U.S. patent application number 10/345696 was filed with the patent office on 2004-07-08 for high contrast inspection and review of magnetic media and heads.
Invention is credited to Hess, Harald F., Mankos, Marian, Soltz, David A..
Application Number | 20040129877 10/345696 |
Document ID | / |
Family ID | 32599693 |
Filed Date | 2004-07-08 |
United States Patent
Application |
20040129877 |
Kind Code |
A1 |
Mankos, Marian ; et
al. |
July 8, 2004 |
HIGH CONTRAST INSPECTION AND REVIEW OF MAGNETIC MEDIA AND HEADS
Abstract
One embodiment disclosed relates to a method for inspecting or
reviewing a magnetized specimen using an automated inspection
apparatus. The method includes generating a beam of incident
electrons using an electron source, biasing the specimen with
respect to the electron source such that the incident electrons
decelerate as a surface of the specimen is approached, and
illuminating a portion of the specimen at a tilt with the beam of
incident electrons. The specimen is moved under the incident beam
of electrons using a movable stage of the inspection apparatus.
Scattered electrons are detected to form image data of the specimen
showing distinct contrast between regions of different
magnetization. The movement of the specimen under the beam of
incident electrons may be continuous, and data for multiple image
pixels may be acquired in parallel using a time delay integrating
detector.
Inventors: |
Mankos, Marian; (San
Francisco, CA) ; Soltz, David A.; (San Jose, CA)
; Hess, Harald F.; (La Jolla, CA) |
Correspondence
Address: |
OKAMOTO & BENEDICTO, LLP
P.O. BOX 641330
SAN JOSE
CA
95164
US
|
Family ID: |
32599693 |
Appl. No.: |
10/345696 |
Filed: |
January 16, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60438649 |
Jan 7, 2003 |
|
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|
Current U.S.
Class: |
250/307 ;
250/310; 369/101; G9B/27.052; G9B/5.024; G9B/5.033; G9B/5.041;
G9B/5.145 |
Current CPC
Class: |
G11B 5/3193 20130101;
G11B 2220/20 20130101; G11B 5/09 20130101; G11B 27/36 20130101;
G11B 5/1272 20130101; G01N 23/2251 20130101; G11B 5/455 20130101;
G11B 5/012 20130101; G11B 5/3166 20130101 |
Class at
Publication: |
250/307 ;
250/310; 369/101 |
International
Class: |
G01N 023/225; G11B
009/10 |
Claims
What is claimed is:
1. A method for inspecting or reviewing a magnetized specimen using
an automated inspection apparatus, the method comprising:
generating a beam of incident electrons using an electron source;
biasing the specimen with respect to the electron source such that
the incident electrons decelerate as a surface of the specimen is
approached; illuminating a portion of the specimen with the beam of
incident electrons at a tilt; moving the specimen under the beam of
incident electrons using a movable stage of the inspection
apparatus; and detecting scattered electrons to form image data of
the specimen showing distinct contrast between regions of different
magnetization.
2. The method of claim 1, wherein the movement of the specimen
under the beam of incident electrons is continuous, and wherein the
detection of the scattered electrons acquires data for multiple
image pixels in parallel and is performed using a time delay
integrating detector.
3. The method of claim 1, wherein the specimen is biased slightly
negative with respect to the mirror potential, such that incident
electrons are primarily reflected above a surface of the
specimen.
4. The method of claim 1, further comprising: adjusting a focus of
the beam of incident electrons by adjusting a strength of an
objective electron lens; and adjusting a tilt of the beam of
incident electrons.
5. The method of claim 1, further comprising: separating the
scattered electrons from the beam of incident electrons using a
beam separator device; projecting the scattered electrons onto an
image forming device; and impinging a second beam of electrons onto
the specimen for controlling surface charge.
6. The method of claim 1, wherein the magnetic specimen comprises a
magnetic storage medium.
7. The method of claim 6, further comprising: extracting binary
data from the image data, wherein the binary data represents
information stored on the magnetic storage medium.
8. The method of claim 1, wherein the magnetic specimen comprises
an array of read/write heads.
9. The method of claim 8, further comprising: inspection of the
read/write heads to detect faulty heads prior to dicing and
individual testing of the heads.
10. A method for recovering data from a magnetic storage medium,
the method comprising: generating a beam of incident electrons
using an electron source; biasing the medium with respect to the
electron source such that the incident electrons decelerate as a
surface of the medium is approached; illuminating a portion of the
medium with the beam of incident electrons at a tilt; detecting
scattered electrons to form image data of the medium showing
distinct contrast between magnetic bits; and extracting binary data
from the image data.
11. The method of claim 10, further comprising: decoding the binary
data to recover data previously stored on the magnetic storage
medium.
12. An automated inspection apparatus configured to inspect arrays
of magnetic read/write heads, the apparatus comprising: an electron
source for generating a beam of incident electrons; a bias circuit
for biasing an array of heads with respect to the electron source
such that the incident electrons decelerate as a surface of the
array of heads is approached; electron optics for illuminating the
array of heads at a tilt with the beam of incident electrons; a
movable stage for moving the array of heads under the beam of
incident electrons; and a detector for detecting scattered
electrons to form image data of the array of heads showing a high
level of magnetic contrast.
13. The apparatus of claim 12, wherein the apparatus is utilized to
inspect the array of heads to detect faulty heads prior to dicing
and individual testing of the heads.
14. The apparatus of claim 12, wherein the movable stage is moved
continuously under the beam of incident electrons, and wherein the
detector comprises a parallel detector that acquires data for
multiple image pixels in parallel to form the image data.
15. The apparatus of claim 14, wherein the parallel detector
comprises a type of time delay integrating detector.
16. The apparatus of claim 12, further comprising: a deflector
which is configured to modify a tilt of the beam of incident
electrons; and an objective lens for adjusting a focus of the beam
of incident electrons.
17. The apparatus of claim 12, wherein the movable stage is biased
78 slightly negative with respect to the mirror potential, such
that incident electrons are primarily reflected above a surface of
the array of heads.
18. The apparatus of claim 12, further comprising: a beam separator
for separating the scattered electrons from the beam of incident
electrons; a projection lens for projecting the scattered electrons
onto an image forming device; and a second electron source for
generating a second beam of electrons for use in controlling
surface charge.
19. An apparatus configured to examine a magnetic storage medium,
the apparatus comprising: an electron source for generating a beam
of incident electrons; a bias circuit for biasing the medium with
respect to the electron source such that the incident electrons
decelerate as a surface of the medium is approached; electron
optics for illuminating the medium at a tilt with the beam of
incident electrons; a detector for detecting scattered electrons to
form image data of the medium showing distinct magnetic contrast;
and an image processor for extracting binary data from the image
data.
20. The apparatus of claim 19, further comprising: a data decoder
for decoding the binary data to recover data previously stored on
the magnetic storage medium.
21. An automated inspection system for inspecting or reviewing a
magnetized specimen, the system comprising: means for generating a
beam of incident electrons using an electron source; means for
biasing the specimen with respect to the electron source such that
the incident electrons decelerate as a surface of the specimen is
approached; means for illuminating a portion of the specimen with
the beam of incident electrons at a tilt; means for moving the
specimen under the beam of incident electrons using a movable stage
of the inspection apparatus; and means for detecting scattered
electrons to form image data of the specimen showing distinct
contrast between regions of different magnetization.
22. A system for recovering data from a magnetic storage medium,
the system comprising: means for generating a beam of incident
electrons using an electron source; means for biasing the medium
with respect to the electron source such that the incident
electrons decelerate as a surface of the medium is approached;
means for illuminating a portion of the medium with the beam of
incident electrons at a tilt; means for detecting scattered
electrons to form image data of the medium showing distinct
contrast between magnetic bits; and means for extracting binary
data from the image data.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to magnetic
specimens. More particularly, the present invention relates to
examining or inspecting magnetic materials or devices.
[0003] 2. Description of the Background Art
[0004] In recent years, the areal density of disk drives has
increased by about 60% to 100% per year. This exponential increase
is comparable to the increase in density of integrated circuit
chips as described by Moore's law (predicting that the density of
IC chips doubles about every 18 months). The areal density
increases have been achieved by developing new materials for
magnetic media and improving read/write heads.
[0005] As the technology of magnetic media and heads continue to
advance, it is desirable to develop and improve techniques for
inspecting or reviewing the magnetic media and/or heads.
Conventional techniques for examining magnetic specimens include
Lorentz microscopy and magnetic force microscopy.
[0006] Lorentz microscopy involves transmission of high energy
electrons through thin samples of magnetic specimens. The magnetic
contrast occurs due to the interaction of the electrons passing
through the magnetic induction due to the magnetization of the
specimen. Components of the magnetic induction normal to the
electron beam cause deflection of the beam. A significant
disadvantage of Lorentz microscopy is that it is applied to
specimens thin enough for electron transmission. This typically
requires substantial sample preparation that is often destructive
of the specimen being examined.
[0007] Magnetic force microscopy (MFM) is a standard technique for
investigating magnetic media. MFM uses a magnetic tip on a small
cantilever to probe a magnetic field above a surface of a specimen.
The magnetic field causes a force that deflects the cantilever. MFM
does not require preparation of an electron thin sample. However,
MFM has various limitations. In particular, MFM requires the entire
area of interest to be scanned or translated under the magnetic
tip. Hence, examining a relatively large area using MFM is a
relatively slow process.
[0008] Another conventional technique for examining magnetic media
involves writing and reading the media on a spin stand with a
magnetic reader head. Such a technique is often used to screen
heads and to characterize media. A further application is to
recover lost data from hard disks by just reading the data with a
flying head. For data recovery to succeed using the conventional
technique the head must fly very low (of order 5-30 nm) over the
spinning disk. This puts stringent demands on the flatness and
perfection of the disk surface, for this method to be viable. For
this reason a crashed or otherwise damaged disk is often not be
recoverable in a disk drive or with a spin stand approach. An
additional data recovery limitation is that the resolution is
limited to that of the read head and one cannot image partially
erased track fragments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 depicts an apparatus for inspection or review of a
magnetized specimen in accordance with an embodiment of the
invention.
[0010] FIG. 2 depicts results of the technique for inspection or
review of a magnetized specimen in accordance with an embodiment of
the invention.
[0011] FIG. 3 is a flow chart showing a method for inspection or
review of a magnetized specimen in accordance with an embodiment of
the invention.
[0012] FIG. 4 is a schematic illustrating the parabolic trajectory
of electrons reflecting off of the electric field of a nonmagnetic
sample when there is a finite incoming angle or tilt in the
incident electrons.
[0013] FIG. 5 is a schematic illustration depicting the surface of
a magnetized specimen and associated magnetic field lines.
[0014] FIG. 6 is a schematic illustration depicting electrons from
a tilted incident beam in accordance with an embodiment of the
invention.
SUMMARY
[0015] One embodiment of the invention pertains to a method for
inspecting or reviewing a magnetized specimen using an automated
inspection apparatus. The method includes generating a beam of
incident electrons using an electron source, biasing the specimen
with respect to the electron source such that the incident
electrons decelerate as a surface of the specimen is approached,
and illuminating a portion of the specimen at a tilt with the beam
of incident electrons. The specimen is moved under the incident
beam of electrons using a movable stage of the inspection
apparatus. Scattered electrons are detected to form image data of
the specimen showing distinct contrast between regions of different
magnetization. The movement of the specimen under the beam of
incident electrons may be continuous, and data for multiple image
pixels may be acquired in parallel using a time delay integrating
detector.
[0016] Another embodiment relates to a method for recovering data
from a magnetic storage medium. The method includes generating a
beam of incident electrons using an electron source, biasing the
medium with respect to the electron source such that the incident
electrons decelerate as a surface of the medium is approached, and
illuminating a portion of the medium at a tilt with the beam of
incident electrons. Scattered electrons are detected to form image
data of the specimen showing distinct contrast between regions of
different magnetization. Finally, binary data is extracted from the
image data. The binary data may be decoded to recover data
previously stored on the magnetic storage medium.
[0017] Another embodiment relates to an automated inspection
apparatus configured to inspect arrays of magnetic read/write
heads. The apparatus includes an electron source for generating a
beam of incident electrons, and a bias circuit for biasing the
array of heads with respect to the electron source such that the
incident electrons decelerate as a surface of the array of heads is
approached. Electron optics is used to illuminate the array of
heads at a tilt with the beam of incident electrons. A movable
stage is used for moving the array of heads under the beam of
incident electrons. Finally, a detector detects scattered electrons
to form image data of the array of heads showing contrast between
regions of different magnetization. The movable stage may be moved
continuously under the beam of incident electrons, and the detector
may comprise a time delay integrating detector which is a type of
parallel detector.
[0018] Another embodiment relates to an apparatus configured to
examine a magnetic storage medium. The apparatus includes an
electron source for generating a beam of incident electrons and a
bias circuit means for biasing the medium with respect to the
electron source such that the incident electrons decelerate as a
surface of the medium is approached. The apparatus also includes
electron optics for illuminating the medium at a tilt with the beam
of incident electrons. A detector for detecting scattered electrons
is used to form image data of the medium showing contrast between
regions of different magnetization. Finally, an image processor for
extracting binary data from the image data. A data decoder may be
utilized to decode the binary data to recover data previously
stored on the magnetic storage medium.
DETAILED DESCRIPTION
[0019] FIG. 1 depicts an apparatus 100 for inspection or review of
a magnetized specimen in accordance with an embodiment of the
invention. The apparatus 100 is a type of low energy electron
microscope. The apparatus 100 as depicted includes an electron gun
or source 102, condensor lenses 104, a deflector 106, an objective
lens 110 which includes an extraction electrode 111, a magnetic
sample or specimen 112, a beam separator 114, a projector lens 116,
and a screen or detector 118. While certain components are
illustrated in FIG. 1 for purposes of discussion, alternate
embodiments of an electron beam apparatus in accordance with the
invention may include other components varying from or adding to
those illustrated.
[0020] The electron gun 102 is a source of electrons for the
incident beam. The electron gun 102 may comprise, for example, a
thermionic electron gun, a field emission gun, or another type of
source. The condensor lenses 104 focuses the electrons from the gun
102 into a beam. The condenser lenses may comprise, for example,
magnetic lenses.
[0021] The deflector 106 may be used to shift or adjust the
direction of the beam of incident electrons. The deflector 106 may
be implemented using a magnetic deflector, an electrostatic
deflector, or using a combined electrostatic-magnetic deflector. In
accordance with an embodiment of the invention, the deflector 106
may be utilized to adjust a tilt angle of the beam of incident
electrons as it impinges upon the magnetic specimen 112. The tilted
beam 108 after deflection is illustrated in FIG. 1. As illustrated,
the beam 108 impinges upon the magnetic specimen 112 at an angle
with respect to the normal from the surface of the specimen
112.
[0022] The tilted electron beam 108 is focused onto the magnetic
specimen 112 by the objective lens 110. The specimen may be set on
a specimen holder (not illustrated). A bias circuit applies a
voltage bias to the specimen. For low energy electron microscopy,
the bias may be a few hundred volts or less with respect to the
source or cathode. When the specimen is biased at the proper
potential with respect to the cathode, the electrons are reflected
and scattered above the surface. This type of imaging mode may be
referred to as mirror electron microscopy, and the potential at
which the electrons are reflected just at the surface of the sample
is referred to as the mirror potential. The value of the mirror
potential depends on the angle of tilt of the beam with respect the
sample, but it typically occurs at a value from near zero to a few
tens of volts positive of the electron source. The scattered
electrons leaving the sample 112 are focused by the objective lens
110 to form an image of the specimen surface.
[0023] A beam separator 114 is utilized to separate apart the
scattered electron beam (the beam coming from the magnetized
specimen 112) from the primary electron beam (the beam coming from
the gun 102). In one embodiment, the beam separator 114 may
comprise a Wien filter that separates the two beams based on their
velocities. Alternatively, the beam separator 114 may comprise
bending magnets configured to separate the beams. The projector
lens 116 images the beam onto the screen or detector 118. The image
formed on the screen or detector 118 is that of the magnetized
specimen 112.
[0024] The image data may be viewed by a user and/or is
electronically processed and analyzed by the inspection or review
system. If the magnetic specimen 112 comprises a magnetic medium,
then binary data may be extracted from the image data, where the
binary data represents information stored on the magnetic medium.
This extraction may be performed by using an image processing
system. If the specimen 112 comprises magnetic read/write heads,
then the image data may be processed to detect faulty heads. Such
inspection may be advantageously performed prior to dicing and
individual testing of the heads.
[0025] In accordance with one particular embodiment, the magnetic
specimen 112 may be moved continuously under the e-beam by a
movable stage during an inspection process. This advantageously
speeds up the process of inspection Such an inspection system may
utilize a time delay integrating (TDI) electron detector as the
detector 118. The operation of an analogous TDI optical detector is
disclosed in U.S. Pat. No. 4,877,326, entitled "Method and
Apparatus for Optical Inspection of Substrates," inventors Chadwick
et al., and assigned at issuance to KLA Instruments Corporation.
The disclosure of U.S. Pat. No. 4,877,326 is hereby incorporated
herein by reference. The image information may be processed
directly from a `back thin` TDI electron detector, or the electron
beam may be converted into a light beam and detected with an
optional optical system and a TDI optical detector. As one
alternative to using a TDI electron detector, such an inspection
system may utilize a camera type detector.
[0026] The apparatus 100 may be configured to have a large incident
beam current and a large field size. Such a configuration would
advantageously provide for high throughput inspection processes. In
addition, a second electron beam (not shown in FIG. 1) may be
advantageously incorporated to maintain charge control at the
surface of the specimen 112. The use of such a second electron beam
is described in further detail in U.S. patent application Ser. No.
09/854,332, entitled "Apparatus for Inspection of Semiconductor
Wafers and Masks Using a Low Energy Electron Microscope with Two
Illuminating Beams," inventors Lee Veneklasen, David L. Adler and
Matthew Marcus, filed May 11, 2001. The aforementioned patent
application is hereby incorporated by reference in its
entirety.
[0027] FIG. 2 depicts results of the technique for inspection or
review of a magnetized specimen in accordance with an embodiment of
the invention. The field of view is 80 micrometers wide in both
images A and B.
[0028] The first image A on the left was obtained experimentally
using a tilted incident beam and shows predominantly magnetic
contrast. The bias on the specimen and focusing by the objective
lens were adjusted to obtain the contrast shown. The horizontal
lines represent magnetic bits recorded onto the hard disk prior to
the experimental viewing. Larger period bits are spaced
approximately 3 micrometers apart and are shown on the left side of
the first image A. Smaller period bits are spaced approximately 1.8
micrometers apart and are shown on the right side of the image
A.
[0029] The second image B on the right shows the same area of the
same specimen as shown in the first image A, but it was obtained
experimentally using a beam normal to the surface. The second image
B shows predominantly topographical contrast.
[0030] Individual magnetic defects (202 and 204) and a group of
magnetic defects 206 are present in the imaged area. The defects
(202, 204, and 206) appear to be somewhat visible in the
topological image B, but the topological image B neither clearly
shows the defects, nor shows whether the defects are magnetic or
non-magnetic in nature. The magnetic image A more clearly reveals
the defects with its high contrast image data and further indicates
the magnetic nature of the defects, differentiating them from
non-magnetic defects. Thus, magnetic and surface topology features
may be advantageously correlated by analyzing both the tilted image
A and the non-tilted image B.
[0031] The distinct contrast in the magnetic image A advantageously
enables the magnetic specimen, whether magnetic media or read/write
heads, to be inspected with a high throughput inspection apparatus.
Furthermore, the magnetic image A shows the high spatial resolution
obtainable with this technique. Such high spatial resolution may
advantageously be used to examine defects in greater detail or to
reveal defects otherwise overlooked with other examination
techniques.
[0032] FIG. 3 is a flow chart showing a method 300 for inspection
or review of a magnetized specimen in accordance with an embodiment
of the invention. A beam of incident electrons is generated 302
using an electron source 102. The beam is tilted 306 such that it
is incident at an angle to the normal of the surface of the
specimen. The tilting may be done, for example, by using a beam
deflector 106.
[0033] The magnetic specimen is biased 306 with respect to the
electron source such that the incident electrons decelerate as a
surface of the specimen is approached. In one embodiment, the
specimen is biased slightly negative with respect to the mirror
potential such that incident electrons are primarily reflected
above a surface of the specimen. The mirror potential is the
potential at which electrons are reflected from the surface of the
sample. The mirror potential varies depending on the tilt of the
beam, but it is typically between near zero and a few tens of volts
positive with respect to the electron source. In another
embodiment, the specimen is biased at or slightly positive to the
mirror potential such that the incident electrons are primarily
reflected at or near a surface of the specimen. In the former case,
the applicants believe that image data obtained has contrast
primarily due to magnetic characteristics. In the latter case, the
applicants believe that the image data obtained includes both
magnetic and topological information.
[0034] In addition, the focus is set 308 to an appropriate level by
adjusting the strength of the objective lens. In one embodiment,
the image may be defocused from the surface of the specimen such
that an area above the surface is in focus.
[0035] With the tilt, bias, and focus parameters set as described
above, the specimen is illuminated 310 with the tilted beam of
incident electrons. In one embodiment, a relatively wide field of
view is illuminated 310 in order to enable parallel imaging of
multiple pixels and achieve high throughput inspection of the
specimens.
[0036] Scattered electrons are detected 314 to form image data of
the specimen showing contrast between regions of different
magnetization. In one particular embodiment, the specimen is moved
312 continuously under the beam. In accordance with such an
embodiment, a time delay integrating detector may be advantageously
utilized, for example.
[0037] The image data may be processed 316 using an image
processing system. The processing may, for example, extract binary
data from the image data, where the binary data represents
information stored on the magnetic medium. As another example, the
processing may be used to inspect read/write heads to detect faulty
heads. This enables inspecting several hundred heads at once while
they are still attached together in a bar after fabrication and
prior to dicing. This advantageously may be used to avoid the slow
and expensive process of mounting and individual testing of each
head.
[0038] FIG. 4 is a schematic illustration depicting the path of the
electrons as they reflect off the surface 402. The electron
trajectory 406 forms a parabola in the yz plane 404 when either the
sample or initial electron direction is tilted in the yz plane.
This represents the case when there is no magnetic field emanating
from the sample surface 402.
[0039] FIG. 5 is a schematic illustration depicting the surface of
a magnetized specimen and associated magnetic field lines. As shown
in the drawing, the surface of the magnetized specimen includes
magnetic bits with the magnetization (dipole) direction to the left
502 and magnetic bits with the magnetization (dipole) direction to
the right 504. Such domains may be present, for example, on a
magnetic medium on which data has been written. Above the surface,
magnetic field lines or flux are illustrated that are associated
with and caused by the magnetic bits (502 and 504). Note that above
the transitions or borders between the domains, the field lines are
either flowing downward 506 or upward 508. The downward flowing
field lines 506 are present above a border that is between magnetic
bits whose magnetization directions are pointed outward or away
from the border. The upward flowing field lines 508 are present
above a border that is between magnetic bits whose magnetization
directions are pointed inward or towards the border.
[0040] Electron trajectories are influenced by such magnetic field
lines in accordance with the Lorentz force equation of physics.
According to the Lorentz force equation, electron trajectories are
not influenced by components of field lines that are parallel to
the trajectories; they are only influenced by components of field
lines that are perpendicular to the trajectories. In other words,
only components of the magnetic field lines that are normal to an
electron trajectory give rise to a deflection of the
trajectory.
[0041] In this case, applicants believe that the electrons from the
untilted beam are not substantially influenced by the downwardly
flowing or upwardly flowing field lines near the borders between
magnetic bits. As such, applicants believe that high magnetic
contrast is problematic to obtain with an untilted incident
beam.
[0042] FIG. 6 is a first schematic illustration depicting electrons
from a tilted incident beam in accordance with an embodiment of the
invention. The electron trajectories 614 and 616 for the tilted
beam are illustrated. These electron trajectories 614 and 616
develop a velocity component coming out of the yz plane 610 and 612
and are deflected either to the right or the left.
[0043] In this case, in accordance with the Lorentz force equation,
applicants believe that the electrons from the tilted beam are
substantially influenced by the downwardly flowing 608 or upwardly
flowing 606 field lines near the borders between magnetic domains
(602 and 604). Specifically, the tilted electrons incident in the
yz plane 612 above the downward flowing field lines 608 are
deflected towards the right following the trajectory 616. This is
due to the Lorentz force acting on the velocity component pushing
the electrons to the right in the horizontal x direction.
Meanwhile, the tilted electrons incident in the yz plane 610 above
the upward flowing field lines 606 are deflected towards the left.
Again, this is due to the Lorentz force acting on the velocity
component pushing electrons to the left in the horizontal x
direction.
[0044] As shown in FIG. 6, applicants believe that the Lorentz
forces cause the tilted electrons to have trajectories such that
the electrons become more concentrated or densely populated above
every other domain. In this specific case, the regions 618 above
the domains with leftward magnetic direction 604 are more populated
with electrons than the regions 618 above the domains with
rightward magnetic direction 602.
[0045] In accordance with an embodiment of the invention, the focus
of the electron inspection apparatus 100 may be set or defocused
such that the above-discussed regions 618 are in focus. In
addition, the specimen 112 may be biased at a slightly negative
voltage with respect to the mirror potential such that the incident
electrons slow down as they approach the surface and are primarily
reflected in the region 618 that is above the surface. In such a
system, applicants believe that high magnetic contrast is
achievable, as demonstrated by the first image A in FIG. 2.
[0046] Note that the above-described technique should also be
usable to inspect magnetic materials where the orientation of the
magnetizations is perpendicular rather than longitudinal. In that
case, the magnetic field lines would flow upward in the regions
above the magnetic bits with upward magnetization direction, and
the magnetic field lines would flow downward in the regions above
the magnetic bits with downward magnetization direction. The
electron trajectories from tilted incident beams would be
concentrated in a similar fashion in particular regions above the
bits, and high magnetic contrast would again be achievable.
[0047] The above-described diagrams are not necessarily to scale
and are intended be illustrative and not limiting to a particular
implementation. The above-described invention may be used in an
automatic inspection or review system and applied to the inspection
or review of magnetic recording media, magnetic read/write heads,
and similar magnetic structures. In the case of inspecting magnetic
media, the high magnetic contrast available with this technique
should enable, for example, the imaging of a typical hard disk in
about an hour or less. Furthermore, in contrast to the conventional
technique of reading the media with a magnetic reader head, the
above-discussed technique should also advantageously provide for
higher spatial resolution. In the case of inspecting read/write
heads, this technique should enable inspection of a full bar of
heads. This contrasts with the expensive and time consuming
conventional technique of dicing, individually mounting, and
individually testing each head. In the future, this technique or a
variation thereof may be advantageously used to inspect or review
advanced magnetic media wherein the magnetic bits are isolated from
each other.
[0048] In the above description, numerous specific details are
given to provide a thorough understanding of embodiments of the
invention. However, the above description of illustrated
embodiments of the invention is not intended to be exhaustive or to
limit the invention to the precise forms disclosed. One skilled in
the relevant art will recognize that the invention can be practiced
without one or more of the specific details, or with other methods,
components, etc. In other instances, well-known structures or
operations are not shown or described in detail to avoid obscuring
aspects of the invention. While specific embodiments of, and
examples for, the invention are described herein for illustrative
purposes, various equivalent modifications are possible within the
scope of the invention, as those skilled in the relevant art will
recognize.
[0049] These modifications can be made to the invention in light of
the above detailed description. The terms used in the following
claims should not be construed to limit the invention to the
specific embodiments disclosed in the specification and the claims.
Rather, the scope of the invention is to be determined by the
following claims, which are to be construed in accordance with
established doctrines of claim interpretation.
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