Focused Ion Beam Machining for Optical Microlens Fabrication

A three-dimensional feature has been fabricated into optical microlens by scanning a focused Ga ion beam. The lens shape is obtained using computer-controlled beam positions and dwell time during sputter machining. We have used this technique to create a micron-sized optical lens surface. The lens surface that is fabricated is a sphere of 1.88 mm radius. When we investigated the distribution of the amount of error between the calculated value of the lens shape and the actual measurement of the lens shape from the center to the circumference, the error increased to the plus side gradually, and it turns out that the error of minus arises in a domain near the perimeter. It is considered that although redeposition in the atom processing becomes significant near the perimeter, the amount of machining increases more than the amount of redeposition because of the increase of the incidence angle.