JP2012135865A - Eddy current sensor and polishing method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an eddy current sensor capable of detecting a metal thin film (or a conductive thin film) on a substrate such as a semiconductor wafer without increasing an oscillation frequency, the amplification degree of an internal circuit, and an exciting voltage, in the eddy current sensor.SOLUTION: In the eddy current sensor provided with a sensor coil 60 disposed in the vicinity of the substrate on which a metal film (or a conductive film) mf is formed, the sensor coil 60 has an oscillation coil 62 connected to a signal source, a detection coil 63 detecting an eddy current formed in the metal film or conductive film mf, and a balance coil 64 connected to the detection coil 63 in series, and the detection coil 63 comprises a coil formed by winding a wire rod or a conductive body by a single row and multiple layers, when the row is defined as a direction perpendicular to the substrate and the layer is defined as a direction parallel to the substrate.

Description

  The present invention relates to an eddy current sensor suitable for detecting a metal film (or conductive film) formed on the surface of a substrate such as a semiconductor wafer. The present invention also relates to a polishing method and apparatus for polishing a substrate and removing the metal film (or conductive film) while monitoring the metal film (or conductive film) formed on the surface of the substrate with an eddy current sensor. It is.

  In recent years, with higher integration and higher density of semiconductor devices, circuit wiring has become increasingly finer and the number of layers of multilayer wiring has increased. When trying to realize multilayer wiring while miniaturizing the circuit, the step becomes larger while following the surface unevenness of the lower layer, so as the number of wiring layers increases, the film coverage to the step shape in thin film formation (Step coverage) deteriorates. Therefore, in order to carry out multilayer wiring, it is necessary to improve the step coverage and perform a flattening process in an appropriate process. Further, since the depth of focus becomes shallower as the optical lithography becomes finer, it is necessary to planarize the surface of the semiconductor device so that the uneven steps on the surface of the semiconductor device are kept below the depth of focus.

Accordingly, in the semiconductor device manufacturing process, a planarization technique for the surface of the semiconductor device is becoming increasingly important. Among the planarization techniques, the most important technique is chemical mechanical polishing (CMP). This chemical mechanical polishing uses a polishing apparatus to slide a substrate such as a semiconductor wafer onto the polishing surface while supplying a polishing solution containing abrasive grains such as silica (SiO ₂ ) onto the polishing surface such as a polishing pad. Polishing in contact.

  When performing the above-described multilayer wiring, a groove for wiring having a predetermined pattern is formed in advance in an insulating layer (dielectric material) on the substrate, and the substrate is immersed in a plating solution, for example, electroless copper (Cu) or Electrolytic plating is performed to form a Cu layer, and then unnecessary portions are selectively removed leaving only the Cu layer formed in the wiring trench by a CMP process. In this case, if the polishing is inadequate and the Cu layer remains on the insulating layer (oxide film), circuit separation is not successful and a short circuit occurs. On the contrary, in the case of excessive polishing, if the Cu layer in the wiring groove is polished together with the insulating layer, the circuit resistance rises, and the entire semiconductor substrate must be discarded, resulting in great damage. This situation is the same when not only the Cu layer but also another metal film such as an Al layer is formed and this metal film is polished by a CMP process.

  A polishing apparatus that performs the above-described CMP process includes a polishing table having a polishing surface made of a polishing pad, and a substrate holding device called a top ring or a polishing head for holding a semiconductor wafer (substrate). . When a semiconductor wafer is polished using such a polishing apparatus, the semiconductor wafer is held by a substrate holding apparatus while pressing the semiconductor wafer against the polishing surface with a predetermined pressure to perform polishing. A metal film on the wafer is removed.

  After the polishing process, if the process proceeds to the next process with a metal remaining film in the semiconductor wafer, a problem such as a short circuit occurs and the semiconductor wafer cannot be used. Therefore, after completion of the polishing process, the remaining film can be confirmed by separating the wafer from the polishing pad (polishing surface) and inspecting for the presence of the metal remaining film. There is a problem that the processing capacity is reduced. If a residual film is detected on the wafer after inspection, re-polishing is required. However, if polishing is performed after the wafer leaves the polishing pad, the processing time per wafer increases. There is a problem of doing. That is, there is a problem that throughput is reduced.

  In order to solve the above-described problem that the throughput decreases due to the inspection of the metal residual film and the re-polishing after the inspection, the present applicant has previously filed Japanese Patent Application No. 2009-167788 (filed on July 16, 2009). ), The inspection time can be shortened by performing an inspection to determine whether there is a metal film (or conductive film) remaining on the substrate such as a semiconductor wafer during polishing. In some cases, a polishing method and a polishing apparatus were proposed that can reduce the processing time by performing additional polishing as it is.

JP 2006-255851 A

In the previously proposed Japanese Patent Application No. 2009-167788, an eddy current sensor that reacts with a metal film of Cu or the like formed on a substrate such as a semiconductor wafer is disposed in the polishing table, and the polishing table is being polished. The eddy current sensor reacts with the metal film on the substrate and outputs a predetermined voltage value as it passes under the substrate, and this output is monitored to detect that the metal film has been removed. I am doing so. In this case, in order to detect the metal thin film as the polishing progresses, the oscillation frequency of the eddy current sensor is increased, the amplification of the internal circuit of the eddy current sensor is increased, or the excitation voltage of the eddy current sensor is increased. By doing that.
However, when the oscillation frequency of the eddy current sensor is increased, there is a problem that the coil resonance frequency is lowered due to the capacitance of the coil itself. Further, when the amplification degree of the internal circuit of the eddy current sensor is increased, there is a problem that the influence of circuit noise becomes large. Further, when the excitation voltage of the eddy current sensor is increased, there is a problem in the stability of characteristics.

The present invention has been made in view of the above circumstances, and without increasing the oscillation frequency of the eddy current sensor, the amplification factor of the internal circuit, and the excitation voltage, a metal thin film (or conductive thin film) on a substrate such as a semiconductor wafer. An object of the present invention is to provide an eddy current sensor capable of detecting the
In addition, the present invention can shorten the inspection time by performing an inspection to determine whether there is a residual film of the metal film (or conductive film) on the substrate during polishing using an eddy current sensor, An object of the present invention is to provide a polishing method and a polishing apparatus capable of reducing the processing time by performing additional polishing as it is when a residual film is detected.

  In order to achieve the above object, an eddy current sensor according to the present invention comprises a sensor coil disposed in the vicinity of a substrate on which a metal film or a conductive film is formed, and an AC signal is supplied to the sensor coil to provide the metal film or An eddy current sensor comprising: a signal source that forms eddy current in a conductive film; and a detection circuit that detects eddy current formed in the metal film or the conductive film based on an output of the sensor coil, The sensor coil includes an oscillation coil connected to the signal source, a detection coil for detecting eddy current formed in the metal film or the conductive film, and a balance coil connected in series to the detection coil. The detection coil includes a coil in which a wire or a conductor is wound in a plurality of layers when a row is defined as a direction perpendicular to the substrate and a layer is defined as a direction parallel to the substrate. .

  According to the eddy current sensor of the present invention, the detection coil in the eddy current sensor is configured by a coil in which a wire or a conductor is wound in a plurality of layers, so that the detection coil can be brought close to the substrate, and the capacitance between the lines Since the component can be reduced, the sensor sensitivity is improved. Therefore, a metal thin film (or conductive thin film) on a substrate such as a semiconductor wafer can be detected without increasing the oscillation frequency of the eddy current sensor, the amplification factor of the internal circuit, and the excitation voltage. The detection coil is formed by spirally winding a plurality of layers of wires or conductors parallel to the surface of the semiconductor wafer (substrate) on which the metal film (or conductive film) is formed, thereby dividing the diameter of the wires or conductors in the column direction. However, the diameter of the wire or conductor may be flat in the column direction by bending the wire or conductor so as to gradually approach (or move away from) the substrate when winding a plurality of layers in a spiral shape. It may be a certain thickness.

According to a preferred aspect of the present invention, the oscillation coil is composed of a coil in which a wire or a conductor is wound in one row and a plurality of layers, or a coil in which a wire or a conductor is wound in a plurality of rows and one or more layers. To do.
According to the present invention, when the oscillation coil in the eddy current sensor is configured by a coil in which a wire or a conductor is wound in a plurality of layers, the oscillation frequency of the coil resonance frequency is improved. In addition, stable thin film detection becomes possible.
According to a preferred aspect of the present invention, the balance coil is formed of a coil in which a wire or a conductor is wound in a plurality of layers in one row.

According to a preferred aspect of the present invention, at least one of the detection coil, the oscillation coil, and the balance coil is configured by connecting a plurality of coils in which a wire or a conductor is wound in a plurality of layers in series. It is characterized by being.
According to the present invention, a plurality of coils in which a wire or a conductor is wound in a plurality of layers are arranged in the column direction, and a gap is formed between the coils so that adjacent coils do not come into contact with each other. Arrange the material. As a result, even if the coils wound in one row and multiple layers become a plurality of rows or multiple rows, the sensor coil can be brought close to the substrate, so that the sensor sensitivity is improved.
In addition, according to the present invention, by connecting a plurality of coils in one row and a plurality of layers in series, the combined inductance of the coils becomes the sum of the inductance for the plurality of coils and the mutual inductance between adjacent coils. As the combined inductance of the coil increases, the sensor output value of the entire coil increases, and the metal film can be detected satisfactorily.

According to a preferred aspect of the present invention, the oscillation coil is formed to be bent so as to approach the substrate as it goes outward in the radial direction.
According to the present invention, the oscillation coil is a coil in which the inner side in the radial direction is recessed toward the balance coil side and is bent into a concave spherical shape so as to approach the detection coil side toward the outer side in the radial direction and wound with a wire or a conductor. is there. Thus, by forming the oscillation coil into a concave spherical shape, the oscillation magnetic field can be converged at the center, and the sensor sensitivity can be increased.

According to a preferred aspect of the present invention, the detection coil and the oscillation coil may have different coil outer diameters.
According to the present invention, by making the outer diameter (diameter) of the detection coil smaller than the outer diameter (diameter) of the oscillation coil (excitation coil), it is possible to detect the metal film of the target finely.

According to a preferred aspect of the present invention, the detection coil, the oscillation coil, and the balance coil are arranged in this order from the substrate side.
According to the present invention, it is preferable that the sensor coil can automatically adjust the zero point of the detection output by the detection coil and the balance coil. By adjusting the zero point, only a change signal with respect to the thickness of the metal film (or conductive film) to be measured can be amplified and detected.

According to a preferred aspect of the present invention, the detection coil, the oscillation coil, and the balance coil are arranged concentrically.
According to the present invention, by arranging the detection coil, the oscillation coil, and the balance coil concentrically, the entire sensor coil can be arranged close to the substrate, and the sensor sensitivity is improved.

According to a preferred aspect of the present invention, the sensor coil is housed in a cylindrical member made of a high magnetic permeability material.
According to the present invention, the magnetic flux from the sensor coil passes through the cylindrical member of the high permeability material located around the sensor coil and passes through the metal film (or conductive film) to be measured (magnetic field). Road). Therefore, the magnetic flux does not pass through the members in the installation environment and is attenuated, and the eddy current due to the sensor coil can be efficiently generated inside the metal film (or conductive film) to be measured. A metal film (or conductive film) can be measured with high sensitivity.

  The polishing method of the present invention is a polishing method for polishing a film on a substrate by pressing a substrate to be polished against a polishing surface on a rotating polishing table, and during the polishing of the substrate, with the rotation of the polishing table, A polishing target surface of the substrate is scanned by an end point detection sensor installed on the polishing table, an output of the end point detection sensor obtained by scanning the polishing surface of the substrate is monitored, and a change in the output of the end point detection sensor After detecting the polishing end point, and detecting the polishing end point, the output of the end point detection sensor or a different sensor is monitored to monitor the remaining film on a part of the substrate, and the end point detection sensor Alternatively, an eddy current sensor is used for a different sensor. In the eddy current sensor, a coil for detecting an eddy current formed in a film on the substrate has a column perpendicular to the substrate and a layer parallel to the substrate. When defined, which comprises using a coil wound wire or conductor in a row a plurality of layers.

  According to the polishing method of the present invention, the end point detection sensor reacts with a film such as a metal film (or a conductive film) on the substrate while passing under the substrate along with the rotation of the polishing table. Since the value is output, the output of this end point detection sensor is monitored, and when the change in output reaches a preset film clear level, the polishing end point is detected. After detecting the polishing end point, the output of the end point detection sensor or a different sensor is monitored, and the remaining film is monitored to detect the remaining film on the substrate, thereby inspecting for the presence of the remaining film during polishing. Can be implemented. For the end point detection sensor or the different sensor, the coil can be brought close to the substrate by using a coil in which a wire or a conductor is wound in a plurality of layers, and the capacitance component between the lines can be reduced. The polishing end point or the remaining film can be reliably detected.

According to a preferred aspect of the present invention, the residual film monitoring is performed by the different sensor having higher sensitivity than the end point detection sensor, and the coil of the different sensor is wound with a wire or a conductor wound in one row and a plurality of layers. A coil is used.
According to the present invention, when only the end point detection sensor having a predetermined sensitivity from the start of polishing to the detection of the polishing end point and the remaining film monitoring is used, when the target film becomes thin or when the area of the film becomes small Makes it difficult to detect the membrane. On the other hand, when the polishing end point is detected using only the thin film sensor, if the initial film is thick, the output is overranged (out of the measurement range), so the polishing process cannot be monitored. . Therefore, in the present invention, two sensors having different sensitivities are used, the output is monitored from the start of polishing until the sensitivity of the end point detection sensor is lost, the polishing end point is detected, the polishing end point is detected, and then the different sensors are used. By switching, the remaining film on the substrate can be reliably detected.

According to a preferred aspect of the present invention, the residual film monitoring is performed by switching the sensitivity of the end point detection sensor, and the sensitivity switching is performed by switching the number of turns of the coil.
According to the present invention, when only the end point detection sensor having a predetermined sensitivity from the start of polishing to the detection of the polishing end point and the remaining film monitoring is used, when the target film becomes thin or when the area of the film becomes small Makes it difficult to detect the membrane. On the other hand, when the polishing end point is detected using only the thin film sensor, if the initial film is thick, the output is overranged (out of the measurement range), so the polishing process cannot be monitored. . Therefore, in the present invention, the sensor sensitivity of the end point detection sensor can be switched in two steps of high and low by switching the number of turns, and the output is overranged (measurement range) as low sensor sensitivity from the start of polishing to the detection of the polishing end point. The remaining film on the substrate can be reliably detected with high sensor sensitivity after the polishing end point is detected.

  According to a preferred aspect of the present invention, the remaining film monitoring is performed by the different sensor having higher sensitivity than the end point detection sensor, and the end point detection sensor and the different sensor form an eddy current in the film on the substrate. An eddy current sensor comprising a detection coil for detecting an eddy current formed on a film on a substrate and a balance coil connected in series to the detection coil, wherein the oscillating coil of the different sensor, As the detection coil and the balance coil, a coil in which a wire or a conductor is wound in a plurality of layers in one row is used.

The polishing apparatus of the present invention has a polishing table having a polishing surface and a top ring that holds a substrate to be polished, and polishes the film on the substrate by pressing the substrate against the polishing surface on the rotating polishing table. In the polishing apparatus, an end point detection sensor that is installed on the polishing table and scans the surface to be polished of the substrate as the polishing table rotates, and an output of the end point detection sensor obtained by scanning the surface to be polished of the substrate And a control device that detects a polishing end point from a change in the output of the end point detection sensor, the end point detection sensor comprising an eddy current sensor, and the eddy current formed in the film on the substrate in the eddy current sensor. The coil for detecting the line is composed of a coil in which a wire or a conductor is wound in a plurality of layers when a row is defined as a direction perpendicular to the substrate and a layer is defined as a direction parallel to the substrate.
According to the polishing apparatus of the present invention, the end point detection sensor reacts with a film such as a metal film (or a conductive film) on the substrate while passing under the substrate as the polishing table rotates. Since the value is output, the output of this end point detection sensor is monitored, and when the change in output reaches a preset film clear level, the polishing end point is detected. Since the coil of the end point detection sensor is constituted by a coil in which a wire or a conductor is wound in a plurality of layers, the coil can be brought close to the substrate, so that the sensor sensitivity is improved and the polishing end point can be detected reliably.

According to a preferred aspect of the present invention, the control device monitors the output of the end point detection sensor or a different sensor after detecting the polishing end point, and detects a film remaining on a part of the substrate. It is characterized by performing.
According to the present invention, after the polishing end point is detected, the output of the end point detection sensor or a different sensor is monitored, and the remaining film is monitored to detect the film remaining on a part of the substrate. Inspection can be performed for the presence or absence of

According to a preferred aspect of the present invention, the remaining film monitoring is performed by the different sensor composed of an eddy current sensor having higher sensitivity than the end point detection sensor, and the coil of the different sensor includes a plurality of rows of wires or conductors. It consists of a coil wound around.
According to the present invention, when only the end point detection sensor having a predetermined sensitivity from the start of polishing to the detection of the polishing end point and the remaining film monitoring is used, when the target film becomes thin or when the area of the film becomes small Makes it difficult to detect the membrane. On the other hand, when the polishing end point is detected using only the thin film sensor, if the initial film is thick, the output is overranged (out of the measurement range), so the polishing process cannot be monitored. . Therefore, in the present invention, two sensors having different sensitivities are used, the output is monitored from the start of polishing until the sensitivity of the end point detection sensor is lost, the polishing end point is detected, the polishing end point is detected, and then the different sensors are used. By switching, the remaining film on the substrate can be reliably detected. Since the coils of the different sensors are composed of coils in which wires or conductors are wound in a plurality of layers in one row, the coils can be brought close to the substrate, so that the sensitivity of the sensor is improved and the remaining film can be detected reliably.

According to a preferred aspect of the present invention, the residual film monitoring is performed by switching the sensitivity of the end point detection sensor, and the sensitivity switching is performed by switching the number of turns of the coil.
According to the present invention, when only the end point detection sensor having a predetermined sensitivity from the start of polishing to the detection of the polishing end point and the remaining film monitoring is used, when the target film becomes thin or when the area of the film becomes small Makes it difficult to detect the membrane. On the other hand, when the polishing end point is detected using only the thin film sensor, if the initial film is thick, the output is overranged (out of the measurement range), so the polishing process cannot be monitored. . Therefore, in the present invention, the sensor sensitivity of the end point detection sensor can be switched in two steps of high and low by switching the number of turns, and the output is overranged (measurement range) as low sensor sensitivity from the start of polishing to the detection of the polishing end point. The remaining film on the substrate can be reliably detected with high sensor sensitivity after the polishing end point is detected.

  According to a preferred aspect of the present invention, the end point detection sensor or the different sensor includes an oscillation coil for forming an eddy current in a film on the substrate and a detection coil for detecting an eddy current formed in the film on the substrate. It comprises an eddy current sensor provided with a sensor coil having a balance coil connected in series to the detection coil.

According to a preferred aspect of the present invention, the oscillation coil is composed of a coil in which a wire or a conductor is wound in one row and a plurality of layers, or a coil in which a wire or a conductor is wound in a plurality of rows and one or more layers. To do.
According to the present invention, when the oscillation coil in the eddy current sensor is configured by a coil in which a wire or a conductor is wound in a plurality of layers, the oscillation frequency of the coil resonance frequency is improved. In addition, stable thin film detection becomes possible.
According to a preferred aspect of the present invention, the balance coil is formed of a coil in which a wire or a conductor is wound in a plurality of layers in one row.

According to a preferred aspect of the present invention, at least one of the detection coil, the oscillation coil, and the balance coil is configured by connecting a plurality of coils in which a wire or a conductor is wound in a plurality of layers in series. It is characterized by being.
According to the present invention, a plurality of coils in which a wire or a conductor is wound in a plurality of layers are arranged in the column direction, and a gap is formed between the coils so that adjacent coils do not come into contact with each other. Arrange the material. As a result, even if the coils wound in one row and multiple layers become a plurality of rows or multiple rows, the sensor coil can be brought close to the substrate, so that the sensor sensitivity is improved.
In addition, according to the present invention, by connecting a plurality of coils in one row and a plurality of layers in series, the combined inductance of the coils becomes the sum of the inductance for the plurality of coils and the mutual inductance between adjacent coils. As the combined inductance of the coil increases, the sensor output value of the entire coil increases, and the metal film can be detected satisfactorily.

According to a preferred aspect of the present invention, the oscillation coil is formed to be bent so as to approach the substrate as it goes outward in the radial direction.
According to the present invention, the oscillation coil is a coil in which the inner side in the radial direction is recessed toward the balance coil side and is bent into a concave spherical shape so as to approach the detection coil side toward the outer side in the radial direction and wound with a wire or a conductor. is there. Thus, by forming the oscillation coil into a concave spherical shape, the oscillation magnetic field can be converged at the center, and the sensor sensitivity can be increased.

According to a preferred aspect of the present invention, the detection coil and the oscillation coil may have different coil outer diameters.
According to the present invention, by making the outer diameter (diameter) of the detection coil smaller than the outer diameter (diameter) of the oscillation coil (excitation coil), the size of the detection end of the sensor can be reduced, and the metal of the target Fine detection of the film becomes possible.

According to a preferred aspect of the present invention, the detection coil, the oscillation coil, and the balance coil are arranged in this order from the substrate side.
According to the present invention, it is preferable that the sensor coil can automatically adjust the zero point of the detection output by the detection coil and the balance coil. By adjusting the zero point, only a change signal with respect to the thickness of the metal film (or conductive film) to be measured can be amplified and detected.

According to a preferred aspect of the present invention, the detection coil, the oscillation coil, and the balance coil are arranged concentrically.
According to the present invention, by arranging the detection coil, the oscillation coil, and the balance coil concentrically, the entire sensor coil can be arranged close to the substrate, and the sensor sensitivity is improved.

According to a preferred aspect of the present invention, the sensor coil is housed in a cylindrical member made of a high magnetic permeability material.
According to the present invention, the magnetic flux from the sensor coil passes through the cylindrical member of the high permeability material located around the sensor coil and passes through the metal film (or conductive film) to be measured (magnetic field). Road). Therefore, the magnetic flux does not pass through the members in the installation environment and is attenuated, and the eddy current due to the sensor coil can be efficiently generated inside the metal film (or conductive film) to be measured. A metal film (or conductive film) can be measured with high sensitivity.

The present invention has the following effects.
(1) Since the detection coil in the eddy current sensor is composed of a coil in which a wire or a conductor is wound in one or more layers, the detection coil can be brought close to the substrate and the capacitance component between the lines can be reduced. Sensitivity is improved. Therefore, a metal thin film (or conductive thin film) on a substrate such as a semiconductor wafer can be detected without increasing the oscillation frequency of the eddy current sensor, the amplification factor of the internal circuit, and the excitation voltage.
(2) Since the oscillation coil in the eddy current sensor is composed of a coil in which a wire or a conductor is wound in a plurality of layers, since the oscillation frequency of the coil resonance frequency is improved, it is stable even if the oscillation frequency is increased. Thin film detection is possible.
(3) By connecting a plurality of coils in one row and multiple layers in series, the combined inductance of the coils becomes the sum of the inductance of the coils and the mutual inductance between adjacent coils. With the increase, the sensor output value of the entire coil increases, and the metal film can be detected satisfactorily.
(4) The inspection time can be shortened by performing an inspection to determine whether there is a remaining film such as a metal film (or conductive film) on the substrate such as a semiconductor wafer during polishing, and the substrate processing capability. Can be improved.
(5) Inspecting whether there is a residual film such as a metal film (or conductive film) on the substrate during polishing, and if the residual film is detected, processing is performed by performing additional polishing as it is. Time can be shortened.
(6) When a remaining film is detected by inspection during polishing, the controller that manages the entire CMP process manages the additional polishing time and the remaining film state, so that the polishing conditions for the next polishing object are optimized. It becomes possible to change to.
(7) It is possible to inspect whether there is a remaining film such as a metal film (or conductive film) on the substrate without separating the substrate such as a semiconductor wafer from the polishing surface (polishing pad).

FIG. 1 is a schematic diagram showing the overall configuration of a polishing apparatus according to the present invention. FIG. 2 is a plan view showing the relationship among the polishing table, the eddy current sensor, and the semiconductor wafer. FIG. 3 is a diagram showing the configuration of the eddy current sensor, FIG. 3 (a) is a block diagram showing the configuration of the eddy current sensor, and FIG. 3 (b) is an equivalent circuit diagram of the eddy current sensor. 4 (a), 4 (b), and 4 (c) are diagrams showing a comparison between the sensor coil of the conventional eddy current sensor and the sensor coil of the eddy current sensor of the present invention, and FIG. FIG. 4B is a schematic diagram illustrating a configuration example of a sensor coil used in the eddy current sensor of FIG. 4, and FIG. 4B is a schematic diagram illustrating a configuration example of the sensor coil of the eddy current sensor of the present invention. ) Is a schematic plan view showing a detection coil of the eddy current sensor of the present invention. FIGS. 5A and 5B are schematic views showing an aspect in which m coils in one row and N layers are connected in series. FIG. 6 is a schematic elevation view showing a positional relationship between a sensor coil of a conventional overcurrent sensor and a sensor coil of the eddy current sensor of the present invention and a semiconductor wafer (substrate). FIG. 7 is a schematic view showing another method of winding the sensor coil. FIG. 8 is a schematic view showing another method of winding the sensor coil. FIG. 9 is a schematic view showing another method of winding the sensor coil. FIG. 10 is a schematic view showing an example in which the oscillation coil is formed in a concave spherical shape. FIG. 11 is a schematic view showing an example in which a cylindrical member made of a high magnetic permeability material is arranged around the sensor coil shown in FIG. FIG. 12 is a schematic view showing an example in which solenoid winding and spiral winding are combined for the three coils of the sensor coil of the eddy current sensor. FIG. 13 is a schematic diagram showing an embodiment in which the diameters of the detection coil, oscillation coil (excitation coil), and balance coil (dummy coil) are changed. FIG. 14 is a schematic diagram showing an example in which three coils of the sensor coil of the eddy current sensor are arranged concentrically. FIG. 15 is a schematic diagram illustrating a connection example of each coil in the sensor coil. FIG. 16 is a block diagram showing a synchronous detection circuit of the eddy current sensor. FIG. 17 is a diagram showing a main configuration of a polishing apparatus provided with an eddy current sensor. FIG. 17A is a diagram showing an overall configuration including a control unit of the eddy current sensor, and FIG. It is an expanded sectional view of an eddy current sensor part. FIG. 18A is a diagram showing the relationship between the locus when the eddy current sensor scans the surface (surface to be polished) of the semiconductor wafer and the output of the eddy current sensor, and FIG. It is a figure which shows the output of the eddy current sensor in the case of a normal semiconductor wafer. FIG. 19A shows the relationship between the polishing process from the start of polishing of the semiconductor wafer until the metal film (or conductive film) on the semiconductor wafer is cleared (eliminated) and the output of the eddy current sensor. FIG. 19B shows a polishing time (t) from the start of polishing of the semiconductor wafer until the metal film (or conductive film) on the semiconductor wafer is cleared (eliminated) and an eddy current sensor. It is a figure which shows the relationship of the change of an output value. FIG. 20 is a flowchart showing the procedure of the polishing process and the monitoring process of the metal film (or conductive film) on the semiconductor wafer. FIGS. 21A and 21B are schematic plan views showing a method of configuring two sensors having different sensitivities by switching the number of turns of a coil using an eddy current sensor having three spirally wound coils. is there. FIG. 22 is a schematic diagram showing the timing of sensor switching in the method of increasing the sensor sensitivity for the purpose of detecting a metal thin film. FIG. 23 is a diagram showing a method of changing the monitoring method for the purpose of detecting a local residual film on the wafer. FIG. 23A shows all the sensor trajectories obtained by one scan. FIG. 23B shows a monitoring method using the output value of each measurement point on the sensor trajectory obtained by one scan, and FIG. 23B shows a monitoring method using the output value obtained by averaging the data of the measurement points. FIG. 23C is a graph showing a case where the monitoring method shown in FIG. 23A is switched to the monitoring method shown in FIG. FIG. 24 is a diagram showing the influence of metal wiring or the like on the lower layer of the wafer when detecting the occurrence of a local residual film by monitoring the output value of each measurement value obtained by the eddy current sensor. FIG. 24A shows a case where there is no influence of the lower layer of the wafer, and FIG. 24B shows a case where it is influenced by metal wiring or the like in the lower layer of the wafer. FIG. 25 is a schematic diagram showing a trajectory of the eddy current sensor scanning on the semiconductor wafer. FIG. 26 is a schematic diagram showing a trajectory of the eddy current sensor scanning on the semiconductor wafer. FIG. 27 is a schematic diagram showing a trajectory that the eddy current sensor scans on the semiconductor wafer. FIG. 28 is a schematic cross-sectional view showing a top ring provided with a plurality of pressure chambers that can be suitably used in the polishing apparatus of the present invention.

  Hereinafter, embodiments of a polishing apparatus according to the present invention will be described in detail with reference to FIGS. In FIG. 1 to FIG. 28, the same or corresponding components are denoted by the same reference numerals, and redundant description is omitted.

FIG. 1 is a schematic diagram showing the overall configuration of a polishing apparatus according to the present invention. As shown in FIG. 1, the polishing apparatus includes a polishing table 100 and a top ring 1 that holds a substrate such as a semiconductor wafer that is an object to be polished and presses the substrate against a polishing surface on the polishing table.
The polishing table 100 is connected to a motor (not shown) disposed below the table via a table shaft 100a, and is rotatable around the table shaft 100a. A polishing pad 101 is affixed to the upper surface of the polishing table 100, and the surface 101 a of the polishing pad 101 constitutes a polishing surface for polishing the semiconductor wafer W. 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 in the polishing table 100.

  The top ring 1 includes a top ring body 2 that presses the semiconductor wafer W against the polishing surface 101a, and a retainer ring 3 that holds the outer peripheral edge of the semiconductor wafer W so that the semiconductor wafer W does not jump out of the top ring. It basically consists of

The top ring 1 is connected to a top ring shaft 111, and the top ring shaft 111 moves up and down with respect to the top ring head 110 by a vertical movement mechanism 124. By moving the top ring shaft 111 up and down, the entire top ring 1 is moved up and down 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.
The vertical movement mechanism 124 that moves the top ring shaft 111 and the top ring 1 up and down 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 column 130. A support base 129 supported by the above-mentioned structure, and an AC servo motor 138 provided on the support base 129. A support base 129 that supports the servo motor 138 is fixed to the top ring head 110 via a support 130.

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

  The top ring shaft 111 is connected to the rotary cylinder 112 via a key (not shown). The rotating cylinder 112 includes a timing pulley 113 on the outer periphery thereof. A top ring motor 114 is fixed to the top ring head 110, and the timing pulley 113 is connected to a timing pulley 116 provided on the top ring motor 114 via a timing belt 115. Accordingly, when the top ring motor 114 is rotationally driven, the rotary cylinder 112 and the top ring shaft 111 rotate together via the timing pulley 116, the timing belt 115, and the timing pulley 113, and the top ring 1 rotates. The top ring head 110 is supported by a top ring head shaft 117 that is 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 W on its lower surface. The top ring head 110 is configured to be pivotable about a top ring shaft 117, and the top ring 1 holding the semiconductor wafer W on the lower surface thereof is rotated from the receiving position of the semiconductor wafer W by the rotation of the top ring head 110. Is moved above. Then, the top ring 1 is lowered to press the semiconductor wafer W 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 is supplied onto the polishing pad 101 from the polishing liquid supply nozzle 102 provided above the polishing table 100. Thus, the surface of the semiconductor wafer W is polished by bringing the semiconductor wafer W into sliding contact with the polishing surface 101a of the polishing pad 101.

FIG. 2 is a plan view showing the relationship among the polishing table 100, the eddy current sensor 50, and the semiconductor wafer W. As shown in FIG. As shown in FIG. 2, the eddy current sensor 50 is installed at a position passing through the center Cw of the semiconductor wafer W being polished held by the top ring 1. Reference symbol _CT denotes the rotation center of the polishing table 100. For example, the eddy current sensor 50 can continuously detect a metal film (conductive film) such as a Cu layer of the semiconductor wafer W on the passage locus (scanning line) while passing under the semiconductor wafer W. 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 FIGS.
FIG. 3 is a diagram illustrating the configuration of the eddy current sensor 50, FIG. 3A is a block diagram illustrating the configuration of the eddy current sensor 50, and FIG. 3B is an equivalent circuit diagram of the eddy current sensor 50. is there.
As shown in FIG. 3A, in the eddy current sensor 50, a sensor coil 60 is disposed in the vicinity of a metal film (or conductive film) mf to be detected, and an AC signal source 52 is connected to the coil. . Here, the metal film (or conductive film) mf to be detected is a thin film such as Cu, Al, Au, W formed on the semiconductor wafer W, for example. The sensor coil 60 is a detection coil, and is disposed 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.

In the eddy current sensor, an eddy current is generated in the metal film (or conductive film) mf, so that the oscillation frequency changes, and a frequency type for detecting the metal film (or conductive film) from this frequency change and an impedance are provided. There is an impedance type that changes and detects a metal film (or conductive film) from this impedance change. That is, in the frequency type, in the equivalent circuit shown in FIG. 3B, when the eddy current I ₂ changes, the impedance Z changes, and the oscillation frequency of the signal source (variable frequency oscillator) 52 changes. The change of the oscillation frequency can be detected at 54, and the change of the metal film (or conductive film) can be detected. The impedance type, in the equivalent circuit shown in FIG. 3 (b), by eddy current I ₂ is changed, the impedance Z is changed, the impedance Z is changed as viewed from the signal source (fixed frequency oscillator) 52, a detection circuit The change of the impedance Z can be detected at 54, and the change of the metal film (or conductive film) can be detected.

  In the impedance type eddy current sensor, signal outputs X, Y, phase, and combined impedance Z are taken out as will be described later. Measurement information of the metal film (or conductive film) Cu, Al, Au, W is obtained from the frequency F, impedance X, Y, or the like. As shown in FIG. 1, the eddy current sensor 50 can be built in a position near the inner surface of the polishing table 100, and is positioned so as to face a semiconductor wafer to be polished via a polishing pad. 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.

  The frequency of the eddy current sensor can be a single radio wave, a mixed radio wave, an AM modulated radio wave, an FM modulated radio wave, a swept output of a function generator or a plurality of oscillation frequency sources, adapted to the film type of the metal film, It is preferable to select an oscillation frequency or modulation method with good sensitivity.

The impedance type eddy current sensor will be specifically described below. The AC signal source 52 is an oscillator having a fixed frequency of about 2 to 8 MHz. For example, a crystal oscillator is used. The current I ₁ flows through the sensor coil 60 due to the AC voltage supplied from the AC signal source 52. When a current flows through the sensor coil 60 disposed in the vicinity of the metal film (or conductive film) mf, this magnetic flux is linked to the metal film (or conductive film) mf, thereby forming a mutual inductance M therebetween. is, eddy current I ₂ flows in the metal film (or conductive film) mf. 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. A metal film (or conductive film) mf 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 52 varies depending on the magnitude of eddy current loss formed in the metal film (or conductive film) mf.

  4 (a), 4 (b), and 4 (c) are diagrams showing a comparison between the sensor coil of the conventional eddy current sensor and the sensor coil of the eddy current sensor of the present invention. 4A is a schematic diagram showing a configuration example of a sensor coil used in a conventional eddy current sensor, and FIG. 4B is a schematic diagram showing a configuration example of the sensor coil of the eddy current sensor 50 of the present invention. FIG. 4 (c) is a schematic plan view showing a detection coil of the eddy current sensor 50 of the present invention.

  As shown in FIG. 4A, a sensor coil 51 of a conventional eddy current sensor includes a coil for forming an eddy current in a metal film (or conductive film), and an eddy current in the metal film (or conductive film). A coil for detecting current is separated from the coil, and is composed of three coils 72, 73 and 74 wound around a bobbin 71. In order to obtain the sensitivity of the sensor, it is necessary to increase the number of turns of the coil. Therefore, the three coils 72, 73, and 74 in the sensor coil 51 are defined when the column is defined as a direction perpendicular to the semiconductor wafer (substrate) W and the layer is defined as a direction parallel to the semiconductor wafer (substrate) W. The bobbin 71 is made of a coil in which the wire ln is solenoidally wound in five rows and two layers (10 turns) on the outer periphery of the bobbin 71. Here, the central coil 72 is an oscillation coil connected to the AC signal source 52. The oscillation coil 72 forms an eddy current in the metal film (or conductive film) mf on the semiconductor wafer (substrate) W disposed in the vicinity by a magnetic field generated by the voltage supplied from the AC signal source 52. A detection coil 73 is arranged on the metal film (or conductive film) side of the bobbin 71 to detect a magnetic field generated by an eddy current formed in the metal film (or conductive film). A balance coil 74 is disposed on the opposite side of the detection coil 73 with the oscillation coil 72 interposed therebetween.

  On the other hand, the sensor coil 60 of the eddy current sensor 50 of the present invention is composed of three coils 62, 63, 64 as shown in FIG. Not. The three coils 62, 63, 64 of the sensor coil 60 are wire rods ln when a column is defined as a direction perpendicular to the semiconductor wafer (substrate) W and a layer is defined as a direction parallel to the semiconductor wafer (substrate) W. Are coils each wound in a spiral with one row and N layer winding. More specifically, the three coils 62, 63, 64 are arranged in a direction perpendicular to the surface of the semiconductor wafer (substrate) W on which the metal film (or conductive film) is formed, and the layer is formed on the semiconductor wafer ( When the substrate is defined as a direction parallel to the surface on which the metal film (or conductive film) of W is formed, it is a coil in which the wire ln is wound in a spiral form with one row and N layers each. N is an integer of 2 or more. For example, N is 10 or more if the number of turns is equal to or greater than the conventional number. In the example shown in FIG. 4B, the coil has one row and 14 layers.

  Of the three coils 62, 63 and 64, the central coil 62 is an oscillation coil connected to the AC signal source 52. The oscillation coil 62 forms an eddy current in the metal film (or conductive film) mf on the semiconductor wafer W disposed in the vicinity by a magnetic field generated by the voltage supplied from the AC signal source 52. A detection coil 63 is disposed on the metal film (or conductive film) side of the oscillation coil 62 to detect a magnetic field generated by an eddy current formed in the metal film (or conductive film). A balance coil 64 is disposed on the opposite side of the detection coil 63 with the oscillation coil 62 interposed therebetween. A spacer S <b> 1 is disposed between the oscillation coil 62 and the detection coil 63 to keep the distance between the oscillation coil 62 and the detection coil 63 constant, and the oscillation coil is interposed between the oscillation coil 62 and the balance coil 64. A spacer S2 for keeping the distance between 62 and the balance coil 64 constant is disposed. A bobbin 61 is disposed adjacent to the balance coil 64. It should be noted that the distance between the oscillation coil 62 and the detection coil 63 and between the oscillation coil 62 and the balance coil 64 need only be wide, and in particular, only a space may be provided without providing a spacer.

  As shown in FIG. 4C, the detection coil 63 is composed of a coil in which a wire ln is wound in a spiral shape in the radial direction by one-row N-layer winding. The detection coil 63 is spirally wound with N layers of a wire rod ln parallel to the surface of the semiconductor wafer (substrate) on which the metal film (or conductive film) mf is formed. It may be flat because the thickness is only the diameter of the wire ln in the direction orthogonal to the wire, and so that the wire ln gradually approaches (or moves away from) the semiconductor wafer (substrate) W when winding the wire ln in N layers spirally. It may be bent to have a predetermined thickness from the diameter of the wire ln in the row direction. Although the detection coil 63 is illustrated in FIG. 4C, the oscillation coil 62 and the balance coil 64 have the same shape as in FIG.

  Further, each of the coils 62, 63, 64 in the sensor coil 60 may be configured by connecting m coils shown in FIG. 4C in which the wire ln is spirally wound with one row and N layer windings in series. . Here, m is an integer of 2 or more. When m coils in a row and N layers are connected in series, the capacitance component increases when the coils come into contact with each other. Therefore, m coils in a row and N layers are arranged in the row direction (perpendicular to the substrate). It is preferable to leave a gap between adjacent coils. Note that a material with low magnetic permeability may be provided in the gap.

ここで、ｋは結合係数、Ｌ_１Ａ，Ｌ_１Ｂは自己インダクタンス［Ｈ］である。
したがって、図５（ａ）に示す例では、合成インダクタンスは、Ｌ_０＝Ｌ_１Ａ＋Ｌ_１Ｂ＋２Ｍとなる。
図５（ｂ）に示す態様では、１列Ｎ層のコイルＡ，コイルＢ，コイルＣを直列に接続している。図５（ｂ）の態様では、コイル３列分のインダクタンスＬ_１Ａ＋Ｌ_１Ｂ＋Ｌ_１Ｃと、隣接するコイル間の相互インダクタンスＭ_１ＡＢ，Ｍ_１ＢＣ，Ｍ_１ＡＣが得られる。相互インダクタンスＭ_１ＡＢ，Ｍ_１ＢＣ，Ｍ_１ＡＣは次式になる。

ここで、ｋ_０，ｋ_１，ｋ_２は結合係数、Ｌ_１Ａ，Ｌ_１Ｂ，Ｌ_１Ｃは自己インダクタンスである。
したがって、図５（ｂ）に示す例では、合成インダクタンスは、Ｌ_０＝Ｌ_１Ａ＋Ｌ_１Ｂ＋Ｌ_１Ｃ＋２Ｍ_１ＡＢ＋２Ｍ_１ＢＣ＋２Ｍ_１ＡＣとなる。
図５（ａ），（ｂ）においては、１列Ｎ層のコイルを２個又は３個直列接続する場合を示したが、１列Ｎ層のコイルをｍ個直列に接続する場合には、コイルの合成インダクタンスＬ_０は、ｍ列分のインダクタンスとｍ列間の相互インダクタンスの和になるため、コイルの合成インダクタンスの上昇に伴い、コイル全体のセンサ出力値は増加することになり、検出を良好に行うことが可能となる。 FIGS. 5A and 5B are schematic views showing an aspect in which m coils in one row and N layers are connected in series.
In the embodiment shown in FIG. 5A, one row N layers of coils A and B are connected in series. 5A, the inductance L _1A + L _1B for two coils and the mutual inductance M between adjacent coils can be obtained. The mutual inductance M between adjacent coils is given by

Here, k is a coupling coefficient, and L _1A and L _1B are self-inductances [H].
Therefore, in the example shown in FIG. 5A, the combined inductance is L ₀ = L _1A + L _1B + 2M.
In the embodiment shown in FIG. 5B, one row N-layer coil A, coil B, and coil C are connected in series. In the mode shown in FIG. 5B, the inductances L _1A + L _1B + L _1C for three coils and the mutual inductances M _1AB , M _1BC and M _1AC between adjacent coils are obtained. The mutual inductances M _1AB , M _1BC , and M _1AC are as follows.

Here, k ₀ , k ₁ and k ₂ are coupling coefficients, and L _1A , L _1B and L _1C are self-inductances.
Therefore, in the example illustrated in FIG. 5B, the combined inductance is L ₀ = L _1A + L _1B + L _1C + 2M _1AB + 2M _1BC + 2M _1AC .
5 (a) and 5 (b) show the case where two or three coils in one row N layers are connected in series, but when m coils in one row N layers are connected in series, combined inductance L ₀ of the coil, since the sum of the mutual inductance between m columns partial inductance and m columns, with increasing total inductance of the coil, results in the sensor output value of the entire coil increases, the detection It is possible to perform well.

  In the example shown in FIGS. 5A and 5B, the number of coils connected in series can be appropriately selected by providing a changeover switch between coils in one row and N layers. Therefore, it is possible to perform optimum detection by switching the number of coils (number of columns) of the detection coil 63, the oscillation coil (excitation coil) 62, and the balance coil (dummy coil) 64 depending on the metal film or film thickness to be detected. It becomes. For example, when the metal film is thin or the metal resistance value is low, the number of coils (number of columns) can be increased. In FIGS. 5A and 5B, there is no space (gap) between the coils A, B, and C, but it is preferable to provide them. A material having a low dielectric constant may be disposed in this space (gap).

FIG. 6 is a schematic elevation view showing the positional relationship between the sensor coil 51 of the conventional overcurrent sensor and the sensor coil 60 of the eddy current sensor of the present invention and the semiconductor wafer (substrate). As shown in FIG. 6, when the detection end 51e of the conventional sensor coil 51 and the detection end 60e of the sensor coil 60 of the eddy current sensor of the present invention are arranged at the same height position, the eddy current sensor 50 of the present invention. The sensor coil 60 is characterized in that it can be disposed closer to the semiconductor wafer W than the sensor coil 51 of the conventional eddy current sensor.
In order to obtain the sensitivity of the sensor, it is necessary to increase the number of turns of the coil. The conventional solenoid-wound sensor coil 51 has five rows and two layers (10 turns) because the wire ln is wound around a bobbin (including an air core), and each coil 73, 72, 74 in the sensor coil 51 and the semiconductor wafer W The distance (L1, L2, L3) between is increased.
Since the sensor coil 60 of the present invention does not have to be wound around the bobbin, each coil 62, 63, 64 is wound in a spiral shape with one row of N layers, and each coil is wound in a thin state. It becomes possible to take a large number. Therefore, since the distance (L1, L2, L3) between each coil 63, 62, 64 and the semiconductor wafer W in the sensor coil 60 can be reduced, the sensor sensitivity is improved. Further, by increasing the number of turns, the L component is also increased, and the sensitivity is improved.

In the conventional solenoid winding method, the coil resonance frequency decreases as the number of turns increases, the capacitance component between the lines increases in parallel connection, and the resonance frequency cannot actually be increased. Can not do.
On the other hand, when the spiral winding of the present invention is carried out, the capacity component between the lines is connected in series and can be reduced because of the one-row N-layer winding. Then, it is possible to increase the number of windings, and it is possible to increase the resonance frequency and increase the oscillation frequency while keeping the L component high.
In FIGS. 4B and 4C, the spiral winding coil is illustrated, but the same effect can be obtained if it is not only spiral winding but also other winding methods as long as one row and N layers are wound. It is.

7 to 9 are schematic views showing other winding methods of the sensor coil having one row and N layers.
In the example shown in FIG. 7, the detection coil 63 is formed by winding a wire ln in a polygonal shape with one row and N layers. As shown in FIG. 7, the polygon may have a polygonal number that increases from the inside in the radial direction to the outside in the radial direction. May be the same.
In the example shown in FIG. 8, the detection coil 63 is formed by winding a wire ln in an elliptical shape with one row and N layers.
In the example shown in FIG. 9, detection is made of a pattern coil in which a conductor 1n is wound around one row N layer by applying a printed wiring PW in a spiral shape with one row N layer winding around a predetermined substrate BP. A coil 63 is formed. In addition to the printed wiring, the pattern coil in which the conductor 1n is wound in one row and N layer can be manufactured by etching or wire cutting a metal member (Cu film, Cu foil, Cu material, etc.). is there. The metal member may be made of other materials such as AL in addition to Cu.
In the examples shown in FIGS. 7 to 9, the various winding methods of the wire or the conductor ln are applied to the detection coil 63, but the present invention can be similarly applied to the oscillation coil 62 and the balance coil 64.

  FIG. 10 is a schematic diagram showing an example in which the shape of the oscillation coil 62 of the three coils 62, 63, 64 of the sensor coil 60 is formed in a concave spherical shape. As shown in FIG. 10, the oscillation coil 62 is a coil in which the inner side in the radial direction is recessed toward the balance coil side, and is wound into a concave spherical shape so as to approach the detection coil side toward the outer side in the radial direction. . Thus, by forming the oscillation coil 62 to be bent into a concave spherical shape, the oscillation magnetic field can be converged on the central portion, and the sensor sensitivity can be increased.

  FIG. 11 is a schematic view showing an example in which a cylindrical member made of a high magnetic permeability material is arranged around the sensor coil shown in FIG. As shown in FIG. 11, the bobbin 61 of the sensor coil 60 and the three coils 62, 63, 64 are surrounded by a cylindrical member 65 made of a high magnetic permeability material. The cylindrical member 65 is manufactured using, for example, a high permeability material (for example, ferrite, amorphous, permalloy, supermalloy, mu metal) having a relative permeability μ = 50, so that the environment around the sensor coil is air. It can pass 50 times more magnetic flux than some cases. In other words, it is possible to pass an equivalent magnetic flux within a thickness of 1/50 as compared with a case where it is installed in an environment surrounding an electrically insulating material such as a ceramic material.

  As shown in FIG. 11, by disposing a cylindrical member 65 made of a high magnetic permeability material around the sensor coil, even when the polishing table 100 is made of a conductive material such as stainless steel (SUS), The magnetic flux formed by supplying current to the oscillation coil 62 of the sensor coil 60 arranged in the cylindrical member 65 generates an eddy current in the polishing table to generate a magnetic flux path (magnetic path) having a magnitude necessary for measurement. ) Is not reduced, and a path for generating an effective eddy current in the metal film of the semiconductor wafer W can be taken. That is, the cylindrical member 65 functions as a path for spreading the magnetic flux generated by the oscillation coil 62 of the sensor coil 60 into the detection space on the semiconductor wafer W side without passing through the conductive base material of the polishing table 100. Can generate a large eddy current in the metal film (or conductive film) mf to be measured. For this reason, even when the polishing table 100 is made of a conductive material such as stainless steel (SUS), the same sensitivity as when it is made of a ceramic material (insulating material) such as SiC can be secured.

  FIG. 12 is a schematic diagram showing an example in which solenoid winding and spiral winding are combined for the three coils 62, 63, 64 of the sensor coil 60 of the eddy current sensor 50. By making the detection coil 63 spirally wound in one row and N layers, the detection coil 63 can be brought closer to the wafer, and the capacitance component between the lines can be connected in series to reduce the performance of the detection coil 63. Can be improved. Therefore, since the sensitivity of the detection coil 63 is improved, as shown in FIG. 12, even if the oscillation coil 62 is a conventional solenoid winding, the sensitivity is better than the conventional sensor. The oscillating coil 62 may be configured with a coil in which a wire or a conductor ln is solenoid-wound around an N-row 1 layer as an M layer. Here, M is an integer of 2 or more. When the coils in the N row 1 layer are made M layers, the capacitance component increases when the coils come into contact with each other. Therefore, M coils in the N row 1 layer are arranged in the layer direction (parallel to the substrate) and adjacent to each other. It is preferable to leave a gap between the coils to be made, and a material with low magnetic permeability may be provided in this gap. In addition, since the balance coil 64 constitutes a detection coil 63 and a bridge circuit (described later), it is preferable that both the coils 63 and 64 have the same characteristics. Therefore, as shown in FIG. 12, the balance coil 64 employs spiral winding.

Next, an embodiment that enables fine detection of a metal film by reducing the size (diameter) of the coil will be described.
FIG. 13 is a schematic view showing an embodiment in which the diameters (outer diameters) of the detection coil 63, the oscillation coil (excitation coil) 62, and the balance coil (dummy coil) 64 are changed. As shown in FIG. 13, the detection coil 63, the oscillation coil 62, and the balance coil 64 do not have to have the same diameter (outer diameter), and the oscillation coil 62, the detection coil 63, and the balance coil 64 have different diameters. May be. In the example shown in FIG. 13, the detection end of the sensor is made smaller by making the diameters of the detection coil 63 and the balance coil 64 smaller than the diameter of the oscillation coil 62. Thereby, the fine detection of the metal film of a target is attained.
As a method for reducing the diameter of the coil, it is conceivable to reduce the number of turns and to reduce the wire diameter (pattern width) and the distance between the wire materials (pattern).
Since the sensor output decreases as the coil becomes smaller, structurally, it is necessary to increase the oscillation coil (excitation coil) or increase the number of stages, but it is also possible to increase the excitation frequency or increase the excitation current. The output can be improved.

  The detection coil of one-row N-layer winding such as spiral winding, polygonal winding, elliptical winding, etc. shown in FIGS. 4 to 9 has a Colpitts circuit by connecting the detection coil and a capacitor in parallel to provide excitation and detection functions. It can also be used as a sensor for detecting the polishing end point from the change in the excitation frequency.

FIG. 14 is a schematic diagram showing an example in which three coils 62, 63, 64 of the sensor coil 60 of the eddy current sensor 50 are arranged concentrically.
As shown in FIG. 14, the three coils 62, 63, 64 of the sensor coil 60 of the eddy current sensor 50 are arranged concentrically. Of the three coils 62, 63, 64, the detection coil 63 is disposed on the outermost periphery, the coil 62 is disposed on the intermediate portion, and the balance coil 64 is disposed on the innermost periphery. Each of the three coils 62, 63, and 64 is a coil in which a wire or a conductor ln is spirally wound with one row and N layers, respectively, and can be integrally formed with printed wiring.
According to the sensor coil 60 in which the three coils 62, 63, 64 are arranged concentrically as shown in FIG. 14, the entire sensor coil is located at a distance L1 from the semiconductor wafer (substrate) W shown in FIG. The sensor sensitivity can be improved because they can be arranged close to each other.

FIG. 15 is a schematic diagram illustrating a connection example of each coil in the sensor coil. As shown in FIG. 15 (a), the coils 62, 63, 64 are formed by spiral winding coils in one row and N layers, and the detection coil 63 and the balance coil 64 are connected in mutually opposite phases.
As described above, the detection coil 63 and the balance coil 64 constitute an antiphase series circuit, and both ends thereof are connected to a resistance bridge circuit 77 including a variable resistor 76. The oscillation coil 62 is connected to the AC signal source 52 and generates an alternating magnetic flux, thereby forming an eddy current in the metal film (or conductive film) mf disposed in the vicinity. By adjusting the resistance value of the variable resistor 76, the output voltage of the series circuit composed of the coils 63 and 64 can be adjusted to zero when there is no metal film (or conductive film). The variable resistors 76 (VR ₁ , VR ₂ ) that enter the coils 63 and 64 in parallel are adjusted so that the signals of L ₁ and 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 ) (1)
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. 15C, the signals of L ₁ and L ₃ before adjustment (indicated by dotted lines in the figure) are made into signals of the same phase and amplitude (indicated by solid lines in the figure).

  When a metal film (or conductive film) is present in the vicinity of the detection coil 63, magnetic flux generated by eddy currents formed in the metal film (or conductive film) is chained to the detection coil 63 and the balance coil 64. However, since the detection coil 63 is arranged closer to the metal film (or the conductive film), the balance of the induced voltages generated in the coils 63 and 64 is lost, thereby causing the metal film (or the conductive film). ) Can be detected. That is, the zero point can be adjusted by separating the series circuit of the detection coil 63 and the balance coil 64 from the oscillation coil 62 connected to the AC signal source and adjusting the balance with a resistance bridge circuit. . Therefore, since it becomes possible to detect the eddy current flowing in the metal film (or conductive film) from the zero state, the detection sensitivity of the eddy current in the metal film (or conductive film) is enhanced. This makes it possible to detect the magnitude of the eddy current formed on the metal film (or conductive film) with a wide dynamic range.

FIG. 16 is a block diagram showing a synchronous detection circuit of the eddy current sensor.
FIG. 16 shows a measurement circuit example of the impedance Z when the sensor coil 60 side is viewed from the AC signal source 52 side. In the impedance Z measurement circuit shown in FIG. 16, a resistance component (R), a reactance component (X), an amplitude output (Z), and a phase output (tan ⁻¹ R / X) accompanying a change in film thickness can be extracted. it can.

  As described above, the signal source 52 that supplies an AC signal to the sensor coil 60 disposed in the vicinity of the semiconductor wafer W on which the metal film (or conductive film) mf to be detected is formed is a fixed crystal oscillator. A frequency oscillator, for example, supplies a voltage having a fixed frequency of 2 MHz or 8 MHz. The AC voltage formed by the signal source 52 is supplied to the sensor coil 60 via the band pass filter 82. A signal detected at the terminal of the sensor coil 60 passes through a high frequency amplifier 83 and a phase shift circuit 84, 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 85 and a sin synchronous detection circuit 86. It is taken out. Here, the oscillation signal formed by the signal source 52 is formed into two signals of the in-phase component (0 °) and the quadrature component (90 °) of the signal source 52 by the phase shift circuit 84, and the cos synchronous detection circuit 85. And the sin synchronous detection circuit 86, 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 87 and 88, the resistance component (R) output which is the cos synchronous detection output, and the reactance component (X which is the sin synchronous detection output) ) Output is taken out respectively. Also, the vector operation circuit 89 obtains an amplitude output (R ² + X ² ) ^1/2 from the resistance component (R) output and the reactance component (X) output. Similarly, the vector operation circuit 90 obtains a phase output (tan ⁻¹ R / X) from the resistance component output and the reactance component output. Here, various filters are provided in the 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 Hz, noise components mixed in the sensor signal being polished can be set. The metal film (or conductive film) to be measured can be measured with high accuracy by removing.

  FIG. 17 is a diagram showing a main configuration of a polishing apparatus provided with an eddy current sensor 50, and FIG. 17 (a) is a diagram showing an overall configuration including a control unit of the eddy current sensor 50, and FIG. ) Is an enlarged sectional view of the eddy current sensor portion. As shown in FIG. 17A, the polishing table 100 of the polishing apparatus is rotatable about its axis as indicated by an arrow. A preamplifier integrated sensor coil 60 including an AC signal source and a synchronous detection circuit is embedded in the polishing table 100. The connection cable of the sensor coil 60 passes through the table shaft 100a of the polishing table 100, passes through the rotary joint 150 provided at the shaft end of the table shaft 100a, and is connected to the control device (controller) via the main amplifier 55 by the cable. 56. Note that the sensor coil 60 may include the main amplifier 55 as an integral unit.

  Here, the control device 56 is provided with various filters for removing 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 Hz, noise components mixed in the sensor signal being polished can be set. The metal film (or conductive film) to be measured can be measured with high accuracy by removing.

  As shown in FIG. 17B, the polishing pad is peeled off by having a coating C of fluorine-based resin such as tetrafluoroethylene resin on the end surface of the eddy current sensor 50 embedded in the polishing table 100 on the polishing pad side. In some cases, both the polishing pad and the eddy current sensor can be prevented from coming off. Further, the end surface on the polishing pad side of the eddy current sensor is installed at a position recessed from 0 to 0.05 mm from the surface of the polishing table 100 (surface on the polishing pad side) made of a material such as SiC near the polishing pad 101, This prevents contact with the wafer during polishing. The difference in position between the polishing table surface and the eddy current sensor surface is preferably as small as possible, but in an actual apparatus, it is often set to about 0.02 mm. For this position adjustment, adjustment by a shim (thin plate) 151m or adjustment means by a screw is taken.

  Here, the rotary joint 150 that connects the sensor coil 60 and the control device 56 can transmit a signal even in the rotating portion, but the number of signal lines to be transmitted is limited. Therefore, the number of signal lines to be connected is limited to eight, and is limited to only the DC voltage source, the output signal line, and the transmission lines for various control signals. The sensor coil 60 can be switched at an oscillation frequency of 2 to 8 MHz, and the gain of the preamplifier can be switched according to the film quality to be polished.

Next, a method of detecting and monitoring a metal film (or conductive film) on a semiconductor wafer being polished in a polishing apparatus having an eddy current sensor configured as shown in FIGS. 1 to 17 will be described. .
FIG. 18A shows the relationship between the locus when the eddy current sensor 50 scans the surface (surface to be polished) of the semiconductor wafer W and the output of the eddy current sensor 50. As shown in FIG. 18A, the eddy current sensor 50 reacts to the metal film (or conductive film) mf of the semiconductor wafer W while passing under the semiconductor wafer W as the polishing table 100 rotates. Thus, a predetermined voltage value (V) is output.
FIG. 18B is a diagram showing the output of the eddy current sensor 50 in the case of a normal semiconductor wafer W. In FIG. 18B, the horizontal axis represents the polishing time (t), and the vertical axis represents the output value (voltage value) (V) of the eddy current sensor 50. As shown in FIG. 18B, in the case of a normal semiconductor wafer W, the eddy current sensor 50 outputs a substantially square pulse-like output (voltage) in response to the metal film (or conductive film) mf on the semiconductor wafer. Value).

  FIG. 19A shows the polishing process from the start of polishing of the semiconductor wafer W until the metal film (or conductive film) mf on the semiconductor wafer W is cleared (removed) and the output of the eddy current sensor 50. It is a figure which shows the relationship. As shown in FIG. 19A, immediately after the start of polishing of the semiconductor wafer W, since the metal film (or conductive film) mf is thick, the output of the eddy current sensor 50 increases. However, as the polishing proceeds, the metal film Since mf becomes thin, the output of the eddy current sensor 50 decreases. When the metal film mf is cleared (lost), the output value of the eddy current sensor 50 disappears.

FIG. 19B shows the polishing time (t) from the start of polishing of the semiconductor wafer W until the metal film (or conductive film) mf on the semiconductor wafer W is cleared (removed) and the eddy current sensor 50. It is a figure which shows the relationship of the change of an output value. When the polishing table 100 rotates once and the eddy current sensor 50 scans the surface (surface to be polished) of the semiconductor wafer W, the eddy current sensor 50 outputs a substantially square pulse output. Each time the eddy current sensor 50 scans the surface of the semiconductor wafer W once, the control device 56 (see FIG. 17) outputs an average value obtained by averaging the output values of the measurement points on the passage locus (scanning line). Output as. The control device 56 monitors the output value as the average value of each measurement point of the eddy current sensor 50 every time the polishing table 100 rotates once, and continues monitoring until the output value of the eddy current sensor 50 disappears.
FIG. 19B shows a change in the output value (average value) of the eddy current sensor 50 depending on the polishing time. As shown in FIG. 19B, by monitoring the output value of the eddy current sensor 50, it is possible to detect a state in which the metal film is uniformly cleared.

FIG. 20 is a flowchart showing the procedure of the polishing process and the monitoring process of the metal film (or conductive film) on the semiconductor wafer W.
As shown in FIG. 20, the polishing apparatus takes out the semiconductor wafer W from the wafer cassette and transfers it to the top ring 1, and presses the semiconductor wafer W against the polishing surface 101 a on the polishing table 100 by the top ring 1 to start polishing. . After starting the polishing, the controller 56 monitors the output value of the eddy current sensor 50, continues the polishing until the polishing end point is detected, and continues the process of monitoring the output value of the eddy current sensor 50. The detection of the polishing end point is to detect that the output value of the eddy current sensor 50 has reached the metal film clear level and to detect that there is no metal remaining film uniformly on the semiconductor wafer W. When the polishing end point is detected, the process shifts to the remaining film monitoring without separating the semiconductor wafer W from the polishing surface (polishing pad).
Residual film monitoring is performed by arbitrarily selecting the following method.
(1) Switching of sensor sensitivity of eddy current sensor (2) Switching of monitoring means The remaining film monitoring method of (1) and (2) will be described later.

  Next, information obtained by monitoring the remaining film is transmitted to a control device (process controller (not shown)) that controls the entire CMP process. The control device (process controller) for controlling the entire CMP process may be a single control device including the control device 56 or may be a control device different from the control device 56. The control device (process controller) determines whether or not it is necessary to perform additional polishing based on the information of the remaining film monitoring. If it is determined that additional polishing is necessary, the additional polishing is performed, the remaining film is monitored, and after confirming that there is no remaining film, the process proceeds to the cleaning process. On the other hand, when it is determined that the CMP process is abnormal, the polishing process is not performed, but a polishing profile abnormality notification is given, and then the process proceeds to the cleaning process. In the cleaning process, after removing the polished semiconductor wafer from the top ring 1, scrub cleaning, pure water cleaning, drying, and the like are performed by a cleaning machine in the polishing apparatus. When the cleaning process is completed, the polished semiconductor wafer W is collected into the wafer cassette.

Next, the remaining film monitoring and additional polishing in the flowchart shown in FIG. 20 will be further described.
Residual film monitoring is performed during water polishing or overpolishing after the main polishing process of the wafer. Here, the water polishing means that polishing is performed while reducing the surface pressure applied to the wafer while supplying pure water (water) to the polishing surface. Further, over polishing refers to a method of performing polishing while supplying slurry to a polished surface after detecting feature points.
The following method is used for monitoring the remaining film.
(1) A method for increasing the sensitivity of a sensor for the purpose of detecting a metal thin film (2) A method for detecting a region to be monitored in order to detect a local residual film from an average of the integrated values of point data. As a film monitoring method, (1) and (2) are arbitrarily combined. In this case, the local metal thin film can be detected by combining the methods (1) and (2).

Further, additional polishing when a residual film is detected is performed as follows.
As a means for performing additional polishing, when a residual film is detected during over polishing, the polishing time for over polishing is changed. In addition, when it is detected by the residual film monitoring that there is a residual film at a specific location on the wafer, additional polishing is performed by changing the pressure of the top ring at the detected specific location, or dedicated polishing conditions are set. And perform additional polishing. The additional polishing conditions are fed back to the polishing conditions when the subsequent semiconductor wafer is polished.

Next, among the above-mentioned residual film monitoring methods, a method that is implemented with increased sensor sensitivity for the purpose of metal thin film detection will be described.
When only a sensor (sensor A) having a predetermined sensitivity is used from the start of polishing to clearing the target metal film, the metal film of the target is thinned or the area of the metal film is reduced. Detection becomes difficult. On the other hand, when the polishing end point is detected using only the thin film sensor (sensor B), if the initial metal film is thick, the output becomes overrange (out of the measurement range). It cannot be monitored.
Therefore, in the present invention, two sensors A and B having different sensitivities are used, the output is monitored from the start of polishing until the sensitivity of the sensor A is lost, and after detecting the polishing end point, the sensor B is switched, Make sure there is no metal residue on the wafer. In this case, the sensor A uses an eddy current sensor including three solenoid-wound coils 72, 73, 74 shown in FIG. 4A, and the sensor B has a spiral winding shown in FIG. An eddy current sensor having three coils 62, 63, 64 is used. Thereby, the sensor A can be a sensor with low sensor sensitivity, and the sensor B can be a sensor with high sensor sensitivity.

Moreover, the eddy current sensor provided with three coils 62, 63, 64 of 1 row N layer windings, such as spiral winding, polygon winding, and elliptical winding shown in FIG.4 (b), FIG.7, FIG.8, FIG.9 etc. Two sensors A and B having different sensitivities can be configured by switching the number of turns of the coil using one of the two.
FIGS. 21A and 21B are schematic diagrams showing a method of configuring two sensors A and B having different sensitivities by switching the number of turns of a coil using an eddy current sensor having three spirally wound coils. It is a top view. 21A and 21B show a method for switching the number of turns of the detection coil 63, but the same switching method is used for the oscillation coil 62 and the balance coil 64. FIG.
As shown in FIG. 21 (a), input terminals T1 and T2 for energizing the spirally wound detection coil 63 are provided, and the input terminal T1 is connected to the outer peripheral side end 63oe of the detection coil 63, The terminal T2 is connected to the changeover switch SW. On the other hand, the inner peripheral end 63ie of the detection coil 63 is connected to the switching terminal TS1, and the intermediate parts 63m1 and 63m2 of the detection coil 63 are connected to the switching terminals TS2 and TS3, respectively.
As shown in FIG. 21 (b), input terminals T1 and T2 for energizing the spirally wound detection coil 63 are provided, and the input terminal T1 is connected to the inner peripheral side end 63ie of the detection coil 63. The input terminal T2 is connected to the changeover switch SW. On the other hand, the outer peripheral side end 63oe of the detection coil 63 is connected to the switching terminal TS1, and the intermediate portions 63m1 and 63m2 of the detection coil 63 are connected to the switching terminals TS2 and TS3, respectively.

  In the detection coil 63 configured as shown in FIGS. 21A and 21B, by connecting the changeover switch SW to the switching terminal TS1, the inner peripheral end 63ie of the detection coil 63 and the input terminal T1, T2 It becomes possible to energize between the outer end 63oe and the number of turns of the coil is maximized. Further, by connecting the changeover switch SW to the switching terminal TS2 or TS3, the intermediate portion 63m1 or 63m2 of the detection coil 63 and the outer peripheral end 63oe (or the inner peripheral end 63ie) from the input terminals T1 and T2 are connected. It becomes possible to energize in the meantime, and the number of turns of the coil is reduced. In this way, the sensor sensitivity can be changed by changing the number of turns of the coil in two steps or three steps, and the sensor A and the sensor can be changed by switching the number of turns of the coil using a single detection coil 63. B can be configured.

  Further, as shown in FIG. 12, an eddy current sensor including a sensor coil 60 in which a detection coil 63 and a balance coil 64 are spirally wound and an oscillation coil 62 is configured by solenoid winding is used as the sensor A, and FIG. An eddy current sensor having three spirally wound coils 62, 63, and 64 shown in FIG.

  FIG. 22 is a schematic diagram showing the timing of sensor switching in the method of increasing the sensor sensitivity for the purpose of detecting a metal thin film. As shown in FIG. 22, when the polishing of the semiconductor wafer W is started, the output of the sensor A is increased because the metal film (or conductive film) mf is thick, but the metal film mf becomes thinner as the polishing progresses. The output of sensor A decreases. When the wafer center metal film clear / wafer edge metal remaining film is present, the sensor A enters a state without sensor sensitivity. Therefore, the sensor A detects the polishing end point. After sensor A detects the polishing end point, it switches to sensor B. Since sensor B is set to be more sensitive than sensor A, the output value on the wafer edge side increases in a mountain shape and detects the state of “wafer center metal film clear / wafer edge metal remaining film”. it can.

Next, among the above-described residual film monitoring methods, a method for changing the monitoring technique for the purpose of detecting a local residual film on the wafer will be described.
From the monitoring by the output value that averaged the data of all the measurement points obtained in one scan used to detect the polishing end point in order to obtain information on the position of the remaining film generation, the size and film thickness of the remaining film Switch to monitoring by output value at each measurement point. In the case where the position of the remaining film does not extend over the entire circumference and is local, the output value changes when the remaining film passes on the locus of the sensor. The distance from the edge (or center) of the wafer can be grasped by grasping the change in the output value. In this case, the metal thin film can be monitored by switching the sensor sensitivity.

FIG. 23 is a diagram showing a method of changing the monitoring method for the purpose of detecting a local residual film on the wafer. FIG. 23A shows a monitoring method using an output value obtained by averaging data of all measurement points on the sensor trajectory obtained by one scan, and FIG. 23B is obtained by one scan. FIG. 23 (c) is a graph showing a case where the monitoring method shown in FIG. 23 (a) is switched to the monitoring method shown in FIG. 23 (b). It is. In FIG. 23 (c), the horizontal axis is the polishing time (t), and the vertical axis is the output value of the eddy current sensor.
As shown in FIG. 23A, each time the eddy current sensor 50 scans the surface of the semiconductor wafer, monitoring is performed using an output value obtained by averaging data measured at all measurement points. Then, as shown in FIG. 23C, the polishing end point is detected by monitoring the output value obtained by averaging the data of all the measurement points on the trajectory of the sensor A. When the polishing end point is detected by the sensor A, the metal film is at a clear level. In this case, the metal thin film having a small local area cannot be detected because the output value of the portion is averaged.

  Therefore, after detecting the polishing end point, the sensor B is switched to the sensor B having high sensitivity. As shown in FIG. 23B, the sensor B outputs an output value measured at each measurement point each time the sensor scans the surface of the semiconductor wafer once. Therefore, when the remaining film is generated, the output value of the sensor B becomes a mountain-shaped output value as shown in the lower part of FIG. 23B, and the metal thin film can be detected. In addition, it is possible to grasp the location where the remaining film is generated. That is, as shown in FIG. 23 (c), after the output value subjected to the averaging process of the sensor A is monitored and the polishing end point is detected, the measurement is switched to the sensor B having a high sensitivity, and each measurement not subjected to the averaging process in the sensor B is performed. By monitoring the output value, it is possible to detect the occurrence of a residual film having a small local area.

FIG. 24 is a diagram showing the influence of the metal wiring or the like on the lower layer of the wafer when the generation of a local residual film is detected by monitoring the output value of each measurement value obtained by the sensor B. FIG. 24A shows a case where there is no influence of the lower layer of the wafer, and FIG. 24B shows a case where it is influenced by metal wiring or the like in the lower layer of the wafer.
As described above, by using the sensor A and averaging the output on the trajectory of the sensor passing through the wafer surface, the influence of the metal wiring in the lower layer of the metal film can be avoided. On the other hand, since the sensor B outputs the output value measured at each measurement point, as shown in FIG. 24 (a), the output value of each measurement value that is not subjected to the averaging process of the sensor B is monitored. Generation of a residual film having a small area can be detected. However, since the output value of the sensor B is the output value of each measurement point, there is a possibility that the output value of the sensor B is affected by the metal wiring or the like under the metal film. Therefore, as shown in FIG. 24B, when there are many points where the output increases, it is determined that the influence is not caused by the remaining film but by the lower layer of the wafer.

Next, a description will be given of the fact that, when a remaining film is detected in the remaining film monitoring in the flowchart shown in FIG. 20, a method for performing additional polishing by CMP and a method for notifying an abnormality of a polishing profile can be selected. .
When the residual film is detected in the residual film monitoring, the metal thin film is usually removed by performing additional polishing. However, even when the flatness of the wafer is maintained by the additional polishing, the CMP process may be abnormal, so that it is possible to notify the polishing apparatus control device of the abnormality of the polishing profile. .

Next, the locus (scanning line) when the eddy current sensor 50 scans the surface of the semiconductor wafer will be described.
In the present invention, the top ring 1 and the top ring 1 are arranged such that the locus drawn by the eddy current sensor 50 on the semiconductor wafer W within a predetermined time (for example, within the moving average time) is distributed almost uniformly over the entire circumference of the surface of the semiconductor wafer W. The rotational speed ratio of the polishing table 100 is adjusted.
FIG. 25 is a schematic diagram showing a trajectory that the eddy current sensor 50 scans over the semiconductor wafer W. As shown in FIG. 25, the eddy current sensor 50 scans the surface (surface to be polished) of the semiconductor wafer W every time the polishing table 100 makes one rotation. A surface passing through the center Cw of the semiconductor wafer W (the center of the top ring shaft 111) is drawn to scan the surface to be polished of the semiconductor wafer W. By making the rotational speed of the top ring 1 different from the rotational speed of the polishing table 100, the locus of the eddy current sensor 50 on the surface of the semiconductor wafer W is scanned as the polishing table 100 rotates as shown in FIG. Lines SL ₁ , SL ₂ , SL ₃ ,. Even in this case, as described above, since the eddy current sensor 50 is disposed at a position passing through the center Cw of the semiconductor wafer W, the locus drawn by the eddy current sensor 50 passes through the center Cw of the semiconductor wafer W every time. .

FIG. 26 shows the locus on the semiconductor wafer drawn by the eddy current sensor 50 within the moving average time (5 seconds in this example), assuming that the rotation speed of the polishing table 100 is 70 min ⁻¹ and the rotation speed of the top ring 1 is 77 min ^−1. FIG. As shown in FIG. 26, under this condition, the trajectory of the eddy current sensor 50 rotates 36 degrees each time the polishing table 100 rotates, so that the sensor trajectory is only half a circle on the semiconductor wafer W after every five scans. Will rotate. Considering the curvature of the sensor trajectory, the eddy current sensor 50 scans the semiconductor wafer W six times within the moving average time, so that the eddy current sensor 50 scans the entire surface of the semiconductor wafer W almost evenly.

In the example described above, the case where the rotation speed of the top ring 1 is higher than the rotation speed of the polishing table 100 is shown, but the case where the rotation speed of the top ring 1 is slower than the rotation speed of the polishing table 100 (for example, the polishing table 100 the rotational speed of 70 min ^-1, rotation speed of the top ring 1 63min ^-1) also, only sensor locus rotates in the opposite direction, the eddy current sensor 50 within a predetermined time drawn to the surface of the semiconductor wafer W The locus is distributed over the entire circumference of the surface of the semiconductor wafer W, which is the same as the above example.

  In the above example, the case where the rotational speed ratio between the top ring 1 and the polishing table 100 is close to 1 has been described, but the rotational speed ratio is 0.5, 1.5, 2 or the like (multiple of 0.5). The same applies to cases close to each other. That is, when the rotational speed ratio between the top ring 1 and the polishing table 100 is 0.5, the sensor locus rotates 180 degrees each time the polishing table 100 rotates, and when viewed from the semiconductor wafer W, the eddy current sensor 50 rotates once. Every time, it moves on the same locus from the opposite direction.

Therefore, the rotational speed ratio between the top ring 1 and the polishing table 100 is slightly shifted from 0.5 (for example, the rotational speed of the top ring 1 is set to 36 min ⁻¹ and the rotational speed of the polishing table 100 is set to 70 min ⁻¹ ). If the sensor trajectory is rotated by (180 + α) degrees each time the table 100 is rotated, the sensor trajectory can be apparently shifted by α degrees. Accordingly, the sensor trajectory is approximately 0.5 times, or approximately N times, or approximately 0.5 + N times on the surface of the semiconductor wafer W within the moving average time (in other words, a multiple of 0.5, that is, 0.5 × N). It is only necessary to set α (that is, set the rotation speed ratio between the top ring 1 and the polishing table 100) so as to rotate by N times (N is a natural number).

  By making the locus drawn by the eddy current sensor 50 on the surface of the semiconductor wafer W approximately evenly distributed over the entire circumference within the moving average time, the rotational speed ratio can be selected in a wide range in consideration of adjustment of the moving average time. Make it possible. Therefore, it is possible to cope with a polishing process in which the rotation speed ratio between the top ring 1 and the polishing table 100 needs to be changed greatly depending on the characteristics of the polishing liquid (slurry).

  By the way, generally, the trajectory drawn on the semiconductor wafer W by the eddy current sensor 50 is curved as shown in FIG. 26 except when the rotational speed of the top ring 1 is exactly half of the rotational speed of the polishing table 100. Therefore, even if the locus drawn by the eddy current sensor 50 on the semiconductor wafer W is distributed over the entire circumference of the semiconductor wafer W within a predetermined time (for example, within the moving average time), the sensor locus is not necessarily strictly in the circumferential direction. It is not evenly distributed. In order to distribute the sensor trajectory strictly and uniformly in the circumferential direction of the semiconductor wafer W, the sensor trajectory needs to rotate exactly N times (N is a natural number) on the circumference of the semiconductor wafer W every predetermined time. . During this time, the eddy current sensor 50 scans the surface of the semiconductor wafer W in a uniform direction and direction in the circumferential direction over the entire circumference. In order to achieve this, for example, while the polishing table 100 is rotated a predetermined number of times (natural number), the polishing is performed so that the top ring 1 is rotated by a number (natural number) different from the number of rotations of the polishing table 100. The rotational speeds of the table 100 and the top ring 1 may be determined. Even in this case, since the sensor trajectory is curved as described above, it cannot be said that the sensor trajectory is distributed at equal intervals in the circumferential direction. However, if two sensor trajectories are considered in pairs, the sensor trajectory has an arbitrary radius. It can be considered that the positions are evenly distributed in the circumferential direction. FIG. 27 is an example showing this, and is a diagram showing a sensor locus on the semiconductor wafer W while the polishing table 100 rotates 10 times under the same conditions as FIG. As described above, the eddy current sensor 50 can acquire data reflecting the average of the entire surface of the semiconductor wafer W as compared with the above example.

  FIG. 28 is a schematic cross-sectional view showing a top ring provided with a plurality of pressure chambers that can be suitably used in the polishing apparatus of the present invention. The top ring 1 includes a circular elastic pad 142 that contacts the semiconductor wafer W and a chucking plate 144 that holds the elastic pad 142. The upper peripheral end of the elastic pad 142 is held by a chucking plate 144, and four pressure chambers (airbags) P1, P2, P3, and P4 are provided between the elastic pad 142 and the chucking plate 144. Yes. Pressurized fluid such as pressurized air is supplied to the pressure chambers P1, P2, P3, and P4 via fluid paths 152, 153, 154, and 155, respectively, or evacuated. The central pressure chamber P1 is circular, and the other pressure chambers P2, P3, P4 are annular. These pressure chambers P1, P2, P3, and P4 are arranged concentrically.

  The internal pressures of the pressure chambers P1, P2, P3, and P4 can be changed independently from each other by a pressure adjusting unit (not shown), whereby four regions of the semiconductor wafer W, that is, a central portion, an inner intermediate portion, The pressing force against the outer intermediate portion and the peripheral portion can be adjusted independently. In this example, the pressure chambers P1, P2, P3, and P4 constitute a pressing mechanism that presses the semiconductor wafer W independently of each other. The film thickness of the metal film (or conductive film) mf of the semiconductor wafer W being polished is measured by an eddy current sensor 50 (see FIG. 1) provided on the polishing table 100, and the film thickness in the radial direction of the semiconductor wafer W is measured. The distribution is acquired by the control device 56 (see FIG. 17). The control device 56 controls the internal pressure of the pressure chambers P1, P2, P3, and P4 according to the film thickness distribution. For example, the film thickness of the central portion of the metal film (or conductive film) mf on the semiconductor wafer W is increased. When the film thickness is thicker than the peripheral edge, the pressure in the pressure chamber P1 is increased higher than the pressure in the pressure chamber P4, and the polishing pressure at the center of the metal film (or conductive film) mf is increased to increase the polishing pressure at the peripheral edge. Achieve the desired polishing profile.

  Although the embodiments of the present invention have been described so far, it is needless to say that the present invention is not limited to the above-described embodiments and may be implemented in various forms within the scope of the technical idea.

DESCRIPTION OF SYMBOLS 1 Top ring 2 Top ring main body 3 Retainer ring 50 Eddy current sensor 52 AC signal source 54 Detection circuit 55 Main amplifier 56 Control apparatus (controller)
60 sensor coil 61 bobbin 62 oscillation coil 63 detection coil 64 balance coil 65 cylindrical member 76 variable resistor 77 resistance bridge circuit 82 band pass filter 83 high frequency amplifier 84 phase shift circuit 85 cos synchronous detection circuit 86 sin synchronous detection circuit 87, 88 low pass Filter 89 Vector arithmetic circuit 100 Polishing table 100a Table shaft 101 Polishing pad 101a Polishing surface 102 Polishing liquid supply nozzle 110 Top ring head 111 Top ring shaft 112 Rotating cylinder 113 Timing pulley 114 Top ring motor 115 Timing belt 116 Timing pulley 117 Top ring Head shaft 124 Vertical movement mechanism 125 Rotary joint 126 Bearing 128 Bridge 129 Support base 130 Post 132 Ball screw 1 8 AC servomotor 132a screw shaft 132b nut 142 elastic pad 144 chucking plate 150 rotary joint 151m shim (thin plate)
152 to 155 Fluid path W Semiconductor wafer mf Metal film (or conductive film)
P1 to P4 pressure chamber

Claims (26)

A sensor coil disposed in the vicinity of a substrate on which a metal film or a conductive film is formed; a signal source for supplying an AC signal to the sensor coil to form an eddy current in the metal film or the conductive film; and the sensor An eddy current sensor comprising a detection circuit for detecting an eddy current formed in the metal film or the conductive film based on an output of a coil,
The sensor coil includes an oscillation coil connected to the signal source, a detection coil for detecting eddy current formed in the metal film or the conductive film, and a balance coil connected in series to the detection coil. And
The detection coil is an eddy current comprising a coil in which a wire or a conductor is wound in a plurality of layers when a row is defined as a direction perpendicular to the substrate and a layer is defined as a direction parallel to the substrate. Sensor.   2. The eddy current sensor according to claim 1, wherein the oscillating coil comprises a coil in which a wire or a conductor is wound in a plurality of layers, or a coil in which a wire or a conductor is wound in a plurality of layers or one layer. .   The eddy current sensor according to claim 1, wherein the balance coil is a coil in which a wire or a conductor is wound in a plurality of layers in one row.   The at least one of the detection coil, the oscillation coil, and the balance coil is configured by connecting a plurality of coils each having a wire or a conductor wound in a plurality of layers in series. Item 4. The eddy current sensor according to any one of Items 1 to 3.   4. The eddy current sensor according to claim 1, wherein the oscillating coil is bent so as to approach the substrate as going outward in the radial direction. 5.   The eddy current sensor according to claim 1, wherein the detection coil and the oscillation coil have different coil outer diameters.   The eddy current sensor according to claim 1, wherein the detection coil, the oscillation coil, and the balance coil are arranged in this order from the substrate side.   The eddy current sensor according to any one of claims 1 to 6, wherein the detection coil, the oscillation coil, and the balance coil are arranged concentrically.   The eddy current sensor according to any one of claims 1 to 8, wherein the sensor coil is accommodated in a cylindrical member formed of a high magnetic permeability material. In a polishing method for polishing a film on a substrate by pressing a substrate to be polished against a polishing surface on a rotating polishing table,
During polishing of the substrate, along with the rotation of the polishing table, the polishing surface of the substrate is scanned by an end point detection sensor installed on the polishing table,
Monitoring the output of the end point detection sensor obtained by scanning the surface to be polished of the substrate, detecting the polishing end point from the change in the output of the end point detection sensor,
After detecting the polishing end point, monitor the output of the end point detection sensor or a different sensor, monitor the remaining film to detect the film remaining on a part of the substrate,
An eddy current sensor is used for the end point detection sensor or a different sensor. In the eddy current sensor, a coil is used to detect an eddy current formed on a film on a substrate, and a column is perpendicular to the substrate and a layer is disposed on the substrate. On the other hand, when defined as a parallel direction, a polishing method using a coil in which a wire or a conductor is wound in a plurality of layers in one row is used.   The residual film monitoring is performed by the different sensor having higher sensitivity than the end point detection sensor, and the coil of the different sensor uses the coil in which a wire or a conductor is wound in a plurality of layers. Item 11. The polishing method according to Item 10.   The polishing method according to claim 10, wherein the remaining film monitoring is performed by switching sensitivity of the end point detection sensor, and the sensitivity switching is performed by switching the number of turns of the coil.   The residual film monitoring is performed by the different sensor having higher sensitivity than the end point detection sensor. The end point detection sensor and the different sensor are provided on the oscillation coil and the film on the substrate for forming an eddy current in the film on the substrate. An eddy current sensor comprising a detection coil for detecting an eddy current formed and a balance coil connected in series to the detection coil, wherein the oscillation coil, the detection coil and the balance coil of the different sensors include The polishing method according to claim 10, wherein a coil in which a wire or a conductor is wound in a plurality of layers is used. In a polishing apparatus having a polishing table having a polishing surface and a top ring for holding a substrate to be polished, and polishing the film on the substrate by pressing the substrate against the polishing surface on the rotating polishing table,
An end point detection sensor that is installed on the polishing table and scans the surface to be polished of the substrate as the polishing table rotates;
A controller that monitors the output of the end point detection sensor obtained by scanning the surface to be polished of the substrate and detects the polishing end point from a change in the output of the end point detection sensor;
The end point detection sensor comprises an eddy current sensor, and the coil for detecting the eddy current formed in the film on the substrate in the eddy current sensor has a row perpendicular to the substrate and a layer parallel to the substrate. A polishing apparatus comprising a coil in which a wire or a conductor is wound in a plurality of layers in one row when defined.   The said control apparatus, after detecting the said polishing end point, monitors the output of the said end point detection sensor or a different sensor, and performs the residual film monitoring which detects the film | membrane which remained on a part on a board | substrate. 14. The polishing apparatus according to 14.   The residual film monitoring is performed by the different sensor composed of an eddy current sensor having higher sensitivity than the end point detection sensor, and the coil of the different sensor is composed of a coil in which a wire or a conductor is wound in a plurality of layers. The polishing apparatus according to claim 15.   The polishing apparatus according to claim 15, wherein the residual film monitoring is performed by switching sensitivity of the end point detection sensor, and the sensitivity switching is performed by switching the number of turns of the coil.   The end point detection sensor or the different sensor is connected in series to an oscillation coil for forming an eddy current in the film on the substrate, a detection coil for detecting an eddy current formed in the film on the substrate, and the detection coil. 16. The polishing apparatus according to claim 14, comprising an eddy current sensor including a sensor coil having a balance coil.   19. The polishing apparatus according to claim 18, wherein the oscillation coil includes a coil in which a wire or a conductor is wound in a plurality of layers in one row or a coil in which a wire or a conductor is wound in a plurality of rows in one layer or a plurality of layers.   The polishing apparatus according to claim 18, wherein the balance coil is a coil in which a wire or a conductor is wound in a plurality of layers in one row.   The at least one of the detection coil, the oscillation coil, and the balance coil is configured by connecting a plurality of coils each having a wire or a conductor wound in a plurality of layers in series. Item 21. The polishing apparatus according to any one of Items 18 to 20.   21. The polishing apparatus according to claim 18, wherein the oscillating coil is bent so as to approach the substrate as it goes radially outward.   The polishing apparatus according to any one of claims 18 to 22, wherein the detection coil and the oscillation coil have different coil outer diameters.   The polishing apparatus according to any one of claims 18 to 23, wherein the detection coil, the oscillation coil, and the balance coil are arranged in this order from the substrate side.   The polishing apparatus according to any one of claims 18 to 23, wherein the detection coil, the oscillation coil, and the balance coil are arranged concentrically.   The polishing apparatus according to any one of claims 18 to 25, wherein the sensor coil is accommodated in a cylindrical member made of a high magnetic permeability material.

Images