Radiant energy – Inspection of solids or liquids by charged particles – Electron probe type
Reexamination Certificate
2002-05-22
2003-09-30
Lee, John R. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Electron probe type
C250S309000, C250S311000, C250S492100
Reexamination Certificate
active
06627889
ABSTRACT:
CLAIM OF PRIORITY
This application claims priority to Japanese Patent Application No. 2001-346849 filed on Nov. 13, 2001.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods and systems for the observation, analysis, and evaluation of thin film samples or fine particles, and more specifically, the present invention relates to systems and methods for analyzing, at multiple stages driving fabrication, electronic devices and/or micro devices such as semiconductor devices, liquid crystal devices, magnetic head devices, that require observation and analysis of not only surfaces of an observation subject but also inner cross sections near the surface thereof.
2. Description of the Background
As a means for obtaining information on the elemental composition of a sample, it is known to detect x-rays generated as a result of electron beam irradiation. X-rays have two components: characteristic radiations with energy specific to the elements comprising the sample, and continuous x-rays whose energy is shorter than the energy of the incident electron beam as a result of Bremsstrahlung radiation. By analyzing the energy spectrum of x-rays, it is possible to find out the elemental composition of the sample. JP-A-68060/1980 discloses a collimator having an opening, which is smaller than an x-ray detector, for taking in x-rays from a sample (Related Art 1).
FIG. 21
shows a schematic view of a device that has been improved from the structure of the Related Art 1.
The improved structure works as follows. Electron beam
8
is irradiated onto a sample
22
, which emits x-rays due to the irradiation. An x-ray detector
16
having an x-ray detecting element
161
provided above in a slanting direction of the sample
22
, and a collimator
162
for restricting the optical path of x-rays disposed between the x-ray detecting element and the sample, detects the x-rays emitted from the sample.
FIG. 23
is a schematic enlarged view showing around the sample
22
in an in-lens electron microscope shown in
FIG. 22. A
micro sample
22
is introduced into a space interposed between an upper magnetic pole
707
and a lower magnetic pole
708
comprising an objective lens. A mesh
26
holds the micro sample
22
, which is attached to a sample holder
706
therethrough. X-rays
401
, secondary electrons
301
, and reflected electrons
205
are generated as an electron beam
8
irradiates the sample
22
. When the micro sample
22
is analyzed for its elemental structure by detecting x-rays thereof, it is ideal if the measured x-rays are only the x-rays
401
. In actuality, however, various aspects generate x-rays as described below.
A part of the reflected electrons
205
generates x-rays
402
with an energy having no bearing to the sample itself by colliding with a surface of the upper magnetic pole
707
. Transmitted electrons
201
and
202
passing. through the sample
22
collides with the sample holder
706
and the lower magnetic poles
708
so as to generate X-rays
403
and
406
. Reflected electrons
207
generated by the transmitted electron
202
being scattered at the lower magnetic pole
708
collide with the sample holder
706
so as to generate x-rays
407
. X-rays generated by the transmitted electron
202
colliding with the lower magnetic pole are incident on the sample holder
706
so as to generate x-rays
405
. Although not shown in any of the figures, there are other x-rays generated by reflected electrons and transmitted electrons colliding with other parts of the sample
22
and the mesh
26
.
These reflected x-rays are called “background x-rays” because they are not generated from the sample. The background x-rays cause to deteriorate accuracy of the elemental analysis. A collimator
162
shown in
FIG. 21
is provided to reduce the above-described background x-rays entering into the x-ray detecting element
161
as much as possible.
Another method for reducing the background x-rays is disclosed in “Principles of Analytical. Electron Microscopy”, edited by David C Joy et al., p.p. 131-135, 1986, Plenum Press, New York (Related Art 2). In this example, as shown in
FIG. 24
, surfaces of upper
707
and lower
708
magnetic poles have plates
501
and
502
, respectively of a light elemental material having a hole for transmitting the electron beam, whereby the reflected electron
205
and transmitted electron
202
from a sample
22
collide with a light elemental plate
501
,
502
rather than directly colliding with the magnetic poles
707
,
708
mainly formed of Fe. In this way, the number of reflected electrons at the magnetic poles, the energy characteristics of the x-rays, and the amount of continuous x-rays are reduced, thus enabling a reduction in the background x-rays as a result thereof.
JP-A-261894/1997 discloses a method for reducing background x-rays generated by reflected electrons and transmitted electrons colliding with places other than an observation point on a sample (Related Art 3). In this method, when creating an observation surface in the form of a thin film from the sample, the observation surface is formed so as to be inclined with respect to a side face of the sample that is not made into a thin film. A carbon film covers a surface of the sample other than the observation point. There is also a method using a sample stage covered by carbon.
The above-described conventional methods have at least the following problems. The method of Related Art 1 prevents x-rays generated from a non-sample portion from entering into a detecting element by providing a collimator
162
between the x-ray detecting element
161
and the sample
22
. In case of using a thin film sample, such a method is not effective with respect to x-rays generated by transmitted electrons that pass through the sample and collide with a sample stage immediately below the sample. Moreover, when a narrow collimator
162
is provided to limit x-rays only from an electron beam irradiation point on the sample
22
, a distance between the detecting element
161
and the sample
22
has to be relatively long, thus lowering detection efficiency due to lack of a proper detection angle.
Furthermore, the x-ray detector
161
must be accurately placed with respect to the sample
22
. Thus, displacement of the sample
22
would result in decreased detection sensitivity.
In Related Art 2, a light elemental material covers the surfaces of upper and lower magnetic poles of the objective lens. The method is effective when a transmission electron microscope that has high accelerating voltage of the electron beam and when a thin sample with a thickness equal to or less than 100 nm is used because of a decrease in the scattering of electron beams transmitted through the sample. However, when a general scanning electron microscope, or a sample with a thickness of 100 nm or more is used, the electron beam transmitted through the sample has a greater scattering angle. Thus, background x-rays due to the collision of electron beams with portions other than the parts of light elemental material covering the magnetic poles or a sample stage increase, thereby deteriorating detection accuracy.
Even in a processing method of a micro sample as shown in Related Art 3, background x-rays generated by a collision of the electron scattered as described above with portions other than a sample stage or a sample chamber are not considered. Thus, the ratio between a signal and a background noise becomes undesirable, and measurement accuracy is also lowered because x-rays from portions other than measurement positions are also detected. The x-rays generated when scattered electrons collide with a carbon film deposited on a sample would be reduced compared to the case without the carbon film, although the degree of reduction is not sufficient. The method for forming a carbon film on a part of the micro sample requires deposition equipment, and the deposition becomes necessary every time a sample is made. Thus, the production of a sample becomes increasingly complicated and requires addition
Fukuda Muneyuki
Ishitani Tohru
Koike Hidemi
Ochiai Isao
Sato Mitsugu
Hitachi , Ltd.
Hughes James P.
Lee John R.
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