High purity synthetic silica and items such as semiconductor jigs manufactured therefrom

A process for the manufacture of an annular transparent synthetic vitreous silica jig of external diameter greater than 400 mm and internal diameter greater than 300 mm and having a chlorine concentration of less than 5 ppM, the process comprising the steps of:

• feeding a chlorine-free silica precursor to the flame of at least one synthesis burner;
• depositing a porous soot body of density greater than 0.4 g/cm3 on an oxidation resistant mandrel of diameter at least 300 mm;
• dehydrating said soot body on a mandrel comprising a material selected from graphite, carbon fibre reinforced carbon, silicon carbide, silicon impregnated silicon carbide, silicon carbide-coated graphite and vitreous silica, under vacuum;
• sintering the dehydrated soot body to transparent pore-free glass under vacuum to produce a hollow ingot;
• and
• slicing the hollow ingot to produce the annular transparent synthetic vitreous silica jig,
• wherein, the hollow ingot is manufactured to a near-net-shape relative to a final shape of the annular transparent synthetic vitreous silica jig as a result of said depositing, dehydrating and sintering steps and without a secondary reflow or resizing process step,
• wherein the transparent vitreous silica of the annular jig has an annealing point (viscosity 1013 Poise) greater than 1,200° C.;
• and
• wherein the annular transparent synthetic vitreous silica jig is not doped with nitrogen and is not doped with fluorine.

A process for the manufacture of an annular transparent synthetic vitreous silica jig of external diameter greater than 400 mm and internal diameter greater than 300 mm and having a chlorine concentration of less than 5 ppM, the process consisting of the steps of:

• feeding a chlorine-free silica precursor to the flame of at least one synthesis burner;
• depositing a porous soot body of density greater than 0.4 g/cm3 on an oxidation resistant mandrel of diameter at least 300 mm;
• dehydrating said soot body on a mandrel comprising a material selected from graphite, carbon fibre reinforced carbon, silicon carbide, silicon impregnated silicon carbide, silicon carbide-coated graphite and vitreous silica, under vacuum;
• sintering the dehydrated soot body to transparent pore-free glass under vacuum to produce a hollow ingot;
• and
• slicing the hollow ingot to produce the annular transparent synthetic vitreous silica jig,
• wherein, the hollow ingot is manufactured to a near-net-shape relative to a final shape of the annular transparent synthetic vitreous silica jig as a result of said depositing, dehydrating and sintering steps and without a secondary reflow or resizing process step,
• wherein the transparent vitreous silica of the annular jig has an annealing point (viscosity 1013 Poise) greater than 1,200° C.,
• wherein the annular transparent synthetic vitreous silica iig is not doped with nitrogen and is substantially free of fluorine.