Realization of Pure Boron/Si Diodes Through a Two-Step Low-Temperature Growth in a Home-Built LP CVD System

For applications such as photodetection and electron microscopy, adopting ultra-shallow pn-junction diodes with ultra-low saturation currents is crucial. One way to realize such diodes is by employing an ultra-thin boron layer (~2-10nm) on top of n-type silicon (Si), i.e., the boron/Si diode. So far, for relatively low process temperatures (T≤400∘C) typically used in standard IC/CMOS processes, the boron/Si interface has not been formed in a controllable way. In this work, through an extensive in-depth growth study, we have developed a two-step growth method for the boron formation for a batch furnace, based on the assumption that the nucleation layer for growing boron is formed at T=250∘C, and subsequently, a higher temperature (T=400∘C) is used for a final rapid deposition of boron in a batch furnace. This approach enables precise control over the growth of thin boron layers. A long deposition at 250 ∘C leads to the formation of a continuous boron layer, significantly reducing the surface roughness and lowering the incubation time at T=400∘C. The improved boron coverage has a direct impact on the ideality factor (η) and saturation current density Js, crucial for the boron/Si diode. As a result, for fully metallized structures a reproducibly low Js of 4.32∙10-16 A/μm has been achieved, with an ideality factor of η≈1.02, and a barrier height ΦB, i.e., a measure of the interface charge that induces the ultrashallow p+ layer, of 0.84 V.