Superheated steam generation method and superheated steam generation device

Abstract

Provided are a superheated steam generation method and a superheated steam generation device that can quickly generate superheated steam and can prevent the superheated steam from becoming excessively high-temperature. In a superheated steam generation method, a heater temperature command value for minimizing a temperature difference is determined in a first heater temperature allowable range (R1) set in a first time interval, and when a measured value of a steam temperature in the first time interval (T1) is less than a target temperature of superheated steam and the temperature difference is greater than a first threshold value, the superheated steam is generated. A second heater temperature allowable range (R2) is determined by increasing the first heater temperature allowable range (R1) by a predetermined amount of increase, and a heater temperature command value for minimizing the temperature difference is determined within the second heater temperature allowable range (R2) set within the second time interval (T2).

Description

Technical Field

[0001] This invention relates to a technique for generating superheated vapor used in regulating the surface temperature of polishing pads for polishing substrates such as wafers. Background Technology

[0002] CMP (Chemical Mechanical Polishing) equipment is used in the manufacturing of semiconductor devices to polish the surface of wafers. A CMP apparatus rotates a wafer with a film on it using a polishing head, and further presses the wafer against a polishing pad on a rotating polishing table, polishing the film forming the wafer surface. During polishing, an polishing slurry (paste) is supplied to the polishing pad. Through the chemical action of the polishing slurry and the mechanical action of the abrasive particles contained in the slurry and / or the polishing pad, the film on the wafer is planarized.

[0003] The polishing rate of a wafer depends not only on the polishing load of the wafer on the polishing pad but also on the surface temperature of the polishing pad. This is because the chemical action of the polishing slurry on the wafer film is temperature-dependent. Therefore, optimal control of the surface temperature of the polishing pad during wafer polishing is crucial to achieving an appropriate polishing rate.

[0004] Therefore, conventionally, a pad temperature regulating device for adjusting the surface temperature of the polishing pad has been used (for example, see Patent Document 1). The pad temperature regulating device is configured to adjust the surface temperature of the polishing pad during wafer polishing to a desired temperature by directing superheated steam and cooling fluid to the surface of the polishing pad.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent document 1: Japanese Patent Application Publication No. 2022-170648.

[0008] The technical problem that the invention aims to solve

[0009] Water is heated by a heater to generate saturated vapor, and then the saturated vapor is further heated to generate superheated vapor. That is, the liquid phase of water is heated by the heater and vaporizes, existing as a mixture of liquid and gas (saturated vapor) for a period of time. When this liquid-gas mixture exists, the heat energy from the heater is consumed in the phase change without producing a temperature change. The heat energy in this state is latent heat. When the enthalpy of the liquid-gas mixture exceeds a critical point, all the liquid turns into vapor. Further heating of this vapor generates superheated vapor. The heat energy in this state is sensible heat.

[0010] The time required for water to generate superheated steam depends on the water volume and the heater's heating temperature. As mentioned above, since water undergoes a phase change to become superheated steam, a certain amount of time is required for this process. Increasing the heater's heating temperature can shorten this time. However, after the latent heat is transferred to sensible heat, the superheated steam is rapidly heated by the high-temperature heater. Excessively high temperatures of superheated steam raise concerns about thermal deformation of steam piping, steam nozzles, etc. On the other hand, lowering the heater's heating temperature results in a longer time required for superheated steam to be generated from water. Summary of the Invention

[0011] The present invention provides a method and apparatus for generating superheated steam that can rapidly generate superheated steam and prevent the superheated steam from becoming excessively hot.

[0012] Technical means for solving technical problems

[0013] In one embodiment, a method for generating superheated steam is provided for generating superheated steam used in adjusting the surface temperature of a polishing pad for polishing a substrate. The method includes: generating steam by heating water using a steam generator equipped with a heater; measuring the temperature of the steam using a steam temperature measuring device; and determining a heater temperature command value, representing a set temperature of the heater, by a feedback control unit. This heater temperature command value is used to minimize a temperature difference between the measured temperature of the steam and a target temperature of the superheated steam. The feedback control unit determines the heater temperature command value by: determining a heater temperature command value that minimizes the temperature difference within a first allowable heater temperature range set in a first time interval; determining a second allowable heater temperature range by increasing the first allowable heater temperature range by a predetermined offset when the measured temperature of the steam within the first time interval is lower than the target temperature of the superheated steam and the temperature difference is greater than a first threshold; and determining a heater temperature command value that minimizes the temperature difference within the second allowable heater temperature range set in a second time interval.

[0014] In one approach, the measured temperature of the steam within the first time interval is the average value of the steam temperature measured by the steam temperature measuring device within the first time interval.

[0015] In one embodiment, the determination of the heater temperature command value by the feedback control unit further includes: determining a heater temperature command value for minimizing the temperature difference within a third heater temperature allowable range set in a third time interval; determining a fourth heater temperature allowable range by decreasing the third heater temperature allowable range by a predetermined decrease offset when the measured temperature of the steam within the third time interval is greater than the target temperature of the superheated steam and the temperature difference is greater than a second threshold; and determining a heater temperature command value for minimizing the temperature difference within the fourth heater temperature allowable range set in the fourth time interval.

[0016] In one embodiment, a superheated steam generating apparatus is provided, comprising: a steam generator having a heater for heating water to generate steam; a steam temperature measuring device for measuring the temperature of the steam; and a feedback control unit that determines a heater temperature command value representing a set temperature of the heater, the heater temperature command value being configured to minimize a temperature difference between the measured temperature of the steam and a target temperature of the superheated steam, wherein the feedback control unit is configured to: determine a heater temperature command value for minimizing the temperature difference within a first allowable heater temperature range set in a first time interval; when the measured temperature of the steam within the first time interval is less than the target temperature of the superheated steam and the temperature difference is greater than a first threshold, increase the first allowable heater temperature range by a predetermined increase offset to determine a second allowable heater temperature range; and within the second allowable heater temperature range set in a second time interval, determine a heater temperature command value for minimizing the temperature difference.

[0017] In one embodiment, the feedback control unit is configured to: calculate the average value of the temperature of the steam measured by the steam temperature measuring device within the first time interval, and use the average value as the measured value of the temperature of the steam within the first time interval.

[0018] In one embodiment, the feedback control unit is configured to: determine a heater temperature command value for minimizing the temperature difference within a third heater temperature allowable range set in a third time interval; when the measured temperature of the steam within the third time interval is greater than the target temperature of the superheated steam and the temperature difference is greater than a second threshold, decrease the third heater temperature allowable range by a predetermined decrease offset to determine a fourth heater temperature allowable range; and within the fourth heater temperature allowable range set in the fourth time interval, determine a heater temperature command value for minimizing the temperature difference.

[0019] The effects of the invention

[0020] During the process of generating superheated steam by heating water through a heater, the feedback control unit determines a heater temperature command value to raise the heater temperature in order to ensure that the measured steam temperature is close to the target temperature of the superheated steam. During a first time interval, the heater temperature command value is limited to a first allowable heater temperature range. Therefore, even if the difference between the measured steam temperature and the target superheated steam temperature is too large, the feedback control unit generates a heater temperature command value that does not exceed the upper limit of the first allowable heater temperature range. This operation suppresses overheating of the heater and prevents the heater from overheating the superheated steam when the heat energy supplied by the heater is transferred from latent heat to sensible heat.

[0021] Furthermore, when the measured temperature of the steam during the first time interval is lower than the target temperature of the superheated steam and the temperature difference is greater than the first threshold, the feedback control unit increases the first heater temperature allowable range by a predetermined offset to determine the second heater temperature allowable range. During the second time interval, a heater temperature command value within the second heater temperature allowable range, which is higher than the first heater temperature allowable range, is determined. The feedback control unit can generate a heater temperature command value higher than the heater temperature command value generated during the first time interval. Therefore, the steam generator can rapidly bring the steam temperature close to the target temperature of the superheated steam. As a result, the steam generator can rapidly generate superheated steam. Attached Figure Description

[0022] Figure 1 This is a schematic diagram illustrating one embodiment of the grinding apparatus.

[0023] Figure 2 This is a cross-sectional view showing one embodiment of a steam generator.

[0024] Figure 3 This is a graph illustrating one embodiment of the operation of the feedback control unit in the process of generating superheated steam from water via saturated steam.

[0025] Figure 4 This is a schematic diagram illustrating other embodiments of the grinding apparatus.

[0026] Explanation of symbols

[0027] W chip

[0028] 1 Grinding head

[0029] 2 grinding tables

[0030] 3 Grinding Pads

[0031] 3a grinding surface

[0032] 4 Grinding fluid supply nozzle

[0033] 6 Grinding Table Rotary Motor

[0034] 10-pad temperature control system

[0035] 24 Pad Heater

[0036] 25 pad cooler

[0037] 32 heaters

[0038] 33 Steam generator

[0039] 35 Steam Temperature Measuring Instrument

[0040] 37 Feedback Control Department

[0041] 39 Water Supply Line

[0042] 40 Voltage Controller

[0043] 41 power lines

[0044] 43 Heater Temperature Measuring Instrument

[0045] 44 Heater Control Section

[0046] 50 Heater Housing

[0047] 51 Thermal Insulation

[0048] 53 heating chamber

[0049] 55 Entry Port

[0050] 56 Export Ports

[0051] 61 Superheated Steam Supply Line

[0052] 62 Heating Flow Control Valve

[0053] 64 Cooling fluid supply line

[0054] 65 Cooling Flow Control Valve

[0055] 67 Valve Control Section. Detailed Implementation

[0056] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0057] Figure 1This is a schematic diagram illustrating one embodiment of the polishing apparatus. The polishing apparatus includes: a polishing table 2 supporting a polishing pad 3; a polishing head 1 pressing a wafer W, which serves as a substrate, onto the polishing pad 3; a polishing table rotation motor 6 for rotating the polishing table 2; and a polishing slurry supply nozzle 4 for supplying polishing slurry (e.g., a slurry containing abrasive particles) onto the polishing pad 3. The surface (upper surface) of the polishing pad 3 constitutes the polishing surface 3a of the wafer W. Specific examples of substrates include wafers, wiring substrates, corner substrates, etc., used in the manufacture of semiconductor devices.

[0058] The polishing of wafer W is performed as follows. The wafer W to be polished rotates via polishing head 1, while polishing pad 3 rotates together with polishing table 2 via polishing table rotation motor 6. In this state, polishing slurry is supplied from polishing slurry supply nozzle 4 to the polishing surface 3a of polishing pad 3, and further, the surface of wafer W is pressed against the polishing surface 3a of polishing pad 3 by polishing head 1. The surface of wafer W is planarized by the chemical action of polishing slurry and the mechanical action of abrasive particles contained in polishing slurry and / or polishing pad 3.

[0059] The grinding apparatus also includes a pad temperature regulating system 10 for regulating the temperature of the grinding surface 3a of the grinding pad 3 (i.e., the surface temperature of the grinding pad 3). The pad temperature regulating system 10 includes a pad heater 24 for heating the grinding surface 3a of the grinding pad 3 and a pad cooler 25 for cooling the grinding surface 3a of the grinding pad 3. The pad heater 24 and the pad cooler 25 are located above the grinding table 2 and the grinding pad 3, and are arranged opposite to the grinding surface 3a of the grinding pad 3. The pad heater 24 and the pad cooler 25 do not contact the grinding surface 3a of the grinding pad 3.

[0060] Superheated steam, used as a heating fluid, is supplied to the pad heater 24. The superheated steam is generated by further heating saturated steam produced from water. A cooling fluid is supplied to the pad cooler 25. Examples of cooling fluids include gases at room temperature (e.g., inert gases such as nitrogen or argon, or air). However, the cooling fluid is not limited to these examples. The cooling fluid can also be a gas cooled to a temperature lower than room temperature, or a gas at a temperature lower than the target temperature of the abrasive surface 3a of the abrasive pad 3.

[0061] The pad temperature control system 10 also includes a superheated steam generating device 30 that supplies superheated steam to the pad heater 24. One embodiment of the superheated steam generating device 30 includes: a steam generator 33 having a heater 32 that heats water to generate steam; a steam temperature measuring device 35 that measures the temperature of the steam generated by the steam generator 33; and a feedback control unit 37 that determines a heater temperature command value representing a set temperature of the heater 32, which is used to minimize the difference between the measured steam temperature and the target temperature of the superheated steam, i.e., the temperature difference. The steam generator 33 is connected to a water supply line 39, through which water is supplied to the steam generator 33. In this embodiment, an electric heater is used as the heater 32. The specific structure of the steam temperature measuring device 35 is not particularly limited; a contact temperature measuring device or a non-contact temperature measuring device can be used.

[0062] The superheated steam generating apparatus 30 includes: a voltage controller 40 connected to a heater 32 via an power line 41; a heater temperature sensor 43 for measuring the temperature of the heater 32; and a heater control unit 44 for controlling the heating temperature of the heater 32 based on the measured temperature value of the heater 32 and a heater temperature command value. The heater temperature sensor 43 is electrically connected to the heater control unit 44, and the measured temperature value of the heater 32 is sent from the heater temperature sensor 43 to the heater control unit 44. One embodiment of the heater control unit 44 is a PID control unit that performs PID operation to minimize the difference between the measured temperature value of the heater 32 and the set temperature of the heater 32 indicated by the heater temperature command value. The specific structure of the heater temperature sensor 43 is not particularly limited, and a contact temperature sensor or a non-contact temperature sensor can be used.

[0063] The heater control unit 44 includes a storage device 44a storing a program and an arithmetic unit 44b performing calculations according to the commands contained in the program. The heater control unit 44 is composed of at least one computer (e.g., a programmable logic controller). The storage device 44a includes a main storage device such as random access memory (RAM), an auxiliary storage device such as a hard disk drive (HDD), or a solid-state drive (SSD). Examples of arithmetic units 44b include a CPU (central processing unit) and a GPU (graphics processing unit). However, the specific structure of the heater control unit 44 is not limited to these examples.

[0064] The heater control unit 44 generates a voltage command value to achieve the set temperature of the heater 32 indicated by the heater temperature command value sent from the feedback control unit 37, and sends the voltage command value to the voltage controller 40. More specifically, the heater control unit 44 generates a voltage command value to minimize the difference between the temperature of the heater 32 measured by the heater temperature sensor 43 and the aforementioned set temperature of the heater 32, and sends the voltage command value to the voltage controller 40. The voltage controller 40 applies the voltage indicated by the voltage command value to the heater 32, thereby enabling the heater 32 to generate heat at the set temperature indicated by the heater temperature command value.

[0065] Figure 2 This is a cross-sectional view showing one embodiment of the steam generator 33. The steam generator 33 includes: a heater housing 50, a heat insulation member 51 disposed within the heater housing 50, a heater 32 surrounded by the heat insulation member 51, a heating chamber 53 surrounded by the heater 32, and an inlet port 55 and an outlet port 56 communicating with the heating chamber 53. The inlet port 55 is connected to a water supply line 39. The entire heat insulation member 51 is covered by the heater housing 50. The heater 32 is in contact with the wall of the heating chamber 53.

[0066] Water flows into the heating chamber 53 through inlet port 55. The water in the heating chamber 53 is heated by the heat from the wall of the heating chamber 53, which is in contact with the heater 32, becoming saturated steam. Further, the saturated steam is heated by the heat from the wall of the heating chamber 53, which is in contact with the heater 32, becoming superheated steam. The superheated steam flows out of the heating chamber 53 through outlet port 56. A heater temperature measuring device 43, which measures the temperature of the heater 32, is in contact with the heater 32.

[0067] Return to Figure 1 The pad temperature control system 10 also includes: outlet port 56 of the steam generator 33 (see reference) Figure 2 The system includes: a superheated steam supply line 61 extending to the pad heater 24; a heating flow control valve 62 controlling the flow rate of superheated steam through the superheated steam supply line 61; a cooling fluid supply line 64 supplying cooling fluid to the pad cooler 25; a cooling flow control valve 65 controlling the flow rate of cooling fluid through the cooling fluid supply line 64; and a valve control unit 67 controlling the operation of the heating flow control valve 62 and the cooling flow control valve 65. The heating flow control valve 62 and the cooling flow control valve 65 are actuator-driven valves such as electric valves, solenoid valves, and pneumatic valves.

[0068] The heating flow control valve 62 and the cooling flow control valve 65 are electrically connected to the valve control unit 67. The operation of the heating flow control valve 62 and the cooling flow control valve 65 (i.e., the flow rate of superheated steam flowing through the superheated steam supply line 61 and the flow rate of cooling fluid flowing through the cooling fluid supply line 64) is controlled by the valve control unit 67. The valve control unit 67 is composed of a computer (e.g., a programmable logic controller) equipped with a storage device storing a program and an arithmetic device that performs calculations according to the commands contained in the program.

[0069] Superheated steam is released from the nozzle 24a of the pad heater 24 onto the grinding surface 3a of the grinding pad 3, thereby raising the temperature of the grinding surface 3a of the grinding pad 3. Cooling fluid is released from the nozzle (not shown) of the pad cooler 25 onto the grinding surface 3a of the grinding pad 3, thereby lowering the temperature of the grinding surface 3a of the grinding pad 3. The valve control unit 67 regulates the flow rates of the superheated steam and cooling fluid supplied from the pad heater 24 and the pad cooler 25 to the grinding surface 3a of the grinding pad 3 by operating the heating flow control valve 62 and the cooling flow control valve 65, thereby controlling the temperature of the grinding surface 3a of the grinding pad 3.

[0070] Although not shown, in one embodiment, the pad temperature control system 10 may also include a suction nozzle adjacent to the pad cooler 25. The suction nozzle has a suction port opposite to the grinding surface 3a of the grinding pad 3. The suction nozzle is connected to a vacuum source such as a vacuum pump. By increasing or decreasing the amount of air drawn from the suction nozzle, the amount of heat of vaporization removed from the grinding fluid on the grinding surface 3a changes, resulting in the ability to adjust the temperature of the grinding surface 3a.

[0071] Next, the operation of the feedback control unit 37 will be described in detail. The feedback control unit 37 includes a storage device 37a storing a program and an arithmetic unit 37b performing calculations according to the commands contained in the program. The feedback control unit 37 is composed of at least one computer (e.g., a programmable logic controller). The storage device 37a includes a main storage device such as random access memory (RAM), an auxiliary storage device such as a hard disk drive (HDD), or a solid-state drive (SSD). Examples of the arithmetic unit 37b include a CPU (central processing unit) and a GPU (graphics processing unit). However, the specific structure of the feedback control unit 37 is not limited to these examples.

[0072] One embodiment of the feedback control unit 37 is a PID control unit that performs feedback control based on PID action. The feedback control unit 37 is configured to determine (generate) a heater temperature command value representing the set temperature of the heater 32, which minimizes the difference between the temperature of the steam measured by the steam temperature sensor 35 and the target temperature of the superheated steam. The steam temperature sensor 35 is installed in the superheated steam supply line 61 and measures the temperature of the steam flowing through the superheated steam supply line 61. The steam temperature sensor 35 is electrically connected to the feedback control unit 37, and the measured temperature value of the steam is sent from the steam temperature sensor 35 to the feedback control unit 37.

[0073] A steam temperature sensor 35 is positioned near the abrasive pad 3, which serves as the point of use for superheated steam. In one embodiment, the steam temperature sensor 35 is located directly upstream of the pad heater 24. For example, the steam temperature sensor 35 is positioned upstream of the pad heater 24 and downstream of the heating flow control valve 62. In another embodiment, the steam temperature sensor 35 may also be positioned within the pad heater 24. For example, the steam temperature sensor 35 may also be positioned near the injection port 24a of the pad heater 24. Thus, since the steam temperature sensor 35 is positioned near the abrasive pad 3, which serves as the point of use for superheated steam, it is able to measure the temperature of the superheated steam before it is released into the abrasive pad 3.

[0074] The feedback control unit 37 monitors the temperature of the steam generated by the steam generator 33 at predetermined time intervals and executes a PID control to minimize the difference between the measured steam temperature and the target temperature of the superheated steam in each time interval. When the steam generated by the steam generator 33 is saturated steam, the temperature difference between the saturated steam and the target temperature of the superheated steam is large. Therefore, the feedback control unit 37 increases the heater temperature command value, which represents the set temperature (heating temperature) of the heater 32. As a result, the steam generated by the steam generator 33 soon becomes superheated steam. Subsequently, the feedback control unit 37 determines a heater temperature command value, representing the set temperature of the heater 32, to minimize the difference between the current temperature of the superheated steam and the target temperature of the superheated steam.

[0075] Figure 3 This is a graph illustrating one embodiment of the operation of the feedback control unit 37 in the process of generating superheated steam from water via saturated steam. The feedback control unit 37 calculates the average temperature of the steam generated by the steam generator 33 in time intervals T1, T2, T3, T4, and T5. More specifically, the feedback control unit 37 calculates the average of multiple steam temperatures measured by the steam temperature measuring device 35 in each time interval. Therefore, the average steam temperature corresponding to time intervals T1, T2, T3, T4, and T5 is calculated.

[0076] In one implementation, time intervals T1, T2, T3, T4, and T5 have the same length (time width). Figure 3 The time intervals T1, T2, T3, T4, and T5 shown are one example; multiple consecutive time intervals of the same length can also continue after time interval T5. In one embodiment, the length of each of the time intervals T1, T2, T3, T4, and T5 is in the range of 5 seconds to 300 seconds. For example, the length of each of the time intervals T1, T2, T3, T4, and T5 is 300 seconds. By extending the time intervals T1, T2, T3, T4, and T5 by a certain extent, even when the distance between the heater 32, which is the object of control, and the steam temperature measuring point is long, the operation of the heater 32 can be controlled based on the average value of the steam temperature measured in each time interval. In one example, the distance between the heater 32 and the steam temperature measuring device 35 is in the range of 50 mm to 500 mm.

[0077] The feedback control unit 37 performs feedback control by using the average value calculated in each time interval as the measured value of the steam temperature in that time interval. For example, the average value of the steam temperature calculated in time interval T1 is used as the measured value of the steam temperature in time interval T1, and the average value of the steam temperature calculated in time interval T2 is used as the measured value of the steam temperature in time interval T2. The same applies to the other time intervals T3 to T5.

[0078] The average value calculated over each time interval can be the arithmetic mean of all measured values ​​of steam temperature obtained in each time interval, or it can be the last moving average calculated from the moving averages of the measured values ​​of steam temperature obtained continuously in each time interval.

[0079] exist Figure 3 In the example shown, time interval T1 is the period during which water boils and turns into steam. The thermal energy of heater 32 during this time is latent heat. From... Figure 3 It is known that the temperature of the steam (or water) within the time interval T1 differs significantly from the target temperature of the superheated steam. In this case, the feedback control unit 37, which is the PID control unit, operates to cause a significant increase in the temperature of the heater 32. However, after the latent heat is transferred to sensible heat, the superheated steam is rapidly heated by the high-temperature heater 32. There is a concern that the excessively high temperature of the superheated steam may cause thermal deformation of the superheated steam supply line 61, the pad heater 24, etc.

[0080] Therefore, in this embodiment, the allowable heater temperature ranges R1, R2, R3, R4, and R5 are preset in time intervals T1, T2, T3, T4, and T5, respectively. The allowable heater temperature ranges R1, R2, R3, R4, and R5 determine the upper and lower limits of the heater temperature command value for the corresponding time intervals T1, T2, T3, T4, and T5. Therefore, within each time interval, the heater temperature command value (i.e., the heating temperature of heater 32) can vary within the corresponding allowable heater temperature range, but the heater temperature command value cannot exceed the upper and lower limits of that allowable range. In one embodiment, the upper and lower limits of at least one of the allowable heater temperature ranges R1, R2, R3, R4, and R5 can also be 0.

[0081] According to this embodiment, even when the difference between the measured temperature of the steam and the target temperature of the superheated steam in each time interval is too large, the feedback control unit 37 generates a heater temperature command value that does not exceed the upper limit of the allowable temperature range of each heater. Such operation can suppress excessive heating of the heater 32, and prevent the heater 32 from overheating the superheated steam when the heat energy of the heater 32 is transferred from latent heat to sensible heat.

[0082] The feedback control unit 37 is configured such that, when the measured value (average value) of the steam temperature in each time interval is lower than the target temperature of the superheated steam, and the difference between the measured value of the steam (or water) temperature and the target temperature of the superheated steam (hereinafter sometimes simply referred to as the temperature difference) is greater than a first threshold, the allowable range of the heater temperature set in that time interval is increased by a predetermined offset, thereby determining a new allowable range of the heater temperature. Furthermore, the feedback control unit 37 is configured to, in the next time interval, determine a heater temperature command value within the newly determined allowable range of the heater temperature to minimize the aforementioned temperature difference.

[0083] More specifically, within the heater temperature allowable range R1 set in time interval T1, the feedback control unit 37 determines a heater temperature command value that minimizes the difference between the measured temperature of the steam (or water) and the target temperature of the superheated steam. When the measured temperature of the steam (or water) in time interval T1 is lower than the target temperature of the superheated steam, and the temperature difference is greater than a first threshold, the heater temperature allowable range R1 is increased by a predetermined offset to determine the heater temperature allowable range R2, and this range is set as the new heater temperature allowable range for use in the next time interval T2. Then, within the heater temperature allowable range R2 set in time interval T2, the feedback control unit 37 determines a heater temperature command value that minimizes the difference between the measured temperature of the steam and the target temperature of the superheated steam. The same control operation is performed in subsequent time intervals T3 to T5.

[0084] Within time interval T2, a heater temperature command value within a heater temperature allowable range R2 that is higher than the heater temperature allowable range R1 is determined. The feedback control unit 37 is able to generate a heater temperature command value that is higher than the heater temperature command value generated within time interval T1. Therefore, the steam generator 33 can rapidly bring the steam temperature close to the target temperature of the superheated steam. As a result, the steam generator 33 can rapidly generate superheated steam.

[0085] If the measured temperature of the steam (or water) within time interval T1 is lower than the target temperature of the superheated steam, but the temperature difference is less than the first threshold, the feedback control unit 37 directly uses the upper and lower limits of the heater temperature allowable range R1 to determine the heater temperature allowable range R2 to be used in the next time interval T2. Therefore, the upper and lower limits of the heater temperature allowable range R2 are the same as the upper and lower limits of the heater temperature allowable range R1.

[0086] The feedback control unit 37 is configured such that, when the measured value (average value) of the steam temperature in each time interval is greater than the target temperature of the superheated steam, and the difference between the measured value of the steam temperature and the target temperature of the superheated steam, i.e., the temperature difference, is greater than a second threshold, the set allowable range of the heater temperature in that time interval is decreased by a predetermined offset, thereby determining a new allowable range of the heater temperature. Furthermore, the feedback control unit 37 is configured to, in the next time interval, determine a heater temperature command value within the newly determined allowable range of the heater temperature to minimize the aforementioned temperature difference.

[0087] More specifically, within the heater temperature allowable range R4 set in time interval T4, the feedback control unit 37 determines a heater temperature command value that minimizes the difference between the measured temperature of the steam (superheated steam) and the target temperature of the superheated steam. If the measured temperature (average value) of the steam within time interval T4 is greater than the target temperature of the superheated steam, and the aforementioned temperature difference is greater than a second threshold, the heater temperature allowable range R4 is decreased by a predetermined shift to determine the heater temperature allowable range R5. The heater temperature allowable range R5 is then set as the heater temperature allowable range to be used in the next time interval T5. Then, within the heater temperature allowable range R5 set in time interval T5, the feedback control unit 37 determines a heater temperature command value that minimizes the difference between the measured temperature of the steam (superheated steam) and the target temperature of the superheated steam.

[0088] Within time interval T5, a heater temperature command value within the heater temperature allowable range R5, which is lower than the heater temperature allowable range R4, is determined. The feedback control unit 37 is able to generate a heater temperature command value that is lower than the heater temperature command value generated within time interval T4. Therefore, the steam generator 33 is able to rapidly bring the temperature of the steam (superheated steam) close to the target temperature of the superheated steam.

[0089] The second threshold may be the same as or different from the first threshold. The upward and downward offsets may also vary based on the temperature difference between the measured temperature of the steam (superheated steam) and the target temperature of the superheated steam.

[0090] If the measured temperature of the steam during time interval T4 is greater than the target temperature of the superheated steam, but the temperature difference is less than the second threshold, the feedback control unit 37 directly uses the upper and lower limits of the allowable heater temperature range R4 to determine the allowable heater temperature range R5 to be used in the next time interval T5. Therefore, the upper and lower limits of the allowable heater temperature range R5 are the same as the upper and lower limits of the allowable heater temperature range R4.

[0091] Figure 4 This diagram illustrates another embodiment of the superheated steam generating apparatus 30. Unless otherwise specified, the structure and operation of this embodiment are referenced. Figures 1-3 The structures and actions described are the same, therefore repeated descriptions are omitted. For example... Figure 4 As shown, the superheated steam generating device 30 does not have... Figure 1 The heater control unit 44 is shown. Instead, the feedback control unit 37 also functions as... Figure 1 The functions of the heater control unit 44 shown are as follows.

[0092] The heater temperature sensor 43 is electrically connected to the feedback control unit 37, and the measured temperature value of the heater 32 is sent from the heater temperature sensor 43 to the feedback control unit 37. The feedback control unit 37 generates a voltage command value to achieve the set temperature of the heater 32 indicated by the heater temperature command value, and sends the voltage command value to the voltage controller 40. More specifically, the feedback control unit 37 generates a voltage command value to minimize the difference between the temperature of the heater 32 measured by the heater temperature sensor 43 and the aforementioned set temperature of the heater 32, and sends the voltage command value to the voltage controller 40. The voltage controller 40 applies the voltage indicated by the voltage command value to the heater 32, thereby enabling the heater 32 to generate heat at the set temperature indicated by the heater temperature command value.

[0093] The embodiments described above are intended to enable those skilled in the art to implement the present invention. Various modifications to the above embodiments can obviously be made by those skilled in the art, and the technical concept of the present invention is also applicable to other embodiments. Therefore, the present invention is not limited to the described embodiments, but should be interpreted as encompassing the broadest scope of the technical concept defined according to the scope of the patent claims.

Claims

1. A method for generating superheated steam, comprising generating superheated steam used in adjusting the surface temperature of an abrasive pad for polishing a substrate, characterized in that, Include: Steam is generated by heating water using a steam generator equipped with a heater. The temperature of the steam is measured using a steam temperature measuring device. The feedback control unit determines a heater temperature command value representing the set temperature of the heater. This heater temperature command value is used to minimize the temperature difference between the measured temperature of the steam and the target temperature of the superheated steam. The heater temperature command value determined by the feedback control unit includes: Within the first allowable heater temperature range set in the first time interval, a heater temperature command value is determined to minimize the temperature difference. When the measured temperature of the steam within the first time interval is lower than the target temperature of the superheated steam and the temperature difference is greater than a first threshold, the allowable temperature range of the first heater is increased by a predetermined offset to determine the allowable temperature range of the second heater. Within the second time interval, within the allowable temperature range of the second heater, a heater temperature command value is determined to minimize the temperature difference.

2. The method for generating superheated steam according to claim 1, characterized in that, The measured value of the steam temperature within the first time interval is the average value of the steam temperature measured by the steam temperature measuring device within the first time interval.

3. The method for generating superheated steam according to claim 1, characterized in that, The determination of the heater temperature command value by the feedback control unit also includes: Within the allowable temperature range of the third heater set in the third time interval, a heater temperature command value is determined to minimize the temperature difference. When the measured temperature of the steam within the third time interval is greater than the target temperature of the superheated steam and the temperature difference is greater than the second threshold, the allowable temperature range of the third heater is decreased by a predetermined offset to determine the allowable temperature range of the fourth heater. Within the fourth time interval, within the allowable temperature range of the fourth heater, a heater temperature command value is determined to minimize the temperature difference.

4. A superheated steam generating device, characterized in that, have: A steam generator having a heater that heats water to generate steam; A steam temperature measuring device that measures the temperature of the steam; and The feedback control unit determines a heater temperature command value representing the set temperature of the heater, which is used to minimize the temperature difference between the measured temperature of the steam and the target temperature of the superheated steam. The feedback control unit is configured as follows: Within the first allowable heater temperature range set in the first time interval, a heater temperature command value is determined to minimize the temperature difference. When the measured temperature of the steam within the first time interval is lower than the target temperature of the superheated steam and the temperature difference is greater than a first threshold, the allowable temperature range of the first heater is increased by a predetermined offset to determine the allowable temperature range of the second heater. Within the second time interval, within the allowable temperature range of the second heater, a heater temperature command value is determined to minimize the temperature difference.

5. The superheated steam generating apparatus according to claim 4, characterized in that, The feedback control unit is configured to: calculate the average value of the steam temperature measured by the steam temperature measuring device within the first time interval, and use the average value as the measured value of the steam temperature within the first time interval.

6. The superheated steam generating apparatus according to claim 4, characterized in that, The feedback control unit is configured as follows: Within the allowable temperature range of the third heater set in the third time interval, a heater temperature command value is determined to minimize the temperature difference. When the measured temperature of the steam within the third time interval is greater than the target temperature of the superheated steam and the temperature difference is greater than the second threshold, the allowable temperature range of the third heater is decreased by a predetermined offset to determine the allowable temperature range of the fourth heater. Within the fourth time interval, within the allowable temperature range of the fourth heater, a heater temperature command value is determined to minimize the temperature difference.

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