ION-INDUCED ETCHING OF ORGANIC POLYMERS IN ARGON AND OXYGEN RADIOFREQUENCY PLASMAS

The authors have studied the etching of novolac-based photoresist, pol yimide, and polymethylmethacrylate in oxygen and argon rf plasmas at p ressures between 0.3 and 10 Pa in a reactive-ion-etching (RIE) reactor . Energy-flux density measurements on the powered electrode were perfo rmed under experimental conditions identical to those used during the etch experiments. In both plasmas the etch rate of these polymers depe nds proportionally on the energy-flux density of the impinging energet ic particles, which are the ions and the energetic neutrals formed by elastic and charge-exchange collisions between ions and neutral gas pa rticles in the sheath. In oxygen and argon plasmas under RIE condition s the etch mechanism of these polymers is ion induced. Average values of the overall carbon yield were determined as a function of the avera ge energy of the impinging energetic particles between 50 and 650 eV a nd as a function of the angle of incidence. The results obtained in ox ygen plasmas were compared with those obtained in argon plasmas and th e chemical enhancement in the presence of oxygen is determined. By mon itoring changes in gas pressure and energy-flux density on the substra te due to polymer etching, details about the oxidation reaction and th e identity of the oxidizing particles in the plasma have been obtained . It is shown that the oxidation reaction occurs mainly with molecular oxygen and for the larger part on the polymer surface.