PHOENIX " When Hans Stork began his engineering career at IBM Corp. in 1982, reliability concerns were "out there on the edge," away from the real action of developing new process technologies.
Now, reliability concerns "are at the very center" of the chip industry. New failure modes threaten as the industry moves to new materials, and to complex system-on-chip solutions with multiple device types on the same die, said Stork, now the chief technology officer at Texas Instruments Inc. (Dallas).
Stork delivered the keynote speech here Tuesday (April 27, 2004) at the International Reliability Physics Symposium (IRPS).
With the difficult integration of copper and low-k dielectrics still ongoing, the chip industry faces another critical test: the move to high-k dielectrics at the critical gate insulation layer.
"The most difficult reliability issues facing us relate to the gate oxide," Stork said, including the move to high-k materials over the rest of this decade.
The high-k oxides, based on hafnium and other metals, present multiple challenges, including electron mobility degradation, shifts in the threshold voltage and incompatibility with polysilicon gates.
Also, TDDB (time-dependent dielectric breakdown) " how the materials degrade and break down over time " is another issue the industry must tackle. "In the old days the oxide would break down and the device would be kaput. Now, we look for graceful degradation," Stork said.
Negative bias temperature instability (NBTI), in which defects in the oxide interface occur over time as the device operates under thermal stress, "is getting worse, with much less headroom.
A massive amount of work needs to be done" to keep NBTI under control, Stork said, including better transistor models, improved processes and providing circuit designers with a level of predictability as to how NBTI will affect designs over time.
Stork said more attention needs to be paid to soft error rates (SER), which grow more important as memory blocks on SoCs grow in size. Errors, caused in part by cosmic rays striking SRAM cells, are becoming an issue for logic as well.
"Logic SER has been deep down in the noise range," Stork said, but that level of relative insignificance is changing as scaling proceeds and logic transistors have less charge. "Logic SER may become as significant as SRAM error rates," he predicted.
About 600 engineers are attending the 2004 IRPS, up from 450 last year. The improving economy, as well as the increasing importance of reliability issues to customers, account for the improved attendance, said Bernie Pietrucha, general chair of the conference.