Nanoabrasives retention and removal mechanisms in polyurethane pads for copper CMP

The continued reduction in integrated circuit (IC) feature size requires similar reductions in surface defectivity. A key source of surface defects in IC fabrication processes stems from nanoabrasives used in chemical-mechanical planarization (CMP) processing. During CMP processing, polished surfaces are more vulnerable to defects including scratching, nanoabrasive particle adhesion and nanoabrasive agglomerate adhesion. The removal of these nano-sized particles is a priority for the IC fabrication industry and is reflected in the 2008 ITRS defect budget. However, there is insufficient technical understanding regarding the retention of residual nanoabrasives on the surfaces of the CMP pad following a CMP process and how they can be removed. Particularly, there are no systematic quantitative studies regarding nanoabrasive transport - specifically, nanoabrasive retention, agglomeration and removal mechanisms at pad surfaces (including micro-pores and asperities) that have been exposed (or not exposed) to polishing.;In this dissertation research regarding the residual nanoabrasive transport in IC1000/SubaIV polyurethane pads following a Cu CMP process is presented. Removal mechanisms of residual nanoabrasive resident at CMP pad pores and asperities via a diamond pad conditioning disk is investigated for a range of conditioning parameters, nanoabrasive particles, and slurry formulations. Qualitative and quantitative analysis of nanoabrasive retention was carried out via conventional and environmental scanning electron microscopy (SEM and ESEM), x-ray photoelectron spectroscopy (XPS) and SEM-based energy dispersion spectroscopy (SEM-EDS). To quantitatively describe the spectroscopic nanoabrasive retention data a semi-empirical model was developed. Quantitative spectroscopic and microscopic analyses on IC1000 CMP pads revealed considerable CMP slurry nanoabrasive retention at pad asperities and open pores that contacted the wafer during Cu CMP. Some of this residual nanoabrasive particle retention was found in individual and other in agglomeration form on the surface of the pad. Distinctive removal mechanisms related to retention of post CMP residual nanoabrasive on polyurethane CMP pad surface had been observed in terms of conditioning parameters, slurries chemistries, nanoabrasive composition, and pad surface location (asperity and open pores). A non-linear nanoabrasive removal model based on a time-dependent removal efficiency best described the nanoabrasive retention data.