Method and apparatus for in-line oxide thickness determination in chemical-mechanical polishing

A chemical-mechanical polishing system comprising:

• means for chemical-mechanical polishing of a dielectric layer on a surface of a workpiece in a polishing slurry, the workpiece having a given level of back-end-of-line (BEOL) structure including junctions;
• means, separate from said chemical-mechanical polishing means, for measuring an in-line thickness measurement of the dielectric film layer subsequent to a prescribed polishing of the dielectric layer of the workpiece by said chemical-mechanical polishing means, said in-line thickness measurement means providing a thickness measurement output signal;
• means for positioning the workpiece between the chemical-mechanical polishing means and said in-line thickness measurement means;
• and
• means for controlling a polishing sequence of the workpiece by said chemical-mechanical polishing means in response to the thickness measurement output signal,
• wherein said in-line thickness measurement means further includes
• a measurement platen;
• a measurement electrode embedded within said measurement platen, wherein said positioning means is further for positioning the workpiece above said measurement electrode with the dielectric layer facing in a direction of said measurement electrode;
• means for maintaining a prescribed level of the polishing slurry above said measurement electrode, the prescribed level to ensure a desired slurry coverage of the workpiece, wherein the polishing slurry further maintains a static electrical contact with the dielectric layer and the workpiece;
• means for sensing a system capacitance C in accordance with an RC equivalent circuit model in which a resistance R is representative of the slurry and workpiece resistances and the system capacitance C is representative of the dielectric material and junction capacitances;
• and
• means for converting the sensed capacitance to a dielectric thickness in accordance with a prescribed system capacitance/optical thickness calibration, wherein the prescribed calibration corresponds to the given level of BEOL structure of the workpiece.

An method for in-line thickness measurement of a dielectric film layer on a surface of a workpiece subsequent to a polishing of the dielectric film layer on a chemical-mechanical polishing machine in a polishing slurry, the workpiece having a given level of back-end-of-line (BEOL) structure including junctions, said method comprising the steps of:

• providing a measurement platen;
• providing a measurement electrode embedded within the measurement platen;
• positioning the workpiece above the measurement electrode with the dielectric layer facing in a direction of the measurement electrode;
• maintaining a prescribed level of the polishing slurry above the measurement electrode, the prescribed level to ensure a desired slurry coverage of the workpiece, wherein the slurry maintains a static electrical contact with the dielectric layer and the workpiece;
• sensing a system capacitance C in accordance with an RC equivalent circuit model in which a resistance R is representative of the slurry and workpiece resistances and the system capacitance C is representative of the dielectric material and junction capacitances;
• and
• converting the sensed capacitance to a dielectric thickness in accordance with a prescribed system capacitance/optical thickness calibration, wherein the prescribed calibration corresponds to the given level of BEOL structure of the workpiece.

A method for chemical-mechanical polishing comprising the steps of:

• chemical-mechanical polishing a dielectric layer on a surface of a workpiece in a polishing slurry, the workpiece having a given level of back-end-of-line (BEOL) structure including junctions;
• measuring an in-line thickness of the dielectric film layer subsequent to a prescribed polishing of the dielectric layer of the workpiece by said chemical-mechanical polishing step, said in-line thickness measurement step providing a thickness measurement output signal;
• positioning the workpiece as appropriate for polishing during said chemical-mechanical polishing step and for thickness measurement during said in-line thickness measurement step;
• and
• controlling a polishing sequence of the workpiece by said chemical-mechanical polishing step in response to the thickness measurement output signal,
• wherein said in-line thickness measurement step includes the steps of
• providing a measurement platen;
• providing a measurement electrode embedded within the measurement platen;
• positioning the workpiece above the measurement electrode with the dielectric layer facing in a direction of the measurement electrode;
• maintaining a prescribed level of the polishing slurry above the measurement electrode, the prescribed level to ensure a desired slurry coverage of the workpiece, wherein the slurry maintains a static electrical contact with the dielectric layer and the workpiece;
• sensing a system capacitance C in accordance with an RC equivalent circuit model in which a resistance R is representative of the slurry and workpiece resistances and the system capacitance C is representative of the dielectric material and junction capacitances;
• and
• converting the sensed capacitance to a dielectric thickness in accordance with a prescribed system capacitance/optical thickness calibration, wherein the prescribed calibration corresponds to the given level of BEOL structure of the workpiece.