METHOD OF SIMULTANEOUSLY COATING AND TEMPERING GLASS AT HIGH TEMPERATURE

Abstract

A method for simultaneously tempering and coating glass, including heating a glass substrate, depositing a textured buffer layer on the glass substrate, depositing a material on the buffer layer, depositing O.sub.2, and rapidly cooling the glass substrate by introducing a gas. This includes coating the glass substrate with crystalline sapphire or a low E film, for example.

Claims

1. A method of simultaneously tempering and coating glass, comprising: heating a glass substrate; depositing a textured buffer layer on the glass substrate; depositing a ceramic material on the buffer layer; depositing O.sub.2; and rapidly cooling the glass substrate by introducing a gas.

2. The method as recited in claim 1, wherein the buffer layer is MgO.

3. The method as recited in claim 1 wherein the ceramic material is aluminum, the aluminum forming a thin film of Al.sub.2O.sub.3 with the deposited O.sub.2.

4. A method of tempering and coating glass with a low E film, comprising: heating a glass substrate; depositing a textured buffer layer on the glass substrate; depositing tin on the buffer layer, forming a tin oxide film; doping the tin oxide film with fluorine; and rapidly cooling the glass substrate by a gas.

5. A method of simultaneously tempering and coating glass, comprising: heating a glass substrate; depositing a photovoltaic absorber coating on the glass substrate; depositing a conducting layer; and rapidly cooling the glass substrate by introducing a gas.

6. The method as recited in claim 1 wherein the gas is O.sub.2, He, H.sub.2, Ar, or N.sub.2.

7. The method as recited in claim 4 wherein the gas is O.sub.2, He, H.sub.2, Ar, or N.sub.2.

8. The method as recited in claim 5 wherein the gas is O.sub.2, He, H.sub.2, Ar, or N.sub.2.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0029] FIG. 1 shows a thin glass sheet with coatings of MgO and Al.sub.2O.sub.3; and

[0030] FIG. 2 shows a thin glass sheet with coatings of MgO and Al.sub.2O.sub.3 in an electron beam evaporation chamber.

DETAILED DESCRIPTION

[0031] FIG. 1 shows a thin sheet of glass 100 having MgO coating 110 and a Al.sub.2O.sub.3 coating 120. Thin glass sheet 100 is 100 m.

[0032] FIG. 2 shows an electron beam evaporation chamber 225. Chamber 225 has substrate holder 205, focusing coils 235, e-beam source 245 and target 255. Substrate holder 205 holds thin sheets of glass 200. Focusing coils 235 direct e-beam source 245 to target 255. Target 255 first holds highly dense MgO and then Al.sub.2O.sub.3 crystals or just Al if O.sub.2 is added to make Al.sub.2O.sub.3 (this target can be any ceramic material). A crystalline MgO layer 215 is first deposited at 550 C. and then a sapphire (Al.sub.2O.sub.3) layer 215 is deposited at 550 C. or slightly above, which is also the melting temperature of the glass. Glass 200 with coating 215 is then cooled rapidly by introducing O.sub.2 230 into chamber 225. 1 atm of O.sub.2 is added. After the cooling from O.sub.2, glass 200 has simultaneously been strengthened and tempered and also has a hard coating. Not only does this cooling temper the glass, but it also tempers Al.sub.2O.sub.3 and MgO layers 215 which increases their hardness. The coatings may be directly deposited on one another and the substrate or may have layers in between. This embodiment includes 2 layers, however, the number of layers is not limited, and multiple layers are possible.

[0033] In a second embodiment, pre-tempered glass is used as the glass substrate on which to deposit the crystalline film coating. The tempered glass, available from say Asahi Glass Company, is put in the chamber and heated to the required deposition temperature for the crystalline coating to be deposited, say 550 C. O.sub.2 is then introduced and like in FIG. 2, the glass with coating is rapidly cooled. Although by heating the already tempered glass to 550 C. the glass becomes un-tempered, or ruined, by rapidly cooling again the glass regains its temper. Although the tempered glass has a hardened surface already, this only helps to improve the overall hardness of the sapphire coating.

[0034] It should be noted that in the present invention, various ceramic materials can be used instead of sapphire and MgO, following the patents and applications by Vispute and Chaudhari. Also, in addition to O.sub.2, other gases can be used, which may also lower the temperature quickly, without negatively influencing the materials. In fact, some gases may not only serve to rapidly lower the temperature, but might also have additional benefits, such as allowing for low E emissivity, or Anti-Reflection Coatings, or doping, or coloring.

[0035] It should be noted that the cooling process disclosed in the present invention is sharply different than the process(es) currently used in the industry described above, which involves high-pressure air blasts on the surface of the glass from an array of nozzles in varying positions.

[0036] In the present invention, the cooling of the glass with coating can take place in various ranges. For example, the glass substrate could be heated to 500 C., 550 C., or 600 C. or 650 C. Also, the cooling of the glass can take place in various ranges and at various speeds. For example, the glass could be cooled from 550 C. to 500 C. in under 1 minute. Or it can be cooled from 550 C. to 400 C. in under 1 minute. And so forth. It is understood that each range and cooling rate will have a certain outcome that may be desirable.

[0037] In the present invention, the tempering of the glass as well as crystalline film growth can take place with glass of various thicknesses. For example, tempering can take place with very thin glass of say 0.7 mm (700 microns), an even thinner glass, 100 microns. thicker glass, 10 mm. or even thicker glass, 100 mm. While the present invention is mostly concerned with soda-lime glass, because it is the least expensive of all glasses, there may be other glasses that are desirable, for example, borosilicate, or quartz.

[0038] In one variation of the present invention, rapid cooling of the tempered glass is not necessary because the crystalline film coating replaces the hard top layer which is brought about by the rapid cooling. This means that once the glass is heated to the melting point, the temperature just needs to be lowered slightly, and the coating then deposited. So in one exemplary iteration the steps are: 1) heating the soda-lime glass to 575 C., where the glass begins to melt, 2) cooling the temperature to 550 C., 3) depositing a crystalline film, and cooling the glass naturally, i.e. it does not require rapid cooling. This process may have a strengthening effect, rather than tempering.

[0039] To be clear, a central distinguishing feature of the present invention is the introduction of gas into the vacuum chamber (e-beam or sputtering) to cause cooling. The gas may be O.sub.2, Ar, or Helium, for example.

[0040] Thermal Impact

[0041] Tempered glass is often used because of its advantageous thermal properties. Regular annealed glass without tempering is easily broken by mechanical stress, impact, and moderate thermal stress. With a ceramic materials as coatings, for example sapphire and MgO, the thermal properties may be greatly enhanced.

[0042] Low E Glass

[0043] Emissivity is the ability of a material to radiate energy. When heat or light energy, typically from the sun or HVAC system, is absorbed by glass it is either shifted away by air movement or re-radiated by the glass surface.

[0044] The glass industry produces a glass product with low emissivity, known a low E glass. The process, which involves the deposition of very thin film coatings on glass is a product with some similarity to the present invention with regard to manufacturing. The low E coatings can be deposited in a vacuum chamber using sputtering for example.

[0045] In the low E glass manufacturing process, the flat glass (soda-lime) is transferred to a vacuum chamber where the needed coating layers, such as SnO.sub.2:F, are deposited on to the glass surface by sputtering in controlled circumstances (vacuum, gas, layer, thickness). However, this method is sharply different from the present invention because not only does the glass temperature always remain below 100 C., but the method does not allow the glass to be re-heated in order to temper it after the coating process. If the glass is re-heated up to the tempering temperature (from 550 C. to 650 C.), the different thermal expansions of the coating and the glass can make the thin layers crack.

[0046] In one embodiment of the present invention, rather than Al.sub.2O.sub.3, low E coatings are deposited on the textured MgO.

[0047] The present invention can be applied to low E coating with significant advantage because it allows for the heating of the glass to high temperature for tempering without ruining the uniformity of the low-E films and causing cracking. The textured MgO buffer layer, or many other types of potential buffer layers such as oxides or nitrides, keeps these low E coatings from cracking by minimizing the thermal expansion effect and enhancing the crystallinity of the films. Moreover, can also help with the light transmission of the low E glass. For example, in many low-E glass products light transmission is 81% or less. In the present invention 89% can be achieved, providing a dramatic improvement.

[0048] The low E coatings, for example Indium Tin Oxide (ITO) can vary in thicknesses, for example 1-10 nm, 10-20 nm, 20-30 nm, 1 um, 5 um or 20 um.

[0049] Thus, the present invention also allows for the simultaneous growth of low E coatings and tempering. In fact, it allows for the simultaneous growth of an unlimited number of coatings, and tempering. The textured buffer layer, say MgO, induces texture in the low E film, and this in turn allows the low E glass product to be used as a substrate for semiconductor film growth, where the semiconductor films also gain texture, providing a whole new application of the low E glass product.

[0050] Finally, the present invention can also be applied to transparent photovoltaic glass (TPV) products, where a tempered or strengthen glass substrate is advantageous. For example, in building integrated photovoltaics (BIPV). In this case, the photovoltaic (PV) absorber coatings, along with conducting layers such as ITO, when applied in an electron beam evaporation chamber, can be grown on glass that is simultaneously tempered or strengthened for BIPV purposes in a similar fashion as discussed above.

[0051] The present invention can be carried out using various common PVD (physical vapor deposition) processes, such as electron beam evaporation (e-beam) or sputtering.

EXAMPLES OF THE INVENTION

Example 1Tempered Glass with Sapphire Coating

[0052] Electron-beam evaporation was used for the growth of tempered sapphire glass, consisting of a thin layer of MgO on soda-lime glass, followed by a thin film of Al.sub.2O.sub.3 grown on top. The evaporator consists of a stainless steel high vacuum chamber capable of reaching 10E-7 Torr with the help of a cryopump. Initial rough vacuum up to 10-3 Torr was achieved with a mechanical dry pump. Prior to vacuuming the chamber, batches of initial soda-lime glass substrates were loaded on a substrate heater that is capable of controlling temperature of the substrates while growing the MgO buffer layer and sapphire layer in reactive deposition mode. A typical buffer layer of MgO was grown from stoichiometric MgO source material. The presence of background pressure of O.sub.2 (10E-4 Torr using O.sub.2 flow need valve)) helps high quality stoichiometric MgO depositions. Substrate temperature was controlled from 300 C. to 650 C. temperature range to control the preferred orientation of the MgO films. Required growth temperature was set using a substrate heater with a typical ramp rate ranging from 15 C./min to 45 C./min. At this stage the system is ready for deposition of the first layer that is MgO. E-beam parameters such as high voltage and emission current were set so that the appropriate evaporation rate of MgO can be achieved. The high voltage (HV approximately 8 KV) for electron beam was setup through potentiometer of the e-beam evaporator system. A good range for setting the bias for Telemark sources is between 17 to 20 A. The electron beam sweep pattern settings can also be judged and finalized without affecting the material. The e-beam system also has joystick that can directly control the e-beam output position, allowing the precondition of the material manually. Once high voltage and emission current is set with desirable evaporation rate of MgO, deposition was conducted for 1 to 2 hours depending upon the film thickness requirement. Studies show varied film thickness of MgO films from a few microns to 7 microns is possible. After MgO deposition, a high purity aluminum (99.999) source was switched for deposition. Initially, the Al source was heated by e-beam to melt the source and the e-beam was adjusted for evaporation of aluminum. Partial pressure was adjusted from 10-4 Torr to 10-6 Torr in order to control reaction of the Al with O.sub.2 on the substrate. Note that the arrival rate of O.sub.2 is adjusted in a way that Al surface mobility can be as high as possible to allow surface migration and then reaction with oxygen so that crystalline properties, grain size, surface smoothness, optical transparency, and interface reaction can be controlled. Thus optimization of aluminum oxide (Al.sub.2O.sub.3) growth includes arrival rates of oxygen background reactive gas atoms and e-beam evaporated aluminum in such a way that aluminum has optimum surface migration for crystallinity and grain size control and reaction with oxygen to form crystalline sapphire (Al.sub.2O.sub.3) or sapphire glass. After the Al.sub.2O.sub.3 film growth is complete the glass substrate must be cooled rapidly to induce tempering in the glass. This is achieved by introducing O.sub.2 into the chamber. The amount of O.sub.2 is 1 atm. (from vacuum to 1 atm.). After cooling, the glass is removed from the chamber. The glass is now both coated with sapphire and tempered.

Example 2Tempered Low E Glass

[0053] Electron-beam evaporation was used for the growth of tempered low E glass, consisting of a thin layer of MgO on soda-lime glass, followed by a thin film of Flourine doped Tin Oxide (FTO) grown on top. The evaporator consists of a stainless steel high vacuum chamber capable of reaching 10E-7 Torr with the help of a cryopump. Initial rough vacuum up to 10-3 Torr was achieved with a mechanical dry pump. Prior to vacuuming the chamber, batches of initial soda-lime glass substrates were loaded on a substrate heater that is capable of controlling temperature of the substrates while growing the MgO buffer layer and sapphire layer in reactive deposition mode. A typical buffer layer of MgO was grown from stoichiometric MgO source material. The presence of background pressure of O2 (10E-4 Torr using O2 flow need valve)) helps high quality stoichiometric MgO depositions. Substrate temperature was controlled from 300 C. to 650 C. temperature range to control the preferred orientation of the MgO films. Required growth temperature was set using a substrate heater with a typical ramp rate ranging from 15 C./min to 45 C./min. At this stage the system is ready for deposition of the first layer that is MgO. E-beam parameters such as high voltage and emission current were set so that the appropriate evaporation rate of MgO can be achieved. The high voltage (HV approximately 8 KV) for electron beam was setup through potentiometer of the e-beam evaporator system. A good range for setting the bias for Telemark sources is between 17 to 20 A. The electron beam sweep pattern settings can also be judged and finalized without affecting the material. The e-beam system also has joystick that can directly control the e-beam output position, allowing the precondition of the material manually. Once high voltage and emission current is set with desirable evaporation rate of MgO, deposition was conducted for 1 to 2 hours depending upon the film thickness requirement. Studies show varied film thickness of MgO films from a few microns to 7 microns is possible. After MgO deposition, a high purity tin (99.999) source was switched for deposition. Initially, the Sn source was heated by e-beam to melt the source and the e-beam was adjusted for evaporation of tin. Partial pressure was adjusted from 10-4 Torr to 10-6 Torr in order to control reaction of the Sn with O.sub.2 on the substrate. Note that the arrival rate of O.sub.2 is adjusted in a way that Sn surface mobility can be as high as possible to allow surface migration and then reaction with oxygen so that crystalline properties, grain size, surface smoothness, optical transparency, and interface reaction can be controlled. Thus optimization of tin oxide growth includes arrival rates of oxygen background reactive gas atoms and e-beam evaporated aluminum in such a way that aluminum has optimum surface migration for crystallinity and grain size control and reaction with oxygen to form crystalline tin oxide. After the tin oxide film growth is complete, it is doped with fluorine which is introduced to the chamber. Finally, the substrate must be cooled rapidly to induce tempering in the glass. This is achieved by introducing O.sub.2 into the chamber. The amount of O.sub.2 is 1 atm. (from vacuum to 1 atm.). After cooling, the glass is removed from the chamber. The glass is now coated with a textured FTO low E coating, and tempered.

Example 3Strengthened Glass with Sapphire Coating

[0054] Electron-beam evaporation was used for the growth of tempered sapphire glass, consisting of a thin layer of MgO on soda-lime glass, followed by a thin film of Al.sub.2O.sub.3 grown on top. The evaporator consists of a stainless steel high vacuum chamber capable of reaching 10E-7 Torr with the help of a cryopump. Initial rough vacuum up to 10-3 Torr was achieved with a mechanical dry pump. Prior to vacuuming the chamber, batches of initial soda-lime glass substrates were loaded on a substrate heater that is capable of controlling temperature of the substrates while growing the MgO buffer layer and sapphire layer in reactive deposition mode. A typical buffer layer of MgO was grown from stoichiometric MgO source material. The presence of background pressure of O.sub.2 (10E-4 Torr using O.sub.2 flow need valve)) helps high quality stoichiometric MgO depositions. Substrate temperature was controlled from 300 C. to 650 C. temperature range to control the preferred orientation of the MgO films. Required growth temperature was set using a substrate heater with a typical ramp rate ranging from 15 C./min to 45 C./min. At this stage the system is ready for deposition of the first layer that is MgO. E-beam parameters such as high voltage and emission current were set so that the appropriate evaporation rate of MgO can be achieved. The high voltage (HV approximately 8 KV) for electron beam was setup through potentiometer of the e-beam evaporator system. A good range for setting the bias for Telemark sources is between 17 to 20 A. The electron beam sweep pattern settings can also be judged and finalized without affecting the material. The e-beam system also has joystick that can directly control the e-beam output position, allowing the precondition of the material manually. Once high voltage and emission current is set with desirable evaporation rate of MgO, deposition was conducted for 1 to 2 hours depending upon the film thickness requirement. Studies show varied film thickness of MgO films from a few microns to 7 microns is possible. After MgO deposition, a high purity aluminum (99.999) source was switched for deposition. Initially, the Al source was heated by e-beam to melt the source and the e-beam was adjusted for evaporation of aluminum. Partial pressure was adjusted from 10-4 Torr to 10-6 Torr in order to control reaction of the Al with O.sub.2 on the substrate. Note that the arrival rate of O.sub.2 is adjusted in a way that Al surface mobility can be as high as possible to allow surface migration and then reaction with oxygen so that crystalline properties, grain size, surface smoothness, optical transparency, and interface reaction can be controlled. Thus optimization of aluminum oxide (Al.sub.2O.sub.3) growth includes arrival rates of oxygen background reactive gas atoms and e-beam evaporated aluminum in such a way that aluminum has optimum surface migration for crystallinity and grain size control and reaction with oxygen to form crystalline sapphire (Al.sub.2O.sub.3) or sapphire glass. After the Al.sub.2O.sub.3 film growth is complete the glass substrate, in contrast to the previous example, does not need to be cooled rapidly to strengthen the glass. This is achieved by simply allowing the samples(s) to cool in the chamber. Mohs scratch testing of the glass (uncoated side) showed a Mohs 7, which is significant improvement in strength given that Mohs for soda-lime glass is normally 5.5 to 6.5.

[0055] In the present invention, the term textured has the following meaning: textured means that the crystals in the film have preferential orientation either out-of-plane or in-plane or both. For example, in the present invention the films could be highly oriented out-of-plane, along the c-axis.

[0056] Although the present invention has been described in conjunction with specific embodiments, those of ordinary skill in the art will appreciate the modifications and variations that can be made without departing from the scope and the spirit of the present invention.