The rf characteristics of a BCl3/Cl2 discharge used to etch aluminum films for semiconductor interconnect applications have been studied in a transformer coupled plasma™ (TCP™) etching system. The impedance (both real and imaginary parts) of the discharge was obtained as a function of process condition by studying the capacitor positions of the matching network attached to the TCP plasma source. By correcting for the contribution of the excitation coil, estimates were made of the plasma resistance and reactance as a function of generator power and chamber pressure. In addition, measurements of rf current and voltage were made using IV probes incorporated into the match as a function of TCP power measured at the generator, pressure, and total gas flow. It was found that the rf current and voltage at the input to the coil were both linearly dependent on power, inversely dependent on total pressure and virtually independent of total gas flow. The current–voltage measurements were correlated with measurements of etch rate and uniformity for both aluminum and oxide films as a function of generator power, pressure, and total gas flow.
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Patrick et al. (1997) studied this question.