Ultraviolet–visible ellipsometry for process control during the etching of submicrometer features

Microelectronics processing of ultralarge-scale-integration devices, which use increasingly thinner films and deep submicrometer design rules, requires sensitive diagnostic techniques to achieve tight process control. Film thickness and etched profiles are commonly characterized by postprocess and/or destructive techniques such as cross-sectional scanning electron microscopy. Because of its sensitivity and compatibility with plasma processing environments, in situ spectroscopic ellipsometry has become an extremely useful diagnostic for plasma etching applications, but until recently it was thought to require a sacrificial, unpatterned area on the wafer to provide film thickness information. We show that the applications of ellipsometry in microelectronics are no longer restricted to the control of uniform films or to unpatterned areas dedicated to film thickness measurement but extend also to monitoring the etching of multilayer stacks during the fabrication of submicrometer devices or gratings with high aspect ratios. Some new interpretation models are developed and presented.