Radiant energy – Inspection of solids or liquids by charged particles – Electron microscope type
Reexamination Certificate
2002-01-24
2004-04-13
Wells, Nikita (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Electron microscope type
C250S305000, C250S3960ML, C250S3960ML
Reexamination Certificate
active
06720558
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transmission electron microscope (TEM) equipped with an energy filter.
2. Description of the Related Art
A transmission electron microscope (TEM) equipped with an energy filter has been heretofore known. An energy filter has a function of energy-dispersing electrons transmitted through a specimen. A TEM equipped with an energy filter is capable of selecting only those electrons transmitted through a specimen which have a certain energy and imaging them. Hence, the contrast and resolution of the image can be improved. Also, this kind of instrument can gain an energy loss spectrum and a two-dimensional distribution of elements constituting the specimen.
An example of the structure of a TEM equipped with an energy filter is shown in FIG.
2
. Shown in this figure are an electron gun
1
, a system of condenser lenses
2
, a specimen stage
3
including a specimen holder, an objective lens
4
, an intermediate lens system
5
, an energy filter
6
, an energy selecting slit
7
, a projector lens system
8
, and an imaging/recording unit
9
.
Note that the “projector lens” referred to herein means a lens located between the energy filter
6
and the imaging/recording unit
9
. The “intermediate lenses” mean one or more lenses positioned between the objective lens
4
and the energy filter
6
. The imaging/recording unit
9
is made of a fluorescent screen, a photography device, or a TV camera.
The energy filter
6
acts to energy-disperse incident electrons. Various kinds of energy filters are known. For example, various energy filters each made up of two or more electromagnets are known as omega, alpha, gamma, and mandolin-type filters according to their orbital geometry of electrons within the energy filter
6
. Furthermore, a Wien filter making use of electric and magnetic fields that are made to overlap with each other is known. Any type can be used as the energy filter
6
shown in FIG.
2
. For convenience, an omega filter is used below.
One known intermediate lens system, such as the intermediate lens system
5
, is made up of a single lens stage. Another known intermediate lens system is made up of two stages of lenses. A further known intermediate lens system consists of three stages of lenses. In the illustrated structure, the intermediate lens system is made of three stages of lenses. Each stage consists of one or more lenses. The projector lens system
8
is made of one or more stages of lenses, and each stage consists of one or more lenses.
Four points or locations are defined within the energy filter
6
. For the description given below, these four locations are described by referring to FIG.
3
. The omega filter is made up of four electromagnets
10
,
11
,
12
, and
13
as shown in FIG.
3
. The electromagnets
10
and
13
are vertically symmetrical with respect to a position indicated by the dot-and-dash line. Similarly, the electromagnets
11
and
12
are vertically symmetrical with respect to the position indicated by the dot-and-dash line. In
FIG. 3
, the central orbit of the electron beam in the omega filter is indicated by the broken line O.
The aforementioned four points are defined in
FIG. 3
, that is, these are an incident crossover point A, an incident image plane B, an exit image plane C, and an exit crossover point D.
The position of the exit image plane C is so set that electrons having different energies are focused at the same position. This plane C is also known as an achromatic image plane. On the other hand, the exit crossover point D is also termed an energy-dispersive plane. The slit
7
is positioned at this exit crossover point D.
These four points A, B, C, and D are defined strictly according to the design of the energy filter, and are important optical positions where they are used as components of the TEM equipped with energy filter. In order to minimize the imaging distortion of the energy filter and to secure the same imaging function as used in an ordinary TEM, these four points must be defined strictly. These four points A-D are defined in any structure including an omega filter.
The operation of each part of the TEM equipped with energy filter is now described.
(1) Action of the intermediate lens system
5
in the TEM equipped with energy filter:
The intermediate lens system
5
acts to vary either the magnification of a TEM image that is a magnified image of a specimen or the camera length for a diffraction pattern.
The intermediate lens system also serves to bring an image and a diffraction pattern formed by the objective lens
4
into positions defined in the energy filter
6
. In particular, where electrons having a desired energy are selected by the slit
7
and an image is observed, the intermediate lens brings the diffraction pattern formed at the back focal plane of the objective lens
4
to the incident crossover point A. Also, the intermediate lens system brings an image formed by the objective lens
4
to the incident image plane B. Where electrons having a desired energy are selected by the slit
7
and a diffraction pattern is observed, the intermediate lens system brings an image formed by the objective lens
4
to the incident crossover point A. Also, the intermediate lens brings a diffraction pattern formed at the back focal plane of the objective lens
4
to the incident image plane B.
In summary, the intermediate lens system
5
performs the following three actions:
(i) The intermediate lens system
5
brings an image or a diffraction pattern that is conjugate with the image to the incident crossover point A defined in the energy filter
6
.
(ii) The intermediate lens system
5
brings a diffraction pattern or an image that is conjugate with the diffraction pattern to the incident image plane B defined in the energy filter
6
.
(iii) In the imaging mode, the intermediate lens system
5
can vary the magnification in minute steps over a wide range. In the diffraction mode, the intermediate lens system
5
can vary the camera length in minute steps over a wide range.
To perform these three actions, it is necessary to fabricate the intermediate lens system
5
from three stages of lenses, because any one lens cannot alone satisfy each of the three conditions described above. Three stages of lenses are so adjusted as to complement each other in satisfying the three conditions.
(2) Action of the energy filter
6
in the TEM equipped with energy filter:
Electrons emitted by the electron gun
1
are focused onto the specimen by the system of condenser lenses
2
. If the thickness of the specimen is only several micrometers or less, the electrons are transmitted through the specimen. During this process, the electrons interact with atoms and electrons constituting the specimen, whereby energy loss takes place. The energy loss is not uniform for all electrons but has a probability distribution that is characteristic of the specimen.
In the TEM equipped with energy filter, electrons are energy-dispersed by the energy filter
6
. The energy loss distribution is analyzed. Thus, the state of electrons, such as free electrons and bound electrons within the specimen, can be known. Furthermore, if the slit
7
is placed in the exit crossover point D in the energy filter
6
, and if only electrons suffering from certain energy loss are selected by the slit
7
and imaged, then a two-dimensional distribution image of energy loss in the specimen can be obtained. This can be applied to analysis of elements constituting the specimen or can be used to improve the image contrast.
In the imaging mode as described above, the intermediate lens system
5
forms a diffraction pattern at the incident crossover point A. Also, the intermediate lens system
5
forms an image at the incident image plane B. The diffraction pattern at the incident crossover point A is focused at the exit crossover point D by the electron-refracting action of the energy filter
6
. The image at the incident image plane B is focused at the exit image plane C.
In the diffraction m
JEOL Ltd.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
Wells Nikita
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