Y. Kitaura et al., LONG-TERM RELIABILITY OF PT AND MO DIFFUSION-BARRIERS IN TI-PT-AU ANDTI-MO-AU METALLIZATION SYSTEMS FOR GAAS DIGITAL INTEGRATED-CIRCUITS, Journal of vacuum science & technology. B, Microelectronics and nanometer structures processing, measurement and phenomena, 12(5), 1994, pp. 2985-2991
Reliability of Ti-Pt-Au and Ti-Mo-Au systems has been investigated for
GaAs integrated circuit first-level metallizations on semi-insulating
GaAs substrates and second-level metallizations on interlayer SiO2 fi
lms using Auger depth profile analysis, residual resistance examinatio
n and temperature storage step-stress testing. Auger analysis and resi
dual resistance examination showed significant reaction between first-
level Ti-Pt-Au and GaAs substrates during metallization processes, whi
le Ti-Mo-Au system with the electron-beam evaporated Mo film showed hi
gher thermal stability because the Mo film acted as a good diffusion b
arrier between GaAs and Au. The second-level Ti-Pt-Au on SiO2 was foun
d to be free from the reaction with GaAs substrates, and its degradati
on was ascribed to interdiffusion of composite metals. The resistance
increase in step-stress testing for the second Ti-Pt-Au was analyzed o
n the basis of a new diffusion-controlled model, and long-term reliabi
lity was estimated. A mean time to failure value of 3X10(5) h at 150 d
egrees C was obtained for a failure defined as 10% increase in resista
nce. Much higher reliability was estimated for Ti-Mo-Au, because the r
esistance continued to decrease as long as 3000 h at 250 degrees C. Th
e decrease in resistance clearly indicates defect annealing with reduc
ed defect scattering in Au layers. This also shows that foreign metal
diffusion into Au, acting as impurity scattering centers, is perfectly
eliminated by Mo diffusion barriers.