Abstract: Amorphous silicon nitride (Si₃N₄) film has outstanding electret properties and it is compatible with the micromachining technology, so it can be used in miniature microphone. But big tensile stress of Si₃N₄ film limits its application. In this paper, the improvement of mechanical property of Si₃N₄ film by boron ion implantation and its influence on the electret properties of the film is discussed. The results show that the boron ion plantation reduces the tensile stress of film effectively,but it also decreases the electret properties of the film. The capability of Si₃N₄ electret film against environmental conditions can be increased by chemistrical surface modification. Therefore, Si₃N₄ film may be used as a vibrating film. After the stability of charge storage is improved,it may be used as electret material for miniature microphones.

Key words: silicon nitride film, electret, boron ion implantation, internal stress