Overlay Measurement Using Phase and Amplitude Modeling

A method for determining overlay in a semiconductor manufacturing process comprising:

• receiving radiation reflected from a metrology target including +1 and −1 diffraction patterns at different wavelengths in a waveband including a maximum of sensitivity of contrast to wavelength;
• analysing the radiation reflected from the metrology target to obtain measured values of overlay and one or both of amplitude and phase corresponding to points distributed over the metrology target, for different wavelengths;
• and
• performing a series of operations on the measured values of overlay to determine an overlay in which it is assumed that the amplitude and phase are unequal in the +1 and −1 diffraction orders.

A system for determining overlay in a semiconductor manufacturing process, the system comprising:

• an illumination system and an imaging system, the illumination system including a radiation source and the imaging system being arranged to direct radiation from the illumination system towards the surface of a target and to receive radiation from the illumination system reflected from the target in the form of diffraction patterns;
• a control unit arranged to control the imaging system or the illumination system or both to obtain diffraction patterns using different values of focal position or wavelength or both;
• and
• an image analysis unit configured to:
• receive radiation reflected from a metrology target including +1 and −1 diffraction patterns at different wavelengths in a waveband including a maximum of sensitivity of contrast to wavelength;
• analyze the radiation reflected from the metrology target to obtain measured values of overlay and one or both of amplitude and phase corresponding to points distributed over the target, for different wavelengths;
• and
• perform a series of operations on the measured values of overlay to determine an overlay in which it is assumed that the amplitude and phase are unequal in the +1 and −1 diffraction orders.