Fused Quartz Properties & Usage Guide

In the semiconductor industry a combination of extreme purity and excellent high temperature properties make fused quartz tubing an ideal furnace chamber for processing silicon wafers. The material can tolerate the wide temperature gradients and high heat rates of the process. And its purity creates the low contamination environment required for achieving high wafer yields. The advent of eight inch wafers combined with today's smaller chip sizes has increased chip production by a factor of four compared to technology in place just a few years ago. These developments have impacted heavily on quartz produced, requiring both large diameter tubing and significantly higher levels of purity. GE Quartz. has responded on both counts. Quartz tubing is available in a full range of sizes, including diameters of 400mm and larger. Diameter and wall thickness dimensions are tightly controlled. Special heavy wall thicknesses are available on request. By finding new and better sources of raw material, expanding and modernizing our production facilities, and upgrading our quality control functions, GE has reduced contaminants levels in its fused quartz tubing to less than 25 ppm, with alkali levels below 1 ppm.

Grade 214LD

224LD - Low Alkali Quartz Tubing

244LD Low Alkali/Low Aluminum Quartz Tubing

Low (OH-)

Fused Quartz Rod & Solids

GE supplies two forms of high purity fused quartz solid shapes for fabricators of quartzware. Type 214 rod has the high purity, elevated temperature characteristics and low coefficient of thermal expansion required for wafer carriers and push rods used in semiconductor wafer processing. The material is available in diameters of 1 to 20 mm. Very tight quality control and special processing of raw materials is used to achieve low levels of trace element contamination. When larger sizes and different shaped starting materials are required, GE supplies fabricators with pieces cut from fused quartz ingots. They are up to 72 inches in diameter, two feet thick, and weigh up to 9000 pounds.

Large Ingots

Lamp Grade Tubing

GE Quartz is the world's leading producer of fused quartz for lighting applications. Four basic types of lamp grade quartz are available, each designed to fulfill specific performance requirements. Together, these materials cover a wide variety of applications. They include:

Type 214

Type 219

Type 254

Type 021

Types 214A, 219A, and 254A

Quartz Crucibles

In the manufacture of silicon metal for semiconductor wafer applications, polysilicon starting materials are placed in fused quartz crucibles, heated to high temperatures and pulled from the melt as a single crystal. Fused quartz is one of the few materials that can combine the high purity and high temperature properties required.

Other Compositions

Fiber Optic Tubing

GE fused quartz series as deposition tubing for one of the major methods of producing optical waveguides, the Modified chemical vapor deposition (MCVD) process. For this application, GE offers high quality quartz tubing that is virtually airline free, with tight dimensional tolerances and low (OH-). This combination of characteristics translates into excellent attenuation for the fiber manufacturer. GE produces fiber optic tubing from either naturally occurring or synthetic quartz. The synthetic grades, combined with GE's unique continuous fusion process, produces fiber optic tubing with all the advantages found in natural occurring quartz, plus the higher tensile strength required for producing long length fibers. Along with waveguide material, GE offers high quality quartz tubing and handles required by the MCVD process. Each waveguide tube produced by GE is serialized, characterized and accompanied by a data slip showing the complete geometry of the tube. If desired, a computer disc can be supplied with the shipment for direct entry into our data bank.

Like any material that is expected to provide a design life at high temperatures, fused quartz demands some care in handling and use to achieve maximum performance from the product.

Storage

Cleaning

Rotation Procedures For Fused Quartz Furnace Tubes

Solarization

Technical Support

Vitreous silica is the generic term used to describe all types of silica glass, with producers referring to the material as either fused quartz or as fused silica. originally, those terms were used to distinguish between transparent and opaque grades of the material. Fused quartz products were those produced from quartz crystal into transparent ware, and fused silica described products manufactured from sand into opaque ware. Today, however, advances in raw material bonification permit transparent fusions from sand as well as from crystal. Consequently, if naturally occurring crystalline silica (sand or rock) is melted, the material is simply called fused quartz. If the silicon dioxide is synthetically derived, however, the material is referred to as synthetic fused silica. Controlled Process: The performance of most fused quartz products is closely related to the purity of the material. GE's proprietary raw material bonification and fusion processes are closely monitored and controlled to yield typically less than 50 ppm total elemental impurities by weight. GE clear fused quartz varieties have a nominal purity of 99.995 W % SiO2. Structural hydroxyl (OH-) impurities are also shown. The strong IR absorption of OH- species in fused quartz provides a quantitative method for analysis. Beta Factor: The term Beta Factor is often used to characterize the hydroxyl (OH-) content of fused quartz tubing. This term is defined by the formula shown below.

Since electrical conductivity in fused quartz is ionic in nature, and alkali ions exist only as trace constituents, fused quartz is the preferred glass for electrical insulation and low loss dielectric properties. In general, the electrical insulating properties of clear fused quartz are superior to those of the opaque or translucent types. Both electrical insulation and microwave transmission properties are retained at very high temperatures and over a wide range of frequencies.

Mechanical properties of fused quartz are much the same as those of other glasses. The material is extremely strong in compression, with design compressive strength of better than 1.1 x 10 9 Pa (160,000 psi). Surface flaws can drastically reduce the inherent strength of any glass, so tensile properties are greatly influenced by these defects. The design tensile strength for fused quartz with good surface quality is in excess of 4.8 x 10 7 Pa (7,000 psi). In practice, a design stress of .68 x 10 7 Pa (1,000 psi) is generally recommended.

Fused quartz is essentially impermeable to most gases, but helium, hydrogen, deuterium and neon may diffuse through the glass. The rate of diffusion increases at higher temperatures and differential pressures. The selective diffusion of helium through fused quartz is the basis for a method of purifying helium by essentially "screening out" contaminants by passing the gas through thin-walled quartz tubes. The diffusion of helium, hydrogen, deuterium and neon through fused quartz is accelerated with increasing temperature. According to General Electric Research Laboratory, the permeability constants for these gases through fused silica at 700 øC are estimated to be: Helium 2.1 x 10 -8 cc/sec/cm2/mm/cm.Hg. Hydrogen 2.1 x 10 -9. Deuterium 1.7 x 10 -9. Neon 9.5 x 10 -10

One of the most important properties of fused quartz is its extremely low coefficient of expansion: 5.5 x 10 -7 mm øC (20-320øC). Its coefficient is 1/34 that of copper and only 1/7 of borosilicate glass. This makes the material particularly useful for optical flats, mirrors, furnace windows and critical optical applications which require minimum sensitivity to thermal changes. A related property is its unusually high thermal shock resistance. For example, thin sections can be heated rapidly to above 1500 øC and then plunged into water without cracking. The residual stress or design, depending on the application, may be in the range of 1.7 x 10 7 to 20.4 x 10 7 Pa (25 to 300 psi). As a general rule, it is possible to cool up to 100øC/hour for sections less than 25 mm thick.

Effects Of Temperature

Viscosity

Devitrification

Cristobalite Growth

An Advantage

Contamination

Resistance To Sag

Type      Al     As      B     Ca    Cd     Cr     Cu    Fe    K   Li     Mg    Mn     Na    Ni    P      Sb   Ti   Zr   OH Type    

214       14   <0.002   <0.2  0.4   <0.01  <0.05  <0.05  0.2  0.6  0.6    0.1  <0.05   0.7  <0.1  <0.2 <0.003  1.1  0.8  <5 214     

219       14   <0.01    <0.2  0.4   <0.01  <0.05  <0.05  0.2  0.6  0.6    0.1  <0.05   0.7  <0.1  <0.2 <0.003  100  0.8  <5 219     

214A      14   <0.002   <0.2  0.4   <0.01  <0.05  <0.05  0.2  0.6  0.6    0.1  <0.05   0.7  <0.1  <0.2 <0.003  1.1  0.8  <1 214A     

214Rod/LD 14   <0.002   <0.2  0.4   <0.01  <0.05  <0.05  0.2  0.6  0.6    0.1  <0.05   0.7  <0.1  <0.2 <0.003  1.1  0.8  10 214Rod/LD

224/Rod   14   <0.002   <0.2  0.4   <0.01  <0.05  <0.03  0.2 <0.2 <0.2    0.1  <0.03  <0.2  <0.1  <0.2  0.003  1.4  0.8  10 224/Rod 

224LD     14   <0.002   <0.2  0.4   <0.01  <0.05  <0.01  0.2 <0.2  0.001  0.1  <0.05  <0.1  <0.1  <0.2  0.003  1.1  0.8  10 224LD   

244/Rod    8   <0.002   <0.1  0.6   <0.01  <0.05  <0.03  0.2 <0.2 <0.2   <0.1  <0.03  <0.2  <0.1  <0.2 <0.03   1.4  0.3  10 244/Rod 

244LD      8   <0.02    <0.1  0.6   <0.01  <0.05  <0.01  0.2 <0.2  0.001 <0.1  <0.03   0.1  <0.1  <0.2 <0.003  1.4  0.3  10 244LD   

124       14   <0.002   <0.2  0.6   <0.01  <0.05  <0.05  0.2  0.6  0.6    0.1  <0.05   0.7  <0.1  <0.2 <0.003  1.1  0.8  <5 124     

144        8   <0.002   <0.1  0.6   <0.01  <0.05  <0.05  0.2 <0.2 <0.2   <0.1  <0.03  <0.2  <0.1  <0.2 <0.03   1.4  0.3  <5 144     

Optical transmission properties provide a means for distinguishing among various types of vitreous silica as the degree of transparency reflects material purity and the method of manufacture. Specific indicators are the UV cutoff and the presence or absence of bands at 245 nm and 2.73 um. The UV cutoff ranges from ~155 to 175 nm for a 10 mm thick specimen and for pure fused quartz is a reflection of material purity. The presence of transition metallic impurities will shift the cutoff toward longer wavelengths. When desired, intentional doping, e.g., with Ti in the case of Type 219, may be employed to increase absorption in the UV. The absorption band at 245 nm characterizes a reduced glass and typifies material made by electric fusion. If a vitreous silica is formed by a "wet" process, either flame fusion or synthetic material, for example, the fundamental vibrational band of incorporated structural hydroxyl ions will absorb strongly at 2.73 um.

UV Cutoff