LAUSR

The coefficient of thermal expansion (α) and biaxial Young's modulus is determined by comparing the differential thermal stress induced in Si-rich silicon nitride thin films deposited on single-crystal Si and sapphire substrates. The amorphous films are deposited in mixtures of dichlorosilane and ammonia, by low pressure chemical vapor deposition, in a temperature range of 1050–1115 K. Temperature-dependent wafer curvature measurements are performed to determine the differential thermal stress, across a temperature range spanning 300–800 K. Observations indicate that both α and the biaxial modulus decrease as the silicon content in the films increases. The trend of reduction in α is consistent with the relative α values for the limiting-case compositions of cubic-Si3N4 and amorphous Si. The decrease in α is attributed to a reduction in anharmonicity associated with Si–Si bonds relative to Si–N bonds. The biaxial modulus is observed to be proportional to the inverse cube root of the amorphous Si volume fra...