Spatial survey of a magnetron sputtering system using a Langmuir probe

Abstract

Summary form only given. Magnetron plasma sputtering systems are a popular thin film deposition technique. Despite the popularity, the structure and physical processes within the plasma are not well understood. A study has been conducted using a Langmuir Probe (LP) to complete spatial surveys of a magnetron plasma to characterize it in terms of electron density (n/sub e/), electron temperature (T/sub e/), plasma potential (V/sub p/), and floating potential (V/sub f/). This survey was conducted in a pure argon environment at both 5 and 40 mtorr. At each pressure lateral surveys through the plasma were done at 3 distances from the planar cathode. Additionally at each pressure, normal surveys were completed for two locations above the cathode face. At 40 mtorr plasma densities up to 6.0 x 10/sup 10/ cm/sup -3/ were observed in conjunction with electron temperatures up to -2 eV near the plasma source. At 5 mtorr plasma densities ranged up to 3.0 x 10/sup 10/ cm/sup -3/ with electron temperatures up to 4 eV. These studies have revealed some interesting results particularly with respect to electron temperature profiles. Electron Energy Distribution Functions (EEDFs) were found that can be described as either Maxwellian or bi-Maxwellian. Though these types of EEDFs have been observed before, the results found in this study suggests the bi-maxwellian distributions observed here are not explained by previously suggested models. Specifically the hot electron temperature appears to increase at greater distances from the cathode while the cold electron temperature decreases over the same spatial extent. It is well known that the flux and energy of particles bombarding a substrate can affect the morphology and chemistry of the resulting thin film. Since magnetrons have been demonstrated as useful in producing films with unique characteristics it is important to understand the collisional and transport processes within the plasma so that the technique may be best exploited.