Image Placement Error Due to Pattern Transfer For EUV Masks

As semiconductor device requirements approach the 70 nm lithography node the development and implementation of a next-generation lithography (NGL) technology and the associated masks becomes of paramount importance. We have been developing Extreme Ultraviolet Lithography (EUVL) mask materials and processes. Fabrication of these masks includes the deposition and patterning of an EUV absorber stack. An understanding of the effect of pattern transfer on image placement is required due to the stringent image placement requirements for NGL masks. This article reports the measurement results of image placement caused by the pattern transfer of resist through final image for a candidate EUVL absorber stack using both bright field and dark field patterned 6025 (6” × 6” × 0.25”) masks. To determine stress related image distortion for EUV masks, an EUV stack consisting of SiON, TaSiN, and Cr was deposited onto Mo/Si coated mask blanks (6025 format) provided by Lawrence Livermore National Laboratory (LLNL). Both dark field and bright field masks were built and the pattern image placement was measured after e-beam lithography and after every etch process. Analysis of the data sets provided the resultant pattern transfer induced image displacement.