This study investigates the mechanical and physical properties of low-temperature plasma-enhanced chemical-vapor-deposited silicon nitride thin films, with particular respect to the effect of deposition temperature. The mechanical properties of the films were evaluated by both nanoindentation and microcantilever beam-bending techniques. The cantilever beam specimens were fabricated from silicon nitride thin films deposited on (100) silicon wafer by bulk micromachining. The density of the films was determined from quartz crystal microbalance measurements, as well as from the resonant modes of the cantilever beams, which were mechanically excited using an atomic force microscope. It was found that both the Young’s modulus and density of the films were significantly reduced with decreasing deposition temperature. The decrease in Young’s modulus is attributed to the decreasing material density. The decrease in density with decreasing deposition temperature is believed to be due to the slower diffusion rates of the deposited species, which retarded the densification of the film during the deposition process.

This study investigated the effect of oxidation on the chemical bonding structures of silicon nitride thin films synthesized by a low-temperature plasma-enhanced chemical vapor deposition ͑PECVD͒ method. These films were heat treated to different temperatures up to 1373 K. The bonding structures were studied by means of x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy. It was found that the amorphous PECVD SiN x films were subjected to oxidation in air at elevated temperatures. The oxidation caused the formation of crystalline silicon dioxide within the matrix of amorphous silicon nitride, conforming to the "random mixing" model. The crystalline silicon dioxide formed is believed to be stoichiometric SiO 2 , whereas the remaining matrix is believed to be a nonstoichiometric silicon oxynitride with a structure conforming to the "random bonding" model.

Thin-film MEMS are essential to realization of intelligent integrated microsystems. Of critical importance in such microsystems is the determination and control of mechanical properties in the thin films used for construction of the MEMS, which can be the decisive factor in the realization and subsequent performance, reliability, and long-term stability of the system. In future microsystems the need to fabricate MEMS on temperature sensitive, non-standard substrates will be of particular importance. In this work, mechanical properties of low-temperature (50−300°C) plasmaenhanced chemical vapour deposited silicon nitride thin films have been investigated using depth sensing indentation. Young's modulus, E, and hardness, H, values obtained for the examined film/substrate bilayers were found to vary asymptotically from the thin film properties for shallow indents to the substrate properties for deep indents. A simple empirical formulation is shown to relate E and H obtained for the film/substrate bilayers to corresponding material properties of the constituent materials via a power-law relation. The temperature of the deposition process was found to strongly influence the thin film mechanical properties. Values of E ~ 150−160GPa and H ~ 14−15GPa were observed for depositions above 225°C. Decreasing the deposition temperature initially caused a moderate and linear decrease in E and H parameters, which was followed by an abrupt decrease in E and H once the deposition temperature was lowered below 100°C, such that E ~ 50GPa and H ~ 3.5GPa at a deposition temperature of 50°C.

In this paper, the Poisson's ratio ν of lowtemperature plasma-enhanced chemical vapor deposited silicon nitride (SiN x H y ) thin films has been determined by a modified double-membrane bulge test. This test method utilizes a square membrane and a large-aspect-ratio rectangular membrane that is fabricated alongside from the same thin film. The Poisson's ratio is determined from the ratio of the bulge deflections of the two membranes under an applied pressure. The method is suitable for determining ν of either stress-free thin films or those containing low tensile residual stresses. Poisson's ratio values of 0.23 ± 0.02 and 0.25 ± 0.01 were measured for SiN x H y films that were deposited at 125 • C and 205 • C, respectively.[ 2006-0065]Index Terms-Amorphous materials, dielectric films, plasma chemical vapor deposition (CVD), thin films.

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