Silicon carbide semiconductor device and method of fabricating the same

A method of fabricating a silicon carbide semiconductor device, comprising the steps of:

• forming a semiconductor layer (2) on a main surface of a semiconductor substrate (1), the semiconductor layer (2) and the semiconductor substrate (1) being of a first conductivity type, the semiconductor layer (2) being made of silicon carbide, the semiconductor substrate (1) being made of silicon carbide, the semiconductor layer (2) being higher in resistivity than the semiconductor substrate (1);
• forming a first gate region (3) in a surface portion of the semiconductor layer (2), the first gate region (3) being of a second conductivity type different from the first conductivity type;
• forming a channel layer (5) of the first conductivity type on the semiconductor layer (2) and the first gate region (3);
• forming a source region (6) of the first conductivity type in the channel layer (5), the source region (6) being opposed to the first gate region (3);
• forming a second gate region (7) in a surface portion of the channel layer (5), the second gate region (7) being of the second conductivity type and containing a positional range opposed to the source region (6);
• forming a recess (8) in the channel layer (5), the recess (8) extending through the second gate region (7) and the source region (6) and reaching the first gate region (3);
• forming a first gate electrode (9, 33, 42), a source electrode (9, 32, 41), and a second gate electrode (10, 32, 43), the first gate electrode (9, 33, 42) being electrically connected with the first gate region (3), the source electrode (9, 32, 41) being electrically connected with the source region (6), the second gate electrode (10, 32, 43) being electrically connected with the second gate region (7);
• and
• forming a drain electrode (12) on a back surface of the semiconductor substrate (1);
• wherein the step of forming the source region (6) and the step of forming the second gate region (7) comprise the sub-steps of:
• (a) placing first and second mask films (21, 22) on the channel layer (5), the first mask film (21) being covered with the second mask film (22);
• (b) forming first and second openings (21A, 22A) in the first and second mask films (21, 22) respectively;
• (c) implanting first ions into a first predetermined place in the channel layer (5) which is assigned to the source region (6) while using the first and second mask films (21, 22) as a mask, the first ions being first impurities corresponding to the first conductivity type;
• (d) implanting second ions into a second predetermined place in the channel layer (5) which is different from the first predetermined place and is assigned to a portion of the second gate region (7) while using the first and second mask films (21, 22) as a mask, the second ions being second impurities corresponding to the second conductivity type;
• (e) oxidating a portion of the first mask film (21) which extends from the first opening (21A) while the first mask film (21) remains covered with the second mask film (22);
• (f) removing the second mask film (22) and the oxidated portion of the first mask film (21);
• (g) implanting third ions into a third predetermined place in the channel layer (5) which is different from the first predetermined place and is assigned to the second gate region (7) while using a remaining portion (21B) of the first mask film (21) as a mask, the third ions being third impurities corresponding to the second conductivity type;
• and
• (h) activating the implanted first, second, and third impurities to form the source region (6) and the second gate region (7).