Trilayer photosensitive system and method for patterning organic devices

Abstract

A trilayer resist system design and method for patterning organic devices, including organic light emitting diode (OLED) devices suitable for high definition light field displays. The trilayer resist system is composed of a fluoropolymer base layer, an inorganic transfer layer, and a top positive photoresist layer that protects the organics formed on the substrate from damage caused by radiation, developers, and solvents used in conventional photolithography techniques, thereby resulting in high resolution, multicolor OLED arrays.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Patent Application No. 63 / 217,776, filed July 2, 2021, the contents of which are incorporated herein by reference in their entirety.

[0002] This disclosure relates to semiconductor processing techniques, and more particularly to photolithography techniques that use photoresist systems to pattern organic devices. [Background technology]

[0003] Organic light-emitting diodes (OLEDs) are inherently difficult to pattern due to the sensitivity of organic materials to temperature and other materials. These structures are traditionally deposited using evaporation through a shadow mask. Deposition through a shadow mask typically involves placing a template in front of the substrate that blocks the substrate everywhere except where the OLED material is desired to be deposited. Traditional patterning methods, such as lithography, are generally not used because OLEDs are composed of organic materials that are susceptible to dissolution or degradation by the solvents required for photoresist techniques found in traditional lithography. Without this limitation, traditional lithography methods would be the simplest method for fabricating OLED structures and other organic devices.

[0004] A common deposition method used to deposit and pattern organic devices, particularly OLED devices, involves the use of a fine metal mask, a type of shadow mask. Shadow masks can generally be large sheets made as thin as possible with small holes. Deposition occurs via a point source where organic material is deposited onto the mask and through these holes. The organic material coming through the point source then ends up on the substrate at the appropriate location dictated by the mask. Among other reasons, there are resolution limits that restrict the feature size and density of the patterned organic material due to limitations on how small the holes in the shadow mask can be, how thin the shadow mask can be, and how close the shadow mask can be placed to the substrate. Among the challenges posed by the physical dimensions of the shadow mask is the shadowing effect, where material is deposited under the masked areas of the shadow mask and the unmasked areas have non-uniform deposition. The shadowing effect occurs during deposition under physically masked areas of the substrate due to the off-normal arrival angle of the deposited material. The thickness of the shadow mask is one factor that determines how much unwanted shadowing effect will be present on the substrate, leading to resolution limits in which organic materials can be patterned. Therefore, it is desirable to have a very thin shadow mask; if the shadow mask is too thin, there is a risk of the mask breaking or deforming. Due to the high-resolution OLED target dimensions for bright-field display technology, photolithography is an ideal deposition technique, as it is mature, well-developed, and often used for small-scale patterning of semiconductors and metals. However, it should be noted that materials commonly used in semiconductor and especially metal fabrication are much less process-sensitive than organic materials. Because organics are often considered contaminants, many microfabrication processes are designed to remove them through development. In particular, standard photolithography cleaning procedures are designed to remove organic contaminants.

[0005] Specially formulated resist systems exist that utilize solvents safe for organic materials. These specially formulated systems typically utilize a two-layer photolithography lift-off method, in which a bottom photolithography layer is used as a sacrificial layer and a top photosensitive resist layer. In one technique, the bottom layer is spun and baked on the wafer before the top layer is spun, baked, and patterned. The basis for this type of photoresist system is that the top and bottom layers dissolve at different rates in different solvents, or at least in the same solvent, allowing for selective etching or removal of each of the two layers. To pattern organics, lift-off techniques are often used, in which an undercut profile is created in the photosensitive resist layer, creating a cavity structure in which the top layer of resist overhangs the opening in the bottom layer of resist. The material to be lifted off is then deposited through the opening, and the cavity below the overhanging resist profile leaves additional space for solvent access to the resist system after deposition of the desired material, thereby leaving the deposited material in the patterned opening.

[0006] It has been demonstrated that exposure to ultraviolet (UV) light, which is necessary for the photolithography process used with these specially formulated resist systems, can damage OLED structures. Some organic safety resist systems use a negative photoresist top layer that must be exposed to UV light during patterning. Negative photoresist is a type of photoresist in which areas of the photoresist exposed to light become insoluble in a photoresist developer. Specifically, negative photosensitive resist materials are strengthened by polymerization or crosslinking in the presence of UV light. After exposing the negative photoresist to light through a light mask, also referred to herein as a photomask, the developer dissolves the areas not exposed to light, leaving a coating of resist in the areas of the negative photoresist layer not exposed to UV light. The photomask has opaque and transparent areas, allowing UV light to pass through to form the desired pattern in the photoresist. The unexposed areas of the photoresist are then dissolved by a photoresist developer, such as a buffered KOH developer. In contrast to negative photoresists, positive photoresists are a type of photoresist in which areas of the photoresist exposed to UV light become soluble in a photoresist developer. In the case of positive photoresists, the photosensitive material is transformed by light, and the developer dissolves the areas exposed to light through the transparent areas of the photomask, leaving the photoresist material beneath the opaque areas of the photomask (i.e., areas not exposed to UV light). The unexposed areas of the photoresist remain insoluble in the photoresist developer and function as a protective layer in the photolithography process. Positive photoresists are well known in the art and are highly controllable, but they have traditionally not been used to pattern OLED structures due to the damaging nature of their developer on organic materials.

[0007] According to Lin (Multilayer Resist Systems, Introduction to Microscopy, Chapter 6, pp. 287–350, 1983), the history of trilayer resists begins in the early 1970s, during the lift-off era of microelectronics. At that time, there was a desire to implement lift-off for microelectronics manufacturing, and trilayer resist systems proved to be a promising candidate. 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. After coating the wafer with the trilayer resist, 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 create undercuts in the resist and remove the imaging layer for an ideal lift-off profile. In projection lithography, it is important that the imaging layers are all coplanar. At that time, planarization techniques such as chemical-mechanical polishing were unavailable, so lithography was performed on the topography.

[0008] In one example of the use of trilayer resist for semiconductor processing, U.S. Patent No. 10,049,876 to Sankarapandian et al. describes a method that involves forming a trilayer resist structure in which a middle layer is disposed between a top layer and a bottom layer. This trilayer resist method is used to directionally remove material from a specific type of transistor without damaging nearby similar transistors. The function of this trilayer resist is to first planarize the surface and then act as a hard mask for the etching process. To remove the middle layer of resist, a material similar to or identical to the bottom layer of the trilayer resist structure is applied to planarize the chemical mechanical polishing (CMP) layer and etch back to the level below the middle layer of resist. The middle layer can then be removed by an etching procedure that would normally damage the rest of the substrate, but due to the additional planarizing layer, the substrate is covered and protected from the etching that would remove the middle layer. The remaining planarizing layer is finally removed using a dry or wet stripping process.

[0009] In conventional bilayer photoresist systems for patterning organic materials, the bottom or base layer is a sacrificial layer that helps create the desired undercut profile for patterning OLEDs. Using a conventional resist for the base layer of an organic-safe resist system requires a developer that first creates the undercut profile using resist that can be removed without damaging the deposited organic material. As previously mentioned, chemical photolithography developers used in conventional photolithography processes (i.e., for positive-tone photoresists) are generally harmful to organic materials. Therefore, there have been barriers to developing photolithography techniques for fabricating small-scale organic devices, specifically nanoscale OLED devices suitable for high-resolution display applications.

[0010] This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. It is not necessarily intended, nor should it be construed, that any of the preceding information constitutes prior art against the present invention. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] U.S. Patent No. 10,049,876 Summary of the Invention

[0012] It is an object of the present invention to provide a three-layer photolithography technique that can be used to pattern organic light emitting diodes (OLEDs).

[0013] In one aspect of the present invention, there is provided a method for patterning an organic device, the method comprising the steps of: depositing a bottom electrode on a substrate; depositing a trilayer resist system on the substrate, the trilayer resist system comprising a fluoropolymer base layer, an intermediate inorganic transfer layer, and a top positive photoresist layer; forming at least one organic device by: patterning the top positive photoresist layer using photolithography to form an image layer aligned with the bottom electrode; 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 bottom electrode; depositing at least one organic layer above the exposed bottom electrode; performing a lift-off procedure to remove remaining components of the trilayer resist system; and depositing a top electrode on the organic layer.

[0014] In one embodiment of the method, the organic device is an organic light emitting diode.

[0015] In other embodiments of the method, the organic device is an organic field effect transistor, an organic solar cell, a photovoltaic device, an organic semiconductor, or an organic laser.

[0016] In another embodiment of the method, etching the fluoropolymer-based layer exposed through the inorganic transfer layer includes exposing the bottom electrode using reactive ion etching.

[0017] In another embodiment of the method, the fluoropolymer base layer has a visible light transmittance of 95% or greater.

[0018] In another embodiment of the method, the positive photoresist layer has a thickness of about 340-500 nm.

[0019] In another embodiment of the method, an undercut region is formed between the positive photoresist image layer and the inorganic transfer layer by etching the inorganic transfer layer through the patterned positive photoresist layer.

[0020] In another embodiment of the method, the fluoropolymer base layer is etched to form a lateral undercut profile and a vertical undercut profile.

[0021] In another embodiment of the method, the length of the lateral undercut profile is ≧0.25 μm.

[0022] In another embodiment of the method, the lift-off procedure utilizes a fluorinated solvent to dissolve the fluoropolymer base layer.

[0023] In another embodiment of the method, the inorganic transfer layer comprises one or more of a metal and a dielectric material.

[0024] In another embodiment of the method, the at least one organic layer comprises one or more of an electron-transporting layer (ETL), an emissive layer (EML), a hole-transporting layer (HTL), and a hole-injection layer (HIL).

[0025] In another embodiment of the method, the light-emitting layer (EML) is at least one of red, green, and blue emitting.

[0026] In another embodiment of the method, an oxide layer is deposited over the substrate and the electrode array prior to deposition of the trilayer resist system. In another embodiment of the method, the oxide layer comprises a transparent conductive oxide.

[0027] In another aspect, a method for patterning an organic device array includes depositing an array of bottom electrodes on a substrate; depositing a trilayer resist system on the substrate using a trilayer resist deposition method, the trilayer resist system comprising a fluoropolymer base layer, an intermediate inorganic transfer layer, and a top positive photoresist layer; and forming a plurality of organic devices for a first set of organic devices using the organic device deposition method, the organic device deposition method including patterning the top positive photoresist layer using photolithography to form an image layer aligned with the set of array of bottom electrodes; and etching the intermediate inorganic transfer layer exposed through the image layer. etching the fluoropolymer-based layer exposed through the inorganic transfer layer to expose a set of arrays of bottom electrodes; depositing at least one organic layer over the exposed set of bottom electrodes; performing a lift-off procedure to remove any remaining components of the tri-layer resist system; and repeating the tri-layer resist deposition method to deposit a tri-layer resist system on the substrate; repeating the organic device deposition method to form a second set of organic devices aligned with the second set of bottom electrodes; and repeating the lift-off procedure to remove any remaining components of the tri-layer resist system.

[0028] In one embodiment, the method further comprises depositing a top electrode over each of the organic devices.

[0029] In another embodiment of the method, the organic devices are OLEDs and the first set of organic devices and the second set of organic devices emit different colors.

[0030] In one embodiment, the method further includes repeating the tri-layer resist deposition method to deposit a tri-layer resist system on the substrate, repeating the organic device deposition method to form a third plurality of organic devices aligned with the third set of bottom electrodes, and performing a lift-off procedure to remove any remaining components of the tri-layer resist system.

[0031] In another embodiment of the method, an undercut region is formed between the positive photoresist image layer and the inorganic transfer layer by etching the inorganic transfer layer through the patterned positive photoresist image layer.

[0032] In another embodiment of the method, the fluoropolymer base layer is etched to form a lateral undercut profile and a vertical undercut profile.

[0033] In another embodiment of the method, the length of the lateral undercut profile is ≧0.25 μm.

[0034] In another embodiment of the method, the lift-off procedure utilizes a fluorinated solvent that interacts with and dissolves the fluoropolymer base layer.

[0035] In another embodiment of the method, the first set of organic devices and the second set of organic devices are each for at least one of red, green, or blue emission.

[0036] In another embodiment of the method, the inorganic transfer layer comprises one or more metal or dielectric materials.

[0037] In another embodiment of the method, the organic layer is an organic stack including one or more of an electron transport layer (ETL), an emissive layer (EML), a hole transport layer (HTL), and a hole injection layer (HIL).

[0038] In another aspect, a method for patterning an organic device array is provided, comprising: depositing a plurality of bottom electrodes on a substrate; depositing a trilayer resist system on the substrate using a trilayer resist deposition method, the trilayer resist system comprising a fluoropolymer base layer, an intermediate inorganic transfer layer, and a top positive photoresist layer; forming a plurality of organic devices using the organic device deposition method, the organic device deposition method comprising: patterning the top positive photoresist layer using photolithography to form an imaging layer aligned with the plurality of bottom electrodes; etching the intermediate inorganic transfer layer exposed through the imaging 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 lift-off procedure to remove any remaining components of the trilayer resist system.

[0039] In another aspect, a method for patterning an organic light emitting diode (OLED) array is provided, comprising: depositing a plurality of bottom electrodes on a substrate in the array; depositing a trilayer resist system, the trilayer resist system comprising a fluoropolymer base layer, an inorganic transfer layer, and a positive photoresist image layer; patterning the positive photoresist image layer by exposing the positive photoresist image layer to ultraviolet light and etching away the patterned positive photoresist image layer exposed to ultraviolet light, thereby forming an array of OLED devices; etching the inorganic transfer layer through the patterned positive photoresist image layer; etching the fluoropolymer base layer exposed through the inorganic transfer layer using reactive ion etching to expose at least a portion of the plurality of bottom electrodes; depositing an organic stack on each of the exposed bottom electrodes; performing a lift-off procedure to remove any remaining components of the trilayer resist system; and depositing a top electrode on the organic stack.

[0040] In one embodiment, an oxide layer is deposited on the substrate prior to deposition of the trilayer resist system.

[0041] In other embodiments, the oxide layer is a transparent conductive oxide.

[0042] In other embodiments, the fluoropolymer base layer has a visible light transmittance of 95% or greater.

[0043] In other embodiments, the fluoropolymer base layer further comprises a light absorbing dye.

[0044] In another embodiment, the positive photoresist image layer has a thickness of 400 to 600 nm.

[0045] In other embodiments, undercut regions are formed between the positive photoresist image layer and the inorganic transfer layer by etching the inorganic transfer layer through the patterned positive photoresist image layer.

[0046] In another embodiment, the fluoropolymer base layer is etched to form a lateral undercut profile and a vertical undercut profile.

[0047] In other embodiments, the length of the lateral undercut profile is ≧0.25 μm.

[0048] In another embodiment, the lift-off procedure utilizes a fluorinated solvent that interacts with and dissolves the fluoropolymer base layer.

[0049] In other embodiments, the inorganic transfer layer comprises one or more metal or dielectric materials.

[0050] In other embodiments, the dielectric material is or includes SiO2 or aluminum.

[0051] In another embodiment, the photolithographic technique includes using a developer that does not penetrate the transfer layer.

[0052] In other embodiments, the developer is a buffered KOH developer.

[0053] In other embodiments, the organic stack is for at least one of red, green, or blue emission.

[0054] In other embodiments, a post-exposure bake process is required after etching the inorganic transfer layer or after etching the fluoropolymer-based layer.

[0055] In other embodiments, the post-exposure bake is carried out at a temperature of ≦120°C.

[0056] In another embodiment, the lift-off procedure involves immersing the substrate in a fluorosolvent that interacts with and dissolves the fluoropolymer base layer but does not interact with the organic stack.

[0057] In another aspect, a method for patterning a multicolor organic light-emitting diode (OLED) array includes depositing a first series of bottom electrodes and a second series of bottom electrodes on a substrate in the array; depositing a trilayer resist system, the trilayer resist system comprising a fluoropolymer base layer, an inorganic transfer layer, and a positive photoresist image layer; patterning the positive photoresist image layer at locations above the first series of bottom electrodes by exposing the positive photoresist image layer to ultraviolet light and etching away the patterned positive photoresist image layer exposed to ultraviolet light, thereby creating a multicolor array of OLED devices; etching the inorganic transfer layer through the patterned positive photoresist image layer; etching the fluoropolymer base layer exposed through the inorganic transfer layer using reactive ion etching to expose at least a portion of the first series of bottom electrodes; and depositing a first color organic stack on the exposed first series of bottom electrodes. performing a lift-off procedure to remove any remaining components of the tri-layer resist system; depositing a tri-layer resist system; patterning the positive photoresist image layer over a second series of bottom electrodes by exposing the positive photoresist image layer to ultraviolet light and etching away the patterned positive photoresist image layer exposed to ultraviolet light; etching the inorganic transfer layer through the patterned positive photoresist image layer; etching the fluoropolymer base layer exposed through the inorganic transfer layer using reactive ion etching to expose at least a portion of the second series of bottom electrodes; depositing a second color organic stack on each of the exposed second series of bottom electrodes; performing a lift-off procedure to remove any remaining components of the tri-layer resist system; and depositing a series of top electrodes on the first color organic stack and the second color organic stack.

[0058] In one embodiment, an oxide layer is deposited on the substrate prior to deposition of the trilayer resist system.

[0059] In other embodiments, the oxide layer is a transparent conductive oxide.

[0060] In other embodiments, undercut regions are formed between the positive photoresist image layer and the inorganic transfer layer by etching the inorganic transfer layer through the patterned positive photoresist image layer.

[0061] In another embodiment, the fluoropolymer base layer is etched to form a lateral undercut profile and a vertical undercut profile.

[0062] In other embodiments, the length of the lateral undercut profile is ≧0.25 μm.

[0063] In another embodiment, the lift-off procedure utilizes a fluorinated solvent that interacts with and dissolves the fluoropolymer base layer.

[0064] In other embodiments, the first color organic stack is for at least one of red, green, or blue emission.

[0065] In other embodiments, the second color organic stack is for at least one of red, green, or blue emission.

[0066] In other embodiments, the organic stack of the first color is different from the organic stack of the second color.

[0067] In other embodiments, a post-exposure bake process is required after etching the inorganic transfer layer or after etching the fluoropolymer-based layer.

[0068] In other embodiments, the post-exposure bake is carried out at a temperature of ≦120°C.

[0069] In other embodiments, the lift-off procedure includes immersing the substrate in a fluorosolvent that interacts with and dissolves the fluoropolymer base layer but does not interact with the first color organic stack or the second color organic stack. [Brief explanation of the drawings]

[0070] These and other features of the present invention will become more apparent in the following detailed description, which refers to the accompanying drawings.

[0071] [Figure 1A] 1 shows a cross section of a substrate after deposition of a fluoropolymer-based layer.

[0072] [Figure 1B] 1 shows a cross section of a substrate after deposition of an inorganic transfer layer.

[0073] [Figure 1C] 1 shows a cross section of a substrate with an electrode substrate after deposition of a positive resist image layer to form a three-layer resist system.

[0074] [Figure 2A] 1 shows a cross section of a substrate with an electrode and a trilayer resist system after photolithography of a positive photoresist image layer.

[0075] [Figure 2B] 1 shows a cross section of a substrate with an electrode and a trilayer resist system after etching of the inorganic transfer layer.

[0076] [Figure 2C] 1 shows a cross section of a substrate with electrodes and a resist system after etching of a fluoropolymer-based layer.

[0077] [Figure 2D] 1 shows a cross section of a substrate with electrodes and a resist system after deposition of an organic stack.

[0078] [Figure 2E]1 shows a cross section of a substrate with electrodes and an organic stack after a lift-off procedure.

[0079] [Figure 2F] 1 shows a cross section of a substrate on which an electrode, an organic stack, and a cathode have been deposited.

[0080] [Figure 3] 1 shows a cross section of the disclosed trilayer resist system on a substrate having a first color OLED structure deposited thereon.

[0081] [Figure 4] 1 shows 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, on which a three layer resist system has been deposited.

[0082] [Figure 5A] 1 shows a cross section of a UV exposure step of photolithography for patterning a second color OLED using the disclosed trilayer resist system on a substrate having a first color OLED structure deposited thereon.

[0083] [Figure 5B] 1 shows a cross section of a substrate with a first color organic stack patterned over a first electrode, a second electrode, and a trilayer resist system, following patterning of a positive photoresist image layer.

[0084] [Figure 5C] 1 shows a cross section of a substrate with a second electrode with a trilayer resist system, a first color organic stack patterned on the first electrode, followed by etching of the inorganic transfer layer.

[0085] [Figure 5D] 1 shows a cross section of a substrate with a first color organic laminate patterned on a first electrode, a second electrode with a resist system, followed by etching of the fluoropolymer base layer.

[0086] [Figure 5E] 1 shows a cross section of a substrate with a second electrode onto which the second organic stack has been deposited, followed by thermal evaporation of the second organic stack, and a first color organic stack patterned onto the first electrode.

[0087] [Figure 5F] 1 shows a cross section of a substrate with a second electrode with a second organic stack and a first color organic stack patterned on the first electrode after a lift-off procedure.

[0088] [Figure 5G] 1 shows a cross section of a multicolor OLED array on a substrate including a second color OLED patterned on a second electrode and a first color OLED patterned on a first electrode.

[0089] [Figure 6A] 1 shows a top view image captured using an optical microscope of the first pattern after development of the tri-layer resist system.

[0090] [Figure 6B] 10 shows a top view image captured using an optical microscope of the second pattern after development of the tri-layer resist system.

[0091] [Figure 6C] 10 shows a top view image captured using an optical microscope of the third pattern after development of the tri-layer resist system.

[0092] [Figure 7] 1 shows the inorganic transfer layer before and after etching.

[0093] [Figure 8A] 1 shows a top view image captured using an optical microscope of the first pattern after wet etching of the inorganic transfer layer.

[0094] [Figure 8B] 10 shows a top view image captured using an optical microscope of the second pattern after wet etching of the inorganic transfer layer.

[0095] [Figure 8C] 10 shows a top view image captured using an optical microscope of the third pattern after wet etching of the inorganic transfer layer.

[0096] [Figure 9A] 1 shows a top view image captured using an optical microscope of the first pattern after dry etching of the fluoropolymer base layer.

[0097] [Figure 9B] 10 shows a top view image captured using an optical microscope of the second pattern after dry etching of the fluoropolymer base layer.

[0098] [Figure 9C] 10 shows a top view image captured using an optical microscope of the third pattern after dry etching of the fluoropolymer base layer.

[0099] [Figure 10] 1 shows a profile image captured by a field emission scanning electron microscope (FESEM) of an undercut in a fluoropolymer base layer.

[0100] [Figure 11A] Shown is a top-view image captured by a field emission scanning electron microscope (FESEM) after successful patterning of the tri-layer resist system for the first pattern.

[0101] [Figure 11B] 10 is a side profile view image captured by FESEM further showing the side profile of the undercut formed in the base layer of the first pattern.

[0102] [Figure 11C] Shown is an isometric image captured by FESEM after successful patterning of the tri-layer resist system for the first pattern.

[0103] [Figure 12] Shown is a top-view image captured by FESEM after successful patterning of the tri-layer resist system for the second pattern.

[0104] [Figure 13A] Shown is a top-view image captured by FESEM after successful patterning of the tri-layer resist system for the third pattern.

[0105] [Figure 13B] Shown is an isometric image captured by FESEM after successful patterning of the tri-layer resist system for the third pattern.

[0106] [Figure 14A] 1 shows a top view image captured using an optical microscope of the first pattern after lift-off of the fluoropolymer base layer.

[0107] [Figure 14B] 10 shows a top view image captured using an optical microscope of the second pattern after lift-off of the fluoropolymer base layer.

[0108] [Figure 14C] FIG. 10 shows a top-view image captured using an optical microscope of the third pattern after lift-off of the fluoropolymer base layer. DETAILED DESCRIPTION OF THE INVENTION

[0109] The present disclosure relates generally to a three-layer photoresist system and method for patterning and fabricating organic devices, such as OLED devices. The method can also be used in patterning OLED arrays and can be used to fabricate OLED devices and OLED arrays for high-resolution, high-density, full-parallax three-dimensional (3D) light field displays.

[0110] Various features of the present invention will become apparent from the following detailed description, taken in conjunction with the illustrative drawings. The design parameters, design methods, configurations, and uses of the three-layer photoresist system and organic device fabrication methods described herein, as well as the microcavity OLED design process and structure disclosed herein, are described with reference to various examples that represent embodiments that are not intended to limit the scope of the invention described and claimed herein. Those skilled in the art to which the present invention pertains will appreciate that there may be other variations, examples, and embodiments of the invention not disclosed herein that can be practiced in accordance with the teachings of the present disclosure without departing from the scope of the present disclosure. definition

[0111] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0112] The use of the word "a" or "an" when used herein in conjunction with the term "comprising" can mean "one," but is also consistent with the meaning of "one or more," "at least one," and "one or more."

[0113] As used herein, the terms "comprising," "having," "including," and "containing," and grammatical variations thereof, are inclusive or open-ended and do not exclude additional, unrecited elements and / or method steps. The term "consisting essentially of," when used herein in connection with a composition, device, article, system, use, or method, indicates that additional elements and / or method steps may be present, but that these additions do not materially affect the manner in which the recited composition, device, article, system, method, or use functions. A composition, device, article, system, use, or method described herein as including particular elements and / or steps can also, in certain embodiments, consist essentially of those elements and / or steps, and in other embodiments, consist of those elements and / or steps, regardless of whether those embodiments are specifically mentioned.

[0114] As used herein, the term "about" refers to about a + / - 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.

[0115] The recitation of ranges herein is intended to convey both the range and the individual values ​​falling within the range, in the same place as the numbers used to denote the range, unless otherwise indicated herein.

[0116] The use of any example or exemplary language, such as "such as," "exemplary embodiment," "illustrative embodiment," and "for example," is intended to illustrate or illustrate aspects, embodiments, variations, elements, or features related to the invention and is not intended to limit the scope of the invention.

[0117] As used herein, the terms "connect" and "connected" refer to any direct or indirect physical association between elements or features of the present disclosure. Thus, these terms may be understood to refer to elements or features that are partially or completely contained within, attached to, coupled, positioned, joined together, in communication with, operably associated with, etc., even if there are other elements or features between the elements or features described as connected.

[0118] As used herein, the term "transparent conductive oxide" or TCO refers to a type of transparent conductive film (TCF), which is a thin film of optically transparent and electrically conductive material. In particular, TCOs are doped metal oxides commonly used in optoelectronic devices. Some examples of 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).

[0119] As used herein, the term "ITO" refers to indium tin oxide, a composition of indium, tin, and oxygen in varying proportions, commonly encountered as an oxygen-saturated composition having a blend of 74% In, 18% O, and 8% Sn by weight. ITO is commonly used as an anode material in OLED structures due to its suitable electrical 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.

[0120] As used herein, the term "organic device" refers to an electronic device comprising an organic layer. As used herein, the term "organic device" includes, but is not limited to, organic light emitting diodes, organic field effect transistors, organic solar cells, photovoltaic devices, organic semiconductors, and organic lasers.

[0121] As used herein, the term "OLED" refers to an organic light-emitting diode, an optoelectronic device that emits light upon the application of an external voltage.

[0122] As used herein, the term "organic layer" refers to a layer in an organic device that comprises carbon-based organic materials, molecules, or structures. Organic materials may be sensitive to degradation under the radiation wavelengths and intensities used in photolithography.

[0123] As used herein, the term "microcavity" refers to a structure formed by reflecting opposite faces of a spacer layer or optical medium, such as an OLED.

[0124] As used herein, the term "microcavity OLED" (MCOLED) refers to an OLED as described above that is bounded within a microcavity defined by two reflective surfaces. The reflective surfaces of an MCOLED can be, for example, a metallic material, a dielectric material arranged to reflect light within a specific range, a combination of a dielectric material and a metallic material, or any other reflective surface.

[0125] As used herein, the term "patterning" refers to a technique used to chemically transfer a pattern into or onto a surface. Photolithography is an example of a patterning technique that uses radiation or light to modify the properties of a lithographic layer. The term patterning as referred to herein includes the photolithography step in which a positive photoresist is exposed to radiation of a wavelength that breaks down the photoresist and makes it soluble in a developer.

[0126] As used herein, the term "photomask" refers to a thin plate or sheet having a plurality of regions that allow or block the transmittance of radiation (e.g., UV light) through the plate to the underlying photoresist material used to pattern said photoresist material during photolithography.

[0127] As used herein, the term "blanket deposition" refers to depositing material without the use of patterning techniques.

[0128] As used herein, the term "wavelength" is a measure of the distance between two identical peaks (high points) or troughs (low points) of a wave, which is a repeating pattern of moving energy such as light or sound. The wavelengths of light used in photolithography are generally in the ultraviolet range (about 10-450 nm), more preferably in the deep ultraviolet range (about 200-300 nm) or wavelengths less than 300 nm. Extreme ultraviolet radiation (about 10-125 nm) and X-ray light (10 picometers-10 nanometers) are also used in some applications of photolithography.

[0129] It is contemplated that any embodiment of the compositions, devices, articles, methods and uses disclosed herein can be implemented by one skilled in the art either as is or by making such modifications or equivalents without departing from the scope of the invention.

[0130] This disclosure relates to semiconductor processing and manufacturing techniques, and more particularly to photolithography techniques using photoresist systems for patterning organic devices, including organic light emitting diodes (OLEDs) and OLED arrays.

[0131] Photoresists are the fundamental photosensitive sacrificial material for photolithography. Photoresist systems generally consist of a polymer, a sensitizer, and a solvent. Exposure to a radiation source, such as UV radiation, changes the polymer structure of the photoresist material. The solvent component allows the photoresist to spin and form a thin layer on the wafer or substrate surface. Finally, a sensitizer or inhibitor controls the photochemical reaction in the polymer phase. Photoresists can be classified as positive photoresists (positive photoresists) or negative photoresists (negative photoresists). The photochemical reaction that occurs in positive photoresists during exposure to a radiation source weakens the polymer, making it more soluble in developer, resulting in a positive pattern. Therefore, in the case of positive photoresists, the photomask used has the same pattern as the desired pattern on the semiconductor layer. Alternatively, in the case of negative photoresists, exposure to a UV radiation source causes polymerization of the polymer. This polymerization renders the areas of the negative photoresist layer exposed to UV light insoluble in the photoresist developer. The areas of negative photoresist exposed to the radiation source remain on the surface of the wafer or substrate after chemical treatment with a developer. Thus, the mask used with negative photoresist contains the inverse or photographic "negative" of the pattern to be transferred.

[0132] A mask, or photomask, controls where a semiconductor wafer or substrate is exposed to radiation by allowing or blocking the transmission of radiation through the photomask to the underlying photoresist material. Areas of the photomask structure that allow radiation transparency result in degradation of the underlying positive photoresist material or polymerization of the underlying negative photoresist material layer (Microfabrication techniques used to create smart devices for industrial applications. Jose M. Quero, Carmen Aracil, in Smart Sensors and MEMs (Second Edition), Woodhead Publishing Series in Electronic and Optical Materials, 2018, Pages 291-311). The radiation used in photolithography is typically ultraviolet (UV) or extreme UV, although X-rays can also be used. The wavelength of the light used determines the minimum feature size that can be applied to the photoresist. UV radiation is generally referred to herein as the photolithography light source, although it is understood that various wavelengths of light can be used depending on the desired process materials and results. A photomask comprises an opaque plate with perforations or transparent areas that allow light to shine through (transmit) at predetermined locations in a specific pattern. Photomask materials can include, for example, fused silica (quartz glass) with a chromium coating pattern. In some cases, photomasks are further coated with Teflon or other low-friction, low-stick coatings to help prevent adhesion problems during contact photolithography. By placing the photomask between the photoresist and a light source capable of dissolving the polymer in positive photoresist, an exact copy of the pattern on the photomask can be created by dissolving the photoresist at the holes or clear areas of the photomask pattern. As mentioned above, in the case of negative photoresist, the photomask has the inverse of the desired pattern. Both negative and positive photoresists have advantages and disadvantages. Advantages of negative photoresist include good adhesion to silicon, low cost, and short processing time.Additionally, more desirable advantages of positive photoresists include improved control, better resolution, and better thermal stability.

[0133] Positive photoresists are suitable for lift-off processes to a limited extent because they do not crosslink or further polymerize upon exposure, thus maintaining the softening point of the photoresist layer at values ​​in the range of approximately 110–130°C. Crosslinking refers to the polymerization or bonding of one polymer chain to another to form a polymer chain or polymer network. In chemical applications, crosslinking can be used to promote changes in the physical properties of a polymer. Temperatures in the 110–130°C range are often used during typical coating processes in semiconductor device fabrication. Resist features are coated entirely, and if positive photoresists polymerize within this temperature range, lift-off becomes difficult or impossible. Additional advantages of using positive photoresists for semiconductor fabrication include the fact that positive photoresists generally do not swell during development, are capable of finer resolution, and are reasonably resistant to plasma processes. Negative photoresists are generally considered a better choice for lift-off processes because these polymers can achieve reproducible undercuts in fabrication layers. This undercut helps prevent the photoresist sidewalls from becoming coated, as cross-linking of the polymer resin in typical negative resists maintains the undercut and facilitates subsequent lift-off of the sacrificial layer.

[0134] Described herein are three-layer photoresist structures and methods for their use. The three-layer system is composed of a fluoropolymer-based layer, an intermediate inorganic layer, and a top positive photoresist layer that can be used to pattern nanoscale organic structures, such as OLEDs, using photolithography techniques. The disclosed three-layer resist system utilizes the advantages of photolithographic patterning using traditional photoresists by including an intermediate inorganic transfer layer between the top positive photoresist, also referred to as the positive photoresist layer, and the fluoropolymer-based layer. By implementing the positive photoresist as the top layer that forms the image layer during patterning, finer patterns can be fabricated through the three-layer photoresist structure, improving the resolution of the resulting organic device and resulting in a more controllable photolithography process. As previously mentioned, when using a photomask with positive photoresist, radiation (UV light) passes through the transparent areas in the mask, defining areas where the positive photoresist material is subsequently removed with a developer. The use of a positive photoresist in conjunction with a photomask is particularly advantageous when patterning high-density OLED arrays, because areas on the underlying substrate with already deposited organic material are shielded from UV light by the opaque areas of the photomask during patterning of subsequent OLED colors. In particular, the combination of a positive photoresist and an opaque photomask prevents photolithographic radiation from penetrating beneath the photomask into areas of the substrate and organic device containing radiation-sensitive organic material. In comparison, when using a negative photoresist bilayer system to pattern organic material, for example, using photolithography and a photomask, the substrate beneath the negative photoresist layer is exposed to the radiation used to polymerize or harden the negative photoresist areas. Therefore, any structure beneath the negative photoresist on the underlying substrate with an existing organic layer deposited thereon will also be exposed to radiation (UV light) during patterning of any subsequent organic stacks (i.e., additional OLED colors), potentially damaging the organic layers.Thus, the radiation exposure required for the curing or polymerization step in negative photoresist processing can penetrate to layers below the negative photoresist, thereby damaging the underlying organic layers.

[0135] The described three-layer resist system comprises a bottom fluoropolymer base layer, an inorganic transfer layer, and a top positive resist forming an 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 application of the top positive resist image layer. The positive photoresist image layer can then be patterned using conventional photolithography techniques for positive photoresists, thereby avoiding degradation of previously deposited organic materials on the substrate caused by UV exposure. The fluoropolymer base layer can be developed and lifted off the substrate using perfluorinated solvents that are not harmful to the organic materials during a lift-off process.

[0136] The term "organic stack" when used with respect to an OLED device refers to a layer in an OLED that includes organic layers through which a light beam is formed between two electrodes. These layers can include one or more electron transport layers, light-emitting layers, hole transport layers, and hole injection layers, where the light-emitting layer is an organic layer and the other layers can be inorganic, organic, or a combination of organic and inorganic. In other organic devices, such as organic solar cells, one or more of each of these layers can include organic materials sensitive to radiation used in photolithography. Thus, the term "organic stack" refers to one or more layers, one of which is formed from organic materials, and can be replaced by a single organic layer in alternative embodiments (i.e., alternative organic devices) of the present disclosure.

[0137] The middle inorganic transfer layer of the disclosed three-layer resist system acts as an important barrier layer by preventing harmful developer solutions used to pattern the top positive photoresist material from penetrating into the underlying fluoropolymer base layer and any organic materials present below said base layer.

[0138] The fluoropolymer base layer is a sacrificial layer that functions to form the desired undercut profile for patterning for organic devices, particularly OLED devices. The three-layer system described herein utilizes a fluoropolymer base layer that is exposed through an intermediate inorganic transfer layer and then etched with oxygen plasma or reactive ion etching (RIE) to form microcavities, preferably with undercuts, through which an organic stack can be deposited.

[0139] The trilayer resist system described herein enables the implementation of photolithography techniques for patterning organic devices and organic light-emitting diodes at the sub-10 μm scale using a highly controllable photoresist as the top positive resist image layer. The described trilayer resist system also enables reliable lift-off of organics, providing high-density OLED arrays that are scalable to substrate sizes not currently possible for patterning OLEDs at the target sub-10 μm dimensions. In contrast, current OLED devices that use shadow masks are not scalable to flat panel displays. While OLED fabrication is provided herein as an example of how the present trilayer photoresist system can be used, it is understood that the same trilayer photoresist fabrication system and method can be used to fabricate other devices comprising organic semiconductor layers, such as organic field-effect transistors, organic solar cells, photovoltaic devices, other organic semiconductor devices, and organic laser devices.

[0140] OLEDs are generally divided into two major classes: those composed of small organic molecules and those composed of organic polymers. OLEDs are light-emitting diodes in which the light-emitting electroluminescent layer comprises a film of organic compounds or components that emit light in response to an electric current. Generally, OLEDs are solid-state semiconductor devices with at least one conductive organic layer disposed between and electrically connected to an anode and a cathode. When an electric current is applied, the anode injects holes, and the cathode injects electrons into the organic layer, which then migrate toward the oppositely charged electrode. When an electron and a hole localize on the same molecule, an exciton is formed, a localized electron-hole pair with an excited energy state. Light is emitted when the exciton relaxes via a light-emitting mechanism. Types of OLEDs include, but are not limited to, active-matrix OLEDs (AMOLEDs), top-emitting OLEDs, and bottom-emitting OLEDs. AMOLEDs have a total layer of cathode, organic molecules, and anode. The anode layer has a thin-film transistor (TFT) plane parallel to it to form a matrix. This helps switch each pixel to its on or off state as desired, thus forming an image. Thus, pixels are turned off whenever they are not needed or when there is a black image on the display, extending the device's battery life. It is the least power-consuming type of OLED and has a faster refresh rate suitable for video. Some applications of AMOLED are computer monitors, large-screen TVs, and electronic signs or billboards. Top-emitting OLEDs have substrates that are either opaque or reflective. Top-emitting OLEDs are more suitable for active-matrix applications because they can be more easily integrated with non-transparent transistor backplanes. Manufacturers use top-emitting OLED displays in devices such as smart cards. An OLED is bottom-emitting when the emitted light passes through a transparent or semi-transparent bottom electrode and substrate.

[0141] Typically, in organic device fabrication, organic layers are deposited onto the organic device through a fine metal mask (FMM) or shadow mask, which allows for the creation of larger pixels (tens of micrometers in size). However, to achieve the pixel density required for high-definition light-field displays, the resolution must be in the sub-10-micrometer range. The disclosed trilayer resist system allows organic layers to be patterned at much finer resolution using conventional photolithography processes. Furthermore, the trilayer system can be used multiple times on a single device, allowing for the fabrication of multiple independent organic stack structures on the same substrate. Previously deposited organic layers are first protected from degradation by radiation through the use of a top layer of positive photoresist (an opaque photomask) and an intermediate inorganic transfer layer, which acts as a critical barrier by preventing harmful developer solutions used to pattern the top layer of positive photoresist material from penetrating the underlying fluoropolymer base layer and any organic materials present below the base layer.

[0142] When patterning a trilayer resist system using photolithography techniques with a photomask, at least one electrode is exposed for deposition of an organic stack or one or more organic layers. For example, when patterning an OLED device (or OLED array), the active area is defined as the area with an exposed bottom electrode deposited on the substrate in an array prior to application of the trilayer photoresist system. Generally, the active area defines the boundary where the first level of electrical connection will be made, predetermining the pattern shape and resolution of the organic device. Therefore, the horizontal offset of the trilayer resist system from the active area also affects organic shadowing, with greater offsets expected to result in less shadowing.

[0143] Alternatively, in the disclosed tri-layer resist system, patterning using maskless photolithography (without a physical mask) is also an option, otherwise known as direct-write lithography. Direct-write lithography refers to any technique that can deposit, remove, dispense, chemically alter, or process various types of materials on different surfaces according to a predetermined layout or pattern. In this application, for example, direct-write lithography can be used to expose a positive photoresist top layer in a desired pattern for depositing an organic layer on a substrate or bottom electrode.

[0144] 1A-1C illustrate the deposition of a three-layer polymer resist system on a substrate containing electrodes. FIG. 1A shows a cross-section of the substrate after deposition of a fluoropolymer-based layer. In this embodiment, substrate 10 has deposited thereon an oxide layer 12, a bottom electrode 14, and a first layer of fluoropolymer resist, referred to herein as fluoropolymer-based layer 16. Bottom electrode 14 can be a transparent material such as indium tin oxide (ITO), or a conductive polymer such as doped polyaniline, a thin layer of a metal such as Ag, Au, or Al, or a combination thereof. The thickness of the bottom electrode material layer can range, for example, from 10 to 100 nm, with the total thickness of the bottom electrode material being 100±10 nm. While a single bottom electrode is shown, it is understood that an organic device can be comprised of multiple bottom electrodes, which can be unpatterned or patterned, such as in rows or columns or other geometric or regularly spaced arrangements. 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 conductive transparent oxide material. Examples of transparent conductive oxide (TCO) materials include, but are not limited to, indium tin oxide (ITO), indium zinc oxide (IZO), and aluminum zinc oxide (AZO). TCOs are conductive materials with relatively low resistivity and relatively high transmittance. In using the three-layer system described herein, the fluoropolymer-based layer 16 can be etched into a cavity with an undercut to accommodate an OLED or other organic stack during fabrication. While the terms "organic stack" and "organic layer" are used herein, it is understood that any semiconductor device including one or more layers of photosensitive material can benefit from the present photolithography methods.

[0145] The fluoropolymers used in the fluoropolymer base layer 16 are generally fluorocarbon-based polymers with multiple carbon-fluorine bonds. Fluoropolymer materials are characterized by high resistance to solvents, acids, and bases, yet can be etched using oxygen plasma or reactive ion etching. Some suitable fluoropolymer base layer materials include amorphous fluoropolymers. The fluoropolymer base layer 16 material used in this system preferably has very high transparency (i.e., visible light transmittance of 95% or greater), as optical transparency may be required for alignment during photolithography. One example of a suitable material for the fluoropolymer base layer is CYTOP®, manufactured by AGC Chemicals, which is classified by its unique amorphous structure. CYTOP® can be dissolved in certain fluorinated solvents and can be used for thin-film coatings to achieve submicron thicknesses. Another example of a suitable fluoropolymer for the fluoropolymer base layer 16 is Teflon® AF1600X (AF). Preferably, the process used to lift off the fluoropolymer should not damage previously deposited OLED stacks or organic layers, so the fluoropolymer does not negatively chemically interact with the organic materials in the OLED device. Spin coating can be used to apply the fluoropolymer in this method. In fabrication, spin coating can be used to apply uniform thin films (420±20 nm) to solid surfaces by applying the film material in a volatile solvent and using centrifugal force to spread the film over the surface. The higher the angular velocity of the spin, the thinner the film. In a typical spin coating procedure, the liquid is placed at the center of a circular surface, and the surface is rapidly spun to produce a uniform film with a thickness of 1-10 μm. In one example, the fluoropolymer base layer 16 is applied by spin coating, spinning to a thickness of 340-500 nm at a speed of 4000 RPM for approximately 20-25 seconds. It should be noted that the thickness of the fluoropolymer base layer 16 is preferably 1.25 times the thickness of the subsequently deposited organic material. Following the spin process, the fluoropolymer base layer 16 is cured.In one example curing process, the first stage (pre-bake) is drying the fluoropolymer base layer 16 at room temperature for 5-30 minutes to remove any air bubbles. To further degas the fluoropolymer base layer 16, an optional bake at 50°C for 10-30 minutes removes any remaining air bubbles. The next stage is another pre-bake followed by a bake at 80-100°C for 30-60 minutes to remove any remaining solvent in the fluoropolymer base layer 16. The final stage is a final bake at 180-250°C for 30-60 minutes to improve adhesion of the fluoropolymer base layer 16 to the substrate 10. Other curing processes for the fluoropolymer base layer can also be used to degas, remove solvent, and improve substrate adhesion, depending on the base layer material. While FIG. 1A shows a substrate covered with an oxide layer, it should be noted that the presence of the oxide layer 12 does not affect the disclosed three-layer resist system, and the fluoropolymer base layer 16 can also be deposited directly onto the substrate. It should also be noted that although spin coating is provided as an example application method, other application methods, such as spray coating or other deposition methods, can be used to apply the fluoropolymer, and that the deposition of the fluoropolymer base layer includes physical deposition and all processing steps (pre-bake and final bake steps).

[0146] The thickness of the fluoropolymer base layer 16 in this method is preferably 100 nm to 2 μm and can be selected based on the thickness of the organic OLED material to be deposited through the fluoropolymer base layer 16. The thickness of the fluoropolymer base layer 16 must also be sufficient to provide the desired planarization. When considering an OLED array, the fluoropolymer should be formed using a solvent that interacts very weakly or does not interact with the OLED material. This is especially important when patterning a second array of OLED devices on a substrate 10 containing OLED devices. Preferably, the minimum thickness or height of the fluoropolymer base layer should be approximately 1.25 times the thickness of the organic material to be deposited on top of the base layer for lift-off. Designing the height of the fluoropolymer base layer to be slightly higher than the deposited stack allows for the deposition of stack layers via a three-layer system with sufficient space to accommodate all layers under the undercut of the fluoropolymer base layer. For example, in an OLED, the 1.25× height of the red organic stack is 308±30.5 nm, the 1.25× height of the green organic stack is 258±30 (12%) nm, and the 1.25× height of the blue organic stack is 238±35 (15%), suggesting minimum fluoropolymer base layer 16 thicknesses of 385 nm, 322.5 nm, and 297.5 nm, respectively. The maximum thickness of the fluoropolymer base layer 16 and the overall height of the trilayer resist system stack can be determined by simulation and / or experimentation. If the layers of the trilayer system are too thick and / or the desired undercut is not properly formed in the fluoropolymer base layer 16, a shadowing effect can occur. This shadowing effect can result in uneven organic layer thickness from the sidewalls of the fluoropolymer base layer 16, blocking or "shadowing" the active area of ​​the bottom electrode 46 and thereby preventing uniform deposition. In general, it is preferred that the overall height of the tri-layer resist stack be minimized as much as possible to generally improve the uniformity of the organic deposits and reduce shadowing effects.According to one embodiment of the present disclosure, the height of the fluoropolymer-based layer 16 should not exceed 530 nm, assuming the positive resist image layer and inorganic transfer layer are limited to thicknesses of 500 nm and 100 nm, respectively. Also, a practical minimum fluoropolymer-based layer 16 thickness is preferably in the range of 340-400 nm, while maintaining a 1.25×organic stack height ratio.

[0147] 1A shows a single bottom electrode 14 on substrate 10 for illustrative purposes, it is understood that substrate 10 may have additional organic or OLED devices and multiple electrodes deposited thereon that are not shown in the enlarged profile view of FIG. 1A. Because the trilayer resist system is removed using lift-off after deposition of the organic and other layers, a lift-off method for the trilayer photoresist system is essential to avoid damaging the deposited organic layers or OLED structures or other chemically sensitive structures.

[0148] FIG. 1B shows a cross section of the substrate after deposition of the inorganic transfer layer. The illustrated substrate 10 is sequentially layered with an oxide layer 12 and a bottom electrode 14, a fluoropolymer base layer 16, and an inorganic transfer layer 18 deposited directly on the fluoropolymer base layer 16. The inorganic transfer layer 18 serves to mask the pattern from the top layer of the three-layer resist system onto the fluoropolymer base layer 16. A variety of dielectrics and metals can be used as suitable materials for the intermediate inorganic transfer layer 18. The strong selectivity of these materials to the photoresist layer material with respect to oxygen plasma allows the intermediate inorganic transfer layer 18 to be relatively thin. Films that are more selective to oxygen plasma etching than fluoropolymer films are suitable materials for use in the intermediate inorganic transfer layer 18. These include, but are not limited to, metals such as aluminum, or dielectrics such as silicon dioxide. Films 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 spin-coating processes. Preferably, the temperature involved in deposition should not exceed approximately 120°C to avoid damage to the organic materials.

[0149] FIG. 1C shows a cross section of an electrode substrate following deposition of a positive photoresist image layer, thereby forming a three-layer resist system. The illustrated substrate 10 comprises, in order, an oxide layer 12, a bottom electrode 14, a fluoropolymer-based layer 16, an intermediate inorganic transfer layer 18, and a top positive photoresist layer, referred to herein as positive photoresist layer 20, deposited directly on the inorganic transfer layer 18. The positive photoresist layer 20 serves to record the image of a photomask used in lithography. When patterned with UV light, the positive photoresist layer 20 is referred to as an image layer. As previously mentioned, photoresists are classified as positive or negative. Positive photoresists chemically transform upon exposure to UV light, becoming soluble to etching. Thus, only the exposed areas of the photoresist are removed by etching, while the unexposed areas of the photoresist remain insoluble. Alternatively, in the case of negative photoresists, the areas of the photoresist exposed to UV light or photolithographic radiation become insoluble to etching. Although UV light is used herein as an example of radiation that can be used for photolithographic patterning, it is understood that various wavelengths can be used depending on the properties of the photoresist layer. Positive photoresists generally maintain their size, can receive radiation patterns, have better etching resistance, have excellent resolution, and have good thermal stability, making them easier to control during photolithography. Photoresist layers can be removed by chemical etching. Chemical etching techniques include, but are not limited to, the use of developers, plasma etching, reactive ion etching, and ion beam milling.

[0150] In the disclosed trilayer resist system, the positive photoresist layer 20 only needs to be thick enough to function as a mask for etching the inorganic transfer layer 18, yet is thin compared to that required in other photolithography systems. The positive photoresist layer 20 is also preferably deposited on a planar surface, in this case the planar inorganic transfer layer 18, and therefore is not limited by a minimum thickness dictated by the topography to be deposited. These factors allow the top positive photoresist layer 20 to be much thinner than is possible in single-layer resist systems, thereby enabling higher-resolution patterns to be imaged thereon, leading to the system's ability to deposit higher-resolution and smaller organic devices. The positive photoresist layer 20 can be deposited using a variety of techniques, such as spin coating, spray-on, or dip coating. Spin coating is the preferred method because it allows for finer control during application and reduced layer thickness. Films of the positive photoresist layer 20 can be as thin as tens of nanometers to several micrometers thick. The baking procedure used during the coating process should be carefully controlled to avoid thermal damage to the organic materials while allowing for curing of the positive photoresist. In this case, it has been found acceptable for the baking temperature limit of the positive photoresist top layer 20 to not exceed 120°C. Reference to the deposition of the top positive photoresist layer 20 is understood to include all processing stages, including the physical deposition of the photoresist, as well as drying, curing, degassing, and baking steps.

[0151] The material selection criteria for the positive photoresist layer 20 should be considered so that the resist material provides strong adhesion to the inorganic transfer layer 18 and is thin enough to be completely removed by oxygen plasma during the fluoropolymer-based layer etching step. Suitable materials for the positive photoresist layer 20 include, but are not limited to, commercially available positive photoresists that are compatible with common developers and strippers of appropriate thickness. In one example, the positive photoresist can be formulated from a phenol-formaldehyde novolac resin. A specific example of a suitable positive photoresist is the AZ® 1500 family of positive photoresists manufactured by Micro Chemicals.

[0152] 2A-2F illustrate a method for patterning a trilayer photoresist system and depositing an organic layer on an exposed electrode according to the present method. The organic layer can be an organic stack or multiple layers, with at least one layer being composed of an organic material. FIG. 2A shows a cross-section of a substrate with an electrode and a trilayer resist system after photolithography of a positive photoresist image layer. The substrate 10 shown has, in order, an oxide layer 12 and a bottom electrode 14 deposited thereon. The disclosed trilayer resist system includes a fluoropolymer-based layer 16, an inorganic transfer layer 18, and a positive photoresist layer 20. Photolithography techniques are used to pattern the positive photoresist layer 20 to expose the inorganic transfer layer 18 above the bottom electrode 14 where the organic layer will be deposited. A photomask can be used to develop the positive photoresist layer 20. In one example of patterning, UV light is irradiated through a photomask onto the positive photoresist layer 20 in a desired pattern, rendering the exposed areas of the positive photoresist layer 20 under the UV-transparent areas of the photomask soluble for etching. An etching process then removes the soluble areas of the positive photoresist layer 20, transferring the desired pattern to the positive photoresist layer 20. In this embodiment, etching is performed using a developer, which may be composed of a hydroxide, such as sodium hydroxide (NaOH), potassium hydroxide (KOH), tetramethylammonium hydroxide, or other suitable material. Developers generally have a limited range of useful dilutions. Highly concentrated dilutions have high sensitivity and allow for faster photospeeds, but are limited by high dark film loss and reduced contrast. More dilute concentrations allow for high contrast and offer greater selectivity between exposed and unexposed resist. These require longer development times or increased exposure energy and are more sensitive to standing wave effects from monochromatic exposure. Sodium-based buffered developers provide optimal process control while minimizing attack on the aluminum surface. Potassium-based buffered developers offer optimal process control while minimizing contamination risks through the use of less mobile potassium ions.In one example process, the developer can have a dilution ratio of about 1:4, a development time of about 15-25 seconds, and a water rinse time of about 55-65 seconds. After exposure to UV light through a photomask, the positive photoresist layer 20 should be developed with the developer, taking care to ensure that the developer does not react, or only reacts to a limited extent, with the inorganic transfer layer 18. If a post-exposure bake process is desired to further remove solvent from the positive photoresist layer 20, the temperature should not exceed a temperature that would destabilize or damage the organic materials, such as 120°C.

[0153] 2B shows a cross section of the substrate, electrodes, and trilayer resist system after etching of the inorganic transfer layer 18. The illustrated substrate 10 has deposited thereon, in order, an oxide layer 12 and a bottom electrode 14, and the disclosed trilayer resist system comprises a fluoropolymer-based layer 16, an inorganic transfer layer 18, and a positive photoresist layer 20. A pattern formed in the top positive photoresist layer 20 is transferred to the inorganic transfer layer 18 by a wet etching process. There are various etching techniques, including wet etching using chemical etchants and dry etching using plasma, also known as plasma etching. Plasma etching is a processing technique that roughens the surface of a raw material on a microscopic scale. This is achieved using a reactive gas, such as oxygen, which changes both the chemical and physical properties of the source material being etched. This chemical effect is imparted by the reactive gas, which reacts and bonds with the surface molecules of the material being etched. High-energy ions physically bombard the surface atoms of the source material, thereby transferring them to the gas phase, resulting in a physical effect. Ideally, the plasma recipe should be relatively high pressure and low power to produce undercuts. In this embodiment, the inorganic transfer layer 18 is etched to transfer the pattern formed in the top positive photoresist layer 20 to the inorganic transfer layer 18. This transfer should preferably produce undercut regions 22. Etching the inorganic transfer layer 18 using a high pressure and low power recipe produces the desired undercut regions 22. For example, for a fluoropolymer base layer 16 thickness of 340-400 nm and an inorganic transfer layer 18 thickness of 100 nm, a minimum offset or undercut length of approximately 0.33-0.35 μm was found to prevent shadowing and uneven deposition of the organic layer on the bottom electrode active region 46. Preferably, the etching plasma and conditions used to remove the inorganic transfer layer 18 beneath the pattern created by the positive photoresist layer 20 do not damage the positive photoresist layer 20 or the underlying fluoropolymer base layer 16. Wet or dry etching can be used to etch the inorganic transfer layer 18 of the disclosed three-layer resist system. Preferably, the conditions during the etching plasma and dry etching used to remove the inorganic transfer layer 18 within the pattern created by the positive photoresist layer 20, or chemical interactions during wet etching, do not damage the positive photoresist layer 20 or the underlying fluoropolymer base layer 16. Depending on the method chosen to etch the inorganic transfer layer 18, small undercuts 22 can be formed, which are ideally minimized during processing.

[0154] FIG. 2C shows a cross-section of the substrate, electrode, and resist system after etching of the fluoropolymer base layer using oxygen plasma or a fluorosolvent. The illustrated substrate 10 sequentially comprises an oxide layer 12 and bottom electrode 14, a fluoropolymer base layer 16, and an inorganic transfer layer 18, followed by pattern transfer from the inorganic transfer layer 18 to the fluoropolymer base layer 16. The pattern transfer procedure can use a reactive ion etching (RIE) process, such as oxygen plasma etching, to remove areas of the fluoropolymer base layer 16 to expose the bottom electrode 14, which are the electrically active areas where the organic stack or organic layers will be deposited. Ideally, the reactive ion etching does not adversely affect or cause damage to the underlying oxide layer 12, bottom electrode 14, or substrate 10 used in OLED or organic device operation. Furthermore, the patterning etch of the fluoropolymer base layer 16 preferably proceeds slightly laterally beneath the remaining inorganic transfer layer 18, creating a lateral undercut profile 24 and a vertical undercut profile 38 that are ideal for lift-off procedures. In one example, the lateral undercut profile 24 can be limited to a length of ≥ 0.25 μm. The underlying bottom electrode 14 can also be made accessible through an opening pattern in the trilayer resist and processed prior to organic deposition. The degree of angle of the vertical undercut profile relative to the normal to the substrate 10 can vary. In a preferred example, the angle of the vertical undercut profile 38 relative to the substrate 10 is preferably at least 30 degrees from the lateral undercut profile. Etching and creating undercuts in the fluoropolymer base layer can be performed using an etching process, such as using UV ozone or oxygen plasma. The lateral undercut profile 24 and the vertical undercut profile 38 can be formed using an etching process in a manner similar to that formed in the inorganic transfer layer 18.The lateral undercut profile 24 and vertical undercut profile 38, the minimum offset required to prevent shading, and overlay accuracy are all inherent to the height of the fluoropolymer base layer 16 and inorganic transfer layer 18 and will change as the height of the organic stack changes. In general, extending the height of the fluoropolymer base layer 16 beyond 530 nm should be avoided unless this is accounted for by increasing the horizontal offset, reducing the sidewall angle, and / or reducing the thickness of other layers. It has been found that maintaining and minimizing the sidewall angle of the fluoropolymer base layer 16 avoids excessive shadowing due to the limiting factor of the top edge on the inorganic transfer layer 18. Note that etching the fluoropolymer base layer 16 above the electrode 14 also substantially removes the remaining positive resist image layer 20.

[0155] Preferably, the bottom fluoropolymer base layer 16 is etched by reactive ion etching (RIE) using oxygen plasma or reactive plasma to remove materials deposited on the substrate. Therefore, the fluoropolymer base layer 16 should have good selectivity in the oxygen or reactive ion etching process. Etch selectivity can be described as the ratio of etch rates between materials. The equation for etch selectivity is:

number

[0156] Selective etching describes the process by which a first material etches more quickly than a second material. The result is the difference in the amount of each material removed in a specific period of time. For example, selective etching of a mask material means that the mask is only thinned slightly, while more material is removed from the material being etched. Selective etching of a mask allows the mask to be made much thinner, enhancing the ability to achieve a more vertical profile in the etched material. In other examples consisting of layers of materials, it can be useful to selectively etch one material and stop selectively on the underlying material. There are various dielectrics and metals that serve as suitable materials for the intermediate inorganic transfer layer 18. These materials have strong selectivity to oxygen plasma over typical first resist layer materials, which also allows this layer to be relatively thin. In optical lithography, another consideration is the alignment of the mask pattern to the features on the substrate 10. This intermediate inorganic transfer layer 18 can be as thin as 10 to 100 nanometers thick. Films can be made of metals such as aluminum or chromium, or dielectrics such as silicon dioxide. It should be noted that any film that is more selective to oxygen plasma etching than fluoropolymer films is 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. Preferably, the temperature involved in deposition should not exceed approximately 120°C to avoid damage to the organic material. It is generally preferred that the inorganic transfer layer 18 be transparent to the wavelength of light used for alignment. Ideally, the inorganic transfer layer 18 has good selectivity to oxygen plasma, since an oxygen plasma etching process is performed to transfer the pattern from the inorganic transfer layer 18 to the fluoropolymer base layer 16. Transparent or semi-transparent material selection is beneficial for alignment purposes; therefore, SiO2 is also a candidate inorganic transfer layer material. One consideration is the low stress of SiO2 to support the deposition of a top positive photoresist image layer.

[0157] FIG. 2D shows a cross section of a substrate with electrodes and a resist system after deposition of an organic stack. The illustrated substrate 10 sequentially includes an oxide layer 12 and a bottom electrode 14, a fluoropolymer-based layer 16 having a lateral undercut profile 24 and a vertical undercut profile 38, and an inorganic transfer layer 18 following pattern transfer from the inorganic transfer layer 18 to the fluoropolymer-based layer 16. FIG. 2D further illustrates an embodiment of the present disclosure after deposition of an organic stack 26 on the active region 46 of the bottom electrode 14. In this embodiment, the organic stack 26 comprises at least one layer of organic material suitable for fabricating an OLED device. In alternative organic device embodiments, the organic stack 26 may be a single organic layer. In one example, the layers of the organic stack 26 are deposited using thermal evaporation. Evaporative deposition can be defined as a thin-film deposition method in which source materials are evaporated in a vacuum. The vacuum allows vapor particles to travel directly to the target object (substrate 10), where they condense and return to a solid state.

[0158] A shadow mask can be used for deposition, allowing deposition gases to pass through the openings in the shadow mask onto the bottom electrode 14, forming a layer of the organic stack 26 on the bottom electrode 14 that corresponds to the width of the bottom of the opening. This prevents the organic stack 26 from creating a shadow effect or reducing the width of the inner and outer shadows during deposition. A shadow mask is typically a microstructure or stencil used to precisely define device regions for various applications, such as deposition, etching, or substrate processing. Precision is particularly important when depositing the organic stack 26 on the bottom electrode 14 to avoid shadowing effects. Shadowing effects can cause the organic stack 26 to not completely cover the active region of the bottom electrode 46, resulting in a reduced layer thickness of the organic stack 26 around the bottom electrode active region 46, resulting in reduced performance and edge effects around the bottom electrode active region. This can further result in suboptimal electrical and optical properties in the OLED device. The shadowing effect can be reduced by using a shadow mask for precise deposition and by creating lateral and vertical undercut profiles 24, 38 in the fluoropolymer base layer during etching. The lateral and vertical undercut profiles 24, 38 allow the organic stack 26 to be deposited over a defined device area that extends the width of the bottom electrode active area 46. The thickness of the organic stack 26 is preferably less than the thickness of the fluoropolymer base layer 16 to create optimal lateral and vertical undercut profiles 24, 38 in the fluoropolymer base layer 16.

[0159] In the case of an OLED device, the organic layers of the organic stack 26 may include, but are not limited to, one or more of an electron-transporting layer (ETL), an emissive layer (EML), a hole-transporting layer (HTL), and a hole-injection layer (HIL). An organic device made in part by the organic stack 26 comprising at least a single organic layer deposited on the bottom electrode 14 may be a microcavity OLED (MCOLED) device. A microcavity organic light-emitting diode (MCOLED) is a device in which the OLED materials are combined within a microcavity defined by two reflective surfaces arranged to reflect light within a specific range, or some combination of dielectric and metallic materials. In an MCOLED device, the organic materials comprising the organic stack 26 are arranged with a material thickness dj with an optical path length of Lj, and the light emitting layer 26 has a thickness dj of 1000 nm. j =n j ×d j and n j is the refractive index of the OLED material. The total optical path length of the material between the reflective surfaces is

number

[0160] FIG. 2E shows a cross section of a substrate with electrodes and an organic stack after a lift-off procedure to remove the trilayer resist system. The organic stack 26 is shown deposited on the bottom electrode 14 and oxide layer 12 on the substrate 10 after the lift-off procedure. Lift-off of the fluoropolymer base layer, the remaining inorganic transfer layer, and the photoresist image layer is achieved by immersing the substrate 10 and its subsequent layers in a fluorinated or fluorosolvent that interacts with and dissolves the fluoropolymer base layer but does not or interacts very weakly with the materials of the organic stack 26. After lift-off, the materials of the organic stack 26 remain on the substrate 10 in the desired pattern. Due to their low surface tension, fluorosolvents (also called fluorinated solvents) remain gentle on the surface of the substrate 10 and are able to penetrate the surface of the fluoropolymer base layer 16. The fluorosolvents are not harmful to the organic stack 26 and form a compatible fluorosolvent for the fluoropolymer base layer, making them ideal for lift-off of the fluoropolymer base layer of the trilayer resist system after the deposition of the organic stack 26. Examples of fluorinated solvents that can be used in the lift-off procedure include, but are not limited to, 92-97% 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether / 3-8% ethanol, 100% 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 46-54% trans-1,2-dichloroethylene / 43-52% 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and 46-55% trans-1,2-dichloroethylene / 43-52% 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether / 1-3% ethanol.

[0161] FIG. 2F shows a cross section of a substrate on which the electrodes, organic stack, and cathode have been deposited. The organic stack 26 is deposited on the bottom electrode 14 and oxide layer 12 on the substrate 10, and further shows the top electrode 28 after deposition. It should be noted that in this configuration, the top electrode 28 is the cathode and the bottom electrode 14 is the anode, resulting in a direct OLED device. It is understood that the electrodes can be reversed, and the disclosed trilayer resist system can be used in both direct and inverted OLED configurations. When the OLED device is inverted, the bottom electrode 14 is the cathode and the top electrode 28 is the anode. The top electrode 28 can be a transparent material such as indium tin oxide (ITO), or a conducting polymer such as 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.

[0162] FIG. 3 shows a cross-section of the disclosed tri-layer resist system on a substrate 10 having a first bottom electrode 14a and a first-color OLED organic stack 26a deposited thereon. To build a multicolor OLED array with multiple OLED organic stacks, each color of the organic stack can be deposited on a different series or set of bottom electrodes on the substrate. The disclosed tri-layer system has a tri-layer structure including a fluoropolymer base layer 16, an inorganic transfer layer 18, and a positive photoresist layer 20. As shown, the substrate 10 has multiple bottom electrodes deposited thereon. In a first-color application, the first bottom electrode 14a is exposed through the tri-layer resist system, the first-color OLED organic stack 26a is deposited thereon, and the remaining tri-layer resist is removed using a fluorosolvent. To prepare substrates and arrays for second or more color OLEDs, the first color OLED organic stack 26a, exposed substrate 10, and other bottom electrodes (one example of which is 14b) are completely covered with a second three-layer resist system comprising a fluoropolymer-based layer 16, an inorganic transfer layer 18, and a positive photoresist layer 20. A second, or continuous, color pattern is then applied to the positive photoresist layer 20 to expose the inorganic transfer layer 18 and pattern the second color OLED organic stack on the second, or continuous, bottom electrode 14b as described above. While a single bottom electrode for the first and second color OLED devices (14a and 14b, respectively) is shown in FIG. 3, it will be understood that one embodiment of this method includes a series or multiple bottom electrodes 14a and a series or multiple bottom electrodes 14b.

[0163] 4 shows a cross-section of a substrate having an OLED device with an electrode in which an OLED stack is deposited on a first electrode and a second electrode 14b without an OLED stack. In this embodiment, an OLED stack 26a is deposited on a first bottom electrode 14a disposed on top of a substrate 10 and includes one or more of a hole-injection layer (HIL) 50, a hole-transport layer (HTL) 52, an emissive layer (EML) 54, an electron-transport layer (ETL) 56, and an electron-injection layer (EIL) 58. In addition to the emissive layer 54, one or more of the hole-injection layer (HIL) 50, the hole-transport layer (HTL) 52, the electron-transport layer (ETL) 56, and the electron-injection layer (EIL) 58 may also be composed of organic materials or molecules and may be considered organic layers. The electron-transport layer (ETL) 56 may be any substantially transparent material capable of facilitating electron transport from the associated electrode to the emissive layer. Examples of materials that can be used for the ETL 56 include, but are not limited to, 2-(4-biphenyl)-5-phenyl-1,3,4-oxadiazole (PBD), butyl PBD, and PBD or butyl PBD doped into an inert polymer such as poly(methyl methacrylate) (PMMA) or poly(carbonate). The emissive layer is composed of organic molecules or polymers that accept electrons from the electrode layer through a hole-injection layer (HIL) 50. The emissive layer (EML) is an organic layer 54 that includes one or more organic materials, including, but not limited to, Alq (tris(8-hydroxyquinolinato)aluminum), aromatic hydrocarbons, poly(phenylene vinylene), oxadiazole, and stilbene derivatives. The EML 54 material can optionally include a stable non-emissive host primary component material doped with an emissive material having an energy gap smaller 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 occurs. Examples of 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)-1,1'-biphenyl-4,4'-diamine) and poly(phenylene vinylene).A fluoropolymer base layer 16, an intermediate inorganic transfer layer 18, and a positive photoresist layer 20 are shown deposited over the OLED stack 26a and the second electrode 14b. The device configuration shown is intermediate fabrication and ready for a second photolithography and etching sequence to expose the second electrode 14b for deposition of a second OLED stack.

[0164] For the fabrication of a trilayer system, in one example, a CYTOP® fluoropolymer base layer was diluted with CT-Solve 180, and any bubbles caused by stirring were removed using a vacuum chamber. The base layer was applied to a substrate using a spin-coating technique to obtain a film of approximately 420 ± 20 nm. The thickness of the base layer was measured using a Filmetrics metrology tool. The fluoropolymer base layer was then baked at room temperature for 15 minutes, followed by a 30-minute bake at 105°C. An inorganic transfer layer was then deposited on top of the CYTOP base layer at room temperature using magnetron sputtering to a thickness of 50–100 nm. The substrate, base layer, and inorganic transfer layer were then spin-coated with AZ® 1505 positive resist (positive resist image layer) to a thickness of 500–600 nm, thus completing the deposition of the trilayer resist system. The resist was then baked at 100°C for 2 minutes and rehydrated for 5 minutes. The trilayer system was then exposed to UV light using direct-write lithography and then developed using AZ® 400K developer.

[0165] FIG. 5A shows a cross-section of the UV exposure step 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. The illustrated substrate 10 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 including a fluoropolymer-based layer 16, an inorganic transfer layer 18, and a positive photoresist layer 20. The trilayer resist system is then used to pattern a second-color OLED organic stack on a second bottom electrode 14b. In the trilayer resist approach, a photolithography process is used to pattern the positive photoresist layer 20. A photomask 34 has transparent regions 42 that allow UV light to pass through and opaque regions 44 that block UV light from reaching the positive photoresist layer 20. The transparent regions 42 of the photomask 34 allow UV light to penetrate to the underlying positive photoresist layer 20 material. Conversely, the opaque regions 44 of the photomask 34 prevent UV light from penetrating into the material below the photomask 34, protecting the organic stack 26a underneath and exposing only the areas above the electrodes onto which the second-color organic stack will be deposited. In the disclosed three-layer resist system, the opaque regions 44 of the photomask 34 cover the material above the first-color OLED organic stack 26a. A positive photoresist is a type of photoresist in which, after UV degradation of the positive resist in the positive photoresist layer 20, the exposed areas of the photoresist become soluble in a photoresist developer. Generally, the UV light has a wavelength preferably between 100 and 450 nm, more preferably between 300 and 450 nm. The unexposed areas of the positive photoresist below the opaque regions 44 of the photomask 34 remain insoluble in the photoresist developer. Positive photoresists are well known in the art and are highly controllable, but have traditionally been unable to be used when patterning organic devices due to the damaging nature of the developer to the organic material: in this case, the developer used to dissolve portions of the positive photoresist exposed to UV light does not penetrate the inorganic transfer layer 18, thus protecting the organic stack below.Negative-tone photoresists are not commonly used because their resolution is limited by swelling of exposed crosslinked regions caused by solvent uptake. The use of positive-tone photoresists in a trilayer resist system can benefit from their etch resistance, excellent resolution, and thermal stability. An additional advantage of implementing positive-tone photoresists with a photomask in this trilayer system is that the first-color OLED organic stack 26a is protected from UV exposure when patterning the second-color OLED structure. During development of the positive-tone photoresist layer 20, the inorganic transfer layer 18 acts as a barrier layer, protecting the organic stack 26a from the developer, which is highly harmful to organic materials. A trilayer resist system is particularly advantageous for patterning multiple organic devices, specifically multicolor OLED arrays, on a single substrate 10. This is achieved by patterning an array of OLEDs for the first color, then patterning the second color and then the third color as needed, with the photomask exposing only the desired bottom electrode for organic stack deposition.

[0166] Figure 5B shows a cross-section of a substrate with a first-color organic stack patterned over the first electrode, second electrode, and tri-layer resist system following patterning of a positive photoresist image layer. An existing first-color OLED structure, including a first-color organic stack 26a, has already been formed on a first bottom electrode 14a, and a second color is formed on a second bottom electrode 14b on the same substrate 10. A tri-layer system, including a fluoropolymer-based layer 16, an inorganic transfer layer 18, and a positive photoresist layer 20, covers the substrate and the electrodes and organic stack thereon. In the next step of the patterning process for the second-color OLED, the desired pattern is transferred to the positive photoresist layer 20 using a photomask and then developed using a developer. The inorganic transfer layer 18 acts as a barrier, protecting the organic stack 26a from the developer. If a post-exposure bake process is required to remove excess solvent, the temperature must not exceed a temperature that could damage the organic layers within the organic stack 26a.

[0167] 5C shows a cross section of a substrate with a second electrode with a trilayer resist system and a first-color organic stack patterned on the first electrode, following etching of the inorganic transfer layer. The substrate 10 has an existing first-color OLED structure thereon, including an oxide layer 12, a first-color organic stack 26a formed on a first bottom electrode 14a on the same substrate 10, and a second bottom electrode 14b, as well as a trilayer system including a fluoropolymer-based layer 16, an inorganic transfer layer 18, and a positive photoresist layer 20. In the next step of the process for patterning the second-color OLED, the pattern formed in the positive photoresist layer 20 is then transferred to the inorganic transfer layer 18 using a first transfer procedure through the openings in the positive photoresist layer 20. The transfer procedure, which etches the inorganic transfer layer 18 under the openings in the positive photoresist layer 20, can be, but is not limited to, wet chemical etching or a dry etching technique such as reactive ion etching (RIE). The first transfer procedure will pattern the inorganic transfer layer 18 so that undercut regions 22 are formed and remaining unpatterned regions 40 of the inorganic transfer layer 18 remain. The undercut regions 22 can be formed through controlled etching of the inorganic transfer layer 18 to replicate a pattern formed in the positive resist image layer 20 using photolithography, and then allowing additional etching time to form the desired undercuts 22. Preferably, the etch selectivity of the positive resist image layer 20 to the inorganic transfer layer 18 is between about 0.78 and 0.82.

[0168] FIG. 5D shows a cross section of a substrate with a first-color organic stack patterned on the first electrode, followed by etching of the fluoropolymer-based layer with a resist system. The substrate 10 has an existing first-color OLED structure, including an optional oxide layer 12, a first-color organic stack 26a formed on the first bottom electrode 14a on the same substrate 10, a second bottom electrode 14b, and the remaining layers of the three-layer resist system: the inorganic transfer layer 18 and the fluoropolymer-based layer 16. To pattern the second-color OLED, the pattern is transferred from the inorganic transfer layer 18 to the fluoropolymer-based 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. The second transfer procedure results in patterning the fluoropolymer-based layer 16 such that lateral undercut profiles 24 and vertical undercut profiles 38 are formed, leaving remaining unpatterned areas 40 of the inorganic transfer layer. The offset value determines the lateral undercut 24. For example, for a fluoropolymer base layer 16 thickness of 340-400 nm and an inorganic transfer layer 18 thickness of 100 nm, a minimum offset of approximately 0.33-0.35 μm is desirable to prevent shadowing and uneven deposition of the organic stack on the bottom electrode active region 46 b. The remaining positive photoresist image layer is removed by a development process that etches the fluoropolymer base layer 16 in FIG. 5C, creating a patterned opening in the trilayer resist system.

[0169] FIG. 5E shows a cross section of a substrate with a second electrode on which the second organic stack has been deposited, and a first-color organic stack patterned on the first electrode, following 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, with a protective fluoropolymer base layer 16 and an inorganic transfer layer 18 underlying the unpatterned region 40. During patterning of the second-color OLED device using a three-layer resist system, the second-color organic stack 26b is deposited on top of the second-color bottom electrode 14b through the patterned openings in the inorganic transfer layer 18 and fluoropolymer base layer 16. The lateral undercut profile 24 and vertical undercut profile 38 of the fluoropolymer base layer 16 allow for organics to be deposited using evaporation deposition. In one example, the second-color organic stack 26b is deposited by thermal evaporation from a point source. A shadow mask can be used for deposition, allowing deposition gases to travel through the openings in the shadow mask onto the bottom electrode 14b, forming an organic stack 26b on the bottom electrode 14b that corresponds to the width of the bottom of the opening. This prevents shadow effects and reduced widths of the inner and outer shadows in the organic stack 26b during deposition. Shadow masks are typically microstructures or stencils used to precisely define device regions for various applications, such as deposition, etching, or substrate processing. Precision is particularly important when depositing the organic stack 26b on the bottom electrode 14b to avoid shadowing effects. Shadowing effects can result in the organic stack 26b not completely covering the bottom electrode active region 46, which can lead to reduced performance and edge effects around the bottom electrode active region 46 due to a reduced thickness of the organic stack 26b layer there. This can further result in suboptimal electrical and optical properties of the OLED device. The shadowing effect can be reduced by using a shadow mask for precision deposition and by creating lateral and vertical undercut profiles 24 and 38 in the fluoropolymer base layer.The lateral undercut profile 24 and the vertical undercut profile 38 allow the organic stack 26 to be deposited over a defined device area that extends the width of the bottom electrode active area 46 .

[0170] FIG. 5F shows a cross section of the substrate with the second electrode and the first-color organic stack patterned on the first electrode after a lift-off procedure. A lift-off procedure is performed to remove the remaining layers of the three-layer resist system, specifically the fluoropolymer base layer, the inorganic transfer layer, and the organic stack formed on the inorganic transfer layer, resulting in the two-color organic stack array shown in the figure. Lift-off is achieved by immersing the substrate 10 in a solvent that interacts with and dissolves the fluoropolymer base layer but does not interact with or interacts very weakly with the organic stacks 26a, 26b. The OLED materials of the organic stacks 26a, 26b are left on the substrate 10 along with the oxide layer 12 in the desired pattern after lift-off. FIG. 5G shows a cross section of a multicolor OLED array on a substrate including a second-color OLED patterned on a second electrode and a first-color OLED patterned on a first electrode. The final fabrication step involves depositing top electrodes 28a, 28b on organic stacks 26a, 26b, resulting in an OLED array as shown. The organic stacks 26a, 26b are formed on bottom electrodes 14a, 14b, respectively. The bottom electrodes 14a, 14b are formed on a substrate 10 including an oxide layer 12, and the top electrodes 28a, 28b are cathodes in this embodiment. The top electrodes 28a, 28b can comprise a reflective metal, a semitransparent thin-film metal, or a transparent conductive oxide, such as indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), indium-doped zinc oxide (IZO), or Ga-doped zinc oxide (ZnO). The bottom electrodes 14a, 14b can be deposited using, for example, sputtering, evaporation, or spin coating techniques.

[0171] Figure 6A shows a top-view image captured using an optical microscope of a first pattern after photolithographic development of the positive photoresist layer of a three-layer resist system. Figure 6B shows a top-view image captured using an optical microscope of a second pattern after photolithographic development of the positive photoresist layer of a three-layer resist system. Figure 6C shows a top-view image captured using an optical microscope of a third pattern after photolithographic development of the positive photoresist layer of a three-layer resist system.

[0172] The inorganic transfer layer was then etched using a wet etching technique, as shown in Figure 7. Figure 7 shows a wafer 60 before etching and an inorganic transfer layer 62 on the same wafer after the etching process. In one embodiment, the etchant can be, for example, one or more of phosphoric acid, nitric acid, acetic acid, and / or water. Additional intermediate etching steps can be performed using different etching methods for the first and second transfer layer wet etching steps.

[0173] Figure 8A shows a top view image captured using an optical microscope of a first pattern after wet etching of the inorganic transfer layer, Figure 8B shows a top view image captured using an optical microscope of a second pattern after wet etching of the inorganic transfer layer, and Figure 8C shows a top view image captured using an optical microscope of a third pattern after wet etching of the inorganic transfer layer.

[0174] Figure 9A shows a top-view image captured using an optical microscope of a first pattern after dry etching of the fluoropolymer base layer. The fluoropolymer base layer was etched with O2 plasma using a dry etching technique. Figure 9B shows a top-view image captured using an optical microscope of a second pattern after dry etching of the fluoropolymer base layer. Figure 9C shows a top-view image captured using an optical microscope of a third pattern after dry etching of the fluoropolymer base layer.

[0175] Figure 10 shows a profile view image captured by a field emission scanning electron microscope (FESEM) of the undercut in the fluoropolymer base layer. The undercut to facilitate lift-off of the CYTOP base layer was created using a high-pressure, low-power O2 plasma process for 30 minutes. During dry etching of the CYTOP base layer with a vertical O2 plasma etch at lower pressure and higher power, strands 48 were found to form, hanging from the sidewall of the inorganic transfer layer and bending toward the undercut region 22, as shown in Figure 10. It was determined that these strands 48 are CYTOP and do not pose a lift-off problem, but a slight modification to the base layer etch was successful in removing them. Figure 11A shows a top view image captured by a field emission scanning electron microscope (FESEM) after successful patterning of the trilayer resist system for the first pattern. Figure 11B is 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. Figure 11C shows an isometric image captured by FESEM after successful patterning of the tri-layer resist system for the first pattern.

[0176] Figure 11A shows a top-view image captured by a field emission scanning electron microscope (FESEM) after successful patterning of the trilayer resist system, prior to deposition of the organic layer for the first pattern. Figure 11B shows a side profile view image captured by the FESEM, further illustrating the side profile of the undercut formed in the fluoropolymer-based layer, prior to deposition of the organic layer for the first pattern. Figure 11C shows an isometric view image captured by the FESEM after successful patterning of the trilayer resist system, prior to deposition of the organic layer for the first pattern.

[0177] FIG. 12 shows a top view image captured by FESEM after successful patterning of the trilayer resist system, before deposition of the organic layer for the second pattern.

[0178] Figure 13A shows a top view image captured by FESEM after successful patterning of the tri-layer resist system before deposition of the organic layer for the third pattern, and Figure 13B shows an isometric view image captured by FESEM after successful patterning of the tri-layer resist system before deposition of the organic layer for the third pattern.

[0179] To achieve lift-off of all remaining components of the tri-layer photoresist system, the substrate was immersed in CT-Solve 100E and sonicated. Figure 14A shows a top-view image of the first pattern captured using an optical microscope after lift-off of the fluoropolymer base layer, demonstrating successful patterning of an array of clean bottom electrodes ready for organic device deposition. Figure 14B shows an image of the second pattern captured using an optical microscope following lift-off of the fluoropolymer base layer, demonstrating successful patterning of an array of clean bottom electrodes ready for organic device deposition. Figure 14C shows an image of the third pattern captured using an optical microscope following lift-off of the fluoropolymer base layer, demonstrating successful patterning of an array of clean bottom electrodes ready for organic device deposition.

[0180] All publications, patents, and patent applications mentioned in this specification are indicative of the level of skill of those skilled in the art to which this invention pertains, and are hereby incorporated by reference. The reference to any prior art herein is not, and should not be taken as, an acknowledgment or any form of suggestion that such prior art forms part of the common general knowledge.

[0181] The invention thus described will be obvious that it may be varied in many ways, and such variations are not to be regarded as a departure from the scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims

1. 1. A method for patterning an organic device, comprising: depositing a bottom electrode on the substrate; depositing a trilayer resist system on the substrate, the trilayer resist system comprising: a fluoropolymer base layer; and an intermediate inorganic transfer layer; a top positive photoresist layer; and at least one organic device; patterning the top positive photoresist layer using photolithography to form an imaging layer aligned with the bottom electrode; etching the intermediate inorganic transfer layer exposed through the image layer; exposing the bottom electrode using reactive ion etching of the fluoropolymer-based layer exposed through the inorganic transfer layer; depositing at least one organic layer over the exposed bottom electrode; performing a lift-off procedure to remove remaining components of the tri-layer resist system; depositing a top electrode on the organic layer; and forming the A method comprising:

2. The method of claim 1 , wherein the organic device is an organic light emitting diode.

3. The method of claim 1 , wherein the organic device is an organic field effect transistor, an organic solar cell, a photovoltaic device, an organic semiconductor, or an organic laser.

4. 4. The method of claim 1, wherein the fluoropolymer base layer has a visible light transmittance of 95% or greater.

5. The method of any one of claims 1 to 3, wherein the positive photoresist layer has a thickness of about 340 to 500 nm.

6. 4. The method of claim 1, wherein the inorganic transfer layer is etched through the patterned positive photoresist layer to form an undercut region between the positive photoresist image layer and the inorganic transfer layer.

7. 4. The method of claim 1, wherein the fluoropolymer base layer is etched to form a lateral undercut profile and a vertical undercut profile.

8. 8. The method of claim 7, wherein the lateral undercut profile length is ≥ 0.25 μm.

9. 4. The method of claim 1, wherein the lift-off procedure utilizes a fluorinated solvent to dissolve the fluoropolymer-based layer.

10. The method of claim 1 , wherein the inorganic transfer layer comprises one or more of a metal and a dielectric material.

11. 4. The method of claim 1, wherein the at least one organic layer comprises one or more of an electron transport layer (ETL), an emissive layer (EML), a hole transport layer (HTL), and a hole injection layer (HIL).

12. 12. The method of claim 11, wherein the light-emitting layer (EML) is at least one of red, green, and blue emitting.

13. 4. The method of claim 1, wherein an oxide layer is deposited on the substrate and electrode array prior to deposition of the trilayer resist system.

14. The method of claim 13 , wherein the oxide layer comprises a transparent conductive oxide.

15. 1. A method for patterning an organic device array, comprising: depositing an array of bottom electrodes on a substrate; depositing a tri-layer resist system on the substrate using a tri-layer resist deposition method, the tri-layer resist system comprising: a fluoropolymer base layer; and an intermediate inorganic transfer layer; a top positive photoresist layer; and forming a plurality of organic devices for a first set of organic devices using an organic device deposition method, the organic device deposition method comprising: patterning the top positive photoresist layer using photolithography to form an imaging layer aligned with the set of arrays of bottom electrodes; etching the intermediate inorganic transfer layer exposed through the image layer; using reactive ion etching of the fluoropolymer-based layer exposed through the inorganic transfer layer to expose the set of arrays of bottom electrodes; depositing at least one organic layer over the set of exposed bottom electrodes; performing a lift-off procedure to remove any remaining components of the tri-layer resist system; repeating the tri-layer resist deposition method to deposit the tri-layer resist system on the substrate; and repeating the organic device deposition method to form a second set of organic devices aligned with a second set of bottom electrodes; repeating the lift-off procedure to remove any remaining components of the tri-layer resist system; A method comprising:

16. The method of claim 15 further comprising depositing a top electrode over each of the organic devices.

17. 17. The method of claim 15 or 16, wherein the organic devices are OLEDs, and the first set of organic devices and the second set of organic devices emit different colors.

18. 17. The method of claim 15 or 16, wherein the inorganic transfer layer is etched through the patterned positive photoresist layer to form an undercut region between the positive photoresist image layer and the inorganic transfer layer.

19. 17. The method of claim 15 or 16, wherein etching the fluoropolymer base layer creates a lateral undercut profile and a vertical undercut profile.

20. 20. The method of claim 19, wherein the length of the lateral undercut profile is ≥ 0.25 μm.

21. 17. The method of claim 15 or 16, wherein the lift-off procedure utilizes a fluorinated solvent to interact with and dissolve the fluoropolymer base layer.

22. The method of claim 15 or 16, wherein the inorganic transfer layer comprises one or more metal or dielectric materials.

23. 17. The method of claim 15 or 16, wherein the organic layer is an organic stack comprising one or more electron transporting layers (ETL), emissive layers (EML), hole transporting layers (HTL), and hole injection layers (HIL).

24. 1. A method for patterning an organic device array, comprising: depositing a plurality of bottom electrodes on a substrate; depositing a tri-layer resist system on the substrate using a tri-layer resist deposition method, the tri-layer resist system comprising: a fluoropolymer base layer; and an intermediate inorganic transfer layer; a top positive photoresist layer; and Forming a plurality of organic devices using an organic device deposition method, the organic device deposition method comprising: patterning the top positive photoresist layer using photolithography to form an imaging layer aligned with the plurality of bottom electrodes; etching the intermediate inorganic transfer layer exposed through the image layer; using reactive ion etching of the fluoropolymer-based layer exposed through the inorganic transfer layer to expose the plurality of bottom electrodes; depositing at least one organic layer over the set of exposed bottom electrodes; and performing a lift-off procedure to remove any remaining components of the tri-layer resist system; A method comprising:

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