Thermomechanical Characterization of Polymer Thin Films. Application for the Conception and the Manufacturing of a 3D Interposer

Abstract

Over the past few years, polymers have appeared almost everywhere in microelectronics. Their conditions of processing and the high variability of their mechanical properties require the use of materials such as glue, passive layer, underfill etc. The mechanical behavior of polymers is characterized by viscoelasticity and so a dependence of the temperature and the frequency of loading. As a result, when we consider the mechanical properties of devices containing polymers, we need to consider the thermo-evolution of the Young modulus (E) and the CTE ($\alpha$) as their properties are not constants. For measuring the evolution of thin films thermomechanical properties, we used a metrology tool called kSAMOS ThermalScan. k-Space Associates Inc developed this thin-film metrology solution composed of an optical module producing and measuring an array of parallel laser beams, a high resolution scanning stage, a rapid thermal processing (RTP) chamber and several accessorial gas control modules. In this work we will present the measurement capabilities of this tool and the results obtained in the case of evolving materials. We will integrate the thermomechanical properties of films in our analytical model for the prediction of the stress distribution “$\text{Sigmap}\varepsilon\text{ps}$”. By means of this model, we consider the whole thermal history of the multilayer system as well as processing conditions which are taken into account for each layer. For the manufacturing of a 3D Silicon Interposer, designers need to stack integrated circuits and connect them vertically. To obtain a functional devise, stresses and strains must be controlled during all the steps of manufacturing. For example, the cutting and the thinning of the substrate increases the strain leading to possible connection problems and consequently difficulties with alignment during assemblies made at high temperatures. Coupling experimental measurements and analytical model allows us to control the bow and the stress distribution in this multi-layered structure.