JP3383163B2 - Temperature measurement method and device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring method for irradiating an object to be measured with a laser beam to measure a physical quantity of the object to be measured, and more particularly to measuring the temperature of a semiconductor substrate in a non-contact manner using the laser beam. Temperature measuring method and device.

[0002]

2. Description of the Related Art In recent years, in the process of manufacturing a semiconductor integrated circuit, its characteristics depend to a large extent on temperature control, and it is required to measure temperature accurately without contacting the semiconductor substrate. . As such a non-contact temperature measuring device for a semiconductor substrate, a temperature measuring method utilizing the fact that the intensity of the interference light due to the reflected light on the surface of the substrate to be measured and the reflected light on the rear surface changes depending on the temperature is disclosed in 3-96247
It is disclosed in the publication. When the temperature changes, the dielectric constant of the measured substrate changes, and the measured substrate expands to change the thickness. Therefore, the change in temperature can be measured by observing the change in the intensity of the interference light. .

However, the temperature measuring method disclosed in Japanese Patent Laid-Open No. 3-96247 cannot determine whether the temperature is rising or falling. JP-A-3-962
A temperature measuring device based on the same principle as the temperature measuring method disclosed in Japanese Patent No. 47, which can measure the direction of temperature change, is disclosed in a document (KLSaenger, et al., "Waveleng.
th-modulated interferometric thermometry for impro
ved substrate temperature measurement ", Rev. Sci.
Instrum. Vol.63, No.8, pp.3862-3868, August 1992.
) Is proposed.

The temperature measuring device described in this document uses a semiconductor laser having an oscillation wavelength of about 1.5 μm, and changes the current injected into the semiconductor laser to emit laser light whose wavelength is modulated to a substrate to be measured. Irradiate. The interference light due to the reflected light from the substrate to be measured is received by the light receiving element and converted into a light receiving signal, and the light receiving signal is wavelength-differentiated by the lock-in amplifier. It is determined whether the temperature is rising or falling based on the differentiated light receiving signal and the non-differentiating light receiving signal.

However, according to the above-mentioned conventional temperature measuring device, many devices and devices such as a laser modulator and a lock-in amplifier are required, which may complicate the structure of the device and increase the cost. It was Also, 1 per second
In order to accurately measure a sudden temperature change such as a change of 00 ° C or more, higher-speed equipment and devices are required,
The cost may have increased. Further, according to the conventional temperature measuring device, since the direction of temperature change can be measured only when the average value of the interference light waveform is crossed, detailed temperature measurement is impossible.

As a temperature measuring method for solving such a problem, the inventors of the present application have specified a temperature measuring method using a semiconductor laser having a feature that the oscillation wavelength of laser light emitted from the semiconductor laser shifts at the rising edge. Wishhei 6
-40274. Japanese Patent Application 6-4
In the temperature measurement method described in the No. 0274 specification, since it is possible to easily obtain laser light of different wavelengths by using the semiconductor laser described above, it is not necessary to perform wavelength differentiation in measurement, and a lock-in amplifier is also unnecessary, An inexpensive temperature measuring device can be realized with a simple configuration.

[0007]

However, in the above-mentioned conventional temperature measuring method, by measuring the change of the interference light caused by changing the temperature of the object to be measured,
The maximum and minimum values of the interference light were obtained after the start of the temperature measurement, and the interference state immediately after the start of the measurement was obtained. Therefore, when the temperature is measured by the conventional temperature measurement method, the maximum value, the minimum value, and the interference state of the interference light necessary for measuring the temperature must be known unless there is a temperature change in which the interference state changes by one cycle or more. I couldn't. Moreover, it was not possible to know in which interference state (phase) the interference light obtained at the start of the measurement was.

Although the desired information can be obtained by changing the temperature of the object to be measured, it is not desirable to change the temperature of the object to be measured for measuring the interference light. Further, it took more time to return the temperature of the measured object to the original value. In particular, the influence was great for measuring an object to be measured placed in a high vacuum. The object of the present invention, without changing the temperature of the measured object,
An object of the present invention is to provide a temperature measuring method and device capable of accurately measuring temperature from the start of measurement.

[0009]

The above object is to irradiate an object with coherent light, and to measure the temperature of the object to be measured based on the intensity of the interference light reflected or transmitted through the object to be measured. In the temperature measuring method for measuring the change amount, before measuring the temperature,
By changing the temperature of the measuring light oscillating section that emits the coherent light to change the wavelength of the coherent light,
A prediction process of predicting the maximum value and the minimum value of the intensity of the interference light, and the temperature of the measured interference light intensity during the temperature measurement, and the amount of change in the temperature of the measured object based on the predicted maximum value and the minimum value. And a measuring process for measuring the temperature. By performing the temperature measurement in this manner, it is not necessary to measure the maximum value and the minimum value of the interference light intensity after the measurement is started, and therefore the temperature can be measured immediately after the measurement is started. Further, the maximum value and the minimum value of the interference light intensity can be predicted without changing the temperature of the object to be measured.

Further, in the above temperature measuring method, it is preferable that the measuring light oscillating section is set to a predetermined temperature and the interference light in the measuring process is brought into a desired interference state. By measuring the temperature in this way, the measurement accuracy can be significantly improved. Further, in the above temperature measuring method, the predetermined temperature of the measuring light oscillating unit is adjusted so that a target measuring temperature is located substantially in the center between the maximum value and the minimum value of the intensity of the interference light. Is desirable. By measuring the temperature in this way, the measurement accuracy can be significantly improved.

In the above temperature measuring method, it is desirable that the coherent light is pulsed laser light. Further, in the above temperature measuring method, when the light source that oscillates the laser light performs pulse oscillation, the oscillation wavelength at the rise of the pulse is 0.5 from the rise.
It is desirable to oscillate a laser beam having a wavelength different from the oscillation wavelength after msec has elapsed. By using such a laser light source, it is possible to easily obtain laser lights of different wavelengths used for temperature measurement.

Further, the above object is to measure the temperature of the measured object by irradiating the measured object with coherent light and measuring the temperature of the measured object based on the intensity of the interference light reflected or transmitted through the measured object. In the device, irradiation means for irradiating the measured object with the coherent light, and the irradiation means are provided to change the temperature of the optical oscillation part of the irradiation means to change the wavelength of the coherent light. By changing the wavelength changing means, and by measuring the wavelength of the coherent light incident on the object to be measured by the wavelength changing means before the temperature measurement, the maximum value and the minimum value of the intensity of the interference light are predicted. A temperature measuring device comprising: a predicting unit that measures the temperature of the object to be measured based on the predicted maximum value and the minimum value of the intensity of the interference light measured during temperature measurement. It is also achieved by the device. By configuring the temperature measuring device in this way, the temperature of the measured object can be measured accurately without changing the temperature of the measured object from the start of measurement.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A temperature measuring method and device according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 7. FIG. 1 shows the configuration of the temperature measuring device according to the present embodiment. In the temperature measuring device according to the present embodiment, the laser light is irradiated to a portion of the semiconductor substrate which is polished on both sides and causes interference of light due to internal reflection with respect to the laser light, and the intensity of the interference light due to the reflected light. The temperature of the substrate to be measured is determined by observing the change.

The semiconductor substrate 6, which is the object to be measured, is housed in the chamber 4 and placed on the heater 5 that heats the semiconductor substrate 6. A pulse power supply 11 is connected to the semiconductor laser 1. The pulse power supply 11 supplies a pulse current of, for example, 50 Hz, whereby the semiconductor laser 1 emits pulsed laser light. Further, the semiconductor laser 1 is provided with a Peltier element 12 whose temperature can be controlled by a computer 10 described later, so that the temperature of the semiconductor laser 1 can be adjusted.

The chamber 4 is provided with an optical window (not shown) for introducing the laser light emitted from the semiconductor laser 1 into the chamber 4. The pulsed laser light emitted from the semiconductor laser 1 is guided to the collimating optical unit 3 via the optical fiber 2. The collimating optical unit 3 collimates the pulsed laser light into parallel light rays, and irradiates the semiconductor substrate 6 in the chamber 4.

The light reflected by the semiconductor substrate 6 is received by the light receiver 7.
Is received by. The light receiver 7 preferably has a rise time of 50 μs or less. The received light signal received by the optical receiver 7 is transmitted to the A / D conversion unit 9 via the data signal line 8. The A / D conversion unit 9 converts the received light signal, which is an analog signal, into a digital signal and outputs the digital signal to the computer 10.

The computer 10 calculates the intensity change of the interference light due to the reflected light from the input digital received light signal,
Based on the calculation result, the temperature change direction is determined together with the measured temperature. In the temperature measuring method according to the present embodiment, when the semiconductor laser 1 emits a pulsed laser beam, the wavelength of the laser beam is shortened by several angstroms at the rising edge of the pulse (first wavelength p1) and then becomes longer (first wavelength p1). Two wavelengths p2) are used.

In order to clarify this, FIG. 2 shows an observed waveform showing the intensity of the interference light obtained when the semiconductor substrate 6 whose temperature is rising is irradiated with the pulsed laser light. Figure 2
Shows the case where a pulsed laser beam having a pulse width of 5 msec is irradiated. The vertical axis represents voltage and 2 V per scale, and the horizontal axis represents time and 1 ms per scale. As shown in FIG. 2, the interference light intensity is strongest immediately after the rise of the pulsed laser light, then gradually decreases, and is stable after about 2 msec. This transient change is not seen when the laser light is pulsed by the chopper. At the time of measurement in FIG. 2, the temperature of the semiconductor substrate 6 is constant.

When the temperature of the semiconductor substrate 6 is constant, the intensity of the interference light depends on the wavelength of the laser light. Therefore, the graph of FIG. 2 shows that the oscillation wavelength of the pulsed laser light changes transiently. Is shown. In this embodiment, a laser beam having a short wavelength is output immediately after the rise of the pulsed laser beam. In the present embodiment, a laser beam having a pulse width of about 10 msec is used, and the laser beam having the first wavelength p1 is sampled at a time point of 0.12 msec after the rise of the pulse, and the second
The laser light having the wavelength p2 is sampled at 8 msec after the rise of the pulse. As the laser light of the first wavelength p1, it is desirable to use laser light that oscillates within about 0.5 msec after rising.

As the semiconductor laser 1 which emits such a laser beam, a III-V group semiconductor laser having an oscillation wavelength of 0.5 μm or more and 3 μm or less can be applied.
In this embodiment, NEC NDL5600 (1310n
InGaAsP phase shift type DF for m optical fiber communication
B-DC-PBH laser diode; output about 0.5m
W) was used. The semiconductor laser 1 has 10
It is desirable to use a semiconductor laser with an APC capable of pulse oscillation of Hz or higher.

Further, it is not necessary to obtain the laser light of the first wavelength p1 and the laser light of the second wavelength p2 from the same pulse.
A laser beam sampled at a time point of 0.12 msec after the rise of a certain pulse is used as the laser beam of the first wavelength p1, and a laser beam sampled at a time point of 8 msec after the rise of another pulse is used as the laser beam of the second wavelength p2. May be used.

Next, the measuring principle of the temperature measuring device according to the present embodiment will be explained with reference to FIGS. Figure 3
Is a graph showing the relationship between measured temperature and interference light intensity,
4A to 4C are graphs showing changes in wavelength and changes in interference light intensity when pulsed laser light is used, and FIG. 5A shows the first wavelength p1 and the second wavelength p2. 5B is a graph showing the intensity of the interference light, and FIG. 5B is a graph showing the time change of the temperature of the semiconductor substrate 6.
FIG. 7C is a diagram illustrating the relationship between the interference light and the temperature change of the semiconductor substrate 6.

In the temperature measuring device of this embodiment, a semiconductor substrate 6 such as a silicon substrate is placed on the heater 5. When the semiconductor substrate 6 is irradiated with the laser light emitted from the semiconductor laser 1, the laser lights reflected from the upper surface and the lower surface of the semiconductor substrate 6 interfere with each other, and the interference light is emitted from the semiconductor substrate 6, as shown in FIG. It becomes reflected light. Then, while heating the semiconductor substrate 6 by the heater 5, the semiconductor substrate 6 is irradiated with the laser light emitted from the semiconductor laser 1 through the collimator optical unit 3. The reflected light from the semiconductor substrate 6 is received by the light receiver 7, and the intensity of the interference light is analyzed by the computer 10.

As a result, as shown by the solid line in FIG.
The interference light intensity characteristic is obtained, and as the temperature of the semiconductor substrate 6 is increased, the intensity of the interference light changes into a periodic waveform shape similar to a sine wave. The principle is as follows. Since the dielectric constant (refractive index) and the thickness of the semiconductor substrate 6 increase as the temperature rises, the optical distance within the semiconductor substrate 6 changes. As a result, the laser light reflected on the lower surface of the semiconductor substrate 6 and emitted from the upper surface and the laser light reflected on the upper surface of the semiconductor substrate 6 undergo a phase change due to a temperature change.

Therefore, the intensity of the interference light reflected from the semiconductor substrate 6 changes sinusoidally due to the temperature change, and
The temperature change ΔT (T) [° C.] of the cycle can be calculated by the following formula, where L is the thickness of the semiconductor substrate 6 and n is the refractive index. ΔT = λ / {2nL (α + β)} However, α = (1 / L) × (dL / dT) β = (1 / n) × (dn / dT) Here, it is difficult to obtain α and β, respectively. . Therefore, (α + β) was determined experimentally.

That is, from the frequency f of the intensity of the interference light calculated by the difference from the initial value of the experiment and the calibration curve of the measured temperature, the temperature change ΔT (T) in one cycle is shown as 5 below.
It was calculated as the following approximate expression. ΔT (f) = 12.278 + 11.012 × f−0.13222 × f2 + 0.0018399 × f3−1.5803 × 10−5 × f4 + 5.5364 × 10−8 × f5 Therefore, the temperature of the semiconductor substrate 6 is , The temperature To [° C.] at the start of heating and the number of cycles of temperature change.

On the other hand, the semiconductor substrate 6 is heated or cooled by the heater 5, and the temperature may rise or fall. Therefore, in order to determine the temperature of the semiconductor substrate 6, it is necessary to know the temperature change direction. The discrimination principle will be described. A pulsed current of about 50 Hz is injected into the semiconductor laser 1 from the pulse power supply 11 to irradiate the semiconductor substrate 6 with pulsed laser light of 50 Hz from the semiconductor laser 1. At this time, the wavelength of the pulsed laser light emitted from the semiconductor laser 1 has a property that the rising time is short and the wavelength becomes long until the steady state, as shown in FIG.

The first wavelength p1 (= λ-Δλ) when the pulsed laser light from the semiconductor laser 1 rises is shorter than the second steady state second wavelength p2 (= λ) by Δλ. The temperature / interference light intensity characteristic indicating the relationship between the reflected light intensity of the semiconductor substrate 6 and the temperature of the laser light of the first wavelength p1 (= λ−Δλ) is as shown by the broken line in FIG.
The phase is advanced by φ from the case of λ).

The first wavelength p1 (= λ-Δλ) of the laser light oscillated within 0.5 ms after the rise of the pulsed laser light from the semiconductor laser 1 and the laser light oscillated thereafter The maximum difference Δλ between the second wavelengths p2 (= λ)
If the relationship of | Δλ | <λ2 / (2nd + λ) is satisfied with respect to the refractive index n of the semiconductor substrate 6 and the thickness d of the semiconductor substrate 6, appropriate interference occurs.

From the above, when the interference light intensity rises in the process of the temperature rise of the semiconductor substrate 6, the interference light intensity I2 of the second wavelength p2 has the first wavelength p1 shorter than that. When the interference light intensity becomes smaller than the interference light intensity I1 and the interference light intensity decreases, conversely, the interference light intensity I2 of the second wavelength p2 becomes larger than the interference light intensity I1 of the shorter first wavelength p1. I understand.

On the other hand, when the interference light intensity rises in the process of the temperature decrease of the semiconductor substrate 6, the interference light intensity I2 of the second wavelength p2 is the first wavelength shorter than that. When the interference light intensity I1 of p1 becomes larger and the interference light intensity decreases, conversely, the interference light intensity I2 of the second wavelength p2 is smaller than the interference light intensity I1 of the shorter first wavelength p1. You can see that it gets smaller.

In contrast to the pulsed laser light reflected from the semiconductor substrate 6 shown in FIG. 4 (a), the interference light intensity increases when the pulsed laser light rises as shown in FIG. 4 (b). In some cases, as shown in FIG. 4C, the intensity of the interference light may decrease when the pulsed laser light rises. 4 (b) corresponds to the change in the interference light intensity at the temperature T1 in FIG. 3, and FIG. 4 (c) shows the temperature T2 in FIG.
Corresponds to the change in the intensity of the interference light, and the circles and the crosses in FIGS. 3 and 4B and 4C correspond to each other.

Therefore, the interference light intensity of the pulsed laser light shown in FIG. 4A with respect to the reflected light from the semiconductor substrate 6 was measured immediately after the rising (X mark) and after a certain period of time (O mark). As shown in FIG. 4B, whether the interference light intensity at the rise of the pulsed laser light is smaller than the interference light intensity after that, and the pulsed laser light as shown in FIG. Whether the intensity of the interference light at the rising edge of is greater than the intensity of the interference light after that, and the first wavelength p1
Intensity I1 of the interference light of the second wavelength or intensity I of the interference light of the second wavelength p2
Judgment is made as to whether the temperature is rising or falling based on which side the interference waveform of 2 is inclined.

That is, when excluding the vicinity of the ridge and the vicinity of the valley of the intensity waveform of the interference light, the time when the intensity I1 of the interference light of the first wavelength p1 or the intensity I2 of the interference light of the second wavelength p2 increases. When the intensity I1 of the interference light of the first wavelength p1 is larger than the intensity I2 of the interference light of the second wavelength p2 (I1> I2), it is determined that the temperature of the semiconductor substrate 6 is rising, When the intensity I1 of the interference light of the first wavelength p1 is smaller than the intensity I2 of the interference light of the second wavelength p2 (I1 <I2
) Determines that the temperature of the semiconductor substrate 6 is decreasing. When the intensity I2 of the interference light I1 of the first wavelength p1 or the interference light I2 of the second wavelength p2 decreases, the first wavelength p
When the intensity I1 of the interference light of 1 is larger than the intensity I2 of the interference light of the second wavelength p2 (I1> I2), it is determined that the temperature of the semiconductor substrate 6 is decreasing, and the interference of the first wavelength p1 When the intensity I1 of the light is smaller than the intensity I2 of the interference light of the second wavelength p2 (I1 <I2), it is determined that the temperature of the semiconductor substrate 6 is rising.

The determination method in this embodiment will be specifically described. First, the semiconductor substrate 1 is irradiated with pulsed laser light from the semiconductor laser 1 at a frequency of 50 Hz. The reflected light is received by the light receiver 7, and the intensity of the interference light is recorded by the computer 10 for each pulse. In this case, as shown in FIGS. 4B and 4C, the interference light intensity I1 by the first wavelength p1 oscillated at one point within 0.5 msec from the rise of the pulsed laser light and 0.5 mse
The interference light intensity I2 due to the second wavelength p2 oscillated after c is extracted and stored.

For example, after the temperature of the semiconductor substrate 6 is raised by the heater 5 in time (to to tm), the temperature is raised in time (t
When the relationship between the intensity of the reflected light from the semiconductor substrate 6 and the time was measured by lowering at m to t2), the measurement result as shown in FIG. 5A was obtained. In FIG. 5A, a solid line having a periodic waveform shape resembling a sine wave represents the interference light intensity at the second wavelength p2 (= λ), and a broken line having a periodic waveform shape resembling a sine wave represents the first wavelength p1 (= λ-Δλ) indicates the interference light intensity.

When the temperature change is obtained from the interference light intensity shown in FIG. 5A obtained in this way, it becomes as shown in FIG. 5B. In the vicinity of the ridge and the vicinity of the valley of the intensity waveform of the interference light, the above physical relationship is opposite. Since the intensity difference between the interference light of the second wavelength p2 and the first wavelength p1 is small in that portion, a predetermined threshold value is set for the intensity difference of the interference light of the second wavelength p2 and the first wavelength p1, The direction of temperature change is determined only when the intensity difference of the interference light occurs.

For example, the interference light intensity I at the first wavelength p1
When the maximum value of 1 is I1max and the intensity of the interference light due to the second wavelength at that time is I2 ', a threshold value Ith = (I1max-I2') is provided for the difference in the intensity of interference light, and | I1-I2 | ≤I
A different algorithm is used for the case of th and | I1 −I2 |> Ith so that the direction of temperature change is correctly determined.

As another method, a ridge of an interference waveform,
Do not decide the temperature change direction between the point of I1 -I2 = 0 near the valley and its ridge and valley, or switch the temperature change direction judgment conditions shown in FIG. 5 (c) during that time. This makes it possible to correctly determine the direction of temperature change. Here, in order to perform such temperature measurement, it is necessary to measure the maximum value and the minimum value of the interference light intensity.
Conventionally, the maximum value, the minimum value, and the interference state of the interference light are measured by changing the temperature of the substrate to be measured and measuring the intensity of the interference light until the intensity of the interference light changes for at least one cycle. However, as described above, it is not desirable to change the temperature of the substrate under measurement.

Therefore, in this embodiment, the maximum value, the minimum value, and the interference state of the interference light are obtained by the following method. The temperature measuring method according to the present embodiment utilizes the fact that the emission wavelength of the semiconductor laser 1 fluctuates according to the temperature change of the semiconductor laser 1, and the maximum value and the minimum value of the interference light are determined from the relationship between the intensity of the interference light and the temperature of the semiconductor laser. , Got an interference condition.

FIG. 6 is a graph showing the relationship between the light intensity of the interference light and the temperature of the measurement light emitting portion when the silicon wafer is irradiated with the laser light. The temperature of the measuring light emitting part is
It is changed by heating the semiconductor laser 1 by the Peltier element 12. As shown in the figure, when the temperature of the measurement light emitting section is raised, the emission wavelength of the semiconductor laser 1 changes, and the light intensity of the interference light periodically increases and decreases. When a silicon wafer having a thickness of 0.53 mm is used as the object to be measured and laser light emitted from an MQW-DFB laser diode (FLD3F7CX manufactured by Fujitsu Ltd.) having an oscillation wavelength of 1310 nm is used as the measurement light, the cycle of the curve is About 11 ℃
Met.

The maximum value and the minimum value of the sinusoidal interference light intensity curve thus obtained correspond to the above-mentioned maximum value Imax and minimum value Imin, respectively. Therefore, the semiconductor substrate 6
If the relationship between the light intensity of the interference light and the temperature of the measurement light emitting portion is measured in advance prior to the temperature measurement, the maximum value Imax and the minimum value Imin of the interference light intensity can be known. Further, it is not necessary to change the temperature of the object to be measured.

Therefore, if the maximum value Imax and the minimum value Imin of the interference light intensity obtained in this way are stored and these values are used when the temperature is measured by the above-mentioned temperature measuring method, it is possible to change the temperature. It is possible to predict where the measured value is located on the interference light intensity curve that changes sinusoidally. That is, the phase of the current measured value in the interference light intensity curve can be known immediately after starting the temperature measurement.

On the other hand, since the temperature change amount ΔT (T) [° C.] corresponding to one cycle change of the interference light intensity curve is known in advance, the temperature of the semiconductor substrate 6 changes and the measured value of the interference light intensity is When it changes, the amount of phase change in the interference light intensity curve is known, and as a result, the amount of temperature change is known. Therefore,
The temperature of the semiconductor substrate 6 can be measured immediately after the measurement of the interference light intensity is started, depending on the temperature at the start of heating and the amount of temperature change.

FIG. 7 shows the temperature measurement result according to the present embodiment with respect to the change in the interference light intensity, in comparison with the temperature measurement result according to the conventional measurement method. FIG. 7 shows the maximum value and the minimum value of the interference light intensity at the time of the main measurement. In the conventional temperature measurement method,
Since the maximum value and the minimum value are obtained from the interference light intensity of about one cycle from the start of the measurement, the measurement can be performed only after the maximum value and the minimum value of the interference light intensity are obtained. Further, in the temperature measuring method according to the present embodiment, the maximum value and the minimum value are measured in advance, so that the temperature change can be measured at the same time when the measurement is started.

As described above, according to this embodiment, the maximum and minimum values of the interference state and the interference state at the start of measurement can be obtained without changing the temperature of the object to be measured. It is possible to improve the temperature measurement accuracy at the time. In the above embodiment, since the semiconductor laser made of the III-V group compound semiconductor is used, highly accurate temperature measurement can be realized. However, the oscillation wavelength of the semiconductor laser of the III-V group compound semiconductor is 1.6 μm at the longest. Therefore, the measurement temperature range of a semiconductor wafer such as silicon or GaAs having a relatively small energy band gap has an upper limit and becomes narrow.

Therefore, in order to solve such a problem, it is possible to use a II-VI group semiconductor laser having a wide oscillation wavelength range. That is, PbSnTe, PbTeS, PbSSe, PbS having a NaCl type crystal structure
II-VI group compound semiconductors such as nSe have a content of 0.04 to 0.3.
It has an energy band gap of eV. The semiconductor laser 1 made of such a semiconductor can oscillate in the wavelength range of 4 to 30 μm due to the difference in composition.

When the semiconductor laser made of the III-V group compound semiconductor used in the first embodiment emits a pulsed laser beam, the wavelength of the laser beam is shortened by several angstroms at the rising edge of the pulse, and then becomes longer. Although it had characteristics, a semiconductor laser made of a II-VI group compound semiconductor, when a pulsed laser beam is emitted, the wavelength of the laser beam is longer than several angstroms at the rise of the pulse, and then becomes shorter. It has the characteristics of
Therefore, the temperature measuring method according to the present embodiment can be applied only by considering this point.

Next explained is a temperature measuring method according to the second embodiment of the invention. FIG. 8 is a graph showing the relationship between the interference light intensity and the temperature of the measurement light emitting portion in the temperature measuring method according to the present embodiment, and FIG. 9 shows the interference light intensity and the temperature of the object to be measured in the temperature measuring method according to the present embodiment. FIG. 10 is a graph showing the relationship, and FIG. 10 is a graph showing the results measured by the temperature measuring method according to the present embodiment.

This embodiment shows a method for improving the accuracy of the measured temperature in the temperature measuring method according to the first embodiment. As is clear from the relationship between the measured temperature and the interference light intensity shown in FIG. 3, in the region between the ridge and the valley of the sinusoidal curve of the interference light intensity, the change of the interference light intensity with respect to the temperature change is large. Therefore, when the measured temperature is located near the center of the ridge and valley of the interference light intensity curve, it is possible to greatly improve the measurement accuracy, and to measure the temperature of the measured object kept at a substantially constant temperature. It is very effective in this case.

On the other hand, the light intensity curve of the interference light has a substantially constant cycle with respect to the temperature of the object to be measured. Therefore, for example, when the temperature is raised from the first temperature to the second temperature and kept constant at the second temperature, if the phase difference between the interference light intensity curves at the first temperature and the second temperature is known, It can be seen how to control the phase of the interference light intensity curve at the first temperature so that the second temperature is located approximately at the center of the ridge and valley of the interference light intensity curve.

By the way, the light intensity of the interference light changes sinusoidally with respect to the temperature of the measurement light emitting section (see FIG. 6). Therefore, the phase of the interference light intensity curve can be arbitrarily changed by controlling the temperature of the measurement light emitting section to a desired value. From the above relationship, the phase difference between the interference light intensities at the first temperature and the second temperature is measured, and the temperature of the light emitting portion of the light source is changed so that the second temperature is almost equal to the ridge and the valley of the interference light intensity curve. If the phase of the interference light intensity curve at the first temperature is controlled so that it is located in the center, the temperature measurement accuracy at the second temperature can be improved.

The temperature measuring method according to this embodiment will be described in detail below. Here, the case where the temperature of the object to be measured is raised from the initial temperature T1 to the temperature T2 and held at the temperature T2 will be described. First, a temperature measuring device is configured as shown in FIG. 1, and the maximum value Imax and the minimum value Imin of the interference light intensity curve are measured in the same manner as the temperature measuring method according to the first embodiment. At the same time, the phase state of the interference light intensity curve at the light emitting portion temperature T0 when the temperature is not controlled by the Peltier element 12 is measured.

In this measurement, it is assumed that, for example, the interference light intensity curve shown in FIG. 8 is obtained, and that the interference light intensity curve at the temperature T0 of the light emitting portion is located substantially at the ridge portion of the curve. Next, the phase difference of the interference light intensity curve between the initial temperature T1 and the target temperature T2 is obtained. As described above, the temperature change amount ΔT (T) [° C.] corresponding to one cycle change of the interference light intensity curve is known in advance.
Based on the temperature difference between the temperature T2 and the temperature T2, the phase of the interference light intensity curve at the temperature T1 can be predicted from the phase of the interference light intensity curve at the temperature T1.

For example, the temperature T1 in the interference light intensity curve
When the temperature T2 and the temperature T2 have a relationship shown by a dotted line in FIG.
The phase at the temperature T1 and the phase at the temperature T2 are shifted by a half cycle (phase difference φ), and the interference light intensity curve at the temperature T2 is located at the valley portion of the curve. As a result, it becomes difficult to measure temperature with high accuracy at the temperature T2. Therefore, the phase of the interference light intensity curve at the temperature T1 is controlled so that the interference light intensity curve at the temperature T2 is located substantially at the center of the ridge and valley of the curve. The phase of the interference light intensity curve at the temperature T1 can be controlled by changing the light emitting section temperature T0 of the light source.

Based on the graph of FIG. 8, when the temperature of the light emitting portion is increased from the temperature T0 to the temperature T0 ', the phase of the interference light intensity curve can be advanced by about 1/4 cycle. As a result, the relationship between the temperature T1 and the temperature T2 in the interference light intensity curve changes as shown by the solid line in FIG. 9, and the interference light intensity curve in the temperature T2 is located approximately at the center of the ridge and valley of the curve. Become. As a result, highly accurate temperature measurement can be performed at the temperature T2.

The measurement results according to this embodiment are shown in FIG. The upper part of FIG. 10 shows the interference light intensity (dotted line) when the initial interference state does not change and the interference light intensity (solid line) when it changes, and the lower part of FIG. 10 shows the semiconductor substrate obtained from each curve. 6 shows the calculated values of temperature (dotted line, solid line) and the temperature measured by the thermocouple (dashed line). As is clear from FIG. 10, when the temperature of the light emitting portion of the light source is adjusted and the initial interference state of the interference light is changed, the calculated temperature and the temperature measured by the thermocouple are compared to the case where the initial interference state is not changed. It can be seen that the two match well.

As described above, according to the present embodiment, the phase of the interference light intensity curve at a desired temperature is adjusted by adjusting the temperature of the light emitting portion of the light source, so that the measurement accuracy at that temperature is significantly improved. You can In the above embodiment, the temperature of the object to be measured is changed from the initial temperature T1 to the temperature T2.
Although the case has been described where the temperature is raised to and maintained at the temperature T2, the present embodiment is not limited to this case.

For example, when there is a process in which the target measured temperature is almost constant, the temperature of the object to be measured is measured by the temperature measuring method according to the present embodiment even in the process of passing through a plurality of temperature processes. It is possible to The present invention is not limited to the above embodiment, and various modifications can be made. For example, in the above embodiment, the temperature of the semiconductor substrate was measured, but if the thickness or the dielectric constant changes depending on the temperature,
Substrates made of other materials may be used. Further, the object to be measured is not limited to the substrate shape and may have another shape.

Although the temperature of the object to be measured is measured in the above embodiment, the first laser light having the first wavelength oscillated immediately after the rise of the pulsed laser light and the laser light oscillated thereafter. A physical quantity other than the temperature may be measured as long as the measurement is performed using the second laser light having the second wavelength.

[0061]

As described above, according to the present invention, the temperature of an object to be measured can be determined based on the intensity of the interference light which irradiates the object to be measured with coherent light and reflects or transmits the object to be measured. In the temperature measuring method for measuring the amount of change, before measuring the temperature, by changing the temperature of the measuring light oscillation part that emits the coherent light to change the wavelength of the coherent light, Prediction process that predicts maximum and minimum values, and during temperature measurement,
Since the temperature is measured by the intensity of the measured interference light and the measurement process that measures the amount of change in the temperature of the DUT based on the predicted maximum and minimum values, the maximum and minimum values of the interference light intensity after the start of measurement Since it is not necessary to measure the value, the temperature can be measured immediately after starting the measurement. Further, the maximum value and the minimum value of the interference light intensity can be predicted without changing the temperature of the object to be measured.

Further, in the above temperature measuring method, the interference light in the measuring process is adjusted to a desired interference state by setting the measuring light oscillating section at a predetermined temperature, so that the measuring accuracy at that temperature is greatly improved. be able to. Further, in the above temperature measurement method, if the predetermined temperature of the measurement light oscillation unit is adjusted so that the target measurement temperature is located at approximately the center between the maximum value and the minimum value of the intensity of the interference light, the measurement accuracy is improved. Can be improved.

In the above temperature measuring method, pulsed laser light can be used as the coherent light. Further, in the above temperature measuring method, when pulse oscillation is performed, a laser light source that oscillates laser light having an oscillation wavelength at the rising edge of the pulse that is different from the oscillation wavelength after 0.5 msec has elapsed from the rising edge,
If it is used as a light source that oscillates laser light, it is possible to easily obtain laser light having different wavelengths for use in temperature measurement.

Further, in the temperature measuring device for irradiating the object to be measured with coherent light and measuring the temperature of the object to be measured based on the intensity of the interference light reflected or transmitted through the object to be measured,
Irradiation means for irradiating the object to be measured with coherent light; wavelength changing means provided in the irradiation means for changing the temperature of the optical oscillation part of the irradiation means to change the wavelength of the coherent light; Before the measurement, by changing the wavelength of the coherent light incident on the object to be measured by the wavelength changing means, a predicting means for predicting the maximum value and the minimum value of the intensity of the interference light, and at the time of temperature measurement,
Since the temperature measuring device is constituted by the intensity of the measured interference light and the measuring means for measuring the temperature of the measured object based on the predicted maximum value and minimum value, without changing the temperature of the measured object, The temperature of the object to be measured can be measured accurately from the start of measurement.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a temperature measuring device according to a first embodiment of the present invention.

FIG. 2 is a waveform showing a change over time in the intensity of interference light when the substrate to be measured is irradiated with pulsed laser light.

FIG. 3 is a graph showing the relationship between the measured temperature and the interference light intensity in the temperature measuring device according to the first embodiment of the present invention.

FIG. 4 is a graph showing changes in wavelength and changes in interference light intensity when pulsed laser light is used in the temperature measuring device according to the first embodiment of the present invention.

FIG. 5 is an explanatory diagram of a measurement principle of the temperature measuring device according to the first embodiment of the present invention.

FIG. 6 is a graph showing the relationship between the interference light intensity and the temperature of the measurement light emitting section.

FIG. 7 is a graph showing a result of temperature measurement by the temperature measuring method according to the first embodiment of the present invention.

FIG. 8 is a graph showing the relationship between the interference light intensity and the temperature of the measurement light emitting section in the temperature measuring method according to the second embodiment of the present invention.

FIG. 9 is a graph showing the relationship between the interference light intensity and the temperature of the measured object in the temperature measuring method according to the second embodiment of the present invention.

FIG. 10 is a graph showing results measured by the temperature measuring method according to the second embodiment of the present invention.

[Explanation of symbols]

1 ... Semiconductor laser 2 ... Optical fiber 3 ... Collimating optics 4 ... Chamber 5 ... Heater 6 ... Substrate to be measured 7 ... Optical receiver 8 ... Data signal line 9 ... A / D conversion unit 10 ... Computer 11 ... Pulse power supply 12 ... Peltier element

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Claims (6)

(57) [Claims] 1. A temperature measuring method for irradiating an object to be measured with coherent light and measuring the amount of change in temperature of the object to be measured based on the intensity of the interference light reflected or transmitted through the object to be measured. In, before the temperature measurement, by changing the temperature of the measuring light oscillation unit that emits the coherent light to change the wavelength of the coherent light, the maximum and minimum values of the intensity of the interference light And a measuring step of measuring the amount of change in the temperature of the measured object based on the predicted maximum value and minimum value of the intensity of the interference light at the time of temperature measurement. How to measure temperature. 2. The temperature measuring method according to claim 1, wherein the measuring light oscillating unit is set to a predetermined temperature, and the interference light in the measuring process is brought into a desired interference state. . 3. The temperature measuring method according to claim 2, wherein the predetermined temperature of the measuring light oscillating unit is such that a target measuring temperature is substantially at a center between the maximum value and the minimum value of the intensity of the interference light. A method for measuring temperature, characterized by adjusting the position. 4. The temperature measuring method according to claim 1, wherein the coherent light is a pulsed laser beam. 5. The temperature measuring method according to claim 4, wherein the light source that oscillates the laser light oscillates when the oscillation wavelength at the rise of the pulse is 0.5 msec after the rise when the pulse oscillation is performed. A temperature measuring method comprising oscillating a laser beam having a wavelength different from the wavelength. 6. A temperature measuring device for irradiating an object to be measured with coherent light and measuring the temperature of the object to be measured based on the intensity of interference light reflected or transmitted through the object to be measured, Irradiation means for irradiating the DUT with the coherent light, and wavelength change for changing the wavelength of the coherent light by changing the temperature of the light oscillation part of the irradiation means provided in the irradiation means. And a predicting means for predicting a maximum value and a minimum value of the intensity of the interference light by changing the wavelength of the coherent light incident on the object to be measured by the wavelength changing means before temperature measurement. A temperature measuring device comprising: a temperature measuring means for measuring the temperature of the object to be measured based on the intensity of the measured interference light and the predicted maximum and minimum values.