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. Different feed gases are used, such as CF4, either nonactivated or activated in a microwave discharge. With these gases well-defined structures are obtained with etch rates of 0.1 μm min−1. Using a gas mixture of CF4 and CCl4, the etching rate can be increased to 1 μm min−1 at room temperature. Smooth etched profiles can be achieved with laser fluences <0.6 J cm−2. The etched Si surfaces are characterized by ex-situ X-ray photoelecton spectroscopy (XPS) and the gas phase reactions are investigated with quadrupole mass spectroscopy (QMS). The formation of ClF3 or ClF is discussed as a critical step within the microwave-assisted laser dry etching (MALDE). The presence of these species correlates with high Si etch rates. A numerical solution of the one-dimensional heat flow equation is used to obtain the laser-induced surface temperature distribution. A numerical model of etching based on thermal evaporation gives etch rates many orders of magnitude smaller than the observed etch rates.