Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
  • C03C3/095—Glass compositions containing silica with 40% to 90% silica, by weight containing rare earths
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C17/00—Surface treatment of glass, not in the form of fibres or filaments, by coating
  • C03C17/06—Surface treatment of glass, not in the form of fibres or filaments, by coating with metals

Definitions

• the present invention relates to glass materials, glass substrates comprising such glass materials, and devices comprising such glass substrates.
• the present invention relates to rare-earth-containing glass materials, high-precision glass substrates, and devices comprising such glass substrates bearing a layer of semiconductor material such as polycrystalline silicon.
• the present invention is useful, e.g., in making glass substrates for LCD displays, especially those based on polycrystalline silicon technology.
• AMLCDs active matrix liquid crystal display devices
• the glass substrates used in the production of AMLCD devices need to have their physical dimensions tightly controlled.
• the downdraw sheet drawing processes and, in particular, the fusion process described in U.S. Patents Nos. 3,338,696 and 3,682,609, both to Dockerty, are capable of producing glass sheets that can be used as substrates without requiring costly post- forming finishing operations such as lapping and polishing.
• the fusion process places rather severe restrictions on the glass properties, which require relatively high liquidus viscosities.
• the multiple heating steps employed during the p-Si TFT manufacture create slightly different fictive temperatures in the glass that cannot be fully compensated for by this pretreatment.
• the thermal stability of the glass becomes closely linked to the details of the p-Si TFT manufacturer, which could mean different pretreatments for different end-users.
• pretreatment adds to processing costs and complexity.
• the glass material has a composition comprising 1-6 mol% MgO 5 in certain other embodiments from 1-5 mol%, in certain other embodiments from 1-4 mol%.
• the glass material has a composition essentially free OfAs 2 O 3 and Sb 2 O 3 .
• the glass material has a composition further comprising:
• the glass material has a composition comprising ZnO and B 2 O 3 , in total, from O to 4 mol%.
• the glass material has a composition having a [R'O]/[A1 2 O 3 ] ratio from 0.75 to 1.8, in certain embodiments from 0.75 to 1.5, in certain embodiments from 0.9 to 1.25, in certain embodiments from 1.0 to 1.25, where [R'O] is defined infra.
• the glass material has an annealing point of higher than 790 0 C, in certain embodiments higher than 800°C, in certain embodiments higher than 805 0 C, in certain embodiments higher than 810 0 C, in certain embodiments higher than 815°C, in certain other embodiments higher than 820 0 C, in certain embodiments higher than 830 0 C; still in certain other embodiments higher than 835 0 C.
• the glass material has a density lower than 3.2 g-cm "3 ; in certain embodiments lower than 3.1 g-cm “ 3 ; in certain embodiments lower than 3.0 g-cm “3 , in certain embodiments lower than 2.95 g-cm , in certain embodiments lower than 2.90 g em " , in certain embodiments lower than 2.85 g-cm " , in certain other embodiments lower than 2.80 g-cm " , in certain other embodiments lower than 2.75 g em "3 , in certain other embodiments lower than 2.70 g-cm " 3 , in certain other embodiments lower than 2.65 g-cm " .
• the glass material has a liquidus temperature lower than 1250 0 C, in certain embodiments lower than 1230 0 C, in certain embodiments lower than 1215°C, in certain embodiments lower than 1200 0 C, in certain embodiments lower than 1190 0 C, in certain embodiments lower than 1180 0 C, in certain other embodiments lower than 1170 0 C, in certain other embodiments lower than 1150 0 C, in certain other embodiments lower than 1130 0 C.
• the glass material has a liquidus viscosity greater than 60 kPoise, in certain embodiments greater than 80 kPoise, in certain embodiments greater than 100 kPoise, in certain embodiments greater than 120 kPoise, in certain embodiments greater than 140 kPoise, in certain embodiments greater than 160 kPoise, in certain embodiments greater than 180kPoise, in certain embodiments greater than 200 kPoise, in certain embodiments greater than 300 kPoise, in certain embodiments greater than 400 kPoise, in certain embodiments greater than 500 kPoise.
• a glass substrate for TFT liquid crystal display, photovoltaic or other opto-electric devices comprising a glass material according to the first aspect of the present invention and the various embodiments thereof, described summarily supra and in greater detail infra.
• the glass substrate is made by a down-draw process such as a fusion down-draw process, or a slot downdraw process.
• the glass substrate is made by a float process.
• a device comprising a substrate according to the second aspect of the present invention and various embodiments thereof, described summarily supra and in greater detail infra.
• the device comprises a thin film of polycrystalline or single-crystalline semiconductor material such as silicon or a semiconductor device made thereof such as a diode, a transistor, and the like, formed over a surface of the substrate.
• the device comprises a thin film of amorphous silicon or a semiconductor device made thereof such as a diode, a transistor, and the like, formed over a surface of the substrate.
• the device comprises a layer of a material differing from the glass material, such as a semiconductor material, formed by a process including a step at a temperature higher than 350°C, in certain embodiments higher than 400 0 C, in certain embodiments higher than 450 0 C, in certain embodiments higher than 500 0 C, in certain embodiments higher than 550 0 C, in certain embodiments higher than 600 0 C, in certain embodiments higher than 650 0 C, in certain embodiments higher than 700 0 C, in certain embodiments higher than 750 0 C.
• mol% or “mole percent” or “percent by mole” of a component, unless specifically stated to the contrary, is based on the total moles of the composition or article in which the component is included. As used herein, all percentages are by mole unless indicated otherwise.
• RO represents, collectively, MgO, CaO, SrO and BaO.
• RE 2 O 3 represents, collectively, rare earth oxides (including but not limited to Sc 2 O 3 , Y 2 O 3 , La 2 O 3 , Pr 2 O 3 , Nd 2 O 3 , Sm 2 O 3 , Eu 2 O 3 , Gd 2 O 3 , Tb 2 O 3 , Dy 2 O 3 , Ho 2 O 3 , Er 2 O 3 , Tm 2 O 3 , Yb 2 O 3 , and Lu 2 O 3 ).
• the mole percentage of an oxide XO in the glass composition is denoted as [XO] with the exception that, however, [R'O] represents, the sum total of [RO] +1.5 X[RE 2 O 3 ].
• T2.3 means the temperature at which the viscosity of the glass having a homogenous composition is 200 poise (20 Pa s).
• the liquidus viscosity of the glass is denoted as ⁇ (liquidus) in the present disclosure.
• the liquidus temperature of a glass is denoted as T(liquidus).
• this composition requires relatively high process temperatures (melting and fining temperatures, e.g. a T2.3 of about 1675°C), and uses antimony as a fining agent.
• next-generation LTPS processes may require a glass substrate with an even higher high-temperature sustainability.
• This invention is thus made, in certain embodiments, to glasses that further increase the low-temperature viscosity to improve dimensional stability while reducing the process and fining temperatures, which could also allow for the removal the need for antimony as a fining agent (though Sb 2 O 3 may still be present).
• the glasses are desired to have resistance to devitrification in the fusion draw machine.
• Devitrification the formation of a crystalline phase from a homogeneous glass
• the liquidus temperature defined as the temperature at which the first crystalline solid is in equilibrium with a melt
• 72 hour gradient boat measurements These measurements are conducted with a platinum boat filled with crushed glass cullet placed into a tube furnace with a thermal gradient imposed upon its length. After 72 hours under these conditions, the temperature at which the first crystal is observed is deemed the liquidus temperature, and the liquidus viscosity is the viscosity of the glass corresponding to this temperature.
• the SiO 2 concentration should be less than or equal to 75 mol% to allow batch materials to be melted using conventional, high volume, melting techniques, e.g., Joule melting in a refractory melter.
• the concentration of SiO 2 goes above 75 mol%, the T2.3 can be too high for conventional melting processes carried out in conventional melting and delivery systems.
• the SiO 2 concentration is from 67 to 74 mol% in certain embodiments, more desirably from 68 to 72 mol% in certain embodiments.
• the glasses of the invention can have T2.3 greater than or equal to 1565°C and less than or equal to 1680 0 C.
• SiO 2 is typically introduced in the form of a crushed sand made of alpha quartz, either from loose sand deposits or mined from sandstone or quartzite. While these are commercially available at low cost, other crystalline or amorphous forms of SiO 2 can be substituted in part or in whole with little impact on melting behavior. Because molten SiO 2 is very viscous and dissolves slowly into alkali- free glass, it is generally advantageous that the sand be crushed so that at least 85% of it passes through a U.S. mesh size of 100, corresponding to mesh opening sizes of about 150 microns. In production, fines may be lofted by batch transfer processes or by air- handling equipment, and to avoid the health hazards this presents it may be desirable to remove the smallest fraction of crushed sand as well.
• Al 2 O 3 is another glass former of the glasses of the invention.
• An Al 2 O 3 concentration greater than or equal to 11 mol% provides the glass with a low liquidus temperature and a corresponding high liquidus viscosity.
• the use of at least 11 mol% Al 2 O 3 also improves the glass strain point and modulus, hi order to achieve a proper melting behavior, the AI 2 O 3 concentration should be at most 17 mol%.
• the Al 2 O 3 concentration is from 12 and 17 mol% in certain embodiments, more desirably from 12 to 16 mol% in certain other embodiments, still more desirably from 13 to 16 mol% in certain other embodiments.
• B 2 O 3 is kept below or equal to 4 mol%, more desirably below 2 mol% in certain embodiments, still more desirably essentially zero in other embodiments.
• the low B 2 O 3 content contributes to enable glass substrates having a strain point higher than 780°C suitable for polysilicon and single-crystalline applications.
• the MgO concentration in the glass and the [RO]/[A1 2 O 3 ] ratio can have significant impact on the performance of the glass and, in particular, with regard to meltability and fining.
• [Al 2 O 3 ] is the mole percent OfAl 2 O 3 and [RO] equals the sum of the mole percentages of MgO, CaO, SrO, and BaO
• [Al 2 O 3 ] is the mole percent OfAl 2 O 3
• [RO] equals the sum of the mole percentages of MgO, CaO, SrO, and BaO
• B As is known in the art, in aluminosilicate glasses, Al 3+ ions seek to be surrounded by four oxygen ions (O 2- ). One means by which this occurs is traditionally called a charge-balance interaction.
• mullite approximately 3 Al 2 O 3 ⁇ SiO 2 , an aluminosilicate containing aluminum in A-, 5- and 6-fold coordination.
• CaAl 2 Si 2 O 8 the calcium aluminosilicate anorthite
• the phase in the lower left is wollastonite, Ca 2 Si 2 O 6 , in which all Si 4+ ions are 4-fold coordinated by oxygen, all Ca 2+ ions are 6-fold coordinated by oxygen, and at least some of the oxygen ions are shared between Ca 2+ and Si 4+ ions.
• the vertical line running through the middle of the triangle denotes compositions for which the CaO/ Al 2 O 3 ratio is exactly 1.0.
• the crystal in question is in equilibrium with a molten glass, and the region of equilibrium between liquid and a particular crystal is referred to as the liquidus phase field of the crystal.
• Eutectics are locations where three crystalline phases simultaneously coexist with a liquid. They are, by definition, local minima in the melting temperature of the particular crystalline assemblage, and therefore are the compositions for which the liquid is most stable relative to any one or combination of the three crystalline phases.
• Two eutectics are seen in FIG. 2. The first, between cristobalite, anorthite and mullite (right-hand side) is a single melt down to 1345 0 C, at which point the three crystalline phases simultaneously come into equilibrium with the liquid.
• the second, between wollastonite, anorthite and cristobalite, is a single melt down to 1170 0 C, at which point those three phases simultaneously come into equilibrium with the liquid.
• F. Were a crystalline assemblage of wollastonite, cristobalite and anorthite heated up from room temperature, the first appearance of a liquid would be at 117O 0 C, and the composition of the liquid would be equivalent to that of the corresponding eutectic composition.
• FIG. 3 shows the liquidus phase diagram of the MgO-Al 2 O 3 -SiO 2 system (data used to prepare this figure are from EM Levin, CR Robbins, HF McMurdie, Phase Diagrams for Ceramists. The American Ceramic Society, Inc., Columbus, OH (1964), p. 246, converted to mole percent).
• This system is unique among RO-Al 2 O 3 -SiO 2 systems in that the magnesium aluminosilicate (cordierite)-mullite-cristobalite eutectic composition has an [R0]/[ Al 2 O 3 ] ratio slightly greater than 1.
• MgO is particularly important with regard to melting and fining.
• the presence of MgO results in lower density and CTE, and a higher chemical durability, strain point, and modulus.
• MgO In terms of concentrations, MgO should be greater than or equal to 1.0 mol% in order to achieve the various benefits associated with MgO described above.
• the MgO concentration is from 1.0 to 5.0 mol%.
• CaO is essential to producing low liquidus temperatures (high liquidus viscosities), high strain points and moduli, and CTE's in the most desired ranges for flat panel applications, specifically, AMLCD applications. It also contributes favorably to chemical durability, and compared to other alkaline earth oxides it is relatively inexpensive as a batch material. Accordingly, the CaO concentration needs to be greater than or equal to 2.0 mol%. However, at high concentrations, CaO increases density and CTE. Accordingly, the CaO concentration of the glasses of the invention is less than or equal to 7.0 mol%. In certain embodiments, the CaO concentration is desirably from 2.0 to 6.0 mol%.
• the remaining alkaline earth oxides ⁇ SrO and BaO ⁇ can both contribute to low liquidus temperatures (high liquidus viscosities) and thus the glasses of the invention will typically contain at least one of these oxides.
• both oxides increase CTE and density and lower modulus and strain point compared to MgO and CaO.
• BaO generally has more adverse effects on glass properties than SrO.
• minimizing or eliminating barium is considered preferable since barium is one of the listed metals in the Resources Conservation and Recovery Act (RCRA) and is therefore classified by the US EPA as hazardous.
• RCRA Resources Conservation and Recovery Act
• Rare earth oxides such as Y 2 O 3 do not form any ternary RE 2 O 3 -Al 2 Oa-SiO 2 phases, unlike the alkaline earth aluminosilicates, hence the minimum liquidus of the system is near the middle of the ternary as shown in FIG. 4.
• rare earth oxides can be used to suppress the liquidus temperatures of alkaline earth aluminosilicates by suppressing the activity of alkaline earth aluminosilicate crystal phases like cordierite, anorthite, and celsian.
• rare earth oxides such as La 2 O 3 and Y 2 O 3 steepen the viscosity curve of the melt relative to the alkaline earth oxides, which simultaneously increases the anneal and strain points while decreasing the T2.3 temperature. This enables attainment of glasses with annealing points up to 840°C while keeping T2.3 less than 1680°C.
• Rare earth oxides also tend to increase elastic modulus to lower sag of the glass during processing. They also increase density and expansion, so their concentration should not be excessive.lt is believed that low amounts of rare earth oxides are incorporated into the glass structure in a manner similar to the alkaline earth oxides in a RO-Al 2 O 3 -SiO 2 glass system.
• the glasses of the invention will also normally contain some alkali as contaminants, in particular, lithium (Li), sodium (Na), and potassium (K).
• a "glass that is substantially free of alkalis” is a glass having a total alkali concentration expressed as R 2 O which is less than or equal to 0.1 mol%, where the total alkali concentration is the sum of the Na 2 O, K 2 O, and Li 2 O concentrations. Desirably the total alkali concentration is less than or equal to 0.07 mol% in certain embodiments.
• the glass materials of the present invention due to their high strain point, relatively low T2.3, are especially advantageous for LCD glass substrates, especially those require a relatively high processing temperature, such as those based on low- temperature polysilicon or single-crystalline technologies.
• a glass substrate for TFT liquid crystal display, photovoltaic or other opto-electric devices comprising a glass material according to the first aspect of the present invention and the various embodiments thereof, described supra.
• the glass substrate can be advantageously made by a down-draw process such as a fusion down-draw process, or a slot down-draw process, or a float process.
• a device comprising a substrate according to the second aspect of the present invention and various embodiments thereof, described supra.
• the device comprises a thin film of polycrystalline or single-crystalline semiconductor material such as silicon or a semiconductor device made thereof such as a diode, a transistor, and the like, formed over a surface of the substrate, hi certain embodiments of the third aspect of the present invention, the device comprises a thin film of amorphous silicon or a semiconductor device made thereof such as a diode, a transistor, and the like, formed over a surface of the substrate.
• the device comprises a layer of a material differing from the glass material, such as a semiconductor material, formed by a process including a step at a temperature higher than 350°C, in certain embodiments higher than 400°C, in certain embodiments higher than 450 0 C, in certain embodiments higher than 500 0 C, in certain embodiments higher than 550 0 C, in certain embodiments higher than 600 0 C, in certain embodiments higher than 650 0 C, in certain embodiments higher than 700 0 C, in certain embodiments higher than 750 0 C.
• a material differing from the glass material such as a semiconductor material
• the device comprises, over a surface of the substrate, a layer of a material differing from the glass material, such as a semiconductor material, formed by a process comprising a step at a temperature higher than the strain point of the glass material, but lower than the softening point of the glass.
• a material differing from the glass material such as a semiconductor material
• One having ordinary skill in the art of thin film semiconductor technology understands how to fabricate a thin film of polisilicon or other semiconductor material on the surface of a glass substrate, such as a glass substrate according to the present invention, and to make semiconductor devices such as transistors from the thin film of semiconductor materials. More recently, intrinsic and doped polysilicon is being used in large-area electronics as the active and/or doped layers in thin-film transistors. Although it can be deposited by LPCVD, plasma-enhanced chemical vapour deposition (PECVD), or solid-phase crystallization (SPC) of amorphous silicon in certain processing regimes, these processes still require relatively high temperatures of at least 300 0 C.
• PECVD plasma-enhanced chemical vapour deposition
• SPC solid-phase crystallization
• step (iii) forming a glass sheet from the fluid glass via a down-draw process.
• the down-draw process comprises a fusion process.
• the as-formed glass is not subjected to a heat treatment at a temperature above T(anneal) — 150°C; in certain embodiments the as-formed glass sheet is not subjected to a heat treatment at a temperature around or higher than the annealing point thereof.
• the as-formed glass sheet is not subjected to a heat treatment at a temperature higher than 300°C.
• a heat treatment at a temperature higher than 300°C.
• the actual batch ingredients may comprise any materials, either oxides, or other compounds, which, when melted together with the other batch components, will be converted into the desired oxide in the proper proportions.
• SrCO 3 and CaCO 3 can provide the source of SrO and CaO, respectively.
• the specific batch ingredients used to prepare the glasses of TABLE I were fine sand, alumina, boric acid, magnesium oxide, limestone, lanthanum oxide, yttrium oxide, barium carbonate or barium nitrate, strontium carbonate or strontium nitrate, zinc oxide, and tin oxide.
• the glass properties set forth in TABLE I were determined in accordance with techniques conventional in the glass art. Thus, the linear coefficient of thermal expansion (CTE) over the temperature range 0-300°C is expressed in terms of x 10 "7 K "1 . and the strain point is expressed in terms of °C. The density in terms of grams/cm 3 was measured via the Archimedes method (ASTM C693).
• the T2.3 in terms of 0 C (defined as the temperature at which the glass melt demonstrates a viscosity of 200 poises) was calculated employing a Fulcher equation fit to high temperature viscosity data measured via rotating cylinders viscometry (ASTM C965-81).
• the liquidus temperature of the glass in terms of °C was measured using the standard gradient boat liquidus method of ASTM C829-81. This involves placing crushed glass particles in a platinum boat, placing the boat in a furnace having a region of gradient temperatures, heating the boat in an appropriate temperature region for 24 hours, and determining by means of microscopic examination the highest temperature at which crystals appear in the interior of the glass.
• the liquidus viscosity in poises was determined from the liquidus temperature and the coefficients of the Fulcher equation. Young's modulus values in terms of Mpsi were determined using a resonant ultrasonic spectroscopy technique of the general type set forth in ASTM E1875-00el.

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• 2009
  • 2009-05-12 TW TW098115765A patent/TWI414502B/zh active
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