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352 MEMS and Microstructures in Aerospace Applications

SOA in terms of temperature, voltage, current, cycles, and power consumption
definitions apply for each device.

16.3 SCREENING, QUALIFICATION, AND PROCESS CONTROLS

16.3.1 DESIGN THROUGH FABRICATION
The selection of the specific tools for the MEMS designer will be driven by
compatibility with the foundry selection. The designer will select the appropriate
foundry and follow the tool guidelines of that entity. Designing MEMS devices
requires a strong link between design and process engineers. Establishing sys-
tematic design principles through a common computer-aided design (CAD)
framework facilitates the design. MEMS design for manufacturing (DFM) tech-
niques focus on process and design qualification through systematic parametric
modeling and testing, from initial development of specifications to manufactur-
ing. The overall result is a MEMS product design framework that incorporates a
top-down design methodology with parametric reusable libraries of MEMS, IC,
and other relevant system components. The framework should be capable of
allowing one to design within a specific process (via a process design kit) that
8
enables virtual manufacturing. The MEMS designers must be able to design
MEMS devices within the process limitations for a working and high yielding
chip. Means are required to inform MEMS designer of those limitations. Design
rules must also communicate the process limitations to those responsible for
developing layout verification and layout design tools. The design rules will
ensure the greatest possibility of successful fabrication and a specific foundry.
Design rules define the minimum feature sizes and spaces for all levels and
minimum overlap and spacing between relevant levels. The minimum line
widths and spaces are mandatory rules. Mandatory rules are given to ensure
that all layouts will remain compatible with the foundries lithographic process
tolerances.
Failure mechanisms in the product may arise in the case of design rule viola-
tions. Violation of minimum line and space rules could potentially result in missing,
undersized, oversized, or fused features. MEMS design rules must become increas-
ingly more specific to reflect the changes in expertise of the people using the rules. 9
Process control monitors are used to verify control of parameters during the
fabrication process. A verification system must be specified and in place to verify
the ability to meet required performance in final application. The procedures to
accept or reject criteria for the screens should be certified by the qualifying activity
(QA). The manufacturer, through the technical review board (TRB), should identify
which tests are applicable to guarantee the quality and reliability of the associated
MEMS fabrication technique or end product (e.g., wafer or die level product,
packaged product, etc.). The manufacturer may elect to eliminate or modify a
screen based on supporting data that indicates that for the specific technology,
the change is justified. If such a change is implemented, the producer is still
responsible for providing a product that meets all the performance, quality,and

© 2006 by Taylor & Francis Group, LLC