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Deliberate Alignment Offset for Contact Hole Etch Depth Accuracy

IP.com Disclosure Number: IPCOM000107894D
Original Publication Date: 1992-Mar-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 1 page(s) / 56K

Publishing Venue

IBM

Related People

Kenyon, NE: AUTHOR [+2]

Abstract

A method for determining contact hole etch depth accuracy in double-metal wafer processing is described that avoids destructive testing. Deliberate alignment offset between the contact holes and the underlying metal studs permits non-destructive SEM viewing from the top surface to discern between the two conditions of (1) residual oxide or (2) no residual oxide over the metal studs.

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Deliberate Alignment Offset for Contact Hole Etch Depth Accuracy

      A method for determining contact hole etch depth accuracy in
double-metal wafer processing is described that avoids destructive
testing.  Deliberate alignment offset between the contact holes and
the underlying metal studs permits non-destructive SEM viewing from
the top surface to discern between the two conditions of (1) residual
oxide or (2) no residual oxide over the metal studs.

      Normally the contact holes are aligned with the underlying
metal studs as shown in Fig. 1.  Non-destructive SEM viewing from the
top surface reveals no apparent difference in brightness across the
bottom of the holes, whether or not the tops of the metal studs are
free from residual oxide after etching.  If the process is modified
as shown in Fig. 2 to deliberately offset the alignment by a distance
d, non-destructive SEM viewing from the top surface is able to
distinguish between two well-defined etch depth conditions.  The
condition of under etching that leaves residual oxide on top of the
studs is very similar in appearance to the normally aligned case.
The bottom of each hole exhibits uniform brightness.  The condition
of sufficient etching leaves no residual oxide on top of the studs.
This condition exhibits a contrast difference between the top of each
bright metal stud and the co-planar material that surrounds each stud
when viewed non- destructively through the contact hole.  Very thin
layers of...