Reduction of the base pressure of an UHV system by using turbomolecular pumps

We present the results on the reduction of the base pressure of an ultra-high-vacuum (UHV) system by using turbomolecular pumps. The UHV range is easily obtained by using a small backing pump, such as a scroll pump, a molecular drag pump, or a turbo-molecular pump. However, the extremely high vacuum range is difficult to achieve due to the low compression ratio and thermal outgassing from the inside of the turbopump. Several tests were done to overcome these difficulties. Among them, hot oxygen injection into the foreline of the pumping system is a possible way to reduce the chamber pressure by converting hydrogen to water molecule. However, a combination pumping approach turned out to be the most effective method of achieving an extremely high vacuum.