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sub-nm 3D metrology inside an EBL tool with atomic force microscopy

Characterization of EBL exposed PMMA resist using a compact sample holder-mounted AFM...

an-afm.jpgThis application note describes a new setup that adds 3D metrology to an e_LiNE plus electron beam lithography and nanofabrication system. Based on an atomic force microscope (AFM) integration and subsequent in situ characterization of PMMA resist exposed by standard electron beam lithography, the paper demonstrates sub-nm surface topography resolution in this setup.

The interesting observation of sub-nm resist shrinking without any ex situ process yields high potential for better understanding of focused electron beam induced energy deposition process characteristics. Moreover, an in situ AFM ideally complements the range of applications within an EBL and nanoengineering tool regarding the determination and control of material growth/etching rates or surface topography analysis – not only for the sake of inspection and metrology but also for nanolithography on non-planar surfaces.

In this application note, is demonstrated a novel technique, which allows the in situ characterization of EBL processes. Instead of the traditional approach of imaging the post-processed resist in a scanning electron microscope (SEM), an easy-tohandle AFM was successfully integrated into the Raith e_LiNE plus, a flexible platform which did not need any modification to accommodate the AFM. In-situ measurements of the EBL resist immediately after the exposure deliver more physically valuable information, such as polymer grain size and distribution.

A resist shrinkage effect was observed for 2 different resist types, which increases linearly with the exposure dose. This enables a step-wise proximity correction or a reexposure of underexposed spots.

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