TRANSMISSION ELECTRON-MICROSCOPY OF NANOMACHINED SILICON-CRYSTALS

Silicon substrate slices in (111) or (001) surface orientation have been machined in two ways: precision ground by a diamond abrasive wheel to a surface roughness R(a) approximate to 11 nm, or turned on a highly stiff single-point diamond turning machine to R(a) approximate to 0.5 nm. Transmission electron microscopy of cross-sections of the machined surfaces has established the following. (1) The mean depth of permanent damage in both cases lies in the range 100-400 nm. (2) In the ground specimens the damage depth is very variable, and the damage consists of regions of well defined dislocation loops on several slip systems, other regions with a very high density of irregular dislocation arrays, and occasional microcracks up to 500 nm deep which do not always intersect the surfaces. Patches of amorphous silicon are also observed. (3) Beneath the turned surfaces the damage appears more homogeneous, consisting of dislocation loops predominantly on a single slip system in any given region of the specimen.