Silicon lenses are widely used for infrared applications. Especially for portable devices the size and weight of the optical
system are very important factors. The use of aspherical silicon lenses instead of spherical silicon lenses results in a
significant reduction of weight and size.
The manufacture of silicon lenses is more challenging than the manufacture of standard glass lenses. Typically
conventional methods like diamond turning, grinding and polishing are used. However, due to the high hardness of
silicon, diamond turning is very difficult and requires a lot of experience. To achieve surfaces of a high quality a
polishing step is mandatory within the manufacturing process. Nevertheless, the required surface form accuracy cannot
be achieved through the use of conventional polishing methods because of the unpredictable behavior of the polishing
tools, which leads to an unstable removal rate.
To overcome these disadvantages a method called Ion Beam Figuring can be used to manufacture silicon lenses with
high surface form accuracies. The general advantage of the Ion Beam Figuring technology is a contactless polishing
process without any aging effects of the tool. Due to this an excellent stability of the removal rate without any
mechanical surface damage is achieved. The related physical process - called sputtering - can be applied to any material
and is therefore also applicable to materials of high hardness like Silicon (SiC, WC).
The process is realized through the commercially available ion beam figuring system IonScan 3D. During the process,
the substrate is moved in front of a focused broad ion beam. The local milling rate is controlled via a modulated velocity
profile, which is calculated specifically for each surface topology in order to mill the material at the associated positions
to the target geometry.
The authors will present aspherical silicon lenses with very high surface form accuracies compared to conventionally