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Claims  |
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What is claimed is:
1. A thin-film forming apparatus in which the elements in a sample produced
in a mechanism by a thin-film forming process in a vacuum chamber are
excited by an excitation source to emit associated fluorescent X-rays,
comprising:
a detector for detecting the associated fluorescent X-rays to insure that
the composition of said sample is consecutively measured in the process of
thin-film formation,
a shield for isolating the detector from light and heat generated in the
mechanism, said shield being heat-resistant and transmissive of at least
fluorescent X-rays containing soft X-rays of 1 keV and below,
a mirror for reflecting the associated flourescent X-rays toward the
detector [is provided either at the entrance or exit of said shield or at
both,
and means defining slits capable of adjusting the incident and exit angles
of said fluorescent X-rays with respect to the mirror, and the ranges of
said angles.
2. The thin-film forming apparatus of claim 1, wherein the mirror is
provided at the entrance of said shield.
3. The thin-film forming apparatus of claim 1, wherein the mirror is
provided at the exit of said shield.
4. The apparatus of claim 8, further comprising a second mirror for
reflecting the associated flourescent X-rays provided at the entrance of
said shield.
5. The thin film forming apparatus of claim 1 wherein the shield comprises
a thin metal film permitting passage of at least soft X rays having an
energy of 1 keV and below;
a support film attached to said thin metal film and having good heat
conductivity;
and a support for supporting the thin metal film and the support film.
6. The thin film apparatus of claim 5 wherein the thin metal film is made
of material of a small atomic number;
wherein the support film is formed of boron nitride;
wherein the support is formed of silicon.
7. The thin film forming apparatus of claim 1 further comprising a vacuum
box for supporting at least the detector;
a gate valve disposed between the vacuum box and the vacuum chamber; and
an exhaust unit for removing air from the vacuum box.
8. The thin film forming apparatus of claim 7 wherein the detector is
disposed in a vessel and further comprising a mechanism attached to the
vessel for opening and closing the vessel 1.
9. The thin film forming apparatus of claim 1 further comprising a vacuum
box for supporting at least the detector;
a gate valve disposed between the vacuum box and the vacuum chamber; and
an exhaust unit for removing air from the vacuum box.
10. The thin film forming apparatus of claim 9 wherein the detector is
disposed in a vessel and further comprising a mechanism attached to the
vessel for opening and closing the vessel.
11. An elemental analyzer comprising:
an excitation source for exciting more than one element present in the
neighborhood of the surface of a sample to emit the characteristic X-ray
of that each element;
means defining a slit for picking up the emitted characteristic X-ray of
each element at angles of a range that includes the angle of total
reflection of each of said characteristic X-rays from the surface of said
sample;
means for ensuring that said characteristic X-rays passing through said
slit are totally reflected at angles corresponding to said individual
elements such that the intensities of X-rays emitted by the elements are
at a similar level; and
an X-ray detector for detecting the characteristic X-rays reflected from
said means for ensuring.
12. The elemental analyzer of claim 11 wherein the means for ensuring that
said characteristic X-rays passing through said slit are totally reflected
at angles corresponding to said individual elements comprises a curved
mirror.
13. The elemental analyzer of claim 11 wherein the means for ensuring that
said characteristic X-rays passing through said slit are totally reflected
at angles corresponding to said individual elements comprises a mirror
assembly comprising a plurality of plane mirrors.
14. The elemental analyzer of claim 11, wherein the electromagnetic wave is
an ion beam generated an ion beam accelerator.
15. The elemental analyzer of claim 11, further comprising a spectrum
analyzer for performing spectrum analysis on the detected X-rays wherein
results of spectrum analysis are stored in a memory.
16. The elemental analyzer of claim 11, further comprising a spectrum
analyzer for performing spectrum analysis on the detected X-rays wherein
results of spectrum analysis are displayed on a display unit.
17. The elemental analyzer of claim 11, wherein the means for ensuring that
each characteristic X-ray picked up at the respective angle of total
reflection is reflected by a mirror at a predetermined angle such that
characteristic X-rays of other energies are attenuated.
18. The elemental analyzer of claim 11, further comprising means for
ensuring that when X-rays are incident at angles at which they are picked
up by the slit, they are reflected by the mirror at respective appropriate
angles.
19. The elemental analyzer of claim 11, wherein the electromagnetic waves
are fluorescent X-rays, wherein the elemental analyzer further comprises
means defining a slit through which X-rays from the X-ray source are
applied to the sample at the angle of total reflection or at nearby
angles, whereby only the elements in the surface of the sample are excited
by the applied X-rays and no fluorescent X-rays are emitted from the
deeper area of the sample.
20. A thin-film forming apparatus comprising:
a mechanism in a vacuum chamber for producing a sample by a thin-film
forming process; and
an elemental analyzer for measuring the composition of said sample as it is
produced, said elemental analyzer comprising:
an excitation source that excites the elements in said sample to emit
characteristic X-rays;
a total reflecting mirror for reflecting said characteristic X-rays;
an X-ray detector for detecting the characteristic X-rays as reflected from
said total reflecting mirror;
means for defining slits that determine the range of incident angles for
the characteristic X-rays that are to be incident on said total reflecting
mirror, as well as the range of exit angles for those characteristic
X-rays which have been reflected from said total reflecting mirror and
which reach said detector; and
a shield for isolating said X-ray detector from light and heat and that is
heat-resistant and transmissive of at least fluorescent X-rays containing
soft X-rays of 1 keV and below.
21. The thin film forming apparatus of claim 20 wherein the shield
comprises a thin metal film permitting passage of at least soft X rays
having an energy of 1 keV and below;
a support film attached to said thin metal film and having good heat
conductivity;
and a support for supporting the thin metal film and the support film.
22. The thin film apparatus of claim 21 wherein the thin metal film is made
of material of a small atomic number;
wherein the support film is formed of boron nitride;
wherein the support is formed of silicon.
23. A method of analyzing more than one element present in the neighborhood
of the surface of a sample, said method comprising the steps of:
applying energy particles to the surface of said sample;
picking up a plurality of electromagnetic waves, emitted by each of the
elements present in the neighborhood of said surface as a result of
excitation due to said step of applying energy particles, at angles of a
range that includes the angles of total reflection of each of said
electromagnetic waves from said surface;
reflecting all of the picked up electromagnetic waves at angles such that
the intensities of X-rays emitted by the elements are at a similar level;
and
subjecting said totally reflected electromagnetic waves to spectroscopy for
detection.
24. The method of claim 23, wherein the sample is a biosample.
25. The method of claim 23, wherein the electromagnetic wave is an electron
beam accelerated by an electron beam accelerator.
26. The method of claim 23, wherein the electromagnetic wave is generated
by a neutral corpuscular beam.
27. A method of analyzing more than one element present in the neighborhood
of the surface of a sample, said method comprising the steps of:
allowing a first electromagnetic wave to fall on the surface of said sample
at angles of a range that includes the angle of total reflection of that
electromagnetic wave from the surface of said sample;
picking up a plurality of second electromagnetic waves, emitted by each of
the elements present in the neighborhood of said surface as a result of
excitation due to said step of allowing, at angles of a range that
includes the angle of total reflection of each of said second
electromagnetic waves from said surface;
reflecting all picked up second electromagnetic waves at angles such that
the intensities of X-rays emitted by the elements are at a similar level;
and
subjecting said totally reflected second electromagnetic waves to
spectroscopy for detection.
28. An elemental analyzer comprising:
an excitation source for exciting more than one element present in the
neighborhood of the surface of a sample to emit the characteristic X-ray
of each element;
means defining a slit for picking up the emitted characteristic X-ray of
each element at angles of a range that includes the angle of total
reflection of each of said characteristic X-rays from the surface of said
sample;
means for causing total reflection of said characteristic X-rays passing
through said slit at angles such that the intensity of X-rays emitted by
the elements is at a similar level; and
an X-ray detector for detecting the characteristic X-rays reflected from
said means for causing total reflection.
29. The elemental analyzer of claim 28 wherein the means for causing total
reflection comprises a mirror assembly comprising a plurality of plane
mirrors having reflecting surfaces made of different materials.
30. The elemental analyzer of claim 28 wherein the means for causing total
reflection comprises a curved mirror having its reflecting surface
composed of different materials in different areas.
31. A method of analyzing more than one element present in the neighborhood
of the surface of a sample, said method comprising the steps of:
applying first electromagnetic waves to the surface of said sample;
picking up a plurality of second electromagnetic waves, emitted by each of
the elements present in the neighborhood of said surface as a result of
excitation due to said step of applying, at angles of a range that
includes the angle of total reflection of each of said second
electromagnetic waves from said surface;
reflecting all picked up second electromagnetic waves at angles such that
the intensities of X-rays emitted by the elements are at a similar level;
subjecting said totally reflected second electromagnetic waves to
spectroscopy for detection.
32. An elemental analyzer comprising:
an excitation source for exciting more than one element present in the
neighborhood of the surface of a sample to emit the characteristic X-ray
of each element;
means defining a slit for picking up the emitted characteristic X-ray of
each element at angles of a range that includes the angle of total
reflection of each of said characteristic X-rays from the surface of said
sample;
a mirror having a curvature in two axial directions, constructed and
arranged so that the characteristic X-rays passing through the slit are
totally reflected and subsequently focused at angles such that the
intensities of X-rays emitted by the elements are at a similar level; and
an X-ray detector for detecting the characteristic X-rays reflected from
said mirror.
33. The elemental analyzer of claim 32, wherein the mirror acts as an
optical filter and focuses reflected X-rays at a predetermined location,
wherein the mirror comprises two cylindrical mirrors having an elliptical
cross-section and wherein a location at which elemental excitation occurs
so as to cause emission of a characteristic X-ray, is brought into
registry with one of the two foci of the ellipsis and the surface of one
mirror is made of an appropriately selected material to provide a
filtering action whereas the other mirror is positioned perpendicular to
the first mirror and focuses incident X-rays to converge at the
predetermined location.
34. The elemental analyzer of claim 33, wherein the X-ray source is a
synchrotron radiator.
35. The elemental analyzer of claim 32, wherein the mirror has a base and a
film formed on the base, wherein the film is made of a layer of gold about
1000 angstroms thick and is evaporated on the base.
36. The elemental analyzer of claim 35, wherein the base is made of silicon
dioxide.
37. The elemental analyzer of claim 35, wherein the base is made of silicon
carbide.
38. The elemental analyzer of claim 35, wherein materials forming the
mirror are varied throughout the surface of the mirror, and wherein the
materials are selected such that materials of a lower density are used to
reflect X-rays that are picked up at larger angles of total reflection
whereas materials of a higher density are used to reflect X-rays that are
picked up at smaller angles of total reflection. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This invention relates to a thin-film forming apparatus for use in the
fabrication of electronic devices, semiconductors, etc. More particularly,
this invention relates to a thin-film forming apparatus that is capable of
consecutively measuring the composition of a sample in the process of
forming the desired thin film on the sample. This invention also relates
to a method and apparatus for analyzing a plurality of elements that are
present on the surface of a material of interest or in its neighborhood,
as well as a thin-film forming apparatus that is capable of measuring the
composition of a sample during thin film formation in the process of
semi-conductor fabrication.
As the scale of integration of electronic devices, semiconductor devices,
etc. has increased while their feature size has decreased today, it has
become apparent that the performance of those devices tends to depend on
the quality of the thin films they use. For example, if the silicon (Si)
to oxygen (O) ratio in a silicon dioxide (SiO.sub.2) deviates from the
stoichiometric value of 1:2, one may conclude that an unwanted substance
other than SiO.sub.2 has entered the film to change its dielectric
constant, whereby desired high-frequency characteristics cannot be
attained. Further, when forming a thin compound film, it is often
difficult to attain the desired composition primarily due to the
differences in sputtering yield and sticking coefficient. Conventionally,
a composition analyzer is used to evaluate the composition of a thin film
after making it with a thin-film forming apparatus. But, in this case, it
has been difficult to form the thin film without any change in its
composition due to variations in the process conditions being properly
corrected during thin film formation. Under these circumstances, attempts
have been made to consecutively measure the change that will occur in the
composition of the thin film being formed.
FIGS. 17 and 18 are diagrammatic views of the prior art thin-film forming
apparatus that is described in Ino et al., "Surface Analysis by RHEED
Excited Total Reflection Angular X-Ray Spectroscopy (TRAXS)" in Oyo
Butsuri (Applied Physics), 56, 7, 1987, pp. 843-850. FIG. 17 shows the
apparatus as it is equipped with an elemental analyzer for measuring the
compositional changes of a sample. Shown by 1 is a vessel for keeping an
X-ray detector in vacuum; 3 is a window that maintains the vacuum
enclosure of the X-ray detector but which admits the passage of X-rays; 6
is a liquid nitrogen dewar vessel for cooling the X-ray detector; 7 is an
X-ray transmitting window; 10 is a thin-film forming vacuum chamber; 12 is
a sample making mechanism; 13 is an exhaust unit for degasifying the
vacuum chamber 10; 21 is a sample; and 31 is an excitation source that
excites the elements in the sample 21 to emit their characteristic X-rays
(fluorescent X-rays). Shown by 51 is a sample holder with a stage 52 for
mounting the sample 21 in position.
FIG. 18 shows the interior of the vessel 1 in detail. Shown by 2 is the
X-ray detector (hereunder sometimes referred to simply as the "detector");
4 is an amplifier for amplifying the output signal from the detector 2;
and 5 is a rod that guides the signal from the amplifier 5 to the outside
of the vacuum enclosure and which lets in a cooling medium for cooling the
detector.
The operation of the apparatus shown in FIGS. 17 and 18 is described below.
To form a thin film of gallium arsenic (GaAs), he activates the mechanism
12 is activated to have gallium (Ga) and arsenic (As) evaporated onto the
sample 21. During the thin-film formation, an excitation beam such as an
electron beam generated from the excitation source 31 such as an electron
gun is incident upon the sample 21, whereby Ga and As are excited to emit
their characteristic X-rays. The emitted X-rays exit from the chamber 10
through the window 7 and travel in air atmosphere to be admitted into the
detector 2 through the window 3 at the front of the vessel 1. Signals
associated with the detected characteristic X-rays are amplified by the
amplifier 4 and the amplified signals pass through the rod 5 to be fed
into a spectrum analyzer (not shown) or some other suitable external
circuit. With this arrangement, the composition of the surface of sample
21 can be analyzed while a thin film is formed on the sample.
The prior art elemental analyzer is described below in detail. FIG. 19 is a
diagrammatic view of the elemental analyzer described in Japanese Patent
Public Disclosure No. 82840/1985. As shown, the analyzer comprises the
detector 2, a vacuum chamber 11, an exhaust port 14 which is connected to
a vacuum pump (not shown) that is operated to keep the inside of the
chamber 11 in vacuum, an electron gun 32 for emitting an electron beam
onto the sample 21, the sample holder 51, the sample mounting stage 52, a
spectrum analyzer 71 for spectrum separating the X-rays detected with the
detector 2, and a memory unit 72 for storing the output of the spectrum
analyzer. The memory unit 72 may be replaced by a display unit.
The operation of the elemental analyzer shown in FIG. 19 is described
below. The sample 21 is to be mounted on the stage 52 at the distal end of
the sample holder 51. In order to facilitate its mounting, an
opening/closing portion is provided in a suitable area of the vacuum
chamber 11 so that the sample 21 can be pushed into the chamber 11 via
said portion. Alternatively, the vessel 11 may be so constructed that the
sample holder 51 can be pulled out for mounting the sample 21 outside the
vessel. The sample holder 51 is equipped with bellows or some other
suitable means for permitting it to rotate or move back and forth so that
the position and inclination of the sample 21 can be freely adjusted.
In response to a current from a power source, the electron gun 32 generates
and emits an electron beam. The emitted electron beam is focused by an
optional electronic lens and a collimator (not shown) to be incident on
the surface of the sample 21. This electron beam excites the elements that
are present on the surface of the sample 21 and in its neighborhood,
whereby X-rays characteristic of the excited elements are emitted for
detection with the detector 2. The detected X-rays are spectrum separated
with the spectrum analyzer 71 and the X-ray spectra supplied from the
spectrum analyzer 71 are stored in the memory unit 72.
The angle at which emitted X-rays are picked up is selected at the angle of
total reflection of electromagnetic waves (generally characteristic
X-rays) emitted from the sample 21, namely the critical angle, or at
nearby angles. The reason for selecting the critical angle as the angle at
which emitted X-rays are to be picked up is described below on the basis
of the disclosures in "Oyo Butsuri (Applied Physics)", 56, 7, 1987, pp.
842-850 and "Japanese Journal of Applied Physics", 24, 6, 1985, pL.
387-390. In the following discussion, each of the angles such as the
critical angle and glancing angle is measured as the angle the incident or
emerging X-ray forms with the surface of the sample.
FIG. 20 shows how X-rays leaving the surface of a material to enter vacuum
are refracted. As shown, the intensity of such X-rays decreases sharply if
they are emitted at smaller angles than a certain critical value
.theta..sub.c. The value of .theta..sub.c coincides with the critical
angle for total reflection that occurs when X-rays of the same energy are
launched from vacuum into the material of interest and it is expressed by:
##EQU1##
where Z, A and .rho. are the atomic number, mass number and density,
respectively, of the material of interest, and .lambda. is the wavelength
of the incoming and outgoing X-ray.
Take, for example, the case where an electron beam is incident on the
surface of the material. The characteristic X-rays are refracted as shown
in FIG. 21 and those which are picked up at angles close to the critical
angle .theta..sub.c contain information from the surface layer whereas
those picked up at angles greater than .theta..sub.c contain information
from deeper areas. As eq. (1) shows, the critical angle .theta..sub.c
varies with the wavelength of incoming and outgoing X-ray and the shorter
its wavelength (hence, the higher its energy), the smaller the critical
angle is. In addition, the characteristic X-rays have energy values
peculiar to the associated elements. For example, the intensity of
characteristic X-rays emitted from the sample 21 having approximately one
atomic layer of silver (Ag) evaporated on the Si surface has a pickup
angle dependency as shown in FIG. 22. The characteristic X-rays emitted by
Ag can be detected with a very high sensitivity by picking them up at the
angle of total reflection of Ag characteristic X-rays with respect to Si
or at nearby angles. In addition, the characteristic X-rays emitted from
the neighborhood of the Si surface can be selectively detected by picking
up the characteristic X-rays emitted by Si at the angle of total
reflection of Si characteristic X-rays with respect to Si or nearby
angles.
To take another example, the intensity of characteristic X-rays emitted
from the sample 21 having calcium (Ca), iron (Fe) or copper (Cu) deposited
as a trace impurity on the Si surface has a pickup angle dependency as
shown in FIG. 23. Obviously, the angle of total reflection of emitted
characteristic X-ray with respect to Si varies with the species of element
that emits the X-ray. If the sample 21 is made of zinc sulfide (ZnS), the
intensity of characteristic X-rays emitted from the sample has a pickup
angle dependency as shown in FIG. 24. Obviously, the angle of total
reflection of the Zn characteristic X-ray with respect to ZnS differs from
that of the S characteristic X-ray with respect to ZnS and at the angle of
total reflection of Zn, the S characteristic X-ray has a very small
intensity whereas at the angle of total reflection of S, the Zn
characteristic X-ray contains more of the information from a deep area of
the sample.
A problem with the prior art elemental analyzer constructed in the manner
described above, is that if more than one element is present in the
neighborhood of the surface of the sample 21, the different values of
energy possessed by X-rays characteristic of the individual elements
provide different angles of total reflection for the sample 21. As a
result, if the characteristic X-ray emitted by a certain element is
detected at an angle in the neighborhood of the angle of total reflection
for that element, the intensity of the characteristic X-ray of another
element will decrease or more of the information from a deeper area will
be detected to reduce the sensitivity of measurement for the surface of
the sample (i.e., more of the unwanted information will be contained in
information about the surface of the sample 21).
The prior art thin-film forming apparatus capable of compositional
measurement of samples, which has the construction shown in FIG. 17, has
had the following disadvantages:
(1) Conventionally, the X-ray transmissive window 7 is formed of a
beryllium (Be) foil which, at a sufficient thickness to keep an ordinary
degree of vacuum, will absorb soft X-rays having an energy of no more than
1 keV and this has made it difficult to measure the characteristic X-rays
of materials such as oxides and carbides that contain light elements;
(2) Even if the X-ray transmissive window 7 is formed of an organic
material that transmits soft X-rays (e.g. Parylene), the heat of radiation
that is generated from the substrate and other sources during thin film
formation can potentially soften or melt the X-ray transmissive window;
(3) Even if the apparatus is so modified as to enable the measurement of
light elements, the efficiency of generation of characteristic X-rays
decreases drastically with the decreasing atomic number of light elements
such as oxygen (O), nitrogen (N) and carbon (C). With compounds containing
such light elements, the yield of characteristic X-rays will vary
considerably with the species of element even if the compositional ratio
of any two elements is 1:1. Accordingly, in performing pulse measurements
on the characteristic X-rays entering the detector 2, the counting rate of
pulses is limited by the higher of the two yields of characteristic X-rays
and the counting rate for the measurement of characteristic X-rays of the
lower of the two yields becomes very low. Under the circumstances, the
time of pulse measurement must be prolonged in order to achieve a higher
precision of measurement. Since it takes a long time to accomplish the
measurement of materials containing light elements, it is difficult to
catch up with the high speed of thin film formation, so has it been to
consecutively measure the composition of the sample 21 in the process of
thin film formation if it contains light elements.
SUMMARY OF THE INVENTION
The present invention has been accomplished under these circumstances and
has as an object providing a thin-film forming apparatus that is capable
of consecutively measuring the composition of a sample in the process of
thin film formation even if it contains light elements.
Another object of the present invention is to provide a method of elemental
analysis by which measurements can be performed on a plurality of elements
present in the neighborhood of a sample surface without deteriorating the
surface sensitivity for any of those elements.
A further object of the present invention is to provide an elemental
analyzer that is capable of performing measurements on a plurality of
elements in the manner described above.
According to one embodiment of the present invention there is provided a
thin-film forming apparatus characterized in that a detector is isolated
from the light and heat generated in a sample making mechanism by means of
a shield that is not only heat-resistant but also transmissive of
fluorescent X-rays containing soft X-rays of 1 keV and below and that a
mirror for total reflection of X-rays that is equipped with slits capable
of adjusting the incident and exit angles of fluorescent X-rays from the
sample excited with an excitation source, as well as the ranges of those
angles is provided either at the entrance or exit of said shield or at
both.
According to another embodiment of the present invention there is provided
a thin-film forming apparatus comprising: an excitation source that
excites the elements in a sample to emit their own characteristic X-rays;
a total reflecting mirror that reflects said characteristic X-rays; an
X-ray detector that detects the characteristic X-rays as reflected from
the total reflecting mirror; slits that determine the range of incident
angles for the characteristic X-rays that are to be incident on the total
reflecting mirror, as well as the range of exit angles for those
characteristic X-rays which have been reflected from the total reflecting
mirror and which reach said detector; and a shield that isolates the
detector from light and heat and that is not only heat-resistant but also
transmissive of fluorescent X-rays containing soft X-rays of 1 keV and
below.
According to still another embodiment of the present invention, there is
provided a method of elemental analysis that comprises: a radiation step
in which energy particles such as an electron beam, an ion beam or a
neutral corpuscular beam or an electromagnetic wave such as X-rays are
applied to the surface of a sample; a pickup step in which a second
electromagnetic wave emitted by each of the elements present in the
neighborhood of the surface of the sample as a result of excitation in the
radiation step is picked up at angles of a range that includes the angle
of total reflection of the second electromagnetic wave from the sample
surface; a reflection step in which all of the second electromagnetic
waves thus picked up are subjected to total reflection; and a detection
step in which the totally reflected second electromagnetic waves are
subjected to spectroscopy for detection.
According to yet another embodiment of the present invention, there is
provided a method of elemental analysis that is similar to the immediately
preceding embodiment above except that the incident electromagnetic wave
is allowed to fall on the surface of the sample at angles of a range that
includes the angle of total reflection of that electromagnetic wave from
the sample surface.
According to another embodiment of the present invention, there is provided
an elemental analyzer comprising: an excitation source that excites more
than one element present in the neighborhood of the surface of a sample to
emit the characteristic X-ray of that element; a slit for picking up the
emitted characteristic X-ray at angles of a range that includes the angle
of total reflection of that characteristic X-ray from the sample surface;
a curved mirror or a mirror assembly that consists of the combination of
two or more plane mirrors, said mirror or mirror assembly causing total
reflection of the characteristic X-rays that have passed through the slit;
and an X-ray detector that detects the characteristic X-ray reflected from
the mirror or mirror assembly.
According to another embodiment of the present invention, there is provided
an elemental analyzer that is similar to the embodiment described
immediately above except that the curved mirror has its reflecting surface
composed of different materials in different areas or that the mirror
assembly consists of the combination of two or more plane mirrors having
reflecting surfaces made of different materials.
According to another embodiment of the present invention, there is provided
an elemental analyzer that is similar to the embodiment described
immediately above same as recited in claim 5 except that the curved mirror
or the mirror assembly has a curvature in two axial directions, whereby
the X-rays passing through the slit are totally reflected and subsequently
focused.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic view showing a thin-film forming apparatus
according to an embodiment of the first aspect of the present invention;
FIG. 2 is a graph showing the relationship between glancing angle and the
reflectance of a total reflecting mirror;
FIG. 3 is a diagrammatic view showing an exemplary shield;
FIG. 4 is a diagrammatic view showing a thin-film forming apparatus
according to another embodiment of the first aspect of the present
invention;
FIG. 5 is a diagrammatic view showing a thin-film forming apparatus
according to yet another embodiment of the first aspect of the present
invention;
FIG. 6 is a diagrammatic view showing a thin-film forming apparatus
according to a further embodiment of the first aspect of the present
invention;
FIG. 7 is a diagrammatic view showing an elemental analyzer according to an
embodiment of the second aspect of the present invention;
FIG. 8 is a graph showing the relationship between the angle of reflection
by a gold (Au) mirror and its reflectance;
FIG. 9 is a diagrammatic view showing an exemplary mirror structure;
FIG. 10 is a diagrammatic view showing another exemplary mirror structure;
FIG. 11 is a diagrammatic view showing still another exemplary mirror
structure;
FIG. 12 is a perspective view showing the principal part of an elemental
analyzer according to another embodiment of the second aspect of the
present invention;
FIG. 13 is a diagrammatic view showing an elemental analyzer according to
still another embodiment of the second aspect of the present invention;
FIG. 14 is a diagrammatic view showing an elemental analyzer according to
yet another embodiment of the second aspect of the present invention;
FIG. 15 is a diagrammatic view showing a thin-film forming apparatus to
which is applied a method of elemental analysis according to an embodiment
of the third aspect of the present invention;
FIG. 16 is a diagrammatic view showing a thin-film forming apparatus to
which is applied a method of elemental analysis according to another
embodiment of the third aspect of the present invention;
FIG. 17 is a diagrammatic view showing a prior art thin-film forming
apparatus;
FIG. 18 is a diagrammatic view showing the structure of a vessel
accommodating an X-ray detector;
FIG. 19 is a diagrammatic view showing a prior art elemental analyzer;
FIG. 20 is a set of diagrams showing how X-rays are refracted;
FIG. 21 is a diagram showing how the characteristic X-rays emitted by
excitation with an electron beam are refracted;
FIG. 22 is a graph showing the pickup angle dependency of the
characteristic X-rays emitted from a sample having approximately one
atomic layer of Ag evaporated on the Si surface;
FIG. 23 is a graph showing the pickup angle dependency of the
characteristic X-rays emitted by various elements, Ca, Fe and Cu that are
deposited in very small amounts on the Si surface; and
FIG. 24 is a graph showing the pickup angle dependency of the
characteristic X-rays emitted from a ZnS sample.
DETAILED DESCRIPTION OF THE INVENTION
The mirror for total reflection of X-rays that is used in the thin-film
forming apparatus of the present invention is such that the higher the
energy of X-rays having a certain glancing angle, the lower the
reflectance of the mirror (M. J. Janiak and T. Arai, Abstr. of 1979
Pittsburgh Conf. and Chem. Appl. Spectros., p. 701) and, therefore, by
properly setting that mirror and the slits which are capable of adjusting
the incident and exit angles of fluorescent X-rays from the sample, as
well as the ranges of those angles, two X-rays having different energy
levels and, hence, different intensities can be processed to have
comparable levels of intensity by means of the combination of the total
reflecting mirror and the slits.
Thus, in accordance with one embodiment of the present invention, the
constituent elements of the thin film to be formed on the sample are
excited with the excitation source to emit fluorescent X-rays and the
total reflecting mirror and the slits which are capable of adjusting the
incident and exit angles of the emitted fluorescent X-rays, as well as the
ranges of those angles are set in such a way that the intensities of those
fluorescent X-rays which are emitted from the respective elements become
comparable to each other. As a result, when counting the number of pulsed
photons in the fluorescent X-rays entering the detector, the counting rate
of pulse measurement is in no way limited by the higher of the-two yields
of incident fluorescent X-rays and the compositional measurement of the
sample can be performed in pace with the rate of thin film formation even
if the thin film to be formed contains light elements.
Further, the thin-film forming apparatus of this embodiment of the present
invention is equipped with a light and heat shield that is not only
heat-resistant but also transmissive of fluorescent X-rays including soft
X-rays of 1 keV and less and this is effective in ensuring that the light
and heat generated in the process of thin film formation will not cause
any adverse effects on the detector, whereby the composition of the sample
can be measured consecutively throughout the process of thin film
formation.
The total reflecting mirror and the slits in the thin-film forming
apparatus of another embodiment of the present invention allow emitted
characteristic X-rays to be supplied to the detector in a selective manner
so that the characteristic X-rays emitted by a plurality of elements will
provide comparable levels of intensity for the detector.
The reflection step of the method for elemental analysis of another
embodiment of the present invention is such that the electromagnetic wave
picked up in the pickup step is reflected at angles including the angle of
total reflection of that electromagnetic wave from the mirror, whereby
information from the neighborhood of the surface of the sample is
selectively supplied to the detection step.
The radiation step of the method for elemental analysis in one embodiment
of the present invention is such that the electromagnetic wave is
permitted to fall on the surface of the sample at angles of a range that
includes the angle of total reflection of that electromagnetic wave for
the sample, whereby only the elements present on the surface of the sample
will be excited.
The slits and mirror in the elemental analyzer in another embodiment of the
present invention are such that characteristic X-rays are picked up from
the sample at angles that include the angle of total reflection while, at
the same time, the picked-up characteristic X-rays are allowed to reflect
at angles including the angle of total reflection of those characteristic
X-rays from the mirror, whereby information from the neighborhood of the
surface of the sample is selectively supplied to the X-ray detector.
The mirror in the elemental analyzer of another embodiment of the present
invention is such that the angle of reflection varies with the angle at
which characteristic X-rays are picked up through the slits, whereby
information from the neighborhood of the surface of the sample is
selectively supplied to the X-ray detector.
The mirror in the elemental analyzer in another embodiment of the present
invention has a curvature in biaxial directions, so that the reflected
X-rays are allowed to converge at a point, thereby enabling the detector
to detect over a smaller area.
Various embodiments of the present invention are described below with
reference to accompanying drawings. FIG. 1 is a diagrammatic view showing
the thin-film forming apparatus that enables the composition of a sample
to be measured even if a thin film containing light elements is to be
formed on the sample. Shown by 42 in FIG. 1 is a mirror, typically made of
soda lime glass, for total reflection of X-rays 43 is a slit that is
provided at both the entrance and exit of the mirror 42 and that is
capable of setting incident and exit angles of fluorescent X-rays that
fall upon and emerge from the mirror 42, as well as the ranges of those
angles; 41 is a shield of the light and heat generated from a sample
making mechanism 12, said shield being not only heat-resistant but also
transmissive of fluorescent X-rays including soft X-ray rays of 1 keV and
below.
The operation of the thin-film forming apparatus is described below in
detail. Fluorescent X-rays entering through the shield 41 can be adjusted
by means of slits 43 in such a way that the fluorescent X-rays emitted by
the individual elements in the sample 21 will have comparable levels of
intensity, which are subsequently detected with a detector 2. The shield
41 effectively isolates detector 2 from any of the light and heat that is
generated in the mechanism 12. Further, the shield 41 is so much
heat-resistant that it will neither deform nor melt by the heat of
radiation from the substrate and other components that are heated during
thin film formation and, therefore, the emitted fluorescent X-rays can be
measured consecutively throughout the process of thin film formation.
FIG. 2 is a graph showing the reflectance of soda lime glass mirror for the
incident characteristic X-rays that are emitted by various elements.
Obviously, the higher the energy of X-rays, the lower the reflectance of
the mirror at a given glancing angle. This feature is utilized in the
present invention in such a way that the ranges of incident and exit
angles of X-rays onto and from the mirror 42 are properly adjusted by
means of the slits 43, whereby the detector 2 can be supplied with two
X-rays having comparable levels of intensity even if X-rays having
different energy levels are emitted from the sample.
In the thin-film forming apparatus, the excitation source 31 excites the
thin film forming on the sample 21 so that the respective elements in the
thin film will emit their own characteristic X-rays. The emitted
characteristic X-rays pass through the slit 43 at the entrance to fall on
the total reflecting mirror 42, from which they are reflected to pass
through the slit 43 at the exit to be supplied to the detector 2. As
already mentioned, the slits 43 are set in such a way that the
characteristic X-rays from the individual elements that have been
reflected by the mirror 42 will have comparable levels of intensity before
they are supplied into the detector 2. Therefore, the respective
characteristic X-rays can be pulse measured with the detector 2 and yet
the counting rate will not be limited by the higher of the yields of those
characteristic X-rays. In other words, the composition of the sample 21
can be measured at a speed in pace with the rate of thin film formation
even if the thin film to be formed on the sample contains light elements.
The shield 41 may typically have a structure as shown in FIG. 3. The shield
has a thin metal film 41 that is made of a material of small atomic number
such as Al or Be, so that it permits the passage of soft X-rays having an
energy of 1 keV and less. The metal film 41a is made to be thinner than
the conventional X-ray transmitting window 7. Because of its thinness, the
metal film 41a is less effective in dissipating the heat of radiation and,
to solve this problem, the shield 41 is provided with a support film 41b
having good heat conductivit | | |
