Control of carrier head sweep and platen shape

Abstract

A controller of a chemical mechanical polishing system is configured to cause a carrier head to sweep across a polishing pad in accord with a sweep profile. The controller is also configured to select values for a plurality of control parameters to minimize a difference between a target removal profile and an expected removal profile. The plurality of control parameters include a plurality of dwell time parameters. A relationship between the plurality of control parameters and a removal rate is stored in a data structure representing a first matrix which includes a plurality of columns including a column for each dwell time parameter and a row for each position on the substrate represented in the expected removal profile, and the controller is configured to, as part of selection of the values, calculate the expected removal profile by multiplying the first matrix by a second matrix representing control parameter values.

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 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;   a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate; and   a controller configured to select values for a plurality of control parameters to minimize a difference between a target removal profile and an expected removal profile, the plurality of control parameters including a first parameter representing a degree of deflection for the flexure, wherein a relationship between the plurality of control parameters and a removal rate is stored in a data structure representing a first matrix which includes a plurality of columns including a column for the degree of deflection of the flexure and a row for each position on the substrate represented in the expected removal profile, and wherein the controller is configured to, as part of selection of the values, calculate the expected removal profile by multiplying the first matrix by a second matrix representing control parameter values.   
     
     
         2 . The polishing apparatus of  claim 1 , wherein the carrier head comprises a plurality of independently pressurizable chambers, and the plurality of polishing control parameters include a plurality of chamber pressure parameters with each respective chamber pressure parameter associated with a respective pressurizable chamber of the plurality of pressurizable. 
     
     
         3 . The polishing apparatus of  claim 2 , wherein the plurality of columns of the first matrix includes a column for each chamber pressure parameter. 
     
     
         4 . The polishing apparatus of  claim 2 , wherein values for the chamber pressure parameters are in units of pressure. 
     
     
         5 . The polishing apparatus of  claim 1 , wherein the platen includes the annular flexure surrounding the central section, and the first matrix includes column for the degree of deflection of the flexure surrounding the central section. 
     
     
         6 . The polishing apparatus of  claim 1 , wherein the platen includes the annular flexure surrounded by the central section, and the first matrix includes column for the degree of deflection of the flexure surrounded by the central section. 
     
     
         7 . The polishing apparatus of  claim 1 , wherein the platen includes a first annular flexure surrounding the central section and a second annular flexure surrounded by the central section, and the first matrix includes a first column for the degree of deflection of the first flexure and a second column for the degree of deflection of the second flexure. 
     
     
         8 . The polishing apparatus of  claim 1 , wherein the degree of deflection of the flexure is units of distance. 
     
     
         9 . The polishing apparatus of  claim 1 , wherein the controller is configured to apply a minimizing algorithm to reduce a difference between an expected thickness profile and a target thickness profile, wherein applying the minimizing algorithm includes iteratively calculating the expected removal profile using different values for the degree of deflection of the flexure. 
     
     
         10 . A chemical mechanical polishing apparatus, comprising:
 a platen to support a polishing pad;   a carrier head to hold a surface of a substrate against the polishing pad;   a motor to control a lateral position of the carrier head on the polishing pad;   a controller configured to cause the motor to sweep the carrier head across the polishing pad in accord with a sweep profile, wherein the controller is configured to select values for a plurality of control parameters to minimize a difference between a target removal profile and an expected removal profile, the plurality of control parameters including a plurality of dwell time parameters with each respective dwell time parameter of the plurality of dwell time parameters representing an amount of time for the carrier head to spend over a different respective zone on the polishing pad, wherein a relationship between the plurality of control parameters and a removal rate is stored in a data structure representing a first matrix which includes a plurality of columns including a column for each dwell time parameter and a row for each position on the substrate represented in the expected removal profile, and wherein the controller is configured to, as part of selection of the values, calculate the expected removal profile by multiplying the first matrix by a second matrix representing control parameter values.   
     
     
         11 . The polishing apparatus of  claim 10 , wherein the carrier head comprises a plurality of independently pressurizable chambers, and the plurality of polishing control parameters include a plurality of chamber pressure parameters with each respective chamber pressure parameter associated with a respective pressurizable chamber of the plurality of pressurizable. 
     
     
         12 . The polishing apparatus of  claim 11 , wherein the plurality of columns of the first matrix includes a column for each chamber pressure parameter. 
     
     
         13 . The polishing apparatus of  claim 11 , wherein values for the chamber pressure parameters are in units of pressure. 
     
     
         14 . The polishing apparatus of  claim 11 , wherein the controller is configured to apply a minimizing algorithm to reduce a difference between an expected thickness profile and a target thickness profile, wherein applying the minimizing algorithm includes iteratively calculating the expected removal profile using different values for each dwell time parameter. 
     
     
         15 . The polishing apparatus of  claim 11 , wherein the controller is configured to calculate a sweep profile from values for the plurality of dwell time parameters. 
     
     
         16 . The polishing apparatus of  claim 15 , wherein the controller is configured to set the sweep profile with a respective speed for each respective annular zone of a plurality of annular zones on the platen. 
     
     
         17 . The polishing apparatus of  claim 16 , wherein the controller is configured to set the respective speed for each respective annular zone of the plurality of annular zones as a constant value within the respective zone. 
     
     
         18 . The polishing apparatus of  claim 17 , wherein values for the dwell time parameters are in units of a fraction of total time. 
     
     
         19 . The polishing apparatus of  claim 17 , wherein the controller is configured to calculate a sweep speed for each respective annular zone of the plurality of annular zones as inversely proportional to the value of the dwell time parameter for the zone. 
     
     
         20 . The polishing apparatus of  claim 10 , wherein the fractional dwell time value for the ith zone.