Optical Properties of Laser Induced Heavily Doped Silicon Layers
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OPTICAL PROPERTIES OF LASER INDUCED HEAVILY DOPED SILICON LAYERS A.SLAOUI *, E.FOGARASSY
P.SIFFERT ,J.F.MORHANGE
,M.BALKANSKI
CENTRE DE RECHERCHES NUCLEA I RES, Laboratoire PHASE, * F-67037 STRASBOURG CEDEX UNIVERSITE Pierre et Marie Curie,Laboratoire de Physique des Solides,F-75230 PARIS CEDEX ABSTRACT: The goal of this paper is to investigate optical properties of heavily doped silicon,performed by laser annealing of implanted layers. The optical properties were investigated by using U.V. and visible light (between 200 and 500 nm)reflectance and Raman spectrometry measurements.The experimental observations have been correlated with the contribution of the supersaturated solid solution of arsenic in the silicon lattice. Furthermore,the absorption coefficent of these layers has been deduced from ellipsometry measurements. INTRODUCTION In the fabrication of sophisticated devices,such as bipolar tsansistors,used in modern electronics,integrated injection transistors I L and solar cells,the use of high dose ion-implanted laser annealed single-crystal silicon allowed the formation (1) of both heavily doped shallow N+ and P+ layers.A high power laser irradiation can anneal the ion-implanted damage region on single crystalline semiconductors. Rapid surface melting and subsequent liquid phase epitaxial regrowth in nano-second pulse annealing make it possible to dope silicon with electrically active impurities well above the thermal equilibrium solid solubility limit (2) and to completely anneal implanted regions without any macroscopic defects, such as dislocations,stacking facets or precipitations (3).Different techniques are used to analyze the structural properties of laser annealed damaged silicon:electron microscopy, He+ backscattering (RBS),Raman scattering and optical spectroscopy (4,5),mainly in the U.V. and visible range.In a recent paper (6), we have attempt to characterize heavily doped silicon layers by U.V. and visible reflectivity experiments and by electrical measurements for very large doping concentrations. In this paper,we correlate these results with the Raman spectroscopy observations to support some arguments of our discussion. EXPERIMENTS Several P-type (l00)oriented silicon wafers,l - 5 ohm.cm in resistivity ,were implanted .•ith 80 keV arsenic ions.The doses ranged from 10 E 15 to 10 E 17 cm .This step was followed by Q-switched pulse YAG laser treatment at a wavelength of 0.532 nm, -2 and a pulse duration of 100 ns,the energy being 2.5 J.cm .After laser annealing,almost all implanted impurities were located in substitutional positions,as confirmed by RBS (Table I).The electrical activity of the implanted arsenic ions was further proved by sheet measurements. The optical reflectivity spectra were performed by using a Beckmann double beam spectrophotometer over the range 250 to Mat. Res. Soc. Syrnp. Proc. Vol. 23 (1984) @Elsevier Science Publishing Co., Inc.
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500 nm. for the structural properties and between 0.9 and 2 microns for the determination of carrier concentrations.An evaporated alu
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