Inside CEA-Leti’s 3D Toolbox

Grenoble-based research institute CEA-Leti’s progress is fueled by a single mission: create innovation and transfer it to industry. The goal is to reach marketability within 5 years. As such, Leti’s focus is less on the feasibility of a technology, and more on the probability of that technology being viable in volume production. When it comes to 3D integration, achieving this goal has resulted in collaborative efforts to establish what Nicolas Sillon, director of Leti’s 3D integration program, calls the 3D toolbox.

It begins with the right environment
Leti’s environment comprises both 200 and 300mm Si capabilities, 8,000 m² clean rooms, and 24/7 operations. One platform supports 3D WLP needs (and also MEMS) in 200mm; with the 300mm platform slated to come online in anticipation of 3D IC integration in Q1/2010. Sillon explained that the concept is to fill this generic 3D toolbox with resources that support both 3D wafer level packaging (3D WLP) and 3D IC technologies. Resources being developed include alignment/bonding processes; interstrata connections; TSV variations including via-last for CIS and interposer technologies, as well as via-mid for high performance TSVs; thinning and handling solutions; and chip/wafer planarization. Target technologies that will utilize these tools include:

  • Via belt Technology: a TSV-free solution that allows wafer-level multi stacking of heterogeneous dies. This process is targeted to assembly companies that have multiple sources of chips without access to new designs.
  • CEA-LetitoolboxTSV Active Si interposer:  a process of chip to wafer heterogeneous stacking with via-last TSV in thinned wafer. This approach is targeted to IDMs with access to design tools.
  • Ultraflat 3D: This 3D IC approach is a high-density 3D solution managed at the circuit level. This approach targets CMOS fabs.

Additionally, the toolbox will contain a complete kit for modeling and characterization, in addition to design tools for optimizing 3D.

Partnerships are the key
Outfitting the toolbox has involved joint development agreements with such materials and equipment suppliers as Semitool, Surface Technology Systems, EV Group, Datacon, R3Logic; as well as common lab agreements with Brewer Science, Replisaurus, and S.E.T.

“Our goal is to have something transferrable one year before market adoption.” notes Sillon. To this end, Leti works in partnership with device manufactures who, based on their application goals and cost, select compatible process flows from the generic toolbox.

Leti’s model in action
The first successful technology transfer based on this business model was last year’s transfer to ST Microelectronics of its CMOS image sensor (CIS) process using via-last TSVs; now in volume production. As Sillon explains, Leti rallied around a via-last approach for TSV formation because it targets short time-to-market applications like CIS and silicon interposers, it requires no change in the CMOS process, it has a wide scale of flexibility with wafer-level assembly processes, and user confidence is high. The latest achievement with this process flow was the transfer to 300mm.

A joint development agreement with Gemalto has resulted in a smart-card application integrating thin 2 die stacks for flash memory. This process flow has achieved electrical validation, and Sillon expects technology transfer to be completed in 2010.

Another notable accomplishment in partnership with ST Microelectronics is a 2-die stack mixing advanced node technology (45nm) with mature node technology (130nm). This demonstration of first-level repartitioning was demonstrated at EMPC 2009. Prototypes exist, and Sillon says the technology will reportedly be ready for transfer in 2011.

Why it works
It all comes down to the bi-lateral partnerships. Sillon credits Leti’s historical link to ST Microelectronics, and the IDM’s aggressive push towards 3D integration for helping to fuel their success with bringing TSVs into production. Partnership with suppliers allows the research entity to prove that processes are scalable for production. If they’re not, there’s no point in further development. This process of elimination and focus on the quick time to market is what sets Leti apart. This organization’s name spells out their recipe for success: Loyalty, Entrepreneurship, Teamwork and Innovation. It seems to be taking hold. We’ll be watching.