STRUCTURAL-PROPERTIES OF N-RICH A-SI-N-H FILMS WITH A LOW ELECTRON-TRAPPING RATE

Hydrogenated amorphous silicon nitride (a-SiNx:H) films with a high ni trogen content were prepared by RF plasma-enhanced chemical vapour dep osition from a mixture of SiH4 and NH3 at 300 degrees C. The influence of the main operating variables on the quality of the material was ex amined. Characteristics and properties of the films were investigated using optical absorption, infrared spectroscopy, x-ray photo-electron spectroscopy and capacitance-voltage measurements. From infrared trans mission and reflection measurements, it was found most of the IR peaks obtained by direct transmission in the range 850-1040 cm(-1), which h ave often been mentioned in the literature, are caused not by absorpti on but rather by a strong reflection due to the Reststrahlen effect. I R studies carried out with polarized light revealed an anisotropic bea m-sample interaction probably due to short-range phonon vibration mode s: a parallel 'LO mode' (1040-1070 cm(-1)), a parallel and perpendicul ar 'TO mode' (840 cm(-1)). For sufficiently high values of the N/Si ra tio, a decreasing percentage of SiH4 or an increasing RF power leads t o a decrease in the trapped charge density which should be related sim ultaneously to an increase in the N/Si ratio and a decrease in the Si- H bond density in the deposited films. It is suggested that, under our experimental conditions, the charged particle bombardment due to the RF discharge does not play an important role in the charge trapping an d that the trapping rate seems to be controlled only by the nature of the traps.