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Browse Prior Art Database

Profile Determination in Heterojunction Bipolar Structures

IP.com Disclosure Number: IPCOM000109158D
Original Publication Date: 1992-Jul-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 1 page(s) / 62K

Publishing Venue

IBM

Related People

DeFresart, E: AUTHOR [+3]

Abstract

Disclosed is the use of spectroscopic ellipsometry with a limited set of parameters to simplify the modelling of spectra from heterojunction bipolar transistors with graded layers. By simulating the front graded layer as a uniform layer of intermediate composition, ignoring doping, and including the lower graded layer with the base, we have limited the number of parameters required in a fit to 6. We have demonstrated that, for an angle of incidence of 75 degrees, these six parameters provide sufficient quality of fit to obtain the required information about real device parameters in samples that require much greater complexity for complete modeling.

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Profile Determination in Heterojunction Bipolar Structures

      Disclosed is the use of spectroscopic ellipsometry with a
limited set of parameters to simplify the modelling of spectra from
heterojunction bipolar transistors with graded layers.  By simulating
the front graded layer as a uniform layer of intermediate
composition, ignoring doping, and including the lower graded layer
with the base, we have limited the number of parameters required in a
fit to 6.  We have demonstrated that, for an angle of incidence of 75
degrees, these six parameters provide sufficient quality of fit to
obtain the required information about real device parameters in
samples that require much greater complexity for complete modeling.

      In preparation of heterojunction bipolar transistors in the
SiGe system, the composition of the base and the gradient of the
composition from the base to the top silicon layer are critical
device parameters.  These are difficult to control during growth to
the precision required, and electrical characterization of these
parameters requires extensive preparation, which delays knowledge of
the results and precludes the use of the tested wafer(s) for the
device fabrication.

      The use of an optical technique such as spectroscopic
ellipsometry appears an ideal choice.  It is non-contact,
nondestructive, and a commonly available technique.  It has not been
applied to this problem because it is known to be sensitive to many
different aspects...