Atomic force microscope (AFM) analysis of photoresist test structures for use in SEM as in-house linewidth standards

摘要

Abstract: Photoresist linewidths are presently controlled by inspecting wafers in plan view with a 'metrology SEM'. No standard reference materials exist for checking this measurement. We show the feasibility of creating an in-house quasi-standard for this purpose. Using a modern i-line stepper (0.54 N.A.), we produced three specimens of 0.5 $mu@m wide photoresist line test patterns which presented both aberrated and good line shapes. We examined the specimens in cross-section using the AFM and in plan view using the SEM. The AFM images had crisp edges defining the line profile. We measured pitch, linewidth, and slope angles from the AFM images and compared these with the pitches and linewidths reported by the SEM. We found differences for features that had curved sidewalls. We discuss the basis for edge contrast in the AFM and propose a method for mathematical analysis. This work shows that the AFM can directly examine resist line profiles and provide images of useful precision, without adding a conductive coating as is commonly done in high resolution SEM. Any added coating should be avoided on a standard, since it would modify both the physical width of the structure and its electron scattering characteristics.!8