Thermo-mechanical characterization and modeling of TSV annealing behavior

Abstract

This paper focuses on the characterization and Finite Element (FE) simulation of thermo-mechanical loads in Through Silicon Vias (TSVs), which emerge due to the annealing process after electro chemical deposition (ECD) of copper. For this purpose a FE-model has been implemented, which calculates the stress state of TSV structures after annealing. To validate the model, measurements using -Raman spectroscopy (RS) were carried out. Results from Finite Element Modeling (FEM) were converted into their corresponding Raman-Shifts to make it comparable to RS measurements. Additionally warpage and copper protrusion were measured to receive a complete picture of the occurring mechanisms and boundary conditions

Effect of annealing after copper plating on the pumping behavior of through silicon vias

“…Annealing temperature 420 is used in IMEC's TSV process flow. [10] 2) Removing overburden before annealing by CMP: according to P. Saettler's research [11], the stress inside TSV release sufficiently without overburden. However we do not want to do a CMP before annealing because of the high cost of CMP.…”

μ-Raman spectroscopy and FE-modeling for TSV-Stress-characterization

“…Additionally, a transformation of the equation into the FE model coordinate system was necessary. [8] and [14] described the procedures in detail. In order to describe the influence of laser intensity on the substrate penetration depth Takahashi assumes exponential behavior in the form of e 2Áa Si ðkÞÁz [19].…”

“…Out of measured peak shifts a direct calculation of concrete stress values is only possible for uni-and biaxial stress states [7]. To overcome these restrictions FE simulations can be used to deliver additional information about the stress distribution [5,[8][9][10][11]. Then, extracted stress values can be converted into their corresponding peak shift, which enables a bilateral validation.…”

Bath chemistry and copper overburden as influencing factors of the TSV annealing

“…To prevent this effect to occur an additional annealing is conducted, which stabilizes the crystal structure of Cu. But this approach has also drawbacks since mechanical stresses are induced due to the CTE mismatches of the materials (Cu-SiO2-Si) [4,5]. This results in an increased risk for the occurrence of delaminations as well as increased wafer warpage.…”

“…Generally, Cu protrusion is found to be a stress relieving mechanism, which can be traced back to the Cu annealing behavior. [3][4][5][6] Based on this knowledge our current work focuses on further influencing factors. For example the improvement of bath chemistry compositions for the electro chemical deposition (ECD) of Cu is an important topic in research.…”