On treatment of ultra-low-k SiCOH in CF plasmas: correlation between the concentration of etching products and etching rate.

Low-pressure rf plasmas have been applied for etching of ultra-low-k SiCOH wafers using an Oxford Plasmalab System 100. In pure CF plasmas, SiCOH layers have been etched for different power values. Using quantum cascade laser absorption spectroscopy in the mid-infrared spectral range, the correlation of online and in situ measured concentrations of two etching products, CO and SiF, with the ex situ determined etching rates has been studied. The concentration of SiF was found to range between 0.6 and 1.4 × 10 molecules cm. In contrast the concentrations of CO were measured to be only about 50 % of the SiF density with 7 × 10 molecules cm in maximum. The production rate of SiF, determined from the time behavior of its concentration after plasma ignition, was found to be between 1 and 5 × 10 cm s. The etching rates varied between 2 and 7 nm s. Both parameters increase nearly linearly with the applied rf power. It was found that for power values of up to 1.1 kW, the etching rate depends nearly linearly on the in situ monitored concentrations of both etching products. Therefore, the concentration of the etching products can be directly used as a measure of the etching rate. [ABSTRACT FROM AUTHOR]