NANOMETER-SCALE LITHOGRAPHY ON SI(001) USING ADSORBED H AS AN ATOMIC LAYER RESIST

We describe nanometer-scale feature definition in adsorbed hydrogen la yers on Si(001) surfaces by exposure to low energy electrons from a sc anning tunneling microscope tip. Feature sizes range from < 5 to > 40 nm as a function of bias voltage (5-30 V) and exposure dose (1-10(4) m u C/cm). We show that the cross section for electron stimulated desorp tion of hydrogen has a threshold at 6-8 eV and is nearly constant from 10 to 30 eV, so that above threshold the feature profiles are a direc t reflection of the electron flux profile at the surface. Radial flux distributions are best fit by a simple exponential function, where the decay length is dependent primarily on the tip-sample separation. Low intensity tails at large radius are also observed for high bias emiss ion. Comparison to field emission simulations shows that our tip has a n ''effective radius'' of approximately 30 nm. Simulations demonstrate that tip geometry and tip-sample separation play the dominant role in defining the electron flux distribution, and that optimum beam diamet er at the sample is obtained at small tip-sample separation (low bias) with sharp tips. We show that adsorbed hydrogen is a robust resist th at can be used as a mask for selective area deposition of metals by ch emical vapor deposition. Fe lines 10 nm wide are deposited by pyrolysi s of Fe(CO)(5) in areas where H has been desorbed, with minimal nuclea tion in the H-passivated areas. (C) 1996 American Vacuum Society.