Selective Etching of Silicon Oxide versus Nitride with Low Oxide Etching Rate

This paper describes both aqueous and solvent-based formulations aimed at etching silicon oxide (SiOx) with etching rates (E/R) of the order of 10-20 A/min with selectivity greater than 5 with respect to silicon nitride (SiNx) . Diluted hydrofluoric acid (dHF) with very low pH was tried first but the selectivity was found to increase only with higher SiOx E/R. Solvent-based formulations derived from previous work also behaved in a similar way, however its SiOx E/R could be reduced by modifying the total fluoride concentration inside formulation. Finally, we found that low SiOx E/R could also be implemented in the diluted buffer-oxide etch (BOE) solution and the selectivity could be adjusted by addition of a specific surfactant at a very low concentration level.