Setsuo Norioka

A cascade diffusion pump system for an electron microscope

Several DP systems have been discussed and evaluated with respect to dynamic evacuation under actual operating conditions of an electron microscope. As a result, a cascade DP system has been found to be the most reasonable for an electron microscope where the column is evacuated by the first DP backed by the second DP, and for the camera chamber by the second DP with a large volume foreline backed by a mechanical pump. A spectrum of the residual gases in an electron microscope with a cascade DP system indicates a very clean vacuum with hydrocarbon partial pressures of less than 3×10−7 Pa.

Practical advantages of a cascade diffusion pump system of a scanning electron microscope

A cascade diffusion pump (DP) system shows a superior performance in dynamic evacuation when switching from roughing to fine pumping, as well as in clean static evacuation. This is particularly true when the DPs have a relatively low tolerable forepressure. Moreover, a cascade DP system shows stable performance during variations of the DP heater voltage. A scanning electron microscope (SEM) with a large specimen chamber was evacuated by a cascade DP system with a buffer tank. With a cascade DP system, the requirements for the vacuum system of a SEM, such as rapid pumping down and a clean vacuum, were almost completely satisfied. This report presents experimental data on the cascade DP system of a SEM, which shows practical advantages over the single DP system.