Method of forming a bottom oxide layer in a trench

A method for forming a bottom oxide layer on a semiconductor substrate, said method comprising:

• etching said semiconductor substrate to form a trench thereon;
• performing a low pressure chemical vapor deposition to form an oxide layer on said semiconductor substrate and on the sidewall and the bottom of said trench;
• depositing a nitride layer along the surface of said oxide layer;
• forming a photo-resist filler in said trench, wherein a portion of said nitride layer on the sidewall of said trench is not covered by said photo-resist layer and is exposed;
• removing said exposed potion of said nitride layer for exposing said oxide layer underneath;
• removing said oxide layer on said semiconductor substrate and on said sidewall of said trench to have a remaining portion of said oxide layer covered by said photo-resist filler on the bottom of said trench;
• removing said photo-resist filler;
• and
• removing said nitride layer to expose said remaining portion of said oxide layer in said trench.

A method of forming a bottom oxide layer in a trench on a semiconductor substrate, said method comprising:

• depositing a nitride layer and an oxide layer on said substrate in sequence;
• defining a trench pattern in said oxide layer and said nitride layer to expose a portion of the surface of said substrate;
• etching said substrate to form a trench therein by applying said oxide layer and said nitride layer to serve as etching masks;
• forming a TEOS material layer on said oxide layer and the surface of sidewall and the bottom of said trench;
• forming a second nitride layer on said TEOS material layer;
• coating a photo-resist layer on said substrate to fill said trench;
• performing the exposing process to cure the lower portion of said photo-resist layer in said trench;
• removing the upper portion of said photo-resist layer to form a photo-resist filler in said trench for exposing a portion of the second said nitride layer on said semiconductor substrate and on the sidewall of said trench;
• removing said exposed portion of said second nitride layer for exposing said TEOS material layer underneath;
• removing said TEOS material layer on said oxide layer and said sidewalls of said trench, wherein a portion of said TEOS material layer remains on the bottom of said trench;
• removing said photo-resist filler;
• and
• removing said second nitride layer to expose said remaining portion of said TEOS material layer in said trench.