Study on anisotropic silicon etching characteristics in various surfactant-added tetramethyl ammonium hydroxide water solutions

Three ion-typed surfactants, including anionic sodium dihexyl sulfosuccinate (SDSS), cationic ammonium salt of poly(ethylene glycol) (ASPEG) and non-ionic poly(ethylene glycol) (PEG), were added to 10 wt% tetramethyl ammonium hydroxide water (TMAHW) solutions to evaluate the silicon anisotropic etching properties of the (1 0 0) silicon plane without agitation and no isopropyl alcohol (IPA) additive. The results indicate that the wetting capacity of the etchants cause the efficacies of the etchants on the roughness reduction to follow the order cationic ASPEG, non-ionic PEG, pure solution and anionic SDSS in TMAHW solutions, especially at high etching temperatures. Moreover, the chemical activities of the etchants cause the efficacies of the etchants on the etching rates to follow the order anionic SDSS, pure solution, cationic ASPEG and non-ionic PEG in TMAHW solutions at a given etching temperature. The cationic ASPEG has a reasonable etching rate of 0.7 νm min^-1 and the lowest surface roughness of 4 nm in TMAHW solutions at an etching temperature of 100 °C. ASPEG and PEG in TMAHW solutions markedly affect aluminum passivation. The undercutting of the convex corners in PEG-added TMAHW solutions can be drastically reduced without using corner compensation; the undercutting ratio obtained using a PEG surfactant is about 45% lower than that obtained in pure TMAHW solution. This finding reveals that non-ionic PEG should be added to TMAHW solutions when accurate profiles are required without extremely deep etching. This study also demonstrated that non-ionic PEG is more appropriate than IPA for anisotropic silicon TMAHW etching.