KR102255963B1 - Determination of gain for eddy current sensor - Google Patents

Abstract

In one aspect, a method of controlling polishing comprises receiving, from an in-line or standalone monitoring system, a measurement of an initial thickness of a conductive film on the first substrate prior to polishing the first substrate, one or more in the polishing system. Polishing the substrates of the-one or more substrates comprising a first substrate-using an eddy current monitoring system to generate a first signal, during polishing of one or more substrates, one or more of the substrates Monitoring the excess substrates, determining a starting value of the first signal for initiation of polishing of the first substrate, determining a gain, based on a measurement of the initial thickness and the starting value, one or more For at least a portion of the first signal collected during polishing of at least one of the substrates, based on the gain and the first signal, calculating a second signal.

Description

DETERMINATION OF GAIN FOR EDDY CURRENT SENSOR

The present disclosure relates to chemical mechanical polishing and, more particularly, to monitoring of conductive layers during chemical mechanical polishing.

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

Chemical mechanical polishing (CMP) is one accepted method of planarization. Such planarization methods typically require the substrate to be mounted on a carrier head. The exposed surface of the substrate is typically placed against a rotating polishing pad. The carrier head provides a controllable load on the substrate to push the substrate against the polishing pad. A polishing slurry with abrasive particles is typically supplied to the surface of the polishing pad.

One problem with CMP is determining whether the polishing process is complete, ie, whether the substrate layer has been planarized to a desired flatness or thickness, or when a desired amount of material has been removed. Variations in the slurry composition, polishing pad condition, relative speed between the substrate and the polishing pad, the initial thickness of the substrate layer, and the load on the substrate can cause changes in the material removal rate. These changes cause changes in the time required to reach the polishing endpoint. Thus, simply determining the polishing endpoint as a function of polishing time can lead to non-uniformities within or between wafers.

In some systems, the substrate is monitored in-situ, during polishing, such as through a polishing pad. One monitoring technique is to induce an eddy current in the conductive layer and detect the change in eddy current as the conductive layer is removed.

In one aspect, a method of controlling polishing comprises receiving, from an in-line or stand-alone monitoring system, a measurement of an initial thickness of a conductive film on the first substrate prior to polishing the first substrate, the polishing system Polishing one or more substrates at-one or more substrates comprising a first substrate-using an eddy current monitoring system to generate a first signal during polishing of one or more substrates Thus, monitoring one or more substrates, determining a starting value of the first signal for initiation of polishing of the first substrate, determining a gain based on the measured value and starting value of the initial thickness. For at least a portion of the first signal collected during polishing of at least one of the one or more substrates, calculating a second signal based on the gain and the first signal, and a second signal Based on, for the at least one substrate, determining at least one of a polishing endpoint or an adjustment to a polishing parameter.

Implementations may include one or more of the following features.

Calculating the second signal may include multiplying the gain.

Calculating the second signal may include calculating V'= V * G + K, where V'is the second signal, V is the first signal, G is the gain, and K is It is an offset.

At least one of the one or more substrates may be the first substrate.

At least one of the one or more substrates may be a second substrate that is polished after the first substrate.

The polishing system may include a rotatable platen, and the eddy current sensor of the eddy current monitoring system is supported on the platen to sweep across one or more substrates.

The first signal may be generated from a portion of the signal generated when the eddy current sensor is not adjacent to the substrate.

A reference value may be determined from a part of a signal generated when the eddy current sensor is not adjacent to the substrate.

An offset can be created by adjusting the reference value to produce a desired value for zero thickness.

Determining the gain may include determining a desired value from a measure of the initial thickness and a calibration function relating the signal strength to the thickness.

To determine the gain,

Depending on, may include calculating the multiplier N,

Here, D is the desired value, S is the starting value, and K is a constant expressing the value of the calibration function for zero thickness.

Determining the gain may include multiplying the old gain by N.

Determining the starting value starts as the value of the function at the approximate starting time of the polishing operation, generating a sequence of measured values from the first signal, fitting the function to the sequence of measured values. It may involve calculating the value.

In another aspect, a computer program product tangibly encoded on non-transitory computer readable media causes a data processing apparatus to perform an operation for performing any of the above methods. Contains instructions operable to cause them to perform.

In another aspect, the polishing system comprises: a rotatable platen for supporting the polishing pad, a carrier head for holding the first substrate against the polishing pad, and generating a first signal according to the thickness of the conductive layer on the substrate. An in-situ eddy current monitoring system comprising a sensor for, and a controller configured to perform any of the above methods.

In another aspect, a method of controlling polishing includes polishing a substrate at a first polishing station, during polishing of the substrate at the first polishing station, using a first eddy current monitoring system to generate a first signal, Monitoring the substrate, determining an end value of the first signal for termination of polishing of the substrate at the first polishing station, determining a first temperature at the first polishing station, and removing the substrate at the first polishing station. After polishing, polishing the substrate at a second polishing station, during polishing of the substrate at the second polishing station, monitoring the substrate, using a second eddy current monitoring system, to generate a second signal, 2 determining a start value of the second signal for the start of polishing of the substrate at the polishing station, determining a gain for the second polishing station based on the end value, the start value, and the first temperature, the second 2 calculating a third signal, based on the gain and the second signal, for at least a portion of the second signal collected during polishing of the at least one substrate at the polishing station, and based on the third signal, at least one And determining at least one of a polishing endpoint or an adjustment to a polishing parameter for the substrate of the.

Implementations may include one or more of the following features.

Determining the gain for the second polishing station may further include measuring a second temperature at the second polishing station.

The gain can be calculated based on the resistivity of the layer being polished at the first and second temperatures.

가 계산될 수 있고, 여기에서, TE_post는 제 1 폴리싱 패드에서의 제 1 온도이고, TE_ini는 제 2 폴리싱 패드에서의 제 2 온도이고, 알파는 폴리싱되는 층의 재료에 대한 저항률 계수이다.

Can be calculated, where TE _post is the first temperature at the first polishing pad, TE _ini is the second temperature at the second polishing pad, and alpha is the resistivity coefficient for the material of the layer being polished.

An ending value of the first signal for ending polishing of the substrate in the first polishing station may be determined.

Determining the end value comprises generating, from the first signal, a first sequence of measured values, fitting a first function to the first sequence of measured values, and an endpoint for polishing at the first polishing station. It may involve calculating the end value as the value of the function in time.

The first thickness may be determined from a calibration function relating the signal strength and thickness, and an end value.

The adjusted thickness may be determined based on the first thickness, the first temperature, and the second temperature.

를 곱하는 것을 포함할 수 있고, 여기에서, TE_post는 제 1 폴리싱 패드에서의 제 1 온도이고, TE_ini는 제 2 폴리싱 패드에서의 제 2 온도이고, 알파는 폴리싱되는 층의 재료에 대한 저항률 계수이다.Determining the adjusted thickness is the first thickness

Wherein TE _post is a first temperature at the first polishing pad, TE _ini is a second temperature at the second polishing pad, and alpha is the resistivity coefficient for the material of the layer being polished to be.

The desired value can be determined from the calibration function and the adjusted value.

A starting value of the second signal for starting polishing of the substrate in the second polishing station may be determined.

Determining the starting value comprises generating, from the second signal, a second sequence of measured values, fitting a second function to the second sequence of measured values, and approximate start of polishing at the second polishing station. It may include calculating the starting value as the value of the second function in time.

To determine the gain,

Depending on, may include calculating the multiplier N,

Here, D is the desired value, S is the starting value, and K is a constant expressing the value of the calibration function for zero thickness.

The first temperature may be the temperature of the first polishing pad in the first polishing station, and the second temperature may be the temperature of the second polishing pad in the second polishing station.

The first temperature can be the temperature of the layer being polished in the first polishing station, and the second temperature can be the temperature of the layer being polished in the second polishing station.

In another aspect, a computer readable object tangibly encoded on non-transitory computer readable media is operable to cause a data processing apparatus to perform operations for performing any of the above methods. .

In another aspect, a polishing system comprises a first in-situ eddy current monitoring system comprising a first platen for supporting a first polishing pad, a first sensor for generating a first signal according to a thickness of a conductive layer on the substrate. , And a first polishing station comprising a first temperature sensor, a second platen for supporting a second polishing pad, and a second sensor for generating a second signal according to the thickness of the conductive layer on the substrate. A second polishing station comprising a two in-situ eddy current monitoring system, a carrier head for holding a substrate, and a controller configured to perform any of the above methods.

Implementations may include one or more of the following advantages. The gain and offset of the monitoring system can be automatically adjusted to compensate for parameters that may affect the eddy current signal. For example, the gain and offset may be adjusted for changes in equipment parameters such as the thickness of the polishing pad or environmental conditions (eg, temperature). The reliability of the endpoint system for detecting the desired polishing endpoint can be improved, and intra-wafer and wafer-to-wafer thickness non-uniformity can be reduced.

Details of one or more implementations are set forth in the description below and in the accompanying drawings. Other aspects, features, and advantages will become apparent from the description and drawings, and from the claims.

1 illustrates a cross-sectional view of an example of a polishing station including an eddy current monitoring system.
2 illustrates a cross-sectional view of an exemplary magnetic field generated by an eddy current sensor.
3 illustrates a top view of an exemplary chemical mechanical polishing station showing the path of a sensor scan across a wafer.
4 illustrates a graph of an exemplary eddy current phase signal as a function of conductive layer thickness.
5 illustrates a graph of an exemplary trace from an eddy current monitoring system.
6 is a flow graph for starting a polishing operation of a substrate in a polishing station.
7 is a flow graph for transferring a substrate from a first polishing station to a second polishing station.
Like reference numbers and designations in the various drawings indicate like elements.

One monitoring technique for controlling the polishing operation is to use an alternating current (AC) drive signal to induce eddy currents in the conductive layer on the substrate. The induced eddy currents can be measured by an eddy current sensor, in-situ, during polishing, to generate a signal. Assuming that the outermost layer undergoing polishing is a conductive layer, the signal from the sensor should depend on the thickness of the layer.

Different implementations of eddy current monitoring systems may use different aspects of the signal obtained from the sensor. For example, the amplitude of the signal can be a function of the thickness of the conductive layer being polished. Additionally, the phase difference between the signal from the sensor and the AC drive signal can be a function of the thickness of the conductive layer being polished.

Due to composition and assembly variations, eddy current sensors may exhibit different gains and offsets when measuring eddy current. Eddy current can also be affected by changes in environmental parameters such as the temperature of the substrate during polishing, for example. Changes in pressure applied on the polishing pad (e.g., in an in-situ monitoring system) or run time changes, such as pad wear, can change the distance between the substrate and the eddy current sensor and , Can also affect the measured eddy current signal. Thus, to compensate for these changes, calibration of the eddy current monitoring system can be performed.

1 illustrates an example of a polishing station 22 of a chemical mechanical polishing apparatus. The polishing station 22 includes a rotatable disk-shaped platen 24 on which a polishing pad 30 is placed. The platen 24 is operable to rotate about an axis 25. For example, the motor 21 may turn the drive shaft 28 to rotate the platen 24. The polishing pad 30 may be a two-layer polishing pad having an outer layer 34 and a softer backing layer 32.

The polishing station 22 may include a supply port or a combined supply-rinse arm 39 for dispensing a polishing liquid 38 such as a slurry onto the polishing pad 30.

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 60, such as a carousel or track, so that the carrier head can rotate about an axis 71, the drive shaft 74 It is connected to the carrier head rotation motor 76 by means of. Optionally, the carrier head 70 may vibrate laterally, for example by rotational oscillation of the carousel itself, or on sliders on the carousel or track 60. In operation, the platen is rotated about the central axis 25 of the platen, the carrier head is rotated about the central axis 71 of the carrier head, and the upper surface of the polishing pad 30 Translated laterally across. In the case where there are multiple carrier heads, each carrier head 70 can have independent control of the polishing parameters of its respective carrier head 70, e.g., each carrier head is The pressure applied to each can be controlled independently.

The carrier head 70 may include a retaining ring 84 for holding a substrate. In some implementations, the retaining ring 84 may include a highly conductive portion, e.g., the carrier ring includes a thin lower plastic portion 86 and a thick upper conductive portion 88 in contact with the polishing pad. can do. In some implementations, the highly conductive portion is a metal such as the same metal as the layer being polished, such as copper, for example.

A recess 26 may be formed in the platen 24 and a thin section 36 may be formed to overlie the recess 26 in the polishing pad 30. The recess 26 and the thin pad section 36 may be positioned so that they pass under the substrate 10 during part of the platen rotation, regardless of the translation position of the carrier head. Assuming that the polishing pad 30 is a two-layer pad, the thin pad section 36 can be constructed by removing a portion of the backing layer 32.

The polishing station 22 may include a pad conditioner device having a conditioning disk 31 for maintaining the condition of the polishing pad.

In some implementations, the polishing station 22 includes a temperature sensor 64 for monitoring the temperature in the system. Although illustrated in FIG. 1 as positioned to monitor the temperature of the slurry 38 and/or the polishing pad 30 on the pad 30, the temperature sensor 64 is used to measure the temperature of the substrate 10. It can be located inside the head.

The polishing station may include an in-situ monitoring system 40. The in-situ monitoring system 40 generates a time varying sequence of values depending on the thickness of the layer on the substrate 10. In particular, the in-situ monitoring system 40 may be an eddy current monitoring system. Similar eddy current monitoring systems are described in US Pat. Nos. 6,924,641, 7,112,960, and 7,016,795, the entire disclosures of which are incorporated herein by reference.

In some implementations, the polishing apparatus includes additional polishing stations. For example, the polishing apparatus may comprise two or three polishing stations. For example, the polishing apparatus may include a first polishing station having a first eddy current monitoring system and a second polishing station having a second eddy current monitoring system.

For example, in operation, bulk polishing of the conductive layer on the substrate can be performed in a first polishing station, and if a target thickness of the conductive layer on the substrate remains, polishing can be stopped. Thereafter, the substrate is transferred to a second polishing station, and the substrate can be polished up to an underlying layer, such as a patterned dielectric layer.

2 illustrates a cross-sectional view of an exemplary magnetic field 48 generated by eddy current sensor 49. Eddy current sensor 49 may be located at least partially in recess 26 (see FIG. 1 ). In some implementations, the eddy current sensor 49 includes a drive coil 44 and a core 42 having two poles 42a and 42b. The magnetic core 42 can receive the AC current in the drive coil 44 and can generate a magnetic field 48 between the poles 42a and 42b. The generated magnetic field 48 can extend through the thin pad section 36 and into the substrate 10. The sensing coil 46 generates a signal according to the eddy current induced in the conductive layer 12 of the substrate 10.

3 illustrates a top view of the platen 24. As the platen 24 rotates, the sensor 49 sweeps under the substrate 10. By sampling the signal from the sensor at a specific frequency, the sensor 49 produces measurements in a sequence of sampling zones 96 across the substrate 10. For each sweep, measurements in one or more of the sampling zones 96 may be selected or may be combined. Thus, over multiple sweeps, the selected or combined measurements provide a time varying sequence of values. In addition, off-wafer measurements can be performed at locations where the sensor 49 is not located under the substrate 10.

1 and 2, in operation, the oscillator 50 is coupled to the drive coil 44, through the body of the core 42 and the two magnetic poles 42a and The drive coil 44 is controlled to generate an oscillating magnetic field 48 that extends into the gap between 42b). At least a portion of the magnetic field 48 extends through the thin pad section 36 of the polishing pad 30 and into the substrate 10.

When a conductive layer 12, such as a metal layer, is present on the substrate 10, the oscillating magnetic field 48 can generate eddy currents in the conductive layer. The generated eddy currents can be detected by the sensing coil 46.

As polishing proceeds, material is removed from the conductive layer 12, making the conductive layer 12 thinner, thus increasing the resistance of the conductive layer 12. Thus, the eddy current induced in the layer 12 changes as polishing proceeds. As a result, the signal from the eddy current sensor changes as the conductive layer 12 is polished. 4 shows a graph 400 illustrating the relationship between the conductive layer thickness and the signal from the eddy current monitoring system 40.

In some implementations, the eddy current monitoring system 40 outputs a signal proportional to the amplitude of the current flowing in the sense coil 46. In some implementations, the eddy current monitoring system 40 outputs a signal proportional to the phase difference between the current flowing in the sense coil 46 and the current flowing in the drive coil 44.

The polishing station 22 also has a position sensor, such as an optical interrupter, to detect when the eddy current sensor 49 is off the substrate and when the eddy current sensor 49 is under the substrate 10. 80). For example, the position sensor 80 may be mounted in a fixed position opposite the carrier head 70. A flag 82 may be attached to the periphery of the platen 24. The length of the flag 82 and the point of attachment are selected so that the flag 82 can signal the position sensor 80 as the core 42 sweeps under the substrate 10.

Alternatively, the polishing station 22 may include an encoder to determine the angular position of the platen 24. The eddy current sensor can sweep under the substrate with each rotation of the platen.

In operation, the polishing station 22 uses the monitoring system 40 to determine when the bulk of the filler layer is removed and/or when the underlying stop layer is exposed. The in-situ monitoring system 40 can be used to determine the amount of material removed from the surface of the substrate.

Turning back to Figures 1 and 3, a universal programmable digital computer 90 can be connected to a sensing circuit 94 capable of receiving eddy current signals. The computer 90 samples the eddy current signal when the substrate is generally overlying the eddy current sensor 49 to store the sampled signals, applies endpoint detection logic to the stored signals, and detects the polishing endpoint. And/or to calculate adjustments to the polishing parameters, such as changes to the pressure exerted by the carrier head, to improve polishing uniformity. Possible endpoint criteria for detector logic include local minimums or maximums, changes in slope, threshold values in amplitude or slope, or combinations thereof.

Components of the eddy current monitoring system other than the coils and core, such as the oscillator 50 and the sensing circuit 94, can be located away from the platen 24 and may be It can be coupled to the components in the platen, or it can be installed on the platen, and can communicate with the computer 90 outside the platen via a rotating electrical union 29.

In addition, the computer 90 also measures the eddy current signal from each sweep of the eddy current sensor 49 under the substrate at a sampling frequency, generating a sequence of measurements for the plurality of sampling zones 96, Calculate the radial position of each sampling zone, divide the amplitude measurements into a plurality of radial ranges, use measurements from one or more radial ranges to determine a polishing endpoint, and/or a polishing parameter. Can be programmed to calculate adjustments for.

Since the eddy current sensor 49 sweeps under the substrate 10 with each rotation of the platen, information about the conductive layer thickness is accumulated on a continuous and real-time basis in-situ. During polishing, measurements from the eddy current sensor 49 may be displayed on the output device 92 to allow the operator of the polishing station 22 to visually monitor the progress of the polishing operation. By arranging the measurements in radial ranges, data for the conductive film thickness in each radial range can be provided to a controller (eg, computer 90) to adjust the polishing pressure profile exerted by the carrier head.

In some implementations, the controller can use eddy current signals to trigger a change in polishing parameters. For example, the controller can change the composition of the slurry.

5 shows a trace 500 generated by the eddy current monitoring system. As described above, the signal may be sampled to generate one or more measurements 510 for each scan of the sensor across the substrate. Thus, over multiple scans, the eddy current monitoring system generates a sequence of measured values 510. This sequence of measured values can be considered a trace 500. In some implementations, measurements within a scan or from multiple scans may be averaged or filtered to generate measurements 510 of trace 500, e.g., a running average calculated. Can be.

The sequence of measured values can be used to determine an endpoint or change to polishing parameters, for example to reduce intra-wafer non-uniformity. For example, a function 520 (of measured value versus time) can be fitted to measured values 510. Function 520 may be a polynomial function, such as a linear function. The endpoint 540 may be predicted based on the calculated time when the linear function 520 reaches the target value 530.

As mentioned above, due to assembly changes and changes over time in environmental or system parameters, the eddy current monitoring system may require calibration. The eddy current monitoring system can be calibrated when the sensor is initially installed on the chemical mechanical polishing station 22. The eddy current monitoring system may be calibrated automatically whenever the substrate is loaded for polishing, and/or may be calibrated during polishing.

The signal from the eddy current sensor can be affected by a drift of environmental parameters, such as the temperature of the eddy current sensor itself, for example. For example, as described in US Pat. No. 7,016,795, drift compensation can be performed to compensate for several changes. However, this drift compensation technique may not handle the various sources of change to the signal and may not satisfy increasingly stringent process requirements.

To calibrate the gain of the eddy current monitoring system, measurements of the substrate from an in-line or standalone metrology station can be used with measurements from an in-situ eddy current sensor. For example, a desired starting signal from an in-situ eddy current sensor can be determined based on a calibration curve and measurements from a metrology station. Thereafter, an adjustment to the gain can be calculated based on a comparison of the actual start signal and the expected start signal from the in-situ eddy current sensor.

In some implementations, corrections can be performed using equation (1) to correct the gain. In equation (1), N is a correction factor for correcting the gain. D is the desired eddy current signal for the measured conductive layer thickness. S is a starting value, that is, a value determined from the measured eddy current signal at the initial time of polishing, and K is a constant expressing the desired value at the off-wafer position. K can be set to a default value.

The new gain G'can be calculated based on the correction factor and the previous gain G, for example G'= G * N.

In some implementations, a correction factor calculated from the values for S and D from one substrate is used to adjust the gain for the in-situ monitoring system for that substrate. For example, the calibration can be expressed as _{G n} = G _{n -1} * N _{n , where G n} is the gain used to adjust the nth substrate, and G _{n -1} is the (n-1)th substrate Is the gain used to adjust _n , and N n is a correction factor calculated from the values for S and D determined from the data from the n-th substrate.

In some implementations, a correction factor calculated from the values for S and D from one substrate is used to adjust the gain for the in-situ monitoring system for a subsequent substrate. For example, the calibration can be expressed as _{G n +1} = G _{n -1} * N _{n , where G n+1} is the gain used to adjust the (n+1)th substrate, and G _{n -1} Is the gain used to adjust the (n-1)-th substrate, and N _n is the correction factor calculated from the values for S and D determined from the data from the n-th substrate.

In some implementations, the desired eddy current signal D can be calculated based on a pre-set (ie, prior to polishing of the substrate) calibration curve that correlates the thickness with the eddy current signal. 4 illustrates an example of a calibration curve 410. In some implementations, the calibration curve is based on eddy current signal values collected from a "golden" polishing station. As a result, ideally, all polishing stations will generate the same eddy current signal for the same conductive layer thickness.

6 shows a process 600 for controlling substrate polishing, such as chemical mechanical polishing. A measurement zone is selected on the substrate (610). The zone can be the radial extent of the substrate. For example, an experimentally determined radial range can be selected based on previous measurements to have low axial asymmetry. For example, the region can be a radial extent excluding both the center and the edge of the substrate. For example, the zone may be in a radial range of 20 to 40 mm from the center of the substrate. In some implementations, the zone may be selected by the user, for example based on input into a graphical user interface.

Prior to polishing, the thickness of the outer conductive layer in the selected area is measured (620). The outer conductive layer may be a metal layer such as copper. The measured thickness is stored as the initial conductive layer thickness. This thickness measurement is not performed by an in-situ monitoring system. Instead, the thickness measurement can be performed by an in-line or standalone metrology system suitable for measuring the conductive layer thickness, such as an eddy current metrology system such ^{as the iMap™ radial scan system available from Applied Materials.}

The substrate is loaded 630 into a polishing station that includes an eddy current monitoring system. Loading of the substrate into the polishing station may occur after the thickness of the initial conductive layer is measured. As an example, a substrate may be loaded into a polishing station 22 with an in-situ monitoring system 40.

The substrate is polished and a "raw" eddy current signal is received (640) from a selected region of the substrate. As an example, the raw eddy current signal may be received by the computer 90 of the polishing station 22. As described above, the computer 90 can receive the raw eddy current signal for the entire substrate, the received signal can be sampled, a location on the substrate for each sampled measurement can be determined, and the sampling The measured values can be classified into a plurality of zones including the selected zone. As described with respect to FIG. 3, computer 90 may also receive a raw eddy current signal from off-wafer locations, eg, when the eddy current sensor is not under the substrate.

The received eddy current data is adjusted 650 by the previously calculated gain and offset. For example, the adjusted signal value V'can be calculated from the original signal value V, based on V'= V * G + K.

In some implementations, for the nth substrate, the gain is calculated based on data from polishing the preceding (n-1)th substrate. for example,

Here, V _'n is n, and the adjustment signal value for the second substrate, V _n is the raw signal value of the n-th substrate, G _{n -1} is the gain used to adjust the second substrate (n-1) And G _{n -2} is the gain used to adjust the (n-2)th substrate, and N _{n -1} is calculated from the values for S and D determined from the data from the (n-1)th substrate. Is the correction factor.

The gain and offset calculations for calibrating the eddy current measurement sensor are described in detail with respect to step 670 below.

In some implementations, for example, when polishing a first substrate, such as a first substrate in a batch or a first substrate after the polishing pad has been replaced, such that the previous data is not reliable or available. , The gain is simply _{set as the default value G 0} , and accordingly,

가 된다.

Becomes.

A new gain (or adjustment to the gain) is calculated based on the received eddy current data and the previously measured initial conductive layer thickness (660). As an example, gain calculations may be performed by the computer 90 of the polishing station 22. For example, the correction factor N for the gain is,

에 따라 계산될 수 있다.

Can be calculated according to.

The initial thickness IT of the conductive layer in the selected area was measured in step 620. The desired value D corresponding to the initial thickness IT can be calculated from the calibration curve 410 (see FIG. 4).

The starting measured value S can be determined from the eddy current data. That is, the eddy current data received during the initial period of polishing must correspond to the initial thickness. For example, if enough data is collected during polishing, the function can be fitted over the sequence of adjusted values. The function may be a polynomial function, such as a linear function.

The value S at the initial time T0 can be calculated from the fitted function (see Fig. 5). The time T0 need not necessarily be an exact start time for the polishing operation, such as the time at which the substrate is lowered into contact with the polishing pad, but may be a few seconds after that, such as 2 or 3 seconds. Without being bound by any particular theory, using the time the substrate is lowered into contact with the polishing pad is due to the fact that, for example, the platen is still ramping up to the target rotation rate, the polishing rate will be reduced. Since it can be initially limited, it can provide unnaturally high signal values.

K may be a default value. K may correspond to the value of the calibration curve 410 for the zero thickness of the layer. For example, as described in US Pat. No. 7,016,795, when drift compensation is performed, the drift compensation can automatically adjust the off-wafer signal back to K in each scan.

After that, a new gain G'can be calculated from the previous gain G, as G'= G * N.

In some implementations, the new gain is used for a subsequent substrate (ie, the substrate after the substrate used to generate values for S and D). In this case, the gain to be used for the (n+1)-th substrate can be expressed as _{G n +1} = G _{n -1} * N _n.

In some implementations, after enough data has been accumulated to determine the starting value S for the current substrate, a new gain is calculated, and using the new gain, a net set of data is calculated for the current substrate. do. In this case, the gain to be used for the n-th substrate can be expressed as _{G n} = G _{n -1} * N _n.

For example, a new gain can be used for the current substrate, for example, when polishing a first substrate, such as the first substrate after the polishing pad has been replaced, or the first substrate in a batch. For substrates that are polished later, a new gain can be used for the subsequent substrate.

In some implementations, the sequence of gain values is filtered to produce a filtered gain value for a given substrate, eg, to attenuate wafer-to-wafer noise such that the gain is changed more smoothly. Thereafter, this filtered gain value can be used instead of G in the above equations. For example, the gain may undergo a recursive notch filter.

In either implementation, the adjusted data is used (670) to change the policing parameters, or to determine the policing endpoint. The adjusted data can represent the thickness of the conductive layer being polished and can be used to trigger a change in polishing parameters. An example of discovering a policing endpoint is described above with reference to FIG. 5.

In some implementations, one or more measurement zones can be selected, and the thickness of more than one zone can be used to calibrate the eddy current sensor. In some implementations, the measurement of the initial thickness is performed at one point in the selected area. In some implementations, measurements are performed at two or more points in the selected area, and the measured data are averaged.

The resistivity of the conductive layer may be changed as the temperature of the conductive layer is changed. The induced eddy currents and thus the measured eddy current signals depend on the resistivity of the conductive layer. Polishing the substrate increases the substrate temperature and reduces induced eddy current signals.

When the substrate is moved from the first in-situ polishing station to the second in-situ polishing station to continue polishing, and both polishing stations use eddy current monitoring, between the two polishing stations Temperature changes affect the eddy current signals. Temperature compensation can be performed as follows.

In the above equations (2) and (3), P _post is the resistivity coefficient of the layer in the second polishing station, and P _ini is the resistivity coefficient of the same layer in the first polishing station. TE _post is the temperature at the second polishing station, and TE _ini is the temperature at the first polishing station. The parameter alpha can be calculated empirically and is a value very close to zero, such as 0.002 to 0.005, such as 0.0032. The parameter alpha can depend on the composition of the layer being polished. In some implementations, the parameter alpha can be selected by user input, eg, the user can select from a menu listing layer compositions, and the parameter alpha corresponding to the selected layer composition is determined from the look-up table. Equation (5) can be used for thickness correction between two polishing stations with different temperatures.

7 shows a process 700 for controlling polishing when transferring a substrate from a first polishing station to a second polishing station. A measurement zone is selected on the substrate (710). As described above, the zone can be the radial extent of the substrate. For example, an experimentally determined radial range can be selected based on previous measurements to have a low axial asymmetry. In some implementations, the zone can be selected by the user, eg, based on input into a graphical user interface.

The substrate is polished at a first polishing station, and a “raw” eddy current raw signal from a selected region of the substrate is received (720). As an example, the eddy current signal may be received by the computer 90 of the polishing station 22. As described above, the computer 90 can receive the eddy current signal of the entire substrate, and the sampled measurements can be classified into different zones, including the selected zone.

The received eddy current data of the selected zone of the first polishing station is adjusted 730 by the first gain and offset. As detailed above for step 670, the gain and offset may be received from previous substrate measurements, or may be calculated from eddy current data of the current substrate being polished. A first function may be fitted to the eddy current data collected at the first polishing station. The first function may be a first polynomial function, such as a first linear function. In some implementations, for a short period of time (eg, 10 seconds) after polishing begins, the eddy current data may not be reliable and may be discarded.

A first temperature of the polishing process at the first polishing station is determined (740). In some implementations, the first temperature is the temperature of the polishing pad. Alternatively or in combination, the temperature of the substrate to be polished can be measured. Contact sensors and/or non-contact sensors (eg, infrared sensors) can be used to measure the temperature. The temperature can be measured periodically and/or around the time when polishing at the first polishing station is stopped.

The substrate is transferred to a second polishing station, and a second temperature of the process at the second polishing station is measured (750). In general, the temperature of the same element as the first polishing station can be measured. For example, if the first temperature is the temperature of the polishing pad in the first polishing station, the second temperature is the temperature of the polishing pad in the second polishing station. Similarly, if the first temperature is the temperature of the substrate at the first polishing station, the second temperature is the temperature of the substrate at the second polishing station. The temperature can be measured periodically and/or around the time at which polishing at the second polishing station begins.

Alternatively, instead of measuring the second temperature at the second polishing station, the system can simply assume that when polishing begins at the second polishing station, the substrate is at a default temperature, eg room temperature, eg 21°C.

The substrate is polished at a second polishing station, and a raw eddy current signal from the selected region of the substrate is received (760). As an example, the eddy current signal may be received by the computer 90 of the polishing station 22. As described above, the computer 90 can receive eddy current raw data of the entire substrate, and the sampled measurements can be classified into different zones, including the selected zone. A second function may be fitted to the eddy current data collected at the second polishing station. The second function may be a second polynomial function, such as a second linear function.

The received eddy current data for the second polishing station is adjusted by the second gain and offset (770). As detailed above for step 670, the gain and offset may be received from previous substrate measurements, or may be calculated from eddy current data of the current wafer being polished. In some implementations, as described in equations (2) and (3), the gain can be adjusted to include the difference between the first and second temperatures.

For example, in the case of switching the substrate from the first polishing station to the second polishing station, the correction factor N for the gain is,

에 따라 계산될 수 있다.

Can be calculated according to.

The starting measured value S'at the second polishing station may be determined from eddy current data collected at the second polishing station. For example, if sufficient data is collected during polishing at the second polishing station, a second function, such as a second linear function, is fitted to the sequence of adjusted values. The value S at the initial time T0 at the second polishing station can be calculated from the second fitted function. The time T0 does not necessarily have to be an exact start time for the polishing operation in the second polishing station, such as the time at which the substrate is lowered into contact with the polishing pad, but may be a few seconds after that, such as 2 or 3 seconds. have.

_{The final thickness T post} of the conductive layer in a selected area at the first polishing station can be determined. In some implementations, the first function is used to calculate the final value DF for the time TF at which polishing was actually stopped at the first polishing station. In some implementations, the final value DF is simply the target value 530. _{The final thickness T post} corresponding to the final value DF may be calculated based on the calibration curve 410 (see FIG. 4 ).

To perform temperature compensation, the adjusted initial thickness T _ini for the second polishing station is calculated based on the temperatures at the two polishing stations and the final thickness T _post. For example, the adjusted initial thickness can be calculated according to _{T ini} = T _post (P _post / P _{ini ).} Thereafter, a desired value D'corresponding to the adjusted initial thickness T _ini can be calculated from the calibration curve 410 (see Fig. 4). After that, the calculation of the gain can proceed as discussed above.

The polishing apparatus and methods described above can be applied to various polishing systems. Either or both of the polishing pad or carrier heads can be moved to provide relative motion between the substrate and the polishing surface. For example, the platen can orbit instead of rotating. The polishing pad may be a circular (or some other shape) pad fixed to the platen. Some aspects of the endpoint detection system may be applicable for linear polishing systems, for example, where the polishing pad is a linearly moving continuous or reel-to-reel belt. The polishing layer may be a standard (eg, polyurethane with or without fillers) polishing material, a soft material, or a fixed-polishing material. Terms of relative positioning are used; It should be understood that the polishing surface and substrate may be held in a vertical orientation or some other orientation.

Embodiments are to control the operation of one or more computer program products, i.e., a data processing device such as a programmable processor, a computer, or multiple processors or computers, or to perform execution by such a data processing device. For this purpose, it may be implemented as one or more computer programs tangibly embodied on non-transitory machine-readable storage media. A number of embodiments of the invention have been described. Nevertheless, it will be understood that various changes may be made without departing from the scope and spirit of the invention. For example, more or fewer calibration parameters may be used. Additionally, calibration and/or drift compensation methods can be changed. Accordingly, other embodiments are within the scope of the following claims.

Claims (30)

As a method of controlling polishing,
Receiving, from an in-line or stand-alone monitoring system, a measurement of an initial thickness of a conductive film on the first substrate prior to polishing the first substrate;
Polishing one or more substrates in a polishing system, the one or more substrates comprising the first substrate;
During polishing of the one or more substrates, monitoring the one or more substrates using an eddy current monitoring system to generate a first signal;
Determining a starting value of the first signal at an initial time of polishing of the first substrate based on the generated first signal;
Determining a gain based on the initial thickness measurement and the starting value;
Calculating a second signal, based on the gain and the first signal, for at least a portion of the first signal collected during polishing of at least one of the one or more substrates; And
Based on the second signal, determining, for the at least one substrate, at least one of an adjustment to a polishing parameter or a polishing endpoint.
Containing,
How to control polishing. The method of claim 1,
The step of calculating the second signal includes multiplying the gain,
How to control polishing. The method of claim 2,
Calculating the second signal includes calculating V'= V * G + K, wherein V'is the second signal, V is the first signal, and G is the gain And, K is an offset,
How to control polishing. The method of claim 1,
The at least one of the one or more substrates is the first substrate,
How to control polishing. The method of claim 1,
The at least one of the one or more substrates is a second substrate polished after the first substrate,
How to control polishing. The method of claim 1,
The polishing system comprises a rotatable platen, and the eddy current sensor of the eddy current monitoring system is supported on the platen to sweep across the one or more substrates,
The above method,
Generating the first signal from a portion of the signal generated when the eddy current sensor is not adjacent to the substrate,
How to control polishing. The method of claim 1,
The determining of the gain comprises determining a desired value of the first signal at the initial time from the measurement of the initial thickness and a calibration function relating the signal strength to the thickness.
How to control polishing. The method of claim 7,
The step of determining the gain,

In accordance with, including the step of calculating a multiplier N,
Wherein D is the desired value, S is the starting value, and K is a constant expressing the value of the calibration function for zero thickness,
How to control polishing. The method of claim 8,
The step of determining the gain comprises multiplying an old gain by N,
How to control polishing. A computer-readable storage medium having stored thereon a program operable to cause a data processing device to perform operations,
The above operations are:
Receiving, from an in-line or standalone monitoring system, a measurement of an initial thickness of a conductive film on the first substrate prior to polishing the first substrate;
Causing a polishing station to perform polishing one or more substrates in a polishing system, the one or more substrates comprising the first substrate;
During polishing of the one or more substrates, monitoring the one or more substrates using an eddy current monitoring system to generate a first signal;
Determining a starting value of the first signal at an initial time of polishing of the first substrate based on the generated first signal;
Determining a gain based on the measured value of the initial thickness and the starting value;
Calculating a second signal, based on the gain and the first signal, for at least a portion of the first signal collected during polishing of at least one of the one or more substrates; And
Based on the second signal, for the at least one substrate, determining at least one of an adjustment to a polishing parameter or a polishing endpoint
Containing,
Computer readable storage media. The method of claim 10,
The operation of determining the gain includes determining a desired value of the first signal at the initial time from the measurement of the initial thickness and a calibration function relating the signal strength and the thickness.
Computer readable storage media. The method of claim 11,
The operation of determining the gain,

In accordance with, including the operation of calculating the multiplier N,
Wherein D is the desired value, S is the starting value, and K is a constant expressing the value of the calibration function for zero thickness,
Computer readable storage media. As a polishing system,
A rotatable platen for supporting the polishing pad;
A carrier head for holding a first substrate against the polishing pad;
An in-situ eddy current monitoring system including a sensor for generating a first signal according to the thickness of the conductive layer on the substrate; And
Controller configured to perform actions
Including,
The above operations are:
Receiving the first signal from the sensor;
Based on the received first signal, determining a starting value of the first signal at an initial time of polishing of the first substrate;
Determining a gain based on the starting value and the measurement of the initial thickness of the conductive layer;
Calculating a second signal based on the gain and the signal, for at least a portion of the signal collected during polishing of the first or subsequent substrate; And
Based on the second signal, for the first substrate or the subsequent substrate, determining at least one of an adjustment to a polishing parameter or a polishing endpoint.
Containing,
Polishing system. The method of claim 13,
The controller is configured to determine a desired value of the first signal at the initial time from the measurement of the initial thickness and a calibration function relating the signal strength to the thickness,
Polishing system. The method of claim 14,
The controller,

According to, by calculating the multiplier N, is configured to determine the gain,
Wherein D is the desired value, S is the starting value, and K is a constant expressing the value of the calibration function for zero thickness,
Polishing system. As a method of controlling polishing,
Polishing the substrate at a first polishing station;
During polishing of the substrate at the first polishing station, monitoring the substrate using a first eddy current monitoring system to generate a first signal;
Determining an end value of the first signal for an end of polishing of the substrate at the first polishing station;
Determining a first temperature at the first polishing station;
After polishing the substrate at the first polishing station, polishing the substrate at a second polishing station;
During polishing of the substrate at the second polishing station, monitoring the substrate using a second eddy current monitoring system to generate a second signal;
Based on the generated second signal, determining a starting value of the second signal at an initial time of polishing of the substrate in the second polishing station;
Determining a gain for the second polishing station based on the end value, the start value, and the first temperature;
Calculating a third signal, based on the gain and the second signal, for at least a portion of the second signal collected during polishing of at least one substrate in the second polishing station; And
Based on the third signal, for the at least one substrate, determining at least one of an adjustment to a polishing parameter or a polishing endpoint.
Containing,
How to control polishing. The method of claim 16,
Determining a gain for the second polishing station further comprises measuring a second temperature at the second polishing station,
How to control polishing. The method of claim 17,
The gain is calculated based on the resistivity of the layer being polished at first and second temperatures,
How to control polishing. The method of claim 18,
Determining an ending value of the first signal for ending polishing of the substrate at the first polishing station,
How to control polishing. The method of claim 19,
The determining of the end value comprises: generating a first sequence of measured values from the first signal, fitting a first function to the first sequence of measured values, and the first polishing Calculating the end value as the value of the function at endpoint time for policing at the station,
How to control polishing. The method of claim 19,
Determining a first thickness from the end value and a calibration function relating signal strength to thickness,
How to control polishing. The method of claim 21,
Determining an adjusted thickness based on the first thickness, the first temperature, and the second temperature,
How to control polishing. The method of claim 17,
The first temperature is a temperature of a first polishing pad in the first polishing station, and the second temperature is a temperature of a second polishing pad in a second polishing station,
How to control polishing. The method of claim 17,
The first temperature is a temperature of the polished layer in the first polishing station, and the second temperature is a temperature of the polished layer in the second polishing station,
How to control polishing. A computer-readable storage medium having stored thereon a program operable to cause a data processing device to perform operations,
The above operations are:
Causing the first polishing station to polish the substrate;
During polishing of the substrate at the first polishing station, receiving a first signal from a first eddy current monitoring system;
Determining an ending value of the first signal for ending polishing of the substrate at the first polishing station;
Determining a first temperature at the first polishing station;
After polishing the substrate at the first polishing station, causing a second polishing station to polish the substrate;
During polishing of the substrate at the second polishing station, receiving a second signal from a second eddy current monitoring system;
Based on the received second signal, determining a starting value of the second signal at an initial time of polishing of the substrate at the second polishing station;
Determining a gain for the second polishing station based on the end value, the start value, and the first temperature;
Calculating a third signal, based on the gain and the second signal, for at least a portion of the second signal collected during polishing of at least one substrate in the second polishing station; And
Based on the third signal, for the at least one substrate, determining at least one of an adjustment to a polishing parameter or a polishing endpoint
Containing,
Computer readable storage media. The method of claim 25,
The operation of determining a gain for the second polishing station further comprises measuring a second temperature at the second polishing station,
Computer readable storage media. The method of claim 26,
The gain is calculated based on the resistivity of the layer being polished at the first and second temperatures,
Computer readable storage media. As a polishing system,
A first platen for supporting a first polishing pad, a first in-situ eddy current monitoring system including a first sensor for generating a first signal according to the thickness of the conductive layer on the substrate, and a first temperature sensor A first polishing station to perform;
A second in-situ eddy current monitoring system comprising a second platen for supporting a second polishing pad and a second sensor for generating a second signal according to the thickness of the conductive layer on the substrate Polishing station;
A carrier head for holding the substrate; And
Controller configured to perform actions
Including,
The above operations are:
During polishing of the substrate at the second polishing station, receiving a second signal from a second eddy current monitoring system;
Based on the received second signal, determining a starting value of the second signal at an initial time of polishing of the substrate at the second polishing station;
The second polishing based on an end value of the first signal, the start value, and a first temperature measured by the first temperature sensor determined for the end of polishing of the substrate at the first polishing station. Determining a gain for the station;
Calculating a third signal, based on the gain and the second signal, for at least a portion of the second signal collected during polishing of at least one substrate in the second polishing station; And
Based on the third signal, for the at least one substrate, determining at least one of an adjustment to a polishing parameter or a polishing endpoint
Containing,
Polishing system. The method of claim 28,
Including a second temperature sensor,
The controller is configured to determine the gain based on a second temperature measured by the second temperature sensor,
Polishing system. The method of claim 28,
The controller is configured to calculate the gain based on the resistivity of the layer being polished at the first and second temperatures,
Polishing system.

Images