Understanding the sensitivity of optical systems thoroughly can lead to improved tolerancing and compensation. An examination into a complex sensitivity analysis is shown. This analysis is used to improve the overall tolerancing and compensation of an optical system. We have developed a tool to facilitate this method of sensitivity analysis. An example of a novel compensation method is presented.
Optical systems often require compensation during operation to accommodate environmental and
process changes. Compensation usually involves the movement of a lens element insitu. Different optomechanical
designs are used to in order to meet the volume, optical and environmental systems requirements
on a case by case basis. Two opto-mechanical designs are presented and compared. The performance and service requirements dictate the methodology used, including component design, flexure construction, actuation and control system. Included will be design constraints, prototype testing, manufacturing issues and implementation problems.
The path to smaller semiconductor feature sizes demands that lens systems operate at higher numerical apertures and shorter wavelengths. Materials available for operation at shorter wavelengths, such as 157nm, exhibit properties that have strong wavelength dependence. Accurate characterization of lens performance must be done at the wavelength of use so as to include these effects. Measurement of optical system performance at 157nm brings with it the necessity to operate in an environment purged of gases and outgasing byproducts. This constraint coupled with increasingly tight tolerances necessary to meet the advancing requirements of the semiconductor industry raise the level of sophistication required of test set-ups. We present an interferometric set-up designed to meet these requirements. The set-up is designed to work with the very low temporal and spatial coherence typical of 157nm laser sources. These coherence properties are used advantageously, reducing coherent noise in the system and achieving high resolution, repeatability and accuracy simultaneously. Specialized instrumentation enables various error-separation techniques to be used. We now measure phase-retardance in the wavefront in order to characterize the error introduced by the intrinsic properties of the material. The combination of these features is required for 'at wavelength' optimization of 157nm lens systems.