Scalable, sub 2μm pitch, Cu/SiCN to Cu/SiCN hybrid wafer-to-wafer bonding technology
This paper presents a novel approach to face-to-face wafer-to-wafer (W2W) bonding using SiCN-to-SiCN dielectric bonding, in combination with direct Cu-Cu bonding using Cu pads of unequal size and surface topography for the top and bottom wafers. The use of SiCN dielectrics allows to obtain a high W2W bonding energy (> 2 J/m2) at low annealing temperature (250 °C). Excellent Cu-Cu bonding is obtained after annealing at 350 °C. A novel CMP process, resulting in a slightly protruding Cu top pad and a slightly recessed Cu bottom pad, is introduced. The difference in pad sizes, allows for the necessary W2W overlay bonding tolerances. Excellent resistivity and yield results are obtained across bonded 300 mm Si wafers for scaled 360 nm top pads bonded to 720 nm bottom pads at 1.44 μm pitch (25% bottom Cu density). Feasibility of smaller pitches has been demonstrated by successfully bonding 180 nm top pads to 540 nm bottom pads at 0.72 μm pitch.
Novel stacked CMOS image sensor with advanced Cu2Cu hybrid bonding
We have successfully mass-produced novel stacked back-illuminated CMOS image sensors (BI-CIS). In the new CIS, we introduced advanced Cu2Cu hybrid bonding that we had developed. The electrical test results showed that our highly robust Cu2Cu hybrid bonding achieved remarkable connectivity and reliability. The performance of image sensor was also investigated and our novel stacked BI-CIS showed favorable results.
Experimental investigation of the geotechnical properties and microstructure of lime-stabilized saline soils under freeze-thaw cycling
Abstract The Song-Nen Plain in northeastern China holds one of the three largest expanses of soda saline-alkali soil in the world. Due to its disadvantageous geotechnical properties, the saline soil in this area is unable to meet the needs of construction projects. This study evaluates the stabilizing effect of adding lime to such soils. Specifically, it investigates how the physicochemical and mechanical properties and microstructure of soda saline-alkali soil are altered by lime and how these changes are affected by both freeze-thaw cycling and the duration of curing. The results reveal that adding lime to saline soil transforms clay particles into sand and silt particles and causes the pore size distribution (PSD) to become bimodal, with small-pore and macropore populations. An increase in lime content leads to an increase in the unconfined compressive strength (UCS) but a gradual decrease in both the cation exchange capacity (CEC) and plastic index. Freeze-thaw cycles break up coarse particles and aggregate finer particles, increasing the diameter of macropores and decreasing the USC; however, the effect on specimens with >9% lime is negligible. It is further shown that the geotechnical properties of the soil change immediately after the addition of lime, indicating that the cation exchange reaction takes place very quickly. Furthermore, the pozzolanic reaction leads to an increase in the percentage of sand-sized particles and a decrease in porosity after 28 days of curing. Overall, these results indicate that it is feasible to use lime to improve the engineering properties of soda saline-alkali soil in this area.