High temperature stability of Al2O3 dielectrics on Si: Interfacial metal diffusion and mobility degradation

Abstract

We have examined the stability of Al2O3/Si heterostructures and show that significant Al diffusion occurs into the silicon for temperatures of 1000 °C and more. This may be caused by dissociation of small quantities of Al2O3 and subsequent dissolution of the Al into the silicon. Such diffusion may be reduced, though not eliminated via an interfacial silicon oxynitride diffusion barrier. Using long channel metal gate Al2O3/Si n field effect transistor data, we show that anneals at 1000 °C result in a degradation of the electron mobility by a factor of 2.

High dielectric constant oxides

“…The mobility is limited mainly by interface roughness over the range of interest. The mobilities in devices with high K gate oxides presently lie well below the universal curve [6,23,32,[121][122][123][124][125]. This is particularly true of NMOS devices.…”

“…Al 2 O 3 does not have soft modes, but it does have a high defect concentration. Thus, the reduced mobility seen in those devices [122] can only arise from charge scattering. [123,131] introduced a general model including the above effects.…”

Ni-salicided CMOS with a poly-SiGe/Al2O3/HfO2/Al2O3 gate stack

“…Secondly, though Al 2 O 3 has been predicted to be thermodynamically stable with Si, dissociation of Al 2 O 3 and subsequent dissolution of the Al into the silicon has recently been shown to occur at high RTA temperatures [14]. It was also suggested that the Al diffusion into the Si substrate causes defects in the high-j dielectric and in the Si substrate.…”

Physical properties of ALD-Al2O3 in a DRAM-capacitor equivalent structure comparing interfaces and oxygen precursors

“…Studies in [2,3] showed different physical properties of ALD-Al 2 O 3 films depending on process conditions. Also the impact of Al 2 O 3 dielectric on semiconductor electrode doping was shown [4]. However, a systematic comparison of available processes and its effect on physical properties was not done so far.…”