Patent ID: 7274465

Claim:
A method of examining a structure formed on a wafer, the structure having a profile, the method comprising: directing an incident pulse at the structure, wherein the incident pulse is a sub-picosecond optical pulse; measuring a diffraction pulse resulting from the incident pulse diffracting from the structure; obtaining a time signal of the incident pulse (E o (t)); convolving the time signal of the incident pulse (E o (t)) with an impulse response (G(t−τ)) of the structure to generate a simulated diffraction pulse; comparing the measured diffraction pulse to the simulated diffraction pulse, wherein a hypothetical profile of the structure is associated with the simulated diffraction pulse; and when the pulses match within a matching criterion, determining a characteristic of the profile of the structure based on the hypothetical profile of the structure associated with the simulated diffraction pulse that matched the measured diffraction pulse.