Partnership between specialists in automation can yield important benefits
to research and OEM users. With each player bringing specific expertise, teamwork
often surpasses what a single organization can achieve.
[Left] FocusTrac™: an innovative laser autofocus module of provides speed and compatibility. [Middle] PIFOC®: High-bandwidth, high-precision piezo actuation provides autofocus responsiveness. [Right]: Typical step/settle response, measured interferometrically, for 250µm wafer edge scanned at 12mm/sec with 10X objective.
A case in point: the engineers at Motion X and PI
have developed a novel, laser-based system that combines Motion X’s high-bandwidth
autofocus sensor with PI’s high-speed piezo driven PIFOC® objective
and Z positioners to provide a big step forward in autofocus responsiveness,
stability and accuracy. The modular and configurable architecture avoids image
degradation and is suitable for commercial and custom microscopes and for substrates
ranging from wafers with sensitive coatings to live biological samples.
Background
Achieving and maintaining a sharp focus can be a critical task for systems engineers
and researchers. Autofocus is important to users of standard microscopes and
designers of custom optical columns alike, and some applications require real-time
autofocus during processes in which the substrate is moved. Several approaches
have been popular but can present significant drawbacks. Probe-based mechanisms
compensate for drift by measuring the position of the sample plate versus the
optical column but are slow, cumbersome to set up and limited in effective resolution
due to the problematic probe/sample mechanical interface. They also only maintain
a mechanical setpoint and cannot correct for variations in sample thickness,
drift between the probe and sample, parfocality errors between objectives, drift
in the optics or the column itself, and so on. By comparison, optical autofocus
techniques have the advantage of evaluating the image via the optics. All mechanical,
thermal and optical issues which can impact focus, including changes and steps
in the sample itself, are compensated.
The teamwork between PI and Motion X married Motion X’s unique FocusTrac™
system to PI’s proven controls and piezo mechanics for plug-and-play autofocus
capability. PI’s PIFOC® piezo objective and Z positioners are typically
10X faster than stepper or servo focusers and can realize the full bandwidth
capability of the Motion X laser autofocus technique. Different laser wavelengths
are easily accommodated, and mechanical options include objective positioners,
turret positioners, sample-positioning and (well-plate) Z-stages and cost-effective
OEM Z-positioning elements. FocusTrac™ works with microscopes from industry
leaders including Olympus, Leica, Nikon, Zeiss and Mitutoyo and is readily integrated
into OEM assemblies as well.
More information: www.pi-usa.us/pdf/Faster_Autofocus_with_Laser_and_Piezo.pdf