Patent Publication Number: US-10319754-B2

Title: Method of fabricating crystalline island on substrate

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. patent application Ser. No. 15/184,429, filed on Jun. 16, 2016 and published as US 2016/0300716, which is incorporated herein by reference in its entirety. U.S. patent application Ser. No. 15/184,429, in turn, is a continuation-in-part of U.S. patent application Ser. No. 14/610,567, filed on Jan. 30, 2015 and published as US 2015/0357192, which is also incorporated herein by reference in its entirety. U.S. Ser. No. 14/610,567, in turn, claims priority from U.S. Provisional Patent Application No. 62/007,624, filed on Jun. 4, 2014, which is also incorporated herein by reference it its entirety. 
    
    
     FIELD 
     The present specification relates to a method of fabricating one or more crystalline islands of an island material abutting a substrate. 
     BACKGROUND 
     Certain electronic applications, such as OLED display back panels, require small islands of high-quality semiconductor material distributed over a large area. This area can be 50 inches diagonally and larger, and exceeds the sizes of crystalline semiconductor wafers that can be fabricated using the traditional boule-based techniques. 
     WO 2013/053052 A1, incorporated herein by reference, discloses fabricating a large number of small, loose, crystalline semiconductor spheres. The spheres are then distributed on a patterned substrate and affixed to the substrate at predetermined locations to form an array of spheres on the substrate. Planarizing the spheres exposes a cross-section of each sphere, thereby providing an array of high-quality, crystalline semiconductor islands for device fabrication on a globally planarized surface. 
     U.S. Pat. No. 4,637,855, incorporated herein by reference, discloses fabricating spheres of silicon on a substrate by applying a slurry of metallurgical grade silicon to the substrate and then patterning the slurry layer to provide regions of metallurgical silicon of uniform size. The substrate is then heated to melt the silicon, which then beads to the surface to form molten spheres of silicon, which are then cooled to crystallize them. The spheres have very weak adhesion to the substrate and are easily detached from the substrate by simply knocking them loose. The loose spheres are collected and undergo further processing. 
     US 2012/0067273 A1, incorporated herein by reference, discloses fabricating silicon wafers by bringing a substrate into contact with a reservoir of molten silicon, forming a layer of solid silicon on the substrate, and subsequently detaching the solid layer from the substrate. The disclosed method can potentially be used to fabricate silicon wafers with large areas. 
     SUMMARY 
     Provided herein is a method of fabricating one or more crystalline islands of an island material abutting a substrate. For each crystalline island, particles of the island material are deposited abutting the substrate, and the substrate and the particles are then heated to melt and fuse the particles to form a respective molten globule. The substrate and the respective molten globules are then cooled to crystallize the molten globules, thereby securing the crystalline islands to the substrate. 
     This method can allow for fabricating crystalline islands using particulate starting materials. In addition, in some implementations the crystalline islands being secured to the substrate can allow for further processing of the islands; for example, planarizing at least a portion of each crystalline island to expose a cross-section of each island. If the crystalline islands are sufficiently high-quality crystalline semiconductors, these cross-sections can then be used to fabricate electronic devices. This method can also allow for fabricating arrays of crystalline islands, distributed over an area potentially exceeding the areas of crystalline semiconductor wafers that can be fabricated using traditional boule-based techniques. 
     According to an aspect of the present specification, there is provided a method of fabricating a crystalline island of an island material, the method comprising depositing particles of the island material abutting a substrate, heating the substrate and the particles of the island material to melt and fuse the particles to form a molten globule, and cooling the substrate and the molten globule to crystallize the molten globule, thereby securing the crystalline island of the island material to the substrate. 
     The crystalline island can comprise a single crystal of the island material or a polycrystalline form of the island material. 
     The method can further comprise planarizing at least a portion of the crystalline island to expose a cross-section of the crystalline island. 
     The securing can comprise the molten globule wetting the substrate at a wetting angle smaller than about 90 degrees and the crystalline island adhering to the substrate. 
     The depositing can comprise defining a depression in the substrate, and transferring the particles of the island material into the depression. 
     When the depositing comprises defining a depression and transferring the particles of the island material into the depression, the securing can comprise a portion of a surface of the depression enveloping a portion of a surface of the crystalline island. 
     When the depositing comprises defining a depression and transferring the particles of the island material into the depression, the depression can be shaped to have at least one vertex. 
     When the depositing comprises defining a depression and transferring the particles of the island material into the depression, the depression can comprise a first depression, and a second depression within the first depression, the second depression smaller and deeper than the first depression. 
     When the depositing comprises defining a depression and transferring the particles of the island material into the depression, the transferring can comprise one or more of doctor-blading the particles of the island material into the depression, and electrostatic deposition of the particles of the island material into the depression using a charged pin. 
     When the depositing comprises defining a depression and transferring the particles of the island material into the depression, the transferring can comprise flowing a suspension onto the substrate and into the depression, the suspension comprising a dispersion of the particles of the island material in a carrier medium, and squeegeeing the suspension located on the substrate outside the depression; and the heating can further comprise eliminating the carrier medium prior to the melting and fusing the particles of the island material. 
     The cooling can comprise one or more of oxidizing an outer surface of the molten globule, super-cooling the molten globule, and applying a physical impact to the substrate. 
     The depositing can comprise transferring particles of the island material into a through hole in the substrate. 
     When the depositing comprises transferring particles of the island material into a through hole in the substrate, pressure can be applied at a second end of the through hole to push the molten globule partially out of a first end of the through hole to form a convex meniscus. 
     When the depositing comprises transferring particles of the island material into a through hole in the substrate, the securing can comprise a portion of a surface of the through hole enveloping a portion of a surface of the crystalline island. 
     When the depositing comprises transferring particles of the island material into a through hole in the substrate, the method can further comprise after the cooling to crystallize the molten globule, planarizing a portion of the meniscus to expose a cross-section of the crystalline island. 
     When the depositing comprises transferring particles of the island material into a through hole in the substrate, a portion of a surface of the substrate outside the through hole and adjacent a first end of the through hole can have a wetting angle with the molten globule of less than about 90 degrees. 
     The depositing can comprise dispersing the particles of the island material in a carrier medium to create a suspension and transferring the suspension onto the substrate, and the heating can further comprise eliminating the carrier medium prior to the melting and fusing the particles of the island material. 
     When the depositing can comprise dispersing the particles of the island material in a carrier medium to create a suspension and transferring the suspension onto the substrate, and the heating can further comprise eliminating the carrier medium prior to the melting and fusing the particles of the island material, the transferring can comprise one or more of stamping the suspension onto the substrate, screen printing the suspension onto the substrate, inkjet printing the suspension onto the substrate, and spin-coating the suspension onto the substrate, and lithographically patterning the spin-coated suspension. 
     The depositing can comprise dispersing the particles of the island material in a carrier medium to create a suspension, forming the suspension into a sheet, causing the sheet to solidify to form a solid sheet, patterning the solid sheet by removing one or more portions of the sheet to form a patterned sheet, and overlaying the patterned sheet on the substrate; and the heating can further comprise eliminating the carrier medium prior to the melting and fusing the particles of the island material. 
     The molten globule can have a first wetting angle with a first portion of a surface of the substrate in contact with the molten globule, and a second wetting angle with a second portion of the surface of the substrate, the second portion abutting the first portion, and the second wetting angle being greater than the first wetting angle. 
     An area of the substrate in contact with the molten globule can comprise one or more of one or more guiding protrusions, one or more guiding depressions, and a metallic grid for controlling initiation of crystallization as the molten globule is cooled. 
     The coefficient of thermal expansion (CTE) of the substrate at a temperature within about 20° C. of the melting point of the island material can match the CTE of the island material at the melting point of the island material. 
     The island material can comprise silicon. 
     The substrate can comprise alumina. 
     The securing can comprise over-coating the crystalline island and the substrate with an over-coating layer to form a stack whereby the crystalline island is sandwiched between the substrate and the over-coating layer. 
     When the securing comprises over-coating the crystalline island and the substrate with an over-coating layer to form a stack whereby the crystalline island is sandwiched between the substrate and the over-coating layer, the method can further comprise planarizing the stack to expose a cross-section of the crystalline island. 
     According to a further aspect of the present specification, there is provided a method of fabricating a crystalline island of an island material, the method comprising depositing particles of the island material on a first substrate, sandwiching the particles of the island material between the first substrate and a second substrate by placing the second substrate adjacent the first substrate, heating the first substrate, the second substrate, and the particles of the island material to melt and fuse the particles to form a molten globule, cooling the first substrate, the second substrate, and the molten globule to crystallize the molten globule, thereby forming the crystalline island of the island material. 
     The cooling can further comprise one or more of applying a pressure pulse to the molten globule, adding a seed crystal to the molten globule, and super-cooling the molten globule. 
     The first substrate can have a first area being a portion of a surface of the first substrate that comes into contact with the molten globule, and the second substrate can have a second area being a portion of a surface of the second substrate that comes into contact with the molten globule, and one or more of the first area and the second area can comprise one or more of one or more protrusions, one or more depressions, a metallic grid, for controlling initiation of crystallization as the molten globule is cooled. 
     According to a further aspect of the present specification, there is provided a method of fabricating a crystalline island of an island material, the method comprising: depositing particles of the island material abutting a substrate; heating the substrate and the particles of the island material to melt and fuse the particles to form a molten disk; cooling the substrate and the molten disk to crystallize the molten disk, thereby securing the crystalline island of the island material to the substrate; and planarizing at least a portion of the crystalline island to expose a cross-section of the crystalline island. 
     According to a further aspect of the present specification, there is provided a method of fabricating a crystalline island of an island material, the method comprising: depositing the island material on a substrate; heating the substrate and the island material, the heating melting the island material to form a first molten disk, the heating also forming a second molten disk comprising oxygen and the island material, the second molten disk disposed between the first molten disk and the substrate; and cooling the substrate, the first molten disk, and the second molten disk to crystallize the first molten disk, thereby forming the crystalline island of the island material. 
     The method can further comprise planarizing at least a portion of the crystalline island to expose a cross-section of the crystalline island. 
     The method can further comprise, after the cooling: over-coating the crystalline island and the substrate with an over-coating layer to form a stack; and planarizing the stack to expose a cross-section of the crystalline island. 
     The method of claim can further comprise, before the depositing: forming an oxide layer on the substrate; and wherein: the depositing can comprise depositing the island material on the oxide layer; and the second molten disk can comprise the oxide layer in a molten state. 
     The forming the oxide layer can comprise depositing on the substrate the oxide layer comprising an oxide of the island material. 
     The depositing can comprise depositing the oxide layer according to a predetermined pattern. 
     The forming the oxide layer can comprise: depositing the island material on the substrate according to a predetermined pattern; and oxidizing the island material. 
     The depositing the island material can comprise one or more of: depositing particles of the island material; and depositing a layer of the island material. 
     The heating can comprise heating the substrate, the island material, and the oxide layer in a non-oxidizing atmosphere. 
     The method can further comprise one or more of, before the depositing: polishing the substrate according to a predetermined pattern; and roughening the substrate according to the predetermined pattern. 
     The depositing can comprise depositing the island material on the substrate in a shape of a plurality of interconnected nodes, each node connected to one or more other nodes. 
     The second molten disk can further comprise aluminum originating from the substrate. 
     The heating can comprises heating the substrate and the island material to at least about 1500° C. 
     The first molten disk can have a maximum thickness that is at least about ten times smaller than the smaller of its maximum length and maximum width. 
     According to a further aspect of the present specification, there is provided a semiconductor device comprising: a substrate; an intermediary disk disposed on the substrate, the intermediary disk comprising oxygen and an island material; and an island disk disposed on the intermediary disk, the island disk comprising the island material, the island disk being crystalline; wherein: the island material is deposited on the substrate; and the intermediary disk is formed by melting and then solidifying the island material on the substrate. 
     The substrate can comprise alumina and the island material comprises silicon. 
     The intermediary disk can further comprise aluminum originating from the substrate. 
     According to a further aspect of the present specification, there is provided a method of fabricating a crystalline island of an island material, the method comprising: depositing the island material on a substrate; heating the substrate and the island material, the heating melting the island material to form a molten corpus, the heating also forming a molten disk comprising oxygen and the island material, the molten disk disposed between the molten corpus and the substrate; and cooling the substrate, the molten corpus, and the molten disk to crystallize the molten corpus to form a crystallized corpus, at least a portion of the crystallized corpus forming the crystalline island of the island material. 
     The method can further comprise planarizing at least a portion of the crystalline island to expose a cross-section of the crystalline island. 
     The method can further comprise, after the cooling: over-coating the crystalline island and the substrate with an over-coating layer to form a stack; and planarizing the stack to expose a cross-section of the crystalline island. 
     The method can further comprise, before the depositing: forming an oxide layer on the substrate; and wherein: the depositing comprises depositing the island material on the oxide layer; and the molten disk comprises the oxide layer in a molten state. 
     The forming the oxide layer can comprise depositing on the substrate the oxide layer comprising an oxide of the island material. 
     The depositing can comprise depositing the oxide layer according to a predetermined pattern. 
     The forming the oxide layer can comprise: depositing the island material on the substrate according to a predetermined pattern; and oxidizing the island material. 
     The heating can comprise heating the substrate, the island material, and the oxide layer in a non-oxidizing atmosphere. 
     The method can further comprise one or more of, before the depositing: polishing the substrate according to a predetermined pattern; and roughening the substrate according to the predetermined pattern. 
     The substrate can comprise alumina. 
     The molten disk can further comprise aluminum originating from the substrate. 
     The island material can comprise silicon and the heating can comprise heating the substrate and the island material to at least about 1500° C. 
     Cooling the molten corpus can form a first solid portion distal from the substrate and a second solid portion proximal the substrate, the first solid portion separating spontaneously from the second solid portion during the cooling, the second solid portion forming the crystalline island. 
     The depositing can comprise: positioning a template on a surface of the substrate, the template comprising a channel having a first end abutting the surface and a second end opposite the first end, the surface capping the first end; and filling at least a portion of the channel with the island material. 
     The method can further comprise: after the cooling, removing the template from the substrate. 
     After the removing, a first portion of the crystallized corpus can remain on the substrate to form the crystalline island and a second portion of the crystallized corpus can remain in the channel. 
     The channel can comprise: a first region proximate the first end, in the first region the channel having a first cross-sectional area; and a second region distal from the first end, in the second region the channel having a second cross-sectional area, the first cross-sectional area different from the second cross-sectional area. 
     An inner surface of the channel can define a vertex separating the first region from the second region. 
     The template can further comprise one or more further channels, each further channel having a corresponding first end abutting the surface and a corresponding second end opposite the corresponding first end, the surface capping the corresponding first end; and the depositing can further comprise filling at least a portion of the one or more further channels with the island material. 
     The second end can be in communication with a reservoir configured to store the island material for at least partially filling the channel with the island material. 
     The reservoir can be integrally formed with the template. 
     The reservoir can comprise a crystallization initiator, the crystallization initiator comprising one or more of a depression into and an extension from a reservoir surface, the crystallization initiator configured to come into contact with the molten corpus and initiate crystallization during the cooling. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the various implementations described herein and to show more clearly how they may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which: 
         FIG. 1  depicts a method of fabricating a crystalline island abutting a substrate, according to non-limiting implementations. 
         FIG. 2  depicts a top perspective view of crystalline islands on a substrate, according to non-limiting implementations. 
         FIG. 3  depicts a top perspective view of a substrate having a depression, according to non-limiting implementations. 
         FIG. 4  depicts a collection of possible shapes for a depression, according to non-limiting implementations. 
         FIG. 5  depicts a top perspective view of a substrate having a depression within a depression, according to non-limiting implementations. 
         FIGS. 6 a - d    depict a cross-section of a substrate having a depression within a depression at different stages of forming a crystalline island in the depressions, according to non-limiting implementations. 
         FIG. 7  depicts a cross-section of a substrate having a depression within a depression, according to non-limiting implementations. 
         FIG. 8  depicts a cross-section of a substrate having a depression within a depression, according to non-limiting implementations. 
         FIGS. 9 a - c    depict a cross-section of a substrate having a through hole, at different stages of forming a crystalline island in the through hole, according to non-limiting implementations. 
         FIG. 10  depicts a method of depositing particles of an island material on a substrate, according to non-limiting implementations. 
         FIG. 11  depicts a cross-section of a crystalline island on a substrate, both over-coated, according to non-limiting implementations. 
         FIG. 12  depicts a cross-section of a crystalline island on a substrate, both over-coated, according to non-limiting implementations. 
         FIG. 13  depicts a method of fabricating a crystalline island sandwiched between two substrates, according to non-limiting implementations. 
         FIG. 14  depicts a cross-section of a molten globule sandwiched between two substrates, according to non-limiting implementations. 
         FIG. 15  depicts a top plan view of an array of pyramids and abutting crystal grains on a substrate, according to non-limiting implementations. 
         FIG. 16  depicts a cross-section of a molten globule sandwiched between two substrates, according to non-limiting implementations. 
         FIGS. 17 a - d    depict in cross-section various stages of fabricating a crystalline island on a substrate, according to non-limiting implementations. 
         FIG. 18  depicts a photomicrograph of a crystalline island on a substrate, according to non-limiting implementations. 
         FIGS. 19 a - c    depict, in side elevation cross-sectional views, various stages of fabricating a crystalline island on a substrate, according to non-limiting implementations. 
         FIGS. 20 a - c    depict, in side elevation cross-sectional views, various stages of fabricating a crystalline island on a substrate, according to non-limiting implementations. 
         FIGS. 21 a - b    depict, in side elevation cross-sectional views, various stages of fabricating crystalline islands on a substrate, according to non-limiting implementations. 
         FIGS. 22 a - b    depict, in top plan views, various stages of fabricating crystalline islands on a substrate, according to non-limiting implementations. 
     
    
    
     DETAILED DESCRIPTION 
     An implementation of the present invention is reflected in method  100  shown in  FIG. 1 . Method  100  can be used to fabricate a crystalline island abutting a substrate, on top of or inside a substrate. First, as shown in box  105 , island material can be deposited abutting the substrate, on or in the substrate. The island material can be in particulate form. Particles of the island material can be deposited at a predetermined location relative to the substrate, which can include, but is not limited to, deposition on all or a portion of the surface of the substrate. Particles of the island material can be deposited as a substantially pure powder, a powder with some additives or impurities, or as particles of the island material suspended in a carrier medium. Additives can be used to dope, alloy, or otherwise compound the island material. 
     Subsequently, as shown in box  110 , the substrate and the particles of the island material can be heated. The heating can be by conduction, convection, and/or radiative heating, and can be performed in a furnace, kiln, or other suitable heating apparatus known to the skilled person. The heating melts and fuses the particles of the island material to form a molten globule of the island material. When a carrier medium is used to deposit the island material, the heating can evaporate, burn off, or otherwise eliminate the carrier medium before the melting and fusing of the island material particles. The island and substrate materials can be chosen so that the substrate does not melt at the temperature required to melt and fuse the particles of the island material. 
     Subsequently, as shown in box  115 , the substrate and the molten globule are cooled to crystallize the molten globule, thereby securing the resulting crystalline island to the substrate. In some implementations, the islands are secured strongly enough to allow mechanical polishing, or other abrasive processing, of the island to expose a cross-section of the island, without dislodging the island from the substrate. 
       FIG. 2  shows an array of crystalline islands  210  formed on substrate  205 . Method  100  can be used to fabricate one or any number of crystalline islands. When a plurality of islands is formed, they can be arranged in an ordered array, or can be distributed on the substrate without perceptible periodic ordering. In some implementations, the position of each island  210  relative to substrate  205  is known to allow for subsequent processing of the islands. 
     Islands  210  can be single-crystalline or poly-crystalline. Nano-crystalline and amorphous islands can also be formed. In some implementations after islands  210  are formed, they are planarized, abraded, or otherwise operated upon so that some material is removed from the surfaces thereof to expose a cross-section of each island. This exposed cross-section can then be used to fabricate electronic devices, for example when the islands are formed from a semiconductor such as silicon. 
     When the starting particulate island material has impurities, the process of melting and crystallizing set out in method  100  can reduce the impurities inside the crystalline islands by pushing the impurities towards the surface of each molten globule as a crystalline lattice begins to form inside the molten globule, a process known as gettering. The lattice then tends to exclude any impurities that would interfere with its ordered arrangement of atoms, thereby excluding at least a portion of the impurities from the inside of the crystal. When the crystalline islands are poly-crystalline, the impurities are pushed to the grain boundaries between the crystals. 
     In some implementations, particles of the island material are deposited onto the substrate by transferring the island material into one or more depressions defined in the substrate surface.  FIG. 3  shows depression  310  in substrate  305 . In some implementations a plurality of depressions can be defined, and they can be arranged into an ordered array. The depressions can be defined lithographically, or using other means known to the skilled person, including but not limited to laser ablation or localized etching using a photolithographically defined mask. 
     The depression  310  contains the molten globule, and can serve to more precisely locate the molten globule, and the resulting crystalline island, relative to the substrate  305 . In addition, the shape of the depression can guide the crystallization process by providing nucleation sites for initiating crystallization. In some implementations, the depression can have one or more vertexes  425  as shown in  FIG. 4  in relation to depressions  405 ,  410 ,  415 , and  420 . The vertex  425  can be at the end of a taper such as in the case of depression  420 , or part of a reverse taper, as shown in depressions  405  and  415 . A depression can have multiple vertexes as shown in depressions  410  and  415 . Having multiple nucleation sites in the form of vertexes  425  increases the likelihood for the island being poly-crystalline and decreases the likelihood of formation of a single-crystalline island. Nucleation sites can also be three-dimensional smaller depressions into or protrusions from the surface of depression  310 . Such smaller depressions can have one or more vertexes (not shown). These vertexes can in turn serve as a nucleation site for crystallization of the molten globule. 
     As shown in  FIG. 5 , in some implementations, substrate  505  can have a larger and shallower depression  510 , within which there can be a smaller and deeper depression  515 . 
       FIGS. 6 a - d    show a cross-section of a substrate  605 , with a larger depression  610  and a smaller and deeper depression  615  within depression  610 . As shown in  FIG. 6 b   , particles of the island material  620  can be deposited to fill both the larger and the smaller depressions  610  and  615 . As shown in  FIG. 6 c   , when the particles are melted, they fuse to form molten globule  625 . The surface tension of the molten globule can pull it into an approximately spherical shape, which is then cooled and crystallizes to form a crystalline island. As shown in  FIG. 6 d   , the crystalline island and/or the substrate  605  can be planarized to yield a crystalline island  630  in substrate  605 . Depression  610  serves as a reservoir for particles of the island material which eventually form the molten globule  625 . Depression  615 , in turn, serves to locate the molten globule  625  and initiate its crystallization using vertexes discussed above in relation to  FIG. 5 . 
     The relative volume of depressions  610  and  615  can determine the size of the molten globule. This, combined with the depth of depressions  610  and  615  can determine the size of cross-section of crystalline island  630  available at different depths of substrate  605 . When particles of island material  620  fuse to form molten globule  625  leaving at least a portion of the volume of depression  610  empty, this empty space can be back-filled after molten globule  625  crystallizes. This back-filling can help to create a planar surface. 
       FIG. 7  shows a side elevation cross-section of a substrate  705  having large depression  710 , and small depression  715  within large depression  710 . As shown in the cross-section, the surface of small depression  715  envelops more than half of molten globule  725  (shown in dotted line) thereby physically securing the crystallized molten globule  725  to the substrate. Even in implementations where the surface of small depression  715  envelops less than half of the molten globule  725 , the enveloping can still contribute to physically securing the crystalline island to the substrate. The shape of depression  715  is not limited to a portion of a sphere. Any suitable shape can be used. When it is desirable to physically secure the crystalline island to the substrate, the shape of depression  715  can be used whereby the molten globule can flow into the shape, but the solid crystalline island cannot be physically removed from depression  715 . An example of such shapes for depression  715  can be any shape where the opening of depression  715  is smaller than the largest dimension of the crystalline island that must pass through the opening in order for the crystalline island to be removed from depression  715 . 
       FIG. 8  shows a side elevation cross-section of a substrate  805  having a large depression  810  and a small depression  815  within large depression  810 . Small depression  815  has protrusion  820  extending into the space to be occupied by molten globule  840 . Protrusion  820  can have at least one vertex  825 . Instead of, or in addition to, protrusion  820 , small depression  815  can have a further depression  830  in the surface of small depression  815 . Further depression  830  may have at least one vertex  835 . Further depression  830  can also be described as a protrusion of the space to be occupied by molten globule  840  into small depression  815 . Depression  815  may have any number or combination of protrusions  820  and further depressions  830 . Vertexes  825  and  835  can form a nucleation site for initiating the crystallization of molten globule  840 . Once molten globule  840  is crystallized, protrusion  820  and further depression  830  can contribute to physically securing the crystallized island into depression  815 , and in turn securing the crystalline island to substrate  805 . 
     The securing means discussed in relation to  FIGS. 7 and 8  can also be used in a single-stage depression such as depression  310  shown in  FIG. 3 . In addition to these means of physically securing the crystalline island to the substrate, surface adhesion can also be used to secure the crystalline island to the substrate. For example, if the molten globule has a wetting angle with the substrate of less than about 90°, the molten globule sufficiently wets the substrate surface and contributes to the adhesion of the crystallized island to the substrate surface. 
     When the particulate island material is in the form of a loose powder, it can be transferred into the depression in the substrate using means including but not limited to: 1) doctor-blading the powder into the depression; and 2) electrostatically depositing the powder into the depression using charged pins to pick and then deposit the powder into the depression. 
     When the particulate island material is in the form of a suspension of the particles in a carrier medium, the suspension can be flowed onto the substrate to fill the depression and then squeegeeing the excess suspension located outside the depression from the surface of the substrate. When such a carrier medium is used, during the heating step it can be evaporated, burnt off, or otherwise eliminated before the melting and fusing of the particulate island material. 
     In the cooling stage, cooling alone can be sufficient to initiate the crystallization of the molten globule. Other techniques can be used to facilitate or more finely control the initiation and progress of the crystallization. For example, the molten globule can be super-cooled below its melting point. Super-cooling can take the form of cooling the molten globule to less than around 300° C. below its melting point before the crystallization starts. Applying a physical impact or shock to the substrate bearing the molten globule can also set off crystallization. This can also be used when the molten globule is super-cooled. In addition, the surface of the molten globule can be exposed to different chemical reactants, such as oxygen, to further guide the crystallization process. The oxygen can form a thin layer or “skin” on the surface of the molten globule which serves to isolate the molten silicon from the substrate and can serve to increase the surface tension of the globule. 
       FIG. 9 a    shows an implementation where substrate  905  has a through hole  910  filled with particulate island material  915 . Hole  910  has a first end  940  and a second end  945 . Hole  910  can be filled with particulate island material  915  using doctor-blading. Hole  910  can also be filled with a liquid suspension comprising the particulate island material dispersed in a carrier medium. The suspension can be flowed onto the substrate and into hole  910 , and then the excess suspension located outside hole  910  can be squeegeed off the surface of the substrate. After filling hole  910 , substrate  905  and island material  915  can be heated to melt and fuse the island material into molten globule  935 . When such a carrier medium is used, during the heating step it can be evaporated, burnt off, or otherwise eliminated before the melting and fusing of the particulate island material. Optionally, substrate  905  can be flipped before the heating. For example, the flipping can be used when hole  910  has a closed end, to point the open end of hole  910  towards the earth&#39;s gravitational force. 
       FIG. 9 b    shows molten globule  935  forming a convex meniscus  920  extending out of the first end  940  of hole  910 . Meniscus  920  can form under the force of gravity. In addition, if surface  925  of substrate  905  adjacent first end  940  of hole  910  has a low wetting angle with the molten globule  935 , this can encourage the molten globule  935  to wet the surface  925  of substrate  905  and for the meniscus  920  to form and extend out of first end  940  of hole  910 . Furthermore, molten globule  930  can be encouraged to extend out of hole  910  and form meniscus  920  if pressure is applied against the molten globule  935  through the second end  945  of hole  910  to push molten globule  935  out of first end  940  of hole  910 . As shown in  FIG. 9 c   , once molten globule  935  crystallizes, meniscus  920  can be polished and/or planarized to expose a cross-section of crystalline island  950  and to form a crystalline island  950  in substrate  905 . 
       FIGS. 9 a - c    show one hole  910 , but a plurality of holes can be used. The holes can be arranged in an ordered array. Crystalline islands can be secured to substrate  905  by respective holes, such as hole  910 , enveloping and physically securing the respective island  950  and/or the surface adhesion of the crystalline island  950  to the surface of hole  910 . Adhesion can be stronger when the wetting angle between the molten globule  935  and the surface of hole  910  is smaller than about 90°. 
     In another implementation (not shown), particles of island material can be dispersed in a carrier medium to form a suspension. The suspension can then be transferred onto the substrate. Next, the substrate and the suspension can be heated, which can evaporate, burn off, or otherwise eliminate the carrier medium. The heating can also melt and fuse the particles of the island material to form a molten globule. The cooling and securing can be carried on as previously described. A wetting angle of less than about 90° between the molten globule and the substrate can contribute to stronger adhesion between the substrate and crystalline island and to securing the crystalline island to the substrate. 
     The suspension can be transferred to the substrate using techniques including, but not limited to, one or more of stamping, screen printing, or inkjet printing of the suspension onto the substrate following procedures known in the art. The suspension can also be spin-coated to form a layer on the substrate. This layer can then be lithographically patterned to define one or more regions on the substrate where particles of the island material are present, and other regions where island material particles are absent. 
     There may not be any depressions in this implementation. However, the substrate surface can be patterned to have areas of higher wetting angle and other areas of lower wetting angle with the molten globule. The molten globule will tend to form on the areas of lower wetting angle. The patterning of areas with low wetting angle can serve as a means of further locating the molten globule, and thus the crystalline island on the substrate. This can be applied to one crystalline island or a plurality of crystalline islands. Methods for patterning a substrate to have high and low wetting angle areas are well known in the art, and can include applying a patterned mask to the surface followed by subjecting the unmasked areas to chemical modification or deposition of other materials, such as SiO 2 , on the unmasked areas. 
       FIG. 10  shows a further implementation of the present invention reflected in method  1000  for depositing particles of the island material on the substrate. First, as shown in box  1005 , the particles can be dispersed in a carrier medium to create a suspension. Next, as shown in box  1010 , the suspension can be formed into a sheet by spreading or spin coating the suspension or using other methods known in the art. Next, as shown in box  1015 , the sheet of the suspension can be transformed into a solid sheet. This can be accomplished by drying, baking, cross-linking, or otherwise solidifying the suspension. Next, as shown in box  1020 , the solid sheet can be patterned by cutting away or removing one or more portions of the sheet to form a patterned sheet. The pattern can be applied using a mechanical punch, lithographically, or using other means known in the art. Next, as shown in box  1025 , the patterned sheet can be overlaid on the substrate. 
     At this stage the remaining steps of heating and cooling-and-securing can be applied as previously described. During heating, the carrier medium can be evaporated, burnt off, or otherwise eliminated before melting and fusing of particles of the island material. A wetting angle of less than 90° between the molten globule and the substrate can contribute to adhesion of the crystalline island to the substrate. This implementation can be used to make a single island or a plurality of crystalline islands on the substrate, which can be arranged in an ordered array. 
     In the implementations where there is no depression, initiation of the crystallization of the molten globule can still be guided and controlled. One or more guiding depressions into and/or guiding protrusion from the substrate surface coming into contact with the molten globule can initiate crystallization. These guiding depressions and protrusions can have at least one vertex to provide an initiation point for the crystallization process. 
     Alternatively, the shape of the contact area of the molten globule with the substrate can be controlled to provide an initiation point for crystallization. By patterning the relatively low and high wetting angle areas on the substrate, the molten globule can be made to wet or contact the substrate along a patterned lower wetting angle shape while avoiding the higher wetting angle areas of the substrate. The shape of the low wetting angle area can be any of the shapes discussed above in relation to  FIG. 4 . The shape can have at least one vertex to provide an initiation point for the crystallization. 
     Another means of controlling initiation of crystallization can be depositing a metallic grid on the substrate, at least over the areas of the substrate that come into contact with the molten globule. The deposited metal can act as an initiation point for the crystallization of the molten globule. The grid can be made of other materials, such as refractories or Ni. The deposited material can have other shapes such as dots or other patterns of deposited material that may not constitute a grid. 
     In other implementations, after the crystalline islands form, the islands and the substrate can be over-coated.  FIG. 11  shows a cross-section of substrate  1105  and crystalline island  1110  over-coated with layer  1115 . This assembly forms a stack where the crystalline island  1110  is sandwiched between substrate  1105  and cover-coating layer  1115 . The stack can then be planarized to remove some of the material comprising the stack and expose a cross-section of the crystalline island. 
     The over-coating layer  1115  can be deposited using any suitable physical or chemical deposition method including but not limited to spin coating or electrostatically-applied powder coating. The layer can be a thin layer, such as layer  1115  in  FIG. 11 , or can be a thicker layer such as layer  1215  shown in cross-section in  FIG. 12 . When an over-coating layer is used, it can physically secure the crystalline island to the substrate by sandwiching the crystalline island between the substrate and the over-coating layer, as shown in  FIGS. 11 and 12 . This securing action of the over-coating layer can contribute to securing to the substrate crystalline islands having a large wetting angle, and therefore small contact area, with the substrate. Large wetting angles can, for example, be angles greater than about 90°. Over-coating can be applied to a plurality of islands on a substrate. 
     Another implementation of the present invention is reflected in method  1300  shown in  FIG. 13 . Box  1305  shows depositing particles of an island material on a first substrate. Particles can be deposited as loose powder or in a suspension as described above. The deposition can be patterned and/or at specified locations relative to the substrate. Next, as shown in box  1310 , the particles of the island material can be sandwiched between the first substrate and a second substrate placed adjacent the first substrate. Next, as shown in box  1315 , the substrate and the particles can be heated to melt and fuse the particles into a molten globule, without melting the first substrate or the second substrate. 
     When the particles are deposited as a suspension in a carrier medium, the heating step can evaporate, burn off, or otherwise eliminate the carrier medium before melting and fusing the particles. Next, as shown in box  1320 , the substrates and the molten globule can be cooled to crystallize the molten globule, thereby forming a crystalline island. 
     The sandwiching, described in box  1310 , and the heating described in box  1315  can be performed in the opposite order, i.e. the molten globule can form before it is sandwiched between the first and the second substrates.  FIG. 14  shows molten globule  1415  sandwiched between first substrate  1405  and second substrate  1410 . 
     When the wetting angle between molten globule  1415  and both first substrate  1405  and second substrate  1410  is large, the crystallized island can adhere more weakly to the substrate. The weak adhesion can facilitate removing the crystallized island from the substrate to form a free-standing wafer. 
     Features on the surfaces of one or both of the first and second substrates can be used to initiate crystallization of the molten globule.  FIG. 15  shows an array of pyramids  1505  that can be formed on the region of the substrate that comes into contact with the molten globule. Pyramids  1505  can protrude from the substrate surface or form depressions into the substrate surface. Instead of a pyramid, other shapes can be used, such as a cone. These shapes can have a vertex, as does pyramid  1505 , to act as an initiation site for the crystallization of the molten globule. 
     Each pyramid  1505  initiates crystallization to form grain  1510 , which eventually abuts upon neighboring grains at grain boundaries  1515 . Using this method, a molten globule can be patterned into a poly-crystalline form. As discussed above, during crystallization at least some of the impurities in the molten globule can be pushed towards the grain boundary regions. This process can leave the central region of grain  1510  with relatively fewer impurities yielding a higher quality crystal for post-processing, such as device fabrication on grain  1510 . This process can isolate the grain boundaries to regions where devices will not be fabricated in subsequent processing. Although  FIG. 15  shows four grains  1510  of uniform size, grains  1510  can also be of different sizes. 
       FIG. 16  shows a cross-section of molten globule  1615  sandwiched between two substrates  1605  and  1610 . As discussed above, one or both of the substrates can include depressions or protrusions to guide the crystallization process. Substrate  1605  can have protrusions  1620  in contact with molten globule  1615 . Substrate  1610 , in turn, can have depressions  1625  in contact with molten globule  1615 . The protrusions  1620  and depressions  1625  can be of different shapes and any numbers of them can be used in/on one or both of first substrate  1605  and second substrate  1610 . In addition or instead of protrusions and depressions, a grid or array of a metal or other material deposited on one or both of the first and the second substrate where those substrates come into contact with the molten globule can also be used to initiate and guide the crystallization process. 
     The cooling as shown in box  1320  of  FIG. 13  can also include super-cooling the molten globule. The super-cooling can include cooling the molten globule to a temperature below about 300° C. below its melting point before crystallization begins. A pressure pulse or mechanical impact can also be applied to the molten globule in a super-cooled state or otherwise. A seed crystal can also be added to the molten globule in a super-cooled state or otherwise. 
     In some implementations, the coefficient of thermal expansion (CTE) of the substrate at a temperature within about 20° C. of the melting point of the island material can be matched to the CTE of the island material at the melting point of the island material. This matching of CTE can reduce stresses between the island material and the substrate as each one cools and contracts. Lower stresses can facilitate making of higher quality crystals with fewer defects, and can improve the adhesion of the crystalline island to the substrate. 
     The island material can include, but is not limited to, semiconductors. Such semiconductor can include, but are not limited to, silicon. The substrate material can include, but is not limited to, silica, alumina, sapphire, niobium, molybdenum, tantalum, tungsten, rhenium, titanium, vanadium, chromium, zirconium, hafnium, ruthenium, osmium, iridium, and combinations and alloys of these materials. 
     The substrate can also be a ceramic or glasses with sufficiently high melting or softening temperatures. The substrate can also be a High-Temperature Co-fired Ceramic (HTCC). HTCC can be worked and mechanically patterned in its green phase. When the island material is silicon, alumina can be a relatively higher wetting angle material and silica a relatively lower wetting angle material. 
     In some implementations, the molten globule of the island material can have a flattened or disk shape. For example, referring to  FIG. 1 , at step  110  heating the substrate and the particles of the island material can melt and fuse the particles to form a molten disk and/or a molten disk-shaped or flattened globule. At step  115 , the cooling can then solidify and crystallize the molten disk, thereby securing the disk-shaped crystalline island of the island material to the substrate. The securing can comprise the crystalline island adhering directly to the substrate. In addition and/or instead, the securing can comprise the crystalline island adhering indirectly to the substrate by adhering to any intermediate and/or interfacial layer secured directly to the substrate. In some implementations, some portions of the crystalline island can adhere directly to the substrate material while other portions can adhere to an interfacial and/or intermediate layer covering at least a portion of the substrate. In some implementations, after the cooling step, at least a portion of the crystalline island can be planarized to expose a cross-section of the crystalline island. 
       FIGS. 17 a - d    show various steps of an exemplary method for fabricating crystalline islands that are disk shaped and/or have a flattened shape.  FIG. 17 a    shows island material  1710  being deposited on a substrate  1705 . Substrate  1705  can be similar to the other substrates described herein, and island material  1710  can likewise be similar to other island materials described herein. 
     While  FIG. 17 a    shows island material  1710  deposited as a heap or mound, it is contemplated that island material  1710  can be deposited in any other suitable manner. For example, island material  1710  can be deposited in powder form. When island material  1710  is deposited in powder form, the powder can be deposited through a screen to form one mound or an array of mounds of powder at predetermined positions on substrate  1705 . The size of the openings in the screen can determine the shape and size of the mounds of powder on substrate  1705 . 
     In other implementations, island material  1710  can be deposited as a layer of material on the substrate. In yet other implementations, the island material  1710  can be suspended in a carrier medium, and the suspension can be deposited on substrate  1705 . Such layers and/or suspensions of island material  1710  can be patterned on substrate  1705  and/or deposited at predetermined positions on substrate  1705 . In some implementations, island material  1710  can be printed on substrate  1705 . 
     Referring to  FIG. 17 b   , once island material  1710  is deposited on substrate  1705 , island material  1710  and substrate  1705  can be heated to melt island material  1710  to form a first molten disk  1715 . The heating can also form a second molten disk  1707  disposed between first molten disk  1715  and substrate  1705 . Second molten disk  1707  can comprise oxygen and the island material. 
     The molten disks can have any generally flattened shape, including but not limited to, a saucer, a pancake, a wafer, a platelet, a discus, a sheet, and/or an oblate shape. The molten disks can have a maximum thickness that is at least about ten times smaller than the smaller of their maximum length and maximum width. In some implementations, molten disks can have a maximum thickness that is at least about five times smaller than the smaller of their maximum length and maximum width. In other implementations, molten disks can have a maximum thickness that is at least about two times smaller than the smaller of their maximum length and maximum width. The first and second molten disks can be largely or entirely immiscible, thereby remaining largely or entirely phase-separated in the molten state. In addition, second molten disk  1707  can have a higher density in the molten state, thereby remaining, under the force of gravity, between substrate  1705  and first molten disk  1715 . 
     After the heating, substrate  1705 , first molten disk  1715  and second molten disk  1707  can be cooled to solidify and/or crystallize first molten disk  1715  to form the crystalline island of the island material. In this process, second molten disk  1707  can also solidify to form an oxide disk. The crystalline island can also have a disk like (or generally flattened) shape similar to the shape of first molten disk  1715 . 
     The crystalline island can be single, poly, and/or nano crystalline. In some implementations, after forming the crystalline island, at least a portion of the crystalline island can be planarized to expose a cross-section of the crystalline island. In some implementations, the island can be mechanically (and/or chemo-mechanically) planarized without becoming detached from the substrate. This can be made possible because the crystalline island can adhere strongly to the oxide disk, which in turn can adhere strongly to the substrate. 
     Several factors can contribute to the strong adhesion of the crystalline island to the substrate. One such factor can be the relatively small wetting angle and thereby relatively large contact area between the crystalline island and the oxide disk and also between the oxide disk and the substrate. If either one of the crystalline island and the oxide disk were to have a large wetting angle, and thereby a tendency to ball-up into a near-spherical shape, there would be much smaller contact area, and weaker adhesion, between the crystalline island, the oxide disk, and the substrate. Such balled-up, near-spherical crystalline islands can adhere only weekly to the substrate such that they would become detached from the substrate during planarization, such as mechanical and/or chemo-mechanical planarization. 
     Another factor contributing to the strong adhesion can be porosity of the substrate, which can also increase the contact surface area between the substrate and the oxide disk and/or crystalline island in contact with the substrate. Yet another factor contributing to the strong adhesion of an alumina substrate to an oxide layer comprising silicon oxide is that often alumina substrates comprise some glass mixed in with the aluminum oxide. Since most glass comprises silicon oxide, the glass component of the alumina substrate can adhere strongly to the oxide disk which can also comprise silicon oxide. 
     In some implementations, as shown in  FIG. 17 c   , after the cooling the crystalline island and substrate  1705  can be over-coated with an over-coating layer  1720  to form a stack. This over-coating layer  1720  can be similar to other over-coating layers described herein. As shown in  FIG. 17 d   , after the over-coating, the stack can be planarized to remove portions of the over-coating layer and the crystalline island, and as a result expose a cross-section  1725  of the crystalline island. 
     In some implementations, second molten disk  1707  can be formed when island material  1710  is heated on substrate  1705  in the presence of oxygen. For example, oxygen can be present in gaseous form if island material  1710  and substrate  1705  are headed in an air atmosphere. In some implementations, second molten disk  1707  can comprise a molten oxide of the island material which phase separates from first molten disk  1715  comprising molten island material. 
     The presence of the second molten disk, combined with temperatures in excess of island material&#39;s melting point during the heating step, can allow the molten globule of the island material to spread into a disk, instead of balling-up into a near-sphere under surface tension forces. Such temperatures can also reduce the viscosity of the molten island material, thereby promoting the ability of the molten island material to spread into a molten disk. In addition, the second molten disk can allow the first molten disk to cool and solidify into a disk and/or flattened shape. Without the second molten disk, as the temperature is reduced to approach the melting point of the island material, the decreasing temperature can cause an increase in the surface tension of the molten island material, thereby causing it to ball-up into a near-sphere. 
     Moreover, the second molten disk can allow the first molten disk to crystallize into a crystalline island while minimizing interference with crystal formation during the cooling step due to lattice and/or CTE mismatches between the island material and the substrate. Reducing these interferences and/or mismatches can also strengthen the mechanical adhesion of the crystalline island, via the oxide disk, to the substrate. 
     In one particular example, crystalline islands of silicon can be fabricated on an alumina substrate. The alumina substrate can comprise Alumina Ceramic Substrate 10×10×0.5 mm, one side polished (ALCeramic101005S1) sold by MTI Corporation. Particles of silicon can be deposited as heaps onto the alumina substrate. The deposition can be carried out using a screen with holes having a diameter of about 1 mm. Then the alumina substrate and the heaps of silicon island material can be heated in an air atmosphere, according to the temperature profile summarized in Table 1 below: 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Temperature Profile 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Ramp rate  
                 Level temp  
                 Dwell time  
               
               
                   
                 Step 
                 (° C./min) 
                 (° C.) 
                 (min) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 1 
                 3 
                 1000 
                 0.1 
               
               
                   
                 2 
                 10 
                 1600 
                 60 
               
               
                   
                 3 
                 10 
                 1200 
                 0.1 
               
               
                   
                 4 
                 5 
                 500 
                 0.1 
               
               
                   
                   
               
            
           
         
       
     
     As can be seen in Table 1, the maximum temperature is 1600° C., which is in excess of the melting point of silicon, which is 1414° C. In other implementations, the maximum temperature can be at least about 1500° C. In the case of silicon deposited on alumina, flattening of the first molten globule into the first molten disk, and consequent formation of a flattened/disk shaped crystalline islands has not been observed at temperatures below 1500° C. At the conclusion of step 4 in the temperature profile, the heater can be turned off, and the sample can be allowed to cool further to facilitate subsequent handling. 
     In addition, while the dwell time at 1600° C. is 60 minutes, dwell times as short as at least 5 minutes at 1600° C. can cause flattening of the molten island material into the first molten disk, and consequent formation of a flattened/disk shaped crystalline island. Generally, in some implementations, the maximum temperature can be at least about 86° C. above the melting point of the island material. In other implementations, the maximum temperature can be at least about 186° C. above the melting point of the island material. 
       FIG. 18  shows a top plan view optical micrograph of a flattened/disk shaped island  1810  of silicon formed on an alumina substrate  1805 , fabricated using the temperature profile summarized in Table 1. When the island material comprises silicon and the substrate comprises alumina, in some implementations the second molten disk, and the oxide disk into which it solidifies, can comprise aluminum in addition to oxygen and silicon. In some implementations, this aluminum can originate from the alumina substrate. In general, in some implementations, the second molten disk can comprise one or more elements originating from the substrate. 
     In the implementations described above, the second molten disk, and the oxide disk into which it solidifies, are formed by heating in the presence of oxygen the island material deposited on the substrate. It is also contemplated that in some implementations an oxide layer can be formed on the substrate before the island material is deposited on the substrate. This oxide layer can comprise the island material and oxygen. In other implementations, the oxide layer can also comprise additional materials including, but not limited to, elements originating from the substrate. 
     In implementations where the oxide layer is initially formed on the substrate, the depositing step can comprise depositing the island material on the oxide layer. In such implementations, the second molten disk can comprise the oxide layer in a molten state. In some implementations, forming the oxide layer can comprise depositing on the substrate the oxide layer, which can comprise an oxide of the island material. In some implementations, the depositing can be according to a predetermined pattern, for example using a mask, printing, lithography, and the like. 
     In other implementations, forming the oxide layer can comprise depositing an initial amount of the island material on the substrate and then oxidizing this initial amount of the island material to form the oxide layer. The deposition of the initial amount of the island material can be according to a predetermined pattern. The initial amount of the island material can be deposited as particles or as a layer of the island material. For example, in the case of silicon island material, the initial amount can be deposited as silicon particles/power and/or as a layer of amorphous, nano-crystalline, and/or poly-crystalline silicon. 
     In implementations where the oxide layer is formed on the substrate prior to depositing the island material on the oxide layer, no further oxide needs to be formed during the heating step. As such, the heating can be performed in a non-oxidizing atmosphere. For example, the atmosphere can be substantially oxygen-free. In some implementations, an inert atmosphere can be used during the heating. For example, the heating can be performed in an argon atmosphere. 
     In some implementations, the island material can be deposited on the substrate in a predetermined pattern. This pattern can comprise an interconnected and/or contiguous pattern, including but not limited to the shape of a plurality of interconnected nodes, with each node connected to one or more other nodes. This can allow for the crystallization of the molten island material to start at one, or a few, nucleation sites in the pattern and then proceed throughout the pattern. This mode of crystallization can allow subsets of the crystalline islands to have similarly oriented crystal lattices. In some implementations, a single crystal can propagate through all or substantially all of the interconnected pattern of the island material. All the means and methods described herein for initiating and/or controlling crystallization can be used to initiate and/or control the crystallization of the molten island material deposited in the predetermined pattern. 
     While the foregoing describes disks of molten material, it is contemplated that the molten material can be of any generally flattened shape, depending on the pattern according to which the island material and/or the oxide layer is deposited and/or formed on the substrate. For example, if the island material is deposited on the substrate according to a pattern of interconnected nodes, then the heating step can produce a generally flattened layer of molten island material also generally in the shape of interconnected nodes. The molten oxide layer can also be generally in the shape of interconnected nodes. Moreover, once the layer of molten island material crystallizes, the resulting crystallized island material can also comprise a generally flattened layer in the shape of interconnected nodes. 
     While the above description relating to  FIGS. 17 a - d    and  FIG. 18  refers to the molten island material being in the shape of a first molten disk, it is contemplated that the molten quantity of the island material need not be in a flattened or disk shape, and can form into the shape of any bounded and contiguous quantity of molten material, which can have any shape dictated by its material properties such as viscosity and surface tension and by external factors such as gravity and the shape of the container/substrate supporting the molten material. Such shapes can be generally and/or colloquially described as a corpus, body, quantity, glob, blob, globule, dab, and the like. These general and/or colloquial descriptions also include flattened and/or disk shaped quantities of the molten island material. 
     As such, the molten globule and/or the molten disk of the island material can also be described as a molten corpus of the island material. When the molten corpus is cooled it can solidify to form a crystallized corpus. All or a portion of this crystallized corpus can, in turn, form the crystalline island of the island material. 
     In some implementations, if the amount and/or volume of the deposited island material is large relative to the footprint of the deposited material on the substrate, then upon heating the volume of the molten island material may be too large for the molten island material to form a flattened or disk shape. Such a larger quantity of molten island material can form a molten corpus that is more rounded, i.e. has a maximum thickness which, relative to its maximum length and maximum width, is larger than the maximum thickness of a flattened or disk shape with the same maximum length and/or maximum width. 
     Moreover, in some implementations, such a more rounded molten corpus can begin to cool and crystallize from a point distal from the substrate. As the wave of crystallization propagates from this point towards the substrate, the wave can create strain and/or other forces internal to the molten corpus. Other examples of other such forces can include, but are not limited to, strain caused by the differences between the coefficient of thermal expansion (CTE) of the crystalized corpus (and/or cooling and crystallizing molten corpus) and the CTE of the solidified oxide disk (and/or cooling and solidifying molten oxide disk). 
     These forces can cause a first solid portion distal from the substrate to spontaneously separate or pop-off from the remainder of the cooling and solidified molten corpus that remains attached to the substrate. This remainder, in turn, can form a second solid portion that is proximal to the substrate and forms the crystalline island. In such a scenario, the crystallized corpus is divided into two portions: the first solid portion and the second solid portion. In some implementations, some or all of the separated first solid portions can be collected and recycled/reused as island material. 
     While the above description of the wave of crystallization refers to the wave starting at a point distal from the substrate, it is contemplated that based on temperature profiles and/or cooling profiles of the components surrounding the molten corpus, in some implementations the wave of crystallization can propagate in the opposite direction, i.e. from a point proximal the substrate towards a point distal from the substrate. In other implementations, the wave of crystallization can propagate in a different direction dictated by the temperature and/or cooling profile of the components surrounding the molten corpus. 
     So long as the wave and/or pattern of crystallization and/or cooling creates sufficient internal strains/forces between the first solid portion and the second solid portion, these two solid portions can spontaneously separate from one another. It is also contemplated that these internal forces may build up as the molten corpus solidifies and continues to cool, and the internal forces can become large enough to cause spontaneous separation when the crystallized corpus is in the cooling phase. 
     In some implementations, the surface roughness of the substrate can be patterned in order to guide where on the substrate the molten oxide layer and/or the molten island material layer form. For example, the substrate can be polished and/or roughened according to a predetermined pattern. Regions of the substrate with different surface roughnesses can have different wettability by the molten oxide and/or molten island material. In addition, regions of the substrate with different surface roughnesses can adhere to the oxide layer with different mechanical strengths. 
     Following the method depicted in  FIGS. 17 a - d   , and/or the other similar methods described herein, a semiconductor device can be fabricated. Such a device comprises a substrate and an intermediary disk disposed on the substrate. The intermediary disk can comprise oxygen and an island material. The intermediary disk can comprise the oxide disk. The semiconductor device also comprises an island disk disposed on the intermediary disk. The island disk can comprise the island material, and can be crystalline. The island material can be formed separately from the substrate and then deposited on the substrate. The intermediary disk can be formed by melting and then solidifying the island material on the substrate. As discussed above, in implementations where the oxide intermediary disk is formed during the heating step, the heating and/or melting can be performed in the presence of oxygen and at a maximum temperature exceeding the melting point of the island material. 
     In addition, while the above description refers to intermediary and island disks, it is contemplated that the intermediary oxide and/or the crystallized island material can be in any layer-like or otherwise flattened shape or configuration. The island disk can have a maximum thickness that is at least about ten times smaller than the smaller of its maximum length and maximum width. In some implementations, the island disk can have a maximum thickness that is at least about five times smaller than the smaller of their maximum length and maximum width. In other implementations, the island disk can have a maximum thickness that is at least about two times smaller than the smaller of their maximum length and maximum width. 
     In some implementations, the substrate can comprise alumina and/or the island material can comprise silicon. Moreover, in some implementations the intermediary disk can also comprise aluminum. This aluminum can originate from the alumina substrate. 
     The planarized cross-sections of the crystalline islands can be used to make electronic devices, such as transistors or other circuit components. As such, the methods and devices described herein can be used in backplanes for active matrix displays such as OLED displays, in electro-optical detector arrays such as X-ray detectors, and in fabricating certain integrated circuits such as those used in amplifiers and op-amps. 
     When multiple crystalline islands are formed on a substrate, and/or when multiple electronic devices are fabricated on a given planarized cross-section, the islands and/or the devices respectively can be appropriately singulated to provide individual crystalline islands and/or electronic devices respectively. When separated crystalline islands (or arrays of crystalline islands) are used to make separate displays and/or detectors, those displays and/or detectors can be tiled together to form a larger tiled display and/or detector. 
     In some implementations, depositing the island material on the substrate can comprise positioning a template on a surface of the substrate, the template comprising a channel having a first end abutting the surface and a second end opposite the first end. The surface can cap and/or cover the first end. At least a portion of the channel can be filled with the island material, either before or after the template is positioned on the substrate.  FIG. 19 a    shows a side elevation cross-section of a template  1915  positioned on a surface  1910  of a substrate  1905 . Template  1915  comprises a channel  1920  having a first end  1925  abutting surface  1910  of substrate  1905  and a second end  1930  opposite first end  1925 . A portion of channel  1920  is filled with island material  1935 . 
     Substrate  1905  can be similar to substrate  1705  and/or the other substrates described herein. Template  1915  can be formed of high temperature co-fired ceramic and/or any other suitable material that does not melt during the operational temperatures described herein and would not react with and/or otherwise contaminate the crystalline island in a manner that would render the crystalline island unsuitable for forming electronic devices. Channel  1920  can have any suitable shape and/or cross-section, including but not limited to, a cylindrical shape and/or a circular cross-section. 
     Once template  1915  and island material  1935  therein are on substrate  1905 , they can all be heated and then cooled in a manner similar to that described above, which heating can cause island material  1935  to melt to form a molten corpus and then solidify to form crystallized corpus  1940 , as shown in  FIG. 19 b   . An oxide layer  1945  can form between substrate  1905  and crystallized corpus  1940 . Formation of crystallized corpus  1940  and oxide layer  1945  can be similar to the formation of the crystalline island and the oxide disk described above in relation to  FIGS. 17 a - d    and  FIG. 18 . 
     At this point, a portion of template  1915  and crystallized corpus  1940  can be removed, e.g. by chemo and/or mechanical planarization, to expose a crystalline island of the island material. This planarization process is not shown in the figures; however, similar planarization steps are shown in  FIGS. 6 d  and 17 d    and described in relation thereto. In some implementations, template  1915  can be selectively etched or otherwise selectively removed, and then crystallized corpus  1940  can be planarized. 
     Moreover, referring to  FIG. 19 c   , in some implementations, template  1915  can be removed by lifting template  1915  off from substrate  1905  to create a crystalline island of the island material secured to substrate  1905 . In this process, a first portion  1950  of crystallized corpus  1940  can remain on and/or secured to substrate  1905  to form the crystalline island and a second portion  1955  of crystallized corpus  1940  can remain in channel  1920 . As template  1915  is lifted off and oxide layer  1945  and first portion  1950  remain on substrate  1905 , oxide layer  1945  and first portion  1950  can leave a corresponding space  1960  in channel  1920 . Space  1960  can be proximate first end  1925  (shown in  FIG. 19 a   ) of channel  1920 . 
     In implementations where template  1915  is lifted off, steps can be taken to reduce stiction between oxide layer  1945  and first portion  1950  and the surface of channel  1920 . For example, and without limitation, the material of template  1915  can be selected to reduce the wettability of the channel surface by the molten oxide material and/or the molten island material. In addition, morphology (e.g. roughness) and/or composition of the surface of channel  1920  can be selected to similarly reduce wettability of the channels surface by the molten oxide material and/or the molten island material. Similar steps, and/or other suitable steps, can be taken to reduce stiction between template  1915  and substrate  1905 . 
     Several different methods can be used to cause and/or facilitate the separation of first portion  1950  from second portion  1955 : in some implementations, second portion  1955  can spontaneously separate and/or pop-off from first portion  1950  in a manner similar to the spontaneous separation described above. In other implementations, the surface of channel  1920  can comprise a stress concentrator and/or separation initiator (not shown in  FIGS. 19 a - c   ) to facilitate the separation of first portion  1950  from second portion  1955 . 
     The stress concentrator and/or separation initiator can comprise a depression into and/or a projection from the surface of channel  1920 . Such a stress concentrator can concentrate internal stresses/strains in crystallized corpus  1940  at the point between first portion  1950  and second portion  1955 . Such a concentration can facilitate the spontaneous separation described above. Instead and/or in addition, when acting as a separation initiator, such a depression and/or projection can allow a mechanical and/or acoustic impulse applied to template  1915  to crack crystallized corpus  1940  and separate first portion  1950  from second portion  1955 . In some implementations, a thermal shock (i.e. rapid change of temperature) can be used instead of and/or in addition to the mechanical and acoustic impulses. 
     In some implementations, the stress concentrator and/or separation initiator can comprise a region or circumferential band where the surface of channel  1920  is roughened or made jagged. In other implementations, the stress concentrator and/or separation initiator can comprise a pattern of pin-shaped projections projecting from the surface of channel  1920 . 
     While  FIGS. 19 b - c    depict formation of oxide layer  1945 , it is contemplated that under different operational conditions, e.g. lower maximum temperatures and/or in the absence of oxygen, there may be no oxide layer, and crystallized corpus  1940  and first portion  1950  can be directly in contact with substrate  1905 . 
     Moreover, while  FIG. 19 c    depicts a smooth border between first portion  1950  and second portion  1955 , it is contemplated that this border can be uneven and/or rough. In such a case, first portion  1950  can be planarized to expose a flat and/or smooth cross-section that can be suitable for formation of electronic devices. 
     In addition, as there is island material remaining (in the form of second portion  1955 ) in channel  1920  of the lifted-off template  1915 , this template can be reused in another heating/cooling cycle to form another crystalline island without necessarily the need to add additional island material to channel  1920 . In this manner, template  1915  can function as a multi-use and/or reusable “print head” for forming and/or “printing” multiple crystalline islands on one or more substrates. Moreover, in some implementations template  1915  can comprise multiple channels, which can have various shapes and/or arrangements. Such a multi-channel template can be used to form and/or “print” crystalline islands of correspondingly different shapes and/or arrangements on one or more substrates. 
     Turning now to  FIGS. 20 a  20 b , and 20 c   , these figures are generally similar to  FIGS. 19 a - c   , with the difference being that channel  2020  is shaped differently than channel  1920 . FIG.  20   a  shows in side elevation cross-section substrate  1905 , and a template  2015  having a channel  2020 , which channel  2020  in turn has first end  2025  and second end  2030  opposite first end  2025 . Channel  2020  is at least partially filled with island material  1935 . Channel  2020  comprises a first region  2065  proximate first end  2025  and a second region  2070  distal from first end  2025 . In first region  2065  channel  2020  has a cross-sectional area that is larger than the cross-sectional area of channel  2020  in second region  2070 . In other implementations, channel  2020  can have a cross-sectional area and/or shape that is different in any other suitable manner between first region  2065  and second region  2070 . 
     Inner surface of channel  2020  defines a vertex  2075  separating first region  2065  from second region  2070 . Vertex  2075  can act as the stress concentrator and/or separation initiator described in relation to  FIGS. 19 b - c    above. While in  FIG. 20 a    vertex  2075  is shown as a right angle, it is contemplated that the vertex can be any other sharp or angular projection from and/or depression into the surface of channel  2020 . 
     Referring now to  FIGS. 20 b - c   , as the cross-sectional area of channel  2020  is larger in first region  2065 , template  2015  can form oxide layers  2045  and first portions  2050  (which from the crystalline island) that have a larger area without the need for having a larger cross-sectional area along the full length of channel  2020 . After the heating and the cooling, the island material  1935  in channel  2020  melts and then solidifies to form crystallized corpus  2040  and oxide layer  2045 . 
     Subsequently, template  2015  can be removed and/or lifted off, whereby first portion  2050  of crystallized corpus  2040  can remains on and/or secured to substrate  1905  and a second portion  2055  of crystallized corpus  2040  can remain inside channel  2020 . As template  2015  is lifted off and oxide layer  2045  and first portion  2050  remain on substrate  1905 , oxide layer  2045  and first portion  2050  can leave a corresponding space  2060  in channel  2020 . 
     Turning now to  FIGS. 21 a  and 21 b   , these figures depict select steps in a method of fabricating a crystalline island similar to the steps depicted in  FIGS. 19 a - c  and 20 a - c   , with the main difference being that the shape of template  2115  is different from the shape of templates  1915  and  2015 . Moreover, the process depicted in  FIGS. 21 a - b    can also have a step/state similar to those shown in  FIGS. 19 b  and 20 b   ; however, this step/state is not shown in  FIGS. 21 a - b    for simplicity. 
     The first difference between templates  1915  and  2015  and template  2115  is that template  2115  comprises two channels  2120   a  and  2120   b . As such, template  2115  can be used to form and/or “print” two crystalline islands at a time. While  FIGS. 21 a - b    show template  2115  as comprising two channels  2120   a,b , it is contemplated that in other implementations template  2115  can comprise one or any number of channels, which channels can be arranged in any suitable way. 
     The second difference between templates  1915  and  2015  and template  2115  is that template  2115  comprises walls  2130  extending from surface  2125  of template  2115  in a direction away from a longitudinal direction of channels  2120   a,b . In other words, walls  2130  can extend from surface  2125  of template  2115  in a direction away from the side and/or surface of template  2115  that is configured to come into contact and/or abut substrate  1905 . Walls  2130  can be formed integrally with template  2115 . Walls  2130  and surface  2125  can cooperate to form a reservoir  2135  configured to store island material  1935 . Reservoir  2135  can be in communication with ends of channels  2120   a,b  such that island material  1935  stored in reservoir  2135  can be transferred into and used to at least partially fill one of more of channels  2120   a,b . Island material  1935  stored in reservoir  2135  can allow template  2115  to be used for forming/“printing” a relatively larger number of crystalline islands before additional island material  1935  needs to be supplied from a source external to template  2115 . 
     Referring now to  FIG. 21 b   , after a cycle of heating to melt island material  1935  to form a molten corpus and then cooling the molten corpus to form a crystallized corpus and an oxide layer  2145   a , template  2115  can be lifted off from substrate  1905 . Upon the lifting off, a first portion  2150   a  of the crystallized corpus can remain secured to substrate  1905  to form the crystalline island, while a second portion  2155  of the crystallized corpus can remain in template  2115 . As template  2115  is lifted off and oxide layer  2145   a  and first portion  2150   a  remain on substrate  1905 , oxide layer  2145   a  and first portion  2150   a  can leave a corresponding space  2160   a  in channel  2120   a . While not numbered or described (for the sake of brevity), as shown in  FIG. 21 b    a similar oxide layer, first portion, and space are also formed corresponding to channel  2120   b.    
     While  FIGS. 21 a - b    show reservoir  2135  having a particular geometry and being integrally formed with template  2115 , it is contemplated that in other implementations the reservoir can have any other suitable dimensions, shape, and/or capacity. In addition, it is contemplated that in other implementations reservoir  2135  can be formed using walls and/or other components that are not integrally formed with template  2115 , but rather are secured and/or connected to template  2115  and/or to channels  2120   a,b . In yet other implementations, the reservoir can comprise a separate container in communication with channels  2120   a,b  to allow the island material to be transferred from the reservoir to channels  2120   a,b.    
     Turing now to  FIGS. 22 a  and 22 b   , top plan views of a template  2215  are shown resting on substrate  1905 . Template  2215  can be generally similar in functionality to template  2115  with one difference being that template  2215  comprises four channels  2220   a , 2220   b , 2220   c , and  2220   d . A circumferential wall  2225  extends from a face of template  2215  in a direction opposite the longitudinal direction of channels  2220   a - d . In other words, wall  2225  extends from the top face of template  2215  being the face that is opposite the face configured to abut substrate  1905 , and wall  2225  extends in a direction generally away from the face configured to abut substrate  1905 . 
     Wall  2225  cooperates with the top face of template  2215  to form a reservoir  2230  for storing island material  1935 . Reservoir  2230  is in communication with channels  2220   a - d  such that island material  1935  can be transferred from reservoir  2230  into channels  2220   a - d  to at last partially fill these channels. Walls  2225  have an inner surface  2235  which can come into contact with island material  1935  stored in reservoir  2230 . Surface  2235  can comprise a notch  2240  having a sharp vertex. 
     During the heating, notch  2240  can come into contact with the portion of the molten corpus in reservoir  2230 , which molten corpus would be contiguous between reservoir  2230  and channels  2220   a - d . During the cooling, notch  2240  and/or its vertex can act as a crystallization initiator allowing the crystallization of the molten corpus to start from a single point and the crystallized corpus to be single crystalline and/or have a uniform crystal orientation. Such uniformity would allow the crystalline islands formed by channels  2220   a - d  to have the same crystal orientation as one another. As some processes used during the fabrication of electronic devices (e.g. oxide growth) can be dependent on the crystal orientation, uniformity between the crystal orientation of the various crystalline islands can allow for greater uniformity in the fabrication of electronic devices on/in those crystalline islands. 
     While  FIGS. 22 a - b    depict notch  2240  as the crystallization initiator, it is contemplated that any other suitable feature in any surface of reservoir  2230  can be used to initiate and/or control crystallization of the molten corpus. For example, and without limitation, the crystallization initiator can comprise a depression into and/or projection from the surface of reservoir  2230 . In some implementations, such depressions and/or projections can comprise a sharp and/or angled feature to promote and/or initiate crystallization. In some implementations, the crystallization initiator can comprise an additional component and/or different material secured to the surface of reservoir  2230  such that the additional component and/or different material would come into contact with the molten corpus. 
     In implementations where the crystallization initiator is a feature in a surface of reservoir  2230 , the cooling profile and/or temperature profile of the components in contact with the molten corpus (e.g. the template, the substrate, and/or any surrounding atmosphere/gases) can be controlled to promote the wave of crystallization starting from the reservoir and propagating through the channels, and towards the substrate to enable the crystallization initiator to influence crystal grain(s) and crystal orientation of the crystallized corpus. 
     While  FIGS. 19-22  depict templates comprising one or more channels formed in the body of the template, it is contemplated that different suitable shapes, geometries, and/or structures can be used for the template. For example, and without limitation, the template can comprise one or more channels that are separately formed and then secured together. In other implementations, the template can comprise multiple pieces that cooperate to form the channels. In such an implementation, when the crystallized corpus and/or the crystalline island(s) is formed, the various pieces of the template can be separated and/or removed from one another to liberate the crystallized corpus and/or the crystalline island(s). 
     The above-described implementations of the invention are intended to be examples of the present invention and alterations and modifications may be effected thereto, by those of skill in the art, without departing from the scope of the invention which is defined solely by the claims appended hereto.