Methods for temporarily bonding a device wafer to a carrier wafer, and related assemblies

A method of bonding a device wafer to a carrier wafer includes disposing a first adhesive over a central portion of a carrier wafer, the first adhesive having a first glass transition temperature, disposing a second adhesive over a peripheral portion of the carrier wafer, the second adhesive having a second glass transition temperature greater than the first glass transition temperature, and bonding the first adhesive to an active front side of the device wafer and the second adhesive to a peripheral portion of the front side of the device wafer. Related assemblies may be used in such methods.

TECHNICAL FIELD

Embodiments disclosed herein relate to fabrication of semiconductor devices. More specifically, embodiments disclosed herein relate to methods for temporarily bonding a device wafer to a carrier wafer for backside processing, and to related assemblies comprising a device wafer and carrier wafer.

BACKGROUND

Temporary bonding of a device wafer to a carrier wafer is an act significant to wafer-level processing techniques used in semiconductor manufacturing. The front side, which may also be characterized as the active surface, of a device wafer is bonded to a carrier wafer to support the device wafer and expose the backside of the device wafer for thinning and exposure of conductive vias (commonly termed through-silicon vias (TSVs)) formed through a partial thickness of the device wafer, as well as passivation of the backside of the thinned device wafer and formation of conductive contact pads and, optionally, a redistribution layer (RDL) thereon. After backside processing is complete, the device wafer may be removed from the carrier wafer, diced, and packaged.

Conventionally, a single thermoplastic adhesive is used for temporarily bonding the device wafer to the carrier wafer.FIGS. 1A through 1Eillustrate a conventional temporary bonding process flow.FIG. 1Ashows a device wafer100and a carrier wafer102with a layer of thermoplastic adhesive104disposed (e.g., spin coated) on a surface thereof. The thickness of the layer of adhesive104may be chosen based on, for example, the topography of an active surface105of the device wafer100. Conventionally, the adhesive104is disposed to a thickness of between about 5 microns and 150 microns. As an example of a conventional device wafer configuration, the device wafer100may be substantially disc-shaped, and may be about 300 mm in diameter and have an initial thickness of about 750 microns. The device wafer100includes a plurality of in-process semiconductor devices, such as semiconductor memory, logic or processor dice, on the active surface105of the device wafer100facing the carrier wafer102. The carrier wafer102is of a similar shape and size to the device wafer100. One conventional thermoplastic adhesive material that has been used for adhesive104is WAFERBOND® HT-10.10, commercially available from Brewer Science, Inc., Rolla, Mo. After application of adhesive104, carrier wafer102with the layer of adhesive104is baked to remove solvents from the adhesive104, e.g., solvents within the as-applied adhesive that facilitate application of the adhesive.

Referring now toFIG. 1B, the device wafer100and the adhesive-coated carrier wafer102are bonded together by applying heat and pressure. For example, the device wafer100and the adhesive-coated carrier wafer102may be mechanically pressed together under elevated temperature conditions sufficient to soften the adhesive layer104and promote adhesion between the device wafer100and the carrier wafer102. The temperature conditions during bonding may be chosen to approach or exceed a glass transition temperature (Tg) of the thermoplastic adhesive material of the adhesive layer104. A portion of the softened adhesive104may squeeze out around a periphery of an interface106between the device wafer100and the carrier wafer102during bonding. Excess adhesive around the periphery of the interface106is removed, e.g., by dissolving the excess adhesive with a solvent.

A backside108of the device wafer100is thinned by a process such as abrasive grinding and/or chemical-mechanical polishing with or without dry etching. The thinning process may reduce the thickness of the device wafer100from an initial thickness of, for example, approximately 750 microns to a thickness of, for example, about 50 microns or less. As noted above, the thinning process may expose ends of conductive vias in the device wafer100on the backside108of the thinned device wafer100. Passivation and formation of contact pads110(shown inFIG. 1C), with or without a redistribution layer (RDL) may follow thinning.

Referring now toFIG. 1D, after thinning and backside processing, the device wafer100may be removed from the carrier wafer102by heating the polymer adhesive104(FIG. 1A) and applying a shear force in direction112(i.e., a force generally parallel to the plane of the interface106(FIG. 1B) between the device wafer100and the carrier wafer102). Heat-induced softening of the adhesive104enables the device wafer100to be slid off of the carrier wafer102. A solvent may be used to clean (i.e., remove) residual adhesive from the device wafer100, and the device wafer100may then be mounted on a film frame support system114.

As shown inFIG. 1E, the device wafer100, after being mounted on the film frame support system114, may be separated, or “singulated,” into individual dice116. The individual dice may then be subsequently packaged or assembled with other dice and packaged to form a semiconductor device or integrated device.

Thermal cycles occurring during processing that take place while the device wafer100is bonded to the carrier wafer102may cause the adhesive104to soften, compromising the adhesion between the device wafer100and the carrier wafer102. Furthermore, differing rates of thermal expansion between the wafer material and metallic features, such as TSVs, of the device wafer100, and differing rates of thermal expansion between the wafer material and the adhesives may lead to warping of the bonded stack (i.e., the device wafer100and the carrier wafer102bonded by the adhesive104) during thermal cycles. During processing, portions of the device wafer100may become non-parallel to the carrier wafer102. For example, peripheral edges of the device wafer100may lift away (e.g., lose adhesion) from the carrier wafer102. Areas of the device wafer100that lift away from the carrier wafer102may be thinned too much or non-uniformly during the thinning process, impacting the ability to use dice subsequently singulated from the device wafer100for three-dimensional integration in the form of stacked die assemblies. Lifting of edges of the device wafer100may also cause the device wafer100to crack or chip and may lead to loss of dice or of an entire device wafer100, significantly reducing yield.

Moreover, adhesive material104that flows from the interface106between the device wafer100and the carrier wafer102may contaminate equipment used for backside processing, leading to costly downtime while the equipment is cleaned.

One other approach to temporary bonding of device wafers and carrier wafers is disclosed in United States Patent App. Pub. No. 2011/0308739 to McCutcheon et al. McCutcheon et al. disclose the use of two different materials in a temporary wafer bonding process.

DETAILED DESCRIPTION

The illustrations included herewith are not meant to be actual views of any particular methods or devices, but are merely idealized representations that are employed to describe embodiments described herein. Elements and features common between figures may retain the same numerical designation except that, for ease of following the description, for the most part, reference numerals begin with the number of the drawing on which the elements are introduced or most fully discussed.

The following description provides specific details, such as material types, material thicknesses, and processing conditions in order to provide a thorough description of embodiments described herein. However, a person of ordinary skill in the art will understand that the embodiments disclosed herein may be practiced without employing these specific details. Indeed, the embodiments may be practiced in conjunction with conventional fabrication techniques employed in the semiconductor industry.

With reference now toFIG. 2, a carrier wafer200including an adhesive202according to the present disclosure is shown. The adhesive202may include a first adhesive204disposed over a central region of the carrier wafer200and a second adhesive208disposed over a peripheral region of the carrier wafer200. The first adhesive204may be a thermoplastic adhesive with a glass transition temperature (Tg) of less than or equal to about two hundred degrees Celsius (200° C.). The first adhesive204may have a shear modulus in the range of 1e5 Pascals (Pa) at the Tg. As a non-limiting example, the first adhesive may be WAFERBOND® HT-10.10 available from Brewer Science, Inc. of Rolla, Mo. Other suitable materials for the first adhesive may include, for example, WAFERBOND® HT-20.20, also available from Brewer Science, Inc., and TA13018A, likewise available from Brewer Science, Inc.

The second adhesive208may be a thermoplastic material with a Tghigher than the Tgof the first adhesive material204. For example, the second adhesive208may have a Tgof about fifteen degrees Celsius (15° C.), or more, higher than the Tgof the first adhesive204. As a non-limiting example, the Tgof the second adhesive208may be between about fifteen degrees Celsius (15° C.) and about twenty-five degrees Celsius (25° C.) greater than the Tgof the first adhesive204. Suitable materials for the second adhesive208may include, without limitation, 9001A, available from Brewer Science, Inc., TA7000M available from Shin Etsu, Tokyo, Japan, or other adhesive materials having the desired characteristics.

Since the second adhesive208has a higher Tgthan the first adhesive204, the second adhesive208may be used to function as a dam around an outer periphery of the carrier wafer200, preventing flow and seepage of the first adhesive204from an interface between a device wafer and carrier wafer200under elevated temperatures encountered during processing of a device wafer bonded to carrier wafer200.

The first adhesive204may be chosen in part based on a desired device feature density and topography of a device wafer to which the carrier wafer200is intended to be bonded. For example, a relatively lower viscosity adhesive may be suitable for a device wafer with a relatively higher feature density or higher topography, as the relatively lower viscosity adhesive may more easily wet and fill the fine features of the semiconductor device wafer.

The first adhesive204and the second adhesive208may be disposed to a thickness of, for example, between about fifty (50) microns and about one hundred fifty (150) microns. As a further non-limiting example, the first adhesive204and the second adhesive208may be disposed to a thickness of between about ninety (90) microns and about one hundred (100) microns. The first adhesive204may be formed on the carrier wafer200by conventional techniques, such as by spin coating, dry film lamination, or spray coating. The second adhesive208may be formed on the outer periphery of the carrier wafer200by conventional techniques, such as spraying, dispensing from a tip dispensing device, e.g., a syringe, or by other methods.

The carrier wafer200may have a substantially circular shape. As a non-limiting example, the carrier wafer200may have a diameter of about three hundred (300) mm and an initial thickness of about six hundred fifty (650) microns.

Now referring toFIGS. 3A through 3I, a process flow according to an embodiment of the present disclosure for temporarily bonding a device wafer to a carrier wafer is shown and described.FIG. 3Ashows a cross-sectional view of a portion of a carrier wafer300. The carrier wafer300includes a bonding surface302with a central portion304and a peripheral portion306adjacent a peripheral edge308of the carrier wafer300. As shown inFIG. 3B, a first adhesive310may be applied to the bonding surface302of the carrier wafer300. The carrier wafer300is shown coated with the first adhesive310. The first adhesive310may be chosen from the materials discussed above with reference to first adhesive204(FIG. 2), or other suitable materials. The first adhesive310may be disposed over substantially the entire bonding surface302, i.e., the first adhesive310may be disposed over the central portion304of the bonding surface302and the peripheral portion306of the bonding surface302. As a non-limiting example, the first adhesive310may be disposed on the bonding surface302by spin coating. Surface tension within the first adhesive310may result in formation of a bead (i.e., a meniscus)312adjacent the peripheral edge308of the carrier wafer300.

A portion of the first adhesive310may be removed from the peripheral portion306of the carrier wafer300, as shown inFIG. 3C. The portion of the first adhesive310removed from the peripheral portion306of the carrier wafer300may include at least a portion of the bead312. For example,FIG. 3Cshows the carrier wafer300after the portion of the first adhesive310has been removed. As a non-limiting example, the first adhesive310may be removed from an area extending from the peripheral edge308inward toward the central portion304(i.e., radially inward) up to about twenty (20) mm. In other embodiments, the first adhesive310may be removed from an area extending from the peripheral edge308inward toward the central portion304more than about twenty (20) mm. That portion of the first adhesive310may be removed by, e.g., dissolving the first adhesive310in a solvent or other edge bead removal process (e.g., dry etch, mechanical abrasion, or other). One example of a suitable solvent for removing WAFERBOND® HT-10.10 adhesive may be dodecene. Other solvents may also be suitable depending on the material used as the first adhesive310. Alternatively or additionally, the first adhesive310may be removed mechanically.

Alternatively, the first adhesive310may be disposed over the central portion304of the carrier wafer300such that the peripheral portion306remains uncoated with the first adhesive310. For example, a spin coating process may be tailored by adjusting, e.g., adhesive volume and spin parameters, to dispose the first adhesive310over the central portion304of the carrier wafer300while leaving the peripheral portion306uncoated, substantially as depicted inFIG. 3C.

Referring now toFIG. 3D, a second adhesive314may be disposed on the peripheral portion306of the carrier wafer300. The second adhesive314may be chosen from the materials discussed above with reference to the second adhesive208(FIG. 2), or other suitable materials. As a non-limiting example, the second adhesive314may be disposed over the area of the peripheral portion306of the carrier wafer300from which the first adhesive310has been removed. A secondary bead316of the first adhesive310may form adjacent an outer edge318of the first adhesive310, e.g., as a result of surface tension within the first adhesive310. The second adhesive314may be disposed on the peripheral portion306by spraying, dispensing from a tip dispensing device such as a syringe, or by other methods.

The second adhesive314may be placed to leave a gap320between the first adhesive310and the second adhesive314, i.e., such that the first adhesive310and the second adhesive314do not contact one another. A width w of the gap320may be selected based on the size of the secondary bead316, the thickness of the first adhesive310, or other factors, and will be discussed further below in connection withFIG. 3G.

A portion of the second adhesive314may be removed from the peripheral portion306of the carrier wafer300. For example, as shown inFIG. 3E, a portion of the second adhesive314may be removed from the peripheral portion306of the carrier wafer300. As a non-limiting example, a portion of the second adhesive314may be removed to expose an area of the bonding surface302extending from the peripheral edge308inward toward the central portion304(i.e., radially inward) about three hundred micrometers (300 μm) to three millimeters (3 mm). The portion of the second adhesive314may be removed, for example, using a solvent, e.g., dodecene, p-Methane, PGMEA, or another suitable solvent.

Following removal of a portion of the second adhesive314, the carrier wafer300may be heated, e.g., baked, to remove undesirable residual solvents, e.g., solvents that may have been used to facilitate application of the adhesives, and/or solvents used to remove portions of the first adhesive310and the second adhesive314. Baking time and temperature may depend on the type and amount of the residual solvents.

Referring now toFIG. 3F, a device wafer324may be aligned with the carrier wafer300. The device wafer324includes a front side325(the front side325may also be characterized as an active side) with an active surface326and a peripheral area328having a surface from and parallel to front side325, with a reduced thickness relative to a thickness of the device wafer324at the active surface326. The active surface326may include active semiconductor components, for example and without limitation, memory or logic circuitry at die locations on the active surface326. The device wafer324may have a first thickness T1from a backside surface332to the active surface326, and a second thickness T2from the backside surface332to the peripheral area328of the front side325. Such a configuration of the device wafer324may be referred to in the industry as a “device edge trim.” As non-limiting examples, the device wafer324may be substantially circular and have a diameter of about 300 mm, and the first thickness T1may be about seven hundred fifty (750) microns. As a further non-limiting example, the second thickness T2may be about one hundred (100) microns less than the first thickness T1.

The device wafer324may be bonded to the carrier wafer300under heat and pressure. For example, the device wafer324may be concentrically aligned with the carrier wafer300by conventional techniques, and the device wafer324and the carrier wafer300may be placed in a mechanical press and pressed together under elevated temperature conditions, such as at a temperature about equal to the Tgof the second adhesive314but higher than the Tgof the first adhesive310. As a non-limiting example, the temperature may be raised to at least about one hundred fifty degrees Celsius (150° C.), and the device wafer324and the carrier wafer300may be pressed together under at least about eight (8) kN up to about thirty (30) kN of force for about two (2) minutes. Bonding conditions of time, temperature, and force may be optimized for viscous interface conditions that depend upon melt viscosity of the first adhesive310and the second adhesive314at the bond temperature and the density and topology of the device architecture. As the device wafer324and the carrier wafer300are pressed together under the elevated temperature conditions, the first adhesive310melts and flows to fill and protect the topography of active surface326of device wafer324while bonding the active surface326to carrier wafer300, while the second adhesive314may soften without excessive flow (i.e., seepage), bonding the carrier wafer300to the peripheral area328of the device wafer324and in some embodiments to lateral surface336extending from active surface326to peripheral area328. Under these conditions, the adhesive material within the secondary bead316(FIG. 3D) may flow and fill the gap320(FIG. 3D) between the first adhesive310and the second adhesive314as the available volume between device wafer324and carrier wafer300decreases. The active surface326of the device wafer324after bonding is substantially parallel to the bonding surface302of the carrier wafer300and the first adhesive310is substantially evenly distributed between the bonding surface302of the carrier wafer300and the active surface326of the device wafer324, as shown inFIG. 3G. As also shown inFIG. 3G, the softened, higher glass transition temperature second adhesive314may bond to a peripheral portion of the device wafer324. For example, the second adhesive314may bond to at least a portion of the peripheral area328and to a peripheral portion of the active surface326of the device wafer324to form a dam structure containing the first adhesive310between carrier wafer300and device wafer324. The second adhesive314may not tend to lift the peripheral area328of device wafer324, as the outer boundary of second adhesive314is unconstrained and allows peripheral expansion of the second adhesive314as device wafer324and carrier wafer300are pressed together.

Referring now toFIG. 3H, material may be removed from the backside surface332of the device wafer324. For example, the backside surface332may be subjected to a thinning process, such as abrasive grinding, chemical-mechanical polishing, wet etch, or combinations thereof. A thickness of material equal to or greater than the thickness T2(FIG. 3F) may be removed from the backside surface332of the device wafer324. In other words, the backside surface332may be thinned to the extent that the peripheral area328(FIG. 3F) of the device wafer324is completely removed, leaving only a portion of the device wafer324including the active surface326, as shown inFIG. 3H.

Referring now toFIG. 3I, after thinning of the backside surface332, excess second adhesive material314may be removed as described above (e.g., by application of a solvent) to leave a relatively small portion334of the second adhesive314extending between the bonding surface302of the carrier wafer300and the active surface326of the device wafer324, as shown inFIG. 3I.

When backside processing of the device wafer324is complete, the device wafer324may be debonded from the carrier wafer300by heating to a temperature above the Tgof the first adhesive310where the shear modulus of the first adhesive310is less than or equal to about 1e5 Pa. to reduce the adhesive bond between device wafer324and carrier wafer300. A mechanical shear force may be applied substantially parallel to the bonding surface302and the active surface326of the device wafer324to slide the carrier wafer300and the device wafer324apart. Because the remaining small portion334of second adhesive314only bonds to a small area at the periphery of carrier wafer300and the active surface326of the device wafer324, the cumulative bonding strength (i.e., the total bonding strength over the entire bonding area) of the second adhesive314may be negligible compared to the cumulative bonding strength of the heated, melted first adhesive310. Thus, the force and temperature utilized to debond the device wafer324from the carrier wafer300using methods of the present disclosure may be similar to that utilized for debonding when only a single adhesive is used, e.g., a process flow similar to that described above in connection withFIGS. 1A through 1E.

The higher Tgof the second adhesive material314relative to the first adhesive material310may enable the second adhesive material314to maintain its integrity during backside processing acts that involve relatively high temperature (e.g., in excess of about 200° C.) thermal cycles. The portion334of the second adhesive314may prevent the first adhesive310from flowing from between the carrier wafer300and the device wafer324under elevated temperatures during backside processing. Eliminating the flow may protect the active surface326of the device wafer324from adhesive squeeze out (i.e., seepage) and contamination during thinning and backside processing acts.

Moreover, adhesive forces between the second adhesive314, the device wafer324, and the bonding surface302of the carrier wafer300may prevent heat-induced warping in the device wafer324from causing a peripheral edge of the device wafer324to lift away from the bonding surface302of the carrier wafer300. During the thinning and backside processing, the second adhesive314may provide sufficient adhesion between the device wafer324and the carrier wafer300at temperatures that reduce the adhesive strength of first adhesive310to reduce or prevent such warping. The disclosed methods may provide increases in thickness uniformity of the thinned device wafer324, prevent crack formation in the device wafer324, and increase yields by a reduction in edge die loss.

The disclosure includes a method of bonding a device wafer to a carrier wafer, the method comprising disposing a first adhesive having a glass transition temperature over a central portion of a carrier wafer. A second adhesive having a glass transition temperature greater than the first glass transition temperature is disposed over a peripheral portion of the carrier wafer. The first adhesive is bonded to at least a portion of a front side of a device wafer and the second adhesive is bonded to a peripheral portion of the front side of the device wafer and to a portion of an active surface of the device wafer.

The disclosure also includes a method of bonding a device wafer to a carrier wafer, the method comprising disposing a first adhesive with a first glass transition temperature over the carrier wafer. The first adhesive is removed from a peripheral portion of the carrier wafer, and a second adhesive with a second glass transition temperature higher than the first glass transition temperature is disposed over the peripheral portion of the carrier wafer. The first adhesive is bonded to a central portion of a device wafer and the second adhesive is bonded to a peripheral portion of the device wafer.

Referring now toFIGS. 4A through 4F, another process flow for bonding a device wafer to a carrier wafer according to an embodiment of the disclosure is shown and described. InFIG. 4A, a carrier wafer400including a bonding surface402is shown. The carrier wafer400may be similar to the carrier wafer300described above in connection withFIGS. 3A through 3I.

Referring now toFIG. 4B, a second adhesive314may be applied to a peripheral portion406of the bonding surface402of the carrier wafer400. The second adhesive314may be applied by, for example, spraying, dispensing from a tip dispensing device such as a syringe, or by other methods. The second adhesive314may be selected as described above in connection withFIGS. 3A through 3I. The area of the peripheral portion406over which the second adhesive314is disposed may extend from adjacent a peripheral edge408inward toward a central portion404of the bonding surface402, for example, up to about twenty (20) mm inward from the peripheral edge408(i.e., radially inward). In other embodiments, the area of the peripheral portion406over which the second adhesive314is disposed may extend from adjacent a peripheral edge408inward toward a central portion404of the bonding surface402by more than about twenty (20) mm. As a non-limiting example, the second adhesive314may be disposed to a thickness of between about fifty (50) to one hundred fifty (150) microns.

Referring now toFIG. 4C, a first adhesive310may be disposed over substantially the entire bonding surface402of the carrier wafer400, including the peripheral portion406over which the second adhesive314is disposed. The first adhesive310may be a material as described in connection withFIGS. 3A through 3Iand may be applied to the carrier wafer400by conventional techniques, such as by spin coating.

As shown inFIG. 4D, an excess portion of the first adhesive310and the second adhesive314may be removed from the bonding surface402of the carrier wafer400. For example, the first adhesive310and the second adhesive314may be dissolved by a solvent, such as dodecene, to leave an outermost area412of the bonding surface402substantially free of the first adhesive310and the second adhesive314.

As shown inFIGS. 4E and 4F, a device wafer424similar to the device wafer324described in connection withFIGS. 3A through 3Imay be bonded to the carrier wafer400in a manner similar to that described with reference toFIGS. 3F and 3G. Remaining process acts, such as thinning a backside surface432and removing excess of the second adhesive314, may be carried out in a manner similar to that described with reference toFIGS. 3H and 3I. The device wafer424may be debonded from the carrier wafer400in a manner similar to that previously described.

The disclosure includes a method of bonding a device wafer to a carrier wafer, the method comprising disposing an adhesive having a first glass transition temperature over a peripheral area of the carrier wafer. Another adhesive having a second glass transition temperature lower than the first glass transition temperature is disposed over the carrier wafer and the adhesive having a first glass transition temperature. A portion of the adhesive having a first glass transition temperature and a portion of the another adhesive having a second glass transition temperature is removed from the peripheral area of the carrier wafer. The adhesive having a first glass transition temperature and the another adhesive having a second glass transition temperature are bonded to a device wafer.

The area of the carrier wafer over which the second adhesive is disposed may be chosen to provide a particular desired bond strength at the periphery of the device wafer. In some embodiments, the second adhesive may be disposed over an area of the carrier wafer such that a greater portion of the second adhesive is disposed between the active surface of the front side of the device wafer and the carrier wafer compared to the embodiments ofFIGS. 3A through 3I and 4A through 4F. For example, the method shown inFIGS. 5A through 5Cmay be similar to the methods shown inFIGS. 3A through 3I and 4A through 4F, but the second adhesive may be disposed over a wider area, such that a greater portion of the second adhesive is disposed between the carrier wafer and an active surface of the device wafer.

Referring now toFIG. 5A, in an additional embodiment, the second adhesive314may be disposed over a peripheral portion506of a bonding surface502of a carrier wafer500such that the second adhesive314bonds to a peripheral area508of an active surface526of a device wafer524. The second adhesive314may extend a distance d inward toward a central portion504of the carrier wafer500(i.e., radially inward) from a lateral surface534surrounding the active surface526of the device wafer524. As non-limiting examples, the distance d may be between about four millimeters (4 mm) and about twenty millimeters (20 mm).

As shown inFIG. 5B, the device wafer524may be thinned as described above in connection withFIG. 3H. Following thinning, an excess portion510of the second adhesive314may be removed to leave an outermost area512of the bonding surface502substantially free of the second adhesive, as shown inFIG. 5C.

In the embodiment ofFIGS. 5A-5C, the second adhesive314disposed between the active surface526of the device wafer524and the bonding surface502of the carrier wafer500over the peripheral distance d (FIG. 5A) may provide increased bond strength adjacent the lateral surface534of the device wafer524compared to the configurations shown and described inFIGS. 3A through 3IandFIGS. 4A through 4F. Such increased bond strength may be desirable when the device wafer524is particularly prone to heat-induced warping. For example, a device wafer524with a relatively high density of features on the active surface526may be more prone to warping than a device wafer with a relatively lower feature density. The peripheral distance d, and thus the area over which the second adhesive314acts to bond the active surface526to the bonding surface502, may be chosen based on the propensity of the device wafer524to warp during heat cycles. For example, a relatively greater peripheral distance d may be chosen for an application involving a wafer device more prone to edge peeling due to heat-induced warping than would be chosen for an application involving a wafer device less prone to such edge peeling. Tailoring the peripheral width and strength of the second adhesive314to the properties of a device wafer affecting its tendency to warp enables effective device wafer warpage management through selective bond strength. In addition, second adhesive314may be tailored with respect to its function as a dam structure in terms of a slightly higher thermal stability in terms of higher melt viscosity to preclude seepage of first adhesive310.

Further, first adhesive310may be optimized to provide interface properties between a device wafer and a carrier wafer with respect to topography and conductive elements (e.g., solder bumps) combined with favorable debonding parameters such as debonding temperature and device wafer slide speed.

Superior adhesion of the device wafer to the carrier wafer by using a two (inner and outer) zone adhesive bonding approach device may eliminate wafer edge chipping, device wafer delamination, crack formation, and loss of die. Overall thickness uniformity of the thinned device wafer is increased, increasing yield by reducing edge die loss. Other processing steps may also be simplified since the incoming device wafer/carrier wafer stack is flat. As a non-limiting example, abrasive processing, such as CMP processing, and device wafer backside plating each benefit from flat, well-adhered device wafer/carrier wafer stacks.

The disclosure includes a method of bonding a device wafer to a carrier wafer, the method comprising disposing a first adhesive having a first glass transition temperature over a portion of the carrier wafer. A second adhesive having a second glass transition temperature is disposed over a portion of the carrier wafer. The first adhesive is bonded to a central portion of an active surface of a device wafer, and the second adhesive is bonded to a peripheral portion of the active surface of the device wafer.

The disclosure also includes an assembly including a carrier wafer and a device wafer having an active surface facing the carrier wafer. A first thermoplastic adhesive material is between the carrier wafer and the device wafer. A second thermoplastic material exhibiting a higher glass transition temperature than a glass transition temperature exhibited by the first thermoplastic adhesive material peripherally surrounds the first adhesive material between the carrier wafer and the device wafer.