Optimization of Si:C Source and Drain Formed by Post-Epi Implant and Activation Anneal: Experimental and Theoretical Ana
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1070-E04-09
Optimization of Si:C Source and Drain Formed by Post-Epi Implant and Activation Anneal: Experimental and Theoretical Analysis of Dopant Diffusion and C Evolution in High-C Si:C Epi Layers Yonah Cho1, Victor Moroz2, Nikolas Zographos3, Sunderraj Thirupapuliyur1, Lucien Date1, and Robert Schreutelkamp1 1 Applied Materials, Inc., 974 E. Arques Ave., Sunnyvale, CA, 94085 2 Synopsys, Inc., 700 East Middlefield Road, Mountain View, CA, 94043 3 Synopsys Switzerland LLC, Zurich, Switzerland ABSTRACT Experimental and simulated P and As dopant diffusion profiles in Si:C epi films containing high C (>1 atomic %) are presented. A new set of physical effects were incorporated to accurately model P or As diffusion in the presence of high level of C. Evolution of substitutional C (Csub) profile in the Si:C epi film through dopant implant and activation anneal was characterized by high-resolution x-ray diffraction (HRXRD) technique. Three-layer analysis was utilized to obtain non-uniform Csub profile. Dependency of Csub retention on anneal thermal budget is studied. It is shown the initial Csub in the epi layer is lost during dopant implantation and conventional spike anneal sequence. Use of advanced millisecond (ms) laser anneal resulted in near 100% Csub retention in P-implanted Si:C epi film without compromising junction depth. Measured Csub (by HRXRD) and total C (by SIMS) profiles are compared with the ones predicted by the newly developed compact modeling in this study. INTRODUCTION nFET device performance improvement using recessed source and drain (S/D) Si:C approach has been demonstrated [1-2] and considered for added strain solution for nFET performance for 32nm technology and beyond. High substitutional C (Csub) is required for high in-film and channel strains. Figure 1 shows the calculated longitudinal (σxx) and vertical (σzz) stress distribution in channel between Si:C S/D of 1.8% Csub and expected channel mobility improvement (Δμe) as a function of Csub in the recessed S/D. 35% 30%
Δμe
25%
NiSi Si:C
NiSi +632 MPa
Si:C
NiSi
NiSi Si:C
-233 MPa
Si:C
20% 15% 10% 5% 0%
SIMULATION
-5% Longitudinal Stress (σxx)
Vertical Stress (σ zz)
0
0.5
1 Csub (%)
1.5
2
(a) (b) Figure 1. (a) Longitudinal (σxx) and vertical (σzz) stress distribution in the channel between Si:C stressors of 1.8% Csub and 80nm thick in a 60nm recess after NiSi formation. (b) Expected mobility improvement is plotted as a function of Csub% based on known piezo-resistance values.
The key challenges are to obtain high Csub Si:C during the epitaxy and to retain it during post-epitaxy integration sequence. As a parallel approach to in-situ doped Si:C epi process, postepi implant and activation anneal of undoped Si:C epi was explore for S/D junction formation. Proper junction formation and retention of Csub in the Si:C S/D for maximum channel strain are critical in fully realizing performance benefit, therefore, accurate prediction of n-dopant and C profiles is necessary. In this paper, a physical model is developed to analyze expe
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