NOVELTY - A square silica composite container has a parallel-plate-shaped porous silica composite board component (100) having a surface layer portion (111,112) containing silica glass, and heat resistant substance having melting point in a internal portion (113) higher than the silica.    USE - Square silica composite container is used for manufacture of silicon ingot (claimed) for solar cell.    ADVANTAGE - The silicon ingot has high quality and is economically manufactured.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) porous silica composite board component. The portion of depth of 1 mm or more from heat-resistant substance contains silica glass. The melting point of heat-resistant substance in internal portion having thickness of 3 or more is higher than silica; and    (2) manufacture of porous silica composite board component, which involves producing silica powder, producing a powder containing heat resistant substance, substituting the inside of the melting container positioned in an electric heating furnace by inert gas atmosphere containing nitrogen, neon, argon, and krypton, supplying silica powder outside the supply position of powder containing heat-resistant substance in the melting container while supplying the supply position, maintaining the inside of the melting container at the inert gas atmosphere, fusing, softening silica powder, heating at 1700 degrees C or more in inert gas atmosphere, melting silica glass, softening, withdrawing continuously molding a composite component with the heat-resistant substance in parallel plate shape through a shape forming tool from the lower portion of the melting container, melting silica glass, softening, disconnecting, and grinding with predetermined dimension.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view of porous silica composite board component.    Porous silica composite board component (100)    Surface (101,102)    Surface layer portion (111,112)    Internal portion (113)