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

Abstract

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 1.4×10 11 cm -2 for 50 °C deposition and 1.1×10 13 cm -2 for 400 °C.

Low temperature pure boron layer deposition for Si diode and micromachining applications

“…5.9. They are all close to the characteristics of implanted p + n diodes for which the current is dominated by hole injection into the substrate [102]. All characteristics displayed a small non-ideality that was similar for all devices including the implanted ones.…”

“…Thus, the layer uniformity and purity are guaranteed. Due to the physical deposition nature, the layer can be deposited at temperatures down to room temperature [102].…”

“…It becomes, just like the Ie, extremely high for the 200℃ and 50℃ depositions. These high values could also indicate that, besides a lower hole concentration, a higher density of interface defects or a weak B-Si bond could also be playing a role for degrading the Rsh [102]. The quality of the MBE B-layers was evaluated by monitoring the removal in Al etchant at room temperature.…”

“…3. THICKNESS AND ROUGHNESS EXTRACTED FROM ELLIPSOMETRY MEASUREMENT FOR MBE B SAMPLES ETCHED IN AL ETCHANT AT ROOMTEMPERATURE FOR DIFFERENT ETCH TIMES[102] …”

On the Many Applications of Nanometer-Thin Pure Boron Layers in IC and Microelectromechanical Systems Technology

“…The name "PureB" diodes was introduced to underline that the attractive characteristics of these diodes are the result of a surface coverage of pure B and not B doping of the bulk Si. The PureB layers discussed in this paper were fabricated from 250 C to 700 C by CVD but electrically active interfaces grown in a molecular beam epitaxy (MBE) system were also fabricated at temperatures down to 50 C [14].…”