JP5377872B2 - Method and apparatus for predicting and detecting the end of polishing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for predicting and detecting a polishing end point capable of minimizing Joule heat loss by an eddy current, precisely uniformizing the surface of a wafer at the end of polishing by reliably detecting the change and changing finish polishing conditions even in a minute magnetic field not penetrating a device wafer, and precisely predicting and detecting a polishing end point. <P>SOLUTION: The method and the device for predicting and detecting a polishing end point bring an inductor 36 in a high-frequency inductor type sensor closer to a prescribed conductive film 28, monitor a change in magnetic flux induced in the prescribed conductive film 28 by magnetic flux formed by the inductor 36, detect a characteristic change based on a peculiar change in magnetic flux, when a film thickness during polishing becomes equal to or close to surface depth determined with the material of the prescribed conductive film 28 as one factor, and change the finish polishing conditions so that the in-plane surface of a wafer W at the end of polishing in the field becomes uniform from the characteristic change. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method and apparatus for predicting / detecting the end of polishing, and in particular, polishing while minimizing Joule heat loss due to eddy current in CMP (Chemical Mechanical Polishing) or the like. The present invention relates to a polishing end point prediction / detection method and apparatus capable of making the wafer inner surface at the end point uniform with high accuracy and predicting and detecting the polishing end point with high accuracy.

  For example, an oxide film is formed on the surface of the semiconductor wafer, and the oxide film is subjected to lithography and etching to form a groove pattern corresponding to the wiring pattern, and a conductive material made of Cu or the like for filling the groove pattern thereon. A process is known in which a film is formed, and unnecessary portions other than the buried portion such as the groove pattern and the through hole portion in the conductive film are removed by chemical mechanical polishing to form a wiring pattern. In the formation of this wiring pattern, it is extremely important to stop the process by reliably detecting the polishing end point when the unnecessary portion of the conductive film has been removed to an appropriate thickness. If the polishing of the conductive film is excessive, the resistance of the wiring increases, and if the polishing is insufficient, an insulation failure of the wiring is caused.

  As a conventional technique related to this, for example, the following in-situ monitoring method for a change in film thickness is known. This prior art is a method for in-situ monitoring of a change in thickness of a conductive film in a method of removing the conductive film from a base body (semiconductor wafer) by chemical mechanical polishing, and is directed to an electromagnetic field. A sensor including a series or parallel resonant circuit of an inductor and a capacitor formed of a coil wound around a ferrite pot type core for shaping so as to bring about a close proximity to the conductive film, and an excitation signal source A sweep output having a frequency of 20 Hz to 40.1 MHz is applied to the sensor via the operating point setting impedance means. Thus, when the sensor is excited, an oscillating current flows through the coil and generates an alternating electromagnetic field. This alternating electromagnetic field then induces eddy currents in the conductive film. When eddy currents are induced in the conductive film, two effects will occur. First, the conductive film acts as a loss resistance, the effect of which is a resistive load on the sensor circuit, which lowers the amplitude of the resonance signal and lowers the resonance frequency. Second, reducing the thickness of the conductive film has the effect of pulling the metal rod out of the inductor coil, thereby causing inductance changes as well as frequency shifts. In this way, the change in the thickness of the conductive film is continuously detected by monitoring the change in the frequency shift associated with the sensor resonance peak due to the change in the thickness of the conductive film. For example, see Patent Document 1).

  As another conventional technique, for example, the following method for planarizing the surface of a semiconductor wafer is known. The prior art includes a first step of identifying a plurality of regions in a polishing process that includes forming a plurality of regions on a wafer and including a plurality of polishing steps, respectively, and a target wafer thickness profile. A second step of polishing the wafer using a plurality of platen stations to obtain, a third step of determining a wafer thickness profile after polishing in the second step, and the target wafer thickness profile And a fourth step of calculating an updated polishing method based on the wafer thickness profile determined in the third step, and performing feedback control of the plurality of platen stations by the calculated updated polishing method. The wafer material removal speed is controlled to flatten the wafer surface (example) If, see Patent Document 2).

  As another conventional technique, for example, the following polishing profile or polishing amount prediction method is known. In this prior art, the top ring in the polishing apparatus has at least two pressing portions, and an arbitrary pressure can be applied to the object to be polished for each pressing portion, and such a polishing device is used. This is a method for predicting a polishing profile or a polishing amount when polishing an object to be polished. Then, during polishing, the pressing portion sets the back pressure at which the corresponding area of the polishing object is pressed, predicts the pressing force distribution at which the polishing object presses the polishing surface from the set back pressure, and then predicts The predicted value of the polishing profile or the polishing amount of the object to be polished is obtained from the pressed pressure distribution. In this way, flatness is obtained by polishing based on the predicted polishing profile or polishing amount (see, for example, Patent Document 3).

As another conventional technique, for example, the following polishing method is known. This prior art sets a polishing rate distribution and a target film thickness distribution of a polishing apparatus. On the other hand, the initial film thickness distribution of the film to be polished deposited on the wafer is measured, and the predicted film thickness distribution after polishing is calculated based on the initial film thickness distribution and the set polishing rate distribution. Next, the predicted film thickness distribution after the polishing is compared with the target film thickness distribution, and an optimum condition (an optimum pressure value for each region of the wafer and the polishing time) is calculated from the comparison result. Then, the polishing apparatus is feedback-controlled so as to satisfy the optimum conditions, thereby flattening the film to be polished (see, for example, Patent Document 4).
Japanese Patent No. 2878178. Japanese Patent Laying-Open No. 2005-520317. JP 2006-43873 A. JP2003-158108A.

  In the prior art described in Patent Document 1, a series or parallel resonance circuit of an inductor and a capacitor, which is a coil wound around a ferrite pot type core, is provided to provide directivity to an electromagnetic field in a sensor. . Then, a sweep output having a frequency of 20 Hz to 40.1 MHz is applied to the sensor in the initial stage of polishing, and a leakage magnetic flux penetrating the conductive film is generated by an alternating electromagnetic field generated from the coil, thereby causing the conduction. Large eddy current corresponding to the thickness of the conductive film is induced from the initial stage of polishing. In order to induce a large eddy current corresponding to the thickness of the conductive film, it is necessary to form a large alternating electromagnetic field, that is, a large magnetic flux that penetrates the conductive film, and the thickness of the conductive film changes. This monitoring is performed by using eddy currents induced in the conductive film from the beginning of polishing to the end of polishing. For this reason, it is necessary to penetrate the magnetic flux in the thickness direction of the conductive film while monitoring the change in film thickness. This is also clear from the fact that in the drawing of the publication according to Patent Document 1, magnetic flux lines penetrating through the conductive film are described in all conductive film portions.

  In general, a solid Cu film (conductive film) is the uppermost layer on the surface of the wafer in the initial stage of polishing. In order to induce eddy currents in all of these innocent Cu films, a very large leakage magnetic flux is required. However, the leakage magnetic flux induces eddy currents, which are eventually consumed as Joule heat in the form of eddy current loss. This Joule heat loss has a relatively small volume resistance with respect to the solid Cu film of the outermost layer, so heat generation is relatively small. However, in the already wired part, the wiring cross-sectional area is small and the volume resistance is small. Therefore, a large eddy current is induced by the penetrating magnetic flux, resulting in a large Joule heat loss locally. This develops into a problem that part of the wiring sometimes melts and breaks. This is a state of so-called induction heating, and in particular, a phenomenon that heat is trapped inside. In particular, in Cu wiring or the like, when Cu is heated, there is a concern that Cu diffuses into a barrier film such as Ta, or in some cases, Cu penetrates the barrier film and diffuses.

  In addition, when multiple layers of wiring are applied to the surface of the wafer, not only the surface Cu film is concerned, but the internal wiring that has already been processed is locally warmed to the surroundings. In some cases, the dopant which diffuses or forms p-type and n-type in the semiconductor substrate further diffuses and changes the characteristics of the in-substrate element. Even when no heat is generated, if excessive eddy current flows through the fine wiring, electromigration may occur and disconnection may occur.

  Furthermore, for example, when processing is performed under different polishing conditions when a predetermined residual film amount near the polishing end point is reached, it is difficult to determine whether the amount is a predetermined residual film amount. This is because it can be estimated from the change from the initial film thickness, but when the initial film thickness varies, the estimate of the predetermined remaining film amount varies. Regarding the determination near the end of polishing, if the gap between the sensor and the conductive film changes minutely due to polishing vibration, the stray capacitance of the entire sensor circuit system changes and the entire resonance frequency shifts. Therefore, even if the threshold value is set when the resonance frequency reaches a certain setting and the polishing end point is determined, if the resonance frequency shifts as a whole, the polishing end point by setting the threshold value Judgment becomes difficult. As described above, in the conventional method, even when the threshold value is set to a certain value at the resonance frequency that monotonously and continuously increases or decreases, the gap between the sensor and the conductive film changes slightly, In many cases, the waveform itself translates vertically as a whole due to the presence of any dielectric material, and as a result, the preset threshold value often does not make sense.

  In the prior art described in Patent Document 2, the platen station is fed back based on the comparison result between the target wafer thickness profile and the wafer thickness profile determined by polishing, and the wafer material removal speed is corrected to correct the wafer surface. Plans to flatten.

  In the prior art described in Patent Document 3, a predicted value of a polishing profile or a polishing amount of a polishing object is obtained, and the surface of the polishing object is flattened by polishing based on the predicted polishing profile or polishing amount. .

  In the prior art described in Patent Document 4, the initial film thickness distribution of the film to be polished is measured, and the predicted film thickness distribution after polishing is calculated based on the initial film thickness distribution and a preset polishing rate distribution. To do. Next, the predicted film thickness distribution based on this prediction is compared with the target film thickness distribution, and the polishing apparatus is feedback-controlled under the optimum condition calculated based on the comparison result, thereby flattening the film to be polished.

  As described above, in each of the conventional techniques described in Patent Documents 2 to 4, the wafer surface is flattened by feedback control of the polishing apparatus based on the data including the predicted value before the polishing.

  Therefore, without exerting a strong magnetic flux to the fine wiring formed in the film, as a result, the generation of eddy currents induced by electromagnetic induction is suppressed, the Joule heat loss due to eddy currents is minimized, and the sensor As a result, the amount of induced eddy current shifts as a whole due to the change in the gap between the conductive film and the intervening state of the dielectric material such as slurry, and the setting of the threshold changes drastically, making it difficult to detect. Even if the magnetic field is so small that it does not penetrate the device wafer, it can reliably detect characteristic changes based on a unique magnetic flux change when the film thickness during polishing is at or near the skin depth. Because of this characteristic change, the final polishing conditions can be changed on the spot to make the wafer inner surface at the end of polishing uniform with high accuracy and to accurately predict and detect the end of polishing. The technical problem to be solved is than arise for, the present invention aims to solve this problem.

The present invention has been proposed in order to achieve the above object, and the invention according to claim 1 is characterized in that the polishing end point when the predetermined conductive film is properly removed by polishing the conductive film is determined. A method for predicting and detecting the end point of polishing for predicting and detecting,
An inductor is brought close to the predetermined conductive film, and eddy currents induced in the predetermined conductive film by the magnetic flux formed by the inductor are monitored at a plurality of locations within the substrate surface to be polished, and polishing is in progress. Oite the thickness of the predetermined conductive film material in the vicinity of the skin depth determined as a factor,
Detecting a point at which the change in the eddy current reaches a maximum point at a plurality of locations in the substrate surface ,
Based on the time when the eddy current at each of the above points becomes the maximum point,
Provided is a prediction / detection method at the end of polishing, in which the pressure distribution condition applied to the substrate surface is changed so that the wafer inner surface at the end of polishing becomes a uniform surface.

  Until the predetermined conductive film reaches a film thickness corresponding to the skin depth by polishing, the magnetic flux induced in the predetermined conductive film passes through the region of the skin depth substantially parallel along the film surface. To do. When polishing progresses and the predetermined conductive film reaches a film thickness that is equal to or near the skin depth, leakage magnetic flux penetrating through the predetermined conductive film begins to be generated. This change in magnetic flux changes the amount of eddy current induced in the predetermined conductive film by electromagnetic induction. As the film thickness decreases, the leakage magnetic flux penetrating the film increases, so that the amount of eddy current induced gradually increases. Due to the eddy current generated in this wide area, a large mutual inductance is generated in the predetermined conductive film. This mutual inductance acts to reduce the self-inductance of the sensor circuit system in the inductance type sensor. Thus, at the initial stage, even if the conductive film is reduced, a constant eddy current is formed when the magnetic flux applied to the conductive film thickness is such that it does not penetrate the wafer. Thereafter, when the film thickness is further decreased to be equal to or less than the film thickness corresponding to the skin depth, a magnetic flux is generated in which a part of the magnetic flux penetrates the conductive film on the wafer and leaks to the back surface of the wafer. At this time, the eddy current induced in the film increases as the leakage magnetic flux increases. Next, although the eddy current formed on the wafer surface increases to a certain thickness, the conductive film itself that generates the eddy current decreases as the conductive film is further removed. The current decreases. As a result, the eddy current increases as the penetrating flux increases once in spite of the monotonous film thickness decreasing process, and then the deposition itself that generates eddy current decreases as the film thickness decreases further. Therefore, a maximum point appears in the mutual inductance corresponding to the induced eddy current. Due to the rapid decrease in eddy current, the mutual inductance also decreases rapidly, and the inductance of the sensor circuit system starts to increase. In this way, eddy current is generated after the predetermined conductive film has reached a film thickness equivalent to or near the skin depth due to the progress of polishing, and then the inductance of the sensor circuit system temporarily decreases due to the rapid decrease thereafter. After that, it starts to increase. Due to this behavior, a peak (inflection point) which is a characteristic change in the waveform of the resonance frequency oscillated from the inductor type sensor is generated. From this characteristic change, the final polishing conditions are changed and the polishing end point is predicted so that the inner surface of the wafer at the end of polishing becomes uniform on the spot.

  Since the peak, which is a characteristic change, appears at the film thickness corresponding to the skin depth, the setting of the threshold varies due to the overall shift of the induced eddy current amount as described above. There is no problem, and a peak constantly appears at a position corresponding to the remaining film thickness. In particular, when the conductive film is, for example, Cu, a peak appears in the vicinity of 710% of the remaining film of Cu. In the case of the W film, a peak appears at 2500 mm where the remaining film of W is a little thicker. This film thickness is different from the actual skin depth, but is a numerical value corresponding to the skin depth. The skin depth δ is an index that conveniently indicates the depth at which the intensity of the electromagnetic wave becomes 1 / e, but this peak position is determined by the conductivity, permeability, applied frequency, etc. of the material. Is also brought about by the skin effect. The present invention is a technique achieved by skillfully utilizing the characteristic change phenomenon that appears due to the skin effect of this material. In particular, since the wiring material has high conductivity in the CMP of the wiring material, the peak position appears as a sharp peak (maximum point) relatively near the end point (710 mm). For this reason, it is possible to detect the time point of changing the finish polishing conditions in a robust manner and to predict and detect the end point without being shaken by various disturbances.

  Further, the inductor type sensor does not monitor the film thickness by intentionally positively generating an eddy current in the film. In the conventional known sensor, the sensor coil is formed so as to have directivity so as to give a magnetic field that penetrates the conductive film. However, in the inductor type sensor according to the present invention, a planar inductor is used. Yes. Thus, the inductor is not intended to give directivity to the magnetic field but to appropriately diverge the magnetic field with respect to the conductive film so as not to penetrate deeply into the conductive film. This is because when the magnetic field penetrates deeply, or when a strong magnetic field is applied to deeply penetrate the magnetic field, the internal wiring is locally overheated by eddy currents, or by electromigration or the like, the wiring itself This is because the wire breaks. Therefore, the planar inductor has an appropriate magnetic flux distribution that does not penetrate the conductive film as much as possible, in other words, does not generate an eddy current that damages the element formed on the wafer. In addition, when the conductive film becomes thin just before the conductive film is removed, even if a magnetic field that causes a moderate divergence is applied, a magnetic flux that partially penetrates the conductive film appears. The rapid change that appears when the state of the thin conductive film near the end point is reached is monitored. Therefore, the algorithm for detecting the frequency, inductor and its signal is configured to maximize the inflection point near the end point.

According to the first aspect of the present invention, an inductor in an inductor type sensor is brought close to a predetermined conductive film, a change in magnetic flux induced in the predetermined conductive film is monitored by a magnetic flux formed by the inductor, and polishing is performed. A characteristic change is detected based on a unique magnetic flux change when the film thickness is equal to or near the skin depth determined by the material of the predetermined conductive film as a factor, and the characteristic change is detected based on the characteristic change. Since the final polishing conditions in the polishing are changed so that the inner surface of the wafer at the end of polishing in the field becomes a uniform surface, the magnetic flux induced in a predetermined conductive film at the initial stage of polishing is It passes through the region of depth almost parallel along the film surface. Thereby, strong magnetic flux is not exerted to the fine wiring etc. formed in the film, and generation of eddy current is suppressed, and Joule heat loss due to the eddy current can be minimized. After the predetermined conductive film has reached a thickness corresponding to the skin depth due to the progress of polishing, a leakage magnetic flux penetrating the predetermined conductive film is generated, and this leakage magnetic flux causes a vortex in the predetermined conductive film. A current is induced. This eddy current gradually increases as the leakage magnetic flux increases as the film thickness decreases, and rapidly decreases because the conductive film itself that generates the eddy current decreases as the film thickness further decreases. Due to this increase in eddy current and subsequent rapid decrease, the inductance of the sensor circuit system once decreases and then increases. Due to this behavior, a waveform of the resonance frequency oscillated from the inductor type sensor, in other words, a peak (inflection point) which is a characteristic change in the magnetic flux induced in the predetermined conductive film is generated. Then, a peak (inflection point), which is a characteristic change, constantly appears at a position corresponding to the remaining film thickness without being fluctuated by various disturbances. For this reason, it is possible to change the final polishing conditions on the spot from a characteristic change and make the wafer inner surface at the end of polishing uniform with high accuracy.
As a result, waste wafers can be reduced. In addition, there is an advantage that the polishing end point can be accurately predicted and detected.

  Without exerting a strong magnetic flux to the fine wiring formed in the film, the generation of eddy currents induced by electromagnetic induction is suppressed as a result. Device, the amount of induced eddy current shifts as a whole due to the change in the gap of the conductive film and the intervening state of the dielectric material such as slurry, and the threshold setting changes drastically. Even with a minute magnetic field that does not penetrate the wafer, a characteristic change is reliably detected based on a unique magnetic flux change when the film thickness during polishing is equal to or near the skin depth. By changing the finish polishing conditions on the spot from the characteristic changes, the wafer inner surface at the end of polishing is made uniform with high accuracy, and the end point of polishing is predicted and detected accurately. In order to achieve the target, a polishing end point prediction / detection method for polishing and predicting a polishing end point when a predetermined conductive film is properly removed by polishing a conductive film, An inductor in a high-frequency inductor type sensor is brought close to a predetermined conductive film, and a change in magnetic flux induced in the predetermined conductive film by a magnetic flux formed by the inductor is monitored. A characteristic change is detected on the basis of a unique magnetic flux change when it is equal to or near the skin depth determined by the material of the conductive film as a factor, and the wafer at the end of polishing in situ from the characteristic change This was realized by changing the final polishing conditions in the polishing so that the in-plane surface was uniform.

  Hereinafter, the method and apparatus for predicting and detecting the end point of polishing according to Embodiment 1 of the present invention will be described in detail with reference to the drawings. 1 is a perspective view of a chemical mechanical polishing apparatus in which a prediction / detection device at the end of polishing is incorporated, FIG. 2 is an enlarged longitudinal sectional view of a polishing head, and FIG. 3 is an illustration of a prediction / detection device at the end of polishing in a platen. FIG. 4 is a partially cutaway schematic side view for explaining a state where the prediction / detection device at the time of completion of polishing is incorporated in the polishing head. It is.

  First, a method for predicting and detecting the end of polishing according to this embodiment and the configuration of the apparatus will be described from the configuration of a chemical mechanical polishing apparatus applied thereto. In FIG. 1, the chemical mechanical polishing apparatus 1 mainly includes a platen 2 and a polishing head 3. The platen 2 is formed in a disk shape, and a rotary shaft 4 is connected to the center of the lower surface thereof. The platen 2 rotates in the direction of arrow A when the motor 5 is driven. A polishing pad 6 is attached to the upper surface of the platen 2, and a slurry that is a mixture of an abrasive and a chemical is supplied onto the polishing pad 6 from a nozzle (not shown).

  As shown in FIG. 2A, the polishing head 3 is mainly composed of a head body 7, a carrier 8, a retainer ring 9, a retainer ring pressing means 10, an elastic sheet 11, a carrier pressing means 16, and control means such as air. Has been.

  The head body 7 is formed in a disk shape smaller than the platen 2, and a rotary shaft 12 (see FIG. 1) is connected to the center of the upper surface thereof. The head body 7 is attached to the rotary shaft 12 and is driven by a motor (not shown) to rotate in the direction of arrow B in FIG.

  The carrier 8 is formed in a disc shape, and is disposed in the center of the head body 7. A dry plate 13 is provided between the center of the upper surface of the carrier 8 and the lower center of the head body 7, and rotation is transmitted from the head body 7 via the pins 14 and 14.

  An operating transformer main body 15a is fixed between the center lower part of the dry plate 13 and the center upper part of the carrier 8, and the core 15b of the operating transformer 15 is fixed to the center upper part of the carrier 8 and is not shown. A polishing state signal of a conductive film made of Cu or the like connected to the control unit and formed on the wafer W (lower side in FIG. 2) is output to the control unit.

  A carrier pressing member 16a is provided at the peripheral edge of the upper surface of the carrier 8, and a pressing force is transmitted from the carrier pressing means 16 to the carrier 8 through the carrier pressing member 16a.

  An air outlet 19 for injecting air from the air float line 17 to the elastic sheet 11 is provided on the lower surface of the carrier 8. The air float line 17 is connected to an air supply pump 21 which is an air supply source through an air filter 20 and an automatic opening / closing valve V1. Air is blown out from the air outlet 19 by switching the automatic opening / closing valve V1.

  A hole 22 is formed in the lower surface of the carrier 8 for blowing out vacuum and, if necessary, DIW (pure water) or air. The suction of the air is executed by driving the vacuum pump 23, and an automatic opening / closing valve V2 is provided in the vacuum line 24. By switching the automatic opening / closing valve V2, the supply of vacuum and DIW is executed via the vacuum line 24. Is done.

  Air supply from the air float line 17, vacuum action from the vacuum line 24, DIW supply and the like are executed by command signals from the control unit.

  The carrier pressing means 16 is disposed at the peripheral edge of the central portion of the lower surface of the head main body 7 and applies a pressing force to the carrier pressing member 16a, thereby transmitting the pressing force to the carrier 8 coupled thereto. The carrier pressing means 16 is preferably composed of a rubber sheet airbag 25 that expands and contracts by air intake and exhaust. The air bag 25 is connected to an air supply mechanism (not shown) for supplying air.

  The retainer ring 9 is formed in a ring shape and disposed on the outer periphery of the carrier 8. The retainer ring 9 is attached to a retainer ring holder 27 provided in the polishing head 3, and the elastic sheet 11 is stretched on the inner peripheral portion thereof.

  The elastic sheet 11 is formed in a circular shape, and a plurality of holes 22 are opened. The elastic sheet 11 is stretched on the inner side of the retainer ring 9 by sandwiching the peripheral portion between the retainer ring 9 and the retainer ring holder 27.

  An air chamber 29 is formed between the carrier 8 and the elastic sheet 11 below the carrier 8 on which the elastic sheet 11 is stretched. The wafer W on which the conductive film is formed is pressed against the carrier 8 through the air chamber 29. The retainer ring holder 27 is attached to an attachment member 30 formed in a ring shape via a snap ring 31. A retainer ring pressing member 10 a is connected to the mounting member 30. The retainer ring 9 is transmitted with the pressing force from the retainer ring pressing means 10 via the retainer ring pressing member 10a.

  The retainer ring pressing means 10 is disposed on the outer peripheral portion of the lower surface of the head body 7, and applies a pressing force to the retainer ring pressing member 10 a to press the retainer ring 9 coupled thereto against the polishing pad 6. The retainer ring pressing means 10 is preferably constituted by a rubber sheet airbag 16b, similar to the carrier pressing means 16. An air supply mechanism (not shown) for supplying air is connected to the airbag 16b.

    The polishing head 3 as shown in FIGS. 2 (b) and 2 (c) has a double pressing force printing structure, and the average pressing force of the entire workpiece is set by pressing the first stage, This is a structure in which the pressing force distribution is changed by the second-stage pressing force mechanism.

  The first-stage pressing is a pressing to which the pressing force is transmitted from the carrier pressing means 16 via the carrier pressing member 16a around the upper surface of the carrier 8 in FIG.

  The second-stage pressing includes a fluid ejection portion that ejects a fluid that applies a pressing force to the surface of the workpiece, and the pressing force on the surface of the workpiece is partially changed corresponding to the fluid ejection portion. It is possible to make it. A fluid supply mechanism (not shown) for supplying fluid is connected.

  Even if the pressing force is changed by the second-stage pressing force mechanism, the average pressure of the entire workpiece does not change. Therefore, if the first-stage pressing force is set, the average pressing force applied to the entire workpiece is constant and stable. Then, when the pressing force distribution is set by the second-stage pressing mechanism, the distribution of the polishing rate within the workpiece is determined while the overall average polishing rate is kept constant.

  Since it has a double pressing force printing structure, it is possible to easily perform setting for obtaining a desired polishing rate distribution while partially changing the pressing force.

  The present invention can be applied to a case where the polishing amount is partially varied by using a polishing apparatus having a double pressing force portion printing pressure structure and capable of partially changing the pressing force.

  As shown in FIG. 2C, the region is divided into P to U regions according to the radius. In the areas of Q, R, T, and U, fluid ejection portions Z1, Z2, Z3, and Z4 each having a fluid ejection port that ejects gas are provided.

  The first to fourth partial pressure regulators corresponding to the fluid ejection portions Z1 (zone pressure 1), Z2 (zone pressure 2), Z3 (zone pressure 3), and Z4 (zone pressure 4) are control signals from the control portion. Controlled by C, C1 to C4.

  Then, as shown in FIG. 3 or FIG. 4, one prediction / detection device 33 at the end of polishing is incorporated in each of the upper part of the platen 2 or the carrier 8 of the polishing head 3 in the chemical mechanical polishing apparatus 1. It is. When the prediction / detection device 33 at the end of polishing is incorporated on the platen 2 side, detection signals such as characteristic changes from the prediction / detection device 33 at the end of polishing are output to the outside via the slip ring 32. Is done.

  Note that two or more prediction / detection devices 33 at the end of polishing may be incorporated in the upper portion of the platen 2 or the carrier 8 portion of the polishing head 3. By incorporating three prediction / detection devices 33 at the end of polishing at positions corresponding to the central portion, intermediate portion, and outer peripheral portion of the wafer W held by the polishing head 3 in the carrier 8 portion of the polishing head 3, which will be described later. As described above, it is possible to monitor the change in the resonance frequency for each of the central portion, the intermediate portion, and the outer peripheral portion in the wafer W plane as the polishing proceeds.

FIG. 5 is a diagram showing a configuration example of the prediction / detection device 33 at the end of polishing, where (a) is a block diagram, (b) is a diagram showing another configuration example of a planar inductor, and (c) is a diagram ( It is sectional drawing of the planar inductor of b). The oscillation circuit 35 constituting the main body of the high-frequency inductor type sensor 34 in the prediction / detection device 33 at the time of completion of polishing has a lumped constant capacitor 37 having a capacitance C _{0 in addition} to a two-dimensional planar inductor 36 having an inductance L. Are connected in series to form an LC circuit. The planar inductor 36 is formed in a meander shape using a conductive material such as Cu on a rectangular substrate 36a made of an insulator.

  In addition to the meander shape shown in FIG. 5 (a), the planar inductor 36 is configured by a square spiral on a rectangular substrate 41a like a planar inductor 41 shown in FIG. 5 (b). Alternatively, a round spiral (not shown) may be used. The two-dimensional planar inductors 36 and 41 are formed by forming a conductive film such as Cu on a substrate 36a or 41a made of an insulating material such as glass, epoxy, paper, or phenol, and then manufacturing the film by etching or the like. As shown in FIG. 5C, the overall shape can be reduced to a square shape having a side of about 23 mm. Further, by miniaturizing the planar inductors 36 and 41, a minute magnetic field can be generated efficiently, and the vicinity of the end point where the conductive film 28 is removed without causing the magnetic field to penetrate deeply into the conductive film 28. It is possible to accurately detect the change behavior of.

  An output signal from the LC circuit is input to an amplifier 38 composed of an operational amplifier or the like, and an output of the amplifier 38 is input to a feedback network 39 composed of a resistor or the like. The output signal of the feedback network 39 is positively fed back to the planar inductor 36, whereby the oscillation circuit 35 is configured including the planar inductor 36.

The oscillation circuit 35 basically has an oscillation frequency band f having an inductance L of the planar inductor 36 and a lumped constant capacitor 37 as shown in the following equation (1), as shown in the configuration example of FIG. It has an oscillation circuit of the Colpitts like determined by the capacitance C _0.

  A frequency counter 40 is connected to the output terminal of the amplifier 38. The frequency counter 40 outputs a detection signal or the like indicating a characteristic change described later in digital form. By digitally transmitting the detection signal output, the influence of noise and output attenuation are prevented. In addition, manageability of the film thickness data can be obtained.

  A high-frequency inductor type sensor 34 including the planar inductor 36 and the frequency counter 40 constitute a polishing end prediction / detection device 33. By arranging the oscillation circuit 35 in the high-frequency inductor sensor 34 and the frequency counter 40 for monitoring the change of the oscillation (resonance) frequency in close proximity, wiring / connection between the oscillation circuit 35 and the frequency counter 40 is performed. A distributed constant circuit is formed in the portion to prevent the inductance and capacitance from becoming unnecessarily large, and a change in magnetic flux accompanying the progress of polishing of the conductive film 28 provided in the vicinity of the high-frequency inductor sensor 34 is accurately detected. It becomes possible.

  In the prediction / detection device 33 at the end of the polishing, other components or circuits excluding the planar inductor 36 are integrated into an IC (integrated circuit) and incorporated in a package 33a. The planar inductor 36 is covered with a thin insulating film and fixed to the surface of the package 33a. When the packaged polishing end prediction / detection device 33 is incorporated in the chemical mechanical polishing device 1, as shown in FIGS. 3 and 4, the planar inductor 36 is a conductive film on the surface of the wafer W. It is incorporated so as to face 28.

  The capacitance of the lumped constant capacitor 37 constituting the oscillation circuit 35 is variable, and the high frequency inductor sensor 34 can select an oscillation frequency within the range of the oscillation frequency band.

  In this embodiment, detection of a characteristic change described later is performed based on the change in magnetic flux when the predetermined conductive film 28 being polished has a film thickness corresponding to the skin depth δ of the predetermined conductive film 28. Is going. The skin depth δ in the predetermined conductive film 28 is determined as shown in Expression (2) depending on the material of the predetermined conductive film 28 and the oscillation frequency f of the high-frequency inductor sensor 34.

  ω: 2πf, μ: permeability, σ: conductivity.

  Then, the high-frequency inductor type is used so that the skin depth δ is smaller than the initial film thickness of the predetermined conductive film 28 and larger than the film thickness of the predetermined conductive film 28 in the portion excluding the buried portion at the end of polishing. The oscillation frequency f of the sensor 34 is selected. When the material of the conductive film 28 to be polished and removed is Cu, the oscillation frequency band is selected to be 20 MHz or higher.

  Here, “the film thickness corresponding to the skin depth” and “the magnetic flux change caused by the skin effect” will be described with reference to FIGS. FIG. 7 is a diagram showing the result of electromagnetic simulation on the direction ((a) to (d) the arrow in the lower part of each figure) in which the magnetic field generated from the coil is arranged on the conductor film. FIG. 4A shows the case where the oscillation frequency from the sensor is 1 MHz and the film thickness of the conductor film is 0.2 μm. FIG. 5B shows the case where the oscillation frequency from the sensor is 1 MHz and the film thickness of the conductor film is 1 μm. FIG. 4C shows the case where the oscillation frequency from the sensor is 40 MHz and the film thickness of the conductor film is 0.2 μm, and FIG. 4D shows the case where the oscillation frequency from the sensor is 40 MHz and the film thickness of the conductor film is 1 μm. .

  In the electromagnetic simulation setting, the inductor that forms the magnetic field is a planar inductor having no directivity. The “film thickness corresponding to the skin depth” means “film thickness at which magnetic flux changes due to the skin effect”. When the oscillation frequency of the sensor is 1 MHz, the magnetic flux on the conductor film existing on the lower side of the coil is directed in the vertical direction. At this frequency, even if the film thickness is 1 μm and 0.2 μm, the magnetic flux penetrates through the conductor film (FIGS. 7A and 7B). When the magnetic flux penetrates through such a conductor film, as shown in the conventional example, the eddy current generated inside the conductor film decreases as the film thickness decreases. Therefore, in the case of 1 MHz, the film thickness is 1 μm or less, which is a monotonous behavior. Therefore, the skin effect does not appear, and the “film thickness corresponding to the skin depth” is also considered to be at least 1 μm thick.

  On the other hand, when the oscillation frequency of the sensor is 40 MHz, the direction of magnetic flux on the conductor surface is clearly horizontal, and when the film thickness is 1 μm, it hardly penetrates into the conductor (FIG. 7 (d)). Obviously, the direction of the magnetic flux entering the conductor film is different from the case where the oscillation frequency is 1 MHz and the film thickness is 1 μm (FIG. 7B).

  However, when the oscillation frequency is 40 MHz and the conductor film is thinned to 0.2 μm (FIG. 7C), only a part of the magnetic flux is directed toward the inside of the conductor film. This indicates that even if the conductor film is Cu, a part of the magnetic flux penetrates the conductor film when the conductor film is thin.

  In the case of the alternating magnetic flux of 40 MHz, the penetration state of the magnetic flux in the conductor film changes corresponding to the skin effect. Due to the effect of gradually increasing the penetrating magnetic flux, the frequency rapidly rises to about 700 mm. When the film thickness is 1 μm or more, the magnetic flux hardly penetrates. Therefore, in this case, the “film thickness corresponding to the skin depth” can be about 1 μm. For this reason, when the oscillation frequency is increased to 40 MHz and a planar inductor is used, almost no magnetic flux enters the 1 μm thick Cu conductor film, which is due to the skin effect.

When the Cu conductor film has an oscillation frequency of 40 MHz and the Cu conductivity is 58 × 10 ⁶ S / m, the skin depth δ is 9.34 μm. In the calculation, if the film thickness is 1 μm, the magnetic flux sufficiently enters the conductor film, but since a planar inductor is used and the magnetic flux has no directivity, the film actually has an oscillation frequency of 40 MHz. Even if the thickness is 1 μm, the magnetic field does not enter the conductor film due to the skin effect. As the conductor film becomes thinner, part of the magnetic flux enters the conductor film and a slight eddy current is generated. From this, instead of actively using eddy currents to measure the film thickness, when a thin film thickness near the end point is reached, a slight leakage / penetration magnetic flux is used due to the skin effect to make the conductor The inflection point (maximum point) of the mutual inductance induced in the film can be used to monitor the film thickness state near the end point of the conductor film.

  Next, the polishing action and the prediction / detection method of the polishing end point of the chemical mechanical polishing apparatus incorporating the polishing end point prediction / detection apparatus configured as described above will be described with reference to FIGS. This will be described with reference to e) and FIGS. 10A to 10E as comparative examples of FIG. FIG. 8 is a diagram for explaining the action of changing the inductance due to the magnetic field generated by electromagnetic coupling in the high-frequency inductor type sensor, and FIG. 9 is an example of the change in magnetic flux and eddy current and the characteristic change due to the removal of the polishing of the conductive film. It is a group diagram for explaining a detection action, (a)-(d) is a figure showing an example of change of magnetic flux and eddy current accompanying polishing removal of a conductive film, and (e) is a film thickness change of a conductive film. It is a characteristic view which shows the example of a change of the resonant frequency with respect to. In FIGS. 9A to 9D, the planar inductor 36 is displayed in a spiral shape for easy viewing of the drawing.

  First, the standby conductive film 28 is placed on a non-polished wafer W at a predetermined position by a moving mechanism (not shown) in the chemical mechanical polishing apparatus 1. Then, the vacuum line 24 of the polishing head 3 is operated, and the air chamber 29 on the lower surface of the elastic sheet 11 is evacuated through the vacuum port 19a and the hole 22 (vacuum hole), whereby the conductive film 28 is unpolished. The wafer W is sucked and held, and the moving mechanism carries the polishing head 3 on which the conductive film 28 sucks and holds the unpolished wafer W onto the platen 2, and the conductive film 28 polishes the wafer W. It is placed on the platen 2 so as to contact the pad 6.

  When the polishing operation of the conductive film 28 on the upper portion of the wafer W is completed, the vacuum line 24 sucks and holds the wafer W by the polishing head 3 again by the operation of the vacuum line 24 and transports it to a cleaning device (not shown). Sometimes used.

  Next, the operation of the vacuum line 24 is released, and air is supplied to the airbag 25 from a pump (not shown) to inflate the airbag 25. At the same time, air is supplied to the air chamber 29 from the air outlet 19 provided in the carrier 8. Thereby, the internal pressure of the air chamber 29 becomes high.

  Due to the expansion of the air bag 25, the conductive film 28 and the retainer ring 9 on the wafer W are pressed against the polishing pad 6 with a predetermined pressure. In this state, the platen 2 is rotated in the direction of arrow A in FIG. 1 and the polishing head 3 is rotated in the direction of arrow B in FIG. 1, and slurry is supplied from a nozzle (not shown) onto the rotating polishing pad 6. The predetermined conductive film 28 is polished.

  Then, as described below, a characteristic change is detected based on a unique change in the magnetic flux accompanying polishing by the magnetic flux formed by the planar inductor 36 in the high-frequency inductor sensor 34, and the characteristic change is detected on the spot. The finish polishing conditions are changed so that the inner surface of the wafer W at the end of polishing becomes a uniform surface.

  The planar inductor 36 is driven at a high frequency oscillated from the oscillation circuit 35, and a magnetic flux φ that changes with time corresponding to the period of the high frequency is generated from the planar inductor 36. The magnetic flux φ induced in the predetermined conductive film 28 in the initial stage of polishing passes only the region having the skin depth δ substantially in parallel along the film surface, and exceeds the skin depth δ in the predetermined conductive film 28. Intrusion of the magnetic flux φ into the area is avoided (FIG. 9A). Further, the resonance frequency oscillated from the high-frequency inductor sensor 34 is also kept constant irrespective of the change in the film thickness of the predetermined conductive film 28 (region a in FIG. 9E).

When the polishing progresses and the predetermined conductive film 28 has a film thickness equal to or near the skin depth δ, a part of the magnetic flux φ penetrates the predetermined conductive film 28 and a leakage magnetic flux φ _L is generated. start. The magnetic flux φ that does not penetrate the predetermined conductive film 28 passes through the film surface almost in parallel. Then, an eddy current Ie is generated in proportion to the number of leakage magnetic fluxes φ _L penetrating into the predetermined conductive film 28 (FIG. 9B).

Moreover the polishing progresses, generated wide region eddy current Ie is increasing leakage flux phi _L is along the film surface of the conductive film 28 (FIG. 9 (c)). As shown in FIG. 8, the eddy current Ie generated in the wide area further creates a magnetic field M, and the magnetic field M acts to cancel the magnetic flux φ _L generated from the original planar inductor 36. As a result, due to the magnetic field M formed by the conductive film 28, the mutual inductance Lm increases, and the apparent inductance L of the original planar inductor 36 decreases. As a result, the oscillation frequency f oscillated from the high-frequency inductor type sensor 34 increases as shown in Expression (3).

  Therefore, due to the mutual inductance, the inductance of the sensor circuit system is equivalently reduced and the resonance frequency oscillated from the high-frequency inductor sensor 34 is increased (regions b and c in FIG. 9E).

Furthermore the leakage flux phi _L with the progress of polishing is increased by saturated. However, the eddy current Ie rapidly decreases as the film thickness volume of the predetermined conductive film 28 decreases (FIG. 9D). Due to the rapid decrease of the eddy current Ie, the mutual inductance also decreases rapidly. This rapid decrease in mutual inductance leads to a decrease in inductance Lm in equation (3). As a result, the inductance of the sensor circuit system increases equivalently, and the resonance frequency oscillated from the high-frequency inductor sensor 34 is increased. Decreases rapidly (region d in FIG. 9E).

  As described above, after the predetermined conductive film 28 becomes a film thickness equivalent to or near the skin depth δ due to the progress of polishing, the eddy current Ie is generated, and the rapid decrease thereafter, the inductance of the sensor circuit system. Decreases once and then increases. This behavior causes a characteristic change V including a peak (inflection point) P in the waveform of the resonance frequency oscillated from the high frequency inductor sensor 34. From this characteristic change V, the change time of the final polishing condition is detected on the spot, and the polishing end time is predicted and detected.

  As will be described later with reference to FIG. 11 (a), the characteristic change V is not limited to the peak (inflection point) P, but the rise start point, the rate of increase before and after the peak (inflection point) P, The amount of increase, the rate of decrease, or the amount of change from increase to decrease is also included. When the predetermined conductive film 28 is Cu, the residual film amount at the time when a peak (inflection point) P at the characteristic change V is detected is about 710 mm, and the final polishing is performed with respect to the residual film amount. The polishing is finished.

  The finish polishing conditions are set, for example, by changing the pressure applied to the wafer W, the rotation speed of the platen 2 and the polishing head 3, the slurry component, the slurry flow rate, the dressing conditions of the polishing pad 6, and the like. Of the characteristic changes V, in particular, from the peak (inflection point) P, a film thickness corresponding to the skin depth, which is the amount of remaining film at the peak (inflection point) P, is set in advance at a required polishing rate. The polishing is finished after polishing for the polishing time. Alternatively, the polishing rate is calculated from the time until the peak (inflection point) P is detected from the initial stage of polishing and the polishing amount until the peak (inflection point) P is reached, and the peak (inflection point) is calculated. ) The required polishing time after detecting the peak (inflection point) P is calculated by dividing the film thickness corresponding to the skin depth, which is the amount of remaining film in P, by the polishing rate. Then, after the peak (inflection point) P is detected, the polishing is finished by polishing for the calculated polishing time.

Next, a comparative example of FIGS. 10A to 10E will be described. In the comparative example, a frequency is applied such that the skin depth δ is larger than the initial film thickness of the conductive film 28. When such a frequency is applied, all the magnetic flux φ induced in the conductive film 28 continuously leaks through the conductive film 28 during monitoring of the film thickness change from the initial polishing to the final polishing. φ _L is generated. Accordingly, during the monitoring of the thickness change, an eddy current Ie is proportional to the leakage magnetic flux phi _L number is generated (in Fig. 10 (a) ~ (d) ). For this reason, a large mutual inductance is generated between the conductive film 28 and the planar inductor due to the eddy current Ie, and the oscillation frequency f oscillated from the sensor by the decrease Lm of the inductance due to the mutual inductance is equal to the initial polishing time. Thus, the above equation (3) is obtained.

  Then, the eddy current Ie sharply decreases as the film thickness decreases due to the progress of polishing (from (b) to (d) in FIG. 10), and the mutual inductance decreases accordingly. The inductance decrease Lm also decreases. As a result, the inductance of the sensor circuit system increases equivalently, and the resonance frequency oscillated from the sensor decreases monotonously ((e) in FIG. 10).

  Thus, in the comparative example, since the resonance frequency has a monotonically decreasing curve, it is possible to estimate the amount of film thickness reduction from the initial stage of polishing, but it is possible to estimate the polishing end point or finish polishing on the spot before the polishing end point. The point of change to the condition cannot be determined accurately. For example, when the stray capacitance C changes due to delicate settings, the overall resonance frequency in FIG. 10E shifts up and down over the entire waveform. For this reason, even if the polishing end point is set when a certain set frequency is reached, the threshold value cannot be set if the overall resonance frequency shifts. Even if the state of the removal amount from the initial film thickness is monitored in real time by changes in eddy current, if the initial film thickness varies, the film thickness at the polishing end point also varies. Since there is no waveform feature, the threshold cannot be set in this case as well.

  (A), (b), and (c) of FIG. 11 are diagrams for explaining detection of characteristic changes when the conductive film to be polished is a Cu film on a barrier film (Ta / TaN). It is. FIG. 4A is a diagram showing the relationship between the thickness of the Cu film and the resonance frequency as the polishing progresses, and FIG. 4B corresponds to the pressing portion of the polishing head 3 and the retainer ring 9 in the diameter direction of the wafer W. The figure which divided into 3 parts, the center part, the intermediate part, and the outer peripheral part which were done, and monitored the change of the resonant frequency in each part, (c) is the example which divided the wafer W surface inside into the center part, the intermediate part, and the outer peripheral part. FIG. The count values on the vertical axis in (a) and (b) of FIG. 11 correspond to the resonance frequency. In FIG. 11A, the initial film thickness of the Cu film is approximately 1.5 μm (15000 mm). As the polishing progresses, the resonance frequency of the Cu film gradually increases from about 1 μm (10000 mm) near the film thickness, and reaches a maximum value near 710 mm, and the characteristic change V has a sharp rise and a sharp fall. It appears as a significant change with an accompanying inflection point (peak) P.

Therefore, the detection of the finish polishing condition change time point on the spot is not limited to the case where the inflection point (peak) P in the characteristic change V is used, but the rising start point Q ₁ in the characteristic change V, increase rate or increase the amount between rising start point Q _1, inflection point (peak) P, falling rate of descent point Q ₂ after the peak, or the inflection point (peak) change in P and fall between falling point Q ₂ Even when at least one of the quantities is used, it is possible to detect the time point of finishing polishing condition change. Thus, the Cu film on the barrier film (Ta / TaN) has a distinctive change V including a peak (inflection point) P, and accurately detects when the final polishing conditions are changed on the spot. Is done.

  FIG. 12 illustrates a part of a process for forming a Cu wiring pattern by polishing a Cu film formed on a groove pattern formed on the surface of a wafer W via a barrier film (Ta / TaN) by CMP. It is a figure for doing. (A) is an initial polishing state, (b) is a state in which the Cu film is flattened by rough polishing, and (c) is a state in which the unnecessary portion of the Cu film is removed under the final polishing conditions changed on the spot and Cu is removed. Each shows a state in which the wiring is formed.

  In the initial polishing state of FIG. 12A, the initial film thickness of the Cu film is generally about 3500 to 35000 mm (350 to 3500 nm). The Cu film is flattened by rough polishing until the residual film thickness is about 500 to 3000 mm (80 to 300 nm) (FIG. 5B). When this residual film thickness is reached, a characteristic change V is detected, and the final polishing conditions are changed so that the in-plane surface of the wafer W becomes uniform on the spot. In the final polishing, polishing is performed until the barrier film (Ta / TaN) is exposed, and Cu wiring is formed ((c) in the figure).

  13, 14, and 15, an example of detecting a characteristic change in the case where the conductive film to be polished is a Cu film and an example of changing the final polishing condition in situ based on the detection of the characteristic change Will be described more specifically. FIG. 13 is a diagram showing the relationship between the film thickness and the resonance frequency with the progress of polishing at the central portion, the intermediate portion, and the outer peripheral portion in the wafer W plane, and FIG. 14 is a detection of characteristic changes in each portion in the wafer W plane. FIG. 15 is a flowchart for explaining an example of changing the shape of the outer peripheral portion by changing the wafer pressure in each part in the wafer W surface in the finish polishing. FIG.

  In the flowchart of FIG. 14, after the smoothing process is performed on the resonance frequency indicated by the count value to remove unnecessary frequency components and the like (step S1), the resonance frequency is subjected to a differentiation process and further subjected to a normalization process. (Steps S2 and S3) Changes in the resonance frequency of each of the central portion, the intermediate portion, and the outer peripheral portion in the wafer W surface accompanying the progress of polishing in the rough polishing state are monitored (Step S4).

As a result of this monitoring, for example, as shown in FIG. 13, the rising start point is first detected at the outer peripheral portion, and then the rising start point is detected in the order of the intermediate portion and the central portion. Further, a peak P ₁ is detected at the outer peripheral portion, and then peaks P ₂ and P ₃ are respectively detected in the order of the intermediate portion and the central portion. At this time, the wafer pressurization to the outer peripheral portion is lowered so that the polishing rate of the outer peripheral portion that has reached the rising start point, which is a characteristic change earlier, becomes slower. FIG. 15 shows an example in which the retainer pressure in the polishing head 3 is changed, for example, from 2.0 psi during rough polishing to 0.5 psi in order to reduce the wafer pressure on the outer peripheral portion.

Then, when a characteristic change including the rising start point and the peaks P ₁ , P ₂ , and P ₃ is detected in all of the wafer W plane, the rough polishing is switched to the final polishing (step S5), The finish polishing conditions are changed so that the inner surface of the wafer W at the end of polishing becomes a uniform surface (step S6). As an example of changing the finish polishing conditions, as will be described later, the wafer pressure is simply lowered at the portion where the characteristic change is detected earlier. Alternatively, a treatment such as increasing the wafer pressure in a portion where no characteristic change is detected is performed. Thereafter, the film thickness corresponding to the skin depth, which is the remaining film amount under the changed final polishing conditions, is polished for a predetermined polishing time at a predetermined polishing rate, and the polishing is finished (step S7).

A specific example of changing the finish polishing conditions in step S6 in the flowchart of FIG. 14 will be described as follows.
(Polishing conditions)
Slurry: Planar Solution 7101 manufactured by Fujimi Incorporated
Pad: IC1400 concentric circular groove manufactured by Nitta House Co., Ltd. (rough polishing conditions)
Wafer / retainer pressure: 1.0 / 2.0 psi
Platen / head rotation speed: 120/120 rpm
Slurry flow rate: 300cc / min
Zone pressurization 1/2/3/4: 0/0/0 / 1.1 psi
(Finishing polishing conditions)
Wafer / retainer pressure: 0.5 / 2.0 psi
Platen / head rotation speed: 120/120 rpm
Slurry flow rate: 300cc / min
Zone pressurization 1/2/3/4: 0/0/0/0 psi
(Interval dress condition)
Dress load: 3kgf
Platen / dress rotation speed: 80/88 rpm
Time: 30sec

  Further, in the step S4, a specific example of changing the polishing conditions for the outer peripheral portion will be described so that the polishing speed of the outer peripheral portion that has reached the rising start point, which is a characteristic change, is slowed as follows. is there.

Wafer / retainer pressure: 0.5 / 0.5 psi
Platen / head rotation speed: 120/120 rpm
Slurry flow rate: 300cc / min
Zone pressurization 1/2/3/4: 0/0 / 0.6 / 0.7 psi
(Interval dress condition)
Dress load: 3kgf
Platen / dress rotation speed: 80/88 rpm
Time: 30sec

FIG. 16 shows a method of detecting a polishing abnormality from characteristic changes detected for each of the central portion, intermediate portion, and outer peripheral portion in the wafer W plane. This method pays attention to, for example, the detection point of the peak P among the characteristic changes in each part in the wafer W plane, and the polishing time difference t between the peak P ₁ detected at the outer peripheral part and the peak P ₂ detected at the intermediate part. _When the polishing time difference t ₂ between the peak P ₂ detected at ₁ and / or the intermediate portion and the peak P ₃ detected at the central portion exceeds a predetermined polishing time, it is determined that the polishing is abnormal.

  17A to 17D show peaks (inflection points) that are characteristic changes with respect to two types of wafers Wa and Wb in which the conductive film to be polished differs in terms of material and conductivity. ) The result of evaluating the occurrence of P is shown. FIG. 4A shows a wafer Wa with a Cu film, FIG. 4B shows an example of a change characteristic of resonance frequency with respect to the film thickness of the Cu film, FIG. 5C shows a wafer Wb with a tungsten (W) film, and FIG. It is a figure which shows the example of a change characteristic of the resonant frequency with respect to the film thickness of a film | membrane, respectively. The sensor output (count value) on each vertical axis in FIGS. 17B and 17D corresponds to the resonance frequency.

  In both the Cu film and the tungsten (W) film, the resonance frequency increases once with the progress of polishing, and then sharply decreases to generate a peak (inflection point) P that is a characteristic change. Based on the characteristic changes including this peak (inflection point) P, the final polishing conditions are changed so that the inner surface of the wafer at the end of polishing is uniform on the spot, and prediction / detection of the end of polishing is performed. Is done. This behavior is clearly more remarkable in the Cu film having a high conductivity shown in FIG. 17B than in the case of the tungsten (W) film shown in FIG.

  FIG. 18 is a diagram showing the relationship between the film thickness in the stationary state and the resonance frequency when the conductive film to be polished is a Cu film. The count value on the vertical axis in the figure corresponds to the resonance frequency. In FIG. 18, the resonance frequency measured with respect to each film thickness of the Cu film in a stationary state shows a maximum value when the film thickness is 710 mm. Therefore, the film thickness of the Cu film having the maximum resonance frequency in the stationary state and the film thickness of the Cu film having the maximum resonance frequency during the progress of the polishing shown in FIG. Yes.

Note that this embodiment, in addition to the mutual inductance of the resonant frequency, the eddy current Ie, it is possible to detect the change V with characteristic based on at least one of a change of the change in leakage flux phi _L. The change in the mutual inductance can be obtained from the change in the oscillation frequency of the high-frequency inductor type sensor 34 using the equation (3). Since the eddy current Ie is proportional to the mutual inductance, the change in the eddy current Ie. it is to seek the can be determined using the change in mutual inductance, also the change of the leakage magnetic flux phi _L is the leakage flux phi _L since it is proportional to the eddy current Ie with the change of the eddy current Ie it can.

As described above, in the method and apparatus for predicting / detecting the end point of polishing according to the present embodiment, the predetermined conductive film 28 is equal to or near the skin depth by the progress of polishing, and the film thickness before the end point of polishing. by leakage flux phi _L underlying changes V detected with features from becomes occurs, the Joule heat loss due to the eddy current Ie generated by the leakage magnetic flux phi _L can be suppressed to a minimum.

  A characteristic change V detected based on a unique magnetic flux change does not fluctuate even with various disturbances, and constantly appears at a position corresponding to the remaining film thickness. For this reason, the finish polishing conditions can be reliably changed from the characteristic change V so that the inner surface of the wafer at the end of polishing is uniform on the spot.

  The characteristic change V of the magnetic flux appears, for example, as a remarkable change in which the remaining film of Cu has a peak P with a sharp rise and a sharp fall in the vicinity of 710 mm (71 nm). The Cu film is removed by rough polishing until the remaining film thickness reaches about 500 to 3000 mm (50 to 300 nm), and the polishing conditions are changed. Therefore, a characteristic change V of the magnetic flux occurs near the time when the polishing conditions are changed between rough polishing and finish polishing, and can be detected with sufficient accuracy.

  The characteristic change V of the magnetic flux appears as a remarkable change having a peak P with a steep rise and a steep fall. Therefore, the detection of the change time of the finish polishing condition on the spot is not limited to the case where the peak P is used, but the rising start point, the rising rate, the rising amount, the falling rate or the changing amount from rising to falling in the characteristic change V. Even at least one of the above can be used with high accuracy.

  When the characteristic change V is detected in all of the central part, intermediate part and outer peripheral part of the wafer W surface, the final polishing conditions are changed so that the wafer inner surface at the end of polishing becomes uniform on the spot. By doing so, the surface in the wafer W surface can be made a uniform surface with higher accuracy.

  The resonance frequency transmission method from the high-frequency inductor sensor 34 is digital output using the frequency counter 40, so that the influence of noise and attenuation of the resonance frequency output are prevented, and the characteristic change V is reliably detected. be able to.

  By making the lumped constant capacitor 37 constituting the high-frequency inductor sensor 34 variable in capacitance, the oscillation frequency can be easily set so that the skin depth δ becomes an appropriate value for the conductive film 28 of different film types. You can choose.

  The planar inductor 36, which is a main component of the high-frequency inductor sensor 34, hardly generates noise and consumes power, and can be reduced in cost because it is relatively inexpensive.

  The present invention can be variously modified without departing from the spirit of the present invention, and the present invention naturally extends to the modified ones.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a chemical mechanical polishing apparatus incorporating a prediction / detection device at the end of polishing according to an embodiment of the present invention. FIG. 2 is an enlarged longitudinal sectional view of a polishing head in the chemical mechanical polishing apparatus of FIG. 1. The longitudinal cross-sectional view which shows the structural example of the grinding | polishing head which can change a pressing force partially. The lower surface cross section which shows the structural example of the polishing head which can change a pressing force partially. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side view showing a partially broken view for explaining a state in which a polishing / ending time prediction / detection device according to an embodiment of the present invention is incorporated in a platen. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially cutaway schematic side view for explaining a state in which a polishing / end prediction / detection device according to an embodiment of the present invention is incorporated in a polishing head. It is a figure which shows the structural example of the prediction and the detection apparatus at the time of completion | finish of grinding | polishing which concerns on the Example of this invention, (a) is a block diagram, (b) is a figure which shows the other structural example of a planar inductor, (c) ) Is a cross-sectional view of the planar inductor of FIG. 6A and 6B are diagrams illustrating a basic configuration example of an oscillation circuit in the prediction / detection device at the time of completion of polishing in FIG. 5, in which FIG. In the Example of this invention, it is a figure which shows the result of carrying out the electromagnetic simulation about what direction the magnetic field generated from the coil was arranged on the conductor film, (a) is a conductor with the oscillation frequency from a sensor of 1 MHz. When the film thickness is 0.2 μm, (b) is when the oscillation frequency from the sensor is 1 MHz and the conductor film thickness is 1 μm, and (c) is when the oscillation frequency from the sensor is 40 MHz and the film thickness of the conductor film. (D) is when the oscillation frequency from the sensor is 40 MHz and the film thickness of the conductor film is 1 μm. The block diagram for demonstrating the change effect of the inductance by the magnetic field which generate | occur | produces by the electromagnetic coupling in the high frequency inductor type sensor which concerns on the Example of this invention. FIG. 2 is a set of views for explaining an example of changes in magnetic flux and the like and detection of characteristic changes associated with polishing removal of the conductive film by the chemical mechanical polishing apparatus of FIG. 1, wherein (a) to (d) are conductive films. The figure which shows the example of a change of the magnetic flux etc. accompanying grinding | polishing deletion of (a), The characteristic view which shows the example of a change of the resonant frequency with respect to the film thickness change of an electroconductive film. FIG. 10 is a group diagram as a comparative example of FIG. 9, in which (a) to (d) are diagrams showing examples of changes in magnetic flux and eddy current accompanying polishing removal of the conductive film, and (e) is a change in film thickness of the conductive film. The characteristic view which shows the example of a change of the resonant frequency with respect to. In the Example of this invention, it is a figure for demonstrating the detection of a characteristic change about the case where the electroconductive film | membrane of grinding | polishing object is Cu film | membrane on a barrier film, (a) is the resonance frequency accompanying progress of grinding | polishing. (B) is a diagram in which the diameter direction of the wafer W is divided into a central part, an intermediate part, and an outer peripheral part, and a change in resonance frequency is monitored in each part. The figure which shows the example which divided the in-plane surface into the center part, the intermediate part, and the outer peripheral part. In the embodiment of the present invention, it is a cross-sectional view for explaining a process of forming a Cu wiring by polishing a Cu film formed through a barrier film on a groove pattern formed on the surface portion of the wafer W, (A) is a diagram of the initial state of polishing, (b) is a diagram of a state in which the Cu film is flattened by rough polishing, and (c) is a state in which the Cu film is removed by finish polishing and a Cu wiring is formed. Figure. In the Example of this invention, the figure which shows the example of a relationship between the film thickness and resonance frequency accompanying progress of grinding | polishing about the center part in a wafer surface, an intermediate part, and an outer peripheral part. 6 is a flowchart for explaining an in-situ finish polishing condition change based on detection of a characteristic change in each part in the wafer surface in the embodiment of the present invention. In the Example of this invention, the figure for demonstrating the example which changes the wafer pressurization of each part in a wafer surface in finish polishing, and changes the shape of an outer peripheral part. The figure for demonstrating the method to detect grinding | polishing abnormality from the characteristic change detected about each part of the center part in a wafer W surface, an intermediate part, and an outer peripheral part in the Example of this invention. In an embodiment of the present invention, the occurrence of a peak (inflection point) P, which is a characteristic change in a Cu film and a tungsten (W) film, in which the conductive film to be polished differs in terms of material and conductivity, is evaluated. (A) is a diagram showing a wafer with a Cu film, (b) is a diagram showing an example of a change characteristic of the resonance frequency with respect to the film thickness of the Cu film, and (c) is with a tungsten (W) film. The figure which shows a wafer, (d) is a figure which shows the example of a change characteristic of the resonant frequency with respect to the film thickness of a tungsten (W) film | membrane. In the Example of this invention, the figure which shows the example of a relationship between the film thickness in a stationary state, and the resonant frequency about the case where the electroconductive film | membrane of grinding | polishing object is a Cu film | membrane.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Chemical mechanical polishing apparatus 2 Platen 3 Polishing head 4 Rotating shaft 5 Motor 7 Head main body 8 Carrier 9 Retainer ring 10 Retainer ring pressing means 11 Elastic sheet 12 Rotating shaft 13 Dry plate 14 Pin 15 Actuating transformer 16 Carrier pressing means 17 Air float line DESCRIPTION OF SYMBOLS 19 Air outlet 20 Air filter 21 Intake pump 22 Hole 23 Vacuum pump 24 Vacuum line 25 Air bag 27 Retainer ring holder 28 Conductive film 29 Air chamber 30 Mounting member 31 Snap ring 32 Snap ring 33 Prediction / detection device at the time of polishing end 34 High Frequency Inductor Type Sensor 35 Oscillation Circuit 36 Planar Inductor 37 Lumped Capacitor 38 Amplifier 39 Feedback Network 40 Frequency Counter 41 Plane A Change W wafer with a inductor V features
P, Q, R, S, T, U wafer surface area
Z1, Z2, Z3, Z4 Q, R, T, U Fluid ejection part provided in the region
Control signals from the C1, C2, C3, and C4 control units to the first to fourth voltage dividing regulators

Claims (1)

A method for predicting and detecting a polishing end time by polishing a conductive film and predicting and detecting a polishing end time when a predetermined conductive film is properly removed,
An inductor is brought close to the predetermined conductive film, and eddy currents induced in the predetermined conductive film by the magnetic flux formed by the inductor are monitored at a plurality of locations within the substrate surface to be polished, and polishing is in progress. Oite the thickness of the predetermined conductive film material in the vicinity of the skin depth determined as a factor,
Detecting a point at which the change in the eddy current reaches a maximum point at a plurality of locations in the substrate surface ,
Based on the time when the eddy current at each of the above points becomes the maximum point,
A prediction / detection method at the end of polishing, characterized in that the pressure distribution condition applied to the substrate surface is changed so that the inner surface of the wafer at the end of polishing is a uniform surface.