Structural and Electrical Properties of ZnO Films Deposited with Low-Temperature Facing Targets Magnetron Sputtering (FTS) System with Changes in H_2 and O_2 Flow Rate

摘要

ZnO has been studied as a strong candidate for high-quality TCO in accordance with increasing demand to replace ITO. The origin of n-doping in ZnO is not clearly understood, but recently, the H_2 effect has received attention due to the role it plays in O-rich and O-poor conditions. In spite of recent rapid developments, controlling the electrical conductivity of ZnO has remained a major challenge. To control the electrical conductivity of ZnO, this study was performed using an FTS system with H_2 and O_2 addition at low processing temperature. The structural and electrical properties of ZnO thin films deposited at various H_2 and O_2 flow rates were investigated using XRD and a sheet resistance meter. In response to changes in H_2 and O_2 flow rates, the crystallization and related grain size of the ZnO films were somewhat changed. The sheet resistance increased from ～10~(-1) to ～10~4 M ohm/sq. when the O_2 flow rate was increased, and the resistance decreased from ～10~(-1) to ～10~(-4) M ohm/sq. when the H_2 flow rate was increased. The increase of sheet resistance with O_2 flow rates could be explained by decrease of oxygen vacancies. The decrease of sheet resistance with H_2 flow rates could be explained by increase of the electrons from interstitial hydrogen atoms. The plasma characteristics were analyzed using optical emission spectroscopy (OES). But, the overall spectrum did not change with the H_2 and O_2 gas flow rates. So, the dramatic changes in the electrical properties of ZnO thin films could be considered to be a result of changes in chemical composition of the thin films rather than the plasma status.