YORKTOWN HEIGHTS, N.Y. Using adaptive optics techniques employed by advanced astronomical telescopes, researchers at IBM Corp.'s Thomas J. Watson Research Center have developed an electron microscope that can make sub-angstrom measurements in finer detail using less power than previous systems.
By crafting and controlling 40 magnetic lenses to correct for the aberrations of the three lenses normally found in electron microscopes, IBM and collaborator Nion Co. (Kirkland, Wash.) were able to focus their microscope's beam down to 0.75 angstrom.
"The term dear to my heart to describe this breakthrough . . . is 'adaptive optics,' " said Philip Batson, the lead scientist on the project at IBM Research, based here. "Our lenses are magnetic, rather than the mirror and glass used in telescopes, but the adaptive optics in both are the same."
For semiconductor makers, the sub-angstrom electron microscope has an additional advantage in its low power of 120 keV, which will not damage chips. Previous technologies, which could only get down to angstrom-sized beams, generated over a million electron-volts.
The electron microscope's 40 magnetic lenses, like a modern telescope's, go through an initial calibration stage at the beginning of each working day, Batson said. Using feedback from a video display of a calibration target, adaptive computer algorithms adjust the parameters on the 40 lenses to correct for up to third-order errors in telescope terms, the "spherical aberration" level of errors.
"When you want to focus 40 lenses the biggest problem is decided which knob to turn, but with the aid of a very fast PC we are able to adaptively focus by controlling all the lenses in real-time," Batson said.
The research team will next attempt to correct fifth-order aberrations. If successful, they expect to be able to focus their beam down to 0.2 angstrom.