Properties of Al2O3 as blocking layer of MANOS memory device were investigated and effects of O infusion by GCIB process were discussed. By introduction of GCIB process, electrical properties were improved such as increasing of program window. GCIB process was able to modify film density and band-gap energy, which was limited to several nm from the surface. The variation of band structure induced by the oxygen infusion contributed to the improvement of electrical properties because reduction of electrical field suppressed F-N tunneling during erase operation.