Spectroscopic diagnostics of temperature-controlled trench etching of silicon

Ernission from the plasma species CCl, CN, CO, N₂, and Si was monitored during trench etching of silicon with a CHCl,₃/ N, chemistry. The temperature of the backside of the wafer was recorded simultaneously. The emission response to experimentally induced perturbations of the plasma was found to be particularly informative. One such perturbation was a sudden change of the wafer temperature through control of the He pressure under the wafer. The other perturbation involved a drastic change of the N₂, flow rate. Our results confirm the mechanism of control of the trench profile through the temperature-dependent rate of deposition of polymers on the sidewalls during etch. Further, N₂, which certainly plays a crucial role in this chemistry, may engage in a surface reaction producing CN radicals; our data are consistent with this surface reaction. Finally, an algorithm was constructed for real-time monitoring of the selectivity of .silicon to the oxide mask; selectivity is shown to be very sensitive to the presence of N₂.