Controlled localised melting in silicon by high dose germanium implantation and ﬂash lamp annealing Matthias Voelskow a, * , Wolfgang Skorupa a , Jörg Pezoldt b , Thomas Kups b a Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf, P.O. Box 510119, 01314 Dresden, Germany b Institute of Micro- and Nanotechnologies, TU Ilmenau, P.O. Box 100565, 98684 Ilmenau, Germany article info Article history: Available online 6 February 2009 PACS: 64.70.dj 61.72.uf 42.72.-g Keywords: Flash lamp annealing Localised melting Doping Ion implantation abstract High intensity light pulse irradiation of monocrystalline silicon wafers is usually accompanied by inho- mogeneous surface melting. The aim of the present work is to induce homogeneous buried melting in sil- icon by germanium implantation and subsequent ﬂash lamp annealing. For this purpose high dose, high energy germanium implantation has been employed to lower the melting temperature of silicon in a pre- determined depth region. Subsequent ﬂash lamp irradiation at high energy densities leads to local melt- ing of the germanium rich buried layer, whereby the thickness of the molten layer depends on the irradiation energy density. During the cooling down epitaxial crystallization takes place resulting in a lar- gely defect-free layer. The combination of buried melting and dopant segregation has the potential to produce unusually buried doping proﬁles or to create strained silicon structures. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction The use of ion implantation as a method for doping of semicon- ductor bulk regions is always connected with the formation of a Gaussian-like concentration/depth proﬁle. Thereby the width of the proﬁle increases with increasing ion energy. Furthermore, annealing of the implantation damage leads to an additional broadening of the dopant distribution. Therefore, using conven- tionally implantation and annealing techniques, it seems impossi- ble to produce at the same time quite deep and sharp doping proﬁles. Pulsed techniques, like laser or ﬂash lamp irradiation, in combi- nation with melting processes have the potential to transfer Gauss- ian-like proﬁles into rectangular or delta like proﬁles in dependence on the segregation coefﬁcient of the implanted ions [1]. However, due to the vertical temperature gradient formed dur- ing the pulse irradiation and due to the high overheating of the material, melting usually starts spontaneous at the surface forming inverse, three-dimensional single molten pyramids, whereby the shape of the molten zones is a result of the anisotropy of the melt- ing velocities. Further heating induce the growth of the single mol- ten regions until they touch each other, forming a continuous molten surface layer. Therefore, the shape of the liquid/solid inter- face is not planar but shows a pronounced zigzag line. During the subsequent solidiﬁcation process the non-planar interface leads to the appearance of horizontal crystallization com- ponents and consequently, in connection with the 5% volume expansion of solidifying silicon, to a quite rough surface relief. A detailed description of the phenomena of facetted melting in sili- con after ﬂash lamp irradiation is given in [2]. Therefore, to form a buried and homogeneous molten layer one has ﬁrst to enforce the start of melting inside the material and sec- ond to homogenize the melting front. In this work, we propose an approach to achieve localised bur- ied melting at a predetermined depth by high dose/high energy Ge implantation and subsequent ﬂash lamp annealing (FLA) to selec- tively melt this zone. A germanium admixture of 20% into silicon, for example, reduces the melting temperature by about 40 degree (see phase diagram [3]). 2. Experimental Germanium implantation at an energy of 190 keV and a dose of 5  10 17 cm 2 into (1 0 0) silicon was used to produce a buried layer with a signiﬁcantly reduced melting temperature. The implantation was carried out at an elevated temperature of 400 °C to avoid amorphisation of the implanted layer as well as any spontaneous crystallization during the subsequent annealing. The pulse annealing was realized using the Rossendorf ﬂash lamp apparatus. The system consists of a process chamber, an upper bank of 12 xenon lamps, a wafer holder, a lower bank of 0168-583X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2009.01.143 * Corresponding author. E-mail address: m.voelskow@fzd.de (M. Voelskow). Nuclear Instruments and Methods in Physics Research B 267 (2009) 1269–1272 Contents lists available at ScienceDirect Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb