TaN EUVL mask fabrication and characterization

The EUV mask patterning process development depends on the choice of EUV mask absorber material, which has direct impact on the mask quality or performance such as CD control, defect control, and registration. In the past, several EUV mask absorber material candidates that include Al-Cu, Ti, TiN, Ta,TaN, and Cr have been evaluated.(1-4) Our research indicated that TaN and Cr are the better candidates among the others evaluated. Cr absorber has been used for many optical lithography generations. Further extending Cr mask absorber to EUV lithography presents minimum impact to the currently mask technology infrastructure. TaN is a new film that has not been used in the currently mask technology. However, Ta based metal compound has been studied previously in x-ray mask technology. Its performance in EUV mask fabrication and printing was found compatible and comparable in many process steps and performance aspects to that of Cr absorber. In this paper, we will present our research and development work on TaN absorber EUV mask fabrication and characterization. The studies include material deposition study, etch development, cleaning compatibility evaluation, and mask printing test. The TaN absorber etch was able to achieve good etch profile and high etch selectivity to the buffer oxide layer. The cleaning benchmarking results showed that TaN absorber is compatible to the currently acid based Cr cleaning procedures and solution. No material damage or loss was found in the case of extreme harsh cleaning conditions used. The TaN thin absorber mask was successfully fabricated and printed in 10x microstepper at Sandia National Lab. Minimum feature of 70nm LIS were obtained.