AFM (Atomic Force Microscopy) for roughness is the gold standard technique for measuring surface roughness at nanometer and sub-nanometer resolution — a sharp probe tip scans the surface using contact, tapping, or non-contact mode, mapping the surface topography with Angstrom-level vertical resolution.

AFM Roughness Measurement

• Tapping Mode: Tip oscillates at resonance frequency, lightly tapping the surface — most common for semiconductor surfaces.
• Scan Sizes: 1×1 µm², 5×5 µm², 10×10 µm² — roughness values depend on scan size and must be reported with scan parameters.
• Metrics: Rq (RMS roughness), Ra (average roughness), Rmax (peak-to-valley), PSD (power spectral density).
• Resolution: Lateral ~5-20 nm, vertical ~0.1 nm (sub-Angstrom) — depends on tip radius.

Why It Matters

• Reference Method: AFM is the reference for calibrating other roughness measurement techniques.
• Process Development: AFM roughness measurements guide CMP slurry development, etch recipe optimization, and surface preparation.
• Limitation: AFM is slow (minutes per scan) and measures small areas — not suitable for in-line, full-wafer monitoring.

AFM for Roughness is the ultimate surface microscope — providing the highest-resolution roughness measurement for semiconductor surface quality control.