MICROSTRUCTURE AND PROPERTIES OF SILICON-NITRIDE THIN-FILMS DEPOSITEDBY REACTIVE BIAS MAGNETRON SPUTTERING

Silicon nitride (SiNx) thin films have been deposited by radio frequen cy (rf) magnetron sputtering of a silicon target in reactive nitrogen- argon atmospheres without intentional substrate heating. The influence of negative substrate bias V-s on the microstructural, compositional, chemical, mechanical, and optical properties of the SiNx films was sy stematically investigated. An extensive analysis of the films was carr ied out using ellipsometry, transmission electron microscopy (TEM), at omic force microscopy (AFM), Rutherford backscattering spectrometry, s econdary ion mass spectrometry (SIMS), Fourier transform infrared (FTI R) spectroscopy, ultraviolet-visible spectroscopy, stress and chemical etch rate measurements. TEM and AFM studies revealed that films produ ced at low bias voltages had a porous columnar structure containing la rge void, typical of zone 1, but that films produced at higher bias vo ltages had relatively smooth surfaces with a highly condensed structur e, typical of zone T. Both FTIR and SIMS analyses showed that an extre mely small amount of hydrogen was contained in the SiNx films deposite d at V-s over -75 V, resulting from the film densification by energeti c bombardment. It was also found that the amount of argon incorporated in the film increased with increasing bias voltage, whereas the oxyge n content decreased. As the substrate bias voltage was increased, the mechanical internal stress in the SiNx films became increasingly compr essive and saturated at a value of about 1.8x10(10) dyne/cm(2) at high er bias voltages. This was found to be well correlated with the increa sed argon content and the film densification. The lowest etch rate in buffered hydrofluoric acid, approximately 72 Angstrom/min, was observe d with the application of a substrate bias of -50 V. A further reducti on in etch rate could be achieved by annealing at 900 degrees C for 1 h in a N-2 ambient. The optical band gap of the SiNx films varied from 4.85 to 4.39 eV depending on the bias voltage. (C) 1998 American Inst itute of Physics. [S0021-8979(98)00810-X].