A Ge thin film deposited by chemical vapor deposition (CVD) was
used to obtain a uniform bonding between Au and Ge films for applications of
wafer level packages (WLPs). This Ge CVD thin film showed selective growth on Au
and Cu metals when the substrate has both metal and oxide. A one-step and
two-step Ge deposition followed by eutectic bonding method was employed to bond
the wafers. The samples were characterized by X-ray diffraction, field emission
scanning electron microscopy equipped with an energy dispersive spectroscopy
(FESEM-EDS), atomic force microscopy, high resolution Field emission
transmission electron microscopy, IR inspection tool and secondary ion mass
spectroscopy (SIMS). According to the IR inspection results, the two-step Ge
deposited sample showed more uniform film compared to one-step deposition after
eutectic bonding. Moreover, an improved bonding quality was obtained from the
two-step process. Based on FESEM observations, a uniform and crater-free
interface was detected between the bonded 4-inch wafers, in which the presence
of Ge beside Au and Si was confirmed by EDS. SIMS profiles proved the formation
of a thin Au-Ge interlayer at the bonded interface, which enhanced the bonding
conditions.
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