Oleg P. Kishkovich

Real-time methodologies for monitoring airborne molecular contamination in modern DUV photolithography facilities

In this paper, the authors discuss the critical airborne molecular contaminants found in DUV photolithography facilities. They present an overview of real-time monitoring methodologies that can detect and measure these contaminants at low concentrations, enabling users to anticipate and resolve AMC challenges before production problems can result. Citing actual examples of how real-time monitoring is being employe din production fabs, the authors examine single point investigate and multi-point process monitoring strategies, compare the different monitoring strategies, compare the different monitoring technologies now is use, and describe critical points to monitor in tracks, steppers, clean rooms, and air filtration systems. As a separate item, the authors describe an innovative, practical approach to quantifying resist environment sensitivity. It is anticipated this work will result in a standard methodology that can be used at individual process sites to determine the resist sensitivity to airborne molecular contamination under local operating conditions.

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.

Accelerated testing technique for evaluating performance of chemical air filters for DUV photolithographic equipment

In this paper, the authors discuss the requirements for chemical air filtration system used in conjunction with modern DUV photolithography equipment. Among the topics addressed are the scope of pollutants, their respective internal and external sources, and an overview of different types of filtration technologies currently in use. Key filtration parameters, including removal efficiency, service life, and spill protection capacity, are discussed and supported by actual data, reflection the total molecular base concentration in operational IC manufacturing facilities. The authors also describe a time-accelerated testing procedure for comparing and evaluating different filtration technologies and designs, and demonstrate how this three-day test procedure can reliably predict an effective filter service life up to ten years.

A practical solution to the critical problem of 193 nm reticle haze

The authors have developed and successfully implemented a practical, yet effective solution to help eliminate haze formation in the production fab. Based on a novel mechanism of haze formation described earlier, along with a thorough understanding of the reticle surface chemistry changes during the manufacturing process, the authors found an unexpectedly simple and straightforward way to prevent haze formation. This is possible regardless of the origin of the reticle, by controlling the purity of the immediate reticle environment.

Real-time amine monitoring and its correlation to critical dimension control of chemically amplified resists for sub-0.25-μm geometries

One such issue is the quantitative control of critical dimension (CD) and how to calibrate fab contamination levels to linewidth control. Since most fabs build several generations of devices, contamination levels for older generations may not be suitable for new generations. Therefore, studies to control CD for each generation are required to determine the effectiveness of filtration schemes. In this paper the authors have investigated CD control for imaging dimensions from 0.25 micrometers to 0.15 micrometers . We have also correlated this data back to chemical monitoring levels to determine CD vs. PED stability for these geometrys to determine the contamination level tolerance. Additionally, the authors have generated process windows to determine the effect such delays have on process windows.

Reticle Haze Control: Global Update and Technology Roadmap

Three years ago Entegris pioneered a novel method of controlling ammonium sulfate (AS) haze by maintaining 193 nm reticles in a low humidity environment. Since then, this approach has became an industry standard and is widely used in production fabs around the world. Based on analysis of practical applications in HVM fabs, this paper describes a successful approach to reticle haze control, outlines its critical elements and explains its limiting factors. In addition to actual fab data, the paper provides a large body of comparative experimental data on humidity dynamics in different reticle storage schemes and arrangements. With this data, the authors explain why some designs work much better than others and provide practical recommendations for lithography practitioners on haze control equipment selections and reticle management strategy development.

More on practical solutions to eliminate reticle haze and extend reticle life in the production environment: specially designed RSPs, internal POD purifiers, and XCDA purged reticle stockers

Use of specially designed reticle SMIF pods (RSPs) - with unique purge flow, internal dual-capture mechanism purifiers and an ultra-low humidity CDA purging system- have provided a practical solution to eliminate reticle haze for the useful life of the reticle in production environments. Prior publications, Kishkovich et al., described newly understood mechanisms of reticle haze formation based on chemical modification of quartz and chrome surfaces and have proposed solutions based on continual purge of the reticle environment with ultra-low humidity purified air [1]. In further publications they reported successful application of this solution in the field on single reticle-pod purge systems. [2] In this paper we provide guidance and advice for high volume manufacturing haze control practitioners, describing some challenges and solutions implemented on reticle stocker equipment, including considerations for materials of construction, purge flow levels and regulation, in-pod moisture/chemical purifiers, and on-tool flow measurement techniques.

Laser pattern generator challenges in airborne molecular contamination protection

The introduction of photomask laser pattern generators presents new challenges to system designers and manufacturers. One of the laser pattern generators environmental operating challenges is Airborne Molecular Contamination (AMC), which affects both chemically amplified resists (CAResist) and laser optics. Similar challenges in CAResist protection have already been addressed in semiconductor wafer lithography with reasonable solutions and experience gained by all those involved. However, photomask and photomask equipment manufacturers have not previously had a comparable experience, and some photomask AMC issues differ from those seen in semiconductor wafer lithography. Culminating years of AMC experience, the authors discuss specific requirements of Photomask AMC. Air sampling and material of construction analysis were performed to understand these particular AMC challenges and used to develop an appropriate filtration specification for different classes of contaminates. The authors portray the importance of cooperation between tool designers and AMC experts early in the design stage to assure goal attainment to maximize both process stability and machine productivity in advanced mask making. In conclusion, the authors provide valuable recommendations to both laser tool users and other equipment manufacturers.

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.