AVS 51st International Symposium
    Electronic Materials and Processing Tuesday Sessions
       Session EM-TuA

Paper EM-TuA7
New Mechanisms for Controlling Transistor Junction Formation through Surface Chemistry

Tuesday, November 16, 2004, 3:20 pm, Room 304B

Session: Defects and Interfaces in Electronic Materials and Devices
Presenter: K. Dev, University of Illinois at Urbana-Champaign
Authors: E.G. Seebauer, University of Illinois at Urbana-Champaign
K. Dev, University of Illinois at Urbana-Champaign
C.T.Z. Kwok, University of Illinois at Urbana-Champaign
R.D. Bratz, University of Illinois at Urbana-Champaign
Correspondent: Click to Email
Forming extremely shallow pn junctions with very low electrical resistance is becoming an insurmountable stumbling block to the continued scaling of microelectronic device performance according to Moore's Law. We have developed a technology based on surface chemistry that holds great promise for simultaneously reducing junction depth and increasing activation for dopants implanted into silicon. The approach uses the surface as a large controllable "sink" that removes Si interstitials selectively over dopant interstitials. We have discovered two distinct ways to employ adsorption at the surface for this task: adjusting the intrinsic loss rate of interstitials to the surface, and reducing the degree of electrical charge built up at the surface. We control the interstitial loss rate to the surface by saturating dangling bonds using adsorbed nitrogen, introduced as ammonia, hydrazine, or a similar simple gas before implantation or the subsequent annealing step. To demonstrate such effects, we have measured SIMS profiles of isotopically labeled Si (mass 30) implanted into a Si host lattice depleted in this isotope, The annealed profiles with an atomically clean surface change relatively little from the as-implanted profile. The annealed profiles with adsorbed N change more, and the profiles with a rather thick layer of adsorbed O has change the most. Electrical charge that builds up at dangling bonds on a surface couples to charged defects in the underlying bulk through an electric field near the surface that strongly repels the bulk defects. The strong repulsion in the near-surface region in effect makes the surface more reflecting of interstitials, thereby changing the concentration profile of the bulk defects and correspondingly in the dopant profile. We have shown by the optical method of photoreflectance that nitrogen adsorption greatly reduces the charge buildup at the surface, and therefore reduces the surface repulsion effect.