profilometry

Profilometry measures surface height profiles to determine step heights, film thicknesses, surface roughness, and wafer-level topography. **Contact (stylus) profilometry**: Diamond stylus dragged across surface. Vertical deflection measured as function of position. **Stylus specifications**: Tip radius 0.1-25 um. Contact force 0.05-50 mg. Vertical resolution ~1nm. **Optical profilometry**: Non-contact methods using white light interferometry or confocal microscopy to measure height without touching surface. **White light interferometry**: Interference fringes from broadband light encode surface height. Sub-nm vertical resolution over large areas. **Applications**: Step height measurement (etched features, deposited films), film stress measurement (wafer bow), CMP surface planarity, photoresist profile. **Wafer bow**: Full-wafer profilometry measures bow and warp. Used to calculate film stress via Stoney equation. **Step height**: Measure height difference between etched and unetched regions or between different film levels. **Limitations of stylus**: Tip radius limits lateral resolution. Stylus contact can scratch soft surfaces. One-dimensional line scan. **Advantages of optical**: Non-contact, 2D surface maps, faster scanning, no surface damage risk. **Scan length**: Stylus can scan from microns to full wafer diameter (200-300mm). Versatile range. **Calibration**: Height standards (NIST traceable step height standards) for calibration. **Vendors**: KLA-Tencor (stylus), Bruker (stylus and optical), Zygo (optical interferometry).