Characterization of advanced etching reactors using novel diagnostic tools

Plasma etching equipment used for sub-micron integrated circuit fabrication at present are exclusively based on 13.56 MHz, capacitively coupled, parallel-plate geometry. The underlying mechanisms of plasma processes in these reactors are not well understood and there is even less understanding of how the etch-tool parameters relate to the plasma discharge characteristics which actually determine the etch process. In this thesis, new diagnostic techniques were applied for the characterization and optimization of plasma etching processes in various reactor configurations. Specifically, diode and triode configurations were studied extensively using tuned scanning Langmuir probes. Both radial and axial distributions of plasma density were measured for a range of process parameters. Extensive mapping of plasma region in these reactors have shown that the plasma density distribution is dramatically different for dissociative molecular etching gases as compared to inert gases. Furthermore, the density distribution was found to be strongly dependent on the electronegativity of the process gas. In the triode configuration, the relative phase between the RF voltage waveforms applied to the electrodes was found to determine both the magnitude and distribution of the plasma density. Typically, higher etch-rates and better etch-uniformity were obtained for out-of-phase excitation(180°) as compared with the in-phase excitation(0°) in the triode. The understanding gained by these studies has lead to the development of a novel magnetic multipole based triode reactor configuration. This new reactor configuration can be operated at low pressures and produces high-rate, low damage etching of submicron features with required profile control. In addition, a new plasma etching diagnostic technique based on thermal imaging of wafer was developed. The technique has been found to be useful for in situ real-time monitoring of end-point and uniformity of etching as well as for inferring wafer temperature and heat transfer characteristics. Also, a simple end-point detection technique based on plasma impedance monitoring was developed which eliminates the need for optical access to the wafer/plasma