METHOD OF MANUFACTURING A POLYSILICON EMITTER AND A POLYSILICON GATE USING THE SAME ETCH OF POLYSILICON ON A THIN GATE OXIDE

摘要

A METHOD OF MANUFACTURING A POLYSILICON EMITTERAND A POLYSILICON GATE USING THE SAME ETCH OFPOLYSILICON ON A THIN GATE OXIDEABSTRACT OF THE DISCLOSUREA method of making bipolar and MOS devicessimultaneously using a single fabrication process. Inone embodiment of the invention, a silicon substrate isdivided into bipolar and MOS regions. A thin layer ofgate oxide, having a thickness in the range of fromapproximately 150 angstroms to 300 angstroms, is thermallygrown on the silicon substrate. A thin layer of polycrys-talline silicon, having a thickness in the range offrom approximately 500 angstroms to 1000 angstroms isdeposited on the gate oxide layer to protect the gateoxide layer during subsequent processing. Both thethin polysilicon layer and the gate oxide layer areremoved from the bipolar region where the emitter is tobe formed. To maintain the integrity of the gate oxidelayer during etching, a photoresist mask used duringthe polysilicon etch is retained during the gate oxideetch, and the gate oxide is etched in a buffered oxidesolution. A thick layer of polysilicon then is depos-ited on the bipolar and MOS regions of the silicon sub-strate, and the substrate is masked and etched for form-ing the emitter and gates of the bipolar and MOS devices,respectively.F5/10272-40