Charge Density and pH Effects on Polycation Adsorption on Poly-Si, SiO₂, and Si₃N₄ Films and Impact on Removal During Chemical Mechanical Polishing

Abstract

The pH-dependent interactions of five aqueous abrasive-free polycationic solutions, all at a concentration of 250 ppm, with poly-Si, SiO(2), and Si(3)N(4) films and IC1000 polishing pads used in chemical mechanical polishing have been investigated and compared with the interaction of poly(diallyldimethyl ammonium chloride) (PDADMAC) that was investigated recently. Three of the polycationic solutions, poly(dimethylamine-co-epichlorohydrin-co-ethylenediamine), poly(allylamine), and poly(ethylene imine) (PEI) enhance poly-Si removal rates (RRs) to the range of about 500 to 600 nm/min at pH 10. In contrast, poly(acrylamide) (PAA) suppressed poly-Si RRs to about 50 nm/min, whereas with a copolymer of PAA and PDADMAC, the RRs were lower than those obtained with PDADMAC but higher than those obtained with PAA. For all the polycationic solutions, the RRs of both SiO(2), and Si(3)N(4) films were ~0 nm/min. These solutions offer a low-defect option for the processing of emerging FinFET devices. The variation in the RR magnitude and dependence on pH among the different polycations is related to the relative charge density of the polycations as well as the films being polished, consistent with ζ potential data. Based on the ζ potential data and earlier published reports, it is suggested that the strong polycation-mediated bridging interactions between the polarized and weakened Si-Si bonds of the poly-Si surface and the polyurethane IC 1000 pad are responsible for the high poly-Si RRs.

Role of Ce3+Ions in Achieving High Silicon Nitride Polish Rates

“…The surface zeta potentials of the PECVD-SiN films in pH-adjusted DI water are similar to those of nitride particles reported earlier 21 with an IEP ∼ 4.6. In the presence of 2.3 mM Ce(NO 3 ) 3 , the zeta potentials of these films increased and stayed positive over the entire tested pH range.…”

The Role of Ce3+ vs. Ce4+ during the Polishing of Silicon Dioxide and Silicon Nitride Films using Ceria Abrasives

“…Since it is well known that commercial ceria particles are available in a variety of forms and colors due to various impurities, we have chosen recently published results [2][3][4][5][6][7][8][9][10][11][12] in silicon dioxide CMP obtained using two types of ceria, one (d m ~180 nm) from Ferro Material Systems (see Table 1 below) and the other (d m ~60 nm) from Rhodia Inc. (Table 2) and different additives -amino acids, amines, carboxylic acids, and polymers. Both the particle size and pH influence these rates, but our focus here is only on understanding the chemical reactivity (the 'C' in CMP) of ceria abrasives in the presence of different additives in determining the silicon dioxide RRs.…”

“…There are also other applications [1] where both silicon dioxide and silicon nitride film removal rates need to be suppressed. To meet these variable requirements, several ceria-based formulations [2][3][4][5][6][7][8][9][10][11][12] containing a variety of additives (amino acids, amines, and polymers) were developed to selectively polish silicon dioxide and silicon nitride films and have been extensively used for many technologically important applications in silicon device manufacturing. Several of these dispersions suppress silicon nitride RRs to <2 nm/min [1][2][3][4]8] but not the oxide RR; a few do the reverse, [7] i.e., suppress silicon dioxide RRs to <2 nm/min, whereas others suppress both silicon dioxide and silicon nitride RRs to <2 nm/min [6].…”

Abrasive-Free Polishing for Extreme Ultraviolet Lithography Mask Substrates

“…17 Later, it was found that several abrasive-free aqueous solutions of 250 ppm of cationic polymers such as poly(diallyldimethyl ammonium chloride) (PDADMAC), poly(ethyleneimine) (PEI), poly(allyl amine) (PAAm) etc., can be used for the polishing of polysilicon films, but only using the harder IC-1000 pads and not the softer politex pads. 10,12,13 The adsorption and desorption of PDADMAC and PEI on polysilicon powders was studied and it was found that PDADMAC adsorbs strongly on a polysilicon surface and can remain as organic contamination whereas the adsorbed PEI on a post-CMP polysilicon surface can be easily removed by buffing with DI water at pH 2. 10 Hence, abrasive-free solutions of one amino acid (ornithine) and one polymer (PEI) were used in our experiments.…”

“…10 Here, we extend this process to EUV mask preparation by depositing ∼150-250 nm a-silicon thin film on the substrate to transfer the defects from it to the silicon surface, followed by polishing using abrasive-free solutions to achieve a high quality surface for the deposition Si/Mo bi-layers. 11 In earlier publications 10,12,13 we investigated the role of polycation charge density, pH, and polishing pad and proposed a polishing mechanism for the removal of polysilicon films using the above mentioned abrasive-free solutions. Here our goal is to apply this process to achieve angstrom level surface smoothness on QZ/ LTEM substrates.…”