Electron Microscopy Studies of Undoped and Phosphorus Doped Si:H and Si,C:H Films
- PDF / 1,482,919 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 10 Downloads / 212 Views
ELECTRON MICROSCOPY STUDIES OF UNDOPED AND PHOSPHORUS DOPED Si:H AND Si,C:H FILMS Y. L. CHEN, J. BENTLEY*, C. WANG, G. LUCOVSKY, AND D. M. MAHER Department of Materials Science and Engineering and Department of Physics North Carolina State University, Raleigh, NC 27695-7916 *Metals and Ceramics Division Oak Ridge National Laboratory, P. O. Box 2008, Oak Ridge, TN 37831-6376 ABSTRACT The microstructure of undoped and phosphorus doped Si:H and Si,C:H films was analyzed by selected-area diffraction, conical dark-field imaging, energy-dispersive x-ray spectroscopy and electron energy-loss spectroscopy in transmission electron microscopes. Thin films were synthesized by remote plasma-enhanced chemical vapor deposition and characterized in terms of degree of crystallinity. The distribution of phosphorus in the Si:H and Si,C:H films, and carbon in the Si,C:H films was evaluated. The results indicate that i) the microstructure of a film may be two phase, consisting of silicon microcrystallites in an amorphous matrix, ii) phosphorus doping as well as the presence of carbon influences the degree of crystallinity by reducing the average size and volume fraction of microcrystallites, iii) the presence of carbon and phosphorus doping completely suppresses the crystalline phase, iv) phosphorus is distributed at approximately the same concentration in both the crystalline and amorphous phases of diphasic films, and v) carbon is detected in the amorphous phase of the Si,C:H films. INTRODUCTION Thin films of microcrystalline Si:H (lic-Si) and microcrystalline Si,C:H (gc-Si,C alloys) and their phosphorus and boron doped counterparts have been synthesized by remote plasma enhanced chemical vapor deposition (RPECVD),1 .2 reactive magnetron sputtering, 3 ,4 and glow discharge. 5- 7 This class of thin films shows interesting electrical and optical properties. 8 ,9 For example, the dark conductivity of a film can be high depending on the microstructure and doping level. Because of these electrical and optical properties, the films are candidates for i) stacked gate electrodes and source/drain contacts in the context of module cluster processing as 14 well as ii) photovoltaic structures and solar cell devices.10Previous studies which combined transmission electron microscopy (including diffraction contrast imaging, selected-area diffraction and high-resolution imaging) and vibrational spectroscopies (including infrared and Raman scattering) 4 ,15 have shown that i) the microstructure of Si:H and Si,C:H films may be two phase, consisting of microcrystallites in an amorphous matrix; ii) the crystalline phase is silicon which has a columnar-like grain structure the major axes of these grains have preferred orientations predominantly along the direction of deposition (i.e. [001]) and the average diameter of columnar-like grains is about 10 nm; iii) the columnar grains are embedded in a matrix of a-Si:H for jic-Si films and a-Si,C:H for the gtcSi,C alloys; iv) the degree of crystallinity depends on both the doping level and the presence of car
Data Loading...
