Series Resistance Analysis of Passivated Emitter Rear Contact Cells Patterned Using Inkjet Printing

Table 1

Processing sequence for IJP PERC cells.

Step	Process	Conditions
(1)	Damage etch/texture	20 min etch in 30% NaOH at 80°C
(2)	Oxidation	Dry oxidation, 1030°C for 4 hr with 1% TCA in O2
(3)	Strip front oxide	Mask rear; strip SiO2 with buffered HF
(4)	Emitter diffusion + oxidation	Diffusion: 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 contacts	Indirect IJP method [5]
(6)	Groove diffusion + drive-in	Diffusion: P solid source, 940°C, 90 min; Drive-in: 1000°C, 3 hr, N2
(7)	IJP the rear contacts	Indirect IJP method [5]
(8)	Evaporate rear Al + sinter	1-2 μm Al, sinter at 400°C, 30 min in forming gas
(9)	Ni plate + anneal	Various plating methods; anneal at 400°C, 10 min in forming gas
(10)	Cu light-induced plate	Cu electroplating solution, 5 min under high-intensity fluorescent light
(11)	Edge isolation	Cut with a 1064 nm Nd : YAG laser from the rear; cut 1/2 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.