Abstract: Photoresist features can be characterized by electron microscopy-based metrology. A protective coating may be deposited on the photoresist with no change or minimal change to the dimensions of the underlying photoresist features, where the protective coating may be conformal and formed in a reactor operated under low temperature and low plasma conditions. In some implementations, the protective coating is formed by plasma-enhanced atomic layer deposition. Reliable and accurate profile information of photoresist features can be captured by metrology using the protective coating.