Fused Quartz Properties & Usage Guide
GE Type 214, 214LD and 124
Properties Index
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
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.
224LD - 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.
244LD 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.
Low (OH-)
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 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
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:
Type 214
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.
Type 219
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.
Type 254
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.
Type 021
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.
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
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.
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
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.
Cleaning
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.
Solarization
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.
Technical Support
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.
Property Typical Values
Density 2.2x10 3 kg/m3
Hardness 5.5 - 6.5 Mohs' Scale 570 KHN 100
Design Tensile Strength 4.8x10 7 Pa (N/m2) (7000 psi)
Design Compressive Strength Greater than 1.1 x l0 9 Pa (160,000 psi)
Bulk Modulus 3.7x10 10 Pa (5.3x10 6 psi)
Rigidity Modulus 3.1x10 10 Pa (4.5x10 6 psi)
Young's Modulus 7.2x1 -10 Pa (10.5x10 6 psi)
Poisson's Ratio .17
Coefficient of Thermal Expansion 5.5x10 -7 cm/cm . øC (20øC-320øC)
Thermal Conductivity 1.4 W/m . øC
Specific Heat 670 J/kg . øC
Softening Point 1683øC
Annealing Point 1215øC
Strain Point 1120 øC
Electrical Resistivity 7x10 7 ohm cm (350øC)
Dielectric Properties (20øC and 1 MHz)
Constant 3.75
Strength 5x10 7 V/m
Loss Factor Less than 4x10 -4
Dissipation Factor Less than 1x10 -4
Index of Refraction 1.4585
Constringence (Nu) 67.56
Velocity of Sound-Shear Wave 3.75x10 3 m/s
Velocity of Sound/Compression Wave 5.90X10 3 m/s
Sonic Attenuation Less than 11 db/m MHz
Permeability Constants (cm3 mm/cm2 sec cm of Hg)
(700øC)
Helium 210x10 -10
Hydrogen 21x10 -10
Deuterium 17x10 -10
Neon 9.5x10 -10
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
Fused quartz is a solid material at room
temperature, but at high temperatures, it behaves like all glasses. It does not
experience a distinct melting point as crystalline materials do, but softens
over a fairly broad temperature range. This transition from a solid to a
plastic-like behavior, called the transformation range, is distinguished by a
continuous change in viscosity with temperature.
Viscosity
Viscosity is the measure of the resistance to flow of a
material when exposed to a shear stress. Since the range in "flowability" is
extremely wide, the viscosity scale is generally expressed logarithmically.
Common glass terms for expressing viscosity include: strain point, annealing
point, and softening point, which are defined as: Strain Point: The temperature
at which the internal stress is substantially relieved in four hours. This
corresponds to a viscosity of 10 14.5 poise, where poise = dynes/cm2 sec.
Annealing Point: The temperature at which the internal stress is substantially
relieved in 15 minutes, a viscosity of 10 13.2 poise. Softening Point: The
temperature at which glass will deform under its own weight, a viscosity of
approximately 10 7.6 poise. The softening point of fused quartz has been
variously reported from 1500 øC to 1670 øC, the range resulting from differing
conditions of measurement.
Devitrification
Devitrification and particle generation are
limiting factors in the high temperature performance of fused quartz.
Devitrification is a two step process of nucleation and growth. In general, the
devitrification rate of fused quartz is slow for two reasons: the nucleation of
the cristobalite phase is possible only at the free surface, and the growth rate
of the crystalline phase is low. Nucleation in fused quartz materials is
generally initiated by surface contamination from alkali elements and other
metals. This heterogeneous nucleation is slower in non stoichiometric fused
quartz, such as GE quartz, than in stoichiometric quartz materials.
Cristobalite Growth
The growth rate of cristobalite from the
nucleation site depends on certain environmental factors and material
characteristics. Temperature and quartz viscosity are the most significant
factors, but oxygen and water vapor partial pressures also impact the crystal
growth rate. Consequently, the rate of devitrification of fused quartz increases
with increasing hydroxyl (OH-) content, decreasing viscosity and increasing
temperature. High viscosity, low hydroxyl fused quartz materials produced by GE
Quartz, therefore, provide an advantage in devitrification resistance. The phase
transformation to Beta-cristobalite generally does not occur below 1000øC. This
transformation can be detrimental to the structural integrity of fused quartz if
it is thermally cycled through the crystallographic inversion temperature range
(250 øC). This inversion is accompanied by a large change in density and can
result in spalling and possible mechanical failure.Thermal Properties, cont
An Advantage
In certain applications, devitrification can be put
to the user's advantage since the cristobalite tends to inhibit sag of the fused
quartz. For example, if a diffusion furnace tube is to be used at high
temperatures for extended periods of time, and is not subject to thermal cycling
below the cristobalite transformation, rotation procedures described on page 24
have been found to be beneficial.
Contamination
Contamination in almost any form is detrimental.
Alkaline solutions, salts, or vapors are particularly deleterious. Handling of
fused quartz with the bare hands deposits sufficient alkali from perspiration to
leave clearly defined fingerprints upon devitrification. Drops of water allowed
to stand on the surface will collect enough contamination from the air to
promote devitrified spots and water marks. Surface contamination affects
devitrification in two ways. First, the contaminant promotes nucleation of the
cristobalite. Second, it acts as a flux to enhance the cristobalite to (high)
tridymite transformation. Under some conditions, the tridymite devitrification
will grow deeply and rapidly into the interior of the fused quartz. Heating
fused quartz to elevated temperatures (ca. 2000 øC) causes the SiO2 to undergo
dissociation or sublimation. This is generally considered to be: SiO2 -> SiO
+ 1/2 O2. Consequently, when flame-working fused quartz, there is a band of haze
or smoke which forms just outside the intensely heated region. This haze
presumably forms because the SiO recombines with oxygen from the air (and
perhaps water) and condenses as extremely small particles of amorphous SiO2. The
haze can be removed from the surface by a gentle heating in the oxy-hydrogen
flame. The dissociation is greatly enhanced when the heating of fused quartz is
carried out in reducing conditions. For example, the proximity or contact with
graphite during heating will cause rapid dissociation of the SiO2.
Resistance To Sag
The most significant chemical factor effecting
the sag resistance of fused quartz is the hydroxyl (OH-) content. GE controls
the (OH-) content in its quartz to meet the specific needs of its customers. To
maximize the performance of tubes used in high temperature semiconductor
processes, it is important to understand the impact of changes in diameter and
wall thickness. In one study using GE 214LD fused quartz tubing, it was found
that the sag rate decreases as the wall thickness of the tube is increased.
Generally, as the wall thickness doubles, the sag rate decreases by a factor of
approximately 3. Also, it was shown that with a fixed wall thickness, the sag
rate decreases as the tube diameter decreases.
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
As the transmission curve in below illustrates, GE Type
214 fused quartz has a UV cutoff (1 mm thickness) at < 160 nm, a small
absorption at 245 nm and no appreciable absorption due to hydroxyl ions. Type
219, which contains approximately 100 ppm Ti, has a UV cutoff at ~230 nm for a 1
mm thick sample. The IR edge falls between 4.5 and 5.0 um for a 1 mm thick
sample. The chart details the percent transmittance for Types 214, 124 and 219
fused quartz, including the losses caused by reflections at both surfaces.
Values represent a 1 mm thick Type 214 sample and a 10 mm thick Type 124 sample.
Type 124 fused quartz is a very efficient material for the transmission of
infrared radiation. Its infrared transmission extends out to about 4 micrometers
with little absorption in the "water band" at 2.73 um.
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