Measurement and control of linewidths in periodic structures using spectroscopic ellipsometry

A method of inspecting a periodic structure having a pitch comprising a feature and a space, comprising:

• directing an incident beam of elliptically polarized light at the periodic structure for obtaining a reflected beam;
• detecting the reflected beam for determining its intensity and polarization at a first wavelength;
• comparing the change in phase between the incident beam and the reflected beam for calculating an angle .DELTA.;
• finding the ratio of the amplitude of the incident beam to the reflected beam for calculating an angle .PSI.;
• detecting the reflected beam for at least one additional wavelength;
• comparing the change in phase between the incident beam and the reflected beam of the at least one additional wavelength for calculating an angle .DELTA.;
• finding the ratio of the amplitude of the incident beam to the reflected beam of the at least one additional wavelength for calculating an angle .PSI.;
• and
• determining the width of the features in the periodic structure.

A method of in-situ process control of a plasma etching process for the generation of a periodic structure having a pitch comprising a feature and a space, comprising:

• directing an incident beam of elliptically polarized light at the periodic structure for obtaining a reflected beam;
• detecting the reflected beam for determining its intensity and polarization at a plurality of wavelengths;
• comparing the change in phase between the incident beam and the reflected beam for calculating an angle .DELTA. at each wavelength;
• finding the ratio of the amplitude of the incident beam to the reflected beam for calculating an angle .PSI. at each wavelength;
• determining the peak of .DELTA. and .PSI. versus wavelength;
• comparing the peaks of .DELTA. and .PSI. to desired reference peak values of .DELTA. and .PSI.;
• and
• changing process parameters to reduce changes between peak values determined during processing to the desired reference peak values of .DELTA. and .PSI..