Supersonic pulse, plasma sampling mass spectrometry: Theory and practice

Supersonic pulse, plasma sampling mass spectrometry is described, with an e mphasis on the physical mechanism by which species originally within the pl asma are incorporated into the supersonically expanding noble gas pulse. Th is new method is based on the release of a short burst of noble gas into th e high vacuum environment of an ECR-microwave plasma. Upon expansion throug h the plasma region, species originally present in the plasma become incorp orated in the noble gas pulse and are detected by quadrupole mass spectrome try. The mechanism of the incorporation process is investigated through mea surement of the time-of-flight velocity distributions of both the noble gas and species incorporated into the pulse. Incorporation is shown to be the result of supercooled noble gas clustering around the incorporated species, which act as nucleation sites for the condensation. It is this unique samp ling method which makes this technique capable of providing a chemical snap shot of the plasma composition. Practical applications of this technique in clude the investigation of the composition of diamond deposition plasmas an d the etching of silicon with chlorine. The investigations of diamond plasm as include the observation of a plasma that contains at least 40% of the ra dical species C2H3.