Experimental Studies of Laterally Seeded Recrystallized Polysilicon on Silicon Dioxide
Banerjee, Sanjay Kumar
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https://hdl.handle.net/2142/69270
Description
Title
Experimental Studies of Laterally Seeded Recrystallized Polysilicon on Silicon Dioxide
Author(s)
Banerjee, Sanjay Kumar
Issue Date
1983
Department of Study
Electrical Engineering
Discipline
Electrical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Abstract
Single crystal silicon films have been grown on silicon dioxide covered silicon substrates by lateral epitaxy by seeded solidification using a scanned graphite strip heater.
Various microscopy techniques have been used to establish that the films consist of large single crystal grains about 1 mm wide which extend indefinitely along the scan direction. These grains contain subgrain boundaries at about 25 (mu)m intervals. The films are fairly smooth and show excellent single crystallinity.
Boron and phosphorus implantations into these films have been studied by secondary ion mass spectrometry and Hall profiling. The diffusion properties of impurities in these films are similar to bulk silicon, the only differences being caused by the presence of the underlying silicon dioxide layer. Electrical activation and carrier mobility in these films approach bulk silicon values over a wide range of doses (10('13) - 10('15) cm('-2)). Electron mobilities as high as 600 cm('2)/V-s are observed for donor concentrations of 5 x 10('16) cm('-3). In contrast, diffusion coefficients in the as-deposited polysilicon films are much higher because of the presence of grain boundaries. These grain boundaries also cause poor activation because of dopant segregation and carrier trapping and reduce carrier mobilities because of grain boundary scattering. The subgrain boundaries in the recrystallized films have a negligible effect in terms of dopant segregation, carrier trapping, or mobility degradation. The mobility results also indicate that the recrystallized films are stress-free.
Junction studies made on these films show that leakage currents are slightly higher in these films than in bulk silicon, presumably because of the generation-recombination centers created by the subgrain boundaries in the depletion region. Reverse breakdown voltages are slightly lower in these films, again probably because of the subgrain boundaries. Minority carrier electron generation lifetimes estimated from reverse leakage current measurements yield values of (TURN) 0.2 - 0.4 (mu)s, which are much superior to values observed in silicon-on-sapphire (SOS). Deep level transient spectroscopy measurements of majority carrier traps using these p-n junctions indicate the presence of one dominant electron trap at E(,C) - 0.57 eV and one dominant hole trap at E(,V) + 0.29 eV.
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