Advanced CAD System for Electromagnetic MEMS Interactive Analysis

3.4.2.3 Process macros
Process emulation macros differ in a significant way from the other process emulation
commands. Namely, while these commands represent common IC processing steps (e.g. dopant
implant and diffusion), the implementation proposed in the standard requires significant
approximations and consist of performing a fixed sequence of steps using other commands from
the CCPDS. For completeness the major steps involved are listed, but the reader is referred to
[11] for the detailed explanation of these macros.
1. Grow
This command is a gross approximation to the growth of thermal oxide on a silicon substrate.
It does not predict residual stress or other physical characteristics of this processing step. It
consists of the following sequence of fundamental steps:
a. etch silicon that would be converted during the thermal oxidation
b. deposit oxide
c. etch oxide where growth would be inhibited by a nitride mask
2. Implant Diffuse
This command allows the user to create multiple solid regions from an initial layer (e.g. to
assign differ material properties to a region of higher doping). It consists of the following
sequence of fundamental steps:
a. etch initial layer
b. deposit layer of higher doping
c. etch layer of higher doping
3.4.2.4 Process emulation
The process emulation commands consist of methods to add material (deposition) and remove
material (etch, mechanical polish) from a given wafer. Recall that these are process emulation
steps in that the user must know the final outcome of the real processing step (e.g. deposition
thickness).
There are three types of emulated deposition supported by the CCPDS standard: conformal,
snowfall, and fill. We will further subdivide conformal deposition into two categories for
implementation purposes: planar and general-topology. Geodesic has an additional physical
deposition type that can be invoked to use process simulation. See the results section (Fig. 3-10,
3-11) for a discussion on process simulation using the level set method. Fig. 3-14 shows the
organization of the deposition commands. The only CCPDS deposition type not explicitly
permitted is “snowfall.” This can be integrated in a straight forward manner by adding an
anisotropic velocity function which takes into account visibility calculations and sticking
coefficients (see [20]). Fig. 3-15 shows graphically the conformal and fill deposition types. The
conformal deposition on a non-planar topology relies heavily on the offset solid algorithm
detailed in [30].
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