Effect of pad surface roughness on material removal rate in chemical mechanical polishing using ultrafine colloidal ceria slurry

In this paper, effect of ultrafine ceria (UFC) particle of which size is as small as 20 nm on CMP performance was investigated. Compared to conventionally used 100 nm abrasive particle which is made by calcination process, almost 80% scratch reduction was obtained by using UFC. However, a UFC slurry showed unstable material removal rate behavior from less than 200 Å/min to over 2000 Å/min, depending on polishing pad surface characteristics. As pad surface roughness increases, oxide removal rate using UFC drops abruptly to less than 200 Å/min. In order to use UFC for scratch reduction, the pad surface roughness optimization is necessary to avoid a sudden drop in the removal rate. This study gives a possible boundary for pad surface roughness for UFC application for CMP.