Patent Application
20060121197
1. Field of the Invention
This invention relates to the coating of substrates, and in particular to a process for the efficient coating of indium tin oxide covered substrates using chemical vapor reaction and gas plasma cleaning.
2. Description of the Related Art
The application of coatings onto substrates and other workpieces is required as a process step in many industrial fields. An example of such a process is the coating of a silicon wafer with a layer of Hexamethyldisalizane (HMDS). This coating process is used to promote the adhesion of organic layers such as photoresist to the inorganic silicon wafer. The HMDS molecule has the ability to adhere to the silicon wafer and also to be adhered to by an organic additional layer. For example, silicon wafers would be baked for 30 minutes in a 150 C oven for 30 minutes to dehydrate them. The silicon wafers would then be sprayed with HMDS. The excess HMDS would then be spun off of the silicon wafer. A typical process of this type would result in a HMDS monolayer on the surface of the silicon wafer.
A problem encountered with the above mentioned process was that if the silicon wafer was not sufficiently dry prior to the application of HMDS, then residual moisture would interfere with the reaction of the HMDS to the silicon wafer. This would result in variations in the HMDS layer reaction and then could lead to voids in the subsequently applied next layer. Another problem with a process of this type is that HMDS would rapidly deteriorate when exposed to air and moisture, and thus such a process required a large amount of HMDS to provide a small amount of reaction.
Because of the problems relating to variations in the HMDS monolayer, processes for the coating of substrates with HMDS evolved. Later processes more thoroughly dehydrated the silicon wafer substrate prior to the application of HMDS, and limited the HMDS from much, if any, exposure to air and moisture. An example of such a process would be as follows. Silicon wafers would be placed in a vacuum chamber and cycled back and forth between vacuum and preheated hot dry nitrogen in order to dehydrate the silicon wafer. For example, the silicon wafer would be exposed to a vacuum of 10 Torr for 2 minutes. At this pressure water boils at about 11 C. The vacuum chamber would then be flooded with preheated nitrogen at 150 C. This part of the process would heat the surface of the silicon wafer so that the high temperature of the wafer would assist in the dehydration process as vacuum was once again applied. After 3 complete cycles, a vacuum of 1 Torr would be applied to complete the dehydration process.
The next step in such a process is to open a valve between the vacuum chamber and a canister of HMDS. At room temperature the HMDS boils at approximately 14 Torr and thus the chamber is flooded with 14 Torr of HMDS vapor. In this process the HMDS is not exposed to air or moisture and the silicon wafer is significantly dryer prior to being coated.
Some coating processes based on the above mentioned type of process require a higher pressure. The HMDS is preheated to create a higher vapor pressure. Typical figures are preheating of the HMDS to 100 C to produce up to 400 Torr pressure of HMDS vapor while limiting the pressure in the process oven at 300 Torr to avoid condensation of the HMDS.
Processes involving the preheating of the deposition chemicals have the drawback that if the deposition chemicals degrade with exposure to heat then the bulk preheating of these chemicals may result in the loss of the unused residual chemical. These chemicals are often very expensive. Also, many of these chemicals are hazardous materials. The less of these chemicals actually being used in the process at any time reduces the potential risk for processing facilities.
A basic building block of many types manufacture products is a substrate topped with an organic silane molecule monolayer. The substrate may consist of silicon or glass or other materials. Earlier processes resulted in silane layers which were inconsistent across their surface area, which was seen in variations in contact angle measurements across the surface area. Variation in the contact angle across a surface would be greater than +/−10.
Across the surface of a glass, silicon, and other substrates are hydroxyl ions entrenched in the substrate itself. The hydrogen of the embedded hydroxyl ion extends away from the surface of the substrate. In a reactive process with silanes, such as silicon trimethyl, the Si of the silicon trimethyl group supplants the hydrogen of the embedded hydroxyl, resulting in a very strong bond to the substrate. This organic/inorganic bridge then allows for the immobilization of another layer onto the substrate.
If the substrate has moisture on its surface, the Si of the silicon trimethyl group may instead supplant the hydrogen of a water molecule on the substrate surface. In contrast to the strong bond to the substrate achieved when the Si is attached to the oxygen atom of the hydroxyl ion, which is embedded in the substrate, there is no such strong bond when the hydrogen of the water molecule is supplanted. The silane layer formed in the presence of moisture on the substrate is therefore inconsistent, with some portions of the silane layer strongly bonded to the substrate while other portions are not. The portion of silane layer which is not strongly bonded to the substrate may not stay attached to the substrate. This loss may occur immediately, upon the first exposure to moisture, or during subsequent processing of the coated substrate.
A method and apparatus for forming a consistent silane layer without, or with a minimum of, moisture related defects is discussed in U.S. patent application Ser. No. 10/656,840, to Moffat and McCoy, with a filing date of Sep. 5, 2003, and is hereby incorporated by reference in its entirety.
Prior silane coated substrates have had some serious drawbacks. Because the layer had numerous areas where the layer was bonded to water on the surface, the surface energy across the surface of a layer would vary, as the weakly bonded areas immediately degraded. These degraded areas would cause quality problems for any product formed during further processing. Another drawback is that of contamination, as many earlier processes involved much handling as the processes were carried out.
The coating of substrates for some applications may require sufficiently dehydrated substrates and insertion into the process chamber of one or more deposition chemicals which have been preheated and/or vaporized prior to insertion. Coatings for some applications are quite expensive. Some coatings are difficult to vaporize and vaporization requires a combination of low pressure and high temperature. Without reduced pressure, the temperature required for vaporization may be too high to retain stability of the chemical to be vaporized. Some applications may require silane deposition onto glass and/or other substrates as a bridge to organic molecules. Among the silanes used are amino silanes, epoxy silanes, and mercapto silanes. These silanes may be used as an adhesion layer between glass substrates and oligonucleotides, for example. Oligonucleotides are a short DNA monomer. Substrates are coated with a monolayer of silane as a bridge between the inorganic substrate and the organic oligonucleotide. A silane coated substrate with an oligonucleotide layer is now a standard tool used in biotech test regimens. One area where this oligonucleotide layer is used is in the formation of DNA microarrays. A uniform and consistent silane layer leads to a more uniform and consistent top surface of the oligonucleotide layer, which in turn leads to more useful test results.
Another technical area in which silane layers may be used as an intermediate layer is the manufacture of liquid crystal displays (LCDs). In this area silane layers may also be used as orientation layers. In some LCD production methods, the liquid crystals are sandwiched between two glass plates that are coated with electrodes, polarizers, color filters, and polyimide layers spin coated onto indium tin oxide. Microscopic grooves in the polymer surface align the liquid crystals.
The microscopic grooves in the polymer surface have typically been created by mechanical rubbing of the of the polymer surface with a rotating velvet cloth. There are significant drawbacks to this approach, as it is a contamination laden process, in addition to being labor intensive. Recently, indium tin oxide-covered plates have been have been coated with silane by immersing them in a solution of silane monomers. The surface contains groove-like structures similar to those in rubbed layers. Nanogrooves on the indium tin oxide plate are believed to act as the base of alignment for the silane layer, and the nanogrooves are amplified by the self-assembly process.
As with other wet silane processes in other technology areas, there are concerns with contamination and with insufficient dehydration of these indium tin oxide coated substrates prior to silane deposition.
What is called for is a process which allows for efficient and consistent coating of indium tin oxide coated substrates. Substrates coated with such a process have reduced contamination, have more consistent layers with better bonds to the substrate, allowing for a more consistent layers during later processing.
A process for the coating of substrates which are at least partially coated with indium tin oxide comprising insertion of a substrate into a process oven, dehydration of the substrate, plasma cleaning of the substrate, vaporizing chemicals in one or more vapor chambers, and transfer of the vaporized chemicals into a process oven, thereby coating the substrate.
In one embodiment of the present invention, as seen in
Chemicals in the fluid reservoirs 106, 107, are withdrawn into fluid input portion 102 by syringe pumps 108, 109. Although syringe pumps are used in this embodiment, other methods of withdrawal may be used, including peristaltic pumps and other appropriate methods. Chemical withdraw valves 116, 117, provide isolation between fluid reservoirs 106, 107, and syringe pumps 108, 109. Chemical withdraw valves 116, 117, are opened prior to withdrawal of chemicals from fluid reservoirs 106, 107.
Chemical infusion valves 113, 114 provide isolation between syringe pumps 108, 109, and the vapor chamber 110. The vapor chamber 110 is surrounded by vapor chamber heater 118. Although the vapor chamber heater is external to the vapor chamber in this embodiment, the vapor chamber heater may be internal to the vapor chamber or integral to the vapor chamber. The vapor chamber heater 110 may be P/N MBH00233 manufactured by Tempco, of Wood Dale, Ill., or other suitable heater. The vapor chamber 110 is fluidically coupled to process oven 104 by heated vapor line 111. The vapor chamber 110 may be isolated from process oven 104 by the operation of heated vapor valve 115. An example of such a heated vapor valve is valve P/N SS-8BK-VV-1C by Swagelok of Sunnyvale, Calif., with heater P/N 030630-41 by Nor-Cal Products of Yreka, Calif. The vapor chamber manometer 112 monitors the pressure inside vapor chamber 110. The process oven 104 may contain one or more trays 105.
In one embodiment of the present invention, as seen in
After withdrawal of chemicals into the syringe body 209, the chemical withdraw valve 116 may be closed to isolate the delivery pipe 203. The chemical infusion valve 113 may then be opened to link the syringe body 209 to the vapor chamber 110. An example of such a chemical infusion valve 113 is P/N 6LVV-DP11811-C manufactured by Swagelok of Sunnyvale, Calif. The syringe pump mechanism 207 may then re-insert the syringe plunger 208 partially or fully into the syringe body 209, forcing the chemical within the syringe body 209 through the T-coupler 205 and then through pipe 210. With the chemical infusion valve 113 open, the chemical then may enter the vapor chamber 110 via pipe 215. Pressure within the vapor chamber 110 is monitored with the vapor chamber manometer 112. An example of such a manometer is a 0-100 Torr heated capacitance manometer P/N 631A12TBFP manufactured by MKS of Andover, Md.
The fluid reservoir 106 is secured with a spring clamp 212 within a source bottle tray 213. The source bottle tray 213 may also act as a spill containment vessel.
In some embodiments of the present invention, the fluid input portion 102 delivers the desired amount of chemical in another way. The chemicals in the fluid reservoirs are withdrawn in a pre-determined amount using a metering pump. For example, the metering pump may withdraw and deliver 2 milliliters per stroke. To deliver a specific quantity of a chemical, the metering pump would be pumped repeatedly until the desired quantity had been delivered. In some embodiments using metering pumps, the chemical withdraw valve and the chemical infusion valve are not necessary. The metering pump itself acts to isolate the fluid reservoir from the vapor chamber. Such embodiments allow for the delivery of the chemical from the fluid reservoir with less required hardware.
One of skill in the art will understand that the fluid input portion may have other embodiments that may use the above described elements in different types of combinations, or may use different typed of elements.
In one embodiment of the present invention, as seen in
The high pressure gas inlet 403 provides gas via a line 464 to the chemical reservoirs 502, 503, and also provides the pressure to actuate valves 463 and valves 480-484. Solenoids 421-427 are directed by a logic controller at I/O locations 440-445 to actuate valves 480-485 using solenoids 421-427. The gas from the high pressure gas inlet 403 is reduced in pressure to 4 psig by a pressure reducer 460 to be fed to the chemical reservoirs.
The solenoid acutated valves 430, 431 are triggered by directions from a logic controller at I/O interfaces 454, 455 to allow for purging of the chemical source bottle feed line 490.
When the solenoid 421 is directed by the logic controller via the I/O interface 440, high pressure gas is directed through a line 471 to actuate the chemical infusion valve 480, which connects the fluid line 510 from the syringe pump 512 to the vaporization chamber 501. When the solenoid 422 is directed by the logic controller via the I/O interface 441, high pressure gas is directed through the line 470 to actuate the chemical infusion valve 481, which connects the fluid line 511 from the syringe pump 513 to the vapor chamber 501.
When the solenoid 426 is directed by the logic controller via the I/O interface 444, high pressure gas is directed through the line 467 to actuate valve 483 which allows for the introduction into the process chamber 500 of gas from the inlet 404. When the solenoid 425 is directed by the logic controller via the I/O interface 443, high pressure gas is directed through the line 465 to actuate the valve 485, which allows for the introduction into the process chamber 500 of gas from the inlet 405.
When the solenoid 427 is directed by the logic controller via the I/O interface 445, high pressure gas is directed through a line 468 to actuate the heated vapor valve 484, which allows for the introduction into the process chamber 500 of vaporized chemical from the vapor chamber 501 via line 554. Temperature indicating controller 524 and temperature alarm high switch are coupled to I/O interface 451.
Solenoid operated valves 428, 429 allow the opening and closing of lines between the chemical reservoirs 502, 503 and the syringe pumps 512, 513. I/O interfaces 458, 459 control the operation of the solenoid operated valves 428, 429.
The level of chemical left in the chemical reservoirs 502, 503 is monitored with level sensors 514, 515 and routed to the logic controller via the I/O interfaces 456, 457. Level sensors 514, 515 are capacitance level switches P/N KN5105 by IFM Effector of Exton, Pa., in this embodiment.
The vapor chamber pressure switch 464 is linked directly by a line 472 to a solenoid actuated valve 423, which, when triggered, in turn triggers the gas actuated overpressurization limit relief valve 463. The overpressurization limit relief valve 463 connects the vapor chamber 501 to the vacuum line inlet 406. The vapor chamber pressure switch 464 triggers when the pressure in the vapor chamber 501 exceeds a preset pressure, which is 650 Torr in this embodiment.
The process oven manometer 461 feeds its signal to the logic controller via an analog interface (not shown). Overtemperature alarm 551 feeds its signal to the logic controller via I/O interface 448. An I/O interface 442 controls the solenoid actuated valve 424, which in turn can trigger the gas actuated heated vacuum valve 482 via a line 466, which links the process oven 500 to the vacuum inlet 406. A temperature monitor 527 monitors the vacuum line temperature and is linked to the logic controller via an I/O interface 460. Temperature alarm high switch 552 is linked to the logic controller via an I/O interface 460.
Temperature monitors 520, 521, 522, 523 monitor the temperature in the process oven 500. Temperature monitors 520, 521, 522, 523 are linked to the logic controller by an RS-485 interface (not shown). Alarms are present in the temperature monitoring system and are linked to the logic controller by I/O interfaces 446, 447, 449, 450.
Temperature monitors 524, 525 connected to I/O interfaces 451, 453 are also used to monitor the temperature of the heated vapor line 526 and the vapor chamber 501. A pressure monitor 462 is linked to the logic controller by an analog interface and overtemperature alarm 553 is linked to the logic controller by an I/O interface 452.
A logic controller may be used to control this apparatus in some embodiments. An example of such a controller is Control Technology Corporation Model 2700 of Hopinkton, Mass. One of skill in the art will understand that the apparatus may be controlled using a variety of suitable methods.
In one embodiment of the present invention, as seen in
A low pressure gas distribution manifold 733 distributes gas such as dry nitrogen for use in dehydration cycles. Inert gas such as dry nitrogen may be used in these lines. A purge manifold 732 allows for the purging of the fluid reservoirs and lines. The low pressure gas input line 522 is split at a T-coupler 723 into two serpentine lines 720. Gas line heaters 721 allow for the pre-heating of the gas prior to delivery of the process chamber. T-couplers 724, 729 further divide the delivery lines prior to input to the chamber at the gas inlets 725, 726, 727, 728.
A high pressure gas distribution manifold 731 provides gas for purge manifold 732 which inserts low pressure nitrogen into the fluid reservoirs 106, 107. A line 730 routes gas to a fluidic coupler 211 in order to replace the volume voided by chemical withdrawal. Inert gas such as dry nitrogen may be used in these lines. The low pressure regulator 741 reduces the pressure from the high pressure gas distribution manifold 731 upstream from purge manifold 732. The low pressure regulator 741 then provides gas to the purge manifold 732.
High pressure gas distribution manifold 731 provides high pressure gas that is routed to the gas actuated valves by the triggering of solenoid actuated valves in valve bank 740.
An alternative process gas distribution inlet 734 provides another inlet for process gas that may be used in some processes using this embodiment of the present invention. In this embodiment, the process gas lines are fluidically coupled to the low pressure gas lines upstream of the serpentine lines 720.
As seen in
[0063] In some embodiments of the present invention, as seen in
FIGS. 14 to 16 show several variations of capacitive plasma generation. Plasma may be generated with an appropriate gas in the presence of a strong electric field at an appropriate pressure. Capacitive plasma generation typically uses parallel plate electrodes to create the electric field. Electrodes may also be used to reduce the charging potential of a plasma and to concentrate the plasma in selected areas.
Capacitive plasma electrodes are commonly referred to as being electrically active, electrically grounded, or electrically floating. An electrically active electrode has a high voltage, typically 400-600 volts, placed on it to create an electric field with respect to other electrodes. The voltage is typically alternating current at a high frequency. The industry standard frequency for plasma equipment is 13.56 MHz. There are advantages to using a lesser frequency in the 40 to 50 KHz range. An electrically grounded electrode is connected to ground with a appropriate conductor so that it remains at ground voltage potential. An electrically floating electrode is isolated from all other electrical potentials and will be at some voltage level that depends on the influence of the plasma upon it.
In some embodiments, the product trays 1404 span the process oven 104. Active electrodes 1402 and ground electrodes 1403 span the process oven 104 horizontally. The RF power supply, cabling, and RF power feed through are known in the art.
In some embodiments, the plasma cleaning cycle may occur before the dehydration process. In an exemplary process, the chamber is evacuated. A gas is then introduced into the chamber and the pressure is stabilized at a low pressure, such as 150-200 milliTorr. In some embodiments, the introduced gas in oxygen. In some embodiments, the introduced gas is a combination of oxygen and argon. In some embodiments, other gasses are used.
The plasma gas generation system allows for plasma gas cleaning of a work piece, such as a slide or substrate, in the same chamber as that in which subsequent process steps will take place. This gives many advantages, including reducing possible contamination that may occur if the work piece is exposed to the environment after plasma cleaning. Also, the plasma gas generation system can be used to clean the oven after the work pieces have been processed and removed. Many of the chemicals that may be used in processes that this chamber supports may leave residues that can interfere with subsequent runs. The plasma gas generation system may be utilized to clean the chamber after a process run and prior to loading the chamber with the work pieces for the next run.
In some embodiments, as seen in
In some embodiments, as seen in
The silane layers according to some embodiments of the present invention have consistent thickness across the surface of the substrate. The silane layer may thicken itself with more processing time as additional silane molecules adhere to silane molecules that have adhered to the substrate in a self-assembling layer.
When the chemical reactive process utilizes substrates that have not been sufficiently dehydrated, the silane layer is formed bonding to both hydroxyl ions and to water on the surface of the substrate. These prior silane layers would thus lose consistency immediately as the weakly bonded portion of the layer was lost. This inconsistency was exacerbated during further processing as the substrate was exposed to moisture and more of the poorly adhered area was lost.
A process for the coating of substrates in a process chamber, which may include dehydrating the substrate, gas plasma cleaning of the substrate, and vaporizing the chemical to be reacted prior to its entry into the process chamber. Subsequent to the processing of the substrate, the chamber may be cleaned using gas plasma.
A substrate for the chemical deposition of different chemicals may be of any of a variety of materials. For biotech applications, a glass substrate, or slide, is often used. Glass substrates may be borosilicate glass, sodalime glass, pure silica, or other types. Substrate dehydration may be performed as part of some processes. The glass slide is inserted into the process chamber. The slide is then dehydrated. Residual moisture interferes with the adhesion of chemicals during the deposition process. Alternatively, dehydration of the slide allows for later rehydration in a controlled fashion. The dehydration process alternates exposing the glass slide to vacuum and then to heated nitrogen, either once or multiple times. For example, the glass slide would be exposed to a vacuum of 10 Torr for 2 minutes. At this pressure water boils at about 11 C. The vacuum chamber would then be flooded with preheated nitrogen at 150 C. This part of the process would heat the surface of the glass slide so that the high temperature of the slide would assist in the dehydration process as vacuum was once again applied. After 3 complete cycles, a vacuum of 1 Torr would be applied to complete the dehydration process.
A gas plasma cleaning cycle may also be used in preparation of the substrate for coating. In a typical process, the substrate is cleaned using gas plasma after the dehydration process. In some embodiments, the plasma cleaning cycle may occur before the dehydration process. In an exemplary process, the chamber is evacuated. A gas is then introduced into the chamber and the pressure is stabilized at a low pressure, such as 150-200 milliTorr. In some embodiments, the introduced gas in oxygen. In some embodiments, the introduced gas is a combination of oxygen and argon. In some embodiments, other gasses are used. After the stabilization of the pressure in the process chamber, the electrodes are powered to generate the plasma. In an exemplary process, the electrodes are powered to 450 Volts cycled at 40 kiloHertz. The power cycle may last for 2 minutes in some embodiments.
After the completion of the dehydration and plasma cleaning cycles, the slide or substrate is ready for chemical reaction. Chemical reservoirs, such as manufacturer's source bottles, provide the chemical for the deposition process. For many processes, silanes are used. Among the silanes used are amino silanes, epoxy silanes, and mercapto silanes. Chemical may be withdrawn directly from the reservoir. A metered amount of chemical is withdrawn from the chemical reservoir. This may be done by opening a valve between the chemical reservoir and a withdrawal mechanism. The withdrawal mechanism may be a syringe pump. Chemical is withdrawn from the reservoir, enters the syringe pump, and then the valve between the chemical reservoir and the syringe pump is closed. The chemical reservoirs may be purged with an inert gas such as nitrogen. This purging allows for the filling of the volume of fluid removed with an inert gas, minimizing contact between the chemical in the reservoir and any air or moisture.
Next, a valve between the syringe pump and a vaporization chamber is opened. The vapor chamber may be pre-heated. The vapor chamber may be a reduced pressure. The syringe pump then pumps the previously withdrawn chemical from the syringe pump to the vaporization chamber. The vapor chamber may be at the same vacuum level as the process oven. In parallel to this delivery of chemical to the vaporization chamber, a second chemical may be undergoing the same delivery process. The two chemicals may vaporize at substantially the same time. Additionally, more chemicals may also be delivered to the vaporization chamber, or to another vaporization chamber.
In some embodiments, the chemical or chemicals to be vaporized may be withdrawn from the reservoir or reservoirs in a specific metered amount. This specific amount of withdrawal and delivery to the vapor chamber may be repeated until the desired amount of chemical or chemicals has been delivered into the vapor chamber. For example, a metering pump may be used. The metering pump may deliver a pre-determined amount of chemical per stroke of the metering pump. The number of pump strokes may be selected, thus delivering a specified amount of chemical.
The reduced pressure in the vapor chamber, and/or the elevated temperature in the vapor chamber may allow for the vaporization of chemicals at pre-determined pressure levels and temperatures.
The vaporized chemical, or chemicals, are then delivered to the process chamber. This may be done by opening a valve between the vaporization chamber and the process oven after the chemical has vaporized in the vaporization chamber. Alternatively, the valve between the vaporization chamber and the process oven may already be open when the chemical, or chemicals, are delivered to the vaporization chamber. The chemical then proceeds into the process chamber and reacts with the substrate.
In some embodiments, the chemical may be added into the vapor chamber with the valve between the vapor chamber and the process chamber open. The chemical may be continued to be added into the vapor chamber until the vapor pressure in the process chamber reaches a desired level. At that time, the valve between the vapor chamber and the process chamber may be closed. The chemical may then remain in the process chamber for the desired amount of time for reaction.
In some embodiments, the chamber may be cleaned using gas plasma subsequent to the processing steps. The chamber may be emptied of all workpieces and then cleaned. The gas plasma cleaning step subsequent to the processing steps helps prepare the process chamber for subsequent processing.
A process for the coating of substrates at least partially coated with indium tin oxide in a process chamber, which may include dehydrating the substrate, gas plasma cleaning of the substrate, and vaporizing the chemical to be reacted prior to its entry into the process chamber.
A substrate for the chemical deposition of different chemicals may be of any of a variety of materials. For LCD applications, indium tin oxide covered glass substrates, or indium tin oxide covered silicon substrates, or other indium tin oxide coated substrates are often used. Substrate dehydration may be performed as part of some processes. The substrate is inserted into the process chamber. The substrate is then dehydrated. Residual moisture interferes with the adhesion of chemicals during the deposition process. Alternatively, dehydration of the substrate allows for later rehydration in a controlled fashion. The dehydration process alternates exposing the substrate to vacuum and then to heated nitrogen, either once or multiple times. For example, an indium tin oxide covered substrate would be exposed to a vacuum of 10 Torr for 2 minutes. At this pressure water boils at about 11 C. The vacuum chamber would then be flooded with preheated nitrogen at 150 C to a pressure of 600 Torr. This part of the process would heat the surface of the indium tin oxide covered substrate so that the high temperature of the substrate would assist in the dehydration process as vacuum was once again applied. After 3 complete cycles, a vacuum of 1 Torr would be applied to complete the dehydration process. In some cases, the substrate may be pre-heated in the chamber prior to the start of the above dehydration process, especially in cases of substrates with large thermal mass.
A gas plasma cleaning cycle may also be used in preparation of the substrate for coating. In a typical process, the substrate is cleaned using gas plasma after the dehydration process. In some embodiments, the plasma cleaning cycle may occur before the dehydration process. In an exemplary process, the chamber is evacuated. A gas is then introduced into the chamber and the pressure is stabilized at a low pressure, such as 150-200 milliTorr. In some embodiments, the introduced gas in oxygen. In some embodiments, the introduced gas is a combination of oxygen and argon. In some embodiments, other gasses are used. After the stabilization of the pressure in the process chamber, the electrodes are powered to generate the plasma. In an exemplary process, the electrodes are powered to 450 Volts cycled at 40 kiloHertz. The power cycle may last for 2 minutes in some embodiments. In some embodiments, the indium tin oxide covered glass substrate will be plasma cleaned in a separate chamber using argon gas.
After the completion of the dehydration and plasma cleaning cycles, the slide or substrate is ready for chemical reaction. Chemical reservoirs, such as manufacturer's source bottles, may provide the chemical for the deposition process. For many processes, silanes are used. Chemical may be withdrawn directly from the reservoir. In some processes, a metered amount of chemical is withdrawn from the chemical reservoir. This may be done by opening a valve between the chemical reservoir and a withdrawal mechanism. The withdrawal mechanism may be a syringe pump. Chemical is withdrawn from the reservoir, enters the syringe pump, and then the valve between the chemical reservoir and the syringe pump is closed. The chemical reservoirs may be purged with an inert gas such as nitrogen. This purging allows for the filling of the volume of fluid removed with an inert gas, minimizing contact between the chemical in the reservoir and any air or moisture.
Next, a valve between the syringe pump and a vaporization chamber is opened. The vapor chamber may be pre-heated. The vapor chamber may be a reduced pressure. The syringe pump then pumps the previously withdrawn chemical from the syringe pump to the vaporization chamber. The vapor chamber may be at the same vacuum level as the process oven. In parallel to this delivery of chemical to the vaporization chamber, a second chemical may be undergoing the same delivery process. The two chemicals may vaporize at substantially the same time. Additionally, more chemicals may also be delivered to the vaporization chamber, or to another vaporization chamber.
In some embodiments, the chemical or chemicals to be vaporized may be withdrawn from the reservoir or reservoirs in a specific metered amount. This specific amount of withdrawal and delivery to the vapor chamber may be repeated until the desired amount of chemical or chemicals has been delivered into the vapor chamber. For example, a metering pump may be used. The metering pump may deliver a pre-determined amount of chemical per stroke of the metering pump. The number of pump strokes may be selected, thus delivering a specified amount of chemical. In some embodiments, the use of a metering pump precludes the need for isolating pumps between the source bottles and the pumps, and between the pumps and the vapor chamber.
In an exemplary process for coating of an indium tin oxide coated substrate, the chemical quantity used is between 4 and 5 milliliters. The metering pump fires 0.1 milliliters per pump. The metering pump is pumped 40 to 50 times, delivering the chemical to the vapor chamber. The heated vapor valve between the vapor chamber and the process chamber is open during the delivery of the chemical to the vapor chamber. The process chamber pressure and the vapor chamber pressure may rise to 4-10 Torr as the chemical is delivered to the vapor chamber. The chemical is vaporized and the duration of the substrate exposure to the vaporized chemical is 5 minutes.
The chemical used for the coating of indium tin oxide coated substrates may be Triethoxy(octyl)silane [CH3(CH2)7Si(OC2H5)3], Perfluorooctyltrichorosilane [CF3(CF2)SCH2CH2SiCL3], and Heptadecafluoro1122tetrahydrodecyltrichlorosilane [C10H4CL3F17Si].
After the exposure of the substrate to the vaporized chemical, a vacuum is drawn for typically 5 minutes and 5 to 10 millitorr to remove the silane from the chambers. A purge cycle, typically repeated three times, adds nitrogen to 600 Torr and is followed by vacuum to 1 Torr.
After the completion of the purge cycles, vacuum is pulled to 1 Torr and the convectron gauge is compared to the diaphragm gauge. If there is agreement, the silane has been removed from the chambers. The chambers are back filled with nitrogen and the substrate may be removed.
In some embodiments, the chamber may be cleaned using gas plasma subsequent to the processing steps. The chamber may be emptied of all workpieces and then cleaned. The gas plasma cleaning step subsequent to the processing steps helps prepare the process chamber for subsequent processing.
As evident from the above description, a wide variety of embodiments may be configured from the description given herein and additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader aspects is, therefore, not limited to the specific details, representative apparatus and illustrative examples shown and described. Accordingly, departures from such details may be made without departing from the spirit or scope of the applicant's general invention.
This application is a continuation in part of U.S. patent application Ser. No. 11/148,543 to Moffat et al., filed Jun. 8, 2005, which is a continuation in part of U.S. patent application Ser. No. 10/656,840 to Moffat et al., filed Sep. 5, 2003. This application claims priority to U.S. patent application Ser. No. 10/843,774 to Moffat et al., filed May 11, 2004, which is hereby incorporated in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10656840 | Sep 2003 | US |
| Child | 11148543 | Jun 2005 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11148543 | Jun 2005 | US |
| Child | 11335945 | Jan 2006 | US |
