Lithography
Figure 2. (Right): Settling time in response to on-board disturbance such as substrate loading is greatly improved by STACIS’ novel “serial” design, helping cycle rates meet exponentiating throughput demands
Together, these describe a challenge for process engineers and researchers alike: the tractability of nanoscale processes worsens with relentlessly diminishing scale, yet the process must be economical. This pushes substrate sizes up and cycle times down, both of which are at cross purposes to the exponentiating resolutions required.
Clearly, yesterday’s vibration isolation techniques are inadequate for tomorrow’s (or even today’s) nanoscale processes. Ambient ground motion can obliterate ever-finer pattern details (Figure 1), and conventional soft isolators do not isolate vibrations below 2Hz and do a poor job of responding to onboard vibration driven by rapid processing (Figure 2).
By comparison, STACIS provides aggressive attenuation starting at sub-Hz levels and is more than 100 times stiffer, directly benefiting settling.
The advancing needs of nanoscale processes are reflected in recent low-threshold Generic Vibration Curves (Figure 3)— a serious challenge to site engineers.
The STACIS Advantage
STACIS active isolators sense the onset of vibration in six degrees of freedom and actively nullify it via cancelling actuation of stiff, piezoelectric actuators acting vertically and horizontally. A real-time digital signal processor performs the necessary
Figure 3. New, more stringent Generic Vibration Curves. Courtesy IEST RP-012, Inst. of Environmental Sciences, Rolling Meadows, IL
calculations rapidly, providing high bandwidth cancellation (0.6-250Hz) and virtually eliminating latencies to minimize settling times and greatly reduce or eliminate the impact of low frequency vibration.
With their inherent stiffness, high load capacity and clean, airless operation, these isolators are popular for both OEM incorporation into leading-edge tools and for deployment beneath isolation platforms for sensitive equipment like optical and e-beam metrology and photolithography tools. And in addition to filling an essential need in the latest fabs, STACIS isolators enable older and noisier fabs to accommodate state-of-the-art tools while providing flexibility of tool placement and floor layout (Figure 4). Tools that already incorporate internal isolation of some sort benefit from STACIS
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www.euroasiasemiconductor.com Issue II 2010
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