Semiconductor device and manufacturing method thereof

Abstract

To improve the reliability of a semiconductor device.SOLUTION: In the present disclosure, in the step of forming a gate insulating film on a silicon carbide substrate, the gate insulating film is formed by an ALD method using a material gas containing a halogen element and a metal element.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a semiconductor device and a manufacturing technique thereof, and more particularly to a semiconductor device having a semiconductor substrate made of a wide band gap semiconductor material having a band gap larger than that of silicon, and a technique that is effectively applicable to the manufacturing technique thereof. [Background technology]

[0002] Japanese Patent Laid-Open Publication No. 2017-228679 (Patent Document 1) describes a technique for improving the reliability of a semiconductor device including a SiC power transistor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-228679 A Summary of the Invention [Problem to be solved by the invention]

[0004] 2. Description of the Related Art In order to improve the performance of semiconductor devices including field effect transistors, studies have been conducted on the use of semiconductor substrates made of wide band gap semiconductor materials having a band gap larger than that of silicon to manufacture the semiconductor devices.

[0005] However, with current technology, a gate insulating film formed on a semiconductor substrate made of a wide band gap semiconductor material does not have as high reliability as a silicon oxide film formed on a silicon substrate. Therefore, in a semiconductor device manufactured using a semiconductor substrate made of a wide band gap semiconductor material, it is desired to form a gate insulating film having high reliability.

[0006] Other objects and novel features will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0007] A method for manufacturing a semiconductor device according to an embodiment includes forming a gate insulating film on a semiconductor substrate made of a wide band gap semiconductor material having a band gap larger than that of silicon, the gate insulating film being formed by chemical vapor deposition using a material gas containing a halogen element and a metal element.

[0008] A semiconductor device according to one embodiment includes a field effect transistor having a gate insulating film formed on a semiconductor substrate made of a wide band gap semiconductor material having a band gap larger than that of silicon, wherein the gate insulating film has a halogen element at a concentration higher than that of carbon. Effect of the Invention

[0009] According to one embodiment, the reliability of the semiconductor device can be improved. [Brief description of the drawings]

[0010] [Figure 1] 1 is a flow chart illustrating an ALD method for use in embodiment embodiments. [Diagram 2] FIG. 1 is a diagram for qualitatively explaining the mechanism by which moisture becomes large in a gate insulating film in an ALD method using trimethylaluminum. [Diagram 3] FIG. 1 is a diagram qualitatively explaining the mechanism by which the moisture content in a gate insulating film is reduced in an ALD method using aluminum trichloride. [Figure 4] 1 is a graph showing the results of measuring the amount of moisture based on a temperature programmed desorption method. [Diagram 5] 1 is a graph showing the results of measuring the carbon concentration in a gate insulating film by SIMS analysis. [Figure 6] 1 is a graph showing the results of measuring the chlorine concentration in a gate insulating film by SIMS analysis. [Figure 7] 1 is a plot showing the relationship between the equivalent silicon oxide thickness of a gate insulating film and the amount of traps present in the gate insulating film. [Figure 8] 1 is a plot showing the relationship between the equivalent silicon oxide thickness of a gate insulating film and the leakage current density flowing through the gate insulating film. [Figure 9] FIG. 1 is a diagram showing an example of the structure of an aluminum oxide film formed by using trimethylaluminum as a material for the ALD method. [Figure 10] FIG. 1 is a diagram showing an example of the structure of an aluminum oxide film formed by using aluminum trichloride as a material for the ALD method. [Figure 11] FIG. 1 is a cross-sectional view showing a configuration of a semiconductor device including a planar SiC field effect transistor. [Figure 12] 11 is a flowchart showing a manufacturing process of a semiconductor device in Application Example 1. [Figure 13] 10 is a flowchart showing a manufacturing process of a semiconductor device in Application Example 1. [Figure 14] FIG. 1 is a cross-sectional view showing a configuration of a semiconductor device including a trench-gate type SiC field effect transistor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] In all the drawings for explaining the embodiments, the same members are generally designated by the same reference numerals, and the repeated explanations thereof will be omitted. In addition, hatching may be applied even to plan views in order to make the drawings easier to understand.

[0012] 2. Description of the Related Art Semiconductor devices including field effect transistors formed on a semiconductor substrate whose main component is a semiconductor material having a band gap larger than that of silicon (hereinafter referred to as wide band gap power semiconductor device) have attracted attention.

[0013] This is because a large band gap means that the material has high dielectric breakdown strength, making it easier to achieve high withstand voltage.

[0014] If the semiconductor material itself has a high dielectric breakdown strength, the withstand voltage can be ensured even if the drift layer that maintains the withstand voltage is thin. For this reason, for example, by thinning the drift layer and increasing the impurity concentration, the on-resistance of the power semiconductor device can be reduced.

[0015] That is, the wide band gap power semiconductor device is superior in that it can improve the breakdown voltage and reduce the on-resistance, which are in a trade-off relationship with each other. Therefore, the wide band gap power semiconductor device is expected to be a semiconductor device that can achieve high performance.

[0016] Examples of semiconductor materials having a band gap larger than that of silicon include silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), diamond, etc. The following description focuses on silicon carbide.

[0017] <Consideration of improvements> In a field effect transistor having a gate insulating film formed on a silicon substrate (referred to as a Si field effect transistor), the gate insulating film is made of, for example, a silicon oxide film formed by a thermal oxidation method. The gate insulating film thus formed is a high-quality film having high reliability. That is, in a Si field effect transistor, the gate insulating film can be made of a high-quality film having high reliability.

[0018] On the other hand, in a field effect transistor having a gate insulating film formed on a silicon carbide substrate (hereinafter referred to as a SiC field effect transistor), the gate insulating film is composed of a silicon oxynitride film (SiON) formed using, for example, NO gas or NO gas. However, it is known that it is difficult to make the gate insulating film thus formed into a film having high reliability.

[0019] Specifically, in the above-mentioned method for forming a gate insulating film, a silicon oxynitride film is formed while cutting the Si-C bonds of silicon carbide by an oxidation reaction. Therefore, interface defects (dangling bonds) are formed at the interface between SiON and SiC. As a result, the density of interface defect states in the gate insulating film is high. This may cause an increase in the on-resistance of the semiconductor device and a shift in the threshold voltage. Thus, in a SiC field effect transistor, it is difficult to form a gate insulating film from a high-quality film.

[0020] Therefore, a method has been proposed for forming a gate insulating film using chemical vapor deposition (CVD), which deposits a film on a silicon carbide substrate, rather than using thermal oxidation. This method is thought to be able to reduce interface defect levels because it does not form a gate insulating film while breaking the Si-C bonds of silicon carbide.

[0021] However, due to the film formation principle, the deposition film formed by the CVD method may contain elements derived from the raw materials as impurities in addition to moisture. In other words, the gate insulating film formed by the CVD method contains moisture and impurities derived from the raw materials as impurities, which is an area for improvement.

[0022] In this regard, the present inventors have obtained the following novel findings.

[0023] (1) Moisture contained in the gate insulating film migrates to the interface and causes an oxidation reaction, which leads to the generation of interface defect levels. For this reason, it is desirable to remove the moisture contained in the gate insulating film. Moisture can be removed by annealing (heat treatment).

[0024] (2) If the source gas for the CVD method contains carbon, the gate insulating film will contain carbon. Carbon is not released from the gate insulating film even when annealed, and it causes deterioration of the quality of the gate insulating film. For this reason, it is desirable to reduce the amount of carbon contained in the gate insulating film.

[0025] (3) If the source gas for the CVD method contains halogen elements, the halogen elements will be contained in the gate insulating film. The halogen elements will not be eliminated from the gate insulating film even when annealed. However, even if halogen elements are contained in the gate insulating film, they are unlikely to deteriorate the film quality.

[0026] Based on the above findings, the present inventors have found a technical idea that allows a gate insulating film to be made of a highly reliable film in a method for forming the gate insulating film by a CVD method. The technical idea that the present inventors have found will be described below.

[0027] <Basic Concept of the Embodiment> The basic idea of ​​the present embodiment is to form a gate insulating film by a CVD method using a material gas containing a halogen element and a metal element in a step of forming a gate insulating film on a silicon carbide substrate. According to this basic idea, the material gas for the CVD method contains a halogen element. As a result, the gate insulating film contains a halogen element. However, even if the gate insulating film contains a halogen element, there is little risk of the film quality being deteriorated. Therefore, according to the basic idea, the gate insulating film can be formed from a film having high reliability.

[0028] That is, according to the basic concept, the CVD method is used to deposit a film without breaking the Si-C bond, instead of the thermal oxidation method, which forms a film while breaking the Si-C bond. This makes it possible to reduce the interface defect level. And, since the material gas used for the CVD method contains a halogen element, which does not easily deteriorate the quality of the gate insulating film, the film quality can be improved.

[0029] In other words, the basic concept is that a high-quality gate insulating film can be formed by combining (1) the use of a CVD method that can suppress the generation of interface defect states, and (2) the use of a material gas containing a halogen element as a material gas for the CVD method.

[0030] Examples of halogen elements include fluorine and chlorine. Examples of metal elements include aluminum (Al), hafnium (Hf), and zirconium (Zr). For example, aluminum is used when the gate insulating film is made of an aluminum oxide film (alumina film). Hafnium is used when the gate insulating film is made of a hafnium oxide film (hafnia film), and zirconium is used when the gate insulating film is made of a zirconium oxide film.

[0031] Thus, in the basic concept, a material gas containing a halogen element and a metal element is used as the material gas for the CVD method. Furthermore, it is desirable that the material gas for the CVD method does not contain carbon and hydrogen. This is because carbon causes deterioration of the film quality of the gate insulating film. Furthermore, if the material gas for the CVD method contains hydrogen, moisture, which is a compound of hydrogen and oxygen, is likely to be contained in the gate insulating film. Moisture moves to the interface and causes an oxidation reaction, which causes the generation of interface defect levels. Therefore, based on the above-mentioned new findings (1), (2), and (3), it is desirable to use a material gas for the CVD method that contains a halogen element and a metal element but does not contain carbon or hydrogen.

[0032] Furthermore, although not essential, it is desirable to have a step of heating the silicon carbide substrate after forming the gate insulating film. As explained in the above-mentioned new finding (1), the gate insulating film formed by the CVD method contains moisture. The moisture migrates to the interface and causes an oxidation reaction, which causes the generation of interface defect levels. Therefore, in order to form a high-quality gate insulating film, it is desirable to remove the moisture contained in the gate insulating film. Therefore, it is desirable to heat the silicon carbide substrate to remove the moisture from the gate insulating film.

[0033] To prevent the silicon carbide from being oxidized due to a reaction between the desorbed moisture and silicon carbide at the silicon carbide interface, the heating temperature (annealing temperature) is desirably lower than 900 degrees Celsius, because the temperature at which oxidation of silicon carbide begins is 900 degrees Celsius. That is, in order to remove moisture in the gate insulating film, it is effective to have a temperature range in which the moisture desorbed from the gate insulating film does not react with silicon carbide.

[0034] In order to remove moisture in the gate insulating film, the heating temperature of the silicon carbide substrate is desirably higher than the formation temperature of the gate insulating film, for example, a temperature of 500 degrees Celsius or higher and lower than 900 degrees Celsius.

[0035] According to the above basic concept, a highly reliable gate insulating film can be formed even when the gate insulating film is formed on a silicon carbide substrate.

[0036] The following describes an embodiment that embodies the basic concept.

[0037] <Embodiment> <<Method of manufacturing semiconductor device>> In the embodiment, a step of forming a gate insulating film included in a manufacturing method of a semiconductor device is described. In particular, in the embodiment, an example in which a gate insulating film formed on a silicon carbide substrate is made of an aluminum oxide film (Al2O3 film) is described. Also, an example in which an atomic layer deposition method (hereinafter referred to as ALD method (Atomic Layer Deposition)), which is a type of CVD method, is used as a method for forming the gate insulating film is described.

[0038] FIG. 1 is a flow chart illustrating an ALD method for use in embodied embodiments.

[0039] In FIG. 1, first, a first material gas containing a halogen element is introduced onto a silicon carbide substrate on which a gate insulating film is to be formed (S1). Then, the first material gas is purged (S2). Next, a second material gas containing oxygen is introduced onto the silicon carbide substrate (S3). Then, the second material gas is purged (S4). Through these steps, a gate insulating film having a thickness at the atomic layer level can be formed on the silicon carbide substrate. If a gate insulating film of the predetermined thickness has not been formed, the film formation process is continued (S5). On the other hand, if a gate insulating film of the predetermined thickness has been formed, the film formation process is terminated (S5). In this manner, a gate insulating film having a desired thickness can be formed.

[0040] Here, the first material gas is AlCl3. The second material gas is any one of H2O, O3, and N2O. The film formation temperature in the ALD method is, for example, 25 degrees Celsius or more and 400 degrees Celsius or less. By using such an ALD method, a highly reliable gate insulating film can be formed according to the embodiment. That is, in the embodiment, the following characteristic points can be obtained by using AlCl3 as the first material gas containing a halogen element in the ALD method. Due to this characteristic point, a highly reliable gate insulating film can be formed according to the embodiment.

[0041] The above-mentioned features will be described below.

[0042] A first characteristic of the embodiment is that the moisture content in the gate insulating film can be reduced by using AlCl3. For example, when the gate insulating film is formed from an aluminum oxide film, trimethylaluminum (Al(CH3)3) is generally used as a material gas for the ALD method. In this regard, the present inventors have newly discovered that the use of trimethylaluminum increases the moisture content in the gate insulating film.

[0043] Therefore, considering that moisture contained in the gate insulating film causes the generation of interface defect levels, it is difficult to form a highly reliable gate insulating film when trimethylaluminum is used.

[0044] In response to this, the present inventors have newly discovered that the use of AlCl3 as a source gas for the ALD method can reduce the amount of moisture contained in the gate insulating film compared to the use of trimethylaluminum. This means that the use of AlCl3 can reduce the amount of moisture in the gate insulating film, which is the cause of the generation of interface defect levels. Therefore, the use of AlCl3 can form a gate insulating film with high reliability.

[0045] Below, we will explain the qualitative mechanism by which the use of trimethylaluminum increases the amount of moisture contained in the gate insulating film, while the use of AlCl3 decreases the amount of moisture contained in the gate insulating film.

[0046] An ALD process using trimethylaluminum has the following steps: (a1) introducing trimethylaluminum; (a2) purging trimethylaluminum. (a3) A step of introducing HO (oxidizing agent). (a4) Purging HO.

[0047] As a result, for example, as shown in FIG. 2, some of the methyl groups in trimethylaluminum are replaced with hydroxyl groups by the oxidizing agent (HO). Then, hydrogen constituting the methyl groups reacts with the hydroxyl groups to generate moisture, which is released. In this way, moisture is easily generated in trimethylaluminum due to the presence of hydrogen, which is a constituent element of moisture. As a result, the use of trimethylaluminum tends to increase the amount of moisture contained in the gate insulating film.

[0048] In contrast, the ALD method using AlCl3 has the following steps: (a1) Introducing AlCl3. (a2) Purging AlCl3. (a3) A step of introducing HO (oxidizing agent). (a4) Purging HO.

[0049] As a result, for example, as shown in FIG. 3, some of the chlorine in AlCl3 is replaced by hydroxyl groups by the oxidizing agent (H2O). Then, multiple hydroxyl groups react with each other to generate moisture, which is then desorbed. In this regard, since AlCl3 does not contain hydrogen, which is a constituent element of moisture, moisture is not easily generated. As a result, the use of AlCl3 makes it easier to reduce the moisture contained in the gate insulating film.

[0050] Fig. 4 is a graph showing the results of moisture content measurement based on thermal desorption spectroscopy. In Fig. 4, the horizontal axis indicates the temperature of the stage on which the silicon carbide substrate with the gate insulating film (aluminum oxide film) formed thereon is placed, while the vertical axis indicates the moisture content contained in the gate insulating film.

[0051] Graph (1) shows an aluminum oxide film formed by ALD using trimethylaluminum (TMA) as the source gas. Graph (2) shows an aluminum oxide film formed by ALD using AlCl3 as the source gas.

[0052] As shown in Figure 4, the moisture content in the aluminum oxide film formed by the ALD method using AlCl3 as the source gas is less than the moisture content in the aluminum oxide film formed by the ALD method using trimethylaluminum (TMA) as the source gas. This proves that the use of AlCl3 can reduce the moisture content in the gate insulating film (aluminum oxide film) more than the use of trimethylaluminum.

[0053] It is also possible to use O3 or N2O as the oxidizing agent instead of H2O. In this case, the moisture in the gate insulating film can be further reduced. This is because H2O contains hydrogen, whereas O3 or N2O does not contain hydrogen, which is a constituent element of moisture, making it difficult for moisture to be generated in the gate insulating film. In other words, from the viewpoint of reducing moisture in the gate insulating film, it is desirable to use O3 or N2O as the oxidizing agent.

[0054] Next, a second feature of the embodiment is that the use of AlCl3 can reduce the amount of carbon present in the gate insulating film. In other words, since AlCl3 does not contain carbon, the amount of carbon contained in the gate insulating film can be reduced. In other words, considering that carbon is a cause of deterioration of the film quality of the gate insulating film, the use of carbon-free AlCl3 as a material gas for the ALD method to reduce the amount of carbon contained in the gate insulating film leads to the formation of a gate insulating film with high reliability.

[0055] For example, trimethylaluminum contains carbon as a methyl group. Therefore, when trimethylaluminum is used as a source gas for the ALD method, the gate insulating film contains a large amount of carbon. As a result, the quality of the gate insulating film is deteriorated by the carbon.

[0056] In contrast, when AlCl3 is used as in the embodiment, since AlCl3 does not contain carbon, the carbon contained in the gate insulating film can be reduced. As a result, according to the embodiment, the carbon that causes deterioration of the film quality of the gate insulating film can be reduced. Therefore, according to the embodiment, a gate insulating film having high reliability can be formed.

[0057] Figure 5 is a graph showing the results of measuring the carbon concentration in a gate insulating film by SIMS analysis. In Figure 5, graph (1) shows a gate insulating film formed using trimethylaluminum. Graph (2) shows a gate insulating film formed using trimethylaluminum and then subjected to a heat treatment at 800 degrees Celsius.

[0058] Graph (3) shows the gate insulating film formed using AlCl3, and graph (4) shows the gate insulating film formed using AlCl3 and then heat-treated at 800 degrees Celsius.

[0059] First, as shown in FIG. 5, by using AlCl3, the carbon concentration in the gate insulating film can be reduced more than when trimethylaluminum is used.

[0060] Even when carbon-free AlCl3 is used as the source gas for the ALD method, it can be seen from Figure 5 that the gate insulating film contains some carbon. This is presumably due to the fact that the gate insulating film is formed on a silicon carbide substrate, and carbon diffuses from the silicon carbide substrate in contact with the gate insulating film into the gate insulating film.

[0061] 5, not only when trimethylaluminum is used, but also when AlCl3 is used, the carbon concentration of the gate insulating film after the heat treatment at 800 degrees Celsius is almost unchanged from the carbon concentration of the gate insulating film before the heat treatment at 800 degrees Celsius. In other words, the carbon contained in the gate insulating film is not desorbed even when the heat treatment at 800 degrees Celsius is performed, regardless of the type of material gas used in the ALD method.

[0062] For this reason, heat treatment is not an effective means for reducing the carbon contained in the gate insulating film. In contrast, the use of AlCl3, which does not contain carbon, instead of trimethylaluminum, which contains carbon, as in the embodiment, is effective from the viewpoint of reducing the carbon contained in the gate insulating film.

[0063] A third feature of the embodiment is that the use of AlCl3 results in an increase in the amount of chlorine present in the gate insulating film. In other words, since AlCl3 contains chlorine, the amount of chlorine present in the gate insulating film increases.

[0064] However, chlorine does not cause deterioration of the quality of the gate insulating film. Considering this, using AlCl3, which contains chlorine, as a material gas for the ALD method does not pose a problem in forming a highly reliable gate insulating film. Rather, using AlCl3 is useful from the viewpoint of forming a highly reliable gate insulating film, since it can reduce carbon, which causes deterioration of the quality of the gate insulating film.

[0065] Figure 6 is a graph showing the results of measuring the chlorine concentration in a gate insulating film by SIMS analysis. In Figure 6, graph (1) shows a gate insulating film formed using trimethylaluminum. Graph (2) shows a gate insulating film formed using trimethylaluminum and then subjected to a heat treatment at 800 degrees Celsius.

[0066] Graph (3) shows the gate insulating film formed using AlCl3, and graph (4) shows the gate insulating film formed using AlCl3 and then heat-treated at 800 degrees Celsius.

[0067] First, as shown in Figure 6, the use of AlCl3 results in a higher chlorine concentration in the gate insulating film than the use of trimethylaluminum. This is because AlCl3 contains chlorine, whereas trimethylaluminum does not.

[0068] Next, from FIG. 6, not only when trimethylaluminum is used, but also when AlCl3 is used, the chlorine concentration of the gate insulating film after the heat treatment at 800 degrees Celsius is almost the same as the chlorine concentration of the gate insulating film before the heat treatment at 800 degrees Celsius. In other words, the chlorine contained in the gate insulating film is not desorbed even when the heat treatment at 800 degrees Celsius is performed, regardless of the type of material gas used in the ALD method. However, even if chlorine remains in the gate insulating film, the chlorine does not deteriorate the film quality of the gate insulating film. Therefore, the chlorine remaining in the gate insulating film is not a problem from the viewpoint of forming a highly reliable gate insulating film.

[0069] As described above, according to the embodiment, the first, second, and third features described above can be obtained by using AlCl3. As a result, in the embodiment, these features enable the formation of a highly reliable gate insulating film.

[0070] <<Verification of effectiveness>> Below, a description will be given of verification results that support the fact that a highly reliable gate insulating film can be formed according to the embodiment.

[0071] FIG. 7 is a plot showing the relationship between the equivalent oxide thickness (EOT) of the gate insulating film and the amount of traps present in the gate insulating film. The horizontal axis indicates the equivalent oxide thickness, and the vertical axis indicates the amount of traps. In FIG. 7, the gate insulating film is an aluminum oxide film. The circles indicate plots showing aluminum oxide films formed by using trimethylaluminum, and the triangles indicate plots showing aluminum oxide films formed by using AlCl3.

[0072] As shown in Fig. 7, the trap amount in the aluminum oxide film formed by using AlCl3 is smaller than the trap amount in the aluminum oxide film formed by using trimethylaluminum. In other words, the defect level density in the aluminum oxide film formed by using AlCl3 is smaller than the defect level density in the aluminum oxide film formed by using trimethylaluminum.

[0073] This means that the aluminum oxide film formed using AlCl3 is a gate insulating film having higher reliability than the aluminum oxide film formed using trimethylaluminum. Therefore, Figure 7 confirms that the aluminum oxide film (gate insulating film) formed by using AlCl3 is a gate insulating film having higher reliability.

[0074] Next, Fig. 8 is a plot showing the relationship between the equivalent oxide thickness (EOT) of the gate insulating film and the leakage current density flowing through the gate insulating film. The horizontal axis shows the equivalent oxide thickness, and the vertical axis shows the leakage current density.

[0075] In Fig. 8, the gate insulating film is an aluminum oxide film. The circles indicate the aluminum oxide film formed by using trimethylaluminum. The triangles indicate the aluminum oxide film formed by using AlCl3.

[0076] As shown in FIG. 8, the leakage current density in the aluminum oxide film formed by using AlCl3 is smaller than the leakage current density in the aluminum oxide film formed by using trimethylaluminum.

[0077] This means that the aluminum oxide film formed using AlCl3 is a gate insulating film having higher reliability than the aluminum oxide film formed using trimethylaluminum. Therefore, Figure 8 proves that the aluminum oxide film (gate insulating film) formed by using AlCl3 is a gate insulating film having higher reliability.

[0078] Below, we will explain the qualitative mechanism by which an aluminum oxide film formed using AlCl3 has a smaller trap amount and leakage current density than an aluminum oxide film formed using trimethylaluminum.

[0079] Fig. 9 is a diagram showing an example of the structure of an aluminum oxide film formed by using trimethylaluminum. As shown in Fig. 9, in an aluminum oxide film formed by using trimethylaluminum, "trap sites" are generated due to the residual or desorbed CHx. As a result, in an aluminum oxide film formed by using trimethylaluminum, the defect level density increases, and as a result, the leakage current density increases.

[0080] Fig. 10 is a diagram showing an example of the structure of an aluminum oxide film formed by using AlCl3. As shown in Fig. 10, in an aluminum oxide film formed by using AlCl3, dangling bonds are terminated by chlorine (Cl). As a result, in an aluminum oxide film formed by using AlCl3, the defect level density is reduced, and as a result, the leakage current density is reduced.

[0081] From the above mechanism, it can be qualitatively understood that an aluminum oxide film formed by using AlCl3 can realize a high-quality gate insulating film with low defect state density and low leakage current density.

[0082] <Application Examples> According to the embodiment, a highly reliable gate insulating film can be formed. Therefore, by manufacturing a field effect transistor using the gate insulating film according to the embodiment, the reliability of a semiconductor device including the field effect transistor can be improved.

[0083] In the following, silicon carbide is taken as an example of a wide bandgap semiconductor material having a bandgap larger than that of silicon. As an application example of the gate insulating film in the embodiment, a SiC field effect transistor having a gate insulating film formed on a silicon carbide substrate is taken as an example and described. In particular, in Application Example 1, a semiconductor device including a planar type SiC field effect transistor is described. In addition, in Application Example 2, a semiconductor device including a trench gate type SiC field effect transistor is described.

[0084] <<Application Example 1>> <<<Configuration of Semiconductor Device>>> Fig. 11 is a cross-sectional view showing the configuration of a semiconductor device including a planar SiC field effect transistor. In Fig. 11, the semiconductor device has a silicon carbide substrate SUB, a back surface high-concentration semiconductor layer BNL, a back surface silicide BSL, and a back surface electrode BE. The semiconductor device also has an epitaxial layer EPI, a channel layer CH, a source region SR, a body contact region PR, and a metal silicide SL. The semiconductor device further has a gate insulating film GOX, a gate electrode GE, an interlayer insulating film IL, a source electrode SE, and a passivation film PAS.

[0085] The silicon carbide substrate SUB is, for example, + The silicon carbide substrate SUB is a silicon carbide semiconductor substrate. + A back surface high-concentration semiconductor layer BNL made of a type semiconductor layer is formed. A back surface silicide BSL is formed so as to contact the back surface high-concentration semiconductor layer BNL. The back surface silicide BSL is made of, for example, nickel silicide. A back surface electrode BE is formed so as to contact the back surface silicide BSL. The back surface electrode BE is made of, for example, a laminated film made of a titanium film, a nickel film, and a gold film.

[0086] Next, an epitaxial layer EPI is formed on the upper surface of the silicon carbide substrate SUB. The epitaxial layer EPI is, for example, - In the epitaxial layer EPI, for example, a plurality of channel layers CH made of p-type semiconductor layers are formed to be spaced apart from each other. A source region SR and a body contact region PR are formed in each of the plurality of channel layers CH so as to be in contact with each other.

[0087] Therefore, as shown in Fig. 11, a plurality of source regions SR and a plurality of body contact regions PR are formed in the semiconductor device. For example, Fig. 11 shows a source region SR1 and a source region SR2 included in the plurality of source regions SR. Each of the plurality of source regions SR is, for example, n +Each of the body contact regions PR is, for example, a p + The semiconductor region is made up of a GaN-type semiconductor region.

[0088] 11, a gate insulating film GOX is formed on the upper surface of the epitaxial layer EPI between the source region SR1 and the source region SR2. In detail, the gate insulating film GOX is formed on the upper surface of the epitaxial layer EPI, on the upper surface of the channel layer CH, on a part of the source region SR1, and on a part of the source region SR2.

[0089] This gate insulating film GOX is made of the gate insulating film described in the embodiment. That is, the gate insulating film GOX is made of an aluminum oxide film formed by using AlCl3 as a material gas for the ALD method. As a result, the gate insulating film GOX has a higher concentration of halogen element (chlorine) than carbon.

[0090] A gate electrode GE is formed on the gate insulating film GOX. The gate electrode GE is made of, for example, a polysilicon film into which n-type impurities (donors) such as phosphorus (P) or arsenic (As) are introduced. An interlayer insulating film IL is formed so as to cover the gate electrode GE. The interlayer insulating film IL is made of, for example, a silicon oxide film.

[0091] In the interlayer insulating film IL thus configured, a contact hole CNT is formed that reaches the source region SR and the body contact region PR. A metal silicide SL is formed on the surface of the source region SR and the body contact region PR exposed from the bottom surface of the contact hole CNT. The metal silicide SL is made of, for example, nickel silicide. A source electrode SE is formed on the interlayer insulating film IL so as to fill the inside of the contact hole CNT. As a result, the source electrode SE is electrically connected to the source region SR and the body contact region PR. The source electrode SE is made of, for example, a laminated film made of a titanium film, a titanium nitride film, and an aluminum film. A passivation film PAS is formed on the source electrode SE. The passivation film PAS is made of, for example, a polyimide resin film.

[0092] In the manner described above, the semiconductor device in Application Example 1 is configured.

[0093] The semiconductor device in Application Example 1 uses the gate insulating film described in the embodiment. Therefore, the gate insulating film GOX of the semiconductor device has high reliability. As a result, the reliability of the semiconductor device in Application Example 1 can be improved.

[0094] <<<Semiconductor Device Manufacturing Method>>> Next, a method for manufacturing the semiconductor device in Application Example 1 will be described.

[0095] 12 and 13 are flowcharts showing the manufacturing process of the semiconductor device in Application Example 1. First, a silicon carbide substrate SUB is prepared (S101). Next, an epitaxial layer EPI is formed on the upper surface of the silicon carbide substrate SUB (S102). The epitaxial layer EPI has an n - The epitaxial layer EPI is an n-type semiconductor layer. The epitaxial layer EPI is formed by growing a silicon carbide layer into which an n-type impurity such as nitrogen is introduced using an epitaxial growth method.

[0096] Next, a channel layer CH is formed inside the epitaxial layer EPI by using photolithography and ion implantation (S103). The channel layer CH is a p-type semiconductor layer. The channel layer CH is formed by introducing p-type impurities such as aluminum into the epitaxial layer EPI. Then, a source region SR is formed inside the channel layer CH by using photolithography and ion implantation (S104). The source region SR is a n + The source region SR is an n-type semiconductor region. The source region SR is formed by introducing an n-type impurity such as nitrogen into the channel layer CH.

[0097] Thereafter, a body contact region PR is formed in the channel layer CH in contact with the source region SR by using a photolithography technique and an ion implantation method (S105). + The body contact region PR is a p-type semiconductor region. The body contact region PR is formed by, for example, introducing a p-type impurity such as aluminum into the channel layer CH. Then, by using an ion implantation method, a back surface high-concentration semiconductor layer BNL is formed on the lower surface of the silicon carbide substrate SUB (S106). The back surface high-concentration semiconductor layer BNL is an n + The back surface heavily doped semiconductor layer BNL is formed by introducing an n-type impurity such as nitrogen into the silicon carbide substrate SUB.

[0098] Next, the silicon carbide substrate SUB is heated to perform activation annealing (S107). The activation annealing is performed, for example, by heating the silicon carbide substrate SUB to 1700 degrees Celsius. This activation annealing activates the conductive impurities introduced into the channel layer CH, the source region SR, the body contact region PR, and the back surface high-concentration semiconductor layer BNL formed by ion implantation.

[0099] Next, a gate insulating film GOX is formed on the upper surface of the epitaxial layer EPI in which the channel layer CH, the source region SR, and the body contact region PR are formed (S108). The gate insulating film GOX is formed by the ALD method using AlCl3 as a material gas. As a result, the gate insulating film GOX is composed of an aluminum oxide film.

[0100] As described in the embodiment, the aluminum oxide film formed by the ALD method using AlCl3 is a high-quality film with low defect level density and leakage current density. Therefore, the gate insulating film GOX has high reliability.

[0101] Here, after forming the gate insulating film GOX, it is effective to heat the silicon carbide substrate SUB at a temperature equal to or higher than the formation temperature of the gate insulating film GOX and lower than 900 degrees Celsius, for example. This is because this heating step makes it possible to remove moisture from the gate insulating film GOX at a temperature (lower than 900 degrees Celsius) at which the silicon carbide substrate SUB is not oxidized.

[0102] Thereafter, a gate electrode GE is formed on the gate insulating film GOX (S109). The gate electrode GE can be formed by using a CVD method and a patterning technique. Specifically, the gate electrode GE can be formed, for example, by depositing a polysilicon film doped with an n-type impurity such as nitrogen, and then patterning the polysilicon film by photolithography and etching techniques.

[0103] Then, an interlayer insulating film IL is formed on the upper surface of the epitaxial layer EPI in which the channel layer CH, the source region SR, and the body contact region PR are formed so as to cover the gate electrode GE (S110). The interlayer insulating film IL is made of, for example, a silicon oxide film. The silicon oxide film can be formed by using a CVD method.

[0104] Next, a contact hole CNT is formed in the interlayer insulating film IL by using photolithography and etching techniques (S111). The contact hole CNT is formed so as to penetrate the interlayer insulating film IL and reach both the source region SR and the body contact region PR.

[0105] Next, a metal silicide SL is formed on the surface of the source region SR exposed from the bottom surface of the contact hole CNT and the surface of the body contact region PR (S112). The metal silicide SL is made of, for example, nickel silicide. The nickel silicide can be formed by forming a nickel film on the interlayer insulating film IL including the bottom surface of the contact hole CNT, and then performing silicide annealing, which is a heat treatment at 1000 degrees Celsius, on the silicon carbide substrate SUB. Here, as described above, it is preferable to heat the silicon carbide substrate SUB after forming the gate insulating film GOX to remove moisture from the gate insulating film GOX. That is, after forming the gate insulating film GOX, a heating step for removing moisture from the gate insulating film GOX may be performed. In this case, the moisture in the gate insulating film GOX is removed at the stage of performing silicide annealing. Therefore, it is possible to suppress oxidation of the silicon carbide substrate SUB by silicide annealing.

[0106] However, the above-mentioned heating step after the gate insulating film GOX is formed can be replaced by silicide annealing. That is, the heating step after the gate insulating film GOX is formed can be omitted, and moisture can be removed from the gate insulating film GOX by silicide annealing. In this way, the silicide annealing can be made to function not only to form the metal silicide SL, but also to remove moisture from the gate insulating film GOX.

[0107] In this case, since the temperature of the silicide annealing is higher than the oxidation temperature of silicon carbide, the moisture released by the silicide annealing reacts with the silicon carbide by oxidation. Therefore, when removing moisture from the gate insulating film GOX by the silicide annealing, it is important to sufficiently reduce the moisture contained in the gate insulating film GOX by adjusting the film forming conditions when forming the gate insulating film GOX.

[0108] Thereafter, the inside of the contact hole CNT with the metal silicide SL formed on the bottom surface is filled, and a source electrode SE is formed on the interlayer insulating film IL (S113). The source electrode SE is composed of a laminated film made of, for example, a titanium film, a titanium nitride film, and an aluminum film. The source electrode SE can be formed by using, for example, a sputtering method. Then, a passivation film PAS is formed on the source electrode SE (S114). The passivation film PAS is a surface protection film. The passivation film PAS is composed of, for example, a polyimide resin film. The polyimide resin film can be formed by, for example, a coating method.

[0109] Next, a back surface silicide BSL is formed in contact with the back surface high-concentration semiconductor layer BNL formed on the lower surface of the silicon carbide substrate SUB (S115). The back surface silicide BSL is made of, for example, nickel silicide. The nickel silicide can be formed by forming a nickel film in contact with the back surface high-concentration semiconductor layer BNL, and then performing silicide annealing, which is a heat treatment at 1000 degrees Celsius, on the silicon carbide substrate SUB.

[0110] Next, a back electrode BE is formed in contact with the back silicide BSL (S116). The back electrode BE is formed of, for example, a laminated film made of a titanium film, a nickel film, and a gold film. The back electrode BE can be formed by, for example, using a sputtering method.

[0111] In this manner, the semiconductor device of Application Example 1 can be manufactured. The semiconductor device of Application Example 1 uses an aluminum oxide film formed by the ALD method using AlCl3. Therefore, the gate insulating film GOX of the semiconductor device of Application Example 1 becomes a gate insulating film having high reliability. As a result, the reliability of the semiconductor device of Application Example 1 can be improved.

[0112] <<Application Example 2>> <<<Configuration of Semiconductor Device>>> Fig. 14 is a cross-sectional view showing the configuration of a semiconductor device including a trench-gate type SiC field effect transistor. In Fig. 14, the semiconductor device has a silicon carbide substrate SUB, a back surface high-concentration semiconductor layer BNL, a back surface silicide BSL, and a back surface electrode BE. The semiconductor device also has an epitaxial layer EPI, a channel layer CH, a source region SR, a body contact region PR, and a metal silicide SL. The semiconductor device further has a trench TR, a gate insulating film GOX, a gate electrode GE, an interlayer insulating film IL, a source electrode SE, and a passivation film PAS.

[0113] The silicon carbide substrate SUB is, for example, + The silicon carbide substrate SUB is a silicon carbide semiconductor substrate. + A back surface high-concentration semiconductor layer BNL made of a type semiconductor layer is formed. A back surface silicide BSL is formed so as to contact the back surface high-concentration semiconductor layer BNL. The back surface silicide BSL is made of, for example, nickel silicide. A back surface electrode BE is formed so as to contact the back surface silicide BSL. The back surface electrode BE is made of, for example, a laminated film made of a titanium film, a nickel film, and a gold film.

[0114] Next, an epitaxial layer EPI is formed on the upper surface of the silicon carbide substrate SUB. The epitaxial layer EPI is, for example, -On the epitaxial layer EPI, a channel layer CH made of, for example, a p-type semiconductor layer is formed. A plurality of source regions SR and a plurality of body contact regions PR are formed inside the channel layer CH. For example, FIG. 14 shows a source region SR1 and a source region SR2 included in the plurality of source regions SR. Each of the plurality of source regions SR is, for example, an n-type semiconductor layer. + Each of the body contact regions PR is, for example, a p + The semiconductor region is made up of a GaN-type semiconductor region.

[0115] 14, a trench TR is formed between the source region SR1 and the source region SR2. The trench TR is formed to penetrate the channel layer CH. The bottom of the trench TR reaches the inside of the epitaxial layer EPI.

[0116] A gate insulating film GOX is formed on the inner wall of the trench TR. This gate insulating film GOX is made of the gate insulating film explained in the embodiment. That is, the gate insulating film GOX is made of an aluminum oxide film formed by using AlCl3. As a result, the gate insulating film GOX has a higher concentration of a halogen element (chlorine) than carbon.

[0117] Next, a gate electrode GE is buried inside the trench TR via a gate insulating film GOX. The gate electrode GE is formed to have a portion buried in the trench TR and a portion protruding above the trench TR. The gate electrode GE is made of, for example, a polysilicon film into which n-type impurities (donors) such as phosphorus (P) or arsenic (As) are introduced. An interlayer insulating film IL is formed so as to cover the gate electrode GE and the channel layer CH in which the source region SR and the body contact region PR are formed. The interlayer insulating film IL is made of, for example, a silicon oxide film.

[0118] In the interlayer insulating film IL thus configured, a contact hole CNT is formed that reaches the source region SR and the body contact region PR. A metal silicide SL is formed on the surface of the source region SR and the body contact region PR exposed from the bottom surface of the contact hole CNT. The metal silicide SL is made of, for example, nickel silicide. A source electrode SE is formed on the interlayer insulating film IL so as to fill the inside of the contact hole CNT. As a result, the source electrode SE is electrically connected to the source region SR and the body contact region PR. The source electrode SE is made of, for example, a laminated film made of a titanium film, a titanium nitride film, and an aluminum film. A passivation film PAS is formed on the source electrode SE. The passivation film PAS is made of, for example, a polyimide resin film.

[0119] In the manner described above, the semiconductor device in Application Example 2 is configured.

[0120] The semiconductor device in Application Example 2 also uses the gate insulating film described in the embodiment. Therefore, the gate insulating film GOX of the semiconductor device is a highly reliable gate insulating film. As a result, the reliability of the semiconductor device in Application Example 2 can be improved.

[0121] <<<Semiconductor Device Manufacturing Method>>> Next, a method for manufacturing the semiconductor device in Application Example 2 will be described. Note that since the method for manufacturing the semiconductor device in Application Example 2 is almost the same as the method for manufacturing the semiconductor device in Application Example 1, the same steps will be omitted and different steps will be mainly described. In particular, the method for manufacturing the semiconductor device in Application Example 2 will be described with reference to Figs. 12 and 13.

[0122] In FIG. 12, steps S101 to S107 are the same as those in the manufacturing method of the semiconductor device in Application Example 1, and therefore will be omitted.

[0123] Next, a trench TR is formed by using photolithography and etching techniques. The trench TR is formed so that it penetrates the channel layer CH in which the source region SR and the body contact region PR are formed, and the bottom of the trench TR reaches the inside of the epitaxial layer EPI (see FIG. 14).

[0124] Next, a gate insulating film GOX is formed on the channel layer CH in which the source region SR and the body contact region PR are formed, and on the inner wall of the trench TR (S108). The gate insulating film GOX is formed by the ALD method using AlCl3 as a material gas. As a result, the gate insulating film GOX is composed of an aluminum oxide film.

[0125] As described in the embodiment, the aluminum oxide film formed by the ALD method using AlCl3 is a high-quality film with low defect level density and leakage current density. Therefore, the gate insulating film GOX is a high-quality gate insulating film with high reliability.

[0126] Thereafter, a gate electrode GE is formed having a portion that fills the trench TR via the gate insulating film GOX and a portion that protrudes above the trench TR (S109). The gate electrode GE can be formed by using a CVD method and a patterning technique. Specifically, the gate electrode GE can be formed by depositing a polysilicon film doped with n-type impurities such as nitrogen on the channel layer CH in which the source region SR and the body contact region PR are formed and inside the trench TR, and then patterning the polysilicon film by photolithography and etching techniques.

[0127] The subsequent steps from step S110 to step S116 shown in FIG. 13 are omitted because they are similar to those in Application Example 1. In this manner, the semiconductor device in Application Example 2 can be manufactured. The semiconductor device in Application Example 2 also uses an aluminum oxide film formed by the ALD method using AlCl3. Therefore, the gate insulating film GOX of the semiconductor device in Application Example 2 is a high-quality gate insulating film with high reliability. As a result, the reliability of the semiconductor device in Application Example 2 can be improved.

[0128] The invention made by the inventor has been specifically described above based on the embodiment thereof. However, it goes without saying that the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the invention. [Explanation of symbols]

[0129] BE Back electrode BNL Backside high concentration semiconductor layer BSL Backside silicide CH Channel Layer CNT contact hole EPI Epitaxial Layer GE gate electrode GOX gate insulating film IL Interlayer insulating film PAS passivation film PR body contact area SE source electrode SL Metal silicide SR Source Region SR1 source region SR2 Source Region SUB Silicon carbide substrate TR Trench

Claims

1. (a) forming a gate insulating film on a semiconductor substrate made of a wide band gap semiconductor material having a band gap larger than that of silicon; Equipped with In the step (a), the gate insulating film is formed by chemical vapor deposition using a material gas containing a halogen element and a metal element.

2. 2. The method of manufacturing a semiconductor device according to claim 1, The method for manufacturing a semiconductor device, wherein the halogen element is chlorine.

3. 2. The method of manufacturing a semiconductor device according to claim 1, The method for manufacturing a semiconductor device, wherein the material gas does not contain carbon or hydrogen.

4. 2. The method of manufacturing a semiconductor device according to claim 1, The material gas is AlCl ３ The method for manufacturing a semiconductor device is as follows.

5. 2. The method of manufacturing a semiconductor device according to claim 1, The method for manufacturing a semiconductor device, wherein the film formation temperature in the step (a) is 25 degrees Celsius or more and 400 degrees Celsius or less.

6. 2. The method of manufacturing a semiconductor device according to claim 1, The chemical vapor deposition method is an atomic layer deposition method, The atomic layer deposition method includes: (a1) introducing a first material gas containing a halogen element; (a2) purging the first material gas; (a3) introducing a second material gas containing oxygen; (a4) purging the second material gas; The method for manufacturing a semiconductor device comprising the steps of:

7. 7. The method of manufacturing a semiconductor device according to claim 6, The first material gas is AlCl ３ and The second material gas is H ２ O, O ３ Or N ２ O. A method for manufacturing a semiconductor device.

8. 2. The method of manufacturing a semiconductor device according to claim 1, (b) heating the semiconductor substrate after forming the gate insulating film; The method for manufacturing a semiconductor device comprising the steps of:

9. 9. The method for manufacturing a semiconductor device according to claim 8, a heating temperature in the step (b) is higher than a forming temperature of the gate insulating film in the step (a).

10. 10. The method of manufacturing a semiconductor device according to claim 9, The method for manufacturing a semiconductor device, wherein the heating temperature is equal to or higher than 500 degrees Celsius and lower than 900 degrees Celsius.

11. 2. The method of manufacturing a semiconductor device according to claim 1, The method for manufacturing a semiconductor device, wherein the step (b) is a silicide annealing step for forming a metal silicide.

12. The semiconductor device includes a field effect transistor having a gate insulating film formed on a semiconductor substrate made of a wide band gap semiconductor material having a band gap larger than that of silicon, The semiconductor device, wherein the gate insulating film has a halogen element at a concentration higher than that of carbon.

13. 13. The semiconductor device according to claim 12, The semiconductor device, wherein the halogen element is chlorine.

14. 13. The semiconductor device according to claim 12, The field effect transistor is a back surface electrode formed on a lower surface of the semiconductor substrate; an epitaxial layer formed on an upper surface of the semiconductor substrate; a plurality of source regions formed in the epitaxial layer; the gate insulating film formed on an upper surface of the epitaxial layer between a first source region and a second source region included in the plurality of source regions; a gate electrode formed on the gate insulating film; The semiconductor device has

15. 13. The semiconductor device according to claim 12, The field effect transistor is a back surface electrode formed on a lower surface of the semiconductor substrate; a source region formed in the semiconductor substrate; a trench formed in the semiconductor substrate extending through the source region; the gate insulating film formed on the inner wall of the trench; a gate electrode including a portion embedded in the trench via the gate insulating film; The semiconductor device has

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