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This paper describes the demonstration of a 4-layer wafer stack using a combination of face-to-face and back-to-back, wafer-to-wafer hybrid bonding process. Details of process flow, process characterization and challenges in multi-layer wafer stacking are included in this paper. Wafer warpage of different pattern density is simulated with 3D finite element analysis (FEA) model. Wafer bow results match with low warpage results of simulation. 4-layer wafer was stacked together without separation. The process development and improvement carries out.

Recently, there has been an increasing use of 3D stack integration for high-performance computing applications. Wafer-to-wafer (W2W) hybrid bonding is a key technology in 3D stacking integration process. However, high-density Cu-Cu hybrid bonding interconnections between W2W can give rise to structural defects, such as misalignment and delamination during the bonding process. The testing and characterization of such defects can also be difficult and challenging. This article investigates the W2W alignment accuracy of hybrid bonding process, and studies the defects in the unbonded zone around the Cu pad bonding area.

This paper presents a 3D advanced numerical modelling methodology to simulate the bonding process for fine pitch TSV wafers using wafer to wafer hybrid bonding (W2W-HB) technology from thermo-mechanical viewpoint. Two critical results affecting bonding integrity, i.e. Cu to Cu bonding area and peeling stresses on both Cu to Cu and dielectric material bonding interfaces, are investigated in details. Bonding integrity could be enhanced by reducing the peeling stresses and achieving more Cu to Cu bonding area concurrently. This paper discusses some of common design and process parameters such as dishing value, annealing temperature and dwell duration, TSV pitch and depth with regard to bonding performance. The purpose of this study is to promote a better understanding on W2W-HB so that shorter development time and better bonding integrity could be achieved.

For Wafer to Wafer Hybrid Bonding (W2W-HB) technology, warpage mitigation and precise Cu to Cu bonding are required to ensure a robust bonding integrity. This paper documents a numerical methodology using the Finite Element Analysis (FEA) tool to investigate the impact of various design and process parameters on two-layer wafer to wafer bonding. The risk of poor bonding integrity associated with inappropriate design and process parameters selected are discussed. The attempt of this paper is to promote a better understanding on the design and process parameters which could be used to establish guidelines for W2W-HB processes.