Influence of roughness on mechanical strength of direct bonded silica and Zerodur® glasses

Abstract

Influence of roughness on mechanical strength of direct bonded silica and Zerodur® glasses Direct bonding is of particular interest for optical system manufacturing for spatial application. This process requires very precise physical and chemical preparations of surface, especially roughness controls. Thus, this paper proposes to understand and discuss the roughness influence on mechanical strength and bonding energy of an elementary mechanical structure after a room temperature bonding and an annealing at optimal temperature. First, surfaces are characterised and roughness is measured. At the same time, the performances of fused silica and Zerodur® glasses are compared. Then interface properties are measured using double shear and wedge tests. At the end of the paper, a discussion, based on literature models, is proposed to explain the existence of an optimum of roughness put in evidence in experimental results.

A cohesive zone model for fracture initiation and propagation of fused silica direct bonding interface

“…In order to improve the model, it could be possible to take into account more precisely the nanometric characteristic size of the direct bonding phenomenon and to insure a better change scale scheme in order to avoid a loss of information such as roughness [16], defects, nature of bonds. As prospects, multiscale methods could be developed and compared with experiments.…”

“…The critical separation distance δ 0 is chosen equal to 0.2 nm based on atomistic considerations (the characteristic distance of hydrogen bond) as in our previous works [16] and highlighted by Kubair in molecular dynamics simulations [24]. The both parameters G c and σ max are determined with the wedge test and the FIT test as described in previous section.…”

“…In order to comply with these standards mechanical experiments: double shear tests, cleavage tests and wedge tests were performed in previous investigations in our laboratory to investigate the influence on the interface mechanical strength of some process parameters, such as annealing time and temperature [15], roughness [16]. Now, there is a need to develop some numerical predictive tools to determine mechanical strength of spatial complex assemblies as slicer or cube corner.…”

Effect of Combined Hydrophilic Activation on Interface Characteristics of Si/Si Wafer Direct Bonding

“…Another important factor in plasma activation wafer bonding is the hydrophily of the wafer surface. The bonding process is the result of the combined influence of micro defects and adsorbed water (H 2 O) molecules on the substrate surface [22,23]. The effect of plasma activation parameters on the hydrophily of wafer surface has been widely investigated.…”

The Flexible Initiation Test (FIT): A new experimental test to characterize fracture initiation in mode I at the free edge of bonded assemblies

“…The mechanical strength of direct bonded interfaces depends on the interface defects and on the nature of the bonds involved as described Cocheteau et al [16,17]. Indeed, Liao et al [18] explained that room temperature bonding needs flatness and roughness perfectly controlled, and no particles contaminations on surfaces.…”