Probing the Film Formation Mechanisms at the Slurry/Substrate Interface Relevant to the Chemical Mechanical Planarization Process

Chemical Mechanical polishing (CMP) has emerged as a critical technology for achieving global planarization of substrates used in advanced technologies such as integrated circuits and data storage media. CMP has been described as a kinetic/thermodynamic balance between the formation of a chemically modified layer and its subsequent abrasion via nanoparticles.  While the nanoparticle in the slurry plays a key role it has been proposed that the chemically modified surface layer is the key activation barrier to achieving desired removal and surface quality. Therefore it is necessary to optimize and balance the rates of chemical modification and mechanical abrasion in the system, which is dependent on the nature of the complexing/passivation chemistry in the slurry.   This presentation will provide insight into the key reaction mechanisms that occur at the slurry/substrate interface relevant to integrated circuit (copper) and data storage substrate (nickel phosphorous) CMP processes.  This worked explored the use of electrochemical techniques (static/dynamic open circuit potential (OCP) and Tafel analysis) to probe the impact of organic additives on the surface redox and film forming mechanisms. More specifically, through monitoring the OCP (under both abrasive and non-abrasive conditions) versus time the film removal rate and subsequent passivation film formation kinetics can be determined as a function of slurry additives (complexing agents).  These results can be correlated to macroscopic performance metrics such as static/dynamic etch rates and overall polishing rates.  Additionally, the surface quality will be measured using atomic force microscopy (AFM) and a correlation between surface roughness and the film formation kinetics will be presented.