Pulsed Excimer Laser (308 nm) Annealing of Ion Implanted Silicon and Solar Cell Fabrication
- PDF / 860,682 Bytes
- 6 Pages / 417.6 x 639 pts Page_size
- 57 Downloads / 195 Views
PULSED EXCIMER LASER (308 nm) ANNEALING OF ION IMPLANTED SILICON AND SOLAR CELL FABRICATION* D. H. LOWNDES, J. W. CLELAND, W. H. CHRISTIE, R. E. EBY, G. E. JELLISON, JR., J. NARAYAN, R. D. WESTBROOK, AND R. F. WOOD Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, and J. A. NILSON AND S. C. DASS Lumonics, Inc., Kanata (Ottawa), Ontario, K2K 1Y3, Canada ABSTRACT A pulsed ultraviolet excimer laser (XeCl, 308 nm wavelength, 40 nsec FWHM pulse duration) has been successfully used for laser TEM, annealing of both boron- and arsenic-implanted silicon. SIMS, and sheet electrical measurements are used to characterize C-V and I-V measurements demonstrate that near-ideal specimens. p-n junctions are formed (diode perfection factor A = 1.2). Electrical activation of implanted ions by single laser pulses is 2 essentially complete for energy densities Ep > 1.4 J/cm , far 2 below the threshold for substantial surface damage -4.5 J/cm . Melting model calculations are in good agreement with observed thresholds for dopant redistribution and for epitaxial regrowth. Changes in annealing behavior resulting from multiple (1,2,5) Finally, we demonstrate the use laser pulses are also reported. of scanned overlapping excimer laser pulses for fabrication of 2 large area (2 cm ) solar cells with good performance characteristics. In contrast to pulsed ruby laser annealing, high open circuit voltages can be obtained without the use of substrate heating. INTRODUCTION Pulsed solid state lasers (both ruby and Nd:YAG) are useful for removal of ion implantation-induced lattice damage [13 and for p-n junction formation [2) However, commercial application of these techniques has been in silicon. limited by several disadvantages inherent to pulsed solid state lasers: (1) Spatial beam nonuniformity which has required using diffuser plates [3] or 2 diffusing light pipes [4] to uniformly anneal even -1 cm areas; (2) low repetition rate (-1 pulse per min) for high energy (Z5 J) pulses; and, (3) high spatial coherence, which causes both troublesome interference patterns ("speckle") and actual damage on a microscopic scale due to diffraction Solid state laser rods and coatings are also susceptible to damage effects. This has led to at high pulse energies, resulting in low duty-cycle operation. the general perception that the necessary scaling up of the single-pulse 2 annealing method to achieve commercially viable areas (-20-80 cm ) and pulse energies (-40-160 J.), could become prohibitively expensive and/or difficult. In contrast, the recent development of excimer lasers is of great interest for potential commercial applications of pulsed laser annealing, such as large Excimer lasers combine a rectangular annealing beam area, area solar cells. with highly uniform (+5%) pulsed energy density and only moderate spatial coherence. Thus, both the need for diffuser plates or light pipes and the most troublesome spatial interference effects are simultaneously eliminated. Excimer lasers also offer high (currently 1-100 Hz) pulse repetition
Data Loading...
