Advanced CAD System for Electromagnetic MEMS Interactive Analysis

The reactive ion etch involves more steps (see Fig. 3-9):
# the offset solid routine works only with polyhedra, so we extract the facets
# from mems_device:
mems_device GetPolyData –result device_polydata 9a
# note: several Vtk procedures are called at this point to merge coincident points and
# consistently orient the triangles of device_polydata. See the example on the CDROM
# for more details.
# offset the solid for a “negative deposition.” That is, we want to move the surfaces
# inward along the surface normal. Since by convention inside of Geodesic the surface
# normals point inwards, we actually specify a positive displacement.
vfab_OffsetSolid –src device_polydata –dst tmp_polydata –offset 1.0 9b
# the output of the offset solid command is a vtkPolyData object, so now we create
# a solid polyhedra
solid_poly3dSolid –result tmp1 –src tmp_polydata –facet Union 9c
# now we subtract the offset solid from the original solid. This effectively leaves us
# with a solid which could be subtracted from the original geometry to do a unit depth
# ion etch over the entire device. However, we only want to etch the area exposed by
# the mask.
# we now want to find the material which should be removed because it is exposed by
# the mask. To do this, we intersect a solid representing the visible area with “tmp1”.
solid_extrudeZ –src myMask –dst tmp2 –dist overall_height 9d
solid_intersect –result tmp3 –a tmp1 –b tmp2 9e
# now do a boolean subtraction of the etch mask from the layer to be etched
solid_subtract –result tmp4 –a etchMe –b tmp3
# now replace the existing object with the desired result
solid_copy –src tmp4 –dst etchMe
We have then emulated a reactive ion etch as desired, with a resulting geometry pictured in Fig.
3-9f.
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9f