Femtosecond laser-induced chemical vapor deposition of tungsten quasi-periodic structures on silicon substrates

A rapid, maskless deposition technique for writing conductive tracks via femtosecond laser-induced chemical vapor deposition has been developed. The technique can be used for a range of applications, one example being writing conductive tracks for the construction of microelectronic devices. The process uses pulsed ultrafast laser with 300 fs pulse length and 1030 nm wavelength for the direct deposition of tungsten tracks on silicon substrates from metal organic tungsten hexacarbonyl precursors. The written tracks consisted of wavy quasi-periodic walls with thickness of 200 nm and a periodicity of 500 nm, aligned perpendicular to the linear polarization of the laser beam. Fixed number of pulses spot dwell experiments revealed that a thin film formed before quasi-periodic structures grew on top of that thin film. The peak intensity threshold for the deposition process (8.64 × 1010 W/cm2) was lower than the threshold for surface modification on the silicon substrate (3.34 × 1011 W/cm2) at the same scanning speed of 10 μm/s and repetition rate of 502 kHz. Negligible damage to the underlying substrate was observed in the cross section. Scan speeds up to 100 μm s−1 were achieved in the process. The elemental composition of the deposits was measured to be 80% by weight tungsten in energy-dispersive x-ray spectroscopy methods and the resistivity of the deposit was measured to be 290 μΩ cm using the transfer length method.