Non-contact method to monitor and quantify effective work function of metals
An example semiconductor wafer includes a semiconductor layer, a dielectric layer disposed on the semiconductor layer, and a layer of the metal disposed on the dielectric layer. An example method of determining an effective work function of a metal on the semiconductor wafer includes determining a surface barrier voltage of the semiconductor wafer, and determining a metal effective work function of the semiconductor wafer based, at least in part, on the surface barrier voltage.
1. A method of determining an effective work function of a metal on a dielectric on a semiconductor wafer, the method comprising:
measuring a surface voltage of the metal using a probe;
determining a surface barrier voltage of the semiconductor wafer from the measured surface voltage of the metal; and
determining the effective work function of the metal on the dielectric on the semiconductor wafer based, at least in part, on the surface barrier voltage.
2. The method of claim 1 , wherein measuring the surface voltage comprises:
measuring a first surface voltage of the metal while the metal is illuminated; and
measuring a second surface voltage of the metal while the metal is not illuminated.
3. The method of claim 2 , wherein the surface barrier voltage corresponds to the second surface voltage minus the first surface voltage.
4. The method of claim 2 , wherein the first and second surface voltages are measured using a Kelvin probe.
5. The method of claim 2 , wherein the first and second surface voltages are measured using a capacitor probe.
6. The method of claim 2 , wherein measuring a first surface voltage of the metal while the metal is illuminated comprises:
illuminating the metal with photon energy larger than an energy gap of the semiconductor wafer.
7. The method of claim 2 , wherein the metal is transparent to the illumination, and
wherein measuring a first surface voltage of the metal while the metal is illuminated comprises directing illumination upon the metal.
8. The method of claim 2 , wherein the metal is opaque to the illumination, and
wherein measuring a first surface voltage of the metal while the metal is illuminated comprises directing illumination upon the semiconductor wafer.
9. The method of claim 1 , wherein the surface barrier voltage is proportional to the effective work function of the metal on the dielectric on the semiconductor wafer.
10. The method of claim 1 , wherein the effective work function of metal on the dielectric on the semiconductor wafer is determined, based at least in part, on a bulk work function of the semiconductor wafer.
11. The method of claim 10 , wherein the effective work function of metal on the dielectric on the semiconductor wafer is determined using the relationship EWF=Φ S −qV SB , where EWF is the effective work function of metal on the dielectric on the semiconductor wafer, Φ S is the bulk work function of the semiconductor wafer, V SB is the surface barrier voltage of the semiconductor wafer, and q is a charge of an electron.
12. The method of claim 11 , wherein determining the surface barrier voltage of the semiconductor wafer comprises determining a spatially dependent map of the surface barrier voltage along a surface of the semiconductor wafer; and
wherein determining the effective work function of the metal on the dielectric on the semiconductor wafer is based, at least in part, on the spatially dependent map.
13. The method of claim 1 , wherein the effective work function of the metal on the dielectric on the semiconductor wafer corresponds to a work function value of the metal at an interface between the metal and the dielectric.
14. A system comprising:
a probe for measuring a surface barrier voltage of a semiconductor wafer, wherein a dielectric disposed on the semiconductor wafer and metal is disposed on the dielectric;
one or more processors in communication with the probe; and
non-transitory memory in communication with the one or more processors, the non-transitory memory storing instructions, which, when executed by the one or more processors, causes the one or more processors to determine an effective work function of the metal on the dielectric on the semiconductor wafer based, at least in part, on the measured surface barrier voltage.
15. The system of claim 14 , wherein the effective work function of the metal on the dielectric on the semiconductor wafer corresponds to a work function value of the metal at an interface between the metal and the dielectric.