Individually rotatable platens and control of carrier head sweep

Abstract

A chemical mechanical polishing apparatus includes: an inner platen to support an inner polishing pad; an annular outer platen to support an outer polishing pad; a carrier head to hold a substrate; one or more motors to rotate the inner platen about a vertical axis at a first rotation rate and to rotate the outer platen about the vertical axis at a second rotation rate; and a controller configured to select values for multiple control parameters to minimize a difference between a target removal profile and an expected removal profile, the multiple control parameters including a first parameter representing a difference in rotational speeds between the inner and outer platens. The outer polishing pad can coaxially surround the inner platen, and an outer edge of the inner platen and an inner edge of the outer platen can be separated by a gap.

What is claimed is: 
     
         1 . A chemical mechanical polishing apparatus, comprising:
 an inner platen to support an inner polishing pad;   an annular outer platen to support an outer polishing pad, wherein the outer polishing pad coaxially surrounds the inner platen, and an outer edge of the inner platen and an inner edge of the outer platen are separated by a gap;   a carrier head to hold a substrate;   one or more motors to rotate the inner platen about a vertical axis at a first rotation rate and to rotate the outer platen about the vertical axis at a second rotation rate; 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 difference in rotational speeds between the inner and outer platens, 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 difference in rotational speeds 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 controller is configured to receive a first rotational speed for the inner platen from a recipe that is stored prior to polishing and to calculate a second rotational speed for the outer platen from the first rotational speed and the difference in rotational speeds. 
     
     
         3 . The polishing apparatus of  claim 1 , wherein the controller is configured to receive a first rotational speed for the outer platen from a recipe that is stored prior to polishing and to calculate a second rotational speed for the inner platen from the first rotational speed and the difference in rotational speeds. 
     
     
         4 . 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 difference in rotational speeds. 
     
     
         5 . The polishing apparatus of  claim 1 , comprising an actuator, and wherein the carrier head is laterally movable by the actuator. 
     
     
         6 . The polishing apparatus of  claim 5 , wherein the controller is configured to cause the actuator to oscillate the carrier head between a first position where the substrate is entirely over the outer polishing pad and a second position where the substrate is partially over the outer polishing pad and partially over the inner polishing pad. 
     
     
         7 . The polishing apparatus of  claim 5 , wherein the controller is configured to cause the actuator to oscillate the carrier head between a first position where the substrate is entirely over the inner polishing pad and a second position where the substrate is partially over the inner polishing pad and partially over the outer polishing pad. 
     
     
         8 . A chemical mechanical polishing apparatus, comprising:
 an inner platen to support an inner polishing pad;   an annular outer platen to support an outer polishing pad, wherein the outer platen coaxially surrounds the inner platen, and an outer edge of the inner platen and an inner edge of the outer platen are separated by a gap;   a carrier head to hold substrate;   a motor to rotate the inner platen about a first vertical axis;   an actuator to move the carrier head to laterally; and   a controller configured to cause the actuator to sweep the carrier head laterally 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 plurality of positions with at least one of the plurality of positions corresponding to substrate being positioned over just one of the inner and outer polishing pads and at least another of the plurality of positions corresponding to substrate being positioned over both the inner and outer polishing pads, 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.   
     
     
         9 . The polishing apparatus of  claim 8 , wherein the controller is configured to calculate a sweep profile from values for the plurality of dwell time parameters. 
     
     
         10 . The polishing apparatus of  claim 9 , 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 each of the inner and outer platens. 
     
     
         11 . The polishing apparatus of  claim 10 , 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 annular zone. 
     
     
         12 . The polishing apparatus of  claim 11 , wherein values for the plurality of dwell time parameters are in units of a fraction of total time. 
     
     
         13 . The polishing apparatus of  claim 10 , 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 values for the plurality of the dwell time parameters for each respective annular zone. 
     
     
         14 . The polishing apparatus of  claim 10 , wherein a fractional dwell time value for the plurality of annular zones is proportional to an oscillation period of the sweep profile. 
     
     
         15 . A method for chemical mechanical polishing comprising:
 rotating an inner platen comprising a first polishing pad at a first rotational speed;   rotating an outer platen comprising a second polishing pad at a second rotational speed different from the first rotational speed, wherein an outer edge of the inner platen and an inner edge of the outer platen are separated by a gap; and   selecting 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 relative rotational speed between the first and second rotational speeds, 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 relative rotational speed and a row for each position on a substrate represented in the expected removal profile, wherein selecting the values for the plurality of control parameters comprises calculating the expected removal profile by multiplying the first matrix by a second matrix representing control parameter values.   
     
     
         16 . The method of  claim 15 , further comprising:
 receiving the first rotational speed for the inner platen from a recipe that is stored prior to polishing; and   calculating the second rotational speed for the outer platen from the first rotational speed and the relative rotational speed.   
     
     
         17 . The method of  claim 15 , further comprising:
 receiving the second rotational speed for the outer platen from a recipe that is stored prior to polishing; and   calculating the first rotational speed for the inner platen from the second rotational speed and the relative rotational speed.   
     
     
         18 . The method of  claim 15 , further comprising:
 applying 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 relative rotational speed.   
     
     
         19 . The method of  claim 15 , further comprising:
 oscillating a carrier head between a first position where the substrate is entirely over the inner polishing pad and a second position where the substrate is partially over the inner polishing pad and partially over the outer polishing pad.   
     
     
         20 . The method of  claim 19 , wherein the plurality of control parameters comprise a plurality of dwell time parameters representing an amount of time for the carrier head to spend over a plurality of positions with at least one of the plurality of positions corresponding to substrate being positioned over just one of the inner and outer polishing pad and at least another of the plurality of positions corresponding to substrate being positioned over both the inner and outer polishing pad. 
     
     
         21 . The method of  claim 20 , further comprising calculating a sweep profile from values for the plurality of dwell time parameters. 
     
     
         22 . The method of  claim 21 , further comprising setting the sweep profile with a respective speed for each respective annular zone of a plurality of annular zones on each of the inner and outer platens. 
     
     
         23 . The method of  claim 22 , further comprising setting the respective speed for each respective annular zone of the plurality of annular zones as a constant value within the respective annular zone.