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DEPOSITION CHEMISTRY AND STRUCTURE OF AMORPHOUS FLUORINATED SILICON NITRIDE MARK A. PETRICH*, RHETT E. LIVENGOOD**, DENNIS W. HESS, and JEFFREY A. REIMER Department of Chemical Engineering, University of California, Berkeley, California 94720-9989 *Current address: Chemical Engineering Department, Northwestern University, Evanston, IL 60208. *Current address: Intel Corporation, SC9-13, P.O.Box 58125,Santa Clara, CA 95052-8125. ABSTRACT The deposition chemistry, optical properties, and structure of plasma-deposited fluorinated silicon nitride films are studied and compared to available results of other researchers. Fluorinated films show an increase in deposition rate and optical band gap, and a decrease in refractive index and film stress compared to unfluorinated silicon nitride films. Fluorine concentration in the films ranges from 5 to 25 atomic percent. The total hydrogen concentration of fluorinated films is lower than that of unfluorinated films. The improved thermal stability of fluorinated films as compared to unfluorinated films is explained by a significant decrease in hydrogen bonded to silicon. All films hydrolyze to some extent and films with large fluorine concentrations hydrolyze rapidly to silicon dioxide. The microstructure of fluorinated films consists of clustered silicon-fluorine and nitrogen-hydrogen regions within an amorphous silicon-nitrogen matrix. INTRODUCTION Plasma-deposited silicon nitride (SiNxHy) films are used for final passivation layers or insulation between metal layers in integrated circuit devices. The complex plasma deposition chemistry produces films which contain up to 30 atomic percent hydrogen. The hydrogen has both deleterious and advantageous effects on electronic device performance. Hydrogen in metal/insulator/semiconductor devices can diffuse to the gate insulator and create traps, causing electrical instabilities such as threshold voltage shifts [1]. Also, hydrogen evolves from SiNxH films during annealing which causes film blistering and peeling. However, some amount hydrogen is required to passivate film defects by formation of covalent bonds. Clearly, the performance and reliability of SiNxH -containing devices depends not only on the amount of hydrogen present but on the type of hyXogen local bonding configurations as well. We report an attempt to improve the hydrogen microstructure, of SiNxHy films by fluorination. Using solid state nuclear magnetic resonance spectroscopy, we are able to elucidate the film microstructure and obtain insight into the deposition chemistry of fluorinated films. EXPERIMENTAL

Film De~ iion

Fluorinated SiNxHy films were deposited in a stainless steel, axial flow, capacitively coupled, radio frequency plasma reactor [2] on substrates using gas mixtures of silane (10 percent diluted in helium), ammonia, nitrogen, nitrogen trifluoride, fluorine (5 percent diluted in helium), and hydrogen. The substrates were silicon ( p-type, 30-50 ohm-cm resistivity), polished carbon, aluminum foil, or quartz depending on subsequent film measurements. Va