Formation of arsenolite crystals at room temperature

Formation of arsenolite crystals at room temperature after very high dose arsenic implantation in silicon Florian Meirer, Damiano Giubertoni, Evgeny Demenev, Lia Vanzetti, Salvatore Gennaro, Michele Fedrizzi, Giancarlo Pepponi, Apurva Mehta, Piero Pianetta, Georg Steinhauser, Vinayak Vishwanath, Majeed Foad, and Massimo Bersani Citation: Applied Physics Letters 101, 232107 (2012); doi: 10.1063/1.4769446 View online: http://dx.doi.org/10.1063/1.4769446 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/101/23?ver=pdfcov Published by the AIP Publishing

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APPLIED PHYSICS LETTERS 101, 232107 (2012)

Formation of arsenolite crystals at room temperature after very high dose arsenic implantation in silicon Florian Meirer,1 Damiano Giubertoni,1 Evgeny Demenev,1 Lia Vanzetti,1 Salvatore Gennaro,1 Michele Fedrizzi,1 Giancarlo Pepponi,1 Apurva Mehta,2 Piero Pianetta,2 Georg Steinhauser,3 Vinayak Vishwanath,4 Majeed Foad,4 and Massimo Bersani1 1

Fondazione Bruno Kessler, Center for Materials and Microsystems, Via Sommarive 18, 38123 Povo, Trento, Italy 2 Stanford Synchrotron Radiation Lightsource, 2575 Sand Hill Rd., Menlo Park, California 94025, USA 3 Atominstitut, Vienna University of Technology, Stadionallee 2, 1020 Vienna, Austria 4 Applied Materials, 3225 Oakmead Village Drive, Santa Clara, California 95052, USA

(Received 26 October 2012; accepted 16 November 2012; published online 5 December 2012) Spontaneous growth of arsenolite micro-crystals at room temperature after high fluence, low energy arsenic trihydride implantation in silicon was observed on the wafer surface after exposure to air. The crystals have been identified unambiguously by x-ray absorption and fluorescence spectroscopy. Thermal treatment easily sublimates the crystals at temperatures as low as 200  C without any relevant in-diffusion of As into the substrate. The deposition of a thin As-rich layer under high fluence implantation conditions is suggested as possible precursor for crystal formation. The same layer can explain the anomalous retained dose increase often observed after C 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4769446] annealing. V

Doping of silicon with arsenic atoms is commonly used in order to create n-type regions in microelectronic devices. Arsenic distributions are typically produced by ion implantation followed by thermal annealing in order to remove lattice damage and electrically activate the dopant atoms. Next generation nanometric devices require challenging specifications in order to ensure low sheet resistance in source and drain areas.1 Particularly, source and drain extensions must have very shallow and highly electrically active dopant distributions in planar complementary metal oxide semiconductor (CMOS) transistors to overcome short channel effects.2 Furthermore, the introduction of tridimensional devices such as fin field-effect transistors requires conformal doping on each side of the structures. Plasma immersion ion implantation and deposition (PIIID) is one approach where the ultimate shallow dopant distribution, high fluences, conformal doping, and high throughput can be achieved.3,4 However, PIIID parameters need to be precisely tuned since plasma immersion not only produces implantation of the doping species in silicon but also sputtering and/or deposition of material depending on the plasma conditions.3,4 Results reported in literature for ultra low energy (ULE) arsenic implantation,5 As pulsed plasma doping (PLAD),6–8 and PIIID9 show the formation of an As-rich silicon oxide when high doses are targeted. However, it is not clear if the layer was deposited during implantation or was formed afterwards, when exposing the irradiated surface to the atmosphere. Surprisingly, it was also reported that after annealing, the retained As dose was found increased with respect to the value measured on “as implanted” samples.8,9 In this work, high fluence low energy As implantation on Si was investigated and insight in the described phenomena was obtained through two pieces of evidence. First, deposition of a thin cap in situ after PIIID prevented the formation of a relatively thick As-rich Si oxide surface layer 0003-6951/2012/101(23)/232107/4/$30.00

as formerly reported,6,8,9 indicating that this layer was not deposited but grown after exposing the irradiated surface to atmosphere. Second, the spontaneous formation of arsenolite crystals (As2O3) was observed after exposing the irradiated surface to air at room temperature for a few weeks if the protective cap was not deposited. The crystals easily sublimate when thermally treated at 200  C without relevant diffusion of arsenic from the crystals to the substrate. It is speculated that the arsenolite crystals formation is due to the deposition of a very thin As-rich layer which triggers spontaneous crystal growth at room temperature when exposed to ambient air. This layer can also explain the discrepancies reported in literature where higher retained As doses were observed after annealing. Silicon (100) CZ wafers were subjected to low energy PIIID with an AsH3/H2 plasma, with bias voltage