JP5499449B2 - Silicon carbide semiconductor device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a silicon carbide semiconductor device and a method for manufacturing the same.

  Conventionally, for example, Patent Documents 1 and 2 propose MOSFETs and J-FETs as silicon carbide semiconductor devices. Among these, in Patent Document 1, an electrode connected to the p-type base region is formed of an Al film through a contact hole of an interlayer insulating film formed on the silicon carbide semiconductor device, and the Al film is formed as a contact hole. A MOSFET structure formed only at a position spaced from the side surface is shown. This prevents the Al film from coming into contact with the gate insulating film and prevents leakage between the gate and the source. Further, the Ni film connected to the n-type source region is formed so as to overlap the Al film. Thereby, the contact resistance with the contact region is reduced.

On the other hand, in Patent Document 2, in a silicon carbide semiconductor substrate in which a p-type region and an n-type region are formed, the p-type region and the n-type region are exposed to the interlayer insulating film formed on the substrate, respectively. A J-FET structure with contact holes is shown. Then, a Ni film as a gate wiring and an alloy film of Ni and Al laminated thereon are formed on the p-type region through each contact hole, and Ni and Al as a source wiring are formed on the n-type region. An alloy layer is formed.
JP 2000-12846 A JP 2005-166724 A

  However, in the above-mentioned Patent Document 1, it is difficult to miniaturize (cell size reduction) due to the necessity of disposing an Al film that becomes a p-type ohmic electrode from the side surface of the contact hole of the interlayer insulating film, and a MOSFET with low on-resistance is obtained. There is a problem that can not be.

  Further, in Patent Document 2, since Al patterning in a miniaturized contact hole is impossible, the formation of an Al film is omitted. That is, a Ni film is formed on the p-type region. As a result, there is a problem that the contact resistance between the Ni film and the p-type region is increased, the switching speed is lowered due to the gate resistance, and the switching loss is increased.

  In view of the above, the present invention can reduce a p-type contact resistance, prevent the switching speed of an element from being lowered, and reduce the on-resistance by miniaturization, and its manufacture It aims to provide a method.

In order to achieve the above object, according to the first aspect of the present invention, the first conductivity type silicon carbide having a lower concentration than the substrate (1) is provided on the substrate (1) made of the first conductivity type silicon carbide. A semiconductor in which a first semiconductor layer (2), a second conductivity type second semiconductor layer (3) made of silicon carbide, and a first conductivity type third semiconductor layer (4, 5) made of silicon carbide are sequentially formed. A substrate (6), a groove (7) formed in the cell portion of the semiconductor substrate (6), passing through the third and second semiconductor layers (3-5) and reaching the first semiconductor layer (2), and a groove A first conductivity type channel layer (8) formed on the inner wall surface of (7), a second conductivity type semiconductor region (9) made of silicon carbide formed on the channel layer (8), and a semiconductor substrate; (6) The interlayer insulating film (11) made of SiO ₂ formed on the second conductive type semiconductor region (9) is exposed. A first contact hole (12) having an interlayer insulating film (11) opened therein and a second contact hole (13) having an interlayer insulating film (11) opened so that the third semiconductor layers (4, 5) are exposed. ), A second conductivity type semiconductor region (9) exposed from the first contact hole (12) in the semiconductor substrate (6), and a third semiconductor layer (4, 5) exposed from the second contact hole (13). Further, an alloy layer (15) made of the same material formed by reaction of silicon carbide, Al, and Ni, respectively, and an alloy layer (15) formed on the second conductivity type semiconductor region (9) The second conductive type semiconductor region (9) is used as a gate layer, and is formed on the gate wiring (16) electrically connected to the gate layer and the third semiconductor layer (4, 5). The third semiconductor layer (4, 5) is formed on the alloy layer (15). As a source layer, a source wiring (17) electrically connected to the source layer, and a drain electrode (19) formed on the back surface of the substrate (1), and Al and Ni in the alloy layer (15) And the elemental composition ratio is 1: 4.6 to 1: 10.6, and the thickness of the alloy layer (15) is 20 nm or more and 100 nm or less.

  According to this, since the element composition ratio of Al and Ni formed by reaction of silicon carbide, Al, and Ni is an alloy layer (15) of 20 nm or more having a ratio of 1: 4.6 to 1: 10.6. The alloy layer (15) can be brought into ohmic contact with the second conductive semiconductor region (9) and the third semiconductor layer (4, 5). Therefore, contact resistance can be reduced. Accordingly, the gate resistance can be reduced, so that the switching speed of the element can be prevented from decreasing.

  Furthermore, since the thickness of the alloy layer (15) is 100 nm or less, it is possible to obtain an element in which the electrical resistance in the first and second contact holes (12, 13) is reduced as much as possible. Therefore, a contact region can be set over the entire surface of the silicon carbide in the first and second contact holes (12, 13) as compared with the conventional case. Therefore, it is possible to realize a low resistance element with a reduced cell size.

According to the second aspect of the present invention, the first conductivity type semiconductor layer (31 made of silicon carbide having a lower concentration than the substrate (30) is formed on the surface side of the substrate (30) made of silicon carbide of the first conductivity type. ) And a second conductivity type base region (32) made of silicon carbide, and a first conductivity type source region formed in a predetermined region of the base region (32). (34), the second conductivity type contact region (35) formed in a predetermined region of the base region (32), the base region (32), and the source region (34) are both penetrated, and the semiconductor layer (31 ), The gate insulating film (40) formed on the inner wall surface of the groove (36), and the gate electrode layer (40) formed inside the gate insulating film (40) in the groove (36). 41) and a source region formed on the gate electrode layer (41) (34) and the contact region and of SiO ₂ interlayer insulating film having a contact hole (43) communicating with (35) (42), the source region exposed from the contact hole (43) in the semiconductor substrate (33) ( 34) and the contact region (35), an alloy layer (44) made of the same material formed by reaction of silicon carbide, Al and Ni, and a source electrode layer (44) formed on the alloy layer (44). 45) and a back electrode layer (47) formed on the back surface of the substrate (30), and the elemental composition ratio of Al and Ni in the alloy layer (44) is 1: 4.6 to 1: 10.6. The thickness of the alloy layer (44) is not less than 20 nm and not more than 100 nm.

  According to this, ohmic contact between the second conductivity type contact region (35) and the first conductivity type source region (34) can be ensured by the same alloy layer (44). Therefore, the contact resistance between the source region (34) and the contact region (35) and the source electrode layer (45) can be reduced. Along with this, it is possible to prevent a decrease in switching speed of the element.

  Moreover, since Al does not react with the gate insulating film (40), the insulation between the gate electrode layer (41) and the source electrode layer (45) can be easily secured. Therefore, the area of the contact hole (43) can be effectively reduced, and a low resistance element with a reduced cell size can be realized. In addition, the effect by the definition of the elemental composition ratio and the thickness of the alloy layer (44) is the same as that of the first aspect.

  The invention according to claim 3 is characterized in that the elemental composition ratio of Al and Ni in the alloy layer is 1: 7.6.

According to this, when the elemental composition ratio of Al and Ni is 1: 7.6, the contact resistivity with respect to the first conductivity type is 2 × 10 ⁻⁴ Ωcm ² or less, and the contact with respect to the second conductivity type. The resistivity is 5 × 10 ⁻³ Ωcm ² or less. For this reason, it is possible to realize a low-resistance element with no deterioration in breakdown voltage.

According to a fourth aspect of the present invention, a first conductive type first semiconductor layer (2) made of silicon carbide having a lower concentration than the substrate (1) is formed on a substrate (1) made of silicon carbide of the first conductive type. A semiconductor substrate (6) in which a second conductivity type second semiconductor layer (3) made of silicon carbide and a first conductivity type third semiconductor layer (4, 5) made of silicon carbide are sequentially formed is prepared. Forming a groove (7) that penetrates the third and second semiconductor layers (3-5) to reach the first semiconductor layer (2) in the cell portion of the semiconductor substrate (6); Forming a first conductivity type channel layer (8) on the inner wall surface, forming a second conductivity type semiconductor region (9) made of silicon carbide on the channel layer (8), and a semiconductor substrate (6) A step of forming an interlayer insulating film (11) made of SiO ₂ and a second conductive type semiconductor region (9) so that the second conductive semiconductor region (9) is exposed; A first contact hole (12) having an opening of an edge film (11) and a second contact hole (13) having an interlayer insulating film (11) opened so that the third semiconductor layers (4, 5) are exposed. Forming the second conductive type semiconductor region (9) and the third semiconductor layer (4, 5) exposed on the interlayer insulating film (11) and exposed from the first and second contact holes (12, 13); On top of that, a Ni film (20) of 10 nm or more and 20 nm or less and an Al film (21) of 2 nm or more and 4 nm or less are laminated in order from the Ni film (20), and heat treatment at 1000 ° C. or less in an oxygen free atmosphere Reacting silicon, Al, and Ni to form an alloy layer (15) in the first and second contact holes (12, 13); and Ni and Al formed on the interlayer insulating film (11) Compound layer (22 Removing the substrate by acid cleaning, and on the alloy layer (15) formed on the second conductive type semiconductor region (9), the second conductive type semiconductor region (9) as a gate layer and the gate layer The electrically connected gate wiring (16) is formed, and the third semiconductor layer (4, 5) is formed on the alloy layer (15) formed on the third semiconductor layer (4, 5). The method includes a step of forming a source wiring (17) electrically connected to the source layer as a source layer, and a step of forming a drain electrode (19) on the back surface of the substrate (1). To do.

  According to this, the second conductive semiconductor region (9) and the third semiconductor layer (4, 4) exposed on the interlayer insulating film (11) and exposed from the first and second contact holes (12, 13). 5) A Ni film (20) of 10 nm or more and 20 nm or less and an Al film (21) of 2 nm or more and 4 nm or less are sequentially laminated on the whole and heat-treated. Therefore, the alloy layer (15) is in ohmic contact with the second conductive semiconductor region (9) and the third semiconductor layer (4, 5) in the first and second contact holes (12, 13). . Therefore, a silicon carbide semiconductor device with reduced contact resistance can be obtained. Along with this, a silicon carbide semiconductor device in which the switching speed of the element is prevented from being reduced can be obtained.

  On the interlayer insulating film (11), the diffusion of Al is suppressed by the underlying Ni, and no reaction layer is formed between the interlayer insulating film (11) and Al. As a result, the excess Ni and Al compound layer (22) on the interlayer insulating film (11) can be removed by acid cleaning.

According to the fifth aspect of the present invention, on the surface side of the substrate (30) made of the first conductivity type silicon carbide, the first conductivity type semiconductor layer (31) made of silicon carbide having a lower concentration than the substrate (30). ) And a second conductive type base region (32) made of silicon carbide, and a first conductive type source in a predetermined region of the base region (32). Forming a region (34) and a second conductivity type contact region (35), and a groove (36) penetrating both the base region (32) and the source region (34) and reaching the semiconductor layer (31) Forming a gate insulating film (40) on the inner wall surface of the trench (36), and forming a gate electrode layer (41) inside the gate insulating film (40) in the trench (36); Interlayer insulating film (42) made of SiO ₂ on the electrode layer (41) Forming a contact hole (43) communicating with the source region (34) and the contact region (35) in the interlayer insulating film (42), and on the interlayer insulating film (42). On the source region (34) and the contact region (35) exposed from the hole (43), an Ni film (20) of 10 nm to 20 nm and an Al film (21) of 2 nm to 4 nm are formed on the Ni film (20). A step of sequentially stacking layers, a step of reacting silicon carbide, Al, and Ni by heat treatment at 1000 ° C. or less in an oxygen-free atmosphere to form an alloy layer (44) in the contact hole (43), an interlayer insulating film A step of removing the Ni and Al compound layer (22) formed on (42) by acid cleaning, and a source electrode layer (45) on the alloy layer (44). A step of forming, characterized in that it contains a step of forming a substrate (30) back electrode layer on the back surface (47).

  According to this, like the above, the alloy layer (44) is in ohmic contact in the source region (34) and the contact region (35) in the contact hole (43). Therefore, the contact resistance can be reduced, and a silicon carbide semiconductor device in which the switching speed of the element is prevented from being reduced can be manufactured.

  In addition, since the reaction layer between the interlayer insulating film (42) and Al is not formed, the insulation between the gate electrode layer (41) and the source electrode layer (45) can be easily secured. That is, an element without gate leakage can be formed.

  Further, since no special patterning is required for the Al film (21), the photo process can be reduced. For this reason, manufacturing cost can also be reduced.

According to the sixth aspect of the present invention, the first conductive type first semiconductor layer (2) made of silicon carbide having a lower concentration than the substrate (1) is formed on the first conductive type silicon carbide substrate (1). A semiconductor substrate (6) in which a second conductivity type second semiconductor layer (3) made of silicon carbide and a first conductivity type third semiconductor layer (4, 5) made of silicon carbide are sequentially formed is prepared. Forming a groove (7) that penetrates the third and second semiconductor layers (3-5) to reach the first semiconductor layer (2) in the cell portion of the semiconductor substrate (6); Forming a first conductivity type channel layer (8) on the inner wall surface, forming a second conductivity type semiconductor region (9) made of silicon carbide on the channel layer (8), and a semiconductor substrate (6) A step of forming an interlayer insulating film (11) made of SiO ₂ and a second conductive type semiconductor region (9) so that the second conductive semiconductor region (9) is exposed; A first contact hole (12) having an opening of an edge film (11) and a second contact hole (13) having an interlayer insulating film (11) opened so that the third semiconductor layers (4, 5) are exposed. Forming the second conductive type semiconductor region (9) and the third semiconductor layer (4, 5) exposed on the interlayer insulating film (11) and exposed from the first and second contact holes (12, 13); On top of this, a Ni film (20) of 20 nm or more and 50 nm or less and an Al film (21) in which the film thickness ratio of the Al film (21) and the Ni film (20) is 1: 3 to 1: 7 are laminated. Forming an alloy layer (15) in the first and second contact holes (12, 13) by reacting silicon carbide with Al and Ni by a heat treatment at 1000 ° C. or less in an oxygen-free atmosphere; Formed on the second conductive type semiconductor region (9). On the layer (15), a gate wiring (16) electrically connected to the gate layer is formed using the second conductivity type semiconductor region (9) as a gate layer, and a third semiconductor layer (4, 5) is formed. Forming a source wiring (17) electrically connected to the source layer on the alloy layer (15) formed on the third semiconductor layer (4, 5) as a source layer; Forming a drain electrode (19) on the back surface of the substrate (1).

  According to this, even if the film thickness of the Ni film (20) and the Al film (21) slightly varies, the film thickness of the alloy layer (15) can be secured. For this reason, the alloy layer (15) can obtain a reliable ohmic contact with respect to the 2nd conductivity type semiconductor region (9) and the 3rd semiconductor layer (4, 5). Therefore, the contact resistance can be reduced, and a silicon carbide semiconductor device in which the switching speed of the element does not decrease can be obtained.

According to the seventh aspect of the present invention, in the step of forming the gate wiring (16) and the source wiring (17), after forming the gate wiring (16) and the source wiring (17), the gate wiring (16) and the source wiring (17) are formed. Using (17) as a mask, a step of removing the compound film (23) made of Ni, Al, and SiO ₂ formed on the interlayer insulating film (11) by dry etching is included.

  Thus, since the compound film (23) on the interlayer insulating film (11) is removed by dry etching using the gate wiring (16) and the source wiring (17) as a mask, no extra patterning is required. The compound film (23) on the interlayer insulating film (11) can be removed. Thereby, a short circuit between the gate and the source can be prevented.

In the invention according to claim 8, in the step of forming the gate wiring (16) and the source wiring (17), Ni, Al, and SiO ₂ formed on the alloy layer (15) and the interlayer insulating film (11). The step of forming a metal film on the compound film (23) by the step, the step of forming a resist on the metal film and patterning, and the metal film and the compound film (23) are continuously formed using the patterned resist as a mask. Then, it is characterized by including a step of forming a gate wiring (16) and a source wiring (17) by removing by dry etching.

  Thus, since the metal film and the compound film (23) are continuously dry-etched, the gate wiring (16) and the source wiring (17) can be formed without extra steps. In addition, the manufacturing cost can be reduced.

According to the ninth aspect of the present invention, the first conductivity type semiconductor layer (31 made of silicon carbide having a lower concentration than the substrate (30) is formed on the surface side of the substrate (30) made of silicon carbide of the first conductivity type. ) And a second conductive type base region (32) made of silicon carbide, and a first conductive type source in a predetermined region of the base region (32). Forming a region (34) and a second conductivity type contact region (35), and a groove (36) penetrating both the base region (32) and the source region (34) and reaching the semiconductor layer (31) Forming a gate insulating film (40) on the inner wall surface of the trench (36), and forming a gate electrode layer (41) inside the gate insulating film (40) in the trench (36); Interlayer insulating film (42) made of SiO ₂ on the electrode layer (41) Forming a contact hole (43) communicating with the source region (34) and the contact region (35) in the interlayer insulating film (42), and on the interlayer insulating film (42). On the source region (34) and contact region (35) exposed from the hole (43), the film thickness ratio of the Ni film (20) of 20 nm to 50 nm, the Al film (21), and the Ni film (20) In a contact hole (43) by reacting silicon carbide, Al and Ni by a step of laminating an Al film (21) having a ratio of 1: 3 to 1: 7 and a heat treatment at 1000 ° C. or less in an oxygen-free atmosphere. Forming an alloy layer (46) on the substrate, forming a source electrode layer (45) on the alloy layer (46), and forming a back electrode layer (47) on the back surface of the substrate (30). Including And said that you are.

  Thus, the same effect as in the fifth aspect can be obtained for the MOSFET.

In a tenth aspect of the present invention, a first conductive type semiconductor layer (31 made of silicon carbide having a lower concentration than the substrate (30) is formed on the surface side of the substrate (30) made of silicon carbide of the first conductive type. ) And a second conductive type base region (32) made of silicon carbide, and a first conductive type source in a predetermined region of the base region (32). Forming a region (34) and a second conductivity type contact region (35), and a groove (36) penetrating both the base region (32) and the source region (34) and reaching the semiconductor layer (31) Forming a gate insulating film (40) on the inner wall surface of the trench (36), and forming a gate electrode layer (41) inside the gate insulating film (40) in the trench (36); On the electrode layer (41), an interlayer insulating film made of SiO ₂ (42 ) In the interlayer insulating film (42), a contact hole (43) communicating with the source region (34) and the contact region (35), and a gate contact hole (48 communicating with the gate electrode layer (41)). And a gate exposed on the interlayer insulating film (42), on the source region (34) and the contact region (35) exposed from the contact hole (43), and on the gate contact hole (48). On the electrode layer (41), an Ni film (20) having a thickness of 20 nm or more and 50 nm or less, and an Al film having a thickness ratio of the Al film (21) to the Ni film (20) of 1: 3 to 1: 7 ( 21) and a heat treatment at 1000 ° C. or less in an oxygen-free atmosphere to cause silicon carbide, Al, and Ni to react with each other in the contact hole (43) and the gate contact. A step of forming an alloy layer (46) in the cut hole (48), a gate wiring (49) on the alloy layer (46) formed on the gate electrode layer (45), and a source region ( 34) and a step of forming a source electrode layer (45) on the alloy layer (46) formed on the contact region (35), and a back electrode layer (47) on the back surface of the substrate (30). And a process.

  Thereby, similarly to the sixth aspect, even if the film thickness of the Ni film (20) and the Al film (21) is somewhat varied, the film thickness of the alloy layer (46) can be ensured. For this reason, the alloy layer (46) can obtain a reliable ohmic contact with the source region (34), the contact region (35), and the gate electrode layer (45), and can reduce the contact resistance. .

In the invention according to claim 11, in the step of forming the gate wiring (49) and the source electrode layer (45), after forming the gate wiring (49) and the source electrode layer (45), the gate wiring (49) and Using the source electrode layer (45) as a mask, a step of removing the compound film made of Ni, Al, and SiO ₂ formed on the interlayer insulating film (42) by dry etching is included.

  Thus, the compound film on the interlayer insulating film (42) can be removed without requiring extra patterning as in the seventh aspect. Thereby, a short circuit between the gate and the source can be prevented.

  In the invention described in claim 12, in the step of laminating the Ni film (20) and the Al film (21), the film thickness ratio of the Al film (21) and the Ni film (20) is 1: 5. It is characterized by.

Thereby, in the alloy layer, the contact resistivity for the first conductivity type is 2 × 10 ⁻⁴ Ωcm ² or less, and the contact resistivity for the second conductivity type is 5 × 10 ⁻³ Ωcm ² or less. For this reason, it is possible to realize a low-resistance element with no deterioration in breakdown voltage.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings. Further, the n− type and n + type shown in the following embodiments correspond to the first conductivity type of the present invention, and the p type and p + type correspond to the second conductivity type of the present invention.

(First embodiment)
A silicon carbide semiconductor device to which an embodiment of the present invention is applied will be described. FIG. 1 is a cross-sectional view of the silicon carbide semiconductor device in the present embodiment. Hereinafter, the structure of the silicon carbide semiconductor device will be described with reference to FIG.

As shown in FIG. 1, the silicon carbide semiconductor device includes an n + type substrate 1 having an impurity concentration of, for example, 1 × 10 ¹⁹ cm ⁻³ or more and, for example, 1 × 10 ^{15 to} 5 × 10 ¹⁶ cm ⁻³ . An n − type drift layer 2 having an impurity concentration, a p + type layer 3 having an impurity concentration of 1 × 10 ^{18 to} 5 × 10 ¹⁹ cm ^{−3, and} an impurity concentration of 5 × 10 ⁻¹⁵ cm ⁻³ , for example. The n − type layer 4 and the n + type layer 5 having an impurity concentration of 1 × 10 ¹⁹ cm ⁻³ , for example, are provided. These n + type substrate 1, n − type drift layer 2, p + type layer 3, n − type layer 4, and n + type layer 5 are made of silicon carbide (SiC), and thereby semiconductor substrate 6 is formed. ing.

  A cell portion having a large number of J-FETs is formed on the inner side of the semiconductor substrate 6. FIG. 1 corresponds to a cross-sectional view showing a part of the cell portion.

On the main surface side of the semiconductor substrate 6 in the cell portion (J-FET formation region), the first reaches the n − type drift layer 2 through the n − type layer 4, the n + type layer 5, and the p + type layer 3. The groove 7 is formed. Although not shown in FIG. 1, all the first grooves 7 are actually formed in a state of being arranged at a predetermined interval. On the inner wall surface of each of the plurality of first grooves 7, for example, an n − type epitaxial layer serving as a channel layer having a thickness of 1 μm or less and an impurity concentration of 5 × 10 ¹⁵ to 1 × 10 ¹⁷ cm ⁻³ ( (Hereinafter referred to as an n− type epi layer) 8 and a p + type layer 9 having an impurity concentration of 1 × 10 ^{18 to} 5 × 10 ²⁰ cm ⁻³ are sequentially formed.

  In the J-FET, the first gate layer and the second gate layer are constituted by the p + -type layers 3 and 9, and the source layer is constituted by the n − -type layer 4 and the n + -type layer 5.

  Further, a second groove 10 is formed at a predetermined position of the semiconductor substrate 6 so as to penetrate the n− type layer 4 and the n + type layer 5 to reach the p + type layer 3.

An interlayer insulating film 11 made of a silicon oxide film (SiO ₂ ) is formed on the surface of the semiconductor substrate 6 and the side wall of the second groove 10. In the interlayer insulating film 11, first to third contact holes 12 to 14 are formed so that the p + -type layer 3, the n + -type layer 5, and the p + -type layer 9 are exposed. An alloy layer 15 formed by reaction of Ni, Al, and SiC is provided at a portion of the semiconductor substrate 6 exposed from the contact holes 12 to 14.

  A gate wiring 16, a source wiring 17, and a gate electrode 18 are formed on the alloy layer 15 and the interlayer insulating film 11. Thereby, the gate wiring 16 is electrically connected to the p + -type layer 9 constituting the first gate layer. On the other hand, a source wiring 17 is electrically connected to the n− type layer 4 and the n + type layer 5 constituting the source layer. The source wiring 17 is electrically isolated from the gate wiring 16 via the interlayer insulating film 11. On the other hand, the gate electrode 18 is electrically connected to the p + type layer 3 constituting the second gate layer.

  Note that the gate wiring 16 functions as a top gate, and the gate electrode 18 functions as a valid gate. Depending on the element control method, the same voltage or different voltages may be applied to the gate wiring 16 and the gate electrode 18.

  A drain electrode 19 as a back surface electrode electrically connected to the n + type substrate 1 is formed on the back surface side of the semiconductor substrate 6, and a cell portion composed of a plurality of J-FETs is configured by such a configuration. . As described above, the silicon carbide semiconductor device provided with the cell portion by J-FET is configured.

  Next, alloy layer 15 of the silicon carbide semiconductor device will be described in detail. As described above, the alloy layer 15 is formed by reaction of Ni, Al, and SiC. The elemental composition ratio of Al and Ni is 1: 4.6 to 1: 10.6, and the thickness of the alloy layer 15 is 20 nm or more and 100 nm or less. In particular, in this embodiment, the elemental composition ratio between Al and Ni is 1: 7.6, and the thickness of the alloy layer 15 is 20 nm.

  In order to derive each of the above numerical values, the inventors examined the dependence of n-type ohmic on the Ni film thickness and the dependence of the contact resistivity on the Ni film thickness / Al film thickness ratio.

First, the inventors conducted an experiment in which a Ni vapor deposition film was formed on an n-type epilayer having an impurity concentration of 1 × 10 ¹⁸ cm ⁻³ to confirm the dependence of n-type ohmic on the Ni film thickness. The experimental procedure is shown in FIG. 2 and the experimental results are shown in FIG.

  First, an n-type epi layer (n epi layer in FIG. 2) is formed on an n + type SiC substrate (n + SiC substrate in FIG. 2) (FIG. 2A), and a thickness is formed on the n type epi layer. A deposited film of Ni having a thickness of 0.4 to 100 nm was formed (FIG. 2B). Thereafter, a current check of the deposited film of Ni was performed (FIG. 2C). Subsequently, a heat treatment was performed at 1000 ° C. in an oxygen-free atmosphere to form an alloy layer (FIG. 2D), and an energization check was performed again (FIG. 2E).

  Regarding the Ni vapor deposition film, Ni film thicknesses of 0.4 nm, 0.6 nm, 1 nm, 2 nm, 10 nm, and 100 nm were prepared, respectively.

  As shown in FIG. 3, the minimum Ni film thickness at which the Ni film is in ohmic contact was 2 nm. It is presumed that the current was not energized before the heat treatment, and Ni was distributed in the form of dots on the n-type epilayer. Although not shown, when TEM observation was performed before and after the heat treatment when the Ni film thickness was 2 nm, Ni was formed in a dot shape on the SiC substrate. After the heat treatment, ohmic contact was observed even when Ni was punctiform. That is, the minimum Ni film thickness showing ohmic characteristics by heat treatment at 1000 ° C. was 2 nm.

  In addition, in Ni vapor deposition, the film thickness is assumed to change from 10 nm to a film shape from 10 nm. Thereby, when forming the vapor deposition film by Ni, it turned out that a film-like Ni vapor deposition film is obtained by making 10 nm into a lower limit.

Next, the inventors examined the dependency of the contact resistivity on the Ni film thickness / Al film thickness ratio. Prepared and p-type epitaxial substrate concentration of the SiC substrate as a 1 × ¹⁰ 18 ^cm n-type epitaxial substrate concentrations ^-3 and 1 × ¹⁰ 18 ^{cm -3,} on each epitaxial substrate, Ni film, Al film (4 nm And then heat-treated at 1000 ° C. in an oxygen-free atmosphere to form an alloy layer. Thereafter, electrical measurements related to the alloy layer were performed to obtain contact resistivity. The result is shown in FIG.

As shown in FIG. 4, the p-type epi substrate and the n-type epi substrate were in ohmic contact when the Ni film thickness / Al film thickness ratio in the range of 1 to 9 based on the Al film thickness. Further, when the Ni film thickness / Al film thickness ratio is in the range of 3 to 7, a p-type contact resistivity of 1 × 10 ⁻² Ωcm ² or less is obtained, and an n-type contact resistivity of 1 × 10 ⁻³ Ωcm ² or less is obtained. It was. Furthermore, when the Ni film thickness / Al film thickness ratio was 5, the p-type contact resistivity was the lowest, indicating 5 × 10 ⁻³ Ωcm ² . Moreover, even with n-type contact resistivity, 2 × 10 ⁻⁴ Ωcm ² showed a low contact resistivity.

In addition, ohmic characteristics were obtained when Ni and Al were deposited in the order of Ni and Al on the surface of the p-type epitaxial substrate and heat-treated at 1000 ° C. (ρ = 5 × 10 ⁻³ Ωcm ² ). In addition, ohmic characteristics were obtained even when Ni and Al were deposited in the order of Ni and Al on the surface of the n-type epitaxial substrate and heat-treated at 1000 ° C. (ρ = 2 × 10 ⁻⁴ Ωcm ² ).

  As described above, a good contact resistivity can be obtained by forming the alloy layer 15 by setting the film thickness ratio of the Al film and the Ni film to 1: 3 to 1: 7. In particular, the film thickness ratio is set to 1: 5. It turned out to be more preferable.

  In the above, the film thickness ratio between the Al film and the Ni film at the time of manufacturing the alloy layer 15 was examined. The ratio of Al to Ni contained in the alloy layer 15 formed by the film thickness ratio is elemental composition. It can be expressed as a ratio.

For Ni, the film thickness ratio is X, the density D1 is 8908 kg / m ³ , and the atomic weight M1 is 58.7. For Al, the film thickness ratio is 1, the density D2 is 2700 kg / m ³ , and the atomic weight M2 is 27.0.

  In this case, the weight composition ratio (wt%) of Ni is represented by D1 · X / (D1 · X + D2), and the element composition ratio (atomic%) is (D1 · X / M1) / (D1 · X / M1 + D2 / M2). Similarly, the weight composition ratio (wt%) of Al is represented by D2 / (D1 · X + D2), and the element composition ratio (atomic%) is represented by (D2 / M2) / (D1 · X / M1 + D2 / M2). Is done.

  When the film thickness ratio of the Al film and the Ni film is converted into the element composition ratio by this conversion, the film thickness ratio of 1: 3 to 1: 7 is the element composition ratio of 1: 4.6 to 1:10. Is the same as .6. Furthermore, the film thickness ratio of 1: 5 is the same as the elemental composition ratio of 1: 7.6.

  That is, in the horizontal axis of the graph of FIG. 4, the Ni film thickness / Al film thickness ratio of “3” corresponds to an element composition ratio of 4.6. Similarly, the Ni film thickness / Al film thickness ratio of “5” corresponds to the element composition ratio of 7.6, and the Ni film thickness / Al film thickness ratio of “7” is the element composition ratio. Corresponds to 10.6.

In addition, it was found that when 10 nm Ni and ₂ nm Al were sequentially laminated on the SiO ₂ surface and heat-treated at 1000 ° C., an alloy layer in which Al and SiO ₂ reacted was not formed, and the Ni / Al film was peeled off. On the other hand, when Ni of 50 nm thickness and Al of 10 nm thickness were sequentially laminated on the SiO ₂ surface and heat-treated at 1000 ° C., an alloy layer in which Al and SiO ₂ reacted was formed, but the depth was It was found to be about 100 nm.

The inventors examined the reason why the alloy layer 15 is formed on SiC and the alloy layer 15 is not formed on SiO ₂ . This will be described with reference to FIG.

  First, as shown in FIG. 5 (a), it is assumed that a Ni film having a thickness of 10 nm and an Al film having a thickness of 2 nm are sequentially formed on SiC and heat-treated at 1000 ° C. or lower. In this case, Ni and SiC have strong interdiffusion, an Ni silicide layer is easily formed, Al is also present in the silicide and on the surface, and is in ohmic contact with the p-type epi layer and the n-type epi layer.

However, as shown in FIG. 5 (b), it is assumed that Ni having a thickness of 10 nm and Al having a thickness of 2 nm are sequentially formed on SiO _{2 at} a temperature of 1000 ° C. or lower. In this case, Ni has the property of not reacting with SiO ₂ originally as disclosed in JP-A-2004-327601. Al interdiffuses with SiO ₂ , but the Ni layer acts as a barrier layer. For this reason, it is considered that a reaction layer of Al and SiO ₂ was not formed with Al having a thickness of 2 nm.

However, when the Al film thickness is 10 nm (Ni is 50 nm), the compound of Al and Ni erodes SiO ₂ . The depth is about 100 nm as described above.

  Here, the reason why the lower limit of the thickness of the alloy layer 15 is set to 20 nm or more is that the minimum film thickness at which Ni is formed in a film shape is 10 nm. This is based on a thickness of 20 nm.

  The upper limit of the thickness of the alloy layer 15 is set to 100 nm or less in consideration of the fact that the alloy layer 15 is formed by eroding the interlayer insulating film 11. That is, based on the fact that when the thickness of the interlayer insulating film 11 is about 500 nm, the maximum thickness of the alloy layer 15 that can prevent all of the interlayer insulating film 11 from being eroded by the alloy layer 15 is 100 nm or less. Yes.

  Next, a method for manufacturing the silicon carbide semiconductor device will be described with reference to FIGS.

  6A, an n + type substrate 1 made of SiC is prepared, and an n− type drift layer 2, a p + type layer 3, an n− type layer 4, on the n + type substrate 1, And the n + type layer 5 is epitaxially grown in order. Thereby, the semiconductor substrate 6 is obtained.

  In the step shown in FIG. 6B, the first groove 7 is formed at a predetermined position of the semiconductor substrate 6. Then, the n − type epi layer 8 and the p + type layer 9 are buried in the first trench 7 in the order of the n − type epi layer 8 and the p + type layer 9, and an excess epi film on the semiconductor substrate 6 is polished and removed. .

  In the step shown in FIG. 6C, the second groove 10 is formed at a predetermined position of the semiconductor substrate 6. Thereafter, an interlayer insulating film 11 is formed on the side wall of the second groove 10 and the surface of the semiconductor substrate 6. Then, first to third contact holes 12 to 14 are formed in the interlayer insulating film 11 so that the p + type layer 3, the n + type layer 5, and the p + type layer 9 are exposed from the interlayer insulating film 11.

  7A, the Ni film 20 having a thickness of 10 nm to 20 nm on the semiconductor substrate 6 and the interlayer insulating film 11 exposed from the first to third contact holes 12 to 14, and 2 nm to 4 nm. Are sequentially formed. In this embodiment, a Ni film 20 having a thickness of 10 nm and an Al film 21 having a thickness of 2 nm are sequentially formed.

  In the step shown in FIG. 7B, the Ni film 20 and the Al film 21 formed are heat-treated at 1000 ° C. in an oxygen-free atmosphere. Thereby, the Ni film 20 / Al film 21 on SiC, which is the semiconductor substrate 6, becomes a silicide layer (ohmic electrode layer) formed by reaction of SiC, Al, and Ni. This silicide layer is the alloy layer 15. On the other hand, the Ni film 20 / Al film 21 on the interlayer insulating film 11 hardly reacts with the interlayer insulating film 11, and remains as a compound layer 22 in which Ni of the Ni film 20 and Al of the Al film 21 are combined.

  The alloy layer 15 is approximately twice as thick as the Ni film 20. If the Ni film 20 is 10 nm or more and 20 nm or less, the thickness of the alloy layer 15 is 20 nm to 40 nm. In this embodiment, since the thickness of the Ni film 20 is 10 nm, the thickness of the alloy layer 15 is 20 nm.

  In the step shown in FIG. 7C, the compound layer 22 on the interlayer insulating film 11 is removed by etching by acid cleaning, and the alloy layer 15 in the first to third contact holes 12 to 14 is left. Thereby, each alloy layer 15 will be in an electrically independent state.

  Thereafter, the gate wiring 16, the source wiring 17, and the gate electrode 18 are formed so as to fill the contact holes 12 to 14, respectively, and the drain electrode 19 is formed on the back surface of the semiconductor substrate 6, as shown in FIG. A silicon carbide semiconductor device provided with a fine J-FET is completed.

  As described above, in this embodiment, since the material of the alloy layer 15 formed on the p + type layer 3, the n + type layer 5, and the p + type layer 9 in the semiconductor substrate 6 is the same, the manufacturing process is performed. It can be simplified. In this case, it can be applied to a fine contact hole of about Φ1 μm, and a low on-resistance can be achieved.

  Further, since the alloy layer 15 that is an ohmic electrode for both the p-type and n-type can be formed by self-alignment with respect to the first to third contact holes 12 to 14, there is an advantage that the process can be simplified.

  Since the alloy layer 15 having an element composition ratio of Al to Ni of 1: 4.6 to 1: 10.6 is formed, the alloy layer 15 is formed of the p + type layer 3, the n + type layer 5, and the p +. Each of the mold layers 9 can be brought into ohmic contact. Therefore, it is possible to reduce the contact resistance, and consequently to prevent the switching speed of the element from decreasing.

  As for the correspondence between the description of the present embodiment and the description of the claims, the n + type substrate 1 corresponds to the substrate of the claims, and the n − type drift layer 2 is the first of the claims. It corresponds to a semiconductor layer. The p + type layer 3 corresponds to the second semiconductor layer in the claims, and the n− type layer 4 and the n + type layer 5 correspond to the third semiconductor layer in the claims. Further, the first groove 7 corresponds to a groove in the claims, and the n− type epi layer corresponds to a channel layer in the claims. The p + type layer 9 corresponds to the second conductivity type semiconductor region in the claims.

(Second Embodiment)
In the present embodiment, only different parts from the first embodiment will be described. FIG. 8 is a cross-sectional view of the silicon carbide semiconductor device in the present embodiment. As shown in this figure, the silicon carbide semiconductor device according to the present embodiment has a structure in which a compound film 23 is formed on the interlayer insulating film 11 with respect to the structure shown in FIG. A gate wiring 16, a source wiring 17, and a gate electrode 18 are formed on the alloy layer 15 and the compound film 23.

  Next, a method for manufacturing the silicon carbide semiconductor device shown in FIG. 8 will be described with reference to FIG. First, the steps shown in FIGS. 7A to 7C are performed to prepare a semiconductor substrate 6 having an interlayer insulating film 11 formed thereon.

  Subsequently, in the process shown in FIG. 9A, the Ni film 20 and the Al film 21 having a thickness of 20 nm to 50 nm are formed on the semiconductor substrate 6 and the interlayer insulating film 11 exposed from the first to third contact holes 12 to 14. An Al film 21 having a film thickness ratio with the Ni film 20 of 1: 3 to 1: 7 is sequentially formed. In particular, the film thickness ratio between the Al film 21 and the Ni film 20 is preferably 1: 5. Therefore, in this embodiment, the Ni film 20 having a thickness of 50 nm and the Al film 21 having a thickness of 10 nm are sequentially formed. Note that the Al film 21 and the Ni film 20 may be formed in this order.

In the step shown in FIG. 9B, the Ni film 20 and the Al film 21 formed are heat-treated at 1000 ° C. in an oxygen-free atmosphere. Thereby, the Ni film 20 / Al film 21 on SiC becomes a silicide layer (ohmic electrode layer), that is, an alloy layer 15 of about 100 nm. Further, the Ni film 20 / Al film 21 on the interlayer insulating film 11 reacts with SiO ₂ which is the interlayer insulating film 11 to become a conductive layer of about 100 nm, that is, a compound film 23.

  In the step shown in FIG. 9C, an Al film is formed and patterned on the alloy layer 15 and the compound film 23 so as to cover the alloy layer 15 formed together with SiC. Thereby, the gate wiring 16, the source wiring 17, and the gate electrode 18 are formed.

  In the step shown in FIG. 9D, using the gate wiring 16, the source wiring 17, and the gate electrode 18 as a mask, the compound film 23 exposed from the mask is removed by dry etching. Thereby, the unnecessary connection between electrodes is interrupted.

  Finally, the drain electrode 19 which is a back electrode is formed on the back surface of the semiconductor substrate 6. Thus, a silicon carbide semiconductor device provided with the fine J-FET shown in FIG. 8 is completed.

  As described above, the stability of the process can be ensured by forming the Ni film 20 and the Al film 21 thicker than in the first embodiment. That is, the film thickness of the alloy layer 15 can be ensured even if the film thicknesses of the Ni film 20 and the Al film 21 slightly vary. Of course, since the alloy layer 15 is in ohmic contact with the p + type layer 3, the n + type layer 5, and the p + type layer 9, contact resistance can be reduced.

(Third embodiment)
In each of the above embodiments, a silicon carbide semiconductor device provided with a J-FET has been described. However, the present invention can also be applied to a MOSFET in which p-type and n-type ohmic electrodes are arranged in one contact hole. This will be described with reference to FIG.

  In the MOSFET shown in FIG. 10, in a semiconductor substrate 33 in which an n + type semiconductor substrate 30, an n − type epi layer 31, and a p type base region 32 are sequentially stacked, an n + type is formed in a predetermined region of the surface layer portion of the p type base region 32. A source region 34 and a p-type contact region 35 are formed.

  Further, a groove 36 is formed in a predetermined region of the n + type source region 34, and this groove 36 penetrates the n + type source region 34 and the p type base region 32 and reaches the n − type epi layer 31. The groove 36 has a side surface 37 substantially perpendicular to the surface of the semiconductor substrate 30 and a bottom surface 38 parallel to the semiconductor substrate 30.

  An n-type semiconductor thin film layer 39 is extended on the surface of the n + -type source region 34, the p-type base region 32, and the n − -type epi layer 31 on the side surface 37 of the groove 36. Further, a gate insulating film 40 is formed on the surface of the n-type semiconductor thin film layer 39 and the bottom surface 38 of the groove 36 in the groove 36. A gate electrode layer 41 is filled inside the gate insulating film 40 in the trench 36. The gate electrode layer 41 is covered with an interlayer insulating film 42.

  Then, via the contact hole 43 formed in the interlayer insulating film 42, the surface of the n + -type source region 34 and the surface of the p-type contact region 35 can be made of a 10 nm thick Ni film and a 2 nm thick Al film. An alloy layer 44 of about 20 nm is formed. A source electrode layer 45 is formed on the alloy layer 44 and the interlayer insulating film 42. The drain electrode 47 is formed on the back surface of the semiconductor substrate 30.

  Also in the alloy layer 44 according to the present embodiment, the element composition ratio of Al and Ni is 1: 4.6 to 1: 10.6 as in the first embodiment, and the thickness of the alloy layer 44 is 20 nm. It is 100 nm or less. In particular, the elemental composition ratio between Al and Ni is preferably 1: 7.6.

  Next, a method for manufacturing the silicon carbide semiconductor device shown in FIG. 10 will be described. First, a semiconductor substrate 33 in which an n− type epi layer 31 made of silicon carbide having a lower concentration than the substrate 30 and a p type base region 32 made of silicon carbide are sequentially formed on the surface side of the n + type semiconductor substrate 30. Prepare.

  Next, an n + type source region 34 and a p + type contact region 35 are formed in a predetermined region of the p type base region 32. In addition, a trench 36 that penetrates both the base region 32 and the source region 34 and reaches the n − -type epi layer 31 is formed. An n-type semiconductor thin film layer 39 is extended on the inner wall surface of the groove 36, and a gate insulating film 40 is formed on the surface of the n-type semiconductor thin film layer 39 and the bottom surface 38 of the groove 36. Then, the gate electrode layer 41 is formed inside the gate insulating film 40 in the trench 36.

Thereafter, an interlayer insulating film 42 made of SiO ₂ is formed on the gate electrode layer 41, and a contact hole 43 communicating with the source region 34 and the contact region 35 is formed in the interlayer insulating film 42. As a result, the source region 34 and the contact region 35 are exposed through the contact hole 43.

  Subsequently, the Ni film 20 having a thickness of 10 nm to 20 nm and the Al film 21 having a thickness of 2 nm to 4 nm are formed on the interlayer insulating film 42 and the source region 34 and the contact region 35 exposed from the contact hole 43. Laminate sequentially. As described above, the film thickness ratio between the Ni film 20 and the Al film 21 is preferably 1: 3 to 1: 7, and the film thickness ratio is adjusted so as to be within the range in this embodiment. In particular, the film thickness ratio between the Al film 21 and the Ni film 20 is preferably 1: 5.

  Next, an alloy layer 44 is formed in the contact hole 43 by reacting silicon carbide, Al, and Ni by heat treatment at 1000 ° C. or less in an oxygen-free atmosphere. The elemental composition ratio of the alloy layer 44 thus formed is 1: 4.6 to 1: 10.6 as described above.

  On the other hand, since the compound layer 22 of Ni and Al is formed on the interlayer insulating film 42, it is removed by acid cleaning. Thereafter, source electrode layer 45 is formed on alloy layer 44 and back electrode layer 47 is formed on the back surface of semiconductor substrate 30 to complete the silicon carbide semiconductor device shown in FIG.

  As described above, even when the silicon carbide semiconductor device is a MOSFET, the alloy layer 44 can be formed similarly to the J-FET, and the same effects can be obtained in terms of contact resistivity and prevention of gate-source leakage. Can do.

  As for the correspondence between the description of the present embodiment and the description of the claims, the n + -type semiconductor substrate 30 corresponds to the substrate made of silicon carbide of the first conductivity type in the claims, and the n − -type epitaxy. The layer 31 corresponds to a semiconductor layer of the first conductivity type made of silicon carbide in the claims.

(Fourth embodiment)
In the present embodiment, only different parts from the third embodiment will be described. FIG. 11 is a cross-sectional view of the silicon carbide semiconductor device according to the present embodiment. In the MOSFET shown in FIG. 11, a gate contact hole 48 is provided so that the gate electrode layer 41 is exposed from the interlayer insulating film 42. Then, the surface of the n + type source region 34, the surface of the p type contact region 35, the surface of the gate electrode layer 41, and the interlayer insulating film 42 are made of a Ni film having a thickness of 50 nm and an Al having a thickness of 10 nm. An alloy layer 46 of about 100 nm is formed.

  A source electrode layer 45 is formed on the source region 34 exposed from the contact hole 43 of the interlayer insulating film 42 and the alloy layer 46 on the contact region 35. Further, a gate wiring 49 is formed on the alloy layer 46 on the gate electrode layer 41 exposed from the gate contact hole 48 of the interlayer insulating film 42.

  When manufacturing a MOSFET having such a structure, an interlayer insulating film 42 is formed as in the third embodiment. Then, a contact hole 43 and a gate contact hole 48 are formed in the interlayer insulating film 42. Thereafter, a Ni film having a thickness of 20 nm or more and 50 nm or less is formed on the interlayer insulating film 42, the source region 34 and the contact region 35 exposed from the contact hole 43, and the gate electrode layer 41 exposed from the gate contact hole 48. 20 and an Al film 21 in which the film thickness ratio of the Al film 21 and the Ni film 20 is 1: 3 to 1: 7. The film thickness ratio between the Al film 21 and the Ni film 20 is preferably 1: 5.

  Thereafter, silicon carbide, Al, and Ni are reacted by heat treatment at 1000 ° C. or less in an oxygen-free atmosphere to form alloy layer 46 in contact hole 43 and gate contact hole 48. Of course, a compound film made of Ni and Al is formed on the interlayer insulating film 42.

  Subsequently, an Al layer is formed on the alloy layer 46 and the compound film and patterned. Thereby, the source electrode layer 45 and the gate wiring 49 are formed.

  Then, using the source electrode layer 45 and the gate wiring 49 as a mask, the compound film exposed from the mask is removed by dry etching. Thereby, unnecessary connection between the electrodes on the interlayer insulating film 42 is cut off. Thus, the MOSFET shown in FIG. 11 is completed. As described above, the alloy layer 46 thicker than the alloy layer 44 shown in the third embodiment can also be formed.

(Other embodiments)
In the first and second embodiments, the silicon carbide semiconductor device in which the J-FET is formed is shown in which the gate electrode 18 functioning as a valid gate is formed. However, the gate electrode 18 is formed. An unstructured structure may be employed.

  The n− type epi layer 8 and the p + type layer 9 may be formed not by epitaxial growth but by ion implantation.

  In the J-FET of FIG. 1 and the like, an example in which the n − type layer 4 is provided on the semiconductor substrate 6 is shown, but the semiconductor substrate 6 having a structure in which the n − type layer 4 is not provided is used. You can also. In this case, the n + type layer 5 is formed on the p + type layer 3.

  In the second embodiment, using the gate wiring 16, the source wiring 17, and the gate electrode 18 as a mask, the compound film 23 exposed from the mask is removed by dry etching. However, after forming the alloy layer 15 and the compound film 23, an Al film serving as a wiring or an electrode is formed thereon, a resist is formed on the Al film, and patterning is performed. Using this resist as a mask, the Al film and the compound film are formed. The film 23 may be continuously dry etched. This makes it possible to reduce the number of processes and manufacturing costs.

  In the MOSFET shown in FIGS. 10 and 11, an n-type semiconductor thin film layer 39 is extended on the inner wall surface of the groove 36, and a gate insulating film 40 is formed on the surface of the n-type semiconductor thin film layer 39 and the bottom surface 38 of the groove 36. This is an example of the structure. That is, the n-type semiconductor thin film layer 39 may not be extended on the inner wall surface of the trench 36, and the gate insulating film 40 may be directly formed on the inner wall surface.

  In the fourth embodiment, the compound film is dry-etched using the source electrode layer 45 and the gate wiring 49 as a mask. However, after forming the alloy layer 46 and the compound film, they are patterned, and the source electrode is formed on the patterned alloy layer 46. The layer 45 and the gate wiring 49 may be formed.

It is sectional drawing of the silicon carbide semiconductor device in 1st Embodiment of this invention. It is the figure which showed the experimental procedure which confirms Ni film thickness dependence on an n-type epilayer. It is the figure which showed the result by the experiment shown by FIG. 2 with the table | surface. It is the figure which showed the Ni film thickness / Al film thickness ratio dependence of contact resistivity. It is a figure for demonstrating each reason with the case where an alloy layer is formed and the case where it is not formed. FIG. 2 is a diagram showing a manufacturing process of the silicon carbide semiconductor device shown in FIG. 1. It is the figure which showed the manufacturing process following FIG. It is sectional drawing of the silicon carbide semiconductor device in 2nd Embodiment of this invention. FIG. 9 is a diagram showing a manufacturing process of the silicon carbide semiconductor device shown in FIG. 8. It is sectional drawing of the silicon carbide semiconductor device in 3rd Embodiment of this invention. It is sectional drawing of the silicon carbide semiconductor device in 4th Embodiment of this invention.

Explanation of symbols

1 n + type substrate 2 n− type drift layer 3 p + type layer 4 n− type layer 5 n + type layer 6 semiconductor substrate 7 first groove 8 n− type epi layer 9 p + type layer 11 interlayer insulating film 12 first contact hole 13 Second contact hole 15 Alloy layer 16 Gate wiring 17 Source wiring 19 Drain electrode

Claims (12)

The first conductivity type first semiconductor layer (2) made of silicon carbide having a lower concentration than the substrate (1), the second conductivity type made of silicon carbide, and the substrate (1) made of silicon carbide of the first conductivity type. A second semiconductor layer (3), a first conductive type third semiconductor layer (4, 5) made of silicon carbide, and a semiconductor substrate (6) formed in order,
A groove (7) formed in a cell portion of the semiconductor substrate (6) and reaching the first semiconductor layer (2) through the third and second semiconductor layers (3-5);
A channel layer (8) of the first conductivity type formed on the inner wall surface of the groove (7);
A second conductivity type semiconductor region (9) made of silicon carbide formed on the channel layer (8);
An interlayer insulating film (11) made of SiO ₂ formed on the semiconductor substrate (6);
A first contact hole (12) in which the interlayer insulating film (11) is opened so that the second conductive semiconductor region (9) is exposed;
A second contact hole (13) in which the interlayer insulating film (11) is opened so that the third semiconductor layer (4, 5) is exposed;
Of the semiconductor substrate (6), the second conductive semiconductor region (9) exposed from the first contact hole (12), and the third semiconductor layer (4, exposed from the second contact hole (13)). 5) and an alloy layer (15) made of the same material formed by the reaction of silicon carbide, Al, and Ni, respectively,
It is formed on the alloy layer (15) formed on the second conductivity type semiconductor region (9), and is electrically connected to the gate layer using the second conductivity type semiconductor region (9) as a gate layer. Connected gate wiring (16);
It is formed on the alloy layer (15) formed on the third semiconductor layer (4, 5), and is electrically connected to the source layer using the third semiconductor layer (4, 5) as a source layer. Connected source wiring (17);
A drain electrode (19) formed on the back surface of the substrate (1),
In the alloy layer (15), the elemental composition ratio between Al and Ni is 1: 4.6 to 1: 10.6, and the thickness of the alloy layer (15) is 20 nm to 100 nm. A silicon carbide semiconductor device. On the surface side of the substrate (30) made of silicon carbide of the first conductivity type, a first conductivity type semiconductor layer (31) made of silicon carbide having a lower concentration than the substrate (30) and a second layer made of silicon carbide. A semiconductor substrate (33) in which a conductive type base region (32) is sequentially formed;
A first conductivity type source region (34) formed in a predetermined region of the base region (32);
A second conductivity type contact region (35) formed in a predetermined region of the base region (32);
A groove (36) penetrating both the base region (32) and the source region (34) and reaching the semiconductor layer (31);
A gate insulating film (40) formed on the inner wall surface of the groove (36);
A gate electrode layer (41) formed inside the gate insulating film (40) in the trench (36);
An interlayer insulating film (42) made of SiO ₂ formed on the gate electrode layer (41) and having a contact hole (43) communicating with the source region (34) and the contact region (35);
Of the semiconductor substrate (33), the source region (34) exposed from the contact hole (43) and the contact region (35) are made of the same material formed by the reaction of silicon carbide, Al, and Ni. An alloy layer (44) comprising:
A source electrode layer (45) formed on the alloy layer (44);
A back electrode layer (47) formed on the back surface of the substrate (30),
In the alloy layer (44), the elemental composition ratio between Al and Ni is 1: 4.6 to 1: 10.6, and the thickness of the alloy layer (44) is 20 nm to 100 nm. A silicon carbide semiconductor device.   3. The silicon carbide semiconductor device according to claim 1, wherein an element composition ratio of Al and Ni in the alloy layer is 1: 7.6. The first conductivity type first semiconductor layer (2) made of silicon carbide having a lower concentration than the substrate (1), the second conductivity type made of silicon carbide, and the substrate (1) made of silicon carbide of the first conductivity type. Preparing a semiconductor substrate (6) in which the second semiconductor layer (3) and the third semiconductor layer (4, 5) of the first conductivity type made of silicon carbide are sequentially formed;
Grooves (7) reaching the first semiconductor layer (2) through the third and second semiconductor layers (3-5) are formed in the cell portion of the semiconductor substrate (6), and the grooves (7 ) Forming a first conductivity type channel layer (8) on the inner wall surface, and forming a second conductivity type semiconductor region (9) made of silicon carbide on the channel layer (8);
Forming an interlayer insulating film (11) made of SiO ₂ on the semiconductor substrate (6);
The first contact hole (12) having the interlayer insulating film (11) opened so that the second conductive type semiconductor region (9) is exposed, and the third semiconductor layer (4, 5) are exposed. Forming a second contact hole (13) having an opening in the interlayer insulating film (11);
On the interlayer insulating film (11) and on the second conductive semiconductor region (9) and the third semiconductor layer (4, 5) exposed from the first and second contact holes (12, 13). A step of laminating a Ni film (20) of 10 nm to 20 nm and an Al film (21) of 2 nm to 4 nm in order from the Ni film (20);
Forming an alloy layer (15) in the first and second contact holes (12, 13) by reacting the silicon carbide with Al and Ni by a heat treatment at 1000 ° C. or less in an oxygen-free atmosphere;
Removing the Ni and Al compound layer (22) formed on the interlayer insulating film (11) by acid cleaning;
On the alloy layer (15) formed on the second conductive type semiconductor region (9), the second conductive type semiconductor region (9) is electrically connected to the gate layer as a gate layer. A gate wiring (16) is formed, and the third semiconductor layer (4, 5) is used as a source layer on the alloy layer (15) formed on the third semiconductor layer (4, 5). Forming a source wiring (17) electrically connected to the source layer;
Forming a drain electrode (19) on the back surface of the substrate (1). A method for manufacturing a silicon carbide semiconductor device, comprising: On the surface side of the substrate (30) made of silicon carbide of the first conductivity type, a first conductivity type semiconductor layer (31) made of silicon carbide having a lower concentration than the substrate (30) and a second layer made of silicon carbide. Preparing a semiconductor substrate (33) in which a conductive type base region (32) is sequentially formed;
Forming a first conductivity type source region (34) and a second conductivity type contact region (35) in a predetermined region of the base region (32);
A trench (36) that penetrates both the base region (32) and the source region (34) and reaches the semiconductor layer (31) is formed, and a gate insulating film (40) is formed on the inner wall surface of the trench (36). Forming a gate electrode layer (41) inside the gate insulating film (40) in the trench (36);
Forming an interlayer insulating film (42) made of SiO ₂ on the gate electrode layer (41);
Forming a contact hole (43) communicating with the source region (34) and the contact region (35) in the interlayer insulating film (42);
On the interlayer insulating film (42) and on the source region (34) and the contact region (35) exposed from the contact hole (43), a Ni film (20) of 10 nm to 20 nm and 2 nm or more A step of laminating an Al film (21) of 4 nm or less in order from the Ni film (20);
Forming an alloy layer (44) in the contact hole (43) by reacting the silicon carbide with Al and Ni by heat treatment at 1000 ° C. or less in an oxygen-free atmosphere;
Removing the Ni and Al compound layer (22) formed on the interlayer insulating film (42) by acid cleaning;
Forming a source electrode layer (45) on the alloy layer (44);
Forming a back electrode layer (47) on the back surface of the substrate (30). A method for manufacturing a silicon carbide semiconductor device, comprising: The first conductivity type first semiconductor layer (2) made of silicon carbide having a lower concentration than the substrate (1), the second conductivity type made of silicon carbide, and the substrate (1) made of silicon carbide of the first conductivity type. Preparing a semiconductor substrate (6) in which the second semiconductor layer (3) and the third semiconductor layer (4, 5) of the first conductivity type made of silicon carbide are sequentially formed;
Grooves (7) reaching the first semiconductor layer (2) through the third and second semiconductor layers (3-5) are formed in the cell portion of the semiconductor substrate (6), and the grooves (7 ) Forming a first conductivity type channel layer (8) on the inner wall surface, and forming a second conductivity type semiconductor region (9) made of silicon carbide on the channel layer (8);
Forming an interlayer insulating film (11) made of SiO ₂ on the semiconductor substrate (6);
The first contact hole (12) having the interlayer insulating film (11) opened so that the second conductive type semiconductor region (9) is exposed, and the third semiconductor layer (4, 5) are exposed. Forming a second contact hole (13) having an opening in the interlayer insulating film (11);
On the interlayer insulating film (11) and on the second conductive semiconductor region (9) and the third semiconductor layer (4, 5) exposed from the first and second contact holes (12, 13). Further, a Ni film (20) having a thickness of 20 nm to 50 nm and an Al film (21) having a film thickness ratio of 1: 3 to 1: 7 between the Al film (21) and the Ni film (20) are laminated. Process,
Forming an alloy layer (15) in the first and second contact holes (12, 13) by reacting the silicon carbide with Al and Ni by a heat treatment at 1000 ° C. or less in an oxygen-free atmosphere;
On the alloy layer (15) formed on the second conductive type semiconductor region (9), the second conductive type semiconductor region (9) is electrically connected to the gate layer as a gate layer. A gate wiring (16) is formed, and the third semiconductor layer (4, 5) is used as a source layer on the alloy layer (15) formed on the third semiconductor layer (4, 5). Forming a source wiring (17) electrically connected to the source layer;
Forming a drain electrode (19) on the back surface of the substrate (1). A method for manufacturing a silicon carbide semiconductor device, comprising: In the step of forming the gate wiring (16) and the source wiring (17), after forming the gate wiring (16) and the source wiring (17), the gate wiring (16) and the source wiring (17) are formed. The step of removing the compound film (23) made of Ni, Al, and SiO ₂ formed on the interlayer insulating film (11) by dry etching, using as a mask, is included in claim 6. The manufacturing method of the silicon carbide semiconductor device of description. In the step of forming the gate wiring (16) and the source wiring (17),
Forming a metal film on the alloy film (23) made of Ni, Al, and SiO ₂ formed on the alloy layer (15) and the interlayer insulating film (11);
Forming and patterning a resist on the metal film; and
Forming the gate wiring (16) and the source wiring (17) by continuously removing the metal film and the compound film (23) by dry etching using the patterned resist as a mask; and The method for manufacturing a silicon carbide semiconductor device according to claim 6, comprising: On the surface side of the substrate (30) made of silicon carbide of the first conductivity type, a first conductivity type semiconductor layer (31) made of silicon carbide having a lower concentration than the substrate (30) and a second layer made of silicon carbide. Preparing a semiconductor substrate (33) in which a conductive type base region (32) is sequentially formed;
Forming a first conductivity type source region (34) and a second conductivity type contact region (35) in a predetermined region of the base region (32);
A trench (36) that penetrates both the base region (32) and the source region (34) and reaches the semiconductor layer (31) is formed, and a gate insulating film (40) is formed on the inner wall surface of the trench (36). Forming a gate electrode layer (41) inside the gate insulating film (40) in the trench (36);
Forming an interlayer insulating film (42) made of SiO ₂ on the gate electrode layer (41);
Forming a contact hole (43) communicating with the source region (34) and the contact region (35) in the interlayer insulating film (42);
On the interlayer insulating film (42) and on the source region (34) and the contact region (35) exposed from the contact hole (43), a Ni film (20) of 20 nm to 50 nm and Al Stacking an Al film (21) having a film thickness ratio of the film (21) and the Ni film (20) of 1: 3 to 1: 7;
Forming an alloy layer (46) in the contact hole (43) by reacting the silicon carbide with Al and Ni by heat treatment at 1000 ° C. or less in an oxygen-free atmosphere;
Forming a source electrode layer (45) on the alloy layer (46);
Forming a back electrode layer (47) on the back surface of the substrate (30). A method for manufacturing a silicon carbide semiconductor device, comprising: On the surface side of the substrate (30) made of silicon carbide of the first conductivity type, a first conductivity type semiconductor layer (31) made of silicon carbide having a lower concentration than the substrate (30) and a second layer made of silicon carbide. Preparing a semiconductor substrate (33) in which a conductive type base region (32) is sequentially formed;
Forming a first conductivity type source region (34) and a second conductivity type contact region (35) in a predetermined region of the base region (32);
A trench (36) that penetrates both the base region (32) and the source region (34) and reaches the semiconductor layer (31) is formed, and a gate insulating film (40) is formed on the inner wall surface of the trench (36). Forming a gate electrode layer (41) inside the gate insulating film (40) in the trench (36);
Forming an interlayer insulating film (42) made of SiO ₂ on the gate electrode layer (41);
In the interlayer insulating film (42), a contact hole (43) communicating with the source region (34) and the contact region (35) and a gate contact hole (48) communicating with the gate electrode layer (41) are formed. Forming, and
The gate electrode layer exposed on the interlayer insulating film (42), on the source region (34) and the contact region (35) exposed from the contact hole (43), and exposed from the gate contact hole (48). On the (41), the Ni film (20) of 20 nm or more and 50 nm or less, and the Al film (21) in which the film thickness ratio of the Al film (21) and the Ni film (20) is 1: 3 to 1: 7 And a step of laminating
Forming an alloy layer (46) in the contact hole (43) and the gate contact hole (48) by reacting the silicon carbide, Al, and Ni by heat treatment at 1000 ° C. or less in an oxygen-free atmosphere; ,
A gate wiring (49) is formed on the alloy layer (46) formed on the gate electrode layer (45), and is formed on the source region (34) and the contact region (35). Forming a source electrode layer (45) on the alloy layer (46);
Forming a back electrode layer (47) on the back surface of the substrate (30). A method for manufacturing a silicon carbide semiconductor device, comprising: In the step of forming the gate wiring (49) and the source electrode layer (45), after the gate wiring (49) and the source electrode layer (45) are formed, the gate wiring (49) and the source electrode layer are formed. The step of removing a compound film of Ni, Al, and SiO ₂ formed on the interlayer insulating film (42) by dry etching using (45) as a mask is included in claim 10. The manufacturing method of the silicon carbide semiconductor device of description.   In the step of laminating the Ni film (20) and the Al film (21), the film thickness ratio of the Al film (21) and the Ni film (20) is 1: 5. Item 12. A method for manufacturing a silicon carbide semiconductor device according to any one of Items 4 to 11.

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