Technology - Lithography
had limitations as gas byproducts from the discharge eventually reach concentrations that are high enough to perturb the system performance. A gas refill with fresh gas has been necessary to enable continued operation, yet this gas refill requires interrupting production for about 20 minutes. The gas “life” is measured in terms of millions of pulses and for argon fluoride systems has typically been 100 million pulses (Mp) between refills. For reference, a typical wafer requires anywhere from 30,000 to 60,000 pulses to be fully exposed, so a high volume fab can reach 100Mp in as little as 24 hours. To this end, Cymer has developed advanced gas management technologies to increase the gas life through more precise control algorithms that take into account actual operating conditions and thus reduce the frequency of refills. The first major step was a ten-fold increase in gas life, to 1 billion pulses (Bp) between refills, with a technology named “GLX” (for Gas Life eXtension), thereby reducing the refill frequency from once per day to once every 10 days in a high volume fab. Further refinements of this technology led to extending it another factor of 2, resulting in a refill frequency of 2Bp. The net time savings over the course of a year has been on the order of more than 100 hours due to minimization of gas refill events. For an ArF immersion scanner running approximately 150 – 180 wafers per hour, this extra uptime has been very significant and has been rapidly adopted by the chipmakers. (Fig. 6) Further developments are under way to continue to reduce the need for refills and provide additional output from the scanner.
Conclusions In summary, as ArF immersion lithography is extended with techniques that include double or multi-patterning, the role of the light source has increased in providing performance advances as well as reducing running costs to keep pace with
Figure 5 - Uptime improvement as a result of introducing the enhanced performance discharge chamber
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chipmaker requirements. In addition to enabling higher power via the XLR 600ix platform, advances in optical performance stability and higher availability have continued to support the demands of high volume production at advanced device nodes.
© 2011 Angel Business Communications. Permission required.
Figure 6. Improvements in gas management technology help reduce the frequency of gas refills and the associated system down time
As ArF immersion lithography is extended with techniques that include double or multi-patterning, the role of the light source has increased in providing performance advances as well as reducing running costs to keep pace with chipmaker requirements
www.euroasiasemiconductor.com Issue IV 2011
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