Dimensional optical metrology on deep sub-wavelength nanostructures

At PTB two different and to a certain degree complementary methods for dimensional optical characterisation of nanostructures have been developed and investigated: Alternating Grazing Incidence Dark field microscopy using UV illumination (UV-AGID) allows measuring individual isolated structures. On the other hand polarisation sensitive DUV scatterometry is capable to measure average dimensional parameters of periodic structures. Both methods have proven the ability to characterise accurately even sub-wavelength structures; example measurement results are shown. Additionally the performance of both methods for linewidths measurement of deep sub-wavelength line structures has been investigated. The theoretical limits have been evaluated by means of numerical simulations of UV-AGID and DUV scatterometry for silicon and chrome line structures with linewidths down to 10 nm. It has been shown that AGID microscopy in the DUV spectral range is in principle capable to measure line structures down to a few 10 nm, depending on the structure material. For scatterometry no fundamental limit has been observed. Sources of technical issues limiting the performance in practise will be discussed.