Method of fabricating programmable read only memory device having trench isolation structure

A method of fabricating a semiconductor integrated circuit, comprising the steps of:

• forming a first gate insulating film selectively on a main surface of a semiconductor substrate;
• forming a first polysilicon layer on said first gate insulating film;
• forming a second gate insulating film on the surface of said first polysilicon layer;
• forming a second polysilicon layer on said second gate insulating film;
• forming trenches for isolating elements by selectively removing said second polysilicon layer, said second gate insulating film, said first polysilicon layer, said first gate insulating film and said semiconductor substrate;
• forming a BPSG film over the entire resulting surface to fill said trenches;
• selectively removing said BPSG film to leave said BPSG film in said trenches;
• forming a word line in contact with said second polysilicon layer;
• selectively etching, by using said work line as a mask, said second polysilicon layer, said second gate insulating film, and said first polysilicon layer;
• forming an insulating layer having contact holes for exposing parts of said semiconductor substrate;
• and
• forming a bit line in contact with said parts of said semiconductor substrate through said contact holes.

A method of fabricating a semiconductor integrated circuit, comprising the steps of:

• forming a first gate insulating film selectively on a main surface of a semiconductor substrate;
• forming a first polysilicon layer on said first gate insulating film;
• forming a second gate insulating film on the surface of said first polysilicon layer;
• forming a second polysilicon layer on said second gate insulating film;
• forming trenches for isolating elements by selectively removing said second polysilicon layer, said second gate insulating film, said first polysilicon layer, said first gate insulating film and said semiconductor substrate;
• filling said trenches with a BPSG film;
• forming an insulating layer having contact holes for exposing parts of said second polysilicon layer;
• and
• forming a word line in contact with said parts of said second polysilicon layer through said contact holes.

A method of providing electrical isolation between devices on a semiconductor substrate, said method comprising the steps of;

• successively growing gate insulating layers on said substrate;
• covering each of said insulating layers with a polysilicon film, wherein beginning at said substrate said layers and films are:
• a first gate oxide film for peripheral transistors, a first polysilicon film, a second gate oxide film, and a second polysilicon film;
• forming separation trenches through said layers and films and between said devices in order to isolate the devices from each other, whereby sections of said gate insulating layers and polysilicon films are isolated for form individual ones of said devices;
• depositing BPSG on said substrate to form a film and fill said trenches, said second polysilicon film protecting said gate insulating layers from deterioration responsive to the deposit of said BPSG.