Tantalum nitride films for the absorber material of reflective-type EUVL mask

Tantalum nitride (TaxN) films were evaluated for use as the absorber material of masks for extreme ultraviolet lithography (EUVL). TaxN films deposited by DC sputtering using an Ar+N-2 gas mixture had a low stress of less than 300 MPa, an amorphous-like structure, and a low deep ultraviolet (DUV) reflectivity. This film provides a DUV contrast of 30% with respect to the Mo/Si multilayer whose top is on Si layer. A TaxN film deposited using a Xe+N-2 gas mixture was found to be better in the following ways: the stress is below 100 MPa, the change in stress is below 30 MPa, and the density is more than 1 g/cm(3) higher. Furthermore, treating the surface of TaxN film with O-2 plasma or sputtering a TaxO film on it using an Ar+O-2 gas mixture improved the DUV contrast because the resulting surface has a lower DUV reflectivity than TaxN film These results indicate that TaxN film is one of the most suitable materials for the absorber of EUVL masks.