Nitridation of thermal SiO2 films by radio-frequency plasma assisted electron cyclotron resonance: Effect of plasma modes and process parameters

Dual-frequency plasma using electron cyclotron resonance(ECR) and radio-fre quency (rf) discharges was used for the nitridation of silicon dioxide (SiO 2) films, which were grown by conventional thermal oxidation. Nitridation w as performed under ion densities less than 10(11) ions/cm(3) and substrate temperatures of 300+/-20 degreesC. The effects of plasma mode (ECR/dc, ECR/ rf, ECR, and rf) and the principal process variables (N-2 pressure, ECR pow er, rf applied voltage, and nitridation time) on formation and growth of th e nitrided layer were studied by spectroscopic ellipsometry, Auger electron spectroscopy, and atomic force microscopy. It was observed that the nitrid ed films were composed of an upper layer of silicon oxynitride (SiOxNy) and an inner layer of SiO2. The plasma mode, N-2 pressure, and rf bias affecte d the reactions and concentration of particles in the gas phase, and theref ore impacted growth of the nitrided layer. Plasma parameters and plasma mod es were optimized to produce a dense upper nitride layer, while minimizing the effect on the inner SiO2 layer, with the goal of preserving the electro nic integrity of the Si-SiO2 interface. (C) 2001 American Vacuum Society. [ DOI: 10.1116/1.1331295].