C. Bryce et D. Berk, KINETICS OF THE DISSOLUTION OF COPPER IN IRON(III) CHLORIDE SOLUTIONS, Industrial & engineering chemistry research, 34(4), 1995, pp. 1412-1418
Wet etching is commonly used to produce patterned copper films for pri
nted circuit boards and semiconductor devices. The investigation of co
pper etching by FeCl3-HCl solutions in a batch stirred-tank reactor wa
s undertaken to determine the intrinsic reaction kinetics. The variati
on of the etch rate with FeCl3 concentration was linear at low concent
rations and gave first-order rate constants of 0.2039, 0.3083, and 0.3
362 mg Cu.kg H2O/cm2.s.mol FeCl3 at 30, 40, and 50-degrees-C, respecti
vely. At approximately 2 mol/kg the etch rate reached a maximum. Etch
rates obtained with 0.85 and 2 mol/L HCl over the range of FeCl3 conce
ntration were similar. The etch rate was substantially reduced with th
e use of Fe(NO3)3-HNO3 solutions and increased uniformly as the chlori
de content of the solution was increased. Concentrations of the chloro
complexes of the iron(III) ion were computed and showed that FeCl2+ a
nd FeCl3(0) are the principal species present in the etchants studied.
The etch rate was found to vary linearly with FeCl2+ concentration at
low (<1 mol/kg) concentrations. The maximum in the etch rate is attri
buted to the inhibition by FeCl3(0), the concentration of which become
s significant in etchants of greater than 2 mol/kg FeCl3.