Origin of Voids at the SiO₂/SiO₂ and SiCN/SiCN Bonding Interface Using Positron Annihilation Spectroscopy and Electron Spin Resonance

Abstract

To obtain reliable 3D stacking, a void-free bonding interface should be obtained during wafer-to-wafer direct bonding. Historically, SiO2 is the most studied dielectric layer for direct bonding applications, and it is reported to form voids at the interface. Recently, SiCN has raised as a new candidate for bonding layer. Further understanding of the mechanism behind void formation at the interface would allow to avoid bonding voids on different dielectrics. In this study, the void formation at the bonding interface was studied for a wafer pair of SiO2 and SiCN deposited by plasma enhanced chemical vapor deposition (PECVD). The presence of voids for SiO2 was confirmed after the post-bond anneal (PBA) at 350°C by Scanning Acoustic Microscopy. Alternatively, SiCN deposited by PECVD has demonstrated a void-free interface after post bond annealing. To better understand the mechanism of void formation at the SiO2 bonding interface, we used Positron Annihilation Spectroscopy (PAS) to inspect the atomic-level open spaces and Electron Spin Resonance (ESR) to evaluate the dangling bond formation by N2 plasma activation. By correlating these results with previous results, a model for void formation mechanism at the SiO2 and the absence of for SiCN bonding interface is proposed.

Facilitating 3D Multichip Integration through Low-Temperature Polymer-to-Polymer Bonding

“…Upon breaking, they react with oxygen to form more stable bonds, such as O−H bonds, resulting in the formation of −OH hydroxyl groups. 14 As observed in the results depicted in Figure 2b, the −OH hydroxyl groups in the wavelength range of 3000−4000 cm −1 exhibit the highest increase after O 2 plasma surface treatment, with additional growth observed after curing. This phenomenon is attributed to the higher oxygen concentration during the O 2 plasma treatment due to the presence of O 2 gas, and during curing on the hot plate, the sample is exposed to the external environment, facilitating its reaction with external oxygen and the generation of −OH hydroxyl groups.…”

“…Consequently, Si–C bonds are less stable and are presumed to be the first to break under external energy. Upon breaking, they react with oxygen to form more stable bonds, such as O–H bonds, resulting in the formation of –OH hydroxyl groups . As observed in the results depicted in Figure b, the –OH hydroxyl groups in the wavelength range of 3000–4000 cm –1 exhibit the highest increase after O 2 plasma surface treatment, with additional growth observed after curing.…”

Temporary Direct Bonding by Low Temperature Deposited SiO2 for Chiplet Applications

“…In the case of the thermal SiO 2 samples in the present work, the bonding energy increased as the PBA temperature was increased up to 250 °C, above which it plateaued. Hydrogen bonds between −OH groups and water molecules at the bonding interface play an important role in SiO 2 –SiO 2 direct bonding. − However, these bonds transition to stronger siloxane bonds (Si–O–Si) during annealing. Therefore, it is likely that PBA at 250 °C was sufficient to promote the formation of such bonds in trials with thermal SiO 2 .…”

The High-Adhesion Die-Cleaning Tape with Dual-Functional Groups for Die to Wafer (D2W) Hybrid Bonding

“…Therefore, the dies on the tape frame should be cleaned to nearly no residuals. 24 Besides, the dies may be activated by the wet chemical treatment; the tape should exhibit not only high adhesion to support the dies but also excellent corrosion resistance to endure harsh chemical environments. The investigation of tape adhesion in the D2W process is of critical importance due to the high precision and reliability demanded by D2W technology.…”

“…The dielectric-to-dielectric will be prebonded at room temperature, and this process is very sensitive to the surface defects. Therefore, the dies on the tape frame should be cleaned to nearly no residuals . Besides, the dies may be activated by the wet chemical treatment; the tape should exhibit not only high adhesion to support the dies but also excellent corrosion resistance to endure harsh chemical environments.…”