Modified Polysilicon Emitter Process
Original Publication Date: 1980-Feb-01
Included in the Prior Art Database: 2005-Feb-13
Polysilicon emitters are conventionally made by depositing polysilicon over the insulator-defined emitter window, implanting arsenic dopant into the polysilicon, and diffusing the dopant out of the polysilicon into the single crystal silicon to the desired emitter junction silicon. In addition to other advantages, the polysilicon is useful in avoiding excessive penetration by the ohmic contacts formed subsequently, such as platinum silicide (PtSi). However, the added polysilicon may slow down the device by providing additional volume for minority charge carrier storage. In addition, the polysilicon must be defined by a separate masking operation prior to forming PtSi, since PtSi is difficult to remove by chemical or reactive ion etchants after formation. Thus, extra masking operations and mask tolerance allowance are needed.