JP2021180295A - Susceptor, manufacturing method of nitride semiconductor device, and nitride semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for suppressing a transition metal contained in graphite of a susceptor from being incorporated into a semiconductor device. SOLUTION: A susceptor is used in a film forming apparatus of a nitride semiconductor apparatus. The susceptor covers the surface of the base material containing graphite as a main component and the surface of the base material, covers the surface of the first layer containing silicon carbide as a main component, and the surface of the first layer, and mainly contains aluminum nitride. A second layer as a component may be provided. [Selection diagram] Fig. 2

Description

The techniques disclosed herein relate to susceptors, methods of manufacturing nitride semiconductor devices and nitride semiconductor devices.

Patent Document 1 discloses a susceptor having a surface composed of graphite, silicon carbide and the like.

Japanese Unexamined Patent Publication No. 2018-070405

Graphite used in the susceptor contains transition metals such as Fe, Ni, and Cr. In the film forming process of a semiconductor device using a susceptor, if a transition metal is incorporated into the semiconductor device from graphite, the performance of the semiconductor device may deteriorate. The present specification provides a technique for suppressing the incorporation of a transition metal contained in graphite of a susceptor into a semiconductor device.

One susceptor disclosed herein is used in a film forming apparatus for a nitride semiconductor apparatus. The susceptor covers the surface of the base material containing graphite as a main component and the surface of the base material, covers the surface of the first layer containing silicon carbide as a main component, and the surface of the first layer, and mainly contains aluminum nitride. A second layer as a component may be provided.

In the above configuration, the graphite-based substrate is covered with a first layer containing silicon carbide as the main component. Therefore, the situation where the transition metal contained in graphite is incorporated into the semiconductor device is suppressed. On the other hand, when the first layer of silicon carbide uses a reducing atmosphere gas such as ammonia in the film forming apparatus, the first layer is liable to be damaged when exposed to the reducing atmosphere gas. According to the above configuration, the first layer is covered with the second layer containing aluminum nitride as a main component. This makes it possible to prevent the first layer from being exposed to the reducing atmosphere. Therefore, it is possible to avoid the situation where the graphite of the base material is exposed from the defect of the first layer. As a result, it is possible to suppress the situation where the transition metal contained in graphite is taken into the semiconductor device from the susceptor.

The first layer may be thicker than the second layer. According to this configuration, by arranging the first layer of silicon carbide relatively thickly on the rough surface of the base material, the surface of the first layer can be made smooth as compared with the base material. As a result, it is possible to suppress the occurrence of defects in the second layer without increasing the thickness of the aluminum nitride, which takes a long time to form a film as compared with silicon carbide.

The first layer may have a thickness of approximately 1000 times the thickness of the second layer. According to this configuration, the film formation time of the second layer can be shortened.

Another susceptor disclosed herein is used in a film forming apparatus for a nitride semiconductor apparatus. The susceptor covers the surface of the base material containing graphite as a main component, the coating layer containing silicon carbide as a main component, and the pores arranged in the coating layer, and is nitrided. A covering member containing aluminum as a main component may be provided.

In the above configuration, the base material containing graphite as a main component is covered with a coating layer containing silicon carbide as a main component. Therefore, the situation where the transition metal contained in graphite is incorporated into the semiconductor device is suppressed. Further, the pores of the coating layer are covered with a coating member of aluminum nitride. This makes it possible to avoid the situation where the graphite of the base material is exposed from the pores of the coating layer. As a result, it is possible to suppress the situation where the transition metal contained in graphite is taken into the semiconductor device from the susceptor.

The method for manufacturing a nitride semiconductor device disclosed in the present specification is a susceptor intermediate including a base material containing graphite as a main component and a coating layer covering the surface of the base material and made of silicon carbide. A manufacturing step of supplying a member containing aluminum nitride as a main component to the surface of the material to manufacture a susceptor in a film forming apparatus in which the susceptor intermediate material is arranged, and an arrangement on the susceptor following the manufacturing step. Even if it is provided with an introduction step of introducing the substrate to be formed into the film forming apparatus and a film forming step of forming a nitride semiconductor layer on the substrate in the film forming apparatus by using a reducing atmosphere gas. good.

In the above configuration, a member containing aluminum nitride as a main component is supplied to the susceptor intermediate material to prepare the susceptor prior to the film forming step using the reducing atmosphere gas. The susceptor intermediate material may have a base material and a coating layer and may not have a member containing aluminum nitride as a main component, or the coating layer of the susceptor may be carbonized by repeated film formation. It may be one in which pores are generated in silicon. In this configuration, aluminum nitride is supplied in the pre-process of the film forming process. Thereby, the film forming step can be executed in a state where the graphite of the susceptor is suppressed from being exposed to the outside. As a result, it is possible to suppress the situation where the transition metal contained in graphite is taken into the semiconductor device from the susceptor.

The nitride semiconductor device disclosed in the present specification is in contact with the p-type conductive layer via an interface, and has an average Fe concentration of 2.0 × 10 ¹⁴ cm ^-3 or less. It may be provided with an n-type conductive layer.

In the nitride semiconductor device manufactured by using the above-mentioned susceptor, the Fe concentration of the n-type conductive layer can be suppressed to a low level. This makes it possible to suppress deterioration in the performance of the semiconductor device due to Fe.

It is the schematic sectional drawing of the film forming apparatus of 1st Example. It is an enlarged sectional view near the surface of the susceptor of 1st Example. It is the schematic sectional drawing of the semiconductor device of 1st Example. It is a flowchart which shows the manufacturing process of the semiconductor device of 1st Example. It is a graph of the measurement result of the Fe concentration of the n-type GaN layer of the semiconductor device of 1st Example. It is a graph of the measurement result of the Fe concentration of the n-type GaN layer of the semiconductor device of the comparative example. It is a graph of the measurement result of the impurity concentration of the semiconductor device of 1st Example. It is an enlarged sectional view near the surface of the susceptor of the 2nd Example.

(First Example)
(Structure of film forming equipment)
FIG. 1 shows a schematic cross-sectional view of the film forming apparatus 2 according to the present embodiment. The film forming apparatus 2 is used to generate a nitride semiconductor apparatus such as GaN. The film forming apparatus 2 forms an n-type conductive layer and a p-type conductive layer on the substrate 101 by using an organic metal vapor phase growth (hereinafter referred to as “MOVPE”) method. The film forming apparatus 2 includes a container 4, a reaction gas supply unit 6, a heater 8, and a susceptor 10.

The container 4 houses the heater 8 and the susceptor 10. A reaction gas supply unit 6 extending from the outside penetrates the container 4. The reaction gas supply unit 6 has a pipe for introducing the reaction gas from the outside of the container 4 into the container 4. The heater 8 adjusts the temperature of the substrate 101 mounted on the susceptor 10.

(Structure of susceptor)
Next, the configuration of the susceptor 10 will be described with reference to FIG. The susceptor 10 has a disk shape. The susceptor 10 is rotatably arranged in the container 4 about a disk-shaped central axis. The susceptor 10 includes a base material 12, a coating layer 14, and a protective layer 16. The base material 12 is made of a material containing graphite as a main component. In addition to graphite, the material of the base material 12 contains a trace amount of transition metals such as Fe, Ni, and Cr as compared with graphite. The base material 12 is covered with a coating layer 14. The coating layer 14 covers the entire surface of the base material 12. The coating layer 14 is made of a material containing silicon carbide as a main component. The coating layer 14 is made of high-purity silicon carbide, and the proportion of impurities contained in the silicon carbide is very small as compared with graphite.

The coating layer 14 has a thickness of 100 μm. The thickness of the coating layer 14 may deviate from 100 μm by a manufacturing error. The covering layer 14 is covered with a protective layer 16. The protective layer 16 covers the entire surface of the covering layer 14. The protective layer 16 is made of a material containing aluminum nitride as a main component. The protective layer 16 is made of high-purity aluminum nitride. The protective layer 16 has a thickness of 0.1 μm. The thickness of the protective layer 16 may deviate from 0.1 μm due to a manufacturing error. The thickness of the covering layer 14 is approximately 1000 times the thickness of the protective layer 16. "Approximately" 1000 times means that the coating layer 14 and the protective layer 16 are 1000 times when manufactured according to the design value, but include a case where the coating layer 14 and the protective layer 16 deviate from 1000 times due to a manufacturing error. ..

In the susceptor 10, the protective layer 16 is exposed in the container 4, and the base material 12 and the coating layer 14 are covered with the protective layer 16 and are not exposed in the container 4.

(Semiconductor device configuration)
Next, the configuration of the semiconductor device 100 will be described with reference to FIG. The semiconductor device 100 is a PN junction diode. The semiconductor device 100 includes a substrate 101, an n-type GaN layer 102, a p-type GaN layer 104, a p-type GaN layer 106, and electrodes 110 and 112. The substrate 101 has an n-type GaN layer. The semiconductor device 100 has a structure in which an n-type GaN layer 102, a p-type GaN layer 104, and a p-type GaN layer 106 are sequentially laminated on the surface of the substrate 101. The electrode 112 is arranged on the surface of the semiconductor device 100, and the electrode 110 is arranged on the surface of the semiconductor device 100.

(Manufacturing method of semiconductor device)
Next, a method of manufacturing the semiconductor device 100 will be described with reference to FIG. When manufacturing the semiconductor device 100, the substrate 101 is housed in the film forming apparatus 2, but before that, in order to complete the susceptor 10, the process of S12 is first executed. In S12, the intermediate material of the susceptor 10 is arranged in the film forming apparatus 2. As shown in FIG. 2, the intermediate material includes a base material 12 and a coating layer 14. Hereinafter, the intermediate material of the susceptor 10 is referred to as an intermediate material (12, 14).

In S12, an aluminum nitride layer, which is a protective layer 16, is formed on the surface of the intermediate material (12, 14). Specifically, in the film forming apparatus 2, the protective layer 16 is generated by using the MOVPE method. The treatment of S12 may also be used for the susceptor 10 that already has the protective layer 16 in order to avoid deterioration of the protective layer 16 over time. In this case, the intermediate material may include the base material 12, the coating layer 14, and the protective layer 16. Further, the process of S12 may not be executed every time, and may be executed, for example, for a predetermined period or every use for a predetermined number of times. Next, in S14, the substrate 101 is placed on the susceptor 10 made in S12. Next, in S16, an n-type GaN layer 102 is generated on the surface of the substrate 101. Specifically, trimethylgallium is used as a raw material for Ga, ammonia gas is used as a raw material for nitrogen, monomethylsilane gas is used as a raw material for n-type impurity silicon, and hydrogen is used as a carrier gas to generate an n-type GaN layer 102 by the MOVPE method. The film formation temperature is maintained at 950 ° C. In S16, for example, an n-type GaN layer 102 having a Si concentration of 2.8 × 10 ¹⁶ cm ^-3 , a carbon concentration of 2 × 10 ¹⁵ cm ^-3 , and a film thickness of 3.2 μm is generated.

Next, in S18, a p-type GaN layer 104 is generated on the surface of the n-type GaN layer 102. Specifically, bis (cyclopentadienyl) magnesium is used as a raw material for the p-type impurity magnesium, and the p-type GaN layer 104 is generated at the same gas and temperature as the n-type GaN layer 102. In S18, for example, a p-type GaN layer 104 having a Mg concentration of 1.4 × 10 ¹⁹ cm ^-3 and a film thickness of 0.5 μm is generated.

Next, in S20, the p-type GaN layer 106 is generated on the surface of the p-type GaN layer 104. In the treatment of S20, as in the treatment of S18, bis (cyclopentadienyl) magnesium is used as a raw material for the p-type impurity magnesium, and the other parts are p-type at the same gas and temperature as the n-type GaN layer 102. Generate the GaN layer 106. In the treatment of S20, bis (cyclopentadienyl) magnesium is adjusted so that the concentration of p-type impurities is higher than that of the treatment of S18. In S20, for example, a p-type GaN layer 106 having a Mg concentration of 9 × 10 ¹⁹ cm ^-3 and a film thickness of 0.1 μm is generated.

Next, in S22, heat treatment is performed on the laminate produced in S20. In the heat treatment, the laminate produced in S20 is heated at 850 ° C. for 5 minutes in a nitrogen atmosphere. As a result, the hydrogen contained in the laminate produced in S20 is released. Next, in S24, etching by dry etching is performed on the laminate after heat treatment in S22 to form a mesa structure penetrating the p-type GaN layers 104 and 106. Next, in S26, electrodes 110 and 112 are generated. Specifically, the electrode 112 which is a Ni / Au ohmic electrode is generated on the front surface of the GaN layer 106, and the electrode 110 which is a Ti / Al ohmic electrode is generated on the back surface of the substrate 101 to generate the semiconductor device 100. .. In S26, it is maintained at 525 ° C. for 5 minutes in an oxygen atmosphere.

If necessary, the semiconductor device 100 may be divided by dicing, or an ion implantation process may be added in order to avoid electric field concentration in the vicinity of the terminal portion of the mesa structure. Further, in order to suppress the leakage current from the surface, a forming treatment for forming a polyimide or an insulating film may be added to the surface after etching.

(Analysis results of semiconductor devices)
Next, the measurement results by the secondary ion mass spectrometry (SIMS) method of the semiconductor device 100 manufactured by the above manufacturing method will be described with reference to FIGS. 5 to 7. FIG. 5 shows the analysis results of the Fe concentration in the substrate 101 of the semiconductor device 100 and the n-type GaN layer 102. FIG. 6 shows, as a comparative example, the susceptor 10 of the film forming apparatus 2 produced by the above-mentioned manufacturing method using a susceptor provided with a base material 12 and a coating layer 14 but not provided with a protective layer 16. The analysis result of the Fe concentration in the substrate and the n-type GaN layer using the semiconductor device of the comparative example is shown. The horizontal axis of FIGS. 5 and 6 indicates the distance from the surface of the n-type GaN layer 102, and the vertical axis indicates the Fe concentration.

In FIG. 5, the analysis results are superimposed and shown at the three SIMS analysis points. In FIG. 6, the analysis result is shown at one analysis point. In this analysis, the lower limit of detection of Fe concentration is 1.0 × 10 ¹⁴ cm ^-3 . Therefore, in FIGS. 5 and 6, when the Fe concentration is 1.0 × 10 ¹⁴ cm ^-3 or less, the Fe concentration is shown as ^{1.0 × 10 14} cm ^-3. In the semiconductor device 100 of this example manufactured by using the susceptor 10, segregation of Fe impurities was not observed, and the Fe concentration was 2.0 × 10 ¹⁴ cm ^-3 or less on average. The individual data points show a maximum ^{value of 5.0 × 10 14} cm ^-3 , but the measured values at the front and back depth positions are low, which is caused by the measurement noise of the SIMS analysis method. Further, Fe detected at a position deeper than the GaN substrate is not derived from the film formation of MOVPE, but is due to impurities originally contained in the obtained GaN substrate. As is clear from comparing FIGS. 5 and 6, in the semiconductor device of the comparative example, the Fe concentration increases as the surface of the n-type GaN layer approaches the interface between the substrate and the n-type GaN layer. Fe impurities are segregated at the interface between the substrate and the n-type GaN layer. Furthermore, as a result of analyzing the electron concentration of the n-type GaN layer 102 by capacitive voltage measurement (that is, CV measurement), the electron concentration of the n-type GaN layer 102 is the Si donor concentration of the n-type GaN layer 102. It was almost the same as the difference from the carbon acceptor concentration. As a result, it was not confirmed that Fe was mixed in the n-type GaN layer 102 to reduce the electron concentration.

FIG. 7 shows the SIMS analysis results of the impurity concentrations in the n-type GaN layer 102 and the p-type GaN layers 104 and 106 of the semiconductor device 100. The horizontal axis of FIG. 7 shows the distance from the surface of the p-type GaN layer 106, and the vertical axis shows the impurity concentration. In this analysis, the concentrations of Mg, Si, carbon, and oxygen as impurities were analyzed. In FIG. 7, the result R1 shows the concentration of Mg, the result R2 shows the concentration of Si, the result R3 shows the concentration of oxygen, and the result R4 shows the concentration of carbon. As shown in FIG. 7, the Si concentration and the Mg concentration that determine the electron concentration and the hole concentration are uniform at the interface between the n-type GaN layer 102 and the p-type GaN layer 104 and other regions, respectively. In the semiconductor device 100, the Fe concentration was 2.0 × 10 ¹⁴ cm ^-3 or less on average, which was 1/100 or less of the Si and Mg concentrations. Therefore, it was not confirmed that the electron and hole concentrations were lowered due to the Fe concentration being mixed in the n-type layer and the p-type layer. In the state where the impurity concentration is "uniform", except for the state where the impurity concentration is the same, the impurity concentration is not the same, but the interface between the n-type GaN layer 102 and the p-type GaN layer 104. The impurity concentration may be lower or higher than the impurity concentration in the other region, and includes a state in which the impurity concentration does not have a high value as compared with the impurity concentration in the other region.

(effect)
In the susceptor 10, the base material 12 is covered with a coating layer 14 containing silicon carbide as a main component. Therefore, the situation where the transition metal contained in the graphite of the base material 12 is taken into the semiconductor device 100 is suppressed. Further, in the susceptor 10, the coating layer 14 is covered with the protective layer 16 containing aluminum nitride as a main component. This makes it possible to prevent the coating layer 14 from being exposed to the reducing atmosphere. As a result, it is possible to suppress the occurrence of defects in the coating layer 14 due to the exposure of the coating layer 14 to the reducing atmosphere gas. According to this configuration, it is possible to manufacture the semiconductor device 100 in which the Fe concentration inside is low and the segregation of Fe is suppressed.

In the susceptor, by using SiC instead of graphite as the base material, the mixing of Fe into the semiconductor device can be suppressed. However, SiC substrates are very expensive compared to industrial graphite. In the susceptor 10 of this embodiment, by arranging the coating layer 14 and the protective layer 16 on the relatively inexpensive graphite base material 12, the internal Fe concentration can be achieved without using the relatively expensive SiC base material. It is possible to realize the semiconductor device 100 in which the segregation of Fe is suppressed. This makes it possible to reduce the manufacturing cost of the semiconductor device 100.

In the susceptor 10, the coating layer 14 is arranged between the base material 12 and the protective layer 16. Since the base material 12 is made of graphite, the surface of the base material 12 has many irregularities. Therefore, when the protective layer 16 is to be arranged directly on the surface of the base material 12, the protective layer 16 must be manufactured with a thickness sufficient to cover the unevenness of the surface of the base material 12. However, the film forming speed of aluminum nitride is slower than the film forming rate of silicon carbide. Therefore, if the protective layer 16 is to be arranged directly on the surface of the base material 12, it takes a long time to form the protective layer 16. On the other hand, the protective layer 16 can be made thinner by arranging a relatively thick covering layer 14 in order to cover the unevenness of the base material 12. Thereby, the generation period of the protective layer 16 can be shortened.

In the above manufacturing method, prior to the film formation of the semiconductor device 100, a process of forming a protective layer 16 on the intermediate material (12, 14) of the susceptor 10 to produce the susceptor 10 is executed. As a result, it is possible to suppress the exposure of the base material 12 due to the deterioration of the coating layer 14 and the protective layer 16, and to prevent the transition metal contained in graphite from being taken into the semiconductor device 100 from the susceptor 10.

(Second Example)
The difference between the susceptor 200 of the second embodiment and the susceptor 10 of the first embodiment will be described with reference to FIG. The susceptor 200 includes a base material 12 and a coating layer 14, but does not include a protective layer 16. The susceptor 200 includes a covering member 116 that is covered with the pores 14a of the covering layer 14. The pores 14a are defects formed by exposing the coating layer 14 to a reducing atmosphere. The covering member 116 also covers the surface of the covering layer 14. The covering member 116 is made of the same material as the protective layer 16, that is, a material containing aluminum nitride as a main component.

According to this configuration, the pores 14a, which are defects of the covering layer 14, are covered with the covering member 116. As a result, it is possible to prevent the base material 12 from being exposed in the container 4.

In the modified example, the susceptor 200 may include the same protective layer 16 as the susceptor 10.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of claims. The techniques described in the claims include various modifications and modifications of the specific examples exemplified above.

(Modification example)
The thickness of the covering layer 14 and the protective layer 16 of the susceptor 10 is not limited to the thickness of the embodiment. Further, the susceptor 10 may have a layer other than the covering layer 14 and the protective layer 16.

The semiconductor device 100 may be a different type of semiconductor device such as a MOSFET, in addition to the diode.

The group III nitride semiconductor constituting the semiconductor device 100 is not limited to GaN, and may be, for example, AlN (aluminum nitride), InN (indium nitride), or a mixed crystal thereof.

Further, the film forming apparatus 2 may have another configuration such as, for example, a film forming apparatus that supplies a pressing gas from above and a reaction gas from the side.

The technical elements described herein or in the drawings exhibit their technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the techniques exemplified in the present specification or the drawings can achieve a plurality of purposes at the same time, and achieving one of the purposes itself has technical usefulness.

2: Film forming device, 10: susceptor, 12: base material, 14: coating layer, 16: protective layer, 100: semiconductor device, 101: substrate, 102: n-type GaN layer, 104, 106: p-type GaN layer, 110, 112: Electrode, 116: Coating member

Claims (6)

It is a susceptor used for film formation equipment of nitride semiconductor equipment.
A base material containing graphite as the main component and
The first layer, which covers the surface of the base material and contains silicon carbide as a main component, and
A susceptor that covers the surface of the first layer and includes a second layer containing aluminum nitride as a main component. The susceptor according to claim 1, wherein the first layer is thicker than the second layer. The susceptor according to claim 2, wherein the first layer has a thickness of about 1000 times the thickness of the second layer. It is a susceptor used for film formation equipment of nitride semiconductor equipment.
A base material containing graphite as the main component and
A coating layer containing silicon carbide as a main component, which covers the surface of the base material,
A susceptor provided with a coating member, which is covered with pores arranged in the coating layer and contains aluminum nitride as a main component. It is a manufacturing method of nitride semiconductor equipment.
A member containing aluminum nitride as a main component is supplied to the surface of a susceptor intermediate material comprising a base material containing graphite as a main component and a coating layer covering the surface of the base material and made of silicon carbide. , The manufacturing process of manufacturing the susceptor in the film forming apparatus on which the susceptor intermediate material is arranged,
Following the manufacturing step, an introduction step of introducing a substrate arranged on the susceptor into the film forming apparatus, and an introduction step.
A method for manufacturing a nitride semiconductor device, comprising a film forming step of forming a nitride semiconductor layer on the substrate in the film forming apparatus using a reducing atmosphere gas. With the p-type conductive layer,
A nitride semiconductor device comprising an n-type conductive layer that is in contact with the p-type conductive layer via an interface and has an average Fe concentration of 2.0 × 10 ¹⁴ cm ^{-3 or less.}

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