ORIGIN OF GAS IMPURITIES IN SPUTTERING PLASMAS DURING THIN-FILM DEPOSITION

The incorporation of alien atoms in thin metal coatings produced by sputtering processes determine the properties of these films. The incorporation depends on the amount of reactive gases in the sputtering gas. The main impurities in the sputtering gas are H-2, H2O, CO/N2 and CO2. We determined the partial pressure of these gases in a sputtering plasma for a typical high vacuum system with a planar magnetron sputtering source. The measurements show that electron stimulated neutral gas desorption, beside thermal desorption of water from the vacuum chamber walls, is one main source for the alien gases. Depending on the deposited metal (Ag, Mo) the above mentioned gases can be gettered in large quantities, whereby the ratio between incorporated reactive gas atoms and deposited metal atoms reaches up to 5%.