Adam S. Fedor

Design and fabrication of customized illumination patterns for low-k1 lithography: a diffractive approach

As CDs continue to shrink, lithographers are moving more towards using off-axis illumination schemes to increase their CD budget. There have been several papers over the last few years describing various custom illumination profiles designed for application specific optimization. These include various annular and quadrupole illumination schemes including weak quadrupole, CQUEST, and QuasarTM. Traditionally, pupil filtering is used to realize these complex illumination modes but this approach tends to introduce significant light loss. Therefore, compromises are made to lithographic performance to minimize the effect on wafer throughput. Diffractive optics, if incorporated into the design of the illumination system, can be used to create arbitrary illumination profiles without the associated light loss, thus maintaining throughput while optimizing system performance. We report on the design and fabrication of such devices for use with KrF, ArF, and potentially F2 scanners. Extension to I-line steppers is also possible.

Binary optic diffuser design

This paper describes the fundamentals of diffractive optics diffuser design, with an emphasis on common pitfalls and important design decisions. In addition, several new design and fabrication methods are presented, which overcome many of the current limitations of multi-level diffractive diffusers. These designs include an easily fabricated white-light diffuser and a uniform, high-NA diffuser design.

Micro integration of VCSELs, detectors, and optics

System alignment is often the cost driver in the production of optical system. In order to both miniaturize and reduce production costs, wafer scale integration of active and passive components is required. This integration relies on a host of techniques to align and bond active and passive devices into a monolithic structure. Moreover, this initial packaging is accomplished while the optics and supporting structures are in wafer form, thereby providing parallel fabrication with resultant cost savings. This paper describes the fundamental techniques for producing IMOS from wafer scale substrates. The relative merits of each approach are discussed, along with design concerns for successful application. Two example systems are discussed, each using a different fabrication technique.

Improvements to optical performance in diffractive elements used for off-axis illumination

As photolithographic tools are pressed to print the ever shrinking features required in todays devices, complex off-axis illumination is taking an ever increasing role in meeting this challenge. This, in turn, is driving tighter, more stringent requirements on the diffractive elements used in these illumination systems. Specifically, any imbalance in the poles of an off-axis illuminator will contribute to reductions in the ultimate imaging performance of a lithographic tool and increased complexity in tool-to-tool matching. The article will focus on improvements to the manufacturing process that achieve substantially better pole balance. The modeling of the possible process contributors will be discussed. Challenges resulting from the manufacturing methodology will be shared. Finally, the improvement in manufacturing process performance will be reported by means of a pole balance capability index.

Design and fabrication of customized illumination patterns for low-k1 lithography--a diffractive approach: II. Calcium fluoride controlled-angle diffusers

As CDs continue to shrink, lithographers are moving more towards using off-axis illumination schemes to increase their CD budget. There have been several papers over the last few years describing various custom illumination profiles designed for application specific optimization. These include various annular and quadrupole illumination schemes including weak quadrupole, CQUEST, and QuasarTM. Diffractive optics, if incorporated into the design of the illumination system, can be used to create arbitrary illumination profiles without the associated light loss, thus maintaining throughput while optimizing system performance. Diffractive optical elements used to generate efficient illumination profiles for 248 nm and 193 nm excimer laser-source scanners, have been reported and realized in fused silica. The fabrication of such elements in calcium fluoride (CaF2), for use in 157 nm wavelength lithographic projection tools has been developed and is presented in this paper. Three different categories of elements are shown: large-diagonal-cluster diffusers, medium- and small-rectangular-cluster diffusers. The diffusers were fabricated as binary phase devices, in order to determine calcium fluoride processing capabilities.

Tolerancing and analysis of a diffractive beam shaper

This paper describes the design and analysis of a deep-UV diffractive beam shaper for converting a collimated Gaussian beam into a collimated flattop beam. Diffractive beam shapers can be manufactured in most common materials to provide good beam control with very low non-uniformity. Beam shapers, however, are generally very sensitive to beam parameters and alignment. Here we examine the sensitivity of the beam shaper to alignment and tilt of the input beam, phase surfaces, and various other fabrication errors. This device was successfully built and comparisons with laboratory measurements show excellent agreement with simulation predictions.

Compact optical encoder approach utilizing novel diffractive optics design

Diffractive optical encoders have quickly established themselves in the marketplace because of their small seize, high accuracy and relaxed alignment tolerances, but current products are still composed of carefully packages, discrete optical and electro-optical components. MicroE and Digital Optics Corporation have been working together on the next generation of these encoders, which replaces all discrete and refractive elements with DOEs and more completely integrates the requisite optical and electro-optical components. In this paper we describe a monolithic source/optics/detector encoder module we have designed and prototyped for a satellite application under a NASA Phase I SBIR contract.