JP2016178336A - Semiconductor device manufacturing method - Google Patents

Abstract

A semiconductor device manufacturing method capable of improving a withstand voltage characteristic is provided. A method of manufacturing JBS1 includes a step of preparing a substrate 10 made of silicon carbide having an n-type region so as to include a main surface 10A, and a step of forming a p-type region in a region including the main surface 10A. And forming the oxide film 20 on the main surface 10A from the n-type region to the p-type region by heating the substrate 10 on which the p-type region is formed at a temperature of 1250 ° C. or higher, The method includes a step of removing the oxide film 20 so that at least a part thereof is exposed, and a step of forming the Schottky electrode 50 in contact with the main surface 10A exposed by removing the oxide film 20. [Selection] Figure 7

Description

  The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor device capable of improving the breakdown voltage characteristics.

  A semiconductor device such as a Schottky Barrier Diode (SBD) or a Junction Barrier Schottky Diode (JBS) has a structure in which a Schottky electrode is formed on a substrate. In order to improve the breakdown voltage characteristics of SBD and JBS, it is necessary to ensure a good contact state between the substrate and the Schottky electrode. On the other hand, for example, it has been proposed to form an oxide film in advance on the substrate surface on which the Schottky electrode is to be formed, and to form the Schottky electrode on a clean substrate surface obtained by removing the oxide film (For example, see Patent Document 1).

JP-A-9-246573

  From the viewpoint of further improving the breakdown voltage characteristics of SBD and JBS, a manufacturing method capable of further improving the contact state between the substrate and the Schottky electrode is required.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a method of manufacturing a semiconductor device capable of improving the breakdown voltage characteristics.

  The method for manufacturing a semiconductor device of the present invention includes a step of preparing a substrate made of silicon carbide having a first conductivity type region so as to include one main surface, and a second conductivity type region in the region including the main surface. And forming the oxide film on the main surface from the first conductivity type region to the second conductivity type region by heating the substrate on which the second conductivity type region is formed at a temperature of 1250 ° C. or higher. And a step of removing the oxide film so that at least a part of the main surface is exposed, and a step of forming a Schottky electrode in contact with the main surface exposed by removing the oxide film. ing.

  The present inventor has conducted detailed studies on measures for improving the breakdown voltage characteristics of a semiconductor device, and has obtained the following knowledge and have come to the present invention.

  In the method of manufacturing a semiconductor device, the present inventor, when forming an oxide film by heating a substrate, the oxidation rate is different due to the difference in the formation rate of the oxide film in the first conductivity type region and the second conductivity type region. It has been found that the roughness of the exposed main surface of the substrate or the interface between the substrate and the oxide film is deteriorated by removing the film. Then, the inventor forms the oxide film by heating the substrate at a temperature of 1250 ° C. or higher, thereby reducing the dependency of the formation rate of the oxide film on the conductivity type as described above. The inventors have further found out that it is possible to reduce the above and have arrived at the present invention.

  In the method of manufacturing a semiconductor device according to the present invention, since the substrate is heated at a temperature of 1250 ° C. or higher in the step of forming the oxide film, the dependency of the formation rate of the oxide film on the conductivity type is reduced, and the film thickness is reduced. An oxide film in which variation is suppressed can be formed. Therefore, the surface roughness of the main surface of the exposed substrate is reduced by removing the oxide film, and as a result, a good contact state between the substrate and the Schottky electrode formed on the main surface of the substrate is obtained. be able to. Therefore, according to the method for manufacturing a semiconductor device according to the present invention, it is possible to provide a method for manufacturing a semiconductor device capable of improving the breakdown voltage characteristics by obtaining a good contact state between the substrate and the Schottky electrode. Can do.

  In the manufacturing method of the semiconductor device, in the step of forming the oxide film, the oxide film may be formed on the main surface by heating the substrate at a temperature of 1300 ° C. or higher. Thereby, the variation in the thickness of the oxide film to be formed can be more effectively suppressed.

  In the semiconductor device manufacturing method, in the step of removing the oxide film, the oxide film may be removed so that a part of the main surface is exposed. In the step of forming the Schottky electrode, a Schottky electrode that contacts the main surface exposed by removing the oxide film and the oxide film may be formed.

  In this way, the remaining oxide film can function as an electric field relaxation FP (Field Plate), and as a result, the breakdown voltage characteristics of the semiconductor device can be further improved. Further, after the step of forming the oxide film by heating the substrate is performed, a step of depositing an oxide film on the oxide film may be performed. In the step of removing the oxide film, The oxide film formed by heating the substrate and the oxide film deposited on the oxide film may be removed so that a part of the main surface is exposed. Thereby, a thicker oxide film can be left, and the function of the oxide film as the electric field relaxation FP can be further improved.

  The semiconductor device manufacturing method may further include a step of heating the substrate on which the oxide film is formed in an atmosphere containing nitrogen before the step of removing the oxide film.

  Thereby, the interface state which exists in the area | region containing the interface of an oxide film and the silicon carbide which comprises a board | substrate can be reduced. As a result, the breakdown voltage characteristics of the semiconductor device can be further improved.

  In the semiconductor device manufacturing method, in the step of forming the oxide film, an oxide film having a thickness of 0.1 μm or more may be formed. Thus, the thickness of the oxide film can be set within a practically appropriate range.

  In the semiconductor device manufacturing method, in the step of removing the oxide film, the oxide film may be removed so that the entire main surface is exposed. Thereby, a semiconductor device having no oxide film functioning as the electric field relaxation FP can be easily manufactured.

  In the semiconductor device manufacturing method, in the step of forming the Schottky electrode, a Schottky electrode including at least one selected from the group consisting of Ti, W, Mo, Ni, Ta, Al, and Au may be formed. .

  As described above, various metals that can make Schottky contact with the substrate can be employed as the metal constituting the Schottky electrode.

  As is apparent from the above description, according to the method for manufacturing a semiconductor device according to the present invention, it is possible to provide a method for manufacturing a semiconductor device capable of improving breakdown voltage characteristics.

It is a flowchart which shows the manufacturing method of JBS schematically. It is a schematic sectional drawing for demonstrating the manufacturing method of JBS. It is a schematic sectional drawing for demonstrating the manufacturing method of JBS. It is a schematic sectional drawing for demonstrating the manufacturing method of JBS. It is a schematic sectional drawing for demonstrating the manufacturing method of JBS. It is a schematic sectional drawing for demonstrating the manufacturing method of JBS. It is a schematic sectional drawing for demonstrating the manufacturing method of JBS. It is a schematic sectional drawing for demonstrating the manufacturing method of JBS. FIG. 10 is a schematic cross-sectional view for illustrating the method for manufacturing a JBS according to the second embodiment. 10 is a schematic cross-sectional view for illustrating the method for manufacturing the JBS according to Embodiment 2. FIG. FIG. 10 is a schematic cross-sectional view for illustrating the method for manufacturing a JBS according to the second embodiment. It is a figure which shows the influence of the heating temperature with respect to the average dispersion | variation in the film thickness of an oxide film.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

(Embodiment 1)
First, a method for manufacturing a semiconductor device according to the first embodiment which is an embodiment of the present invention will be described with reference to FIGS. With reference to FIG. 1, a board | substrate preparation process is first implemented as process (S10). In this step (S10), steps (S11) and (S12) described below are performed to prepare substrate 10 made of silicon carbide.

  First, as a step (S11), a base substrate preparation step is performed. In this step (S11), referring to FIG. 2, for example, by slicing an ingot (not shown) made of 4H—SiC, base substrate 11 made of silicon carbide and having an n-type conductivity is prepared.

  Next, as a step (S12), an epitaxial growth layer forming step is performed. In this step (S <b> 12), referring to FIG. 2, first, electric field stop layer 12 having an n conductivity type is formed on main surface 11 </ b> A of base substrate 11 by epitaxial growth. Similarly, an n-type semiconductor layer 13 is formed on the main surface of the electric field stop layer 12 opposite to the base substrate 11 by epitaxial growth. In this way, the substrate 10 having the main surface 10A, which includes the base substrate 11, the electric field stop layer 12, and the semiconductor layer 13, is prepared.

Next, an ion implantation step is performed as a step (S20). In this step (S20), referring to FIG. 3, first, for example, Al (aluminum) ions are implanted into semiconductor layer 13 as indicated by an arrow in the figure, so that p-type conductivity region is p-type. 15 is formed. Next, for example, Al ions are implanted to the outer edge side of the p region 15 in the semiconductor layer 13, thereby forming the guard ring region 16 having a p-type conductivity. Then, for example, P (phosphorus) ions are implanted to the outer edge side of the guard ring region 16 in the semiconductor layer 13, whereby the field stop region 17 having an n-type conductivity is formed. Thus, in the region including main surface 10A of substrate 10, p region 15 and guard ring region 16 as a p-type (second conductivity type) region, and field stop region as an n-type (first conductivity type) region. 17 is formed. From another viewpoint, the p region 15, the guard ring region 16 surrounding the p region 15, and the field stop region 17 surrounding the p region 15 and the guard ring region 16 are regions including the main surface 10 </ b> A of the substrate 10. It is formed. Further, in the semiconductor layer 13, a region where none of the p region 15, the guard ring region 16, and the field stop region 17 is formed becomes the drift region 14 and constitutes an n-type region together with the field stop region 17. In this step (S20), a mask made of, for example, SiO ₂ (silicon dioxide) is formed on the main surface 10A of the substrate 10 and then ion implantation is performed, so that the inside of the semiconductor layer 13 as shown in FIG. Impurity regions can be formed at desired positions.

  Next, an activation annealing step is performed as a step (S30). In this step (S30), for example, by heating the substrate 10 at a temperature of 1700 ° C. for 30 minutes, the impurities introduced in the step (S20) are activated. As a result, desired carriers are generated in the region where the impurity is introduced.

Next, an oxide film forming step is performed as a step (S40). In this step (S40), referring to FIG. 4, oxide film 20 made of, for example, SiO ₂ (silicon dioxide) is formed to cover main surface 10A of substrate 10. Specifically, by heating the substrate 10 at a temperature of 1250 ° C. or higher in an oxygen-containing atmosphere, the drift region 14 as the n-type region and the field stop region 17 to the p region 15 as the p-type region and the guard An oxide film 20 is formed on main surface 10A over ring region 16.

Next, a nitriding step is performed as a step (S50). In this step (S50), for example, the substrate 10 is heated in an atmosphere containing a gas containing nitrogen atoms such as NO (nitrogen monoxide), NO ₂ (nitrogen dioxide), or N ₂ O (nitrous oxide). Nitrogen atoms are introduced into a region including the interface between oxide film 20 and silicon carbide constituting substrate 10. Although this step (S50) is not an essential step in the method for manufacturing a semiconductor device of the present invention, it is present in a region including the interface between oxide film 20 and silicon carbide constituting substrate 10 by carrying out this step. The interface state can be reduced. As a result, the breakdown voltage characteristics of JBS 1 can be further improved. Further, after the introduction of the nitrogen atoms is completed, SiO ₂ (silicon dioxide) may be further deposited on the oxide film 20 by, eg, CVD (Chemical Vapor Deposition). Although this is not essential in the method of manufacturing a semiconductor device of the present invention, a thicker oxide film 20 can be formed by performing this.

  Next, as a step (S60), an ohmic electrode forming step is performed. In this step (S60), referring to FIG. 5, first, a metal film (not shown) made of Ni is formed on main surface 11B opposite to main surface 11A of base substrate 11, for example, by sputtering. The Then, for example, by heating the metal film at 1000 ° C., at least a part of the metal film is silicided. Thus, the ohmic electrode 30 electrically connected to the base substrate 11 is formed.

  Next, a pad electrode forming step is performed as a step (S70). In this step (S70), referring to FIG. 5, pad electrode 40 made of a conductor such as NiAu or TiAu is formed on ohmic electrode 30, for example, by vapor deposition.

Next, as a step (S80), an oxide film removal step is performed. In this step (S80), oxide film 20 is removed so that a part of main surface 10A of substrate 10 is exposed. Specifically, for example, by dry etching such as RIE (Reactive Ion Etching) or wet etching using hydrofluoric acid, the oxide film is exposed so that a part of drift region 14 and p region 15 are exposed as shown in FIG. 20 is removed. As described above, when SiO ₂ (silicon dioxide) is further deposited on oxide film 20 formed by thermal oxidation in step (S40), in this step (S80), main surface 10A of substrate 10 is formed. The oxide film 20 formed by thermal oxidation and SiO ₂ (silicon dioxide) deposited on the oxide film 20 are removed so that a part is exposed.

  Next, as a step (S90), a Schottky electrode forming step is performed. In this step (S90), referring to FIG. 7, the Schottky electrode is brought into contact with main surface 10A of substrate 10 and oxide film 20 exposed by removing oxide film 20 in step (S80). 50 is formed. Specifically, first, a metal film (not shown) made of Ti or TiAl is formed on main surface 10A and oxide film 20 by, for example, sputtering. Then, for example, by heating the metal film at 500 ° C., at least a part of the metal film is silicided and is in contact with the main surface 10A, with the contact portion being sandwiched from one oxide film 20 to the other. A Schottky electrode 50 having a thickness of 0.1 μm or more is formed over the oxide film 20.

  In this step (S90), a Schottky electrode 50 including at least one metal selected from the group consisting of Ti, W, Mo, Ni, Ta, Al, and Au may be formed. A Schottky electrode 50 made of one selected metal may be formed. Further, Schottky electrode 50 made of an alloy of two or more metals selected from the above metal group such as TiW or TiTa may be formed. Further, the Schottky electrode 50 having a structure in which a metal film made of one metal selected from the metal group and a metal film made of another metal are laminated may be formed. Alternatively, Schottky electrode 50 made of a nitride of one metal selected from the above metal group such as TiN may be formed. As described above, various materials that can make Schottky contact with the substrate 10 can be used as the material constituting the Schottky electrode 50.

  Next, as a step (S100), a wiring formation step is performed. In this step (S100), referring to FIG. 8, wiring 60 made of a conductor such as Al is formed so as to surround Schottky electrode 50, for example, by vapor deposition.

Next, as a step (S110), a passivation film forming step is performed. In this step (S110), referring to FIG. 8, a passivation film 70 made of SiO ₂ (silicon dioxide) is formed on oxide film 20 and wiring 60 by, eg, CVD. By performing the above-described steps (S10) to (S110), JBS 1 is manufactured, and the semiconductor device manufacturing method according to the present embodiment is completed.

  As described above, in the method for manufacturing a semiconductor device according to the present embodiment, substrate 10 is heated at a temperature of 1250 ° C. or higher in the step (S40), so that the formation rate of oxide film 20 depends on the conductivity type. It is possible to form the oxide film 20 which is reduced and variation in film thickness is suppressed. Therefore, the surface roughness of the main surface 10A of the substrate 10 exposed by removing the oxide film 20 is reduced, and as a result, the substrate 10 and the Schottky electrode 50 formed on the main surface 10A of the substrate 10 are good. Can be obtained. Therefore, according to the method for manufacturing a semiconductor device according to the present embodiment, it is possible to manufacture JBS 1 with improved breakdown voltage characteristics by obtaining a good contact state between substrate 10 and Schottky electrode 50.

In the method of manufacturing a semiconductor device according to the present embodiment, the oxide film 20 is removed so that a part of the main surface 10A of the substrate 10 is exposed, and the main surface exposed by removing the oxide film 20 is removed. 10A and Schottky electrode 50 in contact with the remaining oxide film 20 are formed. That is, by making the remaining oxide film 20 function as an electric field relaxation FP (Field Plate), it is possible to avoid electric field concentration at both ends of the Schottky electrode 50, and as a result, the breakdown voltage characteristics of the JBS 1 can be further improved. it can. Further, in the method of manufacturing a semiconductor device according to the present embodiment, since the oxide film 20 is formed by heating the substrate 10 at a temperature of 1250 ° C. or higher as described above, the interface between the substrate 10 and the oxide film 20 is formed. Roughness can also be reduced. Thereby, the function of the oxide film 20 as the electric field relaxation FP can be further improved. As described above, SiO ₂ (silicon dioxide) is further deposited on oxide film 20 formed by thermal oxidation in step (S40), and oxide film 20 formed by thermal oxidation in step (S80). When SiO ₂ (silicon dioxide) deposited on oxide film 20 is removed, thicker oxide film 20 can be left, and the function of oxide film 20 as electric field relaxation FP is further improved. be able to.

  In the method for manufacturing a semiconductor device according to the present embodiment, oxide film 20 having a thickness of 0.1 μm or more may be formed in step (S40). Thus, the thickness of the oxide film 20 is preferably set within a practically appropriate range, that is, within a range necessary for avoiding the dielectric breakdown of the oxide film 20.

(Embodiment 2)
Next, a method for manufacturing a semiconductor device according to the second embodiment which is another embodiment of the present invention will be described. The manufacturing method of the semiconductor device according to the present embodiment is basically performed in the same manner as the semiconductor device according to the first embodiment, and has the same effects. However, the semiconductor device manufacturing method according to the present embodiment is different from the semiconductor device according to the first embodiment in that the oxide film is removed so that the entire main surface of the substrate is exposed in the step of removing the oxide film. It is different from the manufacturing method of the device.

  Hereinafter, a method for manufacturing the semiconductor device according to the present embodiment will be described. Referring to FIG. 1, first, steps (S10) to (S70) are performed in the same manner as in the first embodiment. In the present embodiment, the step (S50) is omitted.

  Next, as a step (S80), an oxide film removal step is performed. In this step (S80), referring to FIG. 9, oxide film 20 is removed so that the entire main surface 10A of substrate 10 is exposed.

  Next, as a step (S90), a Schottky electrode forming step is performed. In this step (S90), referring to FIG. 10, Schottky electrode 50 in contact with main surface 10A exposed by removing oxide film 20 in the step (S80) as in the first embodiment is used. Is formed.

  Next, as a step (S100), a wiring formation step is performed. In this step (S100), referring to FIG. 11, wiring 60 is formed so as to surround Schottky electrode 50, as in the first embodiment.

  Next, as a step (S110), a passivation film forming step is performed. In this step (S110), with reference to FIG. 11, passivation film 70 is formed on main surface 10A of substrate 10 and wiring 60. By performing the above steps (S10) to (S110), JBS 2 is manufactured, and the manufacturing method of the semiconductor device according to the present embodiment is completed.

  As described above, in the method for manufacturing a semiconductor device according to the first and second embodiments of the present invention, the substrate 10 is heated at a temperature of 1250 ° C. or higher in the step (S40). The oxide film 20 in which the dependence on the mold is reduced and the variation in film thickness is suppressed can be formed. Therefore, the surface roughness of the main surface 10A of the substrate 10 exposed by removing the oxide film 20 is reduced, and as a result, the substrate 10 and the Schottky electrode 50 formed on the main surface 10A of the substrate 10 are good. Contact can be obtained. Therefore, according to the method for manufacturing a semiconductor device according to the first and second embodiments of the present invention, it is possible to manufacture JBS 1 with improved breakdown voltage characteristics by obtaining good contact between substrate 10 and Schottky electrode 50. it can.

  In the method for manufacturing a semiconductor device according to the first and second embodiments of the present invention, in the step (S40), the substrate 10 is oxidized on the main surface 10A of the substrate 10 by heating at a temperature of 1300 ° C. or higher. A film 20 may be formed. Thereby, the dispersion | variation in the film thickness of the oxide film 20 can be suppressed more effectively. As a result, the contact between the substrate 10 and the Schottky electrode 50 is further improved, and the breakdown voltage characteristics of the JBSs 1 and 2 can be further improved.

  Further, in the manufacturing method of the semiconductor device according to the first and second embodiments of the present invention, only the JBS in which the p region 15 is formed in the region including the main surface 10A in contact with the Schottky electrode 50 has been described. The manufacturing method of the semiconductor device of the invention is not limited to this. In other words, the method for manufacturing a semiconductor device of the present invention can also be adopted in manufacturing an SBD in which the p region 15 is not formed. Thereby, the roughness at the interface between the oxide film 20 and the substrate 10 is reduced, and an SBD having improved characteristics as the electric field relaxation FP of the oxide film 20 can be manufactured.

An experiment was conducted to confirm the effect of the present invention on the variation in the thickness of the oxide film in the semiconductor device manufacturing method. Specifically, first, a substrate having an n-type region having a (nitrogen) concentration of 8 × 10 ¹⁵ cm ⁻³ so as to include one main surface was prepared. Next, a p-type region in which Al ions are implanted at a concentration of 5 × 10 ¹⁷ cm ⁻³ , 5 × 10 ¹⁸ cm ⁻³ and 5 × 10 ¹⁹ cm ⁻³ into a region including the main surface of the substrate. Formed. Next, the substrate was heated at 1200 ° C., 1250 ° C., and 1300 ° C. to form an oxide film on the main surface from the n-type region to the p-type region. Then, the thickness of the oxide film formed at the heating temperature was confirmed, and the influence of the heating temperature on the average variation in the thickness of the oxide film due to the dependency of the formation rate of the oxide film on the conductivity type was investigated.

  The experimental results will be described with reference to FIG. FIG. 12 shows the influence of the heating temperature on the variation in the thickness of the oxide film. In FIG. 12, the horizontal axis represents the substrate heating temperature (° C.), the left vertical axis represents the oxide film thickness (Å), and the right vertical axis represents the average variation (%) in the oxide film thickness. Here, the average variation is a standard deviation (σ) of the thickness of the oxide film.

  As can be seen from FIG. 12, when the substrate was heated at a temperature of 1250 ° C. or higher, the average variation in the thickness of the oxide film was lower than when the substrate was heated at 1200 ° C. Therefore, in the method of manufacturing a semiconductor device of the present invention, the substrate heating temperature in forming the oxide film is set to 1250 ° C. or higher, preferably 1300 ° C. or higher, thereby suppressing variations in the thickness of the formed oxide film. It was confirmed that

  The embodiments and examples disclosed herein are illustrative in all respects and should not be construed as being restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The method for manufacturing a semiconductor device according to the present invention can be particularly advantageously applied to a method for manufacturing a semiconductor device that is required to improve breakdown voltage characteristics.

  1 JBS, 10 substrate, 11 base substrate, 10A, 11A, 11B main surface, 12 electric field stop layer, 13 semiconductor layer, 14 drift region, 15 p region, 16 guard ring region, 17 field stop region, 20 oxide film, 30 Ohmic electrode, 40 pad electrode, 50 Schottky electrode, 60 wiring, 70 passivation film.

Claims (4)

A plurality of p regions having a conductivity type of p type provided on the main surface of a silicon carbide semiconductor layer having a conductivity type of n type and spaced apart, and a p type guard surrounding the plurality of p regions. A ring region, an n-type field stop region surrounding the guard ring region, and a region where none of the plurality of p regions, the guard ring region and the field stop region is provided on the main surface. Providing a substrate having a drift region having an n-type conductivity,
By heating the substrate at a temperature of 1250 ° C. or higher in an oxygen-containing atmosphere, the substrate has a thickness of 0.1 μm or more from the drift region and the field stop region to the plurality of p regions and the guard ring region. And forming an oxide film having an average thickness variation of 2.25% or less from the drift region and the field stop region to the plurality of p regions and the guard ring region;
Removing the oxide film such that the plurality of p regions and the drift region adjacent to the plurality of p regions are exposed;
Forming a Schottky electrode so as to come into contact with the plurality of p regions and the drift region adjacent to the plurality of p regions.
A method of manufacturing a junction barrier Schottky diode.   2. The method of manufacturing a junction barrier Schottky diode according to claim 1, wherein in the step of forming the oxide film, the oxide film is formed on the main surface by heating the substrate at a temperature of 1300 ° C. or higher.   The junction barrier Schottky diode according to claim 1, further comprising a step of heating the substrate on which the oxide film is formed in an atmosphere containing nitrogen before the step of removing the oxide film. Method.   The step of forming the Schottky electrode forms the Schottky electrode containing at least one metal selected from the group consisting of Ti, W, Mo, Ni, Ta, Al, and Au. The manufacturing method of the junction barrier Schottky diode of any one of these.

Images