Photochemical Deposition of Ni–Cu Patterns onto Conducting Substrates Employing TiO[sub 2]–Pd[sup 2+] Layers

Abstract

The metal photopatterning process employing a thin film of amorphous TiO 2 doped with Pd 2+ and oxalic acid has been developed. The exposure of this photolayer to UV light is believed to yield Pd͑I͒ stabilized in a titanium oxide matrix, while subsequent washing results in formation of Pd nanoparticles through disproportionation. The Pd centers at the exposed areas are capable of inducing electroless nickel plating yielding the adhesive nickel pattern. The electroless copper deposition over patterned Ni allows generation of metal patterns with a resistivity of 4-12 ⍀ cm and a resolution of 7 m on the conducting substrates ͑indium-tin oxide glass, Si͒.Titanium dioxide is known as an excellent heterogeneous photocatalyst. 1-3 Titania-catalyzed photochemical processes involve absorption of suprabandgap photons by semiconductor resulting in the generation of photoexcited electrons ͑e − ͒ and holes ͑h + ͒. The photoelectrons and photoholes diffuse to the surface of the semiconductor where they are consumed due to the interfacial chargetransfer reactions involving adsorbed acceptor and donor molecules and ions. Thus, photoholes can oxidize the organic substances, whereas ions of noble metals ͑Pd, Ag, etc.͒ and some transition metals, having a sufficiently positive electrochemical potential ͑e.g., Cu͒, can be reduced to their elemental forms by the photogenerated electrons. 4-6 The photocatalytically derived metal centers may induce electroless deposition of another metal which thus occurs as a photoselective deposition. 7-10 Different versions of photocatalytic lithography permitting the generation of metal patterns at the dielectric substrates were proposed. 8,10-14 However, these phototechnological processes employing photosensitive layers based on titania microdispersions in synthetic adhesive compositions 7,8,10-12 or annealed polycrystalline TiO 2 layers 10,13,14 which cannot be removed from free areas after metal pattern generation are unsuitable for many potential applications, e.g., production of large-area flat panel displays and microelectronic devices.In our previous papers, 15,16 a photopatterning process permitting the generation of Ni-Cu patterns of 10-12 m resolution with the use of a photosensitive layer consisting of amorphous TiO 2 and water-soluble polyvinyl alcohol was proposed. The main drawback of this phototechnology is that the metal pattern generation cannot be performed on conducting substrates ͓indium-tin oxide ͑ITO͒, n-Si, etc.͔ due to spreading of the photoinduced charges. The aim of the present work was to investigate the possibility of photoselective metal deposition utilizing thin films of hydrated titanium oxide containing both chemical sensitizer ͑photohole scavenging agent͒ and metal ions capable of yielding metal centers which exhibit catalytic activity toward further electroless metal deposition. Such a photolayer, that enables generation of latent metallic image in a single step, is favorable for the formation of metal patterns on conducting substrates and permits one to simplify t...

A direct‐writing approach to the micro‐patterning of copper onto polyimide

“…Laser enhanced electrochemical microfabrication (von Gutfeld et al, 1979(von Gutfeld et al, , 1982von Gutfeld and Sheppard, 1998) Multiple-layer direct-writing of metal wall structures (Wee and Li, 2005) Pd 2+ -ammonia complexes on polyimide (Kordás et al, 2001) Pd-acetate film (Imai et al, 2006) Cu-formate film (Kim et al, 2008) On Al 2 O 3 , SiC, diamond, ZrO 2 (Shafeev, 1998) On polyimide (Wang et al, 2002) On low temperature co-fired ceramics On glass (Manshina et al, 2007) Via microcontact printing (Lee et al, 2003) Via ink-jet printing (Cheng et al, 2005) Ag ink Liu et al, 2005) UV direct-writing of Ag on polyimide for subsequent electroless Cu deposition (Ng et al, 2008) Pd on TiO 2 for selective electroless deposition Byk et al, 2007Byk et al, , 2008 Laser-induced forward transfer by TiO 2 induced decomposition or precursor film (Sakata et al, 2005) Laser assisted Ni deposition on porous Si (Kordás et al, 2001Pap et al, 2002) Laser assisted Au deposition on p-type Si (Toth et al, 2005) Cu-organic mixtures (Condorelli et al, 2003;…”

“…Some recent efforts in utilising semiconductor photocatalysis for metal deposition can be found in Ikeda et al (2001a), Noh et al (2005) and Byk et al (2007Byk et al ( , 2008. These methods are limited by the fabrication process of the semiconductor layer onto the target substrates.…”

Photocatalytic lithography with image inversion

“…This permits the generation of both negative and positive metallic pictures by varying the irradiation dose, which expands the scope for obtaining planar metallic elements with complex structural organization.The feasibility of the photoselective deposition of catalytic metals such as palladium and silver onto the surface of broad-band oxide semiconductors such as TiO 2 , SnO 2 , and ZnO provides conditions for the subsequent chemical precipitation of another metal onto the exposed segments, which, in turn, permits the formation of various metallic elements such as current-conducting pathways, microelectrode assemblies, and catalytic surfaces for growing carbon nanotubes [1][2][3][4][5]. An important advantage of such photocatalytic lithography is the possibility of obtaining metallic pictures with micron resolution on large-format bases without using photoresists and vacuum spraying.…”

Titania-assisted electron-beam and synchrotron lithography

“…This permits the conclusion that electron-beam exposure results in the direct production of palladium nanoparticles in the titania film. The mechanism of e-beam-induced generation of a latent image thus differs considerably from that of palladium nanophase production under UV irradiation which occurs through the intermediate Pd(I) states exhibiting conversion into palladium nanoparticles via disproportionation during the washing stage [8,9]. The xray photoelectron spectra also provides evidence that washing of unexposed TiO 2 -Pd 2+ layers results in efficient removal of Pd 2+ : no signal from palladium is detected after 1 min washing (figure 2, curve (d)).…”

“…We have previously reported on the possibility to fabricate a patterned Pd seed catalyst layer in a single step by UV light exposure of thin films of amorphous titania containing Pd 2+ ions and oxalic acid which behaves as the chemical sensitizer [8][9][10]. These imaging layers permit the generation of nickel patterns on both dielectric and conducting substrates [8,9]. Moreover, very high sensitivity amounting to 10 4 cm 2 J −1 [10] has been demonstrated, which is explained by inherent intrinsic chemical amplification effects.…”