Method for fabricating semiconductor device

A method for fabricating a semiconductor device having a base electrode, an emitter electrode, and a collector electrode, the method comprising the steps of:

• forming first, second, and third buried layers in a semiconductor substrate;
• forming first, second, and third epitaxial layers using the respective buried layers as seeds;
• forming an isolation region between the first and second epitaxial layers;
• forming first, second, and third impurity regions connected to the respective buried layers through the epitaxial layers, respectively;
• forming fourth, fifth, and sixth impurity regions in the epitaxial layers, respectively;
• forming polysilicon layers on the epitaxial layers, respectively;
• defining first, second, and third emitter electrode regions as well as first, second, and third base contact regions in said fourth, fifth and sixth impurity regions, respectively;
• etching portions of the polysilicon layers excluding the respective emitter electrode regions and the respective base contact regions down to a predetermined depth;
• oxidizing the etched portions of said polysilicon layer to grow an oxide layer;
• implanting impurity ions of a first conductivity type into the polysilicon layer of the first and second base contact regions and the third emitter electrode region, respectively, and of a second conductivity type opposite to the first type into the polysilicon layers of the first and second emitter electrode regions and the third base contact region;
• depositing a metal on the polysilicon layer and the oxide layer;
• and
• patterning the metal to be in contact with the polysilicon layers, respectively.