AVS 46th International Symposium
    Electronic Materials and Processing Division Tuesday Sessions
       Session EM-TuA

Paper EM-TuA4
Separate and Independent Reductions in Direct Tunneling in Oxide/Nitride Stacks with Monolayer Interface Nitridation Associated with the i) Interface Nitridation and ii) Increased Physical Thickness

Tuesday, October 26, 1999, 3:00 pm, Room 608

Session: High Dielectric Constant Materials and Thin Oxides
Presenter: Y. Wu, North Carolina State University
Authors: Y. Wu, North Carolina State University
H. Niimi, North Carolina State University
H. Yang, North Carolina State University
G. Lucovsky, North Carolina State University
Correspondent: Click to Email
Reduction of direct tunneling in aggressively-scaled CMOS devices with deposited oxide/nitride stacks and/or oxynitride alloys is crucial for replacement of thermally-grown oxides. We have identified two separate and independent mechanisms for tunnel current reduction that have been combined in oxide/nitride stacks with monolayer interface nitridation to yield current densities <10@super -2@ A/cm@super 2@ for stacks with oxide-equivalent thickness <1.6 nm. Fabrication of these stacks combines remote plasma-assisted nitridation and deposition processes to independently control nitrogen concentration profiles at the atomic layer level at interfaces and in bulk films. The order of interface nitridation is crucial and monolayer concentrations to reduce direct tunneling by ~ten require two 300°C steps: i) first, remote plasma-assisted oxidation of H-terminated Si(100) to form a ~0.6 nm passivating oxide, followed by ii) remote plasma-assisted nitridation to insert a monolayer of N-atoms at the Si-interface. XPS results indicate that the reduction in tunneling derives from differences in interfacial suboxide bonding associated with nitridation. Since tunneling increases exponentially with decreasing film thickness, incorporation of nitride layers in O/N stacks allows use of physically thicker films while maintaining capacitance equivalent to thinner oxides. We find that increases in thickness are in part mitigated by decreases in the product of the tunneling mass and thickness-averaged-barrier-height in the nitrides, limiting tunneling decreases to ~10-20 with respect to single layer oxides. However, using remote plasma-assisted processing to separately control interfacial and bulk dielectric nitrogen profiles, it has been possible to combine these two order of magnitude decreases and achieve reductions in tunneling of more than 200 in N/O/N stacks. These have been included in NMOS- and PMOSFETs which display excellent current drive and high reliability.