UV-assisted curing: an effective technique for toughening low-k organosilicate films

UV-cure processes enable considerable stiffening of organosilicate films in a controlled fashion, such that the porous volume and organosilicate nature of the SiOC:H films are preserved, which is important for maintaining a low dielectric constant. Due to its high degree of bond selectivity, UV radiation can initiate a rearrangement of the backbone Si-O-Si structure towards a more stable network configuration and increase the degree of cross-linking of the matrix. Both phenomena are responsible for improved film mechanical properties. An enhancement of about 40% in elastic modulus and hardness values, as well as a similar increase in cohesive fracture energy was observed for both CVD and spin-on-deposited UV-cured films, accompanied by only a 4-5% increase in dielectric constant. An important factor for the efficiency of UV cure is the mobility of the dielectric matrix, determined by the temperature during the UV cure process and the total amount of energy seen by the film prior to the cure process.