EUV vs. TSV: Which one will become production ready first?

We have a guest contribution today from Israel Beinglass, the CTO of MonolithIC 3D Inc. Israel debates on the answer to an important question that is on everybody's mind these days.

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Like every Semicon West show in the past, where many experts are brought together for showing the latest and greatest semiconductor manufacturing equipment and bringing numerous seminar/panel discussions, this Semicon West of 2013 was no different. Two major issues were discussed, which on the face of it look unrelated, that caught my attention:

Progress in

1. 3D - TSV technology, and
2. EUV

Obviously these two issues are very different, but they are quite similar in respect to the following:

1. As the advanced node progresses to smaller and smaller feature size we are getting closer to the "end of the road map" or the "end of Moore's law".

Going to EUV does alleviate some of the problems related to the current solution of double patterning (or quadruple in the future assuming, EUV doesn't come to fruition soon enough).

As well, utilizing 3D devices with TSV has, in the grand scheme, a similar outcome; namely, advancing the integration via 3D structures rather than continued scaling. Though in the future, 3D devices and advanced nodes could go hand in hand.

2. The big miss of the road map. When one looks at some old road maps from a few years ago, one can ask how did we, the industry, miss by so much?

This actually reminds me of another miss from a few years ago-the low k inter-metal dielectric. Fig. 1 shows the low k dielectric roadmap trend of various ITRS published roadmaps and the prediction in 1999 that by 2004 we would be using k<2 !! Obviously we know what happened and even today 14 years later it is hard to breakthrough a k value of 2.5. 

Figure1: low k Dielectric Road Map

Figures 2 and 3 show the roadmap for EUV and TSV, respectively. Both are of 2009 vintage. In each case the prediction of the road map vs. actual is startling.

Figure 2: EUV road map

Figure 3: TSV road Map

It is not the purpose of this blog to go over the reasons why the roadmaps of EUV and TSV missed the time table by miles, nor to blame anybody for it. There are many articles and discussions published on the subjects. Rather, I will touch on some of the highlights as well as try to make some conclusions regarding the pathway of the industry regarding these two important technologies.

EUV: The EUV technology has so far gone through monumental achievements vis-à-vis the incredible tasks of developing the next generation stepper technology. The amount of engineering and resources poured into it is unprecedented in the short history of the semiconductor industry and maybe so for other industries.

It looks like as I write this blog that the only barrier for the technology from becoming a HVM tool is EUV source power that can provide a high enough throughput. Many experts doubt that it could ever be achieved; however, there are many other experts saying that it is within a reach.

TSV: In this case I could see two totally unrelated issues:

1. Technology driven obstacles

2. Logistics and supply chain issues.

In the case of the TSV it is one of the few cases where the "power point" presentation(s) of the TSV idea are so convincing that it is actually hard to oppose it. However, when it comes to the fine details of the technology development, there are many issues that still need to be addressed and resolved. I believe that it is just a matter of time before the technical obstacles will be resolved and a unified standardized solution emerges. However, on the other hand, I see a real problem from the point of view of logistics, cost and supply chain of the technology, and I have some doubts if it can ever be resolved. For further discussion on this issue, please refer to: 3D IC Supply Chain: Still Under Construction, and to a detailed comment in EE Time published blog and comments re. Semicon West 3D - IC TSV, provided here below.

In summary, I believe that the industry will come with a solution for EUV before TSV becomes a production technology.

Yet there is another alternative to TSV and to EUV - it is the Monolithic 3D methods. Moreover, it is very likely that monolithic 3D will reach volume production before EUV and TSV. As we already see the  NAND Flash vendors ramping up for production of 3D NAND.

The detailed comment fromm EE Times re. Semicon West 3D - IC  TSV:

USER RANK CEO

Re: Semicon Showed Support for 3D ICs  
chipmonk0   7/18/2013 1:46:13 PM

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" same old same old ... " !! With such pollyannaish coverage, I am afraid that TSVs will remain the next hot interconnect tech even 5 years from now !

To provide a counter-point to all this happy talk, SemiCon had invited me to lead a 1 hr discussion at the Show on "Roadmap for TSVs and Alternatives from a Technology perspective ". Since Herb was not there, here are the key points :

1. unlike previous Advanced Packaging technologies like Flip Chip which we developed at IDMs like Motorola & Intel with both deep / broad expertise and product commitments, the development of TSVs has been going on mostly at overseas Govt. funded Laboratories in fits and starts and has then jumped to Foundries / OSATs. Xilinx' use of 2.5-d to integrate poorly yielding FPGAs has led to much irrational exuberance and then disappointment.

2. In the Winter of 2010 - 11 Samsung reported the first Wide I/O DRAM stack using TSVs. Great bandwidth even at 200 MHz & terrific power eff. But what the blogosphere neglected to report was that the yields were down in the mud and since then not much has been heard about Wide I/O from Samsung. Instead they keep bringing out conventional LP DDR at ever higher Clock Rates. JEDEC has actually postponed Wide I/O to 2015. 
3.  The development of TSV technology has been going on in Fabs who do not have to be sensitive to stress issues common in "thick film" type laminates / composites as is the case for filled vias. It is only now that they are waking up to it. Stress effects depend on the sq. of via dia., hence the new interest in shrinking them below 5 um. But integration & reliability problems ( at high Aspect Ratios both get worse ) have not been thought through. Moreover, Bonding stacked chips using the current method ( a sort of pidgin version of the technology I had invented nearly 20 years ago at Motorola for GaAs Power Amps that went into Cell Phones ) also introduces residual stress, affects electron mobility and shifts timing. 

4. While these slow-poke Govt. funded Euro Labs rediscover stress effects on device perf. and the perils of Cu metallurgy applied indiscriminately, there is at least one small Company outside Chicago that has already shifted to the non - obvious ( at least to these TSV-niks ) yet theoretically sound choice of using Tungsten ( a brittle and poor electrical conductor which can be compensated by Design but unlike Cu a close CTE match with Si ).

5. But thats not all Folks - this tiny Co. with just 3 PhDs and Physicists has also solved the biggest TSV integration problem thats keeping all these Labs and various Tool Vendors new to the game ( in Herb's Osterreich they love to build big complex "Maschine" - Physics be damned ) -- intent on optimizing their individual process steps ( e,g. back up wafer bond / debond ) at the risk of compromising the whole process -- awake at night.

6. We did cover more, e,g. as to how to get the electrical benefits of TSVs w/o actually having to drill holes in live Silicon, circuitry and packages that make it possible. We already have some of these Alternatives ( using the concept of Active Interconnects ) under development - especially for the very large Server & SmartPhone markets - and have started publishing.

7. TSV development is orders of magnitude more complex than Flip Chip and would benefit from the same type of brutal, theory-driven Program Management practiced at the world's largest semiconductor Co., but since they have money in the Bank to stay on Moore's Law and thus continue single chip solutions they don't need TSVs that badly. So unless there is a radical shake - up in the TSV programs "outside", incl. at the Foundries, the present slow pace of TSV development will persist.

Morale : give TSVs a fair chance, they need a respite from these overly enthusiastic bloggers, embarassingly out of their depth, and at Conferences lets not blather about Supply Chain Issues, the technical probems are not all solved yet