Critical dimension atomic force microscope (CD-AFM or 3D-AFM) is an important metrology technique for full three-dimensional measurements of linewidth CD and sidewall shape. Recent improvements in the 3D-AFM platform design, including high-precision/low-drift sample stages and high resolution optics, have been coupled with 'enhanced CD' (eCD) scan mode and novel AFM tip design. Especially, the eCD mode features a fast scanning actuator system (FA) and a bottom corner transitional rescan algorithm (TRS). The actuation system utilizes high gain feedback electronics and high bandwidth piezoelectric actuator to pull away a slender tip much faster from a small trench sidewall. The transitional rescan algorithm detects a rising sidewall before rescanning the transition for better bottom corner profiling. The paper presents evaluation data to show these enhancements resulted in improved measurement capability for small trenches required for shrinking device size, better sidewall profiling, more accurate bottom CD and LWR/LER measurement, faster scan speed, and less tip wear . All the improvements ensure 3D-AFM continues to have the lowest measurement uncertainty among all other dimension metrology techniques.