Control of platen shape in chemical mechanical polishing

Abstract

A chemical mechanical polishing apparatus includes a platen to support a polishing pad, an actuator, a carrier head to hold a surface of a substrate against the polishing pad, a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate. The platen has a central section with an upper surface and an annular flexure surrounding or surrounded by the central section and having a top surface with a first edge adjacent to and coplanar with the upper surface and a second edge farther from the central section. The actuator is arranged to bend the annular flexure along an entire circumference of the annular flexure so as to modify a vertical position of the second edge of the annular flexure relative to the central section.

What is claimed is: 
     
         1 . A chemical mechanical polishing apparatus, comprising:
 a platen to support a polishing pad, the platen having a central section with an upper surface and an annular flexure surrounding or surrounded by the central section and having a top surface with a first edge adjacent to and coplanar with the upper surface and a second edge farther from the central section;   an actuator arranged to bend the annular flexure along an entire circumference of the annular flexure so as to modify a vertical position of the second edge of the annular flexure relative to the central section;   a carrier head to hold a surface of a substrate against the polishing pad; and   a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate.   
     
     
         2 . The apparatus of  claim 1 , wherein the annular flexure surrounds the central section of the platen and has an inner edge adjacent to and coplanar with the upper surface and an outer edge farther from the central section, and the actuator is arranged to modify the vertical position of the outer edge. 
     
     
         3 . The apparatus of  claim 2 , wherein the annular flexure comprises no more than an outermost 25% by radius of the platen. 
     
     
         4 . The apparatus of  claim 2 , comprising a second annular flexure surrounded by the central section of the platen and having an inner edge adjacent to and coplanar with the upper surface and an outer edge farther from the central section, and a second actuator is arranged to modify the vertical position of the inner edge of the second annular flexure. 
     
     
         5 . The apparatus of  claim 1 , wherein the annular flexure is surrounded by the central section of the platen and the has an outer edge adjacent to and coplanar with the upper surface and an inner edge farther from the central section, and the actuator is arranged to modify the vertical position of the inner edge. 
     
     
         6 . The apparatus of  claim 5 , wherein the annular flexure comprises no more than an innermost 25% by radius of the platen. 
     
     
         7 . The apparatus of  claim 1 , wherein the annular flexure comprises an annular recess in a lower surface in the platen that extends partially through a thickness of the platen. 
     
     
         8 . The apparatus of  claim 1 , wherein a thickness of the flexure is substantially equal to a thickness of the platen in the central section. 
     
     
         9 . The apparatus of  claim 1 , wherein the flexure comprises a downwardly extending flange, and the actuator is positioned to apply a horizontal force to the flange. 
     
     
         10 . The apparatus of  claim 9 , wherein the actuator comprises pneumatic actuator to press against the flange or an adjustment screw that passes through an aperture in the flange and into a receiving threaded recess. 
     
     
         11 . The apparatus of  claim 1 , wherein the actuator is positioned to apply a vertical force to the annular flexure. 
     
     
         12 . The apparatus of  claim 11 , further comprising a lower platen supporting the central section of the platen. 
     
     
         13 . The apparatus of  claim 12 , wherein the actuator comprises an annular pressurizable chamber positioned between the upper platen and the lower platen. 
     
     
         14 . The apparatus of  claim 13 , comprising an annular seal at an outer edge of the annular flexure. 
     
     
         15 . The apparatus of  claim 1 , wherein the annular flange comprises a tapered edge of the platen. 
     
     
         16 . A method of locally polishing a substrate, comprising:
 supporting a polishing pad with a rotatable platen, the platen comprising at least one annular flexure extending from a central region of the platen and an actuator supported by the platen configured to adjust a vertical height of an edge of the annular flexure relative to the central region along an entire circumference of the annular flexure;   positioning the substrate so that a portion of the substrate is over the annular flexure; moving the annular region of the substrate over the annular section; and   generating relative motion between a polishing pad and a substrate so as to polish an overlying layer on the substrate.   
     
     
         17 . The method of  claim 16 , further comprising:
 determining a thickness profile of the overlying layer;   determining, from the thickness profile, to provide differential polishing to an annular region of the substrate;   adjusting the height of the edge of the annular flexure relative to the central region to provide the differential polishing to an annular region of the substrate.   
     
     
         18 . The method of  claim 17 , further comprising continuing the relative motion between the polishing pad and the substrate until the annular region of the substrate is within a uniformity threshold of the remaining substrate. 
     
     
         19 . The method of  claim 16 , wherein the determining comprises receiving a signal from an in-situ optical monitoring system indicative of a radially-dependent thickness of the overlying layer. 
     
     
         20 . A chemical mechanical polishing apparatus, comprising:
 a platen to support a polishing pad, the platen having a central section with an upper surface and an annular flexure surrounding or surrounded by the central section and having a top surface with a first edge adjacent to and coplanar with the upper surface and a second edge farther from the central section, wherein the annular flexure is tapered to be thinner toward the second edge;   an actuator arranged to bend the annular flexure so as to modify a vertical position of the second edge of the annular flexure relative to the central section;   a carrier head to hold a surface of a substrate against the polishing pad; and   a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate.   
     
     
         21 . A chemical mechanical polishing apparatus, comprising:
 a platen to support a polishing pad, the platen having an upper portion and a lower portion, the upper portion having a central section with an upper surface;   an annular flexure surrounding or surrounded by the central section and having a top surface with a first edge adjacent to and coplanar with the upper surface and a second edge farther from the central section;   a pressurizable chamber between the upper platen and lower platen such that modifying pressurization of the chamber bends the annular flexure so as to modify a vertical position of the second edge of then annular flexure;   a carrier head to hold a surface of a substrate against the polishing pad; and   a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate.