Direct measurement of Leff and channel profile in MOSFETs using 2-D carrier profiling techniques

Different two-dimensional (2-D) carrier profiling tools, based on contact-mode atomic force microscopy (AFM), have been used to investigate the details in the lateral and vertical distribution of the carriers in nMOSFET devices with identical channel profile (4e17 atoms/cm(3)) and gate oxide thickness (5.5 nm) but with different S/D architectures, all relevant for 0.25 mu m CMOS technology (see Table 1). These characterization techniques are: scanning capacitance microscopy (SCM) [1] and scanning spreading resistance microscopy (SSRM) [2]. Two typical 2-D case studies are presented. In the first one, the effective gate length is determined. The measured values are compared with the ones measured by extraction from the electrical characteristics using a modified Shift & Ratio method [3]. In the second study, the vertical channel profile through the centre of the gate is studied as a function of the gate length. Hereby, for the first time, transient enhanced diffusion (TED) effects are directly observed. This type of profile information is not accessible using standard 1-D profiling techniques such as SIMS, SRP, or C-V profiling.