(Invited, Digital Presentation) Probing Triaxial Stress States Using Curvature-Based Methodology for Enabling Highly Robust and Reliable Integrated 3D Systems-on-Package in Advanced Microelectronics Industries
Authors: Budiman Arief , TIppabhotla Sasi 
Published: November 2022

With the nascent of the systems-on-package in advanced 3D microelectronics, mechanical stress states in the system get much more complicated than in the past. Stress states are increasingly triaxial (as opposed to mostly biaxial stress states in the planar semiconductor devices), and with that, the roles of shear stresses in causing relatively new and unique mechanical damages and failures in the 3D stacks of chips and devices (memory, logic, sensors, actuators, data storage, etc.) cannot be undermined. The difficult stress management in a Through-Silicon Via (TSV) as the vertical interconnection between chips on stack has been an early indication of what more to come to the emerging, advanced microelectronics industries in the near, immediate future. Not only the mechanical damages that come into the picture, but also the delicate interrelation between the mechanical straining of the silicon and the corresponding electronic mobility affecting the very working of the semiconductor devices. The methods of stress determination used in the semiconductor industries so far (X-ray Diffraction, Raman Spectroscopy, etc.) have mostly worked under the assumptions of biaxial stress states which were mostly true in the planar semiconductor chip design. Such assumptions may no longer hold true for enabling highly robust and reliable integrated 3D Systems-on-Package in today’s and tomorrow’s microelectronics industries. In addition, once the 3D stacks of devices are fully integrated, it becomes next to impossible to manage the highly convoluted stress states originating from many silicon devices with mostly surface-based Raman techniques and low-penetration depth of conventional laboratory XRD. In this study, we propose to use the curvature-based approaches that would allow determination of the complete 3D stress states in every level of the stacking of silicon devices, and thus by following the stress state evolution during the stacking, the individual and overall resultant of the stress states in the highly integrated 3D systems may be analyzed. The approach originated from our previous work – on TSV for semiconductor chips as well as on thin silicon solar cells for the emerging photovoltaics industry – using synchrotron-based X-ray microdiffraction to determine the origin and evolution of the stress states in the devices (during thermal cycling or subsequent manufacturing steps). However, during those investigations, we realized that the diffraction science is not necessarily needed for highly accurate stress state determination, in fact, just the detection of the local curvature of the surface of the monocrystalline silicon in the devices would suffice to provide for equally highly accurate stress state determination. We have demonstrated the efficacy of this approach since in our work in silicon-based photovoltaics (Tippabhotla et al. Progress in Photovoltaics 2017). As long as we have the silicon surface from each level of devices (individually and after the stacking), a laser-based system could detect the change in local curvature in high spatial resolution and hence could provide with highly accurate stress state determination. No synchrotron radiation would be needed.