Buried contact trench process

A method of forming a buried contact in a semiconductor substrate in the fabrication of a static random access memory (SRAM) integrated circuit comprising:

• providing a layer of gate silicon oxide over the surface of said semiconductor substrate;
• depositing a first polysilicon layer overlying said gate silicon oxide layer;
• etching away said first polysilicon and said gate silicon oxide layers where they are not covered by a buried contact mask to provide an opening to said semiconductor substrate;
• depositing a second layer of polysilicon over said first polysilicon layer and over said semiconductor substrate within said opening;
• doping said second polysilicon layer with dopant;
• driving in said dopant to form a buried contact junction within said semiconductor substrate under said opening;
• depositing a second layer of silicon oxide overlying said second polysilicon layer;
• patterning said second oxide and said first and second polysilicon layers to form a polysilicon contact overlying said buried contact junction wherein a portion of said buried contact within said semiconductor substrate is exposed and wherein a portion of said first polysilicon layer other than that of the contact remains as residue;
• forming a photoresist mask covering said polysilicon contact and extending on either side of said polysilicon contact so that the exposed portion of said buried contact junction within said semiconductor substrate is covered by said photoresist mask;
• and
• etching away said first polysilicon layer residue wherein said photoresist mask protects said exposed portion of said buried contact junction within said semiconductor substrate from said etching completing the formation of said buried contact in the fabrication of said SRAM integrated circuit.

A method of forming a buried contact in a semiconductor substrate in the fabrication of an integrated circuit comprising:

• providing a layer of gate silicon oxide over the surface of said semiconductor substrate;
• depositing a first polysilicon layer overlying said gate silicon oxide layer;
• etching away said first polysilicon and said gate silicon oxide layers where they are not covered by a buried contact mask to provide an opening to said semiconductor substrate;
• depositing a second layer of polysilicon over said first polysilicon layer and over said semiconductor substrate within said opening;
• doping said second polysilicon layer with dopant;
• driving in said dopant to form a buried contact junction within said semiconductor substrate under said opening;
• depositing a second layer of silicon oxide overlying said second polysilicon layer;
• patterning said second oxide and said first and second polysilicon layers to form a polysilicon contact overlying said buried contact junction wherein a portion of said buried contact within said semiconductor substrate is exposed and wherein a portion of said first polysilicon layer other than that of the contact remains as residue;
• forming a photoresist mask covering said polysilicon contact wherein said photoresist mask is formed by using an inverse tone of said buried contact mask wherein said photoresist is patterned to be wider than said polysilicon contact so that the exposed portion of said buried contact junction within said semiconductor substrate is covered by said photoresist mask;
• and
• etching away said first polysilicon layer residue wherein said photoresist mask protects said exposed portion of said buried contact junction within said semiconductor substrate from said etching completing the formation of said buried contact in the fabrication of an integrated circuit.

A method of forming a buried contact in a semiconductor substrate in the fabrication of an integrated circuit comprising:

• providing a layer of gate silicon oxide over the surface of said semiconductor substrate;
• depositing a first polysilicon layer overlying said gate silicon oxide layer;
• etching away said first polysilicon and said gate silicon oxide layers where they are not covered by a buried contact mask to provide an opening to said semiconductor substrate;
• depositing a second layer of polysilicon over said first polysilicon layer and over said semiconductor substrate within said opening;
• doping said second polysilicon layer with dopant;
• driving in said dopant to form a buried contact junction within said semiconductor substrate under said opening;
• depositing a second layer of silicon oxide overlying said second polysilicon layer;
• patterning said second oxide and said first and second polysilicon layers to form a polysilicon contact overlying said buried contact junction wherein a portion of said first polysilicon layer other than that of the contact remains as residue;
• forming a photoresist mask covering said polysilicon contact and extending on either side of said polysilicon contact;
• and
• etching away said first polysilicon layer residue completing the formation of said buried contact in the fabrication of an integrated circuit.