Method for manufacturing silicon carbide semiconductor device

Abstract

To provide a method of manufacturing a silicon carbide semiconductor device capable of suppressing carbon deposition when forming an ohmic electrode.SOLUTION: A method of manufacturing a silicon carbide semiconductor device includes the following steps of: preparing a silicon carbide substrate having a first principal surface; forming a Ni film on the first principal surface, the Ni film having a first portion being at least partially in contact with the first principal surface and a second portion connected with the first portion; forming an Si film on the first portion of the Ni film; performing first heat treatment at a first temperature at which Ni and Si react after forming the Si film; removing the second portion by wet etching after the first heat treatment; and performing second heat treatment at a second temperature higher than the first temperature after removing the second portion.SELECTED DRAWING: Figure 20

Description

[Technical field]

[0001] The present disclosure relates to a method for manufacturing a silicon carbide semiconductor device. [Background technology]

[0002] In the manufacturing process of a silicon carbide semiconductor device, when forming a drain electrode, etc., there is a process in which a Ni (nickel) film is formed on the surface of a silicon carbide substrate and then heat-treated to alloy the Si (silicon) contained in the silicon carbide substrate with the Ni, thereby forming an ohmic electrode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-276978 A [Patent Document 2] JP 2017-175115 A [Patent Document 3] JP 2012-99598 A Summary of the Invention [Problem to be solved by the invention]

[0004] Since silicon carbide substrates contain C (carbon) in addition to Si, when the Si contained in silicon carbide is used for alloying with Ni, unreacted C is generated, and this unreacted C may precipitate on the surface of the alloyed ohmic electrode, etc. Precipitation of C on the surface of the ohmic electrode may lead to a decrease in reliability when a metal wiring layer is formed on the ohmic electrode.

[0005] An object of the present disclosure is to provide a method for manufacturing a silicon carbide semiconductor device that can suppress carbon precipitation during formation of an ohmic electrode. [Means for solving the problem]

[0006] A method for manufacturing a silicon carbide semiconductor device according to the present disclosure includes the steps of preparing a silicon carbide substrate having a first main surface, forming a Ni film on the first main surface, the Ni film having a first portion at least a portion of which is in contact with the first main surface and a second portion connected to the first portion, forming a Si film on the first portion of the Ni film, performing a first heat treatment at a first temperature at which Ni and Si react after the Si film forming step, removing the second portion by wet etching after the first heat treatment, and performing a second heat treatment at a second temperature higher than the first temperature after the second portion removing step. Effect of the Invention

[0007] According to the present disclosure, carbon deposition can be suppressed during the formation of an ohmic electrode. [Brief description of the drawings]

[0008] [Figure 1] 1A to 1C are cross-sectional views (part 1) illustrating a method for manufacturing a silicon carbide semiconductor device according to a reference example. [Diagram 2] 2A to 2C are cross-sectional views (part 2) illustrating a method for manufacturing a silicon carbide semiconductor device according to a reference example. [Diagram 3] 3A to 3C are cross-sectional views (part 3) illustrating a method for manufacturing a silicon carbide semiconductor device according to a reference example. [Figure 4] 4A to 4C are cross-sectional views (part 4) illustrating a method for manufacturing a silicon carbide semiconductor device according to a reference example. [Diagram 5] 5A to 5C are cross-sectional views (part 5) illustrating a method for manufacturing a silicon carbide semiconductor device according to a reference example. [Figure 6] FIG. 6 is a flowchart showing the method for manufacturing the semiconductor device according to the first embodiment. [Figure 7] FIG. 7 is a cross-sectional view (part 1) illustrating the method for manufacturing the semiconductor device according to the first embodiment. [Figure 8] FIG. 8 is a cross-sectional view (part 2) illustrating the method for manufacturing the semiconductor device according to the first embodiment. [Figure 9]FIG. 9 is a cross-sectional view (part 3) illustrating the method for manufacturing the semiconductor device according to the first embodiment. [Figure 10] FIG. 10 is a cross-sectional view (part 4) illustrating the method for manufacturing the semiconductor device according to the first embodiment. [Figure 11] FIG. 11 is a cross-sectional view (part 5) illustrating the method for manufacturing the semiconductor device according to the first embodiment. [Figure 12] FIG. 12 is a cross-sectional view (part 6) illustrating the method for manufacturing the semiconductor device according to the first embodiment. [Figure 13] FIG. 13 is a flowchart showing a method for manufacturing a semiconductor device according to the second embodiment. [Figure 14] FIG. 14 is a cross-sectional view (part 1) showing the method for manufacturing the semiconductor device according to the second embodiment. [Figure 15] FIG. 15 is a cross-sectional view (part 2) showing the method for manufacturing the semiconductor device according to the second embodiment. [Figure 16] FIG. 16 is a cross-sectional view (part 3) showing the method for manufacturing the semiconductor device according to the second embodiment. [Figure 17] FIG. 17 is a cross-sectional view (part 4) illustrating the method for manufacturing the semiconductor device according to the second embodiment. [Figure 18] FIG. 18 is a cross-sectional view (part 5) illustrating the method for manufacturing the semiconductor device according to the second embodiment. [Figure 19] FIG. 19 is a cross-sectional view (part 6) illustrating the method for manufacturing the semiconductor device according to the second embodiment. [Figure 20] FIG. 20 is a cross-sectional view (part 7) illustrating the method for manufacturing the semiconductor device according to the second embodiment. [Figure 21] FIG. 21 is a cross-sectional view (part 8) illustrating the method for manufacturing the semiconductor device according to the second embodiment. [Figure 22] FIG. 22 is a sectional view (part 9) illustrating the method for manufacturing the semiconductor device according to the second embodiment. [Diagram 23] FIG. 23 is a cross-sectional view (part 10) illustrating the method for manufacturing the semiconductor device according to the second embodiment. [Figure 24] FIG. 24 is a cross-sectional view showing an example of a silicon carbide semiconductor device. [Diagram 25] FIG. 25 is a cross-sectional view (part 1) illustrating a method for manufacturing a silicon carbide semiconductor device in accordance with the third embodiment. [Figure 26] FIG. 26 is a cross-sectional view (part 2) illustrating the method for manufacturing the silicon carbide semiconductor device according to the third embodiment. [Figure 27] FIG. 27 is a cross-sectional view (part 3) illustrating the method for manufacturing the silicon carbide semiconductor device in accordance with the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The embodiments for carrying out the invention are described below.

[0010] [Description of the embodiments of the present disclosure] First, the embodiments of the present disclosure will be described. In the following description, the same or corresponding elements are denoted by the same reference numerals, and the same description thereof will not be repeated.

[0011] [1] A method for manufacturing a silicon carbide semiconductor device according to one embodiment of the present disclosure includes the steps of: preparing a silicon carbide substrate having a first main surface; forming a Ni film on the first main surface, the Ni film having a first portion at least a portion of which is in contact with the first main surface and a second portion connected to the first portion; forming a Si film on the first portion of the Ni film; after forming the Si film, performing a first heat treatment at a first temperature at which Ni and Si react with each other; after the first heat treatment, removing the second portion by wet etching; and after removing the second portion, performing a second heat treatment at a second temperature higher than the first temperature.

[0012] In the first heat treatment, most of the Ni in the Ni film is consumed in generating a reaction precursor layer by reacting with Si in the Si film, and the reaction precursor layer contains a small amount of unreacted Ni that has not reacted with Si in the Si film near the first main surface. In the second heat treatment, the small amount of unreacted Ni reacts with Si diffusing from the silicon carbide substrate to form an ohmic electrode. At this time, the amount of Si diffusing from the silicon carbide substrate is small, so that carbon precipitation can be suppressed.

[0013] [2] In the method [1], the first temperature may be equal to or higher than 200° C. and equal to or lower than 400° C. In this case, a reaction precursor layer of nickel silicide is easily formed.

[0014] [3] In the above [1] or [2], the second temperature may be equal to or higher than 800° C. and equal to or lower than 1100° C. In this case, an ohmic electrode can be easily formed from the reaction precursor layer.

[0015] [4] In any one of [1] to [3], the step of forming the Si film may include the steps of forming a first Si film having a third portion on the first portion and a fourth portion on the second portion, and removing the fourth portion by chemical dry etching. In this case, it is easy to control the area where the ohmic electrode is formed.

[0016] [5] In any one of [1] to [4], between the step of preparing the silicon carbide substrate and the step of forming the Ni film, a step of forming an insulating film on the first main surface, and a step of forming a contact hole in the insulating film and exposing the first main surface at a bottom surface of the contact hole may be included, and the first portion may be provided on a bottom surface and a side surface of the contact hole. In this case, an ohmic electrode may be easily formed in the contact hole.

[0017] [6] In [5], the thickness of the Si film at the bottom of the contact hole may be 5 nm or more and 100 nm or less. If the thickness of the Si film is less than 5 nm, even if the local variation in the surface is a few nm, the effect of the local variation cannot be ignored, making it difficult to control the process. Also, if the thickness of the Si film is more than 100 nm, the composition of the reaction precursor layer may not be sufficiently controlled.

[0018] [7] In [5] or [6], the thickness of the Ni film at the bottom of the contact hole may be 5 nm or more and 100 nm or less. If the thickness of the Ni film is less than 5 nm, even if the local variation in the surface is a few nm, the effect of the local variation cannot be ignored, making it difficult to control the process. Also, if the thickness of the Ni film is more than 100 nm, the composition of the reaction precursor layer may not be sufficiently controlled.

[0019] [8] In any one of [1] to [7], in a state where the Si film is formed on the first portion, the number of Si atoms per unit area contained in the Si film and integrated in a thickness direction is defined as N Si The number of Ni atoms per unit area included in the first portion and integrated in the thickness direction is defined as N Ni Then, N Ni ≧N Si The ohmic electrode formed by reacting silicon carbide with nickel has Ni2Si as its main component. Before the reaction, Ni is in excess, and N Ni ≧N Si When the relationship of / 2 is satisfied, it is easy to form an ohmic electrode mainly composed of Ni2Si with good reactivity.

[0020] [Details of the embodiment of the present disclosure] Hereinafter, embodiments of the present disclosure will be described in detail, but the present disclosure is not limited thereto.

[0021] [Reference example] First, a process of forming an ohmic electrode on the surface of a silicon carbide substrate in a method for manufacturing a silicon carbide semiconductor device will be described. When forming an ohmic electrode on the surface of a silicon carbide substrate, a Ni film is formed on the surface of the silicon carbide substrate by sputtering, and then an unnecessary Ni film is removed by wet etching or the like. Then, by heating, Si and Ni contained in the silicon carbide substrate are alloyed to form a nickel silicide film that becomes an ohmic electrode. At this time, Si on the surface of the silicon carbide substrate is taken away for alloying with Ni, and unreacted C precipitates on the surface of the nickel silicide film. Then, when an Al film is formed by sputtering to form a wiring layer, if C precipitates on the surface of the nickel silicide film that becomes an ohmic electrode, the Al film is likely to peel off, which may lead to a decrease in reliability.

[0022] There are various possible measures to address this issue.

[0023] For example, a method is conceivable in which a film containing Ni and Si is formed on the surface of a silicon carbide substrate, and then the film containing Ni and Si is removed from areas other than the desired area, and then heat treatment is performed. In this method, Ni and Si in the film containing Ni and Si are alloyed to form an ohmic electrode, so that when the ohmic electrode is formed, the Si contained in the silicon carbide substrate is hardly taken away. Therefore, it is easy to prevent the precipitation of C.

[0024] However, Ni is difficult to remove by dry etching, and Si is difficult to remove by wet etching. Therefore, a film containing Ni and Si is difficult to remove by either dry etching or wet etching. In addition, a method of forming a film containing Ni and Si in a desired region includes a method of forming the film by lift-off. However, lift-off is not preferable because the peeled film may reattach, which may lead to a decrease in reliability.

[0025] Therefore, in the method of forming a film containing Ni and Si on the surface of a silicon carbide substrate and then performing a heat treatment, it is difficult to remove the film containing Ni and Si from regions other than the desired region, and therefore it is not easy to leave the film containing Ni and Si in the desired region.

[0026] As a method other than the above, a method of forming an ohmic electrode without using a resist, etc. Figures 1 to 5 are cross-sectional views showing a method for manufacturing a silicon carbide semiconductor device according to a reference example.

[0027] 1, an insulating film 20 serving as an interlayer insulating film having a contact hole 21 is formed on a first main surface 10a serving as a surface of a silicon carbide substrate 10, and a TiN film 30 covering the contact hole 21 and the insulating film 20 is formed. Thereafter, the TiN film 30 on the bottom surface 21a of the contact hole 21 is removed to form an opening 30a, and the first main surface 10a of the silicon carbide substrate 10 is exposed.

[0028] 2, Ni film 40 is formed by sputtering. Ni film 40 is formed on first main surface 10a of silicon carbide substrate 10 exposed at bottom surface 21a of contact hole 21 and TiN film 30.

[0029] Next, a heat treatment is performed at a temperature of 500° C. to 700° C. As a result, as shown in Fig. 3, a reaction precursor layer 41 of nickel silicide in which Ni and Si are alloyed is formed at the interface between the silicon carbide substrate 10 and the Ni film 40. The TiN film 30 is formed to prevent Ni from penetrating into the insulating film 20 during this heat treatment.

[0030] 4, the Ni film 40 is removed by wet etching using dilute hydrochloric acid or dilute nitric acid. As a result, a reaction precursor layer 41 remains on the first main surface 10a of the silicon carbide substrate 10 in the opening 30a of the TiN film 30.

[0031] Next, as shown in FIG. 5, the reaction precursor layer 41 is heat-treated at a temperature of about 1000° C. to form an ohmic electrode 41a.

[0032] The ohmic electrode 41a thus formed is extremely thin, having a thickness of only a few nm, and therefore may be removed by reverse sputtering when forming a wiring layer in a subsequent process. Furthermore, with this method, unreacted C precipitates on the surface of the ohmic electrode 41a.

[0033] [First embodiment] (Method for manufacturing silicon carbide semiconductor device) Next, a method for manufacturing the semiconductor device according to the first embodiment will be described. Fig. 6 is a flowchart showing the method for manufacturing the semiconductor device according to the first embodiment. Figs. 7 to 12 are cross-sectional views showing the method for manufacturing the semiconductor device according to the first embodiment.

[0034] 7, a silicon carbide substrate 10 having a first main surface 10a and an opposite second main surface 10b is prepared (step S101), and a Ni film 140 covering the first main surface 10a is formed by sputtering (step S102). The Ni film 140 includes a first portion 141 at least a part of which contacts the first main surface 10a of the silicon carbide substrate 10, and a second portion 142 connected to the first portion 141.

[0035] 8, the Si film 150 is formed on the Ni film 140 by sputtering (step S103). The Si film 150 includes a third portion 153 on the first portion 141 and a fourth portion 154 on the second portion 142.

[0036] Next, as shown in FIG. 9, the fourth portion 154 of the Si film 150 is removed (step S104). Specifically, a resist pattern (not shown) is formed to cover the third portion 153 of the Si film 150, and the fourth portion 154 on which the resist pattern is not formed is removed by chemical dry etching. By removing the fourth portion 154, the second portion 142 of the Ni film 140 is exposed from the third portion 153 of the Si film 150. Thereafter, the resist pattern is removed by an organic solvent or the like. The third portion 153 of the Si film 150 remains on the Ni film 140. The Si film 150 including the third portion 153 and the fourth portion 154 before the removal of the fourth portion 154 is an example of a first Si film.

[0037] Next, a first heat treatment is performed at a temperature of 200° C. or more and 400° C. or less, for example, about 350° C. (step S105). The temperature of the first heat treatment is a temperature at which Ni reacts with Si but Si contained in SiC does not react with Ni. In the first heat treatment, Ni of the first portion 141 of the Ni film 140 reacts with Si of the third portion 153 of the Si film 150, and as shown in FIG. 10, a reaction precursor layer 161 of nickel silicide is formed. At this time, since the fourth portion 154 has been removed from the Si film 150, the second portion 142 of the Ni film 140 does not react with the Si film 150 and remains as it is. In the present disclosure, the temperature of the first heat treatment may be referred to as a first temperature. The first temperature is the temperature of the silicon carbide substrate 10. For example, the first heat treatment is performed using a furnace, and the temperature of the silicon carbide substrate 10 is substantially equal to the temperature in the furnace.

[0038] The reaction between Ni in the Ni film 140 and Si in the Si film 150 progresses from the interface between the Ni film 140 and the Si film 150. The first heat treatment is stopped before all of the Ni in the Ni film 140 reacts with Si. Therefore, the reaction precursor layer 161 contains a small amount of unreacted Ni that has not reacted with Si in the third portion 153 of the Si film 150 near the first main surface 10a.

[0039] 11, the second portion 142 of the Ni film 140 is removed by wet etching (step S106). A reaction precursor layer 161 remains on the first main surface 10a. Unreacted Ni contained in the reaction precursor layer 161 remains in the reaction precursor layer 161 because it is not exposed to the etchant of the wet etching.

[0040] Next, a second heat treatment is performed at a temperature of 800° C. or more and 1100° C. or less, for example, about 1000° C. (step S107). The temperature of the second heat treatment is higher than the first temperature, and is a temperature at which Si contained in SiC reacts with Ni contained in the reaction precursor layer 161. In the second heat treatment, unreacted Ni contained in the reaction precursor layer 161 reacts with Si contained in the silicon carbide substrate 10. As a result, as shown in FIG. 12, an electrode layer 162 in ohmic contact with the first main surface 10a is formed from the reaction precursor layer 161. Si contained in the silicon carbide substrate 10 is diffused into the electrode layer 162, and the electrode layer 162 can function as an ohmic electrode. In the present disclosure, the temperature of the second heat treatment may be referred to as a second temperature. The second temperature is the temperature of the silicon carbide substrate 10. For example, the second heat treatment is performed using a furnace, and the temperature of the silicon carbide substrate 10 is substantially equal to the temperature in the furnace.

[0041] In this embodiment, when the electrode layer 162 is formed, a small amount of unreacted Ni contained in the reaction precursor layer 161 reacts with Si diffusing from the silicon carbide substrate 10. Therefore, the amount of Si diffusing from the silicon carbide substrate 10 is small, and the amount of unreacted C generated is small. Therefore, C is hardly precipitated on the surface of the electrode layer 162. Therefore, even if a wiring layer of Al or the like is formed on the electrode layer 162, peeling of the wiring layer from the electrode layer 162 can be suppressed. The wiring layer may be a film in which TiN and Al are laminated in order.

[0042] In this embodiment, the Si film 150 including the third portion 153 and the fourth portion 154 is formed, and then the fourth portion 154 is removed by chemical dry etching. This makes it easy to control the area in which the electrode layer 162 is formed.

[0043] In addition, the second portion 142 of the Ni film 140 is exposed as the fourth portion 154 is removed. If the fourth portion 154 is removed by reactive ion etching (RIE), Ni may be scattered from the second portion 142 due to ion impact when the second portion 142 is exposed. Since Ni is a magnetic material, if Ni is scattered, the movement of ions may be disturbed and the control of etching may become unstable. In contrast, in this embodiment, the fourth portion 154 of the Si film 150 is removed by chemical dry etching, so that scattering of Ni is suppressed. Even if Ni is scattered, the radicals used in the chemical dry etching are not affected by the magnetism of Ni. Therefore, in this embodiment, etching can be performed stably.

[0044] Since the first temperature is 200° C. or more and 400° C. or less, it is easy to form the nickel silicide reaction precursor layer 161. Since the second temperature is 800° C. or more and 1100° C. or less, it is easy to form the electrode layer 162 that can function as an ohmic electrode from the reaction precursor layer 161.

[0045] Preferably, the number of Si atoms per unit area in the Ni film 140 and the Si film 150 integrated in the thickness direction contained in the Si film 150 is N Si The number of Ni atoms per unit area contained in the Ni film 140 integrated in the thickness direction is N Ni Then, N Ni ≧N Si In this case, Ni is in excess before the reaction, and N Ni ≧N Si Electrode layer 162 mainly composed of NiSi can be easily formed with good reactivity. Note that the thickness direction means the film thickness direction of Ni film 140 and Si film 150, and is the direction perpendicular to the film surfaces of Ni film 140 and Si film 150.

[0046] Second Embodiment Next, a second embodiment will be described. Fig. 13 is a flowchart showing a method for manufacturing a semiconductor device according to the second embodiment. Figs. 14 to 23 are cross-sectional views showing the method for manufacturing a semiconductor device according to the second embodiment.

[0047] 14, a silicon carbide substrate 10 having a first main surface 10a and an opposite second main surface 10b is prepared (step S201), and an insulating film 20 having a thickness of 0.8 μm and serving as an interlayer insulating film is formed on the first main surface 10a of the silicon carbide substrate 10 by a chemical vapor deposition (CVD) method (step S202). The insulating film 20 is, for example, a silicon oxide film.

[0048] Next, as shown in FIG. 15, contact holes 21 are formed in the insulating film 20 (step S203). Specifically, a photoresist is applied to the upper surface 20a of the insulating film 20, and an exposure and development is performed using an exposure device to form a resist pattern (not shown) having an opening in a region where the contact holes 21 are to be formed. Then, the insulating film 20 in a region where the resist pattern is not formed is removed by dry etching such as RIE, and the first main surface 10a of the silicon carbide substrate 10 is exposed to form the contact holes 21. Then, the resist pattern (not shown) is removed by an organic solvent or the like. The contact holes 21 are formed such that the bottom surface 21a becomes the first main surface 10a of the silicon carbide substrate 10 and the side surface 21b becomes the insulating film 20.

[0049] 16, a TiN film 130 is formed by sputtering to cover the bottom surface 21a and side surface 21b of the contact hole 21 and the upper surface 20a of the insulating film 20 (step S204). The thickness t1 of the TiN film 130 is 10 nm or more and 200 nm or less. The thickness t1 of the TiN film 130 is the thickness of the TiN film 130 at the bottom surface 21a of the contact hole 21.

[0050] 17, the TiN film 130 on the bottom surface 21a of the contact hole 21 is removed to form an opening 130a (step S205). As a result, the first main surface 10a of the silicon carbide substrate 10 is exposed from the opening 130a.

[0051] Next, as shown in FIG. 18, a Ni film 140 is formed by sputtering on the exposed first main surface 10a of the silicon carbide substrate 10 and on the TiN film 130 (step S206). The Ni film 140 includes a first portion 141, at least a part of which is in contact with the first main surface 10a of the silicon carbide substrate 10, and a second portion 142 connected to the first portion 141. In this embodiment, the first portion 141 generally covers the bottom surface 21a of the contact hole 21 and covers the side surface 21b via the TiN film 130, and the second portion 142 covers the upper surface 20a of the insulating film 20 via the TiN film 130. The thickness t2 of the Ni film 140 formed is, for example, 5 nm or more and 100 nm or less. The thickness t2 of the Ni film 140 is the thickness of the Ni film 140 at the bottom surface 21a of the contact hole 21. The boundary between the first portion 141 and the second portion 142 does not have to be precise.

[0052] Next, as shown in FIG. 19, the Si film 150 is formed on the Ni film 140 by sputtering (step S207). The Si film 150 includes a third portion 153 on the first portion 141 and a fourth portion 154 on the second portion 142. The thickness t3 of the formed Si film 150 is, for example, 5 nm or more and 100 nm or less. The thickness t3 of the Si film 150 is the thickness of the Si film 150 at the bottom surface 21a of the contact hole 21. In this embodiment, the third portion 153 generally covers the bottom surface 21a and the side surface 21b of the contact hole 21 via the Ni film 140 and the TiN film 130, and the fourth portion 154 covers the upper surface 20a of the insulating film 20 via the Ni film 140 and the TiN film 130. The boundary between the third portion 153 and the fourth portion 154 does not have to be precise.

[0053] 20, the fourth portion 154 of the Si film 150 is removed (step S208). Specifically, a resist pattern (not shown) is formed to cover the third portion 153 of the Si film 150, and the fourth portion 154 on which the resist pattern is not formed is removed by chemical dry etching. By removing the fourth portion 154, the second portion 142 of the Ni film 140 is exposed from the third portion 153 of the Si film 150. Thereafter, the resist pattern is removed by an organic solvent or the like. The third portion 153 of the Si film 150 remains on the Ni film 140.

[0054] Next, a first heat treatment is performed at a temperature of 200° C. to 400° C., for example, about 350° C. (step S209). The temperature of the first heat treatment is a temperature at which Ni reacts with Si but Si contained in SiC does not react with Ni. In the first heat treatment, Ni in the first portion 141 of the Ni film 140 reacts with Si in the third portion 153 of the Si film 150, and a reaction precursor layer 261 of nickel silicide is formed as shown in FIG. 21. At this time, since the fourth portion 154 has been removed from the Si film 150, the second portion 142 of the Ni film 140 does not react with the Si film 150 and remains as it is.

[0055] The reaction between Ni of the Ni film 140 and Si of the Si film 150 progresses from the interface between the Ni film 140 and the Si film 150. The first heat treatment is stopped before all of the Ni of the Ni film 140 reacts with Si. Therefore, the reaction precursor layer 261 contains a small amount of unreacted Ni that has not reacted with Si in the third portion 153 of the Si film 150 near the bottom surface 21a of the contact hole 21.

[0056] 22, the second portion 142 of the Ni film 140 is removed by wet etching (step S210). A reaction precursor layer 261 remains on the bottom surface 21a and the side surface 21b of the contact hole 21. Unreacted Ni contained in the reaction precursor layer 261 remains in the reaction precursor layer 261 because it is not exposed to the etchant of the wet etching.

[0057] Next, a second heat treatment is performed at a temperature of 800° C. to 1100° C., for example, about 1000° C. (step S211). The temperature of the second heat treatment is higher than the first temperature, and is a temperature at which Si contained in SiC reacts with Ni contained in the reaction precursor layer 261. In the second heat treatment, unreacted Ni contained in the reaction precursor layer 261 reacts with Si contained in the silicon carbide substrate 10. As a result, as shown in FIG. 23, an electrode layer 262 including an ohmic region 262a in ohmic contact with the first main surface 10a of the silicon carbide substrate 10 is formed from the reaction precursor layer 261. The ohmic region 262a can function as an ohmic electrode.

[0058] In the ohmic region 262a, Si contained in the silicon carbide substrate 10 is diffused. In this embodiment, when the ohmic region 262a is formed, a small amount of unreacted Ni contained in the reaction precursor layer 261 reacts with Si diffused from the silicon carbide substrate 10. Therefore, the amount of Si diffused from the silicon carbide substrate 10 is small, and the amount of unreacted C generated is small. Therefore, C is hardly precipitated on the surface of the electrode layer 262. Therefore, even if a wiring layer such as Al is formed on the electrode layer 262, peeling of the wiring layer from the electrode layer 262 can be suppressed. The wiring layer may be a film in which TiN and Al are laminated in order.

[0059] Also in this embodiment, the fourth portion 154 of the Si film 150 is removed by chemical dry etching, so that the etching can be performed stably.

[0060] In this embodiment, the first portion 141 of the Ni film 140 is provided on the bottom surface 21a and the side surface 21b of the contact hole 21. This makes it easy to form the electrode layer 262 including the ohmic region 262a in the contact hole 21.

[0061] The thickness of the Si film 150 is preferably 5 nm to 100 nm, more preferably 10 nm to 80 nm. The thickness of the Ni film 140 is preferably 5 nm to 100 nm, more preferably 10 nm to 80 nm. This is to obtain a reaction precursor layer 261 with a stable thickness.

[0062] Preferably, the number of Si atoms per unit area in the bottom surface 21a of the contact hole 21 contained in the Si film 150 in the thickness direction is N Si The number of Ni atoms per unit area contained in the Ni film 140 integrated in the thickness direction is N Ni Then, N Ni ≧N Si In this case, Ni is in excess before the reaction, and N Ni ≧N Si / 2 relationship is established, and the electrode layer 262 containing Ni2Si as a main component can be easily formed with good reactivity.

[0063] (Configuration of Silicon Carbide Semiconductor Device) Next, a description will be given of an example of a silicon carbide semiconductor device manufactured by the method according to the second embodiment. Fig. 24 is a cross-sectional view showing an example of a silicon carbide semiconductor device.

[0064] The silicon carbide semiconductor device 1 is, for example, a vertical MOSFET (metal oxide semiconductor field effect transistor) as shown in FIG. 24. Specifically, the silicon carbide semiconductor device 1 has a silicon carbide substrate 10, an electrode layer 262, a wiring layer 70, a gate insulating film 25, and a gate electrode 71, and the gate electrode 71 is covered with an insulating film 20 that serves as an interlayer insulating film. The silicon carbide substrate 10 has a first n-type layer 11, a second n-type layer 12, a p-type body layer 13, an n-type source region 14, and a p-type region 18. The first n-type layer 11 and the n-type source region 14 are doped with an n-type impurity element at a higher concentration than the second n-type layer 12. The p-type region 18 is doped with an impurity element at a higher concentration than the p-type body layer 13.

[0065] The electrode layer 262 is formed following the first embodiment, and is in ohmic contact with the n-type source region 14 on the first main surface 10a of the silicon carbide substrate 10. The electrode layer 262 has a thickness of, for example, about 100 nm or more and 200 nm or less. A wiring layer 70 is formed on the electrode layer 262 and on the upper surface 20a of the insulating film 20.

[0066] The gate electrode 71 is provided on the first main surface 10a of the silicon carbide substrate 10 via a gate insulating film 25, and faces a channel region 13a on the front surface side of the p-type body layer 13. In addition, a drain electrode 72 is provided on the second main surface 10b of the silicon carbide substrate 10.

[0067] In silicon carbide semiconductor device 1, interconnect layer 70 is unlikely to peel off from electrode layer 262.

[0068] Note that a vertical IGBT (insulated gate bipolar transistor) may be used instead of the vertical MOSFET by forming a p-type collector layer on the side of the silicon carbide substrate 10 facing the drain electrode 72. Also, a structure (trench gate structure) in which a gate electrode is embedded in a trench formed in the silicon carbide substrate 10 via a gate insulating film may be used.

[0069] Third Embodiment Next, a third embodiment will be described. The third embodiment differs from the second embodiment mainly in the ranges of the first portion 141 and the second portion 142 of the Ni film 140 and the ranges of the third portion 153 and the fourth portion 154 of the Si film 150. Figures 25 to 27 are cross-sectional views showing a method for manufacturing a silicon carbide semiconductor device according to the third embodiment.

[0070] In the third embodiment, as shown in FIG. 25, first, similarly to the second embodiment, processing up to the formation of the Si film 150 is performed. In the third embodiment, generally, the first portion 141 covers the bottom surface 21a of the contact hole 21 away from the TiN film 130, and the second portion 142 covers the portion between the first portion 141 of the bottom surface 21a and the TiN film 130, and covers the side surface 21b and the upper surface 20a of the insulating film 20 via the TiN film 130. The third portion 153 is on the first portion 141, and the fourth portion 154 is on the second portion 142. After the Si film 150 is formed, a resist pattern 371 is formed to cover the third portion 153 of the Si film 150.

[0071] Next, similarly to the second embodiment, chemical dry etching is performed on the Si film 150. As a result, as shown in FIG. 26, the fourth portion 154 where the resist pattern 371 is not formed is removed. Thereafter, the resist pattern 371 is removed with an organic solvent or the like. The third portion 153 of the Si film 150 remains on the Ni film 140.

[0072] Next, similarly to the second embodiment, the first heat treatment and the second heat treatment (steps S209 to S211) are performed. As a result, as shown in Fig. 27, an electrode layer 362 in ohmic contact with the first main surface 10a of the silicon carbide substrate 10 is formed inside the opening 130a and away from the TiN film 130. Si contained in the silicon carbide substrate 10 is diffused into the electrode layer 362, and the electrode layer 362 can function as an ohmic electrode.

[0073] The third embodiment also provides the same effects as the second embodiment.

[0074] Although the embodiments have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and changes are possible within the scope of the claims. [Explanation of symbols]

[0075] 1. Silicon carbide semiconductor device 10 Silicon carbide substrate 10a First main surface 10b Second main surface 11 1st n-type layer 12 2nd n-type layer 13 p-type body layer 13a Channel Region 14 n-type source region 18 p-type region 20 Insulating film 20a top surface 21 Contact Hole 21a Bottom 21b Side 25 Gate insulating film 30 TiN film 30a opening 40 Ni film 41 Reaction precursor layer 41a Ohmic electrode 70 wiring layer 71 Gate electrode 72 Drain electrode 130 TiN film 130a opening 140 Ni film 141 Part 1 142 Part 2 150 Si film 153 Part 3 154 Part 4 161 Reaction precursor layer 162 Electrode layer 261 Reaction precursor layer 262 Electrode layer 262a Ohmic region 362 Electrode layer 371 Resist Pattern

Claims

1. providing a silicon carbide substrate having a first main surface; forming a Ni film on the first main surface, the Ni film having a first portion at least a part of which is in contact with the first main surface and a second portion connected to the first portion; forming a Si film on the first portion of the Ni film; a step of performing a first heat treatment at a first temperature at which Ni in the Ni film and Si in the Si film react with each other after the step of forming the Si film, thereby forming a pre-reaction precursor layer; removing the second portion by wet etching after the first heat treatment; performing a second heat treatment at a second temperature higher than the first temperature after the step of removing the second portion; having The pre-reaction precursor layer contains unreacted Ni in the Ni film, In the second heat treatment, unreacted Ni contained in the pre-reaction precursor layer reacts with Si in the silicon carbide substrate.

2. The method for manufacturing a silicon carbide semiconductor device according to claim 1 , wherein the first temperature is not less than 200° C. and not more than 400° C.

3. The method for manufacturing a silicon carbide semiconductor device according to claim 1 , wherein the second temperature is not less than 800° C. and not more than 1100° C.

4. The step of forming the Si film includes: forming a first Si film having a third portion on the first portion and a fourth portion on the second portion; removing the fourth portion by chemical dry etching; The method for manufacturing a silicon carbide semiconductor device according to claim 1 , further comprising the steps of:

5. Between the step of preparing the silicon carbide substrate and the step of forming the Ni film, forming an insulating film on the first main surface; forming a contact hole in the insulating film and exposing the first main surface at a bottom surface of the contact hole; having The method for manufacturing a silicon carbide semiconductor device according to claim 1 , wherein the first portion is provided on a bottom surface and a side surface of the contact hole.

6. 6. The method for manufacturing a silicon carbide semiconductor device according to claim 5, wherein the Si film has a thickness of not less than 5 nm and not more than 100 nm at a bottom surface of the contact hole.

7. 7. The method for manufacturing a silicon carbide semiconductor device according to claim 5, wherein the Ni film has a thickness of not less than 5 nm and not more than 100 nm at a bottom surface of the contact hole.

8. In a state where the Si film is formed on the first portion, the number of Si atoms per unit area contained in the Si film integrated in the thickness direction is defined as N Ｓｉ The number of Ni atoms per unit area included in the first portion and integrated in the thickness direction is N Ｎｉ Then, N Ｎｉ ≧N Ｓｉ 8. The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein a relationship of + / -2 holds.

9. The pre-reaction precursor layer is a first region including unreacted Ni in the Ni film; a second region containing Ni in the Ni film that has reacted with Si in the Si film; having The method for manufacturing a silicon carbide semiconductor device according to claim 1 , wherein the first region is between the silicon carbide substrate and the second region.

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