Ga implantation and interlayer mixing during FIB repair of EUV mask defects

摘要

EUV mask damage caused by Ga focused ion beam irradiation during the mask defect repair was studied. Theconcentration of Ga atom implanted in the multilayer through the buffer layer and distributions of recoil atoms werecalculated by SRIM. The reflectivity of the multilayer was calculated from the Ga distribution below the capping layersurface. To validate the calculation, Ga focused ion beam was irradiated on the buffer layer. The EUV reflectivity wasmeasured after the buffer layer etching process. The measured reflectivity change was considerably larger than the onepredicted from the absorption of light by the implanted Ga. The large reflectivity loss was primarily due to the absorptionof light by chromium silicide residue which was generated by the intermixing of the buffer and the capping layer. Bothlowering 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 ofpatterns with etching residue formed by the intermixing was simulated. When the thickness of the intermixed layerhappened to be 8 nm and the size of the resulting residue was larger than 100 nm, then the impact of the estimatedabsorption by the residue on the linewidth of 32 nm hp line pattern became more than 5 %.