3D IC is only solution for scaling "up," says MonolithIC 3D exec

By Debra Vogler, senior technical editor

March 31, 2011 -- Serial entrepreneur, Zvi Or-Bach, was interviewed by ElectroIQ about his latest startup, MonolithIC 3D. In this podcast interview, Or-Bach explains why the company changed its name (from NuPGA) when its mission changed. "The name change was in response to a strategic change we made once we discovered a path to monolithic 3D ICs," said Or-Bach. He noted that on-chip interconnects are the limiting aspect with respect to scaling, and that after making materials changes (i.e., Al to Cu, and SiO₂ to low-k), the only solution is to go to 3D ICs.

Listen to Or-Bach's interview:  Download (iPod/iPhone users) or Play Now

Interconnect delay → Monolithic 3D		Implant H+ dummy gates	Transfer on top of processed wafer and replace gates (<400°C)
90nm (2005) 45nm (2010) 22nm (2015) 12nm(2020) Transistor delay 1.6ps 0.8ps 0.4ps 0.2ps Delay of 1mm-long interconnect 5 x 102ps 2 x 103ps 1 x 104ps 6 x 104ps Ratio 3 x 102 3 x 103 4 x 104 3 x 105	3D  →
Figure. Next-generation monolithic 3D IC -- leveraging the gate-last process. SOURCE: MonolithIC 3D

Semiconductor scaling costs

Scaling down 0.7x					Scaling up (3D packaging)
Cost:				Capital >$4B	Cost:	Capital: <$200M
				R&D >$1B		R&D  <$100M
Benefits:				Die size 0.5x	Benefits:	Die size 0.5x
				Power 0.5x		Power 0.5x
Speed:				No change	Speed:	No change
Table. The next-generation dilemma -- going up or going down? Companies can do both. SOURCE: MonolithIC 3D.

"While TSVs are a big help with off-chip interconnects, they are not helpful for on-chip interconnects -- they are just too large," explained Or-Bach. "Our vertical interconnect is 10000× more dense than TSVs." The company’s mission is an answer to what Or-Bach calls the next-generation dilemma (table). Whether one chooses to continue to scale down 0.7×, or scale "up" by going to 3D, there are costs. However, the company’s estimates show a glaring difference: capital costs and R&D costs are, respectively, >$4B and >$1B for scaling down; and <$200M and <$100M for scaling up.

3D IC technology

The technology being proposed by Or-Bach uses a combination of four ideas:
1) the gate-last process and proper sequencing of ion-cut (i.e., Smart Cut) technology;
2) low-temperature face-up layer transfer;
3) repeating layouts;
4) innovative alignment.

Or-Bach explains the process in detail (figure) in his audio interview. The technology still requires process development work, but looking ahead, Or-Bach views it as being applicable to both Tier 2 fabs that want to reinvent themselves and compete with leading-edge fabs, and leading-edge fabs that want to add value.

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