JP7257945B2 - 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 takes out the 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.

With regard to the conventional detection method using a bridge circuit, the amount of resistance value adjustment during zero point adjustment is very small compared to the magnitude of the overall resistance value that constitutes the bridge circuit. As a result, the amount of temperature change of the entire resistance value is a non-negligible amount compared to the resistance value adjustment amount at the time of zero point adjustment. The characteristics of the bridge circuit are sensitively affected by changes in the surrounding environment of the resistors due to changes in the resistance value due to temperature changes, changes in the stray capacitance of the resistors, and the like. As a result, there is a problem that the above-mentioned zero point tends to shift and the film thickness measurement accuracy decreases.

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 provide an output signal processing circuit and an output signal processing circuit for an eddy current sensor that is less susceptible to changes in the surrounding environment than conventional sensors. It is to provide a processing method.

In order to solve the above problems, in a first form, an eddy current sensor and an output signal processing circuit that processes an output signal of the eddy current sensor are provided, and the output signal processing circuit includes the output signal, A mixer circuit to which a signal of a predetermined frequency is input, multiplies the two input signals, and outputs an output signal obtained by the multiplication, and the output signal output by the mixer circuit is input. and a low-pass filter for cutting a high-frequency signal contained in the input output signal and outputting at least a DC signal.

In this embodiment, the output signal of the eddy current sensor is connected to the mixer circuit without going through the resistance bridge circuit. Since a resistance bridge circuit, which is susceptible to temperature changes, is not used, it is possible to provide an output signal processing circuit for an eddy current sensor that is less susceptible to changes in the surrounding environment than conventional ones.

Further, in Japanese Patent Application Laid-Open No. 2011-23579, as shown in FIG. 6, a signal detected at a terminal of a resistance bridge circuit passes through a high-frequency amplifier and a phase shift circuit, and then passes through a cos synchronous detection circuit and a sine synchronous detection circuit. A cosine component and a sin component of the detection signal are extracted by the synchronous detection section. A low-pass filter removes unwanted high-frequency components from the synchronously detected signal. Therefore, the high frequency output from the coil becomes a low frequency signal after a long processing step. Since there are many steps that are high-frequency signals, conventional signals have a lot of noise.

In this embodiment, the high-frequency output from the coil becomes a low-frequency signal by the mixer circuit and the low-pass filter. Since there are fewer steps in which the high frequency output is in the high frequency state, the signal will be less noisy than in the prior art. That is, the high-frequency signal, which is easily affected by the surroundings, is converted into the easy-to-handle direct-current signal at an early stage (in a small number of steps), so that stable signal measurement can be performed.

In form 2, output signal processing of an eddy current sensor that processes the first and second output signals output by an eddy current sensor having first and second coils that respectively output first and second output signals a first mixer circuit that receives the first output signal and a signal of a predetermined frequency, multiplies the two input signals, and outputs an output signal obtained by the multiplication; a first low-pass filter that receives the output signal output from the first mixer circuit, cuts a high-frequency signal contained in the input output signal, and outputs at least a DC signal; and a signal of said frequency are inputted, a second mixer circuit for multiplying said two inputted signals and outputting an output signal obtained by said multiplication; said second mixer circuit a second low-pass filter that cuts a high-frequency signal contained in the input output signal and outputs at least a DC signal; and the first low-pass filter that outputs the a first subtraction circuit that receives a DC signal and the DC signal output from the second low-pass filter, obtains a difference between the two input DC signals, and outputs the obtained difference. The configuration of the output signal processing circuit of the eddy current sensor characterized by the following is adopted.

Also in this embodiment, the output signal of the eddy current sensor is connected to the mixer circuit without passing through the resistance bridge circuit. Since a resistance bridge circuit, which is susceptible to temperature changes, is not used, it is possible to provide an output signal processing circuit for an eddy current sensor that is less susceptible to changes in the surrounding environment than conventional ones.

In this embodiment, the subtraction circuit can perform the same detection method using a conventional bridge circuit, in which two coils are used to extract a minute signal change corresponding to the film thickness change. That is, it is possible to obtain the difference between the two DC signals and detect only a minute signal change corresponding to the film thickness change.

In form 3, the output signal processing circuit receives the DC signal output from the first low-pass filter, adjusts the amplitude of the input DC signal, and outputs the adjusted DC signal. The first subtraction circuit receives the DC signal output by the first adjustment circuit and the DC signal output by the second low-pass filter, and 3. The output signal processing circuit of the eddy current sensor according to mode 2, wherein the difference between the two DC signals obtained is obtained and the obtained difference is output.
The configuration is adopted.

In form 4, the output signal processing circuit receives the DC signal output from the first low-pass filter, adjusts the amplitude of the input DC signal, and outputs the adjusted DC signal. The DC signal output by the first adjustment circuit and the second low-pass filter are input, the magnitude of the amplitude of the input DC signal is adjusted, and the adjusted DC signal is output. and a second adjustment circuit, wherein the first subtraction circuit receives the DC signal output from the first adjustment circuit and the DC signal output from the second adjustment circuit. The configuration of the output signal processing circuit of the eddy current sensor according to mode 2 is adopted, which is characterized by obtaining the difference between the two DC signals and outputting the obtained difference.

In forms 3 and 4, it is possible to maintain performance equivalent to that of the conventional detection method using a bridge circuit in which minute signal changes corresponding to changes in film thickness are taken out using two coils by means of an adjustment circuit and a subtraction circuit. can. That is, the level of the phase detection signal from at least one coil is adjusted by the adjusting circuit and then subtracted to detect only minute signal changes corresponding to film thickness changes. The adjustment circuit can improve the accuracy of the zero point adjustment compared to the case without the adjustment circuit. As a result, weak changes in the signal from the zero point can be extracted as described above.

In form 5, the eddy current sensor has third and fourth coils that output third and fourth output signals, respectively, and the output signal processing circuit outputs the third output signal and the frequency a signal of is input, the two signals that are input are multiplied, and an output signal obtained by the multiplication is output; and the output signal output by the third mixer circuit is a third low-pass filter for cutting a high-frequency signal contained in the input output signal and outputting at least a DC signal, the fourth output signal, and a signal of the frequency are input, a fourth mixer circuit that multiplies the two input signals and outputs an output signal obtained by the multiplication; and the output signal that the fourth mixer circuit outputs is input and input a fourth low-pass filter for cutting a high-frequency signal contained in the output signal and outputting at least a DC signal; the DC signal output by the third low-pass filter and the DC output by the fourth low-pass filter A signal is input, a second subtraction circuit obtains the difference between the two input DC signals, and outputs the obtained difference; and an addition circuit for receiving the difference output by the subtraction circuit, adding the two input differences or obtaining the difference between the two differences, and outputting the obtained sum or difference. The configuration of the output signal processing circuit of the eddy current sensor according to any one of modes 2 to 4 is adopted.

In addition to the coil assembly having two coils shown in Embodiments 2 to 4, this embodiment further has a coil assembly having two coils. That is, it has two sets of combinations of two coils. Since there are two sets of combinations, the measurement accuracy is improved by adding the difference between the two DC signals obtained by the two sets or by obtaining the difference between the two DC signals. The reason why the measurement accuracy is improved is as follows. In the case of addition, since the signal output increases, a smaller signal change, that is, a smaller film thickness change can be detected, thereby improving the measurement accuracy.

When the difference is to be obtained, for example, one combination can measure a film thickness in a wider area than the other combination. At this time, by subtracting the output of one combination from the output of the other combination, it is possible to reduce the influence of the film thickness in a wide area and measure only the change in the film thickness in a narrow area more accurately. . That is, the spatial accuracy of measurements can be improved.

In form 6, the step of inputting an output signal of an eddy current sensor and a signal of a predetermined frequency to a mixer circuit, performing multiplication of the two signals by the mixer circuit, and outputting the output signal obtained by the multiplication. and inputting the output signal output from the mixer circuit to a low-pass filter, cutting the high-frequency signal, and outputting at least a DC signal. are taking

In form 7, output signal processing of an eddy current sensor that processes the first and second output signals output by an eddy current sensor having first and second coils that respectively output first and second output signals In the method, the first output signal and a signal of a predetermined frequency are input to a first mixer circuit, the first mixer circuit multiplies the two signals, and the output obtained by the multiplication is performed. outputting a signal; inputting the output signal output from the first mixer circuit to a first low-pass filter, and cutting a high-frequency signal included in the output signal by the first low-pass filter; , outputting at least a DC signal; inputting the second output signal and a signal of the frequency to a second mixer circuit, performing multiplication of the two signals by the second mixer circuit; outputting the output signal obtained by the multiplication; inputting the output signal output by the second mixer circuit to a second low-pass filter so that it is included in the output signal by the second low-pass filter; cutting a high-frequency signal to output at least a DC signal; and inputting the DC signal output from the first low-pass filter and the DC signal output from the second low-pass filter to a first subtraction circuit. and obtaining the difference between the two DC signals by the first subtraction circuit, and outputting the obtained difference. ing.

In form 8, the eddy current sensor has third and fourth coils that output third and fourth output signals, respectively, and the output signal processing method comprises: the third output signal; to a third mixer circuit, multiplying the two signals by the third mixer circuit, and outputting an output signal obtained by the multiplication; a step of inputting an output signal to a third low-pass filter, cutting a high-frequency signal contained in the output signal by the third low-pass filter, and outputting at least a DC signal; inputting the signal of the frequency to a fourth mixer circuit, multiplying the two signals by the fourth mixer circuit, and outputting an output signal obtained by the multiplication; a step of inputting the output signal of the mixer circuit to a fourth low-pass filter, cutting a high-frequency signal contained in the output signal by the fourth low-pass filter, and outputting at least a DC signal; The DC signal output by the low-pass filter and the DC signal output by the fourth low-pass filter are input to a second subtraction circuit, and the difference between the two DC signals is obtained by the second subtraction circuit. , the step of outputting the obtained difference; and the difference output by the first subtraction circuit and the second
inputting the difference output by the subtraction circuit to an addition circuit, adding the two differences or obtaining the difference between the two differences by the addition circuit, and outputting the obtained sum or difference and a method for processing an output signal of an eddy current sensor.

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 schematic diagram showing a configuration example of the coils in the eddy current sensor 50 of this embodiment. FIG. 6 is a schematic diagram showing an output signal processing circuit in another embodiment. FIG. 7 is a diagram showing a resistor bridge circuit. FIG. 8 is a schematic diagram showing a configuration example of an eddy current sensor according to another embodiment. FIG. 9 is a schematic diagram showing a connection example of exciting coils in an eddy current sensor. FIG. 10 is a diagram showing magnetic fields generated by an eddy current sensor. FIG. 11 is a schematic diagram showing an output signal processing circuit in another embodiment. 12 is a perspective view of the eddy current sensor of another embodiment shown in FIG. 8. FIG. FIG. 13 is a schematic diagram showing the internal circuit configuration of the digital signal processor. FIG. 14 shows how the DC signal changes due to the phase difference between the output signal of the eddy current sensor and the signal of the AC signal source.

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 100a to a motor (not shown), which is a driving unit arranged below, and is rotatable about the table shaft 100a. 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 160 . 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 is an oscillator with a fixed frequency of about 2 to 30 MHz, such as 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 the equivalent resistance corresponding to the 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 output signal processing circuit 54 receives the output signal 176 and the signal 180 of a predetermined frequency. The mixer circuit 178 multiplies the two input signals (output signal 176 and signal 180) and outputs an output signal 182 obtained by the multiplication. The output signal processing circuit 54 further has a low pass filter 184 . A low-pass filter 184 receives an output signal 182 output from the mixer circuit 178, cuts high-frequency signals contained in the input output signal 182, and outputs an output signal 186 containing at least a DC signal.

The eddy current sensor 50 has an excitation coil for forming an eddy current in the metal film (or conductive film) on the semiconductor wafer WH and a detection coil for detecting the generated eddy current. For example, an excitation coil and a detection coil are axially arranged on a cylindrical ferrite core. The excitation coil is connected to an AC signal source 52 . The excitation coil 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 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). FIG. 4 does not show the excitation coil. Mixer circuit 178 is supplied from AC signal source 52 with a signal 180 having the same frequency as the voltage supplied to the excitation coil.

Mixer circuit 178 may be an analog multiplier or a digital multiplier. The mixer circuit 178 is a circuit that receives two voltage signals of the same (or different) frequency components f1 and f2 and multiplies both signals. Mixer circuit 178 is also called a mixer, mixing circuit, frequency mixer, frequency mixing circuit, mixer, frequency converter, frequency conversion circuit, frequency converter, and the like. The purpose of the mixer circuit is to multiply two input signals and take out the sum or difference of the frequencies of the two signals (perform frequency conversion). If the two input signals have the same frequency, the phase difference between the two signals can be extracted.

Mixer circuit 178 has an input port 198 , a local oscillator port 200 and an output port 202 . Input port 198 receives output signal 176 from eddy current sensor 50 . A signal 180 from the AC signal source 52 is input to the local oscillator port 200 . Output signal 176 and signal 180 are at the same frequency. The result of multiplying output signal 176 and signal 180 by mixer circuit 178 is output from output port 202 . An output signal 182 output from the output port 202 is input to a low pass filter 184 . By passing through the low-pass filter 184, the amount of phase change (phase difference) between the output signal 176 detected by the eddy current sensor 50 and the signal 180 is extracted as a DC signal (output signal 186). The cutoff frequency of the low-pass filter can be set, for example, in the range of 0.1-10 Hz.

The processing performed by the mixer circuit 178 is as follows. Assume that the output signal 176 is A·sin(ωt+θ _A ). Let signal 180 be B·sin(ωt+θ _B ). A and B are the amplitudes (e.g., mv) of the output signals 176 and 180, respectively; ω is the frequency (1/s); t is the time ( _{S )} ; is the phase of
The output signal 182 of mixer circuit 178 is as follows.
A・sin(ωt+θ _A )・B・sin(ωt+θ _B )＝(1/2)A・B・cos(ωt+θ _A +ωt+θ _B )+(1/2)A・B・ cos(ωt+θ _A −ωt−θ _B )=(1/2)A·B·cos(2ωt+ _θA + _θB )+(1/2)A·B·cos( _θA − _θB ).
When this signal is input to low pass filter 184, the first term in the above equation is removed and the output signal 186 of low pass filter 184 is the second term in the above equation.
(1/2)A·B·cos(θ _A −θ _B ) That is, it becomes a DC signal.

In this embodiment, the output signal 176 of the eddy current sensor 50 is connected to the mixer circuit 178 without going through a resistor bridge circuit. Since the resistor bridge circuit, which is susceptible to temperature changes, is not used, it is possible to provide the output signal processing circuit 54 of the eddy current sensor 50 that is less susceptible to changes in the surrounding environment than in the prior art.

In the prior art, a signal detected at the terminals of a resistance bridge circuit passes through a high-frequency amplifier and a phase shift circuit, and is detected by a synchronous detection section comprising a cosine synchronous detection circuit and a sine synchronous detection circuit. and are taken out. A low-pass filter removes unwanted high-frequency components from the synchronously detected signal. Therefore, the high frequency output from the coil becomes a low frequency signal after a long processing step. Since there are many steps that are high-frequency signals, conventional signals have a lot of noise.

In this embodiment, the high frequency output (output signal 176 ) output by the coil of the eddy current sensor 50 is turned into a low frequency signal (output signal 186 ) by the mixer circuit 178 and the low pass filter 184 . Since the number of steps in which the output signal 176 is a high frequency signal is small, the output signal 186 has less noise than in the conventional art. That is, the high-frequency signal, which is easily affected by the surroundings, is converted into the easy-to-handle direct-current signal at an early stage (in a small number of steps), so that stable signal measurement can be performed.

In FIG. 4, when the signal 180 and the output signal 176 are compared, if the phase change is large and the amplitude change is small between the two signals, it is preferable to measure the film thickness by the phase change. If the phase change between the two signals is small and the amplitude change is small, it is preferable to measure the film thickness by the amplitude change. If the phase change between the two signals is large and the amplitude change is also large, it is preferable to measure the film thickness based on the phase change and the amplitude change. Also, the signal 180 need not be sinusoidal. For example, a square wave with the same frequency as output signal 176 may be used. Furthermore, the frequencies of output signal 176 and signal 180 need not be exactly the same, but may be substantially the same. If there is a large frequency difference between the output signal 176 and the signal 180 , at least one of the frequencies of the output signal 176 and the signal 180 may be adjusted by a frequency adjustment circuit and then input to the mixer circuit 178 .

Another embodiment of the present invention will now be described. FIG. 5 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 structures shown in FIGS. 4, 5 and 8, 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.

FIG. 6 is a schematic diagram showing the output signal processing circuit 54 in this embodiment. The eddy current sensor 50 includes a detection coil 73 (first coil) and a dummy coil 74 (second coil) that respectively output an output signal 176 (first output signal) and an output signal 188 (second output signal). have The output signal processing circuit 54 processes the output signals 182 and 188 output by the eddy current sensor 50 . The output signal processing circuit 54 receives an output signal 176 and a signal 180 having a predetermined frequency output from the AC signal source 52, multiplies the input two output signals 176 and 180, and obtains A mixer circuit 1781 (first mixer circuit) for outputting an output signal 182 obtained by mixing and an output signal 182 output by the mixer circuit 1781 are input. It has a low-pass filter 1841 (first low-pass filter) that outputs an output signal 1861 containing a DC signal.

The output signal processing circuit 54 further receives an output signal 188 and a signal 180 of a predetermined frequency output from the AC signal source 52, multiplies the input output signal 188 and the signal 180, and obtains A mixer circuit 1782 (second mixer circuit) for outputting an output signal 190 and an output signal 190 output by the mixer circuit 1782 are input, a high frequency signal included in the input output signal 190 is cut, and at least a direct current is generated. and a low pass filter 1842 (second low pass filter) that outputs an output signal 1862 containing the signal.

The output signal processing circuit 54 further receives the output signal 1861 output from the low-pass filter 1841 and the output signal 1862 output from the low-pass filter 1842, and obtains the difference between the two input output signals 1861 and 1862, and a first subtraction circuit 1961 (subtraction circuit) that outputs the obtained difference.

In addition, the output signal processing circuit 54 receives the output signal 1861 (DC signal) output from the low-pass filter 1841, adjusts the magnitude of the amplitude of the input output signal 1861, and outputs the adjusted DC signal 1921. A first adjustment circuit 1941 to output and an output signal 1862 (DC signal) output by a low-pass filter 1842 are input, and the magnitude of the amplitude of the input output signal 1862 is adjusted to adjust the DC signal 1922 after adjustment. and a second adjustment circuit 1942 that outputs the difference between the adjusted DC signal 1921 output by the first adjustment circuit 1941 and the adjusted DC signal 1922 output by the second adjustment circuit 1942. and a first subtraction circuit 1961 (subtraction circuit) for obtaining and outputting the obtained difference.

In this embodiment as well, the output signals 176 and 188 of the eddy current sensor 50 are connected to the mixer circuits 1781 and 1782 without passing through the resistance bridge circuit. Since the resistor bridge circuit, which is susceptible to temperature changes, is not used, it is possible to provide the output signal processing circuit 54 of the eddy current sensor which is less susceptible to changes in the surrounding environment than the conventional one.

In this embodiment, the first subtraction circuit 1961 can perform the same detection method using a conventional bridge circuit, in which two coils are used to extract minute signal changes corresponding to film thickness changes. That is, it is possible to obtain the difference between the two DC signals and detect only a minute signal change corresponding to the film thickness change.

Here, a detection method using a bridge circuit as a comparative example will be described with reference to FIG. As shown in FIG. 7, among the three excitation coils 72, detection coils 73, and dummy coils 74, the detection coil 73 and the dummy coil 74 form a series circuit. Its ends are connected to a resistance bridge circuit 204 that includes a variable resistor 206 , a variable resistor 208 and a fixed resistor 210 . By adjusting the balance with the variable resistors 206 and 208 of the resistance bridge circuit 204, it is possible to adjust the zero point so that the output of the resistance bridge circuit 204 becomes zero when the film thickness is zero. The output of resistance bridge circuit 204 is input to synchronous detection circuit 214, as shown in FIG. The synchronous detection circuit 214 extracts the 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. A stray capacitance 212 of the resistor is generated in this circuit.

The amount of adjustment of the resistance values of the variable resistors 206 and 208, that is, the amount of adjustment of the resistance values at the time of zero point adjustment, is very small compared to the overall magnitude of the resistance values forming the bridge circuit. As a result, the amount of temperature change of the entire resistance value is a non-negligible amount compared to the amount of zero point adjustment. The characteristics of the resistor bridge circuit 204 are sensitively affected by changes in the surrounding environment of the resistors due to changes in resistance due to changes in temperature, stray capacitances of resistors, and the like. As a result, there is a problem that the above-mentioned zero point tends to shift and the film thickness measurement accuracy decreases.

Returning to the description of FIG. The first subtraction circuit 1961 receives the DC signal 1921 output from the first adjustment circuit 1941 and the DC signal 1922 output from the second adjustment circuit 1942, and receives the two input DC signals 1921 and 1922. and output the difference. The reason for providing the first adjustment circuit 1941 and the second adjustment circuit 1942 is as follows.

Performance equivalent to the detection method using a conventional resistance bridge circuit, in which minute signal changes corresponding to changes in film thickness are extracted using two coils (detection coil 73 and dummy coil 74) by means of an adjustment circuit and a subtraction circuit. can be maintained. That is, the level of the phase detection signal from at least one coil (however, two detection coils 73 and dummy coils 74 in FIG. 6) is adjusted by an adjustment circuit and then subtracted to obtain a minute signal corresponding to the change in film thickness. Detects only signal changes. The adjustment circuit can improve the accuracy of the zero point adjustment compared to the case without the adjustment circuit. This makes it possible to extract weak changes in the signal from the zero point described above. Only one of the first adjustment circuit 1941 and the second adjustment circuit 1942 may be provided. This is because there are cases in which the level of the phase detection signal can be adjusted by the adjusting circuit to adjust the zero point even with only one of the adjusting circuits.

The first adjustment circuit 1941 and the second adjustment circuit 1942 are, for example, attenuators. An attenuator is a circuit element or device that attenuates a signal input to the attenuator to an appropriate signal level (amplitude). The first adjustment circuit 1941 and the second adjustment circuit 1942 may be amplifiers, for example. The reason for providing the first adjustment circuit 1941 and the second adjustment circuit 1942 is as follows, in addition to the reason resulting from the characteristics of the coil.

A mixer circuit or a low-pass filter may amplify or attenuate the amplitude of an input signal and output it. In that case, a first adjustment circuit 1941 and a second adjustment circuit 1942 may be required to adjust the amplitude of the outputs of the mixer circuit and the low-pass filter.

Another embodiment of the present invention will now be described. 8 and 9 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 W arranged 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. 11) for connecting to the outside come out, respectively.

FIG. 8 is a cross-sectional view of 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. 9, 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. 10 has a structure in which two eddy current sensors of FIG. 5 are arranged concentrically. Accordingly, the output signal processing circuit 54 corresponding to the eddy current sensor of FIG. 10 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. 10 is shown in FIG. The eddy current sensor 50 includes a detection coil 864 (first coil) and a dummy coil 868 (second coil) that respectively output an output signal 176 (first output signal) and an output signal 188 (second output signal). have The eddy current sensor 50 has a detection coil 866 (third coil) and a dummy coil 870 (fourth coil) that output a third output signal 1761 and a fourth output signal 1881, respectively.

The processing of the mixer circuit 1781, the mixer circuit 1782, the low-pass filter 1841, and the low-pass filter 1842 regarding the first output signal and the second output signal is as described above, so the explanation is omitted.

The output signal processing circuit 54 receives the third output signal 1761 and the signal 180 of a predetermined frequency output from the AC signal source 52, multiplies the two input signals, and outputs the output obtained by the multiplication. A third mixer circuit 1783 for outputting a signal 1821 and an output signal 1821 output by the third mixer circuit 1783 are input, a high frequency signal included in the input output signal 1821 is cut, and at least a DC signal is removed. It has a third low pass filter 1843 that outputs an output signal 1863 containing:

The output signal processing circuit 54 receives the fourth output signal 1881 and the signal 180 of a predetermined frequency output from the AC signal source 52, multiplies the two input signals, and outputs the output obtained by the multiplication. A fourth mixer circuit 1784 for outputting a signal 1901 and an output signal 1901 output by the fourth mixer circuit 1784 are input, a high frequency signal included in the input output signal 1901 is cut, and at least a DC signal is removed. It has a fourth low pass filter 1844 that outputs an output signal 1864 containing:

The internal configuration of the digital signal processor 216 is shown in FIG. The output signal processing circuit 54 receives the output signal 1863 output from the third low-pass filter 1843 and the output signal 1864 output from the fourth low-pass filter 1844, and obtains the difference 2222 between the two input DC signals. , and the difference 2221 output by the first subtraction circuit 1961 and the difference 2222 output by the second subtraction circuit 1962 are input to obtain the two input values. and a summing circuit 224 that adds the differences or finds the difference of two differences and outputs the resulting sum or difference as output signal 172 .

In this embodiment, a digital signal processor (DSP) 216 has the functions of first, second, third and fourth adjustment circuits, first and second subtraction circuits, and addition circuits. That is, the digital signal processor 216 receives the output signal 1863 (DC signal) output from the third low-pass filter 1843, adjusts the magnitude of the amplitude of the input output signal 1863, and adjusts the DC signal after adjustment. and the output signal 1864 (direct current signal) output by the fourth low-pass filter 1844 are input, and the magnitude of the amplitude of the input output signal 1864 is adjusted so that after adjustment may have a fourth adjustment circuit 1944 that outputs a DC signal 1924 of . Digital signal processor 216 is a microprocessor suitable for digital signal processing. At least one of the first, second, third and fourth adjusting circuits, the first and second subtracting circuits and the adding circuit may be provided independently as an analog circuit or a digital circuit.

In addition to the coil assembly having two coils shown in FIG. 5, this embodiment further has a coil assembly having two coils. That is, it has two sets of combinations of two coils. Since there are two sets of combinations, the measurement accuracy is improved by adding the difference between the two DC signals obtained by the two sets or by obtaining the difference between the two DC signals. The reason why the measurement accuracy is improved is as follows. In the case of addition, since the signal output increases, a smaller signal change, that is, a smaller film thickness change can be detected, thereby improving the measurement accuracy.

When the difference is to be obtained, for example, one combination can measure a film thickness in a wider area than the other combination. At this time, by subtracting the output of one combination from the output of the other combination, it is possible to reduce the influence of the film thickness in a wide area and measure only the change in the film thickness in a narrow area more accurately. . That is, the spatial accuracy of measurements can be improved.

A perspective view of the eddy current sensor shown in FIG. 8 is shown in FIG. Although top surface 218 is above top surface 220 in FIG. 12 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 FIG. 12, 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.

Also in this embodiment, the output signal of the eddy current sensor is connected to the mixer circuit without passing through the resistance bridge circuit. Since a resistor bridge circuit, which is susceptible to temperature changes, is not used, it is possible to provide an output signal processing circuit for an eddy current sensor that is less susceptible to changes in the surrounding environment than conventional ones.

In this embodiment, the subtraction circuit can perform the same detection method using a conventional bridge circuit, in which two coils are used to extract a minute signal change corresponding to the film thickness change. That is, it is possible to obtain the difference between the two DC signals and detect only a minute signal change corresponding to the film thickness change.

The multiplier circuit and the subtractor circuit may be circuits that multiply the results of multiplication and subtraction by a predetermined constant (the constant may be 1, less than 1, or greater than 1), that is, output an amplified output signal.

FIG. 14 illustrates how output signal 186, which is a DC signal, varies with the phase difference between output signal 176 of eddy current sensor 50 (shown in FIG. 4) and signal 180 of AC signal source 52. indicates 14A, 14B, 14C and 14D are cases where the phase difference is 0 degrees, 30 degrees, 60 degrees and 90 degrees, respectively. As the phase difference increases, the output signal 186 decreases. The horizontal axis of the figure is time (s), and the vertical axis is amplitude (mv).

Next, a method for processing the output signal of the eddy current sensor will be described. In FIG. 4, the output signal 176 of the eddy current sensor 50 and the signal 180 of the AC signal source 52 are input to the mixer circuit 178 . A mixer circuit 178 multiplies the two signals and outputs an output signal 182 resulting from the multiplication. An output signal 182 output from the mixer circuit 178 is input to a low-pass filter 184 to cut high frequency signals and output at least a DC signal 186 .

Next, another method of processing the output signal of the eddy current sensor will be described. In FIG. 6, first and second output signals 176 and 188 output by an eddy current sensor 50 having first and second coils 73 and 74 that output first and second output signals 176 and 188, respectively. process.

A first output signal 176 and a signal 180 from an AC signal source 52 are input to a first mixer circuit 1781, the first mixer circuit 1781 multiplies the two signals, and an output signal 182 obtained by the multiplication is to output The output signal 182 output by the first mixer circuit 1781 is input to the first low-pass filter 1841, and the high-frequency signal included in the output signal 182 is cut by the first low-pass filter 1841 to remove at least the DC signal 1861. Output.

The second output signal 188 and the signal 180 of the AC signal source 52 are input to the second mixer circuit 1782, the two signals are multiplied by the second mixer circuit 1782, and the output signal 190 obtained by the multiplication is to output The output signal 190 output by the second mixer circuit 1782 is input to the second low-pass filter 1842, and the high-frequency signal contained in the output signal 190 is cut by the second low-pass filter 1842 to remove at least the DC signal 1862. Output.

The DC signal 1861 output by the first low-pass filter 1841 and the DC signal 1862 output by the second low-pass filter 1842 are input to the first subtraction circuit 1961, and the first subtraction circuit 1961 divides the two DC signals into Find the difference 172 and output the resulting difference 172 .

Next, another method of processing the output signal of the eddy current sensor will be described. In FIG. 11, the eddy current sensor has third and fourth coils 866, 870 that output third and fourth output signals 1761, 1881, respectively. The third output signal 1761 and the signal 180 of the AC signal source 52 are input to the third mixer circuit 1783, the two signals are multiplied by the third mixer circuit 1783, and the output signal 1821 obtained by the multiplication is to output

The output signal 1821 of the third mixer circuit 1783 is input to the third low-pass filter 1843, the high-frequency signal contained in the output signal 1821 is cut by the third low-pass filter 1843, and at least the DC signal 1863 is output. . The fourth output signal 1881 and the signal 180 of the AC signal source 52 are input to the fourth mixer circuit 1784, the two signals are multiplied by the fourth mixer circuit 1784, and the output signal 1901 obtained by the multiplication is to output

The output signal 1901 of the fourth mixer circuit 1784 is input to the fourth low-pass filter 1844, the high-frequency signal contained in the output signal 1901 is cut by the fourth low-pass filter 1844, and at least the DC signal 1864 is output. . The DC signal 1863 output from the third low-pass filter 1843 and the DC signal 1864 output from the fourth low-pass filter 1844 are input to the second subtraction circuit 1962, and the second subtraction circuit 1962 divides the two DC signals 1863 , 1864 and outputs the difference 2222 obtained. The difference 2221 output from the first subtraction circuit 1961 and the difference 2222 output from the second subtraction circuit 1962 are input to the addition circuit 224 . Addition circuit 224 adds the two differences 2221 and 2222 or finds the difference between the two differences 2221 and 2222 and outputs the resulting sum 172 or difference 172 .

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;
an output signal processing circuit that processes the output signal of the eddy current sensor;
The output signal processing circuit is
a mixer circuit that receives the output signal and a signal of a predetermined frequency, multiplies the two input signals, and outputs an output signal obtained by the multiplication;
An eddy current sensor set, comprising: a low-pass filter that receives the output signal output from the mixer circuit, cuts a high-frequency signal contained in the input output signal, and outputs at least a DC signal. three-dimensional.
Form 2
In an eddy current sensor output signal processing circuit that processes the first and second output signals output by an eddy current sensor having first and second coils that respectively output first and second output signals,
a first mixer circuit that receives the first output signal and a signal of a predetermined frequency, multiplies the two input signals, and outputs an output signal obtained by the multiplication;
a first low-pass filter that receives the output signal output from the first mixer circuit, cuts a high-frequency signal included in the input output signal, and outputs at least a DC signal;
a second mixer circuit that receives the second output signal and a signal of the frequency, multiplies the two input signals, and outputs an output signal obtained by the multiplication;
a second low-pass filter that receives the output signal output from the second mixer circuit, cuts a high-frequency signal included in the input output signal, and outputs at least a DC signal;
The DC signal output by the first low-pass filter and the DC signal output by the second low-pass filter are input, the difference between the two input DC signals is obtained, and the obtained difference is calculated. An output signal processing circuit for an eddy current sensor, comprising: a first subtraction circuit for outputting;
Form 3
The output signal processing circuit receives the DC signal output from the first low-pass filter, adjusts the amplitude of the input DC signal, and outputs the adjusted DC signal. has an adjustment circuit of
The first subtraction circuit receives the DC signal output from the first adjustment circuit and the DC signal output from the second low-pass filter, and obtains a difference between the two input DC signals. 3. The output signal processing circuit for an eddy current sensor according to mode 2, wherein the output signal processing circuit for an eddy current sensor according to mode 2 is characterized by outputting the obtained difference.
form 4
The output signal processing circuit receives the DC signal output from the first low-pass filter, adjusts the amplitude of the input DC signal, and outputs the adjusted DC signal. and an adjustment circuit for
a second adjustment circuit that receives the DC signal output from the second low-pass filter, adjusts the amplitude of the input DC signal, and outputs the adjusted DC signal; ,
The first subtraction circuit receives the DC signal output from the first adjustment circuit and the DC signal output from the second adjustment circuit, and obtains a difference between the two input DC signals. 3. The output signal processing circuit for an eddy current sensor according to mode 2, wherein the output signal processing circuit for an eddy current sensor according to mode 2 is characterized by outputting the obtained difference.
Form 5
The eddy current sensor has third and fourth coils that respectively output third and fourth output signals,
The output signal processing circuit is
a third mixer circuit that receives the third output signal and a signal of the frequency, multiplies the two input signals, and outputs an output signal obtained by the multiplication;
a third low-pass filter that receives the output signal output from the third mixer circuit, cuts a high-frequency signal included in the input output signal, and outputs at least a DC signal;
a fourth mixer circuit that receives the fourth output signal and the signal of the frequency, multiplies the two input signals, and outputs an output signal obtained by the multiplication;
a fourth low-pass filter that receives the output signal output from the fourth mixer circuit, cuts a high-frequency signal included in the input output signal, and outputs at least a DC signal;
The DC signal output by the third low-pass filter and the DC signal output by the fourth low-pass filter are input, a difference between the two input DC signals is obtained, and the obtained difference is calculated. a second subtraction circuit that outputs
the difference output by the first subtraction circuit and the difference output by the second subtraction circuit are input, and the two input differences are added or the difference between the two differences is obtained, An output signal processing circuit for an eddy current sensor according to any one of modes 2 to 4, further comprising an addition circuit for outputting the obtained sum or difference.
Form 6
a step of inputting an output signal of an eddy current sensor and a signal of a predetermined frequency to a mixer circuit, performing multiplication of the two signals by the mixer circuit, and outputting an output signal obtained by the multiplication;
and inputting the output signal output from the mixer circuit to a low-pass filter to cut high-frequency signals and output at least a DC signal.
Form 7
In an eddy current sensor output signal processing method for processing the first and second output signals output by an eddy current sensor having first and second coils that respectively output first and second output signals,
The first output signal and a signal of a predetermined frequency are input to a first mixer circuit, the two signals are multiplied by the first mixer circuit, and the output signal obtained by the multiplication is output. and
The output signal output from the first mixer circuit is input to a first low-pass filter, a high-frequency signal included in the output signal is cut by the first low-pass filter, and at least a DC signal is output. a step;
The second output signal and the signal of the frequency are input to a second mixer circuit, the two signals are multiplied by the second mixer circuit, and the output signal obtained by the multiplication is output. a step;
The output signal output from the second mixer circuit is input to a second low-pass filter, and the second low-pass filter cuts a high-frequency signal included in the output signal to output at least a DC signal. a step;
The DC signal output by the first low-pass filter and the DC signal output by the second low-pass filter are input to a first subtraction circuit, and the two DC signals are divided by the first subtraction circuit. and obtaining a difference, and outputting the obtained difference.
Form 8
The eddy current sensor has third and fourth coils that respectively output third and fourth output signals,
The output signal processing method includes:
The third output signal and the signal of the frequency are input to a third mixer circuit, the two signals are multiplied by the third mixer circuit, and the output signal obtained by the multiplication is output. a step;
inputting the output signal of the third mixer circuit to a third low-pass filter,
a step of cutting a high-frequency signal contained in the output signal by a low-pass filter and outputting at least a DC signal;
inputting the fourth output signal and the signal of the frequency to a fourth mixer circuit, multiplying the two signals by the fourth mixer circuit, and outputting the output signal obtained by the multiplication; a step;
a step of inputting the output signal of the fourth mixer circuit to a fourth low-pass filter, cutting a high-frequency signal contained in the output signal by the fourth low-pass filter, and outputting at least a DC signal;
The DC signal output by the third low-pass filter and the DC signal output by the fourth low-pass filter are input to a second subtraction circuit, and the two DC signals are divided by the second subtraction circuit. obtaining a difference and outputting the obtained difference;
The difference output by the first subtraction circuit and the difference output by the second subtraction circuit are input to an addition circuit, and the addition circuit adds the two differences or divides the two differences. and obtaining a difference, and outputting the obtained sum or difference.
Form 9
a polishing table configured to be attached with a polishing pad for polishing a substrate;
a driving unit configured to rotationally drive the polishing table;
a holding part configured to hold the substrate and press it against the polishing pad;
the eddy current sensor arranged inside the polishing table and configured to detect an eddy current formed in a conductive film formed on the substrate as the polishing table rotates;
an output signal processing circuit of the eddy current sensor according to any one of modes 2 to 5;
an endpoint detection controller configured to calculate film thickness data of the substrate from the output of the output signal processing circuit;
A polishing device with a

DESCRIPTION OF SYMBOLS 50... Eddy current sensor 52... AC signal source 54... Output signal processing circuit 60... Pot core 71... Ferrite core 72... Excitation coil 73... Detection coil 74... Dummy coil 100... Polishing table 101... Polishing pad 102... Polishing liquid supply nozzle 110 Top ring head 174 Eddy current sensor assembly 178 Mixer circuit 184 Low pass filter 198 Input port 200 Local oscillator port 202 Output port 204 Resistive bridge circuit 216 Digital signal processor 218 Upper surface 220 Upper surface 246 End point detection controller 248 Device control controller 860 Exciting coil 862 Exciting coil 864 Detection coil 866 Detection coil 868 Dummy coil 870 Dummy coil 1781 Mixer circuit 1782 Mixer circuit 1783 Third mixer circuit 1784 Third 4 mixer circuits 1841 low-pass filter 1842 low-pass filter 1843 third low-pass filter 1844 fourth low-pass filter 1941 first adjustment circuit 1942 second adjustment circuit 1961 first subtraction circuit

Claims (7)

In an eddy current sensor output signal processing circuit that processes the first and second output signals output by an eddy current sensor having first and second coils that respectively output first and second output signals,
a first mixer circuit that receives the first output signal and a signal of a predetermined frequency, multiplies the two input signals, and outputs an output signal obtained by the multiplication;
a first low-pass filter that receives the output signal output from the first mixer circuit, cuts a high-frequency signal included in the input output signal, and outputs at least a DC signal;
a second mixer circuit that receives the second output signal and a signal of the frequency, multiplies the two input signals, and outputs an output signal obtained by the multiplication;
a second low-pass filter that receives the output signal output from the second mixer circuit, cuts a high-frequency signal included in the input output signal, and outputs at least a DC signal;
The DC signal output by the first low-pass filter and the DC signal output by the second low-pass filter are input, the difference between the two input DC signals is obtained, and the obtained difference is calculated. An output signal processing circuit for an eddy current sensor, comprising: a first subtraction circuit for outputting; The output signal processing circuit receives the DC signal output from the first low-pass filter, adjusts the amplitude of the input DC signal, and outputs the adjusted DC signal. has an adjustment circuit of
The first subtraction circuit receives the DC signal output from the first adjustment circuit and the DC signal output from the second low-pass filter, and obtains a difference between the two input DC signals. 2. The output signal processing circuit of an eddy current sensor according to claim 1 , wherein the obtained difference is output. The output signal processing circuit receives the DC signal output from the first low-pass filter, adjusts the amplitude of the input DC signal, and outputs the adjusted DC signal. and an adjustment circuit for
a second adjustment circuit that receives the DC signal output from the second low-pass filter, adjusts the amplitude of the input DC signal, and outputs the adjusted DC signal; ,
The first subtraction circuit receives the DC signal output from the first adjustment circuit and the DC signal output from the second adjustment circuit, and obtains a difference between the two input DC signals. 2. The output signal processing circuit of an eddy current sensor according to claim 1 , wherein the obtained difference is output. The eddy current sensor has third and fourth coils that respectively output third and fourth output signals,
The output signal processing circuit is
a third mixer circuit that receives the third output signal and a signal of the frequency, multiplies the two input signals, and outputs an output signal obtained by the multiplication;
a third low-pass filter that receives the output signal output from the third mixer circuit, cuts a high-frequency signal included in the input output signal, and outputs at least a DC signal;
a fourth mixer circuit that receives the fourth output signal and the signal of the frequency, multiplies the two input signals, and outputs an output signal obtained by the multiplication;
a fourth low-pass filter that receives the output signal output from the fourth mixer circuit, cuts a high-frequency signal included in the input output signal, and outputs at least a DC signal;
The DC signal output by the third low-pass filter and the DC signal output by the fourth low-pass filter are input, a difference between the two input DC signals is obtained, and the obtained difference is calculated. a second subtraction circuit that outputs
the difference output by the first subtraction circuit and the difference output by the second subtraction circuit are input, and the two input differences are added or the difference between the two differences is obtained, An output signal processing circuit for an eddy current sensor according to any one of claims 1 to 3 , further comprising an addition circuit for outputting the obtained sum or difference. In an eddy current sensor output signal processing method for processing the first and second output signals output by an eddy current sensor having first and second coils that respectively output first and second output signals,
The first output signal and a signal of a predetermined frequency are input to a first mixer circuit, the two signals are multiplied by the first mixer circuit, and the output signal obtained by the multiplication is output. and
The output signal output from the first mixer circuit is input to a first low-pass filter, a high-frequency signal included in the output signal is cut by the first low-pass filter, and at least a DC signal is output. a step;
The second output signal and the signal of the frequency are input to a second mixer circuit, the two signals are multiplied by the second mixer circuit, and the output signal obtained by the multiplication is output. a step;
The output signal output from the second mixer circuit is input to a second low-pass filter, and the second low-pass filter cuts a high-frequency signal included in the output signal to output at least a DC signal. a step;
The DC signal output by the first low-pass filter and the DC signal output by the second low-pass filter are input to a first subtraction circuit, and the two DC signals are divided by the first subtraction circuit. and obtaining a difference, and outputting the obtained difference. The eddy current sensor has third and fourth coils that respectively output third and fourth output signals,
The output signal processing method includes:
The third output signal and the signal of the frequency are input to a third mixer circuit, the two signals are multiplied by the third mixer circuit, and the output signal obtained by the multiplication is output. a step;
a step of inputting the output signal of the third mixer circuit to a third low-pass filter, cutting a high-frequency signal contained in the output signal by the third low-pass filter, and outputting at least a DC signal;
inputting the fourth output signal and the signal of the frequency to a fourth mixer circuit, multiplying the two signals by the fourth mixer circuit, and outputting the output signal obtained by the multiplication; a step;
a step of inputting the output signal of the fourth mixer circuit to a fourth low-pass filter, cutting a high-frequency signal contained in the output signal by the fourth low-pass filter, and outputting at least a DC signal;
The DC signal output by the third low-pass filter and the DC signal output by the fourth low-pass filter are input to a second subtraction circuit, and the two DC signals are divided by the second subtraction circuit. obtaining a difference and outputting the obtained difference;
The difference output by the first subtraction circuit and the difference output by the second subtraction circuit are input to an addition circuit, and the addition circuit adds the two differences or divides the two differences. 6. The method of processing an output signal of an eddy current sensor according to claim 5, further comprising the step of obtaining a difference and outputting the obtained sum or difference. a polishing table configured to be attached with a polishing pad for polishing a substrate;
a driving unit configured to rotationally drive the polishing table;
a holding part configured to hold the substrate and press it against the polishing pad;
the eddy current sensor arranged inside the polishing table and configured to detect an eddy current formed in a conductive film formed on the substrate as the polishing table rotates;
an output signal processing circuit of the eddy current sensor according to any one of claims 1 to 4 ;
an endpoint detection controller configured to calculate film thickness data of the substrate from the output of the output signal processing circuit;
A polishing device with a

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