Semiconductor substrate and method for manufacturing semiconductor substrate

Abstract

To provide a semiconductor substrate that has high channel mobility by reducing interface state density between a silicon carbide substrate and a film on the silicon carbide substrate, and a method of manufacturing the semiconductor substrate.SOLUTION: A semiconductor substrate comprises: a silicon carbide substrate; a first nitride film that is brought into contact with a top surface of the silicon carbide substrate; a second nitride film that is brought into contact with a top surface of the first nitride film; and a silicon oxide film that is brought into contact with a top surface of the second nitride film. Additionally, the first nitride film is a film which is nitrogen-richer than the second nitride film.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to semiconductor substrates and methods for manufacturing the same. [Background technology]

[0002] Patent Document 1 describes a semiconductor device comprising a semiconductor substrate made of silicon carbide and a gate insulating film provided on the surface of the semiconductor substrate, wherein the nitrogen surface density at the interface between the semiconductor substrate and the gate insulating film is 6×10 14 / cm 2 ~1.2×10 15 / cm 2 The present invention discloses a silicon carbide semiconductor device characterized by: [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-149527 Summary of the Invention [Problem to be solved by the invention]

[0004] A high interface state density between a silicon carbide substrate and an upper layer reduces channel mobility, and there is a demand for providing a semiconductor substrate with high channel mobility by reducing the interface state density.

[0005] The present disclosure has been made to solve the above-mentioned problems. An object of the present disclosure is to provide a semiconductor substrate having a reduced interface state density and high channel mobility, and a method for manufacturing the semiconductor substrate. [Means for solving the problem]

[0007] A method for manufacturing a semiconductor substrate according to the present disclosure includes the steps of forming a silicon nitride film on a silicon carbide substrate, forming a silicon film on the silicon nitride film, and oxidizing the silicon film.

[0008] A method for manufacturing a semiconductor substrate according to the present disclosure includes the steps of forming a silicon nitride film on a silicon carbide substrate, oxidizing the silicon nitride film to form silicon oxynitride, and forming a silicon oxide film on the silicon oxynitride. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to provide a semiconductor substrate having a reduced interface state density and high channel mobility, and a method for manufacturing the semiconductor substrate. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view of a semiconductor substrate. [Figure 2] FIG. 10 is a diagram showing an example of an impurity profile. [Figure 3] 1A to 1C are diagrams illustrating a method for manufacturing a semiconductor substrate. [Figure 4] 10A to 10C are diagrams illustrating a method for manufacturing a semiconductor substrate according to another example. DETAILED DESCRIPTION OF THE INVENTION

[0011] The embodiments will be described with reference to the accompanying drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals. Duplicate descriptions of the parts will be appropriately simplified or omitted.

[0012] Embodiment 1 is a cross-sectional view of a semiconductor substrate 10 according to an embodiment. The semiconductor substrate 10 includes a silicon carbide substrate 12.

[0013] According to one example, the silicon carbide substrate 12 is n-type or p-type 4H—SiC. A first nitride film 14 is in contact with the upper surface of the silicon carbide substrate 12. A second nitride film 16 is in contact with the upper surface of the first nitride film 14.

[0014] More specifically, in the case of n-type 4H—SiC, the silicon carbide substrate 12 has a high nitrogen concentration and a low resistivity. +The n-type epitaxial growth layer has a low nitrogen concentration and high resistivity on a wafer. A p-type region and a p-type region are formed on the surface of the n-type epitaxial growth layer by ion implantation or the like. + type area, n + All or part of the mold region may be formed.

[0015] The epitaxial growth layer and the ion implantation region may be switched between n-type and p-type, and the wafer may also be p-type.

[0016] According to one example, first nitride film 14 and second nitride film 16 are silicon oxynitride. According to another example, first nitride film 14 is silicon nitride and second nitride film 16 is silicon oxynitride.

[0017] In either example, the first nitride film 14 can be more nitrogen-rich than the second nitride film 16 .

[0018] In either example, the compound constituting the first nitride film 14 can be made more nitrogen-rich than the stoichiometric composition by, for example, mixing nitrogen atoms or the like between the crystal lattices of the first nitride film 14, or by bonding nitrogen atoms or NH2 to dangling bonds at the interface between the silicon carbide substrate 12 and the first nitride film 14.

[0019] That is, when the first nitride film 14 is silicon oxynitride (SiON), the number of N atoms is greater than the number of Si atoms, and the number of N atoms is greater than the number of O atoms. When the first nitride film 14 is silicon nitride (SiN), the number of N atoms is greater than the number of Si atoms. According to one example, when the first nitride film 14 is silicon nitride, the composition ratio of nitrogen elements to silicon elements (N / Si) can be set to 1.34 or more and 1.45 or less.

[0020] The silicon oxide film 18 is in contact with the upper surface of the second nitride film 16. According to one example, the thickness of the silicon oxide film 18 is greater than the total thickness of the first nitride film 14 and the second nitride film 16.

[0021] According to another example, the thickness of the silicon oxide film 18 is 3 to 50 times the total thickness of the first nitride film 14 and the second nitride film 16 .

[0022] In yet another example, the thickness of the silicon oxide film 18 can be set to 5 to 25 nm or 50 to 250 nm, and the total thickness of the first nitride film 14 and the second nitride film 16 can be set to 1 to 10 nm.

[0023] Any insulating film can be used to replace the silicon oxide film 18. Any insulating film, such as a high-k film, can be formed on the second nitride film 16 so as to obtain a desired equivalent SiO2 thickness.

[0024] Fig. 2 is a diagram showing an example of the concentration of oxygen (O) elements in each layer. In Example 1 in Fig. 2, oxygen elements are present in the first nitride film 14 and the second nitride film 16. No significant incorporation or diffusion of oxygen atoms occurs on the silicon carbide substrate 12 side due to the formation of an oxide film.

[0025] In Example 2 in FIG. 2, oxygen atoms are present in the second nitride film 16, but significant incorporation or diffusion of oxygen atoms due to oxide film formation does not occur on the first nitride film 14 and silicon carbide substrate 12 side.

[0026] In this way, suppressing significant incorporation or diffusion of oxygen into the silicon carbide substrate 12, or suppressing oxidation, maintains the bond between silicon on the top surface (surface) of the silicon carbide substrate 12 and nitrogen or NH at the interface between the silicon carbide substrate 12 and the layer thereon, thereby reducing the interface state density.

[0027] According to another example, the density of O atoms in the silicon carbide substrate 12 is lower than the density of N atoms. Some of the bonds may be bonded with (—NO).

[0028] In the above description, the first nitride film 14 and the second nitride film 16 are described as different films. However, according to one example, the first nitride film 14 and the second nitride film 16 can be made of the same compound. Even in this case, the first nitride film 14 is a film richer in nitrogen than the second nitride film.

[0029] A method for manufacturing a semiconductor substrate will be described with reference to FIG.

[0030] First, as shown in FIG. 3A, a silicon nitride film 20 is formed on a silicon carbide substrate 12.

[0031] The silicon nitride film 20 can be formed by any method, such as plasma CVD, LP (low pressure) CVD, or ALD.

[0032] In plasma CVD, for example, ammonia gas (NH3) is dissociated into reactive ions by plasma energy, and silane gas (SiH4) is dissociated into reactive ions by thermal dissociation or plasma energy, and the dissociated reactive ions react on the silicon carbide substrate 12 to deposit as a silicon nitride film (Si3N4).

[0033] Some reactive ions produce hydrogen (H2) which is exhausted from the reactor. The source gas or reactive ions may be supplied to the reactor and hydrogen may be supplied simultaneously to produce the exhaust stream.

[0034] In LP (low pressure) CVD, for example, silicon nitride film (Si3N4) is produced by thermal dissociation and synthesis reactions while adding nitrogen gas (N2) or hydrogen gas (H2) to dichlorosilane gas (SiH2Cl2) and ammonia gas (NH3).Some of the reaction is discharged from the reactor as hydrochloric acid (HCl) and hydrogen (H2).

[0035] The silicon nitride film 20 can be a nitrogen-rich nitride film. In the step of forming the silicon nitride film 20, the nitrogen atom / silicon atom ratio of the supply gas can be made greater than 1 in order to form a nitrogen-rich nitride film.

[0036] When forming the silicon nitride film 20 by the CVD method, according to one example, first only a gas containing nitrogen atoms is supplied to create a state in which the nitrogen atoms are adsorbed on the surface of the silicon carbide substrate 12, and then a gas containing silicon atoms is also supplied to form the silicon nitride film 20.

[0037] In another example, when forming the silicon nitride film 20 by the CVD method, first hydrogen gas is supplied in addition to a gas containing nitrogen atoms to cause nitrogen atoms and hydrogen atoms to be adsorbed on the surface of the silicon carbide substrate 12, and then a gas containing silicon atoms is also supplied to form the silicon nitride film.

[0038] When forming the silicon nitride film 20 by plasma CVD, for example, first, only a gas containing nitrogen atoms is supplied and turned into plasma, and the plasma is supplied to the surface of the silicon carbide substrate 12 .

[0039] Next, a gas containing silicon atoms is also supplied, and reactive ions dissociated by the plasma are synthesized to form a silicon nitride film 20. The presence of excess reactive ions containing nitrogen atoms causes nitrogen atoms or (-NH2) to bond to dangling bonds on the outermost surface of the semiconductor substrate 10, or nitrogen atoms to become mixed between the lattices of the silicon nitride crystal, resulting in a nitrogen-rich film.

[0040] According to another example, when silicon nitride film 20 is formed by plasma CVD, first, both a gas containing nitrogen atoms and a hydrogen gas are supplied to the surface of silicon carbide substrate 12 in a plasma state.

[0041] Next, a gas containing silicon atoms is also supplied to form a silicon nitride film.

[0042] When forming the silicon nitride film 20 by the LP (low pressure) CVD method, for example, film formation is started by increasing the ratio of the supply amount per unit time of nitrogen atoms contained in a gas containing nitrogen atoms to the supply amount per unit time of silicon atoms contained in a gas containing silicon atoms.

[0043] Thereafter, the amount of nitrogen atoms supplied per unit time is reduced relative to the amount of silicon atoms supplied per unit time, and film formation is continued, whereby the excess nitrogen-containing reactive groups bond with dangling bonds on the surface or mix in between the lattices, thereby making the silicon nitride film 20 nitrogen-rich.

[0044] Forming such a nitrogen-rich nitride film increases the nitrogen surface density on the surface of silicon carbide substrate 12 .

[0045] According to one example, the temperature of the silicon carbide substrate 12 can be set to less than 900°C in the step of forming the silicon nitride film 20. For example, if a plasma CVD method is used, the substrate temperature can be set as low as about 300°C to 400°C.

[0046] In another example, when forming a silicon nitride film 20 by LP (low pressure) CVD, the flow rate ratio of dichlorosilane gas (SiH2Cl2) and ammonia gas (NH3) was fixed, and the temperature of the silicon carbide substrate was set to 700°C to 760°C, and the silicon nitride film 20 was formed.

[0047] Here, the flow rate ratio of dichlorosilane gas to ammonia gas can be fixed at 10.

[0048] By setting the temperature of the silicon carbide substrate to about 700°C to 760°C, a particularly nitrogen-rich film can be formed.

[0049] When the temperature of the silicon carbide substrate was set to 700° C., a silicon nitride film 20 was formed in which the composition ratio of nitrogen element to silicon element (N / Si) was approximately 1.34 to 1.39.

[0050] Furthermore, when the temperature of the silicon carbide substrate was set to 750° C., a silicon nitride film 20 was formed in which the composition ratio of nitrogen element to silicon element (N / Si) was approximately 1.37 to 1.45.

[0051] When the temperature of the silicon carbide substrate was set to 780° C., a silicon nitride film 20 was formed in which the composition ratio of nitrogen element to silicon element (N / Si) was approximately 1.18 to 1.22.

[0052] This process at a temperature of 700° C. to 760° C. can provide the first nitride film 14 having a composition ratio of nitrogen element to silicon element (N / Si) of 1.34 or more and 1.45 or less.

[0053] In addition, when the oxidation rates of silicon nitride films formed at 725°C to 750°C and silicon nitride films formed at 650°C were investigated, it was observed that the oxidation rate of the silicon nitride film formed at 725°C to 750°C was slower.

[0054] The nitrogen to silicon composition ratio (N / Si) of a silicon nitride film formed at 650°C is approximately 1.28 to 1.35, which is smaller than the nitrogen to silicon composition ratio (N / Si) of a silicon nitride film formed at 725°C to 750°C. By depositing a silicon nitride film with a lower composition ratio (N / Si) on a silicon nitride film with a higher composition ratio (N / Si), oxidation can be easily suppressed and / or controlled.

[0055] In another example, when the flow rate ratio of dichlorosilane gas to ammonia was set to 1, the composition ratio of nitrogen element to silicon element (N / Si) was maximized when the temperature of the silicon carbide substrate was 600°C. The composition ratio of nitrogen element to silicon element (N / Si) changed depending on the flow rate ratio and temperature.

[0056] In the present invention, in order to stack a first nitride layer and a second nitride layer having different composition ratios (N / Si), it is preferable to increase the flow rate ratio of dichlorosilane gas to ammonia and adjust the conditions by both the flow rate ratio and the silicon carbide substrate temperature.

[0057] Before forming the silicon nitride film 20 on the surface of the silicon carbide substrate 12, the surface of the silicon carbide substrate 12 may be annealed with ammonia (NH 3 ).

[0058] This allows adsorbed water molecules and oxygen molecules, or oxygen atoms bonded by (-OH) or the like, on the upper surface of the silicon carbide substrate 12 to be removed or replaced with (-NO), (-NH), H, or N bonds. If the temperature of the silicon carbide substrate is high at this time, the surface can be nitrided.

[0059] Next, as shown in FIG. 3B, a silicon film 22 is formed on the silicon nitride film 20.

[0060] The silicon film 22 can be formed by, for example, a sputtering method that does not involve heating the substrate.

[0061] For example, ion beam sputtering or magnetron sputtering can be employed.

[0062] In another example, when forming a silicon film 22 by the CVD method, by switching to supplying only SiH4 or dichlorosilane following the formation of a silicon nitride film, it is possible to form the silicon film 22 continuously in the same reactor.

[0063] 3C, the silicon film 22 is oxidized, resulting in the formation of a silicon oxide film 18. As a result of this oxidation process, all or part of the silicon nitride film 20 becomes silicon oxynitride.

[0064] In the example shown in FIG. 3C, the entire silicon nitride film 20 is made of silicon oxynitride, and the first nitride film 14 and the second nitride film 16 are provided.

[0065] In the example shown in FIG. 3C', a part of the silicon nitride film 20 becomes the second nitride film 16 which is silicon oxynitride, and the remaining part of the silicon nitride film 20 becomes the first nitride film .

[0066] According to one example, the temperature of silicon carbide substrate 12 can be set to a temperature higher than the oxidation start temperature of silicon but lower than the oxidation start temperature of silicon carbide in the step of forming silicon film 22. Such a temperature range is, for example, a temperature range of 800°C or higher and lower than 900°C.

[0067] 4A and 4B are diagrams showing another example of a method for manufacturing a semiconductor substrate. First, as shown in Fig. 4A, a silicon nitride film 20 is formed on a silicon carbide substrate 12. The formation of the silicon nitride film 20 is as described above, and therefore will not be described again.

[0068] 4B, at least a portion of the silicon nitride film 20 is oxidized to form silicon oxynitride, and as a result of this oxidation process, a first nitride film 14 and a second nitride film 16 are provided.

[0069] When the silicon nitride film 20 is entirely oxidized by this oxidation treatment, the first nitride film 14 and the second nitride film 16 are SiON.

[0070] On the other hand, if the silicon nitride film 20 is partially oxidized by this oxidation treatment, the first nitride film 14 will be SiN and the second nitride film 16 will be SiON.

[0071] According to one example, the temperature of the silicon carbide substrate 12 in this step is set to less than 900° C., thereby preventing oxidation of the silicon carbide substrate 12.

[0072] 4C, a silicon oxide film 18 is formed on the second nitride film 16, which is silicon oxynitride. The silicon oxide film 18 can be formed by, for example, a plasma CVD method using nitrogen monoxide (NO) or oxygen (O) and silane (SiH).

[0073] According to one example, the temperature of the silicon carbide substrate 12 can be set to 400° C. or higher and lower than 900° C., and the silicon oxide film 18 can be formed by plasma CVD.

[0074] 3 and 4, the upper surface of silicon carbide substrate 12 is not directly oxidized, and an oxide film is not directly formed on the upper surface. Therefore, bonds such as N, (-NH), and some (-NO) bonded to silicon at the interface between silicon carbide substrate 12 and the film thereon are maintained, and a good interface with a low interface state density is maintained, making it possible to provide a semiconductor substrate with high channel mobility.

[0075] Having described several aspects of at least one embodiment, it should be understood that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the scope of this disclosure.

[0076] It is to be understood that the embodiments of the methods and apparatus described herein are not limited in their application to the details of construction and the arrangement of components set forth in the above description or illustrated in the accompanying drawings, and that the methods and apparatus may be implemented in other embodiments and practiced or carried out in various ways.

[0077] The specific implementation examples are provided here for illustrative purposes only and are not intended to be limiting.

[0078] The phraseology and terminology used in this disclosure are for the purpose of description and should not be regarded as limiting. The use herein of "including," "comprising," "having," "including" and variations thereof means the inclusion of the items listed thereafter and equivalents thereof and additional items.

[0079] References to "or" may be construed as meaning that any term described using "or" refers to one, more than one, and all of the described terms.

[0080] All references to front, back, left, right, top, bottom, top, bottom, width, length, and front and back are intended for convenience of description. Such references do not limit the components of this disclosure to any one positional or spatial orientation. Accordingly, the foregoing description and drawings are by way of example only. [Explanation of symbols]

[0081] 10 semiconductor substrate, 12 silicon carbide substrate, 14 first nitride film, 16 second nitride film, 18 silicon oxide film, 20 silicon nitride film

Claims

1. forming a silicon nitride film on a silicon carbide substrate; forming a silicon film on the silicon nitride film; and a step of oxidizing the silicon film.

2. forming a silicon nitride film on a silicon carbide substrate; a step of oxidizing the silicon nitride film to form silicon oxynitride; and forming a silicon oxide film on the silicon oxynitride.

3. 3. The method for manufacturing a semiconductor substrate according to claim 1, wherein in the step of forming the silicon nitride film, a nitrogen atom / silicon atom ratio contained in the supply gas is greater than 1.

4. The method for manufacturing a semiconductor substrate according to claim 1 , wherein the temperature of the silicon carbide substrate is set to less than 900° C. in the step of forming the silicon nitride film.

5. 4. The method for manufacturing a semiconductor substrate according to claim 1, wherein the temperature of the silicon carbide substrate is set to 300° C. to 400° C. in the step of forming the silicon nitride film.

6. 6. The method for manufacturing a semiconductor substrate according to claim 1, wherein in the step of forming the silicon nitride film, first, only a gas containing nitrogen atoms is supplied to create a state in which nitrogen atoms are adsorbed on the surface of the silicon carbide substrate, and then a gas containing silicon atoms is also supplied to form the silicon nitride film.

7. 6. The method for manufacturing a semiconductor substrate according to claim 1, wherein in the step of forming the silicon nitride film, first, hydrogen gas is supplied in addition to a gas containing nitrogen atoms to create a state in which nitrogen atoms and hydrogen atoms are adsorbed on the surface of the silicon carbide substrate, and then a gas containing silicon atoms is also supplied to form the silicon nitride film.

8. 6. The method for manufacturing a semiconductor substrate according to claim 1, wherein in the step of forming the silicon nitride film, first, a gas containing nitrogen atoms is supplied in a plasma state to the surface of the silicon carbide substrate, and then a gas containing silicon atoms is also supplied to form the silicon nitride film.

9. 6. The method for manufacturing a semiconductor substrate according to claim 1, wherein in the step of forming the silicon nitride film, first, a gas containing nitrogen atoms and a hydrogen gas are both supplied in a plasma state to the surface of the silicon carbide substrate, and then a gas containing silicon atoms is also supplied to form the silicon nitride film.

10. 6. The method for manufacturing a semiconductor substrate according to claim 1, wherein in the step of forming the silicon nitride film, film formation is started by increasing the ratio of the supply amount per unit time of nitrogen atoms contained in a gas containing nitrogen atoms to the supply amount per unit time of silicon atoms contained in a gas containing silicon atoms, and then film formation is continued by decreasing the ratio of the supply amount per unit time of the nitrogen atoms to the supply amount per unit time of the silicon atoms.

11. 2. The method for manufacturing a semiconductor substrate according to claim 1, wherein in the step of oxidizing the silicon film, the temperature of the silicon carbide substrate is set to a temperature higher than an oxidation start temperature of silicon and lower than an oxidation start temperature of silicon carbide.

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