A trace gas mass spectrometer for on‐line monitoring of sputter processes at 10−2 mbar without pressure reduction

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Abstract
For the metallization process of highly integrated semiconductors extremely low contamination levels are mandatory. In the sputter atmosphere (up to 10−2 mbar argon) oxidizing agents like oxygen and water must be limited to a few ppm. Mass spectrometric control must overcome the problems due to the high total pressure of the process gas. Common differential pumping suffers from background interference setting the detection limit to more than 100 ppm. Past attempts for an effective background discrimination method proved to be complex and impracticable. In a recent approach, the ions are produced by electron impact directly at the high process pressure, whereas the mass analyzer and the filament are located in a separately pumped high vacuum chamber. Small orifices with low conductance are provided for the injection of the electron beam into the high pressure region and the extraction of the ions into the mass analyzer. The system is able to detect contaminants in concentrations down to the ppb range. Both the high operating pressure and the high conductance by which such an ionizer can be connected to the process reduce the background problem to a negligible degree. The possible interference of residual background, mainly H2O in the low ppm range, and the influence of high pressure induced side effects are discussed. Results from real sputter processes are demonstrated.

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