Method for debonding temporarily adhesive-bonded carrier-workpiece pair by using chemical and mechanical means

In debonding a temporarily adhesive-bonded carrier-workpiece pair by a combination of chemical and mechanical methods, solvents or chemicals are used to remove the adhesives primarily through dissolution, and a thin wire, filament, or blade is used to exert a cutting or wedging action between the carrier and workpiece. The two methods are used together during the debonding process. In the carrier-workpiece pair, the workpiece can be a semiconductor wafer that has been thinned and processed. The carrier and the workpiece are temporarily bonded using an adhesive dissolvable in a selected chemical or solvent. The chemical and mechanical debonding (CMDB) method can be carried out in solvent immersion or in solvent spray to provide high throughput debonding. The dissolved adhesives can be recycled and later reused, thus lowering the cost of the whole bonding and debonding process.

TECHNICAL FIELD

Embodiments of this disclosure relate generally to bonding and debonding of carrier-workpiece pairs. In particular, various embodiments of debonding temprorarily bonded carrier-workpiece pairs by combination of chemical and mechanical methods are described.

BACKGROUND

In many applications, a workpiece needs to be thinned or processed with the support of a carrier to make the workpiece mechanically stable. The workpiece can be temporarily bonded to the carrier using adhesives. At end of the application, the workpiece needs to be debonded or separated from the carrier, and cleaned of any residue adhesives. For example, in semiconductor wafer thinning process, the workpiece can be a semiconductor wafer or device wafer on which thousands of chips are finally made. Widespread applications of smartphones, tablets, and portable consumer electronics are driving semiconductor packaging towards thinner, smaller, and more integrated directions. Wafer-level packaging (WLP) techniques is rapidly reducing the size of packages for easier integration into mobile electronics. The wafer thinning process used in device miniaturization and packaging has attracted more and more attention. Thin wafers offer the benefits of improved heat dissipation, three-dimensional (3D) stacking, reduced resistance, and substrate flexibility. In through silicon via (TSV) based 3D-IC wafer level packaging, wafers need to be thinned to less than 100 microns (μm). The thinning process needs to be high throughput and low cost to be suitable for volume production.

Wafer thinning is primarily achieved by mechanical grinding (back-grinding), polishing, and chemical etching. Thin wafers, especially ultra-thin wafers (thickness less than 60 microns or even 30 microns) are very unstable, and more susceptible to stress than traditional thick wafers. During processing, thin wafers may be easily broken and warped. Therefore, temporary bonding to a rigid support carrier is required. Thinned device wafers need to be supported for use on the backside in grinding process and subsequent processes such as photolithography, etching, plating, vacuum deposition, reactive ion etching, and so on.

SUMMARY

The present disclosure provides a novel method of debonding or separating a temporarily adhesive-bonded carrier-workpiece pair with the use of a combination of chemical and mechanical methods. The method can be used for processing various workpieces of different shapes such as round, rectangle, or square shapes, of different materials such as silicon, gallium arsenide, sapphire, glass, metal, of different thicknesses, in various applications where the workpieces can be optical lenses, semiconductors, liquid crystal displays (LCD), solar panels, and so on. The method is particularly useful for debonding temporarily adhesive-bonded semiconductor wafers in three-dimensional integrated circuit (3D-IC) semiconductor wafer level packaging.

The chemical and mechanical debonding (CMDB) method provided by this disclosure can advantageously enhance process efficiency, simplify procedures, provide high wafer throughput, and reduce or eliminate defects such as device wafer breakage and internal device damage. The method can greatly increase the range of selection of polymeric adhesives for the use of temporary workpiece bonding and debonding. The use of recyclable polymer adhesive such as thermoplastics is of particular benefit as it can greatly lower the overall cost.

In one aspect of the disclosure, a method of debonding a temporarily bonded carrier-workpiece pair comprises exposing the carrier-workpiece pair in an environment containing a chemical solvent capable of dissolving the adhesive, and exerting a cutting or wedging action to the adhesive with a mechanical component to separate the workpiece from the carrier.

The carrier-workpiece pair may be immersed in a chemical solvent capable of dissolving the adhesive. Alternatively, the carrier-workpiece pair may be sprayed with a chemical solvent capable of dissolving the adhesive.

The cutting or wedge action may be exerted with a wire or blade by moving the carrier-workpiece pair and/or the wire or blade relative to each other. The wire or blade may be in reciprocating saw motion during the moving of the carrier-workpiece pair and/or the wire or blade relative to each other.

The wire or blade may be made of a metal, a metal alloy, a metal coated with a polymer, a polymer, a natural product such as fiber, cloth, cotton, or ceramics, or a composite of different materials as long the materials do not damage the surface of the workpiece or carrier. The wire or blade may have a profile of a triangle, a polygon, a circle, an oval, a rectangle, or a square in cross-section transverse the length of the wire or blade or have a profile of a saw tooth in cross-section along a length of the wire or blade.

In another aspect of the disclosure, a method of debonding a temporarily bonded carrier-workpiece pair comprises exerting a cutting or wedging action to the adhesive in the carrier-workpiece pair with a wire or blade, and applying a lubricant to the carrier-workpiece pair while the cutting or wedging action is exerted to the adhesive with the wire or blade. The cutting or wedge action may be exerted with a wire or blade by moving the carrier-workpiece pair and/or the wire or blade relative to each other. The wire or blade may be in reciprocating saw motion during the moving of the carrier-workpiece pair and/or the wire or blade relative to each other. The wire or blade may be made of a metal, a metal alloy, a metal coated with a polymer, a polymer, a natural product such as fiber, cloth, cotton, or ceramics, or a composite of different materials as long the materials do not damage the surface of the workpiece or carrier. The workpiece in the carrier-workpiece pair may be a device wafer having a thickness of less than 100 microns, or less than 60 microns, or less than 30 microns.

This Summary is provided to introduce selected embodiments in a simplified form and is not intended to identify key features or essential characteristics of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. The selected embodiments are presented merely to provide the reader with a brief summary of certain forms the invention might take and are not intended to limit the scope of the invention. Other aspects and embodiments of the disclosure are described in the section of Detailed Description.

DETAILED DESCRIPTION

Various embodiments of methods for debonding temprorarily bonded carrier-workpiece pair are described. It is to be understood that the disclosure is not limited to the particular embodiments described. An aspect described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced in any other embodiments.

Various embodiments are described with reference to the figures. It should be noted that some figures are not necessarily drawn to scale. The figures are only intended to facilitate the description of specific embodiments, and are not intended as an exhaustive description or as a limitation on the scope of the disclosure. Further, in the figures and description, specific details may be set forth in order to provide a thorough understanding of the disclosure. It will be apparent to one of ordinary skill in the art that some of these specific details may not be employed to practice embodiments of the disclosure. In other instances, well known components may not be shown or described in detail in order to avoid unnecessarily obscuring embodiments of the disclosure.

All technical and scientific terms used herein have the meaning as commonly understood by one of ordinary skill in the art unless specifically defined otherwise. As used in the description and appended claims, the singular forms of “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. The term “or” refers to a nonexclusive “or” unless the context clearly dictates otherwise.

As used herein, the terms “temporarily bonded,” “temporary bonding,” and their grammatical equivalents, refer to embodiments where the bonding between a carrier and a workpiece is temporary and will be removed upon completion of one or more processing steps on the workpiece.

FIG. 1schematically illustrates a process100of temporarily bonding and debonding a carrier-workpiece pair according to embodiments of the disclosure. As shown, a carrier102can be coated with an adhesive106at step150. A workpiece104, which may have been applied with a protective layer (not shown), can be temporarily bonded with the adhesive-coated carrier102at step152, forming a temporarily bonded carrier-workpiece pair110. The temporarily bonded carrier-workpiece pair110can be formed by contacting the workpiece104facedown with the adhesive-coated carrier102under vacuum or pressure. The workpiece104, which is supported by the carrier102through the bonding of the adhesive106, can be then thinned and/or further processed from the backside, as shown at step154. Once the thinning and/or other processing are completed, the workpiece104can be debonded, or separated, from the carrier102, as shown at step156. The workpiece104and carrier102can be then cleaned at step158.

The workpiece104can be a semiconductor device wafer, an optical lens, quartz, a sapphire wafer, display glass, an LED crystal, a thin metal plate, a thin membrane, a film, or the like. The workpiece104can be made of silicon, polysilicon, silicon oxide, silicon-germanium, silicon nitride, gallium arsenide, gallium nitride, gallium phosphide, alumina titanium carbide, or silicon carbon. The workpiece104can also be metals such as copper, aluminum, steel, gold, tungsten, tantalum, low K dielectrics, metal nitrides, metal alloys, silicides, and any combination thereof. Indeed, any suitable workpiece made of any materials in any form can be used in the method of this disclosure.

The carrier102can be any suitable carrier that has sufficient mechanical strength. The carrier102can be made of the same material as that of the workpiece104. In semiconductor temporary wafer bonding and debonding process, the carrier102can be made of silicon, glass, etc. During the debonding step156using such as chemical and mechanical debonding method as will be described below, the carrier102can be applied with a certain degree of pulling force to facilitate separation of the carrier from the workpiece.

Suitable adhesives106that can be used in the temporary bonding process include thermoplastic polymers. Polymers of slight crosslinking and still solvable in a solvent may still be used. In some embodiments, thermoplastic polymeric adhesives are preferred because they can be recycled and reused after post debonding reclaim treatment, and therefore the total cost of the whole bonding and debonding process can be greatly reduced. Any suitable polymers can be used so long they meet the specifications as required by the processing conditions such as low outgassing, film uniformity, solubility in solvents, temperature tolerance, etc. The polymers can be polyimides, rubbers, cyclic olefins, polyacrylates, poly methyl methacrylate, polyurethanes, polycarbonates, polyethylene terephthalate, cellulose, polyesters, polystyrenes, epoxies, silicones, polyamides, polysulfones, etc. or combination thereof. Photoresists such as those manufactured by JSR Corporation of Japan and AZ series photoresists manufactured by AZ Electronic Materials (Merck) of Germany can also be used. In some embodiments, the polymers can be used in formulations which contain polymers as binders and other fillers and additives such as antioxidants, plasticizers. In some embodiments, single polymers are preferred for ease of recycling and reuse of the polymers.

The polymeric adhesives106can be applied to the carrier102using spin coating, spray coating, slot coating, knife coating, and other available coating techniques from solutions. The polymeric adhesives106can also be applied in dry film lamination. The adhesives106should form as uniform films as possible. Bonding of a workpiece such as a device wafer to a carrier wafer coated with adhesives can be accomplished with bonders commercially available from e.g. EVG of Austria, Suss MicroTec of Germany, Tokyo Electron Ltd. of Japan, and other companies, or inhouse made bonders. In some embodiments, the thickness of the polymer adhesive coated on the carrier may range from 1 to 500 microns.

The adhesive bonded carrier-workpiece pair110such as a device wafer-carrier wafer pair can be safely subjected to thinning such as back-grinding and chemical-mechanical polishing (CMP). By way of example, a device wafer104may be thinned to have a thickness of less than 100 microns. In some applications, a device wafer104may be thinned to have a thickness of less than 60 microns or even 30 microns. After thinning, other backside processing can be carried out too, such as through silicon via (TSV) formation, etching such as deep reactive-ion etching (DRIE), metal and dielectric deposition, patterning such as photolithography, via etching, plasma ashing, bonding pads, passivating, annealing, and any combinations thereof. After these processes, the device wafer104is ready to be debonded or separated from the carrier wafer102and cleaned of the adhesive.

The debonding step156can be critical. It is desirable that the debonding step is high throughput, defect less, damage less, and cost effective. The present disclosure provides a chemical and mechanical debonding (CMDB) method, which can enhance process efficiency, simplify procedures, provide high wafer throughput, and reduce or eliminate defects such as device wafer breakage and internal device damage. The debonding method provided by the disclosure also greatly increases the range of selection of polymeric adhesives for use in temporary bonding and debonding as a result of solvent use. The use of recyclable thermoplastics is of particular benefit as it can greatly lower the overall cost. The disclosed debonding method allows separation of the workpiece from the carrier and cleaning to be combined into one integrated step to provide high throughput and lower costs.

In accordance with embodiments of the disclosure, a temporarily adhesive-bonded carrier-workpiece pair can be debonded or separated using a combination of chemical and mechanical means. The carrier-workpiece pair temporarily bonded with an adhesive can be exposed in an environment containing a chemical solvent capable of dissolving the adhesive. A mechanical component may exert a cutting or wedging action to the adhesive to separate the workpiece from the carrier. The carrier-workpiece pair temporarily bonded with the adhesive may be exposed to the chemical solvent by immersing the carrier-workpiece pair in the solvent, or by spraying the carrier-workpiece pair with the solvent. The mechanical component can be a wire, filament, or blade with a suitable cross-sectional profile.

In the chemical and mechanical debonding method of the disclosure, the chemical solvent or solvents used can be a single solvent or a combination of several solvents. The selection of solvents may be dictated by the use of polymer adhesives. The selection of a solvent to a particular polymer generally can be based on the “like dissolves like” principal. Solubility parameter is a factor to consider for selection of a solvent or combination of solvent mixtures. The solvent can also be in the form of a formulation. Many of stripping solutions used in the microelectronics industry can be used. Suitable solvents include n-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), ethyl lactate ethyl acetate, butyl acetate, methyl ethyl ketone (MEK), propylene glycol methyl ethylene acetate (PGMEA), acetone, cyclopentenone, tetrahydrofuran (THF), dimethyl acetamide, hydrocarbons, cyclic hydrocarbons, or strippers made of these solvents as main components. Examples of photoresist removers and strippers include AZ100, Technistrip P1316, P1331, NI555, etc. For example, NMP can be used if polyimide type polymer “durimide” made by Fujifilm Holdings Corporation is used as the temporary bonding adhesive. Water-containing solvents (water content between 0 to 100 percent) can also be used for environmental considerations so long they can carry the adhesive away during chemical and mechanical debonding.

In the chemical and mechanical method for debonding a temporarily adhesive-bonded carrier-workpiece pair such as a device wafer-carrier wafer pair, the mechanical mode may dictate the overall speed of debonding. High throughput is desirable for volume production in 3D-IC manufacturing. According to embodiments of the disclosure, the cutting or wedge action can be exerted by a mechanical component such as a thin wire, thin filament, thin blade, or thin saw. The mechanical component or components should be thin so it they do not cause mechanical damage to the workpiece such as the device wafer during debonding. The wire, filament, or blade can be made of synthetic polymers, natural polymers, metals, ceramics, or combination thereof. An example of the mechanical component is a metal wire coated with polymers. Metal wires, filaments, or blades can be made of copper, gold, silver, stainless steel, tungsten, etc. The thickness of the wire, filament, or blade is preferably less than 5 mm, more preferably less than 1 mm. In some preferred embodiments, the outer surface of the wire, filament, or blade is coated with polymers to avoid scratching or damaging of the surfaces of the workpiece and/or the carrier during mechanical movement. When wires, filaments, or blades comprising polymer coatings are used, the polymers should be selected to not affect the chemical solvents for dissolving the adhesive. Examples of polymer wires include dental floss or filaments made of Nylon (polyamide), and Teflon. The wires, filaments, and blades can be made of other polymers such as polypropylene, silk, cotton, and other fluorinated polymers.

FIG. 5shows profiles of exemplary mechanical components in cross-section transverse the length of the mechanical components which can be used in the debonding method according to embodiments of the disclosure. As shown, the wire, filament, blades, or saw may have various suitable profiles in cross-section transverse the length of the components, such as a triangular, polygonal, circular, oval, rectangular, or square shape. Other regular or irregular profiles in cross-section transverse the length of the mechanical component can also be used so long it gives cutting or wedging action to the carrier-workpiece pair without any detrimental effects.

FIG. 6shows profiles of exemplary mechanical components in cross-section along the length of the mechanical components which can be used in the debonding method according to embodiments of the disclosure. As shown, the wire, filament, or blade may have a profile of a saw tooth in cross-section along a length of the component. Other regular or irregular profiles in cross-section along the length of mechanical component may also be used.

The mechanical component such as a wire, filament, or blaze exerts a cutting or wedging action to the adhesive between the carrier and the workpiece as the carrier-workpiece pair and/or the mechanical component move relative to each other. In applications, the mechanical component may be moved towards the stationary carrier-workpiece pair to exert a cutting or wedging action to the adhesive, or the carrier-workpiece pair may be moved towards the stationary mechanical component while exerting a cutting or wedging action to the adhesive. Alternatively, both the carrier-workpiece pair and the mechanical component may be moved simultaneously towards each other to increase the speed of the debonding process. In various embodiments, the mechanical component such as a wire, filament, or blade may be in a reciprocating saw motion during the relative moving of the carrier-workpiece pair and the mechanical component. The moving direction of the mechanical component should be tangential to the surface of the workpiece and/or the carrier to avoid scratching or damaging of the workpiece and/or the carrier.

FIG. 2schematically illustrates a method200of debonding a temporarily bonded carrier-workpiece pair210according to an embodiment of the disclosure. For illustration purpose, the temporarily bonded carrier-workpiece pair210may include a carrier wafer202and a device wafer204temporarily bonded by a layer of an adhesive206. The device wafer204may be a thinned device wafer having a thickness of e.g. less than 100 microns, or less than 60 microns. The carrier wafer202may be made of e.g. silicon, glass, etc. The adhesive206that temporarily bonds the carrier wafer202and the device wafer204may be a thermoplastic polymer.

FIG. 2on the left shows a view of a cross-section of the carrier wafer-device wafer pair210positioned in a horizontal orientation whereas on the right shows a view from the top of the carrier wafer202. As shown, the adhesive-bonded carrier wafer-device wafer pair210may be immersed in a solvent212in a container214, exposing the carrier wafer-device wafer pair210to the solvent212capable of dissolving the adhesive206. A thin wire or blade216, which can be held at the two ends of the wire or blade, can be aimed at the adhesive206between the carrier wafer202and the device wafer204. As the adhesive206is dissolved by the solvent212from the edge, the thin wire or blade216can be caused to move in a direction across or parallel to the surface of the carrier wafer202, as indicated by arrows218. Alternatively, carrier wafer-device wafer pair210may be caused to move against the thin wire or blade216. At the same time, the thin wire or blade216may be moved in a reciprocating saw motion mode, as indicated by arrows220. The reciprocating saw motion may create a turbulent flow during adhesive dissolution by the solvent. This can greatly increase the debonding speed.

FIG. 3schematically illustrates a method300of debonding a temporarily bonded carrier-workpiece pair310according to another embodiment of the disclosure. For illustration purpose, temporarily bonded carrier-workpiece pair310may include a carrier wafer302and device wafer304temporarily bonded by an adhesive306. The device wafer304may be a thinned device wafer having a thickness of e.g. less than 100 microns, or less than 60 microns. The carrier wafer302may be made of e.g. silicon, glass, etc. The adhesive306that temporarily bonds the carrier wafer302and the device wafer304may be a thermoplastic polymer.

FIG. 3on the left shows a view of a cross-section of the carrier wafer-device wafer pair310positioned in a vertical orientation whereas on the right shows a view from the side of the carrier wafer302. As shown, the adhesive-bonded carrier wafer-device wafer pair310is exposed to a solvent spray312capable of dissolving the adhesive306. For example, the solvent spray312may continuously apply to an edge portion of the carrier wafer-device wafer pair310, allowing the adhesive306to be exposed to the solvent. A thin wire or blade316, which can be held at the two ends of the wire or blade, can be aimed at the adhesive306between the carrier wafer302and the device wafer304. As the adhesive306is dissolved by the solvent spray312from the edge portion of the carrier wafer-device wafer pair310, the thin wire or blade316can be caused to move in a direction across or parallel to the surface of the carrier wafer302, as indicated by arrows318. Alternatively, carrier wafer-device wafer pair310may be caused to move against the thin wire or blade316. At the same time, the thin wire or blade316may be applied a reciprocating saw motion to the adhesive, as indicated by arrows320. The reciprocating saw motion may create a turbulent flow during adhesive dissolution by the solvent. This can greatly increase the debonding speed. When solvents are used in a spray mode, the pressure of the solvent spray may range from 0 to 3000 psi. Due to the use of mechanical perturbation or cutting, the solvents can also act as adhesive removers. While the solvent can be sprayed under a high pressure, spraying under high pressure is not required. In some embodiments for environmental considerations, water-containing solvents (water content between 0 to 100 percent) can be used so long they can carry the adhesive away during chemical and mechanical debonding.

FIG. 4schematically illustrates a method of debonding a temporarily bonded carrier-workpiece pair410according to a further embodiment of the disclosure. For illustration purpose, temporarily bonded carrier-workpiece pair410may include a carrier wafer402and a device wafer404temporarily bonded by a layer of adhesive406. The device wafer404may be a thinned device wafer having a thickness of e.g. less than 100 microns, or less than 60 microns. The carrier wafer402may be made of e.g. silicon, glass, etc. The adhesive406that temporarily bonds the carrier wafer402and the device wafer404may be a thermoplastic polymer.

FIG. 4on the left shows a view of a cross-section of the carrier wafer-device wafer pair410positioned in a vertical orientation whereas on the right shows a view from the side of the carrier wafer402. Different from the embodiments shown inFIGS. 2 and 3, in the embodiment shown inFIG. 4, the carrier wafer-device wafer pair410may not be exposed to a chemical solvent capable of dissolving the adhesive. Instead, a lubricant such as water or any other suitable lubricant such as glycerine, mineral oil, or the like may be applied along the edges of the carrier wafer -device wafer pair410. A thin wire or blade416, which can be held at the two ends of the wire or blade, can be aimed at the adhesive406between the carrier wafer402and the device wafer404, and caused to move in a direction across or parallel to the surface of the carrier wafer402, as indicated by arrows418, exerting a cutting or wedging action to the adhesive406. Alternatively, the carrier wafer-device wafer pair410may be caused to move against the thin wire or blade416. At the same time, the thin wire or blade416may be applied a reciprocating saw motion, as indicated by arrows420. During the mechanical mode, a lubricant such as water can be applied to carry the adhesive away or cool down the carrier wafer -device wafer410and/or the thin wire or blade416.

Embodiments of debonding temprorarily bonded carrier-workpiece pairs have been described. Those skilled in the art will appreciate that various other modifications may be made. All these or other variations and modifications are contemplated by the inventors and within the scope of the invention.