Thickness measurement of nano-metallic film with electromagnetic sensor under large sensor-sample distance

The requirement for noncontact thickness measurement of metallic film with nanometer precision in semiconductor industry is urgent to be satisfied. Using the flat coil model, the magnetic field distributions along the axis of the sensors with close-packed and loose-packed coils were calculated and optimized. The calculation results based on the model have shown that the sensitivity of the sensor made of close-packed coils with a constant height increases with the outer diameter, and decreases with the inner diameters for a given sensor-sample distance. The designed coils with different sizes were fabricated by self-adhered enameled copper wire. The coils were used as the sensor for the thickness measurement of the copper films deposited on silicon wafer. Measurement results verified that the designed coil sensor can achieve the nanometer resolution of thickness measurement under large lift-off, which can be widely used in semiconductor industry.