Structural, Electrical, and Mechanical Properties Development during Curing of Low-k Hydrogen Silsesquioxane Films

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Abstract
Changes in structure and properties of a commercial low dielectric constant (low-k) silsesquioxane (SSQ) material are examined as a function of curing temperature (375-450°C). Curing results in a chemical reaction in which cage-like (HSiO1.5)(HSiO1.5) SSQ oligomers network via -O-Si-O- linkages. A direct consequence of the chemical and structural evolution is a change in electrical and mechanical properties. A correlation is made between chemical and structural changes on curing (quantified by infrared spectroscopy) and the resulting dielectric constant, film stress, hardness, and modulus. In particular, infrared spectroscopy was used to quantify the increased -O-Si-O- oligomer network formed as a result of increased curing temperature. Film modulus and hardness, determined by depth-sensing indentation, were shown to increase as a result of increased networking. Residual film stress, determined by a curvature measurement technique, was determined to be tensile with increased magnitude on increased network formation. Film dielectric constant determined by capacitance measurements of metal dot structures increased as a result of increased network formation. Capping SSQ films with thin layers of SiNxSiNx was shown to greatly improve resistance to stress-corrosion cracking for all levels of network formation. © 2002 The Electrochemical Society. All rights reserved.