Micromechanical characterization of chemically vapor deposited ceramic films
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In this study, nanoindentation is used to determine Young's modulus of chemically vapor deposited films consisting of silicon carbide, silicon nitride, boron carbide, boron nitride, and silicon dioxide. Diethylsilane and ditertiarybutylsilane were used as precursors in the synthesis of the silicon-based material, while triethylamine borane complex was used for the boron-based material. The modulus of these films was observed to be dependent on the processing conditions and resulting composition of the deposits. For the silicon carbide, silicon nitride, boron carbide, and boron nitride films, the carbon content in the films was observed to increase significantly with higher deposition temperatures, resulting in a corresponding decrease in values of Young's modulus. The composition of the silicon dioxide films was near stoichiometry over the investigated deposition temperature range (375-475 °C) with correspondingly small variations in the micromechanical properties. Subsequent annealing of these oxide films resulted in a significant increase in the values of Young's modulus due to hydrogen and moisture removal.
I. INTRODUCTION Dielectric thin films consisting of silicon dioxide and silicon nitride are widely used in a wide range of microelectronic applications that include insulation, isolation, and passivation of devices. Silicon carbide, boron carbide, and boron nitride films are being considered as underlayers for such dielectrics in chemical mechanical polishing processes used in the planarization of integrated circuits. Although extensive information is available on the electrical, optical, and chemical properties of carbides, nitrides, and oxides,1'2 little if any information is available on the mechanical properties of such films. Ceramic thin films are typically synthesized by chemical vapor deposition (CVD) because of the superior step coverage, uniformity, and quality of the resulting deposits. CVD processes used in the synthesis of siliconbased materials typically use silane or chlorosilane as a silicon source. While silane is known to be pyrophoric and explosive, the by-products of the chlorosilanes are corrosive and represent a reliability threat when incorporated in the deposits. Diborane and boron trichloride used in the synthesis of boron carbide and boron nitride films have similar shortcomings. Although the use of organosilanes and amino-borane complexes resolves the safety and film contamination issues, the effect of carbon incorporation on film properties is not well documented and warrants further investigation.3"5 The recent development of a depth-sensing indentation tester (Nanoindenter) has provided the means for determining the micromechanical properties of thin 2072
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J. Mater. Res., Vol. 9, No. 8, Aug 1994
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films. Hardness can be determined from the plastic behavior during the initial indent, and Young's modulus can be calculated from the elastic behavior during subsequent unloading segments.6'7 The applicability of this technique to
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