JP6552361B2 - Sensor and vaporizer - Google Patents

Description

  Embodiments of the present invention relate to sensors and vaporizers.

  In the manufacture of an electronic device such as a semiconductor device, plasma treatment is performed to excite the processing gas supplied into the processing container to generate plasma and expose the object to the plasma to process the object to be processed. There is. In order to perform such plasma processing, a vaporizer that supplies water vapor as a processing gas to a plasma processing apparatus is known. Water vapor may be used for the ashing treatment or may be used as an additive gas for the etching gas.

For example, Patent Document 1 describes a vaporizer including a water storage tank, a heater, a process gas tank, a water vapor pipe, a process gas pipe, and a junction pipe. Pure water is stored in the water storage tank. One end of a steam pipe for transporting the steam generated by the heating of the heater is connected to the upper part of the water storage tank. Further, CF ₄ gas is stored in the process gas tank. One end of a process gas pipe for transporting CF ₄ gas is connected to the process gas tank. The other end of the steam pipe and the other end of the process gas pipe merge with each other and are connected to one end of the merging pipe. The other end of the junction pipe is connected to the plasma processing apparatus. In the apparatus described in Patent Document 1, a mixed gas in which the water vapor generated in the water storage tank and the CF ₄ gas from the process gas tank are mixed is supplied to the plasma processing apparatus via a mixed gas pipe.

Unexamined-Japanese-Patent No. 2004-87952

  By the way, in order to prevent the liquid level in the tank from becoming abnormal such as when the liquid level becomes excessively high or low, the liquid level in the tank is higher than a predetermined height. It is conceivable to use a sensor for detecting whether or not the position is higher. As such a sensor, a sensor as shown in FIG. 12 is used.

  The sensor LS shown in FIG. 12 includes a rod LD, a light emitting element EM, and a light receiving element RE. The rod LD is made of a translucent material and has a tip portion LD1 and a main body portion LD3. The main body portion LD3 has a substantially cylindrical shape, and the distal end portion LD1 is continuous with one end of the main body portion LD3. The distal end portion LD1 has a conical shape which decreases in diameter as it is separated from the other end of the main body portion LD3, that is, the proximal end portion LD2. The rod LD is arranged so that the boundary between the main body part LD3 and the tip part LD1 is located at the reference position RH. The reference position RH is a position in the height direction relative to the bottom of the tank. In FIG. 12, the liquid surface FL represents the water surface in the tank.

  FIG. 13 is an enlarged cross-sectional view of a part of the rod LD including the tip end portion LD1, and is a cross-sectional view showing the rod LD in a plane including the central axis Z1 of the rod LD. The tip portion LD1 has a tip angle α. As shown in FIG. 13, the tip angle α is defined as an angle formed by two lines (indicated by reference numeral “X” in the figure) formed by the surface of the tip portion LD1 in a cross section including the central axis Z1. In other words, the tip angle α is an angle formed by two intersecting lines of a plane including the central axis Z and the surface of the tip portion LD1.

  Returning to FIG. 12, the light emitting element EM and the light receiving element RE are provided on the base end portion LD2. The light emitting element EM is, for example, a light emitting diode, and the light receiving element RE is, for example, a phototransistor. The light emitting element EM emits light to the base end portion LD2. The light incident on the proximal end LD2 propagates in the main body LD3 toward the distal end LD1 and is reflected at the distal end LD1. The light reflected at the tip end portion LD1 propagates again through the main body portion LD3, passes through the base end portion LD2, and is received by the light receiving element RE. The light receiving element RE outputs a voltage corresponding to the intensity of the received light. That is, the light receiving element RE outputs a larger voltage as the intensity of the received light is larger.

  This sensor LS detects the contact state of water at the tip portion LD1 using the difference in refractive index between water and air. As shown in (a) of FIG. 12, when the tip end portion LD1 is not in contact with water, that is, when the liquid level FL is at a position lower than the reference position RH in the height direction, the tip end portion LD1. And the refractive index of the air in contact with the surface of the tip portion LD1 are large, the amount of light reflected at the tip portion LD1 increases, and the intensity of light received by the light receiving element RE increases. On the other hand, as shown in FIG. 12B, when the tip portion LD1 is in contact with water, that is, when the liquid level FL is the same as or higher than the reference position RH. Since the difference between the refractive index of the tip portion LD1 and the refractive index of water in contact with the surface of the tip portion LD1 is small, the amount of light that passes through the water from the tip portion LD1 increases and is received by the light receiving element RE. The light intensity decreases. Thus, since the intensity of the light received by the light receiving element RE changes depending on whether or not the tip portion LD1 is in contact with water, the sensor LS is based on the intensity of the light received by the light receiving element RE. The contact state of water at the tip end portion LD1 can be detected. If it is possible to detect the water contact state of the tip portion LD1, it is detected whether the position in the height direction of the liquid level FL in the tank is the same as or higher than the reference position RH. Can do.

  However, the inventor of the present application uses a sensor as shown in FIG. 12 to detect whether the position in the height direction of the liquid level FL in the tank is at the same position as or higher than the reference position RH. When I tried, I discovered the following problems. For example, as shown in FIG. 14A, when the water in the tank is heated when the position in the height direction of the liquid level FL is lower than the reference position RH, the water droplet D adheres to the tip portion LD1 of the rod LD There is something to do. When the water droplet D adheres to the tip portion LD1, the difference between the refractive index of the rod LD and the refractive index of the water droplet D is small, so the amount of light transmitted from the tip portion LD1 to the water droplet D increases. As a result, the intensity of the light received by the light receiving element RE decreases, and the height of the liquid level FL is high although the position in the height direction of the liquid level FL is lower than the reference position RH by a predetermined distance or more. There is a case where the position in the vertical direction is erroneously detected as being at the same position as or higher than the reference position RH.

  Also, as shown in (b) of FIG. 14, when the water in the tank is heated when the position in the height direction of the liquid level FL is higher than the reference position RH, the water in the tank boils. Bubbles B may adhere to the tip portion LD1 of the rod LD. When the air bubble B adheres to the distal end LD1, the difference between the refractive index of the rod LD and the refractive index of the air bubble B is large, so the amount of light reflected from the distal end LD1 toward the proximal end LD2 increases. As a result, the intensity of the light received by the light receiving element RE is increased, and the height of the liquid level FL is high although the position in the height direction of the liquid level FL is higher than the reference position RH by a predetermined distance or more. It may be erroneously detected that the vertical position is lower than the reference position RH.

  From such a background, it is required to provide a sensor and a vaporizer that can suppress erroneous detection of a contact state with water.

In one embodiment of the present invention, a sensor that outputs different output voltages depending on a contact state with water is provided. This sensor includes a rod, a light emitting element, a phototransistor, an output circuit, a power supply, and an amplifier circuit. The rod is translucent, has a distal end and a proximal end, and extends between the distal end and the proximal end. The tip angle of the tip portion is 97 ° or more and 107 ° or less. The light emitting element outputs light to be propagated into the rod to the proximal end. The phototransistor is provided on the base end and receives the light reflected by the tip of the rod among the light output from the light emitting element. The output circuit is provided between the phototransistor and the ground terminal, includes a resistive element connected in series to the phototransistor, and outputs a voltage having a magnitude corresponding to the current flowing through the phototransistor. The power supply applies an input voltage to a series circuit including a phototransistor and a resistive element. The amplifier circuit amplifies the voltage output from the output circuit and outputs the amplified voltage as an output voltage. When it is assumed that there is no loss of light between the light emitting element and the phototransistor, the input voltage V _in which power is generated, the output voltage V _out of _the amplifier circuit, the following formula (1);
| V _out | = | Gv · V _in | (1)
It has the relationship represented by. In this equation (1), Gv is a gain. In this sensor, the gain is set to a value of 3200 or more and less than 14000.

  In the sensor according to one aspect, the tip of the rod has a tip angle of 97 ° or more and 107 ° or less. By setting the tip angle to 97 ° or more, the output voltage when the tip of the rod is not in contact with water can be increased. This is considered to be because if the tip angle is 97 ° or more, the amount of light reflected by the tip and received by the phototransistor increases. Further, the upper limit value of the tip angle is 107 °. This upper limit value is an angle that is defined so that water droplets attached to the tip end part easily fall. When the water droplet attached to the tip portion falls, the erroneous detection of the sensor due to the water droplet can be reduced.

  Furthermore, in this sensor, the gain is set to 3200 or more and less than 14000. By setting the gain to 3200 or more, the output voltage of the sensor is increased even when water droplets adhere to the tip when the position in the height direction of the liquid level is lower than the above-mentioned predetermined position. can do. Therefore, erroneous detection of the sensor due to water droplets attached to the tip can be reduced. On the other hand, if the gain of the sensor is 14000 or more, when air bubbles adhere to the tip in water, the output voltage of the sensor becomes too large, which may cause false detection. In this sensor, since the gain is set to less than 14000, it is possible to reduce false detection that occurs when air bubbles adhere to the tip in water. Therefore, this sensor can suppress false detection.

  In one embodiment, the rod may be made of a material having a refractive index of 1.414 or more and 1.627 or less. Further, in one embodiment, the rod may be comprised of quartz.

  In one embodiment, the tip may have a wedge shape that includes two sides approaching each other away from the other end. Also, in one embodiment, the tip may have an even number of sides and have a polygonal pyramid shape that tapers away from the other end. Furthermore, in one Embodiment, the front-end | tip part may have the cone shape which diameter-reduces as it leaves | separates from the other end.

  In one embodiment, the holding mechanism may further include a holding mechanism that holds the rod in a state where the axial direction of the rod coincides with the vertical direction, and the holding mechanism may hold the rod by point contact or line contact. When the rod is held by the holding mechanism, in the contact portion between the rod and the holding mechanism, the refractive index of light is different from that of the non-contact portion, so the material of the contact in contact with the rod propagates in the rod Part of the light may leak out of the rod through the contact portion. In one embodiment, the rod is held in point or line contact by the holding mechanism, so that the contact area between the rod and the holding mechanism can be reduced, so that the light generated at the contact portion between the rod and the holding mechanism Loss can be reduced. In one embodiment, the holding mechanism may hold the rod via an O-ring surrounding the outer peripheral surface of the rod. By holding the rod via the O-ring, the contact area between the rod and the holding mechanism can be reduced.

  In one embodiment, the rod is formed with a protrusion which protrudes from the outer peripheral surface of the rod, and the protrusion is located between the distal end and the proximal end in the axial direction of the rod, and the holding mechanism is A movement restricting portion that is provided between the protruding portion and the tip portion and faces the protruding portion in the axial direction of the rod may be included. In such a configuration, when the force directed to the distal end acts on the rod, the movement restricting portion abuts on the protrusion to restrict the movement of the rod. For this reason, the rod can be held securely.

  The vaporizer which concerns on 1 aspect of this invention is equipped with a heater, the above-mentioned at least 1 sensor, a water supply part, and a control part. The heater heats the water in the tank to generate steam. The tip of the sensor is disposed at a predetermined position in the height direction in the space. The water supply unit supplies water into the tank. The control unit controls the supply of water from the water supply unit to the tank according to the output voltage of the amplifier circuit of the sensor.

  The vaporizer according to one aspect includes the above-described sensor to prevent an abnormal state in which the position in the height direction of the liquid level in the tank is extremely high or low. Can.

  In one embodiment, the control unit may control the water supply unit to supply water into the tank when the output voltage of the amplification circuit is equal to or higher than a predetermined threshold. In one embodiment, the at least one sensor includes a first sensor and a second sensor, and the tip of the first sensor is disposed at a first position in the height direction, and the second sensor The front end portion may be arranged at a second position higher than the first position in the height direction.

  According to one aspect and various embodiments of the present invention, false detection of a contact state with water can be suppressed.

It is a figure showing roughly the composition of the plasma treatment apparatus concerning one embodiment. It is a figure showing roughly the 1st sensor and the 2nd sensor. FIG. 5 is an enlarged cross-sectional view of a portion of the rod including the tip. It is a figure which shows a specific example of the circuit structure of a circuit part. It is a figure explaining the principle of operation of the 1st sensor. It is a flowchart which shows the control method of the plasma processing apparatus of one Embodiment. It is a flowchart which shows the control method of the plasma processing apparatus of another embodiment. It is a figure which shows the relationship between the front-end | tip angle of a front-end | tip part, and the output voltage of a sensor. It is a figure which shows the relationship between the gain of a sensor, and an output voltage. It is a figure which shows the time-dependent change of the determination result of whether water is contacting the front-end | tip part, and the time-dependent change of the flow volume of the water vapor | steam which passes a flow controller. It is a figure which shows the time-dependent change of the output voltage of a 1st sensor. It is a figure which shows an example of the conventional sensor. FIG. 5 is an enlarged cross-sectional view of a portion of the rod including the tip. It is a figure explaining the problem of the conventional sensor.

  Hereinafter, various embodiments will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts will be denoted by the same reference numerals.

  First, a plasma processing apparatus provided with the vaporizer of one embodiment will be described. FIG. 1 is a view schematically showing a plasma processing apparatus 1 according to an embodiment. The plasma processing apparatus 1 shown in FIG. 1 includes a main unit 10.

  The main body unit 10 includes a processing container 12. The processing container 12 is configured to accommodate the wafer W. That is, the processing container 12 provides a space S1 for housing the wafer W.

  In one embodiment, the processing vessel 12 includes a first portion 12a and a second portion 12b. The first portion 12 a has a substantially cylindrical shape, and constitutes the side wall and the bottom of the processing container 12. The upper end of the first portion 12a is open. The second portion 12 b is mounted on the upper end of the first portion 12 a and constitutes a ceiling portion of the processing container 12.

  A mounting table 14 is provided inside the processing container 12. The mounting table 14 is configured to hold the wafer W mounted thereon. In one embodiment, the mounting table 14 may have an electrostatic chuck for electrostatically attracting the wafer W. Further, in the mounting table 14, a heater HT is provided. The heater HT is electrically connected to a heater power supply HP provided outside the processing container 12.

  Further, on the side wall of the processing container 12, a passage through which the wafer W can pass is formed. Through this passage, the wafer W is loaded into the processing container 12 and unloaded from the processing container 12 to the outside. The passage formed in the processing container 12 can be opened and closed by a gate valve GVL.

  Further, an exhaust port 12 e is formed at the bottom of the processing container 12. An exhaust device 16 is connected to the exhaust port 12e. The exhaust device 16 is configured to depressurize a space S1 in the processing container 12 and a space S2 in a quartz tube 22 described later.

  Further, a plate 18 is provided in the space S1 in the processing container 12. The plate 18 is provided above the mounting table 14 and faces the upper surface of the mounting table 14. The plate 18 is a plate-like body in which a large number of through holes are formed, and is made of, for example, quartz.

  The main body 10 further includes a plasma generation unit 20. The plasma generation unit 20 is provided on the ceiling portion of the processing container 12, that is, on the second portion 12 b. The plasma generation unit 20 has a quartz tube 22. The quartz tube 22 has a substantially cylindrical shape extending in the vertical direction, and is made of quartz. The quartz tube 22 is provided on the ceiling of the processing container 12 so that the space S2 inside the quartz tube 22 communicates with the space S1.

  A gas inlet 22 a is formed in the quartz tube 22. One end of a pipe 30 is connected to the gas inlet 22a. The other end of the pipe 30 is connected to the first port of the three-way valve V4. One end of a pipe 31 is connected to the second port of the three-way valve V4. The other end of the pipe 31 is connected to the gas supply unit GU. The gas supply unit GU includes a gas supply system GSS1, a gas supply system GSS2, and a gas supply system GSS3.

  The gas supply system GSS1 may include a gas source GS1, a flow rate controller F1, and a valve V1. The gas source GS1 is a gas source of a rare gas. The rare gas is, for example, Ar gas, but may be any rare gas such as He gas, Ne gas, Kr gas, or Xe gas. The flow rate controller F1 is, for example, a flow control system (FCS), and adjusts the flow rate of the rare gas from the gas source GS1. The valve V1 switches between supply and stop of the noble gas from the gas source GS1. The gas supply system GSS1 supplies a rare gas to the space S2 of the main body portion 10.

The gas supply system GSS2 may include a gas source GS2, a flow rate controller F2, and a valve V2. The gas source GS2 is a gas source of O ₂ gas. The flow rate controller F2 is, for example, a flow control system, and adjusts the flow rate of O ₂ gas from the gas source GS2. The valve V2 switches between supply and stoppage of O ₂ gas from the gas source GS2. The gas supply system GSS ₂ supplies O ₂ gas to the space S 2 of the main body 10.

The gas supply system GSS3 may include a gas source GS3, a flow rate controller F3, and a valve V3. The gas source GS3 is a gas source of N ₂ gas. The flow rate controller F3 is, for example, a flow control system, and adjusts the flow rate of N ₂ gas from the gas source GS3. The valve V3 switches between supply and stop of supply of N ₂ gas from the gas source GS3. The gas supply system GSS3 supplies N ₂ gas to the space S2 of the main body 10 and the space S3 of the vaporizer 50 described later.

  Further, the plasma generation unit 20 further includes a plasma source. In one embodiment, the plasma generation unit 20 has a coil 24 as a plasma source. The coil 24 is provided so as to surround the outer peripheral surface of the quartz tube 22 and is electrically connected to the high frequency power supply RG. When the high frequency power from the high frequency power supply RG is supplied to the coil 24, the gas supplied to the space S2 in the quartz tube 22 is excited and a plasma is generated. The coil 24 functions as a plasma generating unit that generates water vapor plasma generated by a vaporizer 50 described later. Active species obtained by the generation of plasma flow from the space S2 to the space S1 and are supplied to the wafer W. Thereby, removal of the organic substance contained in the wafer W or the organic substance adhering to the wafer W is performed. The plasma generation unit 20 further includes a housing 26, and the quartz tube 22 and the coil 24 are accommodated in the housing 26.

The plasma processing apparatus 1 further includes a vaporizer 50. The vaporizer 50 is a mechanism for supplying water vapor, that is, gaseous H ₂ O, to the plasma generation unit 20. The vaporizer 50 includes a tank 52. The tank 52 includes a bottom surface, a side surface, and a top surface, and defines a space S3 for storing water therein. On the upper surface of the tank 52, two through holes 52a and 52b for inserting a sensor described later are formed. O-rings 53 are provided on the inner surfaces of the through holes 52a and 52b (see FIG. 2). A temperature sensor TS is provided on the outer side surface of the tank 52. The temperature sensor TS is, for example, a platinum resistance temperature sensor, and measures the temperature of the water stored in the tank 52. Below the tank 52, a heater 54 is provided. The heater 54 is connected to the power supply 56, generates heat by the power supplied from the power supply 56, and heats the water in the tank 52. When water is heated by the heat from the heater 54, the water in the tank 52 is vaporized to generate steam. The generated water vapor is stored in the upper part of the space S3. At the top of the tank 52, a vent 58 for discharging the water vapor in the tank 52 is provided.

  One end of the pipe 32 is connected to the vent hole 58. The other end of the pipe 32 branches into a pipe 33 and a pipe 34. The pipe 33 is connected to the third port of the three-way valve V4. The three-way valve V4 is a valve that selectively connects one of the pipe 31 and the pipe 33 to the pipe 30. That is, the three-way valve V4 is configured so that any one of the gas from the gas supply systems GSS1, GSS2, and GSS3 and the water vapor from the vaporizer 50 is selectively supplied to the space S2 of the main body 10. Switch the connection. The pipe 32 is provided with a valve V5, and the pipe 33 is provided with a flow rate controller F4. The flow rate controller F4 is a ratio of the flow rate of gas passing through the flow rate controller F4 to the flow rate of gas introduced to the flow rate controller F4 through the pipe 33 (hereinafter referred to as “flow rate controller passing rate”). .) In a range of 0% to 100%. The pipe 32 and the pipe 33 provide a flow path for transporting the water vapor discharged from the vaporizer 50 to the space S2 of the main body 10 through the pipe 30.

The pipe 34 is connected to the gas source GS3 of the gas supply system GSS3. The pipe 34 is provided with a valve V6. The pipe 32 and the pipe 34 provide a flow path for transporting the N ₂ gas from the gas source GS 3 into the tank 52.

  In addition, the vaporizer 50 further includes a first sensor 60a and a second sensor 60b. The first sensor 60a and the second sensor 60b output different output voltages depending on the contact state with water. This output voltage can be adjusted by the rod material, the distance from the liquid level, and the rod tip angle, which will be described later.

  FIG. 2 schematically shows the first sensor 60a and the second sensor 60b. In FIG. 2, the liquid level FL represents the water surface in the tank 52. The first sensor 60 a includes a rod 61 and a circuit unit 65. The second sensor 60 b includes a rod 62 and a circuit unit 66. Each of the rod 61 and the rod 62 is a translucent and long member. In one embodiment, each of the rod 61 and the rod 62 may be composed of any material having a refractive index of 1.414 or more and 1.627 or less. Materials having such a refractive index include quartz (refractive index: 1.46), protein stone (refractive index: 1.47), fluorite (refractive index: 1.43), and optical glass (refractive index: 1 .. 43) and the like.

  The rod 61 has a distal end portion 61a and a main body portion 61c. The main body portion 61 c has a substantially cylindrical shape, and extends in the vertical direction from the outside of the tank 52 to the inside of the tank 52. The tip end portion 61a is continuous with one end, that is, the lower end of the main body portion 61c. The distal end portion 61a has a conical shape which decreases in diameter as it is separated from the other end of the main body portion 61c, that is, the proximal end portion 61b. The tip portion 61a has a tip angle α1. FIG. 3A is an enlarged cross-sectional view of a portion of the rod 61 including the tip portion 61a, and is a cross-sectional view showing the rod 61 in a plane including the central axis Z2 of the rod 61. As shown in (a) of FIG. 3, in the cross section including the central axis Z2, the tip angle α1 is formed by two lines formed by the surfaces of the tip portions 61a contacting each other on the central axis Z2 (reference numeral “61X It is defined as an angle which "is shown". In other words, the tip angle α1 is an angle formed by two intersecting lines 61X of a plane including the central axis Z2 and the surface of the tip 61a in contact with each other on the central axis Z2. The tip angle α1 is set to an angle of 97 ° or more and 107 ° or less.

  The tip portion 61a may have a shape different from the conical shape as long as it has a tip angle α1. For example, the tip portion 61a may have a wedge shape including two side surfaces that approach each other as they move away from the proximal end 61b. In addition, the distal end portion 61a may have an even number of side surfaces and may have a polygonal pyramid shape that tapers away from the proximal end portion 61b. Even when tip portion 61a has a wedge shape or a polygonal pyramid shape, tip angle α1 is an angle formed by the two lines formed by the surfaces of tip portion 61a contacting each other on central axis Z2 in the cross section including central axis Z2. Defined as In one embodiment, the surface of the tip portion 61a is mirror-finished by polishing, and the surface of the main portion 61c may not be mirror-finished.

  In one embodiment, the first sensor 60a may further comprise a holding mechanism 150a. The holding mechanism 150a is a mechanism that holds the rod 61 in a state where the axial direction of the rod 61 coincides with the vertical direction. The holding mechanism 150a holds the rod 61 in a state where the tip end portion 61a is inserted into the inside of the tank 52 through the through hole 52a. Thus, the rod 61 is disposed such that the distal end portion 61 a is located in the tank 52 and the proximal end 61 b is located outside the tank 52. More specifically, the boundary between the main body 61c and the tip 61a of the rod 61 is disposed at a first reference position (first position) H1 in the height direction with the bottom of the tank 52 as a reference.

  The holding mechanism 150 a includes a flange 152, a plate 154, and an annular body 156. The flange 152 is an annular member having an inner diameter slightly larger than the outer diameter of the main portion 61c, and is provided to surround the outer periphery of the main portion 61c. The flange 152 is fixed on the upper surface of the tank 52. The plate 154 is a plate having a substantially L-shaped longitudinal cross section, and includes a first portion 154a and a second portion 154b. The first portion 154a is fixed on the flange 152, and the second portion 154b is provided substantially perpendicular to the first portion 154a. The annular body 156 has an annular shape having an inner diameter slightly larger than the outer diameter of the main body portion 61c, and is provided above the flange 152 so as to surround the outer peripheral surface of the main body portion 61c. The annular body 156 is fixed to the second portion 154 b. In one embodiment, an O-ring 158 is fixed to the annular body 156 along the inner peripheral surface thereof. The O-ring 158 is provided in a compressed state between the annular body 156 and the main body 61c. Thereby, a pressing force is applied to the outer peripheral surface of the main body 61 c through the O-ring 158. The rod 61 is held by the holding mechanism 150 a by this pressing force. Here, since the rod 61 is held by the holding mechanism 150a via the O-ring 158, the contact between the rod 61 and the holding mechanism is substantially linear contact. In FIG. 2, one O-ring is provided between the annular body 156 and the main body 61c. However, in one embodiment, a plurality of O-rings are provided between the annular body 156 and the main body 61c. It may be done. By providing a plurality of O-rings, the rod 61 can be held more reliably.

  The holding mechanism 150a may hold the rod 61 such that the contact between the holding mechanism 150a and the rod 61 is point contact. For example, a plurality of granular elastic bodies are provided in a compressed state between the annular body 156 and the main body portion 61c, and a pressing force is applied to the outer peripheral surface of the main body portion 61c via the plurality of granular elastic bodies. The rod 61 may be held by being applied. Thereby, the rod 61 is substantially held by point contact. In addition, the structure for hold | maintaining the rod 61 is not restricted to the structure mentioned above. For example, an annular elastic body in which a convex portion protruding toward the main body portion 61c is formed is disposed in a state of being compressed between the annular body 156 and the main body portion 61c, and the convex portion is formed in the main body portion 61c. You may make it point-contact. In addition, an annular elastic body, a portion of which is larger in diameter than the other portions, is disposed in a compressed state between the annular body 156 and the main portion 61c, and this enlarged portion is a portion of the main portion 61c. It may be in line contact.

  In the contact portion between the rod 61 and the holding mechanism 150a, the refractive index of light is different from that in the non-contact portion. Therefore, depending on the material of the contact object that is in contact with the rod 61, a part of the light propagating through the rod 61 It may leak to the outside of the rod. On the other hand, in the above configuration, since the rod 61 is held by point contact or line contact, the contact area between the rod 61 and the holding mechanism 150a can be extremely reduced. Thereby, it is possible to reduce the loss of light generated at the contact portion between the rod 61 and the holding mechanism 150a, and to suppress the decrease in sensor sensitivity due to the loss of light. The terms point contact and line contact mentioned above do not mean geometrical point contact and line contact indicating that the contact area is zero, but the substantial point contact and line having a very small contact area Indicates contact. For example, in the configuration shown in FIG. 2, the main body 61 c and the O-ring 158 come into contact with each other in an area corresponding to the amount of elastic deformation of the O-ring 158. Thus, the contact area between the rod 61 and the holding mechanism 150a can be reduced as compared with the method of fixing to the plate 154.

  In one embodiment, a protrusion 61p may be formed at a position between the tip 61a and the base 61b of the rod 61 so as to protrude from the surface of the main body 61c. The protrusion 61p is arranged between the flange 152 and the first portion 154a of the plate 154. The width D in the direction perpendicular to the axial direction of the rod 61 at the position where the protrusion 61 p is formed is smaller than the inner diameter d of the flange 152. Thus, the flange 152 faces the protrusion 61 p in the axial direction of the rod 61. In this configuration, when the force directed to the tank 52 acts on the rod 61, the projection 61p abuts on the upper surface of the flange 152, whereby the entire rod 61 is prevented from being inserted into the tank 52. . That is, the flange 152 functions as a movement restricting portion that restricts the movement of the rod 61 in the direction of the tip portion 61 a.

  Similar to the rod 61, the rod 62 has a tip 62a and a body 62c. The main body portion 62 c has a substantially cylindrical shape, and extends in the vertical direction from the outside of the tank 52 to the inside of the tank 52. The distal end portion 62a is continuous with one end, that is, the lower end of the main body portion 62c. The distal end portion 62a has a conical shape that decreases in diameter as it is separated from the other end of the main body portion 62c, that is, the proximal end portion 62b. The tip portion 62a has a tip angle α2. FIG. 3B is an enlarged cross-sectional view of a portion of the rod 62 including the tip portion 62a, and is a cross-sectional view showing the rod 62 in a plane including the central axis Z3 of the rod 62. As shown in FIG. 3B, the tip angle α2 is defined by two lines formed by the surfaces of the tip 62a that are in contact with each other on the center axis Z3 in the cross section including the center axis Z3 (in the figure, reference numeral “62X”). Is defined as the angle formed by In other words, the tip angle α2 is an angle formed by two intersecting lines 62X of a plane including the central axis Z3 and the surface of the tip 62a in contact with each other on the central axis Z3. The tip angle α2 may be the same as or different from the tip angle α1.

  Similarly to the tip portion 61a, the tip portion 62a may have a shape different from the conical shape as long as it has a tip angle α2. For example, the tip 62a may have a wedge shape that includes two sides approaching each other as it moves away from the proximal end 62b. In addition, the distal end 62a may have an even number of side surfaces and may have a polygonal pyramid shape that tapers away from the proximal end 62b. Even in the case where tip portion 62a has a wedge shape or a polygonal pyramid shape, tip angle α2 is an angle formed by the two lines formed by the surfaces of tip portion 62a contacting each other on central axis Z3 in the cross section including central axis Z3. Defined as In one embodiment, the surface of the distal end portion 62a is mirror-finished by polishing, while the surface of the main portion 62c may not be mirror-finished.

  In one embodiment, the second sensor 60b may further include a holding mechanism 150b. The holding mechanism 150b is a mechanism that holds the rod 62 in a state where the axial direction of the rod 62 coincides with the vertical direction. The holding mechanism 150b holds the rod 62 in a state in which the tip end portion 62a is inserted into the inside of the tank 52 through the through hole 52b. Accordingly, the distal end portion 62 a is positioned in the tank 52, and the proximal end portion 62 b is disposed outside the tank 52. More specifically, the boundary between the main body 62c and the tip 62a of the rod 62 is disposed at the second reference position (second position) H2 in the height direction with the bottom of the tank 52 as a reference. The second reference position H2 is a position above the first reference position H1. The holding mechanism 150b includes a flange 152, a plate 154, and an annular body 156, like the holding mechanism 150a. The holding mechanism 150 b has substantially the same configuration as the holding mechanism 150 a, and thus the description thereof will not be repeated. Further, although the length of the rod 62 is drawn shorter than the length of the rod 61 in FIG. 2, the rod 62 may have a length equal to or longer than the length of the rod 61.

  In one embodiment, a protrusion 62p may be formed at a position between the distal end 62a and the proximal end 62b of the rod 62 so as to protrude from the surface of the main body 62c. The protrusion 62p is disposed between the flange 152 and the first portion 154a of the plate 154. The width in the direction perpendicular to the axial direction of the rod 62 at the position where the protrusion 62 p is formed is smaller than the inner diameter of the flange 152. Therefore, the flange 152 faces the protrusion 62 p in the axial direction of the rod 62. In such a configuration, when the force directed to the tank 52 acts on the rod 62, the projection 62p abuts on the upper surface of the flange 152 to prevent the entire rod 62 from being inserted into the tank 52. . That is, the flange 152 functions as a movement restricting portion that restricts the movement of the rod 62 in the direction of the distal end portion 62a.

  Next, the circuit units included in the first sensor 60a and the second sensor 60b will be described. As shown in FIG. 2, the circuit unit 65 of the first sensor 60 a has a photo reflector 64. The photo reflector 64 includes a light emitting element 104 and a phototransistor 106 which is a light receiving element. The light emitting element 104 and the phototransistor 106 are provided on the base end 61 b. The light emitting element 104 outputs light to the proximal end 61 b. The light incident on the base end portion 61b propagates in the main body portion 61c and enters the distal end portion 61a. All or part of the light incident on the tip portion 61a is reflected. The light reflected by the distal end portion 61 a propagates in the main body portion 61 c, travels toward the proximal end portion 61 b, and is received by the phototransistor 106. The phototransistor 106 outputs a current corresponding to the intensity (light quantity) of received light. The circuit unit 65 generates a voltage corresponding to the current, amplifies the voltage, and generates an output voltage. The circuit unit 66 of the second sensor 60b has the same circuit configuration and function as the circuit unit 65 of the first sensor 60a. In the following, the description of the circuit unit 66 is omitted except when it is particularly necessary to distinguish, and only the circuit unit 65 will be described.

FIG. 4 shows a specific example of the circuit configuration of the circuit unit 65. As shown in FIG. The circuit unit 65 is provided with an alternating current power supply AC. AC power supply AC is, to generate the input voltage _{V in.} One terminal of the alternating current power supply AC is connected to one terminal of the resistance element 102. The other terminal of the AC power supply AC is connected to the ground terminal GND. The other terminal of the resistive element 102 is connected to the anode of the light emitting element 104. The cathode of the light emitting element 104 is connected to the ground terminal GND. The resistive element 102 and the light emitting element 104 are connected in series with each other. The light emitting element 104 is, for example, a light emitting diode, and emits light having an intensity corresponding to the current flowing through the light emitting element 104.

  The circuit unit 65 also includes a phototransistor 106. The phototransistor 106 is connected in parallel to a series circuit including the resistive element 102 and the light emitting element 104. The collector terminal 106C of the phototransistor 106 is connected to one terminal of the AC power supply AC. The emitter terminal 106E of the phototransistor 106 is connected to one terminal of the resistive element 108 connected in series to the phototransistor 106. The other terminal of the resistive element 108 is connected to the ground terminal GND. An input voltage is applied to a series circuit including the phototransistor 106 and the resistive element 108 from an AC power supply AC. The phototransistor 106 changes the current flowing from the collector terminal 106C to the emitter terminal 106E in accordance with the intensity of light received from the light emitting element 104. Specifically, when the intensity of light received by the phototransistor 106 increases, the current flowing from the collector terminal 106C to the emitter terminal 106E increases, and when the intensity of light received by the phototransistor 106 decreases, the current from the collector terminal 106C The current flowing to the emitter terminal 106E is reduced. A voltage corresponding to the current flowing from the collector terminal 106C to the emitter terminal 106E is generated between both ends of the resistive element 108 connected to the phototransistor 106. That is, as the intensity of light received by the phototransistor 106 increases, a larger voltage is generated between both ends of the resistance element 108.

The first terminal 110 a is connected to the emitter terminal 106 E of the phototransistor 106 and one terminal of the resistor 108. Further, the second terminal 110 b is connected to the other terminal of the resistance element 108. Therefore, the voltage between both ends of the resistive element 108 is output as the voltage V _ce between the first terminal 110 a and the second terminal 110 b. The resistance element 108, the first terminal 110a, and the second terminal 110b function as an output circuit 70 for outputting the voltage V _ce . In the circuit example shown in FIG. 4, the voltage _{V ce} is less than the input voltage _{V in.}

Circuit unit 65 amplifies the voltage _{V ce,} further includes an amplifier circuit 120 for outputting the amplified voltage as an output voltage _{V out} between the third terminal 118a and the fourth terminal 118b. The amplifier circuit 120 includes a resistance element 112, a resistance element 114, and an operational amplifier 116. One terminal of the resistance element 112 is connected to the first terminal 110a described above. The other terminal of the resistance element 112 is connected to one terminal of the resistance element 114 and is connected to the inverting input terminal of the operational amplifier 116. The other terminal of the resistive element 114 is connected to the output terminal of the operational amplifier 116 and the third terminal 118 a. The noninverting input terminal of the operational amplifier 116 is connected to the second terminal 110b and to the fourth terminal 118b. The fourth terminal 118 b is connected to the second terminal 110 b.

In this circuit unit 65, assuming that the resistance value of the resistance element 112 is Ri and the resistance value of the resistance element 114 is Rf, the output voltage _Vout and the voltage V _ce have the relationship shown in the following equation (2) . That is, the amplifier circuit 120 is an inverting amplifier circuit that outputs an output voltage _Vout whose phase is inverted with respect to the voltage _Vce .
V _out = − (Rf / Ri) · V _ce (2)

The amplification circuit 120 is not limited to the inverting amplification circuit shown in FIG. 4 as long as it can amplify and output the voltage V _ce . For example, as the amplification circuit 120, a non-inversion amplification circuit that outputs an output voltage V _{out in} phase with the voltage V _ce may be used. In one embodiment, the amplifier circuit 120 further includes a rectifier circuit, which converts the AC voltage generated between the third terminal 118a and the fourth terminal 118b into a DC voltage, and the DC voltage _May be output as the output voltage _Vout . Furthermore, in one embodiment, a DC power supply may be used instead of the AC power supply AC.

  Next, the operation principle of the first sensor 60a and the second sensor 60b will be described. Since the first sensor 60a and the second sensor 60b have the same function and characteristics as each other, the first sensor 60a will be described below unless it is particularly necessary to distinguish. FIG. 5A shows a state in which the position in the height direction of the liquid level FL in the tank 52 is lower than the first reference position H1, that is, a state where the tip 61a of the first sensor 60a is not in water. Show. FIG. 5B shows a state in which the position in the height direction of the liquid level FL in the tank 52 is higher than the first reference position H1, that is, a state in which the tip portion 61a of the first sensor 60a is in water. Show.

As shown in (a) and (b) of FIG. 5, light emitted from the light emitting element 104 of the photo reflector 64 propagates in the rod 61 from the proximal end 61 b toward the distal end 61 a. All or a part of the light reaching the tip portion 61a is reflected at the tip portion 61a. The light reflected by the distal end portion 61 a propagates toward the proximal end portion 61 b and is received by the phototransistor 106. Then, an output voltage _Vout corresponding to the current flowing through the phototransistor 106 is output to the control unit 40 described later.

The amount of light reflected at the tip 61a is determined by the contact state of the tip 61a with water. As shown in (a) of FIG. 5, when the tip portion 61a is not in contact with water, that is, when the liquid level FL is lower than the first reference position H1 in the height direction, the tip is Since the difference between the refractive index of the portion 61a and the refractive index of air in contact with the surface of the tip portion 61a is large, the amount of light reflected at the tip portion 61a is large, and the intensity of light received by the phototransistor 106 is large. Become. On the other hand, as shown in (b) of FIG. 5, when the tip portion 61a is in contact with water, that is, the liquid level FL is the same as the first reference position H1 or higher than the first reference position H1. In the position, the difference between the refractive index of the tip portion 61a and the refractive index of water in contact with the surface of the tip portion 61a is small, so the amount of light transmitted from the tip portion 61a to water becomes large, and the phototransistor The intensity of light received by 106 is reduced. Thus, the amount of light reflected at the tip end portion 61a increases or decreases according to the contact state of the tip end portion 61a with water, so the output voltage V _out output from the circuit portion 65 of the first sensor 60a is predetermined. By comparing the threshold value with the threshold value, it is possible to determine whether the tip portion 61a is in contact with water.

  Further, the amount of light reflected at the tip portion 61a also depends on the tip angle α1 of the tip portion 61a. As an example, consider light that travels in a direction parallel to the central axis Z2 and enters the surface of the tip 61a. This light is incident on the surface of the tip portion 61a at an incident angle of α1 / 2. For example, when the tip angle α1 of the tip portion 61a is 90 °, light incident on the tip portion 61a is reflected twice at a reflection angle of 45 ° on the surface of the tip portion 61a and follows a direction parallel to the central axis Z2. Then, it proceeds again from the distal end portion 61a toward the proximal end portion 61b. When such reflection is performed, the loss of light generated at the surface of the tip portion 61a is minimized. That is, when light traveling in a direction parallel to the central axis Z2 is emitted from the light emitting element 104, the amount of light received by the phototransistor 106 is maximized when the tip angle α1 of the tip portion 61a is set to 90 °. .

  However, in practice, the light emitted from the light emitting element 104 and traveling through the main portion 61c toward the tip portion 61a is divergent light, and not only components traveling in a direction parallel to the central axis Z2, but also various angles It is light having a component. Specifically, the intensity distribution of the light traveling through the main body 61c toward the tip 61a has a Gaussian distribution in the angular direction. It is assumed that such divergent light is efficiently reflected at the tip portion 61a by setting the tip angle α1 to 90 ° or more. As described above, since the tip angle α1 of the tip portion 61a has an angle of 97 ° or more, light emitted from the light emitting element 104 can be efficiently reflected at the tip portion 61a. Further, the tip angle α1 is 107 ° or less. By setting the tip angle α1 to 107 ° or less, water droplets attached to the tip portion 61a can easily fall.

Next, the characteristics of the first sensor 60a will be described. In the first sensor 60a, when it is assumed that there is no loss of light between the light emitting element 104 and the phototransistor 106, the input voltage _{V in,} the output voltage _{V out} of _the circuit portion 65, the following equation (1 ). In the following equation (1), Gv represents the gain of the first sensor 60a. As shown in equation (1), by setting the gain Gv greater, the output voltage _{V out} relative to a constant input voltage _{V in} increases. The gain Gv can be adjusted by changing the resistance value Ri of the resistance element 112 and the resistance value Rf of the resistance element 114.

| V _out | = | Gv · V _in | (1)

In the first sensor 60a, the gain Gv shown in the equation (1) is set to 3200 or more and less than 14000. By setting the gain to 3200 or more, the output voltage V _{out is obtained} even when water droplets adhere to the tip portion 61 a when the position in the height direction of the liquid level FL is lower than the first reference position H1. Can be increased. Therefore, when water droplets adhere to the tip portion 61a, it is suppressed that the output voltage _Vout falls below the predetermined threshold, and as a result, false detection of the sensor due to the water droplets attached to the tip portion 61a can be suppressed. . On the other hand, when the gain is set to 14000 or more, the output voltage _Vout becomes too large when bubbles are attached to the tip portion 61a in water, and erroneous detection may occur. In the first sensor 60a, since the gain is set to less than 14000, the output voltage _Vout is prevented from becoming excessively large. As a result, erroneous detection due to air bubbles attached to the tip portion 61a in water can be detected. It can be suppressed. In addition, as described above, the second sensor 60b has the same configuration, function, and characteristics as the first sensor 60a. Therefore, even with the second sensor 60b, it is possible to suppress false detection of the sensor caused by water droplets attached to the tip 62a, and to suppress false detection caused by air bubbles attached to the tip 62a in water. Can.

  Refer to FIG. 1 again. As shown in FIG. 1, a conduit 72 is provided in the tank 52. The conduit 72 extends in the substantially vertical direction from the outside of the tank 52 to the inside of the tank 52 so that the tip thereof is located at the lower part of the space S3. One end of a pipe 74 is connected to the conduit 72. A water supply unit 76 is connected to the other end of the pipe 74. The water supply unit 76 stores water for water supply and supplies the water into the tank 52 via the pipe 74. A valve V <b> 7 is provided in the middle of the pipe 74. The valve V <b> 7 switches between water supply and supply stop from the water supply unit 76 to the tank 52. A drain pipe 78 is connected to a position on the pipe 74 that is closer to one end of the pipe 74 than the valve V7. The drain pipe 78 discharges the water discharged from the tank 52 through the conduit 72 and the pipe 74 to the outside of the vaporizer 50. A valve V8 is provided in the middle of the drain pipe 78. The valve V8 switches between the discharge of water in the tank 52 and the discharge stop.

The plasma processing apparatus 1 further includes a control unit 40. The control unit 40 controls each unit of the plasma processing apparatus 1. The control unit 40 can be, for example, a computer including a processor, a storage device, an input device, a display device, and the like. The control unit 40 stores a program for controlling each part of the plasma processing apparatus 1 in a storage device, and by executing the program, each part of the plasma processing apparatus 1, for example, valves V1 to V3 and V5 to V5. V8, three-way valve V4, flow controllers F1 to F4, high-frequency power supply RG, heater power supply HP, exhaust device 16 and power supply 56 are controlled. In one example, the control unit 40 controls the supply of water from the water supply unit 76 to the tank 52 in accordance with the output voltage _Vout output from the first sensor 60a and the second sensor 60b.

Next, a control method of the plasma processing apparatus 1 of one embodiment will be described. FIG. 6 is a flowchart showing a control method MT1 of the plasma processing apparatus 1 for performing plasma processing on the wafer W by plasma of rare gas, O ₂ gas, and N ₂ gas.

In the control method MT1, first, in step ST1, O ₂ gas, N ₂ gas, and rare gas are supplied from the gas supply unit GU to the space S2 in the quartz tube 22. In order to supply these gases to the space S2, the control unit 40 opens the valves V1 to V3 and closes the valves V5 to V8. Further, the control unit 40 controls the three-way valve V4 such that the pipe 31 is in communication with the pipe 30. By controlling the valves in this way, O ₂ gas, N ₂ gas, and rare gas from the gas supply unit GU are supplied to the space S2 through the pipe 31 and the pipe 30.

Next, in the control method MT1, a process ST2 is performed. In step ST2, plasma of O ₂ gas, N ₂ gas, and rare gas is generated. For this reason, in the process ST2, high frequency power is supplied from the high frequency power supply RG to the coil 24. With this high frequency power, plasma of O ₂ gas, N ₂ gas, and rare gas is generated in the space S2. Then, the organic species contained in the wafer W and / or the organic matter adhering to the wafer W are removed by the active species of the plasma. That is, ashing processing is performed.

Next, another control method of the plasma processing apparatus 1 will be described. FIG. 7 is a flowchart showing a control method MT2 of the plasma processing apparatus 1 for performing plasma processing on the wafer W with plasma of H ₂ O gas, that is, water vapor.

In the control method MT2, first, in step ST11, the temperature of the water in the tank 52 is controlled to the set temperature. This set temperature is a temperature determined by the volume of the tank 52, the inner diameter and length of the pipes 30, 32, and the flow rate of the H ₂ O gas to be supplied to the space S2, and is, for example, 50 to 78 degrees Celsius. . In order to control the temperature of the water in the tank 52, the controller 40 sends a control signal to the power supply 56 to control the amount of heat generated by the heater 54. When the temperature of the water in the tank 52 reaches the set temperature, then step ST12 is performed. In step ST12, H ₂ O gas is supplied from the vaporizer 50 to the space S2 in the quartz tube 22. In step ST12, in order to supply the H ₂ O gas to the space S2, the control unit 40 opens the valve V5 and closes the valves V1 to V3 and V6 to V8. Further, the control unit 40 controls the three-way valve V4 such that the pipe 33 is in communication with the pipe 30. Thus, by controlling each valve, the H ₂ O gas in the space S3 is supplied to the space S2 through the pipe 32, the pipe 33, and the pipe 30.

Next, in the control method MT2, a process ST13 is performed. In step ST13, plasma of H ₂ O gas is generated. Therefore, in step ST13, high frequency power is supplied from the high frequency power supply RG to the coil 24. The high frequency power generates plasma of H ₂ O gas in the space S2. Then, the organic species contained in the wafer W and / or the organic matter adhering to the wafer W are removed by the active species of the plasma. That is, ashing processing is performed.

Next, in the control method MT2, a process ST14 is performed. In step ST14, it is determined whether the position in the height direction of the liquid level FL in the tank 52 is lower than the first reference position H1. When the effective value of the output voltage V _out of the first sensor 60a (hereinafter simply referred to as “output voltage V _out ”) is equal to or greater than a predetermined threshold, the control unit 40 determines the position of the liquid level FL in the height direction. Is determined to be lower than the first reference position H1. When it is determined in step ST14 that the position in the height direction of the liquid level FL is lower than the first reference position H1, that is, it is determined that the output voltage _Vout of the first sensor 60a is equal to or higher than a predetermined threshold If it has, step ST15 is performed. In step ST15, water is supplied from the water supply unit 76 to the tank 52 so that the position in the height direction of the liquid level FL is the same as the first reference position H1 or higher than the first reference position H1. . In order to supply water into the tank 52, the control unit 40 sends a control signal to the valve V7 to open the valve V7. Thereby, the water stored in the water supply unit 76 is supplied into the tank 52 via the pipe 74 and the conduit 72. Further, when the position in the height direction of the liquid level FL becomes the same as or higher than the first reference position H1, the control unit 40 closes the valve V7 to supply water to the tank 52. Stop.

  On the other hand, when it is determined in step ST14 that the position in the height direction of the liquid level FL is at the same position as or higher than the first reference position H1, step ST16 is performed. Further, the process ST16 is also performed when water is supplied from the water supply unit 76 to the tank 52 in the process ST15. In this step ST16, it is determined whether or not the end condition is satisfied. For example, in step ST16, it is determined whether or not the ashing process in step ST13 has been performed a predetermined number of times. If it is determined in step ST16 that the end condition is not satisfied, step ST11 is performed again. On the other hand, when it is determined in step ST16 that the termination condition is satisfied, the processing is terminated.

Next, experimental results on the tip angle of the tip portion 61a will be described. FIG. 8 shows the experimental results showing the relationship between the tip angle of the tip 61a and the output voltage _Vout when the tip 61a is completely in contact with air. As shown in FIG. 8, when the tip angle of the tip portion 61a is an angle in the range of 80 ° or more and less than 97 °, it is confirmed that the output voltage V _out increases as the tip angle of the tip portion 61a increases. It was done. On the other hand, it was confirmed that when the tip angle of the tip portion 61a is within the range of 97 ° to 107 °, the output voltage _Vout is substantially constant even if the tip angle of the tip portion 61a increases. . As a result, as shown in FIG. 4, the input voltage V _in to a series circuit including a phototransistor 106 and the resistor 108 is applied, the voltage V _ce input voltage generated between both terminals of the resistor element 108 It is presumed that this is caused by not exceeding V _in .

From the above results, it was confirmed that the output voltage _Vout of the sensor when the tip portion 61a is in contact with air is increased by setting the tip angle of the tip portion 61a to 97 ° or more. This result is considered to be obtained because the amount of light reflected at the tip 61a and received by the phototransistor is increased by setting the tip angle to 97 ° or more. Therefore, when the liquid surface FL in the tank 52 is at a position lower than the first reference position H1, water droplets adhere to the tip portion 61a of the rod 61 by setting the tip angle of the tip portion 61a to 97 ° or more. Also, the output voltage V _{out of the} sensor can be increased. As a result, even when water droplets adhere to the tip portion 61a, the output voltage _Vout is less likely to fall below the predetermined threshold, so that false detection of the sensor due to the adhesion of water droplets can be suppressed. Further, by setting the tip angle of the tip portion 61a of the rod 62 to 107 ° or less, the water droplets attached to the tip portion 61a can be easily dropped. Therefore, it can suppress that a water droplet adheres to tip part 61a.

Next, experimental results on the gain Gv of the first sensor 60a will be described. In the experiment from which this experimental result was obtained, the rod 61 was removed from the first sensor 60a in order to simulate total reflection of light at the tip portion 61a, and yellow and different in reflectance from each other directly below the photo reflector 64 Light was emitted from the light emitting element 104 with the purple colored paper placed. Then, when these colored papers were placed, the output voltage _Vout output from the circuit unit 65 was measured. FIG. 9 is a diagram illustrating the relationship between the output voltage _Vout and the gain Gv obtained in the experiment. As shown in FIG. 9, when the gain Gv of the circuit unit 65 is increased, the output voltage _Vout is saturated and becomes substantially constant with respect to the gain Gv greater than a certain value. Here, when the range of the gain Gv in which the rate of increase of the output voltage _Vout is 11% or less when the gain becomes 4 times is defined as the flat range, the gain Gv which is the lower limit of the flat range is 3200. As shown in FIG. 9, when the gain Gv of the first sensor 60a is set to a value included in the flat range, a large output is obtained even when any color paper is disposed immediately below the circuit unit 65. It was confirmed that the voltage V _out was output. That is, by setting the gain Gv of the first sensor 60a to 3200 or more, even if the reflectance at the tip end portion 61a is low and light loss occurs on the surface of the tip end portion 61a, a large output from the first sensor 60a It was confirmed that the voltage V _out can be output. From this, even when water drops adhere to the tip portion 61 a and light leaks from the surface of the tip portion 61 a to the water drop, a large output voltage V _out is output from the first sensor 60 a. It was confirmed that it was possible.

Next, the water in the tank 52 was heated by the heater 54, and the flow rate controller F4 was controlled so that water vapor was intermittently supplied from the tank 52 to the space S2 in the quartz tube 22. And, the temporal change of the judgment result of the first sensor 60a was obtained. The upper graphs in (a) to (c) in FIG. 10 show temporal changes in the determination result of the first sensor 60a when the gain Gv of the first sensor 60a is set to 1400, 3200, and 6500, respectively. It shows. In these graphs, the vertical axis is the determination result of the contact state of water at the tip portion 61a, and the horizontal axis is time. The determination result “1” shown in the upper graph of FIG. 10 indicates that the control unit 40 determines that the tip 61a is in contact with water, and the determination result “0” This indicates that the controller 40 determines that the tip 61a is not in contact with water. As described above, the control unit 40 determines the contact state of water with the tip portion 61a by binarizing the output voltage _Vout from the first sensor 60a based on a predetermined threshold value. Moreover, the graph of the lower stage of (a)-(c) of FIG. 10 has shown the time-dependent change of the flow rate controller passage rate. In these graphs, the vertical axis is the steam flow rate controller passing rate, and the horizontal axis is time. In addition, the time of the horizontal axis of the graph of the upper stage of (a)-(c) of FIG. 10 and the time of the horizontal axis of the lower graph are mutually corresponded.

  As shown by the upper graphs in (a) to (c) of FIG. 10, in this experiment, the determination result of the first sensor 60a changes from “0” to “1” when the time is 46 minutes. There is. This indicates that water has been supplied into the tank 52. In the present experiment, water was not supplied into the tank 52 thereafter. As a result, in the upper graphs of (a) to (c) of FIG. 10, when the time has reached 65 minutes, the determination result of the first sensor 60a changes from "1" to "0".

  After that, when observation was continued, as shown by the graph at the top of FIG. 10A, when the gain Gv is set to 1400, the determination result of the first sensor 60a when the time reaches 71 minutes Changes from "0" to "1" again. In this experiment, since water supply was not performed in the tank 52 after 46 minutes of water supply, the water contacted the tip 61a of the first sensor 60a when the time reached 71 minutes. There should have been no. Therefore, when the time reaches 71 minutes, the determination that the tip 61a is in contact with water is determined to be a false detection. Referring to the lower graph of (a) of FIG. 10, it is understood that this false detection occurs immediately after the flow rate controller passage rate changes from 100% to 0%. When the flow rate controller passing rate changes from 100% to 0%, the communication between the space S3 in the tank 52 and the space S2 in the processing container 12 is released, and the pressure in the tank 52 rises. Along with this, the water vapor in the tank 52 is easily liquefied. From these results, it is presumed that this false detection is caused due to the pressure inside the tank 52 rising and the water drop adhering to the tip portion 61 a of the rod 61. On the other hand, as shown in FIGS. 10B and 10C, when the gain Gv of the first sensor 60a is set to 3200 or 6500, after 65 minutes regardless of the change in the flow rate controller passage rate. The judgment result of was still "0". That is, no false detection was confirmed.

Next, FIG. 11 is referred to. In FIG. 11, when the water in the tank 52 is heated using the heater 54 in a state where the liquid level FL in the tank 52 is higher than the first reference position H1, the first sensor 60a is used. It is a figure which shows the time-dependent change of the output voltage _Vout output. FIG. 11A shows the result when the gain Gv of the first sensor 60a is set to 180, and FIG. 11B shows the result when the gain Gv of the first sensor 60a is set to 14000. It is a result. Here, the threshold value for determining whether or not water is in contact with the tip 61a is 6V.

When the gain Gv of the first sensor 60a is 180, as shown in (a) of FIG. 11, the output voltage _Vout of the first sensor 60a is large even if air bubbles are generated due to the heating of water. It did not increase. On the other hand, when the gain Gv of the first sensor 60a is 14000, the output voltage _Vout of the first sensor 60a greatly increases due to the influence of bubbles generated by the heating of water. Although this output voltage V _out never exceeded 6 V continuously, it exceeded 6 V instantaneously. From this result, it was confirmed that when the gain Gv is set to 14000 or more, there is a high possibility of erroneous detection when bubbles are attached to the tip portion 61a in water. However, when the gain Gv of the first sensor 60a is 14000, the output voltage _Vout does not continuously exceed 6 V. Therefore, when the gain Gv of the first sensor 60a is set to less than 14000 It is considered that the possibility of erroneous detection occurring in the first sensor 60a can be reduced.

  Although the sensor and the vaporizer according to the embodiment have been described above, various modifications can be configured without being limited to the above-described embodiment. For example, the vaporizer 50 supplies water vapor to the plasma processing apparatus 1, but the object to which water vapor is supplied is not limited to the plasma processing apparatus. Moreover, in the embodiment shown in FIG. 1, the whole of the plasma processing apparatus 1 is controlled by the control unit 40. However, in one embodiment, a control unit different from the control unit 40 is provided, and the other control unit The vaporizer 50 may be individually controlled.

  DESCRIPTION OF SYMBOLS 1 ... Plasma processing apparatus, 10 ... Body part, 40 ... Control part, 50 ... Vaporizer, 52 ... Tank, 54 ... Heater, 60a ... 1st sensor, 60b ... 2nd sensor, 61, 62 ... Rod, 61a, 62a ... tip portion, 61b, 62b ... base end portion, 61p, 62p ... projecting portion, 61X, 62X ... intersecting line, 64 ... photo reflector, 65, 66 ... circuit portion, 70 ... output circuit, 72 ... conduit, DESCRIPTION OF SYMBOLS 76 ... Water supply part, 102 ... Resistance element, 104 ... Light emitting element, 106 ... Phototransistor, 106C ... Collector terminal, 106 E ... Emitter terminal, 108 ... Resistance element, 120 ... Amplifier circuit, 158 ... O ring, FL ... Liquid surface, GND: ground terminal, S3: space, α1, α2: tip angle.

Claims (12)

A sensor that outputs different output voltages according to the contact condition with water,
A translucent rod having a distal end portion and a proximal end portion and extending between the distal end portion and the proximal end portion, wherein the distal end angle of the distal end portion is 97 ° to 107 °, With the rod,
A light emitting element for outputting light propagating in the rod to the proximal end;
A phototransistor that is provided on the base end and receives light reflected from the tip of the rod among the light output from the light emitting element;
An output circuit including a resistance element provided between the phototransistor and a ground terminal and connected in series to the phototransistor, wherein the output circuit outputs a voltage having a magnitude corresponding to a current flowing through the phototransistor. When,
A power supply for applying an input voltage to a series circuit including the phototransistor and the resistive element;
An amplifying circuit for amplifying the voltage output from the output circuit and outputting the amplified voltage as the output voltage;
A holding mechanism for holding the rod in a state in which the axial direction of the rod coincides with the vertical direction;
Equipped with
Assuming that there is no light loss between the light emitting element and the phototransistor, the input voltage Vin generated by the power supply and the output voltage Vout of the amplifier circuit are represented by the following formula (1): | Vout | = | Gv · Vin | (1)
In the formula (1), Gv is the gain, the gain is 3200 or more state, and are less than 14000,
The sensor holds the rod by point contact .   The sensor according to claim 1, wherein the rod is made of a material having a refractive index of 1.414 or more and 1.627 or less.   The sensor according to claim 1, wherein the rod is made of quartz.   The sensor according to any one of the preceding claims, wherein the tip has a wedge shape including two sides approaching each other away from the proximal end.   The sensor according to any one of the preceding claims, wherein the tip has an even number of side surfaces and has a polygonal pyramid shape that tapers away from the proximal end.   The sensor according to any one of claims 1 to 3, wherein the distal end portion has a conical shape that decreases in diameter as it goes away from the proximal end portion. The sensor according to any one of claims 1 to 6, wherein the holding mechanism holds the rod via a plurality of granular elastic bodies. The sensor according to any one of claims 1 to 6, wherein the holding mechanism holds the rod via an annular elastic body formed with a convex portion protruding toward the outer peripheral surface of the rod. The rod is formed with a protruding portion that protrudes from the outer peripheral surface of the rod, and the protruding portion is located between the distal end portion and the proximal end portion in the axial direction of the rod,
The sensor according to claim 7 or 8, wherein the holding mechanism includes a movement restricting portion that is provided between the protruding portion and the tip end portion and faces the protruding portion in the axial direction of the rod. A tank defining a space for storing water inside;
A heater for heating water in the tank to generate steam;
The at least one sensor according to any one of claims 1 to 9, wherein the tip portion is arranged at a predetermined position in a height direction in the space;
A water supply unit for supplying water into the tank;
A control unit that controls the supply of water from the water supply unit to the tank according to the output voltage of the amplifier circuit of the sensor.   The said control part controls the said water supply part so that water may be supplied in the said tank, when the said output voltage of the said amplifier circuit is more than a predetermined | prescribed threshold value. The at least one sensor includes a first sensor and a second sensor,
The tip portion of the first sensor is disposed at a first position in the height direction, and the tip portion of the second sensor is a second position higher than the first position in the height direction. The vaporizer according to claim 10 or 11, which is arranged in

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