JP7269871B2 - Eddy current sensor output signal processing circuit and output signal processing method - Google Patents

Description

The present invention relates to an eddy current sensor output signal processing circuit and an output signal processing method.

Eddy current sensors are used for film thickness measurement, displacement measurement, and the like. The eddy current sensor will be described below using film thickness measurement as an example. Eddy current sensors for film thickness measurement are used, for example, in the manufacturing process (polishing process) of semiconductor devices. The eddy current sensor is used in the polishing process as follows. 2. Description of the Related Art As the degree of integration of semiconductor devices advances, circuit wiring is becoming finer and the distance between wirings is becoming narrower. Therefore, it is necessary to planarize the surface of the semiconductor wafer, which is the object to be polished.

The polishing apparatus includes a polishing table for holding a polishing pad for polishing an object to be polished, and a top ring for holding and pressing the object to be polished against the polishing pad. The polishing table and the top ring are each rotationally driven by a driving section (for example, a motor). A liquid (slurry) containing an abrasive is poured onto the polishing pad, and the object to be polished held by the top ring is pressed against it, whereby the object to be polished is polished.

In a polishing machine, if the polishing of the object to be polished is insufficient, insulation between circuits cannot be obtained, and there is a risk of short-circuiting. or the wiring itself is completely removed and the circuit itself is not formed. Therefore, the polishing apparatus is required to detect the optimum polishing end point.

As such a technique, there is one described in JP-A-2011-23579. In this technique, an eddy current sensor using three coils is used to detect the polishing endpoint. As shown in FIG. 5 of Japanese Patent Application Laid-Open No. 2011-23579, the detection coil and the dummy coil among the three coils form a series circuit, and both ends of the series circuit are connected to a resistance bridge circuit including variable resistors. By adjusting the balance in the resistance bridge circuit, it is possible to adjust the zero point so that the output of the resistance bridge circuit becomes zero when the film thickness is zero. The output of the resistance bridge circuit is input to the synchronous detection circuit as shown in FIG. 6 of JP-A-2011-23579. The synchronous detection circuit detects DC components such as resistance component (R), reactance component (X), amplitude output (Z) and phase output (tan ⁻¹ R/X) associated with changes in film thickness from the input signal. Take out.

With regard to the conventional film thickness measurement method using an eddy current sensor, the signal output from the eddy current sensor contains a large amount of noise. Therefore, when detecting minute wiring (for example, Cu wiring), the output signal itself is small, and the output signal may be buried in noise, making it impossible to measure the film thickness. Also, when the magnitude of the output signal is somewhat larger than the noise, the film thickness can be measured, but there is a problem that the measurement accuracy of the film thickness is low.

Japanese Patent Application Laid-Open No. 2011-23579

One aspect of the present invention has been made to solve such problems, and an object of the present invention is to improve the signal-to-noise ratio (S/N: signal-to-noise ratio) as compared with the prior art. An object of the present invention is to provide a sensor output signal processing circuit and an output signal processing method.

In order to solve the above problems, in a first aspect, an eddy current sensor having an excitation coil capable of generating a magnetic field by receiving an excitation signal and a detection coil capable of detecting the magnetic field and outputting a detection signal; an output signal processing circuit for processing the detection signal, the output signal processing circuit being a generation circuit capable of generating a noise reduction signal for reducing noise from the excitation signal or the detection signal; and an addition circuit capable of adding the noise reduction signal generated in the circuit to the detection signal to generate a noise reduction signal in which noise contained in the detection signal is reduced. taking the configuration.

In this embodiment, the noise reduction signal is added to the detection signal to generate the noise reduction signal in which the noise included in the detection signal is reduced, so the S/N is improved as compared with the conventional technique. When an eddy current sensor is used to measure film thickness, the detection accuracy of Cu wiring, etc., is improved compared to conventional technology due to the reduction of the effects of noise, improving the performance of the eddy current sensor.

In form 2, a first excitation coil that receives an excitation signal to generate a first magnetic field, and a first detection coil that detects the first magnetic field and outputs a first detection signal. and processing the first detection signal and the first dummy signal output by an eddy current sensor having a first dummy coil capable of detecting the first magnetic field and outputting a first dummy signal. In an eddy current sensor output signal processing circuit, a first resistance bridge circuit capable of outputting a first difference signal that is a difference between the first detection signal and the first dummy signal; a first generation circuit capable of generating a first noise reduction signal for reducing noise from any one of the first detection signal, the first dummy signal, and the first difference signal; A first noise-reduced signal generated in a generation circuit is added to the first difference signal to generate a first noise-reduced signal in which noise contained in the first difference signal is reduced. and an adder circuit.

In form 3, the eddy current sensor includes a second excitation coil that receives the excitation signal to generate a second magnetic field, and a second excitation coil that detects the first magnetic field and the second magnetic field and a second dummy coil capable of detecting the first magnetic field and the second magnetic field and outputting a second dummy signal; One detection coil is capable of detecting the first magnetic field and the second magnetic field and outputting the first detection signal, and the first dummy coil detects the first magnetic field and the second magnetic field. and outputting the first dummy signal, and the output signal processing circuit is capable of outputting a second difference signal that is a difference between the second detection signal and the second dummy signal. and a second noise reduction signal for reducing noise from any one of the excitation signal, the second detection signal, the second dummy signal, and the second difference signal. and the second noise reduction signal generated in the second generation circuit is added to the second difference signal to generate noise contained in the second difference signal. A second summing circuit capable of generating a reduced second noise reduction signal, and a third summing circuit capable of summing the first noise reduction signal and the second noise reduction signal. The configuration of the output signal processing circuit of the eddy current sensor described in Embodiment 2 is adopted.

In form 4, an excitation signal is input to detect first and second excitation coils capable of generating first and second magnetic fields, respectively, and the first magnetic field and the second magnetic field are detected. First and second detection coils capable of outputting first and second detection signals, detecting the first magnetic field and the second magnetic field, and capable of outputting first and second dummy signals, respectively an eddy current sensor output signal processing circuit for processing the first and second detection signals and the first and second dummy signals output by an eddy current sensor having first and second dummy coils, a first resistor bridge circuit capable of outputting a first difference signal that is the difference between the first detection signal and the first dummy signal; and a difference between the second detection signal and the second dummy signal. and a third addition circuit capable of adding the first difference signal and the second difference signal. It has a configuration of an eddy current sensor output signal processing circuit.

According to this embodiment, since the first difference signal and the second difference signal are added, the output signal of the eddy current sensor becomes larger than in the conventional case, and the accuracy of film thickness measurement is improved.

In form 5, an eddy current sensor having an excitation coil capable of generating a magnetic field upon receiving an excitation signal and a detection coil capable of detecting the magnetic field and outputting a detection signal outputs an eddy current sensor that processes the detection signal. In the current sensor output signal processing method, the steps of generating a noise reduction signal for reducing noise from the excitation signal or the detection signal, adding the generated noise reduction signal to the detection signal, and generating a noise-reduced signal by reducing noise contained in the detection signal.

In form 6, a first excitation coil that receives an excitation signal to generate a first magnetic field, and a first detection coil that detects the first magnetic field and outputs a first detection signal. and processing the first detection signal and the first dummy signal output by an eddy current sensor having a first dummy coil capable of detecting the first magnetic field and outputting a first dummy signal. In an eddy current sensor output signal processing method, the step of outputting a first difference signal that is a difference between the first detection signal and the first dummy signal, the excitation signal, the first detection signal, generating a first noise reduction signal for reducing noise from either the first dummy signal or the first difference signal; applying the generated first noise reduction signal to the first adding to the difference signal to generate a first noise reduction signal in which noise contained in the first difference signal is reduced; and there is

In form 7, the eddy current sensor includes a second excitation coil that receives the excitation signal to generate a second magnetic field, and a second excitation coil that detects the first magnetic field and the second magnetic field to generate a second and a second dummy coil capable of detecting the first magnetic field and the second magnetic field and outputting a second dummy signal; One detection coil is capable of detecting the first magnetic field and the second magnetic field and outputting the first detection signal, and the first dummy coil detects the first magnetic field and the second magnetic field. can be detected to output the first dummy signal, and the output signal processing method outputs a second difference signal that is a difference between the second detection signal and the second dummy signal generating a second noise reduction signal for reducing noise from any one of the excitation signal, the second detection signal, the second dummy signal, and the second difference signal; adding the generated second noise-reduced signal to the second difference signal to generate a second noise-reduced signal in which noise contained in the second difference signal is reduced; The configuration of the eddy current sensor output signal processing method according to mode 6 is characterized by including the step of adding the noise reduction signal and the second noise reduction signal.

In form 8, first and second excitation coils that can generate first and second magnetic fields respectively by receiving an excitation signal and detecting the first magnetic field and the second magnetic field, respectively First and second detection coils capable of outputting first and second detection signals, detecting the first magnetic field and the second magnetic field, and capable of outputting first and second dummy signals, respectively an eddy current sensor output signal processing method for processing the first and second detection signals and the first and second dummy signals output by an eddy current sensor having first and second dummy coils, and outputting a first difference signal that is the difference between the first detection signal and the first dummy signal; and a second difference that is the difference between the second detection signal and the second dummy signal. An eddy current sensor output signal processing method is characterized by comprising a step of outputting a signal, and a step of adding the first difference signal and the second difference signal.

FIG. 1 is a schematic diagram showing the overall configuration of a polishing apparatus according to one embodiment of the present invention. FIG. 2 is a plan view showing the relationship between the polishing table, the eddy current sensor, and the semiconductor wafer. 3A and 3B are diagrams showing the configuration of the eddy current sensor assembly, FIG. 3A is a block diagram showing the configuration of the eddy current sensor assembly, and FIG. It is a circuit diagram. FIG. 4 is a block diagram showing the eddy current sensor assembly of this embodiment. FIG. 5 is a block diagram showing the principle of noise canceling according to this embodiment. FIG. 6 is a block diagram showing the synchronous detection circuit of the eddy current sensor. FIG. 7 is a schematic diagram showing a configuration example of a coil in the eddy current sensor of this embodiment. FIG. 8 is a schematic diagram showing an example of connection of coils in an eddy current sensor. FIG. 9 is a schematic diagram showing a configuration example of an eddy current sensor according to another embodiment. FIG. 10 is a schematic diagram showing a connection example of exciting coils in an eddy current sensor. FIG. 11 is a diagram showing a magnetic field generated by an eddy current sensor. FIG. 12 is a perspective view of the eddy current sensor shown in FIG. 9 and a block diagram showing a connection example. FIG. 13 is a perspective view of the eddy current sensor shown in FIG. 9 and a block diagram showing a connection example. FIG. 14 is a spectrum showing intensity distribution of noise and signal contained in the output signal of the detection coil with respect to frequency. FIG. 15 is a spectrum showing intensity distribution of noise and signal contained in the output signal of the detection coil with respect to frequency.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, in each of the following embodiments, the same or corresponding members may be denoted by the same reference numerals, and redundant description may be omitted. Also, the features shown in each embodiment can be applied to other embodiments as long as they are not mutually contradictory.

FIG. 1 is a schematic diagram showing the overall configuration of a polishing apparatus to which an eddy current sensor 50 according to one embodiment of the invention is applied. As shown in FIG. 1, the polishing apparatus includes a polishing table 100 and a top ring (holding portion) 1 for holding a substrate such as a semiconductor wafer to be polished and pressing it against the polishing surface on the polishing table. there is

The polishing table 100 is connected via a table shaft 170 to a motor (not shown), which is a drive unit arranged below, and is rotatable about the table shaft 170 . A polishing pad 101 is attached to the upper surface of the polishing table 100, and a surface 101a of the polishing pad 101 constitutes a polishing surface for polishing the semiconductor wafer WH. A polishing liquid supply nozzle 102 is installed above the polishing table 100 , and the polishing liquid Q is supplied onto the polishing pad 101 on the polishing table 100 by the polishing liquid supply nozzle 102 . As shown in FIG. 1, an eddy current sensor 50 is embedded inside the polishing table 100 .

The top ring 1 includes a top ring body 142 that presses the semiconductor wafer WH against the polishing surface 101a, and a retainer ring 143 that holds the outer peripheral edge of the semiconductor wafer WH and prevents the semiconductor wafer WH from jumping out of the top ring. is basically composed of

The top ring 1 is connected to a top ring shaft 111 , and the top ring shaft 111 is vertically moved with respect to the top ring head 110 by a vertical movement mechanism 124 . The vertical movement of the top ring shaft 111 raises and lowers the entire top ring 1 with respect to the top ring head 110 for positioning. A rotary joint 125 is attached to the upper end of the top ring shaft 111 .

A vertical movement mechanism 124 for vertically moving the top ring shaft 111 and the top ring 1 includes a bridge 128 that rotatably supports the top ring shaft 111 via a bearing 126, a ball screw 132 attached to the bridge 128, and a support 130. and a servomotor 138 provided on the support base 129 . A support base 129 that supports the servomotor 138 is fixed to the top ring head 110 via a support 130 .

The ball screw 132 has a screw shaft 132a connected to a servomotor 138 and a nut 132b with which the screw shaft 132a is screwed. The top ring shaft 111 moves up and down integrally with the bridge 128 . Therefore, when the servomotor 138 is driven, the bridge 128 moves up and down via the ball screw 132, thereby moving the top ring shaft 111 and the top ring 1 up and down.

Also, the top ring shaft 111 is connected to the rotary cylinder 112 via a key (not shown). The rotating cylinder 112 has a timing pulley 113 on its outer periphery. A top ring motor 114 is fixed to the top ring head 110 , and the timing pulley 113 is connected via a timing belt 115 to a timing pulley 116 provided in the top ring motor 114 . Therefore, when the top ring motor 114 is rotationally driven, the rotating cylinder 112 and the top ring shaft 111 are integrally rotated via the timing pulley 116, the timing belt 115, and the timing pulley 113, and the top ring 1 is rotated. The top ring head 110 is supported by a top ring head shaft 117 rotatably supported by a frame (not shown).

In the polishing apparatus configured as shown in FIG. 1, the top ring 1 can hold a substrate such as a semiconductor wafer WH on its lower surface. The top ring head 110 is configured to be rotatable about a top ring head shaft 117. The top ring 1, which holds the semiconductor wafer WH on its lower surface, moves from the position for receiving the semiconductor wafer WH to the polishing table by the rotation of the top ring head 110. 100 upwards. Then, the top ring 1 is lowered to press the semiconductor wafer WH against the surface (polishing surface) 101 a of the polishing pad 101 . At this time, the top ring 1 and the polishing table 100 are rotated, and the polishing liquid Q is supplied onto the polishing pad 101 from the polishing liquid supply nozzle 102 provided above the polishing table 100 . In this manner, the semiconductor wafer WH is brought into sliding contact with the polishing surface 101a of the polishing pad 101 to polish the surface of the semiconductor wafer WH.

FIG. 2 is a plan view showing the relationship between the polishing table 100, the eddy current sensor 50, and the semiconductor wafer WH. As shown in FIG. 2, the eddy current sensor 50 is installed at a position passing through the center Cw of the semiconductor wafer WH being polished held by the top ring 1 . Polishing table 100 rotates around center of rotation 170 . For example, the eddy current sensor 50 can continuously detect a metal film (conductive film) such as a Cu layer of the semiconductor wafer WH on the passing trajectory (scanning line) while passing under the semiconductor wafer WH. It has become.

Next, the eddy current sensor 50 provided in the polishing apparatus according to the present invention will be described in more detail with reference to the accompanying drawings. 3A and 3B are diagrams showing the configuration of an eddy current sensor assembly including the eddy current sensor 50. FIG. 3A is a block diagram showing the configuration of the eddy current sensor assembly, and FIG. FIG. 4 is an equivalent circuit diagram of the current sensor assembly; As shown in FIG. 3(a), the eddy current sensor 50 is arranged near the metal film (or conductive film) mf to be detected, and an AC signal source 52 is connected to its coil. Here, the metal film (or conductive film) mf to be detected is, for example, a thin film of Cu, Al, Au, W, etc. formed on the semiconductor wafer WH. The eddy current sensor 50 is arranged in the vicinity of, for example, about 1.0 to 4.0 mm with respect to the metal film (or conductive film) to be detected. The coil is usually wound around a magnetic material (not shown) such as ferrite. The eddy current sensor 50 may be an air core coil.

In the signal detection of the eddy current sensor, the impedance changes due to the eddy current generated in the metal film (or conductive film) mf, and the metal film (or conductive film) is detected from this impedance change. there is something That is, in the impedance type, in the equivalent circuit shown in _FIG . The output signal processing circuit 54 can detect the change in the impedance Z to detect the change in the metal film (or the conductive film).

With an impedance type eddy current sensor, it is possible to extract signal outputs X, Y, phase, and combined impedance Z (=X+iY). From the impedance components X, Y, etc., measurement information regarding the film thickness of the metal films (or conductive films) Cu, Al, Au, W can be obtained. The eddy current sensor 50 can be built in a position near the surface inside the polishing table 100 as shown in FIG. A change in the metal film (or conductive film) can be detected from the eddy current flowing in the metal film (or conductive film) on the wafer.

For the frequency of the eddy current sensor, single radio wave, AM modulated radio wave, sweep output of function generator, etc. can be used, and the sensitive oscillation frequency and modulation method can be selected according to the type of metal film. is preferred.

The impedance type eddy current sensor will be specifically described below. The AC signal source 52 has a fixed frequency oscillator 260 (see FIG. 4) on the order of 2-30 MHz. Oscillator 260 is, for example, a crystal oscillator. The AC voltage supplied by the AC signal source 52 causes a current _I1 to flow through the eddy current sensor 50 . When current flows through the eddy current sensor 50 placed near the metal film (or conductive film) mf, this magnetic flux interlinks with the metal film (or conductive film) mf, creating mutual inductance M between them. An eddy current _I2 flows in the metal film (or conductive film) mf. where R1 is the equivalent resistance of the primary including the eddy current sensor and L1 is the self-inductance of the primary including the eddy current sensor as well. On the metal film (or conductive film) mf side, R2 is an equivalent resistance corresponding to eddy current loss, and L2 is its self-inductance. The impedance Z when the eddy current sensor side is viewed from the terminals a and b of the AC signal source 52 changes depending on the magnitude of the eddy current loss formed in the metal film (or conductive film) mf.

FIG. 1 also shows the output signal processing circuitry 54 of the eddy current sensor 50 . As shown in FIG. 2, the polishing table 100 of the polishing apparatus is rotatable around its axis 170 as indicated by the arrow. An AC signal source 52 and an output signal processing circuit 54 are embedded in the polishing table 100 . The eddy current sensor 50, AC signal source 52 and output signal processing circuit 54 may be integrated. The output signal 172 of the output signal processing circuit 54 passes through the table shaft 100a of the polishing table 100, via a rotary joint (not shown) provided at the shaft end of the table shaft 100a, and the end point is detected by the output signal 172. It is connected to controller 246 . At least one of the AC signal source 52 and the output signal processing circuit 54 may be arranged outside the polishing table 100 .

The eddy current sensor assembly 174 is shown in FIG. Eddy current sensor assembly 174 includes eddy current sensor 50 and output signal processing circuitry 54 for processing output signal 176 of eddy current sensor 50 . The eddy current sensor 50 has an excitation coil 72 that receives an excitation signal 250 to generate a magnetic field 308 (see FIG. 8), and a detection coil 73 that detects the magnetic field 308 and outputs an output signal 176 (detection signal). and The output signal processing circuit 54 includes a generation circuit 254 capable of generating a noise reduction signal 252 for reducing noise from the excitation signal 250 or the output signal 176, and the noise reduction signal 252 generated in the generation circuit 254 as an output signal 176. to produce a noise reduced signal 256 that reduces the noise contained in the output signal 176 . In this embodiment, generation circuit 254 generates noise reduction signal 252 from output signal 176 of detection coil 73 . In this embodiment, the output signal 176 is signal-processed by a filter 266 and an amplifier 268 . A generation circuit 254 generates a noise reduction signal 252 from the signal-processed output signal 176 .

AC signal source 52 may include amplifier 262 for amplifying output signal 270 of oscillator 260 and filter 264 for reducing noise contained in output signal 272 of amplifier 262 . Since noise is also amplified by the amplifier 262, a filter 264 is placed after the amplifier 262 for amplified noise reduction. In this embodiment, the output signal of filter 264 is excitation signal 250 .

The eddy current sensor 50 has an excitation coil 72 for forming an eddy current in the metal film (or conductive film) on the semiconductor wafer WH, and a detection coil 73 for detecting the generated eddy current. For example, an excitation coil 72 and a detection coil 73 are arranged axially on a cylindrical ferrite core. The excitation coil 72 is connected to the AC signal source 52 . The excitation coil 72 forms an eddy current in the metal film (or conductive film) mf on the semiconductor wafer WH arranged near the eddy current sensor 50 by the magnetic field formed by the voltage supplied from the AC signal source 52. . A detection coil 73 is arranged above the ferrite core (on the metal film (or conductive film) side) to detect a magnetic field generated by an eddy current formed in the metal film (or conductive film). The eddy current sensor 50 may have a dummy coil 74 as described below.

Output signal 176 is input to generation circuit 254 via filter 266 and amplifier 268 of output signal processing circuit 54 . An amplifier (not shown) is arranged in front of the filter 266 . A filter 266 is provided for amplified noise reduction. The amplifier 268 is placed after the filter 266 because the output signal 176 may be weak if only the amplifier (not shown) is used. Output signal 274 of amplifier 268 is input to generator circuit 254 and summing circuit 258 .

Generation circuit 254 generates noise reduction signal 252 . Generation is performed as follows. Generation circuit 254 includes bandstop filter 276 and phase inverter circuit 278 . Bandstop filter 276 attenuates only frequency signals near a particular frequency signal (eg, 16 MHz) generated by oscillator 260 to a very low level. Bandstop filter 276 passes other frequency signals (ie, noise signals) untouched. The output signal 282 of the bandstop filter 276 is sent to the phase inverter circuit 278 and phase-inverted by the phase inverter circuit 278 . To invert the phase means to advance the phase by 180 degrees.

The output of phase inverter circuit 278 , noise reduction signal 252 , is sent to summing circuit 258 where it is summed with output signal 274 . Noise reduction signal 252 is a signal that cancels out only the noise component contained in output signal 274 . Noise-reduced signal 256, which is the output of summing circuit 258, is a signal with reduced frequencies (ie, noise) generated by oscillator 260 at frequencies other than the specified frequency. Noise reduced signal 256 is sent to detector circuit 280 . The detection circuit 280 extracts the already-described signal outputs X, Y, phase, composite impedance Z (=X+iY), etc. from the high-frequency signal. These are DC signals. The output of detector circuit 280 is output signal 172 .

In this embodiment, the noise reduction signal 252 is added to the detection signal 274 to generate the noise reduction signal 256 in which the noise included in the detection signal 274 is reduced, so the S/N is improved as compared with the prior art. When the eddy current sensor 50 is used for film thickness measurement, the detection accuracy of Cu wiring and the like is improved compared to the conventional technology due to the reduction of the influence of noise, and the performance of the eddy current sensor 50 is improved.

FIG. 5 further illustrates the processing performed in bandstop filter 276, phase inverter circuit 278, and adder circuit 258. FIG. In the following, we assume that noise cancellation is ideal. Bandstop filter 276 outputs an output signal 282 containing only noise components. For clarity of explanation, assume that the output signal 282 is Y1=A sin(ωt). where A is the noise amplitude (eg, in millivolts (mv)), ω is the noise angular frequency (eg, in radians per second (rad/s)), and t is time. (seconds (s)).

Output signal 282 becomes noise reduced signal 252 by phase inverter circuit 278 . If the noise reduction signal 252 is Y2, then Y2=-Y1. Another expression is Y2=A sin(ωt+π). On the other hand, the output signal 274 output from the detection coil 73 includes, as a noise component, the noise component Y3=A sin(ωt) which is the same as the noise component Y1=A sin(ωt).

Summing circuit 258 sums noise reduced signal 252 and output signal 274 to output noise reduced signal 256 . Assuming that the noise component included in the noise reduction signal 256 is Y4, Y4=Y3+Y2. Since Y3 and Y2 have the same amplitude and are out of phase by 180 degrees, Y4=0. Noise reduced signal 256 is a signal that does not contain noise components.

In FIG. 4, noise reduction signal 252 is generated from the output of detection coil 73 or dummy coil 74 . Noise reduction signal 252 may be generated from sources other than the output of detection coil 73 or dummy coil 74 . For example, the noise reduction signal 252 may be generated from the output signal 270 of the oscillator 260 and the excitation signal 250 . Although multiple amplifiers and filters are used in FIG. 4, the noise reduction signal 252 may be generated from signals before or after the amplifiers and filters. Note that when generating the noise reduction signal 252 from the output of the detection coil 73 or the dummy coil 74 , it is preferable to generate the noise reduction signal 252 from the output of the detection coil 73 . Since the signal that is ultimately needed is the output of the detection coil 73, it is preferable to use the output of the detection coil 73 to generate the noise reduction signal 252 in order to remove the noise of the detection coil 73. FIG.

Returning to FIG. 4, the detection circuit 280 will be described. FIG. 6 is a block diagram showing the synchronous detection circuit 280 of the eddy current sensor. This figure shows an example of a circuit for measuring the impedance Z when the side of the eddy current sensor 50 is viewed from the side of the AC signal source 52 . In the impedance Z measurement circuit shown in this figure, the resistance component (R), reactance component (X), amplitude output (Z), and phase output (tan ⁻¹ R/X) associated with changes in film thickness can be taken out. can.

As described above, the signal source 52 supplies an AC signal to the eddy current sensor 50 arranged near the semiconductor wafer WH on which the metal film (or conductive film) mf to be detected is formed. The signal source 52 is a fixed frequency oscillator comprising a crystal oscillator. The signal source 52 supplies voltages at fixed frequencies of, for example, 2 MHz, 8 MHz and 16 MHz. The alternating voltage produced by signal source 52 is supplied to eddy current sensor 50 via bandpass filter 82 . A signal detected at the terminal of the eddy current sensor 50 passes through a high-frequency amplifier 83 and a phase shift circuit 84, and is converted into a cos component and a sine component of a detection signal by a synchronous detection section comprising a cos synchronous detection circuit 85 and a sine synchronous detection circuit 86. is taken out. Here, the oscillation signal formed by the signal source 52 is formed by a phase shift circuit 84 into two signals, an in-phase component (0°) and a quadrature component (90°) of the signal source 52, and cosine synchronous detection circuit 85, respectively. and a sin synchronous detection circuit 86 to perform the above-described synchronous detection.

The synchronously detected signal is filtered by low-pass filters 87 and 88 to remove unnecessary high-frequency components higher than the signal component, and the resistance component (R) output, which is the cosine synchronous detection output, and the reactance component (X) which is the sine synchronous detection output. ) outputs are retrieved respectively. A vector arithmetic circuit 89 obtains an amplitude output (R ² +X ² ) ^1/2 from the resistance component (R) output and the reactance component (X) output. A vector operation circuit 90 similarly obtains a phase output (tan ⁻¹ R/X) from the resistance component output and the reactance component output. Here, various filters are provided in the main body of the measuring device to remove noise components of the sensor signal. Each filter has its own cut-off frequency. For example, by setting the cut-off frequency of a low-pass filter in the range of 0.1 to 10 Hz, noise components mixed in the sensor signal during polishing can be eliminated. The metal film (or conductive film) to be removed and measured can be measured with high accuracy.

Next, a configuration example of the coil in the eddy current sensor 50 of this embodiment will be described. FIG. 7 is a schematic diagram showing a configuration example of the coils in the eddy current sensor 50 of this embodiment. In this embodiment, the eddy current sensor 50 includes an excitation coil 72 for forming eddy currents in the metal film (or conductive film) and a detection coil 73 for detecting eddy currents in the metal film (or conductive film). , and a dummy coil 74 . The eddy current sensor 50 is composed of three layers of coils wound around a ferrite core 71 , an excitation coil 72 , a detection coil 73 and a dummy coil 74 . The structure of the eddy current sensor 50 is not limited to the structure shown in FIG. 7, and any structure can be adopted.

Here the central excitation coil 72 is connected to the AC signal source 52 . This excitation coil 72 forms an eddy current in the metal film (or conductive film) mf on the semiconductor wafer WH arranged in the vicinity of the semiconductor wafer WH by the magnetic field formed by the voltage supplied from the AC signal source 52. . A detection coil 73 is arranged above the ferrite core 71 (on the metal film (or conductive film) side) to detect a magnetic field generated by an eddy current formed in the metal film (or conductive film). A dummy coil 74 is arranged on the opposite side of the excitation coil 72 from the detection coil 73 . The excitation coil 72, the detection coil 73, and the dummy coil 74 are, for example, coils with the same number of turns (1 to 20t). The reason for providing the dummy coil 74 is to enable adjustment so that the output of the output signal processing circuit 54 becomes zero when the metal film (or conductive film) does not exist.

Various methods of processing the outputs of the detection coil 73 and the dummy coil 74 are possible. For example, as shown in FIG. 4, noise canceling and synchronous detection are performed on the outputs of the detection coil 73 and the dummy coil 74, respectively. Subtraction of the two resulting DC signals is then performed. Film thickness measurements can be made based on the subtraction results. The reason for the subtraction is to make the output of the detection coil 73 zero when the metal film does not exist, as described above.

FIG. 8 is a schematic diagram showing another connection example of each coil in the eddy current sensor. In this example, a resistor bridge circuit 77 is used. As shown in FIG. 8A, the detection coil 73 and the dummy coil 74 are connected in opposite phases. The detection coil 73 and the dummy coil 74 constitute a series circuit with opposite phases, and both ends thereof are connected to a resistance bridge circuit 77 including a variable resistance 76 .

Specifically, the signal line 731 of the detection coil 73 is connected to the terminal 773 of the resistance bridge circuit 77 , and the signal line 732 of the detection coil 73 is connected to the terminal 771 of the resistance bridge circuit 77 . A signal line 741 of the dummy coil 74 is connected to a terminal 772 of the resistance bridge circuit 77 , and a signal line 742 of the dummy coil 74 is connected to a terminal 771 of the resistance bridge circuit 77 . Terminal 771 is grounded. Terminal 774 of resistor bridge circuit 77 is the sensor output. The detection coil 73, excitation coil 72, and dummy coil 74 have inductances _L1 , _L2 , and _L3, respectively.

The excitation coil 72 is connected to the AC signal source 52 and generates an alternating magnetic flux to form an eddy current in a metal film (or conductive film) mf arranged nearby. By adjusting the resistance value of the variable resistor 76, the output voltage of the series circuit consisting of the detection coil 73 and the dummy coil 74 can be adjusted to zero when the metal film (or conductive film) does not exist. Variable resistors 76 (VR ₁ , VR ₂ ) connected in parallel to the detection coil 73 and the dummy coil 74 adjust the signals of L ₁ and L ₃ to have the same phase. That is, in the equivalent circuit of FIG. 8(b),
_VR1-1 ×( _VR2-2 + _jωL3 )＝ _VR1-2 ×( _VR2-1 + _jωL1 ) (1)
Adjust the variable resistors VR ₁ (=VR _1-1 +VR _1-2 ) and VR ₂ (=VR _2-1 +VR _2-2 ) so that As a result, as shown in FIG. 8(c), the signals of L ₁ and L ₃ before adjustment (indicated by dotted lines in the figure) are converted to signals of the same phase and amplitude (indicated by solid lines in the figure).

Another embodiment of the present invention will now be described. 9 and 10 are schematic diagrams showing a configuration example of the eddy current sensor 50 of this embodiment and a connection example of exciting coils in the eddy current sensor. The eddy current sensor 50 arranged near the substrate on which the conductive film is formed comprises a pot core 60 and six coils 860, 862, 864, 866, 868 and 870. As shown in FIG. The pot core 60, which is a magnetic body, includes a bottom portion 61a (bottom portion magnetic substance), a magnetic core portion 61b (central magnetic portion) provided in the center of the bottom portion 61a, and a peripheral wall portion 61c provided in the peripheral portion of the bottom portion 61a. (peripheral magnetic body). The peripheral wall portion 61c is a wall portion provided in the peripheral portion of the bottom portion 61a so as to surround the magnetic core portion 61b. In this embodiment, the bottom portion 61a has a circular disc shape, the magnetic core portion 61b has a solid columnar shape, and the peripheral wall portion 61c has a cylinder shape surrounding the bottom portion 61a.

Among the six coils 860 , 862 , 864 , 866 , 868 , 870 , the center coils 860 , 862 are excitation coils connected to the AC signal source 52 . The excitation coils 860 and 862 form eddy currents in the metal film (or conductive film) mf on the semiconductor wafer WH placed nearby by the magnetic field formed by the voltage supplied from the AC signal source 52 . Detection coils 864 and 866 are arranged on the metal film side of the excitation coils 860 and 862 to detect magnetic fields generated by eddy currents formed in the metal films. Dummy coils 868 and 870 are arranged on the opposite side of the detection coils 864 and 866 with the excitation coils 860 and 862 interposed therebetween.

The excitation coil 860 is an internal coil that is arranged on the outer periphery of the magnetic core portion 61b and is capable of generating a magnetic field, forming an eddy current in the conductive film. The excitation coil 862 is an external coil that is arranged on the outer circumference of the peripheral wall portion 61c and is capable of generating a magnetic field, forming an eddy current in the conductive film. The detection coil 864 is arranged on the outer periphery of the magnetic core portion 61b, is capable of detecting a magnetic field, and detects eddy currents formed in the conductive film. The detection coil 866 is arranged on the outer periphery of the peripheral wall portion 61c, is capable of detecting a magnetic field, and detects eddy currents formed in the conductive film.

The eddy current sensor has dummy coils 868, 870 that detect eddy currents formed in the conductive film. The dummy coil 868 is arranged on the outer periphery of the magnetic core portion 61b and is capable of detecting a magnetic field. The dummy coil 870 is arranged on the outer periphery of the peripheral wall portion 61c and is capable of detecting a magnetic field. In this embodiment, the detection coil and the dummy coil are arranged on the outer circumference of the bottom surface portion 61a and the outer circumference of the peripheral wall portion 61c. may be placed only in

The axial direction of the magnetic core portion 61b is orthogonal to the conductive film on the substrate, and the detection coils 864, 866, the excitation coils 860, 862, and the dummy coils 868, 870 are arranged at different positions in the axial direction of the magnetic core portion 61b, Detecting coils 864 and 866, exciting coils 860 and 862, and dummy coils 868 and 870 are arranged in this order from a position close to the conductive film on the substrate toward a position far from the conductive film on the substrate in the axial direction of the magnetic core portion 61b. From the detection coils 864, 866, the excitation coils 860, 862, and the dummy coils 868, 870, lead wires (shown in FIG. 12) for connecting to the outside come out, respectively.

FIG. 9 is a cross-sectional view of the eddy current sensor 50 on a plane passing through the central axis 872 of the magnetic core portion 61b. The pot core 60, which is a magnetic body, includes a disk-shaped bottom portion 61a, a cylindrical magnetic core portion 61b provided in the center of the bottom portion 61a, and a cylindrical peripheral wall portion 61c provided around the bottom portion 61a. have As an example of dimensions of the pot core 60, the diameter L1 of the bottom portion 61a is about 1 cm to 5 cm, and the height L2 of the eddy current sensor 50 is about 1 cm to 5 cm. The outer diameter of the peripheral wall portion 61c is a cylindrical shape that is uniform in the height direction in FIG.

The conductor wires used for the detection coils 864, 866, the excitation coils 860, 862, and the dummy coils 868, 870 are copper, manganin wires, or nichrome wires. By using a manganin wire or a nichrome wire, the temperature change of electric resistance and the like is reduced and the temperature characteristics are improved.

In this embodiment, since the excitation coils 860 and 862 are formed by winding wires around the outer side of the magnetic core portion 61b made of ferrite or the like and the outer side of the peripheral wall portion 61c, the density of the eddy current flowing in the object to be measured is increased. be able to. Moreover, since the detection coils 864 and 866 are also formed outside the magnetic core portion 61b and outside the peripheral wall portion 61c, the generated reverse magnetic field (interlinkage magnetic flux) can be efficiently collected.

In order to increase the density of the eddy current flowing through the object to be measured, in this embodiment, the exciting coils 860 and 862 are also connected in parallel as shown in FIG. That is, the internal coil and the external coil are electrically connected in parallel. The reason for connecting in parallel is as follows. When connected in parallel, the voltage that can be applied to exciting coil 860 and exciting coil 862 increases, and the current flowing through exciting coil 860 and exciting coil 862 increases compared to the case of connecting in series. Therefore, the magnetic field increases. Also, the series connection increases the inductance of the circuit and lowers the frequency of the circuit. It becomes difficult to apply the required high frequency to the exciting coils 860 and 862 . Arrows 874 indicate the directions of currents flowing through exciting coils 860 and 862 .

As shown in FIG. 10, the excitation coils 860 and 862 are connected so that the magnetic field directions of the excitation coils 860 and 862 are the same. That is, currents flow in exciting coils 860 and 862 in different directions. Magnetic field 876 is the magnetic field produced by inner excitation coil 860 and magnetic field 878 is the magnetic field produced by outer excitation coil 862 . As shown in FIG. 10, the magnetic field directions of excitation coil 860 and excitation coil 862 are the same. That is, the direction of the magnetic field generated in the magnetic core portion 61b by the internal coil is the same as the direction of the magnetic field generated in the magnetic core portion 61b by the external coil.

Magnetic field 876 and magnetic field 878 shown in region 880 are in the same direction, so the two fields add together and become larger. Compared to the conventional case where only the magnetic field 876 by the exciting coil 860 exists, in this embodiment, the magnetic field is increased by the magnetic field 878 by the exciting coil 862 .

A detection coil 864, an excitation coil 860 and a dummy coil 868 correspond to the detection coil 73, the excitation coil 72 and the dummy coil 74 in FIG. A detection coil 866, an excitation coil 862, and a dummy coil 870 correspond to the detection coil 73, the excitation coil 72, and the dummy coil 74 in FIG. That is, the eddy current sensor of FIG. 11 has a structure in which two eddy current sensors of FIG. 7 are concentrically arranged. Accordingly, the output signal processing circuit 54 corresponding to the eddy current sensor of FIG. 11 preferably has two output signal processing circuits 54 shown in FIG.

An example of the output signal processing circuit 54 corresponding to the eddy current sensor of FIG. 11 is shown in FIGS. FIG. 12 is a comparative example without the noise canceling function. FIG. 13 has a noise canceling function. 12 and 13 show in perspective view the eddy current sensor shown in FIG. Although top surface 218 is above top surface 220 in FIGS. 12 and 13 for ease of understanding, top surface 218 and top surface 220 are in the same horizontal plane as shown in FIG. Although there are two coil assemblies in FIGS. 12 and 13, there may be three or more coil assemblies. When there are two or more coil assemblies, the measurement accuracy (S/N ratio) is improved because the number of film thickness measurements increases compared to when there is one coil assembly.

First, the configuration of the comparative example will be described. In a comparative example, the detection coil 864 of the inner eddy current sensor 286 and the detection coil 866 of the outer eddy current sensor 288 are connected in series. The dummy coil 868 of the inner eddy current sensor 286 and the dummy coil 870 of the outer eddy current sensor 288 are connected in series. The excitation coils 860 and 862 of the inner and outer eddy current sensors are connected in parallel to the signal source 52 .

Specific connections are as follows. In inner eddy current sensor 286 , sensing coil 864 has signal lines 8641 and 8642 . The exciting coil 860 has signal lines 8601 and 8602 . The dummy coil 868 has signal lines 8681 and 8682 . In outer eddy current sensor 288 , sensing coil 866 has signal lines 8661 and 8662 . The excitation coil 862 has signal lines 8621 and 8622 . The dummy coil 870 has signal lines 8701 and 8702 .

A signal line 8641 of the sensing coil 864 of the inner eddy current sensor 286 is connected to a terminal 773 of the resistive bridge circuit 77 . Signal line 8642 of sensing coil 864 is connected to signal line 8661 of sensing coil 866 of outer eddy current sensor 288 . A signal line 8662 of the detection coil 866 is connected to a terminal 771 of the resistance bridge circuit 77 . A signal line 8681 of the dummy coil 868 of the inner eddy current sensor 286 is connected to a terminal 772 of the resistance bridge circuit 77 . Signal line 8642 of dummy coil 868 is connected to signal line 8701 of dummy coil 870 of outer eddy current sensor 288 . A signal line 8702 of the dummy coil 870 is connected to a terminal 771 of the resistance bridge circuit 77 .

In the comparative example, the output of the detection coil 864 of the inner eddy current sensor 286 and the output of the detection coil 866 of the outer eddy current sensor 288 are in series. has the effect of becoming A terminal 774 of the bridge circuit 77 is connected to the detection circuit 280 . The output of detector circuit 280 is output signal 172 and is connected to endpoint detection controller 246 shown in FIG.

Since the form shown in FIG. 13 has a noise canceling function, it has an advantage that the S/N is improved as compared with the comparative example. This embodiment uses one bridge circuit 77 for the inner eddy current sensor 286 and one for the outer eddy current sensor 288 . Since the output signal processing circuits 54 (the generating circuit 254 and the adding circuit 258) are provided after the resistor bridge circuit 77, the S/N ratio is improved.

The generating circuit 254 for the inner eddy current sensor 286 is generating circuit 2541 and the generating circuit 254 for the outer eddy current sensor 288 is generating circuit 2542 . The generation circuits 2541 and 2542 have the same configuration as the generation circuit 254 . A filter 266 and an amplifier 268 are provided in front of the generation circuit 2541 and the generation circuit 2542 as in FIG. Summing circuit 258 for inner eddy current sensor 286 is summing circuit 2581 and summing circuit 258 for outer eddy current sensor 288 is summing circuit 2582 . Adder circuits 2581 and 2582 have the same configuration as the adder circuit 258 .

The noise-reduced signal 256 obtained by the inner eddy current sensor 286 and the outer eddy current sensor 288 is sent to the detection circuit 280 and the outputs of the two bridge circuits 7710, 7711 are DC. After that, they are added by the adder circuit 284 . Addition improves sensitivity.

The configuration of this embodiment will be specifically described. The inner eddy current sensor 286 includes an exciting coil 860 (first exciting coil) capable of receiving excitation signals 8601 and 8602 from the signal source 52 and generating a first magnetic field 876 (see FIG. 11), and a first A detection coil 864 (first detection coil) capable of detecting the magnetic field 876 and outputting a signal 8641 (first detection signal), and detecting the first magnetic field and outputting a signal 8681 (first dummy signal). possible dummy coil 868 (first dummy coil). In this specification, a signal line and a signal flowing through the signal line may be denoted by the same reference numerals. For example, a signal line 8641 and a signal 8641 .

The output signal processing circuit 290 of this embodiment, which processes the signals 8641 and 8681 output by the inner eddy current sensor 286, is a first resistor capable of outputting a first difference signal 292 which is the difference between the signals 8641 and 8681. It has a bridge circuit 7710 . The output signal processing circuit 290 provides a first signal for reducing noise from any of the excitation signal 8601, the signal 8641 (first detection signal), the signal 8681 (first dummy signal), and the first difference signal 292. has a generation circuit 2541 (first generation circuit) capable of generating the noise reduction signal 252 of . In this embodiment, the first noise reduction signal 252 for noise reduction is generated from the first difference signal 292 output from the terminal 774 .

The output signal processing circuit 290 further adds the first noise reduction signal 252 generated in the generation circuit 2541 to the first difference signal 292 to reduce the noise included in the first difference signal 292 to obtain a first noise signal. It has a first adder circuit 2581 capable of producing a decrease signal 256 .

The outer eddy current sensor 288 includes an exciting coil 862 (second exciting coil) capable of generating a second magnetic field 878 (see FIG. 11) upon receiving an exciting signal 8621, a first magnetic field 876 and a second magnetic field. A detection coil 866 (second detection coil) capable of detecting a magnetic field 878 and outputting a signal 8661 (second detection signal), and a signal 870 by detecting the first magnetic field 876 and the second magnetic field 878.
and a dummy coil 870 (second dummy coil) capable of outputting 1 (second dummy signal).

Detector coils 864 of inner eddy current sensor 286 are capable of detecting first magnetic field 876 and second magnetic field 878 and outputting signal 8641 . The dummy coil 868 can detect the first magnetic field 876 and the second magnetic field 878 and output the first dummy signal. The output signal processing circuit 290 has a second resistance bridge circuit 7711 capable of outputting a second difference signal 294 which is the difference between the signals 8661 and 8701 .

Here, the meaning of the first and second detection coils detecting the first magnetic field 876 and the second magnetic field 878 will be explained. The sensing coil 864 of the inner eddy current sensor 286 senses the film thickness as follows. First, eddy currents are induced on the metal surface by the high-frequency magnetic field generated by the excitation coil. That is, the state of the magnetic field differs depending on whether the wafer (conductive film) is in the vicinity of the magnetic field or not. An excitation coil that can generate a magnetic field on a metal surface is brought close to a conductive metal surface by applying a high frequency (2 MHz or higher) to the excitation coil. A vortex current is generated on a metal surface by a high-frequency magnetic field. Eddy currents flow in directions that partially cancel the magnetic field. A detection coil of the eddy current sensor detects the partially canceled magnetic field. An eddy current sensor measures the thickness of a conductive film on a metal using the correlation between the magnitude of the eddy current and the thickness of the film.

``Detecting the first magnetic field and the second magnetic field'' means ``detecting a magnetic field obtained by synthesizing the first magnetic field and the second magnetic field''. It is different when there is and when there is not. "The first and second detection coils detect the first and second magnetic fields" means that "the combined magnetic field of the first and second magnetic fields generates an eddy current on the metal surface, The magnetic field is partially canceled by the generated eddy currents and the partially canceled magnetic field is detected."

Returning to the description of the outer eddy current sensor 288 . The output signal processing circuit 290 provides a second signal for reducing noise from any of the excitation signal 8621 , the signal 8661 (second detection signal), the signal 8701 (second dummy signal), and the second difference signal 294 . has a generation circuit 2542 (second generation circuit) capable of generating the noise reduction signal 252 of . In this embodiment, the second noise reduction signal 252 for noise reduction is generated from the second difference signal 294 output from the terminal 772 .

The output signal processing circuit 290 adds the second noise reduced signal 252 generated in the generating circuit 2542 to the second difference signal 294 to reduce the noise contained in the second difference signal 294 to obtain a second noise reduced signal. It has a second summing circuit 2582 capable of producing the signal 256 and a third summing circuit 284 capable of summing the first noise reduction signal 256 and the second noise reduction signal 256 .

14 and 15 conceptually show the effects of the configuration shown in FIG. 13 in comparison with the configuration having one eddy current sensor and no noise canceling function. 14 and 15 are spectra showing intensity distributions of noise and signals contained in the output signal of the detection coil with respect to frequency. FIG. 14 shows the spectrum of the eddy current sensor output 300 in a configuration (not shown) with one eddy current sensor and no noise canceling function. FIG. 15 shows the spectrum of the output 302 obtained by adding the outputs of the two eddy current sensors after noise canceling processing in the configuration shown in FIG. 13 having two eddy current sensors and a noise canceling function. 14 and 15, the horizontal axis is frequency (unit: frequency (1/sec)), and the vertical axis is power density (amplitude squared) (unit: millivolt squared) at each frequency. Outputs 300 , 302 include signal 304 present near frequency 296 and noise 306 present outside of frequency 296 .

14 and 15, the magnitude of the output 302 obtained by adding the signals 304 of the two eddy current sensors in the vicinity of the frequency 296 of the excitation signal 8601 is the magnitude of the signal 304 of the single eddy current sensor. about twice as high. The magnitude of the noise 306 contained in the output 302 from the two eddy current sensors outside the vicinity of the frequency 296 of the excitation signal 8601 is greater than the magnitude of the noise 306 contained in the output 300 from one eddy current sensor. considerably reduced.

Note that, as shown in FIG. 13, the first noise reduction signal 256 and the second noise reduction signal 256 are converted into DC signals (the first noise reduction signal 2801 and the second noise reduction signal 2801 through the detection circuit 280, respectively). 2802) and then added by the third adder circuit 284 . 12 and 13, the configuration of FIG. 13 is the same as that of FIG. , a second adder circuit 2582, a detector circuit 280 for the inner eddy current sensor 286, and a third adder circuit 284 are added.

A configuration in which the noise canceling circuit is removed from the configuration of FIG. 13 is also possible. That is, even if the outputs of the two eddy current sensors 286 and 288 are processed by the bridge circuits 7710 and 7711, respectively, converted to direct current by the detection circuit 280 of the respective processed signals, and then added by the third addition circuit 284, good.

Specifically, the output signal processing circuit of this form is a first detection signal capable of outputting a first difference signal 292 which is the difference between the signal 8641 (first detection signal) and the signal 8681 (first dummy signal). a resistance bridge circuit 7710; a second resistance bridge circuit 7711 capable of outputting a second difference signal 294 that is the difference between the signal 8661 (second detection signal) and the signal 8701 (second dummy signal); and a third addition circuit 284 capable of adding the difference signal 292 and the second difference signal 294 via the detection circuit 280 .

In FIG. 13, after DC conversion by the detection circuit 280, addition is performed by the third addition circuit 284, but the DC conversion by the detection circuit 280 may not be performed. That is, AC signals may be added together. However, addition after conversion to direct current has an advantage that will be described later.

When compared with FIG. 12, FIG. 13 has the following advantages. In FIG. 12, by directly connecting the signal line 8642 and the signal line 8661, the outputs of the detection coils 864 and 866 are added. These are high frequency signals and addition of high frequency signals can cause the signals to cancel. As a result, it may not be possible to effectively utilize the output signal. In FIG. 13, after being converted into a direct current by the detection circuit 280, it is added by the third addition circuit 284. In FIG. Since it is the addition of DC signals, the signals do not cancel each other out and the level of the output signal increases.

In the embodiment of FIG. 13, the third summing circuit 284 sums the output of the inner eddy current sensor 286 and the output of the outer eddy current sensor 288, while the third summing circuit 284 adds the output of the inner eddy current sensor 286 The output of outer eddy current sensor 288 may be subtracted from the output of . This time has the following advantages. Because the inner eddy current sensor 286 is small in diameter, it is affected by a small area of the conductive film. As a result, the film thickness of a small area can be measured. Because the outer eddy current sensor 288 has a large diameter, it is affected by a large area of the conductive film. As a result, the film thickness of a large area can be measured. Subtracting the output of the outer eddy current sensor 288 from the output of the inner eddy current sensor 286 removes the effect of the large area conductive film from the output of the inner eddy current sensor 286 . As a result, the film thickness of a small area can be measured more accurately. The term "adding" in the third summing circuit 284 shown in FIG.
including.

9, the inner eddy current sensor 286 and the outer eddy current sensor 288 are integrated, but the inner eddy current sensor 286 and the outer eddy current sensor 288 may be independent eddy current sensors. good. As a manufacturing method of the integrated eddy current sensor shown in FIG. 9, (1) a method of integrally forming the bottom portion 61a, the magnetic core portion 61b, and the peripheral wall portion 61c by cutting, and (2) the bottom portion 61a and the magnetic core portion 61b. , a method in which the peripheral wall portion 61c is manufactured separately, a coil is wound, and then these three pieces are bonded by brazing or the like to be integrated.

The bandstop filter 276, the phase inverter circuit 278, and the adder circuit 258 can be configured by a digital signal processor (DSP). A digital signal processor is a microprocessor suitable for digital signal processing. The bandstop filter 276, the phase inverter circuit 278, and the adder circuit 258 may be analog circuits. The digital signal processor has an analog-to-digital conversion circuit (A/D conversion circuit: ADC: an electronic circuit that converts an analog electrical signal into a digital electrical signal), not shown, in the preceding stage. The digital signal processor has a not-shown digital-analog conversion circuit (D/A conversion circuit: DAC: an electronic circuit that converts a digital electric signal into an analog electric signal) at the subsequent stage. A detector circuit 280 located after the adder circuit 258 can also be configured by a digital signal processor.

In the description of FIG. 5, it is assumed that the noise component Y1 and the noise component Y3 have the same magnitude of the amplitude A for the sake of simplicity of description. may differ in size. For example, the noise component Y1 is generated from the excitation signal 250, and the noise component Y3 is the noise component included in the detection coil 73. FIG. At that time, processing for matching the magnitude of the amplitude A is performed within the DSP. In the explanation of FIG. 5, it was assumed that the phases of the noise component Y1 and the noise component Y3 were the same for the sake of simplicity of explanation. process to cause

Note that the addition circuit 258 in FIG. 4 adds the output signal 274 and a signal obtained by inverting the phase of the output signal 274 . The noise canceling method is not limited to this, and any method can be adopted as long as noise canceling is possible. For example, there is a method of subtracting the signal without inverting the phase. That is, the output signal of the bandstop filter 276 is subtracted from the output signal 274 in the adder circuit 258 without the phase inverter circuit 278 . This method also enables noise cancellation as in the case of using the phase inverter circuit 278 .

Therefore, "adding the phase-inverted signal" and "subtracting the non-phase-inverted signal" have the same effect from the viewpoint of noise canceling. As used herein, the term "adding" includes "addition" and "subtraction" in this sense.

By arranging a temperature sensor inside the eddy current sensor 50, temperature changes inside the eddy current sensor 50 can be detected and the output of the detection coil 73 can be corrected. For example, the correction method is as follows. Before polishing the semiconductor wafer WH, the relationship between the temperature of the eddy current sensor 50 and the output of the detection coil 73 is measured, and this relationship is created as a correction table. Various configurations of the correction table are possible. For example, for each temperature of the eddy current sensor 50, a coefficient by which the output of the detection coil 73 is multiplied is created as a correction table. Alternatively, a polynomial that represents a correction coefficient as a function of temperature is created as a correction table (a table that displays coefficients of each order of the polynomial). By performing correction according to temperature, it becomes possible to cope with temperature changes. The measurement accuracy of the film thickness is improved, and the accuracy of detecting the end of polishing can be improved.

Next, a method for processing the output signal of the eddy current sensor will be described. In FIG. 4, the excitation coil 72 receives an excitation signal 250 to generate a magnetic field. The detection coil 73 detects the magnetic field and outputs a detection signal 176 . A generating circuit 254 generates a noise reduction signal 252 for reducing noise from the excitation signal 250 or the detection signal 176 . A summing circuit 258 adds the generated noise reduced signal 252 to the detected signal 176 to produce a noise reduced signal 256 that reduces the noise contained in the detected signal 176 .

Next, another method of processing the output signal of the eddy current sensor will be described. In FIG. 13, an excitation coil 860 (first excitation coil) receives an excitation signal 250 to generate a first magnetic field 876 . The detection coil 864 (first detection coil) detects the first magnetic field 876 (see FIG. 11) and outputs a signal 8641 (first detection signal). Dummy coil 868 (first dummy coil) detects first magnetic field 876 and outputs signal 8681 (first dummy signal).

In an eddy current sensor output signal processing method for processing signals 8641 and 8681 output by eddy current sensor 286, a first resistive bridge circuit 7710 generates a first difference signal 292 which is the difference between signals 8641 and 8681. to output The generation circuit 2541 generates a first noise reduction signal 252 for reducing noise from any of the excitation signal 250 , the signal 8641 , the signal 8681 and the first difference signal 292 . In FIG. 13, generation circuit 2541 generates first noise reduction signal 252 for noise reduction from first difference signal 292 . The first adder circuit 2581 adds the generated first noise reduced signal 252 to the first difference signal 292 to reduce the noise contained in the first difference signal 292 to produce a first noise reduced signal 2801 . Generate.

Next, another method of processing the output signal of the eddy current sensor will be described. In FIG. 13, an excitation coil 862 (second excitation coil) receives an excitation signal 250 to generate a second magnetic field 878 (see FIG. 11). A detection coil 866 (second detection coil) detects the first magnetic field 876 and the second magnetic field 878 and outputs a signal 8661 (second detection signal). Dummy coil 870 (second dummy coil) detects first magnetic field 876 and second magnetic field 878 and outputs signal 8701 (second dummy signal).

Detection coil 864 detects first magnetic field 876 and second magnetic field 878 and outputs signal 8641 (first detection signal). Dummy coil 868 detects first magnetic field 876 and second magnetic field 878 and outputs signal 8681 (first dummy signal). Second resistive bridge circuit 7711 outputs second difference signal 294 which is the difference between signal 8661 and signal 8701 . A generating circuit 2542 generates a second noise reduction signal 252 for reducing noise from any of the excitation signal 250 , the signal 8661 , the signal 8701 and the second difference signal 294 . A second summing circuit 2582 adds the generated second noise reduced signal 252 to the second difference signal 294 to produce a second noise reduced signal 2802 in which the noise contained in the second difference signal 294 is reduced. Generate. The third adder circuit 284 adds the first noise reduction signal 2801 and the second noise reduction signal 2802 together.

Next, another method of processing the output signal of the eddy current sensor will be described. This embodiment is obtained by removing the noise canceling circuit from the embodiment of FIG. The outputs of the two eddy current sensors 286, 288 are processed by bridge circuits 7710, 7711 respectively. After that, the detection circuit 280 converts it to direct current, and the third addition circuit 284 performs addition. Specifically, excitation coils 860 and 862 receive excitation signal 250 and generate first magnetic field 876 and second magnetic field 878, respectively. Detector coils 864 and 866 (first and second detector coils) detect a first magnetic field 876 and a second magnetic field 878 to generate signals 8641 and 866 respectively.
1 (first and second detection signals) is output. Dummy coils 868 and 870 (first and second dummy coils) detect a first magnetic field 876 and a second magnetic field 878 and output signals 8681 and 8701 (first and second dummy signals), respectively. do.

In the output signal processing method of this embodiment, the signals 8641, 8661 and the signals 8681, 8701 output by the eddy current sensors 286, 288 are processed. The first resistive bridge circuit 7710 outputs a first difference signal 292 which is the difference between signal 8641 (first detection signal) and signal 8681 (first dummy signal). The second resistive bridge circuit 7711 outputs a second difference signal 294 which is the difference between signal 8661 (second detection signal) and signal 8701 (second dummy signal). The first difference signal 292 and the second difference signal 294 are converted to DC in the detection circuit 280 and then added in the third addition circuit 284 .

A method for controlling each part of the polishing apparatus based on the film thickness obtained by the eddy current sensor 50 will be described below. As shown in FIG. 1 , eddy current sensor 50 is connected to endpoint detection controller 246 , which is connected to machine control controller 248 . The output signal of eddy current sensor 50 is sent to endpoint detection controller 246 . The endpoint detection controller 246 performs necessary processing (arithmetic processing/correction) on the output signal of the eddy current sensor 50 to generate a monitoring signal (film thickness data corrected by the endpoint detection controller 246). The equipment controller 248 controls the top ring motor 114, the polishing table 100 motor (not shown), etc. based on the corrected film thickness data.

Although examples of embodiments of the present invention have been described above, the above-described embodiments of the present invention are intended to facilitate understanding of the present invention, and do not limit the present invention. The present invention can be modified and improved without departing from the spirit thereof, and the present invention naturally includes equivalents thereof. In addition, any combination or omission of each component described in the claims and the specification is possible within the range that at least part of the above problems can be solved or at least part of the effect is achieved. is.
As explained above, the present invention has the following aspects.
Form 1
an eddy current sensor having an excitation coil capable of generating a magnetic field by receiving an excitation signal, and a detection coil capable of detecting the magnetic field and outputting a detection signal;
and an output signal processing circuit that processes the detection signal,
The output signal processing circuit is
a generation circuit capable of generating a noise reduction signal for reducing noise from the excitation signal or the detection signal;
and an addition circuit capable of adding the noise reduction signal generated in the generation circuit to the detection signal to generate a noise reduction signal in which noise contained in the detection signal is reduced. three-dimensional.
Form 2
a first excitation coil that receives an excitation signal to generate a first magnetic field; a first detection coil that detects the first magnetic field and outputs a first detection signal; of the eddy current sensor for processing the first detection signal and the first dummy signal output by the eddy current sensor having a first dummy coil capable of detecting a magnetic field and outputting a first dummy signal In the output signal processing circuit,
a first resistance bridge circuit capable of outputting a first difference signal that is a difference between the first detection signal and the first dummy signal;
A first generation circuit capable of generating a first noise reduction signal for reducing noise from any one of the excitation signal, the first detection signal, the first dummy signal, and the first difference signal. and,
The first noise reduction signal generated in the first generation circuit can be added to the first difference signal to generate a first noise reduction signal in which noise contained in the first difference signal is reduced. and a first addition circuit.
Form 3
The eddy current sensor includes a second excitation coil that can generate a second magnetic field by receiving the excitation signal, and a second detection signal by detecting the first magnetic field and the second magnetic field. a second detection coil capable of outputting, and a second dummy coil capable of detecting the first magnetic field and the second magnetic field and outputting a second dummy signal;
The first detection coil is capable of detecting the first magnetic field and the second magnetic field and outputting the first detection signal,
the first dummy coil is capable of detecting the first magnetic field and the second magnetic field and outputting the first dummy signal;
The output signal processing circuit is
a second resistance bridge circuit capable of outputting a second difference signal that is the difference between the second detection signal and the second dummy signal;
A second generation circuit capable of generating a second noise reduction signal for reducing noise from any one of the excitation signal, the second detection signal, the second dummy signal, and the second difference signal. and,
the second noise reduction signal generated in the second generating circuit as the second difference signal;
a second summing circuit capable of generating a second noise-reduced signal in which noise contained in the second difference signal is reduced by adding to
The eddy current sensor output signal processing circuit according to mode 2, further comprising a third adder circuit capable of adding the first noise reduction signal and the second noise reduction signal.
form 4
First and second excitation coils that receive an excitation signal to generate first and second magnetic fields respectively, detect the first magnetic field and the second magnetic field, and detect the first and second magnetic fields, respectively. first and second detection coils capable of outputting two detection signals; and first and second detection coils capable of outputting first and second dummy signals by detecting the first magnetic field and the second magnetic field, respectively. In an eddy current sensor output signal processing circuit that processes the first and second detection signals and the first and second dummy signals output by an eddy current sensor having a second dummy coil,
a first resistance bridge circuit capable of outputting a first difference signal that is a difference between the first detection signal and the first dummy signal;
a second resistance bridge circuit capable of outputting a second difference signal that is the difference between the second detection signal and the second dummy signal;
An output signal processing circuit for an eddy current sensor, further comprising a third addition circuit capable of adding the first difference signal and the second difference signal.
Form 5
Output of an eddy current sensor that processes the detection signal output by an eddy current sensor having an excitation coil capable of generating a magnetic field by receiving an excitation signal and a detection coil capable of detecting the magnetic field and outputting a detection signal. In the signal processing method,
generating a noise reduction signal for reducing noise from the excitation signal or the detection signal;
and adding the generated noise reduction signal to the detection signal to generate a noise reduction signal in which noise contained in the detection signal is reduced.
Form 6
a first excitation coil that receives an excitation signal to generate a first magnetic field; a first detection coil that detects the first magnetic field and outputs a first detection signal; of the eddy current sensor for processing the first detection signal and the first dummy signal output by the eddy current sensor having a first dummy coil capable of detecting a magnetic field and outputting a first dummy signal In the output signal processing method,
outputting a first difference signal that is the difference between the first detection signal and the first dummy signal;
generating a first noise reduction signal for reducing noise from any one of the excitation signal, the first detection signal, the first dummy signal, and the first difference signal;
and adding the generated first noise-reduced signal to the first difference signal to generate a first noise-reduced signal in which noise contained in the first difference signal is reduced. A method for processing an output signal of an eddy current sensor.
Form 7
The eddy current sensor includes a second excitation coil that can generate a second magnetic field by receiving the excitation signal, and a second detection signal by detecting the first magnetic field and the second magnetic field. a second detection coil capable of outputting, and a second dummy coil capable of detecting the first magnetic field and the second magnetic field and outputting a second dummy signal;
The first detection coil is capable of detecting the first magnetic field and the second magnetic field and outputting the first detection signal,
the first dummy coil is capable of detecting the first magnetic field and the second magnetic field and outputting the first dummy signal;
The output signal processing method includes:
a step of outputting a second difference signal that is the difference between the second detection signal and the second dummy signal;
and
generating a second noise reduction signal for reducing noise from any one of the excitation signal, the second detection signal, the second dummy signal, and the second difference signal;
adding the generated second noise-reduced signal to the second difference signal to generate a second noise-reduced signal in which noise contained in the second difference signal is reduced;
and adding the first noise reduction signal and the second noise reduction signal.
Form 8
First and second excitation coils that receive an excitation signal to generate first and second magnetic fields respectively, detect the first magnetic field and the second magnetic field, and detect the first and second magnetic fields, respectively. first and second detection coils capable of outputting two detection signals; and first and second detection coils capable of outputting first and second dummy signals by detecting the first magnetic field and the second magnetic field, respectively. In an eddy current sensor output signal processing method for processing the first and second detection signals and the first and second dummy signals output by an eddy current sensor having a second dummy coil,
outputting a first difference signal that is the difference between the first detection signal and the first dummy signal;
outputting a second difference signal that is the difference between the second detection signal and the second dummy signal;
and adding the first difference signal and the second difference signal.

50 Eddy current sensor 52 AC signal source 54 Output signal processing circuit 72 Exciting coil 73 Detection coil 74 Exciting coil 77 Resistive bridge circuit 172 Output signal 174 Eddy current sensor assembly 176 Detection signal 250 Excitation signal 252 Noise reduction signal, first noise reduction signal, second noise reduction signal 254 Generation circuit 256 Noise reduction signal, first noise reduction signal, second noise reduction signal 258 Addition circuit 278 Phase inverter circuit 280 Detection circuit 284 Adder circuit, third adder circuit 286 Inner eddy current sensor 288 Outer eddy current sensor 290 Output signal processing circuit 292 First difference signal 294 Second difference signal 304... Signal 306... Noise 771... Bridge circuit 860... Exciting coil 862... Exciting coil 864... Detection coil 866... Detection coil 868... Dummy coil 870... Dummy coil 876... First magnetic field 878... Second magnetic field 2541, 2542... Generation circuit 2581 First addition circuit 2582 Second addition circuit 2801 First noise reduction signal 2802 Second noise reduction signal 7710 First resistance bridge circuit 7711 Second resistance bridge circuit

Claims (2)

an eddy current sensor having an excitation coil capable of generating a magnetic field by receiving an excitation signal, and a detection coil capable of detecting the magnetic field and outputting a detection signal;
and an output signal processing circuit that processes the detection signal,
The output signal processing circuit is
a generation circuit capable of generating a noise reduction signal for reducing noise from the excitation signal or the detection signal;
an addition circuit capable of adding the noise reduction signal generated in the generation circuit to the detection signal to generate a noise reduction signal in which noise contained in the detection signal is reduced ;
The generating circuit is capable of generating the noise reduction signal by attenuating a level of a signal having the same frequency as that of the excitation signal among the signals included in the excitation signal or the detection signal. and an eddy current sensor assembly. Output of an eddy current sensor that processes the detection signal output by an eddy current sensor having an excitation coil capable of generating a magnetic field by receiving an excitation signal and a detection coil capable of detecting the magnetic field and outputting a detection signal. In the signal processing method,
generating a noise reduction signal for reducing noise from the excitation signal or the detection signal;
adding the generated noise-reduced signal to the detection signal to generate a noise-reduced signal in which noise contained in the detection signal is reduced ;
In the step of generating the noise reduction signal, among the signals included in the excitation signal or the detection signal, the level of a signal having the same frequency as the excitation signal is attenuated to generate the noise reduction signal. An eddy current sensor output signal processing method characterized by:

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