Abstract:
An apparatus or method for forming a tape-based, epitaxial lift-off film. The epitaxial lift-off film can be for at least one of a solar device, a semiconductor device, and an electronic device. The apparatus can comprise: a tape supply section, the tape supply section providing an unloaded support tape; a lamination section for receiving the unloaded support tape and a plurality of substrates, each substrate containing an epitaxial film thereon, the lamination section adhering the substrates to the unloaded support tape to form a loaded support tape; and an ELO etch section comprising a pressure system for applying pressure on said loaded support tape such that pressure is applied progressively downward and progressively towards a center-line of said loaded support tape when passing through said ELO etch section, the ELO etch section removing the substrates from the loaded support tape, while leaving the epitaxial film on the loaded support tape.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. Ser. No. 61/138,440, filed Dec. 17, 2008, and U.S. Ser. No. 61/257,326, filed Nov. 2, 2009, which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the invention generally relate to apparatuses and methods for the fabrication of solar, semiconductor, and electronic materials and devices, and more particularly to epitaxial lift off (ELO) thin films and devices. 
     2. Description of the Related Art 
     One phase in device fabrication involves handling and packaging of thin films used as photovoltaic or solar devices, semiconductor devices, or other electronic devices. Such thin film devices may be manufactured by utilizing a variety of processes for depositing materials onto and removing material from a substrate or wafer. One uncommon technique for manufacturing thin film devices is known as the epitaxial lift off (ELO) process. The ELO process includes depositing an epitaxial layer or film on a sacrificial layer on a growth substrate, then etching the sacrificial layer to separate the epitaxial layer from the growth substrate. The removed thin epitaxial layer is known as the ELO or epitaxial film or layer and typically includes thin films used as photovoltaic or solar devices, semiconductor devices, or other electronic devices. 
     The thin ELO films are very difficult to manage or handle, such as when bonding to a substrate or while packaging, since the ELO films are very fragile and have narrow dimensions. The ELO films crack under very small forces. Also, the ELO films are very difficult to align due to their extremely narrow dimensions. 
     The sacrificial layer is typically very thin and may be etched away via a wet chemical process. The speed of the overall process may be limited by the lack of delivery or exposure of reactant to the etch front, which leads to less removal of by-products from the etch front. The ELO etching process is a diffusion limited process and when the ELO films are maintained in their as deposited geometries, a very narrow and long opening forms which severely limits the overall speed of the process. To lessen the transport constraint of the diffusion processes, it may be beneficial to open up the resulting opening created by the etched or removed sacrificial layer and bending the ELO film away from the growth substrate. The act of bending while etching forms a crevice between the ELO film and the growth substrate—which geometry of the crevice provides greater angles to increase the transport of species both towards and away the etch front. Reactants move towards the etch front while by-products generally move away from the etch front. 
     The bending of the ELO film however can induce stresses the epitaxial layers within and the amount of bending is limited by the strength of the ELO film. The ELO film usually contains a brittle material, which does not undergo plastic deformation before failure, and as such may be subject to crack induced failures. 
     To minimize the potential for crack propagation, the brittle ELO film may be maintained under a compressive stress. Cracks usually do not propagate through regions of residual compressive stress. The ELO film is placed under tensile stress while bending the ELO film away from the growth substrate since the ELO film is on the outside of the curvature of the crevice. The tensile stress limits the amount of crevice curvature and reduces the speed of the etch process. To overcome this limitation, a residual compressive stress may be instilled within the ELO film before etching the sacrificial layer. This initial compressive stress may be offset by tensile stress caused by the bending and therefore allows for a greater amount of bending during the separation process. 
     Also, the ELO process has always been a cost prohibiting technique for commercially producing the thin ELO film devices. Current ELO processes include transferring a single growth substrate through many fabrication steps while producing a single ELO film. The current processes are time consuming, costly, and rarely produce commercial quality ELO films. 
     Therefore, there is a need for more effective, less time consuming, and less expensive methods and apparatuses to remove and handle ELO thin films. 
     SUMMARY OF THE INVENTION 
     Embodiments of the invention generally relate to apparatuses and methods for producing epitaxial thin films and devices by epitaxial lift off (ELO) processes. The thin film devices generally contain epitaxially grown layers which are formed on a sacrificial layer disposed on or over a growth substrate, such as a wafer. A support tape may be disposed on or over the opposite side of the epitaxial film as the wafer. The support tape may be used to hold the epitaxial films during the etching and removal steps of the ELO process, and thereafter. In various embodiments, the apparatus for removing the epitaxial films from the substrates may include an etch section, substrate and support tape handling devices, and various tension control devices to protect the epitaxial films during the ELO removal process. 
     In one embodiment, a method for forming thin film devices during an ELO process is provided and includes forming an epitaxial film or material over a sacrificial layer on a substrate, adhering an elongated tape support onto the epitaxial film, removing the sacrificial layer during an etching process, and peeling the epitaxial film from the substrate while bending the elongated tape support away from the substrate. 
     In another embodiment, an apparatus for forming a tape-based ELO stack is provided and contains a first end, a second end, and a tape supply section proximate the first end. The tape supply section provides at least one unloaded support tape, a lamination section for receiving the at least one unloaded support tape, and a plurality of substrates having an epitaxial film thereon. The lamination section adheres the substrates to the at least one unloaded support tape to form at least one loaded support tape and an ELO etch section proximate the second end, the ELO etch section removing the substrates from the at least one loaded support tape, while leaving the epitaxial film on the at least one loaded support tape. The tape supply section generally includes at least one roller which has at least one roller with at least one tape wound thereon. 
     Embodiments of the apparatus further provide a splice/punch section disposed between the tape supply section and the lamination section, the splice/punch section forming openings in the elongated, unloaded support tape. The ELO etch section containing etch bath reservoirs or tanks may be configured to continuously remove the substrates from the loaded support tape and may be configured to remove the substrates from the loaded support tape in batches. 
     In some embodiments, the support tape has at least one row of track openings extending the length of the support tape. Other examples provide that each side of the support tape has a row of track openings extending the length of the support tape. In some configurations, the support tape moves around at least two reels, drums, or rollers. The support tape moves around at least one roller having a plurality of pins extending from the roller to engage the track openings. In some examples, the roller contains a sprocket or a cog to engage the track openings. The loaded support tape may contain a plurality of slots extending perpendicular or substantially perpendicular from the outside edges of the support tape. The plurality of slots has pairs of aligned slots which extend from opposite outside edges of the loaded support tape. Each pair of slots is within a region of the loaded support tape, and the region is free of substrates. Each substrate may be coupled to or with the loaded support tape between two consecutive pairs of slots, such as outside the region containing the pair of slots. 
     In another embodiment, a method for forming thin film devices during an ELO process is provided which includes coupling an elongated support tape and a plurality of substrates, wherein each substrate contains an epitaxial film disposed over a sacrificial layer disposed over a wafer, exposing the substrates to an etchant during an etching process while moving the elongated support tape, and etching the sacrificial layers and peeling the epitaxial films from the wafers while moving the elongated support tape. 
     The elongated support tape is coupled with each substrate by the epitaxial film disposed thereon. The plurality of substrates coupled with the elongated support tape generally contains from about 4 substrates to about 100 substrates or more. The elongated support tape may contain multiple layers. In some embodiments, the elongated support tape contains at least one metal, for example, at least one metallic foil. The metallic foil contains a metal such as iron, nickel, cobalt, steel, stainless steel, alloys thereof, derivatives thereof, or combinations thereof. In other embodiments, the elongated support tape contains at least one material such as a plastic material, a polymeric material, a co-polymeric material, an oligomeric material, derivatives thereof, or combinations thereof. In some examples, the elongated support tape may contain polyacrylic materials, polyethylene materials, polypropylene materials, polytetrafluoroethylene materials, fluorinated polymeric materials, isomers thereof, derivatives thereof, and combinations thereof. 
     In some embodiments, the elongated support tape moves around at least two reels, drums, or rollers. At least one side of the elongated support tape contains a row of track openings extending the length of the elongated support tape. In some examples, each side of the elongated support tape contains a row of track openings extending the length of the elongated support tape. The elongated support tape moves around at least one roller having a plurality of pins extending from the roller to engage the track openings. The roller may have a sprocket or a cog as the pins for engaging the track openings. The elongated support tape may have a plurality of slots extending perpendicular or substantially perpendicular from the outside edges of the elongated support tape. The plurality of slots may have pairs of aligned slots which extend from opposite outside edges of the elongated support tape. In some embodiments, each pair of slots may be within a region of the elongated support tape, and the region is free of substrates. Each substrate may be coupled with the elongated support tape between two consecutive pairs of slots. 
     In many embodiments, an adhesive layer is disposed between each substrate and the elongated support tape. The adhesive layer may be formed by applying an adhesive to each substrate and coupling each substrate to the elongated support tape. The adhesive layer may contain a pressure sensitive adhesive, a hot-melt adhesive, a UV-cured adhesive. In some examples, the adhesive layer contains an acrylic adhesive. 
     In some embodiments, the sacrificial layer contains aluminum arsenide, alloys thereof, derivatives thereof, or combinations thereof. The sacrificial layer may have a thickness within a range from about 1 nm to about 20 nm. The sacrificial layer may be exposed to a wet etch solution during the etching process. The wet etch solution may contain hydrofluoric acid, a surfactant, and a buffer. In some examples, the sacrificial layer is etched at a rate of about 5 mm/hr or greater. 
     The epitaxial film or material grown or formed on the wafer may have a plurality of layers. The wafer generally contains gallium arsenide, gallium arsenide alloys, dopants thereof, or derivatives thereof. Each layer of the epitaxial film or material may contain gallium arsenide, aluminum gallium arsenide, indium gallium phosphide, alloys thereof, derivatives thereof, or combinations thereof. In one embodiment, the epitaxial film has a layer containing gallium arsenide and another layer containing aluminum gallium arsenide. The epitaxial film may have a gallium arsenide buffer layer, at least one aluminum gallium arsenide passivation layer, and a gallium arsenide active layer. In some examples, the gallium arsenide buffer layer may have a thickness within a range from about 100 nm to about 500 nm, the aluminum gallium arsenide passivation layer has a thickness within a range from about 10 nm to about 50 nm, and the gallium arsenide active layer has a thickness within a range from about 500 nm to about 2,000 nm. In some specific examples, each epitaxial film contains a photovoltaic or solar cell structure having multiple layers. The photovoltaic cell structure contains at least two materials such as gallium arsenide, n-doped gallium arsenide, p-doped gallium arsenide, aluminum gallium arsenide, n-doped aluminum gallium arsenide, p-doped aluminum gallium arsenide, indium gallium phosphide, alloys thereof, derivatives thereof, or combinations thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  is a schematic isometric view of a substrate containing an ELO thin film stack on a wafer according to embodiments described herein. 
         FIG. 2A  is a side view of an assembly formed of a plurality of substrates adhered to a support tape, according to embodiments of the invention. 
         FIG. 2B  is a plan view of the bottom of the assembly of  FIG. 2A . 
         FIG. 2C  is a side view of an assembly formed of a plurality of epitaxial films attached to a support tape, according to embodiments of the invention. 
         FIG. 2D  is a side view of the assembly of  FIG. 2C  being wound on a support roll, according to embodiments of the invention. 
         FIG. 2E  is a side view of an assembly including the assembly of  FIG. 2C  wound on a support roll, according to embodiments of the invention. 
         FIG. 3  is a schematic plan view of one embodiment of an apparatus for forming tape based ELO films and devices. 
         FIG. 4  is a schematic isometric view of one embodiment of an apparatus for performing an ELO process to remove ELO films from support wafers. 
         FIG. 5  is an enlarged overhead isometric view of the tape drive and tensioning portion of the apparatus of  FIG. 4 . 
         FIG. 6  is an enlarged horizontal isometric view of the tape drive and tensioning portion of the apparatus of  FIG. 4 . 
         FIGS. 6A-6C  are cross sections of the tape and wafer assembly as it proceeds through the apparatus of  FIG. 4 . 
         FIG. 7  is an isometric view of a tape and wafer tank entry assembly for use with embodiments of the ELO process apparatus of the invention. 
         FIG. 8  is an isometric view of a tape extraction assembly for use with embodiments of the ELO process apparatus of the invention. 
         FIG. 9  is an isometric view of a positive substrate detachment assembly for use with embodiments of the ELO process apparatus of the invention. 
         FIG. 10  is a schematic isometric view of a further embodiment of an apparatus for performing an ELO process to remove ELO films from support wafers. 
         FIG. 11  is an enlarged isometric view of the tape drive and tensioning portion of the apparatus of  FIG. 10 . 
         FIGS. 11A-11C  are cross sections of the tape and wafer assembly as it proceeds through the apparatus of  FIG. 10 . 
         FIG. 12  is a schematic isometric view of another embodiment of an apparatus for performing an ELO process to remove ELO films from support wafers. 
         FIG. 13  is an enlarged isometric view of the tape drive and point load tensioning portion of the apparatus of  FIG. 12 . 
         FIG. 14  is an enlarged isometric view of the wafer support and pusher portion of the apparatus of  FIG. 12 . 
         FIG. 15  is a schematic isometric view of another embodiment of an apparatus for performing an ELO process to remove ELO films from support wafers. 
         FIG. 16  is an enlarged isometric view of the tape drive and point load tensioning portion of the apparatus of  FIG. 15 . 
         FIG. 17  is an enlarged isometric view of the wafer support and pusher portion of the apparatus of  FIG. 15 . 
         FIG. 18  is a schematic isometric view of a batch-type embodiment of an apparatus for performing an ELO process to remove ELO films from support wafers. 
         FIG. 19  is an enlarged isometric view of the wafer support and belt drive and point load tensioning portion of the apparatus of  FIG. 18 . 
         FIG. 20  is a cross section through the wafer support and belt drive and point load tensioning portion of the apparatus of  FIG. 18 . 
         FIG. 21  is an enlarged isometric view of the wafer support and belt drive and point load tensioning portion of the apparatus of  FIG. 18  in a loading position. 
         FIG. 22  is a cross section through the wafer support and belt drive and point load tensioning portion of the apparatus of  FIG. 18  in a loading position. 
         FIG. 23  is an enlarged isometric view of the wafer support and belt drive and point load tensioning portion of the apparatus of  FIG. 18  in a point load and finger lowering position. 
         FIG. 24  is a cross section through the wafer support and belt drive and point load tensioning portion of the apparatus of  FIG. 18  in a point load and finger lowering position. 
         FIG. 25  is an enlarged isometric view of the wafer support and belt drive and point load tensioning portion of the apparatus of  FIG. 18  in a point load and finger further lowered position. 
         FIG. 26  is a cross section through the wafer support and belt drive and point load tensioning portion of the apparatus of  FIG. 18  in a point load and finger further lowered position. 
         FIG. 27  is an enlarged isometric view of the wafer support and belt drive and point load tensioning portion of the apparatus of  FIG. 18  in a tape locked position. 
         FIG. 28  is a cross section through the wafer support and belt drive and point load tensioning portion of the apparatus of  FIG. 18  in a tape locked position. 
         FIG. 29  is an enlarged isometric view of the wafer support and belt drive and point load tensioning portion of the apparatus of  FIG. 18  in a lowered belt position. 
         FIG. 30  is a cross section through the wafer support and belt drive and point load tensioning portion of the apparatus of  FIG. 18  in a lowered belt position. 
         FIG. 31  is an enlarged isometric view of the wafer support and belt drive and point load tensioning portion of the apparatus of  FIG. 18  in an initial ELO position. 
         FIG. 32  is a cross section through the wafer support and belt drive and point load tensioning portion of the apparatus of  FIG. 18  in an initial ELO position. 
         FIG. 33  is an enlarged isometric view of the wafer support and belt drive and point load tensioning portion of the apparatus of  FIG. 18  in a continuing ELO position. 
         FIG. 34  is a cross section through the wafer support and belt drive and point load tensioning portion of the apparatus of  FIG. 18  in a continuing ELO position. 
         FIG. 35  is an enlarged isometric view of the wafer support and belt drive and point load tensioning portion of the apparatus of  FIG. 18  in an ELO completed position. 
         FIG. 36  is a cross section through the wafer support and belt drive and point load tensioning portion of the apparatus of  FIG. 18  in an ELO completed position. 
         FIG. 37  is an enlarged isometric view of the wafer support and belt drive and point load tensioning portion of the apparatus of  FIG. 18  in a point load rotated position. 
         FIG. 38  is a cross section through the wafer support and belt drive and point load tensioning portion of the apparatus of  FIG. 18  in a point load rotated position. 
         FIG. 39  is a flow chart illustrating one embodiment of a method for forming ELO thin films and devices that may be performed by the apparatus of  FIG. 3 . 
         FIG. 40  is a flow chart illustrating one embodiment of a batch ELO method that may be performed by the apparatus of  FIGS. 18-38 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  depicts substrate  100  containing an epitaxial lift off (ELO) thin film stack  150 , as described in one embodiment herein. The ELO thin film stack  150  is disposed on or over the wafer  102  and contains an epitaxial film  106  disposed on or over a sacrificial layer  104 . The substrate  100  is a relatively difficult product to handle, requiring each ELO thin film stack  150  to be handled separately. In addition, the wafers  102  used to form the epitaxial layers of the ELO thin film stacks  150  are usually expensive, particularly when made of gallium arsenide. 
     The wafer  102  may contain or be formed of a variety of materials, such as Group III/V materials, and may be doped with other elements. The wafer  102  may be a wafer or a substrate and usually contains gallium arsenide, gallium arsenide alloys or other derivatives, and may be n-doped or p-doped. In one example, the wafer  102  contains n-doped gallium arsenide material. In another example, the wafer  102  contains p-doped gallium arsenide material. 
     The sacrificial layer  104  may contain aluminum arsenide, alloys thereof, derivatives thereof, or combinations thereof. In one example, the sacrificial layer  104  contains at least an aluminum arsenide layer. The sacrificial layer  104  may have a thickness of about 20 nm or less, such as within a range from about 1 nm to about 20 nm, or from about 1 nm to about 10 nm, or from about 4 nm to about 6 nm. 
     The epitaxial film  106  generally contains multiple layers of epitaxial materials. In some embodiments, the epitaxial material of the epitaxial film  106  may contain gallium arsenide, aluminum gallium arsenide, indium gallium phosphide, alloys thereof, derivatives thereof, or combinations thereof. The epitaxial film  106  may contain one layer, but usually contains multiple layers. In some examples, the epitaxial film  106  contains a layer having gallium arsenide and another layer having aluminum gallium arsenide. In another example, the epitaxial film  106  contains a gallium arsenide buffer layer, an aluminum gallium arsenide passivation layer, and a gallium arsenide active layer. The gallium arsenide buffer layer may have a thickness within a range from about 100 nm to about 500 nm, such as about 300 nm, the aluminum gallium arsenide passivation layer may have a thickness within a range from about 10 nm to about 50 nm, such as about 30 nm, and the gallium arsenide active layer may have a thickness within a range from about 500 nm to about 2,000 nm, such as about 1,000 nm. In some examples, the epitaxial film  106  further contains a second aluminum gallium arsenide passivation layer. The second gallium arsenide buffer layer may have a thickness within a range from about 100 nm to about 500 nm, such as about 300 nm. In other embodiments herein, the epitaxial film  106  may have a photovoltaic cell structure containing multiple layers. The photovoltaic cell structure may contain gallium arsenide, n-doped gallium arsenide, p-doped gallium arsenide, aluminum gallium arsenide, n-doped aluminum gallium arsenide, p-doped aluminum gallium arsenide, indium gallium phosphide, alloys thereof, derivatives thereof, or combinations thereof. 
       FIGS. 2A-2E  depict various stages of transferring the epitaxial film  106  from the wafer  102  to a tape substrate on a roll, according to embodiments of the invention.  FIG. 2A  is a side view and  FIG. 2B  is a bottom view of an assembly  200  that includes a plurality (six shown) of the substrates  100  of  FIG. 1 , attached to a support tape  202 . Each of the substrates  100  has a sacrificial layer  104  disposed on or over a wafer  102  and an epitaxial film  106  disposed on or over the sacrificial layer  104 . An adhesive layer  204  may be disposed between each of the substrates  100  and the support tape  202 . 
     In one embodiment, the adhesive layer  204  may be applied to the substrates  100  or the epitaxial films  106  before adhering or coupling with the support tape  202 . Alternatively, the adhesive layer  204  may be applied to the support tape  202  before adhering or coupling with the substrates  100  or the epitaxial films  106 . Also, the adhesive layer  204  may be applied to both the support tape  202  and the substrates  100  or the epitaxial films  106  and subsequently, adhering or coupling together. The adhesive layers  204  may be made of a pressure sensitive adhesive (PSA), a hot melt adhesive, an ultraviolet (UV) curing adhesive, an acrylic adhesive, a rubber adhesive, a natural adhesive (e.g., natural rubber), a synthetic adhesive (e.g., synthetic rubber), derivatives thereof, or combinations thereof. The material of the adhesive layers  204  is at least substantially resistant to the etchant used in the etching process as described below. 
     In some examples, the adhesive layers  204  may be formed from or contain an optical adhesive and/or a UV-curable adhesive that has been exposed to UV radiation during a curing process. Generally, the adhesive may be exposed to the UV radiation for a time period within a range from about 1 minute to about 10 minutes, preferably, from about 3 minutes to about 7 minutes, such as about 5 minutes. The adhesive may be cured at a temperature within a range from about 25° C. to about 75° C., such as about 50° C. An exemplary optical adhesive is commercially available as Norland UV-curable optical adhesive. In some examples, the adhesive layers  204  may contain a mercapto ester compound. In other examples, the adhesive layers  204  may further contain an adhesive material such as butyl octyl phthalate, tetrahydrofurfuryl methacrylate, acrylate monomer, isomers thereof, derivatives thereof, or combinations thereof. In one example, the adhesive layers  204  may contain an acrylic compound or derivatives thereof. 
     In other examples, the adhesive of the adhesive layers  204  may be a silicone adhesive or may contain sodium silicate. In these examples, the adhesive may be cured for a time period within a range from about 10 hours to about 100 hours, preferably, from about 20 hours to about 60 hours, and more preferably, from about 30 hours to about 50 hours, for example, about 42 hours. The adhesive may be cured at a temperature within a range from about 25° C. to about 75° C., such as about 50° C. Also the adhesive may be cured by applying a pressure thereto. The pressure applied to the adhesive may be within a range from about 1 psi (pounds per square inch) to about 50 psi, preferably, from about 3 psi to about 25 psi, and more preferably, from about 5 psi to about 15 psi. In one example, the pressure is about 9 psi. 
     In other examples, the adhesive layers  204  may contain a polymer, a copolymer, an oligomer, derivatives thereof, or combinations thereof. In one embodiment, the adhesive layer  204  contains a copolymer. In one example, the copolymer may be an ethylene/vinylacetate (EVA) copolymer or derivatives thereof. An EVA copolymer which is useful as the adhesive layer  204  is WAFER GRIP adhesive film, commercially available from Dynatex International, located in Santa Rosa, Calif. 
     In one embodiment, the support tape  202  is an elongated thin strip of material. In some embodiments, the support tape  202  is similar in structure to photographic film. The elongated support tape, such as support tape  202 , may be coupled with each substrate  100  through each epitaxial film  106  by an adhesive or adhesive layer  204 . There is a plurality of substrates  100  coupled with the support tape  202 . Generally, there may be 4, 8, 10, 20, 50, 100, or more substrates attached to the support tape  202 . In some embodiments, the support tape  202  may have from about 4 substrates to about 100 substrates or more. 
     The support tape  202  may have a single layer or may contain multiple layers of the same or different materials. The material of the support tape  202 , in some embodiments, includes metallic, plastic, polymeric, co-polymeric, and/or oligomeric materials. In some examples, the support tape  202  may be formed from or contain polyacrylic materials, polyethylene materials, polypropylene materials, polytetrafluoroethylene materials, fluorinated polymeric materials, isomers thereof, derivatives thereof, or combinations thereof. The material of the support tape  202  is at least substantially resistant to the etchant used in the etching process as described below. In some embodiments, the support tape  202  contains at least one metal, or contains at least one metallic foil. The metallic foil may contain at least one metal such as iron, nickel, cobalt, steel, stainless steel, alloys thereof, derivatives thereof, or combinations thereof. 
     The support tape  202  may have a width W 1  that is between about 10 mm and about 1,000 mm, or about 50 mm to about 300 mm, or about 70 mm to about 150 mm, in various embodiments. The overall length (not shown) of the support tape  202 , is only limited by the size of the storage rolls or reels that the support tape  202  is wound upon. In one embodiment the length of the support tape  202  is between about 1 m and about 1,000 m. Each substrate  100  may have a length L 1  in the longitudinal direction of the support tape  202  and a width W 2 , traverse to the support tape  202 . In one embodiment, L 1  is between about 8 mm and about 950 mm, while W 2  is between about 8 mm and about 950 mm. The substrates  100 , in one embodiment, are substantially centered on the tape, and spaced a distance D 1  from each other. In one embodiment, D 1  is between about 2 mm and about 20 mm. 
     The support tape  202  may optionally include track openings  206  along the sides of the support tape  202  for engagement by drive elements as described below with respect to various embodiments of the apparatus. In addition, the support tape  202  may include regularly spaced slots  208 , in some embodiments, to provide a greater degree of flexibility in the transverse direction, as required. The slots  208  are generally centered between two adjacent substrates  100 , and in one embodiment have a width W 3  that is between about 0.5 mm and about 2 mm. In one embodiment, the slots  208  are located between substrates  100  such that between about 2 substrates and about 5 substrates are between adjacent slots  208 . Further, in some embodiments, the slots  208  extend between about 25% and about 90% to the center of the support tape  202 . For example, for tapes having a width W 1  of about 20 mm, and slots  208  that extend for about 7 mm each, then each slot  208  would extend about 70% to the center of the support tape  202 , leaving a connecting edge of about 6 mm between the slots  208 . 
     In  FIG. 2C , a side view of an assembly  210  is shown that includes a plurality (six shown) of the epitaxial films  106  of  FIG. 2A , attached to the support tape  202  by the adhesive layers  204 . There may be 4, 8, 10, 20, 50, 100, or more epitaxial films  106  attached to the support tape  202 . In some embodiments, the support tape  202  may have from about 4 epitaxial films to about 100 epitaxial films or more within the plurality of epitaxial films  106 . 
     In some embodiments, the assembly  210  is formed by exposing the sacrificial layer  104  in the assembly  200  of  FIGS. 2A and 2B  to a wet etch solution during an ELO etching process. In some examples, the wet etch solution contains hydrofluoric acid and may contain a surfactant and/or a buffer. The sacrificial layer  104  may be etched at a rate of about 0.3 mm/hr or greater, preferably, about 1 mm/hr or greater, and more preferably, about 5 mm/hr or greater. In an alternative embodiment, the sacrificial layer  104  may be exposed to an electrochemical etch during the ELO etching process. The electrochemical etch may be a biased process or a galvanic process. Also, the sacrificial layer  104  may be exposed to a vapor phase etch during the ELO etching process in another embodiment described herein. The vapor phase etch includes exposing the sacrificial layer  104  to hydrogen fluoride vapor. The ELO etching process may be a photochemical etch, a thermally enhanced etch, a plasma enhanced etch, a stress enhanced etch, derivatives thereof, or combinations thereof. 
     In  FIG. 2D , a side view is shown of the assembly  210  of  FIG. 2C  being wound on a support reel or a support roll  212 . The assembly  210  includes the support tape  202  with a plurality of epitaxial films  106  attached or adhered thereto as described above. The assembly  210  is shown being wound around roll  212  with the epitaxial films  106  attached to the bottom of the support tape  202  such that the epitaxial films  106  are faced toward the surface of the roll  212 . In an alternate embodiment, the epitaxial films  106  may be above the support tape  202  such that the epitaxial films  106  are faced away from the surface of the roll  212 . A protective film or sheet  214  may be provided to protect the epitaxial films  106  from adjacent surfaces. The roll  212  has a minimum (unloaded) radius of R 1 . In one embodiment, the radius R 1  of the roll  212  is between about 10 cm to about 100 cm. The radius R 1  of the roll  212  is an important design consideration, as the epitaxial films  106  may be cracked or otherwise damaged if they are subjected to a radius of curvature that is too small. Thus the radius R 1  of the roll  212  is chosen based on the structural limitations of the epitaxial films  106 . Once the roll  212  is loaded with an appropriate length of assembly  210 , as shown in  FIG. 2E , a large number of epitaxial films  106  may be handled, transported, or loaded into subsequent processing apparatus as an assembly  220 . 
     In  FIG. 3  is a schematic plan view of one embodiment of an apparatus  300  that is useful for performing a method of forming tape based ELO products such as assembly  220  in  FIG. 2E .  FIG. 39  is a flow chart of a method  3900  that in one embodiment is performed by apparatus  300 . At a first end  350  of the apparatus  300 , a first section  302  includes one or more reels or rolls  354  containing one or more blank or unloaded support tapes  352 . In the embodiment shown in  FIG. 3 , there are six parallel support tapes  352 . However, it should be understood that there may be any number of support tapes  352  loaded on one or more rolls  354 , within the physical restrictions of apparatus  300 . In block  3902  of method  3900 , the unloaded support tapes  352  are unwound from the roll(s), and the unloaded support tapes  352  are fed from the roll(s)  354  into a splice/punch section  304 . In block  3904  of method  3900 , in the splice/punch section  304 , the unloaded support tapes  352  are cut, punched, or a combination of cut and punched to form openings in the tape, as required for handling and other purposes. In one embodiment, for example, the openings formed in the support tapes  352  in the splice/punch section  304 , include the track openings  206  and the slots  208 , as shown in  FIG. 2B . In other embodiments, openings may not be required, and the splice/punch section  304  may be omitted from apparatus  300 . 
     In block  3906  of method  3900 , after block  3904  (if provided), substrates or wafers are laminated onto the unloaded support tapes. As shown in  FIG. 3 , after the splice/punch section  304  (when provided) the unloaded support tapes  352  enter a lamination section  306 . The lamination section  306  receives substrates  356  from a substrate input section  308 . In one embodiment, a robot  310  may be used to load the substrates  356  into the lamination section  306 . The substrates  356  may, in one embodiment, be similar in structure to the substrate  100  of  FIG. 1 . In the lamination section  306 , the substrates are attached, adhered or otherwise bonded to the support tapes  352 , as shown by substrates  358  bonded to the loaded support tapes  368 . In one embodiment, the loaded support tapes  368  are similar in structure to assembly  200  as shown in  FIGS. 2A and 2B . 
     The loaded support tapes  368  enter an accumulation section  312  after leaving the lamination section  306 . In the accumulation section  312 , the loaded support tapes  368  are accumulated prior to entering etch bath reservoirs or tanks within the ELO etch section  314 , as illustrated by block  3908  of method  3900 . 
     After the accumulation section  312 , the loaded support tapes  368  enter etch bath reservoirs or tanks within an ELO etch section  314 . In the ELO etch section  314 , the sacrificial layer (for example sacrificial layer  104  in  FIGS. 1 and 2A ), is etched to remove the sacrificial layer and the wafer (for example, wafer  102  in  FIGS. 1 and 2A ), from the loaded support tapes  368 , in block  3910  of method  3900 . The resulting ELO film loaded support tapes  364 , proceed to tape post etch processing sections, while the unloaded substrates  360  proceed to wafer post etch processing sections, in block  3912  of method  3900 . The unloaded substrates  360  enter a conveyor loading section  316 , where the unloaded substrates  360  are placed on a conveyor, for example, by a robot (not shown). In one embodiment, the wafer post etch processing sections include a first wafer rinsing section  318 , a wafer cleaning section  320 , a second wafer rinsing section  322  and a wafer drying section  324 . The wafer post etch processing sections are designed to prepare the wafers to be reused in the process, by removing contaminates from the wafers. A robot  326  unloads the substrates from the wafer drying section  324  to a wafer output section  328 . The wafers  362  in the wafer output section  328  are ready to have sacrificial and epitaxial material layers redeposited thereon. A conveyor (not shown) may redirect the wafers  362  to a deposition chamber or process. Once the sacrificial layers and epitaxial films are deposited on the substrates, the substrates may be further conveyed to substrate input section  308  as substrates  356 , to be reused in the process. In this manner, the relatively expensive wafers may be used multiple times to grow the desired epitaxial thin films and devices. 
     After removal of the sacrificial layer and the wafer from the loaded support tapes  368 , the resulting ELO film loaded support tapes  364 , proceed to tape post etch processing sections. The tape post etch processing sections, in one embodiment, include a first tape rinsing section  330 , a tape cleaning section  332 , a second tape rinsing section  334  and a tape drying section  336 . In one embodiment, the ELO film loaded support tapes are similar to the assembly  210  as shown in  FIG. 2C . The tape post etch processing sections are designed to clean and dry the ELO film loaded support tapes  364  to remove contaminates from the tape and epitaxial material loaded thereon. 
     Once the ELO film loaded support tapes  364  have been cleaned, they proceed to a tape winding section  338  located at a second end  370  of the apparatus  300 . In the tape winding section  338  the ELO film loaded support tapes  364  are wound onto one or more reels or rolls  366 , such as shown in  FIG. 2D , and in block  3914  of method  3900 . Once the roll  366  is fully loaded, the loaded roll is removed from the tape winding section  338  and is replaced by an empty roll. In one embodiment, the loaded roll is similar to assembly  220  as shown in  FIG. 2E . 
     In  FIGS. 4-6 , a longitudinal geared wedge embodiment of an apparatus  400  for performing an ELO etch process to remove ELO film stacks from support wafers, is shown. The apparatus  400  includes a tape and wafer loading section  402 , an etch bath  404 , a wafer unload section  406 , and a tape unload section  408 .  FIG. 5  shows an overhead view of a portion of the etch bath  404  and the tape drive and tensioning portion of the apparatus  400 . The support tape  202  includes a plurality of openings or track openings  206  along its sides, similar to those shown in  FIG. 2B . The apparatus  400  includes a plurality of drive and tensioning gears  502  that engage the tape in the track openings  206 . The drive and tensioning gears  502  drive the tape through the etch bath  404 , while also maintaining the lateral position of the sides of the support tape  202  by engaging the outside portion  504  of the track openings  206 . The drive and tensioning gears  502  are connected to driven sprockets  506  by drive shafts  508 . The driven sprockets  506  may in turn be attached to a driving sprocket and motor (not shown) by a drive chain or belt (not shown). The driven sprockets  506  and the elements that drive them are, in one embodiment, located above the etch bath  404 . Tape guides  510 , may also be provided to guide the support tape  202  through the etch bath  404 . Referring to  FIGS. 4-6 , a static wedge is shown formed by two ramps  512 . The static wedge progressively applies pressure to remove the wafers  102  from the support tape  202 , while leaving the ELO stack on the support tape  202 . A number of adjustable supports  514  adjustably connect the ramps  512  to an overhead assembly (not shown). The adjustable supports  514  may be threaded, or otherwise adjustable, to provide adjustment of the level of the ramps  512  at the various stages of the etch bath  404 . 
     As depicted in  FIG. 4 , the ramps  512  are spaced apart at their first end adjacent to the tape and wafer loading section  402 , and converge toward one another at their second end adjacent to the tape unload section  408 . The ramps  512  also extend further down into the etch bath  404  from their first end to their second end and thereby increasingly engage the top of the support tape  202  as it travels through the etch bath  404 . The wafers  102  are supported from below by a substrate support (not shown) that supports the wafers  102  near the tape unload section  408  of apparatus  400  using a spring or buoyancy applied force. 
       FIGS. 6A-6C  are schematic diagrams illustrating the relationship between the ramps  512 , the support tape  202 , and wafers  102 , as the support tape  202  and wafers  102  proceed through the etch bath  404  (see  FIG. 4 ). In  FIG. 6A , the support tape  202  and wafer  102  are in an initial position of the etch bath  404 . The ramps  512  are substantially at the initial level of the support tape  202  and the wafers  102 , and the assembly is therefore relatively planar, with little or no pressure being applied to the support tape  202  and wafers  102 . The drive and tensioning gears  502  maintain the position of the ends of the support tape  202 . In the position shown in  FIG. 6B , (approximately half way through the etch bath  404 ), the ramps  512  are extended further into the etch bath  404 , and the center of the tape and the wafer  102  are pushed downward relative to the ends of the support tape  202 . A crevice  600  is therefore formed between the support tape  202  and the wafer  102  (and the ELO stack thereon). In the position shown in  FIG. 6C , (at a point near the tape unload section  408 ), the ramps  512  are extended even further into the etch bath  404 , and the center of the tape and the wafer  102  are pushed further downward relative to the ends of the support tape  202 . The size of the crevice  600 ′ is increased as compared to crevice  600  and the wafer  102  is increasingly removed from the support tape  202 . At a point in the progression slightly after the illustration shown in  FIG. 6C , the adhesion between the support tape  202  and the wafer  102  is minimal, and the wafer  102  is removed from the support tape  202 , and exits through the wafer unload section  406 . 
       FIG. 7  is an isometric view of one embodiment of a tape and wafer tank entry assembly  700  for use in the tape and wafer loading section  402 , (see  FIG. 4 ), of various embodiments of the ELO process apparatus of the invention. The tape and wafer tank entry assembly  700 , includes a tape and wafer guiding block  702 . While in this embodiment, the tape and wafer guiding block  702  has four tapes engaging sides  704 , other numbers of sides may be used. Each tape engaging side  704  includes a plurality of pins  706  for engaging the track openings  206  in the support tape  202 . The tape and wafer guiding block  702  rotates about a shaft (not shown) that extends through a centrally located hole  708 . A shaft support plate  710  is provided on opposite sides of the tape and wafer guiding block  702 , for supporting and guiding the shaft. A slot  712  is provided in each shaft support plate  710 , and allows the shaft to oscillate as the tape and wafer guiding block  702  rotates. The tape and wafer guiding block  702  includes guiding pins  714  on each corner of the sides through which the hole  708  extends. The guiding pins  714  engage sides  716  of the shaft support plates  710 , so that each corner of the wafer guiding block  702  travels substantially vertically down into the etch bath, before traveling horizontally. The combined interaction of these elements, provides a planar support for each wafer  102  on a side  704  of the wafer guiding block  702  to decrease the likelihood that the support tape  202  is torn or otherwise removed from the wafers  102  prior to entering the etch bath  404 . By supporting the wafers  102  in this fashion, the chance of the ELO stack being damaged is reduced as the tape and wafer assembly enters the etch bath  404 . 
     In  FIG. 8 , an embodiment of a tape extraction assembly  800  is shown for use in the tape unload section  408  of the various ELO process apparatuses of the invention. The support tape  202  includes the ELO films that have been removed from the wafers  102  in the etch bath  404  as previously described. The tape extraction assembly  800  includes a tape engaging drum or roller  802  that rotates about a support shaft  804 . The roller  802  includes a plurality of pins  806  that engage the track openings  206  in the support tape  202 . In some embodiments, the pins  806  may be formed by attaching a cog or a sprocket to the roller  802 . Alternatively, the roller  802  containing may be formed or manufactured as a single device. The radius R 2  of the roller  802  is of a sufficient size to avoid damaging the ELO films or stacks on the support tape  202 , as described above with respect to R 1  of  FIG. 2D . In one embodiment, after disengaging from the roller  802 , the support tape  202  with the ELO films or stacks thereon, proceeds to the tape post etch processing sections of apparatus  300  as described above. 
     In some cases, the wafers  102  may not be fully removed from the support tape  202  in the etch bath, due to various processing variables.  FIG. 9  depicts a positive substrate detachment assembly  900 , which may be used with the various embodiments of the ELO process apparatuses of the invention. The positive substrate detachment assembly  900  includes a wafer engaging bar  902  that contacts the leading edge  904  of any wafers  102  remaining on the support tape  202  once the support tape  202  reaches the roller  802 . As the support tape  202  is driven around the roller  802  by pins  806 , the wafer engaging bar  902  peels the wafer  102  from the support tape  202 . While this action may damage the ELO stack, such as epitaxial film  106  associated with the wafer  102 , the positive substrate detachment assembly  900  avoids manual intervention by technicians, thereby decreasing downtime and increasing product throughput. 
     In  FIGS. 10-11 , a longitudinal chain wedge embodiment of an apparatus  1000  for performing an ELO process to remove ELO films or stacks from support wafers, is shown. Those components of apparatus  1000  that are similar in construction to the components in apparatus  400  are labeled with the same reference designators. Similar to the apparatus  400 , apparatus  1000  includes the tape and wafer loading section  402 , an etch bath  404 , a wafer unload section  406  and a tape unload section  408 .  FIG. 11  shows an enlarged view of a portion of the apparatus  1000  that illustrates a tape drive and tensioning portion  1100  of the apparatus  1000 . The support tape  202  includes a plurality of openings or track openings  206  along its sides, similar to those shown in  FIG. 2B . The tape drive and tensioning portion  1100  includes a plurality of drive blocks  1002  that are mounted on a drive belt or drive chain  1006 . The drive chain  1006  is driven and guided by a plurality of driving sprockets  1008  on each side of the etch bath  404 . At least one of the driving sprockets  1008  on each side of the etch bath  404  is attached to a motor (not shown) by a drive shaft (not shown), to rotate the driving sprocket and the drive train  1006 . In some embodiments, two or more of the driving sprockets  1008  may be driven in this manner by an associated motor, drive shaft and/or other driving structure. The drive blocks  1002  also include a pin  1102  that engages the support tape  202  in the track openings  206 . Each drive block  1002  further includes a tensioning roller  1104  that is rotatably mounted on a shaft  1106 . The tensioning rollers  1104  engage a rail  1004  ( FIG. 10 ) to maintain a spaced apart relationship of the drive blocks  1002  on opposite sides of the etch bath  404 , as they are driven therethrough. As the drive blocks  1002  drive the support tape  202  through the etch bath  404 , the lateral position of the sides of the support tape  202  are maintained by the pins  1102  engaging the outside portion  504  of the track openings  206 . 
     As with apparatus  400 , apparatus  1000  includes a static wedge that is formed by two ramps  512 . The static wedge progressively applies pressure to remove the wafers  102  from the support tape  202 , while leaving the ELO stack on the support tape  202 . A number of adjustable supports (not shown) adjustably connect the ramps  512  to an overhead assembly (not shown). The adjustable supports may include an adjustment mechanism to provide adjustment of the level of the ramps  512  at the various stages of the etch bath  404 . 
     As depicted in  FIG. 10 , the ramps  512  are spaced apart at their first end adjacent to the tape and wafer loading section  402 , and converge toward one another at their second end adjacent to the tape unload section  408 . The ramps  512  also extend further down into the etch bath  404  from their first end to their second end and thereby increasingly engage the top of the support tape  202  as it travels through the etch bath  404 . The wafers  102  are supported from below by a substrate support (not shown) that supports the wafers  102  near the tape unload section  408  of apparatus  1000  using a spring or buoyancy applied force. 
       FIGS. 11A-11C  are schematic diagrams illustrating the relationship between the ramps  512 , the support tape  202  and wafers  102 , as the support tape  202  and wafers  102  proceed through the etch bath  404 . In  FIG. 11A , the support tape  202  and wafer  102  are in an initial position of the etch bath  404 . The ramps  512  are substantially at the initial level of the support tape  202  and the wafers  102 , and the assembly is therefore relatively planar, with little or no pressure being applied to the support tape  202  and wafers  102 . The pins  1102  maintain the position of the ends of the support tape  202  as the support tape  202  progresses through the etch bath  404 . The pins  1102  and the drive blocks  1002  are maintained in a spaced apart relationship by the tensioning roller  1104  engaging the rails  1004 . A channel  1108  ( FIG. 11 ) surrounds the bottom portion of the pins  1102 , in one embodiment, to ensure that the pins  1102  do not disengage from the track openings  206 . In the position shown in  FIG. 11B , (approximately halfway through the etch bath  404 ), the ramps  512  are extended further into the etch bath  404 , and the center of the tape and the wafer  102  are pushed downward relative to the ends of the support tape  202 . A crevice  600  is therefore formed between tape  202 , and the wafer  102 . In the position shown in  FIG. 11C , (at a point near the tape unload section  408 ), the ramps  512  are extended even further into the etch bath  404 , and the center of the tape and the wafer  102  are pushed further downward relative to the ends of the support tape  202 . The size of the crevice  600 ′ is increased as compared to crevice  600  and the wafers  102  are increasingly removed from the support tape  202 . At a point in the progression slightly after the illustration shown in  FIG. 11C , the adhesion between the support tape  202  and the wafer  102  is minimal, and the wafer  102  is removed from the support tape  202 , and exits through the wafer unload section  406 . 
       FIGS. 12-14  illustrate another embodiment of an apparatus  1200  for performing an ELO process to remove ELO films or stacks from support wafers. It should be noted that portions of some elements have been omitted from  FIGS. 12-14  for clarity. Apparatus  1200  includes an etch bath  404  and an upper chain drive  1202  with a plurality of longitudinal point loads  1206  mounted in each “cage” formed by the upper chain drive  1202  and a series of transverse support members  1208 . The longitudinal point loads  1206  are rotatably connected at each end  1302  to the transverse support members  1208 , to allow the longitudinal point loads  1206  to rotate downward and apply pressure to the wafers. The longitudinal point loads  1206  rotate about an axis that extends in the longitudinal direction of the apparatus  1200 . The longitudinal point loads  1206  can apply the pressure constantly by their weight, or in another embodiment, the pressure can be positionally controlled using cams (not shown) that engage the longitudinal point loads  1206 . Each “cage” is sized to surround a single wafer such that each longitudinal point load  1206  applies pressure to the wafer located below. 
     Apparatus  1200  further includes a lower chain drive  1204  with a plurality of substrate supports and/or pushers  1402 . The lower chain drive  1204  also includes a series of transverse support members  1404  that form “cages” in the lower chain drive  1204 . Each “cage” includes a pusher  1402  that supports a wafer  102  from beneath the wafer  102 . The pushers  1402  may apply the pressure by a spring force, or by buoyancy within the etch bath  404 . The upper chain drive  1202  further includes a plurality of pins  1304  that extend through the track openings  206  in the support tape  202  and into recesses (not shown) in the lower chain drive  1204  to thereby lock the support tape  202  between the chain drives. The combined action of the pins  1304  maintaining the sides of the support tape  202  as the longitudinal point loads  1206  apply pressure to center of the support tape  202  and the wafer  102  located below it, creates the crevice and separation between the support tape  202  and the wafer  102  as described above with reference to apparatus  400  and apparatus  1000  in  FIGS. 6A-6C  and  11 A- 11 C, respectively. In one embodiment, the upper chain drive  1202  includes a plurality of pins  1306  that snap into receptacles  1308  in the lower chain drive  1204  to lock the chain drives together and hold the support tape  202  securely therebetween. 
       FIGS. 15-17  illustrate another embodiment of an apparatus  1500  for performing an ELO process to remove ELO films or stacks from support wafers. Apparatus  1500  is similar in operation to apparatus  1200 , and similar elements have been labeled with the same reference designator. A significant difference in apparatus  1500  is the use of transverse point loads  1502 . The ends  1604  of the transverse point loads  1502 , are rotatably mounted to the upper chain drive  1202  such that the transverse point loads  1502  rotate about an axis transverse to the longitudinal direction of apparatus  1500 . The transverse support members  1602  of the upper chain drive  1202  include a plurality of pins  1606  that engage the support tape  202  and extend into recesses  1608  in the transverse support members  1610  of the lower chain drive  1204 . The pins  1606  maintain the longitudinal position of each section of the support tape  202  within each “cage” formed by the upper chain drive  1202  and the lower chain drive  1204  and the transverse support members  1602  and  1610 . 
       FIG. 17  depicts each section of the support tape  202  progressively bowed downward by the force of the transverse point loads  1502  acting on the center of each section of the support tape  202 . At section  1702 , the support tape  202  has started to bow, forming a crevice  1710  at each end of the section. At section  1704 , the crevice  1710  has increased to remove a greater portion of the support tape  202  in section  1704  from the wafer  102 . In section  1706  the crevice has increased further, and in section  1708 , the wafer  102  has released from the support tape  202 . The transverse point loads  1502  are not shown in these sections for clarity.  FIG. 17  also illustrates further details of the pushers  1402  that in some embodiments are common to both apparatus  1500  as well as apparatus  1200 . The pushers  1402  are rotatable mounted to the transverse support members  1610  using a shaft (not shown) that extends through hole  1712  in the transverse support members  1610 . A central raised portion  1714  of the pusher  1402  supports the center portion of the wafer  102  located there above. The force applied by the pushers  1402  may be provided by a spring (not shown) or by buoyancy of the pushers  1402  in the etch bath  404 , such that the pushers  1402  move with the wafers  102  as they are progressively released from the support tape  202 . 
       FIGS. 18-20  illustrate a batch-type embodiment of an apparatus  1800  for performing an ELO process to remove ELO films or stacks from support wafers. The apparatus  1800  includes a tape and wafer loading section  1802 , an etch bath  1804 , a wafer unload section  1806  and a tape unload section  1808 . In apparatus  1800 , the wafers  102  are removed from the support tape  202  in batches. For example, in the embodiment illustrated in  FIG. 18 , three wafers are removed from the tape in each batch. Other embodiments may remove more than three or less than three wafers per batch depending on the particular configuration. Apparatus  1800  includes three point loads  1810  that provide downward force to form a crevice between the support tape  202  and the wafers  102 , and to further remove the wafers  102  from the support tape  202 . The point loads  1810  are supported by a finger carrier  1812 , that is lowered and raised to engage or disengage the point loads  1810  from the support tape  202 , respectfully. The finger carrier  1812  also supports a plurality of fingers  1902  that engage the track openings  206  in the support tape  202  to maintain the sides of the support tape  202  in a spaced apart relationship. Two rails  1814  (one shown in the cutaway view of  FIG. 18 ) include recesses  1816  for the fingers  1902  to engage to positively lock the sides of the support tape  202  into place. As is shown in the cross section of  FIG. 20 , when the finger carrier  1812  is lowered, those fingers (labeled as  1902 ′ in  FIG. 20 ) that are aligned with the track openings  206  in the support tape  202 , extend through the support tape  202  and engage the recesses  1816 . As those fingers are flexible, those fingers (labeled as  1902  in  FIG. 20 ) that do not align with the track openings  206  in the support tape  202 , do not extend through the tape but remain in a flexed position above the support tape  202 . 
     Underneath the tape and wafer assembly is a wafer support and handling assembly  1904 . The wafer support and handling assembly  1904  includes two substrate drive belts  1906  and a bottom pusher  2002 . The substrate drive belts  1906  support the wafers  102  as the tape and wafer assembly is fed into the etch bath  404  and transports the wafers  102  to the wafer unload section  1806  once they are removed from the support tape  202 . The bottom pusher  2002  includes two rails  2004  that support the wafers  102  during the ELO process after loading the tape and wafer assembly and prior to release of the wafers  102  from the support tape  202 . 
       FIGS. 21 through 38  illustrate the relationship between the moving parts of apparatus  1800  during various stages of an ELO batch process, as described by some embodiments herein.  FIG. 40  is a flow chart illustrating one embodiment of a method  4000  for a batch ELO process that may be performed by apparatus  1800 . In  FIGS. 21 and 22 , the apparatus  1800  is shown in a loading position where the tape and wafer assembly is loaded into the etch bath  1804  in block  4002  of method  4000 . The pins  806  in roller  802  engage the track openings  206  in tape  202  and load the tape and wafer assembly into the etch bath  1804  as the roller  802  rotates. The substrate drive belts  1906  are in a raised position so that they can support the wafers  102  from below, so that they do not prematurely release from the support tape  202 , which could cause damage to the ELO stack. The substrate drive belts  1906  are mounted on pulleys  2102  of belt carrier  2104 . In one embodiment, the pulleys may be driven by a drive motor and associated mechanisms (not shown) that are synchronized with the drive system of roller  802 . In the raised position of wafer support and handling assembly  1904 , a lever  2106  engages the top of slot  2108  in sidewall  2110  of etch bath  1804 . The lever  2106  operates a mechanism (not shown) within belt carrier  2104  to lower the rails  2004  of bottom pusher  2002 , ( FIG. 20 ) so that they do not engage the wafers as they are loaded into the etch bath  1804 . The finger carrier  1812  is in a raised position such that the point loads  1810  and fingers  1902  are disengaged from the support tape  202 . 
     In some embodiments, the point load and finger carrier  1812  is lowered in block  4004  during method  4000 , after the tape and wafer assembly is loaded into the etch bath  1804 , as shown in  FIGS. 23 through 28 .  FIGS. 23 and 24  show the finger carrier  1812  lowered to a first intermediate position wherein the point loads  1810  initially contact the support tape  202 . Fingers  1902  remain above the support tape  202 . In  FIGS. 25 and 26 , the finger carrier  1812  has further lowered to a further intermediate position wherein the point loads  1810  have not lowered further as they are supported by the tape and wafer assembly. The fingers  1902  still remain above the support tape  202 .  FIGS. 27 and 28  show the finger carrier  1812  fully lowered such that the fingers  1902 ′ that are aligned with the track openings  206  in tape  202  engage with the recesses  1816  to lock the sides of the support tape  202  into the spaced apart relationship. In the positions shown in  FIGS. 23 through 28 , the wafer support and handling assembly  1904  remains in its raised position to support the tape and wafer assembly such that the wafers  102  do not prematurely release from the support tape  202  as previously described. 
     Once the finger carrier  1812  has been fully lowered, the method  4000  proceeds to block  4006  wherein the wafer support and handling assembly  1904  is lowered as shown in  FIGS. 29 and 30 . In the lowered position of wafer support and handling assembly  1904 , the lever  2106  does not engages the top of the slot  2108  in the sidewall  2110  of the etch bath  1804 . The rails  2004  of bottom pusher  2002 , are raised above the top of the wafer support and handling assembly  1904 , but are still located below the wafers  102  such that the wafers  102  are free to move downward, once they are released from the support tape  202 . Once the wafer support and handling assembly  1904  is lowered, the method proceeds to block  4008  and the ELO process is initiated. The ELO process may initiate, in some embodiments, by the weight of the point loads  1810  acting on the tape and substrate assembly to bow the support tape  202  and drive the wafers  102  downward such that crevices  3202  are formed at the edges of the wafers  102 . In other embodiments, a cam or other element (not shown) may apply a force to the top surface  3204  of the point loads  1810  to move the point loads  1810  downward. 
       FIGS. 33 and 34  illustrate that the ELO process continues, with the point loads  1810  further lowered such that the wafers  102  are pushed further down, and the crevices  3202  have increased in size as more of the wafers  102  are removed from the support tape  202 . In  FIGS. 35 and 36 , the point loads  1810  are shown in their fully lowered position, such that the wafers  102  are supported by the rails  2004  of bottom pusher  2002 . The crevices  3202  between the support tape  202  and the wafers  102  have further increased in size such that more of each wafer  102  has been removed from the support tape  202 . 
     Once the point loads  1810  are in their fully lowered position, the method  4000  proceeds to block  4010  where the point loads  1810  are rotated.  FIGS. 37 and 38  show the point loads  1810  in a rotated position. By rotating the point loads  1810 , the pressure point applied to the tape and wafer assembly is moved back and forth (left to right in  FIG. 37 ), to further remove the support tape  202  and ELO stack from the wafer  102 . The point loads  1810  may be rotated by a cam assembly or other mechanism (not shown). After rotating the point loads  1810 , the ELO process is complete and the wafers  102  are removed from the support tape  202 , as indicated in block  4012  of method  4000 . The method  4000  then proceeds to block  4014  and the point load and finger carrier  1812  is raised as shown by its position illustrated in  FIG. 22 . After raising the point load and finger carrier  1812 , the method  4000  proceeds to block  4016 , wherein the wafer support and handling assembly  1904  is partially raised as is also shown in  FIG. 22 . In  FIG. 22 , it should be noted that at this point in the process, the center portion  2202  of the tape and ELO stack is released from the wafers  102 , and the tape and ELO stack form a straight line above and not contacting the wafers  102 . By raising the wafer support and handling assembly  1904  the substrate drive belts  1906  are in contact with the wafers  102  and the rails  2004  of bottom pusher  2002  are retracted as described above. The method  4000  then proceeds to block  4018  and the wafers  102  are transported out of the etch bath  1804  and to the wafer unload section  1806  ( FIG. 18 ) by pulleys  2102  driving the substrate drive belts  1906 . In the wafer unload section  1806 , a series of belts  1818  and pulleys  1820  transport the removed wafers (such as shown by  1822 ) out of the apparatus  1800  and to subsequent processes such as those shown in apparatus  300  of  FIG. 3 . 
     After the removed wafers  102  have been transported out of the apparatus  1800 , the method  4000  proceeds to block  4020 , the wafer support and handling assembly  1904  is raised to its uppermost position as shown in  FIG. 24 . The method  4000  is then restarted at block  4002  and the next batch (length) of tape and wafer assembly is loaded into the etch bath  1804 . 
     In several alternative embodiments, a plurality of substrates  100  may be disposed on a single support substrate. Alternatively, a plurality of ELO thin film stacks  150  may be disposed on a support substrate that contains multiple gallium arsenide wafers or surfaces. Each of the ELO thin film stacks  150  is disposed on or over each gallium arsenide wafer or surface on the support substrate. Therefore, the support substrate may contain at least 2 substrates  100  or ELO thin film stacks  150 , but usually contains 3, 4, 5, 6, 9, 12, 16, 20, 24, 50, 100, or more substrates  100  or ELO thin film stacks  150 . 
     Each ELO thin film stack  150  contains an epitaxial film  106  disposed on or over a sacrificial layer  104 . The support tape  202  may be disposed on or over each of the substrates  100 , such as by the epitaxial film  106 . In some embodiments, each of the ELO thin film stacks  150  may be grown on an individual wafer  100  and then coupled with the support substrate. In other embodiments, each of the ELO thin film stacks  150  may be grown on an individual gallium arsenide wafer or surface already coupled with the support substrate. 
     In some examples, the support substrate may contain at least 2 epitaxial substrates or surfaces, such as gallium arsenide wafers or gallium arsenide surfaces, but usually contains 3, 4, 5, 6, 9, 12, 16, 20, 24, 50, 100, or more epitaxial substrates or surfaces. In some embodiments, the support substrate may contain or be made from columbium, columbium alloys, titanium carbide, magnesium silicate, steatite, tungsten carbide, tungsten carbide cermet, iridium, alumina, alumina ceramics, zirconium, zirconium alloys, zirconia, zirconium carbide, osmium, tantalum, hafnium, molybdenum, molybdenum alloys, oxides thereof, silicates thereof, alloys thereof, derivatives thereof, or combinations thereof. In some examples, the support substrate has no porosity or substantially no porosity. In other examples, the support substrate may be resistant to hydrogen fluoride and hydrofluoric acid. 
     An adhesive may be used to form an adhesive layer between the support substrate and either the wafer  100 , or the gallium arsenide wafers or surfaces. In one example, each wafer  100 , containing an individual ELO thin film stack  150  disposed thereon, may be coupled with the support substrate by an adhesive to form an adhesive layer therebetween. In another example, each individual gallium arsenide wafer or gallium arsenide surface may be coupled with the support substrate by an adhesive to form an adhesive layer therebetween. The adhesive may be the same adhesive as used to form the adhesive layer  204 , as described above. Alternatively, the adhesive may be different than the adhesive used to form the adhesive layer  204 . In some examples, the adhesion layer contains an optical adhesive or an ultraviolet-curable adhesive. In other examples, the adhesion layer may contain a mercapto ester compound and may further contain butyl octyl phthalate, tetrahydrofurfuryl methacrylate, acrylate monomer, derivatives thereof, or combinations thereof. In other examples, the adhesion layer contains silicone or sodium silicate. 
     In another alternative embodiment, a substrate  100  contains a sacrificial layer  104  disposed on a wafer  102 , an epitaxial film  106  disposed over the sacrificial layer  104 , and a support handle is the support tape  202  disposed over the epitaxial film  106 . In some embodiments, the support tape  202  contains multiple layers including a stiff support layer disposed over the epitaxial film  106 , a soft support layer disposed over the stiff support layer, and a handle plate layer disposed over the soft support layer. In other embodiments, the support tape  202  is the handle plate layer and is disposed over the soft support layer, which is disposed over the stiff support layer, which is disposed over the epitaxial film  106 . The support tape  202  is disposed on and maintains compression of the epitaxial film  106 . 
     In some embodiments, the stiff support layer may contain a polymer, a copolymer, an oligomer, derivatives thereof, or combinations thereof. In one embodiment, the stiff support layer contains a copolymer. In one example, the copolymer may be an ethylene/vinylacetate (EVA) copolymer or derivatives thereof. An EVA copolymer which is useful as the stiff support layer is WAFER GRIP adhesion film, commercially available from Dynatex International, located in Santa Rosa, Calif. 
     In other examples, the stiff support layer may contain a hot-melt adhesive, an organic coating, an inorganic material, or combinations thereof. In some examples, the inorganic material contains a single inorganic layer or multiple inorganic layers, such as metal layers or metallic foils. In another example, the stiff support layer may contain wax or derivatives thereof, such as black wax. 
     In another embodiment, the soft support layer may contain an elastomer, such as rubber, foam, or derivatives thereof. Alternatively, the soft support layer may contain a material such as neoprene, latex, or derivatives thereof. The soft support layer may contain a monomer. For example, the soft support layer may contain an ethylene propylene diene monomer or derivatives thereof. 
     In another embodiment, the soft support layer may contain a liquid or a fluid contained within a membrane. Alternatively, the soft support layer may contain a gas contained within a membrane. The membrane may contain a material such as rubber, foam, neoprene, latex, or derivatives thereof. In one example, the membrane contains natural rubber, synthetic rubber, or latex. 
     In another embodiment, the handle plate may contain a material such as plastic, polymer, oligomer, derivatives thereof, or combinations thereof. In one example, the handle plate may contain polyester or derivatives thereof. The handle plate may have a thickness within a range from about 50.8 μm to about 127.0 μm, such as about 23.4 μm. 
     In one embodiment, the method further includes removing the epitaxial film  106  from the wafer  102  and attaching a support substrate, such as the support tape  202 , to an exposed surface of the epitaxial film  106  by an adhesive layer  204 . The support tape  202  may be bonded to the exposed surface of the epitaxial film  106  by an adhesive. In one example, the adhesive layer  204  contains an optical adhesive and/or may be UV-curable, such as commercially available as Norland UV-curable optical adhesive. In some examples, the adhesive may contain a mercapto ester compound. In other examples, the adhesive may further contain a material such as butyl octyl phthalate, tetrahydrofurfuryl methacrylate, acrylate monomer, derivatives thereof, or combinations thereof. 
     In another alternative embodiment, a substrate  100  contains a support substrate, such as support tape  202  disposed over a first surface of the epitaxial film  106 , and the support tape  202  disposed over the other surface of the epitaxial film  106 . An adhesive layer  204  may be disposed between the epitaxial film  106  and the support tape  202 . The support tape  202  contains the stiff support layer disposed over the epitaxial film  106 , the soft support layer disposed over the stiff support layer, and the handle plate disposed over the soft support layer. 
     In one example, the adhesive may be cured by exposing the adhesive to UV radiation. Generally, the adhesive may be exposed to the UV radiation for a time period within a range from about 1 minute to about 10 minutes, preferably, from about 3 minutes to about 7 minutes, such as about 5 minutes. The adhesive may be cured at a temperature within a range from about 25° C. to about 75° C., such as about 50° C. 
     In other examples, the adhesive may be a silicone adhesive or may contain sodium silicate. In these examples, the adhesive may be cured for a time period within a range from about 10 hours to about 100 hours, preferably, from about 20 hours to about 60 hours, and more preferably, from about 30 hours to about 50 hours, for example, about 42 hours. The adhesive may be cured at a temperature within a range from about 25° C. to about 75° C., such as about 50° C. Also the adhesive may be cured at a pressure within a range from about 1 psi (pounds per square inch) to about 50 psi, preferably, from about 3 psi to about 25 psi, and more preferably, from about 5 psi to about 15 psi. In one example, the pressure may be about 9 psi. 
     In other embodiments, the sacrificial layer  104  may be exposed to an etching process to remove the epitaxial film  106  from the wafer  102 . In some embodiments, the sacrificial layer  104  may be exposed to a wet etch solution during the etching process. 
     In some embodiments, the sacrificial layer  104  may be exposed to a wet etch solution during the etching process. The wet etch solution contains hydrofluoric acid and may contain a surfactant and/or a buffer. In some example, the sacrificial layer  104  may be etched at a rate of about 0.3 mm/hr or greater, preferably, about 1 mm/hr or greater, and more preferably, about 5 mm/hr or greater. In an alternative embodiment, the sacrificial layer  104  may be exposed to an electrochemical etch during the etching process. The electrochemical etch may be a biased process or a galvanic process. Also, the sacrificial layer  104  may be exposed to a vapor phase etch during the etching process in another embodiment described herein. The vapor phase etch includes exposing the sacrificial layer  104  to hydrogen fluoride vapor. The etching process may be a photochemical etch, a thermally enhanced etch, a plasma enhanced etch, a stress enhanced etch, derivatives thereof, or combinations thereof. 
     In embodiments herein, the epitaxial materials contained within epitaxial film  106  may include gallium arsenide, aluminum gallium arsenide, indium gallium phosphide, alloys thereof, derivatives thereof, or combinations thereof. The epitaxial film  106  may have a rectangular geometry, a square geometry, or other geometries. The epitaxial film  106  may contain one layer, but usually contains multiple layers. In some examples, the epitaxial film  106  contains a layer having gallium arsenide and another layer having aluminum gallium arsenide. In another example, the epitaxial film  106  contains a gallium arsenide buffer layer, an aluminum gallium arsenide passivation layer, and a gallium arsenide active layer. The gallium arsenide buffer layer may have a thickness within a range from about 100 nm to about 500 nm, such as about 300 nm, the aluminum gallium arsenide passivation layer has a thickness within a range from about 10 nm to about 50 nm, such as about 30 nm, and the gallium arsenide active layer has a thickness within a range from about 500 nm to about 2,000 nm, such as about 1,000 nm. In some examples, the epitaxial film  106  further contains a second aluminum gallium arsenide passivation layer. 
     In other embodiments herein, the epitaxial film  106  may contain a photovoltaic cell structure containing multiple layers. The cell structure may contain gallium arsenide, n-doped gallium arsenide, p-doped gallium arsenide, aluminum gallium arsenide, n-doped aluminum gallium arsenide, p-doped aluminum gallium arsenide, indium gallium phosphide, alloys thereof, derivatives thereof, or combinations thereof. In many examples, the gallium arsenide is n-doped or p-doped. 
     In another embodiment, the sacrificial layer  104  may contain aluminum arsenide, alloys thereof, derivatives thereof, or combinations thereof. In one example, the sacrificial layer  104  contains an aluminum arsenide layer and has a thickness of about 20 nm or less, preferably, within a range from about 1 nm to about 10 nm, and more preferably, from about 4 nm to about 6 nm. 
     While the foregoing is directed to embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.