Semiconductor device and manufacturing method thereof

Abstract

The embodiment of the invention relates to a semiconductor device and a manufacturing method thereof. And the reliability of the semiconductor device is improved. In the present disclosure, a gate insulating film is formed over a silicon carbide semiconductor substrate by an ALD method in a process using a material gas containing a halogen element and a metal element.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The disclosure of Japanese Patent Application No. 2023-126951 filed on August 3, 2023, including the specification, drawings and abstract, is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to a semiconductor device and a manufacturing technology thereof, for example, a technology effective when applied to a semiconductor device including a semiconductor substrate composed of a wide bandgap semiconductor material having a bandgap larger than that of silicon and a manufacturing technology thereof. Background Art

[0004] Japanese Patent Publication No. 2017-228679 (Patent Document 1) describes a technology for improving the reliability of a semiconductor device including a SiC power transistor. Summary of the invention

[0005] In order to improve the performance of semiconductor devices including field effect transistors, it is considered to manufacture the semiconductor devices using a semiconductor substrate composed of a wide bandgap semiconductor material having a larger bandgap than silicon.

[0006] However, with the prior art, the gate insulating film formed on the semiconductor substrate composed of the wide bandgap semiconductor material does not have as high reliability as the silicon oxide film formed on the silicon substrate. Therefore, in the semiconductor device manufactured using the semiconductor substrate composed of the wide bandgap semiconductor material, it is desirable to form a gate insulating film with high reliability.

[0007] Other objects and novel features will become apparent from the description of this specification and the accompanying drawings.

[0008] A method for manufacturing a semiconductor device according to an embodiment includes forming a gate insulating film on a semiconductor substrate composed of a wide bandgap semiconductor material having a larger bandgap than silicon, wherein the gate insulating film is formed by a chemical vapor deposition method using a material gas containing a halogen element and a metal element.

[0009] A semiconductor device according to an embodiment includes a field effect transistor having a gate insulating film formed on a semiconductor substrate composed of a wide bandgap semiconductor material having a bandgap greater than that of silicon. Here, the gate insulating film has a halogen element with a higher concentration than carbon. According to an embodiment, the reliability of the semiconductor device can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a flow chart explaining the ALD method used in the examples.

[0011] Figure 2This is a diagram qualitatively explaining the mechanism of increase in the amount of moisture contained in the gate insulating film in the ALD method using trimethylaluminum.

[0012] Figure 3 This is a diagram for qualitatively explaining the mechanism of reduction of the amount of water contained in the gate insulating film in the ALD method using aluminum trichloride.

[0013] Figure 4 is a graph showing the measurement results of the amount of water based on the temperature-increasing desorption method.

[0014] Figure 5 is a graph showing the results of measuring the carbon concentration in the gate insulating film by SIMS analysis.

[0015] Figure 6 is a graph showing the results of measuring the chlorine concentration in the gate insulating film by SIMS analysis.

[0016] Figure 7 is a graph showing the relationship between the silicon oxide equivalent film thickness of the gate insulating film and the amount of traps present in the gate insulating film.

[0017] Figure 8 is a graph showing the relationship between the silicon oxide equivalent film thickness of the gate insulating film and the leakage current density flowing through the gate insulating film.

[0018] Fig. 9 is a diagram showing an example of the structure of an aluminum oxide film formed by using trimethylaluminum as a material of an ALD method.

[0019] Fig.10 is a diagram showing an example of the structure of an aluminum oxide film formed by using aluminum trichloride as a material of an ALD method.

[0020] Fig.11 is a cross-sectional view showing the structure of a semiconductor device including a planar SiC field effect transistor.

[0021] Fig.12 is a flowchart showing a manufacturing process of a semiconductor device in Application Example 1.

[0022] Fig.13 is a flowchart showing a manufacturing process of a semiconductor device in Application Example 1.

[0023] Fig.14 is a cross-sectional view showing the structure of a semiconductor device including a trench gate type SiC field effect transistor. DETAILED DESCRIPTION

[0024] In all the drawings for explaining the embodiments, the same components are denoted by the same reference numerals in principle, and their repeated description is omitted. It should be noted that even a plan view may be hatched for the sake of clarity.

[0025] It has been noted that a semiconductor device (hereinafter referred to as a wide bandgap power semiconductor device) includes a field effect transistor formed on a semiconductor substrate mainly composed of a semiconductor material having a bandgap larger than that of silicon.

[0026] This is because a larger band gap means it has a higher dielectric breakdown strength, making it easier to achieve high withstand voltage.

[0027] And if the semiconductor material itself has a high dielectric breakdown strength, the breakdown voltage can be ensured even if the drift layer that maintains the breakdown voltage is thin. Thus, for example, by thinning the drift layer and increasing the impurity concentration, the on-resistance of the power semiconductor device can be reduced.

[0028] In other words, the advantage of a wide bandgap power semiconductor device is that it can balance the improvement of breakdown voltage and the reduction of on-resistance, wherein the improvement of breakdown voltage and the reduction of on-resistance are in a trade-off relationship. Therefore, a wide bandgap power semiconductor device is expected to be a semiconductor device capable of achieving high performance.

[0029] Examples of semiconductor materials with a larger band gap than silicon include silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), and diamond. Below, we will focus on silicon carbide.

[0030] (Improvement considerations)

[0031] In a field effect transistor having a gate insulating film formed on a silicon substrate (hereinafter referred to as a Si field effect transistor), the gate insulating film is composed of, for example, a silicon oxide film formed by a thermal oxidation method. The gate insulating film formed in this way is a high-quality film with high reliability. That is, in the Si field effect transistor, the gate insulating film can be composed of a high-quality film with high reliability.

[0032] 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, for example, a silicon oxynitride film (SiON) formed without using a gas or N2O gas. However, it is known that it is difficult to make a gate insulating film formed in this way a film with high reliability.

[0033] In particular, in the method for forming a gate insulating film described above, a silicon oxynitride film is formed while the Si-C bond of silicon carbide is cut off by an oxidation reaction. For this reason, an interface defect (dangling bond) is formed at the interface between SiON and SiC. Therefore, the density of the interface defect level in the gate insulating film is very high. This may lead to an increase in the on-resistance of the semiconductor device and a shift in the threshold voltage. Therefore, in a SiC field effect transistor, it is difficult to form a gate insulating film from a high-quality film.

[0034] Therefore, a method of forming a gate insulating film by depositing a film on a silicon carbide substrate using a chemical vapor deposition method (CVD method) rather than a thermal oxidation method has been proposed. This method is not a method of forming a gate insulating film while cutting the Si-C bond of silicon carbide, so it is believed that the interface defect level can be reduced.

[0035] However, due to the film forming principle of the CVD method, the deposited film formed by the CVD method may inherently contain elements derived from the raw materials as impurities in the deposited film as well as moisture. That is, in the gate insulating film formed by the CVD method, the fact that moisture and impurities derived from the raw materials are included as impurities shows room for improvement.

[0036] In this regard, the present inventors have obtained the following new findings.

[0037] (1) Moisture contained in the gate insulating film may migrate to the interface and cause an oxidation reaction, resulting in generation of interface defect levels. Therefore, it is desirable to remove moisture contained in the gate insulating film. Moisture can be removed by annealing (heat treatment).

[0038] (2) In the case where carbon is included in the raw material gas of the CVD method, the gate insulating film contains carbon. Even during annealing, carbon does not escape from the gate insulating film, and the film quality of the gate insulating film is deteriorated. Therefore, it is desirable to reduce the carbon contained in the gate insulating film.

[0039] (3) In the case where a halogen element is contained in the material gas of the CVD method, the gate insulating film contains the halogen element. Even during annealing, the halogen element is not absorbed from the gate insulating film. However, even if the gate insulating film includes the halogen element, it is unlikely that they will deteriorate the film quality.

[0040] Based on the above findings, the inventors of the present invention have found a technical concept capable of forming a gate insulating film with high reliability in a method of forming a gate insulating film by a CVD method. The technical concept found by the inventors is described below.

[0041] (Basic concept in the embodiment)

[0042] The basic idea in this embodiment is to form a gate insulating film on a silicon carbide substrate using a material gas containing a halogen element and a metal element using a CVD method. According to this basic idea, the material gas of the CVD method contains a halogen element. Therefore, the gate insulating film contains a halogen element. However, even if a halogen element is contained in the gate insulating film, the risk of deteriorating the film quality is small. Therefore, according to the basic idea, the gate insulating film can be formed of a film with high reliability.

[0043] In other words, according to the basic idea, a film is deposited using a CVD method without breaking Si-C bonds, rather than forming a film using a thermal oxidation method while breaking Si-C bonds. Therefore, the interface defect level can be reduced. And since a material gas containing a halogen element that is less likely to deteriorate the film quality of the gate insulating film is used as a material gas for the CVD method, the film quality can be improved.

[0044] In other words, in the basic idea, a high-quality gate insulating film can be formed by combining (1) using a CVD method that can suppress the generation of interface defect levels, and (2) using a material gas containing a halogen element as a material gas for the CVD method.

[0045] Examples of halogen elements include fluorine or chlorine. Examples of metal elements include aluminum (Al), hafnium (Hf) or zirconium (Zr). For example, aluminum is used when the gate insulating film is formed by an aluminum oxide film (aluminum oxide film). Hafnium is used when the gate insulating film is formed by a hafnium oxide film (hafnium dioxide film), and zirconium is used when the gate insulating film is formed by a zirconium oxide film.

[0046] Therefore, in the basic idea, the material gas containing halogen elements and metal elements is used as the material gas of the CVD method. In addition, it is expected that the material gas of the CVD method does not contain carbon and hydrogen. This is because carbon may deteriorate the film quality of the gate insulating film. In addition, if hydrogen is contained in the material gas of the CVD method, the gate insulating film may contain moisture (a compound of hydrogen and oxygen). Moisture can migrate to the interface and cause an oxidation reaction, resulting in the generation of interface defect levels. Therefore, based on the above-mentioned new findings (1), (2) and (3), it is expected to use a material gas containing halogen elements and metal elements but not containing carbon and hydrogen as the material gas of the CVD method.

[0047] In addition, although it is not necessary, it is desirable to have a process for heating the silicon carbide substrate after forming the gate insulating film. As explained in the above new discovery (1), the gate insulating film formed by the CVD method contains moisture. This moisture moves to the interface and causes an oxidation reaction, which is the reason for the formation of the interface defect level. Therefore, in order to form a high-quality gate insulating film, it is desirable to remove the moisture contained in the gate insulating film. For this reason, it is desirable to heat the silicon carbide substrate to remove moisture from the gate insulating film.

[0048] At the silicon carbide interface, in order for silicon carbide not to be oxidized by reaction with the moisture that has left, it is desirable that the heating temperature (annealing temperature) be lower than 900 degrees Celsius. This is because the temperature at which silicon carbide starts to oxidize is 900 degrees Celsius. In other words, in order to remove moisture from the gate insulating film, a temperature range is effective in which the moisture that has left the gate insulating film does not react with silicon carbide.

[0049] In order to remove moisture from the gate insulating film, it is desirable that the heating temperature of the silicon carbide substrate be higher than the temperature at which the gate insulating film is formed. The heating temperature of the silicon carbide substrate is, for example, 500 degrees Celsius or higher and lower than 900 degrees Celsius.

[0050] According to the basic idea as described above, even if a gate insulating film is formed on a silicon carbide substrate, a gate insulating film with high reliability can be formed.

[0051] In the following, implementation modes implementing the basic idea will be described.

[0052] (Example)

[0053] (Method for manufacturing semiconductor device)

[0054] In the embodiment, a process for forming a gate insulating film included in a method for manufacturing a semiconductor device is described. In particular, in the embodiment, an example of a gate insulating film formed on a silicon carbide substrate by configuring an aluminum oxide film (Al2O3 film) is explained. In addition, an example of using an atomic layer deposition method (hereinafter referred to as an ALD method) (a CVD method) as a film forming method of the gate insulating film is explained.

[0055] Figure 1 is a flow chart explaining the ALD method used in the examples.

[0056] exist Figure 1 In the process, 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 cleaned (S2). Next, a second material gas containing oxygen is introduced onto the silicon carbide substrate (S3). Then, the second material gas is cleaned (S4). By undergoing such a process, a gate insulating film having a film thickness at the atomic layer level can be formed on the silicon carbide substrate. If a gate insulating film having a predetermined film thickness has not yet been formed, the film forming process is continued (S5). On the other hand, when a gate insulating film having a predetermined film thickness is formed, the film forming process is terminated (S5). In this way, a gate insulating film having a desired film thickness can be formed.

[0057] Here, the first material gas is AlCl3. In addition, the second material gas is H2O, O3 or N2O. And, the film forming temperature in the ALD method is, for example, above 25 degrees Celsius and below 400 degrees Celsius. According to an embodiment, by using such an ALD method, a gate insulating film with high reliability can be formed. That is, in this embodiment, by using AlCl3 as the first material gas containing a halogen element in the ALD method, the following characteristic point can be obtained. Using this characteristic point, according to an embodiment, a gate insulating film with high reliability can be formed.

[0058] The above-mentioned characteristic points will be explained below.

[0059] The first characteristic point in the embodiment is that the amount of moisture present in the gate insulating film can be reduced by using AlCl3. For example, when a gate insulating film is formed from an aluminum oxide film, trimethylaluminum (Al(CH3)3) is generally used as a material gas of the ALD method. In this regard, the inventors have recently discovered that when trimethylaluminum is used, the amount of moisture contained in the gate insulating film increases.

[0060] Therefore, considering that moisture contained in the gate insulating film becomes a cause of generating interface defect levels, when trimethylaluminum is used, it is difficult to form a gate insulating film with high reliability.

[0061] On the other hand, the present inventors have newly discovered that when AlCl3 is used as a material gas of the ALD method, the amount of moisture contained in the gate insulating film can be reduced compared to when trimethylaluminum is used. Thus, if AlCl3 is used, the moisture in the gate insulating film, which is the cause of the generation of the interface defect level, can be reduced. Therefore, by using AlCl3, a gate insulating film with high reliability can be formed.

[0062] Next, a qualitative mechanism will be explained in which the amount of moisture contained in the gate insulating film increases when trimethylaluminum is used, and the amount of moisture contained in the gate insulating film decreases when AlCl 3 is used.

[0063] When trimethylaluminum is used, the ALD method has the following steps: (a1) a step of introducing trimethylaluminum. (a2) a step of washing out trimethylaluminum. (a3) ​​a step of introducing H2O (oxidant). (a4) a step of washing out H2O.

[0064] So, for example, Figure 2 As shown in , some methyl groups of trimethylaluminum are replaced by hydroxyl groups of an oxidant (H2O). Then, hydrogen and hydroxyl groups constituting the methyl groups react to generate and separate from moisture. In this way, in trimethylaluminum, hydrogen, which is a moisture constituent element, exists, making it easy to generate moisture. Therefore, when trimethylaluminum is used, the amount of moisture contained in the gate insulating film tends to increase.

[0065] In contrast, the ALD method using AlCl3 has the following steps: (a1) a step of introducing AlCl3. (a2) a step of purging AlCl3. (a3) ​​a step of introducing H2O (oxidant). (a4) a step of purging H2O.

[0066] So, for example, Figure 3 As shown in , some of the chlorine in AlCl3 is replaced by the hydroxyl group of the oxidant (H2O). Then, moisture is generated and desorbed by the reaction of multiple hydroxyl groups. In this regard, in AlCl3, since hydrogen, which is a constituent element of moisture, is not present, it is difficult to generate moisture. Therefore, when AlCl3 is used, it is easier to reduce the amount of moisture contained in the gate insulating film.

[0067] Figure 4 is a graph showing the results of measuring the amount of moisture based on the temperature desorption method. Figure 4 In FIG. 1 , the horizontal axis indicates the temperature of the stage on which the silicon carbide substrate on which the gate insulating film (aluminum oxide film) is formed is placed. On the other hand, the vertical axis indicates the amount of moisture contained in the gate insulating film.

[0068] Graph (1) shows an aluminum oxide film formed by an ALD method using trimethylaluminum (TMA) as a material gas. Graph (2) shows an aluminum oxide film formed by an ALD method using AlCl 3 as a material gas.

[0069] like Figure 4 As shown in , it can be seen that the amount of moisture in the aluminum oxide film formed by the ALD method using AlCl3 as the material gas is less than the amount of moisture in the aluminum oxide film formed by the ALD method using trimethylaluminum (TMA) as the material gas. Therefore, it has been confirmed that by using AlCl3, the amount of moisture in the gate insulating film (in the aluminum oxide film) can be reduced compared to when trimethylaluminum is used.

[0070] In addition, instead of H2O, O3 or N2O can also be used as an oxidant. In this case, the amount of moisture in the gate insulating film can be further reduced. This is because, although H2O contains hydrogen, O3 or N2O does not contain hydrogen, which is a constituent element of moisture, resulting in less moisture being generated in the gate insulating film. In other words, from the perspective of reducing the amount of moisture in the gate insulating film, it is desirable to use O3 or N2O as an oxidant.

[0071] Next, the second characteristic point in the embodiment is that by using AlCl3, the amount of carbon present in the gate insulating film can be reduced. That is, 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 deteriorates the film quality of the gate insulating film, the fact that carbon in the gate insulating film can be reduced by using AlCl3 that does not contain carbon as the material gas in the ALD method leads to the formation of a gate insulating film with high reliability.

[0072] For example, trimethylaluminum contains carbon as a methyl group. Therefore, when trimethylaluminum is used as a material gas in the ALD method, the amount of carbon contained in the gate insulating film increases. Therefore, carbon deteriorates the film quality of the gate insulating film.

[0073] In contrast, as in the embodiment, when AlCl 3 is used, since AlCl 3 does not contain carbon, the amount of carbon contained in the gate insulating film can be reduced. Therefore, according to this embodiment, the amount of carbon, which is a factor of deterioration of the film quality of the gate insulating film, can be reduced. Thus, according to the embodiment, a gate insulating film with high reliability can be formed.

[0074] Figure 5 Graph showing the results of measuring the carbon concentration in the gate insulating film by SIMS analysis. Figure 5 Graph (1) shows a gate insulating film formed using trimethylaluminum. Graph (2) illustrates a gate insulating film subjected to heat treatment at 800 degrees Celsius after film formation using trimethylaluminum.

[0075] In addition, graph (3) illustrates a gate insulating film formed using AlCl 3. Graph (4) illustrates a gate insulating film subjected to heat treatment at 800 degrees Celsius after film formation using AlCl 3.

[0076] First, if Figure 5 As shown in , by using AlCl 3 , the carbon concentration in the gate insulating film can be reduced compared to using trimethylaluminum.

[0077] Here, even when AlCl3 containing no carbon is used as a material gas for the ALD method, Figure 5 It is inferred that the gate insulating film contains a small amount of carbon. This can be attributed to the diffusion of carbon from the silicon carbide substrate in contact with the gate insulating film because the gate insulating film is formed on the silicon carbide substrate.

[0078] Next, from Figure 5It can be seen that, regardless of whether trimethylaluminum or AlCl3 is used, the carbon concentration in the gate insulating film after the heat treatment at 800 degrees Celsius does not change significantly compared to the carbon concentration in the gate insulating film before the heat treatment. In other words, regardless of the type of material gas used in the ALD method, the carbon contained in the gate insulating film is not desorbed even after the heat treatment at 800 degrees Celsius.

[0079] It can be concluded that heat treatment is not an effective method for reducing the carbon content in the gate insulating film. On the other hand, as in the embodiment, using AlCl3 that does not contain carbon instead of trimethylaluminum that contains carbon is effective from the perspective of reducing the carbon content in the gate insulating film.

[0080] Next, the third characteristic point in the embodiment is that the use of AlCl 3 leads to a higher chlorine content in the gate insulating film. In other words, because AlCl 3 contains chlorine, the chlorine content in the gate insulating film increases.

[0081] However, chlorine does not deteriorate the film quality of the gate insulating film. Considering this, using AlCl3 containing chlorine as a material gas of the ALD method does not cause a problem in forming a gate insulating film with high reliability. Rather, from the perspective of forming a gate insulating film with high reliability, using AlCl3 is useful because it can reduce the carbon content that causes the film quality of the gate insulating film to deteriorate.

[0082] Figure 6 Graph showing the results of measuring the chlorine concentration in the gate insulating film by SIMS analysis. Figure 6 Graph (1) illustrates a gate insulating film formed using trimethylaluminum. Graph (2) illustrates a gate insulating film subjected to heat treatment at 800 degrees Celsius after film formation using trimethylaluminum.

[0083] In addition, graph (3) illustrates a gate insulating film formed using AlCl 3. Graph (4) illustrates a gate insulating film subjected to heat treatment at 800 degrees Celsius after film formation using AlCl 3.

[0084] First, if Figure 6 As shown in , by using AlCl 3 , the chlorine concentration in the gate insulating film can be increased compared to the case of using trimethylaluminum. This is because AlCl 3 contains chlorine, while trimethylaluminum does not contain chlorine.

[0085] Next, from Figure 6It can be seen that, regardless of whether trimethylaluminum or AlCl3 is used, the chlorine concentration in the gate insulating film after the heat treatment at 800 degrees Celsius does not change significantly compared to the chlorine concentration in the gate insulating film before the heat treatment. In other words, regardless of the type of material gas used in the ALD method, the chlorine contained in the gate insulating film is not desorbed even after the heat treatment at 800 degrees Celsius. However, even if chlorine remains in the gate insulating film, it does not deteriorate the film quality of the gate insulating film. Therefore, from the perspective of forming a gate insulating film with high reliability, the residual chlorine in the gate insulating film does not cause a problem.

[0086] As described above, according to the embodiment, the above-mentioned first feature, second feature, and third feature can be obtained by using AlCl 3. Therefore, in the embodiment, these features enable the formation of a gate insulating film with high reliability.

[0087] (Effect Verification)

[0088] Hereinafter, verification results confirming the ability to form a gate insulating film with high reliability according to the embodiment will be described.

[0089] Figure 7 : is a graph 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 represents the equivalent oxide thickness. The vertical axis represents the amount of traps. Figure 7 In FIG. 1 , the gate insulating film is an aluminum oxide film. In addition, the circle mark is a diagram indicating an aluminum oxide film formed by using trimethylaluminum. In addition, the triangle mark is a diagram indicating an aluminum oxide film formed by using AlCl 3 .

[0090] like Figure 7 As shown in , the amount of traps in the aluminum oxide film formed using AlCl3 is less than the amount of traps in the aluminum oxide film formed using trimethylaluminum. In other words, the defect level density in the aluminum oxide film formed by using AlCl3 is less than the defect level density in the aluminum oxide film formed by using trimethylaluminum.

[0091] This means that the aluminum oxide film formed by using AlCl3 is a gate insulating film having higher reliability than the aluminum oxide film formed by using trimethylaluminum. Figure 7 It was confirmed that the aluminum oxide film (gate insulating film) formed by using AlCl 3 was a gate insulating film with high reliability.

[0092] Next, Figure 8 Graph 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 represents the equivalent oxide thickness. The vertical axis represents the leakage current density.

[0093] exist Figure 8 In FIG. 1 , the gate insulating film is an aluminum oxide film. In addition, a circle mark indicates an aluminum oxide film formed by using trimethylaluminum. In addition, a triangle mark indicates an aluminum oxide film formed by using AlCl 3 .

[0094] like Figure 8 As shown in , the leakage current density in the aluminum oxide film formed using AlCl 3 is smaller than the leakage current density in the aluminum oxide film formed using trimethylaluminum.

[0095] This means that the aluminum oxide film formed by using AlCl3 is a gate insulating film having higher reliability than the aluminum oxide film formed by using trimethylaluminum. Figure 8 It was confirmed that the aluminum oxide film (gate insulating film) formed by using AlCl 3 was a gate insulating film with high reliability.

[0096] Hereinafter, a qualitative mechanism will be described in which the amount of traps and the leakage current density become smaller in the aluminum oxide film formed by using AlCl 3 than in the aluminum oxide film formed by using trimethylaluminum.

[0097] Fig. 9 : is a diagram showing an example of the structure of an aluminum oxide film formed by using trimethylaluminum. Fig. 9 As shown in , in an aluminum oxide film formed by using trimethylaluminum, a "trap site" is generated by the residue and detachment of CHx. Therefore, in an aluminum oxide film formed by using trimethylaluminum, the defect level density increases, resulting in an increase in the leakage current density.

[0098] Fig.10 : is a diagram showing an example of the structure of an aluminum oxide film formed by using AlCl 3. Fig.10 As shown in , in the aluminum oxide film formed using AlCl 3 , dangling bonds are terminated by chlorine (Cl). Therefore, in the aluminum oxide film formed using AlCl 3 , the defect level density is reduced, resulting in a reduction in the leakage current density.

[0099] Through such a mechanism, it can be qualitatively understood that a high-quality gate insulating film with a small defect level density and leakage current density can be realized in an aluminum oxide film formed by using AlCl 3 .

[0100] (Application Example)

[0101] According to the embodiment, a gate insulating film with high reliability can be formed. Therefore, by manufacturing a field effect transistor using the gate insulating film in the embodiment, the reliability of a semiconductor device including the field effect transistor can be improved.

[0102] Hereinafter, silicon carbide is mentioned as an example of a wide bandgap semiconductor material in which the bandgap is larger than that of silicon. Also, as an application example of a gate insulating film in an embodiment, a SiC field effect transistor having a gate insulating film formed on a silicon carbide substrate is explained as an example. In particular, in Application Example 1, a semiconductor device including a planar SiC field effect transistor is described. In Application Example 2, a semiconductor device including a trench gate SiC field effect transistor is described.

[0103] (Application Example 1)

[0104] (Configuration of semiconductor device)

[0105] Fig.11 is a cross-sectional view showing the configuration of a semiconductor device including a planar SiC field effect transistor. Fig.11 In the embodiment, the semiconductor device has a silicon carbide semiconductor substrate SUB, a back high concentration semiconductor layer BNL, a back silicide BSL, and a bottom 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. In addition, the semiconductor device has a gate insulating film GOX, a gate electrode GE, an interlayer insulating film IL, a source electrode SE, and a passivation film PAS.

[0106] The silicon carbide semiconductor substrate SUB is, for example, an n+ type semiconductor substrate. For example, on the bottom side of the silicon carbide semiconductor substrate SUB, a back side high concentration semiconductor layer BNL made of an n+ type semiconductor layer is formed. A back side silicide BSL is formed to contact the back side high concentration semiconductor layer BNL. The back side silicide BSL is composed of, for example, nickel silicide. And a bottom electrode BE is formed so as to contact the back side silicide BSL. The bottom electrode BE is composed of, for example, a laminated film made of a titanium film, a nickel film, and a gold film.

[0107] Next, an epitaxial layer EPI is formed on the upper surface of the silicon carbide semiconductor substrate SUB. The epitaxial layer EPI is made of, for example, an n-type semiconductor layer. Inside the epitaxial layer EPI, a plurality of channel layers CH, for example, made of a p-type semiconductor layer, are formed to be separated from each other. And a source region SR and a body contact region PR that are in contact with each other are formed inside each channel layer of the plurality of channel layers CH.

[0108] Therefore, if Fig.11 As shown in , a plurality of source regions SR and a plurality of body contact regions PR are formed in the semiconductor device. Fig.11 , source region SR1 and source region SR2 included in the plurality of source regions SR are shown. Each of the plurality of source regions SR is composed of, for example, an n+ type semiconductor region. Each of the plurality of body contact regions PR is composed of, for example, a p+ type semiconductor region.

[0109] Next, if Fig.11 As shown in , 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 portion of the source region SR1, and on a portion of the source region SR2.

[0110] The gate insulating film GOX is composed of the gate insulating film described in the embodiment. That is, the gate insulating film GOX is composed of an aluminum oxide film formed by using AlCl3 as a material gas of the ALD method. Therefore, the gate insulating film GOX has a halogen element (chlorine) with a higher concentration than carbon.

[0111] A gate electrode GE is formed on the gate insulating film GOX. The gate electrode GE is composed of a polysilicon film into which an n-type impurity (donor) such as phosphorus (P) or arsenic (As) has been introduced. An interlayer insulating film IL is formed to cover the gate electrode GE. The interlayer insulating film IL is composed of, for example, a silicon oxide film.

[0112] In the interlayer insulating film IL configured in this way, a contact hole CNT reaching the source region SR and the body contact region PR 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, a metal silicide SL is formed. For example, the metal silicide SL is composed of nickel silicide. The source electrode SE is formed to fill the inside of the contact hole CNT and on the interlayer insulating film IL. Therefore, the source electrode SE is electrically connected to the source region SR and the body contact region PR. The source electrode SE is composed of a laminated film composed of, for example, 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 composed of, for example, a polyimide resin film.

[0113] In this way, the semiconductor device in Application Example 1 is configured.

[0114] In the semiconductor device of Application Example 1, the gate insulating film described in the embodiment is used. Therefore, the gate insulating film GOX of the semiconductor device becomes a gate insulating film with high reliability. Therefore, according to the semiconductor device in Application Example 1, the reliability can be improved.

[0115] (Method for manufacturing semiconductor device)

[0116] Next, a method for manufacturing a semiconductor device in Application Example 1 will be described.

[0117] Fig.12 and Fig.131 is a flowchart showing a manufacturing process of a semiconductor device in Application Example 1. First, a silicon carbide semiconductor substrate SUB is prepared (S101). Next, an epitaxial layer EPI is formed on the upper surface of the silicon carbide semiconductor substrate SUB (S102). The epitaxial layer EPI is an n-type semiconductor layer. The epitaxial layer EPI is formed by growing a silicon carbide layer using an epitaxial growth method, into which n-type impurities such as nitrogen have been introduced.

[0118] Next, a channel layer CH is formed inside the epitaxial layer EPI by using a photolithography technique and an ion implantation method (S103). The channel layer CH is a p-type semiconductor layer. The channel layer CH is formed by introducing a p-type impurity such as aluminum into the epitaxial layer EPI. Then, a source region SR is formed inside the channel layer CH by using a photolithography technique and an ion implantation method (S104). 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.

[0119] Subsequently, a body contact region PR in contact with the source region SR is formed inside the channel layer CH 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 introducing a p-type impurity such as aluminum into the channel layer CH. Then, a back side high concentration semiconductor layer BNL is formed on the bottom surface of the silicon carbide semiconductor substrate SUB by using an ion implantation method (S106). The back side high concentration semiconductor layer BNL is an n+ type semiconductor layer. The back side high concentration semiconductor layer BNL is formed, for example, by introducing an n-type impurity such as nitrogen into the silicon carbide semiconductor substrate SUB.

[0120] Next, the silicon carbide semiconductor substrate SUB is heated to perform activation annealing (S107). For example, the activation annealing is performed by heating the silicon carbide semiconductor substrate SUB to 1700 degrees Celsius. Through this activation annealing, the conductive impurities introduced into the channel layer CH, the source region SR, the body contact region PR, and the back high-concentration semiconductor layer BNL formed by the ion implantation method are activated.

[0121] Subsequently, a gate insulating film GOX is formed on the upper surface of the epitaxial layer EPI on which the channel layer CH, the source region SR, and the body contact region PR have been formed (S108). The gate insulating film GOX is formed by an ALD method using AlCl3 as a material gas. Therefore, the gate insulating film GOX is composed of an aluminum oxide film.

[0122] As described in the embodiment, the aluminum oxide film formed by the ALD method using AlCl3 has a small defect level density and a leakage current density, and is a high-quality film. Therefore, the gate insulating film GOX becomes a gate insulating film with high reliability.

[0123] Here, after forming the gate insulating film GOX, it is effective to heat the silicon carbide semiconductor substrate SUB at a temperature lower than 900 degrees Celsius (higher than the temperature at which the gate insulating film GOX is formed). This is because, by this heating process, moisture can be desorbed from the gate insulating film GOX at a temperature (lower than 900 degrees Celsius) at which the silicon carbide semiconductor substrate SUB is not oxidized.

[0124] Subsequently, 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 by depositing a polysilicon film doped with n-type impurities such as nitrogen and then patterning the polysilicon film by photolithography and etching techniques.

[0125] Then, an interlayer insulating film IL is formed on the upper surface of the epitaxial layer EPI on which the channel layer CH, the source region SR and the body contact region PR have been formed so as to cover the gate electrode GE (S110). The interlayer insulating film IL is composed of, for example, a silicon oxide film. The silicon oxide film can be formed by using a CVD method.

[0126] 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 to penetrate the interlayer insulating film IL so as to reach both the source region SR and the body contact region PR.

[0127] Subsequently, 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 (S112). The metal silicide SL is composed of, for example, nickel silicide. 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 on the silicon carbide semiconductor substrate SUB at 1000 degrees Celsius. As described above, it is desirable to remove moisture from the gate insulating film GOX by heating the silicon carbide semiconductor substrate SUB after forming the gate insulating film GOX. That is, a heating process for removing moisture from the gate insulating film GOX can be performed after the gate insulating film GOX is formed. In this case, the moisture in the gate insulating film GOX is removed at the stage of performing silicide annealing. Therefore, oxidation of the silicon carbide semiconductor substrate SUB can be suppressed by silicide annealing.

[0128] However, the above-mentioned heating process after forming the gate insulating film GOX can also be replaced by silicide annealing. In other words, it is allowed to remove moisture from the gate insulating film GOX by silicide annealing without performing a heat treatment process after forming the gate insulating film GOX. Therefore, not only the function of forming the metal silicide SL but also the function of removing moisture from the gate insulating film GOX can be shared by the silicide annealing.

[0129] In this case, since the temperature of silicide annealing is higher than the oxidation temperature of silicon carbide, moisture leaves and silicon carbide is oxidized by silicide annealing. Therefore, when removing moisture from the gate insulating film GOX by 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.

[0130] Subsequently, the inside of the contact hole CNT in which the metal silicide SL has been 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, for example, a laminated film composed of a titanium film, a titanium nitride film, and an aluminum film. The source electrode SE can be formed, for example, by using 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.

[0131] Next, a back side silicide BSL is formed in contact with the back side high concentration semiconductor layer BNL formed on the bottom surface of the silicon carbide semiconductor substrate SUB (S115). The back side silicide BSL is composed of, for example, nickel silicide. The nickel silicide can be formed by forming a nickel film in contact with the back side high concentration semiconductor layer BNL and then performing silicide annealing (heat treatment at 1000 degrees Celsius) on the silicon carbide semiconductor substrate SUB.

[0132] Subsequently, a bottom electrode BE contacting the back side silicide BSL is formed (S116). The bottom electrode BE is composed of, for example, a laminated film composed of a titanium film, a nickel film, and a gold film. The bottom electrode BE can be formed, for example, by using a sputtering method.

[0133] In this way, the semiconductor device in Application Example 1 can be manufactured. In the semiconductor device in Application Example 1, an aluminum oxide film formed by an ALD method using AlCl 3 is used. Therefore, the gate insulating film GOX of the semiconductor device in Application Example 1 becomes a gate insulating film with high reliability. Therefore, according to the semiconductor device in Application Example 1, reliability can be improved.

[0134] (Application Example 2)

[0135] (Configuration of semiconductor device)

[0136] Fig.14 is a cross-sectional view showing the configuration of a semiconductor device including a trench gate type SiC field effect transistor. Fig.14In the embodiment, the semiconductor device has a silicon carbide semiconductor substrate SUB, a back high-concentration semiconductor layer BNL, a back silicide BSL, and a bottom electrode BE. In addition, the semiconductor device has an epitaxial layer EPI, a channel layer CH, a source region SR, a body contact region PR, and a metal silicide SL. In addition, the semiconductor device 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.

[0137] The silicon carbide semiconductor substrate SUB is, for example, an n+ type semiconductor substrate. On the bottom surface of the silicon carbide semiconductor substrate SUB, a back high concentration semiconductor layer BNL, for example, composed of an n+ type semiconductor layer, is formed. A back silicide BSL is formed to contact the back high concentration semiconductor layer BNL. The back silicide BSL is composed of, for example, nickel silicide. Then, a bottom electrode BE is formed to contact the back silicide BSL. The bottom electrode BE is composed of, for example, a laminated film composed of a titanium film, a nickel film, and a gold film.

[0138] Next, an epitaxial layer EPI is formed on the upper surface of the silicon carbide semiconductor substrate SUB. The epitaxial layer EPI is composed of, for example, an n-type semiconductor layer. A channel layer CH composed of, for example, a p-type semiconductor layer is formed on the epitaxial layer EPI. Inside the channel layer CH, a plurality of source regions SR and a plurality of body contact regions PR are formed. For example, Fig.14 The source region SR1 and the source region SR2 included in the plurality of source regions SR are shown. Each of the plurality of source regions SR is composed of, for example, an n+ type semiconductor region. In addition, each of the plurality of body contact regions PR is composed of, for example, a p+ type semiconductor region.

[0139] Next, if Fig.14 As shown in FIG. 1 , 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.

[0140] The gate insulating film GOX is formed on the inner wall of the trench TR. The gate insulating film GOX is composed of the gate insulating film described in the embodiment. That is, the gate insulating film GOX is composed of an aluminum oxide film formed using AlCl3. Therefore, the gate insulating film GOX has a halogen element (chlorine) with a higher concentration than carbon.

[0141] Next, the gate electrode GE is embedded in the trench TR through the gate insulating film GOX. The gate electrode GE is formed to have a portion embedded in the trench TR and a portion protruding above the trench TR. The gate electrode GE is composed of, for example, a polycrystalline silicon film into which n-type impurities (donors) such as phosphorus (P) and arsenic (As) have been introduced. An interlayer insulating film IL is formed to cover the channel layer CH and the gate electrode GE on which the source region SR and the body contact region PR are formed. The interlayer insulating film IL is composed of, for example, a silicon oxide film.

[0142] In the interlayer insulating film IL configured as described above, a contact hole CNT reaching the source region SR and the body contact region PR is formed. 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 composed of, for example, nickel silicide. Then, a source electrode SE is formed to fill the inside of the contact hole CNT and on the interlayer insulating film IL. Therefore, the source electrode SE is electrically connected to the source region SR and the body contact region PR. The source electrode SE is composed of, for example, a laminated film composed 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 composed of, for example, a polyimide resin film.

[0143] In this way, the semiconductor device in Application Example 2 is configured.

[0144] Even in the semiconductor device of Application Example 2, the gate insulating film described in the embodiment is used. Therefore, the gate insulating film GOX of the semiconductor device becomes a gate insulating film with high reliability. Therefore, according to the semiconductor device in Application Example 2, reliability can be improved.

[0145] (Method for manufacturing semiconductor device)

[0146] Next, a method for manufacturing a semiconductor device in Application Example 2 will be described. It should be noted that the method for manufacturing a semiconductor device in Application Example 2 is almost the same as the method for manufacturing a semiconductor device in Application Example 1, so the same steps are omitted and different steps are mainly described. In particular, Fig.12 and Fig.13 A method for manufacturing a semiconductor device in Application Example 2 is described.

[0147] exist Fig.12 In the method for manufacturing the semiconductor device in Application Example 1, steps from S101 to S107 are omitted because they are the same as those in the method for manufacturing the semiconductor device in Application Example 1.

[0148] Next, a trench TR is formed using photolithography and etching techniques. The trench TR is formed to penetrate the channel layer CH where the source region SR and the body contact region PR have been formed so that the bottom of the trench TR reaches the inside of the epitaxial layer EPI (see Fig.14 ).

[0149] Subsequently, a gate insulating film GOX is formed on the channel layer CH where the source region SR and the body contact region PR have been formed and on the inner wall of the trench TR (S108). The gate insulating film GOX is formed by an ALD method using AlCl3 as a material gas. Therefore, the gate insulating film GOX is composed of an aluminum oxide film.

[0150] As described in the embodiment, the aluminum oxide film formed by the ALD method using AlCl3 has a small defect level density and a leakage current density, and is a high-quality film. Therefore, the gate insulating film GOX becomes a high-quality gate insulating film with high reliability.

[0151] After that, a gate electrode GE is formed, which has a portion that fills the trench TR through the gate insulating film GOX and a portion that protrudes above the trench TR (S109). The gate electrode GE can be formed using a CVD method and a patterning technique. In particular, the gate electrode GE can be formed by depositing a polysilicon film to which n-type impurities such as nitrogen have been added on the channel layer CH where the source region SR and the body contact region PR have been formed and inside the trench TR, and then patterning the polysilicon film using photolithography and etching techniques.

[0152] Fig.13 The steps from S110 to S116 shown in the example 1 are omitted because they are the same as those in the example 1. In this way, the semiconductor device in the example 2 can be manufactured. In the semiconductor device of the example 2, an aluminum oxide film formed by the ALD method using AlCl3 is used. Therefore, the gate insulating film GOX of the semiconductor device in the example 2 becomes a high-quality gate insulating film with high reliability. Therefore, according to the semiconductor device in the example 2, the reliability can be improved.

[0153] The invention made by the present inventors has been described in detail above based on the embodiments, but the present invention is not limited to the embodiments described above, and it goes without saying that various modifications can be made without departing from the gist thereof.

Claims

1. A method for manufacturing a semiconductor device, comprising the following steps: (a) forming a gate insulating film on a semiconductor substrate composed of a wide bandgap semiconductor material having a larger bandgap than silicon, wherein In the step (a), the gate insulating film is formed by a chemical vapor deposition method using a material gas containing a halogen element and a metal element.

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

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

4. The method for manufacturing a semiconductor device according to claim 1, wherein The material gas is AlCl3 gas.

5. The method for manufacturing a semiconductor device according to claim 1, wherein In the step (a), the forming temperature is 25 degrees Celsius or higher and 400 degrees Celsius or lower.

6. The method for manufacturing a semiconductor device according to claim 1, wherein The chemical vapor deposition method is an atomic layer deposition method, and The atomic layer deposition method comprises the following steps: (a1) introducing a first material gas containing the halogen element, (a2) cleaning the first material gas, (a3) introducing a second material gas containing oxygen, and (a4) Purging the second material gas.

7. The method for manufacturing a semiconductor device according to claim 6, wherein The first material gas is AlCl3 gas, and The second material gas is one of H2O gas, O3 gas or N2O gas.

8. The method for manufacturing a semiconductor device according to claim 1, further comprising the following steps: (b) After step (a), heating the semiconductor substrate.

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

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

11. The method for manufacturing a semiconductor device according to claim 8, wherein The step (b) is a silicide annealing process for forming metal silicide.

12. A semiconductor device comprising: A field effect transistor having a gate insulating film formed on a semiconductor substrate composed of a wide bandgap semiconductor material having a larger bandgap than silicon, wherein The gate insulating film has a halogen element at a higher concentration than carbon.

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

14. The semiconductor device according to claim 12, wherein The field effect transistor comprises: a bottom electrode formed on a bottom surface of the semiconductor substrate, an epitaxial layer formed on an upper surface opposite to the bottom surface of the semiconductor substrate, a plurality of source regions, including a first source region and a second source region formed in the epitaxial layer, and The gate electrode, wherein In a plan view, the gate insulating film is formed between the first source region and the second source region on the upper surface of the epitaxial layer, and The gate electrode is formed on the gate insulating film.

15. The semiconductor device according to claim 12, wherein The field effect transistor comprises: a bottom electrode formed on a bottom surface of the semiconductor substrate, a source region formed in the upper surface of the semiconductor substrate, a trench formed in the upper surface of the semiconductor substrate such that the trench penetrates the source region, a gate insulating film formed on an inner wall of the trench, and A gate electrode includes a portion filled in the trench via the trench gate insulating film.

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