Study of p-type laser doping using ALD AlOx as a dopant source

The formation of heavily doped p⁺ region on p-type silicon substrates using laser doping through a layer of ALD AlO_x is studied. A 532 nm continuous wave (CW) laser is used to incorporate Al atoms from the AlO_x layers to form p⁺ silicon. The p⁺ regions formed through laser doping are found to be affected by various parameters such as laser speed and power. Sheet resistances as low as 10 Ω/□ were achieved using a power of 15 W and laser scanning speed of 0.5 m/s. The impact of the laser doping process on effective minority carrier lifetime is investigated using only the AlO_x layer as a dopant source, as well as with the addition of a Boron dopant source. Laser doping boron have better protection by introducing a lifetime drop from 67 μs to 57.7 μs after laser doping comparing to the lifetime drop of laser doping AlO_x from 62.5 μs to 46.1 μs. However, the addition of a boron spin on dopant source may induce voids in the laser doped region.