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Active Vibration Control vs. Passive Vibration Control - Part 3

In the third and final part of the Active vs. Passive discussion Wes goes into detail about serial-type active vibration control systems, like the STACIS, and what design features make them the best choice for point-of-use support of very sensitive equipment like SEMs, TEMs, Wafer Metrology and FIBs.

As discussed previously there are two main types of active vibration isolation systems – serial and parallel. TMC’s Electro-Damp is an excellent example of a parallel-type active vibration control system. While these systems are limited in terms of their active bandwidth for floor vibration control, parallel-type active systems like Electro-Damp are ideal for supporting the inspection platform and moving stage inside semiconductor tools, for example wafer metrology instruments that use an electron beam and a moving stage to position the wafer. Mitigating high frequency floor vibration while also canceling the payload deflection and residual motion after the stage moves is critical to improving and maximizing the throughput in semiconductor manufacturing.

Parallel-Type Active

The next type of active vibration control is a Serial-Type system like TMC’s STACIS. These are easier to set up than parallel systems but provide unmatched isolation from low frequency floor vibration. A Serial-Type active vibration cancelation system uses a high frequency rubber spring inside the isolator which acts as a low pass filter and provides a very stiff and stable support for the payload. The active control system is de-coupled from the payload because it is in series with this high frequency rubber spring. The architecture of a serial system enables a much wider active bandwidth than a parallel system, largely because the low pass filter in series keeps any payload resonances or moving stage/on-board control system from interfering with the control loop. The active control loop is downward facing, cancelling floor vibration over a large range of frequencies.

TMCs STACIS system is a prime example of this unique technology. It is the most advanced commercially available active system specifically for cancelling low frequency floor vibration. A control system consisting of high-capacity piezoelectric actuators, inertial sensors, and a feedback loop measure and cancels the floor vibration in real time. A customized rubber mount effectively cancels vibration in both the vertical and horizontal directions, protecting the active control loop while also allowing any on-board (inside the supported tool) isolation/control system to be fully optimized. STACIS is ideal, and often the only option, to support tools that already have either passive or parallel-type active vibration isolation built in. Typical examples include scanning and transmission electron microscopes, CD-SEMS, Wafer Defect Inspection, and Mask Inspection and Repair.

Active Vibration Control

These tools are often installed in environments that have low frequency vibration coming from the floor which will limit the performance of the tools because the pneumatic isolators built into them are not designed to mitigate vibration at very low frequencies. And if the tool includes an internal parallel-type active system, then the industry standard to support this tool in a noisy environment is a serial-type hard-mount active piezoelectric vibration control system such as STACIS. For more information on STACIS piezoelectric vibration isolation systems, click here.

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