Chemical mechanical polishing apparatus and methods with central control of polishing pressure applied by polishing head

Apparatus for controlling a first pressure to be applied to contact areas of a wafer an a polishing pad in chemical mechanical polishing operations, the pressure being applied according to force data specifying the value of a force to be applied to the contact areas, the apparatus comprising:

• a drive system configured to cause relative movement between the wafer and the pad into successive overlapped positions, values of the contact areas being different at each successive overlapped position;
• a central processor for processing data to specify the chemical mechanical polishing operations, the data including a command to the drive system for the relative movement, the data further representing the pressure to be applied to the first contact areas of the wafer and the polishing pad at the successive overlapped position;
• and
• a feedback circuit for providing output signals representing increments of the relative movement;
• the central processor being responsive to both the pressure data and to the output signals representing the actual relative movement, the central processor successively processing a contact area program and a force program to provide successive items of the force data representing successive values of the force to be applied to the contact areas of the wafer and the pad corresponding to the successive overlapped positions.

Apparatus for maintaining a constant pressure to be applied to respective contact areas of a wafer and of a polishing pad in chemical mechanical polishing operations, the apparatus comprising:

• a drive for causing relative movement between the wafer and the pad into a plurality of different overlapped positions;
• a force application system for urging the wafer and the pad against each other so that in each of the different overlapped positions the respective contact areas are in contact and have different values, the system being capable of providing different values of the force for the urging;
• a feedback circuit for providing first and second output signals representing respective first and second increments of the relative movement, the first and second increments being at spaced first and second times;
• and
• a central processor programmed for computing first position data in response to the first output signal, the first position data representing the actual relative movement at the first time;
• the central processor being further programmed for computing second position data in response to the second output signal, the second position data representing the actual relative movement at the second time;
• the central processor being further programmed for computing pressure data representing the constant pressure to be maintained;
• the central processor being further programmed for converting the first position data to first area data representing a value of first contact areas of the contact areas at the first time and at a first of the overlapped positions;
• the central processor being further programmed to process the first area data and the pressure data to output first force data representing a first force to be applied to the first respective contact areas at the first time;
• the force application system being responsive to the first force data for urging the wafer and the pad against each other with the first force to provide the constant pressure on the first contact area at the first time, the respective first contact areas having a first of the different contact area value;
• the central processor being further programmed for converting the second position data to second area data representing the value of second contact areas of the respective contact areas at the second time and at a second of the overlapped positions;
• the central processor being further programmed to process the second area data and the pressure data to output second force data representing a second force to be applied to the respective second contact areas at the second time;
• the force application system being responsive to the second force data for urging the wafer and the pad against each other with the second force to provide the constant pressure on the second contact areas at the second time, the respective second contact areas having a second of the different contact area values.

A method of determining which of first and second processors to use for processing data to control a pressure to be applied to contact areas of a wafer and of a polishing pad in chemical mechanical polishing operations, comprising the operations of:

• providing at least one limit of available processing capacity indicating which of the first and the second processor is capable of real-time processing at a rate sufficient for controlling the pressure to be applied to the contact areas of the wafer and of the polishing pad during the chemical mechanical polishing operation, the at least one limit of processing capacity being based on at least one of the following characteristics:
• values of variations in the pressure, or the time rate of change of the pressure, or the frequency of the relative movement between the wafer and the pad into the overlapped positions, or the rate of the relative movement;
• and
• selecting the second processor as having sufficient available processing capacity to use for the real-time processing of data to control the pressure to be applied to the contact areas of the wafer and of the polishing pad in the chemical mechanical polishing operations that have the characteristics requiring the greatest available processing capacity.