ABSTRACT
As revealed from the data given in Table 9.1, Te, ne and ni increase with the increase of RF power. This is simply attributed to the fact that when the RF power is raised more dissipation of power occurs in the plasma and this eventually leads to the increase in electron energy (or Te). An increase in electron energy will enhance the ionization rate of the Ar atoms and hence n e and ni are also increased with the increase of RF power. During Ar plasma treatment, the DC self-bias voltage (Vb) that is developed on the substrates is observed to be increased from −26 to −74 V with increasing RF power. The DC self-bias voltage is measured using a digital voltmeter connected to the RF electrode through a high impedance (RL = 1.35 × 105 Ώ) inductor. However, the plasma potential (Vp) remains almost constant irrespective of the increase in RF power. With the knowledge of DC self-bias voltage and plasma potential, the maximum energy gained by ions as they travel through the sheath to the substrate is calculated according to the following relation: Emax = q (Vp − Vb) [1.1] where q is the ion charge (Glew et al., 1999). The variation in ion energy at RF power range of 10-30 W is further presented in Table 9.1, which shows an increase in ion energy with higher RF power. In this present work, the ion energy cannot be quantified as the types and charges of the ionized species formed near the plasma sheath are not known (Choudhury et al., 2011a).
