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Punch-Through Guard Ring for Butted Transistor Emitters

IP.com Disclosure Number: IPCOM000062134D
Original Publication Date: 1986-Oct-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Cressler, JD: AUTHOR

Abstract

This article relates generally to semiconductor fabrication and, more particularly, to construction of guard rings for butted emitters to prevent punch-through. A single added implantation step during fabrication of NPN transistors having butted emitters produces a thicker guard ring to prevent emitter-collector punch-through. The construction process is as follows: In Fig. 1, layers of silicon dioxide 1 and silicon nitride 2 are deposited on silicon substrate 3. Photoresist 4 is deposited, exposed and developed to define the active device region. Boron implantation is performed through layers 1 and 2 and produces "transverse straggle" in areas 5 to form the guard ring beneath layer 1 and the mask opening. In Fig.

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Punch-Through Guard Ring for Butted Transistor Emitters

This article relates generally to semiconductor fabrication and, more particularly, to construction of guard rings for butted emitters to prevent punch-through. A single added implantation step during fabrication of NPN transistors having butted emitters produces a thicker guard ring to prevent emitter-collector punch- through. The construction process is as follows: In Fig. 1, layers of silicon dioxide 1 and silicon nitride 2 are deposited on silicon substrate 3. Photoresist 4 is deposited, exposed and developed to define the active device region. Boron implantation is performed through layers 1 and 2 and produces "transverse straggle" in areas 5 to form the guard ring beneath layer 1 and the mask opening. In Fig. 2, reactive ion etching (RIE) is then used to form an opening through the exposed silicon dioxide 1 and silicon nitride 2 into substrate 3. RIE is important since it does not etch laterally to remove implanted boron beneath photoresist 4. Thereafter, the photoresist is stripped and recessed oxide is grown. During this latter step, the boron ions in implantation areas 5 diffuse outwardly enlarging those areas at the edges of the recessed oxide 6, forming the guard ring. Silicon dioxide layer 1 and silicon nitride layer 2 are then removed, as in Fig. 3, and p- type intrinsic base 7 and n-polysilicon emitter 8 are formed. Arsenic ions from the emitter diffuse into the silicon to form a shallow n emit...