Optical temperature sensor and method for manufacturing optical temperature sensor

Provided is an optical temperature sensor including a temperature sensing element having light transmission characteristics that vary with temperature, a hollow holding member that holds the temperature sensing element, and an optical fiber that is arranged inside the holding member, the optical fiber including a tip face that is disposed to face the temperature sensing element at a position separated from the temperature sensing element by a predetermined distance. The temperature sensing element allows light emitted from the tip face of the optical fiber to be incident thereon, allows the incident light to be transmitted therethrough, and allows reflected light of the transmitted light that has been reflected by a measuring object to be transmitted therethrough.

TECHNICAL FIELD

The present invention relates to an optical temperature sensor and a method for manufacturing an optical temperature sensor.

BACKGROUND ART

Optical temperature sensors are known that use a temperature sensing element made of a semiconductor having an energy gap that varies in response to temperature changes (see, e.g., Patent Documents 1-5). Such optical temperature sensors are configured to transmit signal light emitted from a first light emitting element and reference light emitted from a second light emitting element through the temperature sensing element, and detect an external temperature based on the light intensities of the signal light and the reference light that have been transmitted through the temperature sensing element.

PRIOR ART DOCUMENTS

Patent Documents

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

However, values detected by the optical temperature sensors as described above may fluctuate due to the structure of the temperature sensors.

Also, in temperature measuring devices for measuring the temperature of a measuring object based on values detected by optical temperature sensors, measurement accuracy, responsiveness, and stability may be degraded depending on the environmental temperature and individual unit differences of components and the like.

In view of the above problems, it is an object of the present invention to provide an optical temperature sensor and a temperature measuring device that are capable of achieving favorable responsiveness and stability and improved temperature measurement accuracy.

Means for Solving the Problem

According to one aspect of the present invention, an optical temperature sensor is provided that includes a temperature sensing element having light transmission characteristics that vary with temperature, a hollow holding member that holds the temperature sensing element, and an optical fiber that is arranged inside the holding member, the optical fiber including a tip face that is disposed to face the temperature sensing element at a position separated from the temperature sensing element by a predetermined distance. The temperature sensing element allows light emitted from the tip face of the optical fiber to be incident thereon, allows the incident light to be transmitted therethrough, and allows reflected light of the transmitted light that has been reflected by a measuring object to be transmitted therethrough.

According to another aspect of the present invention, a method for manufacturing the above optical temperature sensor is provided, the method including a step of holding the temperature sensing element in the holding member, a step of rotating the holding member in a state where the tip face of the optical fiber is separated from the temperature sensitive element and optimizing a facing position of the tip face of the optical fiber with respect to the temperature sensing element, and a step of arranging the optical fiber at the optimized facing position, which is separated from the temperature sensing element by the predetermined distance.

Advantageous Effect of the Invention

According to an aspect of the present invention, an optical temperature sensor and a temperature measuring device may be provided that are capable of achieving favorable responsiveness and stability and improved temperature measurement accuracy.

EMBODIMENTS FOR IMPLEMENTING THE INVENTION

In the following, embodiments of the present invention are described with reference to the accompanying drawings. Note that in the present descriptions and the drawings, features and elements that are substantially identical are given the same reference numerals and overlapping descriptions may be omitted.

First, an optical temperature sensor1according to an embodiment of the present invention will be described with reference toFIG. 1.FIG. 1is an overall configuration diagram of an optical temperature sensor1according to an embodiment of the present invention. The optical temperature sensor1is a temperature sensor that uses optical fiber and a compound semiconductor chip (thermosensitive element) that changes an optical absorption wavelength as a function of temperature. That is, the optical temperature sensor1is a semiconductor absorption wavelength-based temperature sensor that detects the temperature using a thermosensitive element that changes absorption wavelengths (absorption properties) for transmitted light depending on the temperature.

The optical temperature sensor1includes a thermosensitive element10, a heat transfer aluminum plate11, a holding cylinder12, an optical fiber13, a fixing member14, and a spring15. The thermosensitive element10is made of the compound semiconductor gallium arsenide (GaAs). An aluminum reflection film is formed on an upper face of the thermosensitive element10, and an antireflection film is formed on a lower face of the thermosensitive element10. The thermosensitive element10is an example of a temperature sensing element that has light transmission characteristics that vary with temperature. Note that the temperature sensing element is not limited to the compound semiconductor gallium arsenide (GaAs) as long as it is made of a substance that has light transmission characteristics that vary depending on the temperature.

The heat transfer aluminum plate11that has high thermal conductivity is fixed to the upper face of the thermosensitive element10with an adhesive. With respect to the structure of the tip portion of the optical temperature sensor1, the holding cylinder12has an opening at its tip, and the heat transfer aluminum plate11having the thermosensitive element10adhered thereto is fit into the opening of the holding cylinder12. In this way, the opening of the holding cylinder12may be closed, and the thermosensitive element10is arranged inside the holding cylinder12and fixed at its tip portion. The holding cylinder12is cylindrically shaped and has the optical fiber13arranged therein. The holding cylinder12is an example of a holding member for holding the temperature sensing element. Note that the holding member does not necessarily have to be cylindrically shaped as long as it is a hollow member that can hold the optical fiber13therein.

The optical fiber13has a two-core structure. The fixing member14surrounds the optical fiber13and is fixed to the holding cylinder12with adhesive. In this way, the optical fiber13may be arranged to extend vertically such that its tip face may be positioned at a tip portion of the optical temperature sensor1.

In the present embodiment, an electrostatic chuck (ESC) is illustrated as an example of a temperature measuring object205. The temperature of the temperature measuring object205is transmitted to the thermosensitive element10through the heat transfer aluminum plate11. Note that when heat is exchanged between the thermosensitive element10and the holding cylinder12, the optical fiber13, or the fixing member14, an error may occur in the temperature (detected value) of the temperature measuring object205detected by the thermosensitive element10and the accuracy of the temperature sensor may be degraded.

Accordingly, in the optical temperature sensor1according to the present embodiment, the thermosensitive element10is arranged to not be in contact with the tip faces of and the optical fiber13and the fixing member14. That is, the tip face of the optical fiber13is arranged to face the thermosensitive element10at a position separated from the thermosensitive element10by a predetermined distance. Thus, a hollow portion S is formed between the faces of the optical fiber13and the thermosensitive element10. Note that the distance between the thermosensitive element10and the tip face of the optical fiber13may be optimized with respect to the design value (e.g., 2.55 mm to 2.65 mm) by rotating the holding cylinder12to make fine adjustments to the facing position of the tip face of the optical fiber13with respect to the thermosensitive element10. The optimization of the above distance during a manufacturing process is described below in connection with a method for manufacturing the optical temperature sensor1described below.

Also, the optical temperature sensor1according to the present embodiment is designed such that the temperature of the thermosensitive element10may not be easily transmitted to the holding cylinder12and the optical fiber13. In this way, temperature measurement accuracy may be improved and responsiveness to a temperature change of a measuring object may be improved.

Specifically, the holding cylinder12, which is adhered to the heat transfer aluminum plate11, is made of a material having low thermal conductivity, excellent mechanical strength, and high thermal resistance. The fixing member14is similarly made of a material having low thermal conductivity, excellent mechanical strength, and high thermal resistance. For example, the holding cylinder12and the fixing member14may be made of resin bodies with low thermal conductivity, such as PPS (polyphenylene sulfide).

Also, the area of contact between the holding cylinder12and the heat transfer aluminum plate11is arranged to be as small as possible in order to suppress the heat transfer. Further, the holding cylinder12and the fixing member14are arranged to be as thin as possible in order to reduce heat conduction. In particular, a tip portion of the fixing member14that is positioned near the thermosensitive element10is arranged to have a smaller diameter (thickness) than the diameter (thickness) of a lower portion. That is, a drop shoulder portion14ais formed at the tip portion of the fixing member14to reduce the thickness of the fixing member14near the thermosensitive element10. Thus, a space is created between the side portions of the fixing member14and the holding cylinder12at the drop shoulder portion14a, and the area of contact between the holding cylinder12and the fixing member14may be reduced. With such a configuration, the amount of heat transferred from the thermosensitive element10to the holding cylinder12and the fixing member14may be reduced and responsiveness to a temperature change of a measuring object may be improved.

Also, a protruding portion12bthat protrudes outward and has a larger diameter than an upper portion of the holding cylinder12is formed at a bottom portion of the holding cylinder12. At the protruding portion12b, a space is formed between the holding cylinder12and the optical fiber13accommodated within the holding cylinder12, and a spring15may be arranged in such a space, for example. The holding cylinder12is fit into an aluminum flange21, and the holding cylinder12may be fixed in place by fixing the flange21to a mounting table200using screws22and23, for example. An aluminum bushing24is arranged below the flange21. The spring15may be fixed to the upper surface of the bushing24by fixing the flange21with screws22and23.

The tip portion of the optical temperature sensor1is configured such that the temperature of the measuring object205may be transferred to the thermosensitive element10through the heat transfer aluminum plate11. In the present embodiment, the holding cylinder12is pushed upward by the expansion/contraction of the spring15, and the tip portion of the optical temperature sensor1is pushed against the lower surface of the temperature measuring object205. By pushing the heat transfer aluminum plate11against the lower surface of the temperature measuring object205, stable heat transfer between the temperature measuring object205and the heat transfer aluminum plate11may be performed, and temperature detection by the thermosensitive element10may be stably performed. Note that the reaction force of the spring15may be set to a minimum force required for securing an adequate area of contact between the heat transfer aluminum plate11and the measuring object205for stably measuring the temperature of the measuring object205. The reaction force of the spring15is set to such a minimum force such that excessive force would not be applied to the temperature measuring object205.

LED light output from a temperature measuring device30passes through the optical fiber13and is transmitted through the thermosensitive element10to be reflected by the lower face of the temperature measuring object205. Then, the reflected light is re-transmitted through the thermosensitive element10and is passed through the optical fiber13to be received by the temperature measuring device30.

[Method for Manufacturing Optical Temperature Sensor]

In the following, a method for manufacturing the optical temperature sensor1according to the present embodiment will be described with reference toFIG. 2.FIG. 2illustrates a method for manufacturing the optical temperature sensor1according to one embodiment. Note that before starting the manufacture of the optical temperature sensor1, a cutout portion12aas shown at the bottom ofFIG. 2is formed at a side face of the tip portion of the holding cylinder12.

First, the thermosensitive element10made of gallium arsenide (GaAs) is adhered to the lower face of the heat transfer aluminum plate11.

The heat transfer aluminum plate11, in such a state, is adhered to the holding cylinder12to close the opening at the tip portion of the holding cylinder12.

Then, the optical fiber13that is integrated with the fixing member14is inserted into the holding cylinder12.

Then, the holding cylinder12is rotated while adjusting the distance D between the tip face of the optical fiber13and the thermosensitive element10. At this time, light is output from an LED that is installed in the temperature measuring device30. The light is passed through the optical fiber13, emitted from the tip of the optical fiber13, and transmitted through the thermosensitive element10. The light reflected by the measuring object205is re-transmitted through the thermosensitive element10, is passed through the optical fiber13, and is received by the temperature measuring device30. Based on the light quantity (measured value) of the received reflected light, a suitable position in a rotating direction of the thermosensitive element10at which the optical temperature sensors1would be less likely to exhibit individual unit differences is searched, and a suitable distance D between the tip face of the optical fiber13and the thermosensitive element10is searched. While maintaining an optimized position (distance D) between the thermosensitive element10and the tip face of the optical fiber13obtained from the above search, the side wall of the fixing member14is adhered to the holding cylinder12.

In the above manufacturing method, the hollow portion S with the distance D is created between the tip face of the optical fiber13and the thermosensitive element10. Note that a design reference value is provided for the distance D between the tip face of the optical fiber13and the thermosensitive element10. However, in the method for manufacturing the optical temperature sensor1according to the present embodiment, the holding cylinder12is rotated in a state where the tip face of the optical fiber13is separated from the thermosensitive element10, and the position of the tip face of the optical fiber13is finely adjusted in the vertical direction. In this way, the position in the rotating direction of the thermosensitive element10with respect to a central axis of the holding cylinder12may be adjusted, and at the same time, the distance D between the tip face of the optical fiber13and the thermosensitive element10may be finely adjusted with respect to the design reference value. In this way, the facing position of the tip face of the optical fiber13with respect to the thermosensitive element10may be optimized.

In the following, advantages of optimizing the position in the rotating direction of the thermosensitive element10and the distance D between the tip face of the optical fiber13and the thermosensitive element10in the optical temperature sensor1are described. The optical temperature sensor1detects a temperature using the thermosensitive element10that changes optical absorption wavelengths as a function of temperature. Upon manufacturing the optical temperature sensor1, in the step of adhering the thermosensitive element10to the heat transfer aluminum plate11(step a), the position and angle at which the thermosensitive element10is bonded may not necessarily be constant. Thus, by finely adjusting the distance D between the tip face of the optical fiber13and the thermosensitive element10while rotating the holding cylinder12, the light quantity (measured value) of reflected light that has passed through the thermosensitive element10may be adjusted to be a designated light quantity. In this way, individual unit differences may be reduced in the tip portion structure of the optical temperature sensor1including the thermosensitive element10. Thus, in the method for manufacturing the optical temperature sensor1according to the present embodiment, individual unit differences of the optical temperature sensor1may be reduced, and the accuracy of temperatures measured by the optical temperature sensor1may be improved.

The illustration of step e inFIG. 2is a side view of the tip portion of the optical temperature sensor1as viewed from plane C-C of the illustration of step d. When condensation occurs at the thermosensitive element10, it becomes difficult to make accurate temperature measurements. Accordingly, measures need to be implemented to prevent condensation in the hollow portion S. In this respect, the optical temperature sensor1of the present embodiment has the cutout portion12aformed on a side face of the tip portion of the holding cylinder12. The cutout portion12acommunicates with the hollow portion S. Thus, the space in which the thermosensitive element10is arranged is not sealed, and outside air can flow into the space. Also, dry air may be arranged to flow into the hollow portion S from the cutout portion12aand the dry air may be circulated around the position where the thermosensitive element10is arranged. In this way, water may be prevented from being introduced into the hollow portion S to cause condensation at the tip portion of the optical temperature sensor1. Thus, the temperature of a measuring object may be stably measured.

In the foregoing, the configuration and the method for manufacturing the optical temperature sensor1according to the present embodiment have been described. The optical temperature sensor1according to the present embodiment transmits light emitted from the tip face of the optical fiber13through the thermosensitive element10. The transmitted light is reflected by a surface of the heat transfer aluminum plate11that is in contact with the measuring object. The reflected light is re-transmitted through the thermosensitive element10and enters the optical fiber13by being incident on the tip face of the optical fiber13. The reflected light that has entered the tip face of the optical fiber13passes through the optical fiber13to be output to the temperature measuring device30. The temperature measuring device30measures the wavelength of the light absorbed by the thermosensitive element10based on the input reflected light, and converts the measured wavelength of the absorbed light into a corresponding temperature. In this way, the temperature of the measuring object205is measured.

In the following, one embodiment of the temperature measuring device30that measures the temperature of a measuring object using the optical temperature sensor1having the above-described configuration is described.

FIG. 3is a block diagram of the temperature measuring device30according to an embodiment of the present invention. The temperature measuring device30according to the present embodiment includes a light projecting/receiving module100, a measuring LED driver40, a reference LED driver41, a measuring PD (photodiode) amplifier (amp)42, an LED monitoring PD amplifier (amp)43, a 16-bit A/D converter44, a control unit50, an LED temperature amplifier (amp)52and a heater driver53.

The light projecting/receiving module100according to the present embodiment will be described below with reference toFIG. 4. The light projecting/receiving module100includes a light projecting unit (light projecting module)2for outputting measuring light and reference light, and a light receiving unit (light receiving module)3for receiving reflected light having wavelengths of light absorbed by the thermosensitive element10of the optical temperature sensor1(reflected light of the measuring light and reflected light of the reference light).

The light projecting unit2includes a measuring LED31, a reference LED32, a beam splitter33, an LED SiPD (silicon photodiode)34, and an optical connector35. The light receiving unit3includes a measuring SiPD36and an optical connector37.

The measuring LED31outputs measuring light having a first wavelength. The measuring LED31outputs light (measuring light) of a wavelength band that is transmitted through the thermosensitive element10at varying light quantities depending on the temperature of the thermosensitive element10.

The reference LED32outputs reference light having a second wavelength. The reference LED32outputs light (reference light) of a wavelength band that is transmitted through the thermosensitive element10at a constant light quantity regardless of the temperature of the thermosensitive element10; that is, the reference LED32outputs light (reference light) of a wavelength band that is transmitted through the thermosensitive element10at a light quantity that does not change as a function of the temperature of the thermosensitive element10.

The beam splitter33transmits a part of the incident measuring light and reference light, and reflects a part of the measuring light and reference light. The light transmitted by the beam splitter33is transmitted to the optical temperature sensor1through the optical fiber13that is connected to the optical connector35. The reflected light reflected by the beam splitter33is incident on the LED SiPD (silicon photodiode)34. The LED SiPD34is a photodiode for light projection confirmation. The LED SiPD34outputs current values corresponding to the light quantity of the measuring light and the light quantity of the reference light.

The measuring SiPD36receives the reflected light from the optical temperature sensor1through the optical fiber13that is connected to the optical connector37. The measuring SiPD36outputs a current value corresponding to the light quantity of the input reflected light.

The configuration of the temperature measuring device30other than the light projecting/receiving module100is described below with reference toFIG. 3. The LED monitoring PD amplifier43amplifies and converts a current value output by the LED SiPD34into a corresponding voltage.

The 16-bit A/D converter44converts the voltage output by the LED monitoring PD amplifier43as an analog value into a digital value and inputs the resulting digital value as a monitor value to the control unit50.

The control unit50controls an output value of an LED (the measuring LED31or the reference LED32) to change according to a change in the monitor value of the LED. A pulse value of pulse width modulation (PWM) by the control unit50may be output as a control signal for changing the output value of the LED.

The control unit50includes a CPU (Central Processing Unit)50a, a ROM (Read Only Memory)50b, and a RAM (Random Access Memory)50c. The CPU50aperforms temperature calculation and temperature management based on various types of data stored in a storage area such as the ROM50b. Note that functions of the control unit50may be implemented by software operations, hardware operations, or a combination thereof.

The measuring LED driver40performs feedback control of a current to be supplied to the measuring LED31based on a pulse width of a control signal output by the control unit50.

The reference LED driver41performs feedback control of a current to be supplied to the reference LED32based on a pulse width of a control signal output by the control unit50.

In this way, based on the feedback control of the current values, measuring light with a certain light quantity and reference light with a certain light quantity are respectively output from the measuring LED31and the reference LED32.

According to such a monitoring function, the light emitting intensities of the two types of LEDs used as light sources for emitting measuring light and reference light that are measured by the LED SiPD34, and feedback control of the currents to be supplied to the LEDs is performed such that the light quantities of the measuring light and the reference light may always be constant. Thus, even when the actual light emitting intensities of the measuring LED31and the reference LED32themselves decrease over time due to aging, the light quantities of the measuring light and the reference light output by the measuring LED31and the reference LED32may be controlled to be constant by increasing the current values to be supplied according to such decrease based on feedback control of the current values. In this way, aging of the temperature measuring device30may be suppressed, highly accurate temperature measurement may be enabled, and the service life of the temperature measuring device30may be prolonged.

As described above, the measuring SiPD36receives the reflected light from the optical temperature sensor1through the optical fiber13that is connected to the optical connector37. The measuring SiPD36outputs a current value corresponding to the light quantity of the input reflected light. The measuring PD amplifier42amplifies and converts the current value output by the measuring SiPD36into a corresponding voltage.

The 16-bit A/D converter44converts the voltage output as an analog value by the measuring PD amplifier42into a digital value and inputs the resulting digital value to the control unit50as a measurement value detected by the optical temperature sensor1. The control unit50converts the measurement value into a corresponding temperature.

In the following, a temperature measuring method using the temperature measuring device30according to an embodiment of the present invention is described with reference toFIG. 5.FIG. 5is a flowchart illustrating a temperature measuring method according to an embodiment of the present invention. Note that before starting the temperature measuring method ofFIG. 5, at time T1illustrated in the bottom frame portion ofFIG. 3, an output value (initial value) of the SiPD36is measured in a state where no light is output from the measuring LED31or the reference LED32. Then, at time T2, reflected light (returning light) of light output by the measuring LED31(LED1) is measured by the measuring SiPD36. Then, at time T3, reflected light (returning light) of light output by the reference LED (LED2) is measured by the measuring SiPD36. Note that the above operations of times T1, T2, T3are executed repeatedly. However, in the following, temperature control implemented upon executing the operations of times T1, T2, and T3once is described.

Also, note that the output value measured by the measuring SiPD36at time T1(initial value) is usually a value close to “0”. However, in a case where the measured output value (initial value) is greater than or equal to a predetermined threshold value, the measurement value for the measuring light is corrected by subtracting the output value (initial value) from the measured value of the reflected light of light output by the measuring LED31at time T2. Similarly, in the case where the measured output value (initial value) is greater than or equal to the predetermined threshold value, the measurement value for the reference light is corrected by subtracting the output value (initial value) from the measured value of the reflected light of light output by the reference LED32at time T3. Note that in the temperature measuring method described below, it is assumed that such corrections are not performed, and a description of a case where such corrections are performed is omitted.

First, in step S31, the measuring LED31(LED1) outputs the measuring light having the first wavelength. The measuring light passes through the optical fiber13, and is emitted from the tip face of the optical fiber13to be transmitted through the thermosensitive element10. The measuring light is light in a wavelength band (first wavelength) that is transmitted through the thermosensitive element10at a light quantity that changes in response to a change in the temperature of the thermosensitive element10. The measuring light transmitted through the thermosensitive element10is reflected by the heat transfer aluminum plate11(face in contact with the measuring object). The reflected light of the measuring light is re-transmitted through the thermosensitive element10and enters the optical fiber13by being incident on the tip face of the optical fiber13.

Then, in step S32, the measuring SiPD36receives the reflected light (returning light) from the optical temperature sensor1that has passed through the optical fiber13. The measuring SiPD36outputs a current value I1according to the light quantity of the received reflected light.

Then, in step S33, the reference LED32(LED2) outputs the reference light having the second wavelength. The reference light passes through the optical fiber13, and is emitted from the tip face of the optical fiber13to be transmitted through the thermosensitive element10. The reference light is light in a wavelength band (second wavelength) that is transmitted through the thermosensitive element10at a constant light quantity that does not change even when the temperature of the thermosensitive element10changes. The reference light transmitted through the thermosensitive element is reflected by the heat transfer aluminum plate11(face in contact with the measuring object). The reflected light of the reference light is re-transmitted through the thermosensitive element10and enters the optical fiber13from the tip face of the optical fiber13.

Then, in step S34, the measuring SiPD36receives the reflected light (returning light) from the optical temperature sensor1that has passed through the optical fiber13. The measuring SiPD36outputs a current value12corresponding to the light quantity of the received reflected light.

Then, in step S35, the control unit50obtains a ratio of the current value I1measured from the reflected light of the measuring light to the current value12measured from the reflected light of the reference light, calculates a corresponding temperature, and outputs the calculated temperature.

As described above, in the temperature measuring device30of the present embodiment, the temperature of the temperature measuring object205detected by the optical temperature sensor1is calculated based on the reflected light of the measuring light and the reflected light of the reference light.

Note that it was determined, by experiment, that in the temperature measuring device30of the present embodiment, the temperature can be measured within a period of about 8.3 milliseconds (ms). That is, according to an aspect of the present embodiment, the temperature measuring period can be substantially reduced as compared with conventional applications in which the temperature measuring period is typically about 40 milliseconds (ms).

In measuring the temperature based on the semiconductor absorption wavelength using the optical temperature sensor1, the internal temperature of the light projecting/receiving module100may cause errors in measurement values. Oftentimes, such errors in the measurement values occur due to fluctuations in the measurement values resulting from fluctuations in the environmental temperature of the measuring LED31and the reference LED32. That is, the center wavelength of an LED shifts with temperature. Thus, by controlling the environmental temperature of the LED to be constant, temperature measurement may be stably performed without being affected by the environmental temperature. Also, the center wavelength of an LED may slightly vary depending on each individual LED. Thus, by controlling the environmental temperature of the LED in order to absorb the individual unit differences in the LEDs, temperature measurement may be more stably performed, and individual unit differences in the temperature sensor may be reduced. Accordingly, in the present embodiment, temperature control mechanisms are provided for separately controlling the temperature of the measuring LED31and temperature of the reference LED32. In the following, a temperature control unit including a temperature control mechanism for separately controlling the temperature of the measuring LED31and the temperature of the reference LED32will be described with reference toFIGS. 3 and 6.

First, referring toFIG. 3, the temperature control unit includes a temperature sensor38and a temperature control mechanism6that are included in the light projecting/receiving module100, an LED temperature amplifier (amp)52, a heater driver53, and the control unit50. The temperature control unit performs temperature control of the measuring LED31and temperature control of the reference LED32separately.

Referring toFIG. 6, as shown in the left diagram ofFIG. 6, the measuring LED31and the reference LED32are arranged inside the light projecting unit2. A separate temperature control function (temperature control unit) is provided for each of the measuring LED31and the reference LED32. More specifically, the temperature control function may have a configuration as shown in the middle diagram ofFIG. 6corresponding to a cross-sectional view across line D-D of the left diagram ofFIG. 6. As shown in the middle diagram ofFIG. 6, the outer periphery of the measuring LED31is covered by a cylindrical member60. Similarly, the outer periphery of the reference for LED32is covered by a cylindrical63. The cylindrical members60and63may be made of aluminum, for example.

Aluminum plates62and64that are about 1 mm thick are respectively arranged above the cylindrical members60and63, and Peltier elements61and65are respectively arranged on the aluminum plates62and64. As shown in the middle diagram ofFIG. 6, the Peltier element61(the following descriptions similarly apply to the Peltier element65such that overlapping descriptions are omitted) has the property of transporting heat from one metal to another metal when an electric current is applied to the junction of the two metals. In this way, heat absorption occurs at one side, and heat is generated at the other side. Note that the cylindrical member60, the aluminum plate62, and the Peltier element61constitute an example of a temperature control mechanism6ofFIG. 3, and is also an example of a first temperature control mechanism for heating or cooling a first light source based on the temperature of the first light source. The cylindrical member63, the aluminum plate64, and the Peltier element65constitute another example of the temperature control mechanism6ofFIG. 3and is also an example of a second temperature control mechanism for heating or cooling a second light source based on the temperature of the second light source. Note that in some embodiments, the temperature control mechanism6does not have to include the aluminum plates62and64.

For example, as shown in the middle diagram ofFIG. 6, in a case where the current supplied to the Peltier element61is controlled based on the temperature detected by the temperature sensor38that is provided near the measuring LED31, and a lower surface of the Peltier element61is controlled to give off heat as shown in the middle diagram ofFIG. 6, the measuring LED31is heated via the aluminum plate62and the cylindrical member60having good thermal conductivity. In a case where the current supplied to the Peltier element61is controlled based on the temperature detected by the temperature sensor38, and the lower surface of the Peltier element61is controlled to absorb heat, the measuring LED31is cooled via the aluminum plate62and the cylindrical member60. The above descriptions similarly apply to the reference LED32. That is, by controlling the current supplied to the Peltier element65, the reference LED32may be heated and cooled in a similar manner.

In a conventional light projecting module, a high output heater is required to control the temperature of an overall housing. On the other hand, the temperature control unit of the present embodiment performs local temperature control for controlling the temperature of the measuring LED31and the temperature of the reference LED32. Thus, temperature control may be performed on the measuring LED31and the reference LED32with a small amount of energy.

Further, in order to prevent heat at the cylindrical member60and63from escaping outside, the cylindrical members60and63are designed to be thermally isolated from a housing H that surrounds the outer peripheries of the cylindrical members60and63. That is, spaces are provided around the cylindrical members60and63to reduce the areas of contact between the housing H and the cylindrical members60and63. Note that in some embodiment, insulation rings (not shown) may be arranged between the housing H and the cylindrical members60and63.

The Peltier element61may be placed on the aluminum plate62as shown in the upper right diagram ofFIG. 6. Alternatively, a flat surface60amay be formed at an upper portion of the cylindrical member60as shown in the lower right diagram ofFIG. 6, and the Peltier element61may be placed on the flat surface60a. Note that the Peltier element65may similarly be placed directly on the cylindrical member63rather than via the aluminum plate64.

Returning toFIG. 3, a current value detected by the temperature sensor38is input to the LED temperature amplifier52. The LED temperature amplifier52amplifies and converts the current value into a corresponding voltage value, and outputs the voltage value to the control unit50. The control unit50outputs a control signal for controlling a current value to be output to a heater based on the input voltage value. The heater driver53supplies desired currents to the Peltier elements61and65ofFIG. 6based on the control signal. In this way, the temperatures of the measuring LED31and the reference LED32may be respectively controlled to desired temperatures. Also, temperature control of the measuring LED31and temperature control of the reference LED32are separately and independently performed.

Wavelength distributions of LEDs tend to vary depending on each individual LED. According to the present embodiment, a temperature control unit is provided for each of the measuring LED31and the reference LED32, and temperature control is performed separately for each LED. In this way, individual unit differences and environmental temperature differences in the measuring LED31and the reference LED32may be absorbed.

The light quantity of an LED changes over time and gradually decreases. Therefore, by monitoring the light quantity actually output by the LED and controlling the light quantity output by the LED to be constant, a temperature may be more accurately measured. Accordingly, in the temperature measuring apparatus30according to the present embodiment, the LED SiPD34as shown inFIGS. 3 and 4is provided in order to monitor the light quantities output by the LEDs.

The LED SiPD34is a photodiode for light projection confirmation and outputs a current value corresponding to the light quantity of the measuring light output by the measuring LED31. The LED monitoring PD amplifier43amplifies and converts the current value output by the LED SiPD34into a corresponding voltage value and outputs the voltage value to the control unit50.

The control unit50measures the light quantity output by the LED SiPD34based on the input voltage value, and controls a current to be supplied to the measuring LED31to increase in accordance with a decrease in the measured light quantity.

The measuring light LED driver40performs feedback control of the current to be supplied to the measuring LED31according to the pulse width of a control signal output by the control unit50.

Similarly, the LED SiPD34outputs a current value corresponding to the light quantity of the reference light output by the reference LED32. The LED monitoring PD amplifier43amplifies and converts the current value output by the LED SiPD34into a corresponding voltage value and outputs the voltage value to the control unit50.

The control unit50measures the light quantity output by the LED SiPD34based on the input voltage value input, and controls a current to be supplied to the reference LED32to increase in accordance with a decrease in the measured light quantity.

The LED driver41performs feedback control of the current to be supplied to the reference LED32based on the pulse width of a control signal output by the control unit50.

With the above configuration, the light quantity output by the measuring LED31and the light quantity output by the reference LED32may be monitored in order to control the light quantities output by the LEDs to be constant with respect to the aging of the LEDs.

Note that the LED SiPD34corresponds to an example of a monitoring unit for monitoring the light quantities of the measuring light and the reference light. The measuring LED31corresponds to an example of a first light source for outputting measuring light of a first wavelength. The reference LED32corresponds to an example of a second light source for outputting reference light of a second wavelength.

Example Advantages

FIGS. 7-9show example temperature measurement results according to the present embodiment. Note that in the graphs shown inFIGS. 7-9, the horizontal axis represents the time (seconds), and the vertical axis represents the surface temperature (° C.) of a temperature measuring object.FIG. 7shows detection values detected by temperature sensors of the present embodiment and Comparative Examples 1 and 2 over the course of time indicated by the horizontal axis in a case where the surface temperature of the temperature measuring object was not changed.

According toFIG. 7, in comparing the temperatures detected by the temperature sensors of the present embodiment and Comparative Examples 1 and 2, it can be appreciated that the temperatures detected by the optical temperature sensor1according to the present embodiment have the least amount of variations. The temperatures detected by the temperature sensor of Comparative Example 1 has variations about three times as large as the temperature variations of the optical temperature sensor1according to the present embodiment, and the temperatures detected by the temperature sensor of Comparative Example 2 has variations about twice as large as the temperature variations of the optical temperature sensor1according to the present embodiment. As can be appreciated from the above, favorable output characteristics and stability can be achieved in the optical temperature sensor1of the present embodiment.

Further,FIG. 8shows detection values detected by the temperature sensors of the present embodiment and Comparative Examples 1 and 2 over the course of time indicated by the horizontal axis in a case where the surface temperature of the temperature measuring object was controlled to change from 20° C. to 70° C. According toFIG. 8, in comparing the temperatures detected by the optical temperature sensor1of the present embodiment and the temperature sensors of Comparative Examples 1 and 2, it can be appreciated that the optical temperature sensor1of the present embodiment has higher responsiveness as compared with the temperature sensor of Comparative Example 1. Further, referring to the diagram on the right ofFIG. 8showing an enlarged view of the detection values of the temperature sensors around the temperature rise time, it can be appreciated that the detection values of the optical temperature sensor1of the present embodiment have smaller variations as compared with the detection values of the temperature sensor of Comparative Example 2. As can be appreciated from the above, favorable output characteristics, stability, and responsiveness can be achieved in the optical temperature sensor1of the present embodiment.

Further,FIG. 9shows detection values detected by the temperature sensors of the present embodiment and Comparative Examples 1 and 2 over the course of time indicated by the horizontal axis in a case where the surface temperature of the temperature measuring object was controlled to change from 70° C. to 80° C. According toFIG. 9, in comparing the temperatures detected by the optical temperature sensor1of the present embodiment and the temperature sensors of Comparative Examples 1 and 2, it can be appreciated that the optical temperature sensor1of the present embodiment higher responsiveness as compared with the temperature sensor of Comparative Example 1. Also, referring to the diagram on the right ofFIG. 9showing an enlarged view of the detection values of the temperature sensors at the temperature rise time, it can be appreciated that the optical temperature sensor1of the present embodiment has smaller variations as compared with the detection values of the temperature sensor of Comparative Example 2. As can be appreciated from the above, the optical temperature sensor1of this embodiment, favorable output characteristics, stability, and responsiveness can be achieved in the optical temperature sensor1of the present embodiment even in cases where temperature fluctuations occur in a relatively high temperature region.

As described above, according to the present embodiment, the tip face of the optical fiber and the thermosensitive element are arranged to face each other while being separated from each other by a predetermined distance. In this way, an optical temperature sensor with desirable accuracy, responsiveness, and stability may be provided. Further, according to the present embodiment, a method for manufacturing a low-cost optical temperature sensor that can achieve a predetermined level of performance may be provided.

Further, according to the temperature measuring device30of the present embodiment, temperature measurement may be performed in a short period of time. Further, according to the temperature measuring device30of the present embodiment, the light quantities of the measuring light and the reference light output by the measuring LED31and the reference LED32may be controlled to be constant. In this way, changes in the temperature measuring device30caused by aging may be suppressed, highly accurate temperature measurement may be enabled, and the service life of the temperature measuring device30may be prolonged.

Further, according to the temperature measuring device30of the present embodiment, a temperature control unit is provided for each of the measuring LED31and the reference LED32, and temperature control is separately performed for each of the LEDs. In this way, individual unit differences and environmental temperature differences in the measuring LED31and the reference LED32may be absorbed.

A method for manufacturing an optical temperature sensor and an optical temperature sensor according to the present invention have been described above with respect to illustrative embodiments. Also, a temperature measuring device, a light projecting module, and a temperature measuring method according to the present invention have been described above with respect to illustrative embodiments. However, the present invention is not limited to the above-described embodiments, and various changes and modifications may be made within the scope of the present invention. Also embodiments of the present invention and modifications thereof may be combined to the extent practicable.

For example, an optical temperature sensor, a temperature measuring device, and a temperature measuring method according to the present invention may be applied to temperature measurement of an electrostatic chuck or some other component part of an etching apparatus, an ashing apparatus, or a thin film deposition apparatus.

The present application is based on and claims the benefit of priority of Japanese Patent Application No. 2014-042137 filed on Mar. 4, 2014, the entire contents of which are herein incorporated by reference.

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