Advanced CAD System for Electromagnetic MEMS Interactive Analysis

polyhedra can be directly represented directly in a bRep. The distinguishing characteristic
between these two solid model representations, however, is that a bRep includes analytic
surfaces such as NURBS and swept surfaces.
3.2.3 Surface representation
An important design decision in Geodesic was to use polyhedra instead of analytic surfaces such
as NURBS. The motivation for this was twofold. First, boolean operations on analytic surfaces
can be problematic, particularly on the types of surfaces generated by the techniques discussed
later. Second, all of the process simulators used in this work required discretized geometry.
This would require a translation of the simulation results from polyhedra into more complex
analytic representations which can be difficult.
3.2.4 Process emulation vs. process simulation
Often for complicated structures, or depending on the versatility of the processing steps allowed
in the package, non-physical process steps must be introduced to be able to create geometry that
mimics what is expected. For example, a common processing step in the fabrication of microdevices
is conformal deposition. However, if your geometry engine cannot perform a conformal
deposition, you can sometimes emulate this process using deposition, planarization, and etching
with additional masks. Two of the examples discussed in section 3.3 highlight the differences
between process emulation and simulation. The reactive ion etching example shows that the
results of emulation can be implementation specific, while the level set example shows the
inability to properly capture rounded corners and the results of select etches using emulation.
3.2.5 Accessibility to algorithms which achieve multiple levels of physical accuracy
Since devices and desired levels of simulation accuracy vary significantly, Geodesic was
designed as an integrated environment to permit varying degrees of physical accuracy. It is
important, particularly from a designer perspective, to have a single tool capable of generating
geometry from the earliest conceptual stage to final production when detailed knowledge of the
fabrication processes can be tweaked for higher yield or better reliability. In addition to an
efficient and robust method to create geometry using only solid modeling operations, Geodesic
provides the capability to smoothly incorporate physically based 2-D and 3-D deposition and
etching process simulation results into the geometry. Three key approaches are employed to
achieve varying degrees of physical accuracy: a geometric-based deposition algorithm, domain
decomposition, and level set process simulation (see 3.1.4.3).
First, an efficient geometric-based deposition algorithm (detailed in [30]) and standard solid
modeling operations form the basis of the process emulation capabilities inside of Geodesic.
The algorithm provides for surface angle dependent deposition thickness to allow for nonuniform
sidewall and step coverage. The algorithm was designed to be independent of the solid
modeling kernel used. Additional details can be found in section 3.4. Second, a domain
decomposition algorithm (detailed in [31]) was created to improve the overall computational
efficiency for building complex geometries for devices requiring process simulation. The device
is decomposed (using the etch masks) at each deposition or etching step into regions identified as
needing 1-D, 2-D, or 3-D process simulation. Different geometric and physical approaches to
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