Low-Temperature Oxide Wafer Bonding for 3-D Integration: Chemistry of Bulk Oxide Matters

Abstract

The effect of bulk chemistry of deposited oxide materials on the eventual wafer bonding energy was fundamentally studied. Although low-temperature silicon oxide (LTO) and tetraethyl orthosilicate (TEOS) exhibited the same bulk density, and nitrogen plasma generated a higher degree of surface activation for TEOS than LTO, using LTO as the bonding oxide resulted in a much higher bonding energy than TEOS. This was attributed to the relatively high percentage of hydrogen-bonded silanol groups in LTO, which pointed to the existence of fine defect areas in LTO that would better accommodate the water molecules generated later by the interfacial condensation reactions. A pre-bonding baking step was found favorable for LTO wafer bonding. Index Terms-3-D integration, wafer bonding.

Nanosecond Laser Irradiation for Interface Bonding Characterization

“…a byproduct of the oxidation reaction (6). On the other hand, water also enhances the bonding energy, as previously described in published mechanisms (5,7).…”

“…The square markers represent the series with γ=2.5 J/m 2 , while the round markers represent the series with γ=0.95 J/m 2 . Additionally, on the same graph, we plot equation [7], which depicts the variation of h as a function of R for a given γ.…”

Prototype of multi-stacked memory wafers using low-temperature oxide bonding and ultra-fine-dimension copper through-silicon via interconnects

“…After connecting the A x vias to the F x thin wires on the front side of the wafer, bonding dielectrics are deposited, planarized, and activated for low-temperature oxide bonding (flipped) to the lower wafer (handle or x-1). [12] The bonded wafer is thinned to <7 µm to reveal the A x via bottom from the backside. For x>1 strata, inter-vias (E x , 1 µm in diameter) are fabricated from the backside using a process designed specifically to etch the remaining Si of the x strata and its complex FEOL/BEOL dielectric stack on the front side, the bonding dielectrics, and the interlayer dielectric stack on the back side of the x-1 strata.…”

“…Wafer bonding misalignment is consistently <1.25 µm (6σ), with bonding energy >1.6 J/m 2 as measured using the Maszara method. [12] Figs. 4 and 5 show the well-connected B 1 -A 1 -F 1 and B 1 -E 2 -B 2 -A 2 -F 2 chains, respectively, which play the most critical roles in the present multi-stacking interconnect technology.…”