Adjustment of Measurement Values from In Situ Monitoring Based on Resistivity

Abstract

A method is provided in which a substrate is monitored in situ as it passes through a polishing pad during polishing to induce eddy currents in the conductive layer and detect changes in the eddy currents as the conductive layer is removed. In one embodiment, a first resistivity value and a correlation function relating a thickness of a conductive layer having the first resistivity value to a signal from an in-situ monitoring system are stored. A second resistivity value for the conductive layer on the substrate is received. A series of signal values ​​dependent on the thickness of the conductive layer is received from an in-situ electromagnetic induction monitoring system monitoring the substrate being polished. A series of thickness values ​​is generated based on the series of signal values ​​and the correlation function. For at least some of the thickness values ​​in the series, adjusted thickness values ​​are generated that compensate for variations between the first resistivity value and the second resistivity value to generate a series of adjusted thickness values. A polishing endpoint is detected or adjustments to polishing parameters are determined based on the series of adjusted thickness values.

Description

Technical Field

[0001] The present disclosure relates to chemical mechanical polishing, and more specifically, to the monitoring of conductive layers during chemical mechanical polishing.

Background Art

[0002] Integrated circuits are typically formed on a substrate by sequentially depositing conductive layers, semiconductor layers, or insulating layers on a silicon wafer. Various manufacturing processes require planarization of the layers on the substrate. For example, one manufacturing step involves depositing a fill layer on a non-planar surface and planarizing the fill layer. In certain applications, the fill layer is planarized until the top surface of the patterned layer is exposed. For example, a metal layer can be deposited on a patterned insulating layer to fill the trenches and holes in the insulating layer. After planarization, the remaining portions of the metal in the trenches and holes of the patterned layer form vias, plugs, and lines to provide conductive paths between thin film circuits on the substrate.

[0003]

[0004] One problem in CMP is determining whether the polishing process is complete, i.e., whether the substrate layer has been planarized to the desired flatness or thickness, or when the desired amount of material has been removed. Variations in slurry composition, the condition of the polishing pad, the relative speed between the polishing pad and the substrate, the initial thickness of the substrate layer, and the load applied to the substrate can cause variations in the material removal rate. These variations cause the time required to reach the polishing endpoint to vary. Therefore, simply determining the polishing endpoint as a function of polishing time can result in non-uniformity within or between wafers.

[0005] In some systems, the substrate is monitored in situ, e.g., through a polishing pad, during polishing. One monitoring technique is to induce eddy currents in a conductive layer and detect changes in the eddy currents when the conductive layer is removed. SUMMARY OF THE INVENTION

[0006] In one aspect, a correlation function that associates the thickness of a conductive layer having a first resistivity value and a first resistivity value with a signal from an in-situ monitoring system is stored, a second resistivity value of the conductive layer on the substrate is received, a sequence of signal values that depends on the thickness of the conductive layer is received from an in-situ electromagnetic induction monitoring system that monitors the substrate during polishing, a sequence of thickness values is generated based on the sequence of signal values and the correlation function, and for at least some of the thickness values of the sequence of thickness values, an adjusted thickness value that compensates for variations between the first resistivity value and the second resistivity value is generated to generate a sequence of adjusted thickness values, and based on the sequence of adjusted thickness values, a polishing endpoint is detected or an adjustment of polishing parameters is determined.

[0007] In another aspect, a correlation function that associates the thickness of a conductive layer having a first resistivity value and a first resistivity value with a signal from an in-situ electromagnetic induction monitoring system is stored, a second resistivity value and sheet resistance of the conductive layer on a calibration substrate are received, a first signal value from the in-situ electromagnetic induction monitoring system that is measured when the sensor of the monitoring system is arranged to monitor the conductive layer of the calibration substrate is received, a second signal value from the in-situ electromagnetic induction monitoring system that is measured when the sensor of the monitoring system is not arranged to monitor the conductive layer is received, a threshold signal value that compensates for variations between the first resistivity value and the second resistivity value is calculated from the correlation function based on a target thickness, a sequence of signal values that depends on the thickness of the conductive layer is received from an in-situ electromagnetic induction monitoring system that monitors the substrate during polishing, and a polishing endpoint is detected by comparing the sequence of signal values with the threshold.

[0008] In another aspect, a correlation function that associates the first resistivity value and the thickness of the conductive layer having the first resistivity value with a signal from an in-situ monitoring system is stored, a second resistivity value and a sheet resistance value of the first conductive layer on the calibration substrate are received, a measurement of the first signal value of the first conductive layer on the calibration substrate is performed using an in-situ electromagnetic induction monitoring system, a measurement of the second signal value is performed using the in-situ electromagnetic induction monitoring system without the first conductive layer, and an offset and a gain to be applied to the signal from the in-situ electromagnetic induction monitoring system are calculated to compensate for variations in the in-situ electromagnetic induction monitoring system and to compensate for variations between the first resistivity value and the second resistivity value.

[0009] In another aspect, a correlation function that associates the first resistivity value and the thickness of the conductive layer having the first resistivity value with a signal from an in-situ monitoring system is stored, a second resistivity value of the conductive layer on the substrate is received, the conductive layer on the substrate is polished, and the conductive layer on the substrate is monitored during polishing with an in-situ electromagnetic induction monitoring system that generates a series of signal values depending on the thickness of the conductive layer, a series of thickness values are generated based on the series of signal values and the correlation function, and for at least some of the thickness values of the series of thickness values, adjusted thickness values that compensate for variations between the first resistivity value and the second resistivity value are generated to generate a series of adjusted thickness values, and based on the series of adjusted thickness values, a polishing end point is detected or an adjustment of the polishing parameters is determined.

[0010] Each of these aspects can be applied as a method, as a computer program product tangibly encoded on a non-transitory computer-readable medium including instructions for causing a computer system to execute operations, or as a polishing system including a controller configured to execute operations.

[0011] Embodiments of the method, computer program product, and / or system can include one or more of the following features.

[0012] The adjusted thickness value can be generated by multiplying the thickness value by the ratio of the first resistivity value to the second resistivity value.

[0013] The adjusted thickness value can compensate for temperature variations between the temperature at which the conductive layer has the second resistivity value and the temperature of the substrate during polishing. The first temperature can be stored, and the measured value of the second temperature can be received from the polishing system. The adjusted second resistivity value can be calculated based on the second resistivity value, the first temperature, and the second temperature. Calculating the adjusted resistivity value can include calculating a resistivity ρ T that satisfies the following. ρ T =ρ X [1 + α(T2 - T1)] where T1 is the first temperature, T2 is the second temperature, ρ X is the second resistivity, and α is the temperature coefficient of resistivity of the conductive layer.

[0014] The correlation function can satisfy the following. S = W1·D 2 + W2·D + W3 where S is the signal value, D is the thickness, and W1, W2, and W3 are coefficients.

[0015] The third resistivity value of the second conductive layer on the second substrate can be received. A series of signal values depending on the thickness of the second conductive layer can be received from an in-situ electromagnetic induction monitoring system that monitors the second substrate during polishing. A series of adjusted signal values can be generated by applying an offset and a gain to the signal values from the series of signal values. Based on the series of adjusted signal values and the correlation function, a series of thickness values can be generated. For at least some of the thickness values in the series of thickness values, adjusted thickness values that compensate for variations between the first resistivity value and the third resistivity value can be generated to generate a series of adjusted thickness values. Based on the series of adjusted thickness values, the polishing end point can be detected or adjustments to the polishing parameters can be determined.

[0016] Applying the gain can include calculating an adjusted signal value S' that satisfies the following. S’ = G * S - ΔK Here, G is the gain and ΔK is the offset.

[0017] Calculating the gain G can satisfy the following. G = (S DH - S DL ) / (S1 - S2) Here, S1 is the first signal value, S2 is the second signal value, S DH is the desired high signal value for the second conductive layer, and S DL is the desired low signal value when there is no second conductive layer.

[0018] Calculating the desired high signal value S DH can satisfy the following. TIFF0007693728000001.tif11170 Here, ρ0 is the first resistivity, Rs CAL is the sheet resistance value, and W1, W2, and W3 are coefficients.

[0019] The conductive layer can include a conductive sheet, and the monitoring system can generate eddy currents in the conductive sheet. The conductive layer can include a conductive loop, and the monitoring system can inductively generate a current in the conductive loop.

[0020] The temperature sensor can monitor the temperature related to the conductive layer.

[0021] Embodiments can include one or more of the following advantages. The possible inaccuracy in the correlation between the measured eddy current signal and the thickness of the conductive layer caused by variations in the resistivity of the conductive layer can be reduced. The adjusted eddy current signal or the adjusted thickness of the conductive layer using a compensation process can be more accurate. The adjusted eddy current signal and / or the adjusted conductive layer can be used to determine control parameters during the polishing process and / or to determine the end point of the polishing process. The reliability of determining control parameters and end point detection can be improved, under-polishing of the wafer can be avoided, and non-uniformity within the wafer can be reduced.

[0022] Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other aspects, features, and advantages will become apparent from the description and drawings, as well as from the claims.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figures 3A - 3C

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0024] One monitoring method for the polishing operation is, for example, to induce eddy currents in the conductive layer on the substrate by using an alternating current (AC) drive signal. The induced eddy currents can be measured in situ by an eddy current sensor during polishing to generate a signal. Assuming that the outermost layer being polished is the conductive layer, the signal from the sensor should depend on the thickness of the conductive layer. Based on the monitoring, control parameters of the polishing operation, such as the polishing rate, can be adjusted in situ. In addition, the polishing operation can be terminated based on an indication that the monitored thickness has reached the desired end thickness.

[0025] The accuracy of the correlation between the eddy current signal and the thickness of the conductive layer can be affected by various factors. One factor is the resistivity of the conductive layer. Specifically, even materials with the same composition on the surface (including both chemical composition and, for example, crystal structure) may have different resistivities due to differences in the manufacturing process. For example, copper deposited by electroplating can have a different resistivity from copper deposited by evaporation. When other parameters such as the structure of the eddy current system are the same, the eddy current signals generated from conductive layers of the same thickness will be different if the resistivity of the conductive layer is different.

[0026] Therefore, electromagnetic induction measurements, including the eddy current signal and the measured thickness based on the eddy current signal, are adjusted based on the resistivity of the conductive layer. Furthermore, since the resistivity of the conductive layer may depend on the process by which the conductive layer was formed, it may not be sufficient to simply compensate based on the textbook values of the resistivity of the conductive material.

[0027] In addition, due to assembly variations, the electromagnetic induction sensor may exhibit different gains and offsets. Therefore, the electromagnetic induction monitoring system can be calibrated to compensate for these variations and also taking into account the resistivity of the layers on the substrate used for calibration.

[0028] Figures 1 and 2 illustrate an example of a polishing station 20 of a chemical mechanical polishing system. The polishing station 20 includes a rotatable disk-shaped platen 24, on which a polishing pad 30 is positioned. The platen 24 is operable to rotate about an axis 25. For example, a motor 22 can rotate a drive shaft 28 to rotate the platen 24. The polishing pad 30 can be a two-layer polishing pad having an outer polishing layer 34 and a softer backing layer 32.

[0029] The polishing station 20 can include a supply port or a combined supply rinse arm 39 for dispensing a polishing liquid 38, such as a polishing slurry, onto the polishing pad 30. The polishing station 20 can include a pad conditioning device with a conditioning disk for maintaining the surface roughness of the polishing pad.

[0030] The carrier head 70 is operable to hold the substrate 10 against the polishing pad 30. The carrier head 70 is suspended from a support structure 72, such as a carousel or a track, and is connected to a carrier head rotation motor 76 by a drive shaft 74 so that the carrier head can rotate about an axis 71. Optionally, the carrier head 70 can vibrate laterally, for example, on a slider on the carousel, by movement along a track or by rotational vibration of the carousel itself.

[0031] The carrier head 70 can include a retaining ring 84 for holding the substrate. In some embodiments, the retaining ring 84 can include a highly conductive portion. For example, the carrier ring can include a thin lower plastic portion 86 that contacts the polishing pad and a thick upper conductive portion 88. In some embodiments, the highly conductive portion is a metal, such as the same metal as the layer being polished, for example, copper.

[0032] During operation, the platen rotates about its central axis 25, the carrier head rotates about its central axis 71, and translates laterally across the upper surface of the polishing pad 30. If there are multiple carrier heads, each carrier head 70 can independently control its polishing parameters. For example, each carrier head can independently control the pressure applied to its respective substrate.

[0033] The carrier head 70 can include a flexible membrane 80 having a substrate attachment surface that contacts the back side of the substrate 10, and a plurality of pressurizable chambers 82 that apply different pressures to different zones on the substrate 10, such as different radial zones. The carrier head can further include a retaining ring 84 for holding the substrate.

[0034] In some embodiments, the polishing station 20 includes a temperature sensor 64 for monitoring the temperature of the polishing station or components within the polishing station. In FIG. 1, it is shown disposed for monitoring the temperature of the polishing pad 30 and / or the slurry 38 on the pad 30, but the temperature sensor 64 may be disposed within the carrier head 70 for measuring the temperature of the substrate 10. The temperature sensor 64 can be in direct contact with the outermost layer of the polishing pad or the substrate 10, which can be a conductive layer, to accurately monitor the temperature of the outermost layer (i.e., a contact sensor). The temperature sensor can be a non-contact sensor (e.g., an infrared sensor). In some embodiments, a plurality of temperature sensors are included in the polishing station 22 for measuring the temperature of different components within the polishing station, for example. The temperature can be measured in real time, for example, periodically and / or in relation to real-time measurements performed by an eddy current system. The monitored temperature can be used to adjust the in-situ eddy current measurement values.

[0035] Referring to FIG. 3A, a polishing system can be used to polish a substrate 10 that includes a conductive material on and / or embedded in a patterned dielectric layer. For example, the substrate 10 can be on a dielectric layer 14, such as silicon oxide or a high-k dielectric trench, and can include a layer of conductive material 16, such as a metal, e.g., copper, aluminum, cobalt, or titanium, that fills the trench. Optionally, a barrier layer 18, such as tantalum or tantalum nitride, can cover the trench and separate the conductive material 16 from the dielectric layer 14. The conductive material 16 in the trench can provide vias, pads, and / or interconnects in the finished integrated circuit. The dielectric layer 14 is shown as being directly deposited on the semiconductor wafer 12, but one or more other layers may be inserted between the dielectric layer 14 and the wafer 12.

[0036] Initially, the conductive material 16 is over the entire dielectric layer 14. As polishing proceeds, the bulk of the conductive material 16 is removed and the barrier layer 18 is exposed (see FIG. 3B). Thereafter, as polishing continues, the patterned upper surface of the dielectric layer 14 is exposed (see FIG. 3C). Thereafter, additional polishing can be used to control the depth of the trench containing the conductive material 16.

[0037] In some embodiments, the polishing system includes additional polishing stations. For example, the polishing system can include two or three polishing stations. For example, the polishing system can include a first polishing station equipped with a first electromagnetic induction monitoring system and a second polishing station equipped with a second electromagnetic induction current monitoring system.

[0038] For example, during operation, bulk polishing of the conductive layer on the substrate can be performed at the first polishing station, and polishing can be stopped when the target thickness of the conductive layer remains on the substrate. Next, the substrate can be transferred to the second polishing station and polished down to an underlying layer, such as a patterned dielectric layer.

[0039] Returning to FIG. 1, the polishing system includes an in-situ electromagnetic induction monitoring system 100 that can be coupled to, or considered to include, a controller 90. A rotary coupler 29 is used to electrically connect components within the rotatable platen 24, such as sensors of the in-situ monitoring system, to components external to the platen, such as drive and sensing circuitry or controller 90.

[0040] The in-situ electromagnetic induction monitoring system 100 is configured to generate a signal that depends on the depth of a conductive material 16, such as metal. The electromagnetic induction monitoring system operates by the generation of eddy currents within a conductive material, which can be either a sheet of conductive material on a dielectric layer or conductive material remaining in a trench after the dielectric layer has been exposed, or by the generation of a current in a conductive loop formed in a trench within a dielectric layer on a substrate.

[0041] During operation, the polishing system can use the in-situ monitoring system 100 to determine when a conductive layer has reached a target thickness, such as a target depth of metal in a trench or a target thickness of a metal layer on a dielectric layer, and then stop polishing. Alternatively or additionally, the polishing system can use the in-situ monitoring system 100 to determine the difference in thickness of the conductive material 16 across the substrate 10 and use this information to adjust the pressure within one or more chambers 82 of the carrier head 80 during polishing to reduce polishing non-uniformity.

[0042] A recess 26 can be formed in the platen 24, and optionally, a thin section 36 can be formed in the polishing pad 30 overlying the recess 26. The recess 26 and the thin section 36 can be arranged to pass under the substrate 10 during a portion of the rotation of the platen, regardless of the translational position of the carrier head. Assuming the polishing pad 30 is a two-layer pad, the thin section 36 can be constructed by removing a portion of the backing layer 32 and optionally forming a recess in the bottom of the polishing layer 34. For example, if an in-situ optical monitoring system is integrated into the platen 24, the thin section can optionally be optically transmissive.

[0043] The in-situ monitoring system 100 can include a sensor 102 installed in the recess 26. The sensor 102 can include a magnetic core 104 at least partially disposed within the recess 26 and at least one coil 106 wound around a portion of the core 104. A drive and sense circuit 108 is electrically connected to the coil 106. The drive and sense circuit 108 generates a signal that can be transmitted to the controller 90. Although shown outside the platen 24, some or all of the drive and sense circuit 108 may be installed within the platen 24.

[0044] Referring to FIGS. 1 and 4, the drive and sense circuit 108 applies an AC current to the coil 104 to generate a magnetic field 150 between two poles 152a and 152b of the core 104. During operation, when the substrate 10 intermittently comes over the sensor 102, a portion of the magnetic field 150 spreads into the substrate 10. The circuit 108 can include a capacitor connected in parallel with the coil 106. The coil 106 and the capacitor can together form an LC resonant tank.

[0045] When monitoring the thickness of the conductive layer on the substrate, when the magnetic field 150 reaches the conductive layer, the magnetic field 150 can pass through and generate a current (when the target is a loop), or generate an eddy current (when the target is a sheet). This changes the effective impedance characterizing the LC circuit.

[0046] The drive and sense circuit 108 can include a marginal oscillator coupled to the combined drive / sense coil 106, and the output signal can be the current required to maintain the peak-to-peak amplitude of the sine wave oscillation at a constant value, as described, for example, in U.S. Patent No. 7,112,960. Other configurations are possible for the drive and sense circuit 108. For example, the drive coil and the sense coil may be wound separately around the core. The drive and sense circuit 108 can apply a current at a constant frequency, and the signal from the drive and sense circuit 108 may be the phase shift of the current in the sense coil with respect to the drive coil, or, for example, the amplitude of the sensed current, as described in U.S. Patent No. 6,975,107.

[0047] Referring to FIG. 2, as the platen 24 rotates, the sensor 102 sweeps under the substrate 10. By sampling the signal from the circuit 108 at a specific frequency, the circuit 108 generates measurement values in a series of sampling zones 94 across the substrate 10. For each sweep, the measurement values in one or more of the sampling zones 94 of the sampling zone 94 can be selected or combined. Thus, over a plurality of sweeps, the selected or combined measurement values provide a series of values that change over time.

[0048] The polishing station 20 can also include a position sensor 96, such as an optical interrupter, for sensing whether the sensor 102 is below the substrate 10 and whether the sensor 102 is away from the substrate. For example, the position sensor 96 can be mounted at a fixed position facing the carrier head 70. A flag 98 can be attached around the platen 24. The attachment point and length of the flag 98 are selected such that the flag 98 can send a signal to the position sensor 96 when the sensor 102 sweeps under the substrate 10.

[0049] Alternatively or additionally, the polishing station 20 can include an encoder for determining the angular position of the platen 24.

[0050] Returning to FIG. 1, a controller 90, such as a general-purpose programmable digital computer, receives signals from the sensors 102 of the in-situ monitoring system 100. Since the sensor 102 sweeps under the substrate 10 each time the platen 24 rotates, information regarding the depth of a conductive layer, e.g., a bulk layer or conductive material in a trench, is accumulated in-situ (once per platen rotation). The controller 90 can be programmed to sample measurements from the in-situ monitoring system 100 when the substrate 10 is generally over the sensor 102.

[0051] In addition, the controller 90 can be programmed to calculate the radial position of each measurement and classify the measurements into radial zones. By arranging the measurements into radial zones, data regarding the thickness of the conductive film in each radial zone is supplied to the controller (e.g., controller 90) to adjust the polishing pressure profile applied by the carrier head. The controller 90 can also be programmed to apply endpoint detection logic to a series of measurements generated by the signals of the in-situ monitoring system 100 to detect the polishing endpoint.

[0052] Since sensor 102 sweeps under substrate 10 each time platen 24 rotates, information regarding the thickness of the conductive layer is continuously accumulated in real time in situ. During polishing, the measurement values from sensor 102 can be displayed on an output device so that the operator of the polishing station can visually monitor the progress of the polishing operation.

[0053] As an eddy current monitoring system, electromagnetic induction monitoring system 100 is used to monitor the thickness of the conductive layer by inducing eddy currents in the conductive sheet, or to monitor the depth of the conductive material in the trench by inducing eddy currents in the conductive material. Alternatively, as an induction monitoring system, the electromagnetic induction monitoring system can operate by inductively generating a current in a conductive loop formed in dielectric layer 14 of substrate 10 for monitoring purposes, as described, for example, in U.S. Patent Publication No. 2015-0371907.

[0054] FIG. 5 shows a graph 400 showing a relationship curve 410 between the thickness of the conductive layer and the signal from electromagnetic induction monitoring system 100 for a given resistivity. In graph 400, D START represents the initial thickness of the conductive layer, and S START is the desired signal value corresponding to the initial thickness D START . D FINAL represents the final thickness of the conductive layer, and S FINAL is the desired signal value corresponding to the final thickness. K is a constant representing the value of the signal when the thickness of the conductive layer is zero.

[0055] In addition to the decrease in the thickness of the layer, the difference in resistivity of the conductive layer between substrates can change the output signal from sensor 102. Specifically, when the resistivity is high, the sheet resistance of the conductive layer increases and the layer appears thinner. Conversely, when the resistivity is low, the sheet resistance of the conductive layer decreases and the layer appears thicker. An end point determined based on an incorrect assumption about the value of the conductive layer can lead to under-polishing or over-polishing of the layer.

[0056] As described above, since the resistivity of the conductive layer may depend on the process by which the conductive layer is formed, simply compensating based on the textbook value of the resistivity of the conductive material may not provide sufficient accuracy. Therefore, the controller 90 can be configured to receive the resistivity value and use the measured value to compensate for the difference with respect to the resistivity used to generate the relationship between the signal strength and the layer thickness.

[0057] Due to slight structural differences between the sensors and the possibility of temporal variations due to, for example, changes in the thickness of the polishing pad, the electromagnetic induction monitoring system 100 can be calibrated before being used for substrate polishing.

[0058] The relationship curve 410 can be represented in the controller 90 by a function, for example, a polynomial function, for example, a quadratic function, a cubic function, or a higher-order function. For example, the correlation between the signal S and the thickness D can be represented by the following equation. S = W1·D 2 +W2·D + W3 (Equation 1) Here, W1, W2, and W3 are real-valued coefficients. Therefore, the controller can store the values of the coefficients of the function, for example, W1, W2, and W3, and the resistivity ρ0 to which the relationship curve 410 is applied. Further, this relationship can be represented by a linear function, a Bézier curve, or a non-polynomial function, for example, an exponential function or a logarithmic function.

[0059] Referring to FIG. 5, the calibration method 500 starts with the user manufacturing a calibration substrate formed by a manufacturing process in which the user knows that a relatively thick conductive layer, for example, from 2000 to 20000 angstroms, provides a known resistivity ρ CAL This known resistivity ρ CAL can be set, for example, during the qualification of the manufacturing method by another measurement system.

[0060] The sheet resistance Rs of the conductive layer on this calibration substrate CALis measured, for example, using a four-point probe (step 502). The same four-point probe measurement can be used for all four-point probe measurements for calibration, and the measurement can be performed according to a standard such as ASTM F390-11.

[0061] Next, the thickness of the conductive layer on the calibration substrate can be calculated (step 504). For example, the controller 90 can receive the resistivity ρ CAL and the measured sheet resistance Rs CAL by, for example, user input to a user interface or from a computer-readable medium. The controller can calculate the calibration thickness D CAL = ρ CAL / Rs CAL For example, simply as. Alternatively, the user may simply perform the calculation and input the resistivity ρ CAL and the calibration thickness D CAL into the controller 90. CAL

[0062] Next, two measurements are performed using the in-situ measurement system 100 (step 506). The first measurement is performed with the calibration substrate held at a predetermined position above the sensor 102 by the carrier head. Thereby, a "measured high" first signal S MH is generated. The second measurement is performed with the substrate or the carrier head not on the sensor 102. For example, the platen is rotated to a position where the sensor 102 is not under the carrier head 70. Thereby, a "measured low" second signal S ML is generated. Alternatively, the second measurement may be performed when the sensor is under the carrier head 70 but there is no substrate held by the carrier head 70, or when a completely dielectric substrate is held by the carrier head 70.

[0063] Next, the offset and gain for the in-situ monitoring system 100 can be calculated so that the controller 90 can perform thickness measurements reliably (step 508). ​

[0064] The gain G can be calculated as follows. G=(S DH -S DL ) / (S MH -S ML ) Here, S DH is the "desired high" signal when the layer is polished to the same thickness as the conductive layer on the calibration substrate, and S DL is the "desired low" signal when the layer is removed.

[0065] The "desired low" signal may simply be a set value, for example, 0 or 0.2 or 20%.

[0066] The "desired high" signal takes into account the variation in the resistivity of the conductive layer of the calibration substrate with respect to the resistivity of the layer used for generating the correlation function.

[0067] To calculate the "desired high" signal, the calculated thickness D CAL is multiplied by the ratio of the resistivity ρ0 to which the relationship curve 410 is applied with respect to the known resistivity ρ CAL of the conductive layer of the calibration substrate to generate a corrected thickness, and the "desired high" signal value S DH is calculated from the relationship curve for this corrected thickness. That is, TIFF0007693728000002.tif13170

[0068] D CAL / ρ CAL It is also possible to use 1 / Rs CAL instead of the value of, but since the related values are not very intuitive, it becomes difficult to find inappropriately entered data. However, this eliminates the need to calculate the thickness of the conductive layer of the calibration substrate. Therefore, the calculation can be expressed as follows. TIFF0007693728000003.tif13170

[0069] An offset ΔK that satisfies the following can be calculated. ΔK=G*SML -S DL

[0070] After calibration, the calibrated signal S’ can be generated according to the following. S’ = G * S - ΔK (Equation 2)

[0071] Therefore, when the in-situ monitoring system measures a substrate having a layer with a known resistivity ρ CAL and a predetermined thickness, e.g., a calibration thickness, the gain and offset can be set so that the in-situ monitoring system outputs the same desired high signal value S DH

[0072] To monitor the thickness of the conductive layer 16 during the polishing operation, the controller receives a measured value of the resistivity ρ X of the substrate 10 being polished. This resistivity ρ X may be the same as the calibration resistivity ρ CAL but does not have to be.

[0073] A series of signal values S(t) are received from the in-situ monitoring system over time. Each value is normalized, e.g., using Equation 2 above, to provide a series of calibrated values S’(t). Each calibrated value S’(t) can be used to calculate a thickness value D(t) using a correlation curve to provide a series of thickness values D(t). In addition, each thickness value can be adjusted based on the resistivity of the layer to provide a corrected thickness value, and thus a series of corrected thickness values D’(t) can be provided. The corrected thickness value can be calculated as follows. D’(t) = D(t) * (ρ X / ρ0) (Equation 3)

[0074] The corrected thickness value D’(t) can be used for the control of the polishing parameters, e.g., for the calculation of the polishing pressure to reduce non-uniformity.

[0075] When the corrected thickness value D’(t) reaches the target thickness value D TARGET ​When it reaches, the end point can be determined.

[0076] Alternatively, when the calibrated value S’(t) reaches the target trigger value S TARGET the end point can be determined. For example, S TARGET can be calculated as follows. TIFF0007693728000004.tif11170 The calibrated value S’(t) is compared with the target trigger value S TARGET to determine the polishing end point.

[0077] In addition to the inter-substrate variation in resistivity, changes in the temperature of the layer can cause changes in the resistivity of the conductive layer. For example, as polishing progresses, the conductive layer may become hotter and thus more conductive (lower resistivity). Therefore, the measured thickness determined based on the signal from the electromagnetic induction monitoring system may become smaller than the actual thickness as the temperature of the conductive layer rises. In other words, as the temperature of a layer with a given thickness rises, the layer appears thinner. Due to the end point determined based on such a measured thickness, the polishing process may stop at an actual thickness greater than the measured thickness, so the layer may be under-polished.

[0078] The measured thickness determined based on the signal from sensor 102 can be adjusted to approach the actual thickness, for example, by compensating for the temperature variation of the conductive layer and / or by compensating the measured thickness for the temperature variation of the conductive layer.

[0079] Specifically, the controller executing process 500 can also calculate the resistivity ρ of the conductive layer at the real-time temperature T(t). T In some embodiments, the adjusted resistivity ρ T is calculated based on the following formula. ρ T =ρ X [1 + α(T(t) - T ini )] Here, Tini is the initial temperature of the conductive layer when the polishing process is initiated. Next, the adjusted resistivity ρ T is used instead of the resistivity ρ X , for example, as used in the above equations 3 and 4.

[0080] In situations where the polishing process is carried out at room temperature, T ini can take on a value of approximately 20 o °C. ρ X can be the resistivity of the conductive layer at room temperature T ini . Usually, α is a known value that can be found in the literature or obtained from experiments.

[0081] In some embodiments, the temperatures T and T used for adjusting the measured eddy current signal ini are the temperatures of the conductive layer, measured, for example, by a temperature sensor in the carrier head. In some embodiments, the temperatures T and T ini can be the temperature of the polishing pad or the temperature of the slurry instead of the temperature of the conductive layer.

[0082] Without wishing to be bound by any particular theory, the resistivity ρ T calculated using the temperature of the polishing pad or the slurry is considered to be similar to the resistivity ρ T calculated using the temperature of the conductive layer, because the temperature differences are similar and α is also consistently determined using the temperature of the pad or the slurry.

[0083] The above-described polishing apparatus and method can be applied to various polishing systems. The polishing pad, or the carrier head, or both can be moved to provide relative movement between the polishing surface and the substrate. For example, the platen may orbit rather than rotate. The polishing pad can be a circular (or other shape) pad fixed to the platen. Some aspects of the endpoint detection system can be applicable to a linear polishing system, for example, where the polishing pad is a continuous or reel-to-reel belt that moves linearly. The polishing layer can be a standard (e.g., polyurethane with or without fillers) polishing material, a soft material, or a fixed abrasive material. Expressions of relative arrangement are used. It should be understood that the polishing surface and the substrate may be held in a perpendicular orientation or in other orientations.

[0084] Embodiments can be implemented as one or more computer program products for execution by, or to control the operation of, a data processing apparatus, such as a programmable processor, a computer, or multiple processors or computers, i.e., as one or more computer programs tangibly embodied in a non-transitory machine-readable storage medium. Many embodiments of the present invention have been described. Nevertheless, it should be understood that various modifications can be made without departing from the spirit and scope of the present invention. For example, more or fewer calibration parameters may be used. Further, the calibration and / or drift compensation methods may be changed. Accordingly, other embodiments are within the scope of the following claims.

Claims

1. A computer program product tangibly encoded on a non-transitory computer-readable medium, causing a computer system to store a first resistivity value and a correlation function that associates the layer thickness of a conductive layer having the first resistivity value at a certain temperature with a signal from an in-situ electromagnetic induction monitoring system; receive a second resistivity value for the deposited conductive layer, generated by measurement of the deposited conductive layer on a device substrate to be polished; receive a series of signal values dependent on the thickness of the deposited conductive layer from the in-situ electromagnetic induction monitoring system that monitors the device substrate during polishing; calculate a threshold signal value from a target thickness with the variation between the first resistivity value and the second resistivity value compensated using the correlation function; detect a polishing end point by comparing the series of signal values with the threshold signal value; A computer program product including instructions to cause the above.

2. The computer program product according to claim 1, wherein the instructions for calculating the threshold signal value include instructions for multiplying the target thickness by the ratio of the first resistivity value to the second resistivity value.

3. The computer program product according to claim 1, wherein the correlation function satisfies the following: S = W １ ・D ２ +W ２ ・D+W ３ where S is the signal value, D is the thickness, and W １ 、W ２ 、and W ３ are coefficients.

4. The computer program product according to claim 1, wherein the instructions for calculating the threshold signal value include instructions for compensating for variations in the temperature of the deposited conductive layer on the device substrate to be polished.

5. The computer program product according to claim 1, further comprising instructions for calculating the second resistivity value compensated for fluctuations in the temperature of the deposited conductive layer on the device substrate to be polished.

6. The computer program product according to claim 4, further comprising instructions for storing a first temperature and instructions for receiving a measurement of a second temperature from a polishing system, wherein the instructions for compensating for temperature fluctuations include calculating an adjusted second resistivity value based on the second resistivity value, the first temperature, and the second temperature.

7. Storing a first resistivity value and a correlation function that associates the layer thickness of a conductive layer having the first resistivity value at a certain temperature with a signal from an in-situ electromagnetic induction monitoring system; Receiving a second resistivity value for the deposited conductive layer, generated by measurement of the deposited conductive layer on the device substrate to be polished; Receiving a series of signal values that depend on the thickness of the deposited conductive layer from the in-situ electromagnetic induction monitoring system that monitors the device substrate during polishing; Calculating a threshold signal value from a target thickness that compensates for fluctuations between the first resistivity value and the second resistivity value using the correlation function; Detecting a polishing end point by comparing the series of signal values with the threshold signal value; A polishing method comprising.

8. The method according to claim 7, wherein the conductive layer includes a conductive sheet, and the in-situ electromagnetic induction monitoring system generates eddy currents in the conductive sheet.

9. The method according to claim 7, wherein calculating the threshold signal value includes multiplying the target thickness by the ratio of the first resistivity value to the second resistivity value.

10. The method according to claim 7, wherein the correlation function satisfies the following. S = W １ ・D ２ +W ２ ・D+W ３ However, S is the signal value, D is the thickness, and W １ , W ２ , and W ３ are coefficients. **Claim 11** The method according to claim 7, wherein calculating the threshold signal value includes compensating for fluctuations in the temperature of the deposited conductive layer on the device substrate to be polished. **Claim 12** The method according to claim 7, further comprising calculating the second resistivity value compensated for fluctuations in the temperature of the deposited conductive layer on the device substrate to be polished. **Claim 13** The method according to claim 11, further comprising storing a first temperature, receiving a measurement of a second temperature from a polishing system, and calculating an adjusted second resistivity value based on the second resistivity value, the first temperature, and the second temperature. **Claim 14** A rotatable platen for supporting a polishing pad, A carrier head for holding a substrate against the polishing pad, An in-situ electromagnetic induction monitoring system including a sensor that generates a series of signal values dependent on the thickness of a conductive layer on the substrate, A controller, A polishing system comprising: wherein the controller stores a first resistivity value and a correlation function that associates the layer thickness of a conductive layer having the first resistivity value at a certain temperature with a signal from the in-situ electromagnetic induction monitoring system, receives a second resistivity value for the deposited conductive layer generated by measurement of the deposited conductive layer on the device substrate to be polished, receives a series of signal values dependent on the thickness of the deposited conductive layer from the in-situ electromagnetic induction monitoring system, uses the correlation function to calculate a threshold signal value from a target thickness that compensates for fluctuations between the first resistivity value and the second resistivity value, Detecting the polishing end point by comparing the continuous signal values with the threshold signal value. A polishing system configured as described above.

15. The system according to claim 14, wherein the controller is configured to calculate the threshold signal value by multiplying the target thickness by the ratio of the first resistivity value to the second resistivity value.

16. The system according to claim 14, including a temperature sensor for monitoring the temperature related to the conductive layer.

17. The system according to claim 16, wherein the controller is configured to compensate for the temperature variation by calculating the threshold signal value based on the temperature variation of the deposited conductive layer on the device substrate to be polished.

18. The system according to claim 16, wherein the controller is configured to calculate the second resistivity value with the temperature variation of the deposited conductive layer on the device substrate to be polished compensated.

19. The system according to claim 14, wherein the correlation function satisfies the following. S = W １ · D ２ + W ２ · D + W ３ However, S is the signal value, D is the thickness, and W １ 、W ２ 、and W ３ are coefficients.

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