Investigation of abrasive-free slurry for polysilicon buffing chemical mechanical planarization

Abstract

Abrasive-free slurries which control polysilicon removal and surface roughness are highly desirable for polysilicon buffing chemical mechanical planarization (CMP). Here, we show that the addition of poly(ethylene glycol) (PEG) to poly(diallyldimethylammonium chloride) (PDADMAC) solutions inhibits adsorption of PDADMAC on polysilicon films. The effects of PEG additive on polysilicon static etching and removal behavior during CMP were investigated as a function of PEG concentration. Polysilicon static etching and removal amounts were suppressed with an increase in PEG concentration, and surface roughness was improved by 19.2% and 55.3% compared to those obtained with 250 ppm PDADMAC and 1 wt% silica slurry, respectively, within a certain range of PEG concentrations. The adsorption mechanism of PEG on polysilicon films was investigated using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, contact angle measurements, X-ray photoelectron spectroscopy (XPS) and zeta potential measurements. Our results suggest that PEG adsorbs on the surface of polysilicon films and forms a passivation layer that interferes with the approach of PDADMAC. A possible mechanism for improvement in surface roughness was also proposed based on the inhibition effect of PEG during the CMP process.