Plasma Chamber Environment Control to Enhance Bonding Strength for Wafer-to-Wafer Bonding Processing

In recent years, as scale down in the semiconductor faces a technical bottleneck, 3D architectures and other advanced packages have attracted a lot of attention due to advantages of small form factor, heterogeneous packaging and high performance. Among them, low temperature copper to copper (Cu to Cu) hybrid bonding is in the spotlight due to small form factor, reduced power consumption, high performance. Despite current development, additional research is needed on copper dishing control and ensuring minimum bonding strength (B/S) for subsequent processes such as dicing, etch and deposition. In this study, we present a method of enhancing B/S despite low temperature annealing by controlling the chamber’s environment during wafer surface treatment with N2 plasma. To control the environment of plasma chamber, three types of gases were supplied to chamber, before plasma power was applied. The supplied three type of gases were denoted as gas A, B and C; Gas A is a gas that can contribute to hydroxyl radical (∙OH) generation when plasma power was applied. The gas B was mixture gas of gas A and additional gas (N2 and O2). The gas C was control group that could induce only physical reaction with wafer during plasma treatment. When gas A and B were used, the amount of hydroxyl radical in plasma increased which was identified by optical emission spectrometer (OES) during plasma surface treatment. The change during this surface treatment which was verified by time-of-flight secondary ion mass spectrometry (TOF-SIMS), increased the density of the hydroxyl group in the dielectric portion of the wafer surface after the surface treatment. This induced more hydrogen bonds on the surface between dielectric layers, resulting in more covalent bonds after annealing process, which improving B/S.In addition, through scanning acoustic tomography (SAT) and transmission electron microscope (TEM), it was confirmed that wafer to wafer bonding was successful without a void. Also, it was confirmed through an ellipsometer that controlling the plasma chamber environment did not affect the Cu oxide thickness, suggesting the applicability to Cu to Cu hybrid bonding.