Fabrication process method for increasing an oxide thickness at trench bottom and a trench gate metal-oxide-semiconductor field-effect transistor formed by using the same

A fabrication process method for increasing an oxide thickness at trench bottom, comprising:

• providing a semiconductor substrate and forming a drift region on the semiconductor substrate;
• forming a first heavily doped region in the drift region;
• forming a second heavily doped region and a third heavily doped region respectively on opposite sides of the first heavily doped region, and providing a well region between the first heavily doped region, the second heavily doped region, the third heavily doped region and the drift region;
• depositing a hard mask layer on the first heavily doped region, the second heavily doped region and the third heavily doped region, and using a lithography process to form a trench;
• depositing a pad oxide layer after removing the hard mask layer, wherein the pad oxide layer covers two opposite sidewalls and a bottom of the trench;
• depositing a silicate glass, wherein the silicate glass covers the pad oxide layer on the two opposite sidewalls of the trench to form two spacers, and a spacing is retained between the two spacers;
• and
• performing a thermal process such that the silicate glass flows toward the spacing and fills the spacing and the bottom of the trench, forming a thick oxide layer at the bottom of the trench.