Temperature measuring apparatus utilizing radiation

An apparatus for measuring the temperature of an object placed in a plasma by utilizing radiation includes measuring means for measuring the intensity of radiation from the object and the intensity of plasma light in different directions at the same time. The measuring means includes a first lens for receiving the radiation from the object and the plasma light, a second lens for converting the output beam of the first lens into parallel light rays, a third lens for focusing the parallel light rays, and an interference filter disposed rotatably between the second lens and the third lens.

BACKGROUND OF THE INVENTION 
The present invention relates to a radiation thermometer for detecting the 
thermal radiation of an object placed in a plasma to determine the 
temperature of the object, a sputtering apparatus using the radiation 
thermometer for manufacturing semiconductor devices, and a method of 
measuring the temperature of an object by using radiation. 
Various kinds of radiation thermometers have been known which include a 
monochromatic radiation thermometer for determining the temperature of an 
object to be measured by measuring the intensity of radiation emitted from 
the to-be-measured object (that is, energy emitted from the object), and a 
two-wavelength radiation thermometer for determining the temperature of an 
object to be measured from a ratio of the intensity of one of two 
wavelength components of radiation to the intensity of the other 
wavelength component. 
Technology relating to radiation thermometers of this kind is disclosed in 
a Japanese patent application Post-Exam. Publn. No. Sho 60-58411 
(JP-B-60-58411) and a Japanese patent application Post-Exam. Publn. No. 
Sho 60-58412 (JP-B-60-58412). 
According to the prior art, in a case where a radiator such as a plasma is 
present in the vicinity of an object to be measured, the intensity of 
plasma light is added to the intensity of thermal radiation emitted from 
the to-be-measured object, and thus it is difficult to determine the 
correct temperature of the to-be-measured object. 
Further, since the correct temperature cannot be determined, it is 
impossible to exactly measure the temperature distribution on the surface 
of an object to be measured. In a plasma processing apparatus, it is very 
important for the fabrication of semiconductor devices to exactly measure 
the temperature distribution on the surface of a wafer to be measured. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a radiation thermometer 
capable of determining the correct temperature of a body placed in a 
plasma without being affected by the plasma. 
It is another object of the present invention to provide a method of 
measuring the temperature of a body placed in a plasma by using radiation. 
It is a further object of the present invention to provide a sputtering 
apparatus which uses the above radiation thermometer. 
According to an aspect of the present invention, there is provided a 
temperature measuring apparatus utilizing radiation which apparatus 
comprises: measuring means for measuring the intensity of radiation from a 
to-be-measured object placed in a plasma and the intensity of plasma light 
in different directions at the same time; means for correcting the 
measured value of intensity of the radiation by the measured value of 
intensity of the plasma light to determine the intensity of thermal 
radiation of the to-be-measured object on the basis of the measured values 
being obtained by the measuring means; and means for calculating the 
temperature of the to-be-measured object from the intensity of thermal 
radiation thus determined. 
Further, according to another aspect of the present invention, there is 
provided an imaging spectral analyzer usable as a temperature measuring 
apparatus for determining the spatial distribution of the light intensity 
on a radiator placed in a plasma which analyzer comprises: a first lens 
for receiving radiation from the radiation emitter and plasma light; a 
second lens for converting the output beam of the first lens into parallel 
light rays; a third lens for focusing the parallel light rays; and an 
interference filter disposed rotatably between the second lens and the 
third lens.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will be explained below in detail on the basis of 
embodiments thereof. 
FIG. 1 shows the whole construction of a radiation thermometer which is the 
first embodiment of the present invention. As shown in FIG. 1, the 
radiation thermometer includes a multi-surface mirror 3 for receiving 
radiation from an object 1 to be measured and plasma light from a plasma 2 
in different directions at the same time to reflect the radiation and 
plasma light in the same direction, a camera lens 4 for condensing each of 
the radiation and plasma light reflected from the mirror 3, a first relay 
lens 5 for converting the output beam of the camera lens 4 into parallel 
light rays, an interference filter 6 for transmitting a specified 
wavelength component of the parallel light rays, a second relay lens 7 for 
focusing a light beam having passed through the interference filter 6, and 
an imaging element 8 for converting an image formed of the focused light 
beam into a video signal. The interference filter 6 is coupled with a 
stepping motor 9. When the stepping motor 9 is driven on the basis of a 
command from a personal computer 10, the interference filter 6 turns on an 
axis C-D perpendicular to an optical axis A-B. The video signal from the 
imaging element 8 is supplied to a recording device 11 or the personal 
computer 10 to be processed. 
The intensity distribution of plasma light from the plasma 2 and the 
intensity distribution of the sum of radiation from the to-be-measured 
object 1 and plasma light from the plasma 2 appear on the surface of the 
imaging element 8. In a case where the intensity of plasma light is 
uniform, the intensity of thermal radiation of the to-be-measured object 1 
can be determined on the basis of the intensity distribution of plasma 
light and the geometrical arrangement of the to-be-measured object 1 by 
using the arithmetic unit of the personal computer 10. In a case where the 
intensity of plasma light is not uniform, the intensity of thermal 
radiation of the to-be-measured object 1 can be determined by taking the 
spatial distribution of plasma light into consideration on the basis of 
mathematical processing such as an Abel transformation. 
As mentioned above, the intensity of thermal radiation of the 
to-be-measured object 1 can be determined without being affected by the 
plasma light from the plasma 2. Thus, the correct temperature of the 
to-be-measured object 1 can be determined. 
Next, explanation will be made of a case where the embodiment of FIG. 1 is 
used as a multi-wavelength radiation thermometer. FIG. 2 is a graph for 
explaining the principle of the interference filter 6. In more detail, 
when the wavelength of light which has an incident angle of 0.degree. and 
can pass through the interference filter, and the wavelength of light 
which has an incident angle of .theta. and can pass through the 
interference filter are expressed by .lambda..sub.0 and 
.lambda..sub..theta., respectively, the transmission characteristic of the 
interference filter is given by the following equation: 
##EQU1## 
That is, when the angle of incidence for the interference filter 6 is 
changed, the wavelength of light passing through the interference filter 6 
is varied. The symbol A in the above equation indicates a constant of the 
interference filter 6 which constant depends upon the refractive index and 
thickness of an interference film formed on the filter 6. 
FIG. 3 shows an example of the dependence of the transmitted wavelength of 
an interference filter on the angle of incidence. 
In FIG. 3, the numbers on the abscissa indicate the transmitted wavelength 
.lambda. and the numbers on the ordinate indicate the percent 
transmissivity of the filter. In more detail, FIG. 3 shows how the 
transmitted wavelength of each of P-polarized light and S-polarized light 
is changed when the angle of incidence is varied at an interval of 
10.degree. in a range from 0.degree. to 60.degree.. The term "P-polarized 
light" indicates a polarized component whose electric vector is parallel 
to the plane of incidence of the interference filter (that is, a plane 
defined by an optical axis and a normal to the interference filter), and 
the term "S-polarized light" indicates a polarized component perpendicular 
to the P-polarized light. 
As shown in FIG. 3, when the angle of incidence is set to 0.degree., the 
transmitted wavelength of each of the P-polarized light and the 
S-polarized light is about 590 nm. When the angle of incidence is 
increased to 60.degree., the transmitted wavelength of the P-polarized 
light is about 490 nm. That is, when the angle of incidence is changed 
from 0.degree. to 60.degree., the transmitted wavelength of the 
P-polarized light decreases by about 100 nm. On the other hand, the 
transmitted wavelength of the S-polarized light is about 460 nm at a time 
when the angle of incidence is set to 60.degree.. That is, when the angle 
of incidence is changed from 0.degree. to 60.degree., the transmitted 
wavelength of the S-polarized light decreases by about 130 nm. 
Accordingly, when the interference filter 6 is rotated so that the angle of 
incidence for the interference filter 6 is changed from 0.degree. to 
45.degree., by driving the stepping motor 9 under the control of the 
personal computer 10, the measured wavelength can be changed by about 100 
nm. Thus, the embodiment of FIG. 1 can be used as a multi-wavelength 
radiation thermometer which is excellent in measuring accuracy. 
In this case, an appropriate measured wavelength can be previously 
determined or selected on the basis of a plasma light data base stored in 
the personal computer 10. Thus, the adverse effect of the plasma 2 can be 
appropriately removed. As regards plasma light data, refer to a 
publication entitled "Tables of Spectral Lines of Neural and Ionized 
Atoms" by A. R. Striganov and N. S. Sventitskii (Kurchatov Institute), 
IFI/Pleum (1968), and a publication entitled "The Identification of 
Molecular Spectra" by R. W. B. Pearse and A. G. Gaydon (Imperial College 
London), Chapman & Hall Ltd. (1978). 
FIG. 4 shows the second embodiment of the present invention. In the 
following explanation, the same reference numerals as used in FIG. 1 
designate like parts or devices. 
In the second embodiment of FIG. 4, the angle of incidence for the 
interference filter 6 is set to about 40.degree., and a polarization 
filter 51 is disposed in front of the interference filter 6. The 
polarization filter 51 can be rotated round an optical axis A-B through an 
angle of 90.degree. by a polarization filter driving device 101. Thus, the 
measured wavelength can be selected from two values by utilizing the 
difference in transmitted wavelength between the P-polarized light and the 
S-polarized light shown in FIG. 3. 
In the second embodiment, the transmitted wavelength of the interference 
filter can be changed by about 25 nm, by rotating the polarization filter. 
In the second embodiment, the polarization filter is disposed in front of 
the interference filter. The polarization filter, however, may be disposed 
behind the interference filter, or in front of the camera lens. 
FIG. 5 shows the third embodiment of the present invention viewed in 
directions parallel to the axis of rotation of an interference filter 52. 
FIG. 6 shows the interference filter 52 of FIG. 5 three-dimensionally. As 
shown in FIG. 6, the interference filter 52 includes two interference 
filter plates 111 and 112 having different transmitted wavelengths, and 
the interference filter plates 111 and 112 are combined so as to be 
perpendicular to each other. Further, the side face of each of the 
interference filter plates 111 and 112 is coated with black paint, to 
prevent light from passing through the side face. In a case where two 
wavelengths are to be measured, two interference filter plates capable of 
transmitting one and the other of the above wavelengths are combined to 
form the interference filter 52, and either one of the interference filter 
plates is caused to face the relay lens 7 by turning the rotor of the 
stepping motor 9 through an angle of 90.degree.. Thus, the measured 
wavelength can be changed. 
The present invention is not limited to the above embodiments. For example, 
an interference filter 300 shown in FIG. 7 may be used in the present 
invention. That is, the interference filter is divided into three parts, 
each of which is coated with an interference film capable of transmitting 
a desired measured wave-length. FIG. 8 shows an example of the emission 
spectrum of a radiation emitter which example is measured by using the 
interference filter of FIG. 7. 
The light transmission characteristic of each of interference films 301, 
302 and 303 shown in FIG. 7 is as follows. When the angle of incidence is 
set to 40.degree., the interference film 301 transmits a wavelength 
component .lambda..sub.1. When the angle of incidence is set to 
20.degree., the interference film 302 transmits a wavelength component 
.lambda..sub.2. When the angle of incidence is set to 0.degree., the 
interference film 303 transmits a wavelength component .lambda..sub.3. 
That is, when the interference filter 300 is tilted so that the angle of 
incidence is 40.degree., an image due to the wavelength component 
.lambda..sub.1 is detected by the imaging element. When the interference 
filter 300 is tilted so that the angle of incidence is 20.degree., an 
image due to the wavelength component .lambda..sub.2 is detected by the 
imaging element. When the interference filter 300 is disposed so that the 
angle of incidence is 0.degree., an image due to the wavelength component 
.lambda..sub.3 is detected by the imaging element. 
In the above case, the polarization filter is mounted on the lens system. 
Alternatively, the polarization filter may be bonded to the interference 
filter or the imaging element (for example, a CCD or a vidicon). 
FIG. 9 shows the fourth embodiment of the present invention. In the present 
embodiment, the interference filter 6 is rotated by driving the stepping 
motor 9 under the control of the personal computer 10 so that plasma light 
passing through the interference filter 6 has a maximum intensity, that 
is, the most intense wavelength component of the plasma light passes 
through the filter 6. At this time, the intensity of reflection on the 
to-be-measured object 1 is measured by utilizing light from a part 21 of 
the plasma 2, to determine the reflectivity of the surface of the 
to-be-measured object 1. In this case, it is necessary to determine the 
light intensity distribution in the plasma 2 as in the first embodiment. 
When the reflectivity of the to-be-measured object 1 is determined in the 
above manner, it is possible to determine the temperature of a body whose 
reflectivity varies in a great degree. 
FIG. 10 shows an aluminum sputtering apparatus for manufacturing 
semiconductor devices which apparatus is the fifth embodiment of the 
present invention. Referring to FIG. 10, an argon gas for plasma discharge 
is supplied into a vacuum vessel 40 through a gas inlet 41 so that the 
argon pressure in the vessel 40 is kept at several mTorr. When a 
high-frequency voltage which is produced by a power source 43 and has a 
frequency of 13.56 MHz, is applied between a pair of parallel plate 
electrodes 42, the plasma 2 is generated between the electrodes 42. An 
aluminum target 44 is attached to one of the electrodes 42, and an object 
to be processed (for example, a semiconductor wafer 45) is attached to the 
other electrode. The wafer 45 is heated to a temperature of about 
200.degree. to 400.degree. C. by a heater 47 which is connected to a power 
source 46. 
In the present embodiment, radiation from the semiconductor wafer 45 and 
plasma light from the plasma 2 are led to the above-mentioned radiation 
thermometer through a quartz window 48 mounted on the vacuum vessel 40. In 
the radiation thermometer, an emission spectrum from a region of the 
plasma 2 is measured by tilting the interference filter 6. FIG. 11 shows 
an example of the measured emission spectrum. In this example, not only 
spectral lines of argon (that is, solid lines) but also spectral lines of 
aluminum (that is, broken lines) are observed. In the present embodiment, 
a wavelength of 1.0 .mu.m is used as the measured wavelength. As shown in 
FIG. 12 which is described on page 341 of an article entitled "Spectral 
Emissivity of Silicon" by T. Sato (J.I. Appl. Phys. Vol. 6, 1967), the 
temperature dependence of emissivity of silicon is very little at a 
wavelength of 1.0 .mu.m. The radiation distribution on the silicon wafer 
45 and the light distribution in the plasma 2 are measured to determine 
the temperature distribution on the silicon wafer 45. In this case, during 
a period when plasma processing is carried out, the power source 46 is 
controlled by the personal computer 10 so that the silicon wafer 45 is 
kept at a set temperature. 
Further, in a case where the temperature of the silicon wafer is low, as 
can be predicted from the black body radiation shown in FIG. 13, radiation 
from a to-be-measured body (that is, the silicon wafer) is shifted to the 
long-wavelength side. Thus, each of a wavelength of 1.67 .mu.m and a 
wavelength of 1.6 .mu.m is used as the measured wavelength. It is to be 
noted that the temperature dependence of emissivity of silicon at a 
wavelength of 1.6 .mu.m is large, as shown in FIG. 12. The reflectivity of 
the silicon wafer is determined by using a spectral line of aluminum 
having a wavelength of 1.67 .mu.m. Then, the temperature distribution on 
the silicon wafer is determined by measuring the wave-length component of 
1.6 .mu.m and by using the reflectivity thus obtained. 
FIG. 14 shows a plasma generating apparatus. Referring to FIG. 14, a plasma 
generating region 2 is set in the vacuum vessel 40 made of quartz. A 
mixing gas of CF.sub.4 and O.sub.2 which serves as a reactant gas is 
supplied to the plasma generating region 2 through the gas inlet 41 so 
that the pressure of the reactant gas is kept at several Torr. When a 
high-frequency voltage which is produced by the power supply 43 and has a 
frequency of 13.56 MHz is applied between the parallel plate electrodes 
42, a plasma is generated between the electrodes 42. An object to be 
processed (for example, a semiconductor wafer 45) is disposed in the 
plasma generating region 2 in such a manner that the wafer is placed on 
one of the electrodes 42. The whole of the plasma generating apparatus is 
protected by a cover 62. 
In the above plasma generating apparatus, light from the plasma is led to a 
spectral surface analyzer according to the present invention through an 
aperture formed in the cover 62 and having a hole of a diameter of 10 mm, 
and an optical fiber 53 having a wide angle lens at the end thereof. In 
the imaging spectral analyzer, a wavelength component of the plasma light 
which is emitted from a fluorine radical generated by the decomposition of 
the reactant gas and has a wavelength of 703.7 nm, and a wavelength 
component which is emitted from a CO radical produced from an SiO.sub.2 
film and has a wavelength of 519.8 nm, are measured by rotating the 
interference filter 52. According to the above analyzer, the distribution 
of a chemical species for etching the SiO.sub.2 film can be monitored by 
measuring the distribution of light due to the fluorine radical, and the 
distribution of etching quantity in the surface of the wafer can be 
monitored by measuring the distribution of light due to the CO radical. 
The pressure, flow rate and composition of the plasma generating gas and 
the plasma exciting power are controlled so that the distribution of the 
chemical species and the distribution of the etching quantity are kept 
constant. Further, the constituent elements of the plasma generating 
apparatus and the construction thereof are adjusted so that the above 
condition is satisfied. 
In the above, a plasma etching apparatus is shown as the plasma generating 
apparatus by way of example. The plasma generating apparatus includes a 
plasma CVD apparatus, a plasma ashing apparatus for removing a photoresist 
formed on a semiconductor wafer. Further, the above imaging spectral 
analyzer can be used for maintaining the light generating state of a 
plasma utilization apparatus such as an arc welding apparatus. 
Additionally, the imaging spectral analyzer can be used as a rainy weather 
monitoring apparatus for measuring a ratio of the intensity of infrared 
radiation to the intensity of visible light to obtain information on 
whether the sky becomes clear or cloudy. 
As has been explained in the foregoing, according to the present invention, 
the intensity of radiation from a to-be-measured object placed in a plasma 
and the intensity of plasma light are measured, and the intensity of the 
above radiation is corrected by the intensity of the plasma light. Thus, 
the intensity of thermal radiation from the to-be-measured object can be 
determined without being affected by the plasma, and the temperature of 
the to-be-measured object can be determined correctly. 
Further, the reflectivity of the surface of the to-be-measured object can 
be determined by using the plasma light. Accordingly, the temperature of a 
to-be-measured object whose reflectivity varies greatly with temperature 
can be determined accurately. 
Additionally, according to the present invention, there is provided an 
aluminum sputtering apparatus for manufacturing semiconductor devices 
which apparatus makes it possible to detect the temperature distribution 
on a wafer exactly, and thus can greatly improve the manufacturing yield 
of the wafer.