Multi‐Scale Mechanical Probing Techniques To Investigate The Stability Of BEOL Layer Stacks With Sub‐100 nm Structures

The stress levels induced by chip-package interaction (CPI) impose an increased risk of mechanical failure on advanced backend-of-line (BEOL) layer stacks in microelectronic circuits if they contain fragile ultralow-k (ULK) interlayer dielectric (ILD) films. On the one hand, multilevel finite element modeling is used to assess the potential risk at an early stage of the development of new microelectronic products. On the other hand, the theoretical models need as accurate as possible materials parameters as an input to provide realistic results. Moreover, it is highly desirable to have multi-scale experimental probes available which can provide complementary data to support the modeling calculations. The present paper provides an overview about various mechanical probing techniques which operate on the scale of less than 100nm up to more than 100 mu m. In this way, typical feature sizes are covered which occur from the package level via solder bumps or copper pillars down to small Cu/ULK interconnect structures. The experimental approaches are based on nanoindentation with lateral force detection and in-situ scanning probe microscopy (SPM) imaging capabilities, and they include a novel technique named bump assisted BEOL stability indentation (BABSI) test. Especially, the interrelation between small-scale mechanical properties of ULK dielectric films and stresses acting on larger scales are quantitatively assessed by means of the experimental approaches described here.