Semiconductor device manufacturing method

Abstract

To provide a method for manufacturing a semiconductor device that can reduce crystal defects.SOLUTION: A method for manufacturing a semiconductor device has the steps of: forming a first AlN layer on the first main surface of a single-crystal substrate; forming a plurality of AlN seed crystals from the first AlN layer onto the first main surface by etching a portion of the first AlN layer; and forming a second AlN layer on the first main surface using the AlN seed crystals as growth nuclei.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a semiconductor device. [Background technology]

[0002] A method for manufacturing a semiconductor device is disclosed in which an AlN buffer layer having an uneven upper surface is formed on a SiC substrate, and semiconductor layers such as an electron transit layer and an electron supply layer are formed on the AlN buffer layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-004924 Summary of the Invention [Problem to be solved by the invention]

[0004] Various applications of semiconductor devices using nitride semiconductors are being considered, and depending on the application, it is desirable to further reduce crystal defects such as pits in the nitride semiconductor layer.

[0005] An object of the present disclosure is to provide a method for manufacturing a semiconductor device that can reduce crystal defects. [Means for solving the problem]

[0006] A method for manufacturing a semiconductor device according to the present disclosure includes the steps of: forming a first AlN layer on a first main surface of a single crystal substrate; etching a portion of the first AlN layer to form a plurality of AlN seed crystals on the first main surface from the first AlN layer; and using the AlN seed crystals as growth nuclei to form a second AlN layer on the first main surface. and the average height of the AlN seed crystal is 2.0 times or less the average height of steps present on the first main surface. . [Effects of the Invention]

[0007] According to the present disclosure, crystal defects can be reduced. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a flowchart showing a method for manufacturing a semiconductor device according to the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view (part 1) illustrating the method for manufacturing the semiconductor device according to the first embodiment. [Figure 3] FIG. 3 is a cross-sectional view (part 2) illustrating the method for manufacturing the semiconductor device according to the first embodiment. [Figure 4] FIG. 4 is a cross-sectional view (part 3) illustrating the method for manufacturing the semiconductor device according to the first embodiment. [Figure 5] FIG. 5 is a cross-sectional view (part 4) illustrating the method for manufacturing the semiconductor device according to the first embodiment. [Figure 6] FIG. 6 is a cross-sectional view (part 5) illustrating the method for manufacturing the semiconductor device according to the first embodiment. [Figure 7] FIG. 7 is a schematic diagram (part 1) showing the process of forming the AlN buffer layer in the first embodiment. [Figure 8] FIG. 8 is a schematic diagram (part 2) showing the process of forming the AlN buffer layer in the first embodiment. [Figure 9] FIG. 9 is a schematic diagram (part 3) showing the process of forming the AlN buffer layer in the first embodiment. [Figure 10] FIG. 10 is a cross-sectional view (part 1) showing a method for manufacturing a semiconductor device according to a reference example. [Figure 11] FIG. 11 is a cross-sectional view (part 2) showing a method for manufacturing a semiconductor device according to a reference example. [Figure 12] FIG. 12 is a cross-sectional view (part 3) showing a method for manufacturing a semiconductor device according to a reference example. [Figure 13] FIG. 13 is a flowchart showing a method for manufacturing a semiconductor device according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described.

[0010] [1] A method for manufacturing a semiconductor device according to one embodiment of the present disclosure includes the steps of forming a first AlN layer on a first main surface of a single crystal substrate, etching a portion of the first AlN layer to form a plurality of AlN seed crystals on the first main surface from the first AlN layer, and using the AlN seed crystals as growth nuclei to form a second AlN layer on the first main surface.

[0011] An AlN seed crystal is formed by forming and etching the first AlN layer. The second AlN layer is then formed using the AlN seed crystal as a growth nucleus. This reduces crystal defects in the semiconductor layer formed on the second AlN layer.

[0012] [2] In [1], a nitride semiconductor layer containing Ga may be formed on the second AlN layer, in which case a GaN-based semiconductor device is obtained.

[0013] [3] In the method of [1] or [2], in the step of forming the first AlN layer, the first main surface may be entirely covered with the first AlN layer, which makes it easier to uniformly disperse AlN seed crystals on the first main surface.

[0014] [4] In any of [1] to [3], the step of forming the first AlN layer may include a step of supplying trimethylaluminum gas, ammonia gas, and hydrogen gas into a film formation chamber, and the step of etching the first AlN layer may include a step of sublimating a portion of the first AlN layer by stopping the supply of the trimethylaluminum gas into the film formation chamber while continuing to supply the hydrogen gas into the film formation chamber at a temperature of 1000° C. to 1200° C. In this case, the formation and etching of the first AlN layer can be performed in a common film formation chamber.

[0015] [5] In the method of [4], the supply of the ammonia gas into the deposition chamber may be continued during the step of etching the first AlN layer. When ammonia gas is used to form the second AlN layer, the flow rate of the ammonia gas can be easily stabilized by continuing the supply of the ammonia gas.

[0016] [6] In the methods of [1] to [3], the step of etching the first AlN layer may include the step of removing a portion of the first AlN layer by dry etching the first AlN layer using hydrogen chloride gas at a temperature of 850° C. to 1100° C. In this case, the first AlN layer can be easily etched in a short time.

[0017] [7] In any of [1] to [6], the average height of the AlN seed crystals may be 2.0 times or less the average height of steps present on the first main surface, which makes it easier to reduce variation in size of the AlN seed crystals.

[0018] [8] In any of [1] to [7], the single crystal substrate may be a SiC single crystal substrate, which makes it easier to form a semiconductor layer with good crystallinity.

[0019] [9] A method for manufacturing a semiconductor device according to another aspect of the present disclosure includes the steps of: forming a first AlN layer on a first main surface of a SiC single crystal substrate; etching a portion of the first AlN layer to form a plurality of AlN seed crystals on the first main surface from the first AlN layer; forming a second AlN layer on the first main surface using the AlN seed crystals as growth nuclei; and forming a nitride semiconductor layer containing Ga on the second AlN layer, wherein the step of forming the first AlN layer includes the step of supplying trimethylaluminum gas, ammonia gas, and hydrogen gas into a deposition chamber at a temperature of 1000°C or higher and 1200°C or lower; and the step of etching the first AlN layer includes the step of continuing to supply the ammonia gas and the hydrogen gas into the deposition chamber at a temperature of 1000°C or higher and 1200°C or lower while stopping the supply of the trimethylaluminum gas into the deposition chamber, thereby sublimating a portion of the first AlN layer.

[0020] An AlN seed crystal is formed through the formation and etching of the first AlN layer. Then, the second AlN layer is formed using the AlN seed crystal as a growth nucleus. This reduces crystal defects in the semiconductor layer formed on the second AlN layer. Furthermore, the formation and etching of the first AlN layer can be performed in a common deposition chamber, and when ammonia gas is used to form the second AlN layer, the flow rate of the ammonia gas can be easily stabilized by continuously supplying the ammonia gas.

[0021] [Details of the embodiments of the present disclosure] Hereinafter, embodiments of the present disclosure will be described in detail, but the present disclosure is not limited thereto. In this specification and drawings, components having substantially the same functional configurations may be designated by the same reference numerals to avoid redundant description.

[0022] (First embodiment) First, a first embodiment will be described. The first embodiment relates to a method for manufacturing a semiconductor device including a GaN-based high electron mobility transistor (HEMT). FIG. 1 is a flowchart showing a method for manufacturing a semiconductor device according to the first embodiment. FIGS. 2 to 6 are cross-sectional views showing the method for manufacturing a semiconductor device according to the first embodiment. FIGS. 7 to 9 are schematic views showing a process for forming an AlN buffer layer in the first embodiment.

[0023] In the first embodiment, first, a SiC single crystal substrate 10 is placed in a film formation chamber (Step S11). Next, as shown in FIG. 2, a first AlN layer 11 is formed on an upper surface 10A of the SiC single crystal substrate 10, for example, by metal organic chemical vapor deposition (MOCVD) (Step S12). The SiC single crystal substrate 10 may have an off-axis angle. The upper surface 10A is, for example, the Si surface of the SiC single crystal. The first AlN layer 11 is epitaxially grown on the upper surface 10A. For example, the first AlN layer 11 is formed so as to cover the entire upper surface 10A. The average thickness of the first AlN layer 11 is preferably 1 nm or more and 20 nm or less, and more preferably 3 nm or more and 10 nm or less. When forming the first AlN layer 11, for example, trimethylaluminum (TMA) gas, ammonia (NH) gas, and hydrogen (H) gas are supplied into a deposition chamber accommodating the SiC single crystal substrate 10 at a temperature of 1000° C. to 1200° C. The upper surface 10A is an example of a first main surface.

[0024] As shown in FIG. 7 , the top surface 10A of the SiC single crystal substrate 10 has terraces 21, steps 22, and kinks 23. The steps 22 generally refer to small atomic-level steps that occur during crystal growth, and the relatively flat surface portions of the steps 22 are called terraces 21. The bent portions of the steps 22 are called kinks 23. The first AlN layer 11 is formed by the bonding of Al contained in the TMA gas and N contained in the NH3 gas. In the initial stage of this process, nuclei 31 are generated at multiple locations on the top surface 10A. Nuclei 31 are likely to be generated from the steps 22 and kinks 23; however, due to unavoidable concentration variations in the TMA gas and NH3 gas, and temperature variations on the top surface 10A, it is difficult to control the locations where the nuclei 31 are generated. Furthermore, it is difficult to control the size of the generated nuclei 31.

[0025] Thereafter, as the supply of TMA gas, NH3 gas, and H2 gas into the deposition chamber continues, AlN grows three-dimensionally from the nuclei 31, and a first AlN layer 11 is formed, as shown in Fig. 8. For convenience, the top surface of the first AlN layer 11 is shown as flat in Fig. 8, but the top surface of the first AlN layer 11 may be uneven.

[0026] 3, a portion of the first AlN layer 11 is etched to form a plurality of AlN seed crystals 12 from the first AlN layer 11 on the upper surface 10A of the SiC single crystal substrate 10 (step S13). When etching the first AlN layer 11, for example, NH3 gas and H2 gas are continuously supplied into the deposition chamber at a temperature of 1000°C or higher and 1200°C or lower, and the supply of TMA gas into the deposition chamber is stopped, thereby sublimating a portion of the first AlN layer 11.

[0027] The bond between the AlN constituting the first AlN layer 11 and the SiC constituting the SiC single crystal substrate 10 is stronger at the steps 22 and kinks 23 than at the terraces 21. For this reason, as etching of the first AlN layer 11 proceeds, the first AlN layer 11 remains preferentially at the steps 22 and kinks 23, as shown in Fig. 9, and a plurality of AlN seed crystals 12 are formed. The average height of the AlN seed crystals 12 remaining after etching is preferably 2.0 times or less, and more preferably 1.0 times or less, the average height of the steps 22 present on the upper surface 10A. This is because it is easy to reduce the variation in size of the AlN seed crystals 12 remaining after etching.

[0028] The steps 22 and kinks 23 are dispersed at a relatively uniform density within the upper surface 10A. For this reason, the AlN seed crystals 12 are more likely to be dispersed at a uniform density within the upper surface 10A than the nuclei 31. Furthermore, because the AlN seed crystals 12 are preferentially formed at the steps 22 and kinks 23, the size of the AlN seed crystals 12 is more likely to be uniform than the size of the nuclei 31.

[0029] After the AlN seed crystal 12 is formed, as shown in FIG. 4, a second AlN layer 13 is formed as an AlN buffer layer on the upper surface 10A of the SiC single crystal substrate 10 by, for example, MOCVD using the AlN seed crystal 12 as a growth nucleus (step S14). The second AlN layer 13 is epitaxially grown on the upper surface 10A. For example, the second AlN layer 13 grows in an island shape using the SK growth mode (Stranski-Krastanov growth mode). The average thickness of the second AlN layer 13 is preferably 10 nm to 30 nm, and more preferably 10 nm to 20 nm. When forming the second AlN layer 13, for example, TMA gas, NH gas, and H gas are supplied into a deposition chamber containing the SiC single crystal substrate 10 at a temperature of 1000°C to 1200°C.

[0030] The density and size of the AlN seed crystals 12 within the upper surface 10A vary little, and the second AlN layer 13 grows three-dimensionally using the AlN seed crystals 12 as growth nuclei. Therefore, the density and size of the multiple protrusions 13A included in the second AlN layer 13 grown in an island shape also vary little. Each protrusion 13A is formed so as to surround one of the multiple AlN seed crystals 12.

[0031] After the second AlN layer 13 is formed, as shown in FIG. 5 , an electron transit layer 14, an electron supply layer 15, and a cap layer 16 are formed on the second AlN layer 13 by, for example, MOCVD (step S15). The electron transit layer 14, the electron supply layer 15, and the cap layer 16 are epitaxially grown on the upper surface of the second AlN layer 13. For example, the electron transit layer 14 is a GaN layer, the electron supply layer 15 is an AlGaN layer, and the cap layer 16 is a GaN layer. When forming the electron transit layer 14 and the cap layer 16, for example, trimethylgallium (TMG) gas, NH3 gas, and H2 gas are supplied into a deposition chamber containing the SiC single crystal substrate 10. When forming the electron supply layer 15, for example, TMA gas, TMG gas, NH3 gas, and H2 gas are supplied into a deposition chamber containing the SiC single crystal substrate 10.

[0032] Because there is little variation in density and size among the multiple protrusions 13A included in the second AlN layer 13, the electron transit layer 14 can grow uniformly on the upper surface 10A, and dislocations are less likely to occur in the electron transit layer 14. This prevents the occurrence of crystal defects such as pits. Similarly, the occurrence of crystal defects such as pits is also prevented in the electron supply layer 15 and the cap layer 16.

[0033] After the cap layer 16 is formed, the SiC single crystal substrate 10 on which the second AlN layer 13, the electron transit layer 14, the electron supply layer 15, and the cap layer 16 are formed is removed from the film formation chamber (step S16). Next, as shown in FIG. 6, a portion of the cap layer 16 is removed, and a source electrode 17S and a drain electrode 17D are formed. In addition, a gate electrode 17G is formed on the cap layer 16. Thereafter, a protective film 18 is formed to cover the cap layer 16 (step S17).

[0034] In this manner, a semiconductor device including a GaN-based HEMT can be manufactured.

[0035] In the first embodiment, the AlN seed crystal 12 is formed by forming and etching the first AlN layer 11. Then, the second AlN layer 13 is formed using the AlN seed crystal 12 as a growth nucleus. This makes it possible to suppress variations in density and size among the multiple protrusions 13A included in the second AlN layer 13. This makes it possible to reduce crystal defects in the electron transit layer 14, electron supply layer 15, and cap layer 16 (nitride semiconductor layers) formed on the second AlN layer 13.

[0036] Furthermore, the processes from forming the first AlN layer 11 to forming the cap layer 16 can be performed in a single deposition chamber. This allows these processes to be performed continuously. Also, oxidation and other problems that may occur when the substrate is removed from the deposition chamber can be avoided.

[0037] Here, a reference example will be described for comparison with the first embodiment. Figures 10 to 12 are cross-sectional views showing a method for manufacturing a semiconductor device according to the reference example.

[0038] In the reference example, as shown in Fig. 10, an AlN layer 51 is formed on the upper surface 10A of the SiC single crystal substrate 10, similar to the first AlN layer 11. Next, as shown in Fig. 11, an electron transit layer 14, an electron supply layer 15, and a cap layer 16 are formed on the AlN layer 51. Next, as shown in Fig. 12, a source electrode 17S, a drain electrode 17D, a gate electrode 17G, and a protective film 18 are formed in the same manner as in the first embodiment.

[0039] Nuclei are generated in the early stages of forming the AlN layer 51, but similar to the nuclei 31 in the early stages of forming the first AlN layer 11, it is difficult to control the location and size of the nuclei. As a result, the density and size of the multiple protrusions 51A included in the AlN layer 51 tend to vary. Therefore, compared to the semiconductor device manufactured according to the first embodiment, the semiconductor device manufactured according to the comparative example has more crystal defects in the electron transit layer 14, electron supply layer 15, and cap layer 16. From the other hand, according to the first embodiment, crystal defects can be reduced more than in the reference example.

[0040] The supply of not only the TMA gas but also the NH3 gas to the deposition chamber may be stopped when etching the first AlN layer 11. However, since NH3 gas is supplied when forming the second AlN layer 13 after etching the first AlN layer 11, it is preferable to continue the supply of NH3 gas from the viewpoint of the stability of the flow rate of the NH3 gas.

[0041] (Second embodiment) Next, a second embodiment will be described. The second embodiment differs from the first embodiment mainly in the method of etching the first AlN layer 11. Fig. 13 is a flowchart showing a method of manufacturing a semiconductor device according to the second embodiment.

[0042] In the second embodiment, first, similarly to steps S11 and S12 in the first embodiment, the SiC single crystal substrate 10 is placed in a film formation chamber (step S21), and the first AlN layer 11 is formed (step S22).

[0043] Next, the SiC single crystal substrate 10 on which the first AlN layer 11 has been formed is removed from the deposition chamber (step S23). Next, a portion of the first AlN layer 11 is etched to form a plurality of AlN seed crystals 12 from the first AlN layer 11 on the upper surface 10A of the SiC single crystal substrate 10 (step S24). When etching the first AlN layer 11, for example, the first AlN layer 11 is dry-etched using hydrogen chloride (HCl) gas in an etching apparatus at a temperature of 850°C to 1100°C, thereby removing a portion of the first AlN layer 11. H2 gas or nitrogen (N2) gas may be used as a carrier gas for the HCl gas. In the second embodiment, as shown in FIG. 9, the first AlN layer 11 preferentially remains at steps 22 and kinks 23, and a plurality of AlN seed crystals 12 are formed.

[0044] After the AlN seed crystal 12 is formed, the SiC single crystal substrate 10 on which the AlN seed crystal 12 is formed is placed again in the film formation chamber (step S25). Next, similar to steps S14 to S15 in the first embodiment, the second AlN layer 13 is formed (step S26), and the electron transit layer 14, electron supply layer 15, and cap layer 16 are formed (step S27).

[0045] Next, similar to steps S16 to S17 in the first embodiment, the SiC single crystal substrate 10 on which the second AlN layer 13, the electron transit layer 14, the electron supply layer 15, and the cap layer 16 have been formed is removed from the film formation chamber (step S28), and a protective film 18 is formed (step S29).

[0046] In this manner, a semiconductor device including a GaN-based HEMT can be manufactured.

[0047] In the second embodiment, the second AlN layer 13 is also formed using the AlN seed crystals 12 as growth nuclei, which makes it possible to suppress variations in density and size among the multiple protrusions 13A included in the second AlN layer 13. This makes it possible to reduce crystal defects in the electron transit layer 14, the electron supply layer 15, and the cap layer 16 (nitride semiconductor layers) formed on the second AlN layer 13.

[0048] Furthermore, since the first AlN layer 11 is etched by dry etching using HCl gas, the AlN seed crystal 12 can be formed in a short time.

[0049] The inventors of the present application formed a GaN electron transit layer 14 in accordance with the second embodiment and the above-described reference example, and measured the number density of pits in the electron transit layer 14 for each. The number density in the second embodiment was about 1 / 40 to 1 / 30 of that in the reference example.

[0050] The single crystal substrate is not limited to a SiC single crystal substrate, and may be, for example, an AlN single crystal substrate, a GaN single crystal substrate, a sapphire single crystal substrate, or a Si single crystal substrate.

[0051] Although the embodiments have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and changes are possible within the scope of the claims. [Explanation of symbols]

[0052] 10: SiC single crystal substrate 10A:Top surface 11: 1st AlN layer 12:AlN seed crystal 13: Second AlN layer 13A: Convex part 14: Electron transit layer 15:Electron supply layer 16: Cap layer 17D: Drain electrode 17G: Gate electrode 17S: Source electrode 18:Protective film 21: Terrace 22: Step 23: Kink 31:Nuclear 51:AlN layer 51A: Convex part

Claims

1. forming a first AlN layer on a first main surface of the single crystal substrate; etching a portion of the first AlN layer to form a plurality of AlN seed crystals on the first main surface from the first AlN layer; forming a second AlN layer on the first principal surface using the AlN seed crystal as a growth nucleus; Including, The method for manufacturing a semiconductor device, wherein the average height of the AlN seed crystal is 2.0 times or less the average height of steps present on the first main surface.

2. The method for manufacturing a semiconductor device according to claim 1 , further comprising the step of forming a nitride semiconductor layer containing Ga on the second AlN layer.

3. 3. The method for manufacturing a semiconductor device according to claim 1, wherein in the step of forming the first AlN layer, the first main surface is entirely covered with the first AlN layer.

4. the step of forming the first AlN layer includes the step of supplying trimethylaluminum gas, ammonia gas, and hydrogen gas into a deposition chamber; 4. The method for manufacturing a semiconductor device according to claim 1, wherein the step of etching the first AlN layer comprises a step of sublimating a portion of the first AlN layer by stopping the supply of the trimethylaluminum gas into the film formation chamber while continuing to supply the hydrogen gas into the film formation chamber at a temperature of 1000°C or higher and 1200°C or lower.

5. 5. The method for manufacturing a semiconductor device according to claim 4, wherein the supply of the ammonia gas into the film formation chamber is continued in the step of etching the first AlN layer.

6. 4. The method for manufacturing a semiconductor device according to claim 1, wherein the step of etching the first AlN layer comprises a step of removing a portion of the first AlN layer by dry etching the first AlN layer using hydrogen chloride gas at a temperature of 850°C or higher and 1100°C or lower.

7. 7. The method for manufacturing a semiconductor device according to claim 1, wherein the single crystal substrate is a SiC single crystal substrate.

8. forming a first AlN layer on a first main surface of the SiC single crystal substrate; etching a portion of the first AlN layer to form a plurality of AlN seed crystals on the first main surface from the first AlN layer; forming a second AlN layer on the first principal surface using the AlN seed crystal as a growth nucleus; forming a nitride semiconductor layer containing Ga on the second AlN layer; and the step of forming the first AlN layer includes a step of supplying trimethylaluminum gas, ammonia gas, and hydrogen gas into a film formation chamber at a temperature of 1000° C. or higher and 1200° C. or lower; the step of etching the first AlN layer includes a step of sublimating a portion of the first AlN layer by stopping the supply of the trimethylaluminum gas into the film formation chamber while continuing to supply the ammonia gas and the hydrogen gas into the film formation chamber at a temperature of 1000° C. or higher and 1200° C. or lower; The method for manufacturing a semiconductor device, wherein the average height of the AlN seed crystal is 2.0 times or less the average height of steps present on the first main surface.

Images