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Formation of Thermal Isolation Cap Oxide

IP.com Disclosure Number: IPCOM000101964D
Original Publication Date: 1990-Sep-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 3 page(s) / 83K

Publishing Venue

IBM

Related People

Beyer, KD: AUTHOR [+3]

Abstract

Deep and shallow polysilicon trenches are required in the fabrication of high performance, high density chips and for the reduction of unwanted parasitic capacitance. An oxide cap must be formed on top of such a trench to prevent the polysilicon base from shorting to the trench. This article describes a simple process for forming the cap oxide that eliminates stresses due to vertical bird's beaking during thermal oxidation process steps.

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Formation of Thermal Isolation Cap Oxide

       Deep and shallow polysilicon trenches are required in the
fabrication of high performance, high density chips and for the
reduction of unwanted parasitic capacitance.  An oxide cap must be
formed on top of such a trench to prevent the polysilicon base from
shorting to the trench.  This article describes a simple process for
forming the cap oxide that eliminates stresses due to vertical bird's
beaking during thermal oxidation process steps.

      Referring to Fig. 1, a partially filled trench 1 is shown with
p- doped epitaxial (epi) silicon fill 2 from a selective p-doped epi
process.  Also identified are layers of chemically vapor deposited
(CVD) SiO2 3, Si3N4 4 and SiO2 5.  The partial epi fill could also be
obtained by overfilling the trench with epitaxial silicon,
planarizing the epi silicon trench by chemical-mechanical polishing,
and forming a silicon recess by reactive ion etch (RIE), e.g. with
SF6/C12 .  The top exposed CVD TEOS sidewall is then removed by a
timed dip into buffered HF, providing the structure shown in Fig. 2.
Either a p doped poly layer 6 N1.5 um thickness is next deposited
(see Fig. 3), or a thin CVD Si3N4 deposition 7, e.g., 500 angstroms,
followed by an undoped CVD poly deposition 8, are processed (see Fig.
5).  After planarization of the doped or the undoped poly fill, the
trench fill is recessed N4000- 5000 angstroms by SF6-C12 RIE etching
and subsequently oxidized thermally, prefer...