THE STRUCTURAL AND OPTICAL-PROPERTIES OF A-SINXH PREPARED BY PLASMA-ENHANCED CHEMICAL-VAPOR DEPOSITION

Hydrogenated amorphous silicon nitride (a-SiNx:H) films have been prepared by plasma-enchanced chemical-vapor deposition with a mixture of SiH4 and NH3 at a substrate temperature of 250 and 300-degrees-C. The properties of these films have been investigated using x-ray diffraction, infrared absorption, photoluminescence, and electron probe microanalysis. From the x-ray-diffraction measurement, it is found that the short-range order of a-SiNx:H with a basic unit of 4.31 angstrom appears when the nitrogen-to-silicon ratio in the film exceeds 0.75 at a substrate temperature of 300-degrees-C. In the infrared-absorption measurement, the sample was annealed repeatedly at various temperatures (300-800-degrees-C) to identify the molecular unit responsible for each absorption peak. It is found that part of the infrared-absorption bands between 870 and 1100 cm-1 are caused not by the absorption but by the reflection of infrared radiation due to reststrahlen effect. The absorption peak at 840 cm-1 is assigned to the isolated N in the Si-host network, whereas the peak at 885 cm-1 is assigned to a local bonding arrangement involving a terminal N-H group attached to the amorphous Si network, Si-NH-Si. The transverse optical phonon of crystalline Si3N4 is found to peak at 870 cm-1. Two peaks are observed in photoluminescence experiments when the mole fraction of ammonia in ps phase is smaller than 0.8 indicating the inhomogeneity of the a-SiNx:H films. The higher-energy peak is visible in the red.