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Session F28 - DMP: LASER PROCESSING OF MATERIALS III: APPLICATIONS
Mixed session, Tuesday morning, March 21, 11:00
Empire Room, Fairmont Hotel
3-d structures have been etched directly into silicon with feature sizes in the range of tens of nanometers. The etching process involves local melting of the silicon substrate by a cw laser in an atmosphere of molecular chlorine. The reaction rate for liquid silicon is gas phase transport-limited and several orders of magnitude higher than for solid silicon, resulting in isotropically etched features which are determined by the extent of the melt. Reducing the incident laser power decreases the melt diameter to less than 100 nm for a laser spot size of 600 nm. Our setup is designed to achieve the smallest possible melt size. It is based on a stationary cw beam and high resolution dc motor stages for x/y translation of the sample and z translation of the focusing objective. This allows for a good beam quality and a large access range, while maintaining a high and constant scan velocity for fast etching of continuous trenches. We have etched 10-nm deep trenches with a minimum width of 70 nm and walls between trenches with a minimum width of 40 nm. The radius of curvature of the edge between sidewall and surface is less than 20 nm. Calculations of the spatial temperature distribution, based on an analytical two-phase heat model, show no fundamental limit to the diameter of the melt in this range.