Machine learning and hybrid metrology using HV-SEM and optical methods to monitor channel hole tilting in-line for 3D NAND wafer production

Tilted channel holes affect final yield significantly in High Aspect Ratio (HAR) 3D NAND memory wafer processing. An in-line measurement method is developed to use machine learning that utilizes the spectra from optical metrology to map Tilt-X and Tilt-Y. Reliable reference is provided by high voltage SEM. Results show that the correlation of optical and HV e-Beam measurements has R² more than 0.92. In addition, measurement throughput is improved tremendously by 40% from e-Beam to optical metrology. Combined with other optical metrology on the same platform (thickness, and Optical CD), this method is much efficient for in-line tilt measurement after channel hole etch process.