Energy Flux to a Substrate in ICP Assisted Magnetron Sputtering

Metal-doped ZnO received attention as an alternative transparent conducting material to Sn-doped In2O3 (ITO), since it has advantages over ITO in environment resistance and resource cost. We have applied inductively coupled plasma (ICP) assisted sputtering to the deposition of Al-doped ZnO (AZO), and succeeded in depositing good quality AZO films with good spatial homogeneity without using an intentional substrate heating. To understand the deposition mechanism of AZO films in the ICP assisted sputtering, substrate heating effect in the ICP assisted DC magnetron sputter-deposition of AZO was investigated for various ICP RF power (0 ~ 300 W), DC magnetron power (0 ~ 50 W), and neutral Ar pressures (10 ~ 100 mTorr). The total heat flux to the substrate (J) was measured by thermal probes and compared with Langmuir probe data [1], and metastable Ar density (NAr) and temperature (Tg) were measured by external cavity diode laser absorption spectroscopy (ECDLAS) [2]. As a result, it was found that i) the empirically-determined optimum substrate position to deposit the highest quality AZO film coincided with the position where J took the maximum value of about 3000 Wm for the ICP RF power of 200 W at 30 mTorr, ii) J was predominantly contributed by plasma charged species, iii) energy flux due to neutral Ar species was not more than 10 % of J. In this report, deposition mechanism of AZO thin films is discussed from a viewpoint of plasma-surface interaction.