IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 61, NO. 11, NOVEMBER 2014
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Characterization of the Depth Distribution and Electrical Activation and Deactivation of Ion Implanted Dopants in Silicon Shu Qin, Senior Member, IEEE Abstract— Electrical-assisted diffusion of carriers is proposed as a hypothesis of major dopant deactivation kinetics. New metrology methods, including SIMS/ARXPS and continuous anodic oxidation technique/differential Hall effect methods, are used in this paper to supply supporting evidences and data. The n-type (P- and As-based) implants show more serious deactivation, but similar reactivation to p-type (B-based) implants, which can be interpreted by the electrical-assisted diffusion mechanism. Reactivation occurs only when the excess dopants exist—dopant concentration is higher than its electrically active solid solubility limit. Index Terms— Concentration-dependent diffusion, deactivation, electrical-assisted diffusion, electrically active solid solubility, reactivation, segregation.
I. I NTRODUCTION
T
HE requirement for ultrashallow junctions to include improved R S − x j characteristics, reasonable junction abruptness, and lower junction leakage to realize source and drain (SD) and SD extension (SDE) in Si complementary metal–oxide–semiconductor (CMOS) devices has resulted in a broad use of low-energy implants and an increased variety of annealing processes [1]. A very high degree of dopant electrical activation is required because the sheet resistance (R S ) of SD and SDE regions has to be maintained at a low level. However, it is well-known that high concentrations of dopant are easily deactivated when subjected to subsequent thermal treatments between 500 °C and 800 °C for a relatively long time between a couple minutes to hours of the furnace-based processes. When that happens, R S is significantly increased and CMOS device performance is significantly degraded. The typical low temperature (T ) and long-time (t) thermal treatments are the backend processes after SD and SDE have been formed, including depositions of variety of the dielectric or metal films by CVD, PECVD, or PVD processes. In recent decades, several experimental results and first principle calculations have suggested that the main mechanism behind this deactivation is the clustering of activated dopants (carriers) or precipitates formed with access vacancy or interstitial concentrations [2]–[7].
Manuscript received March 6, 2014; revised June 23, 2014; accepted July 22, 2014. Date of publication August 19, 2014; date of current version October 20, 2014. The review of this paper was arranged by Editor H. S. Momose. The author is with Micron Technology Inc., Boise, ID 83707 USA (e-mail:
[email protected]). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TED.2014.2342535
However, there are several arguments against this theory. First, because of a very small percentage of the activated dopant (carrier) concentration to the Si atomic density, the probability of cluster or precipitate formation is very small. For example, the maximum activated B, P, or As dopants are limited by their electrically active solid solubility, which is only ∼2–4 × 1020 /cm3 concentration after a 1000-°C anneal [8], [9]. It is much 100%, even at 2Anneal due to less deactivation. These data are very consistent to those published in [13]. An activation fraction of >100% is abnormal. It was caused by the artifact or error of the solid solubility data, which was measured by the conventional SIMS method and based on the diffusion doping method. A comparison of the activation fractions of the P-implanted and B-implanted Si demonstrates evidence of the electrical-assisted diffusion mechanism. III. C ONCLUSION Characterization of the depth distribution and electrical activation and deactivation of ion-implanted dopants in silicon demonstrates that electrical-assisted diffusion of carriers could be a hypothesis of a major dopant deactivation kinetics. New metrology methods, including SIMS/ARXPS and CAOT/DHE methods, are used in this paper to supply supporting evidences and data. N-type P implants show more serious deactivation, but similar reactivation to p-type B implants, which can be interpreted by the electrical-assisted diffusion mechanism. Reactivation occurs only when the excess dopants exist—dopant concentration is higher than its electrically active solid solubility limit. R EFERENCES [1] International Technology Roadmap for Semiconductor 2011—Front End Processes, Semiconductor Industry Association, Washington, DC, USA, 2011. [2] P. M. Rousseau, P. B. Griffin, W. T. Fang, and J. D. Plummer, “Arsenic deactivation enhanced diffusion: A time, temperature, and concentration study,” J. Appl. Phys., vol. 84, no. 7, pp. 3593–3601, 1998. [3] O. Dokumaci, P. Rousseau, S. Luning, V. Krishnamoorthy, K. S. Jones, and M. E. Law, “Transmission electron microscopy analysis of heavily As-doped, laser, and thermally annealed layers in silicon,” J. Appl. Phys., vol. 78, no. 2, pp. 828–831, Jul. 1995. [4] M. Ramamoorthy and S. T. Pantelides, “Complex dynamical phenomena in heavily arsenic doped silicon,” Phys. Rev. Lett., vol. 76, pp. 4753–4756, Jun. 1996.
QIN: DEPTH DISTRIBUTION AND ELECTRICAL ACTIVATION AND DEACTIVATION OF ION IMPLANTED DOPANTS IN SILICON
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[14] A. S. Grove, O. Leistiko, Jr., and C. T. Sah, “Redistribution of acceptor and donor impurities during thermal oxidation of silicon,” J. Appl. Phys., vol. 35, no. 9, pp. 2695–2701, Sep. 1964. [15] S. Wolf and R. N. Tauber, Silicon Processing for the VLSI Era, Vol. 1: Process Technology, vol. 1. Sunset, CA, USA: Lattice Press, 1986, p. 228. [16] S. Qin, “Two-dimensional cross-sectional doping profiling study of advanced CMOS devices using electron holography technique,” Solid State Technol., vol. 55, no. 6, pp. 29–35, Jul. 2012. [17] Y. Takamura, S. Jain, P. B. Griffin, and J. D. Plummer, “A study of the deactivation of high concentration, laser annealed dopant profiles in silicon,” in Proc. Mater. Res. Soc. Symp., vol. 669. 2001, pp. J7.3.1–J7.3.6.
Shu Qin (M’94–SM’97) received the Ph.D. degree in electrical engineering from Northeastern University, Boston, MA, USA. He has been a Senior Member Technical Staff with Micron Technology, Inc., Boise, ID, USA, since 2004. His current research interests include advanced semiconductor processing, novel plasma sources and plasma diagnoses, and device and process simulations. He holds more than 40 U.S. and international patents.
