U.S. patent application number 10/964647 was filed with the patent office on 2005-11-24 for method and apparatus for measuring temperature of substrate.
This patent application is currently assigned to MASAFUMI ITO. Invention is credited to Ishii, Nobuo, Ito, Masafumi, Okamura, Yasuyuki, Shiina, Tatsuo.
Application Number | 20050259716 10/964647 |
Document ID | / |
Family ID | 29243329 |
Filed Date | 2005-11-24 |
United States Patent
Application |
20050259716 |
Kind Code |
A1 |
Ito, Masafumi ; et
al. |
November 24, 2005 |
Method and apparatus for measuring temperature of substrate
Abstract
The temperature of the surface and/or inside of a substrate is
measured by irradiating the front surface or rear surface of the
substrate, whose temperature is to be measured, with light and
measuring the interference of a reflected light from the substrate
and a reference light. A method and apparatus for measuring
temperature or thickness which is suitable for directly measuring
the temperature of the outermost surface layer of a substrate, and
an apparatus for treating a substrate for an electronic device,
which uses such method, are provided.
Inventors: |
Ito, Masafumi; (Osaka,
JP) ; Okamura, Yasuyuki; (Santa-shi, JP) ;
Shiina, Tatsuo; (Wakayama-shi, JP) ; Ishii,
Nobuo; (Amagasaki-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
MASAFUMI ITO
Sennan-gun
JP
TOKYO ELECTRON LIMITED
Tokyo
JP
|
Family ID: |
29243329 |
Appl. No.: |
10/964647 |
Filed: |
October 15, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10964647 |
Oct 15, 2004 |
|
|
|
PCT/JP03/04792 |
Apr 15, 2003 |
|
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Current U.S.
Class: |
374/161 ;
374/120; 374/E11.018 |
Current CPC
Class: |
G01J 5/0003 20130101;
G01K 11/12 20130101 |
Class at
Publication: |
374/161 ;
374/120 |
International
Class: |
G01K 011/00; G01K
001/16 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 15, 2002 |
JP |
2002-112733 |
Claims
What is claimed is:
1. A method for measuring temperature, comprising: irradiating with
light the front surface or rear surface of a substrate, whose
temperature is to be measured, and measuring the interference of a
reflected light from the substrate and a reference light, to
thereby measure the temperature of the front surface, rear surface,
and/or inside of the substrate.
2. A method for measuring temperature according to claim 1, wherein
the light is a low-coherence light.
3. A method for measuring temperature according to claim 1, wherein
the reflected light and reference light are the split lights from a
same light source and the reference light is a light corresponding
to a predetermined optical path length.
4. A method for measuring temperature according to claim 1, wherein
the light is applied to the rear surface on the opposite side from
the front surface of the substrate, whose temperature is to be
measured.
5. A method for measuring temperature according to claim 1, wherein
the light is applied to the same side as the front surface of the
substrate, whose temperature is to be measured.
6. A control method comprising the steps of: irradiating with light
the front surface or rear surface of a substrate to be treated,
whose temperature is to be measured, in an apparatus for treating
the substrate to be treated, measuring the interference of a
reflected light from the substrate and a reference light, to
thereby measure the temperature of the front surface, rear surface,
and/or inside of the substrate, and adjusting and/or controlling an
operation variable of the apparatus based on the result of the
measurement.
7. A control method according to claim 6, wherein the light is a
low-coherence light.
8. A control method according to claim 6, wherein the temperature
to be measured is the temperature of the front surface or the
inside of the substrate to be treated, and the variable is the
temperature of a susceptor for holding the substrate to be
treated.
9. A control method according to claim 6, wherein the temperature
to be measured is the temperature of the front surface or the
inside of the substrate to be treated, and the variable is at least
one process parameter selected from the group consisting of; the
total flow rate of a gas to be supplied into a container containing
the substrate to be treated, gas flow rate ratio, gas pressure,
plasma-generating power, and bias power.
10. A control method according to claim 6, wherein the temperature
to be measured is the temperature distribution on the front surface
or inside of the substrate to be treated, and the variable is at
least one selected from the group consisting of: zone control of
the susceptor temperature, attraction force zone control of the
susceptor electrostatic chuck, and zone control of
plasma-generating power.
11. A control method according to claim 6, wherein the temperature
to be measured is the temperature distribution on the front surface
or inside of the substrate to be treated, and the variable is at
least one selected from the group consisting of: the total flow
rate or distribution thereof of a gas to be supplied into a
container containing the substrate to be treated, gas flow rate
ratio or distribution thereof, gas pressure, plasma-generating
power, and bias power.
12. A control method according to claim 6, wherein the temperature
to be measured is the temperature history of the front surface or
inside of the substrate to be treated while the substrate is being
processed, and the adjustment and/or control of the variable is
conducted as part of statistic processing of data with the object
of controlling subsequent device substrate treatment based on the
decision relating to the treatment results.
13. A treatment method comprising the steps of: irradiating with
light the front surface or rear surface of a substrate to be
treated, whose temperature is to be measured, in an apparatus for
treating the substrate to be treated, measuring the interference of
a reflected light from the substrate and a reference light, to
thereby measure the temperature of the front surface, rear surface,
and/or inside of the substrate, and adjusting and/or controlling an
operation variable relating to the treatment of the substrate to be
treated, based on the result of the measurement.
14. A treatment method according to claim 13, wherein the light is
a low-coherence light.
15. A treatment method according to claim 12, wherein the treatment
of the substrate to be treated is the formation of a film on the
substrate to be treated.
16. A treatment method according to claim 15, wherein surface
temperature of the substrate to be treated is measured prior to the
treatment for determining the starting point of the treatment.
17. A treatment method according to claim 15, wherein the
temperature and/or film thickness of the outermost surface layer is
measured during the treatment for determining the end point of the
treatment.
18. A treatment method according to claim 15, wherein the treatment
is started by turning on the plasma-generating power and/or bias
power.
19. A treatment method according to claim 15, wherein the
temperature of the intermediate layer of substrate to be treated is
measured during the treatment and employed as a temperature of the
outermost surface (on which the film is being formed).
20. A treatment method according to claim 16, wherein the
intermediate layer is the second layer from the outermost
surface.
21. A treatment method according to claim 13, wherein the treatment
of the substrate to be treated is etching of the substrate to be
treated.
22. A treatment method according to claim 21, wherein the surface
temperature of the substrate to be treated is measured prior to the
treatment for determining the starting point of the treatment,
23. A treatment method according to claim 21, wherein the treatment
is started by turning on the plasma-generating power and/or bias
power.
24. A treatment method according to claim 21, wherein the
temperature of the second layer from the front surface of the
substrate to be treated is measured during the treatment and the
measured temperature is employed as the temperature of the
outermost surface (which is being etched).
25. An apparatus for measuring temperature, comprising: light
irradiation means for irradiating with light the front surface or
rear surface of a substrate whose temperature is to be measured; a
splitter for splitting the light into a reference light and a
measurement light; reference light reflecting means for reflecting
the reference light; optical path changing means for changing the
optical path length of light reflected from the reference light
reflecting means; and light receiving means for measuring the
interference of the reflected light from the substrate and the
reference light from the reference light reflecting means, wherein
the temperature of the front surface, rear surface and/or inside of
the substrate is measured based on the measurement of the
interference.
26. An apparatus for measuring temperature according to claim 25,
wherein the light is a low-coherence light.
27. An apparatus for measuring temperature according to claim 25,
wherein the interference corresponds to changes in the optical path
length in the reference light.
28. An apparatus for measuring temperature according to claim 25,
wherein the interference corresponds to a phase shift in the
reference light.
29. An apparatus for measuring temperature according to claim 25,
further comprising displacement measurement means for measuring the
displacement of the reference light reflection means.
30. An apparatus for treating a substrate for a device, comprising:
a treatment chamber for conducting a treatment of the substrate for
a device; and temperature measurement means for measuring the
temperature of the front surface, rear surface, and/or the inside
of the substrate to be disposed and treated in the treatment
chamber, wherein the temperature measurement means comprises: light
irradiation means for irradiating with light the front surface or
rear surface of the substrate to be treated and whose temperature
has to be measured; a splitter for splitting the light into a
reference light and a measurement light, reference light reflecting
means for reflecting the reference light; optical path changing
means for changing the optical path length of the light reflected
from the reference light reflecting means; and light receiving
means for measuring the interference of the reflected light from
the substrate and the reference light from the reference light
reflecting means.
31. An apparatus for treating a substrate for a device according to
claim 30, wherein the light is a low-coherence light.
32. An apparatus for treating a substrate for a device according to
claim 30, further comprising control means for adjusting and/or
controlling an operation variable for the treatment.
33. An apparatus for treating a substrate for a device according to
claim 30, wherein the treatment of the substrate to be treated is
the formation of a film on the substrate to be treated.
34. An apparatus for treating a substrate for a device according to
claim 30, wherein the treatment of the substrate to be treated is
etching of the substrate.
35. An apparatus for treating a substrate for a device according to
claim 30, wherein the treatment of the substrate to be treated is
annealing of the substrate.
36. An apparatus for measuring temperature or thickness,
comprising: light source means for irradiating with light the front
surface or rear surface of a substrate whose temperature or
thickness is to be measured, a splitter for splitting the light
into a reference light and a measurement light; reference light
reflecting means for reflecting the reference light; optical path
changing means for changing the optical path length of light
reflected from the reference light reflecting means; and light
receiving means for measuring the interference of the reflected
light from the substrate and the reference light from the reference
light reflecting means, wherein the temperature or thickness of the
front surface, rear surface and/or inside of the substrate is
measured based on the measurement of the interference; wherein the
light source means comprises: one light source or two light sources
having different wavelengths, for measuring the temperature or
thickness of the substrate; and a displacement-measuring light
source for measuring the displacement in the optical path changing
means; and the light receiving means comprises: one or two
light-receiving devices corresponding to the one or two light
sources, for receiving the interference light based on the light
from the one or two light sources, which has been reflected from
the substrate and the reference light reflecting means; and a
displacement-measuring light-receiving device for receiving the
interference light based on the light from the
displacement-measuring light source, which has been reflected from
the substrate and the reference light reflecting means.
37. An apparatus for measuring temperature or thickness according
to claim 36, wherein the light source for measuring the temperature
or thickness of the substrate has a wavelength of 0.3-20 .mu.m, and
a coherence length of 0.1-100 .mu.m.
38. An apparatus for measuring temperature or thickness according
to claim 36, wherein the light source means comprises two light
sources, one of which has a wavelength providing a relatively large
temperature coefficient of change in refractive index of the
substrate, and the other of which has a wavelength providing a
relatively small coefficient of temperature change in the
refractive index of the substrate.
Description
RELATED APPLICATION
[0001] This is a continuation-in-part application of International
Application No. PCT/JP03/04792, filed on Apr. 15, 2003 for METHOD
AND APPARATUS FOR MEASURING TEMPERATURE OF SUBSTRATE.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method and apparatus
capable of accurately measuring the temperature of the front
surface, rear surface, and/or inside of a substrate. More
specifically, the present invention relates to a method and
apparatus capable of accurately measuring the temperature of the
front surface, rear surface, and/or inside of a substrate by using
the interference phenomenon of low-coherence light and to an
apparatus for treating substrates for devices which uses those
method and apparatus.
[0004] The term "device" as used in the present specification means
to include electronic and/or mechanical devices. Thus, in the
present specifically, the term "device" is used in the meaning
including electronic devices (semiconductor devices, liquid-crystal
devices, organic EL devices, and the like) and very small devices
such as the so-called micromachines.
[0005] 2. Related Background Art
[0006] When a physical and/or chemical treatment is conducted on a
variety of substrates, e.g., from silicon, accurately measuring the
temperature of the front surface, rear surface, and/or inside of
the substrate is very important from the standpoint of accurately
controlling properties and physical characteristics of the product
which is to be obtained by the treatment.
[0007] For example, in the field of fine processing based on
lithographic technology in the field of semiconductor processes and
micromachines where surface treatment methods are presently widely
used, the treatment employing gas-phase reactions (for example,
physical vapor deposition (PVD) and chemical vapor deposition
(CVD), which represent deposition processes, and etching, plasma
treatment, and heat treatment such as annealing) are frequently
used.
[0008] In the field of devices, including electronic devices,
primarily semiconductor devices and liquid-crystal devices, which
have to be produced by presently available semiconductor processes,
and micromachines, the requirements placed on quality improvement
of the electronic devices which are the resultant product created a
demand for multilayer structures and quality improvement in each of
thin films constituting the de-vice. Usually, actual products
obtained in those thin film formation processes are extremely
frequently affected by temperature. For this reason, the importance
of temperature control in the outermost surface layer of the
substrate or multilayer structure, which is to be treated,
increases and cannot be underestimated.
[0009] For example, in processes using plasma, the outermost
surface layer of the substrate to be treated, is irradiated with
heat from plasma. In this case, it is clear that there is a
difference between the outermost surface layer and rear surface of
the substrate. Measurement methods employing resistance
thermometers or fluorescent thermometers measuring the temperature
of the rear surface of the substrate have been employed as
temperature measurement methods for measuring the temperature of
the surfaces.
[0010] However, In the above-described conventional processes, it
was very difficult to measure directly the temperature of the
outermost surface layer of the substrate due to restrictions placed
by the structure and operation principle of the apparatus.
DISCLOSURE OF INVENTION
[0011] An object of the present invention to provide a method for
measuring temperature, which resolves the above-described problem
encountered in the prior art.
[0012] Another object of the present invention to provide a method
for measuring temperature, which is capable of directly measuring
the temperature of the outermost surface layer of a substrate.
[0013] As a result of earnest study, the present inventors have
found that measuring the temperature of the surface or the inside
of a substrate by using light interference is very effective for
attaining the above-described object.
[0014] The method for measuring temperature in accordance with the
present invention is based on this discovery. More specifically,
the present invention provides a method for measuring temperature,
comprising:
[0015] irradiating with light the front surface or rear surface of
a substrate, whose temperature is to be measured, and
[0016] measuring the interference of a reflected light from the
substrate and a reference light, to thereby measure the temperature
of the front surface, rear surface, and/or inside of the
substrate.
[0017] The present invention also provides a control method
comprising the steps of:
[0018] irradiating with light the front surface or rear surface of
a substrate to be treated, whose temperature is to be measured, in
an apparatus for treating the substrate to be treated,
[0019] measuring the interference of a reflected light from the
substrate and a reference light, to thereby measure the temperature
of the front surface, rear surface, and/or inside of the substrate,
and
[0020] adjusting and/or controlling an operation variable of the
apparatus based on the result of the measurement.
[0021] The present invention further provides a treatment method
comprising the steps of:
[0022] irradiating with light the front surface or rear surface of
a substrate to be treated, whose temperature is to be measured, in
an apparatus for treating the substrate to be treated,
[0023] measuring the interference of a reflected light from the
substrate and a reference light, to thereby measure the temperature
of the front surface, rear surface, and/or inside of the substrate,
and and a reference light; and
[0024] adjusting and/or controlling an operation variable relating
to the treatment of the substrate to be treated, based on the
result of the measurement.
[0025] The present invention further provides an apparatus for
measuring temperature, comprising:
[0026] light irradiation means for irradiating with light the front
surface or rear surface of a substrate whose temperature is to be
measured;
[0027] a splitter for splitting the light into a reference light
and a measurement light;
[0028] reference light reflecting means for reflecting the
reference light;
[0029] optical path changing means for changing the optical path
length of light reflected from the reference light reflecting
means; and
[0030] light receiving means for measuring the interference of the
reflected light from the substrate and the reference light from the
reference light reflecting means,
[0031] wherein the temperature of the front surface, rear surface
and/or inside of the substrate is measured based on the measurement
of the interference.
[0032] The present invention further provides an apparatus for
treating a substrate for a device, comprising:
[0033] a treatment chamber for conducting a treatment of the
substrate for a device; and
[0034] temperature measurement means for measuring the temperature
of the front surface, rear surface, and/or the inside of the
substrate to be disposed and treated in the treatment chamber,
[0035] wherein the temperature measurement means comprises:
[0036] light irradiation means for irradiating with light the front
surface or rear surface of the substrate to be treated and whose
temperature has to be measured;
[0037] a splitter for splitting the light into a reference light
and a measurement light, reference light reflecting means for
reflecting the reference light;
[0038] optical path changing means for changing the optical path
length of the light reflected from the reference light reflecting
means; and
[0039] light receiving means for measuring the interference of the
reflected light from the substrate and the reference light from the
reference light reflecting means.
[0040] The present invention further provide an apparatus for
measuring temperature or thickness, comprising: light source means
for irradiating with light the front surface or rear surface of a
substrate whose temperature or thickness is to be measured; a
splitter for splitting the light into a reference light and a
measurement light; reference light reflecting means for reflecting
the reference light; optical path changing means for changing the
optical path length of light reflected from the reference light
reflecting means; and light receiving means for measuring the
interference of the reflected light from the substrate and the
reference light from the reference light reflecting means, wherein
the temperature or thickness of the front surface, rear surface
and/or inside of the substrate is measured based on the measurement
of the interference;
[0041] wherein the light source means comprises: one light source
or two light sources having different wavelengths, for measuring
the temperature or thickness of the substrate; and a
displacement-measuring light source for measuring the displacement
in the optical path changing means; and
[0042] the light receiving means comprises: one or two
light-receiving devices corresponding to the one or two light
sources, for receiving the interference light based on the light
from the one or two light sources, which has been reflected from
the substrate and the reference light reflecting means; and a
displacement-measuring light-receiving device for receiving the
interference light based on the light from the
displacement-measuring light source, which has been reflected from
the substrate and the reference light reflecting means.
[0043] In this apparatus for measuring temperature or thickness the
light source for measuring the temperature or thickness of the
substrate may preferably have a wavelength of 0.3-20 .mu.m, and a
coherence length of 0.1-100 .mu.m.
[0044] In this apparatus for measuring temperature or thickness the
light source means comprise may preferably two light sources, one
of which has a wavelength providing a relatively large temperature
coefficient of change in refractive index of the substrate, and the
other of which has a wavelength providing a relatively small
coefficient of temperature change in the refractive index of the
substrate.
[0045] In the present specification "the temperature of the front
surface, rear surface and/or inside of the substrate", which is to
be measured, includes at least one temperature selected from the
group consisting of the following temperatures (1) to (7).
[0046] (1) Temperature of the front surface of the substrate.
[0047] (2) Temperature of the rear surface of the substrate.
[0048] (3) Temperature of the inside of the substrate.
[0049] (4) Temperature of the front surface and rear surface of the
substrate.
[0050] (5) Temperature of the front surface and inside of the
substrate.
[0051] (6) Temperature of the rear surface and inside of the
substrate.
[0052] (7) Temperature of the front surface, rear surface, and
inside of the substrate.
[0053] (8) Average temperature of the front surface, rear surface,
and inside of the substrate.
BRIEF DESCRIPTION OF DRAWINGS
[0054] FIG. 1 is a block diagram illustrating an example of
low-coherence interference that can be used in accordance with the
present invention.
[0055] FIG. 2 is a graph illustrating an example of phase shift
caused by changes in temperature.
[0056] FIG. 3 is a block diagram illustrating an example of a
system configuration for measuring temperature, which can be used
in accordance with the present invention.
[0057] FIG. 4 is a photo illustrating an example of a system
configuration used in the present embodiment.
[0058] FIG. 5 is a graph illustrating a linear expansion
coefficient of Si at various temperatures.
[0059] FIG. 6 is a graph illustrating the temperature coefficient
of changes in the refractive index of Si at a wavelength of 1.55
.mu.m.
[0060] FIG. 7 is a schematic diagram illustrating the configuration
of a Michelson's interferometer.
[0061] FIG. 8 illustrates an SLD interference waveform and LD
interference waveform drawn by a program.
[0062] FIG. 9 is a graph illustrating the output voltage of an LD
interference waveform obtained when the optical system is not
stabilized.
[0063] FIG. 10 is a graph illustrating the output voltage of an LD
interference waveform obtained when the optical system was
stabilized.
[0064] FIG. 11 is a graph illustrating an interference waveform at
the front surface and rear surface of Si based on the analysis
results.
[0065] FIG. 12 is a graph illustrating an enlarged drawing of an
interference waveform in the rear surface position shown in FIG.
11.
[0066] FIG. 13 illustrates mutual arrangement (top) of incident
light and a measurement sample Si, SLD interference waveforms (a),
(c) obtained from the temperature measurement system, and LD
interference waveforms (b), (d) obtained form the displacement
measurement system. Here, (c) and (d) are enlarged drawings of the
substrate on the front surface of the measurement sample Si.
[0067] FIG. 14 is a graph illustrating the surface temperature of a
Si layer in relation to the heater temperature.
[0068] FIG. 15 is a graph illustrating the frequency theoretical
and experimental values of LD interference waveform relating to the
zone between the peaks of the SLD interference waveform that
accompanies temperature increase in a Si monolayer.
[0069] FIG. 16 is a graph illustrating SLD interference waveforms
(e), (g) obtained from the temperature measurement system, and LD
interference waveforms (f), (h) obtained from the displacement
measurement system. (g) and (h) show the enlarged surface
interference waveforms of the measurement sample SiO.sub.2.
[0070] FIG. 17 is a graph illustrating the temperature of the front
surface of a SiO.sub.2 layer, those results being related to a
heater temperature.
[0071] FIG. 18 is a graph illustrating the frequency theoretical
and experimental values of LD interference waveform relating to the
zone between the peaks of the SLD interference waveform that
accompanies temperature increase in a SiO.sub.2 monolayer.
[0072] FIG. 19 is a schematic perspective view illustrating a
multilayer structure used in the embodiments.
[0073] FIG. 20 is a graph illustrating the results obtained in
measuring temperature by using Si and SiO.sub.2 layered
structure.
[0074] FIG. 21 is a graph illustrating the results obtained in
measuring the temperature of Si with a thermocouple, those results
being related to a heater temperature.
[0075] FIG. 22 is a block diagram illustrating another mode of the
apparatus for measuring temperature in accordance with the present
invention.
[0076] FIG. 23 is a schematic cross-sectional view illustrating an
example of employing the apparatus for measuring temperature in
accordance with the present invention in an electronic device
treatment apparatus.
[0077] FIG. 24 is a schematic cross-sectional view illustrating an
example of employing the apparatus for measuring temperature in
accordance with the present invention in an electronic device
treatment apparatus.
[0078] FIG. 25 is a schematic cross-sectional view illustrating
another example of employing the apparatus for measuring
temperature in accordance with the present invention in an
electronic device treatment apparatus.
[0079] FIG. 26 is a schematic cross-sectional view illustrating
another example of employing the apparatus for measuring
temperature in accordance with the present invention in an
electronic device treatment apparatus.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0080] The present invention will be described hereinbelow in
greater detail with reference, when necessary, to the appended
drawings. In the description below, "parts" and "%" representing
weight ratios are based on a mass standard, unless stated
otherwise.
[0081] (Apparatus for Measuring Temperature)
[0082] The apparatus for measuring temperature in accordance with
the present invention comprises light irradiation means for
irradiating with light the front surface or rear surface of the
substrate whose temperature has to be measured, a splitter for
splitting the light into a reference light and a measurement light,
reference light reflecting means for reflecting the reference
light, optical path changing means for changing the optical path
length of the light reflected from the reference light reflecting
means, and light receiving means for measuring the interference of
the reflected light from the substrate and the reference light from
the reference light reflecting means.
[0083] In accordance with the present invention, the
above-described optical system can be composed of a usual optical
system (optical system with spatially matched optical axes).
However, from the standpoint of increasing the degree of freedom in
selecting the disposition of each optical element and reducing the
size of the entire optical system, it is preferred that the optical
system be composed by using optical fibers.
[0084] In accordance with the present invention, any light can be
used, provided that the interference of the reflected light from
the substrate and the reference light can be measured. However, in
order to avoid the damage caused by "excess interference", in order
words, to avoid interference of the reflected light due to the
difference between the front surface and rear surface of the
substrate (usually, about 500-1500 .mu.m), which is to be measured,
and to enable easy measurement of interference of the reference
light with the reflected light from the front surface (or from a
layer inside the substrate) of the substrate, which is to be
measured, it is preferred that a low-coherence light be used. Here,
"the low-coherence light" means a light with a small coherence
length. In accordance with the present invention, for example, the
below-described light can be advantageously used as "a
low-coherence light".
[0085] Central wavelength; preferably 0.3-20 .mu.m, even more
preferably 0.5-5 .mu.m; coherence length: preferably 0.1-100 .mu.m,
even more preferably 3 .mu.m or less
[0086] (Low-Coherence Light Source).
[0087] No specific limitation is placed on the operation principle,
form, size and method of use of the low-coherence light source,
provided it can supply the above-described low-coherence light to
the substrate whose temperature is to be measured. Examples of the
low-coherence light source that can be used in accordance with the
present invention are presented below. SLD (Super Luminescent
Diode), LED, high-luminosity lamps (tungsten lamp, xenon lamp, and
the like), light sources with an ultrawide wavelength band.
[0088] Of those low-coherence light sources, SLD is preferably used
because it has a high luminosity.
[0089] (Splitter)
[0090] In accordance with the present invention, no specific
limitation is placed on the operation principle, form, size and
method of use of the splitter, provided it can split light into a
reference light and a measurement light. Examples of the splitters
that can be used in accordance with the present invention are
presented below.
[0091] Fiber coupler.
[0092] Optical waveguide splitter.
[0093] Semitransparent mirror.
[0094] Of those splitters, an optical fiber coupler is preferred
because of its compatibility with optical fibers.
[0095] (Reference Light Reflection Means)
[0096] In accordance with the present invention, no specific
limitation is placed on the operation principle, form, size and
method of use of the reference light reflection means, provided
that it can reflect the reference light. Examples of the reference
light reflection means that can be used in accordance with the
present invention are presented below.
[0097] Reference mirror (corner cube prism, flat mirror, and the
like).
[0098] Delay line (similar to optical path changing means such as
delay line of a piezoelectric tube type).
[0099] Among those reference light reflection means, the corner
cube prism is preferred because of good parallelism of the
reflected light and incident light.
[0100] (Optical Path Changing Means)
[0101] In accordance with the present invention, no specific
limitation is placed on the operation principle, form, size and
method of use of the optical path changing means, provided that it
can vary the optical path length of the light reflected from the
reference light reflection means. Examples of the optical path
changing means that can be used in accordance with the present
invention are presented below.
[0102] Delay line of a voice coil motor type.
[0103] Delay line of a piezoelectric tube type.
[0104] Delay line of a direct stage type.
[0105] Delay line of a stacked piezoelectric type.
[0106] Of those optical path changing means, the voice coil motor
is preferably used because of its high speed and large variable
optical path length.
[0107] (Light Receiving Means)
[0108] In accordance with the present invention, no specific
limitation is placed on the operation principle, form, size and
method of use of the light receiving means, provided that it can
measure the interference with the reference light from the
reference light reflection means. Examples of the light receiving
means that can be used in accordance with the present invention are
presented below.
[0109] Photodiode.
[0110] Avalanche photodiode.
[0111] Photoelectron multiplier.
[0112] Of those light receiving means, the photodiode is preferably
used because of its low cost and compactness.
[0113] (Method for Converting to Temperature)
[0114] In accordance with the present invention, no specific
lamination is placed on the method for converting the degree of
interference into temperature, provided that the interference of
the reflected light from the above-described substrate (whose
temperature is to be measured) and the reference light from the
reference light reflection means can be used. Examples of the
methods that can be used for such conversion into temperature are
presented below.
[0115] Method using changes in the optical path based on changes in
temperature.
[0116] Method using absorption intensity changes based on changes
in temperature.
[0117] Method combining the two above-described methods.
[0118] Among them, the conversion method using changes in the
optical path based on changes in temperature is preferred from the
standpoint of accuracy and easiness of conversion.
[0119] (Method for Measuring Temperature)
[0120] In accordance with the present invention, the temperature of
the front surface or the inside of a substrate is measured by
irradiating the front surface or rear surface of the substrate
whose temperature is to be measured and measuring the interference
of the reflected light from the substrate and the reference
light.
[0121] (Preferred Modes for Measuring Temperature)
[0122] Examples of the preferred modes for measuring temperature in
accordance with the present invention are presented below.
[0123] (1) A mode of measuring the temperature of the front surface
or inside of a substrate by irradiating the front surface or rear
surface of the substrate, whose temperature is to be measured, with
light and measuring the interference of the reflected light from
the substrate and the reference light, and adjusting and/or
controlling other variables based on the measurement result.
[0124] (2) A mode in which the temperature to be measured is the
temperature of the front surface of the substrate, and the variable
is the temperature of a susceptor for holding the substrate.
[0125] (3) A mode in which the temperature to be measured is the
temperature of the front surface of the substrate, and the variable
is at least one process parameter selected from the group
consisting of the total flow rate of a gas to be supplied into a
container containing the substrate, gas flow rate ratio, gas
pressure, plasma-generating power, and bias power.
[0126] (4) A mode in which the temperature to be measured is the
temperature distribution on the front surface, and the variable is
at least one selected from the group consisting of zone control of
the susceptor temperature, attraction force zone control of the
susceptor electrostatic chuck, and zone control of
plasma-generating power.
[0127] (5) A mode in which the temperature to be measured is the
temperature distribution on the front surface, and the variable is
at least one selected from the group consisting of the total flow
rate of a gas to be supplied into a container containing the
substrate or distribution of the total flow rate, gas flow rate
ratio or distribution thereof, gas pressure, plasma-generating
power, and bias power.
[0128] (6) A mode in which the temperature to be measured is the
temperature history of the front surface while the substrate is
being processed, and the adjustment and/or control of the variable
is conducted as part of APC processing (statistic processing of
data with the object of controlling subsequent device substrate
treatment) based on the decision relating to the treatment
results.
[0129] (Preferred Combinations with Other Processes)
[0130] The above-described method for measuring temperature in
accordance with the present invention may be combined, if
necessary, with other processes. No specific limitation is placed
on "other processes" that have to be thus combined, provided that
they are the processes in which the temperature of the substrate to
be treated, produces a certain effect. From the standpoint of
possibility of the temperature producing an especially large
effect, it is preferred that a combination with etching, film
formation, heat treatment such as annealing, and the like be
employed.
[0131] Examples of preferred combinations with the other processes
preferred in accordance with the present invention are described
below.
[0132] (1) A mode of measuring the temperature of the front surface
or the inside of a substrate by irradiating the front surface or
rear surface of the substrate, whose temperature is to be measured,
with light and measuring the interference of a reflected light from
the substrate and a reference light, and adjusting and/or
controlling a variable relating to the treatment of the substrate
based on the measurement result.
[0133] (2) A mode in which the treatment of the substrate is the
formation of a film on the substrate.
[0134] (3) A mode comprising measuring the surface temperature or
the average temperature inside the substrate prior to the treatment
and determining the starting point of the treatment.
[0135] (4) A mode in which the treatment is started by turning on
the plasma-generating power and/or bias power; a mode comprising
measuring the film thickness during the treatment and determining
the end point of the treatment.
[0136] (5) A mode comprising measuring the temperature of the
second layer from the surface during the treatment and employing it
as a temperature of the outermost surface (the surface of the
substrate where the film has been formed).
[0137] (6) A mode in which the treatment of the substrate is
etching of the substrate.
[0138] (7) A mode comprising measuring the surface temperature or
the average temperature inside the substrate prior to the treatment
and determining the starting point of the treatment.
[0139] (8) A mode in which the treatment is started by turning on
the plasma-generating power and/or bias power.
[0140] (9) A mode comprising measuring the temperature of the
layer, which is to be treated, during the treatment. A mode
comprising measuring the temperature of the second layer from the
surface during the treatment and employing it as a temperature of
the outermost surface (the surface of the substrate where the film
has been formed).
[0141] (Substrate)
[0142] In accordance with the present invention, no specific
limitation is placed on the configuration of the substrate whose
temperature is to be measured. Thus, the temperature measurement in
accordance with the present invention can be conducted on a
substrate composed of a substantially single material and/or a
substrate comprising a plurality of layers or portions. In
accordance with the present invention, substrates for
semiconductors (for example, Si wafers), substrates for
liquid-crystal devices, and substrates for micromachines can be
advantageously used.
[0143] (Examples of Preferred Substrates)
[0144] Examples of substrates on which temperature measurements can
be conducted advantageously in accordance with the present
invention are described below.
[0145] Si substrates.
[0146] Quartz substrates.
[0147] SiO.sub.2 substrates.
[0148] Si.sub.3N.sub.4 substrates.
[0149] Substrates comprising layers of the above-mentioned
materials.
[0150] Substrates used in the LSI fabrication process.
[0151] (Principle of Temperature Measurements)
[0152] In accordance with the present invention, it is preferred
that the temperature of the substrate surface be measured by using
interference based on a low-coherence light. No specific limitation
is placed on the interference measurement method that can be used
in accordance with the present invention. However, it is preferred
that a Michelson's interferometer be used as a base device because
it measures interference from one side of the substrate.
[0153] (Low-Coherence Interferometer)
[0154] A diagram (block diagram) illustrating an example of the
entire low-coherence interferometer that can be advantageously used
in accordance with the present invention is shown in FIG. 1. This
low-coherence interferometer is based on the Michelson's
interferometer. As shown in FIG. 1, a SLD (Super Luminescent Diode)
having a low degree of coherence is used as a light source, the
light emitted from the light source is divided into two beams with
a beam splitter, one of the beams is reflected by each layer toward
the measurement object, and the other beam propagates to a
reference mirror and is reflected. At this time, the respective
light beams are classified as "physical light" and "reference
light". The beams then reach the beam splitter again, where they
are superimposed and undergo interference, followed by the
detection with a light receiving device.
[0155] When such measurements are conducted, the reference mirror
is driven to obtain information in the depth direction of the
measurement object.
[0156] The coherence length of the light from the light source is
small due to a low degree of coherence of the light source.
Therefore, strong interference occurs in zones where the optical
path length of the physical light matches the optical path length
of the reference light (usually, the interference decreases
substantially in other zones). When the reference mirror is driven
back and forth and the optical path length of the reference light
is changed, the reference light and the reflected light caused by
the difference in refractive index in each layer of the measurement
body interfere. As a result, measurements in the depth direction of
the measurement body become possible.
[0157] (Measurement Principle of Low-Coherence Interferometer)
[0158] When the distance from the beam splitter to the reference
mirror in the low-coherence interferometer shown in FIG. 1 is
considered as a distance to the measurement object, if the plane
light waves that are reflected by the reference mirror and
measurement object and reach the light receiving devices are
represented as
e.sub.1(t)=E.sub.1 cos(2.pi.ft-2kl.sub.1-.phi.) (2-1)
e.sub.2(t)=E.sub.2{square root}, {square root over (R)}
cos(2.pi.ft-2kl.sub.2-.phi.) (2-2)
[0159] then the photoelectric current from the light receiving
device will be as follows:
i=.vertline.e.sub.1(t)+e.sub.2(t).vertline..sup.2=i.sub.DC+.sub.1
(2-3)
[0160] Here, .kappa.=2.pi.f/c, f denotes a frequency, c--a light
speed, and R--a reflection factor of the measurement object
surface. In the photoelectric current,
i.sub.DC=(E.sub.1.sup.2+E.sub.2.sup.2)/2 is a direct current
component and
/.sub.1=E.sub.1E.sub.2{square root}{square root over (R)}
cos(4.pi.f.DELTA.l/c) (2-4)
[0161] is an optical interference term in which the difference in
optical path lengths is a variable of a sine function.
[0162] Formula (2-4) presented hereinabove suggests that in optical
interference measurements using a low-coherence interferometer, the
optical interference signal can be considered as a sum of a large
number of sine functions with different periods. This can be
mathematically represented in the following form.
.sub.1.intg.E.sub.1E.sub.2{square root}{square root over (R)}
cos(4.pi.f.DELTA.l/c).multidot.S(f)df (2-5)
[0163] Here, if the function is considered as a Gauss function of a
central frequency, then equation (2-5) can be presented as follows.
1 i ~ 1 = E 1 E 2 R exp { - [ l l c 2 ln 2 ] 2 } cos ( 2 k l ) ( 2
- 6 )
[0164] Here, l.sub.c is a coherence length. When the reference
light mirror is moved as a speed v, then the results are affected
by the Doppler shift and the following representation is possible:
f.sub.D=2v/.lambda..sub.O. .lambda..sub.O is a central wavelength
of the light source.
[0165] (Phase Changes Caused by Changes in Temperature)
[0166] Because the sample of the temperature measurement system is
heated with a heater or the like, the sample is expanded and the
refractive index thereof changes. Therefore, the width of the peak
position of the interference waveform obtained with the temperature
measurement system after the temperature has changed differs from
those prior to changes in temperature. Accordingly, changes in
temperature can be detected by accurately measuring the peak
position, with the interference waveform obtained with the width
displacement measurement system as a standard, or by accurately
measuring the movement time of reference light optical path length
variation means which moves with a constant speed pattern.
[0167] Let us consider measurement samples denoted by A and B in
FIG. 2. Here, the thickness and refractive index of the measurement
sample A is d.sub.1 and n.sub.1, respectively. The thickness and
refractive index of the measurement sample B is d.sub.2 and
n.sub.2, respectively. As for the interference waveform obtained by
using a Michelson's interferometer, it was mentioned above that an
interference waveform shown in the frame in the lower right portion
of FIG. 2 is obtained due to the interference of the reflected
light from the surface of A, boundary surface of A and B, and rear
surface of B, when the incident light and measurement samples A, B
are disposed relative to each other as shown in the figure.
[0168] For example, if we assume that the interference waveform
detected at room temperature has a spacing as shown on the upper
side in the frame, then if the temperature of the measurement
samples is increased, the positions of the peaks in two positions
of the interference waveform peaks located in three positions will
shift with respect to one end as a reference, due to thermal
expansion and changes in the refractive index depending on the
temperature of each measurement sample. This shift, with respect to
thickness, depends on the "linear thermal expansion coefficient
.alpha.", which is inherent to each sample and, with respect to
changes in the refractive index, depends on the "temperature
coefficient .beta. of changes in the refractive index", which is
inherent to each sample. If the thickness and refractive index
after changes in temperature are denoted by d.sub.1' and n.sub.1',
respectively, for the measurement sample A, then they can be
represented as follows:
d'.sub.1=d.sub.1(1+.alpha..sub.A.DELTA.T.sub.1),
n'.sub.1=n.sub.1(1+.beta.- .sub.A.DELTA..sub.T1) (2-7)
[0169] Similarly, if the thickness and refractive index after
changes in temperature are denoted by d.sub.2' and n.sub.2',
respectively, for the measurement sample B, then they can be
represented as follows:
d'.sub.2=d.sub.2(1+.alpha..sub.B.DELTA.T.sub.2),
n'.sub.2=n.sub.2(1+.beta.- .sub.B.DELTA.T.sub.2) (2-8)
[0170] Here, assigning respective indexes to the linear thermal
expansion coefficient a and temperature coefficient .beta. of
changes in the refractive index means that those are the values
inherent to each sample. Furthermore, the temperature in each layer
is supposed to be uniform. If the state changes due to changes in
temperature, then optical path length of the light passing through
each sample will also change. The optical path length is determined
as a product of the thickness and refractive index. Therefore, if
the optical path length of the light that passes through the
measurement sample A prior to changes in temperature is denoted by
1.sub.A, then
1.sub.A=n.sub.1d.sub.1 (2-9)
[0171] and the optical path length after the temperature has
changed by .DELTA.T becomes
1'.sub.A=n'.sub.1d'.sub.1 (2-10).
[0172] Similar changes are also valid for the measurement sample
B.
1.sub.B=n.sub.2d.sub.2 (2-11)
1'.sub.B=n'.sub.2d'.sub.2 (2-12)
[0173] Therefore, the difference in the results before and after
changes in temperature corresponds to the phase shift of the
interference waveform. As a result, the interference waveform shown
in the lower part inside the frame in FIG. 2 is obtained. Reading
this shift in phase caused by changes in temperature makes it
possible to determine changes in temperature of each measurement
sample.
[0174] (System Configuration)
[0175] In accordance with the present invention, no specific
limitation is placed on the measurement system, provided that the
interference between the reflected light from the substrate and the
reference light can be measured by irradiating the substrate, whose
temperature is to be measured, with a low-coherence light. From the
standpoint of accurately reading the phase shift, the
below-described system configuration can be advantageously
used.
[0176] (Example of Preferred System Configuration for Measuring
Temperature)
[0177] A structural diagram (block diagram) illustrating an example
of the system of measuring temperature and characteristics of the
system are shown in FIG. 3 and Table 1. A schematic drawing of the
actual measurement system is shown in FIG. 4.
1 Light source of SLD (Super Luminescent) temperature Wavelength:
1.55 .mu.m, output: 1.5 mW measurement system (MAX), coherence
length: about 50 .mu.m Light source of LD (Laser Diode)
displacement Wavelength: 1.55 .mu.m measurement system Light
receiving Ge photodiode device Sensitivity (1.55 .mu.m): 0.8 A/W
Reference mirror Voice coil motor operation Maximum motion
distance: 6 mm Operating frequency: 0-30 Hz Motion speed (30 Hz
operating): <360 mm/s
[0178] This system is based on the Michelson's interferometer and a
specific feature thereof is that it uses optical fibers.
[0179] As shown in FIG. 3 and Table 1, the present system uses two
2.times.2 optical fiber couplers. One of them provides the light
source with a low coherence ability and high luminosity and uses a
SLD (Super Luminescent Diode) with a central wavelength of 1.55
.mu.m and a coherence length of about 50 .mu.m. Stability of this
light source is ensured by conducting electric current control with
a LD drive unit equipped with a temperature controller. The light
falling from the (a) end of the optical fiber is split to the (b)
end and (c) end, and the light irradiated from the collimator
fibers of the (b) end is reflected by the front surface of each
layer of the layered structure, boundary surfaces, or rear
surfaces. Furthermore, the configuration is such that the light
outgoing from the collimator fiber of the (c) end is reflected by
the corner cube prism used as a reference mirror. The respective
reflected lights are again combined in the optical fiber coupler 1,
and an interference waveform is detected with a PD (Photo Detector)
1 using a Ge photodiode. Those components constitute a temperature
measurement system for measuring changes in temperature occurring
when the measurement sample is warmed with a heater.
[0180] Here, the fixed corner cube prism is driven back and forth
with the voice coil motor employing a speaker drive principle, with
a maximum displacement being 6 mm, in order to change the reference
light optical path length. Thus using the voice coil motor makes it
possible to measure a large depth with a high speed. Therefore, in
terms of depth distance to the measurement sample and measurement
speed, the degree of freedom in designing the system can be
increased with respect to that of a piezoelectric element.
[0181] Another optical fiber coupler uses a LD (Laser Diode) with a
central wavelength of 1.55 .mu.m. Similarly, the light outgoing
from the (b') end and (c') end is reflected by the corner cube
prism and fixed mirror. The respective reflected lights are
combined with a coupler 2 and detected with a PD 2 as an
interference signal. Those components serve as a reference for the
displacement of the above-mentioned voice coil motor and represent
a mechanism for reading the displacement with a high accuracy.
Therefore, they constitute a displacement measurement system.
[0182] The interference waveforms detected by the temperature
measurement system and displacement measurement system are
introduced into a personal computer by using a 12-bit A/D board
with 0.5 Hz-maximum 500 kHz and the phase shift is studied with a
program.
[0183] Using optical fibers in the above-described systems makes it
possible to reduce the effect of the external stray light.
Furthermore, the optical coupler fibers in the temperature
measurement system and displacement measurement system in the
above-described system are coated with a thermally insulating
material in order to eliminate the effect of changes in temperature
caused by the atmosphere or the like. Further, the heater and
measurement sample are accommodated in a case lined with a
thermally insulating material on the inner side. Thus, such
constant temperature control of the system is very desirable for
constantly maintaining the components other than the heater and
measurement samples under identical conditions.
[0184] (Method for Measuring Temperature of a Layered
Structure)
[0185] With the measurement method in accordance with the present
invention, it is possible to measure the temperature not only of a
substrate composed of a single material, but also the temperature
of each layer in a substrate containing a plurality of material
layers. The measurement principle in such a mode of the present
invention will be described below.
[0186] (Temperature Coefficient of Linear Thermal Expansion
Coefficient and Changes in Refractive Index)
[0187] Temperature coefficient of linear thermal expansion
coefficient and changes in the refractive index, which are the
important parameters from the standpoint of conducting temperature
measurement of layered structures, will be explained prior to
describing the measurement method.
[0188] First, linear expansion will be considered. When a rod with
a length l.sub.o at a temperature of 0.degree. C. is heated to a
temperature T.degree.C., the length thereof is increased. Within a
range in which the temperature is not too high, the increased
length generally can be represented by the following formula:
1.sub.T=l.sub.o(1+.alpha.T+.alpha.'T.sup.2) (3-1)
[0189] Here, .alpha., .alpha.' are the constants specific for the
substance. In usual solid bodies, .alpha. is very small and
.alpha.' assumes an even smaller value. In case T is small, the
third term in the right side of equation (3-1) presented above can
be ignored, and l.sub.T can be considered to be increasing
proportionally to T, then the equation:
l.sub.T=l.sub.O(1+.alpha.T), or .alpha.=(1.sub.T-l.sub.O)/l.sub.OT
(3-2)
[0190] shows the ratio of expansion per unit length measured at
0.degree. C. when the temperature increases by 1.degree. C. within
a range from 0.degree. C. to T.degree. C., and this ratio is called
a linear expansion coefficient of the substance. Furthermore, in
this case it can be assumed that the value of .alpha. does not
change even if the temperature prior to expansion is not 0.degree.
C. For example, if l.sub.1, l.sub.2 denote the length of a rod at
any temperature, T.sub.1, T.sub.2.degree. C., then
l.sub.1=l.sub.O(1+.alpha.T.sub.1) or
l.sub.2=l.sub.O(1+.alpha.T.sub.2) (3-3)
.thrfore.l.sub.2=l.sub.1(1+.alpha.T.sub.2)/(1+.alpha.T.sub.1)=l.sub.1(1+.a-
lpha.T.sub.2) (1-.alpha.T.sub.1) (3-4)
[0191] If the temperature T.sub.1, T.sub.2 is not too high,
then
l.sub.2=l.sub.1{1+.alpha.(T.sub.2-T.sub.1)} or
.alpha.=(l.sub.2-l.sub.1)/l- .sub.1(T.sub.2-T.sub.1) (3-5).
[0192] .alpha. can be determined from this equation.
[0193] However, when the third term in the right side of equation
(3-1) cannot be ignored, .alpha. changes with temperature.
Therefore, the linear expansion coefficient has to be considered
for each temperature. If we assume that the rod with a length, l,
at a temperature T.degree. C. expands by .DELTA.l when the
temperature rises by .DELTA.T, then linear expansion coefficient
.alpha..sub.T at temperature T.degree. C. will be represented by
the following formula. 2 T = lim T 0 l l T = 1 l l T ( 3 - 6 )
[0194] Within a temperature range from 0 to 100.degree. C., it is
not necessary to distinguish .alpha. and .alpha..sub.T for usual
substances and any of them can be considered as representing the
linear expansion coefficient of the substance.
[0195] The thickness of Si and SiO.sub.2 samples used in this
example wais 360 .mu.m and 1 mm, respectively, and a temperature
distribution obviously exists inside each of the substances.
However, in multilayer structures, thermal conductivity is most
often differs significantly between the layers and the difference
in average temperature between the layers is larger than the
difference representing temperature distribution in each layer. For
this reason, in the present measurement method, the temperature
distribution inside the substance is ignored and the temperature is
assumed to be uniform. The expansion coefficient of Si has already
been studied and expansion coefficients of Si at different
temperatures have been found, as shown in FIG. 3-3 (J. A.
McCaulley, V. M. Donnelly, M. Vernon, and I. Taha, "Temperature
dependence of the near-infrared refractive index of silicon,
gallium arsenide, and indium phosphide", Phy. Rev. B49, 7408,
1994).
[0196] Here, if the graph is approximated by a curve of second
order in a range from 0.degree. C. to 500.degree. C., then
.alpha..sub.si will be represented by the following formula (the
above-mentioned publication by J. A. McCaulley et al.).
.alpha..sub.si=-7.06.times.10.sup.-11.times.T.sup.2+6.83.times.10.sup.-8.t-
imes.T+2.38.times.10.sup.-6 (3-7)
[0197] Furthermore, because presently there are no sufficient data
for SiO.sub.2, the linear expansion coefficient of SiO2 will be
approximated by a constant value as follows.
.alpha..sub.SiO2=5.times.10.sup.-7 (3-8)
[0198] Further, the temperature coefficient of changes in the
refractive index is an example of one more factor causing a phase
shift of the SLD interference waveform. Research relating to the
temperature coefficient, .beta., of changes in the refractive index
has been conducted. The results are shown by a graph in FIG. 6.
This temperature coefficient is known to depend on a wavelength.
The graph in FIG. 6 also shows that the value of .beta. increases
with the increase in temperature. Therefore, because the optical
path length can be found as a product of refractive index and
distance, it can become a reason why changes in temperature cause a
shift in the peak of the SLD interference waveform.
[0199] If an approximation with a curve of second order is made for
a temperature range from 0.degree. C. to 500.degree. C., similarly
to the linear expansion coefficient, the temperature coefficient
.beta..sub.Si,1.55 of changes in the refractive index of Si with
respect to light with a wavelength of 1.55 .mu.m can be given by
the following formula (the above-mentioned publication by J. A.
McCaulley et al.).
.beta..sub.Si,1.55=-3.33.times.10.sup.-11.times.T.sub.2+6.76.times.10.sup.-
-8.times.T+5.01.times.10.sup.-5 (3-9)
[0200] (Method for Measuring Temperature)
[0201] A measurement method relating to Si and SiO.sub.2 shown in
FIG. 7 as measurement objects will be described below. An
interference waveform from the reflected light from the front
surface and rear surface of each layer and the reference light is
obtained by driving the reference mirror back and forth with a
voice coil motor.
[0202] Referring to FIG. 7, the distance to the surface of
SiO.sub.2 and reference mirror in case the voice coil motor is in a
standard position will be considered the same. Refractive indexes
of Si and SiO.sub.2 prior to changes in temperature will be denoted
by n.sub.si and n.sub.SiO2 and the respective thicknesses will be
denoted by d.sub.si and d.sub.SiO2. In this case, the optical path
length of the light passing through SiO.sub.2 can be represented by
the following formula
1.sub.SiO2=n.sub.SiO2.multidot.d.sub.SiO2 (3-10)
[0203] If the temperature of SiO.sub.2 changes by .DELTA.T.sub.1
under the effect of the heater, then the refractive index changes
as represented by the following formula under the effect of
temperature coefficient .beta..sub.SiO2 of changes in the
refractive index, which depend on the wavelength, and the thickness
changes as represented by the following formula under the effect of
expansion coefficient .alpha..sub.SiO2.
n.sub.SiO2.fwdarw.n.sub.SiO2(1+.beta..sub.SiO2.DELTA.T.sub.1)
(3-11)
d.sub.SiO2.fwdarw.d.sub.SiO2(1+.alpha..sub.SiO2.DELTA.T.sub.1)
(3-12)
[0204] Therefore, the optical path length after the changes in
temperature becomes
l'.sub.SiO2=n.sub.SiO2(1+.beta..sub.SiO2.DELTA.T).multidot.d.sub.SiO2(1+.a-
lpha..sub.SiO.sub.2.DELTA.T) (3-13).
[0205] If the difference between the result obtained before the
changes in temperature and after the changes in temperature is
found, then from
.alpha..sub.SiO2.multidot..beta..sub.SiO2<<.alpha..sub.SiO2,
.beta..sub.SiO2, the following can be obtained.
l'.sub.SiO2-l.sub.SiO2=n.sub.SiO2.multidot.d.sub.SiO2(.alpha..sub.SiO2+.be-
ta..sub.SiO.sub.2).DELTA.T.sub.1 (3-13).
[0206] Thus, changes in temperature .DELTA.T.sub.1 can be found by
examining in advance the temperature coefficient .beta..sub.SiO2 of
changes in the refractive index and linear expansion coefficient
.alpha..sub.SiO2 in SiO.sub.2.
[0207] Similarly, changes in temperature can be found for Si by
examining .alpha..sub.Si and .beta..sub.Si.
[0208] (Method for Finding Changes in Temperature from Interference
Waveform)
[0209] A method for finding changes in temperature from the
interference waveform detected with the present system will be
described. The explanation will be conducted with respect to Si as
an example of the measurement material.
[0210] FIG. 8 shows an image including the SLD interference
waveform obtained with the temperature measurement system according
to a program and the LD interference waveform from the displacement
image system. The reflected lights from the front surface of Si and
rear surface of Si and the reflected light from the corner cube
prism interfere and the interference waveform shown in FIG. 8 is
obtained.
[0211] As shown in FIG. 8, two peaks can be observed in the SLD
interference waveform, but the left and right peaks clearly have
different size. This is because normally incident lights are
reflected on the boundary surface of substances with different
refractive indexes n.sub.1, n.sub.2. Here, the reflection factor of
the light at the boundary surface can be given by the following
equation. 3 = n 1 - n 2 n 1 + n 2 ( 3 - 15 )
[0212] Therefore, the reflected light intensity R becomes 4 R = 2 =
n 1 - n 2 n 1 + n 2 2 ( 3 - 16 )
[0213] The first interference peak is formed by the light reflected
from the front surface of Si. On the other hand, the quantity of
light transmitted through the front surface of Si is reduced by the
light absorption quantity inside the Si and the quantity of
reflected light, and the light that was transmitted through the
front surface undergoes reflection on the rear surface of Si. As a
result, a difference appears between the right and left peaks of
the SLD interference waveform. Those two peaks are detected
according to the program and the positions thereof are stored in a
memory. The wave number between the two points of the peaks and the
phase shift at both ends are then read out with respect to the LD
interference waveform which is a standard. Changes in temperature
are then derived from the aforementioned equation (3-14) by
acquiring the interference waveforms before and after changes in
temperature as described hereinabove and investigating the wave
number of the LD interference waveform between two peaks of the SLD
interference waveform.
[0214] (Several Usual Methods for Measuring Temperature)
[0215] 1) In accordance with the present invention, the value that
can be directly measured by the interference waveform of the
optical system is (n. d) (n is a refractive index, d is a film
thickness).
[0216] (Measurement Method--1)
[0217] In temperature measurements or a substrate treatment
apparatus for electronic devices, the temperature control of the
sample is conduced in a load-lock chamber, or a measurement
chamber, or an OFF-System (separate system) and
(.alpha.+.beta.).sub.m is measured at several temperatures T.sub.m
(including a process temperature T.sub.p). The following formula
can be thus obtained.
(n.sub.m+1d.sub.m+1)-(n.sub.m.multidot.d.sub.m)=(n.sub.m.multidot.d.sub.m)
(.alpha.+.beta.).sub.m(T.sub.m+1-T.sub.m) and then, 5 ( + ) m = ( n
m + 1 d m + 1 ) - ( n m d m ) ( n m d m ) ( T m + 1 - T m ) .
[0218] Here, (.alpha.+.beta.).sub.p is the temperature coefficient
at the initial temperature of the susceptor during the process (it
is preferred that the temperature control of the susceptor be
freely conducted).
[0219] The sample is then transferred onto the susceptor present in
the treatment chamber and a measurement value
(n.sub.t.multidot.d.sub.t) at a transition temperature of the
sample is obtained. If the difference with
(n.sub.p.multidot.d.sub.p) that was determined in advance is within
a certain range, the process is started. A process start signal is
outputted.
[0220] If the process is started, (n.sub.x.multidot.d.sub.x) is
measured. Initially, T.sub.x is not known therefore, T.sub.x is
calculated in the following manner by using (.alpha.+.beta.).sub.p
at the process temperature T.sub.p.
(n.sub.t.multidot.d.sub.t)-(n.sub.p.multidot.d.sub.p)=(n.sub.p.multidot.d.-
sub.p).alpha.+.beta.).sub.p(T.sub.x-T.sub.p) 6 T x = ( n x d x ) -
( n p d p ) ( n p d p ) ( + ) p + T p
[0221] From the next measurement cycle, the measured value of the
optical path length at this point in time is anew considered as
(n.sub.x.multidot.d.sub.x) under an assumption that
T.sub.x.apprxeq.T.sub.m'. At this time, the temperature to be
measured anew, is denoted by T.sub.x and calculated in the
following manner by replacing with the values T.sub.m,
(.alpha.+.beta.).sub.m measured in a temperature zone including,
for example, T.sub.m' from the data representing the temperature
dependence of (.alpha.+.beta.) for which (.alpha.+.beta.).sub.m' at
the temperature T.sub.m' were measured in advance.
(n.sub.x.multidot.d.sub.x)-(n.sub.m.multidot.d.sub.m)=(n.sub.m.multidot.d.-
sub.m)(.alpha.+.beta.).sub.m(T.sub.x-T.sub.m) 7 T x = ( n x d x ) -
( n m d m ) ( n m d m ) ( + ) m + T m
[0222] The temperature of each layer can be then measured by
repeating this operation.
[0223] In order to simplify calculations, all the T.sub.x may be
computed by using the (.alpha.+.beta.).sub.p. Alternatively, when
T.sub.m>T.sub.p, all the T.sub.x may be computed by employing
the arithmetic average value of (.alpha.+.beta.).sub.m as
(.alpha.+.beta.).sub.m'.
[0224] (Measurement Method--2)
[0225] (n.sub.r.multidot.d.sub.r) is measured at room temperature
T.sub.r in the load-lock chamber, or measurement chamber, or
OFF-System.
[0226] The temperature coefficient (.alpha.+.beta.).sub.r is
calculated in the following manner from the above-described
measured values.
[0227] The sample is then transferred onto the susceptor located
inside the treatment chamber and (n.sub.p.multidot.d.sub.p) is
measured at the temperature T.sub.p after the temperature becomes
constant.
[0228] The following result is obtained.
(n.sub.p.multidot.d.sub.p)-(n.sub.r.multidot.d.sub.r)=(n.sub.r.multidot.d.-
sub.r)(.alpha.+.beta.).sub.r(T.sub.p-T.sub.r) 8 ( + ) r = ( n p d p
) - ( n r d r ) ( n r d r ) ( T p - T r )
[0229] The process is then started.
[0230] If the process is started, (n.sub.x.multidot.d.sub.x) is
measured and the temperature T.sub.x is calculated in the following
manner by using the above-described (.alpha.+.beta.).sub.r.
(n.sub.x.multidot.d.sub.x)-(n.sub.p.multidot.d.sub.p)=(n.sub.p.multidot.d.-
sub.p)(.alpha.+.beta.).sub.r(T.sub.x-T.sub.p) 9 T x = ( n x d x ) -
( n p d p ) ( n p d p ) ( + ) r + T p
[0231] (Measurement of Temperature of the Outermost Layer During
Process Execution)
[0232] (1) In case of a heat treatment process, the shape of the
outermost surface is not changed. Therefore, the measurements can
be conducted by the usual measurement method.
[0233] (2) In case of an etching process, the temperature of the
outermost layer can be measured by the usual measurement method by
processing and measuring the interference wavelength determined by
the reflected light from the layer below the mask.
[0234] For example, the etching rate can be calculated by the
following formula after measuring the interference wavelength
determined by the reflected light from the region which is being
etched, if the temperature is considered to be equal to the
temperature below the aforementioned mask. 10 Etching rate = ( n p
d p ) - ( n x d x ) t x
[0235] (t.sub.x is elapsed time)
[0236] Further, the end signal (end point) of the process can be
obtained with (n.sub.x.multidot.d.sub.x)=.phi.. Alternatively, the
process can be ended.
[0237] The etching depth and etching rate can be computed. 11
Etching depth = ( n p d p ) - ( n x d x ) n p Etching rate = ( n p
d p ) - ( n x d x ) n p t
[0238] (n.sub.p.multidot.d.sub.p) is the optical path length below
the mask.
[0239] (n.sub.x.multidot.d.sub.x) is the optical path length of the
region which is being etched.
[0240] (3) In the case of a film deposition process, several
physical properties are obtained in advance at a temperature close
to the process temperature from a sample subjected to film
deposition, by using light with two wavelengths: a wavelength
.lambda..sub.1 at which the changes in the refractive index caused
by temperature are large and a wavelength .lambda..sub.2 at which
the changes in the refractive index are small.
[0241] In the process, the optical path lengths
(n.sub..lambda.1.multidot.- d.sub..lambda.1),
(n.sub..lambda.2.multidot.d.sub..lambda.2) corresponding to
respective two wavelengths are measured and the temperature is
computed from the aforementioned physical properties that were
found in advance. (Preferred measurement method--1) Example of a
method for measuring temperature and film thickness during film
deposition
[0242] In this case, the measurements can be conducted by using two
wavelengths in a low-coherence interferometer. In this case, the
light source means may preferably comprise two light sources, one
of which has a wavelength providing a relatively large temperature
coefficient of change in refractive index of the substrate, and the
other of which has a wavelength providing a relatively small
coefficient of temperature change in the refractive index of the
substrate.
[0243] For example, when silicon is deposited on glass, a LED or
SLD with a wavelength close to 980 nm (.lambda.1), at which the
temperature-induced changes in the refractive index are large, is
preferably used. At .lambda.1, changes in the spacing between the
interference peaks of the front surface and rear surface of a
silicon layer with respect to those at the initial temperature are
measured as changes in the optical path length
n1d(.alpha.+.beta.1).DELTA.T. Then, they are similarly measured as
n2d(.alpha.+.beta.2).DELTA.T at a wavelength close to 1.5 .mu.m.
.DELTA.T is considered as the change in temperature from the
initial temperature. The changes, .beta.2, in the refractive index
caused by temperature at a wavelength close to 1.5 .mu.m are less
than .beta.1 by more than an order of magnitude, as can be judged
by the absorption characteristic. If the ratio is taken, then
n1(.alpha.+.beta.1)/n2(.alpha.+.beta.2) is obtained and d is
eliminated. The dependence of this ratio on temperature is measured
in advance and the temperature is calculated.
[0244] If the dependence of n1 on temperature is found in advance
with the OFF.cndot.System by the method described in "Optical
Technology", p. 305-330, Lecture 6 on Experimental Physics,
published by Kyoritsu Shuppan Co., then when the temperature
T.sub.x is calculated as described hereinabove (for example, in the
form of a table), then the n1.sub.x corresponding thereto can be
inversely calculated, for example, from the table, and the
following expression can be obtained. 12 d = ( n1x d ) n1 x
[0245] (n1.sub.x.multidot.d) is the measured value.
[0246] (Measurement Method--2)
[0247] n1 depends on temperature with respect to .lambda..sub.1
close to process temperature T.sub.p, but n2 is almost constant
with respect to .lambda..sub.2.
[0248] Physical values are measured in advance with the
OFF.cndot.System, while conducting temperature control of materials
after film deposition. For example, close to the initial process
temperature T.sub.p, n1.sub.p with respect to wavelength
.lambda..sub.1, n2 with respect to .alpha.+.beta.1 wavelength
.lambda..sub.2, .alpha.+.beta.2 (.beta.2.apprxeq..phi.).
[0249] A method for measuring the refractive index is described,
for example, in "Optical Technology", p. 305-330, Lecture 6 on
Experimental Physics, published by Kyoritsu Shuppan Co.
[0250] The sample is transferred onto a susceptor located in the
treatment chamber, and after the process is started, the optical
path length (n2.sub.x.multidot.d.sub.x) at the time of temperature
T.sub.x is measured at the wavelength .lambda..sub.2 at which "the
above-described method can be used for the process start timing",
and because n2x.apprxeq.n2(.beta.2.apprxeq..phi.), the following
can be obtained. 13 d x = ( n2 x d x ) n2
[0251] At wavelength .lambda..sub.1, from the formula describing
changes in the optical path, and by using the already known
physical values, the temperature T.sub.x can be calculated in the
following manner.
(n1.sub.x.multidot.d.sub.x)-(nl.sub.p.multidot.d.sub.p)=(nl.sub.p.multidot-
.d.sub.p) (.alpha.+.beta.1) (T.sub.x-T.sub.p)
[0252] 14 T x = ( n1 x x ) - ( n1 p d p ) ( n1 p p ) ( + 1 ) + T
p
[0253] Here, n1.sub.p, (.alpha.+.beta.1) were measured in
advance,
[0254] T.sub.p is already known,
[0255] d.sub.p=d.sub.x.
[0256] Alternatively, the dependence of nl.sub.m on temperature is
represented in advance in the form of a table by using wavelength
.lambda..sub.1, the optical path length (n.sub.x.multidot.d.sub.x)
is measured in the course of the process, and the following can be
obtained at .lambda..sub.2: 15 d x = ( n2 x d x ) n2
[0257] At .lambda..sub.1, the following can be obtained: 16 n1 x =
( n1 x x ) x
[0258] The temperature at the time of nl.sub.x can be calculated by
using inversely the aforementioned table. 30 nm,
.lambda..sub.2.apprxeq.1.5 .mu.m (when the front surface layer is a
deposited Si film).
[0259] (In the Case of Film Deposition Process)
[0260] For example, the interference intensity ratio of the
low-coherence interferometer can be used. An example in which a
two-layer substrate composed of glass and silicon is used for
measurements will be considered below. Usually, when the substrate
does not absorb in the layer where measurements are conducted, the
reflection intensity
{.vertline.n.sub.Si-n.sub.Vac.vertline./{.vertline.n.sub.Si+n.sub.Vac.ver-
tline.}.sup.2 is simply determined from the refractive index at
each boundary. If a wavelength of an order of 1 .mu.m is used, the
light is absorbed. Therefore, the quantity of the light reflected
from the silicon surface is decreased by the absorbed amount and is
equal to
{.vertline.n.sub.Si-n.sub.Vac.vertline./{.vertline.n.sub.Si+n.sub.Vac.ver-
tline.}.sup.2 exp(-a2d) (a is an absorption coefficient, d is a
film thickness).
[0261] The quantity of light reflected from the boundary surface of
silicon and glass does not pass through the silicon layer and
therefore becomes:
{.vertline.n.sub.Si-n.sub.g.vertline./{.vertline.n.sub.Si+n.sub.-
g.vertline.}.sup.2.
[0262] As for the changes in the optical path length caused by
low-coherence interferometer during deposition, changes in the
phase caused by changes in d are usually larger than those caused
by changes in n. Therefore, for the sake of convenience, d is found
by assuming that n is constant, changes in a caused by changes in
temperature are measured in advance, and temperature is calculated
from the decrease in the quantity of the reflected light.
[0263] A method for measuring a is described in "FT-IR Basics and
Applications", p 4 year published by Tokyo Kagaku Dojin Co., Ltd.
or in "Optical Technology", p. 323-330, Lecture 6 on Experimental
Physics, published by Kyoritsu Shuppan Co.
[0264] 5) New signal from measurements during film deposition
process. The following procedure may be employed when d.sub.x has
been measured by the above-described method.
[0265] a) When there is a target thickness, the end signal of the
film deposition process can be outputted.
[0266] Alternatively, the process can be ended.
[0267] b) Film deposition rate=dx/t (t is elapsed time)
[0268] (Example of Configuration of Film Thickness and Temperature
Sensor)
[0269] FIG. 22 is a block diagram illustrating an example of
configuration of the other apparatus for measuring temperature in
accordance with the present invention. The difference between the
apparatus shown in FIG. 22 and that shown in FIG. 3 is in that a
combination of a delay line of a piezoelectric tube type, 3.times.1
coupler, and wavelength separation coupler 2.times.2 coupler is
used. With such an example illustrated by FIG. 22, the entire
optical system is equipped with optical fibers. Furthermore, the
reference optical path is almost equal to the optical path for
temperature measurement. The resultant advantage that can be
obtained is that the system is extremely stable with respect to
disturbances such as vibrations and changes in the external
temperature.
[0270] An example of the apparatus for measuring temperature or
thickness according to this embodiment, may preferably comprise:
light source means for irradiating with light the front surface or
rear surface of a substrate whose temperature or thickness is to be
measured; a splitter for splitting the light into a reference light
and a measurement light; reference light reflecting means for
reflecting the reference light; optical path changing means for
changing the optical path length of light reflected from the
reference light reflecting means; and light receiving means for
measuring the interference of the reflected light from the
substrate and the reference light from the reference light
reflecting means, wherein the temperature or thickness of the front
surface, rear surface and/or inside of the substrate is measured
based on the measurement of the interference;
[0271] wherein the light source means comprises: one light source
or two light sources having different wavelengths, for measuring
the temperature or thickness of the substrate; and a
displacement-measuring light source for measuring the displacement
in the optical path changing means; and
[0272] the light receiving means comprises: one or two
light-receiving devices corresponding to the one or two light
sources, for receiving the interference light based on the light
from the one or two light sources, which has been reflected from
the substrate and the reference light reflecting means; and a
displacement-measuring light-receiving device for receiving the
interference light based on the light from the
displacement-measuring light source, which has been reflected from
the substrate and the reference light reflecting means.
[0273] In this apparatus the light source for measuring the
temperature or thickness of the substrate may preferably have a
wavelength of 0.3-20 .mu.m, and a coherence length of 0.1-100
.mu.m.
[0274] In this apparatus the light source means may preferably
comprise two light sources, one of which has a wavelength providing
a relatively large temperature coefficient of change in refractive
index of the substrate, and the other of which has a wavelength
providing a relatively small coefficient of temperature change in
the refractive index of the substrate.
[0275] (Process Control Based on Temperature Measurements)
[0276] The mode of using the above-described method and apparatus
for measuring temperature in accordance with the present invention
is not limited to the method and apparatus for treating substrates
for devices. For example, when the method and apparatus for
measuring temperature in accordance with the present invention is
used for APC treatment (Advanced Process Control), for example, the
temperature data obtained with the above-described apparatus
(optical circuit) for measuring temperature in accordance with the
present invention can be statistically processed and process
control can be conducted based on the results obtained. In such a
process control, various process parameters (for example, total
flow rate of gas, gas flow rate ratio, gas pressure, susceptor
temperature, temperature of the front surface of the substrate,
plasma-generating power, bias power, and V.sub.dc, V.sub.pp) can be
monitored and if those parameters are within the allowed range,
"GOOD" or "OK" signal can be outputted.
[0277] If some of the parameters are outside the allowed range, an
alarm signal "SUBSTRATE FOR DEVICE (FOR EXAMPLE, WAFER) HAS TO BE
EXAMINED AGAIN" is generated and/or an alarm signal "INITIALIZATION
OR RESET OF TREATMENT SYSTEM IS REQUIRED" is generated.
[0278] (Example of Application to Etching)
[0279] An example in which the above-described method for measuring
temperature in accordance with the present invention is applied to
an apparatus for treating substrates for devices by using etching
is shown in FIG. 23 and FIG. 24.
[0280] FIG. 23 shows an example of controlling a gas flow rate or
the like based on the temperature data (single point of the
substrate) obtained by measuring temperature in accordance with the
present invention. In this case, for example, when the temperature
of the front surface or inside the substrate for a device, which is
to be treated, rises and the adhesion coefficient of gas molecules
contributing to etching decreases, a variety of process parameters
can be controlled so as to increase the flow rate of etching gas
(for example, fluorocarbon gas), decrease the power (dissociation),
decrease the bias, and/or increase the pressure.
[0281] FIG. 24 shows an example of controlling a gas flow rate and
the like based on the temperature data (multiple points on the
substrate; temperature distribution) obtained by measuring the
temperature in accordance with the present invention. In this case,
for example, the above-described various process parameters of the
substrate components corresponding to the measurement points can be
controlled based on the temperature measurement data obtained in
each point.
[0282] For example, when the ambient temperature increased, a
uniform substrate temperature is obtained by conducting zone
control of the attraction force of an electrostatic chuck or zone
control of susceptor temperature, or by increasing the flow rate
ratio of the etching gas on the periphery or decreasing the
plasma-generating power on the periphery.
(Example of Application to Film Deposition)
[0283] An example of using the above-described method for measuring
temperature in accordance with the present invention in the
apparatus for treating substrates for devices by using a film
deposition process is shown in FIG. 25 and FIG. 26.
[0284] FIG. 25 shows an example of controlling the flow rate of the
gas for film deposition based on the temperature data (single point
of a substrate) obtained by measuring temperature in accordance
with the present invention. In this case, for example, when the
temperature on the surface and inside the substrate for a device,
which is to be treated, rises and the separation of the film
formation precursor from the surface becomes significant, various
process parameters can be controlled so as to increase the flow
rate of the gas for film deposition (for example, flow rate of Si),
decrease power (ionization), decrease bias, and/or increase the
pressure.
[0285] FIG. 26 illustrates an example of controlling the flow rate
of the gas for film deposition based on the temperature data
(multiple points of a substrate; temperature distribution) obtained
by measuring temperature in accordance with the present invention.
In this case, for example, various above-described process
parameters can be controlled for a substrate portion corresponding
to the measurement points, based on the temperature measurement
data for each point.
[0286] For example, when the temperature rises in the central
portion, a uniform temperature distribution in the substrate is
obtained by using a zone control function of the electrostatic
chuck for the susceptor temperature. Alternatively, a uniform
distribution of film deposition rate is obtained by conducting
control, for example, such that increases the flow rate ratio of
the gas for film deposition in the central portion.
[0287] The present invention will be described below in greater
detail based on embodiments thereof.
EXAMPLES
Example 1
[0288] (Temperature Measurement Test; Stability of Optical
System)
[0289] A temperature measurement test was conducted by using the
above-described system shown in FIGS. 1, 3 and 4 and Table 1.
[0290] When a temperature measurement test is conducted, it is very
desirable that the stability of the measurement system be ensured
from the very beginning of the test in order to conduct the test
with a high accuracy. This is one of the reasons why optical fibers
are used as a measured against the disturbances in the
interferometer caused by the air. Furthermore, because vibrations
distort the interference waveform, the optical platform where each
component of the optical system is disposed is protected against
vibrations.
[0291] The attention should also be paid to measures relating to
temperature. Referring to the above-described system configuration,
it was mentioned that the light falling from respective light
sources is divided in two with optical fiber couplers in both the
displacement measurement system and the temperature measurement
system of the present system. However, ideally the propagating
light paths in the two split optical paths from the measurement
sample and corner cube prism in the temperature measurement system
and from the fixed mirror and corner cube prism in the displacement
measurement system to the point in which the lights are again
combined with the optical fiber coupler are the same. This is
because if the lights propagate along the paths of different
length, the optical fibers are affected differently and finally a
certain noise will be included in the data obtained. However,
because the reference light and physical body light do not
propagate inside the same optical fibers, the distal ends thereof
were disposed independently to obtain each reflection. However, at
least in order to make them close to one path, the two collimator
fibers of the temperature measurement system and two collimator
fibers of the displacement measurement system are independently
covered with a thermally insulating material and then they are
integrated and covered with a thermally insulating material thereby
eliminating thermal fluctuations from the outside of the
system.
[0292] Further, as was described hereinabove with reference to the
system configuration, the effect produced on the peripheral optical
system by the increase in the temperature of the heater was
eliminated by disposing the measurement sample and the heater in
the same case, and a constant temperature control of the entire
optical system was conducted by covering other components with a
box.
[0293] Measurements (20 sec) were conducted by picking up data from
the displacement measurement system, without driving the voice coil
motor, with respect to a configuration in which the entire optical
system was covered with a box, as shown in FIG. 9, which is
described in the following section, and a configuration in which
the entire optical system was covered with a box, as shown in FIG.
10. Time is plotted against the abscissa and output voltage is
plotted against the ordinate.
[0294] Comparison of FIG. 9 and FIG. 10 confirms that in the
optical system that became unstable, the output voltage varied
within a range of from 3 V to 8 V, as represented by amplitude
width of the graph. The figures also demonstrate that when the
stability of the optical system was not ensured, the stability was
lost in 7 to 8 sec, but when the stability of the optical system
was ensured, the stability was retained for 20 sec.
[0295] Those results suggest that in a stable optical system,
correct results can be obtained if the measurement time is at least
within 20 sec.
Example 2
[0296] (Theoretical Analysis and Test Relating to Si Monolayer)
[0297] With respect to the system configuration used in Example 1,
the analysis was conducted do find how the SLD interference
waveform obtained with the temperature measurement system changes
in a Si monolayer when the heater temperature rises. Linear
expansion coefficient and temperature coefficient of changes in the
refractive index were calculated as follows based on the intensity
of optical interference explained in the "Low-coherence
interferometer" section.
.alpha..sub.si=-7.06.times.10.sup.-11.times.T.sup.2+6.83.times.10.sup.-8.t-
imes.T+2.38.times.10.sup.-6
.beta..sub.Si,1.55=-3.33.times.10.sup.-11.times.T.sup.2+6.76.times.10.sup.-
-8.times.T+5.01.times.10.sup.-5
[0298] FIG. 11(a) and FIG. 11(b) show the analysis results in which
the distance from the front surface to the rear surface is
represented by a wave number in case the thickness of Si is 364.6
.mu.m and the temperature increased from 25.degree. C. to
200.degree. C. FIG. 11(a) shows the interference waveform obtained
by conducting the analysis with respect to the space from the front
surface to the rear surface of Si at a temperature of 25.degree. C.
The results demonstrated that distance between the two peaks was
1618.5 as a wave number determined based on the analysis results.
Similarly, for the distance between the front surface and rear
surface of Si at a temperature of 200.degree. C., as shown in FIG.
11(b), 1641.1 was obtained as a wave number.
[0299] Because the displacement is difficult to evaluate by merely
comparing FIGS. 11(a) and (b), the interference waveform in which
only the right peak is enlarged is shown in FIGS. 12(a), (b) to
confirm the displacement between the peaks, which accompanies the
increase in temperature.
[0300] As a result, on the graph shown in FIG. 12, it is clear that
the difference of about 22.6 fringes is present. This difference in
22.6 fringes is the difference in distance between the front and
rear surfaces as mentioned hereinabove and is clearly based on the
changes caused by the increase in temperature.
[0301] Mere comparison of the two interference waveforms cannot
confirm the difference clearly, For this reason, FIGS. 12(a), (b)
show enlarged abscissa and ordinate of the right peaks of each
interference waveform.
[0302] As shown in those FIGS. 12(a), (b), there is a clear phase
shift between the front surface and rear surface of Si at
temperatures of 25.degree. C. and 200.degree. C.
Example 3
[0303] (Test Relating to Si Monolayer)
[0304] The test on a Si monolayer was conducted by using the system
identical to that of Example 1.
[0305] First, explanation will be conducted based on the detected
interference waveform and data actually obtained from the optical
system of the present system at room temperature (25.degree. C.).
The main parameters of the system used to conduct the test are
described below. Si thickness: about 360 .mu.m, Si layer
temperature: 25.degree. C., voice coil motor movement distance: 3.0
mm, voice coil motor drive frequency: 0.4 Hz. FIGS. 13(a)-(d) show
the SLD interference waveform obtained from the temperature
measurement system and the LD interference waveform obtained from
the displacement measurement system under those conditions.
[0306] In those analysis results, the interference waveform in the
front surface and rear surface of Si is shown. If they are compared
with the interference waveform that was actually obtained, two
peaks on the left and right side can be observed, and it is clear
that there is a distance between interference intensity of the two
interference waveforms. The relationship between the incident light
and the measurement sample Si is shown in a simplified form in the
uppermost portion of FIG. 13. As shown in FIG. 13, in the
measurements, the left side of Si is a front surface, and the right
side is a rear surface. If the refractive index of air is taken as
1, then the refractive index of Si will be 3.44. Therefore, the
reflection factor R on the Si surface in air will be 0.302 and an
about 30% reflection will take place. Furthermore, it is well known
that the absorption of light with a wavelength of 1.55 .mu.m in Si
is extremely small. Therefore, of the remaining 70%, 30% are again
reflected on the rear surface. Thus, about 21% of the initial light
are reflected. Therefore, the left of the two peaks represents
interference results on the front surface of Si, and the right one
represents the interference results on the rear surface of Si.
Those results demonstrate that the difference in interference
intensity is the effect of reflection factor explained in
"Measuring temperature of layered structure".
[0307] From the above-described parameters, the movement speed, v,
of the voice coil motor is about 2.4 mm/sec. Furthermore, the
Doppler shift frequency, f.sub.D, observed in those measurements is
about 3.10 kHz, as calculated from f.sub.D=2v/.lambda.. The
respective enlarged waveforms shown in FIGS. 13(c) and (d)
demonstrate match with the test value in both the SLD interference
waveform and the LD interference waveform.
[0308] The wave number of the LD interference waveform
corresponding to the two peaks of the SLD interference waveform
determined by the wave number count program was 1618.50 at room
temperature (25.degree. C.). In the interferometer using a
reciprocally moving drive mechanism, such as a voice coil motor, if
the movement distance in one direction is set to 1, then the
maximum is reached when the condition 21=m.lambda. (m is integer)
is satisfied. From this result it follows that the distance
equivalent to 1 period of an enlarged waveform in FIG. 13(c) is
0.775 .mu.m half-wavelength. Therefore, the optical path length of
the Si layer corresponding to the wave number of 1618.50 is about
1254.3 .mu.m and the refractive index of Si is 3.44. As a result,
it is clear that the thickness of Si that was found in the test is
364.6 .mu.m and almost complete match is attained.
[0309] (Case where the Temperature of a Heat Source Heater is
Changed)
[0310] Changes in the wave number corresponding to the distance
between the peaks, that is, changes in the interference waveform
within the distance between the front surface and rear surface that
were detected when the temperature of the measurement sample Si
brought into contact with the heater increased due to changes in
the temperature of the heat source heater will be examined
below.
[0311] First, it is necessary to examine the temperature of the Si
layer of the measurement sample, which changes with the increase in
heater temperature. A graph, in which the heater temperature is
plotted against the abscissa and the temperature of the front
surface of the Si layer measured by using a thermocouple is plotted
against the ordinate, is shown in FIG. 14. As for the data plotted
against the abscissa, the heater temperature is measured at room
temperature (25.degree. C.) as the initial value, and then the
measurements are conducted from 40.degree. C. to a maximum of
200.degree. C. with a measurement interval of 20.degree. C. Each
numerical value shown in the graph is given to clarify the
temperature of the Si surface layer on the ordinate. This graph
demonstrates that in the high-temperature portion, the heater
temperature is not transferred to the Si layer at all. This
suggests that part of the heater heat is transferred to the outer
air or the heat of the Si layer is transferred to the outer air and
there is a certain loss.
[0312] In the graph shown in FIG. 15, the heater temperature is
plotted against the abscissa and the wave number found by
theoretical analysis and the results obtained by measuring the
changes between the peaks of the SLD interference waveform detected
with the temperature measurement system at a wave number of the LD
interference waveform obtained from the displacement measurement
system is plotted against the ordinate. The initial values
correspond to room temperature (25.degree. C.), at a temperature
above 40.degree. C., the measurements were conducted for each
20.degree. C.
[0313] From the above-described results, it was obtained that the
thickness of the Si that was used was about 364.6 .mu.m, based on
the test results. The analysis conducted with respect to changes in
temperature based on this value has already been described above
(measurements in Si monolayer). FIG. 15 shows the data obtained in
the test and the theoretic values of the wave number depending on
the increase in temperature and obtained by taking into account the
temperature coefficient of changes in the refractive index and
linear expansion coefficient relating to the above-described
Si.
[0314] The results show that the wave number found from the
theoretic values and the wave number of the LD interference
waveform corresponding to the distance between the peaks of the SLD
interference waveform at each temperature that was obtained in the
test have somewhat different inclinations with respect to
temperature.
[0315] Here, the main factors resulting in this error of the
inclination will be discussed based on formula (3-14). Formula
(3-14) will be explained with SiO.sub.2 as an example, but a
similar formula also relates to Si. Therefore, replacing the
symbols SiO.sub.2 with Si, we can obtained.
.DELTA.l.sub.si=l'.sub.si-l.sub.si=n.sub.sid.sub.si(.alpha..sub.si+.beta..-
sub.si).DELTA.T
[0316] In case of Si, if the following values are considered:
n.sub.si=3.44, d.sub.si=360 .mu.m,
.alpha..sub.si=2-4.times.10.sup.-6 .degree. C..sup.-1,
.beta..sub.si=5-6.times.10.sup.-5 .degree. C..sup.-1,
.DELTA.T=200.degree. C.-25.degree. C.=175.degree. C., then from
.alpha..sub.si<<.beta..sub.si, changes in the optical path
length will be 2.times..DELTA.l.sub.Si. Therefore, we can obtain
the following:
2.DELTA.l.sub.si=2n.sub.Si.multidot.d.sub.Si.multidot..beta..sub.Si.DELTA.-
T
[0317] Changes caused by the optical path displacement in Si as
well as a temperature measured error caused by a thermocouple and
the measurement error of the values cited from reference sources
are considered as the error factors.
[0318] For example, if changes caused by the optical path
displacement are considered as the main factor, then for a 5-fringe
displacement, .DELTA.d.sub.si.apprxeq.94 .mu.m is obtained from
2l.DELTA..sub.Si=5.time- s.1.55 .mu.m, and such a displacement is
difficult to consider. Further, the temperature measurement error
caused by a thermocouple also becomes .DELTA.T.apprxeq.46.degree.
C.pm and this also cannot be considered as a reason for the
aforementioned changes. If the measurement error of .beta..sub.Si
is considered, then .DELTA..beta..sub.Si=1.4.times.10.sup.-- 5
.degree. C..sup.-1 is obtained, and if the measured value of
.beta..sub.Si is about 7.4.times.10.sup.-5 .degree. C..sup.-1 from
6.0.times.10.sup.-5 .degree. C..sup.-1 at 200.degree. C., then the
result can be explained.
[0319] Thus, the error in the inclination of the straight lines can
be assumed to be caused by the measurement error from reference
sources or the measurement error caused by disturbances such as
vibrations in the present system.
[0320] Further, the displacement of measured values from the
straight line can be considered to be mainly due to disturbances
caused by vibrations during measurements.
[0321] The present test results demonstrate a 28.7-fringe
difference at a temperature of Si layer of 25.degree. C. and
193.degree. C. From the present test results, a change in
temperature of about 5.8.degree. C. per 1 fringe can be
established. In order to realize a resolution of 1.degree. C. or
less, a resolution of 1/6 fringe or less is required, and it is
clear that suppression of disturbances such as vibrations is highly
desired.
Example 4
[0322] (Test Relating to SiO.sub.2 Monolayer)
[0323] Test results relating to a SiO.sub.2 monolayer will be shown
similarly to the results of Example 3 (Test relating to Si
monolayer). The main parameters of the system were as follows.
SiO.sub.2 thickness: about 1 mm, Si layer temperature: 25.degree.
C., voice coil motor movement distance: 3.0 mm, voice coil motor
drive frequency: 0.3 Hz. FIGS. 16(e) to (h) show the SLD
interference waveform obtained from the temperature measurement
system and the LD interference waveform obtained from the
displacement measurement system in this case. Two peaks, on the
left and on the right, can be obtained in the interference waveform
that was actually obtained, but this time practically no difference
between the outputs of the two interference waveforms was observed.
Because the refractive index of SiO.sub.2 is 1.46, the reflection
factor R on the SiO.sub.2 surface in air will be 0.035 and an about
3.5% reflection will take place. Of the remaining 96.5%, 3.5% are
again reflected on the rear surface. As a result, about 3.4% of the
initial light are reflected. The left of the two peaks represents
interference waveform on the front surface of SiO.sub.2, and the
right one represents the interference results on the rear surface
of Si. From the above-described parameters, the movement speed, v,
of the voice coil motor becomes about 1.8 mm/s. Furthermore, the
Doppler shift frequency f.sub.D observed in those measurements is
about 2.32 kHz and good match with the test values is obtained in
both the SLD interference waveform and the LD interference
waveform.
[0324] When the wave number of the LD interference waveform
relating to the spacing between the two peaks of the SLD
interference waveform that was determined by the wave number count
program was read, the result was 1927.6. For SiO.sub.2, data
representing the dependence on temperature were not available. For
this reason, the following constant values were used for the linear
expansion coefficient and temperature coefficient, .beta., of
changes in the refractive index.
.alpha..sub.SiO2=5.0.times.10.sup.-7
.beta..sub.SiO2=7.0.times.10.sup.-6
[0325] It follows herefrom that the optical path length inside the
SiO.sub.2 layer corresponding to a wave number of 1927.6 is 1493.9
.mu.m. Further, because the refractive index of SiO.sub.2 is 1.46,
the thickness of SiO.sub.2 found in the test is about 1023.2 .mu.m
and the data almost match. Further, the temperature of the front
surface measured with a thermocouple when the temperature of
SiO.sub.2 was increased was examined by changing the temperature of
the heat source heater. The results are shown in FIG. 17.
[0326] FIG. 18 shows a grain in which the heater temperature is
plotted against the abscissa, and the results obtained in measuring
the optical path length between the peaks of the SLD interference
waveform detected with the temperature measurement system at a wave
number of the LD interference waveform obtained from the
displacement measurement system are plotted against the
ordinate.
[0327] It follows from FIG. 17 that because SiO.sub.2 has a low
thermal conductivity, the surface temperature becomes lower than
that of Si shown in FIG. 14. Furthermore, it follows from FIG. 18
that, similarly to Si, the difference with the theoretic values
increases with the increase in temperature. This result suggests
that an assumption that the .beta.SiO.sub.2 is constant against the
temperature, which was made in the theoretic analysis, is the main
cause of the error. However, the temperature dependence of
.beta.SiO.sub.2 can be inversely evaluated from the measurement
results, and temperature measurements can be conducted by using
this evaluated value.
[0328] The present test results demonstrate a 5.4-fringe difference
at a temperature of SiO.sub.2 layer of 25.degree. C. and
185.degree. C. From the present test results, a change in
temperature of about 29.6.degree. C. per 1 fringe can be
established and in order to realize a resolution of 1.degree. C.,
it is necessary to measure fringes with an accuracy of about
{fraction (1/10)}.
Example 5
[0329] (Temperature Measurements Using Layered Structure of Silicon
and Quartz)
[0330] Measurements were conducted by using a structure of
laminated Si and SiO.sub.2. In this case, the thickness of Si and
SiO.sub.2 layers was 360 .mu.m and 1 mm, respectively, and the
optical path length was 1.23 .mu.m and 1.46 .mu.m, respectively.
Therefore, in case of the laminated structure, the thickness was
1.36 mm and the optical path length was 2.69 mm. Therefore, the
drive distance of 2.69 mm and more is necessary. A voltage of 3.0 V
is applied to the voice coil motor, the drive distance is 3.6 mm,
the operation frequency is 0.1 Hz, and the drive is conducted at a
speed of about 0.36 mm/sec. In this case, too, similarly to a
single body structure, the temperature of the front surface was
directly measured with a thermocouple and the temperature of the
rear surface was measured as a heater temperature.
[0331] As shown in FIG. 19, the temperature was measured when the
layers were laminated so that Si was at the top and SiO.sub.2 was
at the bottom. Measurement results relating to the Si layer, which
is the upper layer, are shown in FIG. 20(a). It follows from those
results that if the approximately straight lines obtained for a Si
single body and a Si layer of the layered structure are compared,
then the inclination of the line obtained for the layered structure
is less than the inclination of the line obtained for the Si single
body. Furthermore, the measured values for Si in a layered
structure are slightly less. This is apparently because the
temperature of the heater was not sufficiently transferred to the
Si layer because SiO.sub.2, which does not have good thermal
conductivity, was placed between the heater and Si. It follows from
FIG. 20(a) and FIG. 14 that in the Si layer of the layered
structure and the Si single body, the difference in temperature is
about 20.degree. C. at a heater temperature of 200.degree. C.
[0332] On the other hand, FIG. 21 shows the temperature of the
front surface of Si measured with a thermocouple as a function of
heater temperature. If this graph is compared with the temperature
of the front surface of the Si single body, which is shown in FIG.
14, then a difference of about 15.degree. C. exists at a
temperature of 200.degree. C. and the results almost match each
other, the difference therebetween being about 5.degree. C.
Further, FIG. 20(b) shows changes in the wave number in the
SiO.sub.2 layer of the layered structure and the SiO.sub.2 single
body. It follows from this figure that there is a certain spread in
the measured values, but it is clear that the two values
practically do not change. This is apparently because the SiO.sub.2
layer is in contact with the heater and the temperature of the
SiO.sub.2 practically does not change with respect to that of the
single body.
[0333] As shown by the above-described embodiments, a system for
measuring the temperature of a layered structure using a
low-coherence interferometer of an optical fiber type was
constructed.
[0334] Using a corner cube prism and a voice coil motor as a
reference mirror drive mechanism of the system made it possible to
stabilize the large depth measurements. Furthermore, using an
optical fiber interferometer employing a semiconductor layer made
it possible to measure the displacement of the reverence mirror
with a high accuracy.
[0335] In the above-described embodiments changes in the optical
path length were examined with respect to a Si substrate single
body by theoretic analysis when the temperature was raised. Then,
actual temperature measurements were conducted with respect to Si
and SiO.sub.2 substrates. The comparison of the interference
wavelength obtained with the temperature measurement system and the
interference wavelength obtained with the displacement measurement
system following increase in temperature confirmed that the optical
path length of each layer changes from a state before the
temperature has changed to a state after the temperature has
changed, following changes in linear expansion coefficient and
refractive index. As a result, changes in the optical path length
caused by the increase in the heater temperature slightly differed
from the theoretic analysis results. Close inspection of this
result suggested that this is due to the accuracy of thermal
coefficient .beta. of changes in the refractive index used in the
theoretic analysis or to the effect of disturbances caused by
vibrations during measurements.
[0336] It followed from the above-described measurement results
that when Si with a thickness of about 360 .mu.m was used and when
SiO.sub.2 with a thickness of about 1000 .mu.m was used, a
respective resolution of no less than 1/6 fringe and {fraction
(1/10)} fringe of the LD interference wavelength was necessary to
obtain a resolution of 1.degree. C.
[0337] Similar measurements were also conducted with respect to a
layered structure composed of Si and SiO.sub.2. The SiO.sub.2 layer
located directly above the heater showed changes in the wave number
almost identical to those of a single body. However, in the Si
layer located above the SiO.sub.2 layer, changes in the wave number
were slightly less than those of the Si single body and almost
matched the value obtained by direct thermocouple measurements on
the front surface of the Si layer.
[0338] It was thus confirmed that with the system used in those
embodiments, the temperature of each layer of the layered structure
can be measured separately.
[0339] As described hereinabove, the present invention can provide
a method for measuring temperature, which is suitable for directly
measuring the temperature of the outermost surface of a substrate
or the like.
[0340] From the invention thus described, it will be obvious that
the invention may be varied in many ways. Such variations are not
to be regarded as a departure from the spirit and scope of the
invention, and all such modifications as would be obvious to one
skilled in the art are intended to be included within the scope of
the following claims.
[0341] The basic International Application No. PCT/JP03/04792,
filed on Apr. 15, 2003, is hereby incorporated by reference.
* * * * *