Detection of Electronic Defects in Strip-Heater Crystallized Silicon Thin Films
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DETECTION OF ELECTRONIC SILICON THIN FILMS
DEFECTS IN STRIP-HEATER
N. M. Johnson, M. D. Moyer, and L. E. Fennell Xerox Palo Alto Research Centers, Palo Alto, CA
CRYSTALLIZED
94304
E. W. Maby and H. Atwater Massachusetts Institute of Technology, Cambridge, MA
02139
ABSTRACT Electronic defects in strip-heater crystallized silicon thin films have been investigated with capacitance-voltage (C-V), deep-level spectroscopic, and scanning-electron microscopic techniques. For electrical characterization the crystallized silicon films were used to fabricate inverted metal-oxide-silicon capacitors in which degenerately doped bulk silicon substrates provided the gate electrode. High-frequency C-V characteristics yield effective fixed-charge densities in the 11 2 oxide of < 2x10 cm- . Trap-emission spectra, recorded with deep-level transient spectroscopy on both p-type and n-type capacitors, indicate a continuous distribution of deep levels throughout the silicon bandgap. The Si-Si0 2 interface is considered to be the principal source of this deep-level continuum, since the films are essentially single crystal with a low density of subgrain boundaries; the effective interface-state density is < 2.5x10 10 eV-1 cm- 2 . A discrete energy level, detectable above the background continuum, appears in the upper half of the silicon bandgap; it may identify a point defect in the bulk of the silicon film with a spatially uniform density of approximately 1X10 13 cm- 3 . On lateral p-n junction diodes, electron-beam- induced -current images
reveal enhanced diffusion of arsenic along structural defects intersecting the junction. INTRODUCTION
The rapid advancements and potential technological impact of beam-crystallized silicon thin films, as evidenced by the numerous papers on the subject in this symposium, have stimulated the need for comprehensive characterization of electronic defects and their correlation with materials processing and device performance. In a recent study [1], deep-level transient spectroscopy (DLTS) was used to measure electronic defect levels in silicon films which had been crystallized with a scanning cw Ar-ion laser. The measurement revealed a continuous distribution of deep levels in the lower half of the silicon bandgap, with the Si-Si0 2 interface considered to be a major source of these levels. In a separate study [2], lateral p - n junction diodes where fabricated in similarly crystallized silicon thin films for analysis of the metallurgical junction with electron -beam -induced currents (EBIC). This investigation revealed that large-angle incoherent grain boundaries provide efficient paths for dopant diffusion during device processing. Mat.
Res.
Soc. Symp.
Proc.
Vol.
13 (1983)
QElsevier Science Publishing Co.,
Inc.
492 In the present study DLTS and capacitance-voltage techniques were applied to detect electronic defect levels and EBIC was used to examine lateral p - n junction profiles in strip-heater crystallized silicon thin films. This crystallization technique has been shown to produce la
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