Aqueous detergent soluble coating and adhesive and methods of temporary bonding for manufacturing
09790407 · 2017-10-17
Inventors
Cpc classification
H01L21/02118
ELECTRICITY
C09J133/26
CHEMISTRY; METALLURGY
International classification
H01L21/02
ELECTRICITY
C09J133/26
CHEMISTRY; METALLURGY
Abstract
Compositions and methods are described for a temporary coating and adhesive with adjustable acidity for use in coating work units as a planarization coating over high topography and also for affixing thin units onto a carrier whereby such compositions provide sufficient properties to support a manufacturing process, and upon completion, the compositions are removed by an aqueous detergent that dissolves and releases the work unit within a rapid time frame without harm to its integrity. The temporary adhesive provides a tunable acidity based upon Lewis acid represented as its acid dissociative constant, K.sub.a, where it is preferred to have K.sub.a≧1×10.sup.−6 (pK.sub.a≦6), more preferred K.sub.a≧1×10.sup.−5 (pK.sub.a≦5), and most preferred K.sub.a≧1×10.sup.−4 (pK.sub.a≦4). The temporary coating and adhesive may be applied and cured in a variety of ways that meet the needs of the work unit and objectives of the manufacturing process. The invention provides benefits of flexibility and reduced cost when establishing practices to handle difficult work units in the manufacture of semiconductors and flat panel displays.
Claims
1. A temporary coating with tunable acidity and further containing a binder, wherein the coating and binder is applied to a work unit and subsequent to a manufacturing process, the acidity allows the removal with an aqueous detergent without harm and without the need for a subsequent cleaning process.
2. The temporary coating of claim 1 wherein the binder comprises an organic resin of one or more chemical families.
3. The temporary coating of claim 2 wherein the organic resin comprises one or more from the group epoxy, acrylate, silicone, urethane, rubber, and engineering polymer.
4. The temporary coating of claim 3 wherein the engineering polymer comprises one or more from the group polyimide, polyamide, polyamideimide, polybenzimidazole, polybenzoxazole, polysulfone, polyethersulfone, polyphenylsulfone, polyarylether, polyetheretherketone, polyvinyidenedifluoride, cyclic olefin copolymer, polyethylene terphthalate, polybutylene terephthalate, polyacrylonitrile, polyaryletherketone, polyketoneketone, styrene-acrylonitrile, polycarbonate, polystyrene, polyvinylchloride, polyphenylene sulfide, polytrimethylene terephthalate, polyvinylidene chloride, acrylonitrile butadiene styrene, and liquid crystal polymer.
5. The temporary coating of claim 3 wherein a mixture of the organic resin contains one or more polymer reaction initiators.
6. The temporary coating of claim 5 wherein the initiators comprise one or more from the group organic acid, photoacid generator, photobase generator, organic amine, thermal free radical, and photo free radical producing.
7. The temporary coating of claim 2 wherein a mixture of the resin contains a filler.
8. The temporary coating of claim 7 wherein the filler comprises one or more from the group nanoparticle, nanofiber, nanometal, fiber, glass bead, glass sphere, ceramic, and cellulose.
9. The temporary coating of claim 1 wherein the work unit comprises a film or foil.
10. The temporary coating of claim 1 wherein the work unit is produced from evaporation.
11. The temporary coating of claim 1 wherein the work unit is produced from plasma deposition.
12. The temporary coating of claim 1 wherein the work unit is produced from electrolytic deposition.
13. The temporary coating of claim 9 wherein the work unit comprises one or more from the group metal, ceramic, glass, organic polymer, and composite.
14. The temporary coating of claim 10 wherein the work unit comprises one or more from the group metal, ceramic, glass, organic polymer, and composite.
15. The temporary coating of claim 11 wherein the work unit comprises one or more from the group metal, ceramic, glass, organic polymer, and composite.
16. The temporary coating of claim 12 wherein the work unit comprises one or more from the group metal, ceramic, glass, organic polymer, and composite.
17. A temporary coating comprising a binder with tunable acidity, wherein the coating is applied to a work unit and subsequent to a manufacturing process, the acidity allows the removal with an aqueous detergent without harm and without the need for a subsequent cleaning process wherein the acidity is from the group Lewis acid.
18. The temporary coating of claim 17 wherein the Lewis acid comprises one or more compounds that exhibit a dissociation constant of >1×10-6 (pKa <6).
19. The temporary coating of claim 18 wherein the Lewis acid exhibits a dissociation constant of >1×10-5 (pKa <5).
20. The temporary coating of claim 19 wherein the Lewis acid exhibits a dissociation constant of >1×10-4 (pKa <4).
21. A manufacturing process where a temporary coating of claim 1 with tunable acidity is applied to a work unit and subsequent to a manufacturing process, the acidity allows the removal with an aqueous detergent without harm and without the need for a subsequent cleaning process, where the process is electronics.
22. The manufacturing process of claim 21 wherein the electronic process comprises semiconductor and display.
Description
DESCRIPTION OF THE PREFERRED EMBODIMENTS
(1) In the case of temporary protection of electronic work units with topography containing features >100 um and the temporary affixing of thin work units to carriers, a need exists for a coating to planarize such features and an adhesive to bond such units. For high volume manufacturing, the coating and adhesive is applied in a manner to achieve rapid curing and affixing, provide resistance to mechanical, thermal, and chemical effects during manufacturing, and to easily remove in aqueous detergent. The models of a coating (e.g. planarizing) and adhesive are given in
(2) A composition with tunable acidity using a Lewis acid is applied to a work unit as a coating or adhesive is sufficient to support a manufacturing process, and upon completion, the composition is removed by exposure to aqueous detergent. An ideal acidity is tuned to be sufficient to hydrolyze and saponify by aqueous detergents.
(3) The Lewis of the invention is desired to be dissociative in water sufficient to achieve a minimum strength such that when alkali materials come into direct contact during aqueous detergent cleaning, the material will begin to break-down, saponify, and hydrolyze to produce complete dissolution where it is then easily rinsed away. Lewis acids comprise regular known acidic compounds, Bronsted-Lowry acids, and virtually all compounds with can accept a pair of electrons. The preferred characteristic to express Lewis acid strength is through the respective dissociation constant of the species. Preferred values of the acid dissociative constant, K.sub.a, is for K.sub.a≧1×10.sup.−6 (pK.sub.a≦6), more preferred, K.sub.a≧1×10.sup.−5 (pK.sub.a≦5), and most preferred, K.sub.a≧1×10.sup.−4 (pK.sub.a≦4). The Lewis acid species may exist singularly or in a mixture that comprises several molecular forms. These forms may include common acidic materials as alkyl-sulfonic acids such as methanesulfonic (MSA), Toluenesulfonic (TSA), and dodecylbenzene sulfonic acid (DDBSA), formic acid, fatty acids, sulfuric acid, nitric acid, or phosphoric acids, weak organic acids as fatty acids such as citric and ascorbic acid, terpene acids, phthalic and terepthalic, and compounds identified with a carboxylic acid group (COOH); Lewis acids also include non-recognizable acidic materials, such as boron trifluoride (BF.sub.3).
(4) This invention describes a mixture that includes a tunable acidity, whereby the system is brought into direct contact with a solid work unit and cured in a variety of ways to produce a final condition. During the application and use of the chemistry, it may be cured by evaporation, initiation, or reacted to effect the desired work function for the manufacturing process. When applying to a surface for protection or adhesion, the result will be dependent upon several factors, including the substrate composition, condition of the substrate surface, texture and/or porosity of the surface, and history of thermal exposure of the coating and/or the work unit. Additionally, the value of adhesion force by peel testing is dependent upon the method includes the peel angle (i.e. 90 or 180 degrees), width of the peel area, and the speed of peeling the specimen. Given these variable conditions are well understood by those familiar with the art, they can been controlled and maintained uniform such that adhesive force may be studied by adjusting the chemistry of the adhesive.
(5) The effect of aqueous detergents upon the coating or adhesive is dependent upon the corresponding changes in the coating chemistry, the Lewis acid chosen, and the amount by weight in the system. Using this understanding, there can be tuning in the Lewis acid in a manner that will govern the measured detergent cleaning speed and effectiveness. In other words, through the selection and adjustment of Lewis acid, the cleaning speed and effectiveness of releasing the work unit may achieve a specific value sufficient to support a manufacturing process yet allow the rapid removal of the work unit without harm or change to its form.
(6) A variety work units may be used with this invention to include inorganic and organic films. Inorganic work units may include films and foils of metals and ceramics. Metal films and foils may be used to include copper (Cu), nickel (Ni), iron (Fe), cobalt (Co), titanium (Ti), tantalum (Ta), tungsten (W), molybdenum (Mo), chromium (Cr), aluminum (Al), gold (Au), silver (Ag), neodymium (Ne), palladium (Pd), platinum (Pt), osmium (Os), iridium (Ir), rhodium (Rh), ruthenium (Ru), nitrides thereof, such as titanium nitride (TiN), and alloys thereof, such as nickel iron (NiFe). Work units may exist initially as foils or may be vacuum deposited onto a temporary coating or adhesive such that the work unit of the metal is completed to a level that its integrity is of a minimum requirement sufficient to proceed with manufacturing and may be removed later by exposure to aqueous detergents. The minimum time to clean and release the work unit may be defined by several properties, to include the amount of Lewis acid present in the composition.
(7) Work units may exist as crystalline and amorphous ceramic materials include silicon, gallium arsenide, quartz, glass, and alloying mixtures thereof. These ceramic and glass materials may exist initially as foils or films. Work units composed of ceramic and glass materials may be produced by vacuum deposition onto a temporary adhesive such that a work unit of the ceramic or glass is completed to a level such that its integrity meets a minimum requirement sufficient to proceed with manufacturing and may be removed later by aqueous detergency. The minimum time to clean and release the work unit may be defined by several properties, to include the amount of Lewis acid present in the composition.
(8) Organic films which represent temporary adhered work units include polyimides such as Kapton® (registered trade mark of E.I. du Pont de Nemours and Company), polyarylether such as Arylite® (registered trade mark of Ferrania), polyesters such as Mylar® (registered trade mark of DuPont Teijin Films), polypropylene, polyethylene, polysulfone (polysulfone, polyethersulfone, polyphenylsulfone) such as Radel® (registered trade mark of Solvay Solexis), polybenzimidazole, polyphenylene sulfide such as Torelina® (registered trade mark of Toray Film Products, Co., Ltd.), polycarbonate, polystyrene, polyacrylic, fluoropolymers as fluoroethylene propylene (FEP), perfluoroalkoxy polymer (PFA), ethyltetrafluoroethylene (ETFE), and ethylene-chlorotrifluoroethylene (ECTE) such as Halar® (registered trade mark of Solvay Solexis), polyvinylidene fluoride (PVDF) such as Kynar® (registered trade mark of Solvay Solexis), polyether ether ketone (PEEK), polyether imide (PEI), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), and various polyamides classified as nylon. Work unit polymers may exist initially as films, may be cast from liquid solutions, or may be vacuum deposited directly onto a coating or temporary adhesive such that a work unit of the polymer is completed to a level such that its integrity reaches a minimum requirement sufficient to proceed with manufacturing and be removed later by aqueous detergents. The minimum time to clean and release the work unit polymer may be defined by several properties, to include the amount of Lewis acid present in the composition.
(9) The tunable acidic coating and adhesive chemistry comprises polymeric resins from at least one specific chemical family and may also be combined with other separate chemical families. The adhesion force is controlled by the content adjustment of mixing resins of different molecular weights or functionality within a chemical family or by mixing between different chemical families. For example, one temporary adhesive may comprise one or more resins from the family of epoxy resins (i.e. alkyl epoxy, novolac epoxy, etc.) whereas, another temporary adhesive may comprise one or more resins from different chemical families (i.e. epoxy and acrylic, etc.). The variation of these resin choices will produce a direct effect on the adhesive force of the system in affixing the thin solid material onto the carrier substrate. Those familiar with the art recognize that in order to effect the reaction of such chemistries, there must also include the necessary initiators. These initiators are considered as cross-linkers, activators, catalysts, or reactors, and represent a small portion of the overall composition. Therefore, it shall be understood that whenever mention is made about the use of a specific chemistry or resin, that chemistry must include the respective initiator, and the choice of the initiator may produce certain subtle differences, the primary emphasis is that an initiator that is matched with the chemistry of choice must be included in the system.
(10) The temporary coating and adhesive chemistry may comprise a variety of base resins. The reactive resins include, but are not limited to, those undergoing cross-linking polymerization mechanisms, including epoxies, acrylates and silicones. These systems undergo thermal, chemical, and photo-initiated polymerization by condensation and addition mechanisms as described in the literature, and described as thermosets. Thermoset chemistries offer rigidity and resistance to the process conditions. Non cross-linking resins include those described as amorphous or thermoplastics. The thermoplastic resins may add strength and durability to the adhesive. Additional properties by amorphous polymers include barrier (gas non-diffusion), temperature resistance, transparency, detergency, and water solubility. The following passages offer more detail on the resins used in the adhesive chemistry. The production of a temporary coating and adhesive for use in this invention is not limited to the resins identified here.
(11) Epoxy resins used for this invention may comprise a single or multiple epoxide functional group, also called oxirane, or ethoxyline, normally identified as a three-membered oxide ring described by the following structures classified as (1) glycidyl ethers, (2) glycidyl esters, (3) gylcidyl amines, (4) linear aliphatics, and (5) cycloaliphatics:
(12) ##STR00001##
where both R, R.sup.1, and R.sup.2 may represent the following: hydrogen (—H), amide (—NH.sub.2), methyl (—CH.sub.3), hydroxyl (—OH), alcohol (—CH.sub.2OH), or any one of the groups represented by the formula —C.sub.nH.sub.(2n), —C.sub.nH.sub.(2n+1), or —C.sub.nH.sub.(2n)OH where n varies from 2-20; cyclic and aromatic hydrocarbon functional groups of the formula —C.sub.6X.sub.5, where X may be substituent groups such as hydrogen (—H), the halogens (—F, —Br, —Cl, —I), hydroxyl (—OH), and —COOH groups, R.sup.3 represents a cyclic or aromatic structure of the formula —C.sub.6X.sub.5, where X may be substituent groups such as hydrogen (—H), the halogens (—F, —Br, —Cl, —I), hydroxyl (—OH), and —COOH groups, all of these variations may exist in multiple substituent formats, or monomers, as given in the example structure (6):
(13) ##STR00002##
wherein structure (6) describes a polymer comprising monomers of glycidyl ether with substituent R and linked by R.sup.1. Such resins may include: CARDOLITE 514 (difunctional glycidyl ether epoxy resin) produced by Cardolite Corporation, ADEKA EP 4088S (epoxy resin and urethane resin curing agent) produced by Adeka Corporation, EBECRYL3605 (partially acrylated bisphenol-A epoxy) produced by Cytec Industries, Inc.
(14) In one embodiment, the epoxy resin includes that of structure (6), wherein the monomeric epoxide substituent is of the novolac variety, also referred to as epoxidized novolac resin, where R represents an aromatic ring of the form C.sub.6X.sub.5, where X may be substituent groups such as hydrogen (—H), the halogens (—F, —Br, —Cl, —I), hydroxyl (—OH), and —COOH groups, and the linkage R.sup.1 is best represented by substituents of the formula —C.sub.nH.sub.(2n). Such epoxy novolac resins include 3-6 epoxide groups per molecule (n=1.6) of the general formula exhibited by the structure (6). General commercialized products which meet this criteria include: DEN 431 and DEN 439 produced by The DOW Chemical Company; EPON 154, EPON 160 and EPON 161 produced by Resolution Performance Products (Hexion), REZICURE 3056 produced by SI Group.
(15) Acrylic monomers and polymers used in this invention include acrylate esters by the general formula described in item (7), where both R.sub.1 and R.sub.2 may represent the following: hydrogen (—H), amide (—NH.sub.2), methyl (—CH.sub.3), hydroxyl (—OH), alcohol (—CH2OH), or any one of the groups represented by the formula —C.sub.nH.sub.(2n+1) or —C.sub.nH.sub.(2n)OH where n varies from 2-20; aromatic hydrocarbon functional groups of the formula —C.sub.6X.sub.5, where X may be substituent groups such as hydrogen (—H), the halogens (—F, —Br, —Cl, —I), hydroxyl (—OH), —COOH; and —COOR.sub.3 groups, wherein R.sub.3 represents the following: hydrogen (—H), amide (—NH.sub.2), methyl (—CH.sub.3), hydroxyl (—OH), alcohol (—CH2OH), or any one of the groups represented by the formula —C.sub.nH.sub.(2n+1) or —C.sub.nH.sub.(2n)OH where n varies from 2-20.
(16) ##STR00003##
It is to be understood that where substituent groups are present, they should be present in a manner such that they do not unduly hinder or interfere with the thermal or photo initiated cure of the acrylic monomer. The preferred acrylic monomers are those represented by item (7), wherein R.sub.1 is a hydrogen (—H), or methyl (—CH.sub.3), defining the molecule as an acrylate or methacrylate, respectively, and R.sub.2 to represent a substituent of the form or —C.sub.nH.sub.(2n)OH where n varies from 2-20. Such preferred acrylics include hydroxyethyl acrylate (CAS #818-61-1), hydroxypropyl acrylate (CAS #25584-83-2), hydroxyethyl methacrylate (CAS #868-77-9), and hydroxy propyl methacrylate (CAS #27813-02-1). The more preferred acrylic monomers are those represented by item (7), wherein R.sub.1 is a hydrogen (—H), or methyl (—CH.sub.3), and R.sub.2 to represent a substituent of the form amide (—NH.sub.2), defining the molecule as an acrylamide. Such preferred acrylics include n,n-dimethylacrylamide (DMAA, CAS #2680-03-7). DMAA has been shown to exhibit high compatibility and solubility for other resins and a significantly faster curing time over the conventional acrylates or methacrylates.
(17) Polysiloxane resins suitable for use herein exist in commerce by multiple suppliers, exhibiting broad classification differences in silicone subcategories, types, and polarities, and reacting through different mechanisms, including addition and condensation polymerization. The use of such materials in the preparation of the adhesive shall consider compatibility and reactivity between the polysiloxanes as a key factor in determining their final behavior. For example, species of similar polarity may be compatible yet be inconsistent in their preferred reaction mechanisms. These include organofunctional polysiloxanes and silicone resin intermediates, both are expected to undergo thermal initiated condensation reactions following hydrolysis. However, vinyl silicones (rubbers) are largely a phobic chemistry and undergo addition reactions with metal catalysts. Therefore, we will differentiate these chemistries accordingly, as their use in an adhesive is expected to follow the same considerations of compatibility and reactivity.
(18) The preferred polysiloxanes include oxysilanes of the formulas represented as (R.sub.1)—[(R.sub.2)(R.sub.3)SiO].sub.n—R.sub.4 or (R.sub.5)O—[(R.sub.3).sub.2SiO].sub.m—R.sub.5, where R.sub.1, R.sub.2, and R.sub.3, may exist as a hydrogen or carbon containing functional group of the variety as alkyl, phenyl, cycloalkyl, alkoxy, hydroxyalkyl, alkoxyalkyl, and hydroxyalkyalkoxy, where these groups may contain up to 6 carbons, and R.sub.4 comprises hydrogen, alkyl, or phenyl, where a minimum of 2 of the groups are oxy substituents used for polymerization, and R.sub.5 is similar to R.sub.4, however, there may exist up to 12 carbons, and n and m varies from 1-5 or to a sufficient number to reach a molecular weight of 500,000.
(19) Siloxane resins suitable for use herein include a broad range of alkyl, aryl, oxygenated, and cyclic substitutions. In the case where thermal resistance is critical, the substitution will be methyl and phenyl. The moieties on the siloxane can also exhibit specific organic functional groups that are well known to interact with the chemistry of the substrate interface. For example, in the case of a mercaptan siloxane moiety, the sulfur group interacts with certain inorganic solid surfaces, such as metals, to increase the interfacial adhesion force. Most importantly, moieties which exhibit epoxy, acrylic, or amine character, are known to interact with a corresponding chemistry within an organic matrix and at the interface of polymeric solid surfaces, resulting in molecular entanglement and van der Waals interactions as hydrogen and covalent bonding, and ultimately, an increase of adhesion.
(20) Silicone resins based on cyclic siloxane molecules are preferred. Useful cyclic silicones are hydroxy functional cyclic silicones classified as liquid resins, flake resins, and silicone intermediates as provided by suppliers Dow Corning (www.dowcorning.com) and Wacker Silicones (Wacker-Chemie GmbH) (www.wacker.com). Preferred cyclic siloxane choices for adhesive development, include those with high compatibility with other polymers, dissolution in a wide range of solvents, and those classified as silanols. These silanol compounds exhibit relatively high capacity for condensation reactivity and include those with two or more hydroxyl groups per cyclic silicone molecular unit and a phenyl/methyl ratio ranging from 50-120% and a molecular weight ranging from 4,000 to 300,000. In all cases, the relative content of silicon dioxide is high, usually greater than 50%.
(21) The choice of initiator is dependent upon the polymer and the application. Epoxy based systems use organic amine and acid materials to open the oxirane ring and initiate cross-linking. These may be promoted by thermal or photo means. Free-radical initiators are used with acrylics, also promoted by applications that apply heat or ultraviolet exposure. Silicone vinyl compounds require metal catalysts to initiate free-radical generation. These classes of initiators and the required media to support polymerization and enable applications of the adhesive to facilitate fixation of the two surfaces. In one embodiment, an epoxy resin system is used with an initiator that is of the polyamine form and of higher molecular weight. Higher molecular weight amine chemistries will remain in the system for longer durations and provide an environment, which efficiently cross-links the epoxy resin. Amines may include triethylenetetramine (TETA), N-methylethanolamine (NMEA), and N-methyldiethanolamine (DMEA) produced by The DOW Chemical Company, and meta-xylenediamine (MXDA) as produced by Mitsubishi Chemical Company. Desirable amine amounts are typically present at levels from about 1% to about 5%, by weight as compared that of the epoxy. A similar approach for epoxies may also be used with acidic materials. The acids tend to have higher reaction rates with epoxies over that of amines. Preferred acids are various sulfonic acids such as toluene, dodecylbenzene, and methane sulfonic acids. The epoxy begins to react upon contact, so the means of mixing and application must be considered. Where acidic reactions are preferred for epoxies are in the case of photo acid generators (PAGs). These systems comprise sulfonium salts that release varying molecular weights of toluene sulfonic acid to cause immediate reaction. This rapid reaction is used in many photoresists. One common photoacid generator is triphenylsulfonium trifluoromethane sulfonate (TPST). Typical amounts of a PAG is in the range of <2% by weight of epoxy.
(22) Initiators for acrylic monomers include thermal (thermal radical initiator, TRI) or photo activated free radical initiators. It is well known from the literature that these free-radical initiated systems will combine with the vinyl group of the acrylic, initiate a chain reaction, whereby the product acrylate free radical combines with other vinyl groups of adjacent acrylics and produce final cross-linked product. These TRI materials include inorganic persulfates such as ammonium persulfate (APS), potassium persulfate, and sodium persulfate, and organic persulfates such as quaternary ammonium persulfates (e.g. tridodecyl ammonium persulfate); peroxides include benzoyl peroxide (BPO), methyl ethyl ketone peroxide, dicumyl peroxide, and benzopinacole (BK), cumene dihydrogen peroxide, and those organic peroxides under the tradename Luperox™ (Arkema, Inc., www.arkema-inc.com), azo-compounds including 2,2′-azobisisobutyrnitrile (AIBN), 4,4-azobis(4-cyanovaleric acid), 1,1′-azobis(cyclohexanecarbonitrile), acetates as peracetic acid, and tert-butyl peracetate. Benzoin photoinitiators are common for use as initiators for acrylic chemistry. One type of benzoin photosensitizer is 2-phenylacetophenone, which undergoes photoscission to release radicals of benzoyl, and benzyl, which become the primary chain polymerization initiators in the curing process. Photochemically generated free radicals react directly with the double bond of the vinyl monomer as a chain-initiating step. The invention involves a cure process between a photoinitiator that is present in the liquid polymer system and actinic radiation from an ultraviolet emission source. Common photoinitiators include benzoin ethers, acetophenones, benzoyl oximes, and acylphosphines. These initiators may include phenylglyoxylate, benzyldimethylketal, ∝aminoketone, ∝hydroxyketone, monoacyl phosphine (MAPO), bisacylphosphine (BAPO), metallocene, and iodonium salt. Preferred initiators include 2-hydroxy-2-methyl-1-phenyl-1-propanone (CAS #7473-98-5) and phosphine oxide phenylbis(2,4,6-trimethylbenzoyl)-(CAS #162881-26-7). A trade name product, which represents these materials, includes Irgacure 2022, as manufactured by CIBA Specialty Chemicals, Basel, Switzerland. The product exhibits absorption maxima at 365 nm, 285 nm, and 240 nm. Concentrations are used anywhere at ≦5% by weight.
(23) Adhesive mixtures which are chosen to use silicone resins may contain anywhere from 20-100% solids of silicone polymers having polysiloxane-vinyl and silyl-hydride character. In the presence of a metal catalyst, the vinyl compounds initiate free radicals that undergo addition polymerization with the silyl-hydride to produce a polymerized final product. To control the reaction rate for application and bonding, there are chelates binding the platinum. During heat exposure, the chelate degrades to release platinum and then triggers polymerization. In the case of silanol polysiloxanes, these monomers will crosslink upon heat exposure, usually in the range 200-250 C.
(24) Additives may also be present to facilitate adjusted adhesion. For example, the use of fluoropolymers are known for surface sensitive activity. The addition of fluoropolymer surfactants meet this objective. Other common surfactants as nonionics or charged species as cationic or anionic may provide surface sensitive adjustments in adhesion and also allowing fluctuations in melt point to give an amorphous character to improve adhesion.
(25) In addition to the resins, initiators, and additives, the chemistry of the temporary adhesive may also contain fillers. These are specifically exemplified by fibrous fillers such as glass fiber, asbestos, alumina fiber, ceramic fiber composed of both alumina and silica, boron fiber, zirconia fiber, silicon carbide fiber, metal fibers, polyester fibers, aramid fiber, nylon fibers, phenolic fibers, natural plant and animal fibers; granular or particulate fillers such as fused silica, precipitated silica, fumed silica, calcined silica, zinc oxide, calcined clay, carbon black, glass beads, alumina, talc, calcium carbonate, clay, aluminum hydroxide, barium sulfate, titanium dioxide, aluminum nitride, silicon carbide, magnesium oxide, beryllium oxide, kaolin, mica, zirconia, and so forth; and mixtures of two or more of the preceding.
(26) There exist several mechanisms for curing, B-staging, reacting, and alike for coating and inserting and affixing the adhesive between a thin solid material and the carrier substrate. As a fundamental characteristic of any coating or adhesive, there must be sufficient wetting between both surfaces. Wetting is defined as the interaction of a lower contact angle (low energy) liquid or semi-solid onto a higher contact angle (higher energy) substrate. In many cases, the difference in surface energy between the adhesive and surface can be as low as 10 dynes/cm, however, the difference is preferably much larger. In optimum conditions, a lower energy adhesive will wet and spread over the higher energy surface of the substrate and achieve good wetting.
(27) Although wetting is fundamental to successful coating, the resulting coating adhesive force is dependent upon the chemistry of the adhesive and the interaction of its chemical functionality with the substrate. This interaction is dependent upon the application, cure, and affixing steps. The coating and adhesive chemistry may comprise organic resins in pure form (i.e. 100% solids) or dissolved into carrier solvents. Cure programs may involve a soft bake step to affix the material to the carrier substrate, followed by a hard bake whereby the thin solid substrate is held in direct contract with the B-stage adhesive affixed to the carrier substrate. The mechanism by which the coating and adhesive is applied, cured, and the thin substrate is brought into contact with the adhesive includes a plurality of approaches which this invention is not limited. Choices on these approaches are based upon many considerations, including the handling of the thin solid material, cure mechanism, and that method which minimizes the existence of trapped air and completely fills any voids. Regardless of the approach, the final objective is to achieve a bonded form where the thin solid material is affixed to the carrier substrate, which now allows the manufacturing process to proceed.
(28) Once the manufacturing process is complete, removal of the work unit is performed. The exact mechanism may vary between conventional batch type cleaning within a wet bench with detergent tanks. The rate of penetration and reaction with the coating and adhesive chemistry is dependent upon the level of Lewis acid and the respective dissociation constant for the acid in the invention chemistry. To reduce harm to the integrity of the work unit, the content and choice of Lewis acid is tuned for maximum performance. The preferred choice in Lewis acid is based upon the respective values of the acid dissociative constant, K.sub.a, is for K.sub.a≧1×10.sup.−6 (pK.sub.a≦6), more preferred K.sub.a≧1×10.sup.−5 (pK.sub.a≦5), and most preferred, K.sub.a≧1×10.sup.−4 (pK.sub.a≦4).
(29) Applications of handling and supporting thin work units are becoming a common challenge in the manufacturing of electronic devices. Due to the reduced cost structures continually promoted, the manufacture of virtually any electronic device is most competitive when it is conducted in Asia. Because cost pressures exist there must be options for a simple design in coating and handling thin work units in electronics. The scenarios vary for semiconductor and display. For example, semiconductor wafer substrates are round, extend to 12″ in diameter, and are robot transferred from tool to cassette. Conversely, display panels are square or rectangular, can extend to more than 60″ on a side, and are conveyorized. In consideration of work units for each market, substrate thickness may vary from as low as 10-100 um (microns). By offering the flexibility to tune or adjust the speed of detergent cleaning and release of the work unit when used with temporary coatings and adhesives, there is a broad range of options in adjusting acidity in the chemistry as it applies in manufacturing. These options reduce the need of new tooling and additional manufacturing steps. Through these practices and others not mentioned here, the invention's novelty and uniqueness is realized.
(30) Prior art for affixing work units, such as silicon wafers, are described in U.S. Pat. No. 7,098,152 (2006) and U.S. Pat. No. 6,869,894 (2005), Moore, describe a rosin-urethane adhesive, whereby the wafer is removed by either chemical penetration through perforated carriers or by thermal slide by applying heat to above the melt point of the adhesive and using shear force onto the thin wafer. U.S. Pat. No. 7,232,770 (2007), Moore et al., describes a cross-linked silicone adhesive that is removed by the method of chemical penetration with a perforated carrier. Both chemical penetration and thermal slide techniques require delicate handling of thin solid materials during the removal process, and the use of large-scale volumes of cleaning chemistry, primarily organic solvents. The use of chemicals, such as organic solvents, in microelectronic manufacturing adds costs, human exposure to toxic substances, and environmental impact by the generation of hazardous waste. It is therefore desired for an adhesive system that does not require organic solvents when handling of work units during removal.
(31) Other applications which describe the adhesive support of work units are described in U.S. Patent Applications 2009/0017248 A1 (2009), Larson et al., 2009/0017323 A1 (2009), Webb et al., and in the International Application WO 2008/008931 A1 (2008), Webb et al. These applications describe the use of a curable acrylate and a photothermal conversion layer that is degraded during removal by a laser irradiation device. Such a device interacts with the substrate by burning or destroying the adhesion interface between the work unit and carrier substrate. Such an interaction can produce by products and residue that are not removable (cleaned), especially when the laser system and adhered surfaces are dynamically changing. Although the use of a laser has been demonstrated as a means of removing a thin solid material, it is generally believed this option will not meet the objectives of high-volume manufacturing of large panels and be made available at a cost that the industry can bear. For these reasons and others which are known by those familiar with the art, removal options which offer simplicity, high volume manufacturing, and low cost, are needed for work units affixed to carrier substrates.
(32) While there is a desire to identify coating and adhesive materials to support work units of various compositions, thicknesses, shapes, and sizes, there also, is a challenge to design a process that affixes the material work unit by a tool, and when finished with the process, will remove the item without deleterious effects to the substrate. The need for flexibility in the adhesive chemistry is great, whereby once the concept to affix and remove the work unit is identified, the need exists to tune the adhesive force such that it fits the interdependence between the properties of the thin solid material and the tooling in the manufacturing line. Since a continuing emphasis exists for the microelectronics industry to be green and improve safety, a desire exists for an adhesive to perform without subsequent surface cleaning of the removed thin solid material. Taking these challenges together, there is a pressing need to provide adhesives that offer tunable acidity in the chemistry of the coating and adhesive to effect removal by aqueous detergency for a broad range of manufacturing by coating or affixing and removing a thin solid material onto a rigid carrier, meeting high throughput, is a green process, and is available at a reduced cost of ownership.
EXAMPLES
(33) The compositions of the invention and the method of making of the examples are described. It is understood, however, that the invention is not meant to be limited to the details described therein. In the examples, the percentages provided are percent (%) by weight unless otherwise stated. The invention is further illustrated, without limitation, by the following examples. The measurement of performance and selectivity of the invention is conducted using practices readily accepted by the industry.
(34) Coatings are produced on a Brewer Science, Inc. CB-100 spin-coater, while spray and encapsulation uses custom tooling designed at Daetec. Metrology data is generated by a XP-1 stylus profiler, AFP-200 atomic force profiler, and a Xi-100 optical profiler (www.kla-tencor.com), using equipment settings 5 mg stylus load, minimum 4 mm distance, and a speed of 0.5 mm/sec. Modified thermogravimetric test methodology for outgas is conducted by typical laboratory scales (+/−0.1 mg). UV cure equipment includes the Intelli-Ray 400 microprocessor controlled light curing system (www.uvitron.com). Furnace support uses box type #ST-1200C-121216 with microprocessor programming, nitrogen purge, and dispersion fan for chamber uniformity (www.sentrotech.com). Force gage M5-series with 90 degree sled and stand ESM301, fixtures, and software (www.mark-10.com).
(35) Silicon wafers and glass plates (˜0.5 mm thick) are used as the inorganic substrate (carrier substrate) upon which the adhesive is applied, cured, and subsequent affixing of a thin solid material is tested. This material forms the basis for the survey, which the invention is demonstrated. Multiple polymers are tested and described for each example.
Example #1
(36) This experiment demonstrates the use of various Lewis concept acids of the variety carboxylic acid (organic acid) as applied as coatings. Water solubility is tested and thermal resistance is indicated for each material. Most of the acids listed here exhibit dissociation values of ≧1×10.sup.−5 (pK.sub.a≦5). The listing and results are in Table 1.
(37) TABLE-US-00001 TABLE 1 Acidic products of the Lewis acid variety (carboxylic acids) and their results for water and detergency solubility. Materials are dissolved in solvents n,n-dimethylacetamide (DMAC). Water Detergency Softening solubility (KOH based # Coating (acidic) Point (C.) (observed) system) 1 1,4-CHDA HP (CAS# 165 Limited/no Yes 1076-92-7) 2 Sokalan DCS (CAS# 120 Limited/no Yes 686603-87-2) 3 Isophthalic acid 300 Limited/no Yes (CAS# 121-91-5) 4 Terephthalic acid 300 Limited/no Partial (CAS# 100-21-0) 5 P-hydroxybenzoic 213 Limited/no Yes acid (CAS# 99-96-7 6 4-Chlorobenzoic acid 240 Limited/no Yes (CAS# 74-11-3) 7 Fumaric Acid (CAS# 300 Limited/no Partial 110-17-9) 8 Phthalic Acid (CAS# 210 Limited/no Yes 88-99-3)
Example #2
(38) Silicone resin intermediate Dow Corning Z-6018 (www.dowcorning) and siloxane Dynasylan 4148 (www.evonik.com) are mixed to determine detergency effect and effects to reduce outgas. Nanoparticle silica as Aerosil R90 (treated silica, Evonik) is used to further condensation of the silicone. Materials are mixed and applied to glass slides (2″×3″), apply 0.25 g of a 25% solids solution. Materials are cured 130 C, 5 min, and 250 C 15 min. Thermal exposures are tested for outgas as material weight loss. Detergent is a standard KOH based system. The results for de-bond are listed in Table 2.
(39) TABLE-US-00002 TABLE 2 Thermal resistance as outgas weight % loss and detergency for several mixtures of tunable acid coating and adhesive for aqueous detergency removal for a silicone resin/polysiloxane. Additives are reviewed for capability to reduce outgassing. Additive & 250 C. 350 C. 350 C. + Water Detergency # amount 30 min 30 min 30 min Soluble Soluble 1 Base -0- 95.4 88.7 86.0 No Yes additive 2 Acid 93.2 83.6 80.5 No Yes addition 3 Base 94.7 85.4 82.1 No Yes addition 4 Nanosilica 100.1 97.4 96.0 No Yes addition 5 Nanosilica 100.5 97.9 96.3 No Yes addition 6 Nanoalumina 98.8 95.7 94.2 No No add
Example #3
(40) This example tests various additives to an acrylic system that has a carboxylic acid present for detergent soluble coating and adhesive systems. The acrylic is n,n-dimethylacrylamide (Kowa American Company, www.chemical.kowa.com), to which 30% w/w of Joncryl HPD 671 (BASF Corp., www.basf.com), mixed and produce a clear, slightly yellow solution. To this several additives are inserted to the mixture, including: lithium styrene sulfonate (LiSS, TOSOH, www.tosoh.co.jp), polysiloxane methacrylic functional Dynasylan MEMO (Evonik, www.evonik.com), and epoxy as Epon 8021 (Resolution Performance Products, www.resins.com). In all cases, UV cure is conducted with 5% w/w of Irgacure 2022 added to each and exposed for 60 sec. Hard bake/temperature resistance is conducted to 300 C for up to 1 hr. Stress is measured on thin glass slides, 100 um thick, and measure height of bending slide. The additives are stated in Table 3 with concentrations and results.
(41) TABLE-US-00003 TABLE 3 Results of systems as stated to given temperatures after UV cure Stress after Stress @ 300 C. # Chemistry UV 130 C. observe 300 C. 1 hr Deterg 1 Base -0- add 12 15 NC Wet Bubbles, cracks Yes 2 10% LiSS 16 19 delam, Soft Bubbles, cracks Yes crack 3 5% LiSS 5 5 delam, Soft Bubbles, cracks Yes crack 4 1% LiSS 6 4 NC Soft No bubbles Yes 5 2% MEMO 18 18 NC Hard Bubbles, cracks Yes 6 5% MEMO Break - - delam, Hard Bubbles, cracks Yes crack 7 10% MEMO 10 10 delam, Hard Bubbles, cracks No, crack flakes 8 2% EPON 5 9 delam, Hard No bubbles Yes crack 9 5% EPON 17 17 NC Hard No bubbles Yes 10 10% EPON 17 19 NC Hard No bubbles No, flakes
BRIEF DESCRIPTION OF THE FIGURES
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