| AVS 55th International Symposium & Exhibition | |
| Plasma Science and Technology | Tuesday Sessions |
| Session PS-TuM |
| Session: | Advanced Gate Etching |
| Presenter: | S.A. Vitale, MIT Lincoln Laboratory |
| Authors: | S.A. Vitale, MIT Lincoln Laboratory J. Kedzierski, MIT Lincoln Laboratory N. Checka, MIT Lincoln Laboratory C.L. Keast, MIT Lincoln Laboratory |
| Correspondent: | Click to Email |
Dual work function band-edge metal gate electrode materials are replacing polysilicon gates at the 45nm technology node for high performance CMOS logic production. At the same time, mid-gap metal gate electrodes are being considered to replace polysilicon gates in novel fully depleted silicon-on-insulator (FDSOI) ultra-low power CMOS devices. A discussion of the physical and electrical requirements of the gate materials for these two technologies will be presented, along with an introduction to the “gate first” vs. “gate last” integration approaches. Titanium nitride metal-gated capacitors and transistors have been successfully fabricated, on a conventional SiO2 gate dielectric. C-V curves have been measured and fit to a quantum-corrected model, with a measured workfunction of 4.55eV. Gate oxide breakdown data reveals a charge-to-breakdown approximately 10x lower than that of conventional polysilicon/SiO2 gates, and a discussion of how this may be improved using a HfO2 high-k gate dielectric will be presented. A key challenge of integrating metal gates is the plasma etching of the gate stack. Conventional etching of a polysilicon layer above the TiN results in a large foot at the base of the polysilicon, due to the presence of the conducting TiN film. TiN etch selectivity over SiO2 in excess of 40:1 is achieved by measuring and exploiting the difference in ion enhanced etching threshold energy between these films. TiN is shown to etch spontaneously in HBr plasmas due to the thermodynamically favorable Ti + Br reaction, but is strongly inhibited in the presence of oxygen. TiN etching in high density plasmas exhibits a strong aspect ratio dependent etching (ARDE) effect, which can be minimized by using a two-step etch process, with different neutral-to-ion flux ratios. *This work was sponsored by the Air Force under contract #FA8721-05-C-0002. Opinions, interpretations, conclusions, and recommendations are those of the author and are not necessarily endorsed by the United States Government.