Fundamental aspects of particulate contamination of tungsten and thermal oxide wafers during chemical-mechanical polishing

Abstract

Chemical-mechanical polishing (CMP) has emerged as a new processing technique for achieving a high degree of planarity (< 10 μm) for submicron devices in very large scale integrated (VLSI) process technology. Metal as well dielectic films can be planarized using CMP. Polishing of tungsten (W) and interlayer dielectric (SiO₂) films is carried out using alumina (Al₂O₃) based slurries which typically contain acids, complexing and oxidizing agents. One of the challenges of CMP is the effective removal of slurry particles (e.g., Al₂O₃) that are deposited on the wafer (e.g., W) surface during polishing. Control of particulate deposition during CMP as well as the development of post CMP cleaning techniques to remove deposited particles require an understanding of the surface and solution chemistry of the wafers and particles under polishing conditions. In this research, an attempt is made to develop an understanding of the importance of the electrostatic interactions in particle deposition using electrokinetic potential data, particle deposition results from small scale polishing experiments and calculated interaction energies between a particle and wafer surface. The electrokinetic potential of tungsten, thermal oxide (SiO₂) wafers and alumina particles were measured as a function of solution chemistry. The measured electrokinetic potential data was used to calculate the interaction energy between an alumina particle and a wafer (e.g., W) surface using the well known DLVO (Derjaguin-Landau-Verwey-Overbeek) theory.