Excimer laser annealing of boron thin-films to fabricate large-area low-defect p+ Si regions

• Pure B deposition on Si is a damage-free B source for excimer laser annealing. • An active B doping concentration of 2.3 × 10 21 cm −3 was reached in the melt zone. • A junction depth of 85 nm with 25 Ω/sq sheet resistance reached for 900 mJ/cm 2 . • About 1 nm B gave large-area ideal junctions for all ELA from 400-900 mJ/cm 2 . • About 1 nm B plus ELA at 600 mJ/cm 2 gave optimal responsivity 0.16 A/W at 406 nm. Boron layers deposited by chemical vapor deposition at 700 °C are exposed to 308 nm excimer laser annealing (ELA). The non-annealed B-deposition is commonly used to form radiation hard p + n PureB photodiodes that have nm-shallow junction depths with low dark currents, i.e., the PureB anode region has a high Gummel number. Here a B-layer thickness ranging from a monolayer to 7 nm was studied for deposition in oxide windows to lightly-doped n-Si wafers, and diode contacting was achieved with an Al/1%Si interconnect layer. The focus was placed on a 1-nm-thin B-layer that, after ELA at fluences from 400 to 900 mJ/cm 2 , delivered ideal diodes with anode Gummel numbers at least as high as PureB counterparts. Fluences above 750 mJ/cm 2 were necessary for melting of the Si to achieve p-region sheet resistance <100 Ω/sq. The maximum active doping level was 2.3 × 10 21 atoms/cm 3 in the melt zone, providing a sheet resistance of 25 Ω/sq at a junction depth of 85 nm for a fluence of 900 mJ/cm 2 . At 600 mJ/cm 2 , about a monolayer of B bonded to Si at the interface remained. This rendered a photodiode with an optimal responsivity of 0.16 A/W at 406 nm and 0.33 A/W at 670 nm wavelengths.