Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K50/00—Organic light-emitting devices
  • H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
  • H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
  • H10K50/125—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers specially adapted for multicolour light emission, e.g. for emitting white light
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K71/00—Manufacture or treatment specially adapted for the organic devices covered by this subclass
  • H10K71/20—Changing the shape of the active layer in the devices, e.g. patterning
  • H10K71/231—Changing the shape of the active layer in the devices, e.g. patterning by etching of existing layers
  • H10K71/233—Changing the shape of the active layer in the devices, e.g. patterning by etching of existing layers by photolithographic etching
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K50/00—Organic light-emitting devices
  • H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
  • H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
  • H10K50/12—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers comprising dopants
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K50/00—Organic light-emitting devices
  • H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
  • H10K50/14—Carrier transporting layers
  • H10K50/15—Hole transporting layers
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K50/00—Organic light-emitting devices
  • H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
  • H10K50/14—Carrier transporting layers
  • H10K50/16—Electron transporting layers
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K50/00—Organic light-emitting devices
  • H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
  • H10K50/17—Carrier injection layers
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
  • H10K59/10—OLED displays
  • H10K59/12—Active-matrix OLED [AMOLED] displays
  • H10K59/1201—Manufacture or treatment
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
  • H10K59/30—Devices specially adapted for multicolour light emission
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K71/00—Manufacture or treatment specially adapted for the organic devices covered by this subclass
  • H10K71/10—Deposition of organic active material
  • H10K71/16—Deposition of organic active material using physical vapour deposition [PVD], e.g. vacuum deposition or sputtering
  • H10K71/166—Deposition of organic active material using physical vapour deposition [PVD], e.g. vacuum deposition or sputtering using selective deposition, e.g. using a mask
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K71/00—Manufacture or treatment specially adapted for the organic devices covered by this subclass
  • H10K71/60—Forming conductive regions or layers, e.g. electrodes
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
  • H10K85/10—Organic polymers or oligomers
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K50/00—Organic light-emitting devices
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/50—Photovoltaic [PV] energy
  • Y02E10/549—Organic PV cells

Definitions

• the present disclosure relates to semiconductor processing techniques, and more particularly, photolithography techniques using photoresist systems for patterning organic devices.
• OLEDs organic light emitting diodes
• Deposition through a shadow mask typically includes placing a template in front of a substrate that blocks the substrate everywhere except the desired deposition locations for the OLED material.
• Conventional patterning methods such as lithography are generally not used since OLEDs are comprised of organic materials and said organic materials are susceptible to being dissolved or degraded by the solvents required for photoresist techniques found in conventional lithography. If it were not for this limitation, conventional lithography methods would be the most straightforward method in fabrication of OLED structures and other organic devices.
• a common deposition method used to deposit and for patterning organic devices and in particular OLED devices involves the use of a fine metal mask, which is a type of shadow mask.
• a shadow mask can be a large sheet that is generally made as thin as possible with small holes. Deposition occurs through a point source in which organics are evaporated onto the mask and through these holes, the organics that come through this point source then end up on the substrate at the appropriate locations as dictated by the mask. Due to limitations in how small the holes in the shadow mask can be, how thin the shadow mask can be made, and how close to the substrate the shadow mask can be placed among other reasons, there is a resolution limit limiting the feature size and density of the patterned organics.
• a lift-off technique is often utilized where an undercut profile is created in the photosensitive resist layers to create a cavity structure where the top layer of resist is overhanging an opening in the bottom layer of resist.
• the material to be lifted off is then deposited through the opening and the cavity under the overhang resist profile leaves additional space for solvents to access the resist system after deposition of the desired material, leaving the deposited material in the patterned openings.
• UV light ultraviolet light
• Some organic-safe resist systems use a negative photoresist top layer, which must be exposed to UV light during patterning.
• a negative photoresist is a type of photoresist wherein the region of the photoresist that is exposed to light becomes insoluble to the photoresist developer. Specifically, the negative photosensitive resist material is strengthened, by polymerization or cross-linking, in the presence of UV light.
• a light mask also referred to herein as a photomask
• the developer will dissolve the regions that were not exposed to light, leaving behind a coating of resist in areas of the negative photoresist layer not exposed to UV light.
• the photomask has opaque and transparent regions to allow UV light to pass through, forming the desired pattern in the photoresist.
• the unexposed region of the photoresist is then dissolved by the photoresist developer, such as, for example, a buffered KOH developer.
• a positive photoresist is a type of photoresist wherein the region of the photoresist exposed to UV light becomes soluble to the photoresist developer.
• the basic elements of this resist system include an imaging layer, an inorganic transfer layer, and a bottom sacrificial layer.
• the bottom sacrificial layer is typically a hard-baked photoresist while the inorganic transfer layer is a metal or dielectric material and the imaging layer is a conventional photoresist.
• the imaging layer is exposed and developed and then the inorganic transfer layer is etched.
• the system is then exposed to an oxygen plasma to transfer the pattern to the sacrificial layer.
• the oxygen plasma can be designed to produce an undercut in the resist and remove the imaging layer for an ideal liftoff profile.
• planarization techniques such as chemical-mechanical polish, were unavailable, therefore lithography was performed over topography.
• United States Patent 10,049,876 to Sankarapandian et al. describes a method that includes forming a trilayer resist structure having a middle layer disposed between a top layer and a bottom layer.
• This trilayer resist method is used to remove a material in a directional way from a specialized type of transistor, while not damaging nearby similar transistors.
• the function of this trilayer resist is to first planarize the surface and then to act as a hard mask for an etching process.
• a material similar to, or the same as, the bottom layer of the trilayer resist structure is applied to planarize and etch back a chemical-mechanical polish (CMP) layer to a level that is below the middle layer of resist.
• CMP chemical-mechanical polish
• the middle layer can then be removed by an etching procedure that would normally harm the rest of the substrate, however due to the additional planarization layer the substrate is covered and protected from the etch that removes the middle layer.
• the remaining planarization layer is finally removed using a dry or wet stripping process.
• the organic device is an organic light emitting diode.
• etching the fluoropolymer base layer exposed through the inorganic transfer layer comprises using reactive ion etching to expose the bottom electrode.
• the positive-type photoresist layer has a thickness of between about 340-500 nm.
• etching the inorganic transfer layer through the patterned positive-type photoresist layer creates an undercut region between the positive- type photoresist image layer and the inorganic transfer layer.
• the liftoff procedure utilizes a fluorinated solvent to dissolve the fluoropolymer base layer.
• the inorganic transfer layer comprises one or more of a metal and a dielectric material.
• the emission layers is at least one of red, green, and blue color emission.
• an oxide layer is deposited on the substrate and electrode array before deposition of the trilayer resist system.
• the oxide layer comprises a transparent conducting oxide.
• the organic device is an OLED, and wherein the first set of organic devices and the second set of organic devices emit different colors.
• the method further comprises repeating the trilayer resist deposition method to deposit a trilayer resist system on the substrate; repeating the organic device deposition method to create a third plurality of organic devices aligned with a third set of bottom electrodes; and performing a liftoff procedure to remove any remaining components of the trilayer resist system.
• etching the inorganic transfer layer through the patterned positive-type photoresist image layer creates an undercut region between the positive-type photoresist image layer and the inorganic transfer layer.
• the lateral undercut profile is > 0.25 pm in length.
• the inorganic transfer layer comprises one or more metal or dielectric material.
• the organic layer is an organic stack comprising one or more electron transport layers (ETL), emission layers (EML), hole transport layers (HTL), and hole injection layers (HIL).
• ETL electron transport layers
• EML emission layers
• HTL hole transport layers
• HIL hole injection layers
• a method for patterning an organic device array comprising: depositing a plurality of bottom electrodes on a substrate; depositing a trilayer resist system on the substrate using a trilayer resist deposition method comprising: a fluoropolymer base layer; an intermediate inorganic transfer layer; and a top positive-type photoresist layer; and creating a plurality of organic devices using an organic device deposition method comprising: patterning the top positive-type photoresist layer using photolithography to create an image layer aligned with the plurality of bottom electrodes; etching the intermediate inorganic transfer layer exposed through the image layer; etching the fluoropolymer base layer exposed through the inorganic transfer layer to expose the plurality of bottom electrodes; and depositing at least one organic layer above the set of exposed bottom electrodes; and performing a liftoff procedure to remove any remaining components of the trilayer resist system.
• an oxide layer is deposited on the substrate before deposition of the trilayer resist system.
• the oxide layer is a transparent conducting oxide.
• the fluoropolymer base layer has a visible light transmission ratio of 95% or greater.
• the thickness of the positive-type photoresist image layer is 400-600 nm.
• etching the inorganic transfer layer through the patterned positive-type photoresist image layer creates an undercut region between the positive-type photoresist image layer and the inorganic transfer layer.
• etching the fluoropolymer base layer creates a lateral undercut profde and a longitudinal undercut profde.
• the lateral undercut profde is > 0.25 pm in length.
• the liftoff procedure utilizes a fluorinated solvent that interacts and dissolves the fluoropolymer base layer.
• the inorganic transfer layer comprises one or more metal or dielectric material.
• the developer is a buffered KOH developer.
• a post exposure bake process is required after etching the inorganic transfer layer or etching the fluoropolymer base layer.
• the post exposure bake process is executed at a temperature ⁇ 120°C.
• the liftoff procedure comprises immersing the substrate in a fluorosolvent to interact with and dissolve the fluoropolymer base layer but does not interact with the organic stack.
• a method for patterning a multi-color organic light emitting diode (OLED) array comprising: depositing a first series of bottom electrodes and a second series of bottom electrodes on a substrate in an array; depositing a trilayer resist system comprising: a fluoropolymer base layer; an inorganic transfer layer; and a positive-type photoresist image layer; and creating a multicolor array of OLED devices by: patterning the positive-type photoresist image layer at locations above the first series of bottom electrodes by exposing the positive-type photoresist image layer to ultraviolet light and removing the patterned positive-type photoresist image layer that has been exposed to the ultraviolet light by etching; etching the inorganic transfer layer through the patterned positive-type photoresist image layer; etching the fluoropolymer base layer exposed through the inorganic transfer layer using reactive ion etching to expose at least some of the first series of bottom electrodes; depositing a trilayer resist system comprising: a fluor
• an oxide layer is deposited on the substrate before deposition of the trilayer resist system.
• etching the fluoropolymer base layer creates a lateral undercut profile and a longitudinal undercut profile.
• the liftoff procedure utilizes a fluorinated solvent that interacts and dissolves the fluoropolymer base layer.
• the first color organic stack is for at least one of red, green, or blue color emission.
• the second color organic stack is for at least one of red, green, or blue color emission.
• the first color organic stack is different from the second color organic stack.
• a post exposure bake process is required after etching the inorganic transfer layer or etching the fluoropolymer base layer.
• the post exposure bake process is executed at a temperature ⁇ 120°C.
• the liftoff procedure comprises immersing the substrate in a fluorosolvent to interact with and dissolve the fluoropolymer base layer but does not interact with the first color organic stack or the second color organic stack.
• FIG. IB illustrates a cross section of a substrate following the deposition of the inorganic transfer layer.
• FIG. 2A illustrates a cross section of a substrate with an electrode and a trilayer resist system following photolithography of the positive-type photoresist image layer.
• FIG. 2B illustrates a cross section of a substrate with an electrode and a trilayer resist system following etching of the inorganic transfer layer.
• FIG. 2C illustrates a cross section of a substrate with an electrode and a resist system following etching of the fluoropolymer base layer.
• FIG. 2D illustrates a cross section of a substrate with an electrode and a resist system following the deposition of an organic stack.
• FIG. 2E illustrates a cross section of a substrate with an electrode and an organic stack following the liftoff procedure.
• FIG. 4 illustrates a cross section of a substrate having an electrode with an OLED stack deposited on a first electrode and a second electrode without an OLED stack with a trilayer resist system deposited thereon.
• FIG. 5A illustrates a cross section of the UV exposure stage of photolithography for patterning a second color OLED using the disclosed trilayer resist system on a substrate with a first color OLED structure deposited thereon.
• FIG. 5B illustrates a cross section of a substrate with a first color organic stack patterned on a first electrode, a second electrode and a trilayer resist system following patterning of the positive-type photoresist image layer.
• FIG. 5D illustrates a cross section of a substrate with a first color organic stack patterned on a first electrode, a second electrode with a resist system following etching of the fluoropolymer base layer.
• FIG. 5E illustrates a cross section of a substrate with a first color organic stack patterned on a first electrode, a second electrode with a second organic stack deposited thereon following the thermal evaporation of the second organic stack.
• FIG. 5F illustrates a cross section of a substrate with a first color organic stack patterned on a first electrode and a second electrode with second organic stack following the liftoff procedure.
• FIG. 6B illustrates a top view image captured using an optical microscope of a second pattern following the development of the trilayer resist system.
• FIG. 6C illustrates a top view image captured using an optical microscope of a third pattern following the development of the trilayer resist system.
• FIG 8A illustrates a top view image captured using an optical microscope of a first pattern following the wet etch of the inorganic transfer layer.
• FIG. 8B illustrates a top view image captured using an optical microscope of a second pattern following the wet etch of the inorganic transfer layer.
• FIG. 8C illustrates a top view image captured using an optical microscope of a third pattern following the wet etch of the inorganic transfer layer.
• FIG. 9C illustrates a top view image captured using an optical microscope of a third pattern following the dry etching of the fluoropolymer base layer.
• FIG. 11 A illustrates a top view image captured by a Field Emission Scanning Electron Microscope (FESEM) following successful patterning of the trilayer resist system for a first pattern.
• FESEM Field Emission Scanning Electron Microscope
• FIG. 11B illustrates a side profile view image captured by the FESEM further illustrating the side profile of the undercut formed in the base layer of the first pattern.
• FIG. llC illustrates an isometric view image captured by the FESEM following successful patterning of the trilayer resist system for the first pattern.
• FIG. 12 illustrates a top view image captured by the FESEM following successful patterning of the trilayer resist system for a second pattern.
• FIG. 13A illustrates a top view image captured by the FESEM following successful patterning of the trilayer resist system for a third pattern.
• FIG. 13B illustrates an isometric view image captured by the FESEM following successful patterning of the trilayer resist system for the third pattern.
• FIG. 14C illustrates a top view image captured using an optical microscope of a third pattern following the liftoff of the fluoropolymer base layer.
• the present disclosure relates generally to a trilayer photoresist system and method for patterning and fabricating organic devices, for example OLED devices.
• the present method can also be used in patterning OLED arrays and can be used for fabricating OLED devices and OLED arrays for high-resolution, high density, full-parallax three dimensional (3D) light field displays.
• compositions, device, article, system, use, or method described herein as comprising certain elements and/or steps may also, in certain embodiments, consist essentially of those elements and/or steps, and in other embodiments consist of those elements and/or steps, whether or not these embodiments are specifically referred to.
• the term “about” refers to an approximately +/-10% variation from a given value. It is to be understood that such a variation is always included in any given value provided herein, whether or not it is specifically referred to.
• TCO transparent conductive oxide
• TCFs transparent conducting fdm
• TCO in particular is a doped metal oxide commonly used in optoelectronic devices.
• TCO materials include but are not limited to Indium Tin Oxide (ITO), Fluorine-doped Tin Oxide (FTO), Aluminum-doped Zinc Oxide (AZO), Indium-doped Zinc Oxide (IZO), and Gallium-doped Zinc Oxide (ZnO).
• ITO refers to Indium Tin Oxide, which is a composition of indium, tin and oxygen in varying proportions, typically encountered as an oxygen- saturated composition with a formulation of 74% In, 18% O2, and 8% Sn by weight. ITO is commonly used as an anode material in an OLED structure due to its suitable conductivity and ability to be deposited by established methods. ITO is also nearly transparent and colorless. ITO can be used to construct the anode layer in OLEDs according to the present disclosure.
• organic device refers to an electronic device comprising an organic layer.
• organic device includes but is not limited to an organic light emitting diode, organic field-effect transistor, organic solar cell, photovoltaic cell device, organic semiconductor, and organic laser.
• organic layer refers to a layer in an organic device that comprises a carbon-based organic material, molecule, or structure.
• Organic materials can be sensitive to degradation under the radiation wavelength and intensity used in photolithography .
• microcavity refers to a structure formed by reflecting faces on two sides of a spacer layer or optical medium, such as, for example, an OLED.
• microcavity OLED refers to an OLED, as previously described, bound in a microcavity defined by two reflective surfaces.
• the reflective surfaces of the MCOLED can be, for example, metallic materials, dielectric materials arranged in such a way to reflect light within a specific range, a combination of dielectric and metallic materials, or any other reflective surfaces.
• photomask refers to a thin plate or sheet having a plurality of regions that either permit or block the transmissivity of radiation (e.g. UV light) through the plate to the underlying photoresist material used for patterning of said photoresist material during photolithography.
• radiation e.g. UV light
• blanket deposition refers to depositing material without using a patterning technique.
• the term “wavelength” is a measure of distance between two identical peaks (high points) or troughs (low points) in a wave, which is a repeating pattern of traveling energy such as light or sound.
• the wavelength of light used in photolithography is generally in the ultraviolet region (about 10-450nm) and more preferably in the deep ultraviolet region (about 200-300nm) or at wavelengths under 300nm. Extreme ultraviolet radiation (about 10-125nm) and x-ray light (10 picometers to 10 nanometers) are also used in some applications of photolithography.
• the present disclosure is directed to semiconductor processing and fabrication techniques, and more particularly, photolithography techniques using photoresist systems for patterning organic devices including organic light emitting diodes (OLEDs) and OLED arrays.
• OLEDs organic light emitting diodes
• Photoresists are light-sensitive sacrificial materials which are fundamental to photolithography.
• Photoresist systems are generally comprised of a polymer, a sensitizer, and a solvent. Upon exposure to a radiation source such as UV radiation, the polymer structure of the photoresist material is altered. The solvent component allows the photoresist to be spun and to form thin layers over a wafer, or substrate surface. Finally, the sensitizer, or inhibitor, controls the photochemical reaction in the polymer phase.
• Photoresists can be classified as positive photoresists (positive-type photoresists) or negative photoresists (negative-type photoresists).
• the photomask used will have the same pattern as that desired for patterning on the semiconductor layer.
• exposure to a UV radiation source causes polymerization of the polymer. This polymerization results in the negative photoresist layer region exposed to the UV light becoming insoluble to the photoresist developer.
• the negative photoresist regions that had been exposed to the radiation source will remain upon the surface of the wafer, or substrate, following the chemical treatment with a developer solution. Therefore, masks used for negative photoresists contain the inverse or photographic “negative” of the pattern to be transferred.
• the wavelength of light used determines the minimum feature size that it can impress on the photoresist.
• UV radiation is generally referred to herein as the photolithography light source, however it is understood that a variety of wavelengths of light may be used according to the desired process materials and results.
• the photomask comprises an opaque plate with perforations or transparent regions that allows light to shine through (transmit) at defined locations in a particular pattern.
• Photomask materials can include, for example, fused silica (quartz glass) with a coating pattern made of chrome. In some cases, the photomask can be further coated with TeflonTM or other low-friction, low- stick coating to help prevent stiction issues during contact photolithography.
• the photomask By placing the photomask between the photoresist and a light source capable of degrading the polymer in the positive photoresist an exact copy of the pattern on the photomask can be created by degrading the photoresist at the holes or transparencies in the photomask pattern.
• the photomask will have the inverse of the desired pattern.
• Both negative and positive photoresists have advantages and disadvantages. Advantages of negative photoresists include good adhesion to silicon, low cost, and short processing time. Further, more desirable advantages of positive photoresists include increased controllability, good resolution, and good thermal stability.
• the resist features will become coated overall, making lift-off difficult or impossible if the positive photoresist were to polymerize within the 110-130°C temperature range. Additional advantages of using positive photoresists for semiconductor fabrication include that a positive photoresist generally does not swell during development, is capable of finer resolution, and is reasonably resistant to plasma processes. Negative photoresists are generally considered to be a better choice for lift-off processes as these polymers can achieve a reproducible undercut in the fabrication layers. This undercut helps to prevent the photoresist sidewalls from being coated as the crosslinking of the polymer resin of common negative resists maintains the undercut, making subsequent lift-off of sacrificial layers easier.
• the trilayer system is comprised of a fluoropolymer base layer, an intermediate inorganic layer, and a top positive-type photoresist layer, that can be used for patterning nano-scale organic structures, such as OLEDs, using photolithography techniques.
• the disclosed trilayer resist system avails of the advantages of photolithographic patterning using conventional photoresists by including an intermediate inorganic transfer layer between a top positive photoresist, also referred to as a positive-type photoresist layer, and a fluoropolymer base layer.
• a positive photoresist as the top layer which forms an image layer upon patterning allows for the fabrication of a finer pattern through the trilayer photoresist structure, leading to increased resolution of the resulting organic devices and a more controllable photolithography process.
• radiation UV light
• UV light is passed through transparent regions in the mask, defining the regions where the positive photoresist material will be subsequently removed with a developer.
• any structures underneath the negative photoresist on the underlying substrate that have an existing organic layer deposited thereon are therefore also exposed to radiation (UV light rays) during patterning of any subsequent organic stack (i.e. an additional OLED color), potentially damaging the organic layer.
• radiation exposure required for the hardening or polymerizing step in a negative photoresist treatment can penetrate into layers below the negative photoresist, thereby damaging underlying organic layers.
• the described trilayer resist system comprises a bottom fluoropolymer base layer, an inorganic transfer layer, and a top positive-type resist which forms the image layer.
• the intermediate inorganic transfer layer acts as a protective barrier for the fluoropolymer base layer.
• the presence of this protective inorganic transfer layer facilitates the implementation of a top, positive-type resist image layer.
• the positive-type photoresist image layer can then be patterned using conventional photolithography techniques for positive-type photoresists, thereby avoiding degradation of previously deposited organic materials on the substrate caused by UV light exposure.
• the fluoropolymer base layer can be developed and lifted off the substrate using a perfluorinated solvent which is not harmful to organic materials during the liftoff process.
• organic stack refers to the layers in the OLED that include an organic layer where a light beam is formed between two electrodes. These layers may include one or more electron transport layer, emission layer, hole transport layer, and hole injection layer, where the emission layer is an organic layer and the other layers can be either inorganic, organic, or combinations of organic and inorganic. In other organic devices, for example, an organic solar cell, one or more of each of these layers can comprise organic materials sensitive to the radiation used in photolithography. Therefore, the term “organic stack” refers to one or more layers, one of which being a layer formed of an organic material and may be replaced by a single organic layer for alternative embodiments of the disclosure (i.e. alternative organic devices).
• the intermediate inorganic transfer layer of the disclosed trilayer resist system acts as a critical barrier layer by preventing penetration of the harmful developer used for patterning the top positive photoresist material, through to the underlying fluoropolymer base layer and any organic material present under said base layer.
• the fluoropolymer base layer is a sacrificial layer that functions to create the desired undercut profiled for patterning for organic devices, and specifically for OLED devices.
• the trilayer system described herein employs a fluoropolymer base layer which, after exposure through the intermediate inorganic transfer layer, is etched with oxygen plasma or reactive ion etching (RIE) to create a microcavity, preferably with an undercut, through which the organic stack can be deposited.
• RIE reactive ion etching
• the presently described trilayer resist system allows for the implementation of photolithography techniques for patterning organic devices and organic light emitting diodes at a sub 10pm scale, with a highly controllable photoresist as the top positive-type resist image layer.
• the described trilayer resist system can further liftoff organics in a reliable way, providing a high-density OLED array, that is scalable to substrate sizes not currently possible for patterning OLEDs at the target sub 10pm dimension.
• present OLED devices using a shadow mask are not scalable to a flat panel display.
• an OLED is a solid-state semiconductor device having at least one conducting organic layer disposed between and electrically connected to an anode and a cathode.
• the anode injects holes
• the cathode injects electrons into the organic layers, and the injected holes and electrons each migrate toward the oppositely charged electrode.
• an exciton which is a localized electron-hole pair having an excited energy state, is formed. Light is emitted when the exciton relaxes via a photoemissive mechanism.
• Types of OLEDs include but are not limited to Active-matrix OLEDs (AMOLEDs), Top-emitting OLEDs, and Bottom-emitting OLEDs.
• AMOLEDs have full layers of cathode, organic molecules, and anode.
• the anode layers have a thin fdm transistor (TFT) plane in parallel to it to form a matrix. This helps in switching each pixel to its on or off state as desired, thus forming an image. Hence, the pixels switch off whenever they are not required or there is a black image on the display, increasing the battery life of the device. This is the least power consuming type of OLED and has quicker refresh rates which makes them suitable for video.
• Some uses for AMOLEDs are in computer monitors, large-screen TVs and electronic signs or billboards.
• Top-emitting OLEDs have a substrate that is either opaque or reflective.
• Top-emitting OLEDs are better suited for active-matrix applications as they can be more easily integrated with a non-transparent transistor backplane. Manufacturers use top-emitting OLED displays in devices such as smart cards. An OLED is bottom emitting if the emitted light passes through the transparent or semi transparent bottom electrode and substrate.
• organic layers are deposited onto an organic device through a fine metal mask (FMM), or shadowmask, which is acceptable for creating larger pixels (10s of pm scale).
• FMM fine metal mask
• shadowmask to achieve the pixel density required for a high-definition light field display must be in the sub- 10 pm range.
• the presently disclosed trilayer resist system allows for the patterning of organics using traditional photolithographic processes at a much finer resolution. Additionally, the present trilayer system can be used in multiple iterations on a single device, enabling fabrication of multiple independent organic stack structures on the same substrate.
• Previously deposited organic layers are first protected from degradation by radiation through use of a positive photoresist top layer (an opaque photomask) and by the intermediate inorganic transfer layer which acts as a critical barrier layer by preventing penetration of the harmful developer, used for patterning the top positive photoresist material, through to the underlying fluoropolymer base layer and any organic material present under said base layer.
• a positive photoresist top layer an opaque photomask
• the intermediate inorganic transfer layer which acts as a critical barrier layer by preventing penetration of the harmful developer, used for patterning the top positive photoresist material, through to the underlying fluoropolymer base layer and any organic material present under said base layer.
• the active area is defined as the region comprising an exposed bottom electrode, which was deposited on the substrate in an array prior to application of the trilayer photoresist system.
• the active area defines the boundaries where first level electrical connections will be made while predetermining the pattern shape and resolution of the organic device(s). Accordingly, the horizontal offset of the trilayer resist system from the active area also affects the shadowing of the organics, with greater offset expected to lead to less shadowing.
• Direct- write lithography refers to any technique that is capable of depositing, removing, dispensing, altering the chemistry, or processing various types of materials over different surfaces following a predetermined layout or pattern.
• direct-write lithography can be used, for example, to expose the positive photoresist top layer in a desired pattern for organic layer deposition on the substrate or bottom electrode.
• FIGs. 1A-1C illustrate the deposition of the trilayer polymer resist system on a substrate comprising an electrode.
• FIG. 1 A illustrates a cross section of a substrate following the deposition of a fluoropolymer base layer.
• Substrate 10 in this embodiment, has deposited thereon an oxide layer 12, bottom electrode 14, and a first layer of a fluoropolymer resist, herein referred to as the fluoropolymer base layer 16.
• the bottom electrode 14 can be a transparent material such as indium tin oxide (ITO) or a conducting polymer such as, for example, doped polyaniline, a thin layer of a metal, such as Ag, Au or Al, or a combination thereof.
• ITO indium tin oxide
• a conducting polymer such as, for example, doped polyaniline
• a thin layer of a metal such as Ag, Au or Al, or a combination thereof.
• Bottom electrode material layer thicknesses can range from, for example, 10-100 nm with an overall bottom electrode material thickness of 100 ⁇ 10 nm. Shown is a single bottom electrode, however it is understood that the organic device may be comprised of a plurality of bottom electrodes which may be unpattemed or patterned, such as into rows or columns or other geometric or regularly spaced arrangement.
• the optional oxide layer 12 is used to achieve improved adhesion between the substrate 10 and the bottom electrode 14 and can be formed, for example, of a conducting transparent oxide material.
• transparent conducting oxide (TCO) materials include, but are not limited to, Indium Tin Oxide (ITO), Indium Zinc Oxide (IZO), and Aluminum Zinc Oxide (AZO).
• TCOs are electrically conductive materials with a relatively low resistivity and relatively high transmittance.
• the fluoropolymer base layer 16 is capable of being etched into a cavity with an undercut for receiving an OLED stack or other organic stack during manufacturing.
• organic stack and ‘organic layer’ are used herein, it is understood that any semiconductor device containing one or more layers of light-sensitive material may benefit from the present photolithography method.
• Fluoropolymers of use in the fluoropolymer base layer 16 are generally fluorocarbon-based polymers with multiple carbon-fluorine bonds. Fluoropolymer materials are characterized by a high resistance to solvents, acids, and bases, but can be etched using oxygen plasma or reactive ion etching. Some suitable fluoropolymer base layer materials include amorphous fluoropolymers. Fluoropolymer base layer 16 materials of use in the present system preferably have extremely high transparency (i.e. a visible light transmission ratio of 95% or greater) as optical transparency may be required for alignment during photolithography.
• a suitable material for the fluoropolymer base layer is CYTOP ® produced by AGC Chemicals, which is classified by its unique amorphous structure. CYTOP ® can be dissolved with certain fluorinated solvents and can be used in thin film coatings to achieve a sub-micron thickness.
• a suitable fluoropolymer for the fluoropolymer base layer 16 is TeflonTM AF1600X (AF).
• the fluoropolymer does not negatively chemically interact with the organic materials of the OLED device, as the process used to lift off the fluoropolymer must not damage any previously deposited OLED stacks or organic layers. Spin coating can be used to apply the fluoropolymer in the present method.
• spin coating can be used to apply a uniform thin fdm (420 ⁇ 20nm) onto a solid surface by applying the fdm material in a volatile solvent and using centrifugal force to spread the fdm out onto the surface. The higher the angular speed of spinning, the thinner the fdm.
• a liquid is placed at the center of a circular surface and the surface is rapidly rotated to produce uniform fdms of 1-lOpm in thickness.
• the fluoropolymer base layer 16 is applied by spin coating, and spun to a thickness of 340-500nm at a speed of 4000RPM for approximately 20-25 seconds.
• the final phase is the final bake, at a temperature of 180-250°C for 30-60 minutes to improve the adhesion of the fluoropolymer base layer 16 to the substrate 10.
• Other curing processes of the fluoropolymer base layer may be also used dependent upon the base layer material, to de-gas, remove solvent and improve adhesion of the base material.
• FIG. 1 A illustrates a substrate covered by an oxide layer, however the presence of said oxide layer 12 does not impact the disclosed trilayer resist system and the fluoropolymer base layer 16 can also be deposited directly upon the substrate.
• spin coating is provided as an example method of application, other methods of application can be used to apply the fluoropolymer, for example, spray coating or other deposition methods and deposition of the fluoropolymer base layer includes the physical deposition and all processing phases (prebake and final baking steps).
• the minimum thickness, or height, of the fluoropolymer base layer should be about 1.25 times the thickness of the organics that will deposited on top of the base layer for liftoff. Designing the fluoropolymer base layer height to be just a bit higher than the deposited stack enables deposition of the stack layers through the trilayer system with enough space to accommodate all layers below the undercut of the fluoropolymer base layer.
• 1.25 c the height of a red organic stack could be 308 ⁇ 30.5 nm
• 1.25 c the height of a green organic stack is 258 ⁇ 30 (12%) nm
• 1.25 c the height of a blue organic stack is 238 ⁇ 35 (15%)
• a fluoropolymer base layer 16 minimum thicknesses of 385 nm, 322.5 nm, and 297.5 nm respectively.
• the maximum thickness of the fluoropolymer base layer 16 and overall trilayer resist system stack height may be determined through simulation and/or experimentation. If the layers in the trilayer system are too thick and/or the desired undercut is not adequately formed in the fluoropolymer base layer 16, a shadowing effect may occur.
• the total height of the trilayer resist stack should preferably be minimized as much as possible to universally improve the uniformity of organics deposition and reduce shadowing effects.
• the height of the fluoropolymer base layer 16 should not exceed 530 nm, assuming that the positive-type resist image layer and inorganic transfer layer are limited to thicknesses of 500 nm and 100 nm respectively. It is also preferred that the actual minimum fluoropolymer base layer 16 thickness should range from 340-400 nm, while maintaining the ratio of 1.25 c the height of the organic stack.
• FIG.1A depicts a single bottom electrode 14 on a substrate 10 for illustrative purposes, however it is understood that the substrate 10 may have additional organic or OLED devices and a plurality of electrodes deposited upon it that are not shown in the magnified profile view of FIG. 1A.
• the trilayer resist system is removed using liftoff after the deposition of the organic and other layer(s), it is imperative that the liftoff method for the trilayer photoresist system avoids damaging any deposited organic layer or OLED structure or other chemically sensitive structure.
• photoresists are categorized as positive or negative-type. Positive photoresists chemically transform and become soluble to etching when exposed to UV light. Therefore, only the exposed regions of the photoresist to light are removed through etching while the unexposed regions of the photoresist remain insoluble. Alternatively, for a negative photoresist, the region of the photoresist that is exposed to UV light or photolithography radiation becomes insoluble to etching. UV light is used herein as an example of radiation that can be used in photolithographic patterning, however it is understood that a range of wavelengths may be used based on the properties of the photoresist layer.
• Positive photoresists are easier to control during photolithography because they generally maintain their size and can receive a radiation pattern, have better etching resistance, have superior resolution, and have good thermal stability.
• the photoresist layer can be removed through chemical etching. Chemical etching techniques include but are not limited to use of a developer, plasma etching, reactive ion etching, and ion beam milling.
• the positive-type photoresist layer 20 needs to be of sufficient thickness to function as a mask for the etch of the inorganic transfer layer 18, which is thin compared to what would be otherwise required in other photolithography systems.
• the positive-type photoresist layer 20 is also preferably deposited on a planar surface, in this case the planar inorganic transfer layer 18, therefore it is not restricted by a minimum thickness dictated by the topography on which it is deposited.
• the positive-type photoresist layer 20 may be deposited using a variety of techniques, for example using a spin coating technique, a spray ed-on technique, or dip application. Spin coating is a preferred method as it allows for finer control during application and a reduced layer thickness.
• the film for the positive-type photoresist layer 20 can be as thin as 10s of nanometers to several micrometers thick. Baking procedures used during the coating process should be carefully controlled to avoid heat damaging of the organic materials while enabling curing of the positive photoresist. In the present case, a baking temperature limit for the positive photoresist top layer 20 not exceeding 120°C has been found to be acceptable. It is understood that reference to deposition of the top positive photoresist layer 20 includes the physical deposition of the photoresist as well as all processing phases including drying, curing, degassing, and baking steps.
• the material selection criterion for the positive-type photoresist layer 20 should be considered such that the resist material provides strong adhesion to the inorganic transfer layer 18, and the positive-type photoresist layer 20 is sufficiently thin to be completely removed by the oxygen plasma during the fluoropolymer base layer etch step.
• Suitable materials for the positive-type photoresist layer 20 include but are not limited to commercially available positive-type photoresists compatible with common developers and strippers with suitable film thickness.
• the positive photoresist can be formulated from a phenol-formaldehyde novolak resin. Specific examples of suitable positive photoresists are those from the AZ ® 1500 family of positive photoresists from Micro Chemicals.
• FIGs. 2A-2F illustrate a method of patterning the trilayer photoresist system and deposition of an organic layer on an exposed electrode in accordance with the present method.
• the organic layer can be an organic stack, or plurality of layers, wherein in at least one layer is comprised of an organic material.
• FIG. 2A illustrates a cross section of a substrate with an electrode and a trilayer resist system following photolithography of the positive-type photoresist image layer.
• the substrate 10 shown has layered upon it, in order, an oxide layer 12 and a bottom electrode 14, and the disclosed trilayer resist system comprising a fluoropolymer base layer 16, an inorganic transfer layer 18, and a positive-type photoresist layer 20.
• a photolithography technique is used to pattern the positive-type photoresist layer 20 to expose the inorganic transfer layer 18 above bottom electrode 14 where the organic layer(s) will be deposited.
• a photomask can be used to develop the positive-type photoresist layer 20.
• UV light is applied to the positive-type photoresist layer 20 in a desired pattern through a photomask, and the exposed regions of the positive-type photoresist layer 20 underneath the UV -transparent regions of the photomask become soluble to etching. The etching process then removes the soluble regions of the positive-type photoresist layer 20 transferring the desired pattern to the positive-type photoresist layer 20.
• etching is performed using a developer that may be comprised of a hydroxide such as, for example, sodium hydroxide (NaOH), potassium hydroxide (KOH), tetramethylammonium hydroxide, or other suitable materials.
• a hydroxide such as, for example, sodium hydroxide (NaOH), potassium hydroxide (KOH), tetramethylammonium hydroxide, or other suitable materials.
• Developers typically have a limited range of useful dilutions. Highly concentrated dilutions have high sensitivity and allow faster photo speeds, but they are limited by high dark fdm losses and reduced contrast. The more dilute concentrations enable high contrast and provide greater selectivity between the exposed and unexposed resist. These require longer development times or increased exposure energy and have greater sensitivity to the effects of standing waves from monochromatic exposure.
• Sodium-based buffered developers provide optimal process control while minimizing the attack on aluminum surfaces.
• FIG. 2B illustrates a cross section of a substrate, an electrode and a trilayer resist system, following etching of the inorganic transfer layer 18.
• the substrate 10 shown has layered upon it, in order, an oxide layer 12 and bottom electrode 14, and the disclosed trilayer resist system comprising a fluoropolymer base layer 16, an inorganic transfer layer 18, and a positive-type photoresist layer 20.
• the pattern formed in the top positive-type photoresist layer 20 is transferred to the inorganic transfer layer 18 by a wet etching process.
• Plasma etching is a processing technique whereby the surface of a source material becomes rougher on a microscopic scale. This is achieved using a reactive gas, such as oxygen, thereby altering both chemical and physical properties of the source material being etched. This chemical effect is imparted by the reactive gas, which steadily reacts and combines with the surface molecules of the material being etched. High energy ions are responsible for the physical effects as they physically hit surface atoms of the source material, thereby moving them to the gas phase.
• the plasma recipe should be at a relatively high pressure and low power so that it is capable of producing an undercut.
• the inorganic transfer layer 18 is etched, transferring the pattern formed in the top positive-type photoresist layer 20 to the inorganic transfer layer 18. This transfer should preferably form an undercut region 22. Etching of the inorganic transfer layer 18 using a high pressure and low power recipe will produce the desired undercut region 22. For example, for a fluoropolymer base layer 16 thickness of 340 - 400 nm and an inorganic transfer layer thickness 18 of 100 nm, about 0.33-0.35 pm of minimum offset or undercut length has been found to prevent shadowing and non-uniform deposition of organic layers over the bottom electrode active area 46.
• the longitudinal undercut profde 38 angle relative to substrate 10 is preferably at least 30 degrees from the lateral undercut profde.
• Etching the fluoropolymer base layer and creating the undercut can be done, using an etching treatment such as, for example, using UV ozone or an oxygen plasma.
• the lateral undercut profde 24 and longitudinal undercut profde 38 can be formed using an etching process in a similar way it is formed in the inorganic transfer layer 18.
• the lateral undercut profde 24 and longitudinal undercut profde 38 which is the minimum offset required to prevent shadowing, and overlay accuracy are all specific to the height of the fluoropolymer base layer 16 and the inorganic transfer layer 18 and change if the organic stack height changes.
• This intermediate inorganic transfer layer 18 can be as thin as 10s of nanometers to 100s of nanometers thick.
• films that can be used include metals such as aluminum, chromium, or dielectrics such as silicon dioxide. It should be noted that any film that is highly selective over fluoropolymer films to an oxygen plasma etch would be suitable.
• the film may be deposited using physical vapor deposition techniques such as evaporation or sputtering, chemical vapor deposition techniques such as plasma enhanced chemical vapor deposition, or a spin coating process.
• the organic stack 26 may be a single organic layer.
• the layers of the organic stack 26 are deposited using thermal evaporation deposition.
• Evaporation deposition may be defined as a method of thin-film deposition wherein the source material is evaporated in a vacuum. The vacuum allows vapor particles to travel directly to the target object (substrate 10), where they condense back to a solid state.
• a shadow mask can be used for evaporation deposition, wherein the evaporation gas travels through the opening in the shadow mask onto the bottom electrode 14, such that an organic stack 26, corresponding to the width of the lower portion of the opening is formed on the bottom electrode 14. This can prevent the generation of shadow effect or reducing the widths of the inner and outer shadows of the organic stack 26 during evaporation.
• Shadow masks are generally micro-structures, or stencils, that are used to define device areas, with precision, for deposition, etching, or a variety of applications suitable for processing a substrate. Precision is particularly important when depositing the organic stack 26 on the bottom electrode 14 to avoid shadowing effects.
• the organic layers of the organic stack 26 may include, but are not limited to, one or more electron transport layers (ETL), emission layers (EML), hole transport layers (HTL), and hole injection layers (HIL).
• the organic device created in part by the organic stack 26 comprising at least a single organic layer, deposited on bottom electrode 14 can also be a microcavity OLED (MCOLED) device.
• MCOLED microcavity organic light emitting diode
• a microcavity organic light emitting diode (MCOLED) is a device in which the materials of an OLED are bound in a microcavity defined by two reflective surfaces arranged in such a way to reflect light within a specific range, or some combination of dielectric and metallic materials.
• the sum of the optical path length of the materials between the reflective surfaces is designed to equal , where L is the peak design wavelength of the MCOLED.
• the optical path length in the MCOLED can be changed by changing the thickness of one or more of the materials between the reflective surfaces, or by adding one or more additional filler material layers.
• the use of a microcavity in an OLED structure decreases the spectral width of the OLED, decreases the angular output, and increases the overall efficiency.
• FIG. 2E illustrates a cross section of a substrate with an electrode and an organic stack following a liftoff procedure to remove the trilayer resist system.
• the organic stack 26 is shown deposited on a bottom electrode 14 and oxide layer 12 on a substrate 10 following the liftoff procedure.
• Liftoff of the fluoropolymer base layer, remaining inorganic transfer layer, and photoresist image layer is achieved by immersing the substrate 10 and its subsequent layers in a fluorinated solvent, or fluorosolvent, that interacts and dissolves the fluoropolymer base layer, but does not interact with, or interacts very weakly with, the materials of the organic stack 26.
• the organic stack 26 materials remain on the substrate 10 in the desired pattern.
• fluorosolvents also referred to as fluorinated solvents
• fluorinated solvents Due to low surface tension, fluorosolvents (also referred to as fluorinated solvents) can penetrate the surface of the fluoropolymer base layer 16 while remaining gentle on the substrate 10 surface. Fluorosolvents are not harmful to the organic stack 26, making the fluoropolymer base layer, and its compatible fluorosolvent, ideal for liftoff of the fluoropolymer base layer of the trilayer resist system following deposition of the organic stack 26.
• FIG. 2F illustrates a cross section of a substrate with an electrode, an organic stack and a cathode deposited thereon.
• the organic stack 26 is deposited on top of a bottom electrode 14 and oxide layer 12 on a substrate 10 and further illustrates the top electrode 28 following deposition.
• the top electrode 28 is a cathode and the bottom electrode 14 is an anode, which results in a direct OLED device.
• the electrodes can also be inverted and the disclosed trilayer resist system can also be used with both direct and inverted OLED configurations. If the OLED device were inverted, the bottom electrode 14 would be a cathode and the top electrode 28 would be an anode.
• the top electrode 28 can be a transparent material such as indium tin oxide (ITO) or a conducting polymer such as, for example, doped polyaniline, or a thin layer of a metal, such as Ag, Au or Al, or a combination thereof and can be deposited by thermal evaporation deposition.
• ITO indium tin oxide
• a conducting polymer such as, for example, doped polyaniline
• a thin layer of a metal such as Ag, Au or Al, or a combination thereof and can be deposited by thermal evaporation deposition.
• FIG. 3 illustrates a cross section of the disclosed trilayer resist system on a substrate 10 with a first bottom electrode 14a and first color OLED organic stack 26a deposited thereon.
• each color of organic stack can be layered onto a different series or set of bottom electrodes on the substrate.
• the disclosed trilayer system as has a three-layer structure with a fluoropolymer base layer 16, an inorganic transfer layer 18, and a positive- type photoresist layer 20.
• the substrate 10 has deposited thereon a plurality of bottom electrodes.
• first bottom electrodes 14a are exposed through the trilayer resist system, on top of which a first color OLED organic stack 26a is deposited and the remaining trilayer resist is removed using a fluorosolvent.
• the first color OLED organic stack 26a, exposed substrate 10, and other bottom electrodes are covered completely in a second trilayer resist system comprising a fluoropolymer base layer 16, an inorganic transfer layer 18, and a positive-type photoresist layer 20.
• the pattern for a second, or successive, color is then applied to the positive-type photoresist layer 20 to expose the inorganic transfer layer 18 for patterning a second color OLED organic stack on a second or successive bottom electrode 14b as previously described. It is noted that while a single bottom electrode for the first and second color OLED devices (14a and 14b respectively) are illustrated in FIG. 3, it is understood that an embodiment of this method would include a series or plurality of bottom electrodes 14a and a series or plurality of bottom electrodes 14b.
• FIG. 4 illustrates a cross section of a substrate having an OLED device comprising an electrode with an OLED stack deposited on a first electrode and a second electrode 14b without an OLED stack.
• the OLED stack 26a is deposited on a first bottom electrode 14a, positioned on top of a substrate 10 and comprises one or more of each of the following layers: an Hole-Injection Layer (HIL) 50, an Hole-Transporting Layer (HTL) 52, an Emissive Layer (EML) 54, an Electron-Transporting Layer (ETL) 56, and an Electron-Injection Layer (EIL) 58.
• HIL Hole-Injection Layer
• HTL Hole-Transporting Layer
• EML Emissive Layer
• ETL Electron-Transporting Layer
• EIL Electron-Injection Layer
• HIL Hole-Injection Layer
• HTL Hole-Transporting Layer
• ETL Electron-Transporting Layer
• EIL Electron-Injection Layer
• ETL Electron-Injection Layer
• EIL Electron-Injection Layer
• Examples of materials that can be used for the ETL 56 include but are not limited to 2-(4-biphenyl)-5-phenyl-l,3,4-oxadiazole (PBD), butyl PBD, and PBD or butyl PBD doped in an inert polymer such as poly(methyl methacrylate) (PMMA) or a poly(carbonate).
• PBD 2-(4-biphenyl)-5-phenyl-l,3,4-oxadiazole
• PBD butyl PBD
• PBD or butyl PBD doped in an inert polymer such as poly(methyl methacrylate) (PMMA) or a poly(carbonate).
• PMMA poly(methyl methacrylate)
• the emissive layer is comprised of organic molecules or polymers that receive electrons from an electrode layer through the Hole-Injection Layer (HIL) 50.
• HIL Hole-Injection Layer
• the Emissive layer (EML) is an organic layer that 54 comprises one or more organic materials that can include but is not limited to Alq (Tris(8- hydroxyquinolinato)aluminum), aromatic hydrocarbons, poly(phenylene vinylenes), oxadiazole and stilbene derivatives.
• the EML 54 material can optionally comprise a stable non-emissive host primary component material doped with an emissive material which has an energy gap that is less than that of the primary component material of the EML 54.
• the hole transport layer (HTL) 52 can be any substantially transparent material that can facilitate the transport of holes to the EML layer 54, where electron-hole recombination takes place.
• suitable materials for the HTL 52 can include but are not limited to organic materials such as diamines (e.g., N, N'-diphenyl-N,N'-bis (3-methylphenyl)-l,l'-biphenyl- 4,4'-diamine) and poly(phenylene vinylenes).
• diamines e.g., N, N'-diphenyl-N,N'-bis (3-methylphenyl)-l,l'-biphenyl- 4,4'-diamine
• Fluoropolymer base layer 16, intermediate inorganic transfer layer 18, and positive-type photoresist layer 20 are shown deposited on top of the OLED stack 26a as well as second electrode 14b.
• the device configuration shown is mid-fabrication and ready for a second photolithography and etching sequence to expose second electrode 14b for deposition of a second OLED stack.
• a CYTOP ® fluoropolymer base layer was diluted with CT-Solvel80 and any bubbles due to stirring were removed using a vacuum chamber.
• the base layer was applied to the substrate using a spin-coating technique to achieve ⁇ 420 ⁇ 20nm film.
• the thickness of the base layer was measured using a Filmetrics measurement tool.
• the fluoropolymer base layer was then baked for 15 minutes at room temperature, followed by a subsequent bake for 30 minutes at 105°C.
• the inorganic transfer layer was then deposited on top of the CYTOP base layer at room temperature, with a thickness of 50-1 OOnm, using magnetron sputtering.
• the substrate, base layer and inorganic transfer layer were then spin coated with positive resist of AZ ® 1505 (positive-type resist image layer) at a thickness of 500-600nm, therefore completing deposition of the trilayer resist system.
• the resist was then baked at 100°C for 2min and rehydrated for 5min.
• the trilayer system was subsequently exposed to UV light using direct write lithography and then developed using an AZ ® 400K developer.
• FIG 5A illustrates a cross section of the UV exposure stage of photolithography for patterning a second color OLED using the disclosed trilayer resist system on a substrate with a first color OLED structure already deposited thereon.
• Substrate 10 shown has deposited thereon, in order, an optional oxide layer 12, a first color OLED organic stack 26a on a first bottom electrode 14a, and a trilayer resist system comprising a fluoropolymer base layer 16, an inorganic transfer layer 18, and a positive-type photoresist layer 20.
• the trilayer resist system is then used for patterning a second color OLED organic stack on a second bottom electrode 14b.
• the positive-type photoresist layer 20 is patterned using a photolithography process.
• the photomask 34 has transparent regions 42 where UV light rays can penetrate and opaque regions 44 which block UV light from reaching the positive-type photoresist layer 20.
• the transparent region 42 of the photomask 34 allows UV light rays to penetrate through to the underlying positive-type photoresist layer 20 material.
• the opaque region 44 of photomask 34 prevents UV light rays from penetrating through to the material under the photomask 34, protecting the organic stack 26a underneath and exposing only the area above the electrodes on top of which the second color organic stack should be deposited.
• the opaque region 44 of the photomask 34 covers the material above the first color OLED organic stack 26a.
• the positive-type photoresist is a type of photoresist in which the region of the photoresist that is exposed to light becomes soluble to the photoresist developer after the positive resist in the positive-type photoresist layer 20 is degraded by ultraviolet light.
• the UV light preferably has a wavelength of 100-450 nm, more preferably 300- 450nm.
• the unexposed region of the positive-type photoresist under the opaque region 44 of the photomask 34 remains insoluble to the photoresist developer.
• Positive photoresists are well known in the art and highly controllable, however, traditionally have not been able to be used when patterning organic devices due to the damaging nature of their developers to organic materials.
• the developer used to dissolve the part of the positive- type photoresist exposed to UV light does not penetrate the inorganic transfer layer 18, thus protecting the organic stack underneath.
• Negative photoresists are not commonly used as the resolution is limited due to swelling in the exposed crosslinked areas caused by solvent uptake.
• Use of a positive photoresist in a trilayer resist system can benefit from the positive photoresist’s etching resistance, superior resolution, and thermal stability.
• a further advantage of the implementation of a positive-type photoresist with a photomask in the present trilayer system is that the first color OLED organic stack 26a is protected from UV exposure when patterning the second color OLED structure.
• the inorganic transfer layer 18 acts as a barrier layer, protecting the organic stack 26a from the developer, which is very harmful to organic materials.
• the trilayer resist system is particularly advantageous for patterning multiple organic devices, specifically, multi-color OLED arrays, on a single substrate 10. This is achieved by patterning an array of OLEDs for a first color, then subsequently patterning a second and then third color, if desired, with the photomask exposing only those bottom electrodes desired for organic stack deposition.
• FIG. 5B illustrates a cross section of a substrate with a first color organic stack patterned on a first electrode, a second electrode and a trilayer resist system following patterning of the positive-type photoresist image layer.
• An existing first color OLED structure comprising a first color organic stack 26a is already formed on a first bottom electrode 14a, and the second color is being formed on a second bottom electrode 14b on the same substrate 10.
• the trilayer system having a fluoropolymer base layer 16, an inorganic transfer layer 18, and a positive-type photoresist layer 20 are covering the substrate and electrodes and organic stacks thereon.
• FIG. 5C illustrates a cross section of a substrate with a first color organic stack patterned on a first electrode, a second electrode with a trilayer resist system following etching of the inorganic transfer layer.
• the substrate 10 has on it an oxide layer 12, an existing first color OLED structure comprising a first color organic stack 26a formed on a first bottom electrode 14a, a second bottom electrode 14b on the same substrate 10, and the trilayer system having a fluoropolymer base layer 16, an inorganic transfer layer 18, and a positive-type photoresist layer 20.
• the pattern formed in the positive-type photoresist layer 20 is then transferred to the inorganic transfer layer 18 using a first transfer procedure through the opening in the positive-type photoresist layer 20.
• the transfer procedure to etch the inorganic transfer layer 18 under the opening in the positive-type photoresist layer 20 can be, but is not limited to, a wet chemical etch or a dry etching technique such as a reactive ion etching (RIE) technique.
• RIE reactive ion etching
• the undercut region 22 can be formed through the controlled etch of the inorganic transfer layer 18 to replicate the pattern formed in the positive-type resist image layer 20 using photolithography, then allowing additional etching time to form the desired undercut 22.
• the etch selectivity of the positive-type resist image layer 20 to inorganic transfer layer 18 is between about 0.78-0.82.
• FIG. 5D illustrates a cross section of a substrate with a first color organic stack patterned on a first electrode, a second electrode with a resist system following etching of the fluoropolymer base layer.
• Substrate 10 has an optional oxide layer 12, an existing first color OLED structure comprising a first color organic stack 26a formed on a first bottom electrode 14a, a second bottom electrode 14b on the same substrate 10, and the remaining layers of the trilayer resist system, namely the inorganic transfer layer 18 and the fluoropolymer base layer 16.
• the pattern is transferred from the inorganic transfer layer 18 to the fluoropolymer base layer 16 using a second transfer procedure, which may be, but is not limited to a reactive ion etching (RIE) procedure, such as an oxygen plasma etching procedure.
• RIE reactive ion etching
• the second transfer procedure results in patterning the fluoropolymer base layer 16 such that a lateral undercut profde 24 and a longitudinal undercut profile 38 are formed, leaving a remaining unpattemed region 40 of the inorganic transfer layer.
• the offset value determines the lateral undercut 24.
• FIG. 5E illustrates a cross section of a substrate with a first color organic stack patterned on a first electrode, a second electrode with a second organic stack deposited thereon following the thermal evaporation of the second organic stack.
• the substrate 10 has an optional oxide layer 12 deposited thereon and a first color OLED structure comprising a bottom electrode 14a and a first color organic stack 26a, and above it a protective fluoropolymer base layer 16 and inorganic transfer layer 18 under the unpattemed region 40.
• a second color organic stack 26b is deposited through the patterning openings in the inorganic transfer layer 18 and the fluoropolymer base layer 16, on top of the second color bottom electrode 14b.
• the lateral undercut profile 24 and the longitudinal undercut profile 38 of the fluoropolymer base layer 16 allow for the organics to be deposited using evaporation deposition.
• the second color organic stack 26b is deposited by thermal evaporation from a point source.
• a shadow mask can be used for evaporation deposition, wherein the evaporation gas travels through the opening in the shadow mask onto the bottom electrode 14b such that an organic stack 26b, corresponding to the width of the lower portion of the opening, is formed on the bottom electrode 14b. This process prevents the generation of shadow effect or reducing of the widths of the inner and outer shadows of the organic stack 26b during evaporation.
• Shadow masks are generally micro-structures, or stencils, that are used to define device areas, with precision, for deposition, etching, or a variety of applications suitable for processing a substrate. Precision is particularly important when depositing the organic stack 26b on the bottom electrode 14b to avoid shadowing effects. Shadowing effects may result in the organic stack 26b not fully covering the bottom electrode active area 46, which can result in decreased performance and edge effects on the perimeter of the bottom electrode active area 46 due to a reduced thickness of the organic stack 26b layers at that perimeter. This may further result in non-optimal electrical properties and optical characteristics of the OLED device.
• Shadowing effects can be reduced by using a shadow mask for precise deposition and by forming a lateral undercut profile 24 and a longitudinal undercut profile 38 in the fluoropolymer base layer.
• the lateral undercut profile 24 and a longitudinal undercut profile 38 allows the organic stack 26 to be deposited on a defined device area that extends the width of the bottom electrode active area 46.
• FIG. 5F illustrates a cross section of a substrate with a first color organic stack patterned on a first electrode and a second electrode with second organic stack following the liftoff procedure.
• a liftoff procedure is performed, and the resulting two-color organic stack array is as shown. Liftoff is achieved by immersing the substrate 10 in a solvent that interacts and dissolves the fluoropolymer base layer but does not interact, or interacts very weakly with the organic stacks 26a, 26b.
• the OLED materials of the organic stacks 26a, 26b will be left on the substrate 10 together with the oxide layer 12 in the desired pattern following liftoff.
• FIG. 5G illustrates a cross section of a multi-colored OLED array on a substrate comprising a first color OLED patterned on a first electrode and a second color OLED patterned on a second electrode.
• the final fabrication step includes depositing the top electrodes 28a, 28b on top of the organic stacks 26a, 26b and the resulting OLED array is as shown.
• the organic stacks 26a, 26b are formed upon bottom electrodes 14a, 14b, respectively.
• the bottom electrodes 14a, 14b are formed upon a substrate 10 comprising an oxide layer 12 and the top electrodes 28a, 28b, in this embodiment are cathodes.
• the top electrode 28a, 28b can comprise, for example, a reflective metal, a semi-transparent, thin-film metal or a transparent conductive oxide such as, for example, Indium Tin Oxide (ITO), Fluorine Doped Tin Oxide (FTO) or Aluminum-doped Zinc Oxide (AZO) and Indium-doped Zinc Oxide (IZO), or Ga-doped Zinc Oxide (ZnO).
• ITO Indium Tin Oxide
• FTO Fluorine Doped Tin Oxide
• AZO Aluminum-doped Zinc Oxide
• IZO Indium-doped Zinc Oxide
• ZnO Ga-doped Zinc Oxide
• the botom electrodes 14a, 14b can be deposited, for example, with sputering, evaporation, or spin coating techniques.
• FIG. 6A illustrates atop view image captured using an optical microscope of a first patern following the photolithographic development of the positive-type photoresist layer of the trilayer resist system.
• FIG. 6B illustrates a top view image captured using an optical microscope of a second patern following the photolithographic development of the positive- type photoresist layer of the trilayer resist system.
• FIG. 6C illustrates a top view image captured using an optical microscope of a third patern following the photolithographic development of the positive-type photoresist layer of the trilayer resist system.
• FIG. 7 shows the inorganic transfer layer on a wafer before etching 60 and the same wafer after the etching process 62.
• the etchant solution can be, for example, one or more of phosphoric acid, nitric acid, acetic acid and/or water. It is possible to perform an additional intermediate etching steps using a different etching method between a first and second transfer layer wet etching step.
• FIG. 8A illustrates a top view image captured using an optical microscope of a first patern following the wet etch of the inorganic transfer layer.
• FIG. 8B illustrates a top view image captured using an optical microscope of a second patern following the wet etch of the inorganic transfer layer.
• FIG. 8C illustrates a top view image captured using an optical microscope of a third patern following the wet etch of the inorganic transfer layer.
• FIG. 9A illustrates a top view image captured using an optical microscope of a first patern following the dry etching of the fluoropolymer base layer.
• the fluoropolymer base layer was etched with an O2 plasma using dry etching technique.
• FIG. 9B illustrates a top view image captured using an optical microscope of a second pattern following the dry etching of the fluoropolymer base layer.
• FIG. 9C illustrates a top view image captured using an optical microscope of a third pattern following the dry etching of the fluoropolymer base layer.
• FIG. 10 illustrates a profile view image captured by a Field Emission Scanning Electron Microscope (FESEM) of an undercut in the fluoropolymer base layer.
• FESEM Field Emission Scanning Electron Microscope
• FIG. 11 A illustrates a top view image captured by a Field Emission Scanning Electron Microscope (FESEM) following successful patterning of the trilayer resist system for a first pattern.
• FIG. 1 IB illustrates a side profile view image captured by the FESEM further illustrating the side profile of the undercut formed in the CYTOP base layer of the first pattern.
• FIG. 11C illustrates an isometric view image captured by the FESEM following successful patterning of the trilayer resist system for the first pattern.
• FESEM Field Emission Scanning Electron Microscope
• FIG. 11 A illustrates a top view image captured by a Field Emission Scanning Electron Microscope (FESEM) following successful patterning of the trilayer resist system, prior to the deposition of an organic layer, for a first pattern.
• FIG. 1 IB illustrates a side profile view image captured by the FESEM further illustrating the side profile of the undercut formed in the fluoropolymer base layer, prior to the deposition of an organic layer, of the first pattern.
• FIG. 11C illustrates an isometric view image captured by the FESEM following successful patterning of the trilayer resist system, prior to the deposition of an organic layer, for the first pattern.
• FIG. 12 illustrates a top view image captured by the FESEM following successful patterning of the trilayer resist system, prior to the deposition of an organic layer, for a second pattern.
• FIG. 13A illustrates a top view image captured by the FESEM following successful patterning of the trilayer resist system, prior to the deposition of an organic layer, for a third pattern.
• FIG. 13B illustrates an isometric view image captured by the FESEM following successful patterning of the trilayer resist system, prior to the deposition of an organic layer, for the third pattern.
• FIG. 14A illustrates a top view image captured using an optical microscope of a first pattern following the liftoff of the fluoropolymer base layer, illustrating the successful patterning of an array of clean bottom electrodes ready for the deposition of organic devices.
• FIG. 14B illustrates an image captured using an optical microscope of a second pattern following the liftoff of the fluoropolymer base layer, illustrating the successful patterning of an array of clean bottom electrodes ready for the deposition of organic devices.
• FIG. 14C illustrates an image captured using an optical microscope of a third pattern following the liftoff of the fluoropolymer base layer, illustrating the successful patterning of an array of clean bottom electrodes ready for the deposition of organic devices.

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