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Method to Reduce Loss of Isolation Trench Insulator

IP.com Disclosure Number: IPCOM000119907D
Original Publication Date: 1991-Mar-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 54K

Publishing Venue

IBM

Related People

Shepard, JF: AUTHOR

Abstract

Semiconductor device isolation is sometimes accomplished by etching a trench in the body of the silicon and filling it with insulating or near insulating materials, such as polysilicon or silicon dioxide. The usual options are to fill the trench completely with SiO2 or cap a poly-filled trench with SiO2 . This could be accomplished, for example, by sputtering or by chemical vapor deposition. The deposited oxide is then planarized to the surrounding area by an etch-back or polishing technique. The desired structure is shown in Fig. 1. Undesirable loss of the trench oxide occurs, however, during subsequent HF dip etches since the deposited oxides have a much higher etch-rate in HF than thermally grown SiO2 .

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Method to Reduce Loss of Isolation Trench Insulator

      Semiconductor device isolation is sometimes accomplished
by etching a trench in the body of the silicon and filling it with
insulating or near insulating materials, such as polysilicon or
silicon dioxide.  The usual options are to fill the trench completely
with SiO2 or cap a poly-filled trench with SiO2 .  This could be
accomplished, for example, by sputtering or by chemical vapor
deposition.  The deposited oxide is then planarized to the
surrounding area by an etch-back or polishing technique.  The desired
structure is shown in Fig. 1.  Undesirable loss of the trench oxide
occurs, however, during subsequent HF dip etches since the deposited
oxides have a much higher etch-rate in HF than thermally grown SiO2 .

      This loss of trench oxide can be minimized by reducing the
etch- rate of the deposited oxide.  This can be accomplished by doing
a blanket ion-implant of Si or W into the surface of the silicon
wafer including the trench oxide. The energy of the implant is chosen
so that it does not penetrate the polishing barriers surrounding the
trench and get into substrate silicon (Fig. 2.)  Any implanted
material in the barrier is therefore removed when the barrier is
removed.  The result is a self-aligned implant into the trench oxide.
Studies show that a silicon implant of dose greater than 1E16 or a
tungsten dose of greater than 5E15 will significantly reduce the
etch-rate of SiO2, thereby provid...