Comparison of laser-doped emitters from as-deposited and thermally diffused APCVD doping glasses on silicon substrates

Abstract

n this comparative study, atmospheric pressure chemical vapor deposited (APCVD) silicate glasses are used as a doping source for laser drive-in applied to mono-crystalline silicon under three conditions: First, laser drive-in from APCVD glasses after being heat treated in a tube furnace, i.e., after forming a shallow emitter; second, laser drive-in from as-deposited APCVD glasses newly deposited after removing the one used to form a shallow emitter; and third, laser drive-in from as-deposited APCVD layers directly on the Si wafer with only a base doping below 1016 cm−3. We analyze sheet resistances and doping profiles after laser-doing of all three approaches within a wide laser parameter space, using APCVD phosphosilicate glass (PSG) and borosilicate glass (BSG) as doping sources. We found that in general, laser doping from as-deposited APCVD doping glasses creates higher surface doping concentrations compared to laser doping from thermally treated APCVD glasses. The presence of shallow emitters (170/146 Ω/□) before laser-doping leads to about 100–200 nm deeper doping profiles compared to laser-doping from glasses on the base substrate. With as-deposited APCVD layers, surface concentrations above 5 · 1019 cm-3 (P) and about 2 · 1019 cm-3 (B) allow for low-ohmic silver contacts. Low sheet resistances of about 18 Ω/□ (P) and 42 Ω/□ (B) are opening wider parameter windows for laser fluence reduction in order to avoid laser-induced defects compared to the application of heat treated APCVD glasses for laser drive in.