Development of Nonuniform Residual Stresses during Anodic Bonding

Abstract

Nonuniform residual stresses may develop during anodic bonding due to variations in wafer curvature prior to bonding or due to nanotopography interactions between the bonding surfaces. In this work, we discuss the significance of nonuniform residual stress in anodically bonded wafer pairs and present a method for measuring local stress variations even in cases when the bonded wafers are apparently defect free based on conventional inspection tools. These residual stresses can vary significantly between two different wafers processed identically, depending on the local interactions, but they are present in all standard bonding methodologies. In some instances, these local residual stresses can significantly alter the resulting wafer curvature in apparently defect free substrates. Currently, anodically bonded devices or substrate wafers are considered "defect free" if no large debonds are found after bonding; however the residual stress state of the wafers cannot be determined using the same conventional techniques.

Engineering Stress in Thin Films: An Innovative Pathway Toward 3D Micro and Nanosystems

“…These methods are likely to produce stress in thin films and substrates. While stresses can be unwanted in the case of wafer bonding, [101,102,111,[103][104][105][106][107][108][109][110] surface passivation, [112][113][114][115][116] laser shock peening, [117,118,127,[119][120][121][122][123][124][125][126] and laser machining [128,129] they are deliberately introduced in thin films and/ or substrates to form 3D structures in other fabrication methods. This section only reviews methods which have been used stress as a tool to produce 3D structures.…”

Anisothermal Anodic Bonding: A Method to Control Global Curvature and Residual Stress

“…Residual tensile stresses may be beneficial to keep thin structures from buckling. On the other hand, tensile stresses may provide a driving force for crack initiation and growth, particularly where features are etched into the silicon substrate (8). In this case, introducing a compressive residual stress globally or in the local vicinity of the initiation sites may provide protection for devices with etched features.…”