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Trench Framed Recessed Oxide Isolation

IP.com Disclosure Number: IPCOM000049325D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Barson, F: AUTHOR [+4]

Abstract

Standard recessed oxide isolation (ROI) produces "bird's beak", a well-known phenomenon, which prohibits butting of the emitter and base of a transistor to the isolation. There is also a significant collector isolation capacitance problem, regardless of the ROI thickness, because a thermal oxide results in an arsenic pile-up. The device density is also limited because the lateral oxidation in ROI limits the minimum dimensions. The present process eliminates the "bird's beak" and epi-isolation isolation capacitance problem. The process also permits the butting of base and emitter to the isolation region.

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Trench Framed Recessed Oxide Isolation

Standard recessed oxide isolation (ROI) produces "bird's beak", a well- known phenomenon, which prohibits butting of the emitter and base of a transistor to the isolation. There is also a significant collector isolation capacitance problem, regardless of the ROI thickness, because a thermal oxide results in an arsenic pile-up. The device density is also limited because the lateral oxidation in ROI limits the minimum dimensions. The present process eliminates the "bird's beak" and epi-isolation isolation capacitance problem. The process also permits the butting of base and emitter to the isolation region.

Fig. 1 shows a subcollector 10 and sub-isolation region 12 formed in a P- substrate 14. The regions 10 and 12 are formed on the substrate by well-known lithographic and diffusion techniques. An N- epi layer 16 is grown to a desired thickness, e.g., 2.0 microns by conventional techniques. Successive layers of thermal oxide 18, polysilicon 20 and chemically vapor deposited silicon dioxide 22 are formed on the epi layer to thicknesses of the order of 100 nm, 300 nm and 650 nm, respectively. The layer 22 serves as a reactive ion etch (RIE) mask layer. A photoresist (not shown) is coated on the layer 22 and patterned to form trench areas 24. The areas 24 are reactive ion etched with a suitable etchant, e.g., CF4/H2. The photoresist (not shown) is removed, and the trenches 24 are etched through the layer 16 and the autodoping peak 12 into the substrate 14 using, for example, Cl2/Ar as the etchant. A thin thermal oxide (not shown) is formed to coat the surfaces of...