Method and apparatus for measuring properties of a polishing pad

Abstract

A comprehensive measurement of properties of a polishing pad of a CMP apparatus is used to create a database by which the CMP apparatus can be maintained and the polishing process can be precisely controlled. The measuring apparatus includes a measuring table and a control section. The measuring table has a flat top surface on which the polishing pad is placed, a camera, a sensor for sensing the relative location of the top surface of the polishing pad, a bracket to which the camera and the sensor are fixed, and an X-Y drive for moving the bracket in X- and Y-directions orthogonal to each other. The control section controls the operation of the camera, the sensor and the X-Y drive, and processes signals from the camera and sensor, so that a profile of the surface of the polishing pad can be discerned and an image of the surface of the polishing pad can be produced. The control section also assigns values to the sensed data and displays the values of the measured data, graphs and a surface image of the polishing pad. The measuring apparatus can also measure the hardness of the polishing pad and the transmittance through a transparent window of the polishing pad.

What is claimed is:  
     
         1 . Apparatus for measuring properties of a polishing pad, comprising: 
 an upper plate having a flat top surface on which the polishing pad is to be placed;    a camera operative to produce signals representative of an image of a surface portion of the polishing pad;    a sensor operative to generate signals representative of a relative location of a surface portion of the polishing pad;    a bracket fixing said camera and said sensor in place above the top surface of said upper plate, whereby the camera is positioned to produce signals representative of an image of a top surface portion of the polishing pad and the sensor is positioned to generate signals representative of the relative location of a top surface portion of the polishing pad when the polishing pad is disposed on said upper plate;    X-axis and Y-axis linear drive mechanisms to which said bracket is connected, said linear drive mechanisms being operable to move said bracket, and the camera and sensor fixed in place by the bracket, in X- and Y-directions extending orthogonal to each other in a plane above the top surface of said upper plate, whereby the top surface of the polishing pad can be scanned by said camera and said sensor when the polishing pad is disposed on the top surface of said upper plate; and    a control system operatively connected to said camera so as to control the operation of said camera and receive the signals produced by said camera, operatively connected to said sensor so as to control the operation of said sensor and receive signals generated by said sensor, and operatively connected to said X-axis and Y-axis linear drive mechanisms so as to control the movement of said camera and said sensor in said X- and Y-directions, and    said control system including a processor configured to process said signals to produce data by which an image of and the profile of the top surface of a polishing pad disposed on the top surface of said upper plate can be discerned.    
     
     
         2 . Apparatus for measuring properties of a polishing pad as claimed in  claim 1 , wherein said upper plate has a plurality of vacuum holes extending through a central portion of the top surface thereof.  
     
     
         3 . Apparatus for measuring properties of a polishing pad as claimed in  claim 1 , wherein said sensor is a non-contacting laser sensor.  
     
     
         4 . Apparatus for measuring properties of a polishing pad as claimed in  claim 1 , and further comprising a hardness-measuring sensor operative to measure hardness of a polishing pad, said hardness-measuring sensor being supported by said X-axis and Y-axis linear drive mechanisms.  
     
     
         5 . Apparatus for measuring properties of a polishing pad as claimed in  claim 1 , and further comprising a transmittance sensor operative to measure transmittance.  
     
     
         6 . Apparatus for measuring properties of a polishing pad as claimed in  claim 5 , wherein said transmittance sensor includes a light-receiving element that is disposed coplanar with the top surface of said upper plate, and a light-emitting element that is disposed above the light-receiving element as spaced therefrom, whereby a polishing pad is insertable between the light-receiving element and the light-emitting element.  
     
     
         7 . Apparatus for measuring properties of a polishing pad as claimed in  claim 1 , wherein said X-axis and Y-axis linear drive mechanisms comprise a Y-axis carrier extending along a first side of said upper plate, a Y-axis guide rail extending parallel to said Y-axis carrier along a second side of the top surface of said upper plate, a Y-axis slider supported by said Y-axis carrier so as to be movable longitudinally therealong, a Y-axis guide rail slider supported by said Y-axis guide rail so as to be movable longitudinally therealong, an X-axis carrier disposed above the top surface of said upper plate and having opposite ends respectively mounted to said Y-axis slider and said Y-axis guide rail slider; and an X-axis slider supported by said X-axis carrier so as to be movable longitudinally therealong between the opposite ends thereof, said bracket being fixed to said X-axis slider so as to move therewith.  
     
     
         8 . Apparatus for measuring properties of a polishing pad as claimed in  claim 7 , wherein said X-axis and Y-axis linear drive mechanisms include a respective feed screw associated with each of said X-axis carrier and said Y-axis carrier.  
     
     
         9 . Apparatus for measuring properties of a polishing pad as claimed in  claim 1 , wherein said control system includes a display comprising a screen, said processor and said display being operative to produce on said screen numeric displays pertaining to a polishing pad disposed on the top surface of said upper plate, a graph of the profile of the top surface of the polishing pad, and an image of the top surface of the polishing pad  
     
     
         10 . A method of measuring properties of a polishing pad of a chemical and mechanical polishing apparatus, comprising the steps of: 
 placing the polishing pad on a table top;    fixing the polishing pad to the table top using suction;    scanning a surface the polishing pad, fixed to the table top, in X- and Y-axis directions orthogonal to each other, and using data derived from said scanning to locate the center of the polishing pad;    once the center of the polishing pad is located, measuring the hardness of the polishing pad at the center of the polishing pad, and displaying a value of the hardness on a screen;    moving a sensor, aimed at the polishing pad fixed to the table top, in the direction of the Y-axis, and using signals from the sensor to discern a profile of the top surface of the polishing pad;    displaying the profile of the polishing pad on the screen;    scanning the surface of the polishing pad, fixed to the table top, with a camera to thereby take pictures of the surface of the polishing pad; and    displaying the pictures on the screen as an image of the surface of the polishing pad.    
     
     
         11 . A method of measuring properties of a polishing pad of a chemical and mechanical polishing apparatus as claimed in  claim 10 , and further comprising the steps of: 
 positioning a transparent window of the polishing pad adjacent a transmittance sensor for measuring transmittance;    measuring transmittance through the transparent window using the transmittance sensor; and    displaying a value of the transmittance on the screen.    
     
     
         12 . A method of measuring properties of a polishing pad of a chemical and mechanical polishing apparatus as claimed in  claim 11 , wherein the step of displaying the value of the transmittance on the screen comprises the substeps of: 
 calculating an error between the measured value and a standard value of the transmittance; and    displaying the measured value, the standard value and the error of the transmittance on the screen.    
     
     
         13 . A method of measuring properties of a polishing pad of a chemical and mechanical polishing apparatus as claimed in  claim 10 , wherein the step of displaying the value of the hardness of the polishing pad on the screen comprises the steps of: 
 calculating an error between the measured value and a standard value of the hardness of the polishing pad; and    displaying the measured value, the standard value and the error of the hardness on the screen.    
     
     
         14 . A method of measuring properties of a polishing pad of a chemical and mechanical polishing apparatus, comprising the steps of: 
 placing a polishing pad, having a transparent window, on a flat surface of a measuring table before the polishing pad is installed in a chemical and mechanical polishing apparatus;    with the polishing pad disposed on the flat surface, scanning the polishing pad with a sensor and using signals derived from the sensor to discern the surface profile of the polishing pad, measuring the hardness of the polishing pad, and measuring a transmittance through the transparent window of the polishing pad;    subsequently installing the polishing pad in the chemical and mechanical polishing apparatus, and polishing a wafer using the polishing pad;    subsequently removing the polishing pad from the chemical and mechanical polishing apparatus and placing the used polishing pad back on the flat surface of the measuring table;    with the used polishing pad disposed back on the flat surface, scanning the used polishing pad with the sensor and using signals derived from the sensor to discern the surface profile of the used polishing pad, measuring the hardness of the used polishing pad, and measuring the transmittance through the transparent window of the used polishing pad; and    filing values of the surface profile, hardness and transmittance of the polishing pad, before and after the polishing pad has been used to polish the wafer, in a database.    
     
     
         15 . A method of measuring properties of a polishing pad of a chemical and mechanical polishing apparatus, as claimed in  claim 14 , and further comprising using the database to create a schedule for the replacing of polishing pads in the chemical and mechanical polishing apparatus.  
     
     
         16 . A method of measuring properties of a polishing pad of a chemical and mechanical polishing apparatus, as claimed in  claim 14 , and further comprising using the database to establish operating parameters of the chemical and mechanical polishing apparatus.