High Sensitivity Real Time Profile Control Eddy Current Monitoring System

Abstract

An apparatus for chemical mechanical polishing includes a platen having a surface to support a polishing pad, and an eddy current monitoring system to generate an eddy current signal. The eddy current monitoring system includes a core and a coil wound around a portion of the core. The core includes a back portion, a first prong extending from the back portion in a first direction normal to the surface of the platen and having a width in a second direction parallel to the surface of the platen, and second and third prongs extending from the back portion in parallel with the first protrusion, the second and third prongs positioned on opposite sides of and equidistant from the first prong. A spacing between each of the second and third prongs and the first prong is approximately equal to twice the width of the first prong.

1 . An apparatus for chemical mechanical polishing, comprising:
 a platen having a surface to support a polishing pad; and   an eddy current monitoring system to generate an eddy current signal, the eddy current monitoring system comprising a core positioned at least partially in the platen and a coil wound around a portion of the core, the core including
 a back portion, 
 a first prong extending from the back portion in a first direction normal to the surface of the platen and having a width in a second direction parallel to the surface of the platen, 
 second and third prongs extending from the back portion in parallel with the first protrusion, the second and third prongs positioned on opposite sides of and equidistant from the first prong, a spacing in the second direction between each of the second and third prongs and the first prong being approximately equal to twice the width of the first prong. 
   
     
     
         2 . The apparatus of  claim 1 , wherein the second and third prongs have a width approximately equal to the width of the first prong. 
     
     
         3 . The apparatus of  claim 1 , wherein the width of the first prong is about 1 mm and the spacing between each of the second and third prongs and the first prong is about 2 mm. 
     
     
         4 . The apparatus of  claim 1 , wherein the first, second and third prongs each have a height in the first direction, the height being greater than the width of the first prong. 
     
     
         5 . The apparatus of  claim 1 , wherein the height is about four times the width. 
     
     
         6 . The apparatus of  claim 1 , wherein the first, second and third prongs each have a length along a third direction parallel to the surface of the platen and perpendicular to the second direction, the length being greater than the width of the first prong. 
     
     
         7 . The apparatus of  claim 6 , wherein the length is at least 10 times the width. 
     
     
         8 . The apparatus of  claim 7 , wherein the length is about 20 times the width. 
     
     
         9 . The apparatus of  claim 6 , wherein the platen is rotatable about an axis of rotation, and the length of the first, second and third prongs is perpendicular to a radius of the platen that extends from the axis of rotation through the core. 
     
     
         10 . The apparatus of  claim 1 , wherein the core has a generally E-shaped cross section in a plane parallel to the first direction and the second direction. 
     
     
         11 . The apparatus of  claim 1 , wherein the coil is wound only around the first prong. 
     
     
         12 . The apparatus of  claim 1 , further comprising the polishing pad, the polishing pad having a backing layer and a polishing layer, wherein the backing layer has an aperture therein, and wherein the prongs of the core extend into the aperture in the backing layer but not past a bottom surface of the polishing layer. 
     
     
         13 . The apparatus of  claim 1 , wherein the eddy current monitoring system has a resonant frequency of about 1.5 to 2 MHz. 
     
     
         14 . An apparatus for chemical mechanical polishing, comprising:
 a platen having a surface to support a polishing pad; and   an eddy current monitoring system to generate an eddy current signal, the eddy current monitoring system comprising a core positioned at least partially in the platen and a coil, the core including
 a back portion, 
 a first prong extending from the back portion in a first direction normal to the surface of the platen and having a height in the first direction, 
 second and third prongs extending from the back portion in parallel with the first protrusion, the second and third prongs positioned on opposite sides of the first prong; 
   wherein the coil is wound around an outer portion of the first prong and is not wound around an inner portion of the first prong that is closer to the back portion than the outer portion, the inner portion extending at least about half the height of the prong.   
     
     
         15 . The apparatus of  claim 14 , wherein the outer portion extends about half the height of the prong. 
     
     
         16 . The apparatus of  claim 14 , further comprising at least one spacer positioned in a gap between the first prong and the second and third prongs to support the coil. 
     
     
         17 . The apparatus of  claim 14 , wherein the first prong has a width in a second direction parallel to the surface of the platen, the second and third prongs are positioned equidistant from the first prong, and a spacing in the second direction between each of the second and third prongs and the first prong is approximately equal to twice the width of the first prong. 
     
     
         18 . The apparatus of  claim 14 , wherein the first, second and third prongs have the same height. 
     
     
         19 . The apparatus of  claim 18 , wherein the first prong has a width in a second direction parallel to the surface of the platen, and the height is greater than the width. 
     
     
         20 . The apparatus of  claim 14 , wherein the first prong has a width in a second direction parallel to the surface of the platen, and wherein the first, second and third prongs each have a length along a third direction parallel to the surface of the platen and perpendicular to the second direction, the length being greater than the width of the first prong. 
     
     
         21 . The apparatus of  claim 14 , wherein the coil is wound only around the first prong. 
     
     
         22 . The apparatus of  claim 14 , further comprising the polishing pad, the polishing pad having a backing layer and a polishing layer, wherein the backing layer has an aperture therein, and wherein the prongs of the core extend into the aperture in the backing layer but not past a bottom surface of the polishing layer. 
     
     
         23 . The apparatus of  claim 14 , wherein the eddy current monitoring system has a resonant frequency of about 1.5 to 2 MHz. 
     
     
         24 . The apparatus of  claim 23 , wherein the coil is wound about 12 times around the first prong. 
     
     
         25 . The apparatus of  claim 24 , wherein the eddy current monitoring system includes a capacitor in parallel with the coil, the capacitor having a capacitance of about 1000 pF.