Hydrophilically activated direct wafer bonding is a technique for gluelessly attaching oxide-coated wafers together. This ability is a vital step in the construction of many microelectronic and microelectromechanical (MEMS) devices. In particular this technique is widely used in the production of 3d interconnected devices due to the lack of interlayer. © 2014 The Electrochemical Society. [DOI: 10.1149/2.007403jss] All rights reserved.Manuscript submitted June 5, 2013; revised manuscript received December 9, 2013. Published February 3, 2014 This review covers the key papers relating to the theory, techniques and quantification of hydrophilically activated silicon wafer bonding. This begins with a review of the history and development of the art. Bond strength characterization is then reviewed followed first by models of physical deformation and then by plasma and radical activation techniques.In the interests of clarity and succinctness this review is not an attempt to exhaustively catalog all direct bonding wafer literature. Excluded are hydrophobic and UHV bonding, and the many papers applying bonding techniques to differing combinations of wafer materials. This paper concludes with a summery of the state of the art of direct wafer bonding and a summation of the current wafer-bonding model derived from the papers reviewed. History and Establishment of the Art

Infra-red video sequences were taken of directly bonded silicon wafer pairs undergoing the razor blade crack length test for bond strength in a specially designed jig. A series of tests were carried out under controlled atmospheres of nitrogen at various relative humidities. Analysis of the video images showed that the crack continues to propagate rapidly for several minutes after the blade has stopped moving, and that the presence of moisture has a strong positive influence on the rate of crack propagation under static loading. A new Maszara protcol is suggested based on modelling crack growth using our experimentally derived constants.

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Using an improved Maszara test we have shown that post anneal bond strength of radical activated wafers and plasma activated wafers varies by up to 50% across the entire wafer surface. We have shown that this is independent of the wafer pre-treatment, the microscale surface geometry and any discontinuities visible in the post anneal infra-red transmission image.

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