Apparatus for accurately measuring local thickness of insulating layer on semiconductor wafer during polishing and polishing system using the same

An apparatus for measuring a thickness of an insulating layer having a first surface held in contact with a first electrode means and a second surface opposite to said first surface and held in contact with a non-conductive liquid spread over a moving member, said second surface being polished, said apparatus comprising:

• a second electrode means stationary with respect to said moving member, changing a relative position with respect to said first electrode means and a first distance to said first electrode means together with said moving member, and forming a first capacitor together with first electrode means, said insulating layer and said non-conductive liquid;
• a third electrode means stationary with respect to said insulating layer and with respect to said first electrode means;
• a fourth electrode means stationary with respect to said moving member, changing a second distance to said third electrode means and forming a second capacitor together with said third electrode means and said non-conductive liquid;
• a source of electric Power connected between said first and third electrode means and said second and fourth electrode means;
• a measuring equipment connected to said second electrode and said fourth electrode for continuously measuring a first capacitance between said first electrode means and said second electrode means and a second capacitance between said third electrode means and said fourth electrode means while said insulating layer is being relatively moved with respect to said moving member, said second electrode means having a plurality of electrodes isolated from one another and selectively connected to said measuring equipment, said plurality of electrodes being opposed to said first electrode means and formed on a major surface of a semiconductor wafer;
• and
• a calculating means connected to said measuring equipment for determining a thickness of said insulating layer on the basis of said first capacitance and said second capacitance.

A polishing system for polishing an insulating layer formed on a semiconductor wafer, said system comprising:

• measuring means for continuously measuring a thickness of more than one portion of said insulating layer responsive to variations of capacitance coupled to said semiconductor wafer during a polishing on said insulating layer;
• a polishing Dad for polishing a surface of said insulating layer;
• feeding means for supplying a non-conductive polishing slurry between said polishing pad and said surface of said insulating layer;
• pressurizing means exerting a variable force on a plurality of portions of said semiconductor wafer for pressing said insulating layer against said polishing pad;
• control means connected to said measuring means and said pressurizing means for instructing said pressurizing means to vary said variable force at said plurality of portions depending upon the thickness of said more than one portion of said insulating layer,
• said measuring means including:
• a first electrode means formed between said semiconductor wafer and said insulating layer,
• a second electrode means attached to said polishing pad, changing a relative position with respect to said first electrode means and a first distance to said first electrode means while said surface of said insulating layer is being polished, said second electrode forming a first capacitor together with first electrode means, and together with said insulating layer and said polishing slurry,
• a third electrode means stationary with respect to said insulating layer and with respect to said first electrode means,
• a fourth electrode means attached to said polishing pad, changing a second distance to said third electrode means and forming a second capacitor together with said third electrode means and said non-conductive polishing slurry,
• a source of electric power connected between said first and third electrode means and said second and fourth electrode means;
• a measuring equipment connected to said second electrode and said fourth electrode for measuring a first capacitance between said first electrode means and said second electrode means and a second capacitance between said third electrode means and said fourth electrode means, said second electrode means having a plurality of electrodes isolated from one another and selectively connected to said measuring equipment, said plurality of electrodes being opposed to said first electrode means formed on a major surface of said semiconductor wafer, and
• a calculating means connected to said measuring equipment for determining said thickness of said more than one portion on the basis of said first capacitance and said second capacitance.