Communication—eliminating thickness measurement uncertainty of capacitive displacement sensor in high resistivity substrate by photoconduction

Capacitive displacement sensors provide non-contact and absolute accuracy thickness measurements. However, if the resistivity of a target substrate is within 10⁵–10⁷ -cm, a measurement uncertainty will occur. Incorporating dopants in the substrate can adjust the resistivity to be outside the range that causes the measurement uncertainty, but also permanently changes the electronic properties. Here, we exploit the photoconductive effect to generate an adequate amount of electron-hole pairs, thereby temporarily decreasing the resistivity and thus enabling the capacitive displacement sensor to accurately measure the thickness at nanoscale resolution. After the measurement is completed, the resistivity of the substrate will return to its original value.