Effects of various ion-typed surfactants on silicon anisotropic etching properties in KOH and TMAH solutions

Etching characteristics of Si{110} in 20 wt% KOH with addition of hydroxylamine for the fabrication of bulk micromachined MEMS

“…Different kinds of additives (e.g. redoxsystem or complexants, oxidizing agent, surfactants, and metal impurities) [13][14][15][16][17] are Open Access *Correspondence: prem@iith.ac.in MEMS and Micro/Nano Systems Laboratory, Department of Physics, Indian Institute of Technology Hyderabad, Kandi, Sangareddy, India added into KOH to get high speed etching and the alcohols/surfactants are incorporated to improve the surface morphology [18][19][20][21][22][23][24]. Moreover, etching at the boiling point of the etchant [11,25], microwave irradiation of the etchant [26], ultrasonic agitation of the etchant [27] have been employed to increase the etch rate.…”

A simple and robust model to explain convex corner undercutting in wet bulk micromachining

“…Triton-X-100, polyethylene glycol (PEG), NC-200, etc.) is added in the etchant [16][17][18][19][20][21][22][23]. In order to explain the mechanism behind the corner undercutting, several models have been proposed [12,[24][25][26][27].…”

“…This is a very simple way of explaining why a convex corner is more vulnerable to undercutting whereas there is no-undercutting at the concave corner. Now the last concern is, why does the undercutting at convex corner decrease dramatically in surfactant-added TMAH [16][17][18][19][20][21][22][23]. The summary of the etching characteristics of the pure and very small amount of surfactant (0.1% by volume) added TMAH solution is presented in Figure 4.…”

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].…”

“…TMAH has several advantages over KOH such as CMOS compatibility, high selectivity between silicon and its oxide/nitride and it can be modified for the etching of silicon wafers containing aluminum metal patterns as the aluminum etch rate can be reduced to zero if adequate amounts of ammonium peroxodisulfate (NH 4 ) 2 S 2 O 8 and silicon are added to the solution [39][40][41][42][43]. Furthermore, the undercutting at convex corners can be minimized to a significantly low level if a small amount of surfactant is added in the solution [31][32][33][34][35][36][37][38]44,45]. As reported in our previous work, the surfactant NC-200 in TMAH reduces the undercutting dramatically [44,45].…”