The opening width of an element isolating trench is Wa'. The opening width of a substrate potential setting trench is Wb'. When the maximum film thickness of a polysilicon film lying on the side wall of each of the trenches is set to t, the opening width Wa' of the element isolating trench...http://www.google.com/patents/US5675173?utm_source=gb-gplus-sharePatent US5675173 - Semiconductor device having a trench for isolating elements and a trench for applying a potential to a substrate 
