Measurement of radial density of Ar metastables in an inductively coupled plasma in Ar/O$_2$

O$_2$ plasma is used for ashing and trimming of the resist in semiconductor production processes, and for the surface modification of metals and polymers. In these processes atomic O radicals play important roles. It is reported that the density of atomic metastables increase in Ar/O$_2$ mixture as compared with that in pure O$_2$ in CCP [1]. We measured the radial profile of the density of Ar metastables (1s3, 1s5) and the temperature in an inductively coupled plasma at 13.56 MHz in Ar/O$_2$ as a function of admixture O$_2$ by using laser absorption spectroscopy. The average densities of metastable Ar are $2 \times 10^{10}$ cm$^{-3}$ (1s3) and $10^{11}$ cm$^{-3}$ (1s5) for 0-20\% O$_2$ fraction, and have the peak at 5-10\%. The temperatures are 2000 K (1s3) and 1600 K (1s5) and are heighest at 10\%. \newline \newline [1] T. Kitajima, T. Nakano, and T. Makabe, Appl. Phys. Lett., \textbf{88}, 091501 (2006).