Patent ID: 8843337

Claim:
An apparatus comprising: a measurement unit that measures a test surface; and a calculation unit that calculates a shape of the test surface using measurement data, wherein the measurement unit sets a plurality of measurement areas in the test surface, each of the plurality of measurement areas being a part of the wafer and measures the test surface such that each of the plurality of measurement areas forms an overlapping region with at least one of other measurement areas, and wherein the calculation unit reads a measurement data item for each of the measurement areas, expresses a measurement error of each measurement as a polynomial including a term that has a coefficient whose value is dependent on setting of the measurement area and a term that has a coefficient whose value is not dependent on the setting of the measurement area, obtains a matrix equation with respect to the coefficients of the polynomial by applying a least-squares method to each of the measurement data items for the overlapping region, assigns data about the terms of the polynomial and each of the measurement data items for the overlapping region to the matrix equation, calculates the coefficients of the polynomial from a singular value decomposition of the matrix equation to which the data has been assigned, and corrects each of the measurement data items for the measurement areas using the calculated coefficients, and calculates the shape of the test surface in the plurality of measurement areas using the corrected measurement data items.