Total physical thickness measurement of a multi-layered wafer using a spectral-domain interferometer with an optical comb.

An interferometric method using an optical comb is proposed and realized to measure the total physical thickness of a multi-layered wafer even if the refractive index of each layer is not given. For a feasibility test, two-layered and three-layered silicon-on-glass wafers were chosen as samples and were measured. An uncertainty evaluation was conducted to estimate the performance capabilities of the proposed method. To verify the measured values, the wafers were also measured by a contact-type standard instrument. For the three-layered wafer, the total physical thickness distribution was determined in a selected area.