Back-end-of-line CMOS-compatible diode fabrication with pure boron deposition down to 50 °C

Pure boron deposited on silicon for the formation of p⁺n-like junctions was studied for deposition temperatures down to 50 °C. The commonly used chemical-vapor deposition method was compared to molecular beam epitaxy with respect to the electrical characteristics and the boron-layer compactness as evaluated by etch tests, ellipsometry and atomic force microscopy. Electrically, the important parameters are minority carrier electron injection into the p-Type region and the sheet resistance along the boron-To-silicon interface which appear to be independent of deposition method for temperatures down to 300 °C. Only with molecular beam epitaxy did we succeed in producing substantial layers for the lower temperatures down to 50 °C. Also, at this very low temperature, p⁺n-like diodes were formed, but the suppression of electron injection was less efficient than at the higher temperatures. From simulations, assuming that the attractive electrical behavior is due to a monolayer of fixed negative charge at the interface, the concentration of holes needed to explain the I-V characteristics is estimated to be 1.4×10¹¹ cm^-2 for 50 °C deposition and 1.1×1013 cm-2 for 400 °C.