Multi-scale Modeling Approach to Assess and Mitigate Wafer Warpage in 3-D NAND Fabrication

Mechanical stresses introduced at various processing steps, combined with large stack thicknesses result in high wafer warpage during 3-D NAND fabrication. We demonstrate a local (device-level) to global (wafer-level) scale finite-element modeling approach that can be used to evaluate wafer warpage with scaling trends and offer potential mitigation strategies. It is shown that the anisotropy in local stresses and asymmetry in warpage are initiated after etching the slits and amplified by wordline metal deposition. Increasing number of layers is shown to significantly increase the magnitude and asymmetry of the warpage. Decreasing layer thicknesses and use of low-stress wordline metal such as Ruthenium and adjusting filler stresses can help reducing wafer-warpage related problems.