Methods, computer program product, and system for eddy current monitoring to detect vibration in polishing

Abstract

The main body is brought into contact with the polishing pad of the polishing system, and polishing fluid is supplied to the polishing pad. When the main body contacts the polishing pad, a relative motion is generated between the main body and the polishing pad. During the relative motion when the main body contacts the polishing pad, a signal from an in-situ eddy current monitoring system is generated, and mechanical vibration in the polishing system is detected based on the signal from the in-situ eddy current monitoring system.

Description

Technical Field

[0001] This case concerns chemical mechanical polishing, and more specifically, eddy current monitoring during polishing. Prior Technology

[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 planarizing the layers on the substrate. For example, one manufacturing step involves depositing a filler layer on a non-planar surface and planarizing that filler layer. For some 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 a patterned insulating layer to fill trenches and holes in the insulating layer. After planarization, the remaining metal in the trenches and holes of the patterned layer forms vias, plugs, and lines to provide conductive paths between thin-film circuits on the substrate.

[0003] Chemical mechanical polishing (CMP) is an acceptable method for planarization. This planarization method typically requires mounting a substrate on a carrier head. The exposed surface of the substrate is typically placed against a rotating polishing pad. The carrier head provides a controlled load on the substrate to push it against the polishing pad. A polishing slurry with abrasive particles is typically supplied to the surface of the polishing pad.

[0004] In some systems, the substrate is monitored in situ during polishing (e.g., using a polishing pad). One monitoring technique involves inducing eddy currents in the conductive layer of the substrate and detecting changes in these eddy currents when the conductive layer is removed. Summary of the Invention

[0005] In one embodiment of a method, computer program product, or polishing system, a signal from an in-situ eddy current monitoring system is generated during the relative motion of a body in contact with a polishing pad, and mechanical vibrations in the polishing system are detected based on the signal from the in-situ eddy current monitoring system.

[0006] In another embodiment, a chemical mechanical polishing method includes: contacting a substrate with a polishing pad; supplying a polishing slurry to the polishing pad; generating relative motion between the substrate and the polishing pad; during polishing of the substrate, causing a sensor of an in-situ eddy current monitoring system to sweep across a path across the substrate; selecting a portion of a signal from the in-situ eddy current monitoring system corresponding to a metal-departure position of the sensor, wherein the metal-departure position excludes at least a location below the substrate; measuring noise in the selected portion of the signal corresponding to the metal-departure position of the sensor; and comparing the measured noise with a threshold to determine whether to generate an alarm.

[0007] In another embodiment, a computer program product tangibly encoded on a non-transitory computer-readable medium has instructions for causing one or more computers to perform the following operations: receiving a signal from an in-situ eddy current monitoring system, the in-situ eddy current monitoring system including a sensor swept below a bearing head of a polishing system; selecting a portion of the signal corresponding to a metal-leaving position of the sensor, wherein the metal-leaving position excludes at least the position of the sensor below the bearing head; measuring noise in the selected portion of the signal corresponding to the metal-leaving position of the sensor; and comparing the measured noise with a threshold to determine whether to generate an alarm.

[0008] In another embodiment, a polishing system includes: a rotatable pressure plate for holding a polishing pad; a carrier head for maintaining contact between a substrate and the polishing pad; a motor for rotating the pressure plate; an in-situ eddy current monitoring system including a sensor position in the pressure plate such that the sensor sweeps between the carrier heads with each rotation of the pressure plate; and a controller. The controller is configured to receive a signal from the in-situ eddy current monitoring system, select a portion of the signal corresponding to a metal-leaving position of the sensor, wherein the metal-leaving position excludes at least a position of the sensor below the carrier heads, measure noise in the selected portion of the signal corresponding to the metal-leaving position of the sensor, and compare the measured noise with a threshold to determine whether to generate an alarm.

[0009] The implementation may include one or more of the following features. The controller may be configured to generate visual or audible alarms to the operator. The body may be a substrate for integrated circuit manufacturing, a retaining ring for a carrier head, or an adjuster disk.

[0010] The implementation may include one or more of the following advantages: It can detect the onset of vibration in the polishing system and generate an alarm to stop polishing or take corrective action. It can reduce or avoid damage to the inner surface of the retaining ring, such as grooving the inner diameter. It can reduce edge over-polishing, thereby improving yield. It can screen polishing processes and hardware to ensure they do not contribute to this vibration. Detection can be implemented with existing hardware, such as existing eddy current monitoring systems, thereby enabling a low-cost solution.

[0011] Details of one or more implementations are set forth in the accompanying drawings and the following description. Other features, characteristics, and advantages will be readily apparent from the description and drawings and from the scope of the claims. Simple Explanation of the Diagram

[0012] Figure 1 shows a schematic cross-sectional view of an example polishing station including an eddy current monitoring system.

[0013] Figure 2 illustrates a schematic top view of an example chemical mechanical polishing station, showing the path of the sensor scanning across the substrate.

[0014] Figure 3 is a schematic cross-sectional view illustrating an example magnetic field generated by the sensor of the eddy current monitoring system.

[0015] Figure 4A is a schematic diagram of the signal from the eddy current monitoring system.

[0016] Figure 4B is a schematic diagram of the signals from the eddy current monitoring system when vibration occurs in the polishing system.

[0017] Figure 5 is a flowchart of a method for monitoring the thickness of the conductive layer. Implementation

[0018] One problem that can arise in chemical mechanical polishing is uneven polishing, such as over-polishing of the substrate edges (typically considered to be the outer 5-10 mm of the substrate). Damage to the inner diameter surface of the retaining ring (e.g., scratches or grooves formed on the inner diameter surface) may be related to some cases of uneven polishing. Without being bound by theory, it is assumed that certain polishing conditions result in high friction and static resistance between the polishing pad and the substrate and / or retaining ring. Theoretically, this high friction causes the substrate and / or retaining ring to undergo slip-stick motion (rather than relatively uniform motion) as it passes over the polishing pad. In particular, it is assumed that the slip-stick motion causes vibration of the substrate relative to the retaining ring, which may cause the substrate edge to chisel into the inner surface of the retaining ring and damage the inner surface of the retaining ring, leaving scratches or grooves. The uneven inner surface of the ring, in turn, leads to uneven polishing, for example, over-polishing at the substrate edges.

[0019] Still not bound by theory, this stick-slip effect is more likely to occur in "aggressive" polishing operations, such as combinations of low slurry flow rates, high temperatures, and high pressures. Such aggressive polishing may be necessary for polishing certain materials to planarize them or to achieve high polishing rates. In some cases, aggressive polishing can be performed without associated retainer ring damage and uneven polishing. However, uneven polishing can rapidly develop after normal polishing of multiple substrates. Again, it is assumed that in aggressive polishing operations, even small changes in temperature, slurry distribution, etc., can be sufficient to trigger the onset of the stick-slip effect. Unfortunately, for many monitoring techniques (e.g., motor torque monitoring), this stick-slip effect is not immediately apparent. Furthermore, due to the combination and effect of other variables (e.g., pad roughness, slurry viscosity, etc.), it may be impossible to specify certain parameters (such as platen motor torque, bearing head torque, or pad temperature) as the boundary for the occurrence of the stick-slip effect.

[0020] However, the stick-slip effect does cause vibrational energy to be transferred to the polishing system. In particular, eddy current monitoring systems can be used to detect mechanical vibrations in the polishing system, such as those caused by the stick-slip effect. This allows for the generation of alarms or modification of command parameters to avoid damage to the retaining ring.

[0021] Figures 1 and 2 illustrate an example of a polishing station 20 in a chemical mechanical polishing system. The polishing station 20 includes a rotatable, disc-shaped pressure plate 24 on which a polishing pad 30 is mounted. The pressure plate 24 is operable to rotate about a central axis 25. For example, a motor 22 can rotate a drive shaft 28 to rotate the pressure plate 24. The polishing pad 30 may be a two-layer polishing pad having an outer polishing layer 34 and a softer backing layer 32.

[0022] Polishing station 20 may include a supply port or combined supply-cleaning arm 39 to dispense polishing fluid 38 (such as abrasive slurry) onto polishing pad 30. Polishing station 20 may include pad conditioner devices, such as a conditioner head 40 with an adjustment disc 42, to maintain the surface roughness of the polishing pad.

[0023] The support head 70 is operable to hold the substrate 10 against the polishing pad 30. The support head 70 is suspended from a support structure 72 (e.g., a carousel or track) and connected to a support head rotation motor 76 by a drive shaft 74, allowing the support head to rotate about a central axis 71. Optionally, the support head 70 can oscillate laterally by movement along the track or by the rotational oscillation of the carousel itself, for example, by oscillating laterally on a slider on the carousel.

[0024] The carrier head 70 may include a retaining ring 84 to hold the substrate. In some implementations, the retaining ring 84 may include highly conductive portions; for example, the retaining ring may include a thin lower plastic portion 86 that contacts the polishing pad, and a thick upper conductive portion 88. In some implementations, the highly conductive portions are metal, for example, the same metal as the layer to be polished, such as copper.

[0025] During operation, the pressure plate rotates about its central axis 25, and the bearing head rotates about its central axis 71 and translates laterally across the top surface of the polishing pad 30. The bearing head 70 may include a flexible membrane 80 having a substrate mounting surface to contact the back side of the substrate 10, and a plurality of pressurizable chambers 82 that apply different pressures to different areas (e.g., different radial areas) of the substrate 10. The bearing head may also include a retaining ring 84 to hold the substrate.

[0026] The polishing system also includes an eddy current monitoring system 100, which may be coupled to or is considered to include the controller 90. A rotary coupling 29 may be used to electrically connect components (e.g., sensors of the in-situ monitoring system) in the rotatable pressure plate 24 to components (e.g., drive and sensing circuitry or the controller 90) outside the pressure plate.

[0027] The in-situ eddy current monitoring system 100 is configured to generate a signal that depends on the depth of the layer of conductive material (e.g., metal, such as copper) on the substrate. In operation, the polishing system can use the in-situ monitoring system 100 to determine when the conductive layer has reached a target thickness (e.g., the target depth of metal in a trench or the target thickness of a metal layer covering the dielectric layer), and then stop polishing. Alternatively or additionally, the polishing system can use the in-situ monitoring system 100 to determine the thickness difference of the conductive material 16 across the substrate 10, and use this information to adjust the pressure in one or more chambers 82 in the bearing head 70 during polishing to reduce polishing non-uniformity.

[0028] A recess 26 may be formed in the pressure plate 24, and optionally, a thin segment 36 may be formed in the polishing pad 30 covering the recess 26. The recess 26 and the thin segment 36 may be positioned such that, regardless of the translational position of the bearing head, both the recess 26 and the thin segment 36 pass under the substrate 10 during a portion of the pressure plate's rotation. Assuming the polishing pad 30 is a two-layer pad, the thin segment 36 may be constructed by removing a portion of the back layer 32 and optionally by forming a recess in the bottom of the outer polishing layer 34. For example, if an in-situ optical monitoring system is integrated into the pressure plate 24, the thin segment may optionally be optically transmissive.

[0029] The in-situ monitoring system 100 may include a sensor 102 mounted in the recess 26. The sensor 102 may include a magnetic core 104 at least partially positioned in the recess 26, and at least one coil 106 wound around a portion of the core 104. A drive and sensing circuit 108 is electrically connected to the coil 106. The drive and sensing circuit 108 generates signals that can be sent to the controller 90. Although illustrated external to the pressure plate 24, some or all of the drive and sensing circuit 108 may be mounted within the pressure plate 24.

[0030] Referring to Figures 1 and 3, the drive and sensing circuit 108 applies an AC current to the coil 106, which generates a magnetic field 150 between the two poles 152a and 152b of the core 104. In operation, a portion of the magnetic field 150 extends into the substrate 10 as the substrate 10 intermittently covers the sensor 102.

[0031] Circuit 108 may include a capacitor connected in parallel with coil 106. Coil 106 and capacitor together may form an LC resonant tank.

[0032] If it is desired to monitor the thickness of a conductive layer on a substrate, when the magnetic field 150 reaches the conductive layer, the magnetic field 150 can penetrate the layer on the substrate and generate eddy currents in the layer on the substrate. This modifies the effective impedance of the LC circuit.

[0033] The driving and sensing circuit 108 may include a marginal oscillator coupled to the combined driving / sensing coil 106, and the output signal may be the current required to maintain the peak-to-peak amplitude of the sinusoidal oscillation at a constant value, for example, as described in U.S. Patent No. 7,112,960. Other configurations of the driving and sensing circuit 108 are also possible. For example, separate driving and sensing coils may be wound on a core. The driving and sensing circuit 108 may apply current at a fixed frequency, and the signal from the driving and sensing circuit 108 may be the phase shift of the current in the sensing coil relative to the driving coil, or the amplitude of the sensed current, for example, as described in U.S. Patent No. 6,975,107.

[0034] Referring to Figure 2, as the pressure plate 24 rotates, the sensor 102 sweeps across the substrate 10. By sampling the signal from the circuit 108 at a specific frequency, the circuit 108 generates measurement results at a series of sampling regions 94 across the substrate 10. For each sweep, the measurement results at one or more sampling regions 94 can be selected or combined. Therefore, after multiple sweeps, the selected or combined measurement results provide a time-varying sequence of values.

[0035] Polishing station 20 may also include a position sensor 96, such as a light interruptor, to sense when sensor 102 is under substrate 10 and when sensor 102 leaves substrate 10. For example, position sensor 96 may be mounted at a fixed position opposite to carrier head 70. Mark 98 may be attached to the periphery of pressure plate 24. The attachment point and length of mark 98 are selected such that the mark signals position sensor 96 when sensor 102 sweeps under substrate 10. Alternatively or additionally, polishing station 20 may include an encoder to determine the angular position of pressure plate 24.

[0036] Referring to Figure 1, a controller 90 (e.g., a general-purpose programmable digital computer) receives signals from a sensor 102 of an in-situ monitoring system 100. As the sensor 102 sweeps beneath the substrate 10 with each rotation of the pressure plate 24, information about the depth of the conductive layer (e.g., a bulk layer or conductive material in a trench) is accumulated in situ (once per pressure plate rotation). The controller 90 can be programmed to sample the measurement results from the in-situ monitoring system 100 when the substrate 10 substantially covers the sensor 102.

[0037] Furthermore, the controller 90 can be programmed to calculate the radial position of each measurement and classify the measurements into radial ranges. By arranging the measurements into radial ranges, data on the conductive film thickness of each radial range can be fed into the controller (e.g., controller 90) to adjust the polishing pressure distribution applied by the bearing head. The controller 90 can also be programmed to apply endpoint detection logic to the sequence of measurement results generated by the in-situ monitoring system 100 and detect the polishing endpoint.

[0038] As the sensor 102 sweeps beneath the substrate 10 with each rotation of the pressure plate 24, information about the thickness of the conductive layer accumulates in situ and on a continuous, real-time basis. During polishing, the measurements from the sensor 102 can be displayed on an output device to allow the polishing station operator to visually monitor the progress of the polishing operation, although this is not required.

[0039] Figure 4A illustrates the time-varying signal 200 output by the eddy current monitoring system 100 during "normal" operation without unexpected mechanical vibration. Peak 202 in signal 200 corresponds to measurements taken when the sensor passes beneath the substrate 10; the interaction of the magnetic field with the metal layers on the substrate and / or the metal portion of the carrier head causes an increase in signal strength. Peak 202 contains a certain amount of "noise" as the sensor traverses various regions with different characteristic densities, metal depths, etc., causing variations in signal strength.

[0040] In contrast, valley 204 in signal 200 corresponds to measurements taken when the sensor is "off-substrate," i.e., not below the substrate. As shown in extended portion 210 of the graph, the signal is approximately flat and has low noise in valley 204. The signal is approximately at its minimum in the absence of a metal layer on the substrate and / or a metal portion of the carrier head to interact with the magnetic field.

[0041] The "step" 206 at the base of peak 202 corresponds to a measurement taken when the sensor passes under the holding ring.

[0042] Figure 4B illustrates a graph showing the change of signal 200' output by eddy current monitoring system 100 over time during the polishing process, during which vibrations may occur, for example, due to stick-slip effects. Similarly, peak 202 in signal 200' corresponds to measurements taken when the sensor passes beneath substrate 10. For some processes, vibrations may not occur immediately. Therefore, the initial valley 204a can be generally flat and have low noise. However, when vibrations occur in the polishing system, they can manifest as noise in some subsequent valleys 204b. Vibrations may occur due to variations in the polishing environment, such as heat accumulated in the polishing pad or changes in slurry distribution over time. Since there is virtually no metal above the sensor during valley 204b, the appearance of noise in valley 204b is undesirable. Again, without being bound by any particular theory, it is assumed that vibrational energy is transmitted to sensor 102, causing sensor 102 to vibrate relative to pressure plate 24 (see Figure 1), causing the element to deviate from its calibration conditions, thus causing signal fluctuations.

[0043] Referring back to Figure 1, the controller 90 can be configured to detect increased or excessive noise in areas where the sensor 102 is located where no signal from metal above the polishing pad is expected (i.e., not below the carrier head 70 (including the substrate 10 and the retaining ring 84)) or below other metal components of the polishing system that may generate signals (e.g., not below the metal adjustment head 40 or the adjustment disc 42) located near and above the polishing pad. The location of the sensor 102 where no signal from metal is expected can be referred to as an "off-metal" location.

[0044] The controller 90 can select the portion of the signal corresponding to the "away from metal" position of the sensor 102 based on data from the position sensor 96. For example, the portion of the signal corresponding to the mark 98 can be excluded. Additional marks can be presented for the adjuster head 40 and / or other metal parts located above the polishing pad, and portions of the signal corresponding to these marks can also be excluded, leaving the remaining portion of the signal corresponding to the "away from metal" position. Alternatively or additionally, the controller can make selections based on angular position data from the encoder, for example by comparing the angular position from the encoder with a set of thresholds (e.g., from a datasheet) indicating which angular positions should be included or excluded. Alternatively or additionally, the controller can make selections based on signal processing of the signal 200 to detect subsequently excluded peaks 202 (see Figures 4A-4B).

[0045] Once the portion of the signal corresponding to the location away from the metal is selected, such as valleys 204a and 204b, the "noise" in each portion can be measured. Typically, each valley 204 produces one noise measurement result. Various techniques can be used to measure the noise of the signal's portion away from the metal, such as standard deviation, minimum-maximum difference, or total trace length. Total trace length is simple to calculate, sensitive to noise, and largely unaffected by the substrate signal. As another possibility, a Fourier transform can be performed on signal 200 to convert the signal into a spectrum (wavelength or wavenumber spectrum would be equivalent), and the power in a pre-selected portion of the spectrum (e.g., in the 1-4 kHz range) can be measured. Any of these techniques produces a measurement indicating the noise in the portion of the signal away from the metal.

[0046] The controller 90 then compares the measured value with a stored threshold. If the noise exceeds the threshold, the controller 90 generates an alarm signal. This can be a visual or audible signal to the operator so that the operator can decide to stop polishing. Alternatively, the alarm signal can cause the controller 90 to automatically stop the polishing process. In either case, the operator can take corrective actions, such as adjusting polishing control parameters (e.g., slurry flow rate, bearing head pressure, or hot or coolant delivery), or replacing parts (e.g., replacing the retaining ring), to prevent uneven polishing on subsequent substrates.

[0047] While the above discussion focuses on the detection of mechanical vibrations during polishing operations, this technique can also be used to screen processes and hardware, such as during the "qualification" of polishing systems or polishing formulations. For example, a polishing system may operate without a substrate present in the carrier head or with a "blank" substrate (rather than a device substrate intended for producing integrated circuits). If mechanical vibrations are detected, the polishing system or polishing formulation is considered unqualified.

[0048] Figure 5 is a flowchart of a method 500 for monitoring mechanical vibration. Assuming a substrate is to be polished (as opposed to a screening operation without a substrate), the substrate is placed in a carrier head and brought into contact with the polishing surface of a polishing pad (step 502). Even without a substrate, the retaining ring of the carrier head will contact the polishing pad. Polishing fluid (e.g., slurry) is supplied to the polishing pad (step 504), generating relative movement between the carrier head and the polishing pad (step 506), such as rotating a pressure plate. During this process, an in-situ eddy current monitoring system is used to monitor the system (step 508) to generate a signal, such as a series of signal values. For the polishing operation, the thickness of the metal layer on the substrate and the polishing endpoint can be detected using the portion of the signal corresponding to the sensor below the substrate. Independently, the portion of the signal corresponding to the sensor at the "out-of-metal" position is selected (step 510). Noise in these "out-of-metal" portions of the signal is measured and compared to a threshold (step 512). If the measured noise exceeds a stored threshold, an alarm can be generated (step 514).

[0049] The polishing equipment and methods described above can be applied to various polishing systems. As long as there is a time interval during which the sensor is in the "away from metal" position, the polishing pad or carrier head, or both, can be moved to provide relative movement between the polishing surface and the substrate. For example, the pressure plate can run around an orbit instead of rotating. The polishing pad can be a circular (or some other shape) pad fixed to the pressure plate. The polishing layer can be a standard (e.g., filled or unfilled polyurethane) polishing material, a soft material, or a fixed abrasive material. The term "relative positioning" is used to refer to relative positioning within the system rather than relative to gravity; it should be understood that the polishing surface and the substrate can be held in a vertical orientation or some other orientation during the polishing operation.

[0050] While the above discussion focuses on the "out-of-metal" portion of the signal, the "on-metal" portion of the signal can also be used to detect mechanical vibrations. Generally, signal changes caused by mechanical vibrations will occur at different frequencies than changes caused by the substrate (e.g., patterned metal). Therefore, the signal can be filtered, for example, using a high-pass or band-pass filter, and the filtered signal can be analyzed to determine whether an alarm should be generated. A specific frequency range for the filter can be determined empirically. Then, the noise in the filtered signal can be compared to a threshold to determine whether an alarm should be generated.

[0051] The functional operation of the controller 90 may be implemented using one or more computer program products (i.e., one or more computer programs tangibly embodied in a non-transitory computer-readable storage medium) for execution by a data processing device (e.g., a programmable processor, a computer, or multiple processors or computers) or for controlling the operation of the data processing device.

[0052] Several embodiments of the invention have been described. However, it will be understood that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the appended claims.

[0053] 10:Substrate 16: Conductive materials 20: Polishing Station 22: Motor 24: Pressure plate 25: Central Axis 26: Depression 28: Drive shaft 29: Rotary coupling component 30: Polishing Pad 32: Back layer 34: Outer polished layer 36: Thin section 38: Polishing fluid 39: Modular Supply - Cleaning Arm 40: Adjustment head 42: Adjustment dial 70: Bearing head 71: Central Axis 72: Supporting structure 74: Drive shaft 76: Bearing head rotary motor 80: Flexible diaphragm 82: Chamber 84: Keeping ring 86: Lower plastic part 88: Upper conductive part 90: Controller 94: Sampling Area 96: Position sensor 98: Logo 100: Eddy Current Monitoring System 102: Sensor 104: Magnetic Core 106: Coil 108: Drive and Sensing Circuits 150: Magnetic Field 152a: Extreme 152b: Extreme 200: Signal 200': Signal 202: Peak 204: Valley 204a: Valley 204b: Valley 206: Steps 210: Extended Section 500: Methods 502: Steps 504: Steps 506: Steps 508: Steps 510: Steps 512: Steps 514: Steps

[0054] Domestic storage information (please note in order of storage institution, date, and number) none Overseas storage information (please note in the order of storage country, institution, date, and number) none

Claims

1. A polishing system, comprising: A rotatable pressure plate for fixing a polishing pad; A support head for fixing a substrate into contact with the polishing pad; a motor for rotating the pressure plate; an in-situ eddy current monitoring system including a sensor position located in the pressure plate such that the sensor sweeps along a path below the support head with each rotation of the pressure plate, the sensor generating a signal including a sequence of signal values. A controller is configured to select a portion of the signal corresponding to several locations below the substrate, determine the thickness of a conductive layer on the substrate at each of the several locations along the path based on the signal values ​​of the selected portion of the signal, measure noise in the selected portion of the signal to detect machine vibration, and compare the measured noise with a threshold to determine whether to generate an alarm.

2. The system of claim 1, wherein the controller is configured to filter the signal from the in-situ eddy current monitoring system to remove acoustic signals from the substrate to generate a filtered signal, and the controller is configured to determine the thickness of the conductive layer from a selected portion of the filtered signal.

3. The system of claim 2, wherein the controller is configured to apply a high-pass filter to the signal.

4. The system of claim 1, wherein the controller is configured to generate an audible alarm or a visual alarm in response to a measured noise exceeding the threshold.

5. The system as requested in item 4, wherein the controller is configured to stop polishing in response to the alarm.

6. The system of claim 1, wherein the controller is configured to measure noise in a selected portion of the signal by calculating one or more of a standard deviation, minimum-maximum difference, or total trace length of the signal.

7. The system of claim 1, wherein the controller is configured to measure noise in a selected portion of the signal by performing a Fourier transform on a selected portion of the signal, and to calculate a power of the signal over a frequency range.

8. The system of claim 1, wherein the system is configured to measure noise by detecting a noise value generated by the sensor during each scan under the substrate.

9. A computer program product tangibly encoded on a non-transitory computer-readable medium, comprising instructions to cause one or more computers to perform the following operations: receiving a signal from an in-situ eddy current monitoring system, the system including a sensor sweeping under a bearing head of a polishing system; selecting a portion of the signal, the portion of the signal corresponding to a plurality of locations under a substrate; determining, by means of a signal value in the selected portion of the signal, the thickness of a conductive layer on the substrate at each of the plurality of locations along a path; measuring noise in the selected portion of the signal to detect machine vibration; and comparing the measured noise with a threshold to determine whether to generate an alarm.

10. The computer program product of claim 9 includes several instructions for filtering the signal from the in-situ eddy current monitoring system to remove acoustic signals from the substrate to generate a filtered signal, and the instructions for determining the thickness of the conductive layer from a selected portion of the filtered signal.

11. The computer program product of claim 10, wherein the instruction for filtering the signal includes an instruction to apply a high-pass filter to the signal.

12. The computer program product of claim 9 includes instructions for generating an audible alarm or a visual alarm in response to measured noise exceeding the threshold.

13. The computer program product, as requested in item 12, includes instructions for stopping polishing in response to the alarm.

14. The computer program product of claim 9, wherein the instructions for measuring noise in a selected portion of the signal include instructions for calculating one or more of a standard deviation, minimum-maximum difference, or total trace length of the signal.

15. The computer program product of claim 9, wherein the instructions for measuring noise in a selected portion of the signal include instructions for performing a Fourier transform on the selected portion of the signal and for calculating a power of the signal over a frequency range.

16. The computer program product of claim 9, wherein the instructions for measuring noise include instructions for detecting each sweep of the sensor under the substrate and instructions for generating a noise value for each sweep.

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