Abstract:
Methods for releasing a device substrate temporarily bonded by a bonding layer to a carrier substrate. A dissolution head is engaged with the carrier substrate and a first dissolution process is performed to partially remove the bonding layer. After the first dissolution process is completed, the dissolution head is disengaged from the carrier substrate, and then re-engaged with the carrier substrate. In response to re-engaging the dissolution head with the carrier substrate, a second dissolution process is performed to further remove the bonding layer remaining after the first dissolution process.

Description:
BACKGROUND 
       [0001]    The invention generally relates to semiconductor manufacturing and, more particularly, relates to methods for debonding a device substrate from a carrier substrate. 
         [0002]    Wafer thinning has been driven by the need to make packages thinner to allow for stacking and high density packaging of chips, and in conjunction with the fabrication of through silicon vias used in stacking. Once thinned, the backside of a device substrate may be subjected to additional operations. To lend mechanical support to the device substrate during thinning and to the thinned device substrate after thinning, the surface of the device substrate bearing the integrated circuits may be adhesively bonded in a temporary manner to a carrier substrate. After the device substrate has been processed in its bonded condition, the substrates are separated by a debonding process. One approach for debonding the device substrate from the carrier substrate relies on a liquid chemical agent, such as a solvent, to dissolve the adhesive temporarily bonding the substrates together. 
         [0003]    Improved methods are needed for debonding a device substrate from a carrier substrate. 
       SUMMARY 
       [0004]    In an embodiment of the invention, a method is provided for releasing a device substrate temporarily bonded by a bonding layer to a carrier substrate. A dissolution head is engaged with the carrier substrate and a first dissolution process is performed to partially remove the bonding layer. After the first dissolution process is completed, the dissolution head is disengaged from the carrier substrate, and then re-engaged with the carrier substrate. In response to re-engaging the dissolution head with the carrier substrate, a second dissolution process is performed to further remove the bonding layer remaining after the first dissolution process. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0005]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various embodiments of the invention and, together with a general description of the invention given above and the detailed description of the embodiments given below, serve to explain the embodiments of the invention. 
           [0006]      FIG. 1  is a cross-sectional view of a head being used in accordance with an embodiment of the invention to dissolve an adhesive layer bonding a device wafer to a carrier wafer. 
           [0007]      FIG. 2  is a diagrammatic view of a control system for controlling the debonder to utilize the head in the removal of the adhesive layer. 
           [0008]      FIG. 3  is a cross-sectional view similar to  FIG. 1  in which the adhesive layer is partially removed and the head is separated from the carrier wafer. 
           [0009]      FIG. 4  is flow chart illustrating a debonding process in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    With reference to  FIG. 1  and in accordance with an embodiment of the invention, a device substrate  10  is temporarily bonded to a carrier substrate  12  by a bonding layer  14 . The carrier substrate  12  may be temporarily bonded by the bonding layer  14  to the device substrate  10 . The carrier substrate  12  operates as a support plate to ensure reliable handling and mechanical support when processing the device substrate  10  under circumstances in which, for example, the device substrate  10  is either thin or flexible. The substrates  10 ,  12  may have similar geometrical shapes (e.g., round) and may have perimeters (e.g., outer diameters) of similar dimensions. 
         [0011]    The device substrate  10  may be comprised of a silicon wafer or another material suitable for the fabrication of an integrated circuit, display, etc. A front surface  10   a  of the device substrate  10  is processed by device fabrication to form, for example, one or more integrated circuits. The carrier substrate  12  may be comprised of a material such as silicon, glass, sapphire, quartz, metal, etc. The material comprising the carrier substrate  12  may have mechanical and thermal properties similar to those of the material comprising the device substrate  10 . For example, the materials for the substrates  10 ,  12  may be chosen to have approximately equivalent coefficients of thermal expansion. The thickness of the carrier substrate  12  may be greater than the thickness of the device substrate  10  to provide mechanical support or lend additional mechanical robustness to the device substrate  10 . 
         [0012]    The bonding layer  14  may be comprised of a polymeric adhesive that is used to adhesively bond the substrates  10 ,  12 . The polymeric adhesive may be a silicone, a polyimide, an acrylate, or another type of polymer, and may be applied by spin coating or spray coating from solution. The device substrate  10  is temporarily bonded to the carrier substrate  12  by the bonding layer  14  such that the device substrate  10  can be easily released without damaging the device substrate  10  or its devices. The bonding layer  14  may have a thickness equal to several microns. The processed front surface  10   a  of the device substrate  10  faces the bonding layer  14 , and the unprocessed back surface  10   b  of the device substrate  10  is accessible for further processing, such as thinning. 
         [0013]    The device substrate  10  may be safely handled and subjected to further processing of the back surface  10   b  that might otherwise have damaged the device substrate  10  in the absence of being bonded to carrier substrate  12 . Thus, the assembly of the composite structure may be safely subjected to backside processing of the back surface  10   b,  such as backgrinding, chemical mechanical polishing, etching, metal and dielectric deposition, patterning (e.g., photolithography and etching), cleaning, etc., without causing separation of the temporarily-bonded substrates  10 ,  12 . For example, backgrinding may be accomplished with mechanical grinding by a multiple-step process involving coarse and fine grinding. The device substrate  10  is thinned to a reduced thickness that is less than its initial thickness when the integrated circuits were fabricated on its front surface  10   a.  For example, the device substrate  10  may be thinned by the processing to a thickness of less than 100 microns, which renders the device wafer extremely fragile. The carrier substrate  12  provides support over the full dimensions of the device substrate  10  to prevent cracking and breakage so that the bonded assembly can be handled in processing tools and cassettes. The bonding layer  14  has a bonding strength to the substrates  10 ,  12  that prevents separation during backside processing. 
         [0014]    After the backside processing of the back surface  10   b  of the device substrate  10  is completed, the device substrate  10  is subsequently removed, or debonded, from the carrier substrate  12  so that the device substrate  10  is separated from the carrier substrate  12 . Debonding may rely on a chemical process using a liquid chemical agent that dissolves or decomposes the material of the bonding layer  14  to provide release. To promote the debonding, the carrier substrate  12  is perforated with passageways  18  that permit the liquid chemical agent to contact the material of the bonding layer  14  and to speed the debonding process using the liquid chemical agent. 
         [0015]    With reference to  FIGS. 1 and 2 , a debonder  20  includes a dissolution head  22 , a vibrator  24 , a motion system  25 , a suction source  27 , a liquid chemical agent source  28 , and a controller  26  coupled with the dissolution head  22 , vibrator  24 , motion system  25 , suction source  27 , and liquid chemical agent source  28 . The debonder  20  may comprise a semi-automated system configured to debond the device substrate  10  from the carrier substrate  12 . The liquid chemical agent source  28  is configured to supply amounts of fresh liquid chemical agent to the dissolution head  22 . The liquid chemical agent may comprise a solvent such as limonene, dodecene, an alcohol, or propylene glycol monomethyl ether (PGME), that is selected to dissolve and/or decompose the material of the bonding layer  14 . In other words, the material of the bonding layer should be susceptible to being removed by the liquid chemical agent. 
         [0016]    The controller  26  may be implemented on one or more computing devices or systems (collectively referred to herein as a computer), such as computer  30 . The computer  30  may include at least one processor  32 , a memory  34 , a mass storage memory device  36 , an input/output (I/O) interface  38 , and a Human Machine Interface (HMI)  40 . The computer  30  may also be operatively coupled to one or more external resources via a network and/or the I/O interface  38 . External resources may include, but are not limited to, servers, databases, mass storage devices, peripheral devices, cloud-based network services, or any other suitable computing resource that may be used by the computer  30 . 
         [0017]    The processor  32  may include one or more devices selected from microprocessors, micro-controllers, digital signal processors, microcomputers, central processing units, field programmable gate arrays, programmable logic devices, state machines, logic circuits, analog circuits, digital circuits, or any other device that manipulates signals (analog or digital) based on operational instructions that are stored in the memory  34 . The memory  34  may include a single memory device or a plurality of memory devices including, but not limited to, read-only memory (ROM), random access memory (RAM), volatile memory, non-volatile memory, static random access memory (SRAM), dynamic random access memory (DRAM), flash memory, cache memory, or any other device capable of storing data. The mass storage memory device  36  may include data storage devices such as a hard drive, optical drive, tape drive, non-volatile solid state device, or any other device capable of storing data. 
         [0018]    The processor  32  may operate under the control of an operating system  46  that resides in the memory  34 . The operating system  46  may manage computing resources so that computer program code embodied as one or more computer software applications, such as an application  48  resident in the memory  34 , may have its instructions executed by the processor  32 . Alternatively, the processor  32  may execute the application  48  directly, in which circumstance the operating system  46  may be omitted. One or more data structures  42  may also reside in the memory  34 , and may be used by the processor  32 , operating system  46 , or application  48  to store or manipulate data. 
         [0019]    The I/O interface  38  may provide a machine interface that operatively couples the processor  32  to the hardware used by the debonder  20  to perform a debonding procedure to separate the substrates  10 ,  12 . The application  48  may thereby work cooperatively with the debonder hardware by communications over the I/O interface  38  to provide the various features, functions, or processes comprising embodiments of the invention. The application  48  may also have program code that is executed by one or more external resources, or otherwise rely on functions or signals provided by other system or network components external to the computer  30 . Indeed, given the nearly endless hardware and software configurations possible, a person of ordinary skill in the art will understand that applications and databases may be located externally to the computer  30 , distributed among multiple computers or other external resources, or provided by computing resources (hardware and software) that are provided as a service over a network, such as a cloud computing service. 
         [0020]    The HMI  40  may be operatively coupled to the processor  32  of computer  30  in a known manner to allow a user to interact directly with the computer  30 . The HMI  40  may include video or alphanumeric displays, a touch screen, a speaker, and any other suitable audio and visual indicators capable of providing data to the user. The HMI  40  may also include input devices and controls such as an alphanumeric keyboard, a pointing device, keypads, pushbuttons, control knobs, microphones, etc., capable of accepting commands or input from the user and transmitting the entered input to the processor  32 . 
         [0021]    A database  44  may reside on the mass storage memory device  36 , and may be used to collect and organize data used by the debonder  20 , such as data providing recipes for procedures to debond the device substrate  10  from the carrier substrate  12 . The database  44  may include data and supporting data structures that store and organize the data. In particular, the database  44  may be arranged with any database organization or structure including, but not limited to, a relational database, a hierarchical database, a network database, or combinations thereof. A database management system in the form of a computer software application executing as instructions on the processor  32  may be used to access the information or data stored in records of the database  44  in response to the initiation of a procedure to debond the device substrate  10  from the carrier substrate  12 . 
         [0022]    The dissolution head  22  includes a body  52 , an inlet  54  and outlets  56  extending through the body  52 , and a sealing member  58  that may have the form of an elastomeric o-ring seated in an o-ring groove in the body  52 . The inlet  54  is coupled with the liquid chemical agent source  28  and may be centrally located in the body  52  of the dissolution head  22 . The liquid chemical agent source  28  may heat the liquid chemical agent that is supplied to the inlet  54  to a temperature greater than room temperature. Each outlet  56  is coupled with the suction source  27  and may be located near an outer edge of the body  52  of the dissolution head  22 . The outlets  56  are arranged in distributed locations about the outer circumference of the dissolution head  22  and, in use, are disposed about the outer circumference of the carrier substrate  12 . 
         [0023]    The sealing member  58 , which may extend about the outer perimeter of the body  52  of the dissolution head  22 , is configured to be compressed to provide a sealed peripheral interface with the carrier substrate  12  when a contacting relationship exists between the dissolution head  22  and the carrier substrate  12 . In an alternative embodiment, the dissolution head  22  may be stationary and the assembly of substrates  10 ,  12  may be moved relative to the dissolution head  22  to provide the physical contact that compresses the sealing member  58 . When the contacting relationship is present, a chamber  62  is defined between the body  52  of the dissolution head  22  and the carrier substrate  12  and interior of the sealed peripheral interface. 
         [0024]    The chamber  62  is coupled with a port  53  of the inlet  54  and with a port  55  of each outlet  56 . During a debonding procedure to dissolve or decompose the material of the bonding layer  14 , the liquid chemical agent flows through the chamber  62  from port  53  to ports  55 . Specifically, when flow is established, the chamber  62  receives fresh liquid chemical agent from the chemical agent source  28  through port  53  of the inlet  54  and the used liquid chemical agent is suctioned from the chamber  62  through the port  55  of each outlet  56 . While in the chamber  62 , the flowing liquid chemical agent is directed through the passageways  18  in the carrier substrate  12  to the location of the bonding layer  14 . 
         [0025]    The vibrator  24  is configured to be activated by the controller  26  of the debonder  20  to transfer ultrasonic energy to the liquid chemical agent in the chamber  62 . The ultrasonic energy may assist with the action of the liquid chemical agent with the dissolution or decomposition of the material of the bonding layer  14 . The vibrator  24  may be physically associated with the dissolution head  22 . 
         [0026]    The motion system  25  is configured to be activated by the controller  26  to move the dissolution head  22  relative to the carrier substrate  12 . The motion system  25  includes a drive mechanism that is capable of imparting bi-directional movement to the dissolution head  22 . The motion system  25  may move the dissolution head  22  in one direction relative to the carrier substrate  12  to engage or re-engage the dissolution head  22  with the carrier substrate  12  to establish physical contact. The sealing member  58  may be compressed between the dissolution head  22  and the carrier substrate  12  to seal the chamber  62  when the contacting relationship is present. The motion system  25  may move the dissolution head  22  in an opposite direction relative to the carrier substrate  12  to disengage the dissolution head  22  from the carrier substrate and thereby end the contacting relationship by creating a condition in which the sealing member  58  is separated from the carrier substrate  12 . 
         [0027]    In use to perform a debonding operation and with reference to  FIGS. 1-4 , the debonding procedure includes multiple dissolution processes that remove the bonding layer in stages or cycles. In one embodiment, that multiple dissolution processes remove the bonding layer by the same mechanism. To that end, the debonder  20  receives the device substrate  10  bonded by the bonding layer  14  to the carrier substrate  12  as an assembly (block  100  of  FIG. 4 ). The bonded assembly may be held in a fixture with the carrier substrate  12  facing toward the dissolution head  22 . 
         [0028]    As shown in  FIG. 1  and in an initial stage or cycle of the debonding procedure, the debonder  20  causes the motion system  25  to move the dissolution head  22  toward the carrier substrate  12  and to place the sealing member  58  in contact with the carrier substrate  12  (block  102 ). Compression of the sealing member  58  between the dissolution head  22  and the carrier substrate  12  forms a peripheral seal extending about the outer circumference of the chamber  62  and carrier substrate  12 . 
         [0029]    A dissolution process is then performed by causing the debonder  20  to supply the liquid chemical agent to the chamber  62  (block  104 ). Specifically, the liquid chemical agent is pumped through the inlet  54  to the chamber  62 , the chamber  62  fills with a volume of the liquid chemical agent, and the liquid chemical agent is suctioned out of the chamber  62  through the outlets  56 . A positive flow of the liquid chemical is thus established through the chamber  62  from the inlet  54  to the outlets  56 . In the representative embodiment, the liquid chemical agent flows outwardly from the centered inlet  54  toward the peripheral outlets  56  and is vacuumed from the chamber  62  of the dissolution head  22  through the port  55  of each outlet  56 . While the liquid chemical agent is present in the chamber  62 , the vibrator  24  is activated to transfer ultrasonic energy to the liquid chemical agent in the chamber  62  and to the bonding layer  14 . 
         [0030]    The flow of liquid chemical agent through the chamber  62  is maintained for a time period during which the liquid chemical agent flows from the chamber  62  through the passageways  18  in the carrier substrate  12  to the location of the bonding layer  14  and wets the bonding layer  14 . Over the time period, the removal of the bonding layer  14  is initiated at the location of the passageways  18  and the liquid chemical agent progressively dissolves the material of the bonding layer  14 . The dissolved material is carried by the liquid chemical agent out of the chamber  62  though the outlets  56 . As a numerical example, the initial time period over which the liquid chemical agent is supplied to the chamber  62  and over which dissolution of the material of the bonding layer  14  occurs may have a duration of, for example, thirty (30) seconds. 
         [0031]    During the initial dissolution process, the material of the bonding layer  14  near the respective outer edges  11 ,  13  of the substrates  10 ,  12  may exhibit a comparatively lower degree of removal by dissolution. In particular, portions of the material of the bonding layer  14  that is localized near the ports  55  of the outlets  56  may exhibit a slower removal rate. Residual material  70 , which represents these portions of the bonding layer  14 , may be only partially removed by the action of the liquid chemical agent during the initial dissolution process. At other locations, the material of the bonding layer  14  may be completely removed, as shown in  FIG. 3 , or may only be thinned by the initial exposure to the liquid chemical agent. In any event, the bonding layer  14  is not completely removed by the initial dissolution process. 
         [0032]    After the supply of liquid chemical agent to the chamber  62  is discontinued, residual liquid chemical agent is vacuumed from the chamber  62  through each port  55  of the outlets  56 . The suction source  27  is switched off to discontinue the suction. Residual amounts of the liquid chemical agent may remain in the outlets  56  and on the exposed surfaces of the substrates  10 ,  12  and residual material  70 . 
         [0033]    As shown in  FIG. 3 , the dissolution head  22  is moved out of contact with the carrier substrate  12  (block  106 ). To that end, the motion system  25  may lift the dissolution head  22  to provide a non-contacting relationship. The vacuum and surface tension between the carrier substrate  12  and dissolution head  22  may allow the carrier substrate  12  to relax and pull slightly away from the device substrate  10 . During this relaxation, the liquid chemical agent in and under the carrier substrate  12  may wick to areas at or near the outer edge  11  at the periphery of the device substrate  10  and may wet the areas of the residual material  70  of the bonding layer  14 . In addition, the liquid chemical agent remaining in the ports  55  of the outlets  56  may backflow back onto the carrier substrate  12  to wet the areas of the residual material  70  of the bonding layer  14 . Subsequent dissolution processes directed at this residual material  70  may be considerably more effective because areas of residual material  70  near the outer edge of the substrates  10 ,  12  and, in particular, areas of residual material  70  near the ports  53 ,  55  proximate to the outer edge of the substrates  10 ,  12  are wetted by the liquid chemical agent. 
         [0034]    Another stage or cycle of the debonding procedure is then performed. After a brief dwell time, the dissolution head  22  is moved back into the contacting relationship with the carrier substrate  12  (block  108 ). Another dissolution process is then performed by causing the debonder  20  to supply the liquid chemical agent to the chamber  62  (block  110 ), as described above, to establish a positive flow. The vibrator  24  is activated to transfer ultrasonic energy to the liquid chemical agent in the chamber  62  and to the bonding layer  14 . 
         [0035]    During this subsequent dissolution process, the flow of liquid chemical agent through the chamber  62  is maintained for a time period during which the liquid chemical agent flows from the chamber  62  through the passageways  18  in the carrier substrate  12  to the location of the bonding layer  14  and wets the bonding layer  14 . The liquid chemical agent progressively dissolves the residual material  70  and any other remaining material of the bonding layer. The dissolved material is conveyed by the liquid chemical agent out of the chamber  62  though the outlets  56 . 
         [0036]    In one embodiment, the duration of the subsequent dissolution process differs from the duration of the initial dissolution process. In another embodiment, the duration of the subsequent dissolution process may be greater than the duration of the initial dissolution process. In another embodiment, the subsequent dissolution process may be at least 50% longer than the initial dissolution process. As a numerical example, the time period over which the liquid chemical agent is supplied to the chamber  62  may have a duration of, for example, ninety (90) seconds. The duration of the dissolution process may be optimized such that the flow of the liquid chemical agent is discontinued shortly after the bonding layer  14  completely removed. 
         [0037]    The supply of liquid chemical agent to the chamber  62  is discontinued, and residual liquid chemical agent is vacuumed from the chamber  62  through each port  55  of the outlets  56 . The suction source  27  is switched off to discontinue the suction and the dissolution head  22  is moved out of contact with the carrier substrate  12 . With the bonding layer  14  removed, the device substrate  10  is released by separation from the carrier substrate  12  (block  112 ). A low mechanical force may be needed to completely separate the substrates  10 ,  12 . 
         [0038]    In an alternative embodiment, the debonding procedure may include additional cycles or stages each including a dissolution process as described above. Each additional dissolution process may have the same duration as one of the preceding dissolution processes, or may have a different duration. The number and duration of the individual dissolution processes may be empirically established. 
         [0039]    The total dissolution time for the debonding procedure is given by the sum of the durations of the individual dissolution processes. The time required to stop and start the flow of liquid chemical agent and to move the dissolution head  22  relative to the carrier substrate  12  may also contribute to the total dissolution time. The utilization of multiple dissolution process that are spaced apart in time, as described herein, may dramatically decrease the total dissolution time in comparison with debonding procedures that rely on a single, lengthier dissolution process. 
         [0040]    In addition, the debonding procedure described herein may eliminate residual material  70  of the bonding layer  14  at the outer edge of the device wafer and near the locations of the ports  55 . By comparison, debonding procedures that rely on a single, lengthier dissolution process may not completely remove the material of the bonding layer  14  at these locations. 
         [0041]    The debonding procedure described herein may work for any thickness of the bonding layer  14 , may not require a redesign of or modification to the dissolution head  22 , may not require solvent resistant tape, and may increases the throughput of the debonder  20  without equipment modification. 
         [0042]    It will be understood that when an element is described as being “connected” or “coupled” to or with another element, it can be directly connected or coupled to the other element or, instead, one or more intervening elements may be present. In contrast, when an element is described as being “directly connected” or “directly coupled” to or with another element, there are no intervening elements present. When an element is described as being “indirectly connected” or “indirectly coupled” to or with another element, there is at least one intervening element present. 
         [0043]    The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.