AFM Surface Roughness and Depth Measurement of Trenches with High Aspect Ratio

Roughness measurements on epitaxial layers before and after etching were done with an atomic force microscope (AFM) with sub-Angstrom repeatability. Furthermore, surface roughness was monitored with AFM after chemical mechanical polishing, before a wafer was bonded to another wafer. It was observed that measuring in non-contact mode reduces the tip wear and extends the life time of AFM tips. We also show that a resist recess in narrow trenches which cannot be measured with scatterometry is easily measured with a high-aspect-ratio tip on AFM. The offset between the AFMs in two different fabs is currently less than 5 nm, when a trench depth recipe is transferred from one tool to another.