EUV and DUV scatterometry for CD and edge profile metrology on EUV masks

Inhalt:
To test the applicability of scatterometry on EUV masks we measured a prototype EUV mask both with an EUV scatterometer and a conventional scatterometer operated at 193 nm and compared the results with AFM and CD-SEM measurements provided to us by the mask supplier. The results of both CD-SEM and EUV- and DUV scatterometry show a quite good agreement in linearity despite constant CD offsets for these different metrology tools. The influences of the multilayer and Si capping layer on top of the multilayer thickness on EUV scatterometry results have been modelled with the help of FEM based simulations. A strong correlation has been found between the thickness of the capping layer and the sidewall angle. In general these results demonstrate the applicability both of EUV and DUV scatterometry for the characterisation of absorber structures on EUV masks. The application of DUV scatterometry allows to omit any influence from multilayer features and is only sensitive to the absorber structure. In this way EUV and DUV scatterometry complement each other for metrology on EUV masks. For applications in process optimisation and in process control the use of a conventional VIS/DUV-scatterometer may be sufficient in many cases.