Pre- and post-metal oxidation sharpening effects on silicon field emitter devices

Oxidation sharpening techniques provide sharp silicon field emitter tips for low voltage operation of vacuum microelectronic devices, as well as for other applications including electron sources for SEMs and high spatial resolution, multi-beam, e-beam lithography. In the baseline fabrication sequence for self-aligned gated silicon field emitter, oxidation sharpening processes can be performed either prior to the gate metal deposition ("pre-metal" case), or after the gate metal is already in place ("post-metal" case). Although sharp tips (2-4 nm radii of curvature) can be obtained with either method, the shape of the sharpened tips is different in the two cases, primarily due to the fact that the nitride caps initially used as etch masks are present in the pre-metal case, but absent in the post-metal case. We present here a series of TEM micrographs illustrating the morphological evolution of silicon field emitter tips as a function of oxidation sharpening time. We also present Auger spectrometry data and sheet resistance measurements performed on the gate metal after the observed agglomeration in the post-metal case.