Semiconductor device and method of fabrication

A method of fabricating a semiconductor device, said method comprising performing the following steps in the following sequence:

• providing a substrate comprising first and second gate regions separated by a trench formed in said substrate wherein said substrate is divided into a first area which includes said first gate region and a first part of said trench and a second area which includes said second gate region and a second part of said trench;
• growing a thin oxide layer on each of said first and second gate regions;
• depositing a polysilicon layer on said thin oxide layer;
• depositing a photoresist layer on said layer of polysilicon, exposing said photoresist and removing said photoresist layer from said second area;
• removing said polysilicon layer from said second area;
• removing said thin oxide layer from said second gate region using a wet etch, wherein said polysilicon layer in said first area protects said thin oxide layer in said first gate region;
• growing a thick oxide layer on said second gate region and on said polysilicon layer in said first area;
• depositing a further photoresist layer on said thick oxide layer, exposing said further photoresist and removing said further photoresist layer from said first area;
• removing said thick oxide layer from said polysilicon layer in said first area;
• depositing a further polysilicon layer over said first and second areas;
• and
• selectively removing portions of said further polysilicon layer using a photoresist and dry etching to form two gates of said semiconductor device.