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Control of Stress in a Metal–Nitride–Metal Sandwich for CMOS-Compatible Surface Micromachining

Published online by Cambridge University Press:  01 February 2011

Rhodri R. Davies ,
David J. Combes ,
Mark E. McNie  and
Kevin M Brunson
Rhodri R. Davies
Affiliation:
QinetiQ Ltd., St. Andrews Road, Malvern, Worcestershire, WR14 3PS, U.K.
David J. Combes
Affiliation:
QinetiQ Ltd., St. Andrews Road, Malvern, Worcestershire, WR14 3PS, U.K.
Mark E. McNie
Affiliation:
QinetiQ Ltd., St. Andrews Road, Malvern, Worcestershire, WR14 3PS, U.K.
Kevin M Brunson
Affiliation:
QinetiQ Ltd., St. Andrews Road, Malvern, Worcestershire, WR14 3PS, U.K.
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Abstract

Further to previous work, which demonstrated the ability to engineer the in- and out-of-plane stress components in PECVD silicon nitride, this paper reports on the control of stress in a metal-nitride-metal sandwich. The addition of a symmetric metallisation to the core nitride layer provides additional functionality by enabling electrical connectivity and electrostatic transduction. This represents a widely applicable structural layer for CMOS-compatible surface micromachining.

The use of advanced test structures coupled with wafer curvature measurements has allowed for detailed analysis of the stress components within the metal-nitride-metal sandwich and enables predictive engineering of the mechanical properties of the structural layer. Relationships between the in- and out-of-plane stress components of the metal-nitride-metal sandwich as a function of the nitride RF deposition power are reported and discussed. In comparison to values measured for nitride-only, a -30MPa/μm stress gradient offset is observed. A mechanism for the decrease in the stress gradient with the addition of the metallisation is proposed and compares well to modelling.

The optimised metal-nitride-metal sandwich can be repeatably engineered to realise low tensile in-plane stress (100MPa) and low out-of-plane stress gradient (0 ± 10MPa/μm). The effective Young's Modulus of the metal-nitride-metal sandwich was determined to be 150GPa; and a value of 195GPa was calculated for the nitride layer using analytical modelling. Work to further reduce the in-plane stress whilst maintaining low stress gradient is in progress by independently tuning the strain of the metal layers.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 782: Symposium A – Micro- and Nanosystems , 2003 , A8.5
Copyright
Copyright © Materials Research Society 2004

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References

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