Control of wafer surface charge during CMP
CMP selectivity, removal rate, and uniformity are controlled both locally and globally by altering electric charge at the wafer surface. Surface charge characterization is performed by an on-board metrology module. Based on a charge profile map, the wafer can be treated in an immersion bath to impart a more positive or negative charge overall, or to neutralize the entire wafer before the CMP operation is performed. If charge hot spots are detected on the wafer, a charge pencil can be used to neutralize localized areas. One type of charge pencil bears a tapered porous polymer tip that is placed in close proximity to the wafer surface. Films present on the wafer absorb ions from, or surrender ions to, the charge pencil tip, by electrostatic forces. The charge pencil can be incorporated into a CMP system to provide an in-situ treatment prior to the planarization step or the slurry removal step.
1. A charge adjustment module, comprising:
a global charge adjustment sub-module configured to substantially neutralize global surface charge on a semiconductor wafer by exposing the semiconductor water to a charge neutralizing fluid;
a first charge pencil configured to adjust local surface charge at a first location on a surface of the semiconductor wafer, the first charge pencil being physically separated from the global charge adjustment sub-module and carrying a positive charge; and
a second charge pencil configured to adjust local surface charge at a second location on the surface of the semiconductor wafer, the second charge pencil being physically separated from the global charge adjustment sub-module and carrying a negative charge, the first charge pencil and the second charge pencil configured to move independently of one another.
2. The charge adjustment module of claim 1 wherein each of the first charge pencil and the second charge pencil further incudes:
a head coupled mechanically and electrically to a motorized assembly; and
a pointed tip removably attached to the head, the pointed tip being tapered.
3. The charge adjustment module of claim 2 wherein the pointed tip is configured to remove charge from specific locations on the surface.
4. The charge adjustment module of claim 2 wherein the pointed tip is configured to deposit charge at specific locations on the surface.
5. The charge adjustment module of claim 2 wherein the pointed tip is configured to apply an ionic solution to specific locations on the surface.
6. The charge adjustment module of claim 2 wherein the pointed tip is an absorbent material.
7. The charge adjustment module of claim 2 wherein the head is configured to receive coordinate locations on the surface that are identified for charge adjustment.
8. The charge adjustment module of claim 7 wherein the head is further equipped to move to the coordinate locations.
9. The charge adjustment module of claim 7 wherein the coordinate locations are received from a metrology module.
10. The charge adjustment module of claim 7 wherein the global charge adjustment sub-module and the first and the second charge pencils are in a chemical polishing (CMP) system.
11. The charge adjustment module of claim 10 wherein the coordinate locations are received from a metrology module of the CMP system.
12. A chemical-mechanical planarization (CMP) system, the system comprising:
a metrology module configured to measure electric charge on a surface of a semiconductor wafer; and
a charge adjustment module configured to apply one or more of a global charge treatment and a local surface charge treatment based on a measurement result of the metrology module, the charge adjustment module including:
a global charge adjustment sub-module configured to substantially, neutralize global surface charge on the semiconductor wafer by exposing the semiconductor wafer to a charge neutralizing fluid;
a first charge pencil configured to adjust local surface charge at a first location on the surface of the semiconductor wafer at a different time period from the exposing the semiconductor wafer to the charge neutralizing fluid, the first charge pencil coupled to a positive charge; and
a second charge pencil configured to adjust local surface charge at a second location on the surface of the semiconductor wafer at a different time period from the exposing the semiconductor wafer to the charge neutralizing fluid, the second charge pencil coupled to a negative charge, the first charge pencil and the second charge pencil configured to move independently of one another.
13. The system of claim 12 , wherein the global charge adjustment sub-module further includes an immersion bath configured to substantially neutralize global surface charge on the entire semiconductor wafer.
14. The system of claim 12 , wherein each of the first charge pencil and the second charge pencil includes a tapered porous polymer tip.
15. A charge adjustment module, comprising:
an immersion bath configured to substantially neutralize global surface charge on a semiconductor wafer; and
a first single discrete charge pencil configured to adjust local surface charge at a first location on a surface of the semiconductor wafer, the first single discrete charge pencil including:
a first head;
a first tip removably attached to the first head, the first tip being tapered to accumulate electric charge at a first point, the first tip configured to accumulate a positive charge; and
a second single discrete charge pencil configured to adjust local surface charge at a second location on the surface of the semiconductor wafer, the second single discrete charge pencil including:
a second head; and
a second tip removably attached to the second head, the second tip being tapered to accumulate electric charge at a second point, the second tip configured to accumulate a negative charge, the first single discrete charge pencil and the second single discrete charge pencil configured to move independently of one another.
16. The charge adjustment module of claim 15 , wherein each of the first tip and the second tip includes a metal biased to a selected bias voltage to control accumulation of the electric charge at the point.
17. The charge adjustment module of claim 16 , wherein the selected bias voltage exceeds an electric potential of surface charge on the semiconductor wafer.
18. The charge adjustment module of claim 17 , wherein the selected bias voltage has opposite polarity from a polarity of the surface charge.
19. The charge adjustment module of claim 15 , wherein each of the first tip and the second tip includes a porous, absorbent material.
20. The charge adjustment module of claim 15 , wherein each of the first tip and the second tip is configured to receive an ionic solution.