Peter,

>From my point of view, large gap optics are a reference to the viewing optics
used for alignment on a contact/proximity aligner (such as an EVG620).

In general, this is a reference to a microscope objective depth-of-focus
limitation when attempting to align a wafer when, due to one reason or another
(thick resist, tall structures, deep cavities), the alignment keys on mask and
wafer cannot be brought close together (near to the depth of focus for the
objective - for example 15 µm for a 10x objective).  Under normal circumstances,
this can make alignment very difficult, since key definition is limited.

Some systems have compensated for this by instituting what are called Large Gap
Optics, which either A)interpose a secondary lens within the optical path for
the microscope to adjust viewing to the different level or B) an attempt at an
optic that uses refocusing.

EVG has actually developed a different process which we call Large Gap
Alignment, which does not rely on highly calibrated (an potentially difficult to
maintain) optics solutions.  Instead, it uses a "locked optic" approach where we
successively place the mask alignment keys and wafer alignment keys into the
same focal plane, and align the live wafer targets to a digitally represented
mask target. This way, no misalignment can be introduced due to movement or mis-
calibration of the optics.

For further details on this process, see:


C.Brubaker, M.Wimplinger, "Advances in Resist Processing and Alignment
Technology for Wafer Level Packaging", Proceedings of IMAPS Device Packaging,
Scottsdale, AZ, March 13 - 16, 2005

Best Regards,
Chad Brubaker


-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of P.E.M. Kuijpers
Sent: Monday, May 15, 2006 1:14 AM
To: [email protected]
Subject: [mems-talk] 3D patterning of cavities

Goodmorning


Who from the MEMS members can give me some info about Large Gap Optics.
What is it, how thus it works etc.
Searching the web didn't give me any clue about this.

regards,
Peter Kuijpers
Philips Applied Technologies/ EP&TF
mailto:[email protected]