HBT Epitaxial Material Matching and Qualification for High Volume Production

Reliable and reproducible epitaxy (epi) materials are
critical to the success of a high volume compound
semiconductor fabrication line. An efficient epi matching and
qualification procedure among different epi reactors and
suppliers is paramount to supporting rapid fab capacity ramp
to keep pace with market demands. Traditional methods of
individual layer thickness and doping matching, such as
Secondary Ion Mass Spectroscopy (SIMS), have limitations
when applied to heterojunctions and subtle interface matching.
Sometimes a subtle epi interface mismatch can create
significant discrepancies in transistor characteristics and RF
module performance. Multiple iterations of lengthy epi
matching as well as RF module level characterization may be
required to resolve the differences. To overcome these
limitations, we developed an epi matching procedure which
greatly shortened the cycle time for epi qualification. After an
initial "quick-lot" matching is performed by our suppliers,
extensive transistor level electrical data is collected and
compared to the historical production distribution. The
measured data of these qualification samples must be within 2.5
sigma of the historical distribution with the same mean. The
in-line DC PCM parameters, for the technology generation, are
a subset collected data. In addition, an extended set of DC and
RF parameters is also matched within the same stringent
criteria. After the transistor level electrical data fully matches
the historical distribution of our database, the qualification
samples then go through transistor level reliability and module
level evaluations. Adequate transistor level reliability and
comparable module level performance are required for a full
production release of a new epi reactor.