Grabenisolation unter Verwendung dotierter Seitenwände

摘要

A P-type substrate 16 is immersed in a solution of potassium hydroxide (KOH) which etches exposed portions of the substrate to form trenches 14 with sidewalls 30 at an angle of 54.7 degrees with respect to the top surface of the substrate. A vertical boron implant is then conducted which implants boron ions into the angled sidewalls of the trenches. A layer of oxide 54, is then deposited over the substrate surface to fill the trenches approximately flush with the surface of the substrate. NMOS transistors may then be formed in the islands surrounded by the trenches so as to be isolated from other NMOS devices. The boron doping of the sidewalls prevents the inversion of the sidewalls due to any charged contaminants in the deposited oxide. This avoids parasitic leakage currents between the N-type source and drain regions of the NMOS transistors which abut the sidewalls of the trenches. <IMAGE>