Low temperature fabrication of amorphous silicon thin film transistors by dc reactive magnetron sputtering

We deposit hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon nitride (a-SiNx:H) films using de reactive magnetron sputtering at 125 and 230 degrees C substrate temperatures, We characterize the structural properties using infrared absorption, thermal hydrogen evolution, and refractive index measurements and evaluate the electrical quality using capacitance-voltage and leakage current measurements, Nitride layers deposited at both temperatures have dominant N-H bonding with hydrogen concentration approximately 10(22)/cm(3). Metal-insulator-semiconductor devices have been fabricatcd on c-Si and show electrical leakage of < 5 x 10(-8) A/cm(2) at 3 MV/cm field, flat band voltage magnitude < 1 V, and hysteresis < 2 V. Low temperature a-Si:H films show monohydride dominant bonding, The photo- to dark conductivity ratio is 5 x 10(5) for films deposited at 125 degrees C. Inverted staggered thin film transistors have been fabricated with the optimized layers, Thin film transistors deposited at 230 degrees C have a field effect mobility of 0.8 cm(2)/V s, an I-on/I-off ratio of 5 x 10(5), a subthreshold slope of 1.2 V/decade, and a threshold voltage of 4 V: those deposited at 125 degrees C have a field effect mobility of 0.3 cm(2)/V s, an I-on/I-off ratio of 5 x 10(5), and a threshold voltage of 3 V. (C) 1997 American Vacuum Society.