Browse Prior Art Database

Autofocus Feedback for Magnetic Low Loss Electron SEM

IP.com Disclosure Number: IPCOM000121503D
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 2 page(s) / 70K

Publishing Venue

IBM

Related People

Hodgson, RT: AUTHOR [+2]

Abstract

Disclosed is a method for keeping low loss electron (LLE) scanning electron microscopes (SEMs) with the specimen in a magnetic field in focus for best resolution. A recently issued patent [*] teaches how to make detectors placed in a magnetic field, where the magnetic field of the SEM or TEM is used to energy filter the electrons backscattered from the surface with little energy loss. It is shown in the patent that the position and shape of the detector is critical to the energy and spatial resolution of the device. However, it was not shown in the patent that the position of the sample was equally as critical. In fact, the sample has to be placed in the exact same position in the microscope as the previous sample if the detector position is to be kept constant and not changed from sample to sample.

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Autofocus Feedback for Magnetic Low Loss Electron SEM

      Disclosed is a method for keeping low loss electron (LLE)
scanning electron microscopes (SEMs) with the specimen in a magnetic
field in focus for best resolution.  A recently issued patent [*]
teaches how to make detectors placed in a magnetic field, where the
magnetic field of the SEM or TEM is used to energy filter the
electrons backscattered from the surface with little energy loss.  It
is shown in the patent that the position and shape of the detector is
critical to the energy and spatial resolution of the device. However,
it was not shown in the patent that the position of the sample was
equally as critical.  In fact, the sample has to be placed in the
exact same position in the microscope as the previous sample if the
detector position is to be kept constant and not changed from sample
to sample. We expect that for ease of use and convenience, the
detector should have to be lined up only once, and then the samples
could then be changed as they are now changed in practice. However,
the sample holders do not normally have the adjustments needed to
bring the device to best focus without changing the detector
position.

      We disclose a method to bring the device to best focus by using
standard automatic focussing devices and feedback of either the
voltage of the SEM beam or the current controlling the magnetic field
(which is a measure of the position of beam focus in the instrument)
to raise or lower the specimen until i...