CCL4-ASSISTED CF4 ETCHING OF SILICON IN A MICROWAVE-ASSISTED LDE (LASER DRY ETCHING)-PROCESS

A combination of microwave excitation and a mask projection scheme is applied for laser-assisted laterally structured etching of silicon. Di fferent feed,eases are used, such as CF4, either nonactivated or activ ated in a microwave discharge. With these gases weil-defined structure s are obtained with etch rates of 0.1 mu m min(-1). Using a gas mixtur e of CF4 and CCl4, the etching rate can be increased to 1 mu m min(-1) at room temperature. Smooth etched profiles can be achieved with lase r fluences < 0.6 J cm(-2). The etched Si surfaces are characterized by ex-situ X-ray photoelecton spectroscopy (XPS) and the gas phase react ions are investigated with quadrupole mass spectroscopy (QMS). The for mation of ClF3 or ClF is discussed as a critical step within the micro wave-assisted laser dry etching (MALDE). The presence of these species correlates with high Si etch rates. A numerical solution of the one-d imensional heat flow equation is used to obtain the laser-induced surf ace temperature distribution. A numerical model of etching based on th ermal evaporation gives etch rates many orders of magnitude smaller th an the observed etch rates.