AVS 49th International Symposium
    Electronic Materials and Devices Tuesday Sessions
       Session EL+SC-TuM

Paper EL+SC-TuM10
Measurement of Fermi Level Pinning Kinetics at Si-SiO@sub 2@ Interfaces: Implications for CMOS Transistor Manufacture

Tuesday, November 5, 2002, 11:20 am, Room C-107

Session: Heterojunctions
Presenter: K. Dev, University of Illinois
Authors: K. Dev, University of Illinois
M.Y.L. Jung, University of Illinois
R. Gunawan, University of Illinois
R.D. Braatz, University of Illinois
E.G. Seebauer, University of Illinois
Correspondent: Click to Email
Excessive transient enhanced diffusion (TED) of boron in silicon has been a major inhibitor to forming ultrashallow junctions for CMOS device applications. Current technology for junction formation relies on ion implantation into Si through SiO@sub 2@ to introduce dopants into the substrate, followed by rapid thermal annealing. We have investigated a previously unknown effect in this process sequence: charge build-up at the Si-SiO@sub 2@ interface and the resulting Fermi level pinning that can occur just after implant. Fundamentally, the charge build-up occurs in response to the ion-induced formation of dangling bonds that introduce energy states into the Si surface bandgap. The present work uses the optical technique of photoreflectance to demonstrate experimentally that these effects indeed exist and to measure their evolution kinetics. Photoreflectance is one of a class of modulation spectroscopies in which a semiconductor is periodically perturbed, and the resulting change in dielectric constant is detected by reflectance. The presence of a photoreflectance spectrum demonstrates unequivocally the existence of Fermi level pinning. The spectral amplitude scales linearly with the magnitude of built-in surface potential. Thus, we can deduce the pinning kinetics from the variation in amplitude. Our data demonstrate the existence of substantial pinning just after implant with 500 eV ions. Healing begins to occur in the vicinity of 400°C - within the temperature stabilization step in which interstitial clusters form. TED simulations using electrostatic boundary conditions derived from the photoreflectance experiments show that pinning deepens the pn junction significantly by transforming the Si-SiO@sub 2@ interface into a reflector of charged bulk interstitials.