Making semiconductor crystals dopant boundaries visible - by etching using high frequency glow discharge and examining with scanning electron microscope

摘要

The boundaries are present in semiconductor crystals, and are esp. pn-junctions in silicon integrated circuits. A sample of the circuit is broken at the zone which is to be examined and then etched via a high frequency (h.f.) glow discharge so the resulting contrast in topography is visible in a scanning electron microscope. The fracture of the sample is pref. made at 90 degrees to the surface of the crystal. When the semiconductor crystal is Si, etching is pref. in a plasma formed from CF4 gas with a sample temp. of =150 degrees C; and the etching time is pref. 2 mins. for revealing n+ zones on p-doped silicon. Plasma etching pref. occurs at a partial pressure of ca. 0.7 torr. with a h.f. source of 200 watts power. Used as an inspection technique in obtaining the min. surface area for individual elements such as diodes, transistors, resistors etc. in integrated circuits, i.e. to achieve the highest packing density.