Patent ID: 9536743
Date: 2017-01-03
CPC Classifications: H01L

Claim:
1. A method for making a power device with a trench-gate structure on a semiconductor substrate, the method comprising: a first etching of the semiconductor substrate to make a first trench having first side walls and a first bottom; coating the first side walls and the first bottom of the first trench with a service insulating layer; forming service spacers on the service insulating layer; a second etching of the semiconductor substrate to make a second trench in the first bottom of the first trench and extending below the first trench, the second trench having second side walls and a second bottom, the second side walls being aligned with the service spacers to define a continuous surface, the second walls and the second bottom comprising exposed surface of the semiconductor substrate; forming a first insulating coating layer over the second side walls and the second bottom, the service spacers preventing forming of the first insulating coating layer on the first side walls of the first trench, the width of the second trench being less than the width of the first trench; after the forming of the first insulating coating layer over the second side walls, removing the service spacers and the service insulating layer, and forming a second insulating coating layer over exposed surfaces of the semiconductor substrate exposed by the removal of the service spacers; and forming electrically conductive material in the first trench and in the second trench; the first and second insulating coating layers having different thicknesses and defining the trench-gate structure with a transition profile that reduces in thickness when progressing into the semiconductor substrate.