Apparatus for detecting an endpoint polishing layer of a semiconductor wafer having a wafer carrier with independent concentric sub-carriers and associated method

A method of operating a polishing system to polish a first side of a semiconductor wafer down to a desired level, said polishing system having a wafer carrier which includes a first sub-carrier and a second sub-carrier which is concentric to said first sub-carrier, comprising the steps of:

• rotating said wafer while said first side of said wafer contacts a polishing surface of a polishing platen in order to remove material from said first side of said wafer;
• applying first pressure to a first radial portion of said wafer with said first sub-carrier in order to press said first radial portion against said polishing surface of said polishing platen;
• applying second pressure to a second radial portion of said wafer with said second sub-carrier in order to press said second radial portion against said polishing surface of said polishing platen;
• determining when said first radial portion of said wafer has been polished down to said desired level and adjusting said first pressure applied to said first radial portion by said first sub-carrier in response thereto;
• and
• determining when said second radial portion of said wafer has been polished down to said desired level and adjusting said second pressure applied to said second radial portion by said second sub-carrier in response thereto.

An apparatus for polishing a first side of a semiconductor wafer down a desired level, comprising:

• a polishing platen having a polishing surface;
• a wafer carrier having a first sub-carrier and a second sub-carrier which is concentric to said first sub-carrier, wherein (i) said first sub-carrier is configured to (a) engage a first radial portion of said wafer by a second side of said wafer, and (b) apply first pressure to said first radial portion in order to press said first radial portion against said polishing surface of said polishing platen, and (ii) said second sub-carrier is configured to (a) engage a second radial portion of said wafer by said second side of said wafer, and (b) apply second pressure to said second radial portion in order to press said second radial portion against said polishing surface of said polishing platen;
• a first endpoint detector operable to (i) transmit a first light signal which propagates through said first radial portion of said wafer such that a first attenuated signal is emanated out of a second side of said wafer, and (ii) cause said first sub-carrier to adjust said first pressure applied to said first radial portion of said wafer based on a first intensity level of said first attenuated signal;
• and
• a second endpoint detector operable to (i) transmit a second light signal which propagates through said first radial portion of said wafer such that a second attenuated signal is emanated out of said second side of said wafer, and (ii) cause said second sub-carrier to adjust said second pressure applied to said second radial portion of said wafer based on a second intensity level of said second attenuated signal.