JP5835309B2 - Method for manufacturing silicon carbide semiconductor device - Google Patents

Description

  The present invention relates to a method for manufacturing a silicon carbide semiconductor device, and more particularly to a method for manufacturing a high breakdown voltage vertical semiconductor device.

  Single crystal silicon carbide (hereinafter referred to as SiC) has a feature that the band gap is wider than that of single crystal silicon (Si) and the electric field strength leading to dielectric breakdown is large. Therefore, by using the SiC substrate, it is possible to manufacture a semiconductor device having a low on-resistance and a high breakdown voltage as compared with the case of using the Si substrate. In particular, in a high voltage semiconductor device, it is expected that a mainstream IGBT (Insulated Gate Bipolar Transistor) is replaced with a SiC-MOSFET (Metal Oxide Semiconductor Field Effect Transistor) with less power loss.

  In addition, metal electrodes are formed on the front surface and the back surface of the semiconductor substrate as a region for extracting current from the semiconductor device. In order to reduce the loss of the applied device, the contact resistance between the metal electrode and the semiconductor substrate becomes a non-negligible factor. Therefore, the junction between the semiconductor substrate and the metal electrode needs to be an ohmic junction having a low contact resistance.

  Therefore, as a widely used method for forming an ohmic junction on the SiC substrate, a nickel film pattern is formed on a portion other than the silicon oxide film on the substrate surface, and after heat treatment at 1000 ° C. or higher, A method of forming a pattern of a second metal film from a nickel film to a silicon oxide film has been proposed (see, for example, Patent Document 1 below).

In the technique of Patent Document 1 described above, in an n-type SiC semiconductor, for example, nickel is used as an electrode material, so that the surface of the n-type SiC region (> 10 ¹⁹ cm ⁻³ ) ion-implanted at a high concentration is 10 ⁻ It is known to show a low contact resistance value of ⁶ Ω · cm ² or less. In other words, it can be said that an n-type SiC semiconductor using nickel as an electrode material is very promising in practical application devices. However, in the technique of Patent Document 1 described above, during the heat treatment, nickel and silicon in the SiC substrate are combined to generate nickel silicide (Ni ₂ Si). Therefore, surplus carbon (C: hereinafter referred to as free carbon) in the SiC substrate forms graphite and is deposited on the inside and the surface of the contact electrode. It is known that the precipitation of graphite causes problems such as an increase in contact resistance and a decrease in adhesion between the SiC substrate and the contact electrode.

  As one of solutions to such a problem, in a semiconductor device using SiC, the material of the ohmic electrode is an alloy of nickel and a metal that easily forms carbide (carbide), and a SiC semiconductor device characterized in that Has been proposed (see, for example, Patent Document 2 below).

  Another method is a method for manufacturing a semiconductor device using a silicon carbide (SiC) substrate, wherein a second metal layer forming step of forming a layer made of a second metal on the surface of the SiC substrate; A first metal layer forming step of forming a layer made of the first metal on the second metal layer, and a heat treatment of heat-treating the SiC substrate on which the second metal layer / the first metal layer is formed at 600 ° C. or more. And the first metal is nickel (Ni) or a nickel alloy, and the second metal is titanium (Ti), tantalum (Ta), or tungsten (W). A method of manufacturing a semiconductor device has been proposed (see, for example, Patent Document 3 below).

Further, as a heat treatment method for forming an ohmic electrode, an ohmic electrode metal is formed on an n-type silicon carbide epitaxial layer formed on a silicon carbide semiconductor substrate, and then 900 ° C. or higher in nitrogen gas (N ₂ ). A method has been proposed in which heat treatment is performed at a temperature of 1000 ° C. or lower to make ohmic contact (see, for example, Patent Document 4 below).

  As another heat treatment method, a method using titanium and aluminum as an electrode material in a p-type SiC semiconductor has been proposed (for example, see Non-Patent Document 1 below).

Further, similarly to the above-described n-type SiC region ion-implanted at a high concentration, a metal electrode using nickel as an electrode material also in a p-type SiC region (> 10 ¹⁹ cm ⁻³ ) ion-implanted at a high concentration. It is known that a good ohmic junction can be formed and a low contact resistance value is exhibited.

JP-A-8-64801 JP 2000-208438 A JP 2006-344688 A Japanese Patent No. 3996282

J. Crofton, 5 others, Titanium and Aluminum Titanium Ohmic Contacts to P Type SIC (TITANIUM AND ALUMINUM-TITANIUM OHMIC CONTACTS TO p-TYPE SiC) Electronics, 1997, Vol. 41, No. 11, p. 1725 to 1729

  However, in an actual semiconductor device, a metal film is partially provided on a SiC substrate. However, in the technique described in Patent Document 2 or 3 described above, a method for forming an electrode pattern in accordance with an actual semiconductor device is used. It is not specified.

  Further, when titanium is used as the metal electrode film, the junction between the n-type SiC substrate and the metal electrode such as titanium is a barrier between the surface of the n-type SiC substrate and the difference between the work function of the metal electrode and the electron affinity of the n-type SiC substrate. Therefore, it becomes a Schottky junction that exhibits a rectifying action. Therefore, as a method of obtaining an ohmic junction in a pseudo manner, there is a method in which a dopant concentration on the surface of the semiconductor substrate is increased so that a current flows by a tunnel effect through the barrier. However, in the case of an n-type SiC substrate, a metal electrode is formed by performing thermal annealing simply by depositing a metal electrode film on a semiconductor substrate due to restrictions in the manufacturing process. Therefore, the junction between the n-type SiC substrate and the metal electrode becomes a Schottky junction, which may be one of the major obstacles in reducing the contact resistance. This is the same even when titanium is used as the metal electrode film in the technique described in Patent Document 4 described above.

  An object of the present invention is to provide a method for manufacturing a silicon carbide semiconductor device having a low contact resistance between a semiconductor substrate and an electrode film in order to solve the above-described problems caused by the conventional technology. Another object of the present invention is to provide a method for manufacturing a silicon carbide semiconductor device in which an electrode film is hardly peeled off from a semiconductor substrate. Another object of the present invention is to provide a more efficient manufacturing process by improving the yield in a method for manufacturing a silicon carbide semiconductor device.

In order to solve the above-described problems and achieve the object, a method for manufacturing a silicon carbide semiconductor device according to the present invention includes a first metal film containing nickel on a surface of a silicon carbide region, and the first metal film. Forming a metal laminated film in which a second metal film containing a metal that easily generates both carbide and nitride is sequentially laminated, and forming an electrode pattern on the metal laminated film by wet etching And a heat treatment step of performing a heat treatment in a nitrogen atmosphere on the silicon carbide region where the metal multilayer film is laminated after the pattern formation step, and the pattern formation step includes A first step of transferring a mask pattern to a resist film coated on the surface of the metal film to form a resist pattern, and the resist on which the resist pattern is formed. Using the resist film as a mask, the second step of removing unnecessary portions of the second metal film, the third step of removing the resist film after the second step, the second step after the third step, And a fourth step of removing unnecessary portions of the first metal film using the metal film as a mask, and the metal forming the second metal film is titanium, zirconium, or tungsten, It is an alloy of two or more types, and the etching chemical used for removing the second metal film in the pattern formation step is ammonia water or hydrogen peroxide water, or a mixed solution of ammonia water and hydrogen peroxide water. In the pattern formation step, the etching chemical used for removing the first metal film is an acid chemical, and in the heat treatment step, the etching chemical was used as a mask in the pattern formation step. A first layer formed by reacting a metal atom in the second metal film with a nitrogen atom in the nitrogen atmosphere on a surface layer of the metal laminated film including the second metal film exposed to the nitrogen atmosphere; Nickel silicide formed by generating a nitride film and reacting nickel atoms in the first metal film with silicon atoms in the silicon carbide region on the surface layer of the metal laminated film on the silicon carbide region side An ohmic junction between the metal laminated film and the silicon carbide region is formed by generating a metal layer containing the metal layer. In order to solve the above-described problems and achieve the object, a method for manufacturing a silicon carbide semiconductor device according to the present invention includes a first metal film containing nickel on the surface of a silicon carbide region, and the first metal. A metal film forming step of forming a metal laminated film in which a second metal film containing a metal that easily generates both carbide and nitride than the film is sequentially laminated; and the silicon carbide in which the metal laminated film is laminated A heat treatment step in which heat treatment is performed on the region in a nitrogen atmosphere, and the metal forming the second metal film is titanium, zirconium, tungsten, or an alloy of two or more of these, In the heat treatment step, a first nitride formed by a reaction between a metal atom in the second metal film and a nitrogen atom in the nitrogen atmosphere on the surface layer of the metal laminated film exposed to the nitrogen atmosphere film And it generates, metal layer including the metal laminate film, a nickel silicide and nickel atoms of the first metal film on the surface layer of the silicon carbide region side and the silicon atoms in the silicon carbide region is reacted By generating, an ohmic junction between the metal laminated film and the silicon carbide region is formed.

The method for manufacturing a silicon carbide semiconductor device according to the present invention is the above-described invention, wherein the electrode pattern is formed by wet etching on the metal laminated film after the metal film forming step and before the heat treatment step. The pattern forming step further includes a first step of forming a resist pattern by transferring a mask pattern to a resist film applied to the surface of the second metal film, and the resist pattern is formed. Using the resist film as a mask, an unnecessary portion of the second metal film is removed using an etching chemical solution made of ammonia water or hydrogen peroxide solution, or a mixture of ammonia water and hydrogen peroxide solution. A step, a third step of removing the resist film after the second step, and a mask of the second metal film after the third step. By using an etching chemical solution consisting of acid chemical solution, characterized in that it comprises a fourth step of removing the unnecessary portion of the first metal film. In the method for manufacturing a silicon carbide semiconductor device according to the present invention, in the above-described invention, in the heat treatment step, the first metal is formed from the surplus carbon atoms precipitated by the formation of the nickel silicide and the second metal film. A carbide film formed by reaction of metal atoms that have penetrated into the film, and a second nitride film formed by reaction of metal atoms that have penetrated into the first metal film and nitrogen atoms in the nitrogen atmosphere. And forming the metal layer in which the carbide film and the second nitride film are mixed and mixed between the microcrystals of the nickel silicide in a network. In the method for manufacturing a silicon carbide semiconductor device according to the present invention, in the above-described invention, the first metal film is formed on a surface of a semiconductor substrate made of n-type silicon carbide, or on a surface of the semiconductor substrate. It is characterized by being laminated on the surface of the concentration n-type region.

  According to the above-described invention, the metal laminated film after the electrode pattern is formed is formed by laminating at least one layer each of a nickel film and a metal film whose main component is a metal that easily forms carbide. Therefore, by performing heat treatment, a contact electrode having a structure in which nickel silicide microcrystals are connected by a carbide (a metal compound generated from a metal that easily forms carbide, the same applies hereinafter) is formed. At this time, carbide is generated from excess carbon (free carbon) in the silicon carbide substrate. Therefore, it is possible to suppress the precipitation of graphite on the inside and the surface of the contact electrode. Thereby, an ohmic junction is formed between the silicon carbide substrate and the contact electrode, and the contact resistance between the silicon carbide substrate and the contact electrode can be kept low. Moreover, since the precipitation of graphite can be suppressed as described above, the adhesion between the silicon carbide substrate and the contact electrode is improved. Further, by using the wet etching method for forming the electrode pattern on the metal laminated film, it is possible to prevent the removed metal laminated film from reattaching to the surface of the silicon carbide substrate. Thereby, the yield of a silicon carbide semiconductor device can be improved. Further, when forming an electrode pattern on the metal multilayer film, the nickel film on the outermost surface layer of the metal multilayer film is etched with an acid chemical solution using the resist film as a mask. Then, the metal film formed in the lower layer of the nickel film is etched with ammonia water or hydrogen peroxide solution, or a mixed solution of ammonia water and hydrogen peroxide solution, using the nickel film remaining in the upper layer as a mask. Further, when a nickel film is formed in the lower layer of the metal film, the nickel film is etched with an acid chemical solution using the metal film left in the upper layer as a mask. At this time, the nickel film is insoluble in ammonia water or hydrogen peroxide solution, or a mixed solution of ammonia water and hydrogen peroxide solution. On the other hand, the metal film is insoluble in the acid chemical solution.

  Further, according to the above-described invention, by performing a thermal annealing process in a nitrogen atmosphere, a network between nickel silicide microcrystals is formed on the surface of the silicon carbide substrate or the surface of the high concentration region of the silicon carbide substrate. A layer connected by a mixed layer of carbide and nitride made of the metal of the second metal film is formed. Thereby, it is possible to prevent the bonding of the silicon carbide substrate and the contact electrode from being a Schottky junction, and to reduce the contact resistance.

  According to the method for manufacturing a silicon carbide semiconductor device of the present invention, there is an effect that the contact resistance between the semiconductor substrate and the electrode film can be lowered. In addition, it is possible to make it difficult to peel the electrode film from the semiconductor substrate. In addition, the yield of the silicon carbide semiconductor device can be improved, and an efficient manufacturing process can be obtained.

FIG. 5 is a cross sectional view showing a process for manufacturing the silicon carbide semiconductor device according to the first embodiment. FIG. 5 is a cross sectional view showing a process for manufacturing the silicon carbide semiconductor device according to the first embodiment. FIG. 5 is a cross sectional view showing a process for manufacturing the silicon carbide semiconductor device according to the first embodiment. FIG. 5 is a cross sectional view showing a process for manufacturing the silicon carbide semiconductor device according to the first embodiment. FIG. 3 is a cross sectional view showing a contact electrode in the process of manufacturing the silicon carbide semiconductor device according to the first embodiment. FIG. 3 is a cross sectional view showing a contact electrode in the process of manufacturing the silicon carbide semiconductor device according to the first embodiment. FIG. 3 is a cross sectional view showing a contact electrode in the process of manufacturing the silicon carbide semiconductor device according to the first embodiment. FIG. 3 is a cross sectional view showing a contact electrode in the process of manufacturing the silicon carbide semiconductor device according to the first embodiment. It is sectional drawing which shows the contact electrode of the silicon carbide semiconductor device concerning this invention. FIG. 6 is a cross sectional view showing a contact electrode in the process of manufacturing the silicon carbide semiconductor device according to the second embodiment. FIG. 6 is a cross sectional view showing a contact electrode in the process of manufacturing the silicon carbide semiconductor device according to the second embodiment. FIG. 6 is a cross sectional view showing a contact electrode in the process of manufacturing the silicon carbide semiconductor device according to the second embodiment. FIG. 9 is a cross sectional view showing a process for manufacturing the silicon carbide semiconductor device according to the third embodiment. FIG. 9 is a cross sectional view showing a process for manufacturing the silicon carbide semiconductor device according to the third embodiment. FIG. 9 is a cross sectional view showing a process for manufacturing the silicon carbide semiconductor device according to the third embodiment. FIG. 7 is a cross sectional view showing a contact electrode of a silicon carbide semiconductor device according to a third embodiment. FIG. 11 is a characteristic diagram showing a current-voltage relationship of the silicon carbide semiconductor device according to the third embodiment. It is a characteristic view which shows the relationship of the electric current-voltage of the silicon carbide semiconductor device concerning a prior art. FIG. 10 is a cross sectional view showing a contact electrode in the process of manufacturing the silicon carbide semiconductor device according to the fourth embodiment. FIG. 10 is a cross sectional view showing a contact electrode in the process of manufacturing the silicon carbide semiconductor device according to the fourth embodiment. FIG. 10 is a cross sectional view showing a contact electrode in the process of manufacturing the silicon carbide semiconductor device according to the fourth embodiment. FIG. 6 is a cross sectional view showing a contact electrode of a silicon carbide semiconductor device according to a fourth embodiment.

  Exemplary embodiments of a method for manufacturing a silicon carbide semiconductor device according to the present invention will be described below in detail with reference to the accompanying drawings. Note that, in the following description of the embodiments and all the attached drawings, the same reference numerals are given to the same components, and duplicate descriptions are omitted.

(Embodiment 1)
1 to 4 are cross-sectional views showing a manufacturing process of the silicon carbide semiconductor device according to the first embodiment. First, the front surface of the n ⁺ type SiC substrate 1 is cleaned by a method such as chemical cleaning or plasma etching. Next, an n ⁻ type SiC epitaxial layer 2 is grown on the front surface of the n ⁺ type SiC substrate 1. Thereafter, a p-type SiC epitaxial layer 3 is continuously grown on the surface of the n ⁻ -type SiC epitaxial layer 2 (FIG. 1). In growing an epitaxial layer on the front surface of the n ⁺ type SiC substrate 1, it is preferable to form the n ⁻ type SiC epitaxial layer 2 and the p type SiC epitaxial layer 3 in succession. The reason is that it is possible to avoid problems such as formation of an oxide film at the interface between the epitaxial layers and contamination of foreign matter. Further, the n ⁻ -type SiC epitaxial layer 2 and the p-type SiC epitaxial layer 3 have a dopant concentration and a film thickness in accordance with electrical characteristics such as breakdown voltage targeted by the semiconductor device.

Next, on the surface of the p-type SiC epitaxial layer 3, a kind of silicon oxide film, for example, tetraethyl silicate (hereinafter referred to as TEOS) is deposited to form a first mask oxide film 4a. Next, dry etching with trifluoromethane (CHF 3) -based gas is performed to open a portion of the first mask oxide film 4 a where the p ⁺ contact region 6 is to be formed, thereby exposing the surface of the p-type SiC epitaxial layer 3 (hereinafter referred to as “the p-type SiC epitaxial layer 3”). First exposed epitaxial layer). Next, a screen oxide film 5 is formed on the exposed portion of the first epitaxial layer, for example, by a thermal oxidation method or the like. The screen oxide film 5 is formed with a thickness of several tens of nm, for example, and protects the exposed portion of the first epitaxial layer. Next, ion implantation is performed on the surface layer of the p-type SiC epitaxial layer 3 from above the screen oxide film 5 to perform an activation process. Thereby, ap ⁺ contact region 6 is formed in the surface layer of p type SiC epitaxial layer 3 (FIG. 2).

Next, wet etching is performed using hydrofluoric acid to remove all the remaining first mask oxide film 4a. Next, TEOS is newly deposited on the surface of the p-type SiC epitaxial layer 3 to form a second mask oxide film 4b. Next, the second mask oxide film 4b in the region that becomes the pn diode is opened to expose the surface of the p-type SiC epitaxial layer 3 (hereinafter referred to as a second epitaxial layer exposed portion). Next, dry etching using sulfur hexafluoride (SF 6) -based gas is performed on the exposed portion of the second epitaxial layer to form a trench reaching the n ⁺ -type SiC substrate 1. At this time, the surface layer of the n ⁺ type SiC substrate 1 is also slightly etched. This trench portion is the element isolation region 7 (FIG. 3).

Next, wet etching is performed using hydrofluoric acid to remove all the remaining second mask oxide film 4b. Next, for example, HTO (High Temperature Oxide), which is a kind of silicon-based oxide film, is applied to the entire surface of the n ⁺ -type SiC substrate 1 (the surface of the p-type SiC epitaxial layer 3, the side walls and the bottom surface of the element isolation region 7). A passivation film 8 is formed by deposition. Next, the passivation film 8 is opened by dry etching using a CHF3-based gas to expose the surface of the p ⁺ contact region 6 (FIG. 4).

Subsequently, a contact electrode is formed on the surface of the p ⁺ contact region 6. 5 to 8 are cross-sectional views showing contact electrodes in the process of manufacturing the silicon carbide semiconductor device according to the first embodiment. First, nickel and titanium are continuously deposited on the surfaces of the n ⁺ type SiC substrate 1 (not shown) and the n ⁻ type SiC epitaxial layer 2, and the first nickel film 9, the second titanium film 10, and the third The nickel films 11 are sequentially laminated. As a result, a three-layer metal laminated film is formed on the surface of the n ⁺ -type SiC substrate 1 (FIG. 5).

Next, a photoresist 12 is applied to the entire surface of the third nickel film 11. Next, photolithography is performed on the photoresist 12 to leave the photoresist 12 only on the p ⁺ contact region 6. Next, using the remaining photoresist 12 as a mask, etching is performed using, for example, an acid-based chemical solution (hereinafter referred to as a first chemical solution) such as a mixed solution of phosphoric acid, nitric acid and acetic acid to form a third nickel film. Unnecessary portions are removed by aligning 11 with a mask (hereinafter referred to as a first metal film removing step). Thereby, as shown in FIG. 6, third nickel film 11 which is the outermost surface layer of n ⁺ type SiC substrate 1 remains only on p ⁺ contact region 6.

Next, all the remaining photoresist (the photoresist 12 in FIG. 6) is dissolved and removed using an organic solvent such as acetone or a stripping solution dedicated to the photoresist. Next, etching is performed using an alkaline chemical solution (hereinafter, referred to as a second chemical solution) such as a mixed solution of ammonia water and hydrogen peroxide solution to remove unnecessary portions of the second titanium film 10 (hereinafter, referred to as “second chemical solution”). A second metal film removing step). At this time, the third nickel film 11 remaining on the upper layer of the second titanium film 10 functions as a mask film, and the second titanium film 10 remains only on the p ⁺ contact region 6 (FIG. 7).

Next, for example, etching is performed using an acid chemical solution (hereinafter, referred to as a third chemical solution) such as a mixed solution of phosphoric acid, nitric acid, and acetic acid to remove unnecessary portions of the first nickel film 9 (hereinafter, referred to as a first chemical solution). 3). At this time, the second titanium film 10 remaining on the upper layer of the first nickel film 9 functions as a mask film, and the first nickel film 9 remains only on the surface of the p ⁺ contact region 6. Further, the remaining third nickel film 11 of the outermost surface layer is also removed by etching with the third chemical solution. As a result, the first nickel film 9 and the second titanium film 10 remain only on the surface of the p ⁺ contact region 6 on the surface of the n ⁺ type SiC substrate 1 (FIG. 8).

Next, the n ⁺ -type SiC substrate 1 is subjected to a heat treatment, for example, at a temperature of 800 to 1000 ° C. in an inert gas atmosphere such as vacuum or argon to form an ohmic junction. FIG. 9 is a cross-sectional view showing a contact electrode of the silicon carbide semiconductor device according to the present invention. By performing the heat treatment, as shown in FIG. 9, a network is formed between the microcrystals of the nickel silicide 13 from the first nickel film 9 and the second titanium film 10 to the surface of the p ⁺ contact region 6. A contact electrode 15 having a structure connected by titanium carbide 14 is formed.

In forming the p ⁺ contact region 6, in order to obtain a contact resistance value of a practical level of 10 ⁴ Ω / sq or less in terms of sheet resistance, the dopant concentration in the p ⁺ contact region 6 should be 10 ¹⁹ cm ⁻³ or more. Is preferred.

Further, when the three-layer metal film is formed on the surface of the n ⁺ -type SiC substrate 1, the film thickness ratio of the first nickel film 9 and the second titanium film 10 in the lowermost layer is 5: 3 to 5: 4. It is preferable to adjust so that. The reason for this is that nickel silicide and titanium carbide can be generated almost in excess and deficiency by thermal annealing treatment after film formation, and precipitation of graphite can be suppressed. This film thickness ratio is calculated from the molar volume ratio when the density of nickel and titanium is assumed to be the reference value described in the science chronology, etc., and is not necessarily limited to this film thickness ratio is not. Further, by making the thickness of the third nickel film 11 thinner than the thickness of the first nickel film 9, complete removal of the third nickel film 11 is facilitated in the third metal film removal step. can do.

  In the first metal film removing step, the second titanium film 10 is formed under the third nickel film 11, so that the first chemical solution is the first lowermost layer of the three metal films. The unexposed portion of the nickel film 9 is not etched. Further, the timing of the end of the process is determined by the etching time calculated from the etching rate and the thickness of the third nickel film 11 by grasping the etching rate of the first chemical solution in advance.

  The reason why the third nickel film 11 functions as a mask film in the second metal film removing step is that the third nickel film 11 is insoluble in the second chemical solution. Further, the timing of the end of the process is determined from the etching rate of the second chemical solution and the thickness of the second titanium film 10 as in the first metal film removal process.

  The reason why the second titanium film 10 functions as a mask film in the third metal film removing step is that the second titanium film 10 is insoluble in the third chemical solution. Further, the timing of the end of the process is determined from the etching rate of the third chemical solution and the thickness of the first nickel film 9 as in the first metal film removal process. As the first nickel film 9 is etched, the passivation film 8, which is the lower layer of the first nickel film 9, is exposed, so that the end timing of the process can also be confirmed visually. At this time, the passivation film 8 hardly dissolves in the acid chemical solution used as the third chemical solution. Further, the third chemical solution may be the same as the first chemical solution as long as it is a chemical solution capable of dissolving both the first nickel film 9 and the third nickel film 11.

In the heat treatment step of the n ⁺ -type SiC substrate 1, the heat treatment is performed in a temperature range that is generally preferable for the heat treatment of the electrode mainly composed of nickel. For details of this temperature range, see, for example, Surface Technology Vol. 55 (2004) No. 1, P29 “Ohmic Contact Formation Technology for Power Devices” and the like.

  In the first embodiment, titanium is used as a metal that easily generates carbide. However, the present invention is not limited to this, and is a metal that easily generates carbide, is soluble in the second chemical solution, and is hexavalent chromium. Any metal that does not generate such harmful by-products may be used. For example, zirconium (Zr) or tungsten may be used. Nickel is used as a metal to be laminated on a metal that is likely to generate carbide. However, it may be a metal that is soluble in the third chemical solution and the first chemical solution and insoluble in the second chemical solution. For example, other metals may be used. Further, although the heat treatment is performed in an argon atmosphere, an inert gas atmosphere other than argon may be used.

As described above, according to the first embodiment, contact electrode 15 made of nickel silicide 13 and titanium carbide 14 is formed on the surface of p ⁺ contact region 6 in the surface layer of n ⁺ type SiC substrate 1. . At this time, the titanium carbide 14 is generated from excess carbon (free carbon) in the n ⁺ -type SiC substrate 1. Therefore, it is possible to suppress the precipitation of graphite on the inside and the surface of the contact electrode 15. Thereby, ohmic contact between the n ⁺ -type SiC substrate 1 and the contact electrode 15 is formed, it is possible to reduce the contact resistance between the n ⁺ -type SiC substrate 1 and the contact electrode 15. Further, as described above, by suppressing the precipitation of graphite, the adhesion between the n ⁺ -type SiC substrate 1 and the contact electrode 15 is improved. This makes it difficult for the n ⁺ -type SiC substrate 1 and the contact electrode 15 to peel off. Further, the first nickel film 9, the second titanium film 10, or the third nickel film 11 that has been removed is reattached to the surface of the n ⁺ -type SiC substrate 1 by using a wet etching method for forming the electrode pattern. Can be prevented. Thereby, the yield of a SiC semiconductor device can be improved. In forming the electrode pattern on the metal film, the third nickel film 11 is etched using the photoresist 12 as a mask, and the second titanium film 10 is etched using the third nickel film 11 as a mask. Further, the first nickel film 9 is etched using the second titanium film 10 as a mask. Therefore, it is not necessary to prepare a new film to be used as a mask for etching, so that the manufacturing process can be made efficient.

(Embodiment 2)
A method for manufacturing the semiconductor device according to the second embodiment will be described. Regarding the description of the second embodiment and the accompanying drawings, the description overlapping with that of the first embodiment is omitted. In the second embodiment, as in the first embodiment, as shown in FIG. 1, to clean the front surface of the n ⁺ -type SiC substrate 1, the front surface of the n ⁺ -type SiC substrate 1 continued The n ⁻ type SiC epitaxial layer 2 and the p type SiC epitaxial layer 3 are continuously grown. Next, as shown in FIG. 2, ion implantation is performed on the surface layer of the p-type SiC epitaxial layer 3, and activation is performed, so that the p ⁺ contact region 6 is formed on the surface layer of the p-type SiC epitaxial layer 3. It is formed. Next, as shown in FIG. 3, an element isolation region 7 is formed in the n ⁺ type SiC substrate 1. Next, a passivation film 8 is formed on the entire surface of the n ⁺ type SiC substrate 1. Next, the passivation film 8 is opened by dry etching to expose the p ⁺ contact region 6 (FIG. 4).

Subsequently, a contact electrode is formed on the surface of the p ⁺ contact region 6. FIGS. 10-12 is sectional drawing which shows the contact electrode of the manufacturing process of the silicon carbide semiconductor device concerning Embodiment 2. FIGS. First, as shown in FIG. 10, titanium and nickel are successively deposited in this order on the surfaces of the n ⁺ type SiC substrate 1 (not shown) and the n ⁻ type SiC epitaxial layer 2, thereby obtaining the second titanium film 10. The first nickel film 16 is sequentially laminated. That is, there is no nickel film (the first nickel film 9 in FIG. 5) formed between the n ⁺ type SiC substrate 1 and the second titanium film 10 in the actual form 1, and the n ⁺ type SiC is present. A two-layer metal laminated film is formed on the surface of the substrate 1.

Next, a photoresist 12 is applied to the entire surface of the n ⁺ type SiC substrate 1. Next, photolithography is performed on the photoresist 12 to leave the photoresist 12 only on the p ⁺ contact region 6. Next, a first metal film removal step is performed. As a result, the first nickel film 16 which is the outermost surface layer of the n ⁺ type SiC substrate 1 remains only on the p ⁺ contact region 6 (FIG. 11).

Next, the remaining photoresist (the photoresist 12 in FIG. 11) is dissolved and removed using an organic solvent such as acetone or a stripping solution dedicated to the photoresist. Next, a second metal film removal step is performed. At this time, the first nickel film 16 remaining in the upper layer of the second titanium film 10 functions as a mask film, and the second titanium film 10 remains only on the surface of the p ⁺ contact region 6 (FIG. 12).

Next, similarly to the first embodiment, the n ⁺ -type SiC substrate 1 is subjected to heat treatment. As shown in FIG. 9, from the second titanium film 10 and the first nickel film 16, a contact electrode made of nickel silicide 13 and titanium carbide 14 is formed on the surface of the p ⁺ contact region 6 as in the first embodiment. 15 is formed.

  In the second metal film removal step, the effect of the first nickel film 16 is the same as the effect of the third nickel film 11 in the first embodiment. The process end timing is also the same as in the first embodiment. Further, since the passivation film 8 which is the lower layer of the second titanium film 10 is exposed as the second titanium film 10 is etched, the timing of the end of the process can be confirmed by visual observation. At this time, the passivation film 8 is soluble in a mixed solution of ammonia water and hydrogen peroxide solution used as the second chemical solution, but its etching rate is slow and can be almost ignored at room temperature.

  As described above, according to the second embodiment, the same effect as in the first embodiment can be obtained.

Further, a contact electrode (hereinafter referred to as a first sample) formed by the technique according to the first embodiment and the second embodiment, and a contact electrode formed using only nickel by the technique according to the conventional technique ( Hereinafter, a tape peeling test was performed on each of the second samples. In the first sample, the contact electrode did not adhere to the tape even after the 10th trial. In the second sample, the contact electrode peeling piece adhered to the tape in the first trial. Thus, it was confirmed that the adhesion was improved in the contact electrode formed by the technique according to the first and second embodiments. Further, contact resistances of the first sample and the second sample were measured. Both the first sample and the second sample had resistance values in the first half of 10 ⁻⁴ Ω · cm ² . As a result, it can be confirmed that the contact electrode formed by the technique according to the first and second embodiments maintains a low contact resistance equivalent to the conventional contact electrode formed using only nickel. It was.

(Embodiment 3)
A method for manufacturing the semiconductor device according to the third embodiment will be described. 13-15 is sectional drawing which shows the manufacturing process of the silicon carbide semiconductor device concerning Embodiment 3. FIGS. Regarding the description of the third embodiment and the attached drawings, the description overlapping with that of the first embodiment is omitted. In the third embodiment, the surface of n ⁺ type SiC substrate 1 is cleaned as in the first embodiment. Next, as shown in FIG. 13, the cleaned n ⁺ type SiC substrate 1 is introduced into, for example, a metal sputtering apparatus, and nickel and titanium are successively deposited on the surface of the n ⁺ type SiC substrate 1 in this order. The first nickel film 9 and the second titanium film 10 are sequentially laminated. As a result, a two-layer metal laminated film is formed on the surface of the n ⁺ -type SiC substrate 1.

  Next, electrode patterns are formed on the first nickel film 9 and the second titanium film 10. As in the first embodiment, a photoresist 12 is applied to the surface of the second titanium film 10. Next, the photoresist 12 is subjected to photolithography, and unnecessary portions of the photoresist 12 are removed to form a desired pattern. Next, unnecessary portions of the second titanium film 10 are removed by wet etching or dry etching using the photoresist 12 as a mask (hereinafter referred to as a fourth metal film removing step) (FIG. 14). Next, as shown in FIG. 15, a third metal film removing step is performed to remove unnecessary portions of the first nickel film 9.

Next, the n ⁺ -type SiC substrate 1 shown in FIG. 15 is introduced into, for example, an annealing furnace, and thermal annealing is performed while flowing high-purity nitrogen gas. FIG. 16 is a cross-sectional view showing a contact electrode of the silicon carbide semiconductor device according to the third embodiment. By performing the thermal annealing treatment, first, the n ⁺ -type SiC substrate 1 and the first nickel film 9 formed on the surface thereof react to generate nickel silicide 17. Further, graphite not shown is deposited. This graphite reacts with titanium that has penetrated into the first nickel film 9 from the second titanium film 10 to produce titanium carbide. At this time, the first nickel film 9 has a structure in which the microcrystals of the nickel silicide 17 are connected with titanium carbide in a network shape. On the other hand, at the initial stage of the heat treatment, titanium in the surface layer of the second titanium film 10 up to a depth of, for example, about 30 nm reacts with nitrogen to produce a titanium nitride (TiN) film 18. In addition, a part of the titanium that has entered the first nickel film 9 also reacts with nitrogen, and a mixed layer 19 of titanium carbide and titanium nitride is generated. Thus, as shown in FIG. 16, on the surface of the n ⁺ -type SiC substrate 1, a layer in which the microcrystals of the nickel silicide 17 are connected in a network by a mixed layer 19 of titanium carbide and titanium nitride, and its surface A contact electrode 20 having a structure in which a titanium nitride film 18 is formed is formed.

The thickness of the first nickel film 9 is preferably at least about 50 nm. The reason is that an ohmic junction can be formed by a thermal annealing treatment after film formation. When the back electrode of the n ⁺ -type SiC substrate 1 is formed, the thickness of the first nickel film 9 is preferably at least about 100 nm. The reason is as follows. When forming the back electrode, a polishing damage layer caused by mechanical polishing with, for example, diamond slurry remains on the back surface of the semiconductor substrate. Therefore, it is preferable to penetrate the first nickel film 9 to a deep part of the polishing damage layer.

  The thickness of the second titanium film 10 is preferably 1.0 to 1.5 times the thickness of the first nickel film 9. This is because, as described above, a sufficient amount of titanium is required to generate titanium carbide and titanium nitride in the thermal annealing process in a nitrogen atmosphere. As in the first embodiment, when thermal annealing is performed in a vacuum or in an inert gas atmosphere such as argon, titanium nitride is not generated. Therefore, the thickness of the second titanium film 10 is the same as that of the first nickel film. The thickness of 9 may be 0.6 to 0.8 times.

In the fourth metal film removing step, when wet etching is performed, it is preferable to use the second chemical solution. By using the second chemical solution, the first nickel film 9 which is the lower layer of the second titanium film 10 is not etched. Moreover, when performing dry etching, it is preferable to use, for example, plasma using a chlorine-based gas as a raw material as an etchant. The etchant is not limited to the above-mentioned etchant, and any etchant that can dissolve the second titanium film 10 and does not dissolve the first nickel film 9 may be used. The effect of performing the third metal film removal step is the same as that of the first embodiment. Further, unnecessary portions of the first nickel film 9 may be removed by dry etching. Further, it is not necessary to form electrode patterns on the first nickel film 9 and the second titanium film 10. Alternatively, a high concentration region may be formed on the surface of the n ⁺ type SiC substrate 1 by ion implantation, for example, and the first nickel film 9 may be formed on the surface of the n type high concentration region.

  The purity of nitrogen introduced in the thermal annealing process may be a purity of about 6N (99.9999%), which is generally used in a semiconductor device manufacturing process. Further, the partial pressure of nitrogen needs to be set higher than when titanium nitride is deposited by reactive sputtering (for example, a partial pressure of about 1 Pa), and is preferably about 100 kPa, for example.

Next, for the silicon carbide semiconductor device according to the third embodiment, a sample for performing measurement based on the transmission line model was produced, and the contact resistance was calculated from the electrical characteristics obtained by the TLM (Transmission Line Matrix) method. FIG. 17 is a characteristic diagram showing a current-voltage relationship of the silicon carbide semiconductor device according to the third embodiment. First, according to the third embodiment, contact electrode 20 was formed on the surface of n ⁺ type SiC substrate 1. A nitrogen-doped n-type bare substrate was used as the n ⁺ -type SiC substrate 1. The surface of the n ⁺ type SiC substrate 1 was finished by mechanical polishing with a 0.5 μm diamond slurry. The thicknesses of the first nickel film 9 and the second titanium film 10 before the thermal annealing treatment were 100 nm and 120 nm, respectively. Electrode patterns were formed on the first nickel film 9 and the second titanium film 10. The gap length between the electrodes was changed every 10 μm from 10 μm to 100 μm. Thermal annealing was performed in a nitrogen atmosphere, and the peak temperature was set to 1000 ° C. The sample thus prepared is taken as a third sample. For comparison, a sample subjected to thermal annealing in vacuum (hereinafter referred to as a fourth sample) was produced. Other conditions were the same as those of the third sample. FIG. 18 shows the current-voltage characteristics of the fourth sample.

As shown in FIG. 17, the third sample showed a linear current-voltage characteristic regardless of the difference in distance between the electrodes, and it was found that no Schottky junction component was included. In the third sample, the contact resistance is 1 × 10 ⁻⁴ Ω · cm ² . On the other hand, in the fourth sample, as shown in FIG. 18, it was found that the Schottky junction component was included in the current-voltage characteristics regardless of the difference in the distance between the electrodes. In the fourth sample, the contact resistance calculated from a range that can be regarded as a substantially straight line is 5 × 10 ⁻³ Ω · cm ² . Thus, it was confirmed that the contact resistance can be reduced by forming the contact electrode according to the third embodiment.

As described above, according to the third embodiment, the same effect as in the first embodiment can be obtained. Further, by performing a thermal annealing treatment in a nitrogen atmosphere, it is possible to prevent the junction between the n ⁺ -type SiC substrate 1 and the contact electrode 20 from being a Schottky junction, and to reduce the contact resistance.

(Embodiment 4)
A method for manufacturing a semiconductor device according to the fourth embodiment will be described. 19 to 21 are cross-sectional views showing contact electrodes in the process of manufacturing the silicon carbide semiconductor device according to the fourth embodiment. Regarding the description of the fourth embodiment and the accompanying drawings, the description overlapping with that of the first embodiment is omitted. In the fourth embodiment, the surface of n ⁺ -type SiC substrate 1 is cleaned as in the first embodiment. Next, as shown in FIG. 19, a p-type region 21 and an n-type region 22 are formed in the surface layer of the front surface of the n ⁺ -type SiC substrate 1 by ion implantation. The p-type region 21 corresponds to a first conductive type first semiconductor region. The n-type region 22 corresponds to a second conductivity type second semiconductor region.

Next, the cleaned n ⁺ -type SiC substrate 1 is introduced into, for example, a metal sputtering apparatus, and titanium and nickel are successively deposited on the front surface of the n ⁺ -type SiC substrate 1 in this order, and the second titanium film 10 and the first nickel film 16 are sequentially laminated. The first nickel film 16 corresponds to a first metal film. The second titanium film 10 corresponds to a second metal film. As a result, a two-layer metal laminated film is formed on the surface of the n ⁺ -type SiC substrate 1.

The film thickness of the second titanium film 10 is preferably 0.6 to 0.8 times the film thickness of the first nickel film 16. The reason is as follows. A reaction satisfying the following formula (1) occurs on the surface of the n ⁺ type SiC substrate 1 by a thermal annealing process to be described later. This is because carbide and silicide can be generated without excess and deficiency, and precipitation of free carbon in the n ⁺ -type SiC substrate 1 can be suppressed.

SiC + 2Ni + Ti → Ni ₂ Si + TiC (1)

The thickness of the first nickel film 16 is preferably 50 nm or more and 200 nm or less. The reason is because it is possible to suppress the n ⁺ -type SiC ohmic junction can be formed to the substrate 1, and n ⁺ -type SiC substrate 1 and the chemical reaction between the first nickel film 16 at a desired depth is there.

  Next, as shown in FIG. 20, the photoresist is subjected to photolithography, and a first resist pattern 31 is formed on the region where the second titanium film 10 is to be left. Next, unnecessary portions of the first nickel film 16 and the second titanium film 10 are removed by performing wet etching or dry etching using the first resist pattern 31 as a mask (hereinafter referred to as fifth metal film). A removal step). Thereby, the first nickel film 16 and the second titanium film 10 remain so as to cover the p-type region 21 and the n-type region 22.

  At this time, when the fifth metal film removal step is performed by wet etching, wet etching is performed using the first resist pattern 31 as a mask to remove unnecessary portions of the first nickel film 16 (for example, the first metal film 16 is removed). Metal film removal step: see FIG. Thereafter, the entire first resist pattern 31 is dissolved and removed. Next, etching may be performed using the first nickel film 16 remaining on the upper layer of the second titanium film 10 as a mask to remove unnecessary portions of the second titanium film 10 (for example, removal of the second metal film). Step: See FIG. The reason is that the first nickel film 16 has high etching resistance (high selectivity) with respect to the alkaline chemical solution. The effect is the same as that of the third embodiment.

  In wet etching, the first nickel film 16 may be removed by using, for example, a first chemical solution (an acid chemical solution such as a mixed solution of phosphoric acid, nitric acid, and acetic acid). Further, for example, a second chemical solution (an alkaline chemical solution such as a mixed solution of ammonia water and hydrogen peroxide solution) may be used to remove the second titanium film 10.

  Next, as shown in FIG. 21, photolithography is performed on the photoresist to form a second resist pattern 32 on the region where the first nickel film 16 is to be left. The second resist pattern 32 may be formed by removing unnecessary portions of the first resist pattern 31. Next, unnecessary portions of the first nickel film 16 are removed by wet etching or dry etching using the second resist pattern 32 as a mask (hereinafter referred to as a sixth metal film removing step). When the sixth metal film removing step is performed by wet etching, for example, a first chemical solution may be used.

Next, the entire second resist pattern 32 is dissolved and removed. Thereafter, although not shown, for example, titanium may be deposited on the back surface of the n ⁺ -type SiC substrate 1 as a material for the back electrode. As a material for the back electrode, for example, nickel may be used. For example, a back electrode in which nickel and titanium are laminated in this order may be formed on the surface of n ⁺ type SiC substrate 1. In that case, the thickness of the titanium film is preferably set to a value obtained by adding 30 to 40 nm to a value obtained by multiplying the thickness of the nickel film by 0.6 to 0.8. The reason is as follows. When the titanium film is the outermost surface layer, in the thermal annealing treatment described later, first, nitrogen introduced into the annealing furnace reacts with titanium having a depth of about 30 to 40 nm from the surface of the titanium film. For this reason, the amount of titanium that reacts with free carbon in the n ⁺ -type SiC substrate 1 is relatively reduced.

Next, the n ⁺ -type SiC substrate 1 shown in FIG. 21 is introduced into, for example, an annealing furnace, and thermal annealing is performed while flowing a high-purity nitrogen gas. The purity and partial pressure of nitrogen introduced in the thermal annealing process may be the same as in the third embodiment. For example, it has been confirmed by the inventor that the nitriding reaction of titanium occurs surely by setting the partial pressure of nitrogen to about 100 kPa.

  FIG. 22 is a cross sectional view showing a contact electrode of the silicon carbide semiconductor device according to the fourth embodiment. By performing the thermal annealing treatment, the following reaction occurs. Since only the second titanium film 10 is formed on the surface of the n-type region 22, the reaction between the second titanium film 10 and nitrogen in the annealing furnace proceeds on the surface of the second titanium film 10. Titanium nitride is produced. On the other hand, the reaction between the second titanium film 10 and the carbon in the n-type region 22 proceeds at the interface between the second titanium film 10 and the n-type region 22, and titanium carbide is generated. Thereby, as shown in FIG. 22, a mixed layer 24 of titanium carbide and titanium nitride is generated as the contact electrode 25.

  On the other hand, since the first nickel film 16 is formed on the second titanium film 10 on the surface of the p-type region 21, the reaction between the second titanium film 10 and nitrogen in the annealing furnace. Does not happen. Further, since the first nickel film 16 that is the outermost surface layer is formed of nickel that does not easily generate nitrides, the first nickel film 16 and nitrogen in the annealing furnace hardly react. On the other hand, at the interface between the second titanium film 10 and the p-type region 21, the reaction between the second titanium film 10 and the carbon in the p-type region 21 proceeds, and titanium carbide is generated. Further, the silicon remaining in the p-type region 21 due to this reaction reacts with the first nickel film 16 to generate nickel silicide. Thereby, as shown in FIG. 22, a mixed layer 23 of titanium carbide and nickel silicide is generated as the contact electrode 25.

  Further, titanium nitride is not generated as a contact electrode on the surface of the p-type region 21. The reason for this is that when titanium and carbon react to change to titanium carbide, the titanium carbide does not change to titanium nitride even if heated in a nitrogen atmosphere. Therefore, the junction between the p-type region 21 and the contact electrode can be avoided from being a Schottky junction, and the contact resistance can be prevented from increasing.

  In the manufacturing method described above, the first nickel film 16 is formed by using nickel as an electrode material. For example, other metals may be used. Further, the second titanium film 10 is formed using titanium as an electrode material. However, any metal that can easily generate both carbide and nitride may be used. Titanium, zirconium, hafnium (Hf), or these Two or more of these alloys may be used.

Next, the number of manufacturing steps of the silicon carbide semiconductor device was verified. The number of manufacturing steps is a single layer electrode film deposition step, a photolithography step, a single layer electrode film etching step, and a thermal annealing treatment step, and the number of steps until the contact electrode is completed is counted. It was. First, according to the manufacturing method described above, a silicon carbide semiconductor device according to the fourth embodiment was manufactured (hereinafter referred to as an example). In the example, the p-type region 21 and the n-type region 22 were formed on the front surface of the n ⁺ -type SiC substrate 1. On the surface of the p-type region 21, a metal laminated film in which titanium and nickel were laminated in this order was formed. The thermal annealing treatment of this metal laminated film was performed in a nitrogen atmosphere. A metal film made of titanium was formed on the surface of the n-type region 22. This metal film was thermally annealed in a nitrogen atmosphere. On the other hand, a metal film made of titanium was formed on the back surface of the n ⁺ type SiC substrate 1. This metal film was thermally annealed in a nitrogen atmosphere.

Next, as a first comparative example, a silicon carbide semiconductor device was fabricated in which the front back electrode on the n ⁺ -type SiC substrate was formed of different electrode materials depending on the conductivity type. In the first comparative example, the p-type region and the n-type region were formed on the front surface of the n ⁺ -type SiC substrate as in the example. A metal laminated film in which titanium and aluminum were laminated in this order was formed on the surface of the p-type region. The thermal annealing treatment of the metal laminated film was performed in a rare gas atmosphere. A metal laminated film in which titanium and nickel were laminated in this order was formed on the surface of the n-type region. The thermal annealing treatment of the metal laminated film was performed in a rare gas atmosphere. On the other hand, a metal film made of titanium was formed on the back surface of the n ⁺ type SiC substrate. This metal film was thermally annealed in a nitrogen atmosphere.

In addition, as a second comparative example, a silicon carbide semiconductor device in which all of the front back electrodes on the n ⁺ type SiC substrate were formed of the same electrode material was manufactured. In the second comparative example, similarly to the example, the p-type region and the n-type region were formed on the front surface of the n ⁺ -type SiC substrate. On the surface of the p-type region, the surface of the n-type region, and the back surface of the n ⁺ -type SiC substrate, metal laminated films in which titanium and nickel were laminated in this order were formed. The thermal annealing treatment of the metal laminated film was performed in a rare gas atmosphere.

  In the above-described example, first comparative example, and second comparative example, the number of manufacturing steps was measured. In the example, the number of manufacturing steps was eight. Further, the junction between the p-type region 21 and the contact electrode and the junction between the n-type region 22 and the contact electrode were ohmic junctions having a low contact resistance.

In contrast, in the first comparative example, the number of manufacturing steps was 14 steps. That is, on the front surface of the n ⁺ -type SiC substrate, a process of laminating a metal film, a process of forming an electrode pattern, and a thermal annealing process must be separately performed on the p-type region and the n-type region, respectively. Because. This is also because the thermal annealing treatment must be performed in an atmosphere different from the thermal annealing treatment performed on the front surface of the back surface electrode of the n ⁺ type SiC substrate.

  In the second comparative example, the number of manufacturing steps was seven. In the second comparative example, the contact resistance increased at any one of the junction between the p-type region and the contact electrode or the junction between the n-type region and the contact electrode. This is because a metal film matching the conductivity type below the contact electrode is not formed. Moreover, it is because the thermal annealing process according to the metal film is not performed.

From the above results, by using the method for manufacturing the silicon carbide semiconductor device according to the fourth embodiment described above, the junction between the n ⁺ -type SiC substrate and the contact electrode can be an ohmic junction having a low contact resistance. I understood. Moreover, it turned out that the number of manufacturing processes can be reduced compared with the past.

As described above, according to the fourth embodiment, the same effect as in the first embodiment can be obtained. Further, the second titanium film 10 and the first nickel film 16 are laminated on the surface of the p-type region 21, and a thermal annealing process is performed in a nitrogen atmosphere, thereby forming a contact electrode formed on the surface of the p-type region 21. Including titanium nitride can be avoided. Therefore, the junction between the p-type region 21 and the contact electrode can be an ohmic junction. Further, by forming only the second titanium film 10 on the surface of the n-type region 22 and performing a thermal annealing process in a nitrogen atmosphere, a contact electrode containing titanium nitride is formed on the surface of the n-type region 22. Can do. Therefore, the junction between the n-type region 22 and the contact electrode can be an ohmic junction. Thereby, even if the p-type region 21 and the n-type region 22 are mixed on the surface of the n ⁺ -type SiC substrate 1, the junction with the contact electrode can be an ohmic junction. In addition, the same electrode material is laminated on regions of different conductivity types on the n ⁺ type SiC substrate, and the same thermal annealing treatment is performed to form an ohmic junction with the contact electrode. Thus, the number of manufacturing steps can be reduced.

  As described above, the present invention is not limited to the above-described embodiment, but can be applied to a silicon carbide semiconductor device formed using a p-type SiC substrate.

  As described above, the method for manufacturing a silicon carbide semiconductor device according to the present invention is useful for a semiconductor device using a silicon carbide substrate, and is particularly suitable for a contact electrode formed by ohmic junction.

2 n ^- type SiC epitaxial layer 3 p-type SiC epitaxial layer 6 p ⁺ contact region 8 passivation film 9 first nickel film 10 second titanium film 11 third nickel film

Claims (5)

A metal formed by sequentially laminating a first metal film containing nickel and a second metal film containing a metal that more easily generates both carbide and nitride than the first metal film on the surface of the silicon carbide region. A metal film forming step for forming a laminated film;
A pattern forming step of forming an electrode pattern on the metal laminated film by wet etching;
After the pattern formation step, a heat treatment step of performing a heat treatment in a nitrogen atmosphere on the silicon carbide region where the metal laminated film is laminated;
Including
The pattern forming step includes
A first step of forming a resist pattern by transferring a mask pattern to a resist film applied to the surface of the second metal film;
A second step of removing unnecessary portions of the second metal film using the resist film on which the resist pattern is formed as a mask;
A third step of removing the resist film after the second step;
After the third step, a fourth step of removing unnecessary portions of the first metal film using the second metal film as a mask,
The metal forming the second metal film is titanium, zirconium or tungsten, or an alloy of two or more of these,
In the pattern forming step, the etching chemical used for removing the second metal film is ammonia water or hydrogen peroxide water, or a mixed liquid of ammonia water and hydrogen peroxide water,
In the pattern forming step, the etching chemical used for removing the first metal film is an acid chemical.
In the heat treatment step, metal atoms in the second metal film are formed on a surface layer of the metal laminated film including the second metal film used as a mask in the pattern forming step on the side exposed to the nitrogen atmosphere. A first nitride film formed by a reaction with nitrogen atoms in the nitrogen atmosphere is generated, and the nickel atoms in the first metal film and the surface layer on the silicon carbide region side of the metal laminated film A silicon carbide semiconductor device characterized in that an ohmic junction is formed between the metal laminated film and the silicon carbide region by generating a metal layer containing nickel silicide formed by a reaction with silicon atoms in the silicon carbide region. Manufacturing method. A metal formed by sequentially laminating a first metal film containing nickel and a second metal film containing a metal that more easily generates both carbide and nitride than the first metal film on the surface of the silicon carbide region. A metal film forming step for forming a laminated film;
A heat treatment step of performing a heat treatment in a nitrogen atmosphere on the silicon carbide region where the metal laminated film is laminated;
Including
The metal forming the second metal film is titanium, zirconium or tungsten, or an alloy of two or more of these,
In the heat treatment step, a first nitridation formed by a reaction between a metal atom in the second metal film and a nitrogen atom in the nitrogen atmosphere on a surface layer of the metal laminated film exposed to the nitrogen atmosphere. A nickel film formed by reacting nickel atoms in the first metal film and silicon atoms in the silicon carbide region on a surface layer of the metal laminated film on the silicon carbide region side of the metal laminated film. A method for manufacturing a silicon carbide semiconductor device, wherein an ohmic junction between the metal laminated film and the silicon carbide region is formed by generating a metal layer including the metal layer. After the metal film forming step, before the heat treatment step, further includes a pattern forming step of forming an electrode pattern by wet etching on the metal laminated film,
The pattern forming step includes
A first step of forming a resist pattern by transferring a mask pattern to a resist film applied to the surface of the second metal film;
Using the resist film on which the resist pattern is formed as a mask, an etching chemical solution made of ammonia water or hydrogen peroxide solution, or a mixed solution of ammonia water and hydrogen peroxide solution is used to form the second metal film. A second step of removing unnecessary portions;
A third step of removing the resist film after the second step;
After the third step, a fourth step of removing an unnecessary portion of the first metal film using an etching chemical solution made of an acid chemical solution with the second metal film as a mask. A method for manufacturing a silicon carbide semiconductor device according to claim 2.   In the heat treatment step, a carbide film formed by a reaction between surplus carbon atoms precipitated by the formation of the nickel silicide and metal atoms entering the first metal film from the second metal film, and the first film A second nitride film formed by a reaction between a metal atom that has penetrated into the first metal film and a nitrogen atom in the nitrogen atmosphere, and the carbide film and 4. The method of manufacturing a silicon carbide semiconductor device according to claim 1, wherein the metal layer connected by a mixed layer formed by mixing the second nitride films is generated. 5.   5. The first metal film is laminated on a surface of a semiconductor substrate made of n-type silicon carbide or a surface of a high concentration n-type region formed on the surface of the semiconductor substrate. The manufacturing method of the silicon carbide semiconductor device as described in any one of these.

Images