1. A computer-implemented method of quantifying a shape of a surface of a semiconductor die comprising: measuring an elevation (z) of the surface of the semiconductor die at a plurality of locations in an x-y plane of the surface comprising measurement data; performing a fit of the measurement data to a series expansion in terms of one or more base functions comprising a series expansion fit, wherein the base functions are generalized monomials; calculating a vector of shape coefficients from the series expansion fit; calculating, based on the vector of shape coefficients, intrinsic surface shape parameters X sag describing an effective bow along a x-axis, Y sag describing an effective bow along a v-axis, and Twist describing an elevation of a fourth corner with respect to a seating plane containing three other corners of a four corner surface; and outputting the intrinsic surface shape parameters.