Application of atomic force microscopy to lithography characterization and control

The characterization and control of high aspect ratio features have typically presented challenges to conventional in-line metrology. For example, the extent to which a top-down CD SEM is capable of detecting scumming in deep trenches and vias varies as a function of feature aspect: ratio and typically must be first verified by independent means before one can rely upon it to control the lithographic process. By necessity, this: verification has been done destructively upon a limited number of samples. The present work uses in-line Atomic Force Microscopy to characterize the lithography of high aspect ratio vias. Operating a Dektak SXM320 in its DT mode, we have scanned vias in excess of 1.5 microns deep with nominal top dimensions of 300 nm, and we have nondestructively explored and characterized the lithographic process window for a variety of process layers representing a range of aspect ratios from 3:1 to 5:1. Analysis of the scan traces by various algorithms will be discussed particularly in the context of process control and the tool's ability to gauge the relative openness of the feature. We will also present our experiences with tip requirements and durability.