Photocatalytic activation of TiO2-functionalized anodic aluminium oxide for electroless copper deposition

We demonstrate conductive copper layer patterning of TiO2-functionalized anodic aluminium oxide (AAO) by means of Cu electroless deposition (Cu-ELD). 4 mu m thick AAO layers were obtained by anodization of Al foil at 140 V in 5% H3PO4 and functionalization with TiO2 by dip-coating in a salicylic-acid-based Ti sol. We show that TiO2 functionalization improves the AAO chemical stability at pH 12.8, allowing its metallization in an alkaline, HCHO-based Cu-ELD bath. In lieu of a noble metal catalyst, surface activation of TiO2/AAO was accomplished by photocatalytic reduction of a Cu[EDTA] complex under ultraviolet (UV) illumination through a photomask. The effects of UV dose on the photocatalytic activation of TiO2/AAO were studied in the range 1.25-20 J cm(-2). Uniform surface coverage of reduction products were obtained at doses <= 7.5 J cm(-2), followed by the formation of 100-500 nm particles upon prolonged UV exposure. XPS analysis revealed a mixed phase Cu+ : Cu2+ composition in a 3 : 1 ratio of the Cu[EDTA] reduction products, which were found to be active as a Cu-ELD catalyst. Conductive Cu patterns with sheet resistance as low as 0.54 omega sq(-1) were obtained within 15 min of Cu-ELD.

Automated summary

In this study, we patterned conductive copper layers on TiO2-functionalized anodic aluminium oxide (AAO) through Cu electroless deposition (Cu-ELD). The functionalization of TiO2 improved the chemical stability of AAO and allowed its metallization in an alkaline environment. The surface activation of TiO2/AAO was achieved by photocatalytic reduction of a Cu[EDTA] complex under UV illumination. Conductive Cu patterns with low sheet resistance were obtained through Cu-ELD.