Patent ID: 9390962
Filing Date: 2016-07-12
CPC Classification: H01L

Claim Text:
1. A method for fabricating a device substrate, the method comprising the steps of: providing a semiconductor substrate with a substrate surface and having a low voltage (LV) region and a second voltage region that is either a medium voltage (MV) region or a high voltage (HV) region; thermally oxidizing a trench-forming area on the substrate surface in the second voltage region to form a silicon oxide layer, wherein the silicon oxide layer has birds beak edges that extend in opposite directions and form rounded trench shoulders of the semiconductor substrate in the second voltage region; forming an LV trench in the semiconductor substrate in the LV region such that the semiconductor substrate has an LV shoulder; forming a trench in the silicon oxide layer and semiconductor substrate in the second voltage region such that the semiconductor substrate has a rounded trench shoulder adjacent a birds beak edge; removing the birds beak edge in the second voltage region; and forming an oxide layer lining each of the LV trench and LV shoulder in the LV region, wherein the LV shoulder and the oxide layer thereon form an LV trench corner; and forming an oxide layer lining each of the trench and rounded trench shoulder in the second voltage region, wherein the rounded trench shoulder in the second voltage region and oxide layer thereon form a rounded trench corner in the second voltage region that is more rounded than the LV corner.