JP7127283B2 - Silicon carbide semiconductor substrate and method for manufacturing silicon carbide semiconductor substrate - Google Patents

Description

The present invention relates to a silicon carbide semiconductor substrate and a method for manufacturing a silicon carbide semiconductor substrate.

Conventionally, a single crystal SiC epitaxial substrate obtained by epitaxially growing a single crystal SiC (hereinafter, epitaxial may be abbreviated as epitaxial) on a single crystal SiC (silicon carbide) substrate has been used as a 1 kV class high voltage Schottky diode, Research and development has progressed as a high voltage MOSFET (Metal Oxide Semiconductor Field Effect Transistor: insulated gate field effect transistor) application, and it has been put to practical use.

However, in order to realize an ultra-high withstand voltage and low loss device of over 10 kV, a low carrier concentration of 1×10 ¹⁴ /cm ³ to 1×10 ¹⁵ /cm ³ is required on a single crystal silicon carbide semiconductor substrate. It is necessary to prepare (manufacture) a single crystal SiC epitaxial substrate by epitaxially growing single crystal SiC. Hereinafter, a single-crystal SiC substrate epitaxially grown on a single-crystal silicon carbide semiconductor substrate may be abbreviated as an epi-substrate. A low-concentration epitaxial layer may also be referred to as a drift layer.

As a low-concentration epitaxial substrate, there is a technique for forming an epitaxial layer with a low nitrogen (N) concentration of about 1×10 ¹⁴ /cm ³ to 1×10 ¹⁷ /cm ³ (see, for example, Patent Document 1 below). Also, there is a technique of forming an epitaxial layer having an impurity concentration of 1×10 ¹⁴ /cm ³ or more and 1×10 ¹⁶ /cm ³ or less by epitaxial growth (for example, see Patent Document 2 below).

JP 2015-002207 A JP 2012-253115 A

However, in the prior art, the drift layer may be formed with a lower carrier concentration than the set carrier concentration, and the drift layer with the set carrier concentration may not be formed. For example, even if the drift layer is formed with a carrier concentration of 4×10 ¹⁴ /cm ³ , the CV (Capacitance-Voltage) measurement value of the carrier concentration of the drift layer is around 1×10 ¹⁴ /cm ³ . Sometimes. As a result, if this epitaxial substrate is used to fabricate an SBD (Schottky Barrier Diode) with a withstand voltage of 10 kV class, for example, with a set film thickness of 135 μm for the drift layer, the on-resistance characteristic may deteriorate.

This is because the set value of the carrier concentration of the drift layer is very low, so the influence of impurities of a conductivity type different from that of the drift layer entering the drift layer in an epitaxial growth apparatus for epitaxial growth of single crystal SiC cannot be ignored. , the drift layer is formed with a lower carrier concentration than the target.

As an example, when an SBD (Schottky barrier diode) was fabricated using an epitaxial substrate on which an n-type drift layer with a set concentration of 4×10 ¹⁴ /cm ³ and a set film thickness of 135 μm was formed, the good epitaxial substrate was RonA ( On-resistance) was about 0.11 Ω/cm ² at room temperature, while the defective epitaxial substrate had about 1.2 Ωcm ² , ten times higher. FIG. 5 is a graph showing current-voltage characteristics of a Schottky barrier diode. As shown in FIG. 5, in a non-defective product, the forward voltage Vf is increased, and when the threshold voltage is exceeded, the forward current If sharply increases. The forward current If increases slowly. SIMS analysis (Secondary Ion Mass Spectrometry) was conducted to investigate the cause of the increase ⁱⁿ on-resistance. cm ³ , and the concentration of boron (B) was also observed to be 2 to 4×10 ¹⁴ /cm ³ . For this reason, it was considered that counterdoping with boron lowered the effective carrier concentration of the drift layer, thereby lowering the on-resistance characteristics of the SBD.

Here, the reason why boron is mixed in the drift layer is considered as follows. FIG. 6 is a cross-sectional view showing the structure of an epitaxial growth apparatus for single crystal SiC. In the epitaxial growth apparatus 6, the material gas, the carrier gas and the dopant gas are introduced and moved horizontally from the gas inlet 66 to the gas outlet 67 in the directions indicated by the arrows. The gas is mainly supplied to the surface side of the semiconductor substrate 65 , the susceptor 61 is heated by a heating device such as an IH (Induction Heating) coil (not shown), and a drift layer is formed on the semiconductor substrate 65 . As the semiconductor substrate, a single-crystal 4H--SiC (four-layer periodic hexagonal silicon carbide) substrate or a single-crystal 6H--SiC (six-layer periodic hexagonal silicon carbide) substrate is used. Moreover, the epitaxial growth apparatus 6 is surrounded by a heat insulating material 64 including a graphite member.

A high-purity carbon material 63 is used as the material of the susceptor 61 , and the surface is covered with a polycrystalline SiC coating layer 62 . However, there is a limit to the purity of the high-purity carbon material 63, and it may contain a trace amount of boron or the like as an impurity. Therefore, immediately after the new susceptor 61 is used, if it is heated during epitaxial growth, a small amount of boron, which contributes as a p-type dopant, is generated as indicated by an arrow 68 and diffuses into the epitaxial growth apparatus 6 . If the set concentration of the drift layer is about ⁵ ×10 ¹⁵ /cm ³ or more, a trace amount of boron contamination on the order of 1× ^{10 14} /cm ³ can be ignored. Then, boron contamination reaches a level that cannot be ignored, and p-type boron is mixed into n-type nitrogen, so that a drift layer with a carrier concentration lower than the target carrier concentration is formed.

An object of the present invention is to provide a silicon carbide semiconductor substrate having a drift layer with a low carrier concentration and a method for manufacturing the silicon carbide semiconductor substrate.

In order to solve the above problems and achieve the object of the present invention, a silicon carbide semiconductor substrate according to the present invention has the following features. The silicon carbide semiconductor substrate has a carrier concentration of 1×10 ¹⁴ /cm ³ or more and 5 ×10 ¹⁴ /cm ³ or less, and among the impurities, each impurity component having a conductivity type different from the impurity that determines the conductivity type. or with epitaxial layers having a total concentration of less than 1×10 ¹⁴ /cm ³ . The crystal structure is 4H—SiC, and the principal plane provided with the epitaxial layer is the (0001) Si plane. A silicon carbide semiconductor substrate for a silicon carbide semiconductor device having a breakdown voltage of 10 kV or higher. The set film thickness of this epitaxial layer is arbitrary.

Further, in the silicon carbide semiconductor substrate according to the present invention, in the invention described above, the impurity that determines the conductivity type is nitrogen in the case of the n-type drift layer, and the impurity that determines the conductivity type has a conductivity type different from that of the impurity that determines the conductivity type. The impurity component is characterized by being boron, or aluminum, or both boron and aluminum. The off angle is 0° or more and 10° or less, and the diameter is 25 mm or more and 200 mm or less. The set film thickness of this epitaxial layer is arbitrary.

In order to solve the above problems and achieve the object of the present invention, a method for manufacturing a silicon carbide semiconductor substrate according to the present invention has the following features. In a method for manufacturing a silicon carbide semiconductor substrate, first, a gas containing hydrogen is supplied into an epitaxial growth apparatus, and the inside of the epitaxial growth apparatus is heated for a predetermined time. Next, a single-crystal silicon carbide substrate is loaded into the epitaxial growth apparatus, and a source gas, a carrier gas, and a dopant gas containing impurities that determine a conductivity type are supplied to form a first epitaxial layer on the single-crystal silicon carbide substrate. A first film forming step is performed to form a first conditional film forming. Next, after the first film formation step, a first measurement step of measuring the impurity concentration and the film thickness of the first epitaxial layer is performed. Next, after the first measurement step, a second film formation step is performed in which the dopant gas is supplied to form a second epitaxial layer on the first epitaxial layer. After the second film formation step, a second measurement step is performed to measure the impurity concentration and film thickness of the second epitaxial layer. Next, calculating the relationship between the impurity flow rate and the impurity concentration of the first epitaxial layer and the impurity concentration of the second epitaxial layer from the measurement results of the first measurement step and the second measurement step, A determination step of determining the flow rate of the dopant gas is performed. Next, after the determining step, a third film forming step is performed to supply the dopant gas and form a third epitaxial layer on the second epitaxial layer by setting a third condition. Next, after the third film formation step, an adjusting step of calculating the film thickness of the third epitaxial layer and the dopant incorporation dependence relationship and adjusting the flow rate of the dopant gas is performed. Next, the dopant gas is supplied at the flow rate adjusted in the adjusting step to form a single-crystal silicon carbide film on the third epitaxial layer by epitaxial growth.

Further, in the method of manufacturing a silicon carbide semiconductor substrate according to the present invention, in the above-described invention, the step of heating for the predetermined time preferably includes heating the inside of the epitaxial growth apparatus to a temperature of at least 1600° C., a gas pressure of 1000 Pa or more, and for 10 minutes or more. is characterized by heating at a temperature of 1725° C. and a gas pressure of 2500 Pa for 3.5 hours. Note that the hydrogen gas flow rate is set arbitrarily within the range in which the gas pressure can be controlled.

Moreover, in the method of manufacturing a silicon carbide semiconductor substrate according to the present invention, in the invention described above, the impurity that determines the conductivity type is nitrogen. In the invention described above, the main surface of the single-crystal silicon carbide substrate on which epitaxial growth is performed is preferably the (0001) Si plane. Further, the off-angle of the silicon carbide semiconductor substrate on which epitaxial growth is performed in the invention described above may be any number within the range of 0 degrees or more and 10 degrees or less. Moreover, the diameter of the epitaxial substrate manufactured in the above-described invention may be any mm within the range of 25 mm or more and 200 mm or less.

According to the invention described above, the n ⁻ -type epitaxial layer has a carrier concentration of 1×10 ¹⁴ /cm ³ or more and 1×10 ¹⁵ /cm ³ or less. Therefore, by setting the film thickness of the n ⁻ -type epitaxial layer of this silicon carbide semiconductor substrate to an appropriate value, a silicon carbide semiconductor device having a high breakdown voltage, for example, 10 kV class or higher can be realized. Further, the carrier concentration of the n ⁻ -type epitaxial layer is set to 1×10 ¹⁴ /cm ³ or more and 5×10 ¹⁴ /cm ³ or less, and the set film thickness of the n ⁻ -type epitaxial layer is set to an appropriate value. , a silicon carbide semiconductor device with a higher withstand voltage, for example, a 13 kV class or higher or a 20 kV class or higher can be realized.

In addition, by heating the inside of the epitaxial growth apparatus for a predetermined time before epitaxially growing the n ⁻ -type epitaxial layer, the boron contained in the carbon constituting the members such as the susceptor in the epitaxial growth apparatus can be released in advance. As a result, the amount of boron mixed into the n ⁻ -type epitaxial layer during epitaxial growth can be reduced, and the concentration of each or the total of p-type impurity components can be less than 1×10 ¹⁴ /cm ³ . For this reason, for example, when a unipolar device such as a 10 kV class SBD is manufactured with the n ⁻ -type epitaxial layer having a set thickness of 135 μm, it is possible to prevent the carrier concentration from becoming lower than the set value. You can prevent it from getting worse.

According to the silicon carbide semiconductor substrate and the method for manufacturing a silicon carbide semiconductor substrate according to the present invention, a silicon carbide semiconductor substrate having a low-concentration drift layer with a carrier concentration of 1×10 ¹⁴ /cm ³ to 1×10 ¹⁵ /cm ³ is manufactured. There is an effect that it can be provided.

1 is a cross-sectional view showing the configuration of a silicon carbide semiconductor substrate according to an embodiment; FIG. 4 is a flow chart of a process for forming a silicon carbide semiconductor substrate according to an embodiment; 5 is a graph showing a correspondence relationship between the flow rate of dopant gas during doping and the carrier concentration of the epitaxial layer in the silicon carbide semiconductor substrate according to the embodiment; 5 is a table showing actual values of SIMS analysis and CV measurement of the n ⁻ -type epitaxial layer of the silicon carbide semiconductor substrate according to the embodiment; 4 is a graph showing current-voltage characteristics of a Schottky barrier diode; 1 is a cross-sectional view showing the structure of an epitaxial growth apparatus for single crystal SiC; FIG.

Preferred embodiments of a silicon carbide semiconductor substrate and a method for manufacturing a silicon carbide semiconductor substrate according to the present invention will be described below in detail with reference to the accompanying drawings. In this specification and the accompanying drawings, layers and regions prefixed with n or p mean that electrons or holes are majority carriers, respectively. Also, + and - attached to n and p mean that the impurity concentration is higher and lower than that of the layer or region not attached, respectively. When the notations of n and p including + and - are the same, it indicates that the concentrations are close, and the concentrations are not necessarily the same. In the following description of the embodiments and the accompanying drawings, the same configurations are denoted by the same reference numerals, and overlapping descriptions are omitted. Also, in this specification, in the notation of the Miller index, "-" means a bar attached to the index immediately after it, and adding "-" before the index indicates a negative index.

(Embodiment)
FIG. 1 is a cross-sectional view showing the configuration of a silicon carbide semiconductor substrate according to an embodiment. As shown in FIG. 1, the silicon carbide semiconductor substrate according to the embodiment includes a first main surface (front surface) of an n-type silicon carbide substrate (single-crystal silicon carbide substrate) 1, for example, the (0001) plane (Si ), an n-type buffer layer 2 is deposited. The n-type buffer layer 2 may be formed or may not be formed. Also, the thickness of the n-type buffer layer 2 may be thinner or thicker than that of the n ⁻ -type drift layer.

N-type silicon carbide substrate 1 is a silicon carbide single crystal substrate. The n-type buffer layer 2 is, for example, a buffer layer with a higher concentration than the n-type silicon carbide substrate 1 . The n-type buffer layer 2 is a film formed by epitaxial growth. An n ⁻ -type epitaxial layer (epitaxial layer) 3 is deposited on the surface of n-type buffer layer 2 opposite to n-type silicon carbide substrate 1 . Note that the n-type buffer layer 2 may have a lower concentration than the n-type silicon carbide substrate 1 .

The n ⁻ -type epitaxial layer 3 has an impurity concentration lower than that of the n-type silicon carbide substrate 1 and the n-type buffer layer 2, and is, for example, a low concentration n ⁻ -type drift layer. N ⁻ -type epitaxial layer 3 is a layer formed by epitaxial growth, and has a carrier concentration of 1×10 ¹⁴ /cm ³ or more and 1×10 ¹⁵ /cm ³ or less. Here, the carrier concentration is the sum of the concentration of n-type impurities such as nitrogen contained in the n ⁻ -type epitaxial layer 3 and the concentration of p-type impurities such as boron and aluminum. Further, in the n ⁻ -type epitaxial layer 3, each or the total concentration of the p-type impurity components is less than 1×10 ¹⁴ /cm ³ . That is, when a plurality of types of p-type impurities are contained, the total concentration of the p-type impurities is less than 1×10 ¹⁴ /cm ³ . Further, the carrier concentration of n ⁻ -type epitaxial layer 3 is more preferably 1×10 ¹⁴ /cm ³ or more and 5×10 ¹⁴ /cm ³ or less. With a carrier concentration of 1×10 ¹⁴ /cm ³ or more and 5×10 ¹⁴ /cm ³ or less, and setting the film thickness of the n ⁻ -type epitaxial layer to an appropriate value, a higher withstand voltage, for example, a 13 kV class As described above, a silicon carbide semiconductor device of 20 kV class or higher can be realized.

(Manufacturing method of silicon carbide semiconductor substrate according to embodiment)
Next, a method for manufacturing a silicon carbide semiconductor substrate according to an embodiment will be described. FIG. 2 is a flow chart of forming steps of the silicon carbide semiconductor substrate according to the embodiment. Moreover, FIG. 3 is a graph showing the correspondence relationship between the flow rate of the dopant gas during doping and the carrier concentration of the epitaxial layer in the silicon carbide semiconductor substrate according to the embodiment. In FIG. 3 , the vertical axis is the concentration of nitrogen in the epitaxial layer formed on the silicon carbide semiconductor substrate in units of /cm ³ , and the horizontal axis is the flow rate of nitrogen in the dopant gas in units of sccm (standard cubic centimeter per minute) or slm (standard litter per minute).

In the method for manufacturing a silicon carbide semiconductor substrate according to the embodiment, first, epitaxial growth apparatus 6 is baked (step S1). A gas containing hydrogen (H ₂ ) is supplied into the epitaxial growth apparatus 6 to heat the inside of the epitaxial growth apparatus 6 for a predetermined time. For example, a gas containing hydrogen is supplied into the epitaxial growth apparatus 6, the temperature inside the epitaxial growth apparatus 6 is increased to at least 1600° C. or higher, the pressure is controlled to 1000 Pa or higher, and the susceptor 61 is heated for 10 minutes or longer. . Preferably, the inside of the epitaxial growth apparatus 6 is heated to 1725° C., the pressure is controlled to 2500 Pa, and the susceptor 61 is heated for 3.5 hours. As a result, boron contained in the high-purity carbon material 63 and the heat insulating material 64 in the susceptor 61 can be released, and boron can be prevented from being released from the high-purity carbon material 63 and the heat insulating material 64 during epitaxial growth.

Next, a first conditional film formation to which nitrogen is added is performed (step S2). For example, the temperature of the silicon carbide semiconductor substrate is set to a desired set temperature within the range of 1580° C. or more and 1725° C. or less, and a silane (SiH ₄ ) gas is applied to the surface of the silicon carbide semiconductor substrate using hydrogen gas as a carrier gas. and propane (C ₃ H ₈ ) gas are supplied at the same time, and a dopant gas containing nitrogen is supplied, and the pressure of the gas is controlled to a desired pressure within the range of 1000 Pa or more and 20000 Pa or less. An epitaxial layer having a thickness of 10 μm is formed. Here, "simultaneous supply" means that the SiH ₄ gas and the C ₃ H ₈ gas, which are source gases, are supplied within several seconds to several tens of seconds, although it does not have to be completely at the same time. After the first conditional film formation, the nitrogen concentration and film thickness of the formed epitaxial layer are measured. The nitrogen flow rate of the dopant gas in the first conditioned deposition and the nitrogen concentration of the formed epitaxial layer are plotted at point 31 in FIG.

Next, a second conditional film formation to which nitrogen is added is performed (step S3). For example, the temperature of the silicon carbide semiconductor substrate is set to a desired set temperature within the range of 1580° C. or higher and 1725° C. or lower, and H ₂ gas is used as a carrier gas to coat the surface of the silicon carbide semiconductor substrate. ₄ gas and C ₃ H ₈ gas are simultaneously supplied, and a dopant gas containing nitrogen is supplied, and the pressure of the gas is controlled to a desired pressure within the range of 1000 Pa or more and 20000 Pa or less, for example, a set film An epitaxial layer with a thickness of 6 μm is formed. After the second conditional film formation, the nitrogen concentration and film thickness of the formed epitaxial layer are measured. The nitrogen flow rate of the dopant gas in the second conditioned deposition and the nitrogen concentration of the formed epitaxial layer are plotted at point 32 in FIG.

Next, the relationship between the flow rate of added nitrogen and the concentration of nitrogen in the epitaxial layer is calculated (step S4). For example, the relationship between the flow rate of added nitrogen and the concentration of nitrogen in the epitaxial layer is calculated by connecting the points resulting from the film formation under the first conditions and the points resulting from the film formation under the second conditions with a straight line. . In FIG. 3, a straight line 33 connecting points 31 and 32 indicates the relationship between the flow rate of added nitrogen and the concentration of nitrogen in the epitaxial layer.

Next, a third conditional film formation is performed to which nitrogen is added (step S5). From the straight line 33 calculated in step S4, it can be seen that the flow rate of nitrogen in the dopant gas should be n2 when forming an epitaxial layer with the concentration dt at point . Therefore, for example, the temperature of the silicon carbide semiconductor substrate is set to a desired set temperature within the range of 1580° C. or more and 1725° C. or less, and H ₂ gas is used as a carrier gas and a raw material gas is applied to the surface of the silicon carbide semiconductor substrate. A certain SiH ₄ gas and C ₃ H ₈ gas are simultaneously supplied, and a dopant gas containing nitrogen is supplied at a flow rate of n2 to control the gas pressure to a desired pressure within the range of 1000 Pa or more and 20000 Pa or less. Then, for example, an epitaxial layer having a set film thickness of 20 μm is formed.

Next, the dependency on the film thickness and nitrogen uptake is calculated (step S6). When an epitaxial layer having a set film thickness of 20 μm is formed in step S5, the nitrogen concentration of the formed epitaxial layer may not be at point 34 but at point 35 in some cases. This is because, for example, when the epitaxial growth apparatus 6 is exposed to the atmosphere for maintenance, nitrogen adheres to the furnace wall, causing the nitrogen uptake rate to change over time. In addition, for example, an n-type by-product (polycrystalline SiC) grows on the susceptor 61 in the epitaxial layer, and the n-type by-product re-sublimes. This is because the C/Si ratio (ratio of carbon to silicon) collapses and the nitrogen uptake rate changes over time. Another reason is that, for example, nitrogen molecules in the air are adsorbed on the surface of the SiC coated susceptor made of carbon.

For example, if the epitaxial layer has a high nitrogen concentration, the flow rate of the dopant gas is adjusted to be low. Conversely, when the nitrogen concentration in the epitaxial layer is low, the flow rate of the dopant gas is adjusted to be high. The amount to be adjusted is determined according to the difference between the desired concentration and the actual concentration.

Next, a low-concentration epitaxial layer is formed by epitaxial growth (step S7). For example, the n-type silicon carbide substrate 1 is carried into the epitaxial growth apparatus 6, the temperature of the n-type silicon carbide substrate 1 is set to a desired set temperature within the range of 1580° C. or more and 1725° C. or less, and the n-type silicon carbide substrate is SiH ₄ gas and C ₃ H ₈ gas, which are raw material gases, were simultaneously supplied to the surface of 1 using H ₂ gas as a carrier gas, and a dopant gas containing nitrogen was supplied, and the gas pressure was set to 1000 Pa. The epitaxial layer is formed by controlling the pressure to a desired value within the range of 20000 Pa or less and setting the film formation time according to the desired set film thickness. The flow rate of nitrogen in the dopant gas is the flow rate determined in step S5.

With this, a series of processes in this flowchart ends. By carrying out this flow chart, an n ^- -type epitaxial layer 3 having a carrier concentration of 1×10 ¹⁴ /cm ³ to 1×10 ¹⁵ /cm ³ is formed on the n-type buffer layer 2 by epitaxial growth.

Incidentally, in the embodiment, film formation under conditions was performed three times for nitrogen, but step S5 may be omitted and film formation under conditions may be performed only twice. This is because the straight line 33 can be calculated and the relationship between the flow rate of the added nitrogen and the concentration of nitrogen in the epitaxially grown film can be obtained by the first two film forming operations.

Next, the result of manufacturing a silicon carbide semiconductor substrate by the manufacturing method described in the embodiment will be shown. Using n-type 4H-SiC as an n-type silicon carbide substrate 1, an n-type buffer layer 2 having a set thickness of about 1.5 μm was epitaxially grown on the Si surface of the n-type 4H-SiC. Next, on the surface of the n-type buffer layer 2, an n ⁻ -type epitaxial layer 3 was formed with a set carrier concentration of 4×10 ¹⁴ /cm ³ and a set film thickness of about 25 μm.

FIG. 4 is a table showing actual values of SIMS analysis and CV measurement of n ⁻ -type epitaxial layer 3 of the silicon carbide semiconductor substrate according to the embodiment. FIG. 4 shows measurement results of n ⁻ -type epitaxial layer 3 of the silicon carbide semiconductor substrate manufactured above. In the SIMS analysis, the concentration was measured at a depth of about 10 μm near the center of the n ⁻ -type epitaxial layer 3 . According to the measurement results, the average nitrogen concentration is 5.6×10 ¹⁴ /cm ³ , the average boron concentration is 5.1×10 ¹³ /cm ³ , and the average aluminum concentration is 7.2×10 ¹³ /cm ³ . Met. As a result, the net impurity concentration was 4.4×10 ¹⁴ /cm ³ , and the p-type impurity (boron, aluminum) concentrations were 5.1×10 ¹³ /cm ³ and 7.2×10 ¹³ , respectively. /cm ³ and less than 1×10 ¹⁴ /cm ³ . Further, the carrier concentration of the n ⁻ -type epitaxial layer 3 by CV measurement was 5.0×10 ¹⁴ /cm ³ and was within the range of 1×10 ¹⁴ /cm ³ to 1×10 ¹⁵ /cm ³ . Thus, according to the method for manufacturing a silicon carbide semiconductor substrate according to the embodiment, the carrier concentration of the n ⁻ -type epitaxial layer is 1×10 ¹⁴ /cm ³ or more and 1×10 ¹⁵ /cm ³ or less, and the p-type It has been found that an n ⁻ -type epitaxial layer 3 is formed in which the concentration of each impurity component is less than 1×10 ¹⁴ /cm ³ .

As described above, according to the silicon carbide semiconductor substrate according to the embodiment, a drift layer with a low carrier concentration can be realized. Specifically, the n ⁻ -type epitaxial layer serving as the drift layer has a carrier concentration of 1×10 ¹⁴ /cm ³ or more and 1×10 ¹⁵ /cm ³ or less. Therefore, by setting the film thickness of the n ⁻ -type epitaxial layer of this silicon carbide semiconductor substrate to an appropriate value, a silicon carbide semiconductor device having a high breakdown voltage, for example, 10 kV class or higher can be realized. Further, the carrier concentration of the n ⁻ -type epitaxial layer is set to 1×10 ¹⁴ /cm ³ or more and 5×10 ¹⁴ /cm ³ or less, and the set film thickness of the n ⁻ -type epitaxial layer is set to an appropriate value. , a silicon carbide semiconductor device with a higher withstand voltage, for example, a 13 kV class or higher or a 20 kV class or higher can be realized.

In addition, by heating the inside of the epitaxial growth apparatus for a predetermined time before epitaxially growing the n ⁻ -type epitaxial layer, impurities acting as p-type dopants such as boron contained in carbon members such as susceptors in the epitaxial growth apparatus are released in advance. can do. As a result, the amount of impurities acting as p-type dopants, such as boron, mixed into the n ⁻ -type epitaxial layer during epitaxial growth is reduced, and the concentration of each or the total of the p-type impurity components is reduced to 1×10 ¹⁴ /cm. Can be less than ³ . Therefore, for example, when a 10 kV-class SBD is manufactured with a set film thickness of 135 μm, it is possible to prevent the carrier concentration from becoming lower than the set value, thereby preventing deterioration of the on-resistance characteristics of the SBD.

Further, the main surface of the silicon carbide semiconductor substrate on which epitaxial growth is performed in the above invention may be the (0001) Si plane, the (000-1) C plane, or any other plane. Further, the off-angle of the silicon carbide semiconductor substrate on which epitaxial growth is performed in the invention described above may be any angle within the range of 0° or more and 10° or less. Moreover, the diameter of the epitaxial substrate manufactured in the above-described invention may be any mm within the range of 25 mm or more and 200 mm or less.

INDUSTRIAL APPLICABILITY As described above, the silicon carbide semiconductor substrate according to the present invention is useful as a semiconductor substrate for high voltage semiconductor devices used in power converters, power supply devices for various industrial machines, and the like.

Reference Signs List 1 n-type silicon carbide substrate 2 n-type buffer layer 3 n ⁻ type epitaxial layer 6 epitaxial growth apparatus 61 susceptor 62 polycrystalline SiC coating layer 63 high-purity carbon material 64 heat insulating material 65 semiconductor substrate 66 gas inlet 67 gas outlet

Claims (7)

The carrier concentration is 1×10 ¹⁴ /cm ³ or more and 5 ×10 ¹⁴ /cm ³ or less, and the concentration of each impurity component having a conductivity type different from the impurity that determines the conductivity type or the total concentration is 1×10 ¹⁴ . / cm ³ of the epitaxial layer,
prepared,
A silicon carbide semiconductor substrate for a silicon carbide semiconductor device having a withstand voltage of 10 kV or more, characterized in that the crystal structure is 4H—SiC, and the main surface provided with the epitaxial layer is a (0001) Si plane. 2. The impurity component according to claim 1, wherein the impurity that determines the conductivity type is nitrogen, and the impurity component having a conductivity type different from that of the impurity that determines the conductivity type is boron, aluminum, or both boron and aluminum. Silicon carbide semiconductor substrate of. 3. The silicon carbide semiconductor substrate according to claim 1, wherein the off-angle is 0[deg.] or more and 10[deg.] or less, and the diameter is 25 mm or more and 200 mm or less. supplying a gas containing hydrogen into an epitaxial growth apparatus to heat the inside of the epitaxial growth apparatus for a predetermined time;
A single-crystal silicon carbide substrate is loaded into the epitaxial growth apparatus, and a source gas, a carrier gas, and a dopant gas containing impurities determining a conductivity type are supplied to form a first epitaxial layer on the single-crystal silicon carbide substrate. A first film forming step of performing a first conditional film forming;
After the first film formation step, a first measurement step of measuring the impurity concentration and the film thickness of the first epitaxial layer;
After the first measurement step, a second film formation step of supplying the dopant gas to form a second epitaxial layer on the first epitaxial layer to perform a second conditional film formation;
After the second film formation step, a second measurement step of measuring the impurity concentration and the film thickness of the second epitaxial layer;
A relationship between the impurity flow rate and the impurity concentration of the first epitaxial layer and the impurity concentration of the second epitaxial layer is calculated from the measurement results of the first measurement step and the second measurement step, and the dopant gas is used. a determining step of determining the flow rate of
After the determining step, a third film-forming step of supplying the dopant gas to form a third epitaxial layer on the second epitaxial layer;
After the third film formation step, an adjustment step of calculating the film thickness of the third epitaxial layer and the impurity incorporation dependency relationship, and adjusting the flow rate of the dopant gas;
supplying the dopant gas at the flow rate adjusted in the adjusting step to form a film of single crystal silicon carbide on the third epitaxial layer by epitaxial growth;
A method for manufacturing a silicon carbide semiconductor substrate, comprising: 5. The method of manufacturing a silicon carbide semiconductor substrate according to claim 4, wherein in the step of heating for the predetermined time, the inside of the epitaxial growth apparatus is heated at least at a temperature of 1600[deg.] C. or higher, at a gas pressure of 1000 Pa or higher, for 10 minutes or longer. 6. The method of manufacturing a silicon carbide semiconductor substrate according to claim 4, wherein the impurity that determines the conductivity type is nitrogen. Claims 4 to 6, wherein the main surface of the single-crystal silicon carbide substrate is a (0001) Si plane, the off-angle is 0° or more and 10° or less, and the diameter is 25 mm or more and 200 mm or less. The method for manufacturing a silicon carbide semiconductor substrate according to any one of .

Images