Anatoly Grayfer

Prevention of optics and resist contamination in 300-mm lithography: improvements in chemical air filtration

Atmospheric pressure deep UV lithography using fast chemically amplified photoresists will be the mainstay of semiconductor production into the foreseeable future. Airborne molecular contamination (AMC) in the form of bases and condensable organic and inorganic materials however, threaten both sensitive optics and modern resists thereby creating a host of yield limiting contamination issues. Past work by Kunz at MIT has described photo-induced organic contamination of lithographic optics as a significant concern in leading-edge lithography. Moreover, Kinkead and Ercken, and Kishkovich and Dean have published work on the impact of base contamination on CD uniformity in modern photoresists. Herein, the authors discuss solutions to control both optics and resist contamination in a single compact filter system for advanced lithography. The results of this work suggest that resist and optics contamination can be controlled as we enter the era of low K1 factor <150nm/300mm-device production.

Contrarian approach to and ultimate solution for 193-nm reticle haze

Despite ample phenomenological evidence of reticle haze in IC manufacturing fabs, the mechanism of reticle haze formation is not well understood. Many attempts to control reticle haze formations are driven by trial-and-error approach and results are frequently contradicting and confusing. The authors apply extensive expertise of airborne molecular contamination (AMC) measurement and control and DUV optics protection [1,2] to develop a potential solution to the issue of 193-nm reticle haze. The authors outline the common mechanism of reticle haze formation and show that chemical modification of the reticle surface during mask manufacturing procedure is largely responsible for mask reticle susceptibility to AMC and surface molecular contamination (SMC). A proposed mechanism well explains available experimental and phenomenological data and the differences seen in chemical compositions of the haze particles observed at different fabs. The authors propose a single elegant solution for controlling multiple types of haze. Effectiveness of this solution is demonstrated through the field data obtained from production fabs.

New filter media development for effective control of trimethysilanol (TMS) and related low molecular weight silicon containing organic species in the photobay ambient

The authors present results of extensive studies on the chemical behavior of low molecular weight silicon-containing species (LMWS) and associated challenges of their analytical determination and control to prevent adverse influence on critical optical elements of exposure tools. In their paper the authors describe a non-traditional approach to the creation of a TMS gaseous source for filter media development and an engineering solution to the challenge of controlling LMWS - a solution that shows a significant advantage over currently existing approaches.

Measurement of low molecular weight silicon AMC to protect UV optics in photo-lithography environments

A new analytical method for semiconductor-specific applications is presented for the accurate measurement of low molecular weight, silicon-containing, organic compounds TMS, HMDSO and D3. Low molecular weight / low boiling point silicon-containing compounds are not captured for extended periods of time by traditional chemical filters but have the same potential to degrade exposure tool optical surfaces as their high molecular weight counterparts. Likewise, we show that capturing these compounds on sample traps that are commonly used for organic AMC analysis does not work for various reasons. Using the analytical method described here, TMS, HMDSO and D3 can be measured artifact-free, with at least a 50:1 peak-to-noise ratio at the method detection limit, determined through the Hubaux-Vos method and satisfying a conservative 99% statistical confidence. Method detection limits for the compounds are 1-6 ppt in air. We present calibration curve, capacity, capture efficiency, break-through and repeatability data to demonstrate robustness of method. Seventy-one real-world samples from 26 projects taken in several fab environments show that TMS is found in concentrations 100 times higher than those of HMDSO and D3. All compounds are found in all environments in concentrations ranging from zero to 12 ppm, but most concentrations were below 50 ppb. All compounds are noticeably higher in litho-bays than in sub-fabs and we found all three compounds inside of two exposure tools, suggesting cleanroom and/or tool-internal contamination sources.

New approach to measurement of photoactive deep-UV optics contaminants at sub parts-per-trillion levels

A new sampling device and collection method has been developed to provide an accurate and convenient means for collecting ultra low levels of condensable organic species. The sample collection and analytical method are optimized to separate, quantify, and identify individual organic components at a detection limit of approximately 0.001 μg/m3, representing a hundred fold improvement over conventional sampling methods. Given the potential threats that these contaminants pose to deep UV lithography optics, the work represents a new step in understanding the long-term risks to production 193nm exposure tools. Devices deployed at an Texas Instruments manufacturing facility have generated data that proves that this sampling device and method is capable of measuring contamination at levels never achieved before. This data will be used to develop correlation of optics degradation with different classes of airborne molecular contamination.