ENHANCED DEPOSITION RATES IN PLASMA SPUTTER-DEPOSITION

Langmuir probe and emission spectroscopic measurements are performed i n a high frequency (100 MHz) argon plasma used for the sputter deposit ion process of thin films of palladium (dedicated to catalysis applica tions). The metal source is a helicoidal palladium wire which is negat ively biased with respect to the plasma potential. This induces sputte ring by the ions present in the plasma. The probe results show that th e presence of the helicoidal wire in the chamber does not affect the t otal ion flux at the substrate location. However, as the bias voltage on the wire and/or the argon pressure are increased, a secondary direc t current (DC) discharge is created inside the helicoidal wire which f ollows a Paschen-like law; the breakdown voltage is lower than in the case of a conventional Ar discharge, probably as a result of the prese nce of primary electrons generated by the main high frequency (HF) pla sma. This second discharge is characterized by a strong Ar+ flux peak inside the helicoidal wire, which probably arises from a hollow cathod e type discharge. From emission spectroscopy and deposition analysis, it is shown that this secondary plasma causes an increase of the sputt ered Pd atom number and, consequently, an enhanced deposition rate.