Phosphorus out-diffusion in laser molten silicon

• Published in: Journal of applied physics 2015-04, Vol.117 (14)
• Main Authors: Köhler, J. R., Eisele, S. J.
• Format: Article
• Language: English
• Subjects: Atomic properties; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; COMPARATIVE EVALUATIONS; Computer simulation; COMPUTERIZED SIMULATION; CONCENTRATION RATIO; DIFFUSION; Diffusion coefficient; Doping; ELECTROMAGNETIC PULSES; ENERGY DENSITY; Flux density; ION MICROPROBE ANALYSIS; IRRADIATION; Laser beams; LASER RADIATION; Lasers; Liquid phases; MASS SPECTROSCOPY; Mathematical models; MELTING; Neodymium lasers; P-N JUNCTIONS; PHOSPHORUS; Secondary ion mass spectroscopy; SILICON; Silicon wafers; SOLIDIFICATION
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.4917048

Laser doping via liquid phase diffusion enables the formation of defect free pn junctions and a tailoring of diffusion profiles by varying the laser pulse energy density and the overlap of laser pulses. We irradiate phosphorus diffused 100 oriented p-type float zone silicon wafers with a 5 μm wide line focused 6.5 ns pulsed frequency doubled Nd:YVO4 laser beam, using a pulse to pulse overlap of 40%. By varying the number of laser scans Ns = 1, 2, 5, 10, 20, 40 at constant pulse energy density H = 1.3 J/cm2 and H = 0.79 J/cm2 we examine the out-diffusion of phosphorus atoms performing secondary ion mass spectroscopy concentration measurements. Phosphorus doping profiles are calculated by using a numerical simulation tool. The tool models laser induced melting and re-solidification of silicon as well as the out-diffusion of phosphorus atoms in liquid silicon during laser irradiation. We investigate the observed out-diffusion process by comparing simulations with experimental concentration measurements. The result is a pulse energy density independent phosphorus out-diffusion velocity vout = 9 ± 1 cm/s in liquid silicon, a partition coefficient of phosphorus 1