JP6302189B2 - Substrate holding device with eddy current sensor - Google Patents

Description

The present invention relates to a substrate holding apparatus including an eddy current sensor that measures the temperature of an object to be measured based on an eddy current generated in the object to be measured.

  There are a contact temperature sensor and a non-contact temperature sensor as temperature sensors for measuring the temperature of a measurement object (object). The contact type temperature sensor includes a thermocouple, a resistance thermometer, and the like, and is widely used for industrial purposes because the temperature can be directly output by an electric signal such as voltage or resistance. Non-contact temperature sensors include a radiation thermometer that measures infrared rays emitted from a measurement object, and can be measured while the measurement object is in operation or moving, and thus is used in various fields.

JP 2001-041828 A

The conventional contact-type temperature sensor and non-contact-type temperature sensor described above have the following problems.
1) In the case of a contact-type temperature sensor, there is a problem regarding the contact portion and wiring when the measurement object moves.
2) When the contact-type temperature sensor is a thermocouple, cable connection between the object to be measured and the thermocouple is required, and the measurement temperature is lower than the true value of the measured temperature due to thermal radiation of the connection part, or measured due to the influence of the cable. The value fluctuates and temperature measurement with high accuracy becomes impossible.
3) When the contact-type temperature sensor is a resistance thermometer, a current flows, but this current causes a self-heating error of the resistor, an error due to a temperature change of the wiring conductor with the resistor, a connection circuit There is a problem that a measurement error occurs due to the contact resistance.
4) In the case of a radiation thermometer which is a typical example of a non-contact type temperature sensor, there is a problem that the temperature cannot be measured accurately depending on the material and state of the object. In addition, the radiation thermometer has a problem that a temperature measurement error occurs due to the influence of disturbance caused by reflection of infrared rays from other than the object to be measured.

The present invention has been made in view of the above circumstances, and can measure a temperature of a measurement object based on an eddy current generated in the measurement object, thereby forming a non-contact temperature sensor. An object of the present invention is to provide a substrate holding device including an eddy current sensor capable of accurately measuring the temperature of an object to be measured without being affected by disturbances other than the above.

In order to achieve the above-described object, a substrate holding apparatus provided with an eddy current sensor according to the present invention is a substrate holding apparatus that holds a substrate and presses it against a polishing surface on a polishing table. A ring main body, an elastic film fixed to the top ring main body and forming a pressure chamber in which pressure fluid is supplied to the inside of the top ring main body, and provided on the back side of the surface holding the substrate in the elastic film A metal film or a conductive film, a sensor coil disposed to face the metal film or the conductive film , and disposed near the metal film or the conductive film ; and supplying an AC signal to the sensor coil a signal source for forming an eddy current in the metal film or the conductive film, the eddy current sensor and a detection circuit for detecting the eddy current formed in the metal film or the conductive film based on an output of the sensor coil so I, from the output of the eddy current sensor, based on the relationship between the output of the temperature and the eddy current sensor in the material of the material and the material of the metal film or the conductive film, the temperature of the metal film or the conductive film And an eddy current sensor to be obtained.

According to the present invention, at least one eddy current sensor is installed in the top ring body of the top ring, and on the back side of the elastic film forming the pressure chamber (opposite side of the substrate holding surface) A metal film or a conductive film having a high thermal conductivity is attached to a position facing the eddy current sensor. Since the metal film or the conductive film has a high thermal conductivity, the metal film or the conductive film becomes approximately equal to the temperature of the portion of the elastic film to which the metal film or the conductive film is attached during polishing. Therefore, the temperature of the elastic film can be measured by the eddy current sensor through the metal film or the conductive film, and the temperature of the substrate can be indirectly measured based on the measured elastic film temperature.
The eddy current sensor has a constant output when the object to be measured is the same metal type and metal film. Even if the object to be measured moves, the sensor side is fixed under a certain condition, and measurement is possible with the same metal thickness. The conditions under which the resistance of the metal changes may be the influence of temperature, the film thickness becomes thin, the material changes. If the film quality and thickness of the metal film are constant in a non-contact state, the temperature can be measured.

According to a preferred aspect of the present invention, the relationship between the temperature of the material of the same material as the material of the metal film or the conductive film and the output of the eddy current sensor is obtained in advance.
According to the present invention, the relationship between the temperature of the material to be measured and the temperature of the same material and the output of the eddy current sensor is obtained in advance, and the temperature of the measurement object is obtained from the output of the eddy current sensor at the time of measurement. be able to.

According to a preferred aspect of the present invention, the output of the eddy current sensor includes an impedance component, and the temperature of the metal film or the conductive film is obtained from a change in the impedance component.
The coil of the eddy current sensor is not affected by temperature, and in that case, the eddy current (I) is constant, so that the output V = Z (R) × I of the eddy current sensor is established. Here, Z is an impedance component. Therefore, the change of the impedance component Z can be obtained from the output V of the eddy current sensor. The temperature can be calculated from the change in the impedance component Z. The impedance component Z is composed of a resistance component (R) and a reactance component (X).

According to a preferred aspect of the present invention, the resistance component and the reactance component of the impedance component are displayed on an orthogonal coordinate axis, and a line connecting the impedance component and a preset reference point coordinate and the resistance component are displayed. An impedance angle which is an angle formed with a parallel straight line is obtained, and the temperature of the metal film or the conductive film is obtained from the impedance angle.
According to a preferred aspect of the present invention, the impedance angle is the same regardless of the distance between the eddy current sensor and the metal film or the conductive film if the thickness of the metal film or the conductive film is constant. It is characterized by being.

According to a preferred embodiment of the present invention, the obtains the variation value of the output of the eddy current sensor over time at the location where the metal film or a conductive film is not present, the metal film or the conductive film by using the variation value The output value of the eddy current sensor obtained at the position where is present is corrected.
At a position where there is no measurement object, the sensor output is essentially zero, but there may be an output over time. Therefore, in the present invention, the sensor output is obtained after a lapse of a certain time at a position where the measurement object does not exist, the fluctuation value of the sensor itself is obtained, and then the output value obtained at the position where the measurement object exists. In addition, the fluctuation value is canceled by adding the fluctuation value of the sensor itself.

The present invention has the following effects.
(1) Since a non-contact type temperature sensor can be constituted by an eddy current sensor, there is no need to make contact with a measurement object, and there is no error in measurement values caused by wiring or connection. Temperature measurement is possible.
(2) Since it is not necessary to pass an electric current through the measurement object, an error due to a self-heating error or a temperature change of the wiring conductor does not occur, and an accurate temperature measurement is possible.
(3) Since the temperature of the measurement object is measured based on the eddy current generated in the measurement object, accurate temperature measurement is possible without being affected by disturbances other than the measurement object, unlike a radiation thermometer. It becomes.

FIG. 1 is a schematic view showing a state in which temperature is measured in a non-contact manner with respect to a measurement object that is moved by an eddy current sensor provided in the substrate holding apparatus of the present invention. FIG. 2 is a diagram showing a basic configuration of the eddy current sensor, FIG. 2 (a) is a block diagram showing the basic configuration of the eddy current sensor, and FIG. 2 (b) is an equivalent circuit diagram of the eddy current sensor. . 3A, 3B, and 3C are schematic views showing the circuit configuration of each coil in the sensor coil. FIG. 4 is a block diagram showing a synchronous detection circuit of the eddy current sensor. FIG. 5A is a graph obtained by converting a change in the impedance component Z measured by the eddy current sensor into a voltage. FIG. 5B is a graph showing the relationship between the output of the eddy current sensor and the object temperature. FIGS. 6A and 6B are graphs showing the results of measuring the temperature of Pt and the output of the eddy current sensor when the metal film is Pt (platinum) in the configuration shown in FIG. FIG. 7A is a graph showing the output of the eddy current sensor when the distance between the eddy current sensor and the measurement object is changed. FIG. 7B is a graph showing the relationship between the output and impedance angle of the eddy current sensor and the object temperature. FIG. 8 is a schematic diagram showing a correction method for canceling the fluctuation of the sensor itself, and is a schematic diagram in which a configuration in which the eddy current sensor can be moved is added to the relationship between the eddy current sensor and the measurement object shown in FIG. It is. FIG. 9 is a schematic perspective view showing the overall configuration of a polishing apparatus to which the eddy current sensor provided in the substrate holding apparatus of the present invention is applied. FIG. 10 is a schematic cross-sectional view showing details of the top ring shown in FIG.

Hereinafter, an embodiment of a substrate holding apparatus provided with an eddy current sensor according to the present invention will be described with reference to FIGS. 1 to 10, the same or corresponding components are denoted by the same reference numerals, and redundant description is omitted.
FIG. 1 is a schematic view showing a state in which temperature is measured in a non-contact manner with respect to a moving measurement object by an eddy current sensor provided in the substrate holding apparatus of the present invention. As shown in FIG. 1, the eddy current sensor 1 is disposed away from the measurement object 2. The measuring object 2 is a movable object, and the eddy current sensor 1 can measure the temperature of the moving measuring object 2. In the example shown in FIG. 1, the measurement object 2 has a configuration in which a metal film 4 is formed on the surface of a non-metallic base part 3. The distance between the metal film 4 and the eddy current sensor 1 is set to L. The base material part 3 is heated by a heating source (not shown), and the metal film 4 is transferred from the base material part 3 and rises to a predetermined temperature. The metal film 4 is made of the same metal species, for example, platinum (Pt).

  The output of the eddy current sensor 1 is constant if the object to be measured is the same metal type and metal film having the same thickness. Even if the object to be measured moves, the sensor side is fixed under a certain condition, and measurement is possible with the same metal thickness. The conditions under which the resistance of the metal changes may be the influence of temperature, the film thickness becomes thin, the material changes. If the film quality and thickness of the metal film are constant in a non-contact state, the temperature can be measured. The eddy current sensor 1 adjusts an excitation frequency, a circuit gain, etc. according to the metal film type and film thickness of the measurement object. Since the eddy current sensor 1 is a non-contact sensor even when the measurement object moves, temperature measurement is possible. Even when the measurement object does not move (when it is fixed), temperature measurement can be performed in the same manner.

Next, the principle of detecting the temperature of the metal film by the eddy current sensor 1 will be described.
The resistance value of the metal film is expressed by equation (1).
R = ρ (T) × (L / S) (1)
L: length, S: cross-sectional area, ρ: resistivity, T: object temperature.
The resistance value is calculated by equation (1). Under the condition that L and S do not change, the resistance value does not change unless the resistivity changes.
The resistivity is affected by temperature and is expressed by equation (2).
ρ (T) = ρ (To) (1 + α (T−To)) (2)
Here, α: resistance temperature coefficient, T: object temperature, To: any temperature near room temperature.
From the equations (1) and (2), the relationship between the resistance value R and the resistance temperature coefficient α is represented by the equation (3).
R (T) = R (To) (1 + α (T−To)) (3)
Since the resistance temperature coefficient α of the metal film is known in advance, a change in resistance value is detected by eddy current, and the temperature is calculated. That is, the coil of the eddy current sensor is not affected by the temperature, and in that case, the eddy current (I) is constant, and the output V = Z (R) × I of the eddy current sensor is established. Here, Z is an impedance component. Therefore, the change of the impedance component Z can be obtained from the output V of the eddy current sensor. The temperature can be calculated from the change in the impedance component Z. The impedance component Z is composed of a resistance component (R) and a reactance component (X).

Next, the output of the eddy current sensor 1 will be described with reference to FIGS.
2 is a diagram showing a basic configuration of the eddy current sensor 1, FIG. 2 (a) is a block diagram showing the basic configuration of the eddy current sensor 1, and FIG. 2 (b) is an equivalent circuit of the eddy current sensor 1. FIG.
As shown in FIG. 2A, in the eddy current sensor 1, a sensor coil 11 is disposed in the vicinity of the metal film 4 of the measurement object 2, and an AC signal source 12 is connected to the coil. The sensor coil 11 is a coil for detection, and is disposed, for example, at a position of about 10 to 40 mm with respect to the metal film to be detected.

In the eddy current sensor, the oscillating frequency changes due to the eddy current generated in the metal film 4, the frequency type for detecting the change in the resistance value of the metal film from the frequency change, the impedance changes, and the impedance change There is an impedance type that detects a change in resistance value of a metal film. That is, in the frequency type, in the equivalent circuit shown in FIG. 2B, when the eddy current I ₂ changes, the impedance Z changes and the oscillation frequency of the signal source (variable frequency oscillator) 12 changes. The change in the oscillation frequency can be detected at 13, and the change in the resistance value of the metal film can be detected. In the impedance type, in the equivalent circuit shown in FIG. 2B, when the eddy current I ₂ changes, the impedance Z changes, and the impedance Z viewed from the signal source (fixed frequency oscillator) 12 changes. The change of the impedance Z can be detected at 13, and the change of the resistance value of the metal film can be detected.

The impedance type eddy current sensor will be specifically described below. The AC signal source 12 is an oscillator having a fixed frequency of about 1 to 32 MHz. For example, a crystal oscillator is used. The current I ₁ flows through the sensor coil 11 due to the AC voltage supplied from the AC signal source 12. When a current flows through the sensor coil 11 disposed in the vicinity of the metal film 4, this magnetic flux is linked to the metal film 4, thereby forming a mutual inductance M therebetween. An eddy current I ₂ is generated in the metal film 4. Flowing. Where R1 is the equivalent resistance of the primary side including the sensor coil, L ₁ is self inductance of the primary side including the sensor coil as well. In the metal film 4 side, R2 is equivalent resistance corresponding to eddy current loss, L ₂ is its self-inductance. The impedance Z when the sensor coil side is viewed from the terminals a and b of the AC signal source 12 varies depending on the magnitude of eddy current loss formed in the metal film 4.

3A, 3 </ b> B, and 3 </ b> C are schematic diagrams illustrating a circuit configuration of each coil in the sensor coil 11.
As shown in FIG. 3 (a), the sensor coil 11 is obtained by separating a coil for forming an eddy current in a metal film and a coil for detecting an eddy current in the metal film. 21, 22, 23. Here, the central coil 21 is an exciting coil connected to the AC signal source 12. The exciting coil 21 forms an eddy current in the metal film 4 disposed in the vicinity by a magnetic field formed by a voltage supplied from the AC signal source 12. A coil 22 is disposed on the upper side (metal film side) of the coil 21 and detects a magnetic field generated by an eddy current formed in the metal film. A balance coil 23 is disposed on the opposite side of the excitation coil 21 from the detection coil 22.

As described above, the detection coil 22 and the balance coil 23 constitute an anti-phase series circuit, and both ends thereof are connected to a resistance bridge circuit 26 including a variable resistor 25. The exciting coil 21 is connected to the AC signal source 12 and generates an alternating magnetic flux, thereby forming an eddy current in the metal film 4 disposed in the vicinity. By adjusting the resistance value of the variable resistor 25, the output voltage of the series circuit composed of the coils 22 and 23 can be adjusted to zero when there is no metal film. The variable resistors 25 (VR ₁ , VR ₂ ) entering in parallel with the coils 22, 23 are adjusted so that the signals of L ₁ , L ₃ are in phase. That is, in the equivalent circuit of FIG.
VR _1-1 × (VR _2-2 + jωL ₃ ) = VR _1-2 × (VR _2-1 + jωL ₁ ) (4)
The variable resistors VR ₁ (= VR _1-1 + VR _1-2 ) and VR ₂ (= VR _2-1 + VR _2-2 ) are adjusted so that As a result, as shown in FIG. 3C, the signals of L ₁ and L ₃ before adjustment (indicated by dotted lines in the figure) are made into signals having the same phase and amplitude (indicated by solid lines in the figure).

  When the metal film is present in the vicinity of the detection coil 22, the magnetic flux generated by the eddy current formed in the metal film is linked to the detection coil 22 and the balance coil 23, but the detection coil 22 is the metal film. Since they are arranged close to each other, the balance of the induced voltages generated in the coils 22 and 23 is lost, whereby the interlinkage magnetic flux formed by the eddy current of the metal film can be detected. That is, the zero point can be adjusted by separating the series circuit of the detection coil 22 and the dummy coil 23 from the exciting coil 21 connected to the AC signal source and adjusting the balance with the resistance bridge circuit. . Therefore, the eddy current flowing in the metal film can be detected from zero, so that the detection sensitivity of the eddy current in the metal film is enhanced. As a result, it is possible to detect the magnitude of the eddy current formed in the metal film with a wide dynamic range.

FIG. 4 is a block diagram showing a synchronous detection circuit of the eddy current sensor.
FIG. 4 shows a measurement circuit example of the impedance Z when the sensor coil 11 side is viewed from the AC signal source 12 side. In the impedance Z measurement circuit shown in FIG. 4, when there is a metal film, a resistance component (R), a reactance component (X), an impedance component (Z), and a phase output (tan ⁻¹ R / X) are extracted. be able to.

  As described above, the signal source 12 that supplies an AC signal to the sensor coil 11 disposed in the vicinity of the metal film 4 of the measurement object 2 is a fixed-frequency oscillator including a crystal oscillator, for example, 1 to 32 MHz. Supply a fixed frequency voltage. The AC voltage formed by the signal source 12 is supplied to the sensor coil 11 via the band pass filter 30. A signal detected at the terminal of the sensor coil 11 passes through a high frequency amplifier 31 and a phase shift circuit 32, and a cos component and a sin component of the detection signal are detected by a synchronous detection unit including a cos synchronous detection circuit 33 and a sin synchronous detection circuit 34. It is taken out. Here, the oscillation signal formed by the signal source 12 is formed by the phase shift circuit 32 into two signals of the in-phase component (0 °) and the quadrature component (90 °) of the signal source 12. And the sin synchronous detection circuit 34, and the synchronous detection described above is performed.

From the synchronously detected signal, unnecessary high frequency components higher than the signal component are removed by the low-pass filters 35 and 36, and an X component output that is a cos synchronous detection output and a Y component output that is a sin synchronous detection output are respectively extracted. It is. Further, the vector operation circuit 37 obtains an impedance component Z = (X ² + Y ² ) ^1/2 from the X component output and the Y component output. Similarly, the vector operation circuit 38 obtains the phase output θ = (tan ⁻¹ Y / X) from the X component output and the Y component output. Here, various filters are provided in the measuring apparatus main body in order to remove noise components of the sensor signal. Each filter has a cut-off frequency corresponding to each filter. For example, by setting the cut-off frequency of the low-pass filter in a range of 0.1 to 10 KHz, the resistance value of the metal film 4 of the measurement object 2 is set. Can be measured with high accuracy.

FIG. 5A is a graph obtained by converting a change in the impedance component Z measured by the eddy current sensor 1 into a voltage. In FIG. 5A, the horizontal axis represents the X component output of the impedance component from the eddy current sensor 1, and the vertical axis represents the Y component output of the impedance component from the eddy current sensor 1.
In FIG. 5A, Z0 is an output when there is no metal film, and Z1 is an impedance component which is an output when there is a metal film 4. An angle θ formed by a straight line connecting Z1 and a preset reference point P and a straight line parallel to the X component is an impedance angle. That is, when the metal film 4 is present on the measurement object 2, the eddy current sensor 1 can obtain the output Z1 and the impedance angle θ.
FIG. 5B is a graph showing the relationship between the output of the eddy current sensor 1 and the object temperature. In FIG.5 (b), a horizontal axis shows time (t) and a vertical axis | shaft shows the magnitude | size and object temperature of a sensor output (Z1). FIG. 5B shows that the sensor output and the object temperature have a correlation.

6A and 6B are graphs showing the results of measuring the temperature of Pt and the output of the eddy current sensor 1 when the metal film is Pt (platinum) in the configuration shown in FIG.
As shown in FIG. 6A, there is a relationship of the following equation between the output (V) of the eddy current sensor 1 and the temperature T (° C.) of Pt.
V = 0.07 × T (° C.) − 1.96 (5)
As shown in FIG. 6B, there is a relationship of the following equation between the output (θ (degree)) of the eddy current sensor 1 and the temperature T (° C.) of Pt.
θ = 2.7 × T (° C.) − 72 (6)
As is apparent from the graphs of FIGS. 6A and 6B, since it is known that the output of the eddy current sensor and the temperature of Pt have a certain relationship, the temperature of Pt is calculated from the output of the eddy current. I can know.
Even when the metal film is made of another material, if the relationship between the metal film of the material and the output of the eddy current sensor is obtained in advance, the temperature of the metal film can be found from the output of the eddy current sensor.

Next, the distance between the eddy current sensor and the measurement object will be described.
When measuring the temperature of the measurement object, the eddy current sensor cannot always be arranged at a constant distance from the measurement object. In addition, there is a case where it is desired to measure the temperature of a thin film in a film forming process in semiconductor manufacturing. However, when there is no metal film at the initial stage and a metal film is formed as the film forming process proceeds, an eddy current sensor is used. It cannot always be placed at a fixed distance from the measurement object.
According to the eddy current sensor provided in the substrate holding apparatus of the present invention, the output distance at a controlled distance and a constant temperature is acquired in advance, and the distance is obtained by comparing with the output characteristic acquired in advance. It is possible to measure the temperature of the measurement object without being affected by the above.

FIG. 7A is a graph showing the output of the eddy current sensor when the distance between the eddy current sensor and the measurement object is changed. That is, FIG. 7A shows a change in the output of the eddy current sensor 1 when the distance L between the metal film 4 and the eddy current sensor 1 is changed in FIG. In FIG. 7A, the horizontal axis indicates the X component output of the impedance component by the eddy current sensor, and the vertical axis indicates the Y component output of the impedance component by the eddy current sensor.
In FIG. 7A, Z0 is an output when there is no metal film. Z1 is an output when the metal film is present, and is an output when the eddy current sensor and the metal film are at a predetermined distance. Z2 is an output when the distance between the eddy current sensor and the metal film is farther than when Z1. Z3 is an output when the distance between the eddy current sensor and the metal film is shorter than the case of Z1. Z1, Z2, and Z3 are impedance components.

If the eddy current sensor has a constant film thickness, even if the distance to the measurement object changes, the straight line connecting each output (Z1, Z2, Z3) and a preset reference point P is parallel to the X component. The impedance angle θ, which is an angle formed with a straight line, has the same characteristic. That is, the output of the eddy current sensor changes depending on the distance to the measurement object, but the impedance angle θ that is an angle with the reference point P does not change. However, it is affected by temperature.
Here, the reference point P is orthogonal to the X component (resistance component) and Y component (reactance component) of the impedance component Z acquired under different conditions between the eddy current sensor and the measurement object. This is the center point where the preliminary measurement straight lines that are displayed on the coordinate axes and connect the coordinates of the X component and the Y component for each film thickness of the measurement object intersect.

FIG. 7B is a graph showing the relationship between the output and impedance angle of the eddy current sensor and the object temperature. In FIG.7 (b), a horizontal axis shows time (t) and a vertical axis | shaft shows the output of an eddy current sensor, impedance angle (theta), and target object temperature.
As shown in FIG. 7 (b), the distance between the eddy current sensor and the metal film is constant before time t1, and the sensor output at that time corresponds to Z1 in FIG. 7 (a). Since the distance between the eddy current sensor and the measurement object increases after time t1, the sensor output decreases. The position where the sensor output is the lowest in FIG. 7B corresponds to Z2 in FIG. During this time, since the object temperature is constant, the impedance angle θ is constant. From time t2 to time t3, the distance between the eddy current sensor and the measurement object does not change, but since the object temperature changes, the sensor output and the impedance angle change. After time t3, the temperature of the object returns to the original temperature. At time t4, the distance between the eddy current sensor and the measurement object is the same as that before time t1, and the sensor output at that time corresponds to Z1 in FIG. Thereafter, at time t5, the distance between the eddy current sensor and the measurement object becomes short, and the sensor output at that time corresponds to Z3 in FIG.
Basically, the relationship between the output of the eddy current sensor and the temperature of the object to be measured can be expressed by a linear expression as in the expressions (5) and (6).
It is necessary to obtain in advance the relationship of the output depending on the distance between the eddy current sensor and the measurement object.

Next, a correction method for canceling the fluctuation of the eddy current sensor itself will be described.
In the eddy current sensor, the output of the eddy current sensor may fluctuate due to a change in use environment or a change with time of the eddy current sensor itself. If there is a fluctuation, the correspondence between the output of the eddy current sensor and the temperature of the object to be measured shifts, and there is a problem that an error occurs in the measured temperature.
FIG. 8 is a schematic diagram showing a correction method for canceling the fluctuation of the sensor itself, and is a schematic diagram in which a configuration in which the eddy current sensor can be moved is added to the relationship between the eddy current sensor and the measurement object shown in FIG. It is.

As shown in FIG. 8, the eddy current sensor 1 is moved and the following values are measured.
(1) Without metal film (xat, yat), (2) With metal film (xbt, ybt).
(3) Measure (1) and (2) above after an arbitrary time. t is the measurement time.
Sensor fluctuation values (δx, δy) are obtained based on vector values without metal film (xat, yat). When there is no metal film, the sensor output is essentially zero, but there may be an output over time, and the sensor output (xat, yat) is observed after a certain time.
For example, when the sensor value at the measurement time 1S is (xa1, ya1) and the sensor value at the measurement time 10S is (xa10, ya10), the sensor fluctuation value is represented by the following equation.
(Δx, δy) = (xa10−xa1, ya10−ya1)
The following correction is made by adding the fluctuation value (δx, δy) of the sensor itself to the measurement value (xbt, ybt) at the measurement time t after the measurement time 10S and canceling the fluctuation. I do.
Sensor output after correction = with metal film (xbt−δx, ybt−δy)

Next, a mode in which the temperature of the substrate being polished is measured using the eddy current sensor provided in the substrate holding apparatus of the present invention will be described.
When polishing a substrate such as a semiconductor wafer using a polishing apparatus, by pressing and sliding the substrate against a polishing pad on a polishing table with a predetermined polishing pressure, the temperature at the contact surface between the substrate and the polishing pad, That is, the polishing temperature increases. Controlling the polishing pressure is important for improving the polishing performance, but measuring and controlling the polishing temperature is also very important for improving the polishing performance. That is, since the polishing pad uses a resin material such as polyurethane foam, the polishing temperature changes the rigidity of the polishing pad and affects the planarization characteristics of the substrate. In addition, chemical mechanical polishing (CMP) is a method that uses a chemical reaction between the polishing liquid (polishing slurry) and the surface to be polished of the substrate, so that the polishing temperature affects the chemical properties of the polishing slurry. Effect. In addition, the polishing rate distribution varies depending on the polishing temperature, resulting in a decrease in yield, or a decrease in the polishing rate, leading to a decrease in productivity of the polishing apparatus. Further, if there is a temperature distribution in the plane of the substrate, the polishing performance in the plane will not be uniform.

In a polishing apparatus, an eddy current sensor is embedded in a polishing table, and during polishing, the polishing pressure is controlled while the film thickness of a metal film on a substrate is monitored by the eddy current sensor.
If an attempt is made to measure the temperature of the metal film on the substrate with an eddy current sensor installed on the polishing table during polishing, there is a problem that the temperature of the metal film cannot be measured because the film thickness of the metal film changes.
Therefore, in the present invention, an eddy current sensor is installed on the top ring for holding the substrate, and the temperature of the substrate is measured from the back side of the surface to be polished.

FIG. 9 is a schematic perspective view showing the overall configuration of a polishing apparatus to which the substrate holding apparatus of the present invention is applied. As shown in FIG. 9, the polishing apparatus includes a polishing table 41 that supports the polishing pad 42, and a top ring 51 that holds a substrate such as a semiconductor wafer as a polishing target and presses the polishing pad 42 on the polishing table 41. And a polishing liquid supply nozzle 43 for supplying a polishing liquid (slurry) onto the polishing pad 42.

  The top ring 51 is configured to hold a substrate such as a semiconductor wafer on its lower surface by vacuum suction. The top ring 51 and the polishing table 41 rotate in the same direction as indicated by arrows, and in this state, the top ring 51 presses the substrate against the polishing pad 42. The polishing liquid is supplied from the polishing liquid supply nozzle 43 onto the polishing pad 42, and the substrate is polished by sliding contact with the polishing pad 42 in the presence of the polishing liquid.

FIG. 10 is a schematic cross-sectional view showing details of the top ring 51 shown in FIG.
As shown in FIG. 10, the top ring 51 basically includes a top ring main body 52 that presses the substrate W against the polishing pad 42 and a retainer ring 53 that directly presses the polishing pad 42. An elastic film (membrane) 54 that is in contact with the back surface of a substrate such as a semiconductor wafer is attached to the lower surface of the top ring body 52. The elastic membrane (membrane) 54 is formed of a rubber material having excellent strength and durability, such as ethylene propylene rubber (EPDM), polyurethane rubber, and silicon rubber. The elastic film (membrane) 54 constitutes a substrate holding surface for holding a substrate such as a semiconductor wafer.

The elastic membrane (membrane) 54 has a plurality of concentric partition walls 54a. By these partition walls 54a, a circular center chamber 55 and an annular ripple are formed between the upper surface of the membrane 54 and the lower surface of the top ring body 52. A chamber 56, an annular outer chamber 57, and an annular edge chamber 58 are formed. That is, a center chamber 55 is formed at the center of the top ring body 52, and a ripple chamber 56, an outer chamber 57, and an edge chamber 58 are formed concentrically in order from the center toward the outer peripheral direction. In the top ring main body 52, a channel 61 communicating with the center chamber 55, a channel 62 communicating with the ripple chamber 56, a channel 63 communicating with the outer chamber 57, and a channel 64 communicating with the edge chamber 58 are formed. Has been. A flow path 61 communicating with the center chamber 55, a flow path 62 communicating with the ripple chamber 56, a flow path 63 communicating with the outer chamber 57, and a flow path 64 communicating with the edge chamber 58 include a pressure chamber pressurization line (see FIG. (Not shown).
In addition, a retainer ring pressure chamber 59 is also formed immediately above the retainer ring 53 by an elastic membrane (membrane) 70.

  As shown in FIG. 10, four eddy current sensors 1 are installed in the top ring body 52 of the top ring 51. Further, a metal film 65 having a high thermal conductivity is attached to the back surface side of the membrane 54 (the side opposite to the substrate holding surface) at a position facing each eddy current sensor 1. Since the metal film 65 has a high thermal conductivity, the metal film 65 becomes approximately equal to the temperature of each part of the membrane 54 to which the metal film 65 is attached during polishing. That is, the four eddy current sensors 1 are arranged so as to face the center chamber 55, the ripple chamber 56, the outer chamber 57, and the edge chamber 58, respectively, and membranes corresponding to the pressure chambers 55, 56, 57, 58, respectively. The temperature of each part 54 can be measured.

According to the present invention, the temperature of the membrane 54 can be measured by the eddy current sensor 1 through the metal film 65, and the substrate temperature can be indirectly measured based on the measured membrane temperature.
According to the polishing apparatus provided with the substrate holding device of the present invention, the pressure of each pressure chamber is changed using the temperature of each part of the substrate measured by the plurality of eddy current sensors 1 to control the polishing pressure of each part of the substrate. can do. That is, during polishing, the temperature measurement value of the substrate corresponding to one pressure chamber (for example, the center chamber 55) is higher than the temperature measurement value of the substrate corresponding to the other pressure chamber (for example, the ripple chamber 56). In this case, the pressure in one pressure chamber (center chamber 55) is reduced to suppress the temperature rise, or conversely, the pressure in the other pressure chamber (ripple chamber 56) is increased to increase the pressure chamber (ripple chamber 56). Promoting the temperature rise is performed. As a result, a desired polishing profile can be obtained by controlling the polishing rate.

In the embodiment, the case of measuring the temperature of the metal film has been described, but the eddy current sensor provided in the substrate holding device of the present invention can also measure the temperature of the conductive film.
Although the embodiment of the present invention has been described so far, the present invention is not limited to the above-described embodiment, and it is needless to say that the present invention may be implemented in various different forms within the scope of the technical idea.

DESCRIPTION OF SYMBOLS 1 Eddy current sensor 2 Measuring object 3 Base material part 4 Metal film 11 Sensor coil 12 Signal source 21 Excitation coil 22 Detection coil 23 Balance coil 25 Variable resistance 26 Resistance bridge circuit 30 Band pass filter 31 High frequency amplifier 32 Phase shift circuit 33 cos Synchronous detection circuit 34 sin synchronous detection circuit 35, 36 Low-pass filter 37 Vector arithmetic circuit 38 Vector arithmetic circuit 41 Polishing table 42 Polishing pad 43 Polishing liquid supply nozzle 51 Top ring 52 Top ring body 53 Retainer ring 54 Elastic membrane (membrane)
54a Bulkhead 55 Center chamber 56 Ripple chamber 57 Outer chamber 58 Edge chamber 59 Retainer ring pressure chamber 61, 62, 63, 64 Flow path 65 Metal film

Claims (6)

In the substrate holding device that holds the substrate and presses it against the polishing surface on the polishing table,
A top ring body that can move up and down to hold the substrate;
An elastic membrane fixed to the top ring body and forming a pressure chamber to which pressure fluid is supplied inside the top ring body;
A metal film or a conductive film provided on the back side of the surface holding the substrate in the elastic film;
A sensor coil disposed so as to face the metal film or the conductive film and disposed in the vicinity of the metal film or the conductive film , and an AC signal is supplied to the sensor coil so as to be applied to the metal film or the conductive film . An eddy current sensor comprising: a signal source that forms an eddy current; and a detection circuit that detects an eddy current formed on the metal film or the conductive film based on an output of the sensor coil. from the output, based on the relationship between the output of the temperature and the eddy current sensor in the material of the material and the material of the metal film or the conductive film, and a eddy current sensor for determining the temperature of the metal film or the conductive film A substrate holding device characterized by the above. 2. The substrate holding apparatus according to claim 1, wherein the eddy current sensor obtains in advance a relationship between a temperature of a material of the same material as the material of the metal film or the conductive film and an output of the eddy current sensor. 3. The substrate holding apparatus according to claim 1, wherein the output of the eddy current sensor includes an impedance component, and the temperature of the metal film or the conductive film is obtained from a change in the impedance component. The resistance component and the reactance component of the impedance component are displayed on an orthogonal coordinate axis, and an angle between a straight line connecting the impedance component coordinate and a preset reference point coordinate and a straight line parallel to the resistance component. 4. The substrate holding apparatus according to claim 3, wherein an impedance angle is obtained, and a temperature of the metal film or the conductive film is obtained from the impedance angle. The impedance angle is the same regardless of the distance between the eddy current sensor and the metal film or conductive film if the thickness of the metal film or conductive film is constant. 5. The substrate holding device according to 4. The eddy current sensor acquires a fluctuation value of the output of the eddy current sensor over time at a position where the metal film or the conductive film does not exist, and the metal film or the conductive film exists using the fluctuation value. 6. The substrate holding apparatus according to claim 1, wherein an output value of the eddy current sensor obtained at the position is corrected.

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