A kinetic model for step coverage by atomic layer deposition in narrow holes or trenches

Highly conformal coatings can be deposited inside narrow features, such as holes, using complementary self-limiting reactions of two vapors with a surface. A simple theory is developed for the conditions needed to deposit coatings with uniform thickness in narrow holes of arbitrary cross section. Two conditions are found to be necessary: 1) certain minimum amounts of vapor must be supplied, and 2) a certain minimum product of vapor pressure and its exposure time at the entrance to the hole. The theory is in good agreement with data from the reaction of hafnium dimethylamide vapor and water vapor to form hafnium dioxide films that are completely conformal in holes with an aspect ratio of 43. The theory provides simple scaling laws to predict the conditions needed to coat holes with other aspect ratios.