TOWARDS A PHYSICAL UNDERSTANDING OF SPREADING RESISTANCE PROBE TECHNIQUE PROFILING

Spreading resistance has become a standard in semiconductor resistivity determination. The method is based on metal-semiconductor point contact measurements. The resulting spreading resistance is generally described by R(s) = rho/4a, wherein rho refers to the bulk resistivity and a to the radius of the contact area. This relation is only valid in the ideal case where the contact area can be considered as a homogenous circular contact. New contact models have introduced the concept of multiple microcontacts in spreading resistance probe technique (SRP) measurements. The physical nature of these contacts has now been studied by an atomic force microscope (AFM). The AFM images show indentations of multiple point contacts penetrating 10-100 nm into the silicon depending on the applied force and the probe characteristics. Time-dependent measurements at constant force revealed a gradual increase in penetration depth and in contact area. An AFM with conducting tip has been developed to study the behavior of a single contact point. I-V curves for such a metallic tip are compared with I-V curves for standard SRP probes.