Substrate polishing device and thickness calculation method

Abstract

The present invention accurately measures the thickness of a polishing target film during polishing of a substrate.　This substrate polishing device comprises: a polishing table which is provided with an eddy current sensor and which is configured so as to be rotatable; a polishing head which faces the polishing table, which is configured so as to be rotatable, and to the polishing-table-facing surface of which a substrate can be attached; and a control unit. The control unit is configured to: use an output signal of the eddy current sensor with respect to a reference substrate to generate mapping data representing the arrangement of one or more metal structures which are locally present on the surface or inside of the reference substrate; during polishing of a polishing target substrate which has the same arrangement of metal structures as the reference substrate, acquire a profile of the output signal of the eddy current sensor when the eddy current sensor passes through a certain path on a surface to be polished of the polishing target substrate; on the basis of the profile, identify a path which corresponds to said profile and along which the eddy current sensor has passed across the surface to be polished of the polishing target substrate; determine, on the basis of the mapping data, whether a metal structure is present on the identified path of the polishing target substrate; correct the profile of the output signal of the eddy current sensor with respect to the polishing target substrate so as to reduce a signal value at the position where it has been determined that the metal structure is present; and calculate the thickness of the polishing target substrate on the basis of the corrected profile of the output signal of the eddy current sensor.

Description

Substrate polishing apparatus and film thickness calculation method

[0001] The present invention relates to a substrate polishing apparatus and a film thickness calculation method.

[0002] A CMP (Chemical Mechanical Polishing) apparatus is one type of semiconductor device manufacturing equipment. A typical CMP apparatus includes a polishing table with a polishing pad attached and a polishing head with a substrate attached. In a typical CMP apparatus, a polishing liquid is supplied to the polishing pad, and the substrate is polished by rotating at least one of the polishing table and the polishing head while the polishing pad is in contact with the substrate.

[0003] Japanese Patent Application Laid-Open No. 2021-058955

[0004] An eddy current sensor can be used to measure the thickness of a film being polished during substrate polishing. The eddy current sensor is mounted on, for example, a polishing table. The eddy current sensor moves along a certain trajectory on the surface of the substrate as the polishing table rotates, measuring the film thickness at each point on the trajectory (see, for example, Patent Document 1). However, if there is a localized metal structure on the substrate in addition to the film (metal film) being polished, this influence makes it difficult to accurately measure the thickness of the film being polished.

[0005] According to one embodiment, a substrate polishing apparatus includes a rotatable polishing table provided with an eddy current sensor, a rotatable polishing head facing the polishing table and configured to rotate, the polishing head being capable of mounting a substrate on a surface facing the polishing table, and a control unit, wherein the control unit uses an output signal of the eddy current sensor for a reference substrate to generate mapping data representing the arrangement of one or more metal structures locally present on the surface or inside of the reference substrate, and during polishing of a target substrate having the same arrangement of metal structures as the reference substrate, the eddy current sensor detects a certain trajectory on the polished surface of the target substrate. a profile of the output signal of the eddy current sensor when the eddy current sensor passes through a surface to be polished of the substrate to be polished, a path of the eddy current sensor that corresponds to the profile and that passes over the surface to be polished of the substrate to be polished is identified based on the profile, whether or not a metal structure is present on the identified path of the substrate to be polished is determined based on the mapping data, the profile of the output signal of the eddy current sensor for the substrate to be polished is corrected to reduce the signal value at the position where the metal structure is determined to be present, and a film thickness of the substrate to be polished is calculated based on the corrected profile of the output signal of the eddy current sensor.

[0006] FIG. 1 is a front view of a substrate polishing apparatus according to an embodiment; FIG. 2 is a cross-sectional schematic diagram showing the structure of an exemplary substrate to be polished by the substrate polishing apparatus; FIG. 3 is a flowchart showing the general operation of a substrate polishing apparatus according to an embodiment; FIG. 4 is a flowchart showing an algorithm of a method according to an embodiment of the present invention; FIG. 5 is a flowchart showing an algorithm of a method according to an embodiment of the present invention; FIG. 6 is a schematic diagram showing an exemplary trajectory of an eddy current sensor passing over a substrate; FIG. 7 is an example of a sensor output map for a reference substrate; FIG. 8 is a conceptual diagram of a process for correcting the position of a maximum value (or minimum value) in a sensor output map; FIG. 9 is an example of mapping data; FIG. 10 is an explanatory diagram of a correction process for a profile of an output signal of an eddy current sensor; FIG. 11 is a flowchart showing a process for identifying the trajectory of an eddy current sensor; FIG. 12 is an example of a sensor output map for a substrate to be polished; FIG. 13 is an example of a profile of an output signal of an eddy current sensor; and FIG. 14 is an example of a profile cut out from a sensor output map.

[0007] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings described below, identical or corresponding components are designated by the same reference numerals, and redundant description will be omitted.

[0008] Fig. 1 is a front view of a substrate polishing apparatus 100 according to one embodiment. The substrate polishing apparatus 100 shown in Fig. 1 is a CMP (Chemical Mechanical Polishing) apparatus. However, the substrate polishing apparatus 100 is not limited to a CMP apparatus. The substrate polishing apparatus 100 may be any apparatus that polishes a substrate by rotating a polishing table provided with an eddy current sensor.

[0009] The CMP apparatus 100 includes a polishing table 110, a polishing head 120, and a liquid supply mechanism 130. The CMP apparatus 100 further includes a control unit 140 for controlling each of the components. The control unit 140 may include, for example, a storage device 141, a processor 142, and an input / output device 143.

[0010] A polishing pad 111 is detachably attached to the upper surface of the polishing table 110. Here, the upper surface of the polishing table 110 refers to the surface of the polishing table 110 facing the polishing head 120. Therefore, the upper surface of the polishing table 110 is not limited to a surface positioned vertically upward. The polishing head 120 is provided to face the polishing table 110. A substrate 121 is detachably attached to the surface of the polishing head 120 facing the polishing table 110. The liquid supply mechanism 130 is configured to supply a polishing liquid such as slurry to the polishing pad 111. Note that the liquid supply mechanism 130 may be configured to supply a cleaning liquid, a chemical liquid, or the like in addition to the polishing liquid.

[0011] The CMP apparatus 100 can lower the polishing head 120 using a vertical movement mechanism (not shown) to bring the substrate 121 into contact with the polishing pad 111. However, the vertical movement mechanism may also be capable of moving the polishing table 110 up and down. The polishing table 110 and the polishing head 120 are rotated by a motor (not shown) or the like. The CMP apparatus 100 polishes the substrate 121 by rotating both the polishing table 110 and the polishing head 120 while the substrate 121 and the polishing pad 111 are in contact with each other.

[0012] The CMP apparatus 100 may further include an air bag 122 divided into a plurality of concentric compartments. The air bag 122 may be provided in the polishing head 120. Additionally or alternatively, the air bag 122 may be provided in the polishing table 110. The air bag 122 is a member for adjusting the polishing pressure of the substrate 121 for each region of the substrate 121. The air bag 122 is configured so that its volume changes depending on the pressure of air introduced therein. A fluid other than air, such as nitrogen gas or pure water, may be introduced into the air bag 122.

[0013] An eddy current sensor 150 is provided inside the polishing table 110. The eddy current sensor 150 is installed at a position such that the eddy current sensor 150 passes through the center of the substrate 121 when the polishing table 110 rotates during polishing. The eddy current sensor 150 is configured to induce an eddy current in the conductive layer on the surface of the substrate 121. The eddy current sensor 150 is further configured to receive a change in impedance caused by a magnetic field generated by the eddy current and output a signal corresponding to the thickness of the conductive layer on the surface of the substrate 121. The output signal from this eddy current sensor 150 can be used to determine the film thickness of the film to be polished on the surface of the substrate 121.

[0014] Here, what affects the output signal of the eddy current sensor 150 is not limited to the film to be polished that is exposed on the top surface of the substrate 121 (a film formed over the entire top surface of the substrate 121). FIG. 2 is a cross-sectional view showing the structure of an exemplary substrate 121 to be polished by the substrate polishing apparatus 100. As shown in FIG. 2, the top surface of this exemplary substrate 121 is covered with a dielectric film (e.g., SiO ２A dielectric film 202 (e.g., a film made of Cu or the like) 202 is formed on the substrate 121, and a metal film (e.g., a film made of Cu or the like) 204 is further formed thereon to cover the dielectric film 202. The metal film 204 is the film to be polished and located on the outermost surface of the substrate 121. The substrate 121 may also have one or more through electrodes 206 for electrical connection between one surface and the other surface. Furthermore, metal wiring 208 may be embedded in the dielectric film 202 on the substrate 121. When the eddy current sensor 150 passes over or near such through electrodes 206 or metal wiring 208, eddy currents are induced in these metal structures as well. This affects the output signal of the eddy current sensor 150, and the signal value changes from the output signal of the eddy current sensor 150 when the eddy current sensor 150 passes over an area of ​​the substrate 121 where no through electrodes 206 or metal wiring 208 exist. That is, the through electrodes 206 and metal wiring 208, which are local metal structures formed on the substrate 121, can cause noise to be generated in the output signal of the eddy current sensor 150. Note that the metal structures are not limited to the through electrodes 206 and metal wiring 208 embedded in the dielectric film 202 as described above, and can also include, for example, wiring and vias exposed on the top surface of the substrate 121.

[0015] FIG. 3 is a flowchart showing an outline of the operation of the substrate polishing apparatus 100 according to an embodiment.

[0016] In step 302, a polishing process is performed. Specifically, the substrate 121 is attached to the polishing head 120, and a slurry is supplied from the liquid supply mechanism 130. While the substrate 121 is pressed against the polishing table 110 by the polishing head 120, both the polishing table 110 and the polishing head 120 rotate, and the substrate 121 is polished. During polishing, a film thickness map showing the in-plane distribution of the film thickness of the film to be polished on the substrate 121 (e.g., the metal film 204 in FIG. 2 ) is created based on the output signal of the eddy current sensor 150. The creation of the film thickness map will be described in detail below. The polishing process in step 302 continues until a predetermined termination condition is met, for example, until a preset polishing time has elapsed to polish the film to be polished by a desired amount. After the polishing process in step 302, the process proceeds to step 304.

[0017] In step 304, it is determined based on the film thickness map created above whether to continue polishing the substrate 121. For example, it is determined whether the desired film thickness or film thickness profile has been achieved over the entire surface of the substrate 121 or over at least a portion of the substrate 121. If the desired film thickness or film thickness profile has not been achieved, the process proceeds to step 306 to continue polishing the substrate 121. On the other hand, if the desired film thickness or film thickness profile has been achieved, the operation of the substrate polishing apparatus 100 is terminated.

[0018] In step 306, the polishing conditions for the polishing process are adjusted. For example, the duration of the additional polishing is set based on the film thickness map. Furthermore, based on the film thickness map, the control unit 140 may increase or decrease the internal pressure of the airbag 122 to increase the polishing pressure in areas where the film thickness is thick (i.e., areas where the polishing progress is low) and decrease the polishing pressure in areas where the film thickness is thin (i.e., areas where the polishing progress is high). This control makes it possible to make the polishing state of the substrate 121 uniform. The polishing process of step 302 is performed again according to the polishing conditions adjusted in this way.

[0019] 4 and 5 are flowcharts showing an algorithm of a film thickness calculation method according to an embodiment of the present invention, which can remove or reduce noise that occurs in the output signal of the eddy current sensor 150 due to local metal structures on the substrate 121. This method includes a preliminary step of creating mapping data (FIG. 4) that represents the arrangement of one or more metal structures that are locally present on the surface or inside of the substrate, and a preliminary step of accurately calculating the film thickness on the substrate by correcting the output signal of the eddy current sensor 150 using the mapping data created in the preliminary step (FIG. 5). The processing of each flowchart may be performed by a processor (e.g., processor 142 of the control unit 140).

[0020] First, the process of creating mapping data will be described with reference to the flowchart in FIG. 4 . In this preliminary preparation stage, a "reference substrate" is used. The reference substrate is a substrate on whose surface no metal film is formed. For example, the reference substrate is the exemplary substrate 121 (hereinafter referred to as the "substrate to be polished") in FIG. 2 , with the metal film 204 removed from the entire surface and the dielectric film 202 exposed on the outermost surface (hereinafter referred to as the "reference substrate 121'" for convenience). For example, one or more of a number of substrates 121 of the same type (i.e., manufactured using the same manufacturing process) that have been polished in advance can be used as the reference substrate 121'. Here, "substrates of the same type" means "substrates having the same wiring pattern formed thereon, at least in terms of design."

[0021] In step 402, an output signal from the eddy current sensor 150 for the reference substrate 121′ is acquired. Specifically, an output signal is acquired from the eddy current sensor 150 while both the polishing head 120 to which the reference substrate 121′ is attached and the polishing table 110 are rotated at predetermined rotational speeds. The eddy current sensor 150 moves relative to the reference substrate 121′ (i.e., as viewed from the reference substrate 121′) along an arc-shaped trajectory that corresponds to the ratio between the rotational speed of the polishing table 110 and the rotational speed of the polishing head 120. With each rotation of the polishing table 110, the eddy current sensor 150 crosses the surface of the reference substrate 121′ along an arc-shaped trajectory with a predetermined curvature determined by the rotational speeds of the polishing table 110 and the polishing head 120. With the next rotation of the polishing table 110, the eddy current sensor 150 passes through an trajectory that has the same curvature as the previous rotation but corresponds to a different arc. Therefore, the eddy current sensor 150 continuously obtains signal values ​​at each point on these multiple arc-shaped trajectories. Note that, since accurate mapping data cannot be created if polishing of the substrate progresses while step 402 is being performed, it is desirable to perform step 402 while supplying water rather than slurry from the liquid supply mechanism 130 (i.e., performing the step as a water polishing process). This makes it possible to acquire signal values ​​from the eddy current sensor 150 corresponding to a large number of trajectories on the reference substrate 121′ while polishing of the reference substrate 121′ does not progress.

[0022] 6 is a schematic diagram showing an exemplary trajectory of the eddy current sensor 150 passing over the substrate 121 (e.g., the reference substrate 121′). In the figure, each curved, arc-shaped arrow represents one trajectory of the eddy current sensor 150 and the direction in which the eddy current sensor 150 moves along that trajectory. The reference numerals "1" to "10" in the figure indicate the order of the trajectories through which the eddy current sensor 150 passes. The eddy current sensor 150 moves over the surface of the substrate 121 in the order of trajectories "1" to "10" in accordance with the rotation of the polishing table 110 and the polishing head 120, outputting a signal value at each point on the trajectory.

[0023] In the example of FIG. 6 , the angular interval θ between adjacent tracks is set to 36 degrees. When the polishing table 110 rotates 10 times, the eddy current sensor 150 follows the same track as before (track "1" again after track "10"). That is, the number of tracks through which the eddy current sensor 150 passes is at most 10 in this example. However, in order to increase the number of measurement points by the eddy current sensor 150, it is preferable that the number of tracks through which the eddy current sensor 150 passes is sufficiently large. Therefore, the angular interval θ between the tracks may be set to, for example, 10 degrees or less, preferably 5 degrees or less, and more preferably 1 degree or less. The angular interval θ between the tracks may be selected so that the measurement points of the eddy current sensor 150 are sufficiently densely arranged on the substrate 121. The angular interval θ between the tracks can be set arbitrarily by combining the rotation speed of the polishing table 110 and the rotation speed of the polishing head 120.

[0024] Next, in step 404, a sensor output map for the reference substrate 121′ is created using the output signal of the eddy current sensor 150 obtained in step 402. The sensor output map is a map that represents the distribution of the magnitude of the output signal of the eddy current sensor 150 over the entire surface of the substrate 121 (here, the reference substrate 121′). As described above, for each of the multiple trajectories on the reference substrate 121′, signal values ​​of the eddy current sensor 150 are obtained for each measurement point on the trajectory. By plotting these signal values ​​on the XY plane, a sensor output map for the reference substrate 121′ can be created. The XY coordinates of each measurement point on the trajectory can be determined based on the shape (curvature) of the trajectory, which is determined by the rotational speed of the polishing table 110 and the polishing head 120, or based on a signal from an encoder provided on the motor that rotates the polishing table 110 and the polishing head 120.

[0025] FIG. 7 shows an example of a sensor output map 700 for the reference substrate 121′ created in step 404. In this example, the distribution of signal values ​​of the eddy current sensor 150 at each measurement point is indicated by shading. The sensor output map 700 has a number of bright spots 702 scattered across the surface of the reference substrate 121′. These bright spots 702 are regions where the signal value of the eddy current sensor 150 is large and correspond to local metal structures (such as the through electrodes 206 and metal wiring 208 in FIG. 2 ) provided on the reference substrate 121′. Note that in the design of a final product (e.g., a semiconductor chip) manufactured from the substrate 121, the through electrodes 206 are often arranged regularly (e.g., so that the through electrodes 206 are aligned linearly and / or at equal intervals).

[0026] Next, in step 406, a maximum value (or minimum value) is searched for in the sensor output map created in step 404, and the position (i.e., XY coordinates) of the found maximum value (or minimum value) is temporarily stored. Any suitable well-known method can be applied as the algorithm for searching for the maximum value (or minimum value), and a detailed description thereof will be omitted here.

[0027] Next, if correction to the positions of the maximum values ​​(or minimum values) is to be applied (Yes in step 408), the process proceeds to step 410. In step 410, the positions of the maximum values ​​(or minimum values) found in step 406 are corrected so that they are aligned in a straight line on the XY plane. In the following step 412, the positions of the maximum values ​​(or minimum values) found in step 406 are corrected so that they are aligned at equal intervals on the XY plane. Either step 410 or step 412 may be omitted. Note that in step 412, correction may be performed to interpolate missing maximum values ​​(or minimum values).

[0028] FIG. 8 is a conceptual diagram for explaining the process of correcting the position of the local maximum value (or local minimum value) in steps 410 and 412. As described above, for example, when a substrate 121 (reference substrate 121′) on which multiple through electrodes 206 are arranged linearly and at equal intervals is used, if the trajectory of the eddy current sensor 150 passes exactly over all of the through electrodes 206, the bright spots 702 on the sensor output map 700 created in step 404 are expected to be aligned precisely linearly and at equal intervals. However, if the eddy current sensor 150 passes a location slightly offset from a certain through electrode 206, the position of the spot 702 on the sensor output map 700 corresponding to that through electrode 206 may deviate from the expected linear and evenly spaced position. In FIG. 8, spot 702a represents such a misaligned spot. On the other hand, the other spots 702b, 702c, ... are not misaligned and are aligned linearly and at equal intervals. The local maximum position 802a identified in step 406 for the misaligned spot 702a is corrected to linear and equally spaced corrected positions 802a' based on the local maximum positions 802b, 802c, ... corresponding to the non-misaligned spots 702b, 702c, ... in steps 410 and 412. This allows the position of a local metal structure (such as the through electrode 206 or the metal wiring 208) provided on the reference substrate 121' to be correctly identified regardless of the trajectory of the eddy current sensor 150.

[0029] Next, in step 414, the size of the local metal structure on the reference substrate 121′ is determined. For example, if the metal structure is a through electrode 206, the diameter of the through electrode 206 is determined. Also, if the metal structure is a metal wiring 208, the width and / or length of the wiring may be determined. For example, the diameter of the through electrode 206 can be determined in advance based on the spot size of the eddy current sensor 150 (i.e., the size of the area where the eddy current sensor 150 can detect a magnetic field), the distance between the eddy current sensor 150 and the reference substrate 121′, the actual dimensions of the through electrode 206 on the reference substrate 121′ (known design dimensions), etc. Alternatively, the diameter of the through electrode 206 may be determined based on the size of the bright spot 702 in the sensor output map 700 created in step 404. The size of the bright spot 702 in the sensor output map 700 may be determined, for example, as a region where the signal value is equal to or greater than a predetermined value, or as a region where the signal value is equal to or greater than a predetermined ratio for each maximum value in the sensor output map 700.

[0030] Next, in step 416, mapping data representing the arrangement of local metal structures on the reference substrate 121′ is generated based on the positions of the local maximum values ​​(or minimum values) on the sensor output map identified in step 406 (or the positions of the local maximum values ​​(or minimum values) corrected in steps 410 and 412) and the size of the metal structures determined in step 414. For example, multiple circles can be defined that are centered on the positions 802a′, 802b, 802c, ... of the local maximum values ​​indicated by Xs in FIG. 8 , and whose radii are the diameters of the through electrodes 206 determined in step 414. Mapping data can be generated so that the inside of the defined circles has a value of “1” and the outside has a value of “0.” This makes it possible to obtain mapping data corresponding to the reference substrate 121′ having multiple through electrodes 206.

[0031] FIG. 9 shows an example of mapping data thus created. The mapping data 900 is composed of coordinate values ​​(XY coordinates) of each point on the XY plane representing the surface of the substrate 121, and a value identifying whether each point on the substrate 121 is a metal structure (such as a through electrode 206 or a metal wiring 208). In the exemplary mapping data 900 of FIG. 9, each point inside a plurality of black circles 902 has a value of "1," indicating that the corresponding region on the substrate 121 is a through electrode 206. On the other hand, each point outside the black circles 902 has a value of "0." By using such mapping data 900, the position of a local metal structure (such as a through electrode 206 or a metal wiring 208) provided on the substrate 121 can be determined.

[0032] Next, a process for correcting the output signal of the eddy current sensor 150 using the mapping data and calculating the film thickness on the substrate will be described with reference to the flowchart in Figure 5. Note that what is used in this process is not the reference substrate 121' but the "substrate to be polished" 121 (i.e., a substrate having a metal film 204 to be polished formed on its surface, as shown in Figure 2, for example).

[0033] First, in step 502, an output signal from the eddy current sensor 150 for the substrate 121 to be polished is acquired. Specifically, the polishing head 120 to which the substrate 121 to be polished is attached and the polishing table 110 are both rotated at a predetermined rotational speed, while an output signal is acquired from the eddy current sensor 150. Step 502 is essentially the same as step 402 in the flowchart of FIG. 4 described above. As the eddy current sensor 150 moves along an arc-shaped trajectory on the surface of the substrate 121 to be polished in conjunction with the rotation of the polishing table 110 and the polishing head 120, signal values ​​at each point on the trajectory of the substrate 121 to be polished are continuously obtained from the eddy current sensor 150. Hereinafter, a series of signal values ​​obtained from the eddy current sensor 150 as the eddy current sensor 150 passes through a particular trajectory is referred to as a "profile" of the output signal from the eddy current sensor 150. Note that step 502 may be performed while the substrate 121 to be polished is being polished in the polishing process of step 302 in the flowchart of FIG. 3 described above.

[0034] Next, in step 504, the trajectory of the eddy current sensor 150 on the substrate 121 being polished is identified based on the profile of the output signal from the eddy current sensor 150. Details of step 504 will be described below with reference to FIG.

[0035] Next, in step 506, a portion of the profile of the output signal of the eddy current sensor 150 obtained in step 502 that corresponds to the outer edge of the substrate 121 (for example, a strip-shaped region extending inward from the edge of the substrate 121 by a few millimeters) is masked. This is because it is expected that the measurement accuracy of the eddy current sensor 150 will not be very good at the outer edge of the substrate 121, and therefore it is preferable to exclude the signal value of the eddy current sensor 150 obtained from this portion from the calculations that follow.

[0036] Next, in step 508, the profile of the output signal of the eddy current sensor 150 after processing in step 506 is normalized.

[0037] Next, in step 510, based on the mapping data created by the processing of the flowchart of Fig. 4, coordinates of the portion of the trajectory of the eddy current sensor 150 identified in step 504 that overlaps with a local metal structure (e.g., the through electrode 206, the metal wiring 208, etc.) of the substrate to be polished 121 are extracted. For example, by overlaying the trajectory of the eddy current sensor 150 on exemplary mapping data 900 shown in Fig. 9, it is possible to identify the portion of the trajectory of the eddy current sensor 150 that overlaps with the local metal structure of the substrate to be polished 121. More specifically, among the points on the trajectory of the eddy current sensor 150, points that correspond to the value "1" on the mapping data 900 (i.e., the black circle 902 in Fig. 9) can be extracted as the portion of the trajectory of the eddy current sensor 150 that overlaps with the local metal structure of the substrate to be polished 121.

[0038] Next, in step 512, the result of step 510 is used to perform correction on the profile of the output signal of the eddy current sensor 150. Specifically, a signal peak is searched for in the profile of the output signal of the eddy current sensor 150 normalized in step 508, and it is determined whether the found peak corresponds to the position of the overlapping portion between the trajectory of the eddy current sensor 150 identified in step 510 and the local metal structure of the substrate to be polished 121. If the peak of the profile corresponds to the position of the overlapping portion, the profile of the output signal of the eddy current sensor 150 is corrected by attenuating the peak of the profile (i.e., reducing the signal value of the peak portion).

[0039] FIG. 10 shows examples of pre-correction and post-correction profiles of the output signal of the eddy current sensor 150 to aid in understanding the correction process in step 512. The horizontal axis of the graph in FIG. 10 indicates the position on the trajectory of the eddy current sensor 150, and the vertical axis indicates the normalized sensor output signal (i.e., the signal value of the eddy current sensor 150 normalized in step 508). In the example of FIG. 10, the pre-correction profile 1002 has peaks Pa, Pb, Pc, Pd, Pe, Pf, Pg, and Ph corresponding to the overlapping portion between the trajectory of the eddy current sensor 150 identified from the mapping data and the local metal structure of the polishing target substrate 121, as well as other peaks Pi, Pj, Pk, Pl, Pm, and Pn. In the post-correction profile 1004, the signal values ​​of the peaks Pa, Pb, Pc, Pd, Pe, Pf, Pg, and Ph in the pre-correction profile 1002 and their neighboring peaks have been changed to predetermined values ​​smaller than the peak values ​​of each peak. More specifically, the signal values ​​in the range corresponding to the overlapping portion between the trajectory of the eddy current sensor 150 and the local metal structure of the polishing target substrate 121 near each of the peaks Pa, Pb, Pc, Pd, Pe, Pf, Pg, and Ph (i.e., the range corresponding to the value "1" in the mapping data 900) are changed to a predetermined value. The predetermined value may be, for example, the peak value of each peak multiplied by a predetermined attenuation rate (e.g., 30%). Note that the attenuation rate may be set to be larger the closer to the center of the peak. On the other hand, the peaks Pi, Pj, Pk, Pl, Pm, and Pn are not subject to correction and remain as they are in the corrected profile 1004.

[0040] In this way, steps 510 and 512 correct the profile of the output signal of the eddy current sensor 150 based on the mapping data, thereby removing or reducing noise that occurs in the output signal of the eddy current sensor 150 due to local metal structures contained in the substrate 121 to be polished.

[0041] Next, in step 514, in order to return the values ​​normalized in step 508 to the original scale, the profile corrected in step 512 is multiplied by the inverse of the ratio by which the signal value of the eddy current sensor 150 was multiplied during normalization.

[0042] Next, in step 516, a moving average in the direction along the trajectory of the eddy current sensor 150 (i.e., a moving average in the horizontal direction in the graph of FIG. 10) is calculated for the profile processed in step 514.

[0043] Next, in step 518, the signal values ​​corresponding to the outer edge of the substrate 121 masked in step 506 are recombined into the post-processing profile of step 516.

[0044] Next, in step 520, a moving average of the profile after processing in step 518 is calculated for a plurality of adjacent orbits of the eddy current sensor 150. The moving average in step 516 corresponds to taking a moving average in the radial direction of the substrate 121, and the moving average in step 520 corresponds to taking a moving average in the circumferential direction of the substrate 121. These moving average processes make it possible to remove fine noise present in the profile of the output signal of the eddy current sensor 150.

[0045] Next, in step 522, a film thickness map of the substrate 121 to be polished is created based on the signal value profiles for multiple trajectories (over the entire substrate) of the eddy current sensor 150 obtained in the processes up to step 520 (see step 302 in FIG. 3 ). For example, for each of the multiple trajectories of the eddy current sensor 150, the film thickness at each point on the trajectory can be calculated from the profile after the process of step 520, and by plotting the film thicknesses at each point on the XY plane, a film thickness map showing the film thickness distribution on the substrate 121 to be polished can be created. As described above, since the profile after the process of step 520 has noise caused by local metal structures on the substrate 121 to be polished removed or reduced, a highly accurate film thickness map can be obtained that is not affected by the through electrodes 206, metal wiring 208, etc. of the substrate 121 to be polished.

[0046] Next, the process of identifying the trajectory of the eddy current sensor 150 in step 504 described above will be described in detail with reference to the flowchart of FIG.

[0047] In step 1102, a sensor output map for the substrate 121 to be polished is created. The sensor output map for the substrate 121 to be polished can be created using the output signal of the eddy current sensor 150 for the substrate 121 to be polished in the same manner as the sensor output map for the reference substrate 121′ created in step 404 of Fig. 4 described above. For example, the sensor output map for the substrate 121 to be polished can be created in advance using one or more substrates 121 to be polished that are the same type as but different from the substrate 121 to be polished used in the process of the flowchart of Fig. 5.

[0048] 12 shows an example 1200 of a sensor output map for the substrate 121 to be polished. The output signal value of the eddy current sensor 150 can be profiled on a line of any shape (such as line A-A' shown in the figure) drawn on the sensor output map 1200. In other words, a profile along any line on the sensor output map 1200 can be calculated.

[0049] Next, in step 1104, a trajectory having a profile most similar to the profile of the output signal of the eddy current sensor 150 acquired in step 502 of the flowchart of Fig. 5 (e.g., the profile obtained during polishing of the substrate 121) is extracted from the sensor output map for the substrate 121 to be polished created in step 1102. Furthermore, in step 1106, the trajectory extracted from this sensor output map is identified as the trajectory on the substrate 121 to be polished that the eddy current sensor 150 has passed through.

[0050] For example, the similarity of the profiles can be determined by calculating the sum of the differences in signal values ​​at corresponding measurement points between a profile on a certain trajectory of the sensor output map created in step 1102 and the profile of the output signal of the eddy current sensor 150 acquired in step 502. As an example, the two profiles may be determined to be most similar when the sum of the differences is the smallest. As another method, the similarity may be determined by comparing at least one of the peak shape, peak position, or peak magnitude of the profile on a certain trajectory of the sensor output map with at least one of the peak shape, peak position, or peak magnitude of the profile of the output signal of the eddy current sensor 150. Any other method for determining the similarity of profiles may be used.

[0051] The processing of steps 1104 and 1106 will be described in more detail with reference to FIGS. 12 to 14. As an example, profiles on trajectories A-A', B-B', and C-C' are extracted from the sensor output map 1200 of FIG. 12. The angular interval θ between each trajectory may be, for example, 0.1 degrees or less, and the number of extracted profiles may be four or more. While trajectories A-A' and the like are shown as straight lines in FIG. 12, the shape of each trajectory may be an arc, similar to the actual trajectory. Here, it is assumed that a profile 1300 of the output signal of the eddy current sensor 150, as shown in FIG. 13, was obtained in step 502 of the flowchart of FIG. 5.

[0052] The control unit 140 acquires a profile on each trajectory of the sensor output map 1200. In this example, there are three trajectories as shown in FIG. 12. Therefore, in this example, three profiles (profile A-A', profile B-B', and profile C-C') are acquired from the sensor output map 1200 as shown in FIG. 14. It should be understood that the profiles in FIG. 14 are not exact reproductions of the profiles of the sensor output map 1200 in FIG. 12.

[0053] The control unit 140 uses any method for similarity comparison to identify the trajectory having the profile most similar to the profile 1300 of the output signal of the eddy current sensor 150. For example, the control unit 140 can normalize the profile 1300 of the output signal of the eddy current sensor 150 and the profile A-A', profile B-B', and profile C-C' obtained from the sensor output map 1200, and then calculate the similarity from the magnitude of the mean square error. In this example, it is assumed that profile C-C' is determined to be most similar to the profile 1300 of the output signal of the eddy current sensor 150. The control unit 140 can identify the trajectory C-C' corresponding to profile C-C' as the trajectory taken by the eddy current sensor 150 on the polishing target substrate 121.

[0054] Although the embodiments of the present invention have been described above based on several examples, the above-described embodiments of the invention are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit thereof, and the present invention naturally includes equivalents thereof. Furthermore, any combination or omission of the components described in the claims and specification is possible within the scope of solving at least part of the above-described problems or achieving at least part of the effects.

[0055] REFERENCE SIGNS LIST 100 Substrate polishing apparatus 110 Polishing table 111 Polishing pad 120 Polishing head 121 Substrate 122 Airbag 130 Liquid supply mechanism 140 Control unit 141 Storage device 142 Processor 143 Input / output device 150 Eddy current sensor 202 Dielectric film 204 Metal film 206 Through electrode 208 Metal wiring

Claims

1. A substrate polishing apparatus comprising: a rotatable polishing table provided with an eddy current sensor; a rotatable polishing head opposed to the polishing table, the polishing head capable of mounting a substrate on a surface opposed to the polishing table; and a control unit, wherein the control unit: generates mapping data representing the arrangement of one or more metal structures locally present on the surface or inside of the reference substrate using an output signal of the eddy current sensor for a reference substrate; acquires a profile of the output signal of the eddy current sensor when the eddy current sensor passes through a certain trajectory on the polished surface of the substrate to be polished, during polishing of the substrate to be polished, the substrate having the same arrangement of metal structures as the reference substrate; identifies, based on the profile, a trajectory along which the eddy current sensor passed on the polished surface of the substrate to be polished that corresponds to the profile; determines, based on the mapping data, whether or not a metal structure is present on the identified trajectory of the substrate to be polished; corrects the profile of the output signal of the eddy current sensor for the substrate to be polished so as to reduce signal values ​​at positions where it is determined that the metal structure is present; and calculates the film thickness of the substrate to be polished based on the corrected profile of the output signal of the eddy current sensor. The substrate polishing apparatus is configured as follows.

2. A substrate polishing apparatus as described in claim 1, wherein the process of generating the mapping data includes a process of correcting the position of each maximum or minimum value so that multiple maximum or minimum values ​​of the output signal of the eddy current sensor over the entire surface of the reference substrate are aligned in a straight line.

3. A substrate polishing apparatus as described in claim 1 or 2, wherein the process of generating the mapping data includes a process of correcting or interpolating the position of each maximum or minimum value so that multiple maximum or minimum values ​​of the output signal of the eddy current sensor are arranged at equal intervals over the entire surface of the reference substrate.

4. A substrate polishing apparatus according to claim 1, wherein the process of correcting the profile includes a process of reducing the peak corresponding to the position of the metal structure and its neighboring portion among a plurality of peaks contained in the profile.

5. A substrate polishing apparatus as described in claim 4, wherein the process of correcting the profile includes a process of reducing the peak corresponding to the position of the metal structure and its surrounding area among the multiple peaks contained in the profile so that they are lower than peaks that do not correspond to the metal structure.

6. The substrate polishing apparatus according to claim 4 or 5, wherein the adjacent portion corresponds to the size of the metal structure.

7. The substrate polishing apparatus according to claim 1, wherein the reference substrate is a substrate having no metal film formed on its surface.

8. The substrate polishing apparatus according to claim 1, wherein the substrate to be polished is a substrate having a metal film to be polished formed on its surface.

9. The substrate polishing apparatus according to claim 1, wherein the metal structure is a through electrode or metal wiring formed on the substrate.

10. The substrate polishing apparatus of claim 1, wherein the process of identifying the trajectory based on the profile includes: a process of generating a sensor output map representing the distribution of the magnitude of the output signal of the eddy current sensor over the entire surface of the substrate to be polished; and a process of extracting from the sensor output map a trajectory having a profile most similar to the profile acquired during polishing of the substrate to be polished, and identifying the extracted trajectory as the trajectory of the eddy current sensor relative to the substrate to be polished.

11. The substrate polishing apparatus according to claim 1, further comprising an air bag capable of adjusting the polishing pressure on the substrate to be polished, and the control unit is further configured to control the internal pressure of the air bag based on the calculated film thickness of the substrate to be polished.

12. A method for calculating a film thickness in a substrate polishing apparatus comprising: a rotatable polishing table provided with an eddy current sensor; and a rotatable polishing head opposed to the polishing table, capable of mounting a substrate on a surface opposed to the polishing table, the method comprising the steps of: generating mapping data representing the arrangement of one or more metal structures locally present on the surface or inside of the reference substrate using an output signal from the eddy current sensor for a reference substrate; acquiring a profile of the output signal from the eddy current sensor when the eddy current sensor passes through a certain trajectory on the polished surface of the substrate to be polished, the trajectory corresponding to the profile, based on the profile; determining whether or not a metal structure is present on the identified trajectory of the substrate to be polished, based on the mapping data; and correcting the profile of the output signal from the eddy current sensor for the substrate to be polished so as to reduce the signal value at the position determined to have the metal structure. calculating a film thickness of the substrate being polished based on a profile of the corrected eddy current sensor output signal.

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