EUV mask damage caused by Ga focused ion beam irradiation during the mask defect repair was studied. The concentration of Ga atom implanted in the multilayer through the buffer layer and distributions of recoil atoms were calculated by SRIM. The reflectivity of the multilayer was calculated from the Ga distribution below the capping layer surface. To validate the calculation, Ga focused ion beam was irradiated on the buffer layer. The EUV reflectivity was measured after the buffer layer etching process. The measured reflectivity change was considerably larger than the one predicted from the absorption of light by the implanted Ga. The large reflectivity loss was primarily due to the absorption of light by chromium silicide residue which was generated by the intermixing of the buffer and the capping layer. Both lowering of the acceleration voltage and using thicker buffer layer were found to be effective in reducing this intermixing. The reduction of the reflectivity loss by using thicker buffer layer was confirmed by our experiments. An aerial image of patterns with etching residue formed by the intermixing was simulated. When the thickness of the intermixed layer happened to be 8 nm and the size of the resulting residue was larger than 100 nm, then the impact of the estimated absorption by the residue on the linewidth of 32 nm hp line pattern became more than 5 %.

Date Published: 17 October 2008
PDF: 11 pages
Proc. SPIE 7122, Photomask Technology 2008, 71222J (17 October 2008);

Published in SPIE Proceedings Vol. 7122:
Photomask Technology 2008
Hiroichi Kawahira; Larry S. Zurbrick, Editor(s)