Deposition and DC electrical characterisation of rf magnetron sputtered silicon nitride thin films

Silicon nitride (Si3N4) is an important insulator, frequently used in VLSI technology and for encapsulation. Conventionally it is prepared by low pressure and plasma-enhanced chemical vapour deposition, but may also be successfully deposited by RF sputtering. In the present work the sputtering process was characterised, together with some measurements on the high-field DC electrical properties in sandwich samples with Au electrodes. Films were Ar-sputtered using a Si3N4 sputtering target at gas pressures up to 2.12 Pa and RF discharge powers of 60–200 W. The deposition rate R was in the range 0.03–0.19 nm s− 1 and was directly proportional to the discharge power and varied linearly with the pressure. Au electrodes formed sandwich structures with thicknesses of 50 nm–1 μm. Conductivity was essentially ohmic below 300 nm, while for the thicker films space-charge limited conductivity, dominated by an exponential distribution of traps, was observed. A mobility value of μ = 2.89 × 10− 6 m2 V− 1 s− 1 was derived from temperature measurements, and further analysis of the J–V data indicated a thermally generated electron concentration of 3.23 × 1019 m− 3 and a trap concentration of 1.57 × 1024 m− 3. It was concluded that this method is suitable for the deposition of thin films, which have similar electrical properties to those prepared by chemical vapour deposition methods.