Abstract: Isopipes for use in making sheet glass by a fusion process are provided which exhibit reduced sag. The isopipes are composed of a zircon refractory which has a mean creep rate (MCR) at 1180° C. and 250 psi and a 95 percent confidence band (CB) for said mean creep rate such that the CB to MCR ratio is less than 0.5, the MCR and the CB both being determined using a power law model. The zircon refractory can contain titania (TiO2) at a concentration greater than 0.2 wt. % and less than 0.4 wt. %. A concentration of titania in this range causes the zircon refractory to exhibit a lower mean creep rate than zircon refractories previously used to make isopipes. In addition, the variation in mean creep rate is also reduced which reduces the chances that the zircon refractory of a particular isopipe will have an abnormally high creep rate and thus exhibit unacceptable sag prematurely.

Abstract: Glasses are disclosed which are used to produce substrates in flat panel display devices. The glasses exhibit a density less than about 2.45 gm/cm3 and a liquidus viscosity greater than about 200,000 poises, the glass consisting essentially of the following composition, expressed in terms of mol percent on an oxide basis: 65–75 SiO2, 7–13 Al2O3, 5–15 B2O3, 0–3 MgO, 5–15 CaO, 0–5 SrO, and essentially free of BaO. The glasses also exhibit a strain point exceeding 650° C.

Abstract: Fused silica stepper lens for photolithographic application are disclosed which are resistant to laser-induced damage, specifically, compaction or densification which can lead to an increase in the optical path length of the lens. The figure compares the phase front distortions of a standard fused silica with the phase front distortions observed in two inventive stepper lens fused silica.

Abstract: A fused silica glass which exhibits low compaction when exposed to high intensity excimer radiation, also exhibits low optical path distortion after exposure to a high intensity radiation dose. Also disclosed is a method for improving the select ratio of fused silica glass for photolithography, by predicting the optical path distortion of the glass under use by determining the intrinsic densification of the glass at a given number of pulses and fluence per pulse. Mathematical modeling methods are also disclosed for use in producing a fused silica stepper lens having low compaction under high intensity excimer radiation; and for determining optical path distortion caused by high energy radiation in fused silica glass.

Abstract: Fused silica boules (19) having improved homogeneity are produced by causing the boule (19) to flow radially during its formation to achieve local mixing between portions of the boule which may have experienced different laydown conditions. The mixing is achieved by one or a combination of: (1) use of a containment vessel (13) having a gently sloping containment wall (22); (2) use of a containment vessel (13) whose inner radius (r.sub.v) is substantially larger than the outermost radius (r.sub.b) of the burners (14) used to produce the boule (19); and/or (3) maintaining the boule (19) at a sufficiently high temperature during laydown so that radial flow is achieved with a minimum head height of glass. Large blanks having high homogeneity can be made from such boules, e.g., blanks having diameters above 200 millimeters and .DELTA.n values of less than 0.25.times.10.sup.-6.