Measurements of friction and wear in chemical mechanical polishing using single particle analog probes

In this work, lateral force microscopy (LFM) was performed with analogs (silica-coated AFM probe and diamond-coated AFM probe) of a nanoscale individual CMP abrasive particle to mimic a chemical mechanical polishing (CMP) process. The silica-coated AFM probes were used to investigate the 2-body friction contribution of an individual silica CMP polishing particle in contact with the polishing pad (JK111) and silica substrates (bulk silica and thermal grown oxide wafer) for load and pH ranging from 10 nN to 50 nN and 7 to 11, respectively. Actual surface deformations of the three samples were obtained to determine the predominant friction involved during LFM. It was shown that the predominant friction mode for the pad surface was plowing friction while the friction of the silica substrates was governed by adhesive friction. This lead to the understanding why the friction results for the pad was higher than other samples. A proper friction model for the bulk silica was determined by fitting the friction results with Carpick's generalized transition equation. It was shown that the friction results at pH 7 and 9 were determined to follow the JKR model while the friction responses at pH 10 and 11 should not be analyzed with adhesive-based friction models because no adhesion force was observed. The diamond-coated AFM probes were used to simulate the surface damage occurring during a CMP process. AFM force lithography was performed on structures composed of various copper-dielectric pattern densities and two dielectric materials under a KOH environment. The damaged surfaces due to lateral force were analyzed to obtain the scratch depth of copper interconnects and line bending of patterned structures. It was observed that the structure with higher pattern densities were susceptible to deformation because they were composed more copper interconnect than the dielectric film. The critical load to initiate the plastic deformation of copper interconnects for the surface deformation was measured. In addition, the structure composed a weaker dielectric film was more susceptible to plastic deformation. For bending of pattern structures, the structure with a similar pattern density but larger dielectric film width or with stiffer dielectric material showed more resistance to bending.