A method for fabricating an integrated circuit (IC) includes etching trenches into a semiconductor surface of a substrate that has a mask thereon. Trench implanting using an angled implant then forms doped sidewalls of the trenches. Furnace annealing after trench implanting includes a ramp-up portion to a maximum peak temperature range of at least 975° C. and ramp-down portion, wherein the ramp-up portion is performed in a non-oxidizing ambient for at least a 100° C. temperature ramp portion with an O2 flow being less than 0.1 standard liter per minute (SLM). The sidewalls and a bottom of the trench are thermally oxidized to form a liner oxide after furnace annealing to form dielectric lined trenches. The dielectric lined trenches are filled with a fill material, and overburden portions of the fill material are then removed to form filled trenches.