To provide a thin film deposition method and a system therefor capable of depositing a thin film of LiNbO3 or LiTaO3 with a constant ratio composition on the surface of a substrate.

In the thin film deposition method where an LiNbO3 thin film is deposited on the surface of a substrate by sputtering, ECR (Electron Cyclotron Resonance) sputtering using LiNbO3 as a main target and sputtering using Li2O as an auxiliary target are simultaneously performed to deposit a film on the surface of a substrate, and also, the sputtering rate in the latter is independently controlled to the sputtering rate in the former.