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

Abstract

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 µm 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.

Fabrication methods based on wet etching process for the realization of silicon MEMS structures with new shapes

“…8. The mechanism behind the change in etching characteristics of pure TMAH when a small amount of surfactant is added into it is discussed elsewhere (Merlos et al 1992;Pal et al 2007b;Sundaram et al 2005;Yang et al 2005;Zubel and Kramkowska 2001). The {100} Si substrate is the most widely used in silicon mainstream technology.…”

“…TMAH has gained wide popularity due to its clean room compatibility. In the last decade, different kinds of ionic and non-ionic surfactants are studied in TMAH to enhance the applications of wet etching in MEMS (Conway and Cunnane 2002;Jeon et al 1996;Pal et al 2007bPal et al , 2009Resnik et al 2005;Sarro et al 2000;Sekimura 1999;Yang et al 2005). The addition of a very small amount of surfactant in TMAH significantly reduces the etch rate of high index planes, resulting in a reduction of the undercutting at sharp convex, curved and non-h110i edges.…”

“…high or low). Hence, TMAH (with and without surfactant) can be exploited to develop new processes/techniques for the formation of new shapes MEMS components in/on silicon wafers (Pal and Sato 2009a, b;Yang et al 2005).…”

Study of corner compensating structures and fabrication of various shapes of MEMS structures in pure and surfactant added TMAH

“…To eliminate the problem of large spatial requirements, more attention must be paid to reduce the undercutting at the convex corners. Several studies for minimizing the undercutting have been reported [28][29][30][31][32][33][34][35][36][37][38]. In case of KOH, IPA is used [28,29], whereas various kinds of surfactants and IPA are reported for TMAH solutions [29][30][31][32][33][34][35][36][37][38].…”

Review paper: Advanced source and drain technologies for low power CMOS at 22/20 nm node and below

“…[32,35] Base concentration and additives in -OH based wet etching chemistries influence the quality of the surface morphology. [36,37,38] Optimization of the pre-treatment of the recess surface before SiGe epi processing is also known to be critical to achieve acceptable SiGe morphology and proper surface cleanliness. [35] The doping concentration of the Si to be etched to form the recess also strongly impacts on the etching: During etching, Boron-doped Si forms borosilicate glass on the exposed Si surface, which acts to create etch stop if the boron doping concentration exceeds 10 18 cm -3 .…”