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Wafer Bonding With Stress-Free Trench Isolation

IP.com Disclosure Number: IPCOM000121083D
Original Publication Date: 1991-Jul-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 2 page(s) / 62K

Publishing Venue

IBM

Related People

Beyer, KD: AUTHOR [+2]

Abstract

The fabrication of a full dielectric isolation by the intersection of deep isolation trenches with SOI (Silicon-On-Insulator) silicon substrates can lead to thermal stresses due to the non-viscous behavior of "buried" oxides during the thermal oxidation of the silicon trench sidewall. Thus, the replacement of the "buried" oxide by an elastic glass, such as borosilicate (BSG), would alleviate this problem.

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Wafer Bonding With Stress-Free Trench Isolation

      The fabrication of a full dielectric isolation by the
intersection of deep isolation trenches with SOI
(Silicon-On-Insulator) silicon substrates can lead to thermal
stresses due to the non-viscous behavior of "buried" oxides during
the thermal oxidation of the silicon trench sidewall.  Thus, the
replacement of the "buried" oxide by an elastic glass, such as
borosilicate (BSG), would alleviate this problem.

      Figs. 1 through 4 show the sequence of a full dielectric
isolation using BSG glass.  According to Figs. 1 and 2, wafer A
coated with a thin (1000 Angstroms) thermal oxide is brought in close
contact with wafer B, which has a trench isolation structure filled
with CVD BSG on a n+ epi/p-silicon substrate.  For a 1.5 mm wide
trench, a 1.5 mm thick CVD BSG film is sufficient to fill the
trenches and to act simultaneously as the source of the joining
dielectric material between wafers A and B.  In order to join wafers
A and B at a relatively low temperature at 900~C, the B2O3 content in
the BSG glass should be near 18%.  After the joining of wafers A and
B, the backside of wafer B is mechanically ground and/or lapped back
within 20 to 30 mm of the trench bottom area of the joined wafer B,
as shown in Fig. 3.  In the final step, the residual mechanical
damage in silicon and the remaining silicon above the trench bottom,
as shown in Fig. 4, is removed by a timed chem.-mech. polishing
process.