Anisotropic etching of surfactant-added TMAH solution

The anisotropic silicon etching characteristics of surfactant-added tetramethyl ammonium hydroxide (TMAH) solution were investigated. It was found that the etch rate of the [110] crystal plane abruptly decreases by more than one order of magnitude and that the etch rate ratio of the etch rate of the [100] crystal plane to the etch rate of the [110] crystal plane is reversed. The roughness of the etched surface of the [110] crystal plane was improved by the addition of surfactant. A peculiar figure was not obtained at wagon wheel pattern etching. Thus, it was visually observed that the anisotropy of surfactant-added TMAH solution was different from that of pure TMAH solution. As a result of the reversal of the etch rate ratio, undercut of convex corners was reduced and slanted [110] planes at 45/spl deg/ to the surface of the [100] crystal plane were obtained.