Vapor growth method and vapor growth apparatus

Abstract

To provide a vapor growth method capable of reducing a crystal defect density in a silicon carbide layer.SOLUTION: A vapor growth method includes steps of: supplying a first process gas onto a silicon carbide substrate 50 in a first gas condition; forming a first silicon carbide layer 52 having a first doping concentration in a first growth rate; supplying a second process gas in a second gas condition after the formation of the first silicon carbide layer; forming a second silicon carbide layer 56 having a second doping concentration in a second growth rate larger than the first growth rate; supplying a third process gas in a third gas condition after the formation of the second silicon carbide layer; and forming a third silicon carbide layer 60 having a third doping concentration lower than the first doping concentration and the second doping concentration in a third growth rate larger than the second growth rate.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a vapor phase growth method and apparatus for forming a film by supplying gas, and to a vapor phase growth apparatus. [Background technology]

[0002] One method for forming high-quality semiconductor films is epitaxial growth, which involves growing a single-crystal film on a substrate such as a wafer using vapor phase growth. In a vapor phase growth apparatus using epitaxial growth, a wafer is placed in a substrate holding section within a reaction chamber maintained at atmospheric pressure or reduced pressure.

[0003] Then, while heating the wafer, process gases such as source gas, which are the raw materials for the semiconductor film, are supplied, for example, from the top of the reaction chamber to the wafer surface inside the reaction chamber. At the wafer surface, thermal decomposition and chemical reactions occur with the source gas, and an epitaxial single crystal film is formed on the wafer surface.

[0004] When a silicon carbide layer is formed on a substrate using epitaxial growth technology, crystal defects are generated in the silicon carbide layer. The presence of crystal defects in the silicon carbide layer can lead to problems, such as reduced reliability of semiconductor devices formed on the layer. Therefore, it is desirable to reduce the density of crystal defects in the silicon carbide layer. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] S. Izumi et al., “Structual analysis and reduction of in-grown stacking faults in 4H-SiC epilayers”, Appl. Phys. Lett., 86 (2005) 202108. [Non-Patent Document 2] T.Hori et al., “Fast homoepitaxial growth of 4H-SiC with low basal-plane dislocation density and low trap concentration by hot-wall chemical vapor deposition”, J.Cryst.Growth, 306 (2007) 297. [Overview of the project] [Problems that the invention aims to solve]

[0006] The problem that this invention aims to solve is to provide a vapor phase growth method that can reduce the density of crystal defects in the silicon carbide layer. [Means for solving the problem]

[0007] A vapor phase growth method according to one aspect of the present invention involves supplying a first process gas containing a carrier gas into a reaction chamber under first gas conditions to form a first silicon carbide layer having a first doping concentration on a silicon carbide substrate at a first growth rate; after forming the first silicon carbide layer, supplying a second process gas containing a carrier gas into the reaction chamber under second gas conditions to form a second silicon carbide layer having a second doping concentration at a second growth rate greater than the first growth rate; after forming the second silicon carbide layer, supplying a third process gas containing a carrier gas into the reaction chamber under third gas conditions to form a third silicon carbide layer having a third doping concentration lower than the first and second doping concentrations at a third growth rate greater than the second growth rate.

[0008] In the vapor phase growth method according to the above embodiment, it is preferable that the thickness of the second silicon carbide layer is greater than the thickness of the first silicon carbide layer, and the thickness of the third silicon carbide layer is greater than the thickness of the second silicon carbide layer.

[0009] In the vapor phase growth method according to the above embodiment, it is preferable that, after forming the first silicon carbide layer, a first transition layer is formed during a first transition time when switching from the first gas conditions to the second gas conditions, and after forming the second silicon carbide layer, a second transition layer is formed during a second transition time when switching from the second gas conditions to the third gas conditions, and the average residence time of the carrier gas in the reaction chamber when forming the first transition layer is shorter than the first transition time, and the average residence time of the carrier gas in the reaction chamber when forming the second transition layer is shorter than the second transition time.

[0010] In the vapor phase growth method according to the above embodiment, it is preferable that the carbon / silicon atom ratio in the second process gas is smaller than the carbon / silicon atom ratio in the first process gas, and the carbon / silicon atom ratio in the third process gas is larger than the carbon / silicon atom ratio in the second process gas.

[0011] A vapor deposition apparatus according to one aspect of the present invention includes a reaction chamber, a carrier gas supply pipe for supplying a carrier gas to the reaction chamber, a first source gas supply pipe for supplying a first source gas containing silicon (Si) to the reaction chamber, a second source gas supply pipe for supplying a second source gas containing carbon (C) to the reaction chamber, a first mass flow controller provided in the carrier gas supply pipe for controlling the flow rate of the carrier gas supplied to the reaction chamber, a second mass flow controller provided in the first source gas supply pipe for controlling the flow rate of the first source gas supplied to the reaction chamber, a third mass flow controller provided in the second source gas supply pipe for controlling the flow rate of the second source gas supplied to the reaction chamber, a pressure adjustment valve for adjusting the pressure in the reaction chamber, and a control unit for controlling the first mass flow controller, the second mass flow controller, the third mass flow controller, and the pressure adjustment valve such that when switching the flow rate of at least one of the first source gas and the second source gas supplied to the reaction chamber at a transition time, the average residence time of the carrier gas in the reaction chamber becomes shorter than the transition time.

Advantages of the Invention

[0012] According to the present invention, it becomes possible to provide a vapor deposition method capable of reducing the crystal defect density in a silicon carbide layer.

Brief Description of the Drawings

[0013] [Figure 1] Schematic diagram of the vapor deposition apparatus of the embodiment. [Figure 2] Schematic cross-sectional view of an example of a silicon carbide layer formed by the vapor deposition method of the embodiment. [Figure 3] Explanation diagram of the vapor deposition method of the embodiment. [Figure 4] Explanation diagram of the vapor deposition method of the embodiment. <0000​​​A schematic cross-sectional view of the silicon carbide layer formed by the vapor phase growth method of the second comparative example. [Figure 7] A diagram illustrating the operation and effects of the vapor phase growth method according to the embodiment. [Figure 8] A schematic diagram of a first modified example of the vapor phase growth apparatus of the embodiment. [Figure 9] A schematic diagram of a second modified example of the vapor phase growth apparatus of the embodiment. [Modes for carrying out the invention]

[0014] Embodiments of the present invention will be described below with reference to the drawings.

[0015] In this specification, identical or similar components may be denoted by the same reference numeral.

[0016] In this specification, the direction of gravity when the vapor phase growth apparatus is installed in a manner that enables film formation is defined as "down," and the opposite direction is defined as "up." Therefore, "lower part" means the position in the direction of gravity relative to a reference, and "downward" means the direction of gravity relative to a reference. Furthermore, "upper part" means the position in the opposite direction to the direction of gravity relative to a reference, and "upward" means the opposite direction to the direction of gravity relative to a reference. Also, "vertical direction" refers to the direction of gravity.

[0017] Furthermore, in this specification, "process gas" is a general term for gases used for film deposition on a substrate, and includes, for example, carrier gas, source gas, dopant gas, assist gas, and mixtures thereof. Carrier gas may be used to form the main gas stream after being introduced into the reaction chamber and to transport source gas, dopant gas, assist gas, and other gases to the wafer within the reaction chamber. Carrier gas may also be used to be mixed with source gas, dopant gas, assist gas, and other gases by connecting a gas supply pipe before introduction into the reaction chamber, and then transported to the reaction chamber.

[0018] The vapor phase growth method of the embodiment involves supplying a first process gas containing a carrier gas into a reaction chamber under first gas conditions to form a first silicon carbide layer having a first doping concentration on a silicon carbide substrate at a first growth rate; after forming the first silicon carbide layer, supplying a second process gas containing a carrier gas into the reaction chamber under second gas conditions to form a second silicon carbide layer having a second doping concentration at a second growth rate greater than the first growth rate; after forming the second silicon carbide layer, supplying a third process gas containing a carrier gas into the reaction chamber under third gas conditions to form a third silicon carbide layer having a third doping concentration lower than the first and second doping concentrations at a third growth rate greater than the second growth rate.

[0019] Furthermore, the vapor phase growth apparatus of the embodiment includes a reaction chamber, a carrier gas supply pipe for supplying a carrier gas to the reaction chamber, a first source gas supply pipe for supplying a first source gas containing silicon (Si) to the reaction chamber, a second source gas supply pipe for supplying a second source gas containing carbon (C) to the reaction chamber, a first mass flow controller provided in the carrier gas supply pipe for controlling the flow rate of the carrier gas supplied to the reaction chamber, a second mass flow controller provided in the first source gas supply pipe for controlling the flow rate of the first source gas supplied to the reaction chamber, a third mass flow controller provided in the second source gas supply pipe for controlling the flow rate of the second source gas supplied to the reaction chamber, a pressure regulating valve for adjusting the pressure inside the reaction chamber, and a control unit that controls the first mass flow controller, the second mass flow controller, the third mass flow controller, and the pressure regulating valve so that when switching the flow rate of at least one of the first source gas and the second source gas supplied to the reaction chamber in a transition time, the average residence time of the carrier gas inside the reaction chamber is shorter than the transition time.

[0020] Figure 1 is a schematic diagram of a vapor phase growth apparatus according to an embodiment. The vapor phase growth apparatus 100 of the embodiment is, for example, an epitaxial growth apparatus for epitaxially growing a single-crystal silicon carbide layer on a single-crystal silicon carbide substrate.

[0021] The vapor phase growth apparatus 100 of the embodiment includes a reaction chamber 10, a susceptor 12, a heater 14, a carrier gas supply pipe 15, a first source gas supply pipe 16, a second source gas supply pipe 17, a dopant gas supply pipe 18, an assist gas supply pipe 19, a first mass flow controller 25, a second mass flow controller 26, a third mass flow controller 27, a fourth mass flow controller 28, a fifth mass flow controller 29, exhaust piping 30, a pressure regulating valve 31, an exhaust pump 32, and a control unit 34. The control unit 34 includes a process condition storage unit 34a, an average residence time calculation unit 34b, a transition time determination unit 34c, a flow rate command unit 34d, and a valve opening command unit 34e.

[0022] The reaction chamber 10 is made of, for example, stainless steel. The reaction chamber 10 has, for example, cylindrical walls. A silicon carbide layer is formed on the surface of the wafer W inside the reaction chamber 10. The wafer W is an example of a substrate.

[0023] The susceptor 12 is installed inside the reaction chamber 10. The susceptor 12 has the function of holding the wafer W. The susceptor 12 may have an opening in its center.

[0024] The heater 14 is located inside the reaction chamber 10. The heater 14 is located below the susceptor 12. The heater 14 has the function of heating the wafer W. In addition, the reaction chamber 10 may be provided with a heater (not shown) positioned parallel to the side of the reaction chamber 10. The heater (not shown) positioned parallel to the side of the reaction chamber 10 can heat the wafer via a hot wall (not shown) positioned inside it.

[0025] The carrier gas supply pipe 15 is connected to the reaction chamber 10. Multiple carrier gas supply pipes 15 may be connected to the reaction chamber 10. The carrier gas supply pipe 15 supplies carrier gas to the reaction chamber 10. The carrier gas is, for example, hydrogen gas, argon gas, or helium gas. The carrier gas may be introduced into the reaction chamber 10 alone, or it may be mixed with other gases such as source gas, dopant gas, and assist gas before being introduced into the reaction chamber 10.

[0026] The first source gas supply pipe 16 is connected to the reaction chamber 10. The first source gas supply pipe 16 may also be connected to the carrier gas supply pipe 15, thereby connecting to the carrier gas supply pipe 15 and thus to the reaction chamber 10 via the carrier gas supply pipe 15. The first source gas supply pipe 16 supplies a first source gas containing silicon (Si) to the reaction chamber 10. The first source gas is a raw material for forming the silicon carbide layer. The first source gas is, for example, monosilane (SiH4) gas.

[0027] The second source gas supply pipe 17 is connected to the reaction chamber 10. The second source gas supply pipe 17 may also be connected to the carrier gas supply pipe 15, thereby connecting to the carrier gas supply pipe 15 and thus to the reaction chamber 10 via the carrier gas supply pipe 15. The second source gas supply pipe 17 supplies a second source gas containing carbon (C) to the reaction chamber 10. The second source gas is a raw material for forming the silicon carbide layer. The second source gas is, for example, propane (C3H8) gas.

[0028] The dopant gas supply pipe 18 is connected to the reaction chamber 10. The dopant gas supply pipe 18 may also be connected to the carrier gas supply pipe 15, thereby connecting to the carrier gas supply pipe 15 and connecting to the reaction chamber 10 via the carrier gas supply pipe 15. The dopant gas supply pipe 18 supplies dopant gas to the reaction chamber 10. The dopant gas contains n-type impurities or p-type impurities that act as dopants in the silicon carbide layer. An example of an n-type impurity is nitrogen (N). An example of a p-type impurity is aluminum (Al) or boron (B). An example of a dopant gas for an n-type impurity is nitrogen gas. An example of a dopant gas for a p-type impurity is trimethylaluminum ((CH3)3Al) gas or diborane (B2H6) gas.

[0029] The assist gas supply pipe 19 is connected to the reaction chamber 10. The assist gas supply pipe 19 may also be connected to the carrier gas supply pipe 15, thereby connecting to the carrier gas supply pipe 15 and thus to the reaction chamber 10 via the carrier gas supply pipe 15. The assist gas supply pipe 19 supplies assist gas to the reaction chamber 10. The assist gas suppresses, for example, the clustering of silicon (Si). The assist gas is, for example, hydrogen chloride (HCl) gas.

[0030] The first mass flow controller 25 is installed in the carrier gas supply pipe 15. If multiple carrier gas supply pipes 15 are connected to the reaction chamber 10, the first mass flow controller 25 may be installed in each carrier gas supply pipe 15. The first mass flow controller 25 has the function of monitoring the flow rate of the carrier gas supplied to the reaction chamber 10 and controlling the flow rate of the carrier gas. The carrier gas is, for example, hydrogen gas, argon gas, or helium gas.

[0031] The second mass flow controller 26 is installed in the first source gas supply pipe 16. The second mass flow controller 26 has the function of monitoring the flow rate of the first source gas supplied to the reaction chamber 10 and controlling the flow rate of the first source gas. The first source gas is, for example, monosilane gas.

[0032] The third mass flow controller 27 is installed in the second source gas supply pipe 17. The third mass flow controller 27 has the function of monitoring the flow rate of the second source gas supplied to the reaction chamber 10 and controlling the flow rate of the second source gas. The second source gas is, for example, propane gas.

[0033] The fourth mass flow controller 28 is installed in the dopant gas supply pipe 18. The fourth mass flow controller 28 has the function of monitoring the flow rate of the dopant gas supplied to the reaction chamber 10 and controlling the flow rate of the dopant gas. The dopant gas is, for example, nitrogen gas.

[0034] The fifth mass flow controller 29 is installed in the assist gas supply pipe 19. The fifth mass flow controller 29 has the function of monitoring the flow rate of the assist gas supplied to the reaction chamber 10 and controlling the flow rate of the assist gas. The assist gas is, for example, hydrogen chloride gas.

[0035] The exhaust pipe 30 is connected to the reaction chamber 10. The exhaust pipe 30 has the function of discharging process gas from the reaction chamber 10.

[0036] The pressure regulating valve 31 has the function of adjusting the pressure inside the reaction chamber 10 to a desired pressure by controlling the flow rate of process gas discharged from the reaction chamber 10. The pressure regulating valve 31 is, for example, a throttle valve or a butterfly valve.

[0037] The exhaust pump 32 has the function of discharging gas from the reaction chamber 10. The exhaust pump 32 is, for example, a vacuum pump.

[0038] The control unit 34 controls the operation of the vapor phase growth apparatus 100. For example, the control unit 34 controls the operation of the first mass flow controller 25, the second mass flow controller 26, the third mass flow controller 27, the fourth mass flow controller 28, the fifth mass flow controller 29, the pressure regulating valve 31, and the exhaust pump 32.

[0039] The control unit 34 is, for example, a control circuit. The control unit 34 is, for example, an electronic circuit. The control unit 34 includes, for example, hardware and software.

[0040] The control unit 34 includes a process condition storage unit 34a, an average residence time calculation unit 34b, a transition time determination unit 34c, a flow rate command unit 34d, and a valve opening command unit 34e.

[0041] The process condition storage unit 34a has the function of storing process conditions for, for example, forming a silicon carbide layer on a wafer W. Process conditions include, for example, the gas conditions, wafer temperature, reaction chamber pressure, or duration for each process step when forming the silicon carbide layer. Gas conditions include, for example, the type of gas or gas flow rate. The process condition storage unit 34a also stores, for example, the reaction chamber volume.

[0042] The process condition storage unit 34a is, for example, a memory device. The process condition storage unit 34a is, for example, a semiconductor memory.

[0043] The average residence time calculation unit 34b has the function of calculating the average residence time tx of the carrier gas in the reaction chamber 10. The average residence time tx of the carrier gas in the reaction chamber 10 means the average time from when the carrier gas is supplied into the reaction chamber 10 until the carrier gas is discharged outside the reaction chamber 10. The average residence time tx can be expressed, for example, by the following formula. Note that the carrier gas flow rate may be approximately the exhaust flow rate, and the same applies to the following description. In addition, the reaction chamber volume in the following formula is the volume of the space enclosed by the walls of the reaction chamber 10 minus the volume occupied by the various components placed in the reaction chamber, and the same applies to the following description. tx = reaction chamber pressure [Pa] × reaction chamber volume [m³] 3 ] / Carrier gas flow rate [Pa·m 3 / s]

[0044] The average residence time calculation unit 34b calculates the average residence time tx from, for example, the carrier gas flow rate, reaction chamber pressure, and reaction chamber volume stored in the process condition storage unit 34a.

[0045] The average dwell time calculation unit 34b is, for example, an average dwell time calculation circuit. The average dwell time calculation unit 34b is, for example, an electronic circuit. The average dwell time calculation unit 34b includes, for example, hardware and software.

[0046] The transition time determination unit 34c has the function of determining the transition time t required to transition from one process step to the next process step, for example, when forming a silicon carbide layer. The transition time determination unit 34c also has the function of determining the length of the transition time t when switching the flow rate of the source gas supplied to the reaction chamber 10 at a transition time t. The transition time t is, for example, the time required from the start to the end of the change in the flow rate of the source gas.

[0047] The transition time determination unit 34c determines the transition time t, for example, such that the average residence time tx of the carrier gas in the reaction chamber 10 is shorter than the transition time t. The transition time determination unit 34c determines the transition time t based on the average residence time tx of the carrier gas calculated by the average residence time calculation unit 34b.

[0048] The flow rate command unit 34d has the function of commanding the gas flow rate to, for example, the first mass flow controller 25, the second mass flow controller 26, the third mass flow controller 27, the fourth mass flow controller 28, and the fifth mass flow controller 29.

[0049] The flow rate command unit 34d is, for example, a flow rate command circuit. The flow rate command unit 34d is, for example, an electronic circuit. The flow rate command unit 34d includes, for example, hardware and software.

[0050] The valve opening command unit 34e has the function of commanding the pressure regulating valve 31 to a predetermined opening degree, for example, so that the reaction chamber pressure is maintained at the pressure stored in the process condition storage unit 34a.

[0051] The valve opening command unit 34e is, for example, a valve opening command circuit. The valve opening command unit 34e is, for example, an electronic circuit. The valve opening command unit 34e includes, for example, hardware and software.

[0052] When the control unit 34 switches the flow rate of at least one of the first and second source gases supplied to the reaction chamber 10 at a transition time t, for example, it controls the first mass flow controller 25, the second mass flow controller 26, the third mass flow controller 27, and the pressure regulating valve 31 so that the average residence time tx of the carrier gas in the reaction chamber 10, represented by the following formula, becomes shorter than the transition time t. tx = reaction chamber pressure [Pa] × reaction chamber volume [m³] 3 ] / Carrier gas flow rate [Pa·m 3 / s]

[0053] Figure 2 is a schematic cross-sectional view of an example of a silicon carbide layer formed by the vapor phase growth method of the embodiment. The silicon carbide layer formed by the vapor phase growth method of the embodiment is formed on a silicon carbide substrate 50. The silicon carbide substrate 50 is an example of a substrate.

[0054] The silicon carbide layer formed by the vapor phase growth method of the embodiment includes a first buffer layer 52, a first transition layer 54, a second buffer layer 56, a second transition layer 58, and a drift layer 60.

[0055] The silicon carbide substrate 50 (substrate), the first buffer layer 52 (first silicon carbide layer), the first transition layer 54, the second buffer layer 56 (second silicon carbide layer), the second transition layer 58, and the drift layer 60 (third silicon carbide layer) are single-crystal 4H-SiC silicon carbide. The silicon carbide substrate 50, the first buffer layer 52, the first transition layer 54, the second buffer layer 56, the second transition layer 58, and the drift layer 60 contain nitrogen (N), an n-type impurity, as a dopant.

[0056] The silicon carbide substrate 50 is an example of a substrate. The first buffer layer 52 is an example of a first silicon carbide layer. The second buffer layer 56 is an example of a second silicon carbide layer. The drift layer 60 is an example of a third silicon carbide layer.

[0057] The nitrogen concentration of the silicon carbide substrate 50 is, for example, 1E18 / cm³. 3 More than 2E19 / cm 3The following is true. The thickness of the silicon carbide substrate 50 is, for example, 300 μm or more and 500 μm or less.

[0058] The first buffer layer 52 is provided on the silicon carbide substrate 50. The first buffer layer 52 has a function of improving the crystallinity of the drift layer 60, for example.

[0059] The nitrogen concentration of the first buffer layer 52 is, for example, 1E17 / cm 3 or more and 2E19 / cm 3 or less. The nitrogen concentration of the first buffer layer 52 is, for example, lower than the nitrogen concentration of the silicon carbide substrate 50. The thickness of the first buffer layer 52 is, for example, 0.05 μm or more and 0.50 μm or less.

[0060] The first transition layer 54 is provided on the first buffer layer 52. The first transition layer 54 is provided between the first buffer layer 52 and the second buffer layer 56.

[0061] The nitrogen concentration of the first transition layer 54 is, for example, 1E17 / cm 3 or more and 2E19 / cm 3 or less. The thickness of the first transition layer 54 is, for example, 0.01 μm or more and 0.15 μm or less.

[0062] The second buffer layer 56 is provided on the first transition layer 54. The second buffer layer 56 has a function of improving the crystallinity of the drift layer 60, for example.

[0063] The nitrogen concentration of the second buffer layer 56 is, for example, 1E17 / cm 3 or more and 2E19 / cm 3 or less. The nitrogen concentration of the second buffer layer 56 is, for example, lower than the nitrogen concentration of the silicon carbide substrate 50. The thickness of the second buffer layer 56 is, for example, 0.5 μm or more and 5 μm or less.

[0064] The second transition layer 58 is provided on the second buffer layer 56. The second transition layer 58 is provided between the second buffer layer 56 and the drift layer 60.

[0065] The nitrogen concentration in the second transition layer 58 is, for example, 1E13 / cm³. 3 More than 2E19 / cm 3 The following applies: The thickness of the second transition layer 58 is, for example, 0.01 μm or more and 0.15 μm or less.

[0066] The drift layer 60 is provided on the second transition layer 58. A semiconductor device is formed in or on the drift layer 60.

[0067] The nitrogen concentration in the drift layer 60 is lower than the nitrogen concentrations in the first buffer layer 52 and the second buffer layer 56. The nitrogen concentration in the drift layer 60 is, for example, 1E13 / cm³. 3 More than 2E16 / cm 3 The following applies: The thickness of the drift layer 60 is, for example, between 5 μm and 500 μm.

[0068] Next, an example of a vapor phase growth method according to the embodiment will be described. The vapor phase growth method according to the embodiment uses the vapor phase growth apparatus 100 shown in Figure 1.

[0069] The following explanation will use the example of forming a single-crystal 4H-SiC silicon carbide layer on the surface of a silicon carbide substrate 50, in which nitrogen is doped as an n-type impurity. Furthermore, the following explanation will use the example of forming the silicon carbide layer with hydrogen gas as the carrier gas, monosilane gas as the first source gas, propane gas as the second source gas, nitrogen gas as the dopant gas, and hydrogen chloride gas as the assist gas.

[0070] Figures 3, 4(a), and 4(b) are explanatory diagrams of the vapor phase growth method of the embodiment. Figure 3 shows the change in the growth rate of the silicon carbide layer over time when forming the silicon carbide layer. Figure 4(a) shows the change in the gas flow rate of the process gas over time when forming the silicon carbide layer. Figure 4(b) shows the change in the carbon / silicon atom ratio (C / Si) in the process gas over time when forming the silicon carbide layer.

[0071] The vapor phase growth method of the embodiment comprises a first process step of forming a first buffer layer 52, a second process step of forming a first transition layer 54, a third process step of forming a second buffer layer 56, a fourth process step of forming a second transition layer 58, and a fifth process step of forming a drift layer 60. The first, second, third, fourth, and fifth process steps are carried out continuously within the same reaction chamber 10 without removing the substrate from the reaction chamber 10.

[0072] First, the susceptor 12 on which the wafer W is placed is brought into the reaction chamber 10. The wafer W is a silicon carbide substrate 50. The wafer W is an example of a substrate.

[0073] The nitrogen concentration of the silicon carbide substrate 50 is, for example, 1E18 / cm³. 3 More than 2E19 / cm 3 The following applies:

[0074] Next, the wafer W is heated using the heater 14. The temperature of the wafer W is, for example, between 1550°C and 1750°C.

[0075] In the first process step, a first buffer layer 52 is formed on the wafer W. The first buffer layer 52 has a first nitrogen concentration. The first buffer layer 52 is formed by supplying a first process gas containing a carrier gas into the reaction chamber 10 under first gas conditions. The first buffer layer 52 is formed at a first growth rate. The first buffer layer 52 is formed between time t0 and time t1.

[0076] The first nitrogen concentration is, for example, 1E17 / cm³. 3 More than 2E19 / cm 3 The following applies:

[0077] The first gas condition is, for example, the type of process gas supplied into the reaction chamber 10 in the first process step, and the flow rate of each process gas.

[0078] In the first process step, hydrogen gas, monosilane gas, propane gas, nitrogen gas, and hydrogen chloride gas are supplied to the reaction chamber 10 at predetermined flow rates as the first process gas.

[0079] The first growth rate is, for example, between 1 μm / h and 10 μm / h. The first growth rate depends, for example, on the silicon / hydrogen atom ratio (Si / H) in the process gas. The first growth rate depends, for example, on the ratio of the flow rate of monosilane gas to the flow rate of hydrogen gas in the process gas. The silicon / hydrogen atom ratio (Si / H) in the first process step is, for example, between 5.28E-5 and 4.65E-4.

[0080] The carbon / silicon atom ratio (C / Si) under the first gas conditions is, for example, between 0.5 and 3.5. The chlorine / silicon atom ratio (Cl / Si) under the first gas conditions is, for example, between 1 and 30.

[0081] The thickness of the first buffer layer 52 is, for example, 0.05 μm or more and 0.50 μm or less.

[0082] In the second process step, a first transition layer 54 is formed on the first buffer layer 52. The first transition layer 54 is formed between time t1 and time t2. The difference between time t2 and time t1 is the first transition time ta.

[0083] The thickness of the first transition layer 54 is, for example, thinner than the thickness of the first buffer layer 52.

[0084] In the third process step, a second buffer layer 56 is formed on the first transition layer 54. The second buffer layer 56 has a second nitrogen concentration. The second buffer layer 56 is formed by supplying a second process gas containing a carrier gas into the reaction chamber 10 under second gas conditions. The second buffer layer 56 is formed at a second growth rate. The second buffer layer 56 is formed between time t2 and time t3.

[0085] The second nitrogen concentration is, for example, 1E17 / cm³. 3 More than 2E19 / cm 3 The following applies:

[0086] The second gas condition is, for example, the type of process gas supplied into the reaction chamber 10 in the third process step, and the flow rate of each process gas.

[0087] In the third process step, hydrogen gas, monosilane gas, propane gas, nitrogen gas, and hydrogen chloride gas are supplied to the reaction chamber 10 at predetermined flow rates as process gases.

[0088] As shown in Figure 3, the second growth rate is greater than the first growth rate. The second growth rate is, for example, between 40 μm / h and 100 μm / h. The second growth rate depends, for example, on the silicon / hydrogen atom ratio (Si / H) in the process gas. The second growth rate depends, for example, on the ratio of the flow rate of monosilane gas to the flow rate of hydrogen gas in the process gas. The silicon / hydrogen atom ratio (Si / H) in the third process step is, for example, between 5.28E-4 and 4.65E-3.

[0089] As shown in Figure 4(a), the flow rate of monosilane gas under the second gas condition is greater than that under the first gas condition. Furthermore, the silicon / hydrogen atom ratio (Si / H) under the second gas condition is greater than that under the first gas condition. Because the silicon / hydrogen atom ratio (Si / H) under the second gas condition is greater than that under the first gas condition, the second growth rate tends to be greater than the first growth rate. Note that the flow rate of hydrogen gas under the second gas condition is, for example, equal to that under the first gas condition. Alternatively, the flow rate of hydrogen gas under the second gas condition may be adjusted, for example, within a range of 0.90 to 1.10 times the flow rate of hydrogen gas under the first gas condition.

[0090] As shown in Figure 4(a), the flow rate of propane gas under the second gas condition is greater than the flow rate of propane gas under the first gas condition.

[0091] The carbon / silicon atom ratio (C / Si) under the second gas condition is, for example, between 0.5 and 2.0. The chlorine / silicon atom ratio (Cl / Si) under the second gas condition is, for example, between 1 and 30.

[0092] As shown in Figure 4(b), for example, the carbon / silicon atomic ratio (C / Si) under the second gas condition is smaller than the carbon / silicon atomic ratio (C / Si) under the first gas condition.

[0093] The thickness of the second buffer layer 56 is, for example, 0.5 μm or more and 5 μm or less.

[0094] In the second process step, the gas conditions are switched from the first gas conditions to the second gas conditions. In the second process step, the gas conditions are switched from the first gas conditions to the second gas conditions during a first transition time ta. The first transition time ta is the time required from the start of the change to the first gas conditions to the completion of the change to the second gas conditions.

[0095] As shown in Figure 4(a), in the second process step, for example, the flow rate of monosilane gas changes in a direction that increases. Also, as shown in Figure 4(a), in the second process step, for example, the flow rate of propane gas changes in a direction that increases. In the second process step, for example, the flow rate of hydrogen gas is equal to the flow rate of hydrogen gas under the first gas conditions. Alternatively, for example, the flow rate of hydrogen gas may be adjusted to a range of 0.90 to 1.10 times the flow rate of hydrogen gas under the first gas conditions.

[0096] In the second process step of forming the first transition layer 54, the average residence time tx of the hydrogen gas in the reaction chamber 10 is made shorter than the first transition time ta. The average residence time tx of the hydrogen gas in the reaction chamber 10 is expressed by the following formula. tx = reaction chamber pressure [Pa] × reaction chamber volume [m³] 3 ] / Carrier gas flow rate [Pa·m 3 / s]

[0097] In the second process step, the average residence time tx of the hydrogen gas in the reaction chamber 10 is, for example, 0.5 seconds or more and 10 seconds or less.

[0098] In the fourth process step, a second transition layer 58 is formed on the second buffer layer 56. The second transition layer 58 is formed between time t3 and time t4. The difference between time t3 and time t4 is the second transition time tb.

[0099] The thickness of the second transition layer 58 is, for example, thinner than the thickness of the second buffer layer 56.

[0100] In the fifth process step, a drift layer 60 is formed on the second transition layer 58. The drift layer 60 has a third nitrogen concentration. The drift layer 60 is formed by supplying a third process gas containing a carrier gas into the reaction chamber 10 under third gas conditions. The drift layer 60 is formed at a third growth rate. The drift layer 60 is formed between time t4 and time t5.

[0101] The third nitrogen concentration is lower than the first and second nitrogen concentrations. The third nitrogen concentration is, for example, 1E13 / cm³. 3 More than 2E16 / cm 3 The following applies:

[0102] The third gas condition is, for example, the type of process gas supplied into the reaction chamber 10 in the fifth process step, and the flow rate of each process gas.

[0103] In the fifth process step, hydrogen gas, monosilane gas, propane gas, nitrogen gas, and hydrogen chloride gas are supplied to the reaction chamber 10 at predetermined flow rates as process gases.

[0104] As shown in Figure 3, the third growth rate is greater than the second growth rate. The third growth rate is, for example, between 45 μm / h and 100 μm / h. The third growth rate depends, for example, on the silicon / hydrogen atom ratio (Si / H) in the process gas. The third growth rate depends, for example, on the ratio of the flow rate of monosilane gas to the flow rate of hydrogen gas in the process gas. The silicon / hydrogen atom ratio (Si / H) in the fifth process step is, for example, between 5.28E-4 and 4.65E-3.

[0105] As shown in Figure 4(a), the flow rate of monosilane gas under the third gas condition is preferably equal to the flow rate of monosilane gas under the second gas condition, but it may be adjusted within a range of 0.95 to 1.40 times the flow rate of monosilane gas under the second gas condition. Also, for example, the flow rate of hydrogen gas under the third gas condition is equal to the flow rate of hydrogen gas under the second gas condition. Also, for example, the flow rate of hydrogen gas under the third gas condition may be adjusted within a range of 0.90 to 1.10 times the flow rate of hydrogen gas under the second gas condition.

[0106] As shown in Figure 4(a), the flow rate of propane gas under the third gas condition is greater than the flow rate of propane gas under the second gas condition.

[0107] The carbon / silicon atom ratio (C / Si) under the third gas condition is, for example, between 0.5 and 2.0. The chlorine / silicon atom ratio (Cl / Si) under the third gas condition is, for example, between 1 and 30.

[0108] As shown in Figure 4(b), for example, the carbon / silicon atomic ratio (C / Si) under the third gas condition is greater than the carbon / silicon atomic ratio (C / Si) under the second gas condition. For example, by making the carbon / silicon atomic ratio (C / Si) under the third gas condition greater than the carbon / silicon atomic ratio (C / Si) under the second gas condition, the third growth rate can be made greater than the second growth rate.

[0109] The thickness of the drift layer 60 is, for example, between 5 μm and 500 μm.

[0110] In the fourth process step, the gas conditions are switched from the second gas conditions to the third gas conditions. In the fourth process step, the gas conditions are switched from the second gas conditions to the third gas conditions during a second transition time tb. The second transition time tb is the time required from the start of the change to the second gas conditions to the completion of the change to the third gas conditions.

[0111] As shown in Figure 4(a), in the fourth process step, for example, the flow rate of propane changes in a direction that increases.

[0112] In the fourth process step of forming the second transition layer 58, the average residence time tx of the hydrogen gas in the reaction chamber 10 is made shorter than the second transition time tb. The average residence time tx of the hydrogen gas in the reaction chamber 10 is expressed by the following formula. tx = reaction chamber pressure [Pa] × reaction chamber volume [m³] 3 ] / Carrier gas flow rate [Pa·m 3 / s]

[0113] In the fourth process step, the average residence time tx of the hydrogen gas in the reaction chamber 10 is, for example, 0.5 seconds or more and 10 seconds or less.

[0114] The silicon carbide layer shown in Figure 2 is formed by the vapor phase growth method described above.

[0115] Next, the operation and effects of the vapor phase growth method and vapor phase growth apparatus of the embodiment will be described.

[0116] When a silicon carbide layer is formed on a substrate using epitaxial growth technology, crystal defects are generated in the silicon carbide layer. Examples of crystal defects include basal plane dislocations (BPDs) and stacking faults (SFs). The presence of crystal defects in the silicon carbide layer can lead to problems such as reduced reliability of semiconductor devices formed on the silicon carbide layer. Therefore, it is desirable to reduce the density of crystal defects in the silicon carbide layer.

[0117] Figure 5 is a schematic cross-sectional view of the silicon carbide layer formed by the vapor phase growth method of the first comparative example. The vapor phase growth method of the first comparative example differs from the vapor phase growth method of the embodiment in that a second buffer layer 56 is not formed between the first buffer layer 52 and the drift layer 60. In other words, it differs from the vapor phase growth method of the embodiment in that a second buffer layer 56 with a growth rate greater than that of the first buffer layer 52 is not formed between the first buffer layer 52 and the drift layer 60. Note that defects present in the silicon carbide substrate 50 are not shown in Figure 5.

[0118] A transition layer 59 is formed between the first buffer layer 52 and the drift layer 60.

[0119] As shown in Figure 5, the vapor phase growth method of the first comparative example makes it easier to suppress the formation of stacking faults SF from the interface between the silicon carbide substrate 50 and the first buffer layer 52, and to suppress the formation of stacking faults SF extending into the drift layer 60. Stacking faults SF in the drift layer 60 grow, for example, during the bipolar operation of the semiconductor device, increasing the electrical resistance of the drift layer 60. Therefore, stacking faults SF are problematic because they degrade the reliability of the semiconductor device.

[0120] According to the vapor phase growth method of the first comparative example, the generation of stacking faults SF extending into the drift layer 60 can be suppressed. Therefore, the degradation of the reliability of semiconductor devices caused by stacking faults SF formed by epitaxial growth can be suppressed.

[0121] On the other hand, in the vapor phase growth method of the first comparative example, basal plane dislocations (BPDs) that reach the surface of the silicon carbide substrate 50 from within the silicon carbide substrate 50 are propagated to the first buffer layer 52 and easily reach the surface of the first buffer layer 52. Furthermore, basal plane dislocations (BPDs) that reach the surface of the first buffer layer 52 are easily propagated to the vicinity of the first buffer layer 52 within the drift layer 60. Basal plane dislocations (BPDs) that have propagated to the vicinity of the first buffer layer 52 within the drift layer 60 are converted, for example, into threading edge dislocations (TEDs) within the drift layer 60.

[0122] Thus, basal plane dislocations (BPDs) are easily converted to through-edge dislocations (TEDs) near the first buffer layer 52 in the drift layer 60. In other words, basal plane dislocations (BPDs) are present up to the vicinity of the first buffer layer 52 in the drift layer 60. When basal plane dislocations (BPDs) are present in the drift layer 60, for example, during the bipolar operation of the semiconductor device, the basal plane dislocations (BPDs) are converted to stacking faults (SFs). Stacking faults (SFs) increase the electrical resistance of the drift layer 60, for example. Therefore, the reliability of the semiconductor device deteriorates, which becomes a problem.

[0123] As described above, the vapor phase growth method of the first comparative example makes it possible to reduce the density of stacking faults SF in the drift layer 60 formed by epitaxial growth. On the other hand, the vapor phase growth method of the first comparative example makes it difficult to reduce the density of basal plane dislocations BPD extending to the vicinity of the first buffer layer 52 in the drift layer 60. Therefore, the vapor phase growth method of the first comparative example suffers from a problem of degradation in the reliability of the semiconductor device due to basal plane dislocations BPD and stacking faults SF formed by conversion from basal plane dislocations BPD.

[0124] Figure 6 is a schematic cross-sectional view of the silicon carbide layer formed by the vapor phase growth method of the second comparative example. The vapor phase growth method of the second comparative example differs from the vapor phase growth method of the embodiment in that a first buffer layer 52 is not formed between the silicon carbide substrate 50 and the second buffer layer 56. In other words, it differs from the vapor phase growth method of the embodiment in that a first buffer layer 52, which has a slower growth rate than the second buffer layer 56, is not formed between the silicon carbide substrate 50 and the second buffer layer 56. Note that defects present in the silicon carbide substrate 50 are not shown in Figure 6.

[0125] A transition layer 59 is formed between the second buffer layer 56 and the drift layer 60.

[0126] As shown in Figure 6, according to the vapor phase growth method of the second comparative example, for example, basal plane dislocations BPD extending from the interface between the silicon carbide substrate 50 and the second buffer layer 56 are more easily converted into through-edge dislocations TED within the second buffer layer 56. Therefore, it is possible to reduce the density of basal plane dislocations BPD in the drift layer 60.

[0127] It is known that the influence of through-edge dislocations (TEDs) on the properties of semiconductor devices is minor compared to, for example, basal plane dislocations (BPDs) and stacking faults (SFs).

[0128] According to the vapor phase growth method of the second comparative example, the density of basal plane dislocations (BPDs) in the drift layer 60 can be reduced. Therefore, the degradation of semiconductor device reliability caused by basal plane dislocations (BPDs) can be suppressed.

[0129] On the other hand, as shown in Figure 6, in the vapor phase growth method of the second comparative example, stacking faults SF are easily formed at the interface between the silicon carbide substrate 50 and the second buffer layer 56, and it is difficult to suppress the formation of stacking faults SF extending to the drift layer 60. Therefore, the degradation of the reliability of the semiconductor device due to stacking faults SF becomes a problem.

[0130] As described above, the vapor phase growth method of the second comparative example can reduce the density of basal plane dislocations (BPDs) in the drift layer 60 formed by epitaxial growth, thereby suppressing the degradation of the reliability of the semiconductor device characteristics caused by basal plane dislocations (BPDs). On the other hand, the vapor phase growth method of the second comparative example makes it difficult to reduce the density of stacking faults (SFs) extending into the drift layer 60. Therefore, the vapor phase growth method of the second comparative example suffers from a problem of degradation of the reliability of the semiconductor device caused by stacking faults (SFs).

[0131] Figure 7 is an explanatory diagram of the operation and effects of the vapor phase growth method of the embodiment. Figure 7 is a schematic cross-sectional view of an example of a silicon carbide layer formed by the vapor phase growth method of the embodiment.

[0132] In the vapor phase growth method of this embodiment, a first buffer layer 52 is formed at a first growth rate before forming a drift layer 60 on a silicon carbide substrate 50, and then a second buffer layer 56 is formed at a second growth rate greater than the first growth rate. By forming the first buffer layer 52, it is easier to suppress the formation of stacking faults SF from the interface between the silicon carbide substrate 50 and the first buffer layer 52, and the density of stacking faults SF extending into the drift layer 60 can be reduced. Furthermore, by forming the second buffer layer 56, basal plane dislocations BPD that have reached the surface of the silicon carbide substrate 50 from the interior are more easily converted into through-edge dislocations TED in the second buffer layer 56, and the density of basal plane dislocations BPD in the drift layer 60 can be reduced. Therefore, the density of both stacking faults SF and basal plane dislocations BPD in the drift layer 60 can be reduced. Thus, according to the vapor phase growth method of this embodiment, the degradation of the reliability of semiconductor devices caused by crystal defects can be suppressed.

[0133] The first growth rate when forming the first buffer layer 52 is preferably 1 μm / h or more and 10 μm / h or less, more preferably 2 μm / h or more and 8 μm / h or less, and even more preferably 3 μm / h or more and 6 μm / h or less. Exceeding the lower limit shortens the formation time of the first buffer layer 52 and improves the productivity of the silicon carbide layer. Furthermore, below the upper limit can further reduce the density of stacking faults SF in the drift layer 60.

[0134] From the viewpoint of setting the first growth rate when forming the first buffer layer 52 to be 1 μm / h or more and 10 μm / h or less, it is preferable that the silicon / hydrogen atom ratio (Si / H) when forming the first buffer layer 52 is 5.28E-5 or more and 4.65E-4 or less.

[0135] The second growth rate when forming the second buffer layer 56 is preferably 40 μm / h or more and 100 μm / h or less, more preferably 45 μm / h or more and 80 μm / h or less, and even more preferably 50 μm / h or more and 60 μm / h or less. Exceeding the lower limit can further reduce the density of basal plane dislocations (BPDs) in the drift layer 60. Also, below the upper limit can improve the crystallinity and surface morphology of the drift layer 60.

[0136] From the viewpoint of setting the second growth rate when forming the second buffer layer 56 to 40 μm / h or more and 100 μm / h or less, it is preferable that the silicon / hydrogen atom ratio (Si / H) when forming the second buffer layer 56 is 5.28E-4 or more and 4.65E-3 or less.

[0137] The thickness of the first buffer layer 52 is preferably 0.05 μm or more and 0.5 μm or less. Exceeding the lower limit further reduces the density of stacking faults SF in the drift layer 60. Also, below the upper limit shortens the formation time of the first buffer layer 52 and improves the productivity of the silicon carbide layer.

[0138] The thickness of the second buffer layer 56 is preferably 0.5 μm or more and 5 μm or less. Exceeding the lower limit further reduces the density of basal plane dislocations (BPDs) in the drift layer 60. Also, below the upper limit shortens the formation time of the second buffer layer 56 and improves the productivity of the silicon carbide layer.

[0139] The thickness of the second buffer layer 56 is preferably greater than the thickness of the first buffer layer 52. In other words, the thickness of the first buffer layer 52 is preferably thinner than the thickness of the second buffer layer 56. By reducing the thickness of the first buffer layer 52, which has a low growth rate, the formation time of the first buffer layer 52 is shortened, and the productivity of the silicon carbide layer is improved.

[0140] In the second process step of forming the first transition layer 54, it is preferable that the average residence time tx of the hydrogen gas in the reaction chamber 10 is shorter than the first transition time ta. The average residence time tx of the hydrogen gas in the reaction chamber 10 is expressed by the following formula. tx = reaction chamber pressure [Pa] × reaction chamber volume [m³] 3 ] / Carrier gas flow rate [Pa·m 3 / s]

[0141] By making the average residence time tx in the hydrogen gas reaction chamber 10 shorter than the first transition time ta, it becomes easier to control the film thickness and doping concentration of the first transition layer 54.

[0142] In the fourth process step of forming the second transition layer 58, it is preferable that the average residence time tx of the hydrogen gas in the reaction chamber 10 is shorter than the second transition time tb. The average residence time tx of the hydrogen gas in the reaction chamber 10 is expressed by the following formula. tx = reaction chamber pressure [Pa] × reaction chamber volume [m³] 3 ] / Carrier gas flow rate [Pa·m 3 / s]

[0143] By making the average residence time tx in the hydrogen gas reaction chamber 10 shorter than the second transition time tb, it becomes easier to control the film thickness and doping concentration of the second transition layer 58.

[0144] The average residence time tx of hydrogen gas in the reaction chamber 10 is preferably 0.5 seconds or more and 10 seconds or less, from the viewpoint of suppressing the formation of step bunching in the silicon carbide layer. Furthermore, the average residence time tx of hydrogen gas in the reaction chamber 10 is preferably 10 seconds or less, from the viewpoint of reducing the thickness of the first transition layer 54 and the second transition layer 58.

[0145] It is preferable that the carbon / silicon atomic ratio (C / Si) under the second gas conditions for forming the second buffer layer 56 is smaller than the carbon / silicon atomic ratio (C / Si) under the first gas conditions for forming the first buffer layer 52. In other words, it is preferable that the carbon / silicon atomic ratio (C / Si) under the first gas conditions for forming the first buffer layer 52 is larger than the carbon / silicon atomic ratio (C / Si) under the second gas conditions for forming the second buffer layer 56.

[0146] When forming a nitrogen-doped silicon carbide layer, increasing the carbon / silicon atom ratio (C / Si) in the process gas can suppress the introduction of nitrogen into the silicon carbide layer. This is because a high carbon / silicon atom ratio (C / Si) in the process gas suppresses the entry of nitrogen atoms into the carbon sites of the silicon carbide. This phenomenon occurs when the carbon / silicon atom ratio (C / Si) in the process gas at the wafer surface exceeds 1.

[0147] The carbon / silicon atomic ratio (C / Si) under the third gas conditions for forming the drift layer 60 is preferably greater than the carbon / silicon atomic ratio (C / Si) under the second gas conditions for forming the second buffer layer 56.

[0148] By increasing the carbon / silicon atom ratio (C / Si) under the third gas conditions when forming the drift layer 60, the density of carbon vacancies in the drift layer 60 can be reduced. Carbon vacancies function as lifetime killers of minority carriers, for example, when operating bipolar semiconductor devices. Reducing the density of carbon vacancies in the drift layer 60 can improve the properties of bipolar semiconductor devices.

[0149] In the vapor phase growth method of the embodiment, it is preferable that the process gas used to form the first buffer layer 52, the first transition layer 54, the second buffer layer 56, the second transition layer 58, and the drift layer 60 contains hydrogen chloride (HCl) gas as an assist gas. By including hydrogen chloride (HCl) gas in the process gas, the formation of silicon droplets and deterioration of the surface morphology of the silicon carbide layer can be suppressed. By suppressing the formation of silicon droplets and deterioration of the surface morphology of the silicon carbide layer, it is possible to reduce the crystal defect density in the silicon carbide layer, for example.

[0150] The chlorine / silicon atom ratio (Cl / Si) in the process gas used to form the first buffer layer 52, the first transition layer 54, the second buffer layer 56, the second transition layer 58, and the drift layer 60 is preferably between 1 and 30. By satisfying the above range for the chlorine / silicon atom ratio (Cl / Si), the formation of silicon droplets and deterioration of the surface morphology of the silicon carbide layer can be further suppressed.

[0151] The vapor phase growth apparatus 100 of this embodiment includes a control unit 34 that controls a first mass flow controller 25, a second mass flow controller 26, a third mass flow controller 27, and a pressure regulating valve 31 so that when switching the flow rate of at least one of the first source gas and the second source gas supplied to the reaction chamber 10 at a transition time t, the average residence time tx of the carrier gas in the reaction chamber 10, represented by the following formula, is shorter than the transition time t. tx = reaction chamber pressure [Pa] × reaction chamber volume [m³] 3 ] / Carrier gas flow rate [Pa·m3 / s]

[0152] The vapor phase growth apparatus 100 of this embodiment includes a control unit 34, which makes it easier to control the thickness of the transition layer and the doping concentration.

[0153] As described above, the vapor phase growth method of the embodiment can reduce the density of crystal defects in the silicon carbide layer. Furthermore, the vapor phase growth apparatus of the embodiment can improve the uniformity of the silicon carbide layer.

[0154] Figure 8 is a schematic diagram of a first modified example of the vapor phase growth apparatus of the embodiment. The vapor phase growth apparatus 110 of the first modified example shows another configuration example of the vapor phase growth apparatus 100 of the embodiment.

[0155] The vapor phase growth apparatus 110 comprises a reaction chamber 10, a susceptor 12, a heater 14, a carrier gas supply pipe 15, a first source gas supply pipe 16, a second source gas supply pipe 17, a dopant gas supply pipe 18, an assist gas supply pipe 19, a first mass flow controller 25, a second mass flow controller 26, a third mass flow controller 27, a fourth mass flow controller 28, a fifth mass flow controller 29, exhaust piping 30, a pressure regulating valve 31, an exhaust pump 32, and a control unit 34.

[0156] In the vapor phase growth apparatus 110 shown in Figure 8, the first source gas supply pipe 16, the second source gas supply pipe 17, the dopant gas supply pipe 18, and the assist gas supply pipe 19 are connected to the carrier gas supply pipe 15. In this way, the carrier gas may be mixed with gases such as the source gas, dopant gas, and assist gas and introduced into the reaction chamber 10.

[0157] Furthermore, in the vapor phase growth apparatus 110 shown in Figure 8, the first source gas supply pipe 16, the second source gas supply pipe 17, the dopant gas supply pipe 18, and the assist gas supply pipe 19 are connected to the reaction chamber 10 via the carrier gas supply pipe 15. In this way, the first source gas supply pipe 16, the second source gas supply pipe 17, the dopant gas supply pipe 18, and the assist gas supply pipe 19 may also be connected to the carrier gas supply pipe 15, thereby connecting them to the reaction chamber 10 via the carrier gas supply pipe 15.

[0158] Figure 9 is a schematic diagram of a second modified example of the vapor phase growth apparatus of the embodiment. The vapor phase growth apparatus 120 of the second modified example shows yet another configuration example of the vapor phase growth apparatus 100 of the embodiment.

[0159] The vapor phase growth apparatus 120 comprises a reaction chamber 10, a susceptor 12, a heater 14, a carrier gas supply pipe 15, a first source gas supply pipe 16, a second source gas supply pipe 17, a dopant gas supply pipe 18, an assist gas supply pipe 19, a first mass flow controller 25, a second mass flow controller 26, a third mass flow controller 27, a fourth mass flow controller 28, a fifth mass flow controller 29, exhaust piping 30, a pressure regulating valve 31, an exhaust pump 32, and a control unit 34.

[0160] In the vapor phase growth apparatus 120 shown in Figure 9, multiple carrier gas supply pipes 15 are provided. Thus, multiple carrier gas supply pipes 15 may be connected to the reaction chamber 10.

[0161] In the vapor phase growth apparatus 120 shown in Figure 9, the first source gas supply pipe 16 and the assist gas supply pipe 19 are connected to one of the multiple carrier gas supply pipes 15. The second source gas supply pipe 17 and the dopant gas supply pipe 18 are connected to another of the multiple carrier gas supply pipes 15. Yet another of the multiple carrier gas supply pipes 15 is connected to the reaction chamber 10 without being connected to the first source gas supply pipe 16, the second source gas supply pipe 17, the dopant gas supply pipe 18, or the assist gas supply pipe 19.

[0162] Thus, the carrier gas may be introduced into the reaction chamber 10 alone, or it may be mixed with other gases such as source gas, dopant gas, and assist gas before being introduced into the reaction chamber 10. In the vapor phase growth apparatus 120 shown in Figure 9, each of the multiple carrier gas supply pipes 15 is equipped with a first mass flow controller 25. In this way, when multiple carrier gas supply pipes 15 are connected to the reaction chamber 10, each of the carrier gas supply pipes 15 may be equipped with a first mass flow controller 25.

[0163] Furthermore, the vapor phase growth apparatus 100 of the embodiment and its modified vapor phase growth apparatus can improve the uniformity of the transition layer and the silicon carbide layer adjacent to the transition layer by including a control unit 34. In the control unit 34, the average residence time tx can be easily calculated, and the transition time t can be easily determined from the calculated average residence time tx, so the transition time determination unit 34c is not necessarily required.

[0164] The embodiments and modifications thereof of the present invention have been described above with reference to specific examples. The above embodiments are merely given as examples and do not limit the present invention. Furthermore, the components of each embodiment may be combined as appropriate.

[0165] In the embodiments and their modifications, examples were given of cases where the carrier gas, source gas, dopant gas, and assist gas are supplied independently into the reaction chamber 10 (Figure 1), where two or more of the carrier gas, source gas, dopant gas, and assist gas are mixed (Figure 9), or where all of them are mixed and supplied into the reaction chamber 10 (Figure 8). However, other methods are also acceptable.

[0166] In the embodiments and their modifications, the case in which the silicon carbide layer contains n-type impurities as dopants was described as an example, but the silicon carbide layer may also contain p-type impurities as dopants.

[0167] In the embodiments and their modifications, descriptions of parts not directly necessary for explaining the present invention, such as the apparatus configuration and manufacturing method, have been omitted. However, the necessary apparatus configuration and manufacturing method can be appropriately selected and used. Furthermore, all vapor phase growth methods and vapor phase growth apparatuses that possess elements of the present invention and can be appropriately modified by those skilled in the art are included within the scope of the present invention. The scope of the present invention is defined by the claims and the scope of equivalents thereof. [Explanation of Symbols]

[0168] 10 Reaction Chamber 15 Carrier gas supply pipe 16. First source gas supply pipe 17. Second source gas supply pipe 25. First Mass Flow Controller 26. Second Mass Flow Controller 27. Third Mass Flow Controller 31 Pressure regulating valve 34 Control Unit 50 Silicon carbide substrate (substrate) 52 First buffer layer (first silicon carbide layer) 54 First transition layer 56. Second buffer layer (second silicon carbide layer) 58 Second transition layer 60. Drift layer (third silicon carbide layer) 100 Vapor-phase growth apparatus

Claims

1. supplying a first process gas containing a carrier gas into a reaction chamber under first gas conditions to form a first silicon carbide layer having a first doping concentration on a silicon carbide substrate at a first growth rate; After forming the first silicon carbide layer, supplying a second process gas containing a carrier gas under second gas conditions into the reaction chamber to form a second silicon carbide layer having a second doping concentration at a second growth rate greater than the first growth rate; a vapor phase growth method including: supplying, into the reaction chamber under third gas conditions, a third process gas containing a carrier gas after forming the second silicon carbide layer; and forming a third silicon carbide layer having a third doping concentration lower than the first doping concentration and the second doping concentration, at a third growth rate higher than the second growth rate.

2. 2. The vapor phase growth method according to claim 1, wherein the second silicon carbide layer is thicker than the first silicon carbide layer, and the third silicon carbide layer is thicker than the second silicon carbide layer.

3. forming a first transition layer during a first transition time for switching from the first gas condition to the second gas condition after forming the first silicon carbide layer; forming a second transition layer during a second transition time for switching from the second gas condition to the third gas condition after forming the second silicon carbide layer; an average residence time of the carrier gas in the reaction chamber when forming the first transition layer is shorter than the first transition time; 3. The vapor phase growth method according to claim 1, wherein an average residence time of the carrier gas in the reaction chamber when the second transition layer is formed is shorter than the second transition time.

4. the carbon / silicon atomic ratio in the second process gas is less than the carbon / silicon atomic ratio in the first process gas; 4. The vapor phase growth method according to claim 1, wherein the carbon / silicon atomic ratio in the third process gas is greater than the carbon / silicon atomic ratio in the second process gas.

5. A reaction chamber; a carrier gas supply pipe for supplying a carrier gas to the reaction chamber; a first source gas supply pipe for supplying a first source gas containing silicon (Si) to the reaction chamber; a second source gas supply pipe for supplying a second source gas containing carbon (C) to the reaction chamber; a first mass flow controller provided in the carrier gas supply pipe and configured to control the flow rate of the carrier gas supplied to the reaction chamber; a second mass flow controller provided in the first source gas supply pipe and configured to control a flow rate of the first source gas supplied to the reaction chamber; a third mass flow controller provided in the second source gas supply pipe and configured to control a flow rate of the second source gas supplied to the reaction chamber; a pressure regulating valve for regulating the pressure in the reaction chamber; a control unit that controls the first mass flow controller, the second mass flow controller, the third mass flow controller, and the pressure adjustment valve so that an average residence time of the carrier gas in the reaction chamber is shorter than a transition time when switching a flow rate of at least one of the first source gas and the second source gas to be supplied to the reaction chamber over a transition time; A vapor phase growth apparatus comprising:

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