Method of manufacturing a bipolar junction transistor including undercutting regions adjacent to the emitter region to enlarge the emitter region

A method used in forming an intermediate structure in a bipolar junction transistor, comprising:

• disposing a first oxide layer between a semiconductor substrate and a base polysilicon layer;
• forming a dielectric layer outwardly from the base polysilicon layer;
• forming an emitter region having sidewalls by removing a portion of the dielectric layer and a portion of the base polysilicon layer;
• forming a first nitride layer on the sidewalls of the emitter region;
• removing a portion of the first oxide layer to form undercut regions adjacent the emitter region and to enlarge the emitter region thereby exposing the semiconductor substrate;
• forming a second oxide layer on all surfaces of the undercut regions and outwardly from the semiconductor substrate in the emitter region;
• forming a second nitride layer on the second oxide layer;
• anisotropically etching the second nitride layer in the emitter region to expose a portion of the second oxide layer;
• forming a third oxide layer outwardly from the portion of the second oxide layer in the emitter region;
• removing the first and second nitride layers;
• coupling the base polysilicon layer with the semiconductor substrate by forming a second polysilicon layer in the cavities;
• forming a fourth oxide layer on the sidewalls of the emitter region;
• and
• removing the oxide pad.

A method for manufacturing a bipolar junction transistor, comprising:

• forming a first oxide layer outwardly from a semiconductor substrate;
• forming a base polysilicon layer outwardly from the first oxide layer;
• forming a second oxide layer outwardly from the first polysilicon layer;
• forming a first nitride layer outwardly from the second oxide layer;
• etching a portion of the first nitride layer, the second oxide layer, and the base polysilicon layer to form an emitter region having sidewalls, wherein a portion of the first oxide layer forms a base of the emitter region;
• forming a second nitride layer on the sidewalls of the emitter region;
• etching the first oxide layer to remove the base of the emitter region thereby exposing the semiconductor substrate, and to form undercut regions adjacent the emitter region, the undercut regions disposed between the semiconductor substrate and the base polysilicon layer;
• forming a third oxide layer outwardly from the semiconductor substrate in the emitter region and the undercut regions, and inwardly from the base polysilicon layer in the undercut regions;
• forming a third nitride layer on the third oxide layer;
• anisotropically etching the third nitride layer in the emitter region to expose a portion of the third oxide layer;
• forming a fourth oxide layer outwardly from the portion of the third oxide layer in the emitter region;
• removing the first, second, and third nitride layers;
• etching the third oxide layer in the undercut regions and at least a portion of the fourth oxide layer thereby leaving an oxide pad disposed outwardly from the semiconductor substrate in the emitter region;
• coupling the base polysilicon layer with the semiconductor substrate by forming a first polysilicon layer in the undercut regions;
• forming a fifth oxide layer on the sidewalls of the emitter region;
• removing the oxide pad;
• and
• forming a second polysilicon layer in the emitter region.