Thin films and surface topography measurement using reduced library

An apparatus for determining properties of a surface of an object, the apparatus comprising:

• a radiation source for producing radiation to be incident on the surface;
• a detector for detecting the radiation after the radiation interacts with the surface and producing a measurement signal;
• and
• a computer with memory coupled to receive the measurement signal from the detector and a computer-usable medium having computer-readable program code embodied therein for causing said computer to:
• process the measurement signal to remove a height contribution from the measurement signal leaving a film contribution in the measurement signal to produce a film measurement signal;
• compare the film measurement signal to a plurality of film signals in a library stored in the memory to determine film parameters of the surface of the object, the library comprising the plurality of film signals and a plurality of full signals, wherein the plurality of film signals are associated with the plurality of full signals and the plurality of film signals are produced by removing height contributions from the plurality of full signals;
• generate a reduced set of full signals using the film parameters of the surface, the reduced set of full signals having fewer signals than the plurality of film signals;
• compare the measurement signal to the reduced set of full signals to determine a height parameter of the surface of the object;
• and
• store the height parameter and the film parameters in the memory.