Superheated steam generation method and superheated steam generation apparatus

Abstract

The present invention provides a superheated steam generation method that can rapidly generate superheated steam and prevent the superheated steam from becoming excessively hot. [Solution] The superheated steam generation method determines a heater temperature command value to minimize the temperature difference within a first heater temperature tolerance range R1 set in a first time interval T1. If the measured steam temperature within the first time interval T1 is smaller than the target temperature of the superheated steam and the temperature difference is larger than a first threshold, the first heater temperature tolerance range R1 is raised by a predetermined upward shift amount to determine a second heater temperature tolerance range R2, and a heater temperature command value to minimize the temperature difference is determined within the second heater temperature tolerance range R2 set in the second time interval T2.

Description

Technical Field

[0005]

[0001] The present invention relates to a technique for generating superheated steam used for adjusting the surface temperature of a polishing pad for polishing a substrate such as a wafer.

Background Art

[0002] A CMP (Chemical Mechanical Polishing) apparatus is used in the process of polishing the surface of a wafer in the manufacture of semiconductor devices. The CMP apparatus rotates a wafer having a film by a polishing head, and further presses the wafer against a polishing pad on a rotating polishing table by the polishing head to polish the film constituting the surface of the wafer. During polishing, a polishing liquid (slurry) is supplied to the polishing pad. The film of the wafer is planarized by the chemical action of the polishing liquid and the mechanical action of the abrasive grains contained in the polishing liquid and / or the polishing pad.

[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 liquid on the film of the wafer depends on temperature. Therefore, in order to achieve an appropriate polishing rate of the film, it is important to optimally control the surface temperature of the polishing pad during wafer polishing.

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

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] Superheated steam is produced by heating water with a heater to create saturated steam, and then further heating the saturated steam. That is, the liquid phase water is heated by the heater and vaporizes, and for a while, liquid and gas (saturated steam) coexist. While the liquid-gas mixture exists, the thermal energy from the heater is spent on the phase change, and no temperature change occurs. The thermal energy in this state is latent heat. When the enthalpy of the liquid-gas mixture exceeds the critical point, all of the liquid turns into steam. Superheated steam is produced when this steam is further heated. The thermal energy in this state is sensible heat.

[0007] The time required to generate superheated steam from water depends on the amount of water and the heating temperature of the heater. As mentioned above, water undergoes a phase change to transform into superheated steam, so it takes a certain amount of time to generate superheated steam from water. Increasing the heating temperature of the heater can shorten the time it takes to generate superheated steam from water. However, immediately after the transition from latent heat to sensible heat, the superheated steam is rapidly heated by the high-temperature heater. Superheated steam that becomes excessively hot may cause thermal deformation of steam pipes and steam nozzles. On the other hand, lowering the heating temperature of the heater will result in a longer time for superheated steam to be generated from water.

[0008] The present invention provides a superheated steam generation method and a superheated steam generation apparatus that can rapidly generate superheated steam and prevent the superheated steam from becoming excessively hot. [Means for solving the problem]

[0009] In one embodiment, a superheated steam generation method is provided for generating superheated steam used to adjust the surface temperature of a polishing pad for polishing a substrate, comprising: generating steam by heating water with a steam generator equipped with a heater; measuring the temperature of the steam with a steam temperature measuring instrument; and determining a heater temperature command value indicating the set temperature of the heater to minimize the temperature difference, which is the difference between the measured temperature of the steam and the target temperature of the superheated steam, by a feedback control unit, wherein the determination of the heater temperature command value by the feedback control unit is determined to minimize the temperature difference within a first heater temperature tolerance range set in a first time interval; if the measured temperature of the steam within the first time interval is smaller than the target temperature of the superheated steam and the temperature difference is larger than a first threshold, the first heater temperature tolerance range is raised by a predetermined upward shift amount to determine a second heater temperature tolerance range; and the heater temperature command value to minimize the temperature difference is determined within the second heater temperature tolerance range set in the second time interval.

[0010] In one embodiment, the measured value of the steam temperature within the first time interval is the average of the steam temperatures measured by the steam temperature measuring instrument within the first time interval. In one embodiment, determining the heater temperature command value by the feedback control unit further includes determining the heater temperature command value to minimize the temperature difference within the third heater temperature tolerance range set in the third time interval, and if 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, lowering the third heater temperature tolerance range by a predetermined downward shift amount to determine the fourth heater temperature tolerance range, and determining the heater temperature command value to minimize the temperature difference within the fourth heater temperature tolerance range set in the fourth time interval.

[0011] In one embodiment, a superheated steam generating device is provided, comprising: a steam generator equipped with a heater that heats water to generate steam; a steam temperature measuring instrument for measuring the temperature of the steam; and a feedback control unit that determines a heater temperature command value indicating the set temperature of the heater to minimize the temperature difference, which is the difference between the measured temperature of the steam and the target temperature of the superheated steam. The feedback control unit is configured to determine the heater temperature command value to minimize the temperature difference within a first heater temperature tolerance range set in a first time interval, and if the measured temperature of the steam within the first time interval is smaller than the target temperature of the superheated steam and the temperature difference is larger than a first threshold, it raises the first heater temperature tolerance range by a predetermined upward shift amount to determine a second heater temperature tolerance range, and determines the heater temperature command value to minimize the temperature difference within the second heater temperature tolerance range set in the second time interval.

[0012] In one embodiment, the feedback control unit is configured to calculate the average of the steam temperature measured by the steam temperature measuring instrument within the first time interval and to use the average as the measured value of the steam temperature within the first time interval. In one embodiment, the feedback control unit is configured to determine a heater temperature command value to minimize the temperature difference within a third heater temperature tolerance range set in a third time interval, and if 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, it lowers the third heater temperature tolerance range by a predetermined downward shift amount to determine a fourth heater temperature tolerance range, and determines a heater temperature command value to minimize the temperature difference within the fourth heater temperature tolerance range set in the fourth time interval. [Effects of the Invention]

[0013] In the process of heating water with a heater to generate superheated steam, the feedback control unit determines a heater temperature command value to increase the heater temperature in order to bring the measured steam temperature closer to the target temperature of the superheated steam. In the first time interval, the heater temperature command value is limited to the first heater temperature tolerance range. Therefore, even if the difference between the measured steam temperature and the target temperature of the superheated steam is too large, the feedback control unit generates a heater temperature command value that does not exceed the upper limit of the first heater temperature tolerance range. This operation suppresses excessive heating of the heater and prevents the heater from overheating the superheated steam when the thermal energy supplied from the heater transitions from latent heat to sensible heat.

[0014] Furthermore, if the measured steam temperature within 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 raises the first heater temperature tolerance range by a predetermined upward shift amount to determine the second heater temperature tolerance range. In the second time interval, a heater temperature command value within the second heater temperature tolerance range, which is higher than the first heater temperature tolerance range, is determined. The feedback control unit can generate a heater temperature command value higher than the heater temperature command value generated in the first time interval. Therefore, the steam generator can quickly bring the steam temperature closer to the target temperature of the superheated steam. As a result, the steam generator can quickly generate superheated steam. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic diagram showing one embodiment of a polishing apparatus. [Figure 2] This is a cross-sectional view showing one embodiment of a steam generator. [Figure 3] This graph illustrates one embodiment of the operation of the feedback control unit in the process of generating superheated steam from water via saturated steam. [Figure 4] This is a schematic diagram showing another embodiment of the polishing apparatus. [Modes for carrying out the invention]

[0016] Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a schematic diagram showing one embodiment of a polishing apparatus. The polishing apparatus includes a polishing table 2 that supports a polishing pad 3, a polishing head 1 that presses a wafer W, which is an example of a substrate, against the polishing pad 3, a table rotation motor 6 that rotates the polishing table 2, and a polishing liquid supply nozzle 4 for supplying polishing liquid (for example, a slurry containing abrasive particles) onto the polishing pad 3. The surface (top surface) of the polishing pad 3 constitutes the polishing surface 3a for polishing the wafer W. Specific examples of substrates include wafers used in the manufacture of semiconductor devices, wiring boards, and rectangular substrates.

[0017] The wafer W is polished as follows: The wafer W to be polished is rotated by the polishing head 1, while the polishing pad 3 is rotated together with the polishing table 2 by the table rotation motor 6. In this state, polishing fluid is supplied from the polishing fluid supply nozzle 4 to the polishing surface 3a of the polishing pad 3, and the surface of the wafer W is pressed against the polishing surface 3a of the polishing pad 3 by the polishing head 1. The surface of the wafer W is flattened by the chemical action of the polishing fluid and the mechanical action of the abrasive particles contained in the polishing fluid and / or the polishing pad 3.

[0018] The polishing apparatus further includes a pad temperature control system 10 for adjusting the temperature of the polishing surface 3a of the polishing pad 3 (i.e., the surface temperature of the polishing pad 3). The pad temperature control system 10 includes a pad heater 24 for heating the polishing surface 3a of the polishing pad 3 and a pad cooler 25 for cooling the polishing surface 3a of the polishing pad 3. The pad heater 24 and pad cooler 25 are located above the polishing table 2 and the polishing pad 3 and are positioned opposite the polishing surface 3a of the polishing pad 3. The pad heater 24 and pad cooler 25 are not in contact with the polishing surface 3a of the polishing pad 3.

[0019] The pad heater 24 is supplied with superheated steam as a heating fluid. The superheated steam is generated by further heating the saturated steam generated from water. The pad cooler 25 is supplied with a cooling fluid. Examples of the cooling fluid include a gas at room temperature (e.g., an inert gas such as nitrogen or argon, or air). However, the cooling fluid is not limited to this example. The cooling fluid may be a gas cooled to a temperature lower than room temperature, or a gas at a temperature lower than the target temperature of the polishing surface 3a of the polishing pad 3.

[0020] The pad temperature control system 10 further includes a superheated steam generator 30 that supplies superheated steam to the pad heater 24. One embodiment of the superheated steam generator 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 indicating the set temperature of the heater 32 to minimize the temperature difference, which is the difference between the measured value of the steam temperature and the target temperature of the superheated steam. The steam generator 33 is connected to a water supply line 39, and water is supplied to the steam generator 33 through the water supply line 39. In this embodiment, an electric heater is used as the heater 32. The specific configuration of the steam temperature measuring device 35 is not particularly limited, and a contact-type temperature measuring device or a non-contact-type temperature measuring device may be used.

[0021] The superheated steam generator 30 includes a voltage controller 40 connected to the heater 32 by a power line 41, a heater temperature measuring device 43 that measures the temperature of the heater 32, and a heater control unit 44 that controls the heat generation temperature of the heater 32 based on the measured value of the temperature of the heater 32 and the heater temperature command value. The heater temperature measuring device 43 is electrically connected to the heater control unit 44, and the measured value of the temperature of the heater 32 is transmitted from the heater temperature measuring device 43 to the heater control unit 44. One embodiment of the heater control unit 44 is a PID control unit that performs a PID operation to minimize the difference between the measured value of the temperature of the heater 32 and the set temperature of the heater 32 indicated by the heater temperature command value. The specific configuration of the heater temperature measuring device 43 is not particularly limited, and a contact-type temperature measuring device or a non-contact-type temperature measuring device may be used.

[0022] The heater control unit 44 includes a storage device 44a storing a program and an arithmetic unit 44b that executes arithmetic operations according to instructions included in the program. The heater control unit 44 is composed of at least one computer (for example, a programmable logic controller). The storage device 44a includes a main storage device such as a random access memory (RAM) and auxiliary storage devices such as a hard disk drive (HDD) and a solid state drive (SSD). Examples of the arithmetic unit 44b include a CPU (central processing unit) and a GPU (graphics processing unit). However, the specific configuration of the heater control unit 44 is not limited to these examples.

[0023] The heater control unit 44 generates a voltage command value for realizing the set temperature of the heater 32 indicated by the heater temperature command value transmitted 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 for minimizing the difference between the temperature of the heater 32 measured by the heater temperature measuring device 43 and the above set temperature of the heater 32, and transmits 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, whereby the heater 32 can generate heat at the set temperature of the heater 32 indicated by the heater temperature command value.

[0024] FIG. 2 is a cross-sectional view showing an embodiment of the steam generator 33. The steam generator 33 includes a heater housing 50, a heat insulating material 51 disposed within the heater housing 50, a heater 32 surrounded by the heat insulating material 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 the water supply line 39. The entire heat insulating material 51 is covered by the heater housing 50. The heater 32 is in contact with the wall surface of the heating chamber 53.

[0025] Water flows into the heating chamber 53 through the inlet port 55. The water in the heating chamber 53 is heated by the heat from the wall of the heating chamber 53 in contact with the heater 32, becoming saturated steam. Furthermore, the saturated steam is heated by the heat from the wall of the heating chamber 53 in contact with the heater 32, becoming superheated steam. The superheated steam flows out of the heating chamber 53 through the outlet port 56. The heater temperature measuring instrument 43, which measures the temperature of the heater 32, is in contact with the heater 32.

[0026] Returning to Figure 1, the pad temperature control system 10 further comprises a superheated steam supply line 61 extending from the outlet port 56 of the steam generator 33 (see Figure 2) to the pad heater 24, a heating flow control valve 62 that controls the flow rate of superheated steam flowing through the superheated steam supply line 61, a cooling fluid supply line 64 that supplies cooling fluid to the pad cooler 25, a cooling flow control valve 65 that controls the flow rate of cooling fluid flowing through the cooling fluid supply line 64, and a valve control unit 67 that controls 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 air-operated valves.

[0027] The heating flow control valve 62 and the cooling flow control valve 65 are electrically connected to the valve control unit 67, and 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 consists of a computer (e.g., a programmable logic controller) equipped with a storage device that stores a program and an arithmetic unit that performs calculations according to the instructions contained in the program.

[0028] Superheated steam is released from the nozzle 24a of the pad heater 24 onto the polishing surface 3a of the polishing pad 3, thereby raising the temperature of the polishing surface 3a of the polishing pad 3. Cooling fluid is released from the nozzle (not shown) of the pad cooler 25 onto the polishing surface 3a of the polishing pad 3, thereby lowering the temperature of the polishing surface 3a of the polishing pad 3. The valve control unit 67 controls the flow rate of superheated steam and cooling fluid supplied from the pad heater 24 and pad cooler 25 to the polishing surface 3a of the polishing pad 3 by operating the heating flow control valve 62 and the cooling flow control valve 65, thereby controlling the temperature of the polishing surface 3a of the polishing pad 3.

[0029] Although not shown in the figures, in one embodiment the pad temperature control system 10 may further include a suction nozzle adjacent to the pad cooler 25. The suction nozzle has a suction port facing the polishing surface 3a of the polishing 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 in from the suction nozzle, the amount of heat of vaporization removed from the polishing liquid on the polishing surface 3a changes, and as a result, the temperature of the polishing surface 3a can be adjusted.

[0030] Next, the operation of the feedback control unit 37 will be described in detail. The feedback control unit 37 comprises a storage device 37a in which a program is stored, and an arithmetic unit 37b that performs calculations according to the instructions contained in the program. The feedback control unit 37 consists of at least one computer (e.g., a programmable logic controller). The storage device 37a comprises a main memory such as random access memory (RAM) and an auxiliary storage device such as a hard disk drive (HDD) or solid-state drive (SSD). Examples of arithmetic units 37b include a CPU (central processing unit) and a GPU (graphics processing unit). However, the specific configuration of the feedback control unit 37 is not limited to these examples.

[0031] One embodiment of the feedback control unit 37 is a PID control unit that performs feedback control according to PID operation. The feedback control unit 37 is configured to determine (generate) a heater temperature command value that indicates the set temperature of the heater 32 to minimize the difference between the steam temperature measured by the steam temperature sensor 35 and the target temperature of the superheated steam. The steam temperature sensor 35 is attached to 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 values ​​of the steam temperature are transmitted from the steam temperature sensor 35 to the feedback control unit 37.

[0032] The steam temperature sensor 35 is positioned close to the polishing pad 3, which is the point of use for the superheated steam. In one embodiment, the steam temperature sensor 35 is positioned immediately 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 other embodiments, the steam temperature sensor 35 may be positioned inside the pad heater 24. For example, the steam temperature sensor 35 may be positioned near the nozzle 24a of the pad heater 24. In this way, since the steam temperature sensor 35 is positioned close to the polishing pad 3, which is the point of use for the superheated steam, the steam temperature sensor 35 can measure the temperature of the superheated steam just before it is released onto the polishing pad 3.

[0033] The feedback control unit 37 monitors the temperature of the steam generated by the steam generator 33 at predetermined time intervals and performs PID operation to minimize the difference between the measured steam temperature in each time interval and the target temperature of the superheated steam. If the steam generated by the steam generator 33 is saturated steam, the difference between the temperature of 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 indicates the set temperature (exothermic temperature) of the heater 32. As a result, the steam generated by the steam generator 33 eventually becomes superheated steam. Subsequently, the feedback control unit 37 determines the heater temperature command value, which indicates 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.

[0034] Figure 3 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 each of the 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 instrument 35 in each time interval. Therefore, the average steam temperature corresponding to each of the time intervals T1, T2, T3, T4, and T5 is calculated.

[0035] In one embodiment, time intervals T1, T2, T3, T4, and T5 have the same length (time width). The time intervals T1, T2, T3, T4, and T5 shown in Figure 3 are just an example, and multiple consecutive time intervals of the same length may follow time interval T5. In one embodiment, the length of each time interval T1, T2, T3, T4, and T5 is in the range of 5 seconds to 300 seconds. For example, the length of each time interval T1, T2, T3, T4, and T5 is 300 seconds. By making each of the time intervals T1, T2, T3, T4, and T5 somewhat long, the operation of the heater 32 can be controlled based on the average of the measured steam temperature in each time interval, even when the distance between the heater 32, which is the object to be controlled, and the steam temperature measurement point is long. In one example, the distance between the heater 32 and the steam temperature measuring instrument 35 is in the range of 50 mm to 500 mm.

[0036] The feedback control unit 37 performs feedback control by using the average calculated in each time interval as the measured value of the steam temperature within that time interval. For example, the average 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 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.

[0037] The average calculated in each time interval may be the arithmetic mean of all steam temperature measurements taken in each time interval, or it may be the last moving average calculated from the moving averages of steam temperature measurements taken continuously in each time interval.

[0038] In the example shown in Figure 3, time interval T1 is the period when water boils and turns into steam. The thermal energy of heater 32 at this time is latent heat. As can be seen from Figure 3, the temperature of the steam (or water) within time interval T1 is far from the target temperature of the superheated steam. In such a case, the feedback control unit 37, which is the PID control unit, operates to significantly increase the temperature of heater 32. However, immediately after the transition from latent heat to sensible heat, the superheated steam is rapidly heated by the high-temperature heater 32. The excessively high temperature of the superheated steam may cause thermal deformation of the superheated steam supply line 61, pad heater 24, etc.

[0039] Therefore, in this embodiment, heater temperature tolerance ranges R1, R2, R3, R4, and R5 are set in advance for each time interval T1, T2, T3, T4, and T5. The heater temperature tolerance ranges R1, R2, R3, R4, and R5 define the upper and lower limits of the heater temperature command value in the corresponding time intervals T1, T2, T3, T4, and T5. Consequently, within each time interval, the heater temperature command value (i.e., the heating temperature of the heater 32) may fluctuate within the corresponding heater temperature tolerance range, but the heater temperature command value cannot exceed the upper and lower limits of that heater temperature tolerance range. In one embodiment, at least one of the upper and lower limits of the heater temperature tolerance ranges R1, R2, R3, R4, and R5 may be 0.

[0040] According to this embodiment, even when the difference between the measured steam temperature within each time interval and the target temperature of the superheated steam is too large, the feedback control unit 37 generates a heater temperature command value that does not exceed the upper limit of the allowable range for each heater temperature. This operation suppresses excessive heat generation by the heater 32 and prevents the heater 32 from overheating the superheated steam when the thermal energy of the heater 32 transitions from latent heat to sensible heat.

[0041] The feedback control unit 37 is configured to raise the heater temperature tolerance range set for that time interval by a predetermined upward shift amount when the measured value (average) of the steam temperature within each time interval is smaller 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 larger than the first threshold value, thereby determining a new heater temperature tolerance range. Then, in the next time interval, the feedback control unit 37 is configured to determine a heater temperature command value that minimizes the above temperature difference within the newly determined heater temperature tolerance range.

[0042] More specifically, the feedback control unit 37 determines a heater temperature command value to minimize the temperature difference between the measured temperature of the steam (or water) and the target temperature of the superheated steam within the heater temperature tolerance range R1 set in the time interval T1. If the measured temperature of the steam (or water) within the time interval T1 is lower than the target temperature of the superheated steam, and the temperature difference is greater than the first threshold, the heater temperature tolerance range R1 is increased by a predetermined upward shift amount to determine the heater temperature tolerance range R2, and the heater temperature tolerance range R2 is set as the new heater temperature tolerance range to be used in the next time interval T2. Then, the feedback control unit 37 determines a heater temperature command value to minimize the temperature difference between the measured temperature of the steam and the target temperature of the superheated steam within the heater temperature tolerance range R2 set in the time interval T2. The same control operation is performed in the subsequent time intervals T3 to T5.

[0043] In time interval T2, a heater temperature command value is determined that is higher than the heater temperature tolerance range R1 and within the heater temperature tolerance range R2. The feedback control unit 37 can generate a heater temperature command value higher than the heater temperature command value generated in time interval T1. Therefore, the steam generator 33 can quickly bring the steam temperature closer to the target temperature of superheated steam. As a result, the steam generator 33 can quickly generate superheated steam.

[0044] 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 uses the upper and lower limits of the heater temperature tolerance range R1 as is to determine the heater temperature tolerance range R2 to be used in the next time interval T2. Therefore, the upper and lower limits of the heater temperature tolerance range R2 are the same as the upper and lower limits of the heater temperature tolerance range R1.

[0045] The feedback control unit 37 is configured to lower the heater temperature tolerance range set for that time period by a predetermined downward shift amount when the measured (average) steam temperature within each time period is greater than the target temperature of the superheated steam, and the temperature difference between the measured steam temperature and the target temperature of the superheated steam is greater than the second threshold. Then, in the next time period, the feedback control unit 37 is configured to determine a heater temperature command value that minimizes the temperature difference within the newly determined heater temperature tolerance range.

[0046] More specifically, the feedback control unit 37 determines a heater temperature command value to minimize the temperature difference, which is the difference between the measured temperature of the steam (superheated steam) and the target temperature of the superheated steam, within the heater temperature tolerance range R4 set in the time interval T4. If the measured (average) temperature of the steam in the time interval T4 is greater than the target temperature of the superheated steam, and the temperature difference is greater than the second threshold, the heater temperature tolerance range R4 is lowered by a predetermined downward shift amount to determine the heater temperature tolerance range R5, and the heater temperature tolerance range R5 is set as the heater temperature tolerance range to be used in the next time interval T5. Then, the feedback control unit 37 determines a heater temperature command value to minimize the temperature difference, which is the difference between the measured temperature of the steam (superheated steam) and the target temperature of the superheated steam, within the heater temperature tolerance range R5 set in the time interval T5.

[0047] In time interval T5, a heater temperature command value is determined that is lower than the heater temperature tolerance range R4, within the heater temperature tolerance range R5. The feedback control unit 37 can generate a heater temperature command value lower than the heater temperature command value generated in time interval T4. Therefore, the steam generator 33 can quickly bring the temperature of the steam (superheated steam) closer to the target temperature of the superheated steam.

[0048] The second threshold may be the same as or different from the first threshold. The upward and downward shift amounts may be variable according to the temperature difference, which is the difference between the measured temperature of the steam (superheated steam) and the target temperature of the superheated steam.

[0049] If the measured steam temperature within 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 uses the upper and lower limits of the heater temperature tolerance range R4 as is to determine the heater temperature tolerance range R5 to be used in the next time interval T5. Therefore, the upper and lower limits of the heater temperature tolerance range R5 are the same as the upper and lower limits of the heater temperature tolerance range R4.

[0050] Figure 4 shows another embodiment of the superheated steam generator 30. The configuration and operation of this embodiment, which are not specifically described, are the same as those described with reference to Figures 1 to 3, so redundant descriptions are omitted. As shown in Figure 4, the superheated steam generator 30 does not have the heater control unit 44 shown in Figure 1. Instead, the feedback control unit 37 also performs the function of the heater control unit 44 shown in Figure 1.

[0051] The heater temperature measuring device 43 is electrically connected to the feedback control unit 37, and the measured temperature of the heater 32 is transmitted from the heater temperature measuring device 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 measuring device 43 and the set temperature of the heater 32, and transmits 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 allowing the heater 32 to generate heat at the set temperature indicated by the heater temperature command value.

[0052] The embodiments described above are intended to enable persons with ordinary skill in the art to implement the present invention. Various modifications of the above embodiments can be made naturally by those skilled in the art, and the technical idea of ​​the present invention can be applied to other embodiments as well. Therefore, the present invention is not limited to the embodiments described, but is to be interpreted in the broadest sense according to the technical idea defined by the claims. [Explanation of symbols]

[0053] W wafer 1 Polishing head 2 Polishing Tables 3. Polishing pads 3a Polished surface 4. Polishing fluid supply nozzle 6 Table Rotation Motor 10 Pad Temperature Control System 24 Pad Heaters 25 Pad Cooler 32 Heater 33 Steam generator 35. Steam temperature measuring instrument 37 Feedback Control Unit 39 Water supply lines 40 Voltage Controllers 41 Power lines 43 Heater temperature measuring instrument 44 Heater control unit 50 Heater Housing 51 Insulation 53 Heating chamber 55 Entrance Port 56 Exit Ports 61 Superheated steam supply line 62 Heating flow control valve 64 Cooling fluid supply line 65 Cooling flow control valve 67 Valve control unit

Claims

1. A method for generating superheated steam used to control the surface temperature of a polishing pad for polishing a substrate, A steam generator equipped with a heater heats water to produce steam, The temperature of the steam is measured using a steam temperature measuring instrument. The feedback control unit includes determining a heater temperature command value that indicates the heater's set temperature to minimize the temperature difference, which is the 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 is Within the first time interval set, the heater temperature command value is determined to minimize the temperature difference within the first heater temperature tolerance range. If 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 the first threshold, the first heater temperature tolerance range is increased by a predetermined upward shift amount to determine the second heater temperature tolerance range. A method for generating superheated steam, comprising determining a heater temperature command value to minimize the temperature difference within the second heater temperature tolerance range set within a second time interval.

2. The superheated steam generation method according to claim 1, wherein the measured value of the steam temperature within the first time interval is the average of the steam temperatures measured by the steam temperature measuring instrument within the first time interval.

3. The heater temperature command value determined by the feedback control unit is Within the allowable temperature range of the third heater set for the third time interval, the heater temperature command value is determined to minimize the temperature difference. If 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 tolerance range of the third heater temperature is lowered by a predetermined downward shift amount to determine the tolerance range of the fourth heater temperature. The superheated steam generation method according to claim 1, further comprising determining the heater temperature command value for minimizing the temperature difference within the fourth heater temperature tolerance range set within the fourth time interval.

4. A steam generator equipped with a heater that heats water to produce steam, A steam temperature measuring instrument for measuring the temperature of the steam, The system includes a feedback control unit that determines a heater temperature command value indicating the heater's set temperature to minimize the temperature difference, which is the difference between the measured temperature of the steam and the target temperature of the superheated steam. The feedback control unit, Within the first time interval set, the heater temperature command value is determined to minimize the temperature difference within the first heater temperature tolerance range. If 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 the first threshold, the first heater temperature tolerance range is increased by a predetermined upward shift amount to determine the second heater temperature tolerance range. A superheated steam generator configured to determine the heater temperature command value for minimizing the temperature difference within the second heater temperature tolerance range set within a second time interval.

5. The superheated steam generator according to claim 4, wherein the feedback control unit is configured to calculate the average of the steam temperature measured by the steam temperature measuring instrument within the first time interval and to use the average as the measured value of the steam temperature within the first time interval.

6. The feedback control unit, Within the allowable temperature range of the third heater set for the third time interval, the heater temperature command value is determined to minimize the temperature difference. If 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 tolerance range of the third heater temperature is lowered by a predetermined downward shift amount to determine the tolerance range of the fourth heater temperature. The superheated steam generator according to claim 4, configured to determine the heater temperature command value for minimizing the temperature difference within the fourth heater temperature tolerance range set within the fourth time interval.

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