R. Buchhold et al., MECHANICAL-STRESS IN MICROMACHINED COMPONENTS CAUSED BY HUMIDITY-INDUCED INPLANE EXPANSION OF THIN POLYMER-FILMS, Thin solid films, 312(1-2), 1998, pp. 232-239
Thin polymer films have found widespread application in silicon-based
microelectronic devices and micromechanical systems due tc, their uniq
ue material properties. When exposed to ambient humidity polymers tend
to expand due to the uptake of moisture in the film. In most microele
ctronic applications. this characteristic is rather undesirable due to
associated reliability problems. We have investigated humidity-depend
ent mass uptake and expansion for a range of polymers at room temperat
ure and have found that the isotherms are generally nonlinear. Based o
n the obtained relationships. the polymer process can be optimized in
viers of reduced mass uptake and reduced mechanical stress in the poly
mer. Results are given for polyimide PI2540. Both mass uptake and swel
ling can be approximated by a linear humidity dependence with an error
of about 10%. Based on these results, the empirical quantities swelli
ng ratio and stress coupling factor are defined, and linearized sorpti
on parameters are discussed. (C) 1998 Elsevier Science S.A.