IMPROVED CURRENT-VOLTAGE CHARACTERISTICS OF DOWNSTREAM PLASMA-ENHANCED CHEMICAL-VAPOR-DEPOSITION SINX DEPOSITED AT LOW-TEMPERATURE BY USINGHE AS A DILUTION

We have compared the current-voltage characteristics of silicon nitrid es prepared from the two gas combinations N-2/NH3/SiH4 (N-2-SiNx) and He/NH3/SiH4 (He-SiNx) at temperatures between 100 and 350 degrees C. A downstream plasma enhanced chemical vapor deposition reactor with a n on-ECR microwave plasma source has been used. While N-2-SiNx with reas onable electrical properties requires deposition temperatures of about 350 degrees C, the characteristics of He-SiNx even improve at decreas ing process temperatures. Almost identical current-voltage characteris tics are found for both N-2-SiNx and He-SiNx prepared at 350 degrees C exhibiting an Ohmic behavior at low fields and a Poole-Frenkel (PF) c onduction at high fields. At a deposition temperature of 100 degrees C the He-SiNx with a dielectric strength of 1.13x10(7) V/cm and an onse t field strength of the PF conduction of 6.9x10(6) V/cm is in contrast to the N-2-SiNx with a dielectric strength of 4.3x10(6) V/cm and a PF onset field strength of as low as 2x10(5) V/cm resulting in many orde rs of magnitude higher current flow. In order to find a correlation be tween the dielectric and the structural properties of the silicon nitr ides several analyses are performed. The He-SiNx proves to be superior to the N-2-SiNx concerning refractive index, mass density and buffere d HF etch rate at every deposition temperature and the deterioration w ith decreasing deposition temperature is weaker. All SiNx films are fo und to be nitrogen-rich at a N:Si ratio of 5:3. As expected, the hydro gen content increases with decreasing deposition temperature, being lo wer for the He-SiNx than for the N-2-SiNx. In all layers most of the h ydrogen is bonded to the nitrogen atoms. A simple model is proposed th at explains the difference between the two kinds of low-temperature Si Nx by the microscopic void structure of the material. (C) 1997 America n Vacuum Society.