JP5437592B2 - Semiconductor device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a technique effectively applied to a semiconductor device using silicon carbide as a semiconductor material and a manufacturing method thereof.

  Silicon carbide semiconductor (SiC) is characterized by a large band gap and a dielectric breakdown electric field that is about one digit larger than that of a silicon semiconductor. For this reason, it is regarded as a promising next-generation power device, and various devices such as diodes and transistors have been studied. However, it is known that when manufacturing a MOS transistor, there is a big problem peculiar to silicon carbide.

  When manufacturing a MOS transistor with a silicon semiconductor, a silicon substrate is usually thermally oxidized to form a silicon oxide film, which is used as a gate insulating film. Similarly, a silicon carbide substrate can be thermally oxidized to form a silicon oxide film, but due to carbon generated by oxidation, it has an interface state that is orders of magnitude larger than that of a silicon semiconductor. For this reason, when a silicon oxide film formed by thermal oxidation of a silicon carbide substrate is used as a gate insulating film, various problems such as fluctuations in threshold voltage of MOS transistors and reduction in channel mobility occur.

  Another problem is that silicon carbide semiconductors differ greatly in the rate of thermal oxidation depending on the crystal plane. From the viewpoint of channel mobility, a trench MOS transistor in which a channel is formed on the side wall of a trench provided on the substrate has been studied. In this case, the rate of thermal oxidation differs greatly between the substrate surface and the trench side wall. .

  Therefore, studies have been made to reduce the amount of thermal oxidation of the silicon carbide semiconductor as much as possible. Japanese Patent Application Laid-Open No. 2003-243653 (Patent Document 1) describes a method of reducing the interface state density by suppressing the thickness of thermal oxidation and adding an insulating film after the thermal oxidation. In Japanese Patent Laid-Open No. 2006-269924 (Patent Document 2), an amorphous silicon film having a thickness of 50 nm is formed on a silicon carbide substrate, and this amorphous silicon is thermally oxidized to form a silicon oxide film independent of the plane orientation of silicon carbide. A method is described.

JP 2003-243653 A JP 2006-269924 A

  However, even if the above-described method is used, it can be said that the amount of thermal oxidation of the silicon carbide semiconductor is insufficient. That is, when a method of suppressing the thickness of thermal oxidation and adding a shortage of film thickness as a gate insulating film is used, the silicon carbide semiconductor is directly thermally oxidized after all. In the case of a method in which an amorphous silicon film is formed on a silicon carbide substrate and thermally oxidized, the amorphous silicon film to be thermally oxidized is thick, so that the amorphous silicon film is fully thermally oxidized. As a result, the silicon carbide substrate is thermally oxidized as a result. For example, when a 50 nm amorphous silicon film formed on the (0001) surface of 4H—SiC is thermally oxidized to form a silicon oxide film of about 100 nm, if extra oxidation is performed with a margin of 10%, for example, 1 nm To the extent the silicon carbide substrate is oxidized. In the case of the trench side wall, the thermal oxidation is several times faster than the (0001) plane, so that the silicon carbide substrate is oxidized about several nm. Therefore, although it is possible to form a gate insulating film whose film thickness does not depend on the plane orientation, it can be said that it is insufficient as a method for suppressing oxidation of silicon carbide in order to reduce the interface state.

  Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows.

  That is, in the method for manufacturing a semiconductor device according to the present invention, first, an amorphous silicon film having a thickness of 10 nm or less and a silicon oxide film serving as a cap are formed on a silicon carbide substrate. Next, a thermal oxide film is formed on the silicon carbide by thermally oxidizing the amorphous silicon film with the surface protected by the silicon oxide film.

  Of the inventions disclosed in the present application, effects obtained by typical ones will be briefly described as follows.

  According to the present invention, the silicon film formed on silicon carbide is oxidized under conditions that substantially do not oxidize silicon carbide, thereby suppressing the generation of carbon during silicon carbide oxidation, and a good silicon carbide / silicon oxide film interface. Can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In all the drawings for explaining the embodiments, the same reference numerals are given to the same members in principle, and the repeated explanation thereof is omitted. In particular, for functions corresponding to different embodiments, the same reference numerals are given even if there are differences in shape, impurity concentration, crystallinity, and the like.

Example 1
FIGS. 1A to 1C are explanatory views showing a partial cross-sectional structure of a manufacturing process of a semiconductor device in Example 1 of the present invention.
In the semiconductor device according to the first embodiment, as shown in FIG. 1A, for example, an impurity is implanted into a region desired to be n-type and a region desired to be p-type in a silicon carbide substrate 1 having an n-type conductivity type. Then, annealing for impurity activation is performed. Here, for example, nitrogen is used as an impurity to be implanted into a region to be n-type, and aluminum is used as an impurity to be implanted into a region to be p-type.
Subsequently, as shown in FIG. 1B, an intrinsic amorphous silicon film 2 having a thickness of about 5 nm and a thickness of, for example, about 40 nm are formed on the silicon carbide substrate 1 by, for example, a CVD (Chemical Vapor Deposition) method. A silicon oxide film 3 is deposited. Since the deposited amorphous silicon film 2 is amorphous, there are no crystal grains, and since it is a very thin film having a thickness of 10 nm or less, the film thickness is excellent in uniformity.

Further, as shown in FIG. 1C, the amorphous silicon film 2 is thermally oxidized in a dry O ₂ atmosphere at 1000 ° C. or lower to form a silicon oxide film 4, thereby forming silicon oxide film 4 and silicon formed by a CVD method. A laminated structure of the oxide film 3 is formed.
For example, an amorphous silicon film is thermally oxidized in a dry O ₂ atmosphere at 900 ° C. to form a silicon oxide film. Since the silicon oxide film formed at this time is about twice as thick as the amorphous silicon film, it is about 10 nm. If thermal oxidation is performed within a time period in which the thermal oxide film is formed to have a thickness of about 12 nm with a margin, thermal oxidation in which a silicon oxide film is formed to a maximum of about 2 nm is performed on the silicon carbide substrate. In the case of the (0001) plane of 4H—SiC, the rate of thermal oxidation is about 1/10 times that of silicon. For this reason, the thermal oxide film formed on the silicon carbide substrate is about 0.2 nm at the maximum, and only the amorphous silicon film 2 can be oxidized without substantially oxidizing the silicon carbide substrate 1.

Non-Patent Literature (Shiro Hino, Tomohiro Hatayama, Jun Kato, Naruhisa Miura, Tatsuo Oomori, Eisuke Tokumitsu, “Anomalously high channel mobility in SiC-MOSFETs with Al ₂ O ₃ / SiOx / SiC gate structure”, International Conference Silicon Carbide and Related Materials 2007, We18-We19.) States that a good silicon carbide / silicon oxide film interface can be obtained by suppressing the oxidation of the silicon carbide substrate surface to 1 nm or less. For this reason, if the thickness of the silicon oxide film formed on the surface of the silicon carbide substrate is suppressed to 0.5 nm or less in view of a margin in the manufacturing process, the thickness of the amorphous silicon film 2 is controlled to about 10 nm or less. There is a need.

As described above, in the manufacturing process of the semiconductor device shown in the first embodiment, the CVD silicon oxide film 3 is deposited on the thinly deposited amorphous silicon film 2 and then the amorphous silicon carbide substrate 1 is amorphous under the condition that the silicon carbide substrate 1 is not substantially oxidized. By oxidizing the silicon film 2, a silicon carbide / silicon oxide film interface can be obtained without oxidizing silicon carbide. Further, since the CVD silicon oxide film 3 is deposited on the amorphous silicon film 2 and then oxidized, the aggregation of the amorphous silicon film 2 can be suppressed and the silicon oxide film 4 having a uniform thickness can be obtained.
In the first embodiment, the case where silicon carbide substrate 1 is of the n-type conductivity has been described, but it may be of p-type conductivity.

  In the first embodiment, the amorphous silicon film 2 deposited on the silicon carbide substrate 1 is thermally oxidized to form the silicon oxide film 3. However, before the thermal oxidation is performed, the amorphous silicon film 2 is crystallized by annealing. May be. In this case, it is necessary to perform annealing at a temperature higher than the temperature for crystallizing thick amorphous silicon of about 10 nm or more, for example, about 900 ° C. Since the silicon oxide film 3 is deposited on the surface of the thin amorphous silicon film 2 as a cap, it is considered that movement and crystallization of silicon atoms are suppressed. Due to the cap effect of the silicon oxide film 3, the polycrystalline silicon film crystallized by annealing is excellent in uniformity as in the amorphous film.

  In the first embodiment, the silicon oxide film 3 on the amorphous silicon film 2 is formed by the CVD method. However, if a uniform silicon oxide film can be obtained, another deposition method such as a sputter deposition method is used. Also good.

(Example 2)
In the second embodiment, a semiconductor device having a so-called MOS (Metal-Oxide-Semiconductor) structure as shown in FIGS. 2A to 2C will be described. In this semiconductor device, the silicon carbide / silicon oxide film structure described in the first embodiment is used as a gate insulating film of a MOS structure.

  2A to 2C show application examples to a semiconductor device having a MOS structure. 2A shows a structure in which the source 6 and the drain 7 are arranged in a direction parallel to the substrate surface (hereinafter referred to as horizontal MOS), and FIG. 2B shows that the source 6 and the drain 7 are arranged in a direction perpendicular to the substrate surface (hereinafter referred to as vertical MOS). FIG. 2C shows a structure in which a source 6 and a drain 7 are arranged in a direction perpendicular to the substrate surface, and a channel serving as a current path is formed on a sidewall of a groove formed in the substrate (hereinafter referred to as a trench MOS).

Hereinafter, application to the vertical MOS structure shown in FIG. 2B will be described. 3 to 7 are cross-sectional views in each process when manufacturing the vertical MOS transistor of the second embodiment.
In addition, in order to avoid complexity, the cross-sectional view shows only the configuration of the main part in the process, and does not correspond to an accurate cross-sectional view.
First, for example, a semiconductor substrate having a stacked structure of high-concentration n-type (n +) silicon carbide single crystal / low-concentration n-type (n) silicon carbide single crystal is prepared, impurities are ion-implanted into a desired region, and annealing is further performed. To form a p-type region and an n + region. For example, in FIG. 3, an n + region serving as the source 6 of the transistor is formed inside the p-type region.
After performing predetermined cleaning, as shown in FIG. 4, an amorphous silicon film 2 having a thickness of about 5 nm, for example, a CVD silicon oxide film 3 having a thickness of about 20 nm is deposited on the semiconductor substrate.

Subsequently, as shown in FIG. 5, the amorphous silicon film 2 is oxidized in a dry O ₂ atmosphere at 900 ° C. At this time, since the silicon oxide film 3 is deposited on the surface of the amorphous silicon film 2 as a cap, the film thickness nonuniformity due to the aggregation of silicon does not occur, and the silicon oxide film 4 having a uniform film thickness is obtained.
Subsequently, as shown in FIG. 6, a gate material film 5 made of an n-type polycrystalline silicon film having a thickness of about 200 nm is deposited.

Subsequently, as shown in FIG. 7, the gate material film 5 is etched using the resist as a mask to form the gate 8 of the MOS transistor.
Subsequently, a normal silicide electrode process, an interlayer insulating film forming process, a process for forming contacts to the source 6 and the gate 8, and a process for forming wirings are performed to complete the semiconductor device.
As described above, a high-quality silicon oxide film 4 can be obtained without substantially oxidizing silicon carbide by changing only the formation method of the gate insulating film in the process of manufacturing a normal MOS transistor. . In addition, the MOS structures shown in FIGS. 8A to 8C can be similarly applied by changing the method for forming the gate insulating film. Therefore, when applied to the trench MOS structure shown in FIG. 8C, a thermally oxidized silicon oxide film is formed on silicon carbide substrate 1 without considering the difference in thermal oxidation rate due to the difference in crystal orientation of silicon carbide. can do.

  In Example 2, an n-type silicon carbide single crystal semiconductor substrate was used. However, since the semiconductor substrate is not directly thermally oxidized, for example, a p-type silicon carbide substrate may be used. In this case, the MOS structure can be formed by reversing the polarity of impurity ion implantation into each region for forming the MOS structure.

  In the second embodiment, an n-type polycrystalline silicon film is used as the gate material film 5. However, even when a p-type polycrystalline silicon film or a metal is applied to the gate, the gate material film 5 is effective as the gate material film 5 described above. is there. In this case, since the threshold voltage of the MOS transistor fluctuates, a material having a desired threshold voltage can be selected.

(A), (b), (c) is explanatory drawing which shows the cross-sectional structure in the manufacturing process of the semiconductor device in the present Example 1. FIG. It is explanatory drawing which shows the cross-section of the semiconductor device in the present Example 2 (in the case of a lateral MOS structure). It is explanatory drawing which shows the cross-section of the semiconductor device in the present Example 2 (in the case of a vertical MOS structure). It is explanatory drawing which shows the cross-sectional structure (trench MOS structure) of the semiconductor device in the present Example 2. It is explanatory drawing which shows the cross-sectional structure in the manufacturing process of the semiconductor device in the present Example 2. FIG. 4 is an explanatory diagram showing a cross-sectional structure during the manufacturing process of the semiconductor device following FIG. 3; FIG. 5 is an explanatory diagram illustrating a cross-sectional structure during the manufacturing process of the semiconductor device following FIG. 4; FIG. 6 is an explanatory diagram showing a cross-sectional structure during the manufacturing process of the semiconductor device following FIG. 5; FIG. 7 is an explanatory diagram illustrating a cross-sectional structure during the manufacturing process of the semiconductor device following FIG. 6; It is explanatory drawing which shows the cross-section of the conventional semiconductor device. It is explanatory drawing which shows the cross-section of the conventional semiconductor device. It is explanatory drawing which shows the cross-section of the conventional semiconductor device.

Explanation of symbols

1 ... silicon carbide substrate,
2. Amorphous silicon film,
3 ... Silicon oxide film,
4 ... A silicon oxide film obtained by oxidizing an amorphous silicon film,
5 ... Gate material film,
6 ... Sauce,
7 ... drain,
8 ... Gate.

Claims (4)

A method of manufacturing a semiconductor device comprising the following steps:
(A) forming an amorphous silicon film on a silicon carbide substrate by a deposition method ;
(B) forming a silicon oxide film on the amorphous silicon film by a deposition method;
(C) A step of oxidizing the amorphous silicon film to form a silicon oxide film from the amorphous silicon film.   2. The method of manufacturing a semiconductor device according to claim 1, wherein a CVD method or a sputtering method is used for the deposition method.   2. The method of manufacturing a semiconductor device according to claim 1, wherein a film thickness of the amorphous silicon film formed in the step (a) is 10 nm or less. Silicon carbide semiconductor device, which comprises using as the gate insulating film a silicon oxide film formed by the manufacturing method of any one of a semiconductor device of claims 1 to 3.

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