Wafer-Level Simultaneous Film Thickness and Thermal Conductivity Characterizations for Bonded Si-on-Si

Abstract

Wafer bonding and thinning processes in three-dimensional Si−Si bonding technology may cause the nonuniform thickness of the Si thin film. This in turn will lead to nonuniform thermal conductivity (TC) as phonon boundary scattering dominates TC at the submicron scale. The simultaneous scanning thickness and TC of the Si thin film are challenging. In this paper, we experimentally investigate the transient thermoreflectance (TTR) technique's capability and effectiveness of simultaneously measuring the TC and thickness of the Si thin film for bonded Si−Si samples. Uniform samples, combined with scanning electron microscopy and phononbased thermal conductivity models, were used to verify the technique's capability. A small deviation (∼10%) was found between TTR and SEM measurements for a film thickness less than 1 μm. From the Monte Carlo error analysis, we obtained a fitting error of ∼3% for the film thickness and ∼10−25% for TC. The fitting uncertainty was then elaborated through sensitivity analysis. We also developed a wafer-level highthroughput thickness scanning system, achieved by a high-precision automatic scanning stage combined with the deep learningbased fast-fitting algorithm. We performed the scanning measurements on the sample with a nonuniform thickness, observing local inhomogeneity, which is difficult to detect with the general single-point method. The scanning area is 16 mm × 6 mm and the spatial resolution is ∼60 μm. The TTR technique enables a platform to characterize the structure and thermal properties of advanced Si−Si bonded materials.