Advanced Surface Finishing Process for Single-Crystal Aluminum Nitride Utilizing Chemical Mechanical Polishing Technology

Single-crystal aluminum nitride (AlN) substrates are intrinsically characterized by high hardness and high brittleness, properties that pose significant difficulties for achieving ultra-precision surface fabrication. Despite the substantial potential of AlN in various applications, effective and efficient polishing techniques specifically tailored for single-crystal AlN substrates have been scarcely investigated. To address this technological shortcoming, this research puts forward an enhanced CMP strategy tailored to surface finishing of single-crystal AlN, structured around a sequential three-step process: initial grinding, intermediate rough polishing, and final fine polishing. The most favorable processing conditions were identified by systematically examining how the rotation speed and applied pressure of the polishing plate impact the resulting surface roughness. Upon completion of the fine polishing step, the AlN substrate surface exhibited exceptional uniformity and an extremely low average roughness (Ra) of only 1.16 nm, coupled with a low coefficient of variation of 12.84%. These results provide an essential foundation for producing exceptionally uniform, atomically smooth surfaces in a wide range of brittle semiconductor substrates and hard, with AlN serving as a representative example. • An enhanced three-step chemical mechanical polishing process is developed for single-crystal crystals aluminum nitride substrates. • The effects of platen speed and downforce on material removal rate and surface roughness are clarified. • A maximum material removal rate of 878.9 μm/h is achieved with good overall surface flatness. • Ultrasmooth crystals aluminum nitride surfaces with a minimum ra of 1.16 nm are obtained after fine polishing. • The proposed chemical mechanical polishing strategy enables highly uniform finishing of hard and brittle substrates.