Local doping of silicon by a point-contact microwave applicator

The feasibility of local doping in silicon by an open-end coaxial applicator with a tip made of the doping material, e.g. aluminum or silver, is studied in this paper. In these experiments, localized microwave power of 100-350 W at 2.45 GHz was applied for ∼1 min to obtain doped regions of ∼1-mm width and ∼0.3-μm depth. Independent measurements of secondary ion mass spectroscopy (SIMS) and junction built-in potential measured by atomic-force microscopy (AFM) were used to estimate the activated doping concentrations in the order of 10¹⁹ and 10²² cm ^-3 for aluminum and silver doping, respectively. Potential barriers (pn junctions) of 0.5-0.7 V were measured across the aluminum-doped regions, and I-V characteristics were observed. The doping experiments were conducted in air atmosphere, hence oxidation effects were observed as well. The localized-microwave doping concept presented here could be useful in small-scale semiconductor processes, integrated optics, and MEMS applications.