VLSI – DRAM Technology
With the VLSI Syymposia just a little over a month away, I will wrap up my picks for papers to watch for by looking at DRAM. For the Technology Symposium, Samsung is over-represented with five out of the seven presentations split between two sessions.
Two of Samsung’s articles will discuss aspects of their FinFET DRAM cell, touted as the enabler for sub-50nm devices. The second paper appears to provide more details of the process and cell performance. If enough details are provided at the conference, it could be enough to predict Samsung as the first to make it to production with a FinFET device.
Qimonda is the only other vendor presenting a technology paper. In their forward-looking work, carbon is proposed as a new capacitor electrode material for DRAM. The technology includes a high-K dielectric for the trench capacitor, so Qimonda moves to carbon-based materials for better thermal stability. Qimonda’s other paper promotes trench technology beyond 40nm with a discussion of an array transistor that is self-aligned to the trench.
But the best paper for insight into production technology is provided in the final DRAM paper. Samsung announces it’s 56nm, 1Gb technology patterned on an ArF immersion tool. A 0.19 square micron cell size is reported. To achieve this scaled cell, Samsung moves to an elevated source / drain structure for the first time. Micron has used a similar structure for a few generations now. The capacitor dielectric is “ZAZ” which is a sandwich of zirconium and aluminum oxides for increased K value. Based on some work shown by Kinam Kim at IEDM 2005, I expect that the higher aspect ration capacitors at 56nm could use the Samsung “MESH-CAP” design for mechanical stability.
In yet another article, Samsung talks about hafnium dielectrics for DRAM. Of course, we have already seen this used in capacitors, but this work describes hafnium in a HfSiON dielectric for the access transistor.
Samsung is the DRAM dominator, and they lead this conference along with many others in presenting their technology developments. Unfortunately, I will not have a chance to see any of these papers first hand, but my good friend and colleague, Ramesh Kuchibatla will be in Kyoto and provide both scoops and scams he discovers at the event.