distribution of the doping density of the film epitaxially grown in this way was measured. The measurement was performed by the CV method using an Hg probe, and as shown in FIG. 4, a total of 25 points were measured with a concentric pattern on the obtained SiC wafer. As a result, σ / mean (standard deviation / average value) obtained from the measured 25 points was 4.7% and good.

(Examples 2 to 11)
Epitaxial growth was carried out on the Si surface of a SiC single crystal substrate having a 4H type polytype, which was sliced, roughened, normally polished, and subjected to CMP in the same manner as in Example 1. The procedure from etching before growth to the end of growth and the growth film thickness are the same as in Example 1, but the substrate off-angle, aperture, SiH ₄ during growth, C ₃ H ₈ , N ₂ flow rate, C / Si ratio, The growth pressure was changed as shown in Table 1. With respect to the obtained SiC wafer, the in-plane distribution of the doping density of the epitaxial film was measured in the same manner as in Example 1. Table 1 shows the growth rate confirmed after growth, the P × R value calculated from the growth rate, and σ / mean of the doping density. From Table 1, all σ / mean values were within 10% or less, which was good. When evaluating a 6-inch substrate, r in FIG. 4 is 14 mm, 28 mm, 42 mm, 56 mm, and 70 mm, and the total number of measurement points is 41 points.

(Comparative Examples 1-6)
Epitaxial growth was carried out on the Si surface of a SiC single crystal substrate having a 4H type polytype, which was sliced, roughened, normally polished, and subjected to CMP in the same manner as in Example 1. The procedure from etching before growth to the end of growth and the growth film thickness are the same as in Example 1, but the substrate off-angle, aperture, SiH ₄ during growth, C ₃ H ₈ , N ₂ flow rate, C / Si ratio, The growth pressure was changed as shown in Table 2. With respect to the obtained SiC wafer, the in-plane distribution of the doping density of the epitaxial film was measured in the same manner as in Example 1. As a result, it can be seen that in Comparative Examples 1 and 2, σ / mean is larger than 10% because the P × R value is too small. In Comparative Example 3, since the C / Si ratio is small, the P × R value is 45 or more but σ / mean is large due to the influence of residual impurities. In Comparative Example 4, the killer is large because the C / Si ratio is large. Many defects occur and σ / mean is large. Furthermore, in Comparative Example 5, the growth temperature was too low and many killer defects occurred, and in Comparative Example 6, the growth temperature was too high and surface roughness occurred. Yes. In Comparative Example 7, the P × R value was too large, that is, since a high growth rate was set under a high growth pressure, the raw material SiH ₄ formed two-dimensional nuclei, and Si droplets were generated, resulting in a mirror-like surface. As a result of not being able to obtain an epitaxial film and normal doping, σ / mean is large.

  According to the present invention, it is possible to produce a SiC wafer having a high-quality epitaxial film excellent in in-plane uniformity of doping density in epitaxial growth on a SiC single crystal substrate. Therefore, if an electronic device is formed on such a SiC wafer, it can be expected that the characteristics and yield of the device are improved.

Claims (4)

  On a silicon carbide single crystal substrate in an epitaxial growth furnace, a silicon-based and carbon-based material gas having a carbon to silicon atomic ratio (C / Si ratio) of 1.0 or more and 2.0 or less, a doping gas, a carrier gas, In the method of manufacturing an epitaxial silicon carbide single crystal wafer by epitaxially growing silicon carbide by a thermal CVD method at a growth temperature of 1550 ° C. or higher and 1700 ° C. or lower, the growth conditions of the epitaxial growth are the pressure in the growth furnace during epitaxial growth. Silicon carbide is epitaxially grown by adjusting the product of P (kPa) and the growth rate R (μm / hr.) Of the resulting epitaxial layer to be in the range of 45 to 100 (45 ≦ P × R ≦ 100) A method for producing an epitaxial silicon carbide single crystal wafer, comprising:   The method for manufacturing an epitaxial silicon carbide single crystal wafer according to claim 1, wherein the growth rate R of the epitaxial layer is controlled by adjusting a flow rate of a material gas.   The method for manufacturing an epitaxial silicon carbide wafer according to claim 1, wherein an off angle of the silicon carbide single crystal substrate is 4 ° or less.   The method for manufacturing an epitaxial silicon carbide wafer according to claim 1, wherein the silicon carbide single crystal substrate has a diameter of 4 inches (100 mm) or more.

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