Browse Prior Art Database

Dispositioning Method for Aligning Masks to Wafers

IP.com Disclosure Number: IPCOM000102366D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 72K

Publishing Venue

IBM

Related People

Dioguardi, SJ: AUTHOR

Abstract

This article concerns an improved method of aligning photomasks to wafers and, more specifically, a measurement disposition process in which the overlay of masks is matched to the point of set management through a unique program utilizing a "least squares" algorithm. The methodology of this technique results in a more positive approach for maximizing overlay and final test yield while minimizing rework, product and mask scrap.

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Dispositioning Method for Aligning Masks to Wafers

       This article concerns an improved method of aligning
photomasks to wafers and, more specifically, a measurement
disposition process in which the overlay of masks is matched to the
point of set management through a unique program utilizing a "least
squares" algorithm.  The methodology of this technique results in a
more positive approach for maximizing overlay and final test yield
while minimizing rework, product and mask scrap.

      An inefficiency in mask dispositioning arises from the present
lack of conformity in mask alignment techniques employed between two
stages of the mask manufacturing process, i.e., the mask house and
the manufacturing line. In the former, a Nikon 2i instrument is used
to measure 17 selected sites on the mask with respect to
corresponding sites on a theoretically perfect grid, as contained in
an APL computer program.  Data from the 15 product sites (2
additional sites are the auto-alignment sites) on the mask are
manipulated by the program to perform a "least squares" fit
calculation to corresponding sites on the theoretically perfect grid.
Results of this calculation are applied to the measured values to
give "best fit" values, which represent the distances between the
selected sites and the corresponding "perfect grid" sites after the
"least squares" fit has been performed.  The "new values" are then
compared to the specification value (limit).  Masks are rejected if
any of these values exceed the specified value and accepted if all
are found equal or less than that value.

      The manufacturing line, on the other hand, uses a procedure
wherein the mask is aligned at 2 sit...