JP5298691B2 - Silicon carbide semiconductor device and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silicon carbide semiconductor device capable of achieving high channel mobility with improved reproducibility, and to provide a manufacturing method of the silicon carbide semiconductor device. <P>SOLUTION: The silicon carbide semiconductor device has: a semiconductor layer made of silicon carbide having, on the surface, a groove with a sidewall made of a crystal surface inclined within a range of not less than 50&deg; and not more than 65&deg; with respect to ä0001} plane; and an insulation film formed in contact with the sidewall of the groove. The maximum value of nitrogen concentration, in a region within 10 nm from the interface between the sidewall of the groove and the insulation film is not less than 1&times;10<SP>21</SP>cm<SP>-3</SP>. The silicon carbide semiconductor device has a channel direction within a range of &plusmn;10&deg;, in a direction orthogonal to &lt;-2,110&gt; direction in the sidewall of the groove. The silicon carbide semiconductor device is manufactured by the manufacturing method. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a silicon carbide semiconductor device and a manufacturing method thereof, and more particularly, to a silicon carbide semiconductor device exhibiting excellent electrical characteristics and a manufacturing method thereof.

Conventionally, a silicon carbide semiconductor device using silicon carbide (SiC) is known, and an example thereof is described in, for example, International Publication No. WO01 / 018872 (hereinafter referred to as “Patent Document 1”). . Patent Document 1 describes a MOS field effect transistor (MOSFET) as a silicon carbide semiconductor device having a plane orientation of approximately {03-38} and formed using a 4H type polytype SiC substrate. In the MOSFET described in Patent Document 1, the gate oxide film is formed by dry oxidation, and high channel mobility (about 100 cm ² / Vs) can be realized.
International Publication No. 01/018872 Pamphlet

  In order to stably exhibit the excellent electrical characteristics of the silicon carbide semiconductor device using SiC, it is required to realize high channel mobility with good reproducibility.

  However, as a result of studies by the present inventors, it has been found that the channel mobility may not be sufficiently high even in the MOSFET described in Patent Document 1.

  In view of the above circumstances, an object of the present invention is to provide a silicon carbide semiconductor device capable of realizing high channel mobility with high reproducibility and a method for manufacturing the same.

According to the present invention, a semiconductor layer made of silicon carbide having a groove with a side wall made of a crystal plane inclined within a range of 50 ° or more and 65 ° or less with respect to the {0001} plane, and a contact with the side wall of the groove And the maximum value of the nitrogen concentration in the region within 10 nm from the interface between the sidewall of the groove and the insulating film is 1 × 10 ²¹ cm ⁻³ or more, and within the sidewall of the groove A silicon carbide semiconductor device having a channel length direction within a range of ± 10 ° in a direction orthogonal to the <−2110> direction.

Further, the present invention includes a substrate made of silicon carbide of the first conductivity type, and a first conductivity type impurity formed on the substrate and having a lower concentration than the substrate, and is 50 ° to 65 ° with respect to the {0001} plane. A semiconductor layer made of silicon carbide of the first conductivity type having a groove with a side wall made of a crystal plane inclined within the following range on the surface, a second conductivity type impurity diffusion layer formed on the side wall of the groove, At least a part of a region other than the first conductive type impurity diffusion layer formed in the surface of the semiconductor layer, the insulating film formed so as to be in contact with the sidewall of the groove, and the insulating film forming portion on the surface of the semiconductor layer A source electrode formed so as to be in contact with the gate electrode, a gate electrode formed on the insulating film, and a drain electrode formed on the surface of the substrate opposite to the side on which the semiconductor layer is formed. Nitrogen concentration in the region within 10 nm from the interface with the film A is a large value less than 1 × 10 ²¹ cm ^-3, silicon carbide semiconductor device having a channel length direction in a range of directions ± 10 ° orthogonal to the <-2110> direction in the side wall of the trench.

  Here, in the silicon carbide semiconductor device of the present invention, the surface of the source electrode is preferably striped.

  In the silicon carbide semiconductor device of the present invention, it is preferable that the surface of the source electrode has a honeycomb shape.

  In the silicon carbide semiconductor device of the present invention, the sidewall of the groove is preferably made of a crystal plane inclined within a range of ± 5 ° with respect to the {03-38} plane.

Furthermore, the present invention provides a step of forming a groove having a side wall made of a crystal plane inclined within a range of 50 ° or more and 65 ° or less with respect to the {0001} plane on the surface of a semiconductor layer made of silicon carbide, Forming an insulating film in contact with the side wall of the groove so that the channel length direction is formed within a range of ± 10 ° in a direction perpendicular to the <−2110> direction, and the side wall of the groove and the insulating film And a step of adjusting the nitrogen concentration so that the maximum value of the nitrogen concentration in a region within 10 nm from the interface is 1 × 10 ²¹ cm ⁻³ or more.

Here, in the method for manufacturing a silicon carbide semiconductor device of the present invention, the channel length is within a range of ± 10 ° in the direction orthogonal to the <−2110> direction in the sidewall of the groove based on the orientation of the defect included in the semiconductor layer. It is preferable to form a direction.

  In the method for manufacturing a silicon carbide semiconductor device of the present invention, the step of adjusting the nitrogen concentration preferably includes a step of heat-treating the semiconductor layer on which the insulating film is formed in an atmosphere of a nitrogen-containing gas.

  In the method for manufacturing a silicon carbide semiconductor device of the present invention, the step of adjusting the nitrogen concentration preferably includes a step of heat-treating the semiconductor layer after the heat treatment in an inert gas atmosphere.

  ADVANTAGE OF THE INVENTION According to this invention, the silicon carbide semiconductor device which can implement | achieve high channel mobility with sufficient reproducibility, and its manufacturing method can be provided.

  Embodiments of the present invention will be described below. In the drawings of the present invention, the same reference numerals represent the same or corresponding parts.

  In addition, when expressing the crystal plane and direction, it should be expressed by adding a bar on the required number. However, because there are restrictions on the expression means, in the present invention, the required number Instead of the expression with a bar above, “−” is added in front of the required number. In the present invention, the individual orientation is represented by [], the collective orientation is represented by <>, the individual plane is represented by (), and the collective plane is represented by {}.

  FIG. 1 shows a schematic cross-sectional view of an example of a vertical trench gate MOSFET (Metal Oxide Semiconductor Field Effect Transistor) which is an example of the silicon carbide semiconductor device of the present invention.

  A silicon carbide semiconductor device 1 shown in FIG. 1 includes, for example, a substrate 11 made of silicon carbide of n-type and polytype 4H—SiC, and a semiconductor layer 12 made of n-type silicon carbide formed on the surface 11 a of the substrate 11. A groove 20 formed in the surface 12a of the semiconductor layer 12, a second conductivity type impurity diffusion layer 14 which is a p-type region formed in the surface 12a of the semiconductor layer 12, and a second conductivity type impurity diffusion layer. The first conductivity type impurity diffusion layer 15 which is an n-type region formed in the surface of the semiconductor layer 12 (also in the surface 12a of the semiconductor layer 12), and a part of the surface 12a of the semiconductor layer 12 on the side wall 19 of the groove 20 Insulating film 13 formed so as to contact, source electrode 16 formed in a region other than the region where insulating film 13 is formed on surface 12 a of semiconductor layer 12, and gate electrode 17 formed on the surface of insulating film 13 And the board And a drain electrode 18 formed on the rear surface of the 1.

  Here, as the surface 11a of the substrate 11 on which the semiconductor layer 12 is formed, for example, a crystal plane composed of {2-1-10} plane can be used.

Further, as the semiconductor layer 12, for example, it can be used such as a layer of a low have n-type silicon carbide in the n-type impurity concentration than the substrate 11.

  Further, the side wall 19 of the groove 20 formed on the surface 12a of the semiconductor layer 12 is composed of a crystal plane inclined within a range of 50 ° to 65 ° with respect to the {0001} plane.

  As the insulating film 13, for example, an oxide film formed by dry oxidation (thermal oxidation) or the like can be used. The insulating film 13 is not limited to a one-layer structure, and may be composed of two or more layers.

  In addition, as the second conductivity type impurity diffusion layer 14, for example, a p type region formed by diffusing a p type impurity as the second conductivity type impurity in the surface 12a of the semiconductor layer 12 can be used. Here, as the p-type impurity as the second conductivity type impurity, for example, aluminum, boron or the like can be used. Further, the second conductivity type having a higher concentration than the second conductivity type impurity diffusion layer 14 is formed in at least a part of the region other than the formation region of the first conductivity type impurity diffusion layer 15 in the surface of the second conductivity type impurity diffusion layer 14. A p + -type region containing a p-type impurity as an impurity may be formed.

  In addition, as the first conductivity type impurity diffusion layer 15, for example, an n type region formed by diffusing an n type impurity as the first conductivity type impurity in the surface 12 a of the semiconductor layer 12 can be used. In addition, the n-type impurity concentration of the first conductivity type impurity diffusion layer 15 can be higher than the n-type impurity concentration of the semiconductor layer 12. Here, as the n-type impurity as the first conductivity type impurity, for example, nitrogen, phosphorus or the like can be used.

  The source electrode 16, the gate electrode 17, and the drain electrode 18 can each be made of a conventionally known metal, for example.

Further, in the silicon carbide semiconductor device 1 shown in FIG. 1, the maximum value of the nitrogen concentration in the region within 10 nm from the interface between the sidewall 19 of the groove 20 and the insulating film 13 is 1 × 10 ²¹ cm ⁻³ or more. . Here, the region within 10 nm from the interface between the side wall 19 of the groove 20 and the insulating film 13 refers to the side wall 19 side of the groove 20 perpendicular to the interface from the interface between the side wall 19 of the groove 20 and the insulating film 13. This is a region obtained by adding a region advanced by 10 nm and a region advanced by 10 nm from the interface between the side wall 19 of the trench 20 and the insulating film 13 to the insulating film 13 perpendicular to the interface.

  FIG. 2 is a schematic plan view of silicon carbide semiconductor device 1 shown in FIG. 1 viewed from the gate electrode 17 side. Here, the surface of the source electrode 16 and the surface of the gate electrode 17 are formed so as to extend in the <-2110> direction in stripes. The source electrode 16 and the gate electrode 17 are alternately arranged along the <03-38> direction which is a direction perpendicular to the <−2110> direction, and one gate is provided between the two source electrodes 16. An electrode 17 is disposed. Further, the surface of the insulating film 13 is exposed from the gap between the source electrode 16 and the gate electrode 17. Thus, when the surface of the source electrode 16 is striped, as will be described later, the side wall 19 of the groove 20 (the crystal plane tilted within the range of 50 ° to 65 ° with respect to the {0001} plane) ), The channel direction tends to be easily formed within a range of ± 10 ° in a direction perpendicular to the <−2110> direction. In the present invention, the channel direction means a direction in which carriers move in the side wall 19 of the groove 20.

  Here, the channel direction of the silicon carbide semiconductor device 1 configured as described above is within the side wall 19 of the groove 20 formed of a crystal plane inclined within a range of 50 ° to 65 ° with respect to the {0001} plane. It is formed so as to be included in a range of a direction ± 10 ° perpendicular to the <−2110> direction.

  Hereinafter, an example of the manufacturing method of the silicon carbide semiconductor device 1 having the above-described configuration will be described. First, as shown in the schematic cross-sectional view of FIG. 3, a substrate 11 made of silicon carbide (4H—SiC) having a surface 11 a made of, for example, a {2-1-10} crystal plane is prepared.

  Next, as shown in the schematic cross-sectional view of FIG. 4, the semiconductor layer 12 is formed on the surface 11 a of the substrate 11.

Here, the semiconductor layer 12 can be formed by, for example, epitaxially growing the semiconductor layer 12 made of n-type silicon carbide having n-type impurities at a lower concentration than the substrate 11 on the surface 11 a of the substrate 11. it can. When the semiconductor layer 12 is formed by the above-described epitaxial growth, the crystal plane of the surface 11a of the substrate 11 can be inherited by the surface 12a of the semiconductor layer 12. Therefore, for example, the surface 11a of the substrate 11 is {2-1-10. }, The surface 12a of the semiconductor layer 12 can also be a {2-1-10} crystal plane as shown in the schematic plan view of FIG.

  Next, as shown in the schematic cross-sectional view of FIG. 6, the second conductivity type impurity diffusion layer 14 is formed in the surface 12 a of the semiconductor layer 12. In this example, the second conductivity type impurity diffusion layer 14 is formed in a stripe shape extending in the <-2110> direction, but is not limited to this shape.

  Here, the second conductivity type impurity diffusion layer 14 is formed, for example, after an ion implantation prevention mask is provided in a region other than the formation region of the second conductivity type impurity diffusion layer 14 in the surface 12 a of the semiconductor layer 12. A p-type impurity ion as a type impurity can be formed by ion implantation into the surface 12 a of the semiconductor layer 12. As the ion implantation preventing mask, for example, an oxide film patterned by photolithography and etching can be used.

  Next, as shown in the schematic cross-sectional view of FIG. 7, the first conductivity type impurity diffusion layer 15 is formed in the surface of the second conductivity type impurity diffusion layer 14 formed as described above. In this example, the first conductivity type impurity diffusion layer 15 is also formed in a stripe shape extending in the <−2110> direction, but is not limited to this shape.

  Here, the first conductivity type impurity diffusion layer 15 is formed, for example, after an ion implantation prevention mask is provided in a region other than the formation region of the first conductivity type impurity diffusion layer 15 in the surface 12 a of the semiconductor layer 12. An n-type impurity ion as a type impurity can be formed by ion implantation into the surface 12 a of the semiconductor layer 12. Here, as the ion implantation preventing mask, for example, an oxide film patterned by photolithography and etching can be used.

  Next, activation annealing treatment is performed on the semiconductor layer 12 after the second conductivity type impurity diffusion layer 14 and the first conductivity type impurity diffusion layer 15 are formed as described above. Thus, the p-type impurity as the second conductivity type impurity in the second conductivity type impurity diffusion layer 14 ion-implanted as described above and the n type impurity as the first conductivity type impurity in the first conductivity type impurity diffusion layer 15 are obtained. Can be activated.

  Here, the activation annealing treatment is performed at a temperature of about 1700 ° C., for example, on the semiconductor layer 12 after the formation of the second conductivity type impurity diffusion layer 14 and the first conductivity type impurity diffusion layer 15 in an argon gas atmosphere. This can be done by heating for about a minute.

  Next, as shown in the schematic cross-sectional view of FIG. 8, a groove 20 having a side wall 19 is formed on the surface 12 a of the semiconductor layer 12. The groove 20 is removed by, for example, installing an etching mask in a region other than the region where the groove 20 is formed on the surface 12a of the semiconductor layer 12, and then etching and removing the region of the surface 12a of the semiconductor layer 12 where the etching mask is not installed. Can be formed.

  Here, for example, when the channel direction is made coincident with the extending direction of the side wall 19 of the groove 20, a direction orthogonal to the <−2110> direction is specified on the basis of the defect formed in the semiconductor layer 12, for example, FIG. As shown in the schematic plan view, the groove 20 is formed so that the extending direction (upward direction in FIG. 9) of the side wall 19 of the groove 20 is included in the range of ± 10 ° in the direction orthogonal to the <−2110> direction. It is preferable to do.

  In the manufacturing process of the silicon carbide semiconductor device 1, defects may be formed in certain locations of the semiconductor layer 12, and therefore by using the position of the defects formed in certain locations of the semiconductor layer 12 as a reference, For example, when the channel direction coincides with the extension direction of the side wall 19 of the groove 20, the extension direction of the side wall 19 of the groove 20 is included in a range of ± 10 ° perpendicular to the <−2110> direction. This is because it can be easily formed.

  Further, for example, as shown in the schematic perspective view of FIG. 10, the side wall 19 of the groove 20 is a crystal plane that is inclined with respect to the {0001} plane within an angle α ° of 50 ° to 65 ° (see FIG. 10). 10 hatched portions). Further, the side wall 19 of the groove 20 is preferably also a crystal plane inclined within a range of ± 5 ° with respect to the {03-38} plane, as shown in the schematic cross-sectional view of FIG. When the sidewall 19 of the groove 20 is a crystal plane inclined within a range of ± 5 ° with respect to the {03-38} plane, the electrical characteristics such as channel mobility of the silicon carbide semiconductor device 1 are improved. There is a tendency. Further, from the viewpoint of further improving the electrical characteristics such as channel mobility of the silicon carbide semiconductor device 1, a crystal in which the side wall 19 of the groove 20 is inclined within a range of ± 3 ° with respect to the {03-38} plane. More preferably, the side wall 19 of the groove 20 is a {03-38} plane. A crystal plane inclined within a range of ± 5 ° with respect to the {03-38} plane and a crystal plane inclined within a range of ± 3 ° with respect to the {03-38} plane are each {03 Needless to say, the −38} plane is included.

  Next, as shown in the schematic cross-sectional view of FIG. 12, the insulating film 13 is formed so as to be in contact with the side wall 19 of the groove 20 formed as described above. The insulating film 13 is formed so as to be in contact with the side wall 19 of the groove 20 whose extension direction is controlled so that the extension direction of the side wall 19 of the groove 20 is included in a range of ± 10 ° perpendicular to the <−2110> direction. Accordingly, the channel direction can be formed within a range of ± 10 ° in the direction orthogonal to the <−2110> direction.

  Here, as the insulating film 13, for example, an oxide film formed by dry oxidation (thermal oxidation) or the like can be used. The dry oxidation (thermal oxidation) is performed by heating the surface 12a of the semiconductor layer 12 in which the groove 20 is formed as described above, for example, in air at a temperature of about 1200 ° C. for about 30 minutes. it can.

Next, a nitrogen annealing process is performed on the semiconductor layer 12 after the formation of the insulating film 13. Thus, the nitrogen concentration is adjusted so that the maximum value of the nitrogen concentration in the region within 10 nm from the interface between the sidewall 19 of the trench 20 and the insulating film 13 is 1 × 10 ²¹ cm ⁻³ or more.

Here, the above-described nitrogen annealing treatment is performed, for example, at a temperature of about 1100 ° C. on the semiconductor layer 12 after the formation of the insulating film 13 in an atmosphere of nitrogen-containing gas such as nitrogen monoxide (NO) gas. By performing the heating for about 120 minutes, the maximum value of the nitrogen concentration in the region within 10 nm from the interface between the side wall 19 of the groove 20 and the insulating film 13 can be set to 1 × 10 ²¹ cm ⁻³ or more.

  Further, it is preferable that the semiconductor layer 12 after the nitrogen annealing treatment is further subjected to an inert gas annealing treatment in an atmosphere of an inert gas such as argon gas. When the above-described inert gas annealing process is performed on the semiconductor layer 12 after the nitrogen annealing process, there is a greater tendency for the silicon carbide semiconductor device 1 to achieve high channel mobility with good reproducibility. .

  Here, the above-described inert gas annealing treatment can be performed by heating the semiconductor layer 12 after the above-described nitrogen annealing treatment at a temperature of about 1100 ° C. for about 60 minutes, for example, in an atmosphere of argon gas. .

  Next, as shown in the schematic sectional view of FIG. 13, the insulating film 13 is patterned by removing a part of the insulating film 13 formed as described above.

  Here, the patterning of the insulating film 13 is performed by removing a part of the insulating film 13 so that at least a part of the surface of the first conductivity type impurity diffusion layer 15 in the surface 12a of the semiconductor layer 12 is exposed. .

  The insulating film 13 is partially removed by, for example, forming an etching mask patterned on the surface of the insulating film 13 so that the removed portion of the insulating film 13 is exposed by photolithography and etching. 13 can be formed by removing the exposed portion by etching.

  Next, as shown in FIG. 1, the source electrode 16 is formed so as to be in contact with the surface of the first conductivity type impurity diffusion layer 15 in the surface 12 a of the semiconductor layer 12 exposed from the removed portion of the insulating film 13.

  Here, the source electrode 16 is formed by, for example, sputtering a conductive film made of a metal such as nickel on the surface 12a of the semiconductor layer 12 exposed after the etching of the insulating film 13 and the surface of the etching mask. After the formation, it can be formed by removing the etching mask. That is, the conductive film formed on the surface of the etching mask is removed (lifted off) together with the etching mask, and only the conductive film formed on the surface 12 a of the semiconductor layer 12 remains as the source electrode 16.

  In addition, it is preferable that the semiconductor layer 12 after the formation of the source electrode 16 is subjected to heat treatment for alloying.

  Here, as the heat treatment for alloying, the semiconductor layer 12 after the formation of the source electrode 16 is heated at a temperature of about 950 ° C. for about 2 minutes in an atmosphere of an inert gas such as argon gas, for example. Can be done.

  Next, as shown in FIG. 1, a gate electrode 17 is formed on the surface of the insulating film 13. Here, the gate electrode 17 is, for example, a resist mask having an opening in a portion where the gate electrode 17 is formed by photolithography and etching so as to cover the entire surface of the insulating film 13 and the surface of the source electrode 16. After forming a conductive film made of a metal such as aluminum on the surface of the resist mask and the surface of the insulating film 13 exposed from the opening of the resist mask by, for example, sputtering, the resist mask is removed. Can be formed. That is, the conductive film formed on the surface of the resist mask is removed (lifted off) together with the resist mask, and only the conductive film formed on the surface of the insulating film 13 remains as the gate electrode 17.

  Next, as shown in FIG. 1, the drain electrode 18 is formed on the back surface of the substrate 11. Here, the drain electrode 18 can be formed by, for example, forming a conductive film made of a metal such as nickel on the back surface of the substrate 11 by, for example, sputtering.

Thus, silicon carbide semiconductor device 1 having the configuration shown in FIG. 1 can be manufactured.
In silicon carbide semiconductor device 1 of the present invention, for example, as shown in the schematic plan view of FIG. 14, the surface of source electrode 16 is formed in a honeycomb shape, and a partial region surrounding the outer periphery of source electrode 16 is formed. The excluded region can also be formed as the gate electrode 17.

  As described above, when the surface of the source electrode 16 is formed in a honeycomb shape, the surface of each source electrode 16 is formed in a hexagonal shape, and in particular, it may be formed in a regular hexagonal shape. preferable. When the surface of each source electrode 16 is formed in a regular hexagonal shape, the number of silicon carbide semiconductor devices 1 that can be formed can be increased even when the same size substrate 11 is used. There is a tendency that the silicon carbide semiconductor device 1 having a high degree can be manufactured with higher reproducibility and higher manufacturing efficiency. In this case, each of the second conductivity type impurity diffusion layer 14 and the first conductivity type impurity diffusion layer 15 can also be formed in a hexagonal shape such as a regular hexagonal shape.

  Other configurations of silicon carbide semiconductor device 1 having source electrode 16 and gate electrode 17 configured as shown in FIG. 14 can be the same as described above.

  In silicon carbide semiconductor device 1 having the configuration described above, for example, when a negative voltage is applied to source electrode 16 and a positive voltage is applied to gate electrode 17 and drain electrode 18, carriers injected from source electrode 16 are injected. (Electrons in the above example) move to the drain electrode 18 through the surface of the first conductivity type impurity diffusion layer 15, the side wall 19 of the groove 20, the inside of the semiconductor layer 12, and the inside of the substrate 11.

  Even when a negative voltage is applied to the source electrode 16 and a positive voltage is applied to the drain electrode 18, when a positive voltage is not applied to the gate electrode 17, carriers injected from the source electrode 16 (in the above example) The movement of electrons) is limited in the surface of the second conductivity type impurity diffusion layer 14 on the side wall 19 of the groove 20.

In silicon carbide semiconductor device 1 of the present invention, for example, as shown in FIG. 15, the maximum value of the nitrogen concentration in the region within 10 nm from the interface between side wall 19 of trench 20 and insulating film 13 is 1 × 10 ²¹ cm ^{−. 3} or more. Therefore, in the silicon carbide semiconductor device 1 of the present invention, the interface state generated when the insulating film 13 is formed by dry oxidation (thermal oxidation) or the like at the interface between the side wall 19 of the groove 20 and the insulating film 13 is reduced. Therefore, carrier mobility (channel mobility) can be stably improved particularly in the channel immediately below the insulating film 13 (the side wall 19 portion of the groove 20 in contact with the insulating film 13).

FIG. 15 shows an example of the nitrogen concentration in the vicinity of the interface between side wall 19 of trench 20 and insulating film 13 in silicon carbide semiconductor device 1 having the configuration described above. Here, in FIG. 15, the vertical axis represents the nitrogen concentration (cm ⁻³ ), and the horizontal axis represents the distance (nm) from the interface between the side wall 19 of the trench 20 and the insulating film 13. Further, in FIG. 15, the position where the horizontal axis distance (nm) is 0 (nm) means the interface between the side wall 19 of the trench 20 and the insulating film 13, and the horizontal axis distance (nm) is 0 (nm). ) Toward the insulating film 13 side as it proceeds to the left side, and proceeds toward the side wall 19 side of the groove 20 as the distance (nm) on the horizontal axis proceeds from the location of 0 (nm) to the right side. It means that.

  Furthermore, since silicon carbide semiconductor device 1 having the above-described configuration has a channel direction within a range of ± 10 ° in a direction perpendicular to the <−2110> direction in side wall 19 of groove 20, the channel direction Since the carrier movement in the channel becomes smooth and the carrier mobility and current characteristics in the channel direction can be improved, the on-resistance of the silicon carbide semiconductor device 1 can be reduced.

  FIG. 16 shows that <−2110 in the side wall 19 of the groove 20 of the silicon carbide semiconductor device 1 having the above-described configuration (a crystal plane inclined within a range of 50 ° to 65 ° with respect to the {0001} plane). > An example of the relationship between the angle (°) relative to the direction and the channel mobility (relative value) is shown. In FIG. 16, the vertical axis represents channel mobility (relative value), and the horizontal axis represents an angle (°) with respect to the <−2110> direction in the side wall 19 of the groove 20. Note that the angle (°) of the horizontal axis in FIG. 16 is not limited to the direction of inclination with respect to the <−2110> direction. For example, 80 ° on the horizontal axis is inclined by + 80 ° with respect to the <−2110> direction. And a direction inclined by −80 ° is meant.

  Further, the channel mobility (relative value) on the vertical axis in FIG. 16 is expressed as a relative value when the channel mobility in the direction orthogonal to the <−2110> direction in the side wall 19 of the groove 20 is 1. Yes. Further, the 90 ° portion of the horizontal axis in FIG. 16 indicates a direction orthogonal to the <−2110> direction in the side wall 19 of the groove 20.

  As shown in FIG. 16, in the side wall 19 of the groove 20, the channel mobility is highest when the channel direction is in a direction whose angle with respect to the <-2110> direction is 90 ° (direction orthogonal to the <−2110> direction). Thus, it can be seen that the channel mobility tends to decrease as the deviation from the direction orthogonal to the <−2110> direction in the side wall 19 of the groove 20 increases. Note that the tendency shown in FIG. 16 is established for any crystal plane in which the side wall 19 of the groove 20 is inclined within a range of 50 ° to 65 ° with respect to the {0001} plane.

  Therefore, from the viewpoint of realizing high channel mobility, the channel direction is <− in the side wall 19 of the groove 20 (a crystal plane inclined within a range of 50 ° to 65 ° with respect to the {0001} plane). The case where the direction is orthogonal to the 2110> direction (that is, the direction ± 0 ° orthogonal to the <-2110> direction) is considered most preferable.

  However, as shown in FIG. 16, the angle with respect to the <−2110> direction in the side wall 19 of the groove 20 is in the range of 80 ° to 90 ° (that is, within a range of ± 10 ° in the direction orthogonal to the <−2110> direction). In the case where the channel direction is present in the direction (1), the channel mobility (relative value) is higher than 0.99, and therefore the channel mobility of the silicon carbide semiconductor device 1 varies somewhat due to manufacturing problems or the like. However, it is unlikely that the channel mobility will drop significantly.

  Therefore, in the silicon carbide semiconductor device 1 of the present invention having the channel direction within the range of ± 10 ° in the direction orthogonal to the <−2110> direction in the side wall 19 of the groove 20, high channel mobility is realized with good reproducibility. be able to. Further, in the silicon carbide semiconductor device 1 of the present invention, in order to realize high channel mobility with good reproducibility, the channel direction may be formed in a direction perpendicular to the <−2110> direction in the side wall 19 of the groove 20. Most preferred is as described above.

  In the above description, the case where the first conductivity type is n-type and the second conductivity type is p-type has been described. However, in the present invention, in the configuration of the silicon carbide semiconductor device 1 described above, the first conductivity-type is used. May be p-type and the second conductivity type may be n-type.

(Production of vertical trench gate MOSFET)
A silicon carbide semiconductor device as a vertical trench gate MOSFET of the example was manufactured as follows.

  First, as shown in FIG. 3, a substrate 11 made of an n-type silicon carbide crystal (4H—SiC) having a thickness of 400 μm was prepared. Here, the substrate 11 has a surface 11a made of a {2-1-10} crystal plane.

Next, as shown in FIG. 4, on the surface 11a of the substrate 11, a semiconductor layer 12 made of n-type silicon carbide crystal doped with nitrogen as an n-type impurity (n-type impurity concentration: 5 × 10 ¹⁵ cm ^{−). 3} ) was epitaxially grown to a thickness of 10 μm by a CVD (Chemical Vapor Deposition) method.

  Here, the surface 12a of the semiconductor layer 12 has a {2-1-10} plane having a <-2110> direction and a <03-38> direction orthogonal to the <-2110> direction, as shown in FIG. It was composed of crystal planes.

Next, as shown in FIG. 6, a second conductivity type impurity diffusion layer 14 (p-type impurity concentration: 1 × 10 ¹⁷ cm ⁻³ ) was formed in the surface 12 a of the semiconductor layer 12. Here, the second conductivity type impurity diffusion layer 14 is an oxide film patterned using photolithography and etching in a region other than the formation region of the second conductivity type impurity diffusion layer 14 in the surface 12a of the semiconductor layer 12. Then, using the oxide film as an ion implantation prevention mask, boron, which is a p-type impurity, is implanted by ion implantation. The second conductivity type impurity diffusion layer 14 was formed in a stripe shape extending in the <-2110> direction.

Next, as shown in FIG. 7, the first conductivity type impurity diffusion layer 15 (n-type impurity concentration: 5 × 10 ¹⁹ cm ⁻ is formed in the surface of the second conductivity type impurity diffusion layer 14 formed as described above. ³ ) and a p + type region (not shown) (p type impurity concentration: 3 × 10 ¹⁹ cm ⁻³ ). Here, the first conductivity type impurity diffusion layer 15 is formed in a stripe shape extending in the <−2110> direction, and the p + -type region is formed outside the first conductivity type impurity diffusion layer 15 shown in FIG. A stripe shape extending in the <−2110> direction so as to be in contact with the conductive impurity diffusion layer 15 was formed.

  The first conductivity type impurity diffusion layer 15 forms an oxide film patterned using photolithography and etching in a region other than the formation region of the first conductivity type impurity diffusion layer 15 in the surface 12a of the semiconductor layer 12. Then, the oxide film was used as an ion implantation preventing mask, and phosphorus, which is an n-type impurity, was ion implanted. The p + -type region also forms an oxide film patterned by photolithography and etching in a region other than the formation region of the p + -type region in the surface 12a of the semiconductor layer 12, and the oxide film is ion-implanted. A p-type impurity boron was ion-implanted as a prevention mask.

  Next, the second conductivity type impurity diffusion layer 14, the first conductivity type impurity diffusion layer 15 and the semiconductor layer 12 formed with the p + type region as described above are heated in an argon gas atmosphere at 1700 ° C. for 30 minutes. Thus, activation annealing treatment was performed.

  Next, as shown in FIG. 8, a groove 20 having a side wall 19 is formed on the surface 12 a of the semiconductor layer 12. For example, the groove 20 is formed by providing an etching mask in a region other than the region where the groove 20 is formed on the surface 12 a of the semiconductor layer 12, and then forming a region where the etching mask is not formed on the surface 12 a of the semiconductor layer 12. It can be formed by etching and removing perpendicular to the surface 12a of the semiconductor layer 12. Here, the groove 20 is formed by specifying a direction orthogonal to the <−2110> direction on the basis of the defect formed in the semiconductor layer 12 and setting the channel direction to the side wall 19 of the groove 20 as shown in FIG. 9. In order to coincide with the extension direction, the groove 20 was formed so that the extension direction of the side wall 19 of the groove 20 was included in a range of ± 10 ° in a direction perpendicular to the <−2110> direction. As a result, the side wall 19 of the groove 20 was composed of a {03-38} plane which is a crystal plane inclined at an angle of about 55 ° with respect to the {0001} plane. Further, the side wall 19 of the groove 20 extends in a direction perpendicular to the surface 12 a ({2-1-10} plane) of the semiconductor layer 12.

  Next, as shown in FIG. 12, the surface 12a of the semiconductor layer 12 is heated in air at 1200 ° C. for 30 minutes for dry oxidation (thermal oxidation), whereby an insulating film in contact with the entire surface 12a of the semiconductor layer 12 is obtained. 13 was formed.

  Next, nitrogen annealing treatment was performed by heating the semiconductor layer 12 after the formation of the insulating film 13 at 1100 ° C. for 120 minutes in a nitrogen monoxide (NO) gas atmosphere.

  Next, an inert gas annealing process was performed by heating the semiconductor layer 12 after the above-described nitrogen annealing process in an argon gas atmosphere at 1100 ° C. for 60 minutes.

  Next, as shown in FIG. 13, the insulating film is exposed so that a part of the surface of the first conductivity type impurity diffusion layer 15 and the surface of the p + -type region (not shown) in the surface 12 a of the semiconductor layer 12 are exposed. Part of 13 was removed and the insulating film 13 was patterned. Here, the patterning of the insulating film 13 is performed by forming an etching mask patterned on the surface of the insulating film 13 so as to expose the removed portion of the insulating film 13 by photolithography and etching, and then exposing the insulating film 13. This was done by removing the portion by etching.

  Next, nickel having a regular hexagonal surface as shown in FIG. 14 is formed on the surface of the first conductivity type impurity diffusion layer 15 and the p + type region (not shown) exposed from the removed portion of the insulating film 13. A source electrode 16 having a thickness of 0.1 μm was formed.

  Next, heat treatment for alloying was performed by heating the semiconductor layer 12 after the formation of the source electrode 16 at 950 ° C. for 2 minutes in an argon gas atmosphere.

  Next, a 1 μm thick gate electrode 17 made of aluminum having a surface shape as shown in FIG. 14 was formed on the surface of the insulating film 13.

  Next, a drain electrode 18 made of nickel and having a thickness of 0.1 μm was formed on the entire back surface of the substrate 11.

  Thus, silicon carbide semiconductor device 1 as a vertical trench gate MOSFET of the example was manufactured.

  Channel length of silicon carbide semiconductor device 1 as the vertical trench gate MOSFET of the embodiment manufactured as described above (extending direction of side wall 19 of first conductivity type impurity diffusion layer 15 exposed at side wall 19 of groove 20) Was 2 μm.

  For comparison, a silicon carbide semiconductor device as a vertical trench gate MOSFET of a comparative example was fabricated in the same manner as described above except that the channel direction in the surface 12a of the sidewall 19 of the groove 20 was set to the <-2110> direction. .

(Evaluation of vertical trench gate MOSFET)
Regarding the vertical trench gate MOSFETs of the example and the comparative example manufactured as described above, the distribution in the depth direction of the nitrogen concentration in the vicinity of the interface between the side wall 19 of the groove 20 and the insulating film 13 is expressed as SIMS (secondary ion mass). Analysis).

As a result, in each of the vertical trench gate MOSFETs of the example and the comparative example, the maximum value of the nitrogen concentration in the vicinity of the interface between the side wall 19 of the groove 20 and the insulating film 13 is 1 × 10 ²¹ cm ⁻³ or more, respectively. It was. Therefore, in each of the vertical trench gate MOSFETs of the example and the comparative example, the maximum value of the nitrogen concentration in the region within 10 nm from the interface between the side wall 19 of the trench 20 and the insulating film 13 is 1 × 10 ²¹ cm ⁻³ or more. It was confirmed that

  Further, channel mobility was evaluated for the vertical trench gate MOSFETs of the example and the comparative example. The following method was used as the channel mobility evaluation method. First, with the source-drain voltage VDS = 0.1 V, the gate voltage VG was applied to measure the source-drain current IDS (the gate voltage dependency was measured). Then, as gm = (δIDS) / (δVG), the maximum value of the channel mobility with respect to the gate voltage was obtained by the following equation (1), and the maximum value was calculated as the channel mobility.

Channel mobility μ = gm × (L × d) / (W × ε × VDS) (1)
In the above equation (1), L represents the channel length, d represents the thickness of the insulating film 13, W represents the channel width, and ε represents the dielectric constant of the insulating film 13.

As a result, the channel mobility of the vertical trench gate MOSFET of the example was 100 cm ² / Vs, and the channel mobility of the vertical trench gate MOSFET of the comparative example was 40 cm ² / Vs.

  Therefore, the channel mobility of the vertical trench gate MOSFET of the example is 2.5 times the channel mobility of the vertical trench gate MOSFET of the comparative example, and accordingly, the source-drain current value is 2.5 times. Therefore, it was confirmed that the on-resistance is greatly reduced.

  Therefore, according to the configuration of the vertical trench gate MOSFET of the embodiment, even if the channel mobility varies somewhat due to a manufacturing problem, it is unlikely that the channel mobility will be greatly reduced, so high channel mobility is reproduced. It can be realized with good performance.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. 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.

  According to the present invention, it is possible to provide a silicon carbide semiconductor device capable of realizing high channel mobility with good reproducibility and a method for manufacturing the same. Therefore, the present invention provides a vertical trench gate MOSFET using SiC, for example. There is a possibility that it can be suitably used.

It is typical sectional drawing of an example of the vertical trench gate MOSFET which is an example of the silicon carbide semiconductor device of this invention. It is the typical top view which looked at the silicon carbide semiconductor device shown in FIG. 1 from the gate electrode side. It is typical sectional drawing illustrating a part of manufacturing process of an example of the manufacturing method of the silicon carbide semiconductor device of this invention. It is typical sectional drawing illustrating a part of manufacturing process of an example of the manufacturing method of the silicon carbide semiconductor device of this invention. It is a typical top view illustrating an example of the surface of the semiconductor layer in the present invention. It is typical sectional drawing illustrating a part of manufacturing process of an example of the manufacturing method of the silicon carbide semiconductor device of this invention. It is typical sectional drawing illustrating a part of manufacturing process of an example of the manufacturing method of the silicon carbide semiconductor device of this invention. It is typical sectional drawing illustrating a part of manufacturing process of an example of the manufacturing method of the silicon carbide semiconductor device of this invention. It is a typical top view illustrating an example of the side wall of the groove | channel in this invention. It is a typical perspective view illustrating an example of the crystal plane of the side wall of the groove | channel in this invention. It is typical sectional drawing illustrating a preferable example of the crystal plane of the side wall of the groove | channel in this invention. It is typical sectional drawing illustrating a part of manufacturing process of an example of the manufacturing method of the silicon carbide semiconductor device of this invention. It is typical sectional drawing illustrating a part of manufacturing process of an example of the manufacturing method of the silicon carbide semiconductor device of this invention. It is the typical top view which looked at another example of the silicon carbide semiconductor device of this invention from the gate electrode side. It is a figure which shows an example of distribution of the nitrogen concentration in the interface vicinity of the side wall of a groove | channel and an insulating film in an example of the silicon carbide semiconductor device of this invention. It is a figure which shows an example of the relationship between the angle (degree) with respect to the <-2110> direction and the channel mobility (relative value) in the side wall of the groove | channel in an example of the silicon carbide semiconductor device of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Silicon carbide semiconductor device, 11 board | substrate, 11a surface, 12 semiconductor layer, 12a surface, 13 insulating film, 14 2nd conductivity type impurity diffusion layer, 15 1st conductivity type impurity diffusion layer, 16 source electrode, 17 gate electrode, 18 Drain electrode, 19 side walls, 20 grooves.

Claims (9)

A semiconductor layer made of silicon carbide having on its surface a groove with a side wall made of a crystal plane inclined within a range of 50 ° or more and 65 ° or less with respect to the {0001} plane;
An insulating film formed in contact with the side wall of the groove,
The maximum value of the nitrogen concentration in a region within 10 nm from the interface between the sidewall of the trench and the insulating film is 1 × 10 ²¹ cm ⁻³ or more,
A silicon carbide semiconductor device having a channel length direction within a range of ± 10 ° in a direction perpendicular to the <−2110> direction in the side wall of the groove. A substrate made of silicon carbide of the first conductivity type;
A sidewall formed of a crystal plane formed on the substrate and containing a first conductivity type impurity at a lower concentration than the substrate and tilted within a range of 50 ° to 65 ° with respect to the {0001} plane is provided. A semiconductor layer made of silicon carbide of the first conductivity type having grooves on the surface;
A second conductivity type impurity diffusion layer formed on the side wall of the groove;
A first conductivity type impurity diffusion layer formed in the surface of the semiconductor layer;
An insulating film formed in contact with the side wall of the groove;
A source electrode formed so as to be in contact with at least a part of a region other than a portion where the insulating film is formed on the surface of the semiconductor layer;
A gate electrode formed on the insulating film;
A drain electrode formed on the surface of the substrate opposite to the side on which the semiconductor layer is formed,
The maximum value of the nitrogen concentration in a region within 10 nm from the interface between the sidewall of the trench and the insulating film is 1 × 10 ²¹ cm ⁻³ or more,
A silicon carbide semiconductor device having a channel length direction within a range of ± 10 ° in a direction perpendicular to the <−2110> direction in the side wall of the groove.   The silicon carbide semiconductor device according to claim 2, wherein a surface of the source electrode has a stripe shape.   The silicon carbide semiconductor device according to claim 2, wherein a surface of the source electrode has a honeycomb shape.   5. The silicon carbide semiconductor according to claim 1, wherein the side wall of the groove is formed of a crystal plane inclined within a range of ± 5 ° with respect to a {03-38} plane. apparatus. Forming a groove having a side wall made of a crystal plane inclined within a range of 50 ° to 65 ° with respect to the {0001} plane on the surface of the semiconductor layer made of silicon carbide;
Forming an insulating film in contact with the side wall of the groove so that a channel length direction is formed within a range of ± 10 ° in a direction perpendicular to the <−2110> direction in the side wall of the groove;
Adjusting the nitrogen concentration so that the maximum value of the nitrogen concentration in the region within 10 nm from the interface between the sidewall of the trench and the insulating film is 1 × 10 ²¹ cm ⁻³ or more. Manufacturing method. 7. The channel length direction is formed within a range of ± 10 ° in a direction perpendicular to the <−2110> direction in the side wall of the groove based on the orientation of defects included in the semiconductor layer. A method for producing a silicon carbide semiconductor device according to claim 1.   The carbonization according to claim 6 or 7, wherein the step of adjusting the nitrogen concentration includes a step of heat-treating the semiconductor layer on which the insulating film is formed in an atmosphere of a gas containing nitrogen. A method for manufacturing a silicon semiconductor device.   The method for manufacturing a silicon carbide semiconductor device according to claim 8, wherein the step of adjusting the nitrogen concentration includes a step of heat-treating the semiconductor layer after the heat treatment in an atmosphere of an inert gas.

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