Control of microstructure shape and morphology in femtosecond laser ablation of imprint rollers

With increasing demand for microstructure shape accuracy for MEMS and optoelectronic devices, controllability of shape and morphology in micro-fabrication has become increasingly crucial. In this paper, the effects of processing parameters on the shape and morphology of microstructures in femtosecond laser fabrication of imprint roller are explored. An optimized fabrication process is proposed to acquire high accuracy microstructures, in which a two-step inclination ablation process and optimal laser focus position are adopted. Adjusting and matching the processing parameters is a basic method to acquire well-defined shapes, but the ablation results indicate that the draft angle of microstructures can only be adjusted in a limited range due to the intensity distribution of laser beam. A two-step inclination ablation process is adopted to increase the draft angle. In the two-step inclination ablation process, the laser beam irradiates the target surface with an angle and the microstructure with a much steeper draft angle forms after the two-step fabrication. Laser focus position is explored as an important parameter affecting the morphology, and an optimal laser focus position is obtained to enhance the ablation quality. By matching the laser fluence and laser focus position, this morphology enhancement method can realize the high-quality ablation of microstructures with a wide range of dimensions without changing the focusing objective lens.