Silicon microlens structures fabricated by scanning-probe gray-scale oxidation.

We report on the micromachining of silicon microlens structures by use of scanning-probe gray-scale anodic oxidation along with dry anisotropic etching. Convex, concave, and arbitrarily shaped silicon microlenses with diameters as small as 2 microm are demonstrated. We also confirm the high fidelity of pattern transfer between the probe-induced oxides and the etched silicon microlens structures. Besides the flexibility, the important features of scanning-probe gray-scale anodic oxidation are small pixel size and pitch (of the order of tens of nanometers), an unlimited number of gray-scale levels, and the possibility of creating arbitrarily designed microlens structures with exquisite precision and resolution. With this approach, refractive, diffractive, and hybrid microlens arrays can be developed to create innovative optical components.