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We report for the first time a fully 300-mm stacking-compatible capacitor-less DRAM cell with >400s retention time by integrating two IGZO-TFTs in a 2T0C configuration. We optimize the single IGZO-TFT performances by engineering the materials surrounding the IGZO layer and the transistor layout parameters. We thus introduce a novel IGZO-TFT device and demonstrate a scaled transistor (W = 70 nm, L = 45 nm) with optimal V th reproducibility on 300-mm wafers. By integrating the IGZO-TFTs in a 2T0C configuration, we systematically assess reproducible long retention time for different transistor dimensions, thanks to the extremely low extracted IGZO-TFT off-current (~3x10-19A/µm).

Buried power rail (BPR) is a key scaling booster for CMOS extension beyond the 5 nm node. This paper demonstrates, for the first time, the integration of tungsten (W) BPR lines with Si finFETs. The characteristics of CMOS in close proximity to floating BPR are found to be similar to the characteristics of CMOS without BPR. Moreover, W-BPR interface with Ru via contact can withstand more than 320 h of electromigration (EM) stress at 4 MA/cm 2 and 330°C, making Ru a candidate for via metallization to achieve low resistance contact strategy to BPR.

3D sequential integration is shown to be compatible with a back gate implementation suitable for dynamic V th tuning of the FDSOI top tier devices. The back gate is inserted seamlessly into the 3D sequential process flow during the top Si layer transfer, providing a close proximity to the top tier device, as well as a uniform and high quality thermal back oxide. A threshold voltage tuning of ~103mV/V and ~139mV/V is obtained in p-and nMOS top tier junction-less devices, respectively, over a back gate bias range of +/-2V. BTI reliability measurements show no detrimental impact of the back gate bias. Back-gating can therefore be used to enhance the $I_{ON}$ performance with no reliability penalty. The buried metal line is also shown to lower crosstalk by metal shielding insertion between top and bottom tier metal lines, with a reduction larger than 10dB up to 45GHz.

3 Dstacking using a sequential integration approach is demonstrated for finfet devices on 300mm wafers at a 45nm fin pitch and 110nm poly pitch technology. This demonstrates the compatibility of the 3D sequential approach for aggressive device density stacking at advanced nodes thanks to the tight alignment precision of the first processed top layer to the last processed bottom layer through the top silicon channel and bonding stack during 193nm immersion lithography. The top devices are junction-less devices fabricated at low temperature $(\mathrm{T}\leq 525^{\circ}\mathrm{C})$ in a top Si layer transferred by wafer-to-wafer bonding with a bonding dielectric stack down to 170nm. The top devices offer similar performance as the high temperature bulk finfet technology for LSTP applications. The use of TiN/TiA1/TiN/HfO 2 gate stack provides the proper threshold voltage adjustment while the insertion of the LaSiO x dipole improves device performance and brings the BTI reliability within specification at low temperature.

In this paper, we review the current progress on 3D sequential device stacking, highlighting the main integration challenges and the possible technological solutions. Junction-less devices are shown to be attractive top tier devices for low temperature processing, low complexity of fabrication and meeting reliability specification despite without the use of “reliability” anneal. Next, we explore the potential benefits of 3D sequential stacking at transistor level, CMOS level and for hybrid circuits.

In this paper, we review the current progress on 3D sequential device stacking, highlighting the main integration challenges and the possible technological solutions. Next, we explore the potential benefits of 3D sequential stacking at transistor level, CMOS level and for hybrid circuits.

Ruthenium has been recently considered as a promising candidate to replace copper as the BEOL interconnect material for sub-5nm technology nodes. In this work, single level Ru interconnects were fabricated in imec's 300-mm pilot line using EUV lithography and the subtractive etch of Ru films. Lines with critical dimension smaller than 10.5 nm were formed and electrically tested to assess the line resistance of patterned Ru. Using the TCR method, structures with resistivity of 15 μΩ.cm and cross-sectional area of 200 nm2 were obtained and benchmarked against analogous Ru and Cu damascene processes. Ru lines with aspect ratio up to 3.8 were fabricated and measured having line resistance below 500 Ω/μ $m$ at 12 nm CD. Ru is expected to outperform damascene Cu at this scale, supporting the potential insertion of Ru metal patterning for advanced technology nodes.

Extreme thinned wafer transfer technologies have been demonstrated by combining a selected set of temporary and permanent bonding materials. The extreme thinning was performed on the backside of a top wafer bonded on carrier wafer with the temporary glue material, subsequently followed by grinding, polishing and plasma dry etching to a final thickness of 5 µm. The properties of the temporary adhesive have been selected to be compatible with a permanent thermocompression bond of the extreme thin wafer to a final target substrate. Thus, the high thermal deformation resistance of the temporary adhesive is key. As we are dealing with extremely thin substrate, the required process uniformity and total thickness variation of each material are crucial. Hence after the spin-coating, the permanent bond polymer was planarized by a surface planer process. The performance benefit brought by this process and the final transfer steps will also be discussed.