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BUTTING STRATEGY FOR PAGE-WIDTH HYBRID CIRCUITS

IP.com Disclosure Number: IPCOM000026058D
Original Publication Date: 1990-Feb-28
Included in the Prior Art Database: 2004-Apr-05
Document File: 2 page(s) / 142K

Publishing Venue

Xerox Disclosure Journal

Abstract

The boron doping level required to stop EDP etchant is in the high 1019 cm-3 doping range (J. Electrochem SOC. 131, pg. 166 [1984J). It is also known that boron does not fit particularly well in the silicon lattice due to the fact that boron's covalent radius is O.SSA, while that of silicon is l.lOA. (Solid-state Electronics 15, pg. 259 [1972]). A consequence of lattice mismatch and high doping is the presence of a critical doping level: Above 1.5 x 1016 boron cm-2, networks of misfit dislocations are generated on the heavily doped wafer surface (Jap JAP 44, 269 [1974]). Therefore, it is desirable to reduce boron concentration to eliminate dislocations but to increase the concentration to produce an effective etch stop. A tradeoff can be made to satisfy etch stop requirements while producing surface crystal quality, but substantial work would be required to qualify the process for production quantities.

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XEROX DISCLOSURE JOURNAL

BUTTING STRATEGY FOR PAGE- WIDTH HYBRID CIRCUITS U.S. C1.156/626 William G. Hawkins

Proposed Classification

Int. C1. HOll21/306

12

F-

FIG. 1

The boron doping level required to stop EDP etchant is in the high 1019 cm-3 doping range (J. Electrochem SOC. 131, pg. 166 [1984J). It is also known that boron does not fit particularly well in the silicon lattice due to the fact that boron's covalent radius is O.SSA, while that of silicon is l.lOA. (Solid-state Electronics 15, pg. 259 [1972]). A consequence of lattice mismatch and high doping is the presence of a critical doping level: Above 1.5 x 1016 boron cm-2, networks of misfit dislocations are generated on the heavily doped wafer surface (Jap JAP 44, 269 [1974]). Therefore, it is desirable to reduce boron concentration to eliminate dislocations but to increase the concentration to produce an effective etch stop. A tradeoff can be made to satisfy etch stop requirements while producing surface crystal quality, but substantial work would be required to qualify the process for production quantities.

XEROX DISCLOSURE JOURNAL - Vol. 15, No. 1 JanuaryIFebruary 1990 1

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BUTTING STRATEGY FOR PAGE-WIDTH HYBRID CIRCUITS

(Cont'd)

An alternative approach is to use electrochemical etch stopping rather than high boron doping. The electromechanical approach (IE3 Electron Device Letters (EDL-2, pg. 44 [1981]) uses a reverse biased junction to passivate silicon against the EDP etchant. The mechanism of etch stopping is that electrons are required at the silicon surface in order for etching to occur. In p+ material, the electron density is suppressed because there are so many holes for electrons to combine with. In a similar fashion, electrons can be depleted from the etching surface by a p-n junction with appropriate bias potential applied. The key advantage of using the electromechanical etch stop rather than a doping etch stop is that very low doping levels are required. For example, one coul...