| As semiconductor device technology evolves, the industry continues to place more stringent limits on the acceptable physical and electrical properties of materials used to make transistors. Of these materials, the gate dielectric is one of the most critical to thin film and CMOS transistor performance. We have investigated very low temperature (<150°C) plasma enhanced chemical vapor deposited hydrogenated silicon nitride, SiNxH y, as the gate dielectric in thin film transistors used in liquid crystal displays. Traditionally deposited at 300–400°C, the development of good quality <150°C silicon nitride thin films would allow the manufacture of these displays on rugged, flexible, transparent plastics. Silane and nitrogen are used as the reactants while helium is used as a diluent. The addition of helium enabled the control of the film stoichiometry so that similar films could be made at low temperatures as at higher temperatures. The affect of He on the plasma chemistry was monitored using optical emission spectroscopy and mass spectrometry and a plasma kinetic model was developed to predict film property trends. Complementary metal oxide semiconductor, CMOS, transistors, used in logic chips, are made with thermally grown SiO2 as the gate dielectric. The dimensions of these devices are continuously scaled down to make chips faster and cheaper. Within 10 years the thickness of the SiO 2 (k = 4) gate dielectric is expected to decrease from 30 Å to less then 15 Å. At this thickness the tunneling of electrons will be too excessive for transistor operation. For continued transistor dimension scaling, an alternate high dielectric constant insulator is necessary. We have deposited Ta2O5 and Al2O3 (k = 25 and 12 respectively) thin films using metal organic chemical vapor deposition from various precursors and have characterized them using transmission infra-red spectroscopy and current vs. voltage/capacitance vs. voltage electrical measurements on metal/oxide/semiconductor (MOS) devices. The feasibility of the use of these materials in future technology will be discussed. |
