We attempted to improve the dielectric properties of sputter deposited Y2O3 thin film on Si for the buffer layer of Ferroelectric Random Access Memory (FeRAM) application. Although the use of Xe as a sputtering gas was effective to improve the crystallinity of Y2O3 film On Si compared to that of the film deposited using Ar gas, oxygen deficiency in the film was enhanced by use of Xe gas. Increasing the total sputtering gas pressure was effective for improving the oxygen deficiency. The Y2O3 film sputtered at the total gas pressure of 20 mTorr has little positive charges and shows excellent dielectric properties as insulator. Effect of the substrate cleaning was also studied for decreasing the interface state density and the shift of flat band voltage.