Spectroscopic Ellipsometry for the Characterization of the Morphology of Ultra-thin Thermal CVD Amorphous and Nanocrysta
- PDF / 191,865 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 110 Downloads / 213 Views
Spectroscopic Ellipsometry for the Characterization of the Morphology of Ultra-thin Thermal CVD Amorphous and Nanocrystalline Silicon Thin Films Sukti Hazra, Mitsuyuki Yamanaka, Isao Sakata, Toshiyuki Tsutsumi, Tatsuro Maeda, Hirohisa Taguchi and Eiichi Suzuki Electron Devices Division, Electrotechnical Laboratory, 1-1-4 Umezono, Tsukuba, Ibaraki 305 8568, Japan. ABSTRACT Ultra-thin hydrogenated amorphous silicon thin films have been deposited by thermal chemical vapor deposition (CVD) to prepare smooth top surface of the films avoiding the ion bombardment. Rapid thermal oxidation of thermal CVD a-Si:H results in nanocrystalline dots in the ultra-thin silicon films. Spectroscopic ellipsometry (SE) and high resolution transmission electron microscopy (TEM) have been used to investigate the optical and structural properties of both ultra-thin a-Si:H and nanocrystalline silicon films. To analyze the ellipsometric data of ultra-thin a-Si:H films, a new parameterization i.e., the combination of Sellmeier law and four Lorentz peaks, has been successfully introduced. Width of the Lorentz peaks are directly related with the change of optical functions with the thickness of a-Si:H films. It has been certified that the dense Si matrix with smaller degree of disorder is formed when the thickness exceeds 8nm and the films with the thickness of less than 3.8 nm becomes voided. To interpret the ellipsometric data for nanocrystalline silicon films, three layer model (SiO2, poly-Si+a-Si+void and SiO2) has been adapted. It is inferred from SE and TEM analyses that the size and the density of nanocrystalline dots can be controlled by the morphology of initial ultra-thin a-Si:H films and RTO conditions. INTRODUCTION In the last years, there has been a considerable increase of the applications of silicon thin films in the microelectronic devices viz., thin film solar cells [1], thin film transistors [2, 3] etc. In this regard, extensive works are needed for the proper fabrication of silicon thin films for any particular device. In the present work, we have concentrated to develop and characterize the ultra-thin (2-10 nm) silicon films with nanocrystalline dots for the application in single electron memory transistor. Memory action of these single electron transistors will be reported elsewhere. To fabricate the nanocrystalline silicon dots, rapid thermal oxidation (RTO) [4, 5] of ultra-thin hydrogenated amorphous silicon (a-Si:H) has been used. Thermal chemical vapor deposition (Thermal CVD) has been preferred to deposit a-Si:H films instead of the most commonly used plasma enhanced chemical vapor deposition (PECVD) to avoid ion bombardment. Ion bombardment makes the top surface of the films rough which is an obstacle for our device application. Optical and structural properties of both amorphous and nanocrystalline silicon films have been characterized by the spectroscopic ellipsometry (SE) and high resolution transmission electron microscopy (TEM). To analyze the properties of ultra-thin hydrogenated amorphous silicon films, a new par
Data Loading...
