BNL-112215-2016-CP Molecular ion sources for low energy semiconductor ion implantation 1 2 3 A. I. Hershcovitch , V. I. Gushenets , D. N. Seleznev , 2 4 2 3 B. A. S. Bugaev , S. Dugin , E. M. Oks , T. V. Kulevoy , 4 3 3 C. O. Alexeyenko , A. Kozlov , G. N. Kropachev , 3 3 2 2 D. R. P. Kuibeda , S. Minaev , A. Vizir , G. Y. Yushkov 1Brookhaven National Laboratory, Upton, NY 11973 USA 2High Current Electronics Institute, Siberian Branch of Russian Academy of Sciences, Tomsk 634055 Russia 3Institute for Theoretical and Experimental Physics, Moscow 117218 Russia 4State Scientific Center of the Russian Federation State Research Institute for Chemistry and Technology of Organoelement Compounds, Moscow Russia Presented at the 16th International Conference on Ion Sources New York Marriott Marquis Hotel, New York, NY August 23 – 28, 2015 May 2016 Collider-Accelerator Department Brookhaven National Laboratory U.S. Department of Energy Office of Science, Office of Nuclear Physics Notice: This manuscript has been authored by employees of Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy. The publisher by accepting the manuscript for publication acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or any third party’s use or the results of such use of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof or its contractors or subcontractors. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Molecular ion sources for low energy semiconductor ion implantationa) A. Hershcovitch1,b), V. I. Gushenets2, D. N. Seleznev3, A. S. Bugaev2, S. Dugin4, E. M. Oks2, T. V. Kulevoy3, O. Alexeyenko4, A. Kozlov3, G.N. Kropachev3, R. P. Kuibeda3, S. Minaev3, A. Vizir2, and G. Yu. Yushkov2 1Brookhaven National Laboratory, Upton, New York 11973, USA 2High Current Electronics Institute, Siberian Branch of Russian Academy of Sciences, Tomsk 634055, Russia 3Institute for Theoretical and Experimental Physics, Moscow 117218, Russia 4State Scientific Center of the Russian Federation State Research Institute for Chemistry and Technology of Organoelement Compounds, Moscow, Russia (Presented XXXXX; received XXXXX; accepted XXXXX; published online XXXXX) Smaller semiconductors require shallow, low energy ion implantation, resulting space charge effects, which reduced beam currents and production rates. To increase production rates, molecular ions are used. Boron and phosphorous (or arsenic) implantation are needed for P-type and N-type semiconductors respectively. Carborane, which is the most stable molecular boron ion leaves unacceptable carbon residue on extraction grids. A self-cleaning carborane acid compound (C4H12B10O4) was synthesized and utilized in the ITEP Bernas ion source resulting in large carborane ion output, without carbon residue. Pure gaseous processes are desired to enable rapid switch among ion species. Molecular phosphorous was generated by introducing phosphine in dissociators via 4РН3 = Р4 + 6Н2 generated molecular phosphorous in a pure gaseous process, was then + injected into the HCEI Calutron-Bernas ion source, from which Р4 ion beams were extracted. Results from devices and some additional concepts are described. I. INTRODUCTION Modern semiconductor technology requires an increase in the efficiency and reliability of highly integrated circuits One of the last remaining frontiers of the (ICs), enhancement of their functional capabilities, and a semiconductor industry, as well as a major research and decrease in the cost of IC elements and structures. A development thrust for the semiconductor ion implantation technique to do this is to increase the integrated circuit industry, is low energy ion implantation1. Since the density by decreasing the size of IC elements and invention of the transistor, the trend has been to increasing their number per unit crystal area, which miniaturize semiconductor devices. As devices get smaller, simultaneously decreases their depth. These tasks inspire shallower ion implantation for semiconductor continuous improvement and development of manufacturing is needed. Consequently, lower energy ion technological equipment for IC manufacturing. Decreasing beams are needed. However, low energy ion beam have the modification depth necessitates a decrease in dopant limited intensity (current), due to space charge blow-up as ion energy; hence the need for shallow implantation and the Child Law limit is exceeded. Low intensity ion beams the resultant space charge issues. result in low production rates. Therefore, low energy ion 1 Although most implanters still rely on xenon plasma implanters have low production rates. Consequently, for neutralization, a better approach for mitigating the increasing the current of pure, low energy ion beams is of space charge problem is to utilize molecular ion beams (or paramount importance to the semiconductor industry clusters terminology used by the semiconductor) for nowadays. Ion beams are usually extracted from ion implantation. sources, in which ions are generated by electrical discharge Boron and phosphorous clusters have been used by the of gases or vapors. At a given extraction energy, ion semiconductor ion implantation industry. Much of the current is limited by the space charge of the ion beam development of boron clusters ion sources has been known as the Child law. Neutralizing plasmas, utilized in 2 pioneered at SemEquip lead by Tom Horsky in generating today’s implanters, to reduce space charge offer only a decaborane (B H ) and octadecaborane (B H ) ion partial solution and often result in implanting undesirable 10 14 18 22 beams; though molecular boron compounds were invented impurities. in the Soviet Union as rocket fuel. Similarly, tetratomic a) th Invited talk paper, published as part of the Proceedings of the 16 phosphorus (P4) and its ions are of interest as prototypes of International Conference on Ion Sources, New York City, NY, USA small clusters. Horsky3 at SemEquip also generated August, 2015. b) molecular phosphorus ion beams. Both boron and Electronic mail: [email protected]. phosphorous clusters are very promising for high-dose The use of red phosphorus as a P4 molecular vapor very-low-energy ion implantation in semiconductor source involves a series of problems associated with industry. multiphase nature of red phosphorus, its evaporation rate The use of clusters (with n atoms) is promising instability, thermodynamic instability (a possibility to because at a given accelerating voltage and at the same ion transform from one allotropic state to another), and low beam current density, for the cluster ions implanted dose evaporation kinetics. The foregoing factors considerably rate increases in n2 times compared to that for monatomic lengthen the time during which equilibrium vapor pressure ions3. This may be connected to lower implanted energy is established over the heated phosphorus surface and per cluster atom and shorter the mean path of the ions in a result in unstable vapor supply to the discharge chamber of target. The use of polyatomic molecules for implantation an ion source. And, equally important for the ion provides, along with the increase in beam perveance and implantation industry is that the use of ovens is time implanted dose, the following significant advantages: consuming when switching among implantation species; 1) Eliminate the so-called energy contamination and therefore, many manufacturers implant P+ even for shallow high-energy tail characteristic of low-energy implantation implantations. with a retarding field; An alternative source of phosphorus as a plasma- 2) Greatly improves the quality of a low-energy ion forming medium is phosphine – a gaseous compound of beam (decreases its angular expansion and ensures better phosphorus with hydrogen (PH3) under normal conditions. angular and spatial distributions) at a target; and In discharge systems of ion sources, phosphine is used 3) Allow using the existing doping technology for mainly to obtain singly charged monatomic phosphorus shallow p-n junctions. ions. In addition to phosphorus ions, the beam contains + + Molecular ion generation that is the subject of this ions of phosphorus compounds with hydrogen: РН , РН3 . + + paper has advantages over currently used techniques: The total current of РН , РН3 ions is rather high and can 5 boron generation is based on carborane (C2B10H12) that is reach 25–30% of the total beam current . The use of the the most stable of multi-boron molecules that does not gaseous compound allows control