Patent ID: 6911368
Filing Date: 2005-06-28
Classification: H01L

Abstract:
1. A method in the fabrication of an emitter-base portion of a bipolar double-poly transistor, comprising the steps of depositing and doping a layer of base silicon on a silicon substrate, depositing a first layer of silicon dioxide on the base silicon layer, forming a photo mask on the first layer of silicon dioxide, etching an emitter window through the first layer of silicon dioxide and the base silicon layer by using said photo mask, forming a notch in the emitter window wall by means of etching part of the first layer of silicon dioxide in the interface between the first layer of silicon dioxide and the layer of base silicon while the photo mask is till present to prevent upper portions of the first layer of silicon dioxide from being etched, removing the photo mask, forming a second layer of silicon dioxide in the emitter window and in the notch, forming silicon nitride spacers on the second layer of silicon dioxide in the emitter window by deposition of silicon nitride and reactive ion etching, whereupon the notch is filed by the silicon nitride, removing the second layer of silicon dioxide from the bottom of the emitter window, and depositing emitter silicon in the emitter window and on top of and in contact with said first layer of silicon dioxide, wherein said steps of forming a notch and depositing silicon nitride create a silicon nitride seal isolating the base silicon from the emitter silicon.