Abstract: In a scheme in which a top ring is held to an end portion of a swing arm, the present invention improves accuracy of polishing end point detection. A polishing apparatus for polishing between a polishing pad 10 and a semiconductor wafer 16 disposed opposed to the polishing pad 10 includes a polishing table 30A for holding the polishing pad 10 and a top ring 31A for holding the semiconductor wafer 16. A swing shaft motor 14 swings a swing arm 110 for holding the top ring 31A. The arm torque detection section 26 detects arm torque applied to the swing arm 110. An end point detection section 28 detects a polishing end point indicating an end of polishing based on the detected arm torque.

Abstract: A method and apparatus for on-line measurement of the wafer thinning and grinding force, related to the field of ultra-precision machining of semiconductor wafer materials. The grinding force measuring apparatus comprises a semiconductor wafer, a worktable, a bearing table, a thin film pressure sensor, and a data processing and wireless transmission module. The grinding force measuring method includes sensor calibration based on the testing device and on-line measurement of grinding force. Using the grinding force measuring device and method provided by the invention, the grinding force in the semiconductor wafer grinding process can be monitored in real time, which is of great significance for semiconductor processing and reducing grinding damage.

Abstract: The present disclosure describes an apparatus and a method for a chemical mechanical polishing (CMP) process that recycles used slurry as another slurry supply. The apparatus includes a pad on a rotation platen, a first feeder and a second feeder where each of the first and the second feeder is fluidly connected to a respective flow regulator and configured to dispense a first and a second slurry on the pad, a flotation module configured to provide a recycled slurry, and a detection module configured to detect a polishing characteristic associated with polishing the substrate. The flotation module further includes an inlet configured to provide a fluid sprayed from the pad and a tank configured to store chemicals that include a frother and a collector configured to chemically bond with the fluid.

Abstract: A polishing apparatus capable of accurately determining a service life of a light source, and further capable of accurately measuring a film thickness of a substrate, such as a wafer, without calibrating an optical film-thickness measuring device, is disclosed. The polishing apparatus includes a spectrometer configured to decompose reflected light from a substrate in accordance with wavelength and measure an intensity of the reflected light at each of wavelengths a film thickness of the substrate is determined based on a spectral waveform indicating a relationship between the intensity of the reflected light and wavelength. An optical-path selecting mechanism is configured to selectively couple either a light-receiving fiber or an internal optical fiber to the spectrometer.

Abstract: The invention simulates polishing amount taking into account pressure concentration that occurs in the vicinity of the edge of a substrate when a small-diameter buffing pad overhangs the substrate to be buffed. One embodiment of the invention provides a method for simulating polishing amount in a case where a polishing pad of a smaller size than a substrate is used to buff the substrate. The method includes measuring distributions of pressure that is applied from the polishing pad to the substrate according to each overhang amount of the polishing pad relative to the substrate by using a pressure sensor, and correcting the pressure that is used in the polishing amount simulation in accordance with the overhang amounts and the measured pressure distributions.

Abstract: An end point detection method is provided for detecting an end point based on a drive current supplied to a drive unit that rotates and drives one of a polishing table and a holding unit. The end point detection method includes: a step (S102) of determining whether a polishing condition of a polishing process to be executed coincides with a preset specific polishing condition; a step (S103) of adjusting a current control parameter in a drive control unit that controls the drive current, the current control parameter related to a change in the drive current with respect to a change in a driving load of the drive unit, if it is determined that the polishing condition coincides with the specific polishing condition; and a step (S105) of detecting the drive current supplied to the drive unit based on the adjusted current control parameter.

Abstract: A polishing apparatus 100 includes a first electric motor 14 that rotationally drives a polishing table 12, and a second electric motor 22 that rotationally drives a top ring 20 that holds a semiconductor wafer 18. The polishing apparatus 100 includes: a current detection portion 24; an accumulation portion 110 that accumulates, for a prescribed interval, current values of three phases that are detected by the current detection portion 24; a difference portion 112 that determines a difference between a detected current value and the accumulated value, where the detected current value is detected in an interval that is different than the prescribed interval; and an endpoint detection portion 29 that detects a polishing endpoint that indicates the end of polishing of the surface of the semiconductor wafer 18, based on a change in the difference that the difference portion 112 outputs.

Abstract: A semiconductor manufacturing apparatus includes: a treatment chamber treating a treated film of a wafer using a desired chemical fluid; a film thickness measurement unit measuring an initial film thickness of the treated film before treatment and a final film thickness of the treated film after treatment; and a main body controlling unit calculating a treatment speed of the chemical fluid from the initial film thickness, the final film thickness, and a chemical fluid treatment time taken from the initial film thickness to the final film thickness to calculate a chemical fluid treatment time for a wafer to be treated next from the calculated treatment speed.

Abstract: A polishing system includes a polishing station including a platen to support a polishing pad, a support to hold a substrate, an in-line metrology station to measure the substrate before or after polishing of a surface of the substrate in the polishing station, and a controller. The in-line metrology station includes a color line-scan camera, a white light source, a frame supporting the light source and the camera, and a motor to cause relative motion between the camera and the support along a second axis perpendicular to the first axis to cause the light source and the camera to scan across the substrate. The controller is configured to receive a color data from the camera, to generate a 2-dimensional color image from the color data, and to control polishing at the polishing station based on the color image.

Abstract: A polishing pad is provided. The polishing pad, suitable for a polishing procedure using a slurry containing water, includes a polishing track region and a first reactant. The polishing track region includes a central region and a peripheral region surrounding the central region. The first reactant is disposed in the central region of the polishing track region, wherein the first reactant is able to react endothermically with the water in the slurry.

Abstract: The present disclosure relates to a method of forming a CMP slurry that is free of pH-adjusters (i.e., chemicals added solely for the purpose of adjusting a pH of a CMP slurry), and an associated a pH-adjuster free CMP slurry. In some embodiments, the method is performed by forming a CMP slurry having a first pH value. A desired pH value of the CMP slurry is determined. A chelating agent configured to bond to metallic ions is provided to the CMP slurry. The chelating agent is configured to adjust a pH value of the CMP slurry from the first pH value to the desired pH value. By using the chelating agent to adjust a pH value of the CMP slurry to achieve a desired pH value, the method is able to form a CMP slurry that is free of pH-adjusters, thereby reducing the cost and complexity of the CMP slurry.

Abstract: A substrate holding unit of a liquid processing apparatus holds a circular substrate horizontally and rotates the substrate about a vertical axis, and a chemical liquid nozzle supplies a chemical liquid to the peripheral edge of the substrate while the substrate is being rotated in order to remove a film of the peripheral edge. An image capture unit captures an image of the peripheral edge, and a determination unit calculates an actually removed value for a removed width of the film based on a result of the image capturing and determines whether the removed width is suitable or not.

Abstract: The present invention improves the accuracy of film thickness detection. A film thickness signal processing apparatus 230 is provided with a receiving unit 232 for receiving film thickness data output from an eddy-current sensor 210 for detecting the film thickness of a polishing object 102 along a surface to be polished thereof; an identifying unit 236 for identifying the effective range of the film thickness data on the basis of the film thickness data received by the receiving unit 232; and a correcting unit 238 for correcting the film thickness data within the effective range identified by the identifying unit 236.

Abstract: During polishing of a first substrate at a first polishing station, a sequence of measurements by a first in-situ monitoring system is monitored to determining a first time at which the first sequence exhibits a first predefined feature indicating a predetermined thickness of an overlying layer, and during polishing of the first substrate at a second polishing station, a sequence of measurements by a second in-situ monitoring system is monitored to determine a second time indicating clearance of the overlying layer and exposure of the underlying layer. The first time is used to calculate a first adjusted polishing pressure for a second substrate at the first polishing station, and the second time is used to calculate a second adjusted polishing pressure for the second substrate at the second polishing station.

Abstract: The present disclosure provides a method of fabricating a semiconductor device. The method includes providing a semiconductor structure including a metal gate (MG) layer formed to fill in a trench between two adjacent interlayer dielectric (ILD) regions; performing a chemical mechanical polishing (CMP) process using a CMP system to planarize the MG layer and the ILD regions; and cleaning the planarized MG layer using a O3/DIW solution including ozone gas (O3) dissolved in deionized water (DIW). The MG layer is formed on the ILD regions.

Abstract: Provided is a chemical mechanical polishing (CMP) apparatus that includes a swing unit installed apart from a platen, on which a CMP pad to be conditioned is placed, at a predetermined interval, a connector installed on an upper end of the swing unit at one end thereof in a perpendicular direction to the swing unit and pivoting around the swing unit above the CMP pad, a rotator rotatably installed on the other end of the connector, a CMP pad conditioner coupled to the rotator and conditioning the CMP pad when rotated, and a vibration meter installed on the connector and detecting vibrations to measure a vibration acceleration of the CMP pad conditioner, thereby predicting a wear rate of the CMP pad based on the vibration acceleration and a state in which the CMP pad conditioner is installed or being used.

Abstract: To provide a polishing apparatus capable of more accurately determining a polishing end point. The polishing apparatus includes a turntable 12, a first electric motor 14 configured to rotationally drive the turntable, a top ring 20 configured to hold a workpiece together with the turntable, and a second electric motor 22 configured to rotationally drive the top ring. The polishing apparatus further includes a weighting unit configured to perform weighting so as to make the current ratios of the respective phases different from each other, and a torque variation detecting unit configured to detect a change in a phase current greatly weighted by the weighting unit and thereby detects a change in torque of the electric motor, the change being generated by performing the polishing.

Abstract: A substrate polishing system includes a platen to support a polishing surface, a carrier head configured to hold a substrate against the polishing surface during polishing, a light source configured to direct a light beam onto a surface of the substrate, a detector including an array of detection elements, and a controller. The detector is configured to detect reflections of the light beam from an area of the surface, and is configured to generate an image having pixels representing regions on the substrate having a length less than 0.1 mm. The controller is configured to receive the image and to detect clearance of a metal layer from an underlying layer on the substrate based on the image.

Abstract: Disclosed is a liquid processing apparatus capable of accurately determining a holding state of a substrate without being influenced by, for example, material or surface condition of a substrate. The liquid processing apparatus includes a substrate holding unit that holds a substrate, a camera that photographs a region where a peripheral edge portion of substrate is present when substrate is properly held by the substrate holding unit, and a control unit that determines a holding state of the substrate held by the substrate holding unit based on an image photographed by the camera.

Abstract: A projecting/receiving unit (52) projects a laser light to a peripheral portion (30) and receives the reflected light while a liquid is being fed to a substrate (14) and is flowing on the peripheral portion (30). A signal processing controller (54) processes the electric signal of the reflected light to decide the state of the peripheral portion (30). The state of the peripheral portion being polished is monitored. Moreover, the polish end point is detected. A transmission wave other than the laser light may also be used. The peripheral portion (30) may also be enclosed by a passage forming member thereby to form a passage properly. The peripheral portion can be properly measured even in the situation where the liquid is flowing on the substrate peripheral portion.

Abstract: Various embodiments of a semiconductor processing fluid delivery system and a method delivering a semiconductor processing fluid are provided. In aspect, a system for delivering a liquid for performing a process is provided that includes a first flow controller that has a first fluid input coupled to a first source of fluid and a second flow controller that has a second fluid input coupled to a second source of fluid. A controller is provided for generating an output signal to and thereby controlling discharges from the first and second flow controllers. A variable resistor is coupled between an output of the controller and an input of the second flow controller whereby the output signal of the controller and the resistance of the variable resistor may be selected to selectively control discharge of fluid from the first and second flow controllers.

Abstract: A method includes performing a semiconductor fabrication process on a plurality of substrates. The plurality of substrates are divided into a first subset and a second subset. A rework process is performed on the second subset of the plurality of substrates but not on the first subset. A respective mean value of at least one exposure parameter for a lithography process is computed for each respective one of the first and second subsets of the plurality of substrates. A scanner overlay correction and a mean correction are applied to expose a second plurality of substrates on which the rework process has been performed. The mean correction is based on the computed mean values.

Abstract: Methods of etching exposed titanium nitride with respect to other materials on patterned heterogeneous structures are described, and may include a remote plasma etch formed from a fluorine-containing precursor. Precursor combinations including plasma effluents from the remote plasma are flowed into a substrate processing region to etch the patterned structures with high titanium nitride selectivity under a variety of operating conditions. The methods may be used to remove titanium nitride at faster rates than a variety of metal, nitride, and oxide compounds.

Abstract: Systems, methods and apparatus for polishing a substrate edge without mechanical contact are disclosed. The apparatus includes a rotatable chuck configured to secure a substrate, an ion milling machine configured to project an ion beam on an edge of the substrate and to sputter off matter from the substrate, and an endpoint detection sensor configured to determine if a material removal endpoint of the substrate has been reached. Numerous additional features are disclosed.

Abstract: A system for tunable removal rates and selectivity of materials during chemical-mechanical polishing using a chemical slurry or solution with increased dissolved oxygen content. The slurry can optionally include additives to improve removal rate and/or selectivity. Further selectivity can be obtained by varying the concentration and type of abrasives in the slurry, using lower operating pressure, using different pads, or using other additives in the dispersion at specific pH values.

Abstract: An apparatus for processing a substrate is disclosed. The apparatus includes a polishing section configured to polish a substrate, a transfer mechanism configured to transfer the substrate, and a cleaning section configured to clean and dry the polished substrate. The cleaning section has plural cleaning lines for cleaning plural substrates. The plural cleaning lines have plural cleaning modules and plural transfer robots for transferring the substrates.

Abstract: A polishing pad enabling a highly precise optical endpoint sensing during the polishing process and thus having excellent polishing characteristics (such as surface uniformity and in-plane uniformity) is disclosed. A polishing pad enabling to obtain the polishing profile of a large area of a wafer is also disclosed. A polishing pad of a first invention comprises a light-transmitting region having a transmittance of not less than 50% over the wavelength range of 400 to 700 nm. A polishing pad of a second invention comprises a light-transmitting region having a thickness of 0.5 to 4 mm and a transmittance of not less than 80% over the wavelength range of 600 to 700 nm. A polishing pad of a third invention comprises a light-transmitting region arranged between the central portion and the peripheral portion of the polishing pad and having a length (D) in the diametrical direction which is three times or more longer than the length (L) in the circumferential direction.

Abstract: The present invention relates to an apparatus for measuring surface properties of a polishing pad which measures surface properties such as surface topography or surface condition of a polishing pad used for polishing a substrate such as a semiconductor wafer. The apparatus for measuring surface properties of a polishing pad includes a laser beam source configured to emit a laser beam, and a photodetector configured to detect scattered light that is reflected and scattered by the polishing pad, an optical Fourier transform being performed on the detected scattered light to produce an intensity distribution corresponding to a spatial wavelength spectrum based on surface topography of the polishing pad. The laser beam is applied to the polishing pad at such an incident angle that the laser beam does not reach a bottom portion of a pore formed in the surface of the polishing pad.

Abstract: A method of controlling polishing of a substrate is described. A controller stores a library having a plurality of reference spectra. The controller polishes a substrate and measures a sequence of spectra of light from the substrate during polishing. For each measured spectrum of the sequence of spectra, the controller finds a best matching reference spectrum from the plurality of reference spectra and generates a sequence of best matching reference spectra. The controller uses a cell counting technique for finding the best matching reference spectrum. The controller determines at least one of a polishing endpoint or an adjustment for a polishing rate based on the sequence of best matching reference spectra.

Abstract: In accordance with an embodiment, a film thickness monitoring method includes applying light to a laminated body, detecting reflected light from the laminated body and outputting signals corresponding to the detected light, and judging whether a film thickness of an opaque film which is a polishing target has reached a desired film thickness. The laminated body includes a transparent film and the opaque film on the transparent film. A comparison value between the signal before polishing the opaque film and the signal after starting the polishing is obtained at predetermined time intervals, and whether the film thickness of the opaque film has reached the desired film thickness is judged based on a relationship between the comparison value of the signals and a predetermined threshold value.

Abstract: In accordance with an embodiment, a film thickness monitoring method includes applying light to a substrate, which is a processing target, in a semiconductor manufacturing process involving rotation of the substrate, detecting reflected light from the substrate, and calculating a thickness of a film on the substrate. The thickness of the film is calculated from intensity of the reflected light detected in an identified time zone in which incident light passes a desired region on the substrate during the semiconductor manufacturing process.

Abstract: A chemical mechanical polishing to that can provide uniform polishing across a wafer even when polishing hard wafers such as AlTiC wafers used in the formation of magnetic recording sliders. The chemical mechanical polishing to has a wafer carrier that includes a diaphragm or bladder that is configured such that an inner portion of the bladder can be pneumatically pressurized so as to bow outward, while outer portions remain unpressurized.

Abstract: In a Cu wiring forming method for forming a Cu wiring by filling Cu in a recess which is formed in a substrate in a predetermined pattern, a barrier film formed of a TaAlN film is formed at least on the surface of the recess by thermal ALD or thermal CVD. Then a Cu film is formed to fill the recess with the Cu film. Further, the Cu wiring is formed in the recess by polishing the entire surface of the substrate by CMP.

Abstract: A method includes performing a semiconductor fabrication process on a plurality of substrates. The plurality of substrates are divided into a first subset and a second subset. A rework process is performed on the second subset of the plurality of substrates but not on the first subset. A respective mean value of at least one exposure parameter for a lithography process is computed for each respective one of the first and second subsets of the plurality of substrates. A scanner overlay correction and a mean correction are applied to expose a second plurality of substrates on which the rework process has been performed. The mean correction is based on the computed mean values.

Abstract: A wafer polishing system including a platen configured to rotate in a first direction, and a polishing head configured to hold a wafer, the polishing head configured to rotate in a second direction. The wafer polishing system further includes an optical sensing system configured to detect a thickness of the wafer at a first location on the platen and a second location on the platen. A first distance from a center of the platen to the first location is different than a second distance from the center of the platen to the second location.

Abstract: A pressure control assembly for a carrier head of a polishing apparatus includes a pressure supply line configured to fluidically connect to a chamber of a carrier head, a sensor to responsive to pressure in the chamber and configured to generate a signal representative of the pressure, and a pneumatic control unit configured to receive the signal, to control a pressure applied to the pressure supply line, and to record the signal in a non-transitory storage media of a storage device removably attached to the pneumatic control unit.

Abstract: According to one embodiment, a wafer processing device includes a processed number counting unit that counts a number of processed wafers, and a maintenance post-processing unit that executes a dummy lot process and a QC lot process after a maintenance process. A wafer preparation device prepares the dummy lot and the QC lot, when a first processed number is counted by the processed number counting unit. When a second processed number is counted by the processed number counting unit, a carrier device carries the dummy lot and the QC lot to the wafer processing device simultaneous with the maintenance process, before the maintenance process is completed.

Abstract: Methods of determining a polishing endpoint are described using spectra obtained during a polishing sequence. In particular, techniques for using only desired spectra, faster searching methods and more robust rate determination methods are described.

Abstract: A chemical mechanical polishing apparatus includes a carrier head including a retaining ring having a plastic portion with a bottom surface to contact a polishing pad, an in-situ monitoring system including a sensor that generates a signal that depends on a thickness of the plastic portion, and a controller configured to receive the signal from the in-situ monitoring system and to adjust at least one polishing parameter in response to the signal to compensate for non-uniformity caused by changes in the thickness of the plastic portion of the retaining ring.

Abstract: A chemical mechanical polishing system includes a platen to support a polishing pad, two carrier heads configured to hold two substrates against the polishing pad at the same time, two actuators to sweep the two carrier heads laterally across the polishing pad, an in-situ polishing monitoring system including a two current sensors to sense two currents supplied to the two actuators and generate two signals, and a controller to receive the two signals and independently detect a two endpoints for the two substrates based on the two signals.

Abstract: Sensors can be located in a carrier head for a chemical mechanical polishing system. In some implementations the carrier head includes a flexible membrane, and a thermocouple is positioned on the lower surface of the flexible membrane or embedded in the flexible membrane adjacent the lower surface. In some implementations, the carrier head optical sensor is secured to the head and positioned to sense a reflectivity of a spot on a back surface of a substrate held in the carrier head, and a controller is configured to receive a signal from the optical sensor and determine precession of the substrate based on the signal.

Abstract: A chemical mechanical polishing (CMP) apparatus includes a process controller operable to execute a multi-step CMP algorithm implementing delivering a first chemical composition onto the wafer surface while on a platen for a first time duration, and without removing the wafer from the platen, delivering a second chemical composition different from the first chemical composition onto the wafer surface for a second time duration. CMP is performed with a polishing pad contacting the wafer surface using a slurry including the first chemical composition during the first time duration or the second chemical composition during the second time duration, and a non-polishing process without any contact of the polishing pad to the wafer surface using the other of the first and second chemical composition during the other of the time durations, and repeating the multi-step CMP comprising process a plurality of times on the wafer.

Abstract: A polishing system receives one or more target parameters for a selected peak in a spectrum of light, polishes a substrate, measures a current spectrum of light reflected from the substrate while the substrate is being polished, identifies the selected peak in the current spectrum, measures one or more current parameters of the selected peak in the current spectrum, compares the current parameters of the selected peak to the target parameters, and ceases to polish the substrate when the current parameters and the target parameters have a pre defined relationship.

Abstract: A method of controlling polishing includes storing a desired ratio representing a ratio for a clearance time of a first zone of a substrate to a clearance time of a second zone of the substrate. During polishing of a first substrate, an overlying layer is monitored, a sequence of measurements is generated, and the measurements are sorted a first group associated with the first zone of the substrate and a second group associated with the second zone on the substrate. A first time and a second time at which the overlying layer is cleared is determined based on the measurements from the first group and the second group, respectively. At least one adjusted polishing pressure is calculated for the first zone based on a first pressure applied in the first zone during polishing the first substrate, the first time, the second time, and the desired ratio.

Abstract: The present disclosure provides a chemical mechanical polishing (CMP) system. The CMP system includes a pad designed for wafer polishing, a motor driver coupled with the pad and designed to drive the pad during the wafer polishing, and a controller coupled with the motor driver and designed to control the motor driver. The CMP system further includes an in-situ rate monitor designed to collect polishing data from a wafer on the pad, determine CMP endpoint based on a life stage of the pad, and provide the CMP endpoint to the controller.

Abstract: Chemical-mechanical polishing (CMP) systems comprising apparatus and methods which allow the physical and chemical characteristics of a CMP slurry to be monitored during the polishing process, both on the pad and in the fresh slurry, are provided. The methods and apparatus of the invention also furnish the CMP operator with real-time information about the polishing process, which can provide insight into various chemical and physical mechanisms involved in chemical-mechanical polishing. The data provided by the sensors also make available valuable information about the stability and reproducibility of the particular CMP process being observed.

Abstract: A polishing apparatus has a polishing section (302) configured to polish a substrate and a measurement section (307) configured to measure a thickness of a film formed on the substrate. The polishing apparatus also has an interface (310) configured to input a desired thickness of a film formed on a substrate to be polished and a storage device (308a) configured to store polishing rate data on at least one past substrate therein. The polishing apparatus includes an arithmetic unit (308b) operable to calculate a polishing rate and an optimal polishing time based on the polishing rate data and the desired thickness by using a weighted average method which weights the polishing rate data on a lately polished substrate.

Abstract: A substrate polishing apparatus is provided for preventing excessive polishing and insufficient polishing, and enabling a quantitative setting of an additional polishing time. The substrate polishing apparatus comprises a mechanism for polishing a substrate to be polished; a film thickness measuring device for measuring the thickness of a thin film deposited on the substrate; an interface for entering a target thickness for the polished thin film; a storage area for preserving past polishing results; and a processing unit for calculating a polishing time and a polishing rate. The substrate polishing apparatus builds an additional polishing database for storing data acquired from the result of additional polishing in the storage area.

Abstract: Apparatus and methods for plasma etching are disclosed. In one embodiment, an apparatus for etching a plurality of features on a wafer comprises a chamber, a feature plate disposed in the chamber for holding the wafer, a gas channel configured to receive a plasma source gas, an anode disposed above the feature plate, a cathode disposed below the feature plate, a radio frequency power source configured to provide a radio frequency voltage between the anode and the cathode so as to generate plasma ions from the plasma source gas, a pump configured to remove gases and etch particulates from the chamber, and a clamp configured to clamp the wafer against the feature plate. The clamp includes at least one measurement hole for passing a portion of the plasma ions to measure a DC bias of the feature plate.

Abstract: A device for measuring a thickness of a slurry used in a chemical mechanical polishing apparatus and a method using the same are provided. The chemical mechanical polishing apparatus comprises a polishing head (10), a rotary table (20), a polishing platen (30) and a polishing pad (40). The device for measuring the thickness of the slurry comprises: a distance sensor (50) disposed in the polishing platen (30) for measuring a distance between the distance sensor (50) and a wafer (11) in the polishing head (10); a processing unit (70) (60) disposed in the rotary table (20) and connected to the distance sensor (50) for converting a measuring signal from the distance sensor (50) into standard electrical signal; a processing unit (70) connected to distance converters (60) for acquiring the standard electrical signal to obtain a thickness of the slurry between the polishing head (10) and the polishing pad (40).