The adaptation of turbomolecular pumps to plasma etching processes

Abstract

A summary of the requirements vacuum pumps have to meet during their application with plasma etchers is given. In particular the modification of turbomolecular pumps will be discussed. Two pumps with a pumping speed of 330 l s −1 and 510 l s −1 for N 2 have been adapted and extensively tested with plasma etchers under production conditions. The pumps have been equipped with a gas purge system. The purge gas is admitted directly into the rotor bearing area of the turbomolecular pump and generates a gas flow from there to the forevacuum port. Due to inbuilt restrictors, a laminar flow in the ring gaps of the bearing area by the corrosives is achieved. In addition the internal surfaces of the pump have special corrosion resistant coatings. The adapted turbomolecular pumps have shown a high operational life (up to now approx 7000 h without failures) and reliability. The pressure range of sputtering and plasma etching processes is above the optimum operating range of the high vacuum pumps used with these processes. These pumps, however, can be used in the 5 × 10 −3 mbar to 1 × 10 −1 mbar range by placing a throttle valve between the pump and the work chamber. The paper describes the design of a corrosion resistant conductance limiter, the flow conductance of which can be adjusted in the range from 0.1 to 1000 l s −1. This conductance limiter can be used as a pressure and a flow control, due to the high reproducibility of the positioning of the valve plate.