Epitaxial growth device for silicon carbide semiconductor

Abstract

This epitaxial growth device for a SiC semiconductor is provided with: a chamber (1) having an internal space; a susceptor (2) that is disposed within the chamber (1) and constitutes a placement surface for the SiC semiconductor substrate (9); a reaction vessel (3) surrounding the susceptor (2) and constituting a growth space (11) in which the SiC semiconductor layer (10) is epitaxially grown on the SiC semiconductor substrate (9); a first gas nozzle (4) that introduces a raw material gas of SiC into the reaction vessel (3); a second gas nozzle (5) for introducing a dopant gas containing V at a position separated from the first gas nozzle (4); a gas discharge pipe (6) for discharging the gas flowing out of the growth space (11) from the chamber (1); and a heating device (7) that heats the reaction vessel (3). As a result, the epitaxial growth apparatus can suppress the generation of V-Si in the nozzle.

Description

Technical Field

[0001] The present disclosure relates to an epitaxial growth apparatus capable of epitaxially growing a silicon carbide (hereinafter referred to as SiC) semiconductor. Background Art

[0002] Patent Document 1 previously disclosed an epitaxial growth apparatus for SiC semiconductor layers capable of being simultaneously doped with p-type and n-type impurities. The epitaxial growth apparatus comprises a reaction vessel constituting a growth space and first to fourth supply paths for supplying various gases into the reaction vessel. The first supply path supplies a Si feedstock gas containing Si (silicon). The second supply path supplies a C feedstock gas containing C (carbon). The third supply path supplies a dopant gas containing n-type impurities. The fourth supply path supplies a dopant gas containing p-type impurities. Each supply path is equipped with an MFC (mass flow controller) capable of controlling the gas flow rate flowing through each path. Furthermore, the first to fourth supply paths converge in front of a gas nozzle, which serves as a gas inlet pipe for the reaction vessel, and various gases are supplied into the reaction vessel through a single gas nozzle. This allows a SiC semiconductor layer doped with n-type and p-type impurities to be epitaxially grown on a SiC semiconductor substrate disposed within the reaction vessel.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2014-187113 Summary of the Invention

[0006] However, it has been confirmed that when forming a V (vanadium)-doped SiC semiconductor layer, V-Si products form within the nozzle that introduces gas from the supply path into the growth space, causing nozzle clogging. Specifically, to prevent nozzle clogging caused by SiC growth, the nozzle outlet temperature must be kept below 1400°C. However, V-Si is generated when doping at temperatures below 1400°C.

[0007] An object of the present disclosure is to provide an epitaxial growth apparatus for a SiC semiconductor capable of suppressing the generation of V-Si in a nozzle.

[0008] An epitaxial growth apparatus according to one aspect of the present disclosure comprises: a chamber having an internal space; a susceptor arranged in the chamber and constituting a mounting surface for a silicon carbide semiconductor substrate; a reaction vessel surrounding the susceptor and constituting a growth space for epitaxially growing a silicon carbide semiconductor layer on the silicon carbide semiconductor substrate; a first gas nozzle for introducing a raw material gas of silicon carbide into the reaction vessel; a second gas nozzle arranged at a position separated from the first gas nozzle and for introducing a dopant gas containing vanadium into the reaction vessel; a gas exhaust pipe for exhausting the gas flowing out of the growth space from the chamber; and a heating device for heating the reaction vessel.

[0009] In the epitaxial growth apparatus thus configured, the source gas and the V dopant gas are introduced from separate nozzles. Therefore, even if the gas outlets of the first and second gas nozzles are at 1400° C. or lower, the generation of V—Si at the gas outlets can be suppressed.

[0010] Therefore, when the SiC semiconductor layer is epitaxially grown, it is possible to suppress clogging of the gas outlets of the first gas nozzle and the second gas nozzle by the V—Si product. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a cross-sectional view of the epitaxial growth apparatus according to the first embodiment of the present disclosure.

[0012] Figure 2 It is a cross-sectional view of an epitaxial growth apparatus according to a second embodiment of the present disclosure.

[0013] Figure 3 It is a cross-sectional view of an epitaxial growth apparatus according to a third embodiment of the present disclosure.

[0014] Figure 4 It is a cross-sectional view of an epitaxial growth apparatus according to a fourth embodiment of the present disclosure. DETAILED DESCRIPTION

[0015] Hereinafter, embodiments of the present disclosure will be described based on the drawings. In addition, the same or equivalent parts of each embodiment, including other embodiments described below, will be denoted by the same reference numerals for description.

[0016] (First embodiment)

[0017] Reference Figure 1 A SiC semiconductor epitaxial growth apparatus according to a first embodiment of the present invention will be described.

[0018] Figure 1The epitaxial growth apparatus shown includes a chamber 1 , a susceptor 2 , a reaction vessel 3 , a first gas nozzle 4 , a second gas nozzle 5 , a gas exhaust pipe 6 , a heating device 7 , a cooling unit 8 , etc., for epitaxially growing a SiC semiconductor layer 10 on the surface of a SiC semiconductor substrate 9 .

[0019] The chamber 1 is hollow, having an upper surface 1a, a bottom surface 1b, and side surfaces 1c. A susceptor 2, a reaction vessel 3, and the like are arranged within the interior space. In this embodiment, the chamber 1 has a generally cylindrical shape, with the upper surface 1a and bottom surface 1b being circular, and the side surface 1c being cylindrical. The chamber 1 can be constructed of a material capable of withstanding the temperatures encountered during epitaxial growth. For example, the chamber 1 can be constructed of a metal such as SUS.

[0020] The upper surface 1a has an opening 1aa and an opening 1ab formed at positions separated from each other. The first gas nozzle 4 is arranged in the opening 1aa, and the second gas nozzle 5 is arranged in the opening 1ab. In addition, an opening 1ba is also formed around the base 2 in the bottom surface 1b, and a gas exhaust pipe 6 is arranged. Figure 1 In FIG. 1 , the openings 1 ba are shown on both sides of the base 2 in the radial direction, but they may be provided at a plurality of locations at equal intervals in the circumferential direction around the base 2 or at only one location.

[0021] The susceptor 2 forms a mounting surface for the SiC semiconductor substrate 9 on which epitaxial growth is to be performed. In the present embodiment, the susceptor 2 is arranged at the center of the bottom surface of the chamber 1, and the SiC semiconductor substrate 9 is mounted on the upper surface of the susceptor 2 as the mounting surface. During epitaxial growth, the susceptor 2 is rotated by a rotation mechanism (not shown) with the normal direction of the surface of the SiC semiconductor substrate 9 as the central axis direction and the center of the SiC semiconductor substrate 9 as the rotation center. This achieves uniform impurity doping concentration and film thickness distribution of the grown SiC semiconductor layer 10. For example, the susceptor 2 is made of graphite, or is composed of graphite coated with a high-melting-point metal carbide such as TaC (tantalum carbide) or NbC (niobium carbide), or is entirely composed of a high-melting-point metal carbide. In addition, the high-melting-point metal carbide referred to here refers to a metal carbide that does not melt even at the temperature used in the growth of the SiC semiconductor layer 10 (for example, around 1600°C).

[0022] Reaction vessel 3 is a wall member that partitions the interior of chamber 1 to form a chamber for gas introduction. It is arranged to surround susceptor 2 and form growth space 11 for epitaxial growth. Reaction vessel 3 is made of graphite, or graphite coated with a high-melting-point metal carbide such as TaC, NbC, or SiC, or is entirely composed of a high-melting-point metal carbide. In this embodiment, reaction vessel 3 is cylindrical, slightly smaller than side surface 1c, and is positioned inside side surface 1c of chamber 1, with a space between it and side surface 1c of chamber 1.

[0023] Furthermore, a gap is provided between the inner wall of the reaction vessel 3 and the susceptor 2, and an opening 1ba and a gas exhaust pipe 6 are disposed in this gap. Therefore, the growth space 11 formed within the reaction vessel 3 is connected to the gas exhaust pipe 6 via the gap between the inner wall of the reaction vessel 3 and the susceptor 2.

[0024] The first gas nozzle 4 is a tubular member formed within the opening 1aa of the upper surface 1a of the chamber 1 and is made of, for example, SUS or graphite. The first gas nozzle 4 introduces Si source gas, such as a silane-based gas like SiH4, and C source gas, such as a propane-based gas like C3H8. A carrier gas, such as H2 (hydrogen), is introduced through the first gas nozzle 4 along with the Si source gas and the C source gas. In this embodiment, the first gas nozzle 4 is configured as a tubular member within the opening 1aa of the upper surface 1a of the chamber 1. However, the opening 1aa may alternatively constitute the first gas nozzle 4.

[0025] The second gas nozzle 5 is also a tubular member formed within the opening 1ab of the upper surface 1a of the chamber 1 and is made of, for example, SUS or graphite. The second gas nozzle 5 introduces a dopant gas containing V, such as VCl4. In addition to the dopant gas containing V, a carrier gas, such as H2, is introduced through the second gas nozzle 5. In this embodiment, the second gas nozzle 5 is a tubular member disposed within the opening 1ab of the upper surface 1a of the chamber 1. However, the opening 1ab may also constitute the second gas nozzle 5.

[0026] When the dopant gas containing V is introduced in this manner, V is doped into the SiC semiconductor layer 10. When a SiC semiconductor device including a diode is formed using the SiC semiconductor substrate 9 having the SiC semiconductor layer 10 formed thereon, V has the effect of suppressing current-carrying degradation of the diode.

[0027] For example, a SiC semiconductor substrate 9 having a SiC semiconductor layer 10 formed thereon can be used to form a SiC semiconductor device having a switching element such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). In this case, a built-in diode is formed. If the SiC semiconductor device is applied to an inverter circuit, etc., and the built-in diode performs bipolar action due to the backflow action during switching, the basal plane dislocation (hereinafter referred to as BPD) may expand to a Shockley-type stacking fault (hereinafter referred to as SSF). That is, the holes passing near the BPD recombine with the electrons in the n-type layer to generate a large recombination energy, so the BPD expands to the SSF. Compared with the BPD, the SSF occupies a larger area and is a defect that easily causes a decrease in the electrical characteristics of the SiC semiconductor device and the so-called power-on degradation of the diode, so it is desirable to suppress the expansion of the BPD to the SSF. V has this inhibitory effect.

[0028] The first gas nozzle 4 and the second gas nozzle 5 can be arranged at any position as long as they are spaced at a predetermined distance or more. Here, they are arranged at the same distance from the center on both sides of the center of the circular upper surface 1a in the radial direction.

[0029] The gas exhaust pipe 6 exhausts unnecessary gas from the chamber 1. In this embodiment, the gas exhaust pipe 6 is provided on the bottom of the chamber 1 to exhaust unreacted Si and C raw material gases and carrier gas flowing out of the growth space 11.

[0030] Heating device 7 heats reaction vessel 3, thereby raising the temperature of growth space 11. Heating device 7 can be a device that performs heating using either direct heating or induction heating. In this embodiment, a device that performs heating using direct heating is employed as heating device 7. Reaction vessel 3 is heated by heating device 7, thermally decomposing the Si and C source gases introduced into growth space 11, thereby creating an atmosphere suitable for epitaxial growth.

[0031] The epitaxial growth apparatus also includes a cooling unit 8 for cooling the first and second gas nozzles 4 and 5. In this embodiment, the cooling unit 8 is constructed by integrating a water flow path for cooling water 8a into the upper surface 1a of the chamber 1. The cooling unit 8 is configured to surround the first and second gas nozzles 4 and 5 and to extend between them. However, any layout is sufficient as long as the temperature is maintained at or below 1400°C at least in the vicinity of the first gas nozzle 4.

[0032] Thus, the epitaxial growth apparatus for SiC semiconductors according to this embodiment is constructed. In this epitaxial growth apparatus, when epitaxially growing SiC semiconductor layer 10, heating device 7 heats reaction vessel 3, heating SiC semiconductor substrate 9 to, for example, 1600-1750°C. At this time, the gas outlets of first gas nozzle 4 and second gas nozzle 5 are heated by radiant heat from reaction vessel 3, SiC semiconductor substrate 9, and the like, but the temperature is kept below 1400°C, for example, within the range of 500-1200°C. Therefore, the gas outlets of first gas nozzle 4 and second gas nozzle 5 are prevented from becoming clogged by SiC growth.

[0033] On the other hand, although the temperature is 1400°C or lower, at which V-Si can be generated, in this embodiment, the Si source gas and the C source gas are introduced from the first gas nozzle 4, and the V dopant gas is introduced from the second gas nozzle 5, which is separate from the first gas nozzle 4. In this way, since the Si source gas and the V dopant gas are introduced from separate gas nozzles, the generation of V-Si at the gas outlets of the first gas nozzle 4 and the second gas nozzle 5 can be suppressed even if the gas outlets of the first gas nozzle 4 and the second gas nozzle 5 are 1400°C or lower.

[0034] Therefore, when epitaxially growing the SiC semiconductor layer 10 , it is possible to suppress clogging of the gas outlets of the first gas nozzle 4 and the second gas nozzle 5 by the V—Si product, thereby enabling stable growth of the SiC semiconductor layer 10 .

[0035] (Second embodiment)

[0036] The second embodiment of the present disclosure is described below. This embodiment is similar to the first embodiment except that gas is introduced from the first gas nozzle 4 and further gas nozzles are added. Therefore, only the differences from the first embodiment will be described.

[0037] like Figure 2 As shown, in this embodiment, in addition to the Si source gas, the C source gas, and the carrier gas, HCl is also introduced as an etching gas from the first gas nozzle 4. By introducing the etching gas in addition to the Si source gas and the C source gas, the formation of SiC polycrystals and the like in the first gas nozzle 4 can be further suppressed.

[0038] In addition to the first gas nozzle 4 and the second gas nozzle 5, a third gas nozzle 20 is also provided. The placement of the third gas nozzle 20 is arbitrary, but in this case, it is placed between the first gas nozzle 4 and the second gas nozzle 5. In other words, the third gas nozzle 20 is placed closest to the center of the upper surface 1a of the chamber 1, and the first gas nozzle 4 and the second gas nozzle 5 are placed outside the third gas nozzle 20.

[0039] In addition to openings 1aa and 1ab, an opening 1ac is formed on the upper surface 1a of the chamber 1. The third gas nozzle 20 is a tubular member disposed within the opening 1ac and is made of, for example, SUS or graphite. The third gas nozzle 20 introduces NH3 as an n-type dopant gas containing N, which serves as an n-type impurity. Here, a carrier gas, such as H2, is introduced through the third gas nozzle 20 along with the NH3 serving as the n-type dopant gas.

[0040] Thus, when introducing an n-type dopant gas, a third gas nozzle 20 is provided independently of the first and second gas nozzles 4 and 5, and the gas is introduced from the third gas nozzle 20. When using NH3 as the n-type dopant gas, if the gas introduced from the first gas nozzle 4 contains the Cl element, or if VCl4 containing the Cl element is used as the V dopant gas, NH4Cl is generated within the gas nozzle, potentially clogging the gas nozzle. However, in this embodiment, these gases are introduced from separate gas nozzles, namely the first gas nozzle 4, the second gas nozzle 5, and the third gas nozzle 20, which are separately arranged. Therefore, in addition to suppressing the generation of V-Si by separating the first and second gas nozzles 4 and 5, the generation of NH4Cl can also be suppressed by separating the third gas nozzle 20 from the first and second gas nozzles 4 and 5.

[0041] Therefore, when epitaxially growing the SiC semiconductor layer 10 , it is possible to suppress clogging of the gas outlets of the gas nozzles by V—Si products or NH 4 Cl, thereby enabling the SiC semiconductor layer 10 to grow stably.

[0042] While the case of introducing HCl as an etching gas is exemplified herein as a case where the gas introduced from the first gas nozzle 4 contains the Cl element, there are also cases where chlorosilanes such as SiHCl3 are used as SiC raw material gas. Suppressing the generation of NH4Cl is also effective when either the gas introduced from the first gas nozzle 4 that introduces the Si raw material gas or the C raw material gas, that is, the gas used as the SiC raw material, or the gas introduced together with it, contains the Cl element. While this embodiment illustrates a case where both the first gas nozzle 4 and the second gas nozzle 5 contain the Cl element, it is preferable to suppress the generation of NH4Cl even with only one of the gases.

[0043] (Third embodiment)

[0044] The third embodiment of the present disclosure will now be described. This embodiment differs from the first and second embodiments in that the structure of the second gas nozzle 5 is modified. Otherwise, the same as the first and second embodiments, so only the differences will be described. While this example illustrates the application of the structure of this embodiment to an epitaxial growth apparatus equipped with a third gas nozzle 20, as in the second embodiment, it can also be applied to an epitaxial growth apparatus that does not have a third gas nozzle 20, as in the first embodiment.

[0045] like Figure 3 As shown, in the epitaxial growth apparatus of this embodiment, the gas outlet of the second gas nozzle 5 is positioned below the gas outlets of the first gas nozzle 4 and the third gas nozzle 20, that is, closer to the susceptor 2. In other words, the second gas nozzle 5 extends toward the high-temperature side. Preferably, the second gas nozzle 5 is positioned on the outer periphery of the upper surface 1a, that is, closer to the reaction vessel 3, so that the portion of the second gas nozzle 5 protruding from the upper surface 1a is along the inner wall surface of the reaction vessel 3. More preferably, the lower end of the second gas nozzle 5 is positioned near the portion of the reaction vessel 3 where the heating device 7 is disposed. For example, the lower end of the second gas nozzle 5 is positioned below the upper end of the heating device 7 so that the upper end of the heating device 7 overlaps with the gas outlet of the second gas nozzle 5 when viewed horizontally.

[0046] This further separates the V dopant gas from the Si raw material gas. This further suppresses the formation of V-Si and prevents clogging of the gas nozzles by V-Si products. Furthermore, by extending the second gas nozzle 5, which introduces the V dopant gas, to a higher temperature, the mixing point of V and Si is located at a higher temperature, further suppressing the formation of V-Si. In particular, the second gas nozzle 5 is positioned further outboard of the third gas nozzle 20 and closer to the heating device 7, allowing the second gas nozzle 5 to reach a higher temperature more easily.

[0047] (Fourth embodiment)

[0048] The fourth embodiment of the present disclosure will be described. Compared to the third embodiment, this embodiment mixes the gases introduced from the first gas nozzle 4 and the second gas nozzle 5 and introduces them into the growth space 11. Otherwise, this embodiment is the same as the first and second embodiments, so only the differences from the third embodiment will be described.

[0049] like Figure 4As shown, in this embodiment, the second gas nozzle 5 is positioned on the upper surface 1a of the chamber 1, outboard of the first and third gas nozzles 4 and 20. In this embodiment, as in the third embodiment, the second gas nozzle 5 is extended downward and positioned at multiple locations on the upper surface 1a, outboard of the first and third gas nozzles 4 and 20. Furthermore, a shower plate 30, serving as a partition plate and having multiple holes 30a, is provided below the gas outlets of the first and third gas nozzles 4 and 20, located inboard. This creates a mixing space 31 above the growth space 11. Within this mixing space 31, Si and C source gases, etc., from the first gas nozzle 4 are mixed with a dopant gas containing an impurity element, etc., from the third gas nozzle 20, to form a mixed gas. Furthermore, the mixed gas is introduced into the growth space 11 in a shower-like manner through the multiple holes 30a formed in the shower plate 30, thereby supplying each element uniformly distributed within the surface of the SiC semiconductor substrate 9.

[0050] In this way, if the mixed gas is introduced into the growth space 11 after being converted into the mixed gas, the film thickness and carrier concentration of the SiC semiconductor layer 10 can be made more uniform.

[0051] Generally, for epitaxial growth films, high uniformity of ±10% in film thickness and ±15% in carrier concentration is required. On the other hand, if V is 1×10 14 cm -3 The above results in an effect of suppressing the conduction degradation of the diode. If the impurity concentration of V is too high, defects may occur. However, if it is 1×10 16 cm -3 The generation of defects can be suppressed as follows. That is, if the impurity concentration of V is 1×10 14 cm -3 Above and 1×10 16 cm -3 This suppresses both diode degradation and defects. The V impurity concentration has a wide setting range and can be easily adjusted, eliminating the need for uniform introduction of V-containing gases through the shower plate 30. Consequently, V-containing gases can be introduced to a location with a higher temperature at the gas outlet without passing through the shower plate 30. Furthermore, Si source gases, for example, can be uniformly introduced using the shower plate 30.

[0052] (Other embodiments)

[0053] The present disclosure is described based on the above-mentioned embodiments, but is not limited to the embodiments and includes various modifications and variations within the scope of the equivalents. In addition, various combinations and configurations, as well as other combinations and configurations including only one element, more than one element, or less than one element, also fall within the scope and spirit of the present disclosure.

[0054] For example, the shapes of the chamber 1, susceptor 2, and reaction vessel 3, as well as the types of gases introduced from the gas nozzles, described in the first to fourth embodiments are merely examples; other shapes and gas types may also be used. Furthermore, in the second to third embodiments, the introduction of an n-type dopant, that is, the case where the SiC semiconductor layer 10 is made n-type, is described as an example. This is also merely an example; the epitaxial growth apparatus described in the above embodiments can also be provided when a p-type dopant is introduced to make the SiC semiconductor layer 10 p-type. Examples of p-type dopant gases include TMA (Trimethylaluminum) gas and B2H6. Furthermore, while the first gas nozzle 4 is a single gas nozzle that introduces both the Si source gas and the C source gas, it may also be divided into two gas nozzles: one for the Si source gas and the other for the C source gas.

[0055] Furthermore, in the above embodiments, the reaction vessels 3 are disposed within the chamber 1 and are independent of each other. However, the chamber 1 itself may also constitute the reaction vessels 3. In other words, as long as the reaction vessels 3 surround the susceptor 2 and form the growth space 11, the reaction vessels 3 may be constituted by the chamber 1 itself or may be separate from the chamber 1. Any of these is acceptable.

Claims

1. An epitaxial growth device for silicon carbide semiconductor, characterized in that: have: a chamber, having an interior space; a susceptor, disposed in the chamber and constituting a mounting surface for the silicon carbide semiconductor substrate; a reaction container surrounding the susceptor and constituting a growth space for epitaxially growing a silicon carbide semiconductor layer on the silicon carbide semiconductor substrate; a first gas nozzle for introducing a raw material gas of silicon carbide into the reaction container; a second gas nozzle disposed at a position away from the first gas nozzle and introducing a dopant gas containing vanadium into the reaction container; a gas exhaust pipe for exhausting the gas flowing out of the growth space from the chamber; and A heating device is used to heat the reaction container.

2. The epitaxial growth apparatus according to claim 1, wherein: The gas outlet of the second gas nozzle extends further toward the susceptor than the first gas nozzle.

3. The epitaxial growth apparatus according to claim 1 or 2, wherein: The epitaxial growth apparatus includes a third gas nozzle disposed at a position separated from the first gas nozzle and the second gas nozzle, and introducing a dopant gas containing an element that imparts n-type or p-type impurities to the silicon carbide semiconductor layer.

4. The epitaxial growth apparatus according to claim 3, wherein: The chamber is a hollow shape having an upper surface, a bottom surface and side surfaces, The first gas nozzle, the second gas nozzle, and the third gas nozzle are arranged at different positions on the upper surface of the chamber. The second gas nozzle is arranged on the upper surface at an outer side than the third gas nozzle.

5. The epitaxial growth apparatus according to claim 4, wherein: On the upper surface, the second gas nozzle is arranged outside the first gas nozzle and the third gas nozzle. A shower plate is provided below the gas outlet of the first gas nozzle and the gas outlet of the third gas nozzle. The shower plate has a plurality of holes formed therein and serves as a partition plate constituting a mixing space above the growth space. The raw material gas introduced from the first gas nozzle and the dopant gas containing the element serving as the impurity introduced from the third gas nozzle are mixed in the mixing space and then introduced into the growth space through the plurality of holes. The dopant gas containing vanadium introduced from the second gas nozzle is introduced into the growth space without passing through the mixing space.

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