Method and system for optical metrology in patterned structures

An optical metrology system for use in determining one or more parameters of a patterned upper structure located on top of an underneath layered structure on a semiconductor wafer, the system comprising:

• measurement apparatus configured to
• perform first optical measurements on a first site of a semiconductor wafer comprising the underneath layered structure, thereby obtaining first measured data indicative of at least spectral response to incident radiation,
• perform second optical measurements on the first site or on a second site of the semiconductor wafer comprising the patterned upper structure on top of the underneath layered structure, thereby obtaining second measured data Smeas indicative of at least spectral response to incident radiation, and
• provide preliminary complex spectral measured data PMD of the underneath layered structure based on at least the first measured data, the PMD being a function ƒ of spectral intensity Iλ and phase ϕ, expressed as PMD=ƒ(Iλ;ϕ), the PMD being indicative of a complex spectral response of the underneath layered structure to incident radiation;
• and
• a computer system comprising a processor and a memory, the computer system configured to analyze the second measured data Smeas to determine values for one or more parameters of the patterned upper structure, wherein the parameters represent physical characteristics of the patterned upper structure, by:
• obtaining a modeled optical response Smodel of the patterned upper structure to incident radiation,
• providing a general function F(Smodel;PMD) describing a relation among
• a) a theoretical optical response Stheor of a semiconductor wafer sample to incident radiation, the sample including the patterned upper structure on top of the underneath layered structure,
• b) the modeled optical response Smodel of the patterned upper structure, and
• c) the complex spectral response PMD of the underneath layered structure, wherein the relation is expressed as Stheor=F(Smodel;PMD) and wherein Smodel and an optical response of the underneath layered structure that contributes to a total optical response of the patterned upper structure on top of the underneath layered structure are combined to form Stheor,
• utilizing the general function F(Smodel;PMD) for comparing the second measured data Smeas and the theoretical optical response Stheor in a fitting procedure, and
• determining the one or more parameters of the patterned upper structure from the theoretical optical response Stheor corresponding to a best fit condition between the second measured data Smeas and the theoretical optical response Stheor.