Effect of Hydrogen on GaAs MMICs in Hermetic Packages.

Presence of hydrogen in a hermetic package containing GaAs semiconductor devices can adversely affect performance and reliability of the GaAs devices. The problem is believed to be caused by conversion of molecular hydrogen to atomic hydrogen through the catalytic reaction with platinum or palladium in the gate structure of a GaAs device, which then diffuse into the active area of the device affecting its electrical performance. The primary source of hydrogen in the package is the trapped hydrogen in the ferrous metals used in package fabrication, and hydrogen that gets absorbed in the nickel plating during electroplating of the package. Past studies have shown that performance of GaAs device can degrade severely at hydrogen level as low as fraction of a percent. The device fabrication process and gate structure/metallurgy also impact the sensitivity to the hydrogen level. This paper presents the results of a study on the level of hydrogen in gold/nickel plated aluminum package as a function of different high temperature bake, and presents the Residual Gas Analysis (RGA) results for hydrogen in hermetic hybrids with GaAs MMICs that have successfully completed 1000 hour life test as a part of Telcordia Hybrid Qualification. The results show that hydrogen content in a hermetic package can be reduced to less than 1000 ppm by high temperature bake, and for telecommunication applications (operating ambient 60°C or less) hydrogen poisoning of GaAs MMIC in hermetic hybrid is not a concern so long as the hydrogen level is kept below 5000 ppm