US 9,812,548 B2
Power device having a polysilicon-filled trench with a tapered oxide thickness
Richard A. Blanchard, Los Altos, CA (US); Mohamed N. Darwish, Campbell, CA (US); and Jun Zeng, Torrance, CA (US)
Assigned to MAXPOWER SEMICONDUCTOR, INC., San Jose, CA (US)
Filed by MaxPower Semiconductor, Inc., San Jose, CA (US)
Filed on Aug. 25, 2016, as Appl. No. 15/247,510.
Claims priority of provisional application 62/215,563, filed on Sep. 8, 2015.
Claims priority of provisional application 62/218,375, filed on Sep. 14, 2015.
Prior Publication US 2017/0069727 A1, Mar. 9, 2017
Int. Cl. H01L 21/04 (2006.01); H01L 29/66 (2006.01); H01L 29/78 (2006.01); H01L 29/40 (2006.01); H01L 29/10 (2006.01); H01L 29/06 (2006.01); H01L 29/16 (2006.01); H01L 21/265 (2006.01); H01L 29/423 (2006.01); H01L 29/08 (2006.01); H01L 29/417 (2006.01)
CPC H01L 29/66068 (2013.01) [H01L 21/047 (2013.01); H01L 21/26586 (2013.01); H01L 29/0623 (2013.01); H01L 29/0634 (2013.01); H01L 29/0878 (2013.01); H01L 29/1037 (2013.01); H01L 29/1095 (2013.01); H01L 29/16 (2013.01); H01L 29/407 (2013.01); H01L 29/42368 (2013.01); H01L 29/66734 (2013.01); H01L 29/7813 (2013.01); H01L 29/1608 (2013.01); H01L 29/41766 (2013.01)] 18 Claims
OG exemplary drawing
 
1. A method of forming a semiconductor device comprising
providing a silicon-containing substrate having a top surface;
epitaxially growing at least one first layer over the top surface of the substrate;
etching a first trench into the at least one first layer to a first depth;
implanting nitrogen ions into at least sidewalls of the first trench at a plurality of angles to create a tapered nitrogen dopant concentration along the sidewalls, wherein the nitrogen dopant concentration along the sidewalls increases from a bottom of the first trench to a top of the first trench to create the tapered nitrogen dopant concentration;
annealing the sidewalls to form a tapered thickness of silicon nitride along the sidewalls;
oxidizing the sidewalls to form silicon dioxide along the sidewalls, wherein a thickness of the silicon dioxide is tapered along the sidewalls due to the tapered thickness of the silicon nitride variably inhibiting growth of the silicon dioxide so that the silicon dioxide near the bottom of the trench is substantially thicker than the silicon dioxide near the top of the trench;
at least partially filling the first trench with a conductive material;
forming a first electrode overlying the at least one first layer; and
forming a second electrode, wherein current is conducted between the first electrode and second electrode when the device is turned on.