Ceramic coating as an ultrahigh vacuum compatible protective surface treatment for aluminum alloys against reactive species

From its extremely low out gassing rate, the aluminum-alloy UHV system possesses substantial advantages in the fabrication processes of next-generation semiconductor devices. In order to realize the advantages, however, its vacuum properties must be tested under actual fabrication circumstances where the inner surface of the chamber is continuously irradiated with chemically reactive species or energetic ions and photons. In this study, the effects of reactive gas (dichlorosilane: SiH₂Cl₂) on the outgassing rates of aluminum-alloy surfaces were examined for three different surface treatments: the ethanol lathing (EL), the special extrusion (EX), and the ceramic coating (CC). Without exposures to the reactive gas, all three surfaces, after having been baked, resulted in extremely low outgassing rates below the experimental limit of 10_-12Torr l/s cm₂ to prove their usefulness as UHV materials. After an exposure to the reactive gas, however, the outgassing rates of EL and EX increased by about a factor of 50, while that of CC remained basically of the same order. Changes in the surface morphology and the surface layer compositions were also examined by scanning electron microscopy and energy dispersive x-ray analyzer, respectively, which revealed the extent of their corrosions to be in the order EX > EL ⪢ CC. Ceramic coating technique will provide us with a promising surface treatment for aluminum alloy used in reactive semiconductor processes.