etched using the photoresist 110 as a mask to provide the structure shown in fig2 after removal of the photoresist 110 oxide is grown on the resulting structure forming oxide layer 109 and a layer of nitride 113 is deposited thereon photoresist 112 is patterned over the layer of nitride 113 and the nitride 113 is etched using the photoresist 112 as a mask fig2 the photoresist 112 is then removed the oxide 109 and substrate 100 are then etched fig2 using the nitride 113 as a mask to define a recess 114 in the substrate 100 the recess surfaces are then oxidized 117 successive layers of polysilicon 115 and nitride 116 are deposited over the resulting structure a layer of photoresist 118 is deposited over the nitride layer 116 and portions of the photoresist layer 118 are removed to provide the structure shown in fig2 successive etching steps are undertaken using the photoresist 118 as a mask etching in turn the nitride layer 116 and the polysilicon layer 115 the photoresist 118 is then removed leaving the structure shown in fig2 an oxidation step is then undertaken wherein the polysilicon 115 is oxidized to form the oxide insulating material portions 120 122 these oxide insulating portions 120 122 are positioned on either side of the recess 114 and are tapered inward in the direction inward of the recess 114 subsequently the nitride 116 113 and the polysilicon 115 are removed by appropriate steps and the oxide is etched to expose the substrate 100 at.