Role of Poly(diallyldimethylammonium chloride) in Selective Polishing of Polysilicon over Silicon Dioxide and Silicon Nitride Films

Abstract

A cationic polymer, poly(diallyldimethylammonium chloride), or PDADMAC (MW ≈ 200,000), at a concentration of 250 ppm was used to enhance polysilicon removal rates (RRs) to ∼600 nm/min while simultaneously suppressing both silicon dioxide and silicon nitride RRs to <1 nm/min, both in the absence or in the presence of ceria or silica abrasives during chemical mechanical polishing (CMP). These results suggest that aqueous abrasive-free solutions of PDADMAC are very attractive candidates for several front-end-of-line (FEOL) CMP processes. Possible mechanisms for the enhancement of poly-Si RR and the suppression of oxide and nitride RRs are proposed on the basis of the RRs, contact angle data on poly-Si films, zeta potentials of polishing pads, polysilicon films, silicon nitride particles, and silica and ceria abrasives, thermogravimetric analysis, and UV-vis spectroscopy data.

Use of anionic surfactants for selective polishing of silicon dioxide over silicon nitride films using colloidal silica-based slurries

“…In the absence of any additive, the RRs of oxide films decrease from ∼70 nm/min at pH 2 to ∼20 nm/min at pH 4 and 8, and then increase to about 40 nm/min at pH 10. Similar oxide RRs were reported in our earlier publication [13,14]. The decrease in the oxide RRs from pH 2 to 4 is presumably due to the increase in the electrostatic repulsion between the negatively charged silica abrasives and the oxide surface [15] while the increase in the oxide RRs at higher basic pH values can be attributed to an increase in oxide solubility [16].…”

“…In the absence of any additive, the nitride RRs drop from ∼45 nm/min at pH 2 to ∼15 nm/min at pH 4 and thereafter follow a trend that is similar to the RRs of oxide films. Similar nitride RRs were reported earlier using the same silica abrasives [14] and discussed based on the electrostatic interactions between the nitride surface and the abrasives. More interestingly, adding either DBSA or SDS suppressed the nitride RRs to ∼1 nm/min at both pH 2 and 3 and to ∼4 nm/min at pH 4.…”

“…5 shows the potential values of 1 wt% silicon nitride particles dispersed in water with and without adding the surfactants. In the absence of any additives, the IEP of silicon nitride particles is ∼5, same as that reported earlier [12,14,27]. The additives reversed the charge of the silicon nitride surface (except for SLS below pH 3) for pH <5 with the potential reaching relatively high negative values, except for SLS and K 2 SO 4 .…”

Ceria-Based Slurries for Non-Prestonian Removal of Silicon Dioxide Films

“…31 The negligible adsorption of DADMAC implies that a large amount of positively charged free ions (DADMA + ) remain in the dispersion. These combined with an equal number of Cl − ions dissociated from DADMAC molecules in the dispersion can compress the electrical double layer near the particle surface, resulting in a significant reduction in the range of the electrostatic forces and, hence, a reduction of the zeta potential, similar to the effect of increasing the ionic strength.…”

“…7. In fact, Penta et al 31 showed that PDADMAC, the polymer form of DADMAC, adsorbs on a silica surface primarily due to the electrostatic attraction between the negatively charged oxide surface and the positively charged PDADMAC at all pH values in the range of 2 to 12.…”