JP2015143168A - Silicon carbide epitaxial substrate and method for manufacturing silicon carbide epitaxial substrate - Google Patents

Abstract

A silicon carbide epitaxial substrate having good surface properties and a sufficiently reduced background concentration of nitrogen atoms and a method for manufacturing the same are provided. A silicon carbide epitaxial substrate includes a base substrate having a C-plane as a main surface and a silicon carbide epitaxial layer disposed on the C-plane of the base substrate. Silicon carbide epitaxial layer 2 includes a layer having a background concentration of nitrogen atoms of 3 to 10 @ 15 cm @ -3 or less. In the step of forming silicon carbide epitaxial layer 2, the ratio C / Si of the number of carbon atoms to the number of silicon atoms in the raw material gas is set to 1.7 to 2.1 and the epitaxial growth temperature ranges from 1600 ° C. to 1800 ° C. To do. Furthermore, the background concentration of nitrogen atoms of silicon carbide epitaxial substrate 10 can be reduced by setting the nitrogen concentration of the member constituting the silicon carbide growth apparatus to 10 ppm or less and reducing the nitrogen released from the member. [Selection] Figure 1

Description

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

  Conventionally, silicon (Si) has been widely used as a material constituting semiconductor devices. In recent years, the use of silicon carbide (SiC) as a material constituting a semiconductor device has been promoted in order to enable a semiconductor device to have a high breakdown voltage and low loss.

  Silicon carbide is a wide band gap semiconductor having a larger band gap than silicon. By adopting silicon carbide as a material constituting the semiconductor device, it is possible to achieve high breakdown voltage of the semiconductor device, reduction of on resistance, and the like. Furthermore, a semiconductor device that employs silicon carbide as a material also has an advantage that a decrease in characteristics when used in a high-temperature environment is smaller than a semiconductor device that employs silicon as a material.

  Due to the crystal structure of silicon carbide, a silicon carbide wafer generally has two types of main surfaces called Si plane and C plane. Conventionally, a silicon carbide layer has been formed by epitaxial growth on the Si surface of a silicon carbide wafer (see, for example, Non-Patent Document 1).

Kazutoshi Koiima, Satoshi Kuroda, Haiime Okumura, and Kazuo Aral, "Nitrogen incorporation characteristics on a 4H-SiC epitaxial layer", APPLIED PHYSICS LETTERS, vol. 88, pp. 21907-1-021907-3

  In recent years, it has been studied to improve device characteristics by using the C-plane of a silicon carbide substrate. Therefore, the importance of a uniform epitaxial growth technique on the C plane is increasing.

  In order to control the impurity concentration of the silicon carbide epitaxial layer, it is necessary to consider not only the concentration of the impurity introduced into the silicon carbide epitaxial layer by the dopant gas but also the background concentration of the silicon carbide epitaxial layer. Found. In this specification, “background concentration” refers to the concentration of impurities contained in an epitaxial layer as a result of epitaxial growth without using a dopant gas. Typically, nitrogen can be an impurity contained in the silicon carbide epitaxial layer.

  Furthermore, it is also important in epitaxial growth that good surface properties can be obtained on the main surface of the epitaxial layer. However, Patent Document 1 does not mention a manufacturing method for obtaining a silicon carbide epitaxial substrate that has good surface properties and a sufficiently reduced background concentration of nitrogen atoms.

  The present invention has been made to solve the above-described problems. A main object of the present invention is to provide a silicon carbide epitaxial substrate having good surface properties and a sufficiently reduced background concentration of nitrogen atoms, and a method for producing the same.

A silicon carbide epitaxial substrate according to an aspect of the present invention includes a silicon carbide base substrate having a C plane as a main surface, and a silicon carbide epitaxial layer disposed on the C plane of the silicon carbide base substrate. The layer includes a layer having a background concentration of nitrogen atoms of 3 × 10 ¹⁵ cm ⁻³ or less.

  A method for manufacturing a silicon carbide epitaxial substrate according to another aspect of the present invention includes a step of preparing a silicon carbide base substrate having a C-plane as a main surface, and forming a silicon carbide epitaxial layer on the silicon carbide base substrate. And a step of forming a silicon carbide epitaxial layer on the C-plane of the silicon carbide base substrate by supplying the raw material gas used for the above and heating the silicon carbide base substrate to the epitaxial growth temperature. In the step of forming the silicon carbide epitaxial layer, the ratio C / Si of the number of carbon atoms to the number of silicon atoms in the raw material gas is 1.7 or more and 2.1 or less, and the epitaxial growth temperature is 1600 ° C. or more and 1800 ° C. or less. It is a range.

  ADVANTAGE OF THE INVENTION According to this invention, the surface property is favorable and the silicon carbide epitaxial substrate by which the background concentration of the nitrogen atom was fully reduced can be provided.

It is sectional drawing for demonstrating the silicon carbide epitaxial substrate which concerns on embodiment of this invention. It is a flowchart which shows the manufacturing method of the silicon carbide epitaxial substrate which concerns on embodiment of this invention. It is sectional drawing for demonstrating the silicon carbide growth apparatus which concerns on embodiment of this invention. FIG. 4 is a sectional view taken along line IV-IV in FIG. 3. In the silicon carbide growth apparatus which concerns on embodiment of this invention, it is sectional drawing which shows the structure of a substrate holder periphery. In the silicon carbide growth apparatus which concerns on embodiment of this invention, it is a top view which shows the structure of a substrate holder periphery. Background concentration of silicon carbide epitaxial substrate (Embodiment of the present invention) having an epitaxial layer formed on C-plane and silicon carbide epitaxial substrate (Comparative Example) having an epitaxial layer formed on Si-plane It is the figure which showed the relationship between and carrier density in-plane uniformity. In the manufacturing method of the silicon carbide epitaxial substrate which concerns on embodiment of this invention, it is a figure for demonstrating the relationship between the material of substrate holder 11 and the heat generating body 12, and background concentration. It is sectional drawing for demonstrating the silicon carbide epitaxial substrate which concerns on other embodiment of this invention.

[Description of Embodiment of Present Invention]
Embodiments of the present invention will be described below with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated.

First, outlines of embodiments of the present invention will be listed.
(1) A silicon carbide epitaxial substrate (10) according to an embodiment of the present invention includes a silicon carbide base substrate (1) having a C surface as a main surface (1A) and a C surface of the silicon carbide base substrate (1). And a silicon carbide epitaxial layer (2) disposed on the surface. Silicon carbide epitaxial layer (2) includes a layer having a background concentration of nitrogen atoms of 3 × 10 ¹⁵ cm ⁻³ or less.

  According to the above configuration, it is possible to provide a silicon carbide epitaxial substrate that has good surface properties and a sufficiently reduced background concentration of nitrogen atoms.

  (2) Preferably, the outer diameter of the silicon carbide epitaxial substrate (10) is 100 mm or more.

  According to the above configuration, it is possible to provide a large-diameter silicon carbide epitaxial substrate that has good surface properties and has a sufficiently reduced background concentration of nitrogen atoms.

  (3) Preferably, the ratio of the standard deviation of the nitrogen concentration in the surface layer to the average value of the nitrogen concentration in the surface layer of the silicon carbide epitaxial layer (2) including the main surface of the silicon carbide epitaxial layer (2) is in-plane When defined as uniformity, the in-plane uniformity of the nitrogen concentration is 15% or less.

  According to the above configuration, the in-plane uniformity of the nitrogen concentration contained in silicon carbide epitaxial layer 2 is high. Therefore, if a plurality of silicon carbide semiconductor devices are manufactured on the silicon carbide epitaxial substrate according to the present embodiment, a plurality of silicon carbide semiconductor devices having the same characteristics can be obtained with a high yield.

(4) Preferably, the nitrogen concentration in the silicon carbide epitaxial layer (2) is 2 × 10 ¹⁶ cm ⁻³ or less.

  According to the above configuration, if a silicon carbide semiconductor device is manufactured using the silicon carbide epitaxial substrate according to the present embodiment, variation in characteristics can be suppressed and carbonization suitable for a device that requires high breakdown voltage. A silicon semiconductor device can be obtained.

  (5) A method for manufacturing a silicon carbide epitaxial substrate according to another embodiment of the present invention includes a step of preparing a silicon carbide base substrate (1) having a C-plane as a main surface (1A), and a silicon carbide base substrate By supplying a raw material gas used for forming the silicon carbide epitaxial layer (2) to (1) and heating the silicon carbide base substrate (1) to the epitaxial growth temperature, a silicon carbide base substrate ( 1) forming a silicon carbide epitaxial layer (2) on the C-plane. In the step of forming the silicon carbide epitaxial layer (2), the ratio C / Si of the number of carbon atoms to the number of silicon atoms in the source gas is 1.7 or more and 2.1 or less, and the epitaxial growth temperature is 1600 ° C. or more and 1800 It is the range below ℃.

  According to the above configuration, it is possible to manufacture a silicon carbide epitaxial substrate having good surface properties and a sufficiently reduced background concentration of nitrogen atoms.

  (6) Preferably, epitaxial growth temperature is the range of 1600 degreeC or more and 1700 degrees C or less.

  According to the above configuration, the material gas for forming the silicon carbide epitaxial layer is sufficiently thermally decomposed, and the deterioration of the silicon carbide growth apparatus member and the detachment of Si atoms from the silicon carbide base substrate can be suppressed. it can.

  (7) The manufacturing method further includes a step of disposing the silicon carbide base substrate (1) in the silicon carbide growth apparatus (100) prior to the step of forming the silicon carbide epitaxial layer (2). The silicon carbide growth apparatus (100) includes a member (11) that is in contact with the source gas and is heated to an epitaxial growth temperature. The nitrogen concentration of the member (11) is 10 ppm or less.

  According to the above configuration, the background concentration of nitrogen atoms in the silicon carbide epitaxial substrate can be sufficiently reduced.

(8) The outer diameter of the silicon carbide base substrate (1) is 100 mm or more.
According to the above configuration, when a silicon carbide layer is formed by epitaxial growth on a so-called large-diameter silicon carbide base substrate, the surface properties are good and the background concentration of nitrogen atoms is sufficiently reduced. An epitaxial substrate can be manufactured.

[Details of the embodiment of the present invention]
Next, details of the embodiment of the present invention will be described. In the crystallographic description in this specification, the individual orientation is indicated by [], the collective orientation is indicated by <>, the individual plane is indicated by (), and the collective plane is indicated by {}. In addition, a negative crystallographic index is usually expressed by adding a “-” (bar) above a number, but in this specification a negative sign is added before the number. Yes.

  With reference to FIG. 1, a silicon carbide epitaxial substrate 10 according to an embodiment of the present invention will be described. Silicon carbide epitaxial substrate 10 according to the present embodiment includes a base substrate 1 and a silicon carbide epitaxial layer 2.

  Base substrate 1 is made of single crystal silicon carbide. The outer diameter of the base substrate is, for example, 100 mm or more. Therefore, the outer diameter of silicon carbide epitaxial substrate 10 is also 100 mm or more. The base substrate 1 has a first main surface 1A.

Silicon carbide constituting base substrate 1 has a hexagonal crystal structure, for example, and preferably has a crystal polymorph (polytype) of 4H—SiC. Base substrate 1 contains an n-type impurity such as nitrogen (N) at a high concentration, and its conductivity type is n-type. The impurity concentration of the base substrate 1 is, for example, about 1.0 × 10 ¹⁸ cm ⁻³ or more and 1.0 × 10 ¹⁹ cm ⁻³ or less.

  The first main surface 1A of the base substrate 1 is a C surface. The “C plane” is a plane in which the outermost surface atoms are carbon (C) atoms, and can be expressed as a (000-1) plane. In this specification, the “C plane” may include not only the (000-1) plane but also a plane whose off angle with respect to the (000-1) plane is a predetermined angle (for example, 10 °) or less. .

  Silicon carbide epitaxial layer 2 is made of silicon carbide. Silicon carbide epitaxial layer 2 is formed on first main surface 1A of base substrate 1 by epitaxial growth.

  Silicon carbide epitaxial layer 2 has second main surface 2A. The surface roughness (Ra) of the second main surface 2A is 0.6 nm or less, preferably 0.4 nm or less, and more preferably 0.2 nm or less. Here, the surface roughness (Ra) of the second main surface 2A can be measured by, for example, an atomic force microscope (AFM). On the second main surface 2A, the growth conditions such as the C / Si ratio or the growth temperature are adjusted so that step bunching and the formation of triangular defects are suppressed. By adjusting the C / Si ratio, the growth of the silicon carbide epitaxial layer 2 can be a step flow growth. As a result, surface flatness and occurrence of surface defects can be suppressed.

Silicon carbide epitaxial layer 2 includes an n-type impurity such as nitrogen (N). Therefore, the conductivity type of silicon carbide epitaxial layer 2 is n-type. The impurity concentration of silicon carbide epitaxial layer 2 may be lower than the impurity concentration of base substrate 1. The impurity concentration (nitrogen concentration) of silicon carbide epitaxial layer 2 is, for example, 3.0 × 10 ¹⁵ cm ⁻³ or less, preferably 1.0 × 10 10 when impurity (nitrogen) is not intentionally doped. ¹⁵ cm ⁻³ or less. On the other hand, the impurity concentration (nitrogen concentration) of silicon carbide epitaxial layer 2 is 2.0 × 10 ¹⁶ cm ⁻³ or less when impurities are intentionally doped. That is, in silicon carbide epitaxial layer 2, the background concentration of impurities (nitrogen) is 3.0 × 10 ¹⁵ cm ⁻³ or less. Preferably, the background concentration of nitrogen atoms in silicon carbide epitaxial layer 2 is 1.0 × 10 ¹⁵ cm ⁻³ or less. The nitrogen concentration can be measured by, for example, a secondary ion mass spectrometry (SIMS) apparatus.

  In-plane uniformity (σ / Ave.) In the surface layer including the second main surface 2A of the nitrogen concentration in the silicon carbide epitaxial layer 2 is 15% or less, preferably 10% or less, more preferably 5% or less. Here, the in-plane uniformity is determined by the standard deviation (σ) of the nitrogen concentration measured at a predetermined interval (for example, nine measurement points) in the radial direction and the average value (Ave.) of the measured nitrogen concentration. Represented. That is, in silicon carbide epitaxial layer 2, the nitrogen concentration is extremely low and the in-plane uniformity of the nitrogen concentration is high. Thereby, if a plurality of silicon carbide semiconductor devices are manufactured on silicon carbide epitaxial substrate 10, a plurality of silicon carbide semiconductor devices having the same characteristics can be obtained with a high yield. Silicon carbide epitaxial layer 2 has a film thickness of, for example, about 5 μm to 40 μm.

  Next, with reference to FIG. 2, the manufacturing method of the silicon carbide epitaxial substrate which concerns on this Embodiment is demonstrated. The method for manufacturing a silicon carbide epitaxial substrate according to the present embodiment includes a step of preparing base substrate 1 (S11), a step of disposing base substrate 1 in silicon carbide growth apparatus 100 (see FIG. 3) (S12), By supplying a raw material gas used for forming silicon carbide epitaxial layer 2 to base substrate 1 and heating base substrate 1 to an epitaxial growth temperature, silicon carbide epitaxial layer 2 is formed on base substrate 1. Forming (S13).

  First, base substrate 1 having first main surface 1A having an outer diameter of, for example, 100 mm and made of single crystal silicon carbide is prepared (step (S11)). The base substrate 1 having an outer diameter of 100 mm may be prepared by any method. The outer diameter of the base substrate 1 may be 5 inches or more (for example, 6 inches) (1 inch is about 25.4 mm).

  Next, base substrate 1 is arranged in silicon carbide growth apparatus 100 (step (S12)). Silicon carbide growth apparatus 100 according to the present embodiment is a CVD (Chemical Vapor Deposition) apparatus as an example.

  Referring to FIGS. 3 and 4, base substrate 1 is placed on substrate holder 11 in silicon carbide growth apparatus 100. The substrate holder 11 is surrounded by a heating element 12, a heat insulating material 13, a quartz tube 14, and an induction heating coil 15. Specifically, the substrate holder 11 is disposed, for example, in a recess formed in the heating element 12. The substrate holder 11 can be installed in a state in which the substrate holder 11 can rotate while being disposed on the heating element 12. The heating element 12 has a semi-cylindrical hollow structure, and has a curved surface and a flat surface along an arc.

  In silicon carbide growth apparatus 100, two heating elements 12 are arranged so that the flat surfaces face each other. As a result, a reaction chamber surrounded by the flat surface of the heating element 12 is formed. The concave portion is provided on one flat surface of the heating element 12 forming the reaction chamber.

  The heat insulating material 13 is disposed so as to surround the outer periphery of the heating element 12. The quartz tube 14 is disposed so as to surround the outer peripheral side of the heat insulating material 13. The induction heating coil 15 includes a plurality of coil members, and is provided so as to wind, for example, the outer peripheral side of the quartz tube 14. When the induction heating coil 15 is used as a high frequency coil and a high frequency current is passed through it, the heating element 12 is induction heated by electromagnetic induction. As a result, the base substrate 1 and the source gas supplied to the base substrate 1 can be heated to a predetermined temperature.

  The substrate holder 11 and the heating element 12 are conductive members having high heat resistance, and are composed of members having a very low nitrogen concentration. As shown in FIG. 5, the substrate holder 11 includes a substrate holder base material 11a and a holder coat portion 11b that covers the substrate holder base material 11a. Moreover, the heat generating body 12 is comprised by the heat generating body base material 12a and the heat generating body coat | court part 12b which covers the heat generating body base material 12a.

  The substrate holder base material 11a and the heating element base material 12a are made of, for example, a carbon material. The carbon material constituting the substrate holder base material 11a and the heating element base material 12a has a nitrogen concentration of 10 ppm or less, preferably 5 ppm or less.

  The holder coat part 11b and the heating element coat part 12b are made of SiC. SiC constituting the holder coat part 11b and the heating element coat part 12b has a nitrogen concentration of 10 ppm or less, preferably 5 ppm or less.

  Next, silicon carbide epitaxial layer 2 is formed on first main surface 1A of base substrate 1 (“C plane” defined above) (step (S13)). In silicon carbide growth apparatus 100, source gas used to form silicon carbide epitaxial layer 2 is supplied to base substrate 1, and base substrate 1 is heated to an epitaxial growth temperature, whereby base substrate 1 is heated. Silicon carbide epitaxial layer 2 is formed on first main surface 1A.

As shown in FIG. 4, the source gas is introduced into the CVD apparatus 100 through the pipe 16. The source gas includes monosilane (SiH ₄ ), propane (C ₃ H ₈ ), ammonia (NH ₃ ), and the like. Further, a carrier gas containing hydrogen (H ₂ ) is introduced in addition to the source gas. At this time, any source gas is introduced into the reaction chamber so as to be sufficiently thermally decomposed when supplied onto the first main surface 1A of the base substrate 1.

  Among the source gases, particularly ammonia gas used as a dopant gas, it is preferable that the ammonia gas is preliminarily decomposed by preheating before being supplied onto the base substrate 1. By preheating, the ammonia gas is supplied to the base substrate 1 in a state of being reliably thermally decomposed. Thereby, in the step of forming silicon carbide epitaxial layer 2, the nitrogen concentration close to a linear distribution on first main surface 1 </ b> A of base substrate 1 on which epitaxial growth proceeds or on the epitaxial growth surface of silicon carbide epitaxial layer 2. Distribution is possible. As a result, the uniformity of the concentration distribution of nitrogen doped in silicon carbide epitaxial layer 2 can be improved.

  The preheating with respect to the ammonia gas is performed by, for example, a preheating mechanism 17 attached to the pipe 16. The preheating mechanism 17 has a room heated to, for example, 1300 ° C. or higher. After the ammonia gas is circulated through the preheating mechanism 17, the ammonia gas is supplied to the silicon carbide growth apparatus 100. As a result, the ammonia gas can be sufficiently thermally decomposed without causing a large disturbance in the gas flow.

  The “room” provided in the preheating mechanism 17 means a space for heating the flowing gas, and includes a long and thin tube heated from the outside, a room in which a heat transfer coil is installed, It includes a wide space in which fins and the like are formed on the wall surface. The upper limit of the temperature of the wall surface of the room is preferably 1350 ° C. or higher in order to perform reliable thermal decomposition even if the length of the room is somewhat short, and is preferably 1600 ° C. or lower from the viewpoint of thermal efficiency.

  The preheating mechanism 17 is sufficient if the ammonia gas is thermally decomposed sufficiently and without disturbing the flow until the ammonia gas arrives on the base substrate 1 on which the epitaxial growth is performed. For this reason, the preheating mechanism 17 may be separate from the reaction vessel or may be integrated with the reaction vessel. Furthermore, the raw material gas containing ammonia gas may be preheated integrally, or after preheating only the ammonia gas, another raw material gas may be mixed.

  Each gas may be mixed before being introduced into the reaction chamber of silicon carbide growth apparatus 100, or may be mixed in the reaction chamber of silicon carbide growth apparatus 100.

The base substrate 1 disposed on the substrate holder 11 is supplied with the carrier gas and the source gas while being heated. Thereby, silicon carbide epitaxial layer 2 doped with nitrogen (N) atoms is formed on first main surface 1A. Specifically, silicon carbide epitaxial layer 2 is formed under conditions of a growth temperature of 1600 ° C. or higher and 1800 ° C. or lower and a pressure of 1 × 10 ³ Pa or higher and 3 × 10 ⁴ Pa or lower. At this time, the n-type impurity concentration in the silicon carbide epitaxial layer 2 is set to a desired concentration by adjusting the flow rate of the NH ₃ gas. For example, the n-type impurity concentration in silicon carbide epitaxial layer 2 is set to about 2 × 10 ¹⁶ cm ⁻³ or less. Thereby, for example, a silicon carbide semiconductor device having a desired breakdown voltage can be manufactured.

  When the growth temperature is less than 1600 ° C., it is difficult to sufficiently thermally decompose the source gas. On the other hand, when the growth temperature exceeds 1800 ° C., the deterioration of the silicon carbide growth apparatus member (substrate holder 11 and the like) is promoted and silicon (Si) atoms are easily detached from the base substrate 1. The growth temperature of the silicon carbide epitaxial layer 2 is 1600 ° C. or higher and 1800 ° C. in order to suppress deterioration of the member for the silicon carbide growth apparatus and detachment of Si atoms from the base substrate 1 while sufficiently thermally decomposing the source gas. The temperature is preferably 1600 ° C. or higher and more preferably 1600 ° C. or lower and 1700 ° C. or lower.

  The n-type impurity concentration in silicon carbide epitaxial layer 2 can be determined according to the characteristics of a device manufactured using silicon carbide epitaxial substrate 10. However, the concentration of nitrogen atoms doped in silicon carbide epitaxial layer 2 with the source gas is higher than the background concentration.

  The thickness of silicon carbide epitaxial layer 2 is about 15 μm. In this step (S13), the substrate holder 11 and the base substrate 1 disposed on the substrate holder 11 are rotating.

  In the source gas used for forming silicon carbide epitaxial layer 2 in this step (S13), the ratio of the number of C atoms to the number of Si atoms (C / Si ratio) is 1.7 or more and 2.1 or less. .

  When a source gas having a C / Si ratio exceeding 2.2 is used, crystal defects such as triangular defects or step bunching are likely to occur in the formed silicon carbide epitaxial layer 2. On the other hand, when the C / Si ratio is less than 1.7, nitrogen atoms are easily taken into carbon atom positions (C sites) in the silicon carbide crystal during epitaxial growth of the silicon carbide layer. For this reason, when a source gas having a C / Si ratio of less than 1.7 is used, background nitrogen atoms are also easily taken into silicon carbide epitaxial layer 2. Therefore, the C / Si ratio is preferably 1.7 or more and 2.1 or less.

  Silicon carbide epitaxial substrate 10 according to the present embodiment includes a silicon carbide base substrate having a C surface as a main surface, and a silicon carbide epitaxial layer formed on the C surface of the silicon carbide base substrate and including the main surface. . Silicon carbide semiconductor devices manufactured using the C-plane have attracted attention from the viewpoint of characteristics. Therefore, silicon carbide epitaxial substrate 10 according to the present embodiment can improve the characteristics of the silicon carbide semiconductor device. On the other hand, when a silicon carbide epitaxial layer is grown on the C plane, nitrogen atoms are easily taken into the silicon carbide epitaxial layer. For this reason, the background concentration of nitrogen atoms tends to be high.

  Silicon carbide epitaxial substrate 10 according to the present embodiment has good surface properties and a high in-plane control with a low background concentration of nitrogen atoms, even if the outer diameter is 100 mm or more and a large diameter. Uniformity. Therefore, by manufacturing a silicon carbide semiconductor device using silicon carbide epitaxial substrate 10 according to the present embodiment, variation in characteristics is suppressed, and silicon carbide semiconductor device particularly suitable for a device that requires high breakdown voltage Can be obtained at a high yield.

  With reference to FIG. 5 and FIG. 6, the method for manufacturing the silicon carbide epitaxial substrate according to the present embodiment will be described in more detail.

  In the step of forming silicon carbide epitaxial layer 2 on first main surface 1A of base substrate 1 (S13), base substrate 1 is placed on substrate holder 11 in silicon carbide growth apparatus 100 and rotates (FIG. 6). In the direction of arrow R). Therefore, while the step (S13) is being performed, the outer peripheral region of the base substrate 1 is adjacent to the members such as the substrate holder 11 and the heating element 12 as compared with the inner region, and the flow direction G1 of the source gas is increased. It will be located upstream. That is, nitrogen released from the members constituting silicon carbide growth apparatus 100 is supplied to the inner region through the outer peripheral region of base substrate 1.

  As described above, silicon carbide epitaxial layer 2 easily takes in nitrogen. Therefore, when the process (S13) is performed under the epitaxial growth conditions that can form silicon carbide epitaxial layer 2 having good surface properties using a conventional silicon carbide growth apparatus, base substrate 1 (or silicon carbide epitaxial substrate 10) More nitrogen is taken into the region on the outer peripheral side of the.

  Therefore, a difference in nitrogen concentration occurs between the outer peripheral region and the inner region, and the in-plane uniformity of the nitrogen concentration of silicon carbide epitaxial substrate 10 deteriorates. This tendency is particularly remarkable when the flow rate of the dopant gas is reduced. In addition, the in-plane uniformity of silicon carbide epitaxial substrate 10 having a nitrogen concentration deteriorates as the substrate diameter increases.

  On the other hand, the substrate holder 11 and the heating element 12 as the members for the silicon carbide growth apparatus according to the present embodiment include the substrate holder base material 11a, the holder coating portion 11b, the heating body base material 12a, and the heating body coating portion 12b. Each nitrogen concentration is 10 ppm or less. As a result, the amounts of nitrogen gas G2 released from substrate holder 11 and nitrogen gas G3 released from heating element 12 are sufficiently reduced to such an extent that no problem occurs in silicon carbide epitaxial substrate 10. That is, the nitrogen gas G2a released from the substrate holder base material 11a, the nitrogen gas G2b released from the holder coat part 11b, the nitrogen gas G3a released from the heating element base material 12a, and the heat generator coat part 12b are released. The amount of nitrogen gas G3b is sufficiently reduced.

  Therefore, according to the present embodiment, the step (S13) of forming silicon carbide epitaxial layer 2 can be performed under a condition in which the background concentration of nitrogen atoms is reduced. As a result, silicon carbide epitaxial layer 2 having high in-plane nitrogen concentration uniformity can be formed even under epitaxial growth conditions that can improve the surface properties of silicon carbide epitaxial layer 2. That is, according to the embodiment of the present invention, silicon carbide epitaxial substrate 10 including silicon carbide epitaxial layer 2 having good surface properties and high in-plane uniformity of nitrogen concentration can be manufactured.

In the method for manufacturing the silicon carbide epitaxial substrate according to the present embodiment, ammonia gas is used as the dopant gas in the step (S13) of forming silicon carbide epitaxial layer 2, but this is not restrictive. For example, nitrogen (N ₂ ) gas may be used. In this case, the same effects as those of the method for manufacturing the silicon carbide epitaxial substrate according to the present embodiment can be achieved by appropriately controlling the flow rate of N ₂ gas and the like.

Even when the dopant gas is N ₂ gas, it is preferable that the N ₂ gas is supplied to the silicon carbide growth apparatus 100 after being circulated through the preheating mechanism 17 (see FIG. 5). Thus, before supplying N ₂ gas on the base substrate 1 can be sufficiently thermally decomposing the N ₂ gas. The heating temperature in the preheating mechanism 17 should just be a temperature which can fully thermally decompose nitrogen gas, for example, should just be about 1600 degreeC.

  Hereinafter, an example of a manufacturing method according to an embodiment of the present invention and a silicon carbide epitaxial substrate manufactured by the manufacturing method will be described.

  FIG. 7 shows a silicon carbide epitaxial substrate (an embodiment of the present invention) having an epitaxial layer formed on the C plane and a silicon carbide epitaxial substrate (comparative example) having an epitaxial layer formed on the Si surface. FIG. 5 is a diagram showing the relationship between background density and carrier density in-plane uniformity.

  Referring to FIG. 7, the numerical values in the graph represent the C / Si ratio. The vertical axis of the graph represents the in-plane uniformity value of the carrier concentration (nitrogen atom concentration). The in-plane uniformity value is the above-mentioned σ / Ave. Is a value obtained by Therefore, the smaller the in-plane uniformity value of the carrier concentration, the higher the in-plane uniformity of the carrier concentration. The horizontal axis of the graph represents the background concentration of nitrogen atoms in the silicon carbide epitaxial layer.

  In the formation of a silicon carbide epitaxial substrate (shown as “C-plane” in FIG. 7) having an epitaxial layer formed on the C-plane, the C / Si ratio was selected to be 1.5 and 1.9. The epitaxial growth temperature was 1620 ° C., for example.

When 1.5 was selected as the C / Si ratio, the background concentration was 8.0 × 10 ¹⁴ / cm ³ and the in-plane uniformity of the carrier concentration was 10%. On the other hand, when 1.9 was selected as the C / Si ratio, the background concentration was 5.0 × 10 ¹⁴ / cm ³ and the in-plane uniformity of the carrier concentration was 4%.

  On the other hand, in the formation of a silicon carbide epitaxial substrate (shown as “Si surface” in FIG. 7) having an epitaxial layer formed on the Si surface, the C / Si ratio was selected to be 1.0 and 1.2. The epitaxial growth temperature was 1620 ° C., for example.

When 1.0 is selected as the C / Si ratio, the background concentration of nitrogen atoms in the silicon carbide epitaxial layer is about 8.5 × 10 ¹⁴ / cm ³ , and the in-plane uniformity of the carrier concentration is 11%. Met. When 1.2 was selected as the C / Si ratio, the background concentration of nitrogen atoms was 6.0 × 10 ¹⁴ / cm ³ and the in-plane uniformity of the carrier concentration was 5%.

  As shown in FIG. 7, in the method for manufacturing a silicon carbide epitaxial substrate according to the present embodiment, the C / Si ratio in the source gas is 1 when the silicon carbide layer is formed on the C surface of the base substrate by epitaxial growth. The epitaxial growth temperature is selected in the range of 1600 ° C. or higher and 1800 ° C. or lower. Thereby, not only the background concentration of nitrogen atoms can be lowered, but also the in-plane uniformity of the carrier concentration can be improved.

  Nitrogen contained in the members constituting substrate holder 11 and heating element 12 shown in FIG. 5 affects the background concentration of the silicon carbide epitaxial substrate. FIG. 8 is a diagram for explaining the relationship between the material of substrate holder 11 and heating element 12 and the background concentration in the method for manufacturing a silicon carbide epitaxial substrate according to the embodiment of the present invention.

  Referring to FIG. 8, conventional members are used for substrate holder 11 and heating element 12 in forming a silicon carbide epitaxial substrate having an epitaxial layer formed on a C-plane silicon carbide base substrate. Specifically, the holder coat portion 11b and the heating element coat portion 12b are films made of tantalum carbide (TaC). The nitrogen concentration of the substrate holder base material was 10 ppm, and the nitrogen concentration of the holder coat part was 900 ppm. The nitrogen concentration of the heating element base material was 30 ppm, and the nitrogen concentration of the heating element coating portion was 2%.

A silicon carbide epitaxial substrate was prepared under two conditions with a C / Si ratio of 1.5 and 1.9. The epitaxial growth temperature was 1620 ° C. When the C / Si ratio was 1.5, the background concentration of nitrogen atoms in the silicon carbide epitaxial layer was about 2.0 × 10 ¹⁵ / cm ⁻³ . On the other hand, when the C / Si ratio was 1.9, the background concentration of nitrogen atoms was about 1.3 × 10 ¹⁵ / cm ⁻³ .

  Also from this result, the C / Si ratio in the source gas is selected within the range of 1.7 to 2.1 and the epitaxial growth temperature is selected within the range of 1600 ° C. to 1800 ° C. It can be seen that the background concentration of nitrogen atoms can be reduced.

  On the other hand, the silicon carbide epitaxial substrate according to the present embodiment was formed using a member (high purity member) in which holder coat portion 11b and heating element coat portion 12b are SiC films. The substrate holder used was composed of a substrate holder base material having a nitrogen concentration of 2 ppm and a holder coat portion having a nitrogen concentration of 0.4 ppm. As the heating element, a heating element base material having a nitrogen concentration of 2 ppm and a heating element coating portion having a nitrogen concentration of 0.4 ppm was used. The C / Si ratio was 1.9. The epitaxial growth temperature was 1620 ° C.

As a result of forming the silicon carbide epitaxial layer on the C-plane of the base substrate using the high purity member, the background concentration of nitrogen atoms in the silicon carbide epitaxial layer was 5 × 10 ¹⁴ / cm ⁻³ . Therefore, it can be seen that the background concentration of the silicon carbide epitaxial substrate can be reduced by using the SiC-coated member in the silicon carbide growth apparatus as compared with the TaC-coated member.

Further, from the relationship between the C / Si ratio and the background concentration when the conventional member is used for the substrate holder 11 and the heating element 12, when the high purity member is used, the C / Si ratio is 1.7. It can be estimated that a background density | concentration can be 1.0x10 < ¹⁵ > / cm < ^-3 > or less by setting it as the range of -2.1.

In the above embodiment, silicon carbide epitaxial layer 2 is a single layer in which the background concentration of nitrogen atoms is 3 × 10 ¹⁵ cm ⁻³ or less. However, as shown in FIG. 9, for example, silicon carbide epitaxial layer 2 may be composed of silicon carbide epitaxial layers 21 and 22. At least one of silicon carbide epitaxial layers 21 and 22 may have a background concentration of nitrogen atoms of 3 × 10 ¹⁵ cm ⁻³ or less. Furthermore, silicon carbide epitaxial layer 2 is composed of more than two silicon carbide epitaxial layers, and at least one of the silicon carbide epitaxial layers has a nitrogen atom background concentration of 3 × 10 ¹⁵ cm ⁻³ or less. Good.

In the above method for manufacturing a silicon carbide epitaxial substrate, before or after the step (S13) of forming the silicon carbide epitaxial layer 2, the flow rate and partial pressure of the source gas are changed to continue the step (S13). A silicon carbide epitaxial layer having an impurity concentration or the like different from that of silicon carbide epitaxial layer 2 is formed. Even if it does in this way, there can exist an effect similar to the manufacturing method of the silicon carbide epitaxial substrate which concerns on this Embodiment. That is, the background concentration of nitrogen atoms in at least one of the plurality of silicon carbide epitaxial layers can be 3 × 10 ¹⁵ cm ⁻³ or less. In other words, when the whole of the plurality of silicon carbide epitaxial layers is regarded as one silicon carbide epitaxial layer, the silicon carbide epitaxial layer includes a layer having a background concentration of nitrogen atoms of 3 × 10 ¹⁵ cm ⁻³ or less.

  The embodiment disclosed this time is to be considered as illustrative in all points 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.

  The present invention is particularly advantageously applied to a silicon carbide semiconductor device that requires a high breakdown voltage.

DESCRIPTION OF SYMBOLS 1 Base substrate 1A 1st main surface 2,21,22 Silicon carbide epitaxial layer 2A 2nd main surface 10 Silicon carbide epitaxial substrate 11 Substrate holder 11a Substrate holder base material 11b Holder coat part 12 Heat generating body 12a Heat generating body base material 12b Heating element coating part 13 Heat insulating material 14 Quartz tube 15 Induction heating coil 16 Pipe 17 Preheating mechanism 100 Silicon carbide growth apparatus G1 Flow direction G2a, G2b, G2, G3b, G3, G3a Nitrogen gas R Arrow

Claims (8)

A silicon carbide base substrate having a C-plane as a main surface;
A silicon carbide epitaxial layer disposed on the C-plane of the silicon carbide base substrate,
The silicon carbide epitaxial layer includes a layer having a nitrogen atom background concentration of 3 × 10 ¹⁵ cm ⁻³ or less.   The silicon carbide epitaxial substrate according to claim 1, wherein an outer diameter of the silicon carbide epitaxial substrate is 100 mm or more. When the ratio of the standard deviation of the nitrogen concentration in the surface layer to the average value of the nitrogen concentration in the surface layer of the silicon carbide epitaxial layer including the main surface of the silicon carbide epitaxial layer is defined as in-plane uniformity,
The silicon carbide epitaxial substrate according to claim 1 or 2, wherein the in-plane uniformity of the nitrogen concentration is 15% or less. 4. The silicon carbide epitaxial substrate according to claim 1, wherein the nitrogen concentration in the silicon carbide epitaxial layer is 2 × 10 ¹⁶ cm ⁻³ or less. 5. Preparing a silicon carbide base substrate having a C-plane as a main surface;
By supplying a source gas used for forming a silicon carbide epitaxial layer to the silicon carbide base substrate, and heating the silicon carbide base substrate to an epitaxial growth temperature, the C of the silicon carbide base substrate is obtained. Forming the silicon carbide epitaxial layer on the surface,
In the step of forming the silicon carbide epitaxial layer,
The ratio C / Si of the number of carbon atoms to the number of silicon atoms in the source gas is 1.7 or more and 2.1 or less,
The method for manufacturing a silicon carbide epitaxial substrate, wherein the epitaxial growth temperature is in a range of 1600 ° C. or higher and 1800 ° C. or lower.   The method for manufacturing a silicon carbide epitaxial substrate according to claim 5, wherein the epitaxial growth temperature is in a range of 1600 ° C. or higher and 1700 ° C. or lower. Prior to the step of forming the silicon carbide epitaxial layer, further comprising the step of disposing the silicon carbide base substrate in a silicon carbide growth apparatus,
The silicon carbide growth apparatus includes a member that is in contact with the source gas and heated to the epitaxial growth temperature,
The manufacturing method of the silicon carbide epitaxial substrate of Claim 5 or Claim 6 whose nitrogen concentration of the said member is 10 ppm or less.   The method for manufacturing a silicon carbide epitaxial substrate according to claim 5, wherein an outer diameter of the silicon carbide base substrate is 100 mm or more.

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