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newbie question help: L-Edit / Cadence layouts for MEMS/MST



Jan 1, 1970
Hi All,

I have some basic newbie questions about microfabrication with respect to
MEMS designs (a course I am taking). I hope this is the right forum for
these questions. (If not, I apologize):

1. Using Cadence or L-Edit with the appropriate technology files (3-layer
Polysilicon - PolyMUMPS), is it safe to say that the layers available in
L-Edit are really the masks (as compared to the actual material design
layers)? So when you send a MEMS layout to CMC (or elsewhere) for
fabrication, the submitted layout really reflects the masks. So as I
understand it, the fab will automatically deposit _complete_ layers of your
sacraficial layers and your structrual layers uniformily across the entire
wafer so when designing your MEMS structure in L-Edit, the different layers
are the MASKs that are going to pattern each layer. Is that a correct

(I guess the confusing thing for me is that the PolyMUMPS handbook using the
convention where the masks are in uppercase (POLY0, POLY1, etc) and the
actual design layers only have the first letter capitalized (Poly0, Poly1,
etc). And L-Edit, when using the PolyMUMPS technology file, has the layers
indicated as Poly0, etc implying that they are the actual material layers
.... but aren't they the actual masks that are used to pattern the
sacraficial and structural layers?)

2. In L-Edit with the PolyMUMPS tech file, it has a Silicon nitride and
outline masks. When would you use Silicon nitride? I understand that it
can be used as a sacraficial layer and additionally, its the first layer on
the wafer (irregardless to prevent charge feedthrough), but if my
intrepretation is correct above, the tools allows you to specify MASKs not
the actual material layers so where/why would Silicon nitride be available
as a mask?

3. In the same manners as #2, how about the outline layer/mask that's
available on the left hand side of L-edit? I presume since you are
specifying masks layouts (to pattern the material layers), that the masks,
depending on your design won't span the full dimensions of your device, so
the outline layer/mask just allows you to put some boundaries on your
layout. Is this correct? Any other reasons?

4. With regards to the various masks (POLY0, DIMPLE, ANCHOR1, POLY1,
ANCHOR2, P1_P2_VIA, POLY2, METAL), is it correct to say the structural masks
(POLY0, POLY1, POLY2, METAL) use the subtractive pattern transfer
lithography process where these masks determine the dimensions of the
underlying structural material that _remains_ after etching.

And the DIMPLE, ANCHOR1, ANCHOR2, P1_P2_VIA masks use the additive pattern
transfer lithography process where these masks determine the dimensions of
the underlying sacraficial layer that is to be _removed_ by etching.

Is this correct?

5. I also noticed that the PolyMUMPS handbooks indicates that POLY0 could
be HOLE0. Is this an example of where the designer can use an additive
pattern transfer lithographic process on a structural layer to specify the
dimesions of the structural layer to _remove_ (instead of retain)?

Thanks in advance for any and all feedback!