AVS 50th International Symposium
    Surface Science Monday Sessions
       Session SS1-MoA

Paper SS1-MoA1
Growth of Ordered and Disordered Arrays of Silicon Pillars During Laser-Assisted Etching

Monday, November 3, 2003, 2:00 pm, Room 326

Session: Stimulated Processes at Surfaces
Presenter: K.W. Kolasinski, Queen Mary, University of London, UK
Authors: D. Mills, Queen Mary, University of London, UK
K.W. Kolasinski, Queen Mary, University of London, UK
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We report on the formation of conical silicon pillars on a Si(111) substrate by etching with a nanosecond pulsed excimer laser in the presence of SF@sub 6@, HCl or NF@sub 3@. The change in the silicon surface morphology was monitored as the number of shots from the XeCl (308 nm) excimer laser was varied from one to several hundred, for all experiments the energy density at the silicon surface was kept at about 1 J cm@super -2@. Significant changes in pillar morphology result from changing the process gas. This is a clear indication that gas-phase/plasma chemistry occurring in the laser ablation plume and plume/surface interactions are instrumental in the pillar formation mechanism. Initial surface morphology also affects pillar dimensions. Exposure of an unpolished surface results in much sharper pillars for a given number of laser shots than does exposure of the polished side. Modulation of the laser intensity profile by the effects of diffraction can be used to enhance the order of the pillars. For instance, the diffraction profile resulting from irradiation of a Gaussian shaped interface produces concentric rings of pillars. Large areas of pillars, on the order of 1 cm@super 2@, have been formed by rastering the beam across the Si sample under continual laser irradiation at 20-50 Hz. Progress has also been made with the production of ordered arrays of the pillars using near field diffraction effects from fine wires and grids. Further investigation will examine the effects of varying the pressure of the process gas, the partial pressure of process gas mixtures, pre-heating of the surface with an argon ion laser, the effects of pulse repetition rate and diffraction on the pillar height, width and packing densities.