Microfabrication by UV femtosecond laser ablation of Pt, Cr and indium oxide thin films

We demonstrate the direct deposition of Pt, Cr and In2O3 microstructures on glass using a femtosecond laser assisted technique. A metal (Pt, Cr) or ox ide (In2O3) source film is first deposited on an optically transparent quar tz carrier and is brought in intimate contact with a receiver glass substra te using an especially designed vacuum cell. An ultrashort excimer laser pu lse ablates the source film at the quartz/film interface and results in the forward-transfer deposition of material onto the nearby glass receiver. Th e morphology of the ablated and transferred features was studied by means o f scanning electron and atomic force microscopies. It was found that the go od adhesion of the pre-deposited source film on the quartz substrate and th e intimate contact between the source and receiver glass are two critical f actors for achieving efficient transfer printing. The optimal deposited mor phology in terms of spatial resolution and dispersion was produced using 30 -40 nm and 50-60 nm thick source films of metals and In2O3 respectively. In addition, the laser fluence had to be just above the threshold for printin g (E-pr). This was 150 +/- 20 mJ/cm(2) for Pt, Cr and 60 +/- 20 mJ/cm(2) fo r the In2O3. Fluences greater than E-pr lead to the development of crater l ike features with excessive spread on the periphery rim. Similar behaviour was observed for micro-prints obtained using a backward-transfer configurat ion. Sub-micron Pt dots were obtained from a 30 nm thick Pt source film, ir radiated with a 3 mu X 3 mu m spot at a fluence of similar to 150 mJ/cm(2). The production of these sub-micron dots was possible due to limited therma l diffusion and sharp ablation threshold existent in fs laser processing. ( C) 1999 Elsevier Science B.V. All rights reserved.