Browse Prior Art Database

Method of Removing Stress in Optical Silica-on-Silicon Films

IP.com Disclosure Number: IPCOM000104341D
Original Publication Date: 1993-Apr-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 55K

Publishing Venue

IBM

Related People

Liu, K: AUTHOR [+2]

Abstract

Disclosed is a method to reduce or remove the stress in silica-on-silicon optical waveguides after processing, enabling polarization-independent devices to be made. A typical process for making silica integrated optics involve a heated substrate, so strong stress-induced birefringence resultsfrom the mismatch in thermal expansion coefficients between the silica and the silicon. The stress induced birefringence cannot be removed by annealing since that process also takes place at elevated temperatures. Some techniques to reduce or compensate for the birefringence rely on specific device structures. For example, stress-releasing grooves can be etched on either side of a channel waveguide are effective only for narrow channel waveguides.

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Method of Removing Stress in Optical Silica-on-Silicon Films

      Disclosed is a method to reduce or remove the stress in
silica-on-silicon optical waveguides after processing, enabling
polarization-independent devices to be made.  A typical process for
making silica integrated optics involve a heated substrate, so strong
stress-induced birefringence resultsfrom the mismatch in thermal
expansion coefficients between the silica and the silicon.  The
stress induced birefringence cannot be removed by annealing since
that process also takes place at elevated temperatures.  Some
techniques to reduce or compensate for the birefringence rely on
specific device structures.  For example, stress-releasing grooves
can be etched on either side of a channel waveguide are effective
only for narrow channel waveguides.  Similarly, another technique
relies on a stress-applying film to trim the birefringence to a
specific value rather than eliminate it generally.  It should be
noted that the problem of stressed thin-films is commonly encountered
in electronics as well.  However, most of the attention in that
community has been directed towards reducing wafer warpage.  It
should be clarified that wafer warpage and its solutions are quite a
distinct from the problemof birefringent optical waveguides.  For
example, the wafer warpage could be eliminated by growing a film of
silica on the back side of the substrate, or a film of  with large
thermal expansion on top of the silica. ...