Modifying residual stress and stress gradient in LPCVD Si3N4 film with ion implantation

This study presents a method for modifying residual stress in low-pressure chemical vapor deposition (LPCVD) Si3N4 films. Utilizing ion implantation technology, the residual stress and stress gradient in the Si3N4 film has been successfully modified with a wide adjustable range. Compressive stress is introduced by the ion implantation and offsets the intrinsic tensile stress in the film. Besides the distribution of the induced stress can modify the stress gradient in the film. An analytical model has been developed to describe the modifications. The dosage and energy of ion implantation can be controlled accurately, and therefore the presented method can modify stress level precisely. With this method, the mean residual stress in the Si3N4 film was adjusted from 1.2 GPa tensile to −0.1 GPa compressive continuously. Moreover, cantilever curling caused by the stress gradient was reduced efficiently, which demonstrates the modification of the stress gradient. The ion implantation slightly increased the film's etch rate in HF and KOH, and degrade the mechanical properties, hardness and elastic modulus, due to damage caused by atomic collision. Thermal annealing was used to recover the damage.