Radiant energy – Inspection of solids or liquids by charged particles
Reexamination Certificate
1999-03-19
2001-11-06
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
C250S307000, C250S305000, C250S310000
Reexamination Certificate
active
06313461
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of electron microscopy. More particularly, the present invention relates to a system and a method for magnetic and spectroscopic imaging.
2. Description of the Related Art
Magnetic media presently used for disk drives are thin films that have grains that are about 15 nm across. Soon the grain size will be under 10 nm. To better understand how the magnetic microstructure of the media affects magnetic recording processes, magnetic imaging having a resolution of less than 5 nm is required. Currently, only transmission electron microscopy (TEM) provides an imaging resolution that is on the order of 5 nm. TEM, however, is limited by requiring a sample to be processed to be about 100 nm thick. Further, TEM is insensitive to ultra-thin films, that is, films, that are on the order of 20 nm thick or less.
Many techniques have been developed for extracting various types of image information from a scanning probe microscope (SPM). One technique uses a scanning near-field optical probe, but has a low efficiency for collecting emitted photons. Collection efficiency is improved by using photoemission so that electrons are emitted from the surface of a sample and collected using a positively-biased scanning probe, such as disclosed by K. Tsuji et al., X-Ray Excited Current Detected with Scanning Tunneling Microscope Equipment, Jpn. J. Appl. Phys, Vol, 34, pp. LI 506-LI 508, 1995. Nevertheless, this approach is limited by the noise of the collection current amplifier (Johnson noise). Another limiting factor with this approach in practice is an interfering signal caused by emission from the scanning tip. There are also difficulties associated with sufficiently limiting the collecting area for achieving good spatial resolution.
Stohr et al., Element-specific Magnetic Microscopy Using Circularly Polarized X-rays, Science, Vol. 259, p. 658, 1993, discloses a photoemission microscope that is capable of magnetic imaging by using conventional electron microscope optics for imaging photoemitted electrons. This approach efficiently collects electrons and has a theoretical resolution of about 10 nm, but the high voltages inherent in this approach makes the microscope susceptible to breakdown and arcing.
What is needed is a technique having nm-scale resolution for imaging magnetic and spectroscopic features that does not require sample thinning and can image an ultrathin film without the application of high voltages,
SUMMARY OF THE INVENTION
The present invention provides a technique having nm-scale resolution for imaging magnetic and spectroscopic features and does not require sample thinning and can image an ultrathin film. The advantages of the present invention are provided by a scanning-aperture electron microscope system and method in which a particle or radiation source generates a beam that causes electrons to be ejected from the sample material. The preferred embodiment employs a radiation source such that a laser, or synchrotron beams to cause photoemission of electrons from the target. For this preferred radiation source, magnetic imaging is performed by using a polarization rotator to polarization the incident beam. Alternative radiation beams that can be used include electrons, ions, x-rays, visible and ultraviolet light.
A scanning-aperture probe having an aperture is positioned in proximity to the surface of the sample material so that some of the photoelectrons emitted from the surface of the sample material pass through the aperture. An electron detector detects the photoelectrons that pass through the aperture. The electron detector outputs a signal in response to the detected photoelectrons that is used for imaging magnetic and/or spectroscopic features of the surface of the sample material According to the invention, the resolution of the imaged features is about equal to the size of the aperture.
In one embodiment of the present invention, an optical element can be disposed between the aperture of the scanning-aperture probe and the electron detector and a barrier having a pinhole is disposed between the optical element and the electron detector. The optical element and the pinhole operate together for directing photoelectrons emitted from the surface of the sample material having a predetermined electron energy and having a predetermined emission path to the electron detector. In another embodiment of the present invention, a measurement controller can be used to generate a trigger signal in response to a magnetic field pulse event that is applied to the surface of the sample material. For this embodiment, the radiation source is responsive to the trigger signal by generating a pulsed emission radiation been so that an image having known temporal relationship with the rapid magnetic field pulse can be generated.
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Kouichi Tsuji et al., X-Ray Excited Current Detected with Scanning Tunneling Microscope Equipment, Jpn. J. Appl. Phys., vol. 34 (1995) pp. L 1506-L 1508, Part 2, No. 11A, Nov. 1, 1995.
McClelland Gary Miles
Rettner Charles Thomas
Samant Mahesh Govind
Weller Dieter Klaus
Banner & Witcoff , Ltd.
Berthold, Esq. Thomas R.
International Business Machines Corp.
Nguyen Kiet T.
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