Direct laser writing on electrolessly deposited thin metal films for applications in micro- and nanofluidics

This paper presents a method that uses a tightly focused laser beam to write features on thin metal films with a resolution of several hundred nanometers to a few micrometers. Owing to the ease of fabricating electrolessly and electrolytically deposited Ni layers, we also evaluated with scanning electron microscopy the suitability of such thin Ni films as a substrate for laser writing and subsequently as an etch resist in HF etching and as a photomask in contact photolithography. Using atomic force microscopy, we characterized the feature sizes that can be obtained from three commonly used lasers: the 488 nm of a continuous wave (CW) Ar⁺ laser, the 1064 nm of a CW Nd:YAG laser, and the 337 nm of a pulsed (3 ns pulse width) N₂ laser. The smallest feature sizes that we can generate routinely are approximately 0.5 μm for the Ar⁺ laser, 1.3 μm for the YAG laser, and 2.3 μm for the N₂ laser. Using the laser-patterned Ni film as an etch mask, we have produced HF-etched channels (1.5 μm in width) in glass. In addition to Ni films, we demonstrate the flexibility of this strategy to create photomasks by writing directly on sputtered gold films and on commercially available chrome blanks.