Abstract: Apparatus of quartz or silicon carbide for use in horizontal or vertical furnace tubes, applicable to both diffusion/oxidation processes and to low pressure chemical vapor deposition process. The primary objectives include the adjustment of process gas flow distribution to improve film growth and composition uniformity to increase film growth rate and to reduce the consumption of reactant gases.The apparatus consists of four major types of components, namely a plurality of substrate carriers or boats, a plurality of gas distribution discs, front and rear manifold link fixtures and primary and secondary gas injection tubes. Substrate carriers or boats are constructed of quartz or silicon carbide or other chemically nonreactive, thermally resistant materials which support a plurality of substrates on edge in machined slots in the substrate carriers interiorly along the length of a furnace tube. The substrates rest perpendicular to the longitudinal axis of the furnace tube.