Experimental Evidence of Long-Range Point Defect-Phosphorous Pair Diffusion in Silicon
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1155-C05-06
Experimental Evidence of Long-Range Point Defect-Phosphorous Pair Diffusion in Silicon
Ammar M. Nayfeh and Viktor I. Koldyaev Innovative Silicon, 4800 Great America Parkway, Suite 500 Santa Clara Ca 95054 Phone: 408-969-9555 x2043 Fax 408-969-2367, Email: [email protected]
ABSTRACT Point Defect (PD) mediated diffusion of phosphorous in silicon is studied in order to address the long standing open problem of PD-Dopant pair lifetime. A novel experimental method is suggested to increase PD-P pair lifetime for better observability and experimental resolution. In the experiment, phosphorous is implanted, followed by low temperature poly-Si deposition with in-situ doped phosphorous. The P profile shows, after low temperature (550◦C), Transient Enhanced Diffusion (TED) due to interstitials created by P implantation decays significantly faster than the poly-Si deposition time (annealing for interstitials). For such low P dose the interstitial concentration is below a critical one for T>550◦C so that no rod-like defects or dislocation loops can be created. Only TED related to dissolution of rod-like defects resulting in short-term TED and dislocation loop dissolution resulting in a long-term TED might be affecting our quantification method for the decay of the P concentration in the peak (δP). Error bars (Figure 4) in P-I diffusivity extraction reflects this small effect as well as other error sources. Figure 1 is a cartoon diagram showing experimental features.
X=0 P source
P Concentration P marker Implant Figure 1 Diagram illustrating idea for increased observability of pair diffusion
Due to P implant and P drive-in, SiI concentration is at the level of supersaturation while Si Vacancy (Siv) concentration is undersaturated.
PDrive− In → SiI :
Supersaturation; SiV − Understaturation
(1)
During injection of I into the Si substrate, P-SiI pairs are formed with a generation rate (τg) τ
g Ps + SiI → CPI : Pair − Formation − ( Kick − out − Mechanism)
(2)
After P-SiI pair formation, the pair diffuses in the Si lattice with diffusivity DPI. The following differential equation governs pair formation, diffusion and dissociation.
∂CPI ∂t
= DCPI ∇ 2C PI +
Ps
τg
−
C PI
τp
:
(3)
Finally, P-SiI pair will dissociate governed by pair lifetime (τp) τ
p CPI → PS + SiI − Pair − Dissociation
(4)
The actual experimental steps are as follows. First, P is implanted as a marker layer at a shallow depth followed by Si surface cleaning and conditioning. Next highly P doped Poly-Si is deposited by CVD at low temperature and finally P profile is measured by SIMS. Figure 2 shows a cross sectional view highlighting interstitial injection, pair formation, diffusion and dissociation.
Figure 2 Cross Section of sample during experiment highlighting interstitial injection, pair formation, diffusion and dissociation
RESULTS The phosphorus concentration after low temperature poly deposition was studied with SIMS and a typical result is plotted in Figure 3.
Figure 3 (1) Gaussian Profile simulated with TCAD coinci
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