Fast Si (100) etching with a smooth surface near the boiling temperature in surfactant-modified tetramethylammonium hydroxide solutions

The etching characteristics of the commonly utilised Si (100) facet at high temperatures near the boiling point in surfactant-modified tetramethylammonium hydroxide (TMAH) solutions are investigated. Solutions of 25 wt% TMAH are selected because of the etching stability and the rate of addition of the surfactant Triton-X-100 [C₁₄H₂₂O(C₂H₄O)n, n = 9-10] ranges from 0.01 to 1% v/v. The etching rates of Si (100) facets close to the boiling point are three to four times higher than those at 80°C in the surfactant-modified 25 wt% TMAH solutions. In particular, at 115°C, the very near temperature of the boiling point, the silicon sample possessing a high etching rate of 1.45 μm/min and the smooth etched Si (100) surface with an average roughness of about 1 nm is obtained. Moreover, the samples do not demonstrate much undercut difference at the etched convex corners near the boiling point. These results are useful for the fabrication of microelectromechanical systems and indeed provide an efficient etching method for industry products.