Applications of a laser assisted defect detection system for chemical mechanical planarization (CMP) slurry development in rigid disk polishing

A laser assisted optical surface analyser (OSA) was applied for inspecting scratch defects on rigid disks used for hard disk drives (HDDs). The disk samples were polished with a chemical mechanical planarization (CMP) technique beforehand. Since it has been recognized that the CMP slurry formulation highly affects the scratch performance of rigid disks, a reliable defect evaluation system is required for efficient slurry development. In this paper, the capability of the OSA tool (Candela C10, KLA-Tencor Corp.) for scratch evaluation is discussed with reference to the scratch data acquired with a conventional dark field microscope (DFM) technique. A gauge repeatability and reproducibility (R&R) study revealed that the Candela had more than three times better R&R performance than the DFM. Scratch counts measured using the two tools were correlated, but not matched, due to the differences in the detection systems. The linear regression correlation coefficient (R2) was found to be 71% for the relatively larger size (>1 mm) of scratch categories. Another study was conducted using a scratch control additive in CMP slurry. The results showed that the effect of the additive was readily detected by the Candela, but was not obvious for the DFM detection. Based on the findings, the similarities and differences of the Candela and the DFM techniques are discussed. It was also found that the tuning capability of the Candela analysis recipe allowed consistent scratch counts with another type of laser assisted defect evaluation tool. This flexibility of the Candela system is a main characteristic which can be effectively used for CMP slurry development. An approach to targeted slurry designs is suggested in conjunction with the advantages and opportunities of the Candela method.