Abrasive and additive interactions in high selectivity STI CMP slurries

• Silicon dioxide to silicon nitride removal rate selectivity evaluated.
• Ceria purity and crystal structure influence selectivity.
• l-glutamic acid yields high selectivity with all ceria and is robust.
• l-proline yields high selectivity only with one ceria and is less robust.

Ceria based slurries with additives are widely used in shallow trench isolation (STI) chemical mechanical planarization (CMP) process to obtain high selective removal of silicon dioxide over silicon nitride. In this study ceria from different sources were used as abrasives and l-proline and l-glutamic acid were used as additives, with a focus on identifying the interactions between abrasives and additives and their effect of selectivity. Ceria particles were characterized using X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) while the additive abrasive interactions were evaluated by UV–Visible spectroscopy and inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis. While slurries with l-proline yielded high selectivity only with certain type of ceria, slurries with l-glutamic acid were found to be less sensitive to the ceria source than those with l-proline, and yielded high selectivity regardless of the source of ceria used. The purity of the abrasive and its crystal structure appear to play a significant role in determining the selectivity.

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