Advanced CAD System for Electromagnetic MEMS Interactive Analysis

Fig. 3-16 shows schematically the steps involved in using the offset solid algorithm to perform a
conformal deposition. In a preliminary step, all of the current layers and wafer for the device are
unioned together simplifying all internal boundaries. This leaves a solid with only exterior walls
(i.e. free surfaces) as seen in Fig 3-16 (a). Conceptually, we want to generate a new solid (d) that
we can subtract the original geometry (a) from and have the result be the deposited material.
This requires four major steps. First, the bottom and sides of the wafer are identified (b) and
fixed so they cannot move. This can be thought of as only wanting to deposit material on top of
the wafer. Second, infinite planes representing the remaining faces are offset in the direction of
the normal by the specified deposition thickness (this can be a function of the normal direction).
Third, the vertices of the model are cycled over. At each vertex, the intersection of all infinite
planes representing the faces meeting at the vertex is calculated. Assuming the topology of the
device doesn’t change, these vertices along with the original connectivity define the new
geometry shown in (d). The final step consists of doing a boolean subtracting of (a) from (d) to
get the desired result.
Original geometry (a)
New Geometry (d)
Fix sides and bottom (b)
Subtract original
geometry
Figure 3-16: Using the offset solid algorithm in Geodesic to generate a conformal
deposition. Conceptually, we want to generate a new solid (d) that we can subtract the
original geometry (a) from and have the result be the deposited material.
There are three types of etching defined in the CCPDS: Sacrificial, Surface, and Bulk. In
addition, Geodesic has an additional type of etching using the level set kernel for physical
process simulation. For implementation purposes, we further subdivide surface etching into two
categories: ideal, and undercut with angled-sidewalls. The standard also subdivides surface
etching into two types: inside and outside. Fig. 3-17 shows the organization of the etch
commands.
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Offset planes and
intersect (c)
Deposited layer (e)