Polishing device and method for evaluating work-affected layer in polishing device

Abstract

A new evaluation method for a work-affected layer using an eddy current sensor is provided.　A polishing device for polishing a workpiece having a work-affected layer is provided. This polishing device comprises: a first holder configured to hold and rotate the workpiece; a second holder configured to hold and rotate a polishing tool for polishing the workpiece so as to face the workpiece; at least one eddy current sensor provided at one of the first holder and the second holder; and a controller. The controller is configured to acquire an output signal of the eddy current sensor during polishing of the workpiece, calculate an electric resistance value of a polished layer in the workpiece on the basis of the output signal of the eddy current sensor, and determine the thickness of the work-affected layer in the workpiece on the basis of a deviation of the calculated electric resistance value of the polished layer from a predetermined reference.

Description

Polishing apparatus and method for evaluating the processed altered layer in the polishing apparatus

[0001] The present invention relates to a polishing apparatus and a method for evaluating the processed and altered layer in a polishing apparatus.

[0002] One type of semiconductor device manufacturing equipment is a CMP (Chemical Mechanical Polishing) machine. A typical CMP machine comprises a polishing table to which a polishing pad is attached and a polishing head to which a substrate is attached. In a typical CMP machine, a polishing solution 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 and the substrate are in contact.

[0003] On the surface of a workpiece such as a substrate, a processed layer may be formed during processing steps such as cutting, which are pre-processing steps before polishing. This processed layer is a layer whose physical properties have changed from the original material, and it is required to be completely removed by polishing. Reference 1 discloses a technique for detecting this processed layer using an eddy current sensor.

[0004] Japanese Patent Publication No. 2018-189603

[0005] One objective of this invention is to provide a new evaluation method for processed and altered layers using eddy current sensors.

[0006] According to one embodiment, a polishing apparatus for polishing a workpiece having a processed altered layer is provided, comprising: a first holder configured to hold and rotate the workpiece; a second holder configured to hold and rotate a polishing tool for polishing the workpiece so as to face the workpiece; at least one eddy current sensor provided on one of the first holder and the second holder; and a control unit, wherein the control unit acquires the output signal of the eddy current sensor during polishing of the workpiece, calculates the electrical resistance value of the layer to be polished on the workpiece based on the output signal of the eddy current sensor, and determines the thickness of the processed altered layer on the workpiece based on the deviation of the calculated electrical resistance value of the layer to be polished from a predetermined standard.

[0007] In the above embodiment, the predetermined criterion may be the relationship between the thickness of the polished layer and the electrical resistance value in a workpiece that does not have a processed altered layer.

[0008] In the above embodiment, the determination may include calculating the magnitude of the deviation from a predetermined standard based on the thickness of the polished layer and the calculated electrical resistance value of the polished layer, and determining the thickness of the processed altered layer in the polished object based on the magnitude of the deviation from the predetermined standard.

[0009] In the above embodiment, the determination may include calculating the second derivative of the calculated electrical resistance value of the polished layer with respect to the thickness of the polished layer, and determining that the thickness of the processed and altered layer in the polished object is zero when the value of the second derivative of the polished layer with respect to the electrical resistance value becomes zero.

[0010] In the above embodiment, it may include estimating the time when the value of the second derivative becomes zero using the calculated values ​​of the multiple second derivatives.

[0011] In the above embodiment, the determination may include calculating the rate of change of the calculated electrical resistance value of the polished layer with respect to the thickness of the polished layer, and determining that the thickness of the processed and altered layer in the polished object has reached its minimum value when the rate of change of the electrical resistance value of the polished layer becomes constant.

[0012] In the above embodiment, the eddy current sensor may be driven using a drive frequency that changes from a first frequency to a second frequency that is higher than the first frequency during the polishing of the workpiece.

[0013] In the above embodiment, the system further comprises an airbag capable of adjusting the polishing pressure applied to the workpiece, and the control unit may be further configured to control the internal pressure of the airbag based on the thickness of the processed altered layer in the workpiece.

[0014] In the above embodiment, the first holder may be provided with a plurality of eddy current sensors, and the plurality of eddy current sensors may be arranged in a line along the circumferential or radial direction of the first holder.

[0015] In the above embodiment, the first holder may comprise a first portion that does not rotate and a second portion configured to rotate relative to the first portion, wherein the first portion of the first holder is provided with the at least one eddy current sensor, and the second portion of the first holder holds the workpiece to be polished.

[0016] Furthermore, according to one embodiment, a method is provided for evaluating the processed altered layer of a workpiece in a polishing apparatus for polishing a workpiece having a processed altered layer, wherein the polishing apparatus comprises a first holder configured to hold and rotate the workpiece, a second holder configured to hold and rotate a polishing tool for polishing the workpiece so as to face the workpiece, and at least one eddy current sensor provided on one of the first holder and the second holder, and the method includes the steps of: acquiring an output signal from the eddy current sensor during polishing of the workpiece; calculating the electrical resistance value of the polished layer in the workpiece based on the output signal from the eddy current sensor; and determining the thickness of the processed altered layer in the workpiece based on the deviation of the calculated electrical resistance value of the polished layer from a predetermined standard.

[0017] This is a front view of a polishing apparatus according to one embodiment of the present invention. This is a schematic cross-sectional view showing the structure of an exemplary substrate to be polished by the polishing apparatus. This is an exemplary model showing the relationship between the depth x from the surface of the substrate and the electrical resistivity ρ at that location. This is the sheet resistance R of the substrate obtained by the model in Figure 3. Ｓ This graph shows the relationship between the sheet resistance R of the substrate obtained using the model in Figure 3. Ｓ This is another type of graph showing the relationship between and thickness t. This figure shows the estimation of the point in time when the thickness of the processed altered layer becomes zero. This is a flowchart showing the control method of a polishing apparatus according to one embodiment of the present invention. The sheet resistance R of the substrate obtained by the model in Figure 3. ＳThis is yet another type of graph showing the relationship between and thickness t. This is a front view of the polishing apparatus according to the second embodiment of the present invention. This is a top view of the substrate holder of the polishing apparatus according to the second embodiment of the present invention. This is a cross-sectional view showing a modified example of the substrate holder of the polishing apparatus according to the second embodiment of the present invention. This is a front view of a modified example of the polishing apparatus according to the second embodiment of the present invention.

[0018] Embodiments of the present invention will be described below with reference to the drawings. In the drawings described below, the same or corresponding components are denoted by the same reference numerals, and redundant descriptions are omitted.

[0019] <First Embodiment> Figure 1 is a front view of a polishing apparatus 100 according to one embodiment. The polishing apparatus 100 shown in Figure 1 is a CMP (Chemical Mechanical Polishing) apparatus. However, the polishing apparatus 100 is not limited to a CMP apparatus. The polishing apparatus 100 can be any apparatus that polishes an object to be polished, such as a substrate, by rotating a polishing table equipped with an eddy current sensor.

[0020] The CMP apparatus 100 comprises a polishing table 110, a polishing head 120, and a liquid supply mechanism 130. The CMP apparatus 100 further comprises a control unit 140 for controlling each component. The control unit 140 may include, for example, a storage device 141, a processor 142, and an input / output device 143.

[0021] On the upper surface of the polishing table 110, a polishing pad 111 is detachably attached. Here, the upper surface of the polishing table 110 refers to the surface of the polishing table 110 that faces the polishing head 120. Therefore, the upper surface of the polishing table 110 is not limited to the surface positioned vertically upward. The polishing head 120 is provided so as to face the polishing table 110. A substrate 121 is detachably attached to the surface of the polishing head 120 that faces the polishing table 110. The substrate 121 is an example of an object to be polished. The substrate 121 may be, for example, a Si (silicon) substrate, a SiC (silicon carbide) substrate, a GaN (gallium nitride) substrate, etc. Not limited to such semiconductor substrates, any object may be used as the object to be polished. 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 or a chemical solution in addition to the polishing liquid.

[0022] The CMP apparatus 100 can lower the polishing head 120 by a vertical movement mechanism (not shown) to bring the substrate 121 into contact with the polishing pad 111. However, the vertical movement mechanism may be able to move the polishing table 110 vertically. 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.

[0023] The CMP apparatus 100 may further include an airbag 122 divided into a plurality of concentric sections. The airbag 122 may be provided on the polishing head 120. As an addition or alternative, the airbag 122 may be provided on the polishing table 110. The airbag 122 is a member for adjusting the polishing pressure of the substrate 121 for each region of the substrate 121. The airbag 122 is configured such that its volume changes according to the pressure of the air introduced into it. A fluid other than air, such as nitrogen gas or pure water, may be introduced into the airbag 122.

[0024] Inside the polishing table 110, an eddy current sensor 150 is provided. 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 the 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. By using the output signal from this eddy current sensor 150, the thickness of the film to be polished on the surface of the substrate 121 can be obtained.

[0025] FIG. 2 is a schematic cross-sectional view showing the structure of an exemplary substrate 121 to be polished by the polishing apparatus 100. As shown in FIG. 2, this exemplary substrate 121 has a processed altered layer 121a on its outermost surface. The processed altered layer 121a is a surface layer that has changed in material properties by performing processing such as cutting on the substrate 121. Material changes include, for example, disorder and increase of lattice defects on the surface, deformation and refinement of crystal grains, or surface flow. For example, the base portion of the substrate 121 may be a crystal layer, while the processed altered layer 121a may be an amorphous layer. The substrate 121 also includes a layer to be polished 121b. The layer to be polished 121b is a layer that is planned to be removed from the substrate 121 by polishing with the polishing apparatus 100. The processed altered layer 121a may be included in the layer to be polished 121b. In one example, as shown in FIG. 2, the layer to be polished 121b may extend to a position deeper than the lowermost (deepest) part of the processed altered layer 121a. In another example, the thickness of the layer to be polished 121b may be the same as the thickness of the processed altered layer 121a.

[0026] Here, in order to examine the behavior of the measurement values obtained by performing measurement with the eddy current sensor 150 on the exemplary substrate 121 of FIG. 2, consider the following model. FIG. 3 is an exemplary model showing the relationship between the depth x from the surface of the substrate 121 and the electrical resistivity ρ at that location. In the model represented by the graph of FIG. 3, x = 0 on the horizontal axis of the graph corresponds to the surface of the substrate 121, and the thicknesses of the substrate 121 and the processed altered layer 121a are t and x, respectively. ｄThat is, the machined affected layer 121a exists in the range from depth x = 0 to x = x ｄ and the original crystal layer of the substrate 121 that has not been affected by machining exists in the range from depth x = x ｄ to x = t. Also, the electrical resistivity of the original crystal layer of the substrate 121 is ρ ０ , and it is assumed that the electrical resistivity of the machined affected layer 121a decreases as it approaches the surface of the substrate 121.

[0027] In such a model, the electrical resistance dR of a microelement with thickness dx, width W, and length L (cross-sectional area dA = Wdx) cut out from the substrate 121 is expressed by the following equation.

[0028]

[0029] Assuming the electrical resistance of the entire substrate 121 is R, the equation for the combined resistance of a circuit in which a large number of such microelements are connected in parallel can be written as follows.

[0030]

[0031] From the above equation, the overall electrical resistance R and sheet resistance R Ｓ of the substrate 121 with thickness t in this model are as follows.

[0032]

[0033] FIG. 4 is a graph showing the relationship between the sheet resistance R Ｓ of the substrate 121 obtained from the above model and the thickness t of the substrate 121. The horizontal axis of the graph in FIG. 4 is the thickness t of the substrate 121, and the vertical axis represents the reciprocal R Ｓ －１ of the sheet resistance of the substrate 121. In the graph of FIG. 4, the sheet resistance R Ｓ of the substrate 121 based on the above model (calculated, for example, by numerical integration of the above equation) is shown by the solid line 402. Also, for comparison, the sheet resistance for a substrate of the same type without a machined affected layer is shown by the dotted line 404. Here, since the sheet resistance of a substrate without a machined affected layer is R Ｓ －１ = t / ρ ０ , the dotted line 404 has a slope of 1 / ρ ０This is a straight line. As shown in Figure 4, if a processed altered layer 121a is present on the substrate 121, the reciprocal of the sheet resistance R of the substrate 121 based on the model in Figure 3 is... Ｓ －１ The value of (solid line 402) is greater than the reciprocal value of the sheet resistance in a substrate without a processed altered layer (dotted line 404). As polishing progresses and the thickness t of the substrate 121 decreases, the difference between the two (the difference between solid line 402 and dotted line 404) decreases, and when the processed altered layer 121a is completely gone, the difference becomes zero.

[0034] Therefore, for example, by monitoring the deviation of the sheet resistance of the substrate 121 having the processed and altered layer 121a, as measured by the eddy current sensor 150 (for example, a point on the solid line 402 in Figure 4), from the sheet resistance of the substrate without the processed and altered layer (for example, the straight line 404 in Figure 4), the amount of the processed and altered layer 121a present on the surface of the substrate 121 can be determined. Specifically, the current substrate thickness t of the substrate 121 and the reciprocal R of the measured sheet resistance of the substrate 121 can be used to determine the amount of the processed and altered layer 121a present on the surface of the substrate 121. Ｓ －１ By plotting the points determined by on the graph in Figure 4, it is possible to identify the amount of deviation from the reference (straight line 404). The current substrate thickness t of the substrate 121 is the initial value t of the thickness of the substrate 121 at the start of polishing, assuming that the polishing speed of the substrate 121 is constant. ０ This can be calculated from the elapsed time since the start of polishing. Alternatively, the current substrate thickness t of the substrate 121 may be determined based on the amount of elevation of the polishing head 120 measured by the vertical movement mechanism that controls the vertical position of the polishing head 120, or by using a film thickness sensor (e.g., an optical film thickness sensor) provided separately from the eddy current sensor 150. In one embodiment, for example, when it is detected that the above-mentioned displacement has become zero, it can be determined that the thickness of the processed altered layer 121a has become zero, that is, that the processed altered layer 121a has been completely removed by polishing. Furthermore, the determination that the processed altered layer 121a has been completely removed can also be made by, for example, the method described below.

[0035] Figure 5 shows the sheet resistance R of the substrate 121 obtained using the model in Figure 3. ＳThis is another type of graph showing the relationship between the thickness t of the substrate 121 and the resistance R of the substrate 121. In the graph of Figure 5, the horizontal axis is the thickness t of the substrate 121, and the vertical axis is the reciprocal of the sheet resistance R of the substrate 121. Ｓ －１ This represents the second derivative with respect to the substrate thickness t. The graph in Figure 5 shows the reciprocal R of the sheet resistance of the substrate 121 having the processed altered layer 121a. Ｓ －１ The second derivative with respect to is shown by the solid line 502, and for comparison, the second derivative with respect to the reciprocal of the sheet resistance of the same type of substrate without the processed and altered layer is shown by the dotted line 504. As described above, the dotted line 404 in Figure 4, which corresponds to the sheet resistance of the substrate without the processed and altered layer, is a straight line, so the dotted line 504 in Figure 5, which is its second derivative, is a straight line representing a constant value of 0 for all t (i.e., a straight line that coincides with the horizontal axis). Therefore, the sheet resistance R of the substrate 121 having the processed and altered layer 121a obtained by measurement with the eddy current sensor 150 is... Ｓ Therefore, its reciprocal R Ｓ －１ By calculating the second derivative with respect to the substrate thickness t, and detecting that the value of the second derivative becomes zero, it is possible to determine that the thickness of the processed altered layer 121a has become zero, that is, that the processed altered layer 121a has been completely removed by polishing. Note that it is necessary to know the current substrate thickness t of the substrate 121 when calculating the second derivative, but as mentioned above, assuming that the polishing speed is constant, the initial value t of the thickness of the substrate 121 at the start of polishing can be used. ０ From the elapsed time since the start of polishing, the current substrate thickness t can be determined, and using this, the reciprocal R of the sheet resistance of the substrate 121 obtained by measurement can be calculated. Ｓ －１ The second derivative with respect to the substrate thickness t can be calculated. Alternatively, the second derivative may be calculated using the current substrate thickness t obtained from the amount of elevation of the polishing head 120 or from measurement by an optical film thickness sensor, as described above.

[0036] Furthermore, as the remaining thickness of the processed altered layer 121a decreases (i.e., in the region where the solid line 402 approaches the dotted line 404 in the graph of Figure 4), the accuracy of the second derivative calculation may deteriorate due to the limit of the resolution of the signal from the eddy current sensor 150. Therefore, as shown in Figure 5A, it is convenient to use the data 502a obtained before the remaining thickness of the processed altered layer 121a decreases to estimate the point in time 506 when the thickness of the processed altered layer 121a becomes zero. For example, by extrapolating the curve 502a of the second derivative calculation results obtained up to a certain point during the polishing of the processed altered layer 121a with a predetermined function equation, the thickness t of the substrate 121 corresponding to the state in which the processed altered layer 121a has been completely removed can be estimated. ｆｉｎ It is possible to predict this. Based on this prediction, the substrate thickness t is monitored (as described above), and if the substrate thickness is t ｆｉｎ When this occurs, it can be determined that the processed altered layer 121a has been completely removed.

[0037] Figure 6 is a flowchart showing a control method for a polishing apparatus 100 according to one embodiment of the present invention. The processing in this flowchart may be carried out by a processor (for example, the processor 142 of the control unit 140).

[0038] First, in step 602, the output signal of the eddy current sensor 150 to the substrate 121 is acquired. Specifically, the output signal is acquired from the eddy current sensor 150 while both the polishing head 120, to which the substrate 121 to be polished is attached, and the polishing table 110 are rotated at predetermined rotational speeds. The eddy current sensor 150 moves in an arc-shaped trajectory relative to the substrate 121 (i.e., from the perspective of the substrate 121), corresponding to the ratio of the rotational speed of the polishing table 110 to the rotational speed of the polishing head 120. The eddy current sensor 150 passes through a different trajectory on the substrate 121 each time the polishing table 110 rotates. Signal values ​​at each point along these multiple arc-shaped trajectories are continuously obtained from the eddy current sensor 150.

[0039] Next, in step 604, the processor 142 of the control unit 140 calculates the electrical resistance of the polished layer 121b of the substrate 121 based on the output signal of the eddy current sensor 150 for each point on the trajectory of the substrate 121 that the eddy current sensor 150 has passed through. Specifically, the output signal obtained from the eddy current sensor 150 is a signal that reflects the change in impedance caused by eddy currents induced in the substrate 121, and the processor 142 calculates the sheet resistance R of the substrate 121 from the resistance component of this impedance. Ｓ It is possible to calculate this.

[0040] Next, in step 606, the processor 142 controls the sheet resistor R of the substrate 121 obtained in step 604. Ｓ Based on the deviation from a predetermined standard, the thickness of the processed and altered layer 121a present on the surface of the substrate 121 is determined. The predetermined standard is the relationship between the thickness of the substrate without the processed and altered layer (or the thickness of the polished layer on the substrate) and the electrical resistance value. More specifically, the predetermined standard may be, for example, the relationship between the reciprocal of the sheet resistance of the substrate without the processed and altered layer and the substrate thickness, as shown by the dotted line 404 in Figure 4, and the processor 142 determines the sheet resistance R of the substrate 121 obtained in step 604. Ｓ Find the reciprocal of and the reciprocal R Ｓ －１ The processor determines how much the point determined by the current substrate thickness t of the substrate 121 deviates from the dotted line 404 in Figure 4, and from the amount of deviation, it is possible to determine the thickness of the processed altered layer 121a or whether the processed altered layer 121a has been completely removed. Alternatively, the predetermined criterion may be, for example, the relationship between the second derivative of the reciprocal of the sheet resistance in a substrate without a processed altered layer and the substrate thickness, as shown by the dotted line 504 in Figure 5, and the processor 142 obtains the sheet resistance of the substrate 121 obtained in step 604 and its reciprocal R Ｓ －１ The second derivative with respect to the substrate thickness t is calculated, and if the value of the second derivative is zero, it can be determined that the processed altered layer 121a has been completely removed.

[0041] Next, in step 608, the processor 142 determines whether the thickness distribution of the processed altered layer 121a within the substrate plane is uniform. If the thickness distribution of the processed altered layer 121a within the substrate plane is not uniform, the process proceeds to step 610, where the processor 142 increases or decreases the internal pressure of the airbag 122 to control the polishing pressure so that it is higher in areas where the processed altered layer 121a is thick (i.e., areas where the degree of polishing is low) and lower in areas where the processed altered layer 121a is thin (i.e., areas where the degree of polishing is high). This control allows the processed altered layer 121a to be polished while ensuring a uniform polishing state.

[0042] Next, in step 612, the processor 142 determines whether the processed altered layer 121a of the substrate 121 has been completely removed by polishing. If the processed altered layer 121a has been completely removed, the process proceeds to step 614, where the processor 142 determines the in-plane thickness distribution of the substrate 121 (with the processed altered layer 121a removed) based on the output signal from the eddy current sensor 150, and determines whether the in-plane distribution has reached the target profile. If the in-plane thickness distribution of the substrate 121 has not reached the target profile, the process proceeds to step 616, where the processor 142 controls the internal pressure of the airbag 122 to increase or decrease, similar to step 610 above. Finally, in step 618, the processor 142 determines whether the thickness of the substrate 121 has reached the target thickness, and if it has reached the target thickness, the process of this flowchart ends.

[0043] Furthermore, during the polishing process according to the flowchart above, the processor 142 may control the drive frequency (the oscillation frequency of the current flowing through the sensor coil of the eddy current sensor 150) that drives the eddy current sensor 150. For example, the eddy current sensor 150 may be driven at a first drive frequency in the initial stages of polishing, and then driven at a second drive frequency higher than the first drive frequency once the polishing has progressed to a certain extent (for example, when 80% of the polishing is complete relative to the target polishing amount). Increasing the drive frequency increases the detection sensitivity of the eddy current sensor 150, making it possible to more accurately determine when the processed altered layer 121a has been completely removed and to determine the final polishing completion timing.

[0044] Although the above description has focused on an embodiment where the polishing apparatus is a CMP apparatus 100, the present invention is also applicable to polishing apparatuses other than CMP apparatuses, such as lapping apparatuses. In a lapping apparatus, the polishing pad 111 is made of a hard metal plate. Therefore, when a substrate 121 having a processed altered layer 121a is polished with a lapping apparatus, the processed altered layer 121a can be thinned to a certain extent, but if polishing is continued further with the lapping apparatus, a new processed altered layer will be generated due to the frictional pressure from the hard metal plate, and the net thickness of the processed altered layer cannot be reduced below a certain film thickness value (i.e., the processed altered layer settles at a certain film thickness).

[0045] Figure 7 shows the sheet resistance R of the substrate 121 being polished by a lapping device. Ｓ This graph, corresponding to Figure 4 above, shows the relationship between and the substrate thickness t. When the substrate 121 is polished with a lapping device, the processed and altered layer ultimately becomes a constant thickness, so as shown in Figure 7, the sheet resistance R of the substrate 121 Ｓ The solid curve 702, which represents the reciprocal of R, approaches a straight line with a constant slope (a straight line parallel to the straight line 404 in Figure 4) as polishing progresses and the substrate thickness t decreases. Thus, unlike in the case of a CMP apparatus, the difference between the solid line 702 and the dotted line 404 is not zero, but as a result of polishing, when the film thickness of the processed and altered layer settles to its minimum value, the slope (rate of change) of the solid line 702 becomes constant. Therefore, in the embodiment in which a lapping polishing apparatus is used, the current substrate thickness t of the substrate 121 and the reciprocal R of the measured sheet resistance of the substrate 121 are... Ｓ －１ The points determined by and are plotted continuously on a graph, and when it is detected that the slope of the resulting curve (for example, the solid line 702 in Figure 7) has become constant, it can be determined that the thickness of the processed altered layer has reached its minimum value. Since it is not possible to make the processed altered layer any thinner with a lapping polishing device, the processed altered layer can then be further polished using a CMP device.

[0046] <Second Embodiment> Figure 8 is a front view of a polishing apparatus 200 according to another embodiment. The polishing apparatus 200 comprises a substrate holder 210 for holding a substrate 121, a grinding wheel holder 220 for holding a grinding wheel 221, and a control unit 140. The control unit 140 is the same as the control unit 140 of the polishing apparatus 100 according to the first embodiment described above, and controls the polishing apparatus 200 in the same manner as in the first embodiment (see Figure 6). The polishing apparatus 200 according to this embodiment differs from the first embodiment in that the polishing head 120 and polishing table 110 in the polishing apparatus 100 of the first embodiment are replaced by the substrate holder 210 and the grinding wheel holder 220, respectively. Unless otherwise specified, in other respects, the polishing apparatus 200 is configured and operates in the same manner as the polishing apparatus 100.

[0047] A grinding wheel 221 is detachably mounted on the surface of the grinding wheel holder 220 facing the substrate holder 210. Similarly, a substrate 121 is detachably mounted on the surface of the substrate holder 210 facing the grinding wheel holder 220. For example, the substrate holder 210 and the grinding wheel holder 220 may be positioned such that the substrate 121 and the grinding wheel 221 face each other in the horizontal direction (lateral direction in the figure), as shown in Figure 8.

[0048] The polishing device 200 moves the substrate holder 210 toward the grinding wheel holder 220 by a drive mechanism (not shown), thereby bringing the substrate 121 into contact with the grinding wheel 221. The polishing device 200 may also move the grinding wheel holder 220 toward the substrate holder 210. The substrate holder 210 and the grinding wheel holder 220 are rotated by a motor (not shown) or the like. The polishing device 200 polishes the substrate 121 by rotating both the substrate holder 210 and the grinding wheel holder 220 while the substrate 121 and the grinding wheel 221 are in contact. The "polishing" device 200 may also be configured as a "grinding" device.

[0049] An eddy current sensor 150 is provided inside the substrate holder 210. The eddy current sensor 150 is the same as the eddy current sensor 150 described above for the polishing apparatus 100 of the first embodiment, and it induces eddy currents in the conductive layer on the surface of the substrate 121 and outputs a signal to the control unit 140 corresponding to the magnetic field generated by the eddy currents. From the output signal of this eddy current sensor 150, the thickness of the conductive layer on the surface of the substrate 121 (for example, the thickness of the processed and altered layer 121a) can be determined in the same manner as in the first embodiment.

[0050] Unlike the polishing apparatus 100 of the first embodiment, in this embodiment, the eddy current sensor 150 is provided on the substrate holder 210, so the relative position between the eddy current sensor 150 and the substrate 121 is fixed. Therefore, with a configuration using only one eddy current sensor 150, it is not possible to obtain film thickness measurements over a wide area of ​​the substrate 121.

[0051] Figure 9 is a top view of the substrate holder 210 of the polishing apparatus 200 according to this embodiment. The substrate holder 210 is provided with a plurality of eddy current sensors 150 across the mounting surface of the substrate 121 to the substrate holder 210. The plurality of eddy current sensors 150 include a plurality of eddy current sensors arranged in a line along the circumferential direction 211 of the substrate holder 210 and a plurality of eddy current sensors arranged in a line along the radial direction 212 of the substrate holder 210. Each eddy current sensor 150 detects a magnetic field generated by an eddy current induced at a proximity position of the eddy current sensor in the conductive layer on the substrate 121 and outputs a detection signal to the control unit 140. By using these signals corresponding to multiple locations in the conductive layer on the substrate 121, the in-plane thickness distribution of the conductive layer on the substrate 121 (for example, the thickness distribution along the circumferential direction 211 or the thickness distribution along the radial direction 212) can be determined. Note that the number and arrangement of eddy current sensors 150 shown in Figure 9 are merely examples and not limited to any particular configuration. A different number of eddy current sensors 150 may be provided, or multiple eddy current sensors 150 may be installed in a different arrangement.

[0052] Figure 10 is a cross-sectional view showing a modified example of the substrate holder 210 of the polishing apparatus 200 according to this embodiment. The substrate holder 210 according to this modified example has a first portion 210A that constitutes the inner core of the substrate holder 210 and a second portion 210B that constitutes the outer shell of the substrate holder 210. The second portion 210B is arranged to cover the first portion 210A. As shown in Figure 10, in this modified example, the substrate 121 is held by the second portion 210B of the substrate holder 210, and the eddy current sensor 150 (for example, one eddy current sensor) is attached to the first portion 210A of the substrate holder 210. The second portion 210B of the substrate holder 210 is connected to a motor (not shown), and the rotation of the motor can rotate the substrate 121 held by the second portion 210B. On the other hand, the first portion 210A of the substrate holder 210 is not connected to a motor and does not rotate. Therefore, the eddy current sensor 150 attached to the first part 210A does not rotate, and its position remains fixed. Consequently, in the substrate holder 210 of this modified example, as the substrate 121 held by the second part 210B rotates, the eddy current sensor 150 moves on the substrate 121 in a trajectory of a predetermined radius relative to the substrate 121. Thus, by using the output signals from the eddy current sensor 150 at each point along the trajectory, the thickness distribution of the conductive layer on the substrate 121 (for example, a thickness profile along the trajectory) can be determined. Although only one eddy current sensor 150 is shown in Figure 10, multiple eddy current sensors 150 may be installed at positions with different radii from the rotation center of the substrate 121. This makes it possible to obtain thickness profiles of the conductive layer along multiple different trajectories on the substrate 121.

[0053] Figure 11 is a front view of a modified example of the polishing apparatus 200 according to this embodiment. This modified example differs from the configuration in Figure 8 in that the eddy current sensor 150 is provided on the grinding wheel holder 220 side instead of the substrate holder 210 side. In this modified example, the eddy current sensor 150 moves along a predetermined trajectory on the substrate 121 as the substrate holder 210 and grinding wheel holder 220 rotate. Therefore, as in the case of Figure 10, the thickness distribution of the conductive layer on the substrate 121 (for example, a thickness profile along the trajectory) can be determined by using the output signals from the eddy current sensor 150 at each point along the trajectory.

[0054] While embodiments of the present invention have been described above based on several examples, the embodiments described above are intended to facilitate understanding of the present invention and do not limit it. The present invention can be modified and improved without departing from its spirit, and of course, its equivalents are included. Furthermore, any combination or omission of the components described in the claims and specification is possible to the extent that at least some of the above-mentioned problems can be solved or at least some of the effects can be achieved.

[0055] 100 Polishing device 110 Polishing table (second holder) 111 Polishing pad (polishing tool) 120 Polishing head (first holder) 121 Substrate (workpiece to be polished) 121a Processed altered layer 121b Polished layer 122 Airbag 130 Liquid supply mechanism 140 Control unit 141 Storage device 142 Processor 143 Input / output device 150 Eddy current sensor 200 Polishing device 210 Substrate holder (first holder) 220 Grinding wheel holder (second holder) 221 Grinding wheel (polishing tool)

Claims

1. A polishing apparatus for polishing a workpiece having a processed altered layer, comprising: a first holder configured to hold and rotate the workpiece; a second holder configured to hold and rotate a polishing tool for polishing the workpiece so as to face the workpiece; at least one eddy current sensor provided on one of the first holder and the second holder; and a control unit, wherein the control unit is configured to acquire the output signal of the eddy current sensor during polishing of the workpiece, calculate the electrical resistance value of the layer to be polished on the workpiece based on the output signal of the eddy current sensor, and determine the thickness of the processed altered layer on the workpiece based on the deviation of the calculated electrical resistance value of the layer to be polished from a predetermined standard.

2. The polishing apparatus according to claim 1, wherein the predetermined standard is the relationship between the thickness of the polished layer and the electrical resistance value in a workpiece that does not have a processed altered layer.

3. The polishing apparatus according to claim 2, wherein the determination includes calculating the magnitude of the deviation from a predetermined standard based on the thickness of the polished layer and the calculated electrical resistance value of the polished layer, and determining the thickness of the processed altered layer in the polished object based on the magnitude of the deviation from the predetermined standard.

4. The polishing apparatus according to claim 2, wherein the determination includes calculating the second derivative of the calculated electrical resistance value of the polished layer with respect to the thickness of the polished layer, and determining that the thickness of the processed and altered layer in the polished object is zero when the value of the second derivative of the polished layer with respect to the electrical resistance value becomes zero.

5. The polishing apparatus according to claim 4, comprising using the calculated values ​​of the multiple second derivatives to estimate the time when the value of the second derivative becomes zero.

6. The polishing apparatus according to claim 2, wherein the determination includes calculating the rate of change of the calculated electrical resistance value of the polished layer with respect to the thickness of the polished layer, and determining that the thickness of the processed and altered layer in the polished object has reached its minimum value when the rate of change of the electrical resistance value of the polished layer becomes constant.

7. The polishing apparatus according to any one of claims 1 to 6, wherein during the polishing of the workpiece, the eddy current sensor is driven using a drive frequency that changes from a first frequency to a second frequency higher than the first frequency.

8. The polishing apparatus according to any one of claims 1 to 6, further comprising an airbag capable of adjusting the polishing pressure applied to the workpiece, wherein the control unit is further configured to control the internal pressure of the airbag based on the thickness of the processed altered layer in the workpiece.

9. The polishing apparatus according to any one of claims 1 to 6, wherein a plurality of eddy current sensors are provided on the first holder, and the plurality of eddy current sensors are arranged in a line along the circumferential or radial direction of the first holder.

10. The polishing apparatus according to any one of claims 1 to 6, wherein the first holder comprises a first portion that does not rotate and a second portion configured to rotate relative to the first portion, the first portion of the first holder is provided with the at least one eddy current sensor, and the second portion of the first holder holds the object to be polished.

11. A method for evaluating the processed layer of a workpiece in a polishing apparatus for polishing a workpiece having a processed layer, the polishing apparatus comprising: a first holder configured to hold and rotate the workpiece; a second holder configured to hold and rotate a polishing tool for polishing the workpiece so as to face the workpiece; and at least one eddy current sensor provided on one of the first holder and the second holder, the method comprising: acquiring an output signal from the eddy current sensor during polishing of the workpiece; calculating the electrical resistance value of the polished layer in the workpiece based on the output signal from the eddy current sensor; and determining the thickness of the processed layer in the workpiece based on the deviation of the calculated electrical resistance value of the polished layer from a predetermined standard.

12. The method according to claim 11, wherein the predetermined standard is the relationship between the thickness of the polished layer and the electrical resistance value in a workpiece that does not have a processed altered layer.

13. The method according to claim 12, wherein the determination step includes: calculating the magnitude of the deviation from a predetermined standard based on the thickness of the polished layer and the calculated electrical resistance value of the polished layer; and determining the thickness of the processed altered layer in the polished object based on the magnitude of the deviation from the predetermined standard.

14. The method according to claim 12, wherein the determination step includes: calculating the second derivative of the calculated electrical resistance value of the polished layer with respect to the thickness of the polished layer; and determining that the thickness of the processed altered layer in the polished object is zero when the value of the second derivative of the polished layer with respect to the electrical resistance value becomes zero.

15. The method according to claim 12, wherein the determination step includes: calculating the rate of change of the calculated electrical resistance value of the polished layer with respect to the thickness of the polished layer; and determining that the thickness of the processed altered layer in the polished object has reached a minimum value when the rate of change of the electrical resistance value of the polished layer becomes constant.

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