Effects of annealing in silicon nitride film deposited by inductively coupled plasma CVD on GaN

摘要

Silicon nitride (SiN_x) films on GaN were deposited, using the inductively coupled plasma chemical vapor deposition (ICPCVD) method with different radio-frequency chuck power (RF power). After deposition, all the films were annealed at 750°C in N_2, and some pins and bubbles were observed on the surface of some films, but this phenomenon was not observed on the films which were deposited with RF power=0W, as well as films deposited by a two-step-deposition method, which was consisted of setting RF power=0W at the beginning, and setting RF power=2W after that. To study the mechanism of origin of these pins and bubbles, Atomic force microscopy(AFM) was performed to study surface morphology and measure the height of the pins and bubbles, it was found that the height of bubbles was about 300nm, and the depth of pins was about 300nm, which were almost the same as the film thickness. It was showed that the pins and bubbles were originated from gas escaping from the inner films after high-temperature annealing. X-ray photoelectron spectra(XPS) was used to characterize the chemical composition of the films before and after annealing, independently. It was found that, on GaN-SiN_x interface and SiN_x film surface, the N element content decreased a lot after annealing, but N content remained almost the same in those films with RF power=0W. which indicated that reducing of N content was closely related with those pins and bubbles. RF power increased the plasma energy and caused GaN surface damage. The ion bombardment broke some N-Si bonds and N-Ga bonds, as a result some N reactants didn't perform as Si-N bond, but performed in other bonds such as N-H bonds or N-N bonds, and a high-temperature annealing process would cause NH_3 or N_2 escape from the film. The pins were voids which resulted from the film broken by the gas, and the bubbles came from bulge resulted from gas escape.