THE BLACK SILICON METHOD - A UNIVERSAL METHOD FOR DETERMINING THE PARAMETER SETTING OF A FLUORINE-BASED REACTIVE ION ETCHER IN DEEP SILICONTRENCH ETCHING WITH PROFILE CONTROL

Very deep trenches (up to 200 mu m) with high aspect ratios (up to 10) in silicon and polymers are etched using a fluorine-based plasma (SF6 /O-2/CHF3). Isotropic, positively and negatively (i.e. reverse) tapere d as well as fully vertical walls with smooth surfaces are achieved by controlling the plasma chemistry. A convenient way to find the proces sing conditions needed for a vertical wall is described: the black sil icon method. This new procedure is checked for three different reactiv e ion etchers (RIE), two parallel-plate reactors and a hexode. The inf luence of the RF power, pressure and gas mixture on the profile will b e shown. Scanning electron microscope (SEM) photos are included to dem onstrate the black silicon method, the influence of the gases on the p rofile, and the use of this method in fabricating microelectromechanic al systems (MEMS).