Browse Prior Art Database

Etching Process for Boron-Doped Silicon Structures

IP.com Disclosure Number: IPCOM000102160D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 84K

Publishing Venue

IBM

Related People

Bassous, E: AUTHOR [+2]

Abstract

Disclosed is a non-toxic, dual-bath silicon etchant system that is useful in the fabrication of silicon microstructures containing high boron dopant concentrations in excess of 9x1019/cm3 . Examples of such P++ silicon microstructures include large-area membranes, diaphragms, free-standing bridges and cantilevers. Silicon etchants for P++ doped silicon structures must display good etching uniformity and high etch selectivity, i.e., fast, uniform etching of lightly-doped silicon and very high etch-resistance of P++ silicon, respectively.

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Etching Process for Boron-Doped Silicon Structures

       Disclosed is a non-toxic, dual-bath silicon etchant
system that is useful in the fabrication of silicon microstructures
containing high boron dopant concentrations in excess of 9x1019/cm3 .
Examples of such P++ silicon microstructures include large-area
membranes, diaphragms, free-standing bridges and cantilevers.
Silicon etchants for P++ doped silicon structures must display good
etching uniformity and high etch selectivity, i.e., fast, uniform
etching of lightly-doped silicon and very high etch-resistance of P++
silicon, respectively.

      The disclosed etchant system is based on hot potassium
hydroxide (KOH) solutions which possess all the attributes and none
of the drawbacks of conventional silicon etchants which employ
mixtures of ethylenediamine (E), pyrocatechol (P) and water (W).  The
KOH etchant system is non-toxic, low-cost, simple to use, and
environmentally safe.  In contrast, EPW etchants are costly,
extremely toxic and corrosive, and their use and disposal require
special handling procedures.  Solutions of EPW are universally
employed due to their uniform etching at a rate that is 500-1000
times greater on (100)-oriented lightly-doped silicon than on
heavily-doped P++ silicon (1,2).

      Aqueous KOH solutions etch (100)-silicon uniformly but their
etch selectivity relative to P++ Si is not sufficiently high to apply
to structures such as thin, large-area, boron-doped silicon membranes
(3).  Adding isopropyl alcohol (IPA) to aqueous KOH solutions has the
effect of increasing the etch selectivity without appreciably
affecting the etch rate on lightly-doped (100)-Si.  In IPA-saturated
KOH solutions the selectivity increases to a maximum that is equal to
EPW etchants. Aqueous KOH-IPA solutions are, however, not suitable
for prolonged etching of (100)-Si.

      A KOH-based etchant system that is comparable to EPW in
performance, i.e., displaying high etching uniformity as well as high
etch selectivity, is made up of two different KOH solutions in the
composition and temperature range indicated below....