A large aluminum alloy molecular beam epitaxy chamber with an ultimate pressure of 7.5×10−12 Torr

Abstract

An ultimate pressure of 7.5×10−12 Torr was reached in a large molecular beam epitaxy (MBE) chamber made of aluminum alloy A1050, after baking and after liquid nitrogen was introduced. Most of the components were made of aluminum alloys, except a gauge and the Ti-sublimation pump. For the seals between aluminum and stainless steel flanges, aluminum gaskets or helicoflexes were used and no problems resulted. It was also found that the Ti-sublimation pump was effective in the 10−10 Torr range but not in the lower 10−11 Torr range. The pressure limits of the turbomolecular pump used in the system was 6×10−11 Torr. Pumping speeds of the ion pump and the shroud cooled with liquid nitrogen were about 60 and 250 l/s, respectively. The outgassing rate of the chamber was estimated to be 1×10−13 Torr ⋅ l/s cm2. After a situation in which the ion pump was turned off at room temperature and in a second case in which the liquid nitrogen supply was stopped, surface conditions of the system were studied.