Method of making laser recrystallized silicon-on-insulator nonvolatile memory device

A method of making a nonvolatile semiconductor memory device on a substrate comprising:

• forming a conductive polysilicon gate on a surface portion of the substrate;
• forming a silicon nitride layer on said gate and the remaining surface portion of the substrate;
• forming a relatively thick silicon dioxide layer on said nitride;
• removing said thick oxide corresponding to a central portion of the gate thereby exposing the nitride thereunder;
• thermally oxidizing said exposed nitride layer to form a relatively thin oxide layer thereon;
• forming a doped polysilicon layer on said thin oxide layer and the thick oxide layer;
• subjecting said polysilicon layer to a laser beam to convert the polysilicon layer into a recrystallized silicon layer;
• patterning the recrystallized silicon layer into an active area;
• masking the recrystallized silicon layer in correspondence with the gate;
• and
• forming source and drain regions in said recrystallized silicon in alignment with the gate.

A method of making a nonvolatile silicon gate field effect transistor on a substrate comprising:

• forming a conductive n-type polysilicon gate on a surface portion of said substrate;
• forming a first silicon nitride layer on said gate and the remaining surface portion of the substrate;
• forming a relatively thick silicon dioxide layer on said first nitride layer;
• removing said thick oxide corresponding to a central portion of the gate thereby exposing the first nitride layer thereunder;
• thermally oxidizing the structure to form a relatively thin silicon oxynitride-silicon dioxide dual layer on said exposed first nitride and densifying said thick oxide;
• forming a polysilicon layer on said thick and thin oxide layers;
• implanting said polysilicon layer with p-type impurities;
• forming a second silicon nitride layer on said polysilicon layer;
• converting said polysilicon layer into recrystallized silicon by subjecting the polysilicon layer via said second nitride to laser radiation;
• removing said second nitride-layer;
• patterning said recrystallized silicon into the transistor active area;
• masking the portion of said patterned recrystallized silicon in correspondence with the underlying gate;
• and
• implanting n-type ions in the unmasked portion of said recrystallized silicon forming therein source and drain regions in alignment with the gate.