LOW-PRESSURE CHEMICAL VAPOR-DEPOSITION OF ALPHA-SI3N4 FROM SIF4 AND NH3 - NUCLEATION AND GROWTH-CHARACTERISTICS

The crystal structure and surface morphology of Si3N4 prepared by LPCVD were characterized as a function of processing conditions. Temperature was the most dominant variable which affected the coating microstructure. Strongly faceted crystalline Si3N4 was deposited at temperatures above approximately 1410-degrees-C. In the temperature range of 1300-degrees to 1410-degrees-C, crystalline and amorphous phases were codeposited. The content of the crystalline phase rapidly decreased with decreased temperature. In this temperature range, the coating crystallinity was also influenced by kinetic factors such as deposition rate and reagent depletion. For example, Si3N4 became more crystalline as the deposition rate was decreased by either decreasing the flow rate or increasing the NH3/SiF4 molar ratio. At approximately 1300-degrees-C, the coating surface appeared fully botryoidal, and the coatings were mostly amorphous. Changes in the orientation and size of Si3N4 crystallites were parametrically documented. As the temperature was increased, the Si3N4 grains generally became more preferentially oriented to the (102) and/or (l0l) where l = 1,2,3,.., directions. The average facet size increased with coating thickness.