Early manufacture and use of 157nm high NA lenses has presented significant challenges including: intrinsic birefringence correction, control of optical surface contamination, and the use of relatively unproven materials, coatings, and metrology. Many of these issues were addressed during the manufacture and use of International SEMATECH’s 0.85NA lens. Most significantly, we were the first to employ 157nm phase measurement interferometry (PMI) and birefringence modeling software for lens optimization. These efforts yielded significant wavefront improvement and produced one of the best wavefront-corrected 157nm lenses to date. After applying the best practices to the manufacture of the lens, we still had to overcome the difficulties of integrating the lens into the tool platform at International SEMATECH instead of at the supplier facility. After lens integration, alignment, and field optimization were complete, conventional lithography and phase ring aberration extraction techniques were used to characterize system performance. These techniques suggested a wavefront error of approximately 0.05 waves RMS--much larger than the 0.03 waves RMS predicted by 157nm PMI. In-situ wavefront correction was planned for in the early stages of this project to mitigate risks introduced by the use of development materials and techniques and field integration of the lens. In this publication, we document the development and use of a phase ring aberration extraction method for characterizing imaging performance and a technique for correcting aberrations with the addition of an optical compensation plate. Imaging results before and after the lens correction are presented and differences between actual and predicted results are discussed.
Significant improvement in 157nm optical components lifetime is required for successful implementation of pilot and production scale 157nm lithography. To date, most of the 157nm optics lifetime data has been collected in controlled laboratory conditions by introducing predetermined concentrations of contaminants and monitoring degradation in terms of transmission loss. This publication compliments prior work by documenting field experience with the 157nm Exitech Microstepper currently in operation at International SEMATECH. Failure mechanisms of various optical components are presented and molecular contamination levels in purge gas, tool enclosure, and clean room are documented. Finally the impacts of contaminant deposition and degradation of components on imaging performance is discussed.
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.
The Advanced Mirror System Demonstrator program sponsored by NASA, the Space Based Laser Joint Venture Team, and the National Reconnaissance Office provides an opportunity to design and build a demonstration model of the next generation primary mirrors that will be needed for future space programs. This paper discusses the history of this technology at Kodak and provides an overview of the analysis techniques used in the design and performance prediction process.
Advanced optical systems, currently under consideration, propose the use of lightweight, segmented, long radii elements. Reaction-bonded silicon carbide (RB SiC) is quickly becoming a contender in the materials market for these large, lightweight mirrors due, in part, to its relatively low thermal expansion and high stiffness to weight ratio. The RB SiC manufacturing processes can be considered advanced in comparison to the polishing and finishing processes on bare RB SiC, or on clad RB SiC substrates. In an effort to improve the polishing and finishing techniques, Eastman Kodak Company has investigated a polishing process for physical vapor deposited silicon (PVD Si) coated RB SiC optics and has demonstrated this process on a lightweight, concave, PVD Si-coated RB SiC hexagonal optic. This discussion includes the modification and redesign of an existing conventional planetary table, durability test results on the PVD Si/RB SiC coating bond, process approach and results for the hexagonal demonstration piece, and the thermal stability analysis of the hexagonal mirror upon completion of polishing and ion figuring the front surface of the mirror.
Conference Committee Involvement (2)
Optical Manufacturing and Testing VI
31 July 2005 | San Diego, California, United States
Optical Manufacturing and Testing V
3 August 2003 | San Diego, California, United States