Investigations of Production Processes of Ti+ in High-Pressure Magnetron Sputtering Plasmas

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We investigate production processes of Ti+ in magnetron sputtering plasmas to explain the finding that Ti+ density is enhanced significantly in the downstream region of a high-pressure discharge [N. Nafarizal et al.: Jpn. J. Appl. Phys. 44 (2005) L737]. We examined the contributions of the following five production processes: 1) electron impact ionization ($\text{Ti}+\text{e}\rightarrow\text{Ti$^{+}$}+\text{2e}$), 2) Penning ionization ($\text{Ti}+\text{Ar$^{\text{M}}$}\rightarrow\text{Ti$^{+}$}+\text{Ar}+\text{e}$), 3) charge exchange collision with Ar+ ($\text{Ti}+\text{Ar$^{+}$}\rightarrow\text{Ti$^{+}$}+\text{Ar}$), 4) three-body recombination ($\text{Ti$^{2+}$}+\text{e}+\text{e}\rightarrow\text{Ti$^{+}$}+\text{e}$), and 5) two-step ionization via metastable Ti ($\text{Ti}+\text{e}\rightarrow\text{Ti$^{\text{M}}$}+\text{e}$ followed by $\text{Ti$^{\text{M}}$}+\text{e}\rightarrow\text{Ti$^{+}$}+\text{2e}$). However, the experimental results indicated that none of the five processes listed above was the dominant production mechanism of Ti+ in the high-pressure magnetron sputtering plasma. We consider charge exchange collision with Ar$_{2}^{+}$ ($\text{Ti}+\text{Ar$_{2}^{+}$}\rightarrow\text{Ti$^{+}$}+\text{2Ar}$) as a possible mechanism that explains the increase in Ti+ density in the high-pressure discharge.
2009-12-25