Effects of Energetic Ion Bombardment on Structural and Electrical Properties of Al-Doped ZnO Films Deposited by RF-Superimposed DC Magnetron Sputtering

The bombardment of various types of energetic ions during rf-superimposed dc magnetron sputter deposition was investigated in detail and their effects on the structural and electrical properties of Al-doped ZnO (AZO) films were analyzed. Aside from the expected energetic negative oxygen ions (i.e., O - and O 2 - ), various other negative ions (i.e., AlO - , AlO 2 - , AlO 3 - , ZnO - , and ZnO 2 - ) with a high energy were clearly observed. Such negative ions were found to be generated on the target surface and accelerated towards the substrate by the full cathode voltage. Furthermore, we found that the energy of these negative ions decreased with decreasing plasma impedance by superimposing rf power on dc sputtering. The resistivity of the AZO films deposited using the rf-superimposed dc sputtering was much lower than that of the films deposited using conventional dc sputtering. Such a decrease in resistivity should be attributed to reducing the damage of AZO films by suppressing the bombardment energies of various types of energetic negative ions impinging on a growing film surface.