In situ monitoring of silicon plasma etching using a quantum cascade laser arrangement

In etch plasmas used for semiconductor processing, concentrations of the precursor gas NF3 and of the etch product SiF4 are measured online and in situ using a new diagnostic arrangement, the Q-MACS Etch system, which is based on quantum cascade laser absorption spectroscopy (QCLAS). In addition, the etch rates Of SiO2 layers and of the silicon wafer are monitored including plasma-etching endpoint detection. For this purpose the Q-MACS Etch system is working as an interferometer arrangement. The experiments are performed in an industrial, dual-frequency, capacitively coupled, magnetically enhanced, reactive ion etcher (MERIE), which is a plasma reactor developed for dynamic random access memory (DRAM) technologies. In the spectral range 1028 +/- 0.3 cm(-1), the absorption cross-sections of SiF4 and NF3 are determined to be sigma = (7.7 +/- 0.7) x 10(-18) cm(2) molecule(-1) and sigma= (8.7 +/- 0.8) x 10(-20) cm(2) molecule(-1), respectively.