Table 1: Processing sequence for IJP PERC cells.

StepProcessConditions

(1)Damage etch/texture20 min etch in 30% NaOH at 80°C
(2)OxidationDry oxidation, 1030°C for 4 hr with 1% TCA in O2
(3)Strip front oxideMask rear; strip SiO2 with buffered HF
(4)Emitter diffusion + oxidationDiffusion: P solid source, 850°C, 15 min
Oxidation: 1100°C, 5 hr, 1% TCA in O2, 15 min anneal in N2
(5)IJP the front contactsIndirect IJP method [5]
(6)Groove diffusion + drive-inDiffusion: P solid source, 940°C, 90 min
Drive-in: 1000°C, 3 hr, N2
(7)IJP the rear contactsIndirect IJP method [5]
(8)Evaporate rear Al + sinter1-2 μm Al, sinter at 400°C, 30 min in forming gas
(9)Ni plate + annealVarious plating methods; anneal at 400°C, 10 min in forming gas
(10)Cu light-induced plateCu electroplating solution, 5 min under high-intensity fluorescent light
(11)Edge isolationCut with a 1064 nm Nd : YAG laser from the rear; cut way thru wafer then snapped

Ni plating was done in one of two ways: (i) electroless Ni using Transene EN solution [9], 80°C for 3 min; or (ii) BA-LIP Ni, 25–30°C for 30 s under high-intensity fluorescent light. The BA-LIP Ni consisted of Watt’s solution in the ratios 10 g Ni2SO4, 20 g NiCl2, 4 g boric acid in 100 mL deionized water [13].
The electroplating solution for the Cu plating used 12 g CuSO4, 11 mL H2SO4, and 50 mL deionized water.