Observation of Polymer Additive Absorption on Substrates for STI CMP Slurries

Abstract

High SiO2 to SiN removal rate selectivity and SiN removal rate suppression are indispensable for the shallow trench isolation (STI) CMP slurry and those characteristics are achieved by the polymer additives such as poly-acrylic acid (PAA). Recently, it is reported that the polymers containing hydrophobic and hydrophilic moieties show high selectivity and SiN removal rate suppression [1, 2]. For further improvement of these characteristics, it is important to clarify the mechanisms of the effects of the polymer additives. Several studies have reported that polymer additives preferentially adsorbs on the SiN film resulting high rate selectivity [2, 3]. However, evaluation of adsorption properties of the polymer additives are limited to thermal or electrochemical analysis and few studies have been reported on the direct observation of adsorbed polymers on the SiO2 and SiN surfaces. In this study, we have investigated adsorption properties of the polymer additives by using surface enhanced Raman scattering (SERS) suitable for analysis of trace organic substance on surface in water.Figure 1 schematically illustrates the measurements of SERS spectra. The SiN/SiO2=30/70 m patterned wafer chip with 1% polymer solution is putted on the quartz glass with Ag nanoparticles, resulting high Raman scattering intensity. Figure 2 show the spectra measured on the SiO2 and SiN films in PAA solution. The peak of CH stretching mode of the PAA polymer chain was observed at approximately 2935 cm-1 on the SiO2 and SiN. This result implies that the polymer is adsorbed both on the SiO2 and SiN. Meanwhile, the case in the polymer containing hydrophobic moiety, the peak attributed to the hydrophobic group is observed at approximately 1000 cm-1. Its intensity is stronger on the SiO2 than SiN, indicating the preferential adsorption of polymer on the SiO2 surface.The ratio of peak intensity of polymer on the SiN to SiO2 (SiN/SiO2) for PAA (0.26) is higher than the polymer containing hydrophobic moiety (0.03), implying that the adsorption of polymer with hydrophobic moiety to the SiN film is lower than PAA. This suggests that the nitride removal suppression effect is not caused by the adsorption of the polymer on the SiN surface. The influence of other components, such as abrasive, dispersant, pH adjuster is under investigation.[1] T. Otsuki, US Pat. 2019/0136089 (2019).[2] N. K. Penta et. al, Appl. Surf. Sci., 283, 986(2013)[3] S. Kim et. al., J. Colloid Interface Sci., 319, 48 (2008). Figure 1