Beyond SRP: Quantitative carrier profiling with M4PP

Abstract

Understanding dopant diffusion and activation mechanisms is a key issue for future sub-45-nm CMOS technologies. This understanding requires the availability of accurate chemical and electrically active dopant profiles. In this work we will focus on the accurate and reliable characterization of carrier depth profiles for ultra-shallow (USJ) structures. Typically conventional means such as spreading resistance probe (SRP), which uses two high-pressure probes (10GPa) with a contact radius of about 1μm and a separation of 30μm, are running out of steam in the sub-30-nm depth regime. This is mainly due to the need to apply for multi-layer structures quite large Laplace-based deconvolution correction factors (>1000) on the raw data causing excessive noise amplification. These correction factors can be circumvented by performing a series of microscopic four-point probe (M4PP) measurements along a beveled sample with a small enough angle (few minutes). In M4PP, the probe tips make an elastic (non-penetrating) contact with a 1.5μm pitch leading to an enhanced dynamic range because of the reduced sampling size and penetration. Subsequently, the underlying resistivity and carrier depth profiles can be easily extracted by the simple calculation of the differential sheet resistance for each of the sub-layers.