A measurement of F metastables by laser absorption spectroscopy in a two frequency CCP

Fluorine-containing plasmas are used in SiO$_{2}$ etching. The degree of dissociation of CF$_{4}$ is a critical factor for bottom etching and sidewall polymer deposition and determines the absolute density of F atom. Relative density is of F atom in metastables and grand state are experimentaly reported in an ECR plasma[1]. In the present study, we have observed the absolute density of F metastables by using a tunable diode laser absorption spectroscopy(LAS) in a capacitively-coupled plasma (CCP) in Ar/CF$_{4}$. The transition line used for absorption spectroscopy of F metastables is $3s4p_{3/2}-3p4D_{5/2}$ at 690.25nm. The metastable density, $6.0\times10^{9}cm^{-3}$ on the center of electrodes is measured at conditions that the CCP is sustained at 100MHz with 50W and a pressure of 100mTorr. Consequently we performed a measurement of absolute density of F metastables in the low and middle-density plasma.\newline [1]Kazuki Takizawa, Koichi Sasaki and Kiyoshi Kadota. Jpn. J. Appl. Phys. Vol40(2001)pp. 5130-5133