Use of zeta potential during chemical mechanical polishing for end point detection

In a linear polisher for performing chemical-mechanical polishing (CMP) on a first surface of a substrate or of a layer formed on the substrate, and in which the substrate is placed upon a linearly moving polishing pad for polishing the first surface, wherein the first surface is associated with a first zeta potential and overlies a second surface associated with a second zeta potential, an apparatus for determining a polishing end point for polishing the first surface comprising:

• a fluid bearing disposed along an underside of a linearly moving belt having the pad disposed thereon, the fluid bearing for dispensing fluid along a gap between the fluid bearing and the underside of the belt;
• a sensor coupled to the fluid bearing to measure a pressure change of the fluid when the end point for polishing the first surface is reached;
• a slurry dispensed onto the polishing pad for polishing the first surface, the slurry having a selected pH value so that a zeta potential of the slurry is different from the second zeta potential, wherein upon completion of the polishing of the first surface, the difference between the zeta potential of the slurry and the second zeta potential provides a pressure change of the fluid measured by the sensor;
• and
• a controller coupled with the sensor and operative to terminate polishing in response to the sensor measuring the pressure change provided by the difference in zeta potentials.

In a linear polisher for performing chemical-mechanical polishing (CMP) on a first material layer formed on a semiconductor wafer, and in which the first material layer is polished to expose an underlying second material layer, wherein the first and second material layers are respectively associated with a first and second zeta potential, an apparatus for determining a polishing end point for stopping the polishing when the second material layer is exposed comprising:

• a fluid bearing disposed along an underside of a linearly moving belt having the pad disposed thereon, the fluid bearing for dispensing fluid along a gap between the fluid bearing and the underside of the belt;
• a sensor coupled to the fluid bearing to measure a pressure change of the fluid when the end point for polishing the first material layer is reached;
• a slurry dispensed onto the polishing pad for polishing the first material layer, the slurry having a selected pH value so that a zeta potential of the slurry is different from the second zeta potential, wherein upon completion of the polishing of the first material layer, the difference between the zeta potential of the slurry and the second zeta potential provides a pressure change of the fluid measured by the sensor when the second material layer is exposed to the slurry;
• and
• a controller coupled with the sensor and operative to terminate polishing in response to the sensor measuring the pressure change provided by the difference in zeta potentials.

A method of determining a polishing end point for polishing a first surface associated with a first zeta potential, the first surface overlying a second surface associated with a second zeta potential, the method comprising:

• dispensing a slurry onto a polishing pad for polishing the first surface, the slurry having a selected pH value so that detection of a change from the first zeta potential to the second zeta potential indicates a completion of the polishing of the first surface;
• polishing the first surface;
• detecting a change from the first zeta potential to the second zeta potential, thereby detecting a completion of the polishing of the first surface;
• and
• terminating polishing in response to the detected change from the first zeta potential to the second zeta potential.

In a linear polisher for performing chemical-mechanical polishing (CMP) on a first material layer formed on a semiconductor wafer, and in which the first material layer is polished to expose an underlying second material layer, wherein the first and second material layers are respectively associated with a first and second zeta potential, a method of determining a polishing end point for stopping the polishing when the second material layer is exposed comprising:

• dispensing a slurry onto a polishing pad for polishing the first material layer, the slurry having a selected pH value so that a zeta potential of the slurry is different from the second zeta potential, wherein upon completion of the polishing of the first material layer, the difference between the zeta potential of the slurry and second zeta potential provides a pressure change of a fluid dispensed along an underside of the pad or a belt upon which the pad is mounted;
• polishing the first material layer;
• measuring the pressure change of the fluid when the second material layer begins to be polished;
• and
• terminating polishing in response to the measured pressure change provided by the difference between the zeta potential of the slurry and second zeta potential.

For use with a chemical-mechanical polishing (CMP) tool comprising a polishing pad operative to polish a first material layer formed on a semiconductor wafer positioned adjacent the polishing pad to expose an underlying second material layer, the first and second material layers respectively associated with a first and second zeta potential, a method of determining a polishing end point, the method comprising:

• dispensing a slurry onto the polishing pad, the slurry having a pH value selected so that a zeta potential of the slurry is opposite in polarity from the second zeta potential;
• exposing the second material layer by polishing the first material layer with the polishing pad;
• when the second material layer is polished, measuring a pressure change of a fluid dispensed along an underside of the polishing pad, the pressure change being in response to the polarity difference between the zeta potential of the slurry and second zeta potential;
• and
• terminating polishing in response to the measured pressure change.