Alternative Gate Stack PMOS Presented by: Valarie Welsh Senior Research Proposal February 18, 2004

CMOS Issues with Poly-Si Gate High Gate Resistance High Gate Resistance Premature Gate Depletion Premature Gate Depletion Boron Penetration Boron Penetration Current Leakage Current Leakage

High Gate Resistance Resistances should be minimized for switching speeds Resistances should be minimized for switching speeds Alternative gate materials, specifically conductors are attractive for this purpose Alternative gate materials, specifically conductors are attractive for this purpose

Gate Depletion Dopant from poly can diffuse into and through thin Dopant from poly can diffuse into and through thin

Boron Penetration Ultimate in dopant migration can affect channel length. Ultimate in dopant migration can affect channel length.

Current Leakage P-type regions beneath very thin gate with n+ doped poly are susceptible to tunneling effects opposite of the gate depletion and boron penetration mechanism

Gate Stack Engineering Refers to finding new gate and new dielectrics materials Refers to finding new gate and new dielectrics materials Work on alternative gate material Work on alternative gate material Material should: Material should: –Be compatible with gate dielectric –Have appropriate work function –Fit into to existing manufacture processes

Alternative Gate Material Molybdenum – transition metal Molybdenum – transition metal Tg=2617°C Tg=2617°C Stable contact with SiO2 to 1000°C Stable contact with SiO2 to 1000°C WK Fcn 4.7 Variable with process WK Fcn 4.7 Variable with process

Potential Solution to: High Gate Resistance High Gate Resistance Premature Gate Depletion Premature Gate Depletion Boron Penetration Boron Penetration Current Leakage Current Leakage

Process Plan A

Potential Problems Finding previous work on self aligned gate process using Mo. Is there a reason why? Finding previous work on self aligned gate process using Mo. Is there a reason why? Looking for Mo application specs (sputter or other) usable in RITs fab Looking for Mo application specs (sputter or other) usable in RITs fab Source/Drain implants must be recalculated to compensate for gate treatment Source/Drain implants must be recalculated to compensate for gate treatment

Process Plan B Same 5 Lith levels but no self aligning gate Same 5 Lith levels but no self aligning gate Apply Mo outside RIT FAB Apply Mo outside RIT FAB

To Do: Locate Mo application and etch process for use at RIT Locate Mo application and etch process for use at RIT Simulation to establish whether workfunction adjustment is warranted Simulation to establish whether workfunction adjustment is warranted Final establishment of process Final establishment of process Certifications Certifications

References: – P. Ranade, Molybdenum as a gate electrode for deep sub-micron CMOS technology, Mat. Res. Soc. Symp. Vol. 611,2000, p.C3.2.1 – K. Han, Gate Stack Engineering: Advanced Process Integration for VLSI, Research Paper. Fall 2001 – C.H. Choi et.al., Direct Tunneling Current Model for Circuit Simulation, Center for Integrated Systems, Stanford University, Stanford, CA – R.P.S. Thakur, Y.Chen, E.H.Poindexter, and R.Singh, Silicon-Based Ultrathin Dielectrics, The Electrochemical Society Interface, Summer 1999

Questions…?