Amorphous silicon nitride fibers grown from the vapor phase

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Amorphous silicon nitride fibers grown from the vapor phase Frederick T. Wallenberger Department of Materials Science and Engineering, University of Illinois, 1304 West Green Street, Urbana, Illinois 61801

Paul C. Nordine Containerless Research, Incorporated, 735 Carriage Way, Deerfield, Illinois 60015 (Received 13 May 1993; accepted 25 October 1993)

Using high reactor pressures ( > 1 bar) and a unique rate control mechanism, three fibers were recently obtained by laser assisted chemical vapor deposition (LCVD) having elemental (i.e., boron, carbon, and silicon) compositions, small diameters (>9 /itm), and surprisingly high growth rates (0.3-1.1 mm/s). By reacting silane and ammonia at high pressures ( > 1 bar) near the focus of a Nd-YAG laser beam, we have now obtained the first LCVD fibers with binary (i.e., silicon-nitrogen and silicon nitride) compositions having small diameters and high growth rates (0.34-0.74 mm/s). These fibers were amorphous.

Growth of small diameter fibers directly from the vapor phase by laser assisted chemical vapor deposition (LCVD) is a containerless process. A CO 2 , Nd-YAG, or Ar + laser beam is focused onto a point inside a reactor where, under suitable conditions, localized heating promotes vapor deposition in the direction of the laser. The growing fiber is not in contact with reactor walls or foreign materials. It is chemically pure and suitable for optical uses, and structurally uniform, i.e., stronger than surface flawed analogs. The applied physics community1"3 uses LCVD as a research tool to study the kinetics of chemical vapor deposition (CVD) reactions. (1) Rate studies by LCVD require only a very small cross-sectional area, that of the fiber, and those by conventional CVD require a much larger surface area, that of the entire film. (2) Temperature control by laser heating is more uniform than that by radiant heating from reactor walls. (3) The low pressure regime (