Patent ID: 8860956

Claim:
A method of measuring a dimension of a material layer in a material stack, said method comprising: measuring at least one optical spectrum from a stack of material layers; generating a material stack model that approximates said stack of material layers from a database that includes refractive index curves and extinction coefficient curves for a plurality of materials; generating a plurality of modulated extinction coefficient curves by scaling an extinction coefficient curve, as acquired from said database, of a target material within said material stack model through multiplication of a plurality of scalars; generating, for each selected modulated extinction coefficient curve among said plurality of modulated extinction coefficient curves, a data set representing an estimated thickness of one of said material layers by fitting a modified material stack model with said at least one measured optical spectrum, wherein said modified material stack model is derived from said material stack model by substitution of said selected modulated extinction coefficient curve for said extinction coefficient curve; determining a best-fit function by fitting said data sets with a fitting function while employing said plurality of scalars as discrete values for a variable of said fitting function; estimating a physical thickness of said one of said material layers by selecting a value of said best-fit function corresponding to a value of 1 of said variable; and outputting said estimated physical thickness of said one of said material layers as an approximation of a true physical thickness of said one of said material layer by storing in a non-transitory machine-readable data storage medium, or by displaying in a human-perceptible format, said estimated physical thickness of said one of said material layers.