Ultra-shallow p+-junction formation in silicon by excimer laser doping: a heat and mass transfer perspective

• Published in: International journal of heat and mass transfer Vol. 39; no. 18; pp. 3835 - 3844
• Main Authors: Zhang, X., Ho, J.R., Grigoropoulos, C.P.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.12.1996; Elsevier
• Subjects: Applied sciences; Electronics; Exact sciences and technology; Microelectronic fabrication (materials and surfaces technology); Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Microelectronic fabrication; Impurity density; Junction; Silicon; Laser irradiation; Experimental study; Doping profile
• ISSN: 0017-9310; 1879-2189
• DOI: 10.1016/0017-9310(96)00043-9

Heat and mass transfer at the nanosecond time scale and the nanometer length scale in pulsed laser fabrication of ultra-shallow p +-junctions is studied in this work. A new technique is developed to fabricate the ultra-shallow p +-junctions with pulsed laser doping of crystalline silicon with a solid spin-on-glass (SOG) dopant, through the nanosecond pulsed laser heating, melting, and boron mass diffusion in the 100 nm thin silicon layer close to the surface. High boron concentration of 10 20 atoms cc −1 and the ‘box-like’ junction profile are achieved. The key mechanism determining the ‘box-like’ junction shape is found to be the melt-solid interface limited diffusion. The ultra-shallow p +-junctions with the depth from 30 to 400 nm are successfully made by the excimer laser. The optimal laser fluence condition for SOG doping is found about 0.6–0.8 J cm −2 by studying the ultra-shallow p +-junction boron profiles measured by the secondary ion mass spectroscopy (SIMS) vs the laser fluence and the pulse number. The one-dimensional numerical analysis agrees reasonably with the experiment, within the available physical picture. Possible mechanisms such as boron diffusivity dependence on the dopant concentration in the molten silicon are proposed.