Evaluation of substrate degradation in plasma etch processes using thermal wave analysis

The evaluation of plasma etching damage with thermal wave analysis is discussed. In particular the degradation of single crystal silicon substrates by plasma etch processes developed for the fabrication of trench capacitor cells in multi Mbit DRAMs was investigated since damage induced by these processes has direct impact on the electrical device performance. The etch experiments were performed in a triode system, in a magnetically confined reactor with triode RF configuration operating at very low gas pressure, and in a magnetically enhanced RIE system. To identify qualitatively the obtained thermal wave signals as structural damage bias voltage measurements during the dry etch processes, Auger and TEM analyses and electrical yield measurements on processed wafers were performed. The obtained results demonstrate that the thermal wave analysis exhibits a rapid and reliable nondestructive and contactless evaluation technique to access damage occuring during plasma processing; under specific conditions it can even be used to predict the electrical performance of fully processed DRAMs. (orig.)