PureB diode fabrication using physical or chemical vapor deposition methods for increased back-end-of-line accessibility

Several methods of depositing pure boron (PureB) layers on silicon are examined with respect to their potential for fabricating advanced PureB (photo)diodes with back-end-of-line (BEOL) CMOS compatibility. PureB devices were fabricated in two different batch furnace chemical-vapor deposition (CVD) systems or by electron-beamassisted physical-vapor deposition (EBPVD), and their electrical characteristics were found to be comparable to those of devices previously fabricated using single-wafer CVD and molecular beam epitaxy (MBE) systems. For all methods, the material properties of the B-layers and the I-V characteristics of the PureB diodes follow the same temperature dependence over the range 50 degrees C-400 degrees C. This was also the case for the EBPVD layers which were deposited at 50 degrees C and then annealed at higher temperatures, instead of being deposited at these temperatures as for the other methods. At 400 degrees C, the ability to achieve an optimal suppression of the electron injection into the PureB anode regions, corresponding to an electron current density of similar to 20 pA/cm(2), was verified for all methods. The advantages and disadvantages of each deposition method is evaluated with respect to equipment availability, B-layer selectivity, conformality, and thickness control. The batch furnace systems could be attractive for high-volume production, but hardware improvements as discussed here would be needed to reduce the effects of gas depletion. On all points except conformality, EBPVD appears to be a very good option for fabricating nm-thin B-layers suitable for fabricating high-performance 400 degrees C PureB diodes.