Non Destructive Determination of the Threading Dislocation Density of Smooth Simox Substrates using Atomic Force Microscopy

Atomic force microscopy (AFM) has been used extensively in recent years to study the topographic nature of surfaces in the nanometer range. Its high resolution and ability to be automated have made it an indispensable tool in semiconductor fabrication. Traditionally, AFM has been used to monitor the surface roughness of substrates fabricated by separation by implanted oxygen (SIMOX) processes. It was during such monitoring that a novel use of AFM was uncovered.A SIMOX process requires two basic steps - a high dose oxygen ion implantation (1017 to 1018 cm-3) followed by a high temperature anneal (>1200°C). The result of these processes is to form a buried oxide layer which isolates a top single crystal silicon layer from the underlying substrate. Pairs of threading dislocations can form in the top silicon layer during the high temperature anneal as a result of damage caused during the high dose oxygen implant.