Browse Prior Art Database

Through-Substrate Monitor of Film Thickness Changes by Substrate-Compensated Laser Interferometry

IP.com Disclosure Number: IPCOM000104882D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 81K

Publishing Venue

IBM

Related People

Saenger, KL: AUTHOR

Abstract

Interferometric techniques are widely used to monitor film thickness changes, typically in configurations in which (i) the light source is incident on the film (front) side of the film/substrate sample and (ii) the substrate is opaque at the monitored wavelength(s) to avoid substrate interference effects. However, tooling constraints and process conditions sometimes preclude reliable front-side access to the sample. For example, it may not be possible to add a window to an existing system, or existing windows may get coated during a deposition process. While interferometric techniques can, in principle, be implemented from the back side, the requirement for a transparent substrate introduces additional interference effects (e.g., intricate beating patterns in the reflectance vs.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Through-Substrate Monitor of Film Thickness Changes by Substrate-Compensated Laser Interferometry

      Interferometric  techniques  are widely used to monitor film
thickness changes, typically in configurations in which  (i) the
light source is incident on the film (front) side of the
film/substrate  sample and (ii) the substrate is opaque at the
monitored wavelength(s) to avoid substrate  interference effects.
However,   tooling   constraints  and  process conditions sometimes
preclude reliable front-side access  to the  sample.  For  example,
it may not be possible to add a window to an existing system, or
existing  windows  may  get coated  during  a deposition process.
While interferometric techniques can, in principle, be implemented
from  the  back side, the requirement for a transparent substrate
introduces additional  interference  effects  (e.g.,  intricate
beating patterns in the reflectance  vs.  time  trace  and/or  extra
fringes  due  to thermal effects).  The disclosed method for
substrate-compensated  interferometry  allows   conventional
interferometric  techniques  to be used without modification on
transparent  substrates  with  back  (or   front)   side
illumination, significantly advancing their utility.

      Since  interference  effects  tend  to  wash out if the optical
thickness of the sample  is  not  uniform  over  the probed  area,
the  interference-compensated  substrate  can either be (i) a wedge
(a well-known option in wide  use  for spectroscopic  measurements)
or (ii) a parallel-sided wafer lithographically patterned to suppress
interference  effects (at   a   single   selected  monitoring
wavelength).    The lithographic patterning  can  be  applied  over
the  entire wafer,  or  restricted  to  the area of the wafer site
being monitored (typically several mm sup 2 ).

      Provided here  is  an  example  of  a  lithographically defined
pattern  which  can suppress substrate interference effects.   This
particular  example  requires  two  etching steps.    The  mask
patterns  for each etch step consist of parallel lines on centers
spaced by twice the (typically % similar % 50 % mu m ) line width.
For the first etch step, the lines are etched to a depth of Delta L %
identical % lambda...