A novel test method for simultaneous measurement of thermal conductivity, CTE, residual stress and Young´s modulus of suspended thin films using a laser doppler vibrometer

This paper presents a novel test method that uses a laser Doppler vibrometer (LDV) for measuring the thermal conductivity (κ) of suspended thin films. Unlike traditional thermal conductivity measurement techniques, the present method also yields the coefficient of thermal expansion (CTE), the Young´s modulus E and the residual stress σ₀ of the film. The method relies on the absorption of the LDV´s laser light by the thin film. The amount of absorbed laser power is first calibrated using a dedicated test structure. After this calibration step, the resonance frequency of a series of clamped-clamped beams is measured using the same LDV. The material properties κ, E, CTE and σ₀ are then extracted from those measurements. The method is illustrated for a 3.5μm-thick poly-SiGe layer; the obtained material properties are κ = 3.0W/(m·K), E = 117GPa, σ₀ = 56MPa and CTE = 4.7ppm/°C.