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Semiconductor Grade Fused Quartz Tubing
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.
This is the large diameter grade of industry standard 214 quartz tubing. For all but the highly specialized operations, this low cost tubing offers the levels of purity, sag resistance, furnace life and other properties that diffusion and CVD processes require. For superior performance at elevated temperatures GE type 214 LD furnace tubing gives process engineers a better balance between the effects of higher temperatures and heavier wafer loads.
Low Alkali Quartz Tubing As the semiconductor industry moves toward higher densities, furnace atmosphere contaminant becomes an increasingly critical factor in controlling wafer yields. One potential contaminant is sodium, which occurs naturally in the silica sand used to make fused quartz. This highly mobile ion can effectively destabilize the electrical characteristics of MOS and bipolar devices if not removed. For these critical applications GE has developed Grade 224 low alkali fused quartz tubing. It is made in a special process that eliminates up to 90 % of the naturally occurring alkalis. The process achieves a typical sodium level of 0.1 ppm (vs. a normal 0.7 ppm), greatly reduces potassium, and virtually eliminates lithium
Low Alkali/Low Aluminum Quartz Tubing This grade has been specially developed for quartz users concerned about the aluminum level in fused quartz. 244 has a typical aluminum level of 8 ppm.
One reason that GE fused quartz tubing can withstand the wide thermal gradients and chemical environments of wafer processing operations is its (OH-) content of less than 10 ppm water in most grades. Low OH- minimizes the sag rate at diffusion temperatures, and effectively retards the progress of devitrification. Because of its low hydroxyl content, GE Quartz tubing does not require special coatings that could potentially release contaminants at elevated temperatures.
Fused Quartz Rod & Solids
GE supplies two forms of high purity fused quartz solid shapes for fabricators of quartz ware. 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.
GE Type 124 ingots have been the semiconductor industry's material of choice for fabricating diffusion and CVD furnace components for a number of years. The advent of larger wafer sizes, tighter device geometries, and the drive for lower contaminant levels has stimulated GE's development of an even higher purity grade. Type 144 is specially processed to reduce alkali content by up to 90%. Sodium is held to 0.2 ppm or lower, potassium is significantly reduced while lithium is about 0.2 ppm. Type 012 provides the ultra high purity of synthetic fused silica, while maintaining low (OH) at < 5 ppm.
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:
The worldwide standard for clear fused quartz lamp tubing. GE 214 is a high purity, high transmittance, high temperature material with a low hydroxyl (OH-) content. It is suitable for a broad range of mercury, halogen and other quartz lamp applications.
Known as "Ozone-Free" or "Germicidal" quartz tubing. GE 219 transmits UV-A and UV-B while blocking the deep, high energy wavelengths that cause ozone generation and pose the greatest exposure risks. Type 219 transmits the 253.7 nanometer mercury emission very efficiently, making it an ideal material for disinfection applications and various other UV treatments.
A doped quartz material that blocks virtually all UV-B and UV-C radiation. Type 254 has a transmittance cutoff wavelength between 350 and 400 nanometers. It is ideal for lamps requiring maximum visible transmittance with nearly complete UV protection. Applications for GE 254 are those where UV exposure to people or property is undesirable, including some quartz halogen and metal halide lamps and other UV sources.
This is a dry synthetic fused silica material providing high transmittance in the deep ultraviolet range. It combines the advantages of low hydroxyl content with ultra high purity to yield superior UV transmittance and resistance to solarization for a variety of UV lamp applications including water purification, ozone generation, paint and ink curing, and chemical processing.
Types 214A, 219A, and 254A
These are identical to the standard types but are produced with a lower hydroxyl content. "A" products contain <1 ppm (OH-) and are intended for metal halide lamps and other applications where the quartz must be devoid of hydroxyl as well as all dissolved gases.
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.
To keep pace with the increasingly stringent purity requirements of the industry, GE now offers a variety of compositions in its quartz crucibles. Each type is designed to address specific micro-contamination concerns. However. other options are also available. GE's "Crucible Team" is prepared to work with you on your specific crucible designs
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.
Guidelines for Users of Fused Quartz
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.
Space permitting, fused quartz should be stored in its original shipping container. If that is not practical, at least the wrapping should be retained. In the case of tubing, the end coverings should be kept in place until the product is used. This protects the ends from chipping and keeps out dirt and moisture which could compromise the purity and performance of the tubing.
For applications in which cleanliness is important, General Electric recommends the following procedure: The product, particularly tubing, should be washed in deionized or distilled water with a degreasing agent added to the water. The fused quartz should then be placed in a 7% (maximum) solution of ammonium bifluoride for no more than ten minutes, or a 10 vol % (maximum) solution of hydrofluoric acid for no more than five minutes. Etching of the surface will remove a small amount of fused quartz material as well as any surface contaminants. To avoid water spotting which may attract dirt and cause devitrification upon subsequent heating, the fused quartz should be rinsed several times in de-ionized or distilled water and dried rapidly. To further reduce the possibility of contamination, care should be used in handling fused quartz. The use of clean cotton gloves at all times is essential. Washing of translucent tubing is not recommended because the water or acid solution tends to enter the many capillaries in the material. This may cause the quartz to burst if the pieces are subsequently heated rapidly to very high temperatures.
Rotation Procedures For Fused Quartz Furnace Tubes
The following procedure has been used to create an even layer of crystobalite on diffusion tubes in order to increase resistance to devitrification. Place the tube in a furnace at 1200øC, and rotate it 90ø every two hours for the first 30 hours. If the working schedule does not permit adherence to this procedure, the following suggestion is offered. Place the tube in a furnace at 1200øC and rotate it 90ø every two hours for the first 8 hours, then reset the furnace to operating temperature.
Fused quartz made from natural raw material solarizes or discolors upon prolonged irradiation by high energy radiation (such as short UV, x-rays, gamma rays and neutrons). Resistance to this type of solarization increases with the purity of fused quartz. Hence, synthetic fused silica is highly resistant to solarization. Solarization in fused quartz can be thermally bleached by heating it to about 500øC.
An important consideration for today's users of fused quartz is the availability of technical product support. GE Quartz backs its products with fully equipped analytical and development lab oratories and a staff of materials and fusion experts available to support customer requirements. State-of-the-art analytical equipment assures optimal production quality and also enables certification and subsequent verification of GE Quartz product compliance with stringent industry standards. Physical properties and other information shown on pages 14 through 24 was developed from a number of sources, including GE's technical laboratories, text books and technical publications. While GE believes that this information is accurate, it is not an exhaustive review of the subjects covered and, accordingly, GE makes no warranty as to the accuracy or completeness of the data. Customers are advised to check references to ensure that the product is suitable for the customer's particular use or requirements. Additional technical assistance from our engineering team is available by calling or faxing our world headquarters.