Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Backside Infrared Wafer Leveling System

IP.com Disclosure Number: IPCOM000108438D
Original Publication Date: 1992-May-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 1 page(s) / 55K

Publishing Venue

IBM

Related People

Chiu, GL: AUTHOR [+2]

Abstract

Disclosed is an optical system whereby wafers are leveled through their backside using infrared light. This enables tight focusing control for lenses with short working distances.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 68% of the total text.

Backside Infrared Wafer Leveling System

      Disclosed is an optical system whereby wafers are leveled
through their backside using infrared light.  This enables tight
focusing control for lenses with short working distances.

      The present invention uses a sub-bandgap infrared laser source
with wavelengths around 1.3mm.  For example, the InP-based laser
diode or Nd:YAG laser is suitable for this application.  The silicon
or GaAs wafer is transparent at these sub-bandgap wavelengths.  The
wafer plane can thus be sensed through the backside.  The dwindling
lithographic projection lens' working distance no longer poses any
problem in this approach.

      A distance measuring interferometer can be set up below the
wafer chuck to pinpoint the top surface of the wafer. Here the spots
on the top surface of the wafer whose z heights are to be measured
are coated with infrared reflectors, using, e.g., metal.  The
reflected infrared light combined with the reference beam results in
fringes for distance measurement in the usual way.  If the metal
reflectors are patterned globally for the wafer, it results in a
global leveling scheme.  If the metal reflectors are patterned in or
around (kerf) each chip, a die-by-die leveling scheme is
accomplished.  Typically 3 to 4 beams are used to sense distances and
the plane is then determined through these 3 or 4 points.  The plane
is then servoed to make it coincide with the lens image plane.  The
zero point of the...