Two-step oxide trench silicon carbide mosfet

A semiconductor device comprising:

• a semiconductor substrate of a first conductivity type, wherein the semiconductor substrate is formed by Silicon Carbide (SiC);
• a drift region of the first conductivity type formed on the semiconductor substrate;
• a channel of a second conductivity type opposite to the first conductivity type formed on the drift region;
• a source region of the first conductivity type formed on the channel;
• a trench that penetrates through the source region and the channel and reaches the drift region;
• an oxide region that lines the trench, wherein:
• the oxide region comprises a bottom portion, a lower side portion and an upper side portion;
• a thickness of the bottom portion is greater than a thickness of the upper side portion;
• and
• a thickness of the lower side portion is greater than the thickness of the upper side portion;
• at least one gate electrode formed in the trench lined with the oxide region;
• and
• a shield region of the second conductivity type in contact with the bottom portion of the trench and a width of the shield region is at most equal to a width of the trench.

A method of forming a semiconductor device, comprising:

• forming a first oxide layer having a first thickness to line a trench formed in a Silicon Carbide (SiC) substrate;
• forming a conductive material on a bottom portion of the trench lined with the first oxide layer;
• forming a nitride layer above the conductive material and along sidewalls of the trench;
• using the nitride layer as hardmask to etch the conductive material;
• conducting a first oxidation process on a remaining portion of the conductive material to form a bottom portion and a lower side portion of an oxide region within the trench;
• removing the nitride layer;
• cleaning exposed sidewalls of the trench;
• conducting a second oxidation process on the exposed sidewalls of the trench to form an upper side portion of the oxide region;
• and
• forming a gate electrode in the trench lined with the oxide region.