Doping Process for 3-D N-Type Trench Transistors-2-D Cross-Sectional Doping Profiling Study

Comparison study of doping a 3-D trench transistor structure is carried out by beam-line (BL) implant and plasma doping (PLAD) methods. Electron holography (EH) is used as a powerful characterization method to study 2-D cross-sectional doping profiles of arsenic-based doping processes. Quantitative definitions of junction depths x_j in both vertical and lateral directions can be obtained. Good correlations of 2-D EH dopant profiles, 1-D secondary ion mass spectrometry/angle-resolved X-ray electron spectroscopy impurity profiles, and device electrical parameters are demonstrated. The results reveal an advantage of PLAD over BL implant: a much larger effective implant area for 3-D trench bottom. It leads to a deeper vertical junction depth x_j(V) with a larger lateral junction depth x_j(L). It is due to the PLAD technology with less angle variation issues and no line of sight shadowing effect. Enhancing the dopant lateral straggle by PLAD at the trench bottom is particularly useful for nonplanar device structures with low resistance buried dopant layers.