Polishing monitoring method, polishing end point detection method, and polishing apparatus

Abstract

A method of monitoring a thickness of a conductive film on a substrate during polishing of the substrate with use of an eddy current sensor is provided. This method includes: polishing the conductive film by pressing the substrate against a polishing surface on the rotating polishing table; obtaining output signal of the eddy current sensor during polishing; calculating an amount of output adjustment of the eddy current sensor using the output signal obtained when the substrate is not present above the eddy current sensor; with use of the amount of output adjustment, correcting the output signal obtained when the substrate is present above the eddy current sensor; and monitoring the thickness of the conductive film based on the corrected output signal.

1 . A method of monitoring a thickness of a conductive film on a substrate during polishing of the substrate with use of an eddy current sensor provided in a polishing table, said method comprising:
 polishing the conductive film by pressing the substrate against a polishing surface on the rotating polishing table;   obtaining output signal of the eddy current sensor during polishing;   calculating an amount of output adjustment of the eddy current sensor using the output signal obtained when the substrate is not present above the eddy current sensor;   with use of the amount of output adjustment, correcting the output signal obtained when the substrate is present above the eddy current sensor; and   monitoring the thickness of the conductive film based on the corrected output signal.   
     
     
         2 . The method according to  claim 1 , wherein:
 a resistance component and reactance component of impedance of electric circuit including a coil of the eddy current sensor are defined as coordinates on a coordinate system;   the coordinates are rotated and moved such that a distance between an origin of the coordinate system and a point specified by the coordinates is reduced in accordance with a decrease in the thickness of the conductive film; and   the output signal of the eddy current sensor is represented by the rotated and moved coordinates.   
     
     
         3 . The method according to  claim 2 , wherein said correcting of the output signal is performed by moving the origin of the coordinate system. 
     
     
         4 . The method according to  claim 3 , wherein said monitoring the thickness of the conductive film based on the corrected output signal comprises monitoring the thickness of the conductive film based on the distance between the moved origin of the coordinate system and the point specified by the coordinates of the impedance. 
     
     
         5 . The method according to  claim 1 ; further comprising:
 obtaining resistance components and reactance components of impedance of electric circuit including a coil of the eddy current sensor at each of different thicknesses of the conductive film under conditions of various distances between a coil end of the eddy current sensor and the conductive film;   plotting the resistance components and the reactance components onto rectangular coordinate axes;   drawing preliminary measurement linear lines each connecting points specified by coordinates consisting of the resistance components and the reactance components at each thickness of the conductive film; and   determining in advance a reference point at which the preliminary measurement linear lines intersect with each other.   
     
     
         6 . The method according to  claim 5 , wherein said correcting of the output signal is performed by moving the reference point that has been determined in advance. 
     
     
         7 . The method according to  claim 6 , wherein said monitoring the thickness of the conductive film based on the corrected output signal comprises monitoring the thickness of the conductive film based on an angle of a line connecting the moved reference point to a point specified by coordinates of the impedance. 
     
     
         8 . The method according to  claim 1 , wherein said correcting of the output signal is performed by using an average of the output signal obtained when the substrate is not present above the eddy current sensor while the polishing table makes N revolutions. 
     
     
         9 . The method according to  claim 1 , wherein said calculating of the amount of output adjustment comprises calculating the amount of output adjustment of the eddy current sensor using only output signal obtained from a region where a top ring for holding the substrate is not present on or above the polishing surface, among the output signal obtained when the substrate is not present above the eddy current sensor. 
     
     
         10 . The method according to  claim 9 , wherein said calculating of the amount of output adjustment comprises calculating the amount of output adjustment of the eddy current sensor using only output signal obtained from a region where a dresser for dressing the polishing surface and an atomizer for cleaning the polishing surface are not present on or above the polishing surface, among the output signal obtained when the substrate is not present above the eddy current sensor. 
     
     
         11 . A method of monitoring a thickness of a conductive film on a substrate during polishing of the substrate with use of an eddy current sensor provided in a polishing table, said method comprising:
 polishing the conductive film by pressing the substrate against a polishing surface on the rotating polishing table;   obtaining resistance components and reactance components of impedance of electric circuit including a coil of the eddy current sensor at each of different thicknesses of the conductive film under conditions of various distances between a coil end of the eddy current sensor and the conductive film;   plotting the resistance components and the reactance components onto rectangular coordinate axes;   drawing preliminary measurement linear lines each connecting points specified by coordinates consisting of the resistance components and the reactance components at each thickness of the conductive film;   determining a reference point at which the preliminary measurement linear lines intersect with each other;   correcting the reference point using output signal of the eddy current sensor obtained during polishing, before polishing, or after polishing; and   monitoring the thickness of the conductive film based on an angle of a line connecting the corrected reference point to a point specified by coordinates of the impedance.   
     
     
         12 . A polishing apparatus, comprising:
 a rotatable polishing table having a polishing surface;   a top ring configured to press a substrate against the polishing surface to polish a conductive film on the substrate;   an eddy current sensor arranged in said polishing table; and   a monitoring device for monitoring a thickness of the conductive film based on output signal of said eddy current sensor,   wherein said monitoring device is configured to
 obtain the output signal of said eddy current sensor during polishing, 
 calculate an amount of output adjustment of said eddy current sensor using the output signal obtained when the substrate is not present above said eddy current sensor, 
 with use of the amount of output adjustment, correct the output signal obtained when the substrate is present above said eddy current sensor, and 
 monitor the thickness of the conductive film based on the corrected output signal. 
   
     
     
         13 . The polishing apparatus according to  claim 12 , wherein:
 a resistance component and reactance component of impedance of electric circuit including a coil of said eddy current sensor are defined as coordinates on a coordinate system;   the coordinates are rotated and moved such that a distance between an origin of the coordinate system and a point specified by the coordinates is reduced in accordance with a decrease in the thickness of the conductive film; and   the output signal of said eddy current sensor is represented by the rotated and moved coordinates.   
     
     
         14 . The polishing apparatus according to  claim 13 , wherein said monitoring device is configured to correct the output signal by moving the origin of the coordinate system. 
     
     
         15 . The polishing apparatus according to  claim 14 , wherein said monitoring device is configured to monitor the thickness of the conductive film based on the distance between the moved origin of the coordinate system and the point specified by the coordinates of the impedance. 
     
     
         16 . The polishing apparatus according to  claim 12 , wherein said monitoring device is configured to:
 obtain resistance components and reactance components of impedance of electric circuit including a coil of the eddy current sensor at each of different thicknesses of the conductive film under conditions of various distances between a coil end of the eddy current sensor and the conductive film;   plot the resistance components and the reactance components onto rectangular coordinate axes;   draw preliminary measurement linear lines each connecting points specified by coordinates consisting of the resistance components and the reactance components at each thickness of the conductive film; and   determine in advance a reference point at which the preliminary measurement linear lines intersect with each other.   
     
     
         17 . The polishing apparatus according to  claim 16 , wherein said monitoring device is configured to correct the output signal by moving the reference point that has been determined in advance. 
     
     
         18 . The polishing apparatus according to  claim 17 , wherein said monitoring device is configured to monitor the thickness of the conductive film based on an angle of a line connecting the moved reference point to a point specified by coordinates of the impedance. 
     
     
         19 . The polishing apparatus according to  claim 12 , wherein said monitoring device is configured to correct the output signal by using an average of the output signal obtained when the substrate is not present above the eddy current sensor while the polishing table makes N revolutions. 
     
     
         20 . The polishing apparatus according to  claim 12 , wherein said monitoring device is configured to calculate the amount of output adjustment of the eddy current sensor using only output signal obtained from a region where a top ring for holding the substrate is not present on or above the polishing surface, among the output signal obtained when the substrate is not present above the eddy current sensor. 
     
     
         21 . The polishing apparatus according to  claim 20 , wherein said monitoring device is configured to calculate the amount of output adjustment of the eddy current sensor using only output signal obtained from a region where a dresser for dressing the polishing surface and an atomizer for cleaning the polishing surface are not present on or above the polishing surface, among the output signal obtained when the substrate is not present above the eddy current sensor. 
     
     
         22 . A method of detecting a polishing end point, said method comprising:
 rotating a top ring and a polishing table while the top ring is pressing a substrate against a polishing pad on the polishing table to polish a film of the substrate;   during polishing of the substrate, sweeping an eddy current sensor across a surface of the substrate;   obtaining resistance component X and inductive reactance component Y of impedance of the eddy current sensor;   plotting coordinates X and Y, which consist of the resistance component X and the inductive reactance component Y, onto a XY coordinate system on which a plurality of impedance areas are defined in advance, the plurality of impedance areas including a reference impedance area and at least one offset impedance area;   calculating a plurality of film thickness index values in the plurality of impedance areas, respectively, using plural pairs of coordinates X and Y which belong respectively to the plurality of impedance areas; and   determining polishing end points of the substrate in the plurality of impedance areas, respectively, using the plurality of film thickness index values.   
     
     
         23 . The method according to  claim 22 , wherein said plurality of impedance areas are obtained by:
 polishing a substrate identical to the substrate to be polished;   obtaining the resistance component X and the inductive reactance component Y during polishing of the identical substrate;   plotting coordinates X and Y, which consist of the resistance component X and the inductive reactance component Y obtained, onto the XY coordinate system to form an initial impedance area; and   dividing the initial impedance area along its longitudinal direction.   
     
     
         24 . The method according to  claim 22 , wherein said reference impedance area is obtained by:
 polishing a substrate identical to the substrate to be polished;   obtaining the resistance component X and the inductive reactance component Y in a center of the identical substrate; and   plotting coordinates X and Y, which consist of the resistance component X and the inductive reactance component Y obtained, onto the XY coordinate system.   
     
     
         25 . The method according to  claim 22 , wherein said offset impedance area has the same width as that of the reference impedance area. 
     
     
         26 . The method according to  claim 22 , wherein the film thickness index value is represented by a distance between a point specified by the coordinates X and Y and an origin of the XY coordinate system. 
     
     
         27 . The method according to  claim 22 , further comprising:
 translating the offset impedance area until the offset impedance area overlaps the reference impedance area.   
     
     
         28 . The method according to  claim 22 , wherein the film thickness index value is represented by an angle between a linear line connecting a point specified by the coordinates X and Y to a predetermined reference point and a predetermined reference line extending through the reference point. 
     
     
         29 . The method according to  claim 28 , further comprising:
 multiplying the angle obtained in the offset impedance area by a coefficient such that the angle obtained in the offset impedance area is equal to the angle obtained in the reference impedance area.   
     
     
         30 . A method of detecting a polishing end point, said method comprising:
 rotating a top ring and a polishing table while the top ring is pressing a substrate against a polishing pad on the polishing table to polish a film on the substrate;   obtaining output signal of an eddy current sensor provided in the polishing table while sweeping the eddy current sensor across a surface of the substrate;   obtaining output signal of the eddy current sensor while sweeping the eddy current sensor across the surface of the substrate in the same path as that when the previous output signal is obtained;   calculating a film thickness index value from the output signal of the eddy current sensor; and   determining a polishing end point of the substrate from a change in the film thickness index value.   
     
     
         31 . The method according to  claim 30 , wherein the number of revolutions of the polishing table required for the eddy current sensor to describe the same path is calculated from a ratio of a rotational speed of the top ring to a rotational speed of the polishing table. 
     
     
         32 . The method according to  claim 31 , wherein a time required for the polishing table to make one revolution is measured, and the rotational speed of the polishing table is calculated from the measured time. 
     
     
         33 . The method according to  claim 31 , wherein a time required for the top ring to make one revolution is measured, and the rotational speed of the top ring is calculated from the measured time. 
     
     
         34 . The method according to  claim 30 , further comprising:
 sorting the output signal of the eddy current sensor in accordance with a plurality of zones defined in advance on the surface of the substrate,   wherein said calculating of the film thickness index value comprises calculating film thickness index values for the respective zones on the substrate from the sorted output signal.   
     
     
         35 . A method of detecting a polishing end point, said method comprising:
 rotating a top ring and a polishing table while the top ring is pressing a substrate against a polishing pad on the polishing table to polish a film on the substrate;   during polishing of the substrate, sweeping an eddy current sensor across a surface of the substrate, said eddy current sensor being provided in the polishing table;   obtaining output signal of the eddy current sensor;   producing a film thickness profile from the output signal of the eddy current sensor;   judging whether a salient portion appearing in the film thickness profile is due to the film remaining on the substrate or due to metal lying under the film based on a change in position of the salient portion appearing in the film thickness profile; and   determining a polishing end point of the substrate based on a size of the salient portion that appears due to the film remaining on the substrate.   
     
     
         36 . A polishing apparatus, comprising:
 a rotatable polishing table for supporting a polishing pad;   a top ring configured to press a substrate against the polishing pad on said rotating polishing table while rotating the substrate;   an eddy current sensor arranged in said polishing table so as to sweep a surface of the substrate; and   a monitoring device for monitoring a film thickness of the substrate from output signal of said eddy current sensor,   wherein said monitoring device is configured to   obtain resistance component X and inductive reactance component Y of impedance of said eddy current sensor,   plot coordinates X and Y, which consist of the resistance component X and the inductive reactance component Y, onto a XY coordinate system on which a plurality of impedance areas are defined in advance, the plurality of impedance areas including a reference impedance area and at least one offset impedance area,   calculate a plurality of film thickness index values in the plurality of impedance areas, respectively, using plural pairs of coordinates X and Y which belong respectively to the plurality of impedance areas, and   determine polishing end points of the substrate in the plurality of impedance areas, respectively, using the plurality of film thickness index values.   
     
     
         37 . A polishing apparatus, comprising:
 a rotatable polishing table for supporting a polishing pad;   a top ring configured to press a substrate against the polishing pad on said rotating polishing table while rotating the substrate;   an eddy current sensor arranged in said polishing table so as to sweep a surface of the substrate; and   a monitoring device for monitoring a film thickness of the substrate from output signal of said eddy current sensor,   wherein said monitoring device is configured to   obtain output signal of said eddy current sensor while said eddy current sensor is sweeping the surface of the substrate,   obtain output signal of said eddy current sensor while said eddy current sensor is sweeping the surface of the substrate in the same path as that when the previous output signal is obtained,   calculate a film thickness index value from the output signal of said eddy current sensor, and   determine a polishing end point of the substrate from a change in the film thickness index value.