This paper presents the results of surface energy measurements performed in situ during annealing of silicon wafers. The method allows conclusions to be drawn about the progress of silanol condensation while surface energy increases. The effects of wafer conditioning by atmospheric pressure plasmas, chemical post-treatments after plasma exposure but before bonding, and annealing temperatures on silanol condensation is investigated. Using nitrogen or nitrogen/oxygen gas mixtures for plasma activation, higher fracture surface energies γ are obtained at room temperature compared with oxygen plasma activation. Upon annealing, an increase in surface energies starts below
100°C
. Possible reasons responsible for the effects of nitrogen plasma treatment and post-treatments with ammonia are discussed. Upward bent
γ(t)
curves are obtained during annealing at
200°C
, independently of the type of wafer preconditioning, in contrast with the implications of existing chemical-kinetic models of the bonding process. Aside from a self-enhancement of the process due to facilitated water removal from the interface, the hypothesis of the nucleation and growth of covalently bonded microareas is able to explain the observed behavior qualitatively.
An experimental study of low-temperature bonding of plasma-treated borosilicate glass and fused silica wafers as well as silicon substrates carrying thin films of silicon dioxide, silicon nitride, silicon oxynitride, and indium tin oxide, respectively, is reported. Plasma process parameters were optimized in order to maximize bond energy. Surface energy measurements were carried out in situ during annealing, helping to understand the kinetics of the bonding process. Power spectral density measurements on debonded wafers support the idea of the strong impact of micro-contact formation on bonding kinetics.
Differences in surface tensions of individual fluid phases in multiphase mixtures can be utilized to achieve a phase separation. A new fabrication method for a microfluidic phase separator combines micropatterning methods with atmospheric‐pressure plasma‐based surface coating, allowing an inexpensive manufacturing and, if required upscaling by numbering‐up. Of particular importance for the functioning of the novel Y‐shaped separator are coatings with different surface free energies on opposite surfaces in the divergence zone of the main channel and in the two diverting channels. This paper presents the principle of the method and first results regarding the coatings and applications.
Dynamic measurements of interfacial fracture surface energies J have been carried out during the annealing of pairs of silicon, fused silica and borosilicate glass wafers, resp. Pronounced maxima of the resulting J(t) curves could be detected in several cases, especially for plasma activated wafer pairs. In the present article the different phases of the bonding process are discussed and an interpretation is given for the formation of the J(t) maxima.Moreover, influences of plasma activation at atmospheric pressure and at low pressure on the increase in surface energy during annealing are compared. Based on AFM roughness measurements, power spectral densities were determined for two debonded wafer pairs and the influence of the bond strength is discussed here.
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