By Debra Vogler, SEMI
A forum of industry experts at SEMICON West 2016 will discuss the challenges associated with getting from node 10 — which seems set for HVM — to nodes 7 and 5. Confirmed speakers at the “Node 10 to Node 5 ─ Dealing with the Slower Pace of Traditional Scaling (Track 2)” session on Tuesday, July 12, 2:00pm-4:00pm, are Lode Lauwers (imec), Guy Blalock (IM Flash), Kelvin Low (Samsung), Mike Chudzik (Applied Materials), Kevin Heidrich (Nanometrics), and David Dutton (Silvaco). SEMI interviewed Lauwers and Chudzik to see what challenges they see ahead as the industry progresses from node 7 to node 5.
According to Mike Chudzik, senior director, Cross-Business Unit Modules Team at Applied Materials, “The top tw or three process development challenges facing the industry at node 7 are RC reduction, RC reduction, and RC reduction,” Chudzik told SEMI. “At the 7nm node, parasitic resistance and parasitic capacitance delays are predicted to be greater than the inherent transistor delay.” Among the solutions he cites are new materials such as cobalt for the contact fill, lower-k spacers, and integration solutions, such as air-gap and replacement contact schemes. “While FinFETs are expected to scale to the 7nm node, their days are numbered. If you want to scale to the true historical 0.7X 7nm node, it’s a challenge for FinFETs because continuing to scale the gate length requires scaling the fin width.” He also explained that the variability in patterned fins will cause serious device performance challenges at near 5nm fin width on account of quantum confinement. “Something new like gate-all-around (GAA) devices are needed to fuel the next-generation of device scaling.”
Among the materials challenges in getting to nodes 7 and 5 are cobalt implementation for the contact, and Si/SiGe superlattices for the 5nm node, explained Chudzik. “The former challenge concerns replacing tungsten in the contact plug, and the latter is needed to form horizontal GAA structures.” Figure 1 shows that at the 7nm node (CD of 13nm) the resistance of the TiN/W fill material for the contact plug is expected to become higher than the interfacial contact resistance. “A TiN/Co solution provides relief.”
In addition to improving the performance of the interconnect, Lode Lauwers, VP, business development for CMOS technology at imec, told SEMI that getting to node 7 will require very advanced fin technology combined with a patterning solution. Looking ahead to node 5, he said it is expected that the fin will still be the reference technology, along with the introduction of new materials such as SiGe, and a high concentration of Ge in the channel as a mobility improvement, and possibly even the consideration of III-V materials (particularly at N5) (see Figures 2 and 3).
In looking out towards the horizon, Lauwers pointed out that the industry has to consider alternatives to the fin because there is an engineering limit to how small the fin dimensions can be made. “There is the possibility that at node 5 the industry will consider alternatives to the traditional fin, said Lauwers. “For example, the GAA structure (also referred to as a lateral or horizontal nanowire, HGAA) is superior in terms of gate control and will have better leakage control. That means you will be able to have better performance over a lower supply voltage with a lower threshold voltage.”
Beyond HGAA structures, Lauwers observed that the industry could move to a vertical nanowire structure (VGAA). But there are several contenders (see Figure 2). “It’s not up to imec to choose and it’s too early to say what will be the right option,” Lauwers told SEMI. “Maybe for certain applications or a certain technology positioning, a device maker might make a different compromise.”
In addition to imec and Applied Materials, speakers from IM Flash, Nanometrics, Samsung, and Silvaco will present at the “Scaling: Node 10 to Node 5” session of the three-day Advanced Manufacturing Forum (see Schedule-at-a-Glance) at SEMICON West 2016 which takes place July 12-14 in San Francisco, Calif.