June 16, 2006 – At this recent Symposium on VLSI Technology, SEMATECH engineers reviewed technical details on metal electrode materials that can be used to build low-threshold-voltage (Vt) nMOS transistors with high-k dielectric, and discussed a new approach for creating advanced, low-standby-power transistors for the 45nm technology generation.

The first presentation outlined achievements previously announced this spring, involving nMOSFETs with metal electrodes showing an effective workfunction of ~4.0eV. The identification of nMOS metal gate electrode materials, capping a three-year project, represents a major milestone in the quest to fabricate working CMOS devices using metal gate and high-k dielectric stacks, the organization stated. “From this work, we developed an understanding of how metal electrode materials and high-k dielectrics react, and how the effective workfunction of metal electrodes can be controlled to yield an effective workfunction close to that of doped polysilicon gates,” stated Byoung Hun Lee, manager of SEMATECH’s advanced gate stack program.

In a second presentation, S.C. Song, material evaluation test structure project manager, described a dual high-k, dual metal gate (DHDMG) process for CMOS field-effect transistors (FETs), also unveiled earlier this year, which offers several advantages over previously reported dual metal gate integration approaches for creating advanced, low-power transistors usable at the 45nm technology node. The DHDMG process allows high-k dielectric materials and their associated metal gates to be optimized in separate processing steps, eliminating the difficult integration problems that have plagued more conventional methodologies. The new process allows for use of a second different high-k film for nMOSFETs, if needed, as well as dual metal electrodes for pMOSFETs. Thus nMOSFETs and pMOSFETs can be optimized independently, avoiding intermixing of gate stack materials that typically degrades threshold voltage and other performance characteristics.

“We have demonstrated a manufacturable solution for one of the most vexing problems facing advanced transistor development,” Song stated, adding that the process details have been transferred to SEMATECH member companies for consideration, and eventual implementation.