Amorphous indium-zinc-oxide films were deposited in the "transition region" by reactive sputtering using an In-Zn alloy target with a specially designed double feedback system. The cathode voltage showed a V- and circle-shaped curve as a function of O2 gas flow in the transition region, which differs from the S-shaped curve in Berg's model for reactive sputtering depositions. In-situ analyses with a quadrupole mass spectrometer combined with an energy analyzer revealed that the negative ions O-, O2-, InO-, and InO2-, with high kinetic energies corresponding to the cathode voltage, were generated at the partially oxidized target surface. Furthermore the positive ions O +, Ar+, In+, and Zn+ with rather low kinetic energies (around 10 eV) were confirmed to be generated by the charge exchange of sputtered neutral O, Ar, In and Zn atoms, respectively.
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