JP2014069255A - Polishing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To more correctly determine an end point of polishing.SOLUTION: A polishing apparatus includes: a polishing table 12; a first electric motor 14 which rotationally drives the polishing table; a top ring 20 which, together with the polishing table, can hold a workpiece; and a second electric motor 22 which rotationally drives the top ring. The polishing table is rotated by the first electric motor and the top ring is rotated by the second electric motor, so that the workpiece is polished while being sandwiched between the polishing table and the top ring, and surface of the workpiece can be planarized. At least one of the first electric motor and the second electric motor includes a winding of a plurality of phases. The polishing device further includes: a weighting part which performs weighting to give a current ratio difference in each phase; and a detecting part which detects a change in current of the phase greatly weighted by the weighting part to thereby detect torque fluctuation of the electric motor caused by polishing.

Description

  The present invention relates to a polishing apparatus, and more particularly to a polishing apparatus that polishes the surface of a workpiece (polishing object) such as a semiconductor wafer flatly.

  In recent years, as semiconductor devices are highly integrated, circuit wiring is becoming finer and the distance between wirings is becoming narrower. In particular, in the case of optical lithography of 0.5 μm or less, the depth of focus becomes shallow, so that the flatness of the imaging surface of the stepper is required. Therefore, it is necessary to flatten the surface of the semiconductor wafer, and polishing (polishing) is performed by a polishing apparatus as one means of this flattening method.

  Conventionally, this type of polishing apparatus has a turntable with a polishing cloth affixed to the upper surface and a top ring, each rotating at an independent rotational speed. Then, a liquid (slurry) containing an abrasive is poured onto a polishing pad affixed to a turntable, and a semiconductor wafer as a workpiece set on the top ring is pressed thereon to flatten the surface of the semiconductor wafer. And it is polished to a mirror surface.

  The polishing speed of this type of polishing apparatus varies due to variations in the surface state of the semiconductor wafer generated in the previous process, the wear state of the polishing pad, and subtle changes in the slurry. If the polishing is insufficient, insulation between the circuits may not be obtained and a short circuit may occur, and if excessive polishing occurs, the resistance value increases due to the reduced cross-sectional area of the wiring, or the wiring itself is completely removed. Therefore, there is a problem that the circuit itself is not formed. For this reason, this type of polishing apparatus is equipped with a polishing end point detection device to detect the optimum polishing end point.

  As one of the polishing end point detection means of the polishing apparatus described above, there is known a method of detecting a change in polishing friction force when polishing is transferred to a different material. A semiconductor wafer, which is an object to be polished, has a laminated structure made of different materials such as semiconductors, conductors, and insulators, and has a different friction coefficient between different material layers. This is a method for detecting a change in frictional force. According to this method, when the polishing reaches a different material layer, the end point of the polishing is reached. Also, the polishing device detects that the surface of the semiconductor wafer has been flattened by detecting the change in polishing friction force when the surface of the semiconductor wafer is flattened by removing the unevenness. You can also

  Here, the change in the abrasive friction force is detected as follows. Since the polishing frictional force acts at a position eccentric from the rotation center of the turntable, it acts as a load torque on the rotating turntable. For this reason, the polishing friction force can be detected as torque acting on the turntable. When the means for rotationally driving the turntable is an electric motor, the load torque can be measured as a current flowing through the motor. Therefore, the end point of the polishing is detected by monitoring the motor current with an ammeter and applying appropriate signal processing.

FIG. 7 shows a configuration example of a method for detecting the polishing end point based on a change in the current input to the drive motor. It is driven by an AC commercial power supply 512 via an electric motor 500 and an inverter device 510. In the inverter device 510, the AC commercial power supply 512 is converted into a DC power supply by the converter unit 514, DC power is accumulated in the capacitor 516, and the inverter unit 518 converts it back to an arbitrary frequency and voltage, via the three-phase cable 520. Thus, AC power is supplied to the electric motor 500. The three-phase cables of the inverter 510 that supply AC power to the electric motor 500 are connected to the three-phase field windings of the electric motor 500, respectively. Motor current is detected by interposing a current converter (CT) 522 in one phase, for example, V phase, of the three-phase cable 520 that supplies power to the electric motor 500. The motor current flowing in the current supply line to the electric motor 500 is detected by the ammeter 524 in the current value flowing in the V phase and sent to the end point detection means of the control circuit of the polishing apparatus (not shown). The end point of polishing is determined.

JP 10-202523 A

  In recent years, as the integration of semiconductor devices is further advanced, circuit wiring is becoming finer and the distance between wirings is becoming narrower than ever. Therefore, there is a demand for flattening a semiconductor wafer. However, as described above, it is not sufficient to detect the current value flowing in one phase with an ammeter and determine the polishing end point from the change in the current value to flatten the semiconductor wafer more than ever. Met.

The present invention has been made in view of the above problems, and is a polishing apparatus for flattening the surface of a workpiece,
A polishing table;
A first electric motor that rotationally drives the polishing table;
A substrate holding unit capable of holding a workpiece;
A second electric motor that rotationally drives the substrate holder,
The polishing table is rotated by the first electric motor, and the substrate holding portion is rotated by the second electric motor to press the workpiece against the polishing table while holding the workpiece by the substrate holding portion. The surface of the workpiece can be flattened by polishing,
At least one of the first and second electric motors includes a plurality of phases of windings,
The polishing apparatus includes: a weighting unit that performs weighting that makes a difference in the current ratio of each phase; and the electric motor that is generated by the polishing by detecting a change in current of a phase that is set to have a large weighting by the weighting unit. A polishing apparatus is provided that includes a detection unit that detects torque fluctuations.

  The polishing apparatus may further include an end point detection unit that detects an end point of the polishing process indicating the flattening of the surface of the workpiece based on the torque fluctuation of the electric motor detected by the detection unit. .

In the polishing apparatus, at least one of the first and second electric motors may include at least a three-phase winding of a U phase, a V phase, and a W phase.
In the polishing apparatus, the first electric motor may include at least a three-phase winding of a U phase, a V phase, and a W phase.

In the polishing apparatus, the first electric motor may be a synchronous or inductive AC servomotor.
In the polishing apparatus, the weighting unit may set a large weight to one phase.

In the polishing apparatus, the one phase may be a V phase.
In the polishing apparatus, the weighting unit may include a current amplifier.
In the polishing apparatus, the polishing apparatus may include a first inverter device for controlling the first electric motor.

In the polishing apparatus, the weighting unit is connected in parallel to the first inverter device, and a second inverter device for controlling the first electric motor;
A switching circuit for adding a current output from the second inverter device to an output current of the first inverter device.

  The polishing apparatus further includes a motor driver that drives at least one of the first and second electric motors, and the motor driver includes a current command value for each of the phases and the electric motor. A current compensator that compensates the current of each phase based on a deviation from an actual current value supplied; and the weighting unit sends a command signal of a current ratio of each phase to the current compensator The current compensator can also add a difference to the current ratio of each phase based on the current ratio command signal input from the weighting unit.

  The polishing apparatus further includes a motor driver that drives at least one of the first and second electric motors, the motor driver based on a detected value of a rotational position of the electric motor. An electric calculator for obtaining the rotational speed of the motor, and the electric motor based on a deviation between a command value for the rotational speed of the electric motor input via the input interface and the rotational speed of the electric motor obtained by the arithmetic unit. Based on a speed compensator that generates a command signal for current supplied to the motor, an electrical angle signal that is generated based on a detected value of the rotational position of the electric motor, and a command signal for current that is generated by the speed compensator And a converter that generates current command values for at least two of the phases, and the weighting unit applies to the converter The command signal of the current ratio of at least two phases of each phase is input, and the converter receives at least two commands of the current ratio input from the weighting unit. It is also possible to make a difference in the current ratio of the phases.

  The polishing apparatus further includes an inverter device that drives at least one of the first and second electric motors, and the weighting unit is provided at a subsequent stage of the inverter device and is output from the inverter device. And an amplifier that individually amplifies the current of each phase and supplies the electric motor to the electric motor, receives a command signal of the amplified value of the current of each phase, and the amplifying unit receives the amplified value of the received current By amplifying the current of each phase based on the command signal, the current ratio of each phase can be differentiated.

  According to this invention of the present application, in the phase in which the weighting is set to be large, the change in the current value becomes large with respect to the change in the torque, and thereby, the change in the torque can be detected more accurately. The polishing end point can be accurately determined. In accordance with this, the yield of the planarized workpiece can be improved.

FIG. 1 is a block diagram according to the first embodiment of the present invention. FIG. 2 is a diagram for explaining the processing contents of the two-phase to three-phase converter. FIG. 3 is a diagram illustrating an example of a manner of detecting the end point of polishing. FIG. 4 is a graph showing the relationship between load torque and current obtained as experimental values in the first embodiment. FIG. 5 is a block diagram according to the second embodiment of the present invention. FIG. 6 is a block diagram according to the third embodiment of the present invention. FIG. 7 is a more detailed block diagram of the control unit and the weighting unit shown in FIG. FIG. 8 is a block diagram of a current amplifier according to the fourth embodiment of the present invention. FIG. 9 is a block diagram of a current amplifier according to the fifth embodiment of the present invention. FIG. 10 is a diagram showing a circuit configuration of a conventional endpoint detection method using input power of a drive motor.

Hereinafter, a polishing apparatus according to an embodiment of the present invention will be described with reference to the drawings.
<First Embodiment>
FIG. 1 is a diagram showing an overall configuration of a polishing apparatus according to a first embodiment of the present invention.

  The polishing apparatus includes a turntable 12 on which the polishing cloth 10 can be attached to the upper surface, a first electric motor 14 that directly rotates the turntable 12 without using a gear, and the rotational position of the first electric motor. Detecting the torque of the position detection sensor 16, the top ring (substrate holding part) 20 capable of holding the semiconductor wafer 18, the second electric motor 22 for rotationally driving the top ring 20, and the turntable 12. An end point detection device 30 for detecting an end point of polishing of the semiconductor wafer 18 is provided.

  The top ring 20 can be moved closer to or away from the turntable 12 by a holding device (not shown). When polishing the semiconductor wafer 18, the top ring 20 is brought close to the turntable 12 so that the semiconductor wafer 18 held on the top ring 20 is brought into contact with the polishing pad 10 attached to the turntable 12. In this embodiment, the torque of the first electric motor 14 that directly rotates the turntable 12 is detected to detect the end point of the polishing state of the semiconductor wafer 18. The end point of the polishing state of the semiconductor wafer may be detected by detecting the torque of the second electric motor that is driven to rotate.

  When polishing the semiconductor wafer 18, the top ring 20 holding the semiconductor wafer 18, which is an object to be polished, in a state where the turntable 12 with the polishing cloth 10 attached to the upper surface is rotationally driven by the first electric motor 14. Thus, the semiconductor wafer 18 is pressed against the polishing pad 10. Further, the top ring 20 rotates around an axis line 21 that is eccentric from the rotating shaft 13 of the turntable 12. When polishing, a polishing abrasive liquid containing an abrasive is supplied from the abrasive supply device 24 to the upper surface of the polishing pad 10, and the semiconductor wafer 18 set on the top ring 20 is pressed thereon. In other words, when polishing the semiconductor wafer 18, the semiconductor wafer 18 is pressed against the turntable 12 while being held by the top ring 20 and polished to flatten the surface of the semiconductor wafer 18.

  The first electric motor 14 is preferably a synchronous or induction type AC servo motor having at least three windings of U phase, V phase and W phase. In the present embodiment, the first electric motor 14 is composed of an AC servo motor having three-phase windings. The three-phase windings cause currents that are 120 degrees out of phase to flow in the field windings provided around the rotor in the electric motor 14, thereby rotating the rotor. The rotor of the electric motor 14 is connected to the motor shaft 15, and the turntable 12 is rotationally driven by the motor shaft 15.

  In addition, the polishing apparatus receives and receives a command signal for the rotation speed of the first electric motor 14 from the operator via the motor driver 100 that rotationally drives the first electric motor 14 and an input interface such as a keyboard or a touch panel. An input unit 200 that inputs a command signal to the motor driver 100 and a weighting unit 300 that performs weighting by adding a difference to the ratio of the current supplied to the three-phase winding of the first electric motor 14 are provided.

  The motor driver 100 includes a differentiator 102, a speed compensator 104, a two-phase / three-phase converter 106, an electrical angle signal generator 108, a U-phase current compensator 110, a U-phase PWM modulation circuit 112, A V-phase current compensator 114, a V-phase PWM modulation circuit 116, a W-phase current compensator 118, a W-phase PWM modulation circuit 120, a power amplifier 130, and current sensors 132 and 134 are provided.

  The differentiator 102 generates an actual speed signal corresponding to the actual rotational speed of the first electric motor 14 by differentiating the rotational position signal detected by the position detection sensor 16. That is, the differentiator 102 is an arithmetic unit that obtains the rotational speed of the first electric motor 14 based on the detected value of the rotational position of the first electric motor 14.

  The speed compensator 104 is based on a speed deviation signal corresponding to the deviation between the rotational speed command signal (target value) input via the input unit 200 and the actual speed signal generated by the differentiator 102. The rotational speed of the electric motor 14 is compensated. That is, the speed compensator 104 receives the rotation speed command value of the first electric motor 14 input via the input interface (input unit 200) and the rotation speed of the first electric motor 14 obtained by the differentiator 102. Based on the deviation, a command signal for the current to be supplied to the first electric motor 14 is generated.

  The speed compensator 104 can be configured by, for example, a PID controller. In this case, the speed compensator 104 adds the proportional control for changing the operation amount in proportion to the deviation between the rotational speed command signal input from the input unit 200 and the actual speed signal of the first electric motor, and the deviation. Integral control that changes the operation amount in proportion to the value and differential control that captures the rate of change of the deviation (that is, the speed at which the deviation changes) and outputs the operation amount proportional to this, to achieve the compensated rotation speed A corresponding current command signal is generated. The speed compensator 104 can also be configured by a PI controller.

The electrical angle signal generator 108 generates an electrical angle signal based on the rotational position signal detected by the position detection sensor 16.
The two-phase to three-phase converter 106 is based on the current command signal generated by the speed compensator 104 and the electrical angle signal generated by the electrical angle signal generator 108, and the V-phase current command signal and the V-phase A current command signal is generated. That is, the two-phase to three-phase converter 106 is based on the electrical angle signal generated based on the detected value of the rotational position of the first electric motor 14 and the current command signal generated by the speed compensator 104. , A converter that generates current command values for at least two of the phases.

  Here, the processing of the two-phase / three-phase converter 106 will be described in detail. FIG. 2 is a diagram for explaining the processing contents of the two-phase to three-phase converter. A current command signal Ic as shown in FIG. 2 is input from the speed compensator 104 to the two-phase / three-phase converter 106. Further, the U-phase electrical angle signal Sinφu as shown in FIG. 2 is input to the 2-phase-3 phase converter 106 from the electrical angle signal generator 108. Although not shown in FIG. 2, the V-phase electrical angle signal Sinφv is also input to the two-phase / three-phase converter 106.

  For example, consider a case where the U-phase current command signal Iuc is generated. In this case, the two-phase to three-phase converter 106 multiplies the current command signal Ic (i) at a certain time ti by the U-phase electrical angle signal Sinφu (i), thereby obtaining the U-phase current command signal Iuc. (I) is generated. That is, Iuc (i) = Ic (i) × Sinφu (i). Similarly to the U phase, the two-phase to three-phase converter 106 multiplies the current command signal Ic (i) at a certain time ti by the V-phase electrical angle signal Sinφv (i). The V-phase current command signal Ivc (i) is generated. That is, Ivc (i) = Ic (i) × Sinφv (i).

The current sensor 132 is provided on the U-phase output line of the power amplifier 130 and detects the U-phase current output from the power amplifier 130.
The U-phase current compensator 110 corresponds to a deviation between the U-phase current command signal Iuc output from the two-phase / three-phase converter 106 and the U-phase detection current Iu * detected by the current sensor 132 and fed back. Based on the U-phase current deviation signal, U-phase current compensation is performed. The U-phase current compensator 110 can be constituted by, for example, a PI controller or a PID controller. The U-phase current compensator 110 performs U-phase current compensation using PI control or PID control, and generates a U-phase current signal corresponding to the compensated current.

  The U-phase PWM modulation circuit 112 performs pulse width modulation based on the U-phase current signal generated by the U-phase current compensator 110. The U-phase PWM modulation circuit 112 generates two systems of pulse signals corresponding to the U-phase current signal by performing pulse width modulation.

The current sensor 134 is provided on the V-phase output line of the power amplifier 130 and detects the V-phase current output from the power amplifier 130.
The V-phase current compensator 114 corresponds to a deviation between the V-phase current command signal Ivc output from the two-phase / three-phase converter 106 and the V-phase detection current Iv * detected by the current sensor 134 and fed back. V-phase current compensation is performed based on the V-phase current deviation signal. The V-phase current compensator 114 can be constituted by, for example, a PI controller or a PID controller. The V-phase current compensator 114 compensates for the V-phase current using PI control or PID control, and generates a V-phase current signal corresponding to the compensated current.

  The V-phase PWM modulation circuit 116 performs pulse width modulation based on the V-phase current signal generated by the V-phase current compensator 114. The V-phase PWM modulation circuit 114 generates two systems of pulse signals corresponding to the V-phase current signal by performing pulse width modulation.

  The W-phase current compensator 118 includes a W-phase current command signal Iwc generated based on the U-phase current command signal Iuc and the V-phase current command signal Ivc output from the two-phase / three-phase converter 106, and a current sensor 132. , 134, and W phase current compensation is performed based on a W phase current deviation signal corresponding to a deviation between the U phase detection current Iu * and the V phase detection current Iv * fed back. The W-phase current compensator 118 can be constituted by, for example, a PI controller or a PID controller. The W-phase current compensator 118 performs compensation of the W-phase current using PI control or PID control, and generates a W-phase current signal corresponding to the compensated current.

  The W-phase PWM modulation circuit 120 performs pulse width modulation based on the W-phase current signal generated by the W-phase current compensator 118. The W-phase PWM modulation circuit 118 generates two systems of pulse signals corresponding to the W-phase current signal by performing pulse width modulation.

  The power amplifier 130 is configured by the inverter device 510 described in FIG. Two systems of pulse signals generated by the U-phase PWM modulation circuit 112, the V-phase PWM modulation circuit 116, and the W-phase PWM modulation circuit 120 are applied to the inverter unit 518 of the power amplifier 130 (inverter device 510). . The power amplifier 130 drives each transistor of the inverter unit 518 according to each applied pulse signal. Thereby, the power amplifier 130 outputs AC power for each of the U phase, the V phase, and the W phase, and rotationally drives the first electric motor 14 with the three-phase AC power.

Next, the weighting setting device 300 will be described. The weighting setter 300 receives from the input unit 200 command signals for weighting the currents of the U phase, V phase, and W phase of the first electric motor 14. Then, the weighting setter 300 gives a weighting command signal (current of each phase) to each of the U-phase current compensator 110, the V-phase current compensator 114, and the W-phase current compensator 118. Input the ratio command signal. For example, the weight setting device 300 gives weights of 0.8 to the U phase, 1.2 to the V phase, and 1.0 to the W phase.

  In this case, the U-phase current compensator 110 outputs a current corresponding to 0.8 times the current originally output from the U-phase current compensator 110, and the V-phase current compensator 114 is the V-phase current compensator 114. Outputs a current corresponding to 1.2 times the current output from. W-phase current compensator 118 outputs the current originally output from W-phase current compensator 118 as it is. That is, each of the U-phase current compensator 110, the V-phase current compensator 114, and the W-phase current compensator 118 corresponds to the phase of each compensator based on the current ratio command signal input from the weighting setter 300. Make a difference in the current ratio.

  In this way, the weighting setting device 300 can weight the currents output from the U phase, the V phase, and the W phase, so the current of a specific phase (for example, the V phase) is increased. be able to.

  In the present embodiment, the second current sensor 31 is provided for the phase (for example, V phase) in which the current is set to be large by the weighting setting device 300. More specifically, the second current sensor 31 is provided in a V-phase current path between the motor driver 100 and the first electric motor 14. The second current sensor 31 detects a V-phase current and outputs it to the sensor amplifier 32.

The sensor amplifier 32 amplifies the detection current output from the second current sensor 31 and outputs it to the end point detection unit 30 as a detection current signal.
The end point detection unit 30 determines the polishing end point of the semiconductor wafer 18 based on the detection current signal output from the sensor amplifier 32. More specifically, the end point detection unit 30 determines the polishing end point of the semiconductor wafer 18 based on the change in the detected current signal output from the sensor amplifier 32.

  Determination of the polishing end point of the end point detection unit 30 will be described with reference to FIG. FIG. 3 is a diagram illustrating an example of a manner of detecting the end point of polishing. In FIG. 3, the horizontal axis indicates the polishing time, and the vertical axis indicates the torque current (I) and the differential value (ΔI / Δt) of the torque current. For example, when the torque current 30a (V-phase motor current) changes as shown in FIG. 3, the end point detection unit 30 polishes the semiconductor wafer 18 when the torque current 30a becomes smaller than a preset threshold value 30b. It is determined that the end point has been reached. In addition, the end point detection unit 30 obtains the differential value 30c of the torque current 30a, and indicates that the slope of the differential value 30c has changed from negative to positive in the period between the preset time threshold values 30d and 30e. If detected, it can be determined that the polishing of the semiconductor wafer 18 has reached the end point. That is, the time thresholds 30d and 30e are set to an approximate period that is considered to be the polishing end point based on an empirical rule, and the end point detection unit 30 performs polishing in the period between the time thresholds 30d and 30e. Perform end point detection. For this reason, the polishing of the semiconductor wafer 18 has reached the end point, even if the slope of the differential value 30c has changed from negative to positive outside the period between the time threshold values 30d and 30e. Not determined. For example, immediately after the start of polishing, when the differential value 30c hunts due to the effect of unstable polishing and the slope changes from negative to positive, it is prevented from being erroneously detected as the polishing end point. Because. Hereinafter, a specific example of determination of the polishing end point of the end point detection unit 30 will be shown.

For example, consider a case where the semiconductor wafer 18 is laminated with different materials such as a semiconductor, a conductor, and an insulator. In this case, since the friction coefficient is different between the different material layers, the motor torque of the first electric motor 14 is changed when the polishing is shifted to the different material layer. In response to this change, the V-phase motor current (detection current signal) also changes. The end point detection unit 30 determines the end point of polishing of the semiconductor wafer 18 by detecting that the motor current has become larger or smaller than the threshold value. The end point detection unit 30 can also determine the polishing end point of the semiconductor wafer 18 based on the change in the differential value of the motor current.

  Further, for example, consider a case where the polished surface is flattened by polishing from a state in which the polished surface of the semiconductor wafer 18 is uneven. In this case, when the polishing surface of the semiconductor wafer 18 is flattened, the motor torque of the first electric motor 14 changes. In response to this change, the V-phase motor current (detection current signal) also changes. The end point detection unit 30 determines the polishing end point of the semiconductor wafer 18 by detecting that the motor current has become smaller than the threshold value. The end point detection unit 30 can also determine the polishing end point of the semiconductor wafer 18 based on the change in the differential value of the motor current.

Next, the operation of the polishing apparatus according to this embodiment will be described.
The operator drives the first and second electric motors 14 and 22 via the input unit 200 to operate the polishing apparatus. Although the torque required for the first electric motor 14 varies depending on the polishing state of the semiconductor wafer 18, the turntable 12 needs to be rotated at a constant speed. For this reason, the speed compensator 104 controls the current passed through each winding of the first electric motor 14 by PID control or the like. The speed compensator 104 rotates and drives the first electric motor 14 at a constant speed even if the torque required for the electric motor 14 varies according to the polishing state of the semiconductor wafer 18, so that the turntable 12 is constant. Rotate at a speed of. That is, based on the difference between the speed command set in the input unit 200 and the actual speed of the first electric motor 14 generated by the differentiator 102, the speed compensator 104 performs each phase by PID control or the like. The current command value to be passed through the winding is calculated and the current command for each phase is output.

  Here, when the weighting control is not performed as in the past, the weighting command is not given to the U-phase current compensator 110, the V-phase current compensator 114, and the W-phase current compensator 118 from the input unit 200. For this reason, the U-phase current compensator 110, the V-phase current compensator 114, and the W-phase current compensator 118 output the command values of the respective phases as they are without giving weights to the current command values of the respective phases. Therefore, currents having substantially the same amplitude and different phase differences of 120 ° are supplied to the windings of the respective phases, and the electric motor 14 generates rotational torque based on this current.

  On the other hand, when each phase is weighted in order to perform end point detection more appropriately, the weighting value is input from the input unit 200 via the weighting setter 300, the U-phase current compensator 110, and the V-phase current compensation. 114 and the W-phase current compensator 118. For example, when a weighting of 0.8 for the U phase, 1.2 for the V phase and 1.0 for the W phase is given, based on this, the U phase current compensator 110, the V phase current compensator 114, and The W-phase current compensator 118 controls the current of each phase so as to give a weight to the current command value of each phase. That is, the U-phase current compensator 110 outputs a current corresponding to 0.8 times the current originally output from the U-phase current compensator 110, and the V-phase current compensator 114 is output from the V-phase current compensator 114. A current corresponding to 1.2 times the current output is output. W-phase current compensator 118 outputs the current originally output from W-phase current compensator 118 as it is.

  When weighting is given in this way, a difference is given to the amplitude of the current flowing through the winding of each phase of the first electric motor 14. The second current sensor 31 detects the current flowing through the winding through which the most current flows, that is, the V-phase winding. The end point detection device 30 detects the polishing end point of the polishing apparatus based on the detected current value.

FIG. 4 is a diagram showing an actual measurement example of the motor current of each phase winding with respect to the load torque of the electric motor for driving the turntable when weighted in this way. The horizontal axis in FIG. 4 indicates the load torque (Nm), and the vertical axis indicates the electric motor current (effective current). In FIG. 4, a diagram 100 is a plot of the U phase, a diagram 150 is a plot of the W phase, and a diagram 200 is a plot of the V phase. When weighting control is performed on the V phase in this way, the slope of the diagram 200 increases as shown in FIG. 4, and a large current change can be detected with respect to a slight load torque fluctuation.

  When looking at FIG. 4 from the viewpoint of current sensitivity to rotational load fluctuation, in the example obtained by synthesizing the three phases, the reciprocal of 12.5 Nm / A, ΔI≈0.08ΔT, and in the example given weighting, A reciprocal of 10.4 Nm / A, ΔI≈0.1ΔT, is obtained, and the current sensitivity can be improved by about 20%.

  As described above, an effective current (DC current) is calculated based on a plurality of phase currents, and even if the electric motor has the same torque constant (Km = torque / effective current), which is the ratio between the load torque and the effective current, By providing the weighting control, the V-phase torque constant Km of the electric motor to be weighted can be reduced. As a result, when the rotational load fluctuation occurs, the current of the phase with a large weighting fluctuates greatly, and the end point detection sensitivity can be improved.

In the present embodiment, the second current sensor 31 is provided in the V-phase current path between the motor driver 100 and the first electric motor 14, and the current value detected by the second current sensor 31 is calculated. Although the example which outputs to the sensor amplifier 32 was shown, it is not restricted to this. For example, the V-phase current value detected by the current sensor 134 can be output from the motor driver 100 and output to the sensor amplifier 32 without providing the second current sensor 31.
Second Embodiment
FIG. 5 is a diagram showing an overall configuration of a polishing apparatus according to the second embodiment of the present invention. The polishing apparatus of the second embodiment is different from the first embodiment only in the aspects of the weighting setting device and the two-phase / three-phase converter, and the other configurations are the same as those of the first embodiment. . Therefore, in the second embodiment, only the weighting setter and the two-phase / three-phase converter will be described, and the description of other configurations will be omitted.

  As shown in FIG. 5, the weighting setter 400 has at least two of the U-phase, V-phase, and W-phase (the U-phase in this embodiment) with respect to the two-phase / three-phase converter 410. And a V-phase current ratio command signal. For example, the weight setting unit 400 inputs a weighting command signal of 0.8 for the U phase and 1.2 for the V phase to the two-phase / three-phase converter 410.

  Based on the current ratio command signal input from the weighting setter 400, the two-phase / three-phase converter 410 calculates a difference in the current ratio of at least two phases (for example, the U phase and the V phase) of each phase. wear.

  More specifically, when generating the U-phase current command signal Iuc, the two-phase / three-phase converter 410 generates the current command signal Ic (i) at a certain time ti and the U-phase electrical angle signal. A U-phase current command signal Iuc (i) is generated by multiplying Sinφu (i) by the U-phase weight (0.8). That is, Iuc (i) = Ic (i) × Sinφu (i) × 0.8.

  When generating the V-phase current command signal Ivc, the two-phase to three-phase converter 410 and the current command signal Ic (i) at a certain time ti and the V-phase electrical angle signal Sinφv (i) And the V-phase weighting (1.2) are multiplied to generate the V-phase current command signal Ivc (i). That is, Ivc (i) = Ic (i) × Sinφv (i) × 1.2.

Even when a weighting command signal is input from the weighting setting device 400 to the two-phase / three-phase converter 410 as in the second embodiment, a specific phase (for example, The V phase current can be increased relative to the other phases. Therefore, the V-phase current sensitivity with respect to the rotational load fluctuation of the first electric motor 14 can be improved. As a result, when the rotational load fluctuation of the first electric motor 14 occurs, the current of the phase with a large weighting fluctuates greatly, so that the sensitivity of the end point detection can be improved.
<Third Embodiment>
FIG. 6 is a block diagram according to the third embodiment of the present invention.

  In 3rd Embodiment, since the structure of the turntable 12, the 1st electric motor 14, the top ring 20, the 2nd electric motor 22, etc. is the same as that of 1st, 2nd embodiment, description is abbreviate | omitted.

  The polishing apparatus of the third embodiment includes a speed sensor 506 that detects the speed of the first electric motor, and an end point detection device 530 that detects the end point of polishing of the semiconductor wafer 18 by detecting the torque of the turntable 12. ing.

  When an electric motor is constituted by an AC servomotor having three-phase windings, the electric motor is preferably driven by an inverter device 550. The inverter device 550 is configured as described with reference to FIG. 10. The inverter unit 550 converts the AC commercial power source 552 into a DC power source by the converter unit, accumulates DC power in the capacitor, and inversely converts it to an arbitrary frequency and voltage in the inverter unit. Thus, AC power is supplied to the first electric motor 14.

  The first electric motor 14 is provided with a speed sensor 506 for detecting the rotational speed of the rotor of the electric motor. The speed sensor 506 can be composed of a magnetic encoder, an optical encoder, a resolver, and the like. When a resolver is employed, it is preferable that the resolver rotor is directly connected to the rotor of the electric motor. When the resolver rotor rotates, a sin signal and a cos signal are obtained in the secondary coil arranged 90 ° apart, and based on these two signals, the rotor position of the electric motor is detected and a differentiator is used. Thus, the speed of the electric motor can be obtained.

  The polishing apparatus includes a weighting unit 560 that performs weighting with a difference in the ratio of the current supplied to the three-phase winding of the first electric motor 14, a control unit 570 that controls the weighting unit, and the control unit 570 includes a current sensor (detection unit) 580 that detects a change in torque of the electric motor caused by the polishing by detecting a change in current of a phase whose weight is set to be large by 570, and an end point detection device 530 is provided. The end point of polishing is determined from the change in the current value from the current sensor 580.

  The current sensor 580 includes a current converter (CT) provided in one phase, for example, the V phase, of the three-phase cable 22 that supplies electric power to the electric motor. A motor current value flowing in the phase is detected. The current sensor 580 is connected to the end point detection device 530 of the polishing apparatus, and the current value flowing in the V phase detected by the current sensor 580 is sent to the end point detection device 530, and the end point detection device 530 receives the current value. The end point of the polishing is determined from the change in. The current sensor 580 is also connected to the control unit 570. An input unit 590 is connected to the control unit 570, and the weighting unit 560 is controlled based on the difference between the current value detected by the current sensor 580 and the set value from the input unit 590. Thus, the current flowing in the V phase is amplified by a predetermined range. Thus, the current value flowing in the V phase is larger than the current values flowing in the other U phase and W phase, thereby improving the sensitivity of end point detection in the end point detection device 530.

The weighting unit 560 is for making a difference in the ratio of the current flowing through the windings of the respective phases of the first electric motor 14, and as shown in FIG. 7, the U-phase current amplifier 562 and the V-phase A current amplifier 564 and a W-phase current amplifier 566 are provided. The U-phase current amplifier 562, the V-phase current amplifier 564, and the W-phase current amplifier 566 are provided between the inverter device 550 and the first electric motor 14 (after the inverter device 550), and the first electric motor 14 Is an amplifier that individually amplifies the current of each phase and supplies it to the first electric motor 14. The weighting unit 560 is connected to the inverter device 550, and the current output from the inverter device 550 is supplied to the electric motor 14 after the current flowing in each phase is amplified by the weighting unit 560 by a predetermined ratio. The U-phase cable, V-phase cable, and W-phase cable of the inverter device 550 are connected to the U-phase current amplifier 562, the V-phase current amplifier 564, and the W-phase current amplifier 566 of the weighting unit 560, respectively. The weighting unit 560 makes a difference in the current amplitude of each phase based on the command from For example, when adopting a configuration in which only the current flowing in the V phase is amplified and the current flowing in the U phase and the W phase is not amplified, the weighting unit 560 can be configured by only the V phase current amplifier 564.

  The control unit 570 includes a compensator 572 and a current command calculation unit 574. An input unit 590 is connected to the control unit 570, and the speed value of the first electric motor 14 is supplied to the compensator 572 by manual input at the input unit 590, and the weight value is the current command calculation unit 574. To be supplied.

  The compensator 572 can be composed of a PID controller, and is used to calculate the deviation between the speed of the electric motor as the target value input from the input unit 590 and the actual value from the speed sensor 16 that detects the speed of the electric motor. Proportional control that changes the operation amount proportionally, integral control that adds the deviation and changes the operation amount in proportion to the value, and operation proportional to the deviation rate (that is, the speed at which the deviation changes) It performs differential control that produces quantity. By performing this PID control, the current command value of each phase is output-controlled so that the speed of the electric motor 14 becomes the speed as the target value input from the input unit 590. The compensator 572 may be composed of a PI controller.

  The current command calculation unit 574 is connected to the compensator 572 and the input unit 590. The weighting information of each phase input to the input unit 590 and the current command value of each phase output from the compensator 572 Based on this, the U-phase current amplifier 562, the V-phase current amplifier 564, and the W-phase current amplifier 566 are controlled. As described above, when only the current flowing from the V-phase cable of inverter device 550 to the V-phase winding of electric motor 14 is amplified, current command calculation unit 574 outputs an amplification command value of a predetermined multiple by V-phase current amplifier 564. The U-phase current amplifier 562 and the W-phase current amplifier 566 output an amplification command value of 1 time. The weighting unit 560 receives the command signal of the amplified value of the current of each phase from the current command calculation unit 574. The U-phase current amplifier 562, the V-phase current amplifier 564, and the W-phase current amplifier 566 amplify the current of each phase based on the received command signal of the amplification value of the current, and thus the difference in the current ratio of each phase. Can be attached.

  The input unit 590 includes a keyboard, a touch panel, and the like. The operator sets the speed value of the electric motor and the weighting value) via the input unit 590 based on the result obtained based on the experiment performed in advance or the result obtained by the simulation.

Next, the operation of the polishing apparatus according to this embodiment will be described.
The operator drives the first and second electric motors 14 and 22 via the input unit 590 to operate the polishing apparatus. Although the torque required for the electric motor 14 varies depending on the polishing state of the semiconductor wafer 18, the turntable 12 needs to be rotated at a constant speed. For this reason, even if the compensator 572 of the control unit 570 controls the current flowing through each winding of the electric motor 14 by PID control, and the torque required for the electric motor 14 varies according to the polishing state of the semiconductor wafer, The electric motor 14 is rotationally driven at a constant speed, and the turntable 12 rotates at a constant speed. That is, the speed command set in the input unit 590,
Based on the difference between the actual speed of the electric motor 14 detected by the speed sensor 16, the compensator calculates a current command value to be passed through the winding of each phase by PID control, and the compensator 572 outputs the current command value. Current command value is output.

  Here, when the weighting control is not performed in the same manner as before, the weighting command is not given to the current calculation commanding unit 574 from the input unit 590. For this reason, the current calculation command unit 574 outputs the current command value to the current amplifier of each phase as it is without giving a weight to the current command value of each phase output from the compensator 572. Therefore, each phase current amplifier supplies the current output from the inverter to the electric motor without being amplified. For this reason, currents having substantially the same amplitude and different phase differences of 120 ° are supplied to the windings of the respective phases, and the electric motor 14 generates rotational torque based on this current.

  On the other hand, when weighting each phase in order to perform end point detection more appropriately, a weighting value is given from the input unit 590 to the current calculation command unit 574. For example, when a weighting of 0.8 is assigned to the U phase, 1.2 to the V phase, and 1.0 to the W phase, the current calculation command unit 574 outputs each weight output from the compensator 572 based on this weighting. The current amplifiers 562, 564, and 566 for each phase are controlled so that the current command values for the phases are weighted. That is, the current output from the inverter device 550 to the U-phase cable of the inverter device is supplied to the U-phase current amplifier 562, and the amplitude value is multiplied by 0.8 by the U-phase current amplifier. Supplied to the phase winding. On the other hand, the current output to the V-phase cable of the inverter device 550 is supplied to the V-phase current amplifier 564, the amplitude value of which is multiplied by 1.2 by the V-phase current amplifier, and the current is output to the V-phase winding of the electric motor 14. Supplied. Further, the current output to the W-phase cable of the inverter device is supplied to the W-phase current amplifier 566, the amplitude value of which is multiplied by 1.0 by the W-phase current amplifier, that is, without being amplified at all. , Supplied to the W-phase winding of the electric motor 14.

  When weighting is given in this way, a difference is made in the amplitude of the current flowing through the winding of each phase of the electric motor 14, and the winding through which the current flows most, that is, the current flowing through the V-phase winding is expressed as current. It is detected by a sensor and used to detect the polishing end point of the polishing apparatus based on the current value.

Even if the current amplifiers 562, 564, and 566 of each phase are controlled so as to give weights to the current command values of the respective phases output from the compensator 572 as in the third embodiment, the first embodiment Similarly, the current of a specific phase (for example, V phase) can be increased with respect to other phases. Therefore, the V-phase current sensitivity with respect to the rotational load fluctuation of the first electric motor 14 can be improved. As a result, when the rotational load fluctuation of the first electric motor 14 occurs, the current of the phase with a large weighting fluctuates greatly, so that the sensitivity of the end point detection can be improved.
<Fourth embodiment>
In the above embodiment, the current amplifier is composed of a power transistor or the like. However, the present invention is not limited to this, and other configurations may be adopted. FIG. 8 is a block diagram of a current amplifier according to the fourth embodiment of the present invention. As shown in FIG. 8, a plurality of (for example, two) inverter devices 600 and 610 may be connected in parallel, and a switching circuit 620 may be provided between the two inverter devices. When weighting the V-phase current, the switching circuit 620 closes the V-phase of the two inverters, and the current flowing in the V-phase winding of the electric motor can be superimposed. Each of inverter devices 600 and 610 has the same configuration as the inverter device shown in FIG.
<Fifth Embodiment>
FIG. 9 is a block diagram of a current amplifier according to the fifth embodiment of the present invention. As shown in FIG. 9, transformers 630 and 640 are provided on the output sides of the inverter devices 600 and 610, respectively.
May be provided to further amplify the current value.

  In the present embodiment, a current sensor for detecting a current value flowing in the V phase is provided. In accordance with this, it is possible to amplify only the current flowing in the V phase and control not to amplify the current flowing in the U phase and the W phase. However, by providing a current sensor for detecting the current value flowing in each phase, each phase current amplifier is controlled based on the weighting information of each phase input to the input unit, and the current flowing in each phase is It may be amplified.

  In each of the above embodiments, an electric motor having three-phase windings is used. However, the present invention is not necessarily limited to this, and an electric motor having two or more phase windings may be used. good.

  In the above embodiment, weighting control is performed on the motor current of the electric motor that drives the turntable. However, when end point detection is performed using the electric motor that rotationally drives the top ring, the electric motor that rotationally drives the top ring. The motor current can be weighted.

DESCRIPTION OF SYMBOLS 10 Polishing cloth 12 Turntable 14 1st electric motor 16 Speed sensor 18 Semiconductor wafer 20 Top ring 22 2nd electric motor 30 End point detection apparatus 50 Inverter apparatus 100 Motor driver 200 Input part 300 Weighting setting device

Claims (13)

A polishing apparatus for flattening the surface of a workpiece,
A polishing table;
A first electric motor that rotationally drives the polishing table;
A substrate holding unit capable of holding a workpiece;
A second electric motor that rotationally drives the substrate holder,
The polishing table is rotated by the first electric motor, and the substrate holding portion is rotated by the second electric motor to press the workpiece against the polishing table while holding the workpiece by the substrate holding portion. The surface of the workpiece can be flattened by polishing,
At least one of the first and second electric motors includes a plurality of phases of windings,
The polishing apparatus includes: a weighting unit that performs weighting that makes a difference in the current ratio of each phase; and the electric motor that is generated by the polishing by detecting a change in current of a phase that is set to have a large weighting by the weighting unit. A polishing apparatus comprising: a detecting unit that detects torque fluctuations of the polishing machine. The polishing apparatus according to claim 1, further comprising:
A polishing apparatus, comprising: an end point detection unit that detects an end point of polishing processing indicating flattening of a surface of the workpiece based on torque fluctuation of the electric motor detected by the detection unit. The polishing apparatus according to claim 1 or 2,
At least one of the first and second electric motors includes at least a three-phase winding of a U phase, a V phase, and a W phase. The polishing apparatus according to claim 3, wherein
The polishing apparatus, wherein the first electric motor includes at least a three-phase winding of a U phase, a V phase, and a W phase. The polishing apparatus according to claim 4, wherein
The polishing apparatus according to claim 1, wherein the first electric motor is a synchronous or induction type AC servo motor. The polishing apparatus according to any one of claims 1 to 5,
The polishing apparatus according to claim 1, wherein the weighting unit sets a large weight to one phase. The polishing apparatus according to claim 6, wherein
The polishing apparatus according to claim 1, wherein the one phase is a V phase. The polishing apparatus according to any one of claims 1 to 7,
The polishing apparatus according to claim 1, wherein the weighting unit includes a current amplifier. The polishing apparatus according to claim 1, wherein
The polishing apparatus includes a first inverter device for controlling the first electric motor. The polishing apparatus according to claim 1, wherein
The weighting unit is
A second inverter device connected in parallel to the first inverter device for controlling the first electric motor;
A polishing apparatus, comprising: a switching circuit that adds a current output from the second inverter device to an output current from the first inverter device. The polishing apparatus according to claim 1, further comprising:
A motor driver for driving at least one of the first and second electric motors;
The motor driver has a current compensator that compensates the current of each phase based on a deviation between each current command value of each phase and an actual current value supplied to the electric motor;
The weighting unit inputs a command signal of the current ratio of each phase to the current compensator,
The polishing apparatus according to claim 1, wherein the current compensator makes a difference in the current ratio of each phase based on a current ratio command signal input from the weighting unit. The polishing apparatus according to claim 1, further comprising:
A motor driver for driving at least one of the first and second electric motors;
The motor driver
A computing unit for obtaining a rotational speed of the electric motor based on a detected value of a rotational position of the electric motor;
Generates a command signal for the current to be supplied to the electric motor based on a deviation between the command value of the rotation speed of the electric motor input via the input interface and the rotation speed of the electric motor obtained by the calculator. A speed compensator to
Based on the electrical angle signal generated based on the detected value of the rotational position of the electric motor and the current command signal generated by the speed compensator, the current command value of at least two phases of the phases. A converter for generating
The weighting unit inputs a command signal of a current ratio of at least two phases of the phases to the converter,
The polishing apparatus according to claim 1, wherein the converter makes a difference between the current ratios of at least two of the phases based on a current ratio command signal input from the weighting unit. The polishing apparatus according to claim 1, further comprising:
An inverter device for driving at least one of the first and second electric motors;
The weighting unit includes an amplifier that is provided in a subsequent stage of the inverter device and individually amplifies the current of each phase output from the inverter device and supplies the current to the electric motor. Receive command signal,
The amplifying unit amplifies a current of each phase based on a command signal of an amplification value of the received current, thereby differentiating a current ratio of each phase.

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