Pulsed Excimer Laser (308 nm) Annealing Of Ion Implanted Silicon and Solar Cell Fabrication

Abstract

ABSTRACTA pulsed ultraviolet excimer laser (XeCl, 308 nm wavelength, 40 nsec FWHM pulse duration) has been successfully used for laser annealing of both boron- and arsenic-implanted silicon. TEM, SIMS, and sheet electrical measurements are used to characterize specimens. C-V and I-V measurements demonstrate that near-ideal p-n junctions are formed (diode perfection factor A = 1.2). Electrical activation of implanted ions by single laser pulses is essentially complete for energy densities Eℓ≥ 1.4 J/cm2 , far below the threshold for substantial surface damage ∽4.5 J/cm2. 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) laser pulses are also reported. Finally, we demonstrate the use of scanned overlapping excimer laser pulses for fabrication of large area (2 cm2 ) 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.