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Shallow Emitter Process for Bipolar Transistors

IP.com Disclosure Number: IPCOM000051570D
Original Publication Date: 1981-Feb-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 3 page(s) / 79K

Publishing Venue

IBM

Related People

Horng, CT: AUTHOR [+2]

Abstract

Arsenic-doped polysilicon can be used as a diffusion source for formin defect-free shallow emitters in epitaxial silicon. The lateral motion of the dopant from the polysilicon would be approximately equal to the vertical motion. However, due to the increase of the effective emitter depth, fabricated polysilicon emitter devices have a greater emitter delay time.

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Shallow Emitter Process for Bipolar Transistors

Arsenic-doped polysilicon can be used as a diffusion source for formin defect-free shallow emitters in epitaxial silicon. The lateral motion of the dopant from the polysilicon would be approximately equal to the vertical motion. However, due to the increase of the effective emitter depth, fabricated polysilicon emitter devices have a greater emitter delay time.

An ideal shallow emitter structure can be made by using a consumable polysilicon emitter process. Briefly, the process uses a thin arsenic-doped polysilicon as emitter diffusion source. The process uses a lower temperature (800-850 degrees C) oxidation cycle to consume Ndoped polysilicon and to push arsenic into the epitaxial silicon. Low temperature oxidation is practical for the Ndoped silicon because of its enhanced oxidation property. A higher temperature, for example 950 degrees C in nitrogen ambient, drive-in cycle is then used to diffuse the piled-up arsenic to the desired emitter depth. The oxide formed is etched back to the silicon by reactive ion etching (RIE), leaving a side- oxide around the emitter contact edge.

The preferred process is as follows:

The device uses Pdoped polysilicon layer 8 for doping the external base 10 and also making contact to the transistor base. The internal base 12 is formed by a boron implant into the emitter contact window. The device structure prior to formation of the emitter is shown in Fig. 1, wherein the device is isolated from other devices by recessed oxide region 14. The Ncollector contact region is isolated by oxide region 15 from the base area. The Ncontact region contacts subcollector regi...