Neutron reflectivity (NR) was applied to measure the concentration of
water at the buried interfaces between an amorphous polyimide and sili
con single crystal wafers. Excess water was discovered within 30 Angst
rom of the metal/polymer interface, where the water concentration reac
hed 17% (by volume) for the samples without a coupling agent and 12% f
or the ones with coupling agent. Beyond the interface, the water conce
ntration was measured at 2 to 3%, which is typical of bulk polyimide.
The above results demonstrate conclusively the unique power of NR in d
etermining water concentration near a buried interface, and provide th
e first quantitative evidence for a water concentration profile which
peaks in the interface region.