Semiconductor device manufacturing method

Abstract

To provide a technique capable of manufacturing a semiconductor device of which dopant concentration is uniform in a technique capable of performing epitaxial growth of a SiC layer.SOLUTION: A manufacturing method of a semiconductor device (10), comprises a step of performing epitaxial growth of a SiC layer (28a) onto a lower ground layer (28b) by introducing first raw material gas containing Si, second raw material gas containing C, and doping gas into a chamber (90) into which the lower ground layer is arranged. In the step of performing the epitaxial growth of the SiC layer, the second raw material gas and the doping gas are introduced into the chamber before the first raw material gas is introduced.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a technology for epitaxially growing a SiC layer. [Background technology]

[0002] Patent Document 1 discloses a technique for epitaxially growing a SiC layer, in which a doping gas is introduced into a chamber containing an underlayer at an earlier timing than the source gas, thereby increasing the doping gas concentration in the chamber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-152487 Summary of the Invention [Problem to be solved by the invention]

[0004] In the technology of Patent Document 1, a source gas containing Si and a source gas containing C are introduced into a chamber at the same time. The source gas containing Si and the source gas containing C are decomposed in the chamber. The source gas containing Si is more easily decomposed than the source gas containing C. Therefore, when the source gas containing Si and the source gas containing C are introduced into the chamber simultaneously, the ratio of decomposed C to Si present in the gas in the chamber (hereinafter referred to as the "C / Si ratio") is low at the beginning of epitaxial growth. Thereafter, the C / Si ratio increases.

[0005] The dopant concentration of the SiC layer formed by epitaxial growth depends on the C / Si ratio in the chamber. As described above, if the C / Si ratio is low at the beginning of epitaxial growth and then increases, the dopant concentration in the formed SiC layer changes as the growth progresses. As such, it has been difficult to achieve a uniform dopant concentration in the SiC layer using conventional manufacturing methods.

[0006] This specification provides a technique for epitaxially growing an SiC layer, which is capable of manufacturing a semiconductor device with a uniform dopant concentration. [Means for solving the problem]

[0007] This specification discloses a method for manufacturing a semiconductor device (10). The method includes a step of epitaxially growing a SiC layer (28a) on an underlayer (28b) by introducing a first source gas containing Si, a second source gas containing C, and a doping gas into a chamber (90) in which the underlayer (28b) is disposed, and in the step of epitaxially growing the SiC layer, the second source gas and the doping gas are introduced into the chamber before the first source gas.

[0008] According to the above manufacturing method, the second source gas containing C and the doping gas are introduced into the chamber before the first source gas containing Si, and the SiC layer is epitaxially grown. This suppresses a decrease in the C / Si ratio in the chamber at the beginning of epitaxial growth, compared to when the first source gas and the second source gas are introduced into the chamber simultaneously. As a result, the C / Si ratio in the chamber can be made substantially uniform throughout the entire epitaxial growth. As a result, the dopant concentration in the SiC layer formed by epitaxial growth can be made uniform. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view of a semiconductor device according to a first embodiment. [Figure 2] 2A to 2C are diagrams for explaining the manufacturing process of the semiconductor device according to the first embodiment. [Figure 3] 1 is a schematic diagram of an apparatus for epitaxial growth. [Figure 4] 2A to 2C are diagrams for explaining the manufacturing process of the semiconductor device according to the first embodiment. [Figure 5]10 is a graph showing the introduction timing and introduction amount of each gas in a conventional manufacturing method. [Figure 6] 10 is a graph showing the distribution of nitrogen concentration in a first drift region formed by a conventional manufacturing method. [Figure 7] 4 is a graph showing the introduction timing and introduction amount of each gas in the manufacturing method of this embodiment. [Figure 8] 10 is a graph showing the distribution of nitrogen concentration in the first drift region formed by the manufacturing method of this embodiment. [Figure 9] FIG. 10 is a schematic cross-sectional perspective view of a semiconductor device according to a second embodiment. [Figure 10] 10 is a graph showing the introduction timing and introduction amount of each gas in the manufacturing method of Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0010] In one example manufacturing method disclosed in the present specification, the underlayer may be made of SiC containing a dopant, and in the step of epitaxially growing the SiC layer, the SiC layer may be formed to have a dopant concentration higher than the dopant concentration of the underlayer.

[0011] In one example manufacturing method disclosed in the present specification, the step of epitaxially growing the SiC layer may include a first step of epitaxially growing the SiC layer at a first growth rate, and a second step of epitaxially growing the SiC layer at a second growth rate higher than the first growth rate after the first step.

[0012] Example 1 The semiconductor device 10 of this embodiment shown in FIG. 1 is a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). That is, the semiconductor device 10 is a switching element. The semiconductor device 10 has a semiconductor substrate 12. The semiconductor substrate 12 is made of silicon carbide (SiC). A source electrode 80 is disposed on an upper surface 12a of the semiconductor substrate 12. A drain electrode 84 is disposed on a lower surface 12b of the semiconductor substrate 12.

[0013] A plurality of trenches 34 are formed in the upper surface 12a of the semiconductor substrate 12. As shown in FIG. 1, the plurality of trenches 34 are arranged at intervals in the left-right direction of the page. A gate insulating film 38 and a gate electrode 40 are formed in each trench 34. The gate insulating film 38 is made of, for example, silicon oxide, and covers the inner surface of the trench 34. The gate electrode 40 is insulated from the semiconductor substrate 12 by the gate insulating film 38. The upper surface of the gate electrode 40 is covered by an interlayer insulating layer 36. The gate electrode 40 is insulated from the source electrode 80 by the interlayer insulating layer 36.

[0014] The semiconductor substrate 12 has a source region 22, a contact region 24, a body region 26, a drift region 28, and a drain region 30. Each of the regions 22, 24, 26, 28, and 30 is made of SiC.

[0015] A plurality of source regions 22 are formed in the semiconductor substrate 12. Each source region 22 is an n-type region. Each source region 22 is exposed on the upper surface 12a of the semiconductor substrate 12. Each source region 22 is in ohmic contact with the source electrode 80. Each source region 22 contacts the gate insulating film 38 at the upper end of the trench 34.

[0016] A plurality of contact regions 24 are formed in the semiconductor substrate 12. Each contact region 24 is a p-type region. Each contact region 24 is exposed on the upper surface 12a of the semiconductor substrate 12 at a position adjacent to the source region 22. Each contact region 24 is in ohmic contact with the source electrode 80.

[0017] The body region 26 is a p-type region. The body region 26 has a lower p-type dopant concentration than each of the contact regions 24. The body region 26 contacts the source region 22 and the contact region 24 from below. The body region 26 contacts the gate insulating film 38 below the source region 22.

[0018] The drift region 28 is an n-type region. The drift region 28 contacts the body region 26 from below. The drift region 28 is separated from the source region 22 by the body region 26. The drift region 28 contacts the gate insulating film 38 below the body region 26. The drift region 28 has a first drift region 28a and a second drift region 28b. The n-type dopant concentration of the first drift region 28a is higher than the n-type dopant concentration of the second drift region 28b.

[0019] The first drift region 28a contacts the body region 26 from below. The second drift region 28b contacts the first drift region 28a from below.

[0020] The drain region 30 is an n-type region. The n-type dopant concentration of the drain region 30 is higher than the n-type dopant concentration of the first drift region 28a. The drain region 30 contacts the second drift region 28b from below. The drain region 30 is exposed at the lower surface 12b of the semiconductor substrate 12. The drain region 30 is in ohmic contact with the drain electrode 84.

[0021] Next, the operation of the semiconductor device 10 will be described. A higher potential is applied to the drain electrode 84 than to the source electrode 80. When a potential equal to or higher than the gate threshold is applied to the gate electrode 40, a channel is formed in the body region 26 near the gate insulating film 38. Then, electrons flow from the source electrode 80 toward the drain electrode 84 via the source region 22, the channel in the body region 26, the drift region 28, and the drain region 30. In other words, the semiconductor device 10 is turned on. Furthermore, when the potential of the gate electrode 40 is lowered to a potential lower than the gate threshold, the channel disappears, the flow of electrons stops, and the semiconductor device 10 is turned off.

[0022] Next, a method for manufacturing the semiconductor device 10 will be described with reference to Figures 2 to 4. Figures 2 and 4 show cross sections corresponding to Figure 1. The semiconductor device 10 is manufactured from a semiconductor substrate 12 (i.e., an unprocessed semiconductor substrate 12) that includes a drain region 30. First, the second drift region 28b is epitaxially grown on the drain region 30.

[0023] Specifically, as shown in FIG. 3, a semiconductor substrate 12 including a drain region 30 is placed in a chamber 90. The semiconductor substrate 12 is heated in the chamber 90. Then, silane gas (SiH), propane gas (C3H8), and doping gas (N2) are introduced into the chamber 90. As shown in FIG. 3, the silane gas is introduced into the chamber 90 by being supplied from a carrier gas supply source to a gas supply path leading to the chamber 90. Similarly, the propane gas and the doping gas are also introduced into the chamber 90 by being supplied from a carrier gas supply source to a gas supply path leading to the chamber 90. As shown in FIG. 3, the gas supply paths through which the silane gas, propane gas, and doping gas are respectively supplied are different from one another.

[0024] When silane gas, propane gas, and doping gas are introduced into chamber 90, second drift region 28b is formed by epitaxial growth above drain region 30, as shown in FIG.

[0025] After the second drift region 28b is formed, the first drift region 28a is formed by epitaxial growth on the second drift region 28b. The introduction timing and introduction amount of each gas in the process of epitaxially growing the first drift region 28a on the second drift region 28b will be described later.

[0026] Thereafter, the body region 26, the source region 22, and the contact region 24 are formed in the semiconductor substrate 12. The body region 26, the source region 22, and the contact region 24 can be formed by, for example, epitaxial growth or ion implantation.

[0027] 4, a plurality of trenches 34 are formed by selectively etching the upper surface 12a of the semiconductor substrate 12. Here, each trench 34 is formed so as to penetrate the source region 22 and the body region 26 and reach the drift region 28 (particularly the first drift region 28a).

[0028] Next, using techniques such as CVD (Chemical Vapor Deposition) or sputtering, the interlayer insulating layer 36, the gate insulating film 38, the gate electrode 40, the source electrode 80, and the drain electrode 84 are formed, completing the semiconductor device 10 shown in FIG. 1.

[0029] Next, with reference to Figures 5 to 8, the timing and amount of introduction of each gas in the process of epitaxially growing the first drift region 28a on the second drift region 28b will be described. The graph in Figure 5 shows the timing and amount of introduction of each gas in a conventional manufacturing method. The graph in Figure 6 shows the distribution of nitrogen concentration (i.e., n-type dopant concentration) in the first drift region 28a formed by the conventional manufacturing method. The graph in Figure 6 shows the distribution of nitrogen concentration in the thickness direction of the first drift region 28a. In Figure 6, position A is the position at the start of growth, and position B is the position at the end of growth.

[0030] 5, in the conventional technology, first, at time t1, only the doping gas is introduced into the chamber 90 before the silane gas and propane gas. Then, at time t2, the silane gas and the propane gas are introduced into the chamber 90 at the same time. Here, the silane gas and the propane gas are introduced into the chamber 90 so that the gas supply ratio into the chamber 90 is constant.

[0031] The silane gas and propane gas introduced into the chamber are decomposed in the chamber. The decomposition of the silane gas produces reactive silicon material. The decomposition of the propane gas produces reactive carbon material. The reactive silicon material and the reactive carbon material react on the upper surface 12a of the semiconductor substrate 12, growing the second drift region 28b on the semiconductor substrate 12. Hereinafter, the ratio of the reactive carbon material to the reactive silicon material present in the chamber is referred to as the C / Si ratio. That is, the C / Si ratio is the value obtained by dividing the number of moles of reactive carbon material by the number of moles of reactive silicon material. The bond energy of silane gas is lower than that of propane gas. That is, silane gas decomposes more easily than propane gas. Therefore, when silane gas and propane gas are simultaneously introduced into the chamber 90 at time t2, the C / Si ratio is low at the beginning of epitaxial growth. Thereafter, the C / Si ratio increases over time and converges to a constant value.

[0032] Furthermore, the dopant concentration of the SiC layer (e.g., first drift region 28a) formed by epitaxial growth depends on the C / Si ratio in the chamber. Specifically, the n-type dopant nitrogen (N) is incorporated into SiC by coordinating with C. Therefore, the lower the C / Si ratio in the chamber (i.e., the smaller the amount of C in the gas), the more easily the n-type dopant is incorporated into SiC. In other words, the lower the C / Si ratio, the higher the n-type dopant concentration in SiC formed by epitaxial growth.

[0033] 6, the n-type dopant concentration is high in the portion of first drift region 28a formed in the early stage of epitaxial growth (i.e., the period when the C / Si ratio is low), while the n-type dopant concentration is stable at a low value in the portion of first drift region 28a formed in the later stage of epitaxial growth (i.e., the period when the C / Si ratio is stable at a high value).

[0034] Thus, in the conventional technology, a portion with a high n-type dopant concentration is formed in the first drift region 28a at the beginning of epitaxial growth. That is, a portion with a high n-type dopant concentration is formed in the first drift region 28a near the upper surface of the second drift region 28b. The presence of such a portion with a high n-type dopant concentration in the first drift region 28a can result in a decrease in the breakdown voltage of the semiconductor device 10, an increase in leakage current in the semiconductor device 10, and the like.

[0035] 7, in this embodiment, first, at time t1, propane gas and doping gas are introduced into chamber 90 before silane gas. Then, at time t2, silane gas is introduced into chamber 90. Note that in this embodiment, the difference between time t2 and time t1 is 10 seconds, but in modified examples, the difference between time t2 and time t1 may be less than 10 seconds or may be greater than 10 seconds.

[0036] As described above, silane gas decomposes more easily than propane gas. In this embodiment, propane gas is introduced into the chamber 90 before the easily decomposable silane gas is introduced into the chamber 90. Therefore, at time t2 when the silane gas is introduced into the chamber 90, a large amount of reactive carbon material is present in the gas in the chamber 90. Therefore, the C / Si ratio in the chamber 90 is high at the beginning of the epitaxial growth. This allows the C / Si ratio in the chamber 90 to be kept substantially constant throughout the entire epitaxial growth. As a result, as shown in the graph of FIG. 8, the n-type dopant concentration in the first drift region 28a can be made uniform. As a result, a semiconductor device 10 with high breakdown voltage and low leakage current can be manufactured.

[0037] Furthermore, when the growth of the SiC layer is started at a high growth rate in a state where the C / Si ratio in the chamber 90 is high, deterioration is likely to occur on the surface of the SiC layer.

[0038] In this regard, as shown in FIG. 7 , in the process of forming the first drift region 28a in this embodiment, the flow rate of the silane gas is gradually increased when the introduction of the silane gas begins. As a result, the growth rate can be kept low in the early stages of epitaxial growth. This suppresses deterioration of the surface of the SiC layer to be formed. After time t3, the flow rate of the silane gas is maintained constant at a high value, allowing the SiC layer to grow stably at a high growth rate. The low growth rate in the period from time t2 to time t3 is an example of a first growth rate. The high growth rate in the period after time t3 is an example of a second growth rate. Note that the method for keeping the growth rate low in the early stages of epitaxial growth is not limited to the above-described method. For example, the growth rate may be kept low by lowering the temperature.

[0039] In the above-described first embodiment, the second drift region 28b and the first drift region 28a correspond to examples of the "underlying layer" and the "SiC layer", respectively.

[0040] Example 2 Next, a second embodiment will be described with reference to FIG. 9 . In a semiconductor device 100 of the second embodiment, a first drift region 28a and a second drift region 28b have a superjunction structure. Other configurations of the semiconductor device 100 of the second embodiment are similar to those of the semiconductor device 10 of the first embodiment. In the first drift region 28a, a plurality of n-type columns 150 and a plurality of p-type columns 152 are alternately arranged in a repeated manner in the horizontal direction. In the second drift region 28b, a plurality of n-type columns 160 and a plurality of p-type columns 162 are alternately arranged in a repeated manner in the horizontal direction. The direction in which the p-type columns 152 extend intersects with the direction in which the p-type columns 162 extend. The p-type columns 162 are connected to the body region 126 via the p-type columns 152.

[0041] In the manufacturing method of the semiconductor device 100 of Example 2, first, an n-type second drift region 28b is formed by epitaxial growth, similar to Example 1. Next, p-type dopants are selectively implanted into the second drift region 28b to form p-type columns 162. The regions of the second drift region 28b where the p-type columns 162 are not formed become n-type columns 160. Next, similar to Example 1, a first drift region 28a is grown on the second drift region 28b. Therefore, the first drift region 28a has a uniform n-type dopant concentration. Next, p-type dopants are selectively implanted into the first drift region 28a to form p-type columns 152. The regions of the first drift region 28a where the p-type columns 152 are not formed become n-type columns 150.

[0042] The first drift region 28a is formed so that the amount of p-type dopant in the p-type columns 152 and the amount of n-type dopant in the n-type columns 150 are balanced. If a region with a high concentration of n-type dopant were formed during epitaxial growth of the first drift region 28a, as shown in FIG. 6 , it would be difficult to balance the dopants between the n-type columns 150 and the p-type columns 152. In this case, the breakdown voltage of the semiconductor device 100 would be reduced. On the other hand, the manufacturing method of Example 2 can uniformly distribute the n-type dopant concentration in the first drift region 28a. Therefore, it is possible to balance the dopants between the n-type columns 150 and the p-type columns 152, and a semiconductor device with a high breakdown voltage can be manufactured.

[0043] Example 3 Next, Example 3 will be described with reference to Figure 10. In Example 3, as shown in Figure 10, at time t1, propane gas and doping gas are introduced into chamber 90 before silane gas. Then, at time t2, silane gas is introduced into chamber 90. Between time t2 and time t3, the flow rates of propane gas and silane gas are gradually increased. After time t3, the flow rates of propane gas and silane gas are maintained constant at high values.

[0044] In this configuration, between time t2 and time t3, not only the flow rate of silane gas but also the flow rate of propane gas is gradually increased, thereby suppressing fluctuations in the supply ratio of propane gas to silane gas into chamber 90. This prevents the C / Si ratio from becoming excessively high, thereby suppressing deterioration of the surface of the SiC layer.

[0045] A modification of the above embodiment will now be described. In the above embodiment, an example of doping with an n-type dopant was described, but the technique described in this specification is also useful in the case of doping with a p-type dopant into SiC.

[0046] For example, consider an example in which trimethylaluminum (hereinafter referred to as "TMA") is used as the doping gas. In this example, aluminum (Al) is the p-type dopant. The p-type dopant Al is incorporated into SiC by coordinating with Si. Therefore, the lower the C / Si ratio in the chamber (i.e., the greater the amount of Si), the more difficult it is for the p-type dopant to be incorporated into SiC. In other words, the lower the C / Si ratio, the lower the p-type dopant concentration in SiC formed by epitaxial growth.

[0047] Therefore, when silane gas and propane gas are simultaneously introduced into chamber 90, a region with a low p-type dopant concentration is formed in the early stage of epitaxial growth. After that, when the C / Si ratio converges to a constant value, the p-type dopant concentration in the first drift region becomes approximately the same.

[0048] On the other hand, if propane gas is introduced into chamber 90 prior to the introduction of silane gas, which is easily decomposed, a certain amount of C is already present in the gas in chamber 90 when silane gas is introduced into chamber 90. That is, the C / Si ratio in chamber 90 is higher at the beginning of epitaxial growth than when silane gas and propane gas are introduced into chamber 90 simultaneously. Therefore, the C / Si ratio in chamber 90 can be made substantially uniform throughout the entire epitaxial growth. As a result, the p-type dopant concentration in first drift region 28a can be made uniform.

[0049] In the above example, the doping gas and the propane gas were introduced into the chamber 90 at the same time t1 (see the graph on the left side of FIG. 5(B)). In a modified example, the doping gas and the propane gas may be introduced into the chamber 90 at different times, as long as they are introduced before the time t2 at which the silane gas is introduced into the chamber 90.

[0050] The configurations of the manufacturing method disclosed in this specification are listed below. (Configuration 1) A method for manufacturing a semiconductor device (10), comprising: a step of epitaxially growing a SiC layer (28a) on an underlayer (28b) by introducing a first source gas containing Si, a second source gas containing C, and a doping gas into a chamber (90) in which the underlayer (28b) is disposed; In the step of epitaxially growing the SiC layer, the second source gas and the doping gas are introduced into the chamber before the first source gas. (Configuration 2) the underlayer is made of SiC containing a dopant, 2. The manufacturing method according to claim 1, wherein the step of epitaxially growing the SiC layer forms the SiC layer having a dopant concentration higher than a dopant concentration of the underlayer. (Configuration 3) the step of epitaxially growing the SiC layer comprises: a first step of epitaxially growing the SiC layer at a first growth rate; a second step of epitaxially growing the SiC layer at a second growth rate higher than the first growth rate after the first step; 3. The method of manufacturing according to claim 1 or 2, comprising:

[0051] Although specific examples of the technology disclosed in this specification have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility either alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives itself has technical utility. [Explanation of symbols]

[0052] 10, 100: semiconductor device, 12: semiconductor substrate, 22: source region, 24: contact region, 26: body region, 28: drift region, 28a: first drift region, 28b: second drift region, 30: drain region, 34: trench, 36: interlayer insulating layer, 38: gate insulating film, 40: gate electrode, 80: source electrode, 84: drain electrode, 150, 160: n-type column, 152, 162: p-type column

Claims

1. A method for manufacturing a semiconductor device (10), comprising: The method includes a step of epitaxially growing a SiC layer (28a) on an underlayer (28b) by introducing a first source gas containing Si, a second source gas containing C, and a doping gas into a chamber (90) in which the underlayer (28b) is disposed; In the step of epitaxially growing the SiC layer, the second source gas and the doping gas are introduced into the chamber before the first source gas.

2. the underlayer is made of SiC containing a dopant, The manufacturing method according to claim 1 , wherein the step of epitaxially growing the SiC layer forms the SiC layer having a dopant concentration higher than a dopant concentration of the underlayer.

3. the step of epitaxially growing the SiC layer comprises: a first step of epitaxially growing the SiC layer at a first growth rate; a second step, after the first step, of epitaxially growing the SiC layer at a second growth rate higher than the first growth rate; The manufacturing method according to claim 1 or 2, comprising:

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