CN103370800A - A method and apparatus for forming a thin lamina - Google Patents

Abstract

A method for producing a lamina from a donor body includes implanting the donor body with an ion dosage and heating the donor body to an implant temperature during implanting. The donor body is separably contacted with a susceptor assembly, where the donor body and the susceptor assembly are in direct contact. A lamina is exfoliated from the donor body by applying a thermal profile to the donor body. Implantation and exfoliation conditions may be adjusted in order to maximize the defect-free area of the lamina.

Description

Method and apparatus for forming thin-layer sheets

Related applications

This application is a continuation-in-part of U.S. Patent Application No. 12/980,424, "A Method to Form a Device by constructing a support Element on a Thin Semiconductor Lamina," filed December 29, 2010, by Murali et al. owned by the assignee of and is hereby incorporated by reference. Pursuant to 35 U.S.C. §119(e), this application claims priority to the filing date of U.S. Provisional Patent Application Serial No. 61/510,477, filed July 21, 2011, "Detection Methods in Exfoliation of Lamina”; U.S. Provisional Patent Application Serial No. 61/510,476, filed July 21, 2011, “Support Apparatus and Methods For Production of Silicon Lamina”; U.S. Provisional Patent Application Serial No., filed July 21, 2011 No. 61/510,478, "Ion Implantation and Exfoliation Methods"; and U.S. Provisional Patent Application Serial No. 61/510,475, filed July 21, 2011, "Apparatus and Methods for Production of Silicon Lamina"; the disclosure of these applications incorporated herein by reference.

Background technique

A conventional prior art photovoltaic cell comprises a p-n diode; an example is shown in FIG. 1 . A depletion region forms at the p-n junction, creating an electric field. Incident photons (incident light indicated by arrows) knock electrons from the valence band to the conduction band, creating free electron-hole pairs. Within the electric field located at the p-n junction, electrons tend to migrate towards the n-region of the diode while holes migrate towards the p-region, resulting in a current called photocurrent. Typically one region has a higher dopant concentration than the other regions, so the junction is either a p+/n- junction (as shown in Figure 1 ) or an n+/p-junction. The lightly doped region is called the base of the photovoltaic cell, while the more heavily doped region of the opposite conductivity type is called the emitter. Most charge carriers are generated in the base, and it is usually the thickest part of the cell. The base and emitter together form the active area of the cell.

Ion implantation is a known method for forming cleave planes in semiconductor materials to form lamina utilized in photovoltaic cells. The ion implantation and exfoliation steps in these methods can have a significant effect on the quality of the laminate produced. It would be desirable to improve methods and apparatus for producing laminates.

Contents of the invention

A method for producing a laminate from a donor body includes implanting the donor body with a dose of ions, and heating the donor body to an implantation temperature during implantation. The donor body is in separate contact with a susceptor assembly with which the donor body is in direct contact. The ply is exfoliated from the donor body by applying a thermal profile to the donor body. Implantation and exfoliation conditions can be adjusted to maximize the defect-free area of the laminate.

Description of drawings

Each of the aspects and embodiments of the invention described herein can be used alone or in combination with each other. Aspects and embodiments are now described with reference to the drawings.

Figure 1 is a cross-sectional view of a prior art photovoltaic cell.

2A through 2D are cross-sectional views illustrating stages in the formation of a photovoltaic device of Sivaram et al., US Patent Application No. 12/026,530.

3 is a flowchart illustrating steps of an example method according to aspects of the invention.

4A and 4B are cross-sectional views illustrating stages of ply formation according to an embodiment of the present invention.

5A and 5B are cross-sectional views illustrating ply separation according to an embodiment of the present invention.

6A and 6B are cross-sectional views illustrating ply separation according to an embodiment of the present invention.

7A and 7C are cross-sectional views illustrating stages in the formation of a photovoltaic device with a structured metal support element.

8A and 8B are perspective cutaway and perspective top views of an example base assembly of the present invention.

9A and 9B are top views illustrating embodiments of susceptor trays of the present invention.

10A and 10B are perspective cutaway views illustrating a split chuck of an embodiment of the present invention.

Detailed ways

Methods and apparatus are described in which individual plies are formed and separated from a donor body without adhesive or permanent bonding to a support element. The methods and apparatus of the present invention include implanting a dose of ions on a first surface of a donor body and heating the donor body to an implantation temperature during implantation. The first surface of the donor body is separately contacted with the base assembly, and the laminate is peeled from the donor body by applying a thermal profile to the donor body. The laminate can then be separated from the donor body. In some embodiments, the separation method comprises applying a deforming force to the surface of the laminate or donor body. Implantation and exfoliation conditions can be adjusted according to the material of the donor body in order to maximize the defect-free area of the thin individual laminates.

Conventional photovoltaic cells formed from silicon bulks include p-n diodes where the depletion region is formed at the p-n junction, as shown in FIG. 1 . Silicon donors used to form photovoltaic cells are typically about 200 to 250 microns thick. Thinner lamellae formed from silicon donors can be used to form photovoltaic Battery. Typically, the lamina thus formed must either incorporate a support element into any resulting photovoltaic cell, or be engaged during a stripping step to remove the support element. Described in this invention are methods and apparatus in which thin, free-standing laminates can be formed and separated from a donor body without adhesion or permanent bonding to a support element, and without the need for stripping or cleaning steps prior to photovoltaic cell fabrication . In the present invention, the donor body is implanted through the first surface to form a cleavage plane. The first surface of the donor body can then be placed adjacent to the support element. A heating step is performed to exfoliate the laminate from the first surface to create the second surface. This process occurs without support elements already bonded to the laminate. Ion implantation and exfoliation conditions can have a significant effect on the quality of the laminates produced by this method, and can be optimized to reduce the amount of physical defects that can form in individual laminates. A method for separation of exfoliated thin individual plies is also described.

U.S. Patent Application No. 12/026.530 of Sivaram et al., filed February 5, 2008, owned by the assignee of the present invention and hereby incorporated by reference, "Method to Form a Photovoltaic Cell Comprising a Thin Lamina" describes Fabrication of photovoltaic cells from thin semiconducting lamellae formed of non-deposited semiconducting materials. Referring to FIG. 2A , in an embodiment of Sivaram et al., semiconductor donor 20 is implanted through first surface 10 with one or more gas ions, such as hydrogen and/or helium ions. The implanted ions define a cleave plane 30 within the semiconductor donor volume. As shown in FIG. 2B , donor body 20 is attached to receiver 60 at first surface 10 . Referring to FIG. 2C , the annealing step causes the lamella 40 to cleave from the donor body 20 at the cleave plane 30 , creating the second surface 62 . In the Sivaram et al. embodiment, additional processing before and after the cleaving step forms a photovoltaic cell comprising a semiconductor lamella 40 having a thickness between about 0.2 and about 100 microns, for example between about 0.2 and about Between 50 microns, such as between about 1 and about 20 microns, in some embodiments between about 1 and about 10 microns, or between about 4 and about 20 or between about 5 and about 15 microns, although within the specified range Any thickness is possible. Figure 2D shows the structure inverted during operation in some embodiments, with receiver 60 at the bottom. Receiver 60 may be a discrete receiver element having a maximum width no greater than 50% greater than that of donor body 10, and preferably about the same width, as described in Herner, U.S. Patent Application No. 12/057,265, "Method to Form a Photovoltaic Cell Comprising a ThinLamina Bonded to a Discrete Receiver Element", filed March 27, 2008, owned by the assignee of the present invention and hereby incorporated by reference. Alternatively, multiple donors can be attached to a single larger receiver and laminates cleaved from each donor.

Using the method of Sivaram et al., photovoltaic cells are formed from thin semiconductor lamellae rather than from sliced wafers without loss through kerf or wasting silicon by the fabrication of unnecessarily thick cells, thus reducing cost. The same donor wafer can be re-used to form multiple laminates, further reducing cost, and can be re-sold for some other use after peeling of multiple laminates.

In the present invention, individual lamellae are formed by implanting a semiconductor donor body with ions to define a cleave plane and exfoliating the semiconductor lamina from the donor body at the cleave plane. The ply has a non-bonded first surface and a non-bonded second surface opposite the first surface. After the exfoliation step, the laminate is separated from the donor and fabricated into a photovoltaic cell, wherein the laminate contains the base region of the photovoltaic cell. The thickness of the laminates may be between about 4 microns and about 20 microns. One, two or more layers may be formed on the first surface of the lamina prior to incorporation of the lamina into a photovoltaic cell. One, two or more layers may be formed on the second surface of the individual plies. The thickness of the laminate is determined by the depth of the cleavage plane. In many embodiments, the thickness of the laminate is between about 1 and about 10 microns, such as between about 2 and about 5 microns, such as about 4.5 microns. In other embodiments, the thickness of the laminate is between about 4 and about 20 microns, such as between about 10 and about 15 microns, such as about 11 microns. The second surface is created by cleaving. Although different processes are possible, thin-layer boards are generally provided without permanent or adhesive fixation to the support element. In most embodiments, it has been exfoliated and separated from a larger donor body such as a wafer or ingot.

Turning to Figure 3, where the method of the present invention is outlined, the cleavage plane is formed by first implanting the donor with ions through the first surface (step 1, Figure 3). Implantation conditions can be adjusted to mitigate apparent physical defects (such as cracks, fissures, splits, wavefront defects, radial striations, flaking, or any combination thereof) in the final formed laminate. In one embodiment the physical defect comprises a crack and the method of the invention provides an individual ply wherein the total length of the cracks is less than 100 mm. Physical defects include any defects that can cause shunting or degrade performance in a completed cell. Laminar regions containing physical defects can be equivalent to reflecting unusable regions in photovoltaic cells. Implantation conditions that can be adjusted to maximize substantially defect-free areas in the cleaved lamina include temperature and/or pressure applied to the donor body during implantation. In some embodiments, the injection temperature may be maintained between 25 and 300°C, such as between 100 and 200°C or between 120 and 180°C. One aspect of the invention is that the implantation temperature can be adjusted, depending on the material and orientation of the donor. In some embodiments, the material is {111} oriented silicon and the implantation temperature may be between 150 and 200°C. In other embodiments, the material is {100} oriented silicon and the implantation temperature may be between 25 and 150°C. The methods disclosed here can also be applied to any other orientation of semiconductor donors, such as {110} oriented silicon or {001}. Implantation temperature can be optimized for any silicon orientation and implantation temperature. Other implant conditions that may be adjusted may include initial process parameters such as dopant dose and ratio of implanted ions (eg H:He ratio). In some embodiments, implantation conditions may be optimized in combination with exfoliation conditions such as exfoliation temperature, exfoliation susceptor vacuum, heating rate, and/or exfoliation pressure to maximize the area present in the laminate that is substantially free of physical defects. In some embodiments, greater than 90% of the surface area of the ply produced by the methods of the invention is free of physical defects.

After injection to form the cleave plane, the donor body can be exposed to a temporary support element (Fig. 3, step 2) such as a base assembly for further processing. Typically, donor bodies, laminates or photovoltaic cells at various stages of fabrication can be attached to a temporary carrier with adhesives or via chemical bonding. When adhesives are used, additional steps are required to initiate peeling of the laminate and/or to clean the surface of the photovoltaic cells and temporary carrier after disassembly. Alternatively, the support element may dissolve or otherwise be removed and rendered unavailable for further support steps. In one aspect of the invention, the donor body is separately contacted to a support member, such as a base assembly, without an adhesive or permanent bond to stabilize the laminate during exfoliation. The contact may be direct contact between the donor body and the support element and not involve an adhesive or bonding step requiring chemical or physical steps to break the contact after merely lifting the donor body or laminate from the base. The base can then be reused as a support element without further processing. In some embodiments of the methods of the present invention, the injected donor body may be separately contacted with a support member, such as a base assembly, wherein the interaction force between the donor body and the base during exfoliation is only exerted on the base. body weight or just the weight of the base assembly on the donor body. In cases where contact is established solely by the weight of the donor body, the donor body may be oriented with the injected side down and in contact with the base. Alternatively, the donor body may be oriented with the injected side up and out of contact with the susceptor. In this case, the cover sheet can be used to stabilize the laminate during and after peeling. In other embodiments the contact may further comprise a vacuum force between the base and the donor body. A vacuum force may be applied to the donor body to temporarily secure the donor body to the base assembly without the use of adhesives, chemical reactions, electrostatic pressure, or the like.

As in the present invention, contacting the plies to the non-bonded support member during the steps of exfoliation and damage annealing provides several significant advantages. The steps of exfoliation and annealing occur at relatively high temperatures. If the preformed support element is attached to the donor body prior to the high temperature step, for example with adhesives or chemicals, it must be exposed to high temperature like any intervening layers and plies. Many materials cannot easily tolerate high temperatures, and if the coefficients of thermal expansion (CTE) of the support element and the laminate are mismatched, the heating and cooling cause stresses that can damage the thin laminate. Thus, the non-bonded support elements provide an optimized surface for laminate fabrication independent of the bonding and debonding procedures that potentially prevent the formation of defect-free layers. Annealing can occur before or after separation of the lamina from the donor body.

Following contact of the donor body to the base assembly, heat may be applied to the donor body to cleave the laminate from the donor body at the cleaving plane. Peeling conditions can be optimized to cleave the laminate from the donor body (Fig. 3, step 3) to minimize physical defects in the peeled laminate without adhesive support elements. The exfoliation parameters can be optimized for a particular donor. Flaking can occur under ambient stress. An exfoliation thermal profile with one, two or more thermal ramps can be applied. In some embodiments the exfoliation conditions may comprise a single rapid thermal ramp to a peak exfoliation temperature greater than 600°C. The thermal ramp rate may be 100°C/minute, 200°C/minute or greater. The material of the susceptor may have a lower heat capacity than the donor body and may resist thermal degradation at the final exfoliation temperature to facilitate exfoliation by this method. In other embodiments the final exfoliation temperature may be between 400 and 600°C, where the ramp rate is any speed, but the temperature is applied substantially uniformly across the surface area of the ply. The susceptor assembly may contain a thermally anisotropic material to promote a uniform thermal profile across the surface of the donor body during exfoliation. In some embodiments, the donor body can be transported to a region of higher temperature so that the heating of the donor body is transferred from one end of the donor body to the other in a uniform manner. In one embodiment, the donor body is moved from a lower temperature zone to a higher temperature zone (eg, a belt furnace). The rate of movement can provide rapid changes in the temperature of the donor, for example 60°C/minute, 200°C/minute or more.

The exfoliated laminate may be separated from the donor body by any means, for example by applying a deforming force to the first surface of the donor body away from the opposing surface of the newly formed laminate (Figure 3, step 4). In some embodiments the donor body can be deformed away from the exfoliated laminate. In other embodiments the exfoliated ply can be deformed away from the donor body. After exfoliation, the surface of the individual ply that is the first surface of the donor body may be separately contacted with a support means such as a base assembly. In some embodiments the contact force may comprise a vacuum force between the laminate and the base plate. In some embodiments the contact force may simply be the weight of the donor on the laminate. The chuck may be bonded to the donor body on the surface opposite the laminate. Bonding in some embodiments may be a vacuum force applied to the donor body through a porous chuck. Vacuum pressure can be applied through the chuck, thus bonding the donor body to the chuck. The chuck may be coupled to a deflection device such as a deflection arm or a deformable disk or the like. Force applied to the deflection means may deform the donor body away from the laminate. This force can deform any portion of the donor body away from the laminate, such as an edge or other area. Deformation may separate the donor body to a distance greater than 1 mm from a portion of the laminate surface, releasing the edges of the donor body for subsequent complete separation of the laminate from the donor body. The separated plies can remain on the base plate or be transferred to different temporary or permanent support elements for further processing. In some embodiments the permanent support can be constructed on separate plies.

One aspect of the invention encompasses a process for fabricating photovoltaic cells from individual plies, starting with a donor of a suitable semiconductor material. A suitable donor may be a single crystal silicon wafer of any practical thickness, for example from about 200 to about 1000 microns thick. Typically wafers have a Miller index of {100} or {111}, although other orientations may be used. In alternative embodiments, the donor wafer can be thicker; the maximum thickness is limited only by wafer handling practicability. Alternatively, polycrystalline or polycrystalline silicon may be used, as may be microcrystalline silicon, or wafers or ingots of other semiconductor materials including germanium, silicon germanium, or III-V or II-VI semiconductor compounds such as GaAs, InP, etc. Other materials can be used, such as SiC, LiNbO ₃ , SrTiO ₃ , sapphire, etc. The term polycrystalline in this context generally refers to semiconductor materials having grains of the order of one millimeter or larger in size, while polycrystalline semiconductor materials have smaller grains of the order of one thousand Angstroms. The grains of microcrystalline semiconductor material are very small, for example about 100 angstroms. Microcrystalline silicon, for example, may be fully crystalline or may comprise the crystallites in an amorphous matrix. It is understood that a polycrystalline or polycrystalline semiconductor is completely or substantially crystalline. Those skilled in the art recognize that the term "monocrystalline silicon" as it is customarily used does not exclude silicon with occasional blemishes or impurities such as conductivity enhancing dopants.

The process of forming monocrystalline silicon generally results in circular wafers, but the donor body can have other shapes as well. For photovoltaic applications, cylindrical monocrystalline ingots are often processed into octagonal cross-sections before wafer dicing. Wafers can also be other shapes such as square. Square wafers have the advantage over circular and hexagonal wafers that they can be aligned edge-to-edge on photovoltaic modules with minimal gaps between them. The diameter or width of the wafer can be any standard or custom size. For simplicity, this disclosure describes single crystal silicon wafers as semiconductor donors, but it is understood that other types and materials of donors may be used.

Preferably ions of hydrogen or a combination of hydrogen and helium are implanted into the donor body through the first surface so as to define a cleave plane, as previously described. The total depth of the cleave plane is determined by several factors including implant energy. The depth of the cleave plane may be between about 0.2 and about 100 microns from the first surface, for example between about 0.5 and about 20 or about 50 microns, for example between about 1 and about 10 microns, between about 1 or 2 and about 5 microns or between 6 microns, or between about 4 and about 8 microns. Alternatively, the depth of the cleave plane may be between about 5 and about 15 microns, such as about 11 or 12 microns.

The temperature and dose of ion implantation can be adjusted according to the material to be implanted and the desired depth of the cleave planes in order to provide free-standing laminations substantially free of physical defects. The ion dose may be any dose such as between 1.0×10 ¹⁴ and 1.0×10 ¹⁸ H/cm ² . The injection temperature may be any temperature eg greater than 140°C (eg between 150 and 250°C). Implantation conditions can be adjusted based on the Miller index of the donor and the energy of the implanted ions. For example, a single crystal silicon with a Miller index of {111} may require a different set of implant conditions than a single crystal silicon wafer with a Miller index of {100}. One aspect of the invention involves adjusting the implant conditions to maximize the substantially defect-free area in the laminate. In some embodiments, the implant dose may be less than 1.3 x ¹⁰¹⁷ H/ ^cm2 in combination with an implant temperature greater than 25°C, eg, between 80°C and 250°C. In some embodiments, a single crystal silicon donor having a Miller index of {111} can be implanted at a temperature between 150 and 200°C. In some embodiments, a single crystal silicon donor having a Miller index of {100} can be implanted at a temperature between 100 and 150°C. In some embodiments, higher injection temperatures can result in more uniform exfoliation.

Referring to FIG. 4A , the injected surface 10 of the donor body 20 may be separately contacted with a support member, such as a base assembly 400 . The base assembly can be in contact with the donor body while remaining unbonded to the donor body. The contact force between the donor body and the base assembly during exfoliation may simply be the weight of the donor body. Alternatively, the entire assembly and donor body could be inverted, and the contact force could be the weight of the base assembly on the donor body. In some embodiments, the contact force between the donor body and the base can be enhanced by the vacuum force between the base and the donor body. The material properties of the base component can facilitate spallation of the substantially defect-free laminate from the donor body. The susceptor assembly 400 may comprise a monolithic susceptor disk that is flat as in FIG. 4A. In some embodiments the surface of the susceptor assembly may comprise a material having substantially the same coefficient of thermal expansion (CTE) as the donor body over a wide range of temperatures (eg, 0 to 1000°C). The susceptor assembly may comprise a material having a thermal capacity substantially the same as or lower than the thermal capacity of the donor body so as to support rapid thermal ramping to exfoliation temperatures greater than 400°C.

In other embodiments, as shown in FIG. 4B , base assembly 401 may contain multiple discs to provide suitable conditions for processing laminates from donor body 20 . The contact force between the susceptor assembly 401 and the donor body in some embodiments may be a vacuum force applied to the porous susceptor disc 405 of the susceptor assembly through the vacuum channel 410 (as shown in FIG. 4B ). When vacuum forces are used to support the donor body, susceptor disk 405 may be porous graphite or any material that is permeable to vacuum pressure. For example, the material of porous disc 405 may comprise porous graphite, porous boron nitride, porous silicon, porous silicon carbide, laser-drilled silicon, laser-drilled silicon carbide, aluminum oxide, aluminum nitride, silicon nitride, or any combination thereof. Vacuum pressures in the range of about 0 to about -100 psi (eg, between 0 psi and about -15 psi) may be used. Susceptor assembly 401 may include a first disk 405 having a coefficient of thermal expansion (CTE) similar to or substantially the same as that of donor body 20 . In some embodiments the thermal profile applied during exfoliation can be substantially uniform across the surface of the donor body, thereby promoting successful exfoliation of individual plies. To achieve a uniform thermal profile across the surface of the donor body, the susceptor assembly may include a second disk 415 adjacent to the first disk 405, wherein the second disk 415 has a higher thermal conductivity on a surface parallel to the donor body than on a surface perpendicular to the donor body. Apparently higher is preferred. Thermally anisotropic materials such as pyrolytic graphite are well suited to facilitate in this way the application of a substantially uniform thermal profile on the donor body. The susceptor assembly may optionally include an insulating disc 425, such as a quartz disc, disposed below the thermally anisotropic disc 415 to facilitate maintenance of the thermal profile required for exfoliation by insulating the donor body from potentially cooling forces such as an operating vacuum manifold.

Following contact of the donor body to the base assembly, a thermal expansion protocol may be applied that results in cleaving of the individual plies substantially free of physical defects from the donor body 20 at the cleavage plane 30 . The expansion protocol may comprise one or two or more thermal ramps to one or two or more peak exfoliation temperatures followed by a thermal soak for a period of, for example, less than 1, 2, 3, 4, 5 or 6 minutes ( thermal soak). The peak exfoliation temperature may be between 350 and 900°C, such as between 350 and 500°C or between 500 and 900°C. The ramp rate during the thermal exfoliation profile can also be optimized. The thermal ramp rate can range from, for example, 0.1°C/sec to 20°C/sec. The exfoliation pressure can be ambient pressure or higher. The thermal exfoliation profile can be optimized based on the material and orientation of the donor body so as to form free-standing laminates substantially free of physical defects.

In some embodiments, a monocrystalline silicon lamina can be exfoliated from a donor in {111} orientation by applying an exfoliation thermal profile comprising a single thermal ramp rate 15°C/sec faster than the final exfoliation temperature greater than 600°C. The peak exfoliation temperature can be maintained for 100, 50, 25 seconds or less. In other embodiments the thermal profile may comprise a ramp rate of between 0.1 and 5°C/sec to a peak profile temperature between 400 and 600°C, wherein the thermal ramp rate is substantially the same across the surface area of the laminate . The peak exfoliation temperature may be maintained for less than 3 minutes, 1 minute, or less than 30 seconds. The susceptor may contain a thermally anisotropic material such as the second disc 415 of FIG. 4B to facilitate the uniform application of a uniform thermal profile across the surface of the donor during exfoliation.

Alternatively, exfoliation may involve two or more thermal ramps to provide a more controlled exfoliation process. Multiple thermal scales can accommodate donors with Miller indices of {111}, {100}, or other orientations. For example, a thermal profile may include a first thermal ramp rate of between 10 and 20°C/sec to a peak temperature between 350 and 500°C, and a first thermal ramp rate to a peak temperature between 600 and 800°C at about Second thermal ramp rate between 5 and 20°C/sec. The peak exfoliation temperature may be maintained for less than 60 seconds after each thermal ramp, followed by cooling or further processing to anneal or separate the exfoliated plies. In some embodiments the exfoliation protocol may comprise two or more thermal ramps under thermally anisotropic conditions, thereby providing a more controlled exfoliation process. Other examples of multiple thermal ramp rates include a first thermal ramp of between 0.5 and 10°C/sec to a peak temperature between 350 and 450°C, followed by a A second thermal ramp of between about 0.1 and 5°C/sec of peak temperature. The peak exfoliation temperature may be maintained for less than 10 seconds after each thermal ramp, followed by cooling or further processing to anneal or separate the exfoliated plies. The thermal profile can be imposed by moving the susceptor assembly and/or the cleaved donor body from a first region of one temperature to a second region of a different temperature. The first temperature may be lower than the second temperature. The process can be carried out via a belt furnace or other conveying means.

The step of implanting to define cleave planes has been found to result in damage to the crystal lattice of the polycrystalline donor wafer. This damage can impair battery performance if not repaired. In the present disclosure, annealing can remove residual physical defects in exfoliated laminates. Relatively high temperature annealing, for example at greater than 800, 850, 900 or 950°C, repairs most implant damage in the bulk of the laminate. After peeling off, the individual plies can contact the base with the donor remaining on top. The donor body can be deformed away from the exfoliated laminate by applying a deforming force to the surface of the donor body opposite the laminate. This method can apply a sufficiently gentle force to detach the donor from a lamina less than 50 μm thick without damaging the lamina. The vacuum gripper device is then placed on top of the donor body so as to make contact with the donor body surface opposite the lamina. The first chuck of the vacuum clamping apparatus may cover the entire surface opposite the ply (chuck 515 ) as in FIG. 5 , or a portion of the surface opposite the ply (chuck 615 ) as in FIG. 6 . The first chuck may be a porous chuck (such as porous graphite, porous boron nitride, porous silicon, porous silicon carbide, laser drilled silicon, laser drilled silicon carbide, alumina, aluminum nitride, silicon nitride, or any combination) or contain a vacuum channel. Vacuum is applied through the first chuck, which grips the donor body. Next, the first chuck is deflected. Pressure can be applied to the backside of the flexure, which causes a slight deflection of the flexure, bringing the disk into contact with the vacuum-held donor. One aspect of these vacuum chuck methods is that the edge of the donor body is pulled away from the laminate first, allowing air to rush between the donor and the laminate surface. This action eliminates suction on the newly formed surface of the ply that can cause physical defects to appear.

Referring now to FIGS. 5A and 5B , in some embodiments separation of the lamina from the donor body can occur by using a deflection device to deform the donor body away from the lamina. Deformation can facilitate the separation of the donor body from the individual lamina in a manner that minimizes the formation of defects in the individual lamina. Figure 5A shows a first step in an embodiment of the method in which the donor body 20 is coupled to a separation fixture 500, such as a vacuum fixture. The jig 500 may include a first chuck 515 that may be supported to a surface 520 of the donor body 20 opposite the laminate 40 via vacuum pressure applied through a vacuum channel 525 or any other adhesive force. The first chuck 515 may be coupled to a flexure device such as a flexible arm, a flexure arm, a flex disk 535, or the like. The flexure may be coupled to the rear pan 545 or to a support arm, pivot point, or the like. The peeled ply 40 may be separately contacted in the base assembly 402 to the base plate 405 . Additionally contact force may be applied to susceptor disk 405 via vacuum pressure applied via vacuum channel 410 . Separation is achieved by applying a force to a deflection device that deflects the donor surface opposite the laminate. This detached embodiment is shown in FIG. 5B , showing the deflection of the flexible disk 535 and the resulting deformation of the donor body 20 away from the laminate 40 . In this embodiment, positive pressure is applied to the rear side of the flex disc 535 via channel 555 , which causes a slight deformation of the flex disc 535 , first chuck 515 and clamped donor body 20 . Positive pressure can be applied by any means, such as air flow between the flex disk 535 and the back disk 545 . A portion of the donor body 20 may deform between 1 and 3 mm or more from the lamina, thereby initiating separation of the donor body from the cleaved lamina 40 held stationary on the susceptor disc 405 . In an alternative embodiment, the donor body may remain fixed to the base pan, while the cleaved plies are attached to the chuck and detached from the donor body as described above.

6A and 6B illustrate an embodiment of the separation process in which the separation fixture comprises a first chuck 615 bonded to only a portion of the surface of the donor body 20 opposite the laminate 40 and coupled to a Flexure means for rigid arm 635. The bond between first chuck 615 and donor body 20 may utilize vacuum force delivered through vacuum channel 625 . The first chuck 615 may be porous. Rigid arm 635 may be coupled to pivot point 645 or any device designed to move the rigid arm away from the donor body. The laminate 40 may be fixed to or simply contact the base plate 405 . Deflecting the rigid arm 635 away from the laminate 40 as shown in FIG. 6B causes a portion of the donor body 20 to deform away from the laminate 40 which remains stationary on the base plate 405 . In an alternative embodiment, the donor body may remain fixed to the base plate, while the cleaved laminate is attached to the chuck 615 and detached from the donor body as described above. The annealing step may be performed at any stage in the process, for example after separation of individual laminae, in order to repair damage to the lattice caused throughout the body of the laminae during implantation, exfoliation steps or separation steps. Annealing may be performed in any amount while the laminate remains in place on the base assembly, for example at a temperature greater than 500°C, for example at a temperature of 550, 600, 650, 700, 800, 850°C or greater, for example about 950°C time. The structure can be annealed, for example, at about 650°C for about 45 minutes, or at about 800°C for about ten minutes, or at about 950°C for about 120 seconds or less. In many embodiments the temperature exceeds 850°C for at least 60 seconds. In some embodiments, it is advantageous to remove the donor prior to annealing the laminate to temperatures above 700°C, thus preserving the structural and electronic properties of the donor for subsequent iterations of the implant-exfoliation process.

Photovoltaic devices can be fabricated from individual thin-layer sheets after the sheets have been annealed. Laminates may be transferred to temporary or permanent supports for further processing therefor, as in U.S. Patent Application No. 12/980,424 filed December 29, 2010, owned by the assignee of the present application, and hereby incorporated by reference Described in "A Method to Form a Device by Constructing a Support Element on a Thin Semiconductor Lamina". This can be done, for example, using vacuum paddles (not shown). To effect this transfer, a vacuum paddle can be placed on the second surface while the vacuum on the first surface is released. After transfer to the vacuum paddle, the second surface is supported by vacuum while the first surface is exposed. Referring to Figure 7A, the ply 40 may be attached to a temporary carrier 50, for example using adhesive. The adhesive must tolerate moderate temperatures (up to about 200°C) and must be easily releasable. Suitable binders include, for example, polyesters with maleic anhydride and rosin, which are soluble in hydrocarbons; or polyisobutylene and rosin, which are soluble in detergents. Temporary carrier 50 may be any suitable material, such as glass, metal, polymer, silicon, and the like. After transfer, the first surface 10 is supported by the adhesive to the temporary carrier 50, while the second surface 62 is exposed.

As shown in Figure 7B, further processing to form a photovoltaic device may be as follows. The etching step to remove damage caused by spalling can be performed, for example, by applying a mixture of hydrofluoric (HF) acid and nitric acid or using KOH. It may be found that annealing is sufficient to remove all or nearly all damage and this etching step is unnecessary. The surface can be cleaned with a dilute HF solution; eg 10:1 HF for two minutes to remove organic material and residual oxides. After this wet process, an amorphous silicon layer 72 is deposited on the second surface 62 . The layer 72 may be heavily doped silicon and may have a thickness, for example, between about 50 and about 350 Angstroms. FIG. 7B shows an embodiment that includes an intrinsic or near-intrinsic amorphous silicon layer 74 between and in direct contact with second surface 62 and doped layer 72 . In other embodiments, layer 74 may be omitted. In this example, the heavily doped silicon layer 72 is heavily doped n-type of the same conductivity type as the lightly doped n-type lamina 40 . The lightly doped n-type lamella 40 contains the base region of the photovoltaic cell to be formed, and the heavily doped amorphous silicon layer 72 provides electrical contact to the base region. If included, layer 74 is sufficiently thin so that it does not prevent electrical connection between laminate 40 and heavily doped silicon layer 72 .

A transparent conductive oxide (TCO) layer 110 is formed on and in direct contact with the amorphous silicon layer 74 . Suitable materials for TCO 110 include indium tin oxide and aluminum doped zinc oxide. The layer may be, for example, between about 500 and about 1500 Angstroms thick, such as about 750 Angstroms thick. This thickness enhances the reflection from the reflective layer to be deposited. In some embodiments, the layer can be substantially thin, such as about 100 to about 200 Angstroms. Amorphous silicon layer 76 may also be applied to the second surface after annealing of the laminate.

As seen in the completed device shown in FIG. 7C , incident light enters the laminate 40 at the first surface 10 . After passing through the lamella 40 , light that is not absorbed leaves the lamella 40 at the second surface 62 and then passes through the TCO layer 110 . The reflective layer 12 formed on the TCO layer 110 reflects the light back into the cell for an absorbed second chance, improving performance. A conductive reflective metal can be used for the reflective layer 12 . Various layers or stacks can be used. In one embodiment, reflective layer 12 is formed by depositing a very thin layer of chromium, such as about 30 or 50 Angstroms to about 100 Angstroms, on TCO layer 110, followed by about 1,000 to about 3,000 Angstroms of silver. In an alternative embodiment not pictured, reflective layer 12 may be aluminum having a thickness of about 1000 to about 3000 Angstroms. In the next step, layers are formed by plating. Conventional plating cannot be performed onto an aluminum layer, so if aluminum is used for the reflective layer 12, an additional layer or layers can be added to provide a seed layer for the plating. In one embodiment, a titanium layer, eg, between about 200 and about 300 Angstroms thick, is followed by a seed layer, eg, cobalt, which may be of any suitable thickness, eg, about 500 Angstroms.

A metal support element 60 is formed on the reflective layer 12 (chrome/silver stack in this embodiment). In some embodiments metal support member 60 is formed by electroplating. The temporary carrier 50 and the laminates 40 and associated layers are immersed in the electrolytic bath. Electrodes are attached to the reflective layer 12, and current is passed through the electrolyte. Ions originating from the electrolytic cell accumulate on the reflective layer 12 forming a continuous metal support element 60 . Metal support element 60 may be, for example, an alloy of nickel and iron. Iron is less expensive, while nickel's coefficient of thermal expansion better matches silicon, reducing stress during later steps. The thickness of metal support member 60 may be as desired. The metal support member 60 should be thick enough to provide structural support for the photovoltaic cell to be formed. Thicker support elements 60 are less prone to bending. Conversely, minimizing thickness reduces cost. One skilled in the art selects the appropriate thickness and iron:nickel ratio to balance these considerations. The thickness of metal support member 60 may be, for example, between about 25 and about 100 microns, such as about 50 microns. In some embodiments, the iron-nickel alloy is between about 55% and about 65% iron, such as 60% iron.

The lightly doped n-type stack 40 contains the base of the photovoltaic cell, and the heavily doped p-type amorphous silicon layer 76 serves as the emitter of the cell. The heavily doped n-type amorphous silicon layer 72 provides good electrical contact to the base of the cell. Electrical contact must be made to both sides of the cell. Contacts to the amorphous silicon layer 76 are made by gridlines 57 via the TCO layer 112 . The metal support element 60 is electrically conductive and is in electrical contact with the base contact 72 via the conductive layer 12 and the TCO layer 110 .

FIG. 7C shows the completed photovoltaic assembly 80 comprising the photovoltaic cells and the metal support element 60 . In an alternative embodiment, by varying the dopants used, the heavily doped amorphous silicon layer 72 may serve as the emitter, while the heavily doped amorphous silicon layer 76 serves as the contact to the base. Amorphous silicon layers 72 and 76 may be in direct contact with the first and second surfaces of the individual laminates, respectively. Incident light (indicated by arrows) falls on TCO 112 , enters the cell at heavily doped p-type amorphous silicon layer 76 , enters lamina 40 at first surface 10 , and passes through lamina 40 . The reflective layer 12 serves to reflect some light back into the cell. In this embodiment, the receiver element 60 serves as the substrate. The receiver element 60 and the laminate 40 and associated layers form a photovoltaic assembly 80 . A plurality of photovoltaic assemblies 80 may be formed and attached to a support substrate 90, or alternatively attached to a support substrate (not shown). Each photovoltaic assembly 80 includes photovoltaic cells. The photovoltaic cells of the module are typically connected electrically in series.

base device

Referring now to FIGS. 8A and 8B , a susceptor assembly as previously described in FIGS. 4A and 4B may comprise one or more susceptor disks. The susceptor assembly 400 may be disposed in the lower portion of the susceptor chamber 800 as shown in FIG. 8B and configured to support appropriate conditions for exfoliation, annealing, or separation of the individual plies. In FIG. 8A, a first disc 405 may be used to contact the first surface of the donor body and provide a detachable support for the lamina during exfoliation, separation, annealing, or any combination thereof. The first susceptor disk 405 may be used throughout the ply production process, or a separate disk with separation properties optimized for a particular step may be used. For example, the donor body may be in contact with a first susceptor disc during implantation, a second susceptor disc during exfoliation and a third susceptor disc during detachment. An optional upper surface (eg, a clamp not shown) may be used to contact a second surface of the donor body opposite the first surface. The susceptor assembly 400 provides physical support for the thin-layer board after spalling and also provides thermal characteristics that facilitate the spalling and annealing procedures utilized. In some embodiments, the first susceptor disk 405 can be an inert solid such as graphite. In some embodiments of the invention, the donor body or ply is separately contacted to the vacuum permeable base assembly. A porous material may be used for the first susceptor disk 405 to enable vacuum pressure to support the donor body or laminate to the substrate during exfoliation. The porous material may comprise porous graphite, porous boron nitride, porous silicon, porous silicon carbide, laser-drilled silicon, laser-drilled silicon carbide, aluminum oxide, aluminum nitride, silicon nitride, or any combination thereof.

Vacuum can be achieved by applying negative gauge pressure in the ambient environment (eg, air or nitrogen), or by direct vacuum pressure through a series of vacuum channels 410 . The choice of porous susceptor disk material to facilitate process flow is important to the exfoliation process. Material properties that facilitate the exfoliation process include: low static coefficient of friction (CSF with values such as 0.1-0.5), low hardness (<10 on the Mohs scale), average pore diameter of less than about 15 microns, ability to be machine flattened (i.e., ability to use conventional mechanical techniques/materials on these susceptors), low roughness (<1µm roughness), flatness (<10µm waviness on the main body), prevention of electrostatic charge between laminate and susceptor sufficient conductivity to occur, and so on. In one embodiment the first susceptor plate 405 can have a CTE that is substantially the same as the coefficient of thermal expansion (CTE) of the donor body. In other embodiments the susceptor plate may have the same or lower thermal capacity than the donor body. In some embodiments the donor is single crystal silicon, and the heat capacity of the susceptor is about the same as silicon (about 19.8 J/mol-°K).

Due to these constraints, many engineered ceramics and other materials can be selected to provide the first susceptor plate 405 with these properties. In one embodiment, Ringsdorff ^™ graphite grade R6340 can be used because it has a CTE similar to that of silicon. This is important to prevent lateral forces from being applied to the donor body or laminate during heat treatment associated with spalling or annealing. These temperature changes can lead to wrinkling or tearing of the laminates due to graphite having a CTE not similar to the silicon CTE. Due to the CTE-matched graphite, the laminates can be held under light or no vacuum retention during these temperature changes. A bulk etch can be applied to graphite to improve purity. A common bulk etch process consists of a 24 hour high temperature bake in a vacuum chamber into which chloride gas has been introduced.

In other embodiments of the exfoliation process, a rapid high temperature thermal profile is applied. In these embodiments it is desirable to have a susceptor plate that is resistant to outgassing or decomposition at temperatures up to 800 or 900 or 1000°C. The susceptor material may have properties that prevent contamination of the donor body, such as being able to withstand the temperature and atmospheric exposure of the process without undergoing material decomposition. The material can be inherently resistant to decomposition, or coated with a material that acts as a barrier to donor contamination at high temperatures. For example, porous silicon carbide, which is rigid, durable, and has a good CTE match, can be coated with boron nitride, which is soft and has low CSF and high purity. In other embodiments, optimized porous/laser drilled materials may be utilized. Laser drilled materials allow to differentiate between the necessity of the volume of the fixture (porosity, CTE, flatness/machinability) and the necessity of the surface material (low CSF, soft, high purity, etc.). For example, a material that provides an interface having the desired properties listed above can be coated over a stock material having the properties desired for the base block. In other embodiments, metal oxides, carbides, nitrides, ceramics, and superalloys meeting the previously mentioned specifications are candidates for use. The properties of the susceptor material described above are beneficial in improving the quality of the laminates produced, including laminate mechanical properties, uniformity and purity.

In another embodiment of the invention, a uniform temperature profile can be applied to the donor body during exfoliation. In FIG. 8A, a thermally anisotropic second susceptor disk 415 may be disposed adjacent to the first disk 405, thereby providing a preferably higher thermal conductivity in a plane parallel to the donor body than in a direction perpendicular to the donor body, In order to facilitate the application of a uniform thermal profile. The uniformity of the exfoliation temperature profile can be imposed by the presence of pyrolytic carbon, a graphite material with high thermal conductivity across the cleave plane compared to normal to the cleave plane and thus is an ideal planar thermal conductor. The thermally anisotropic second plate may contain vacuum channels 410 to facilitate the distribution of vacuum pressure to the bottom side of the first susceptor plate 405 . Additional features may include vacuum channels 455 machined into the surface of the susceptor plate to improve vacuum pressure distribution. In the embodiment shown in Figure 9A, a second susceptor disk 915 with a set of vacuum channels 955 shown as concentric rings connected by radial paths can be used to distribute vacuum pressure to separate porous susceptor disks. Vacuum channels on the periphery 925 of the second susceptor disk 915 may be used to distribute vacuum pressure around the periphery of the susceptor disk in order to secure one susceptor disk to another device or disk.

In some embodiments, a heating source for the susceptor apparatus may be provided, for example, by embedding heat lamps within the susceptor chamber. The heating source may be any source capable of providing the temperature required for implantation, exfoliation or annealing, for example up to 1000°C. In other embodiments, a heating source may be located separately from the susceptor chamber, such as, but not limited to, a quartz heating or induction heating element disposed within the susceptor chamber to heat the susceptor assembly and/or donor body.

In a further embodiment, different vacuum channels may be used on the base plate to separate the vacuum holding the plates 405 and 415 together from the vacuum supporting the donor body to the base assembly 400 . 8A illustrates an example susceptor assembly with differential vacuum channels. To vary the support force, the vacuum pulling through the base may require throttling. To decouple the effect of pulling through the porous material (eg graphite) onto the laminate versus pulling on the first susceptor plate itself, differential vacuum channels for the two may be employed. A first set of channels 410 is centrally located and these control the suction on the laminate itself. A second set of vacuum channels 460 and annulus 470 are located around the edges of the first and second susceptors that support the first susceptor in place, independent of the clamping on the donor body in the center. By employing this system, it is possible to remove the laminates while still keeping the base assembly together.

In some embodiments, vacuum force is applied to secure the laminate to the base assembly during the annealing or exfoliation process, which can aid in the cooling of the base assembly. To achieve the high temperatures required for the annealing process or the exfoliation process, the susceptor assembly may contain a disc that provides a thermal break between the donor body and the lower vacuum manifold. A third susceptor disk 475 acting as a thermal break can be added to the susceptor assembly 400 of FIG. 8A between the vacuum manifold (not shown) and the first 405 or second 415 susceptor disk. In an alternative embodiment, the first or second susceptor disk may act as a thermal break between the vacuum manifold and the laminate. In some embodiments of the invention, thermal fracturing during annealing and/or exfoliation can be accomplished with a quartz disk such as disk 975 shown in Figure 9B. The number of pans can be, for example, one or two, depending on the desired temperature range and uniformity. Instead of quartz, other insulating materials such as high temperature ceramics that can withstand the annealing temperature can be used. The quartz disks are machined to allow vacuum to pass through them while still separating the inner and outer annulus of the different vacuum channels. This thermal rupture disk can be critical when using a vacuum manifold beneath a water-cooled base assembly. Thermal cracking can prevent heat loss from the first susceptor disk 405, which can potentially facilitate achieving the temperatures needed to achieve annealing and/or spalling. Properties of thermally ruptured susceptor disk 475 that may facilitate the annealing process include: low content of highly diffused foreign matter (less than 20 PPM impurities), similar thermal expansion coefficient to silicon (eg, within 20% of silicon CTE), and high temperature capability (eg, 1000°C ), and low resistivity.

Note that although the base assembly with differential channels is shown in FIG. 8A with a thermal stack, the differential channel 460/470 and thermal stack 475 features can be used independently of each other. Similarly, thermal stacks may be utilized in any situation where the top surface of the supporting laminate operates at a different temperature than the components underlying the thermal rupture element. Furthermore, the individual elements of the thermal stack (as thermally fractured quartz separating the top surface from the lower surface at different temperatures) can be used individually, in different orders, or in different configurations.

separation equipment

In Figures 10A and 10B, an embodiment of a separation jig 100 for separating a donor body from a laminate in the method of Figure 5B is shown. In operation, the surface of the donor body opposite the laminate is placed against the separation fixture, and the peeled (but not yet separated) laminate body is placed on the base assembly. Alternatively, the donor/lamina can be reversed in the device. The separation fixture 100 of Figures 10A and B involves a disc stack comprising a porous disc 115 (eg graphite), a flexure means such as a flexible disc 135 (eg aluminum or PEEK) and a rigid support disc 145 (eg aluminum). Porous disk 115 is referred to in this disclosure as graphite; however, other materials are possible as described later. Rigid disk 145 has distribution channels 150 therein to apply positive pressure to the backside of flexible disk 135 . The distribution channels can be configured, for example, as concentric rings connected by radial channels, or as a rectilinear grid. The flexible disc 135 may be secured to a rigid disc 145 around its circumference. When a positive pressure is applied, the central portion of the flexible disk 135 deflects into a convex shape such as that shown in Figure 10B, forcing the porous disk 115 to follow that shape. The flex disc may deflect, for example, by about 1 or 2 or more millimeters. The operating pressure of the device may be any pressure, for example 0.1-5 bar. This pressure depends on the thickness of the material in the device. The three needs of a flex disk are mechanical strength to withstand the pressure applied to it, compliance to elastic bending (as opposed to rupture), and impermeability to pressurized air. In one embodiment, the porous layer 115 is about 3 mm thick and the impermeable flexible disk 135 is about 5 mm thick. Other material options for the flexible layer 135 include soft metals such as aluminum, thin gauge steel or polymers, elastomeric or rubber based materials. In some embodiments, a donor body (not shown) can be supported against porous disk 115 by applying a vacuum between the flexible disk and the porous disk. Since the graphite disk is porous, a vacuum can be applied to the distribution channel 160 behind the disk 115 via the vacuum inlet to the vacuum body, thereby providing uniform suction through the porous disk 115 .

Example

Laminar Formation Derived from {111} Single Crystal Donor Wafers

The process starts with a donor wafer with a Miller index of {111}. A first surface is provided that is substantially flat but may have some pre-existing texture. The donor was implanted with a total ion dose of 4.0×10 ¹⁶ H atoms/cm ³ at 400 keV. The injection temperature is about °C. This implantation resulted in a cleavage plane 4.5 μm from the first surface of the donor body. The donor is doped with an n-type dopant such as boron to a resistivity between 1 and 3 ohm-cm.

After implantation, the implanted surface of the donor wafer is contacted with the susceptor assembly. The susceptor assembly comprises a susceptor disk of porous graphite. Additionally, the porous graphite has been machine smoothed with a 1500 grit sandpaper, thus providing an evenly flat and smooth surface. No vacuum pressure is applied to the wafer. Once in contact with the base component, apply a thermal exfoliation profile consisting of two thermal ramps. The following ramp sequence starting at room temperature was applied: 15°C/sec ramp to 400°C, hold at 400°C for 60 seconds, followed by 10°C/sec ramp to 700°C. At this point the lamina had peeled off from the donor wafer and was annealed by ramping at 10°C/sec to 950°C and holding for 1 minute. The wafer is then allowed to cool to room temperature.

The donor body is detached from the laminate at room temperature while the first surface of the laminate (formerly the donor body) remains fixed to the base plate. A vacuum force of -13 psi is applied to the perforated disc in the base assembly, securing the laminate to the base assembly. A portion of the second surface of the donor body opposite the first surface contacts the porous disk of the separation fixture coupled to the vacuum line. The porous disc separating the fixture is coupled to a rigid arm containing a pivot point. When vacuum is applied to the porous disk of the separation fixture, a portion of the disk against the donor body causes the rigid arm to rotate at a pivot point, lifting a portion of the donor body off the deck. After initial separation from the shelf, the donor body is manually lifted from the shelf and returned to the process line. The laminates are further processed to form photovoltaic devices. The separation process takes place at ambient temperature and pressure.

Laminates derived from {100} single crystal donor wafers

The process starts with a donor wafer with a Miller index of {100}. A first surface is provided that is substantially flat but may have some pre-existing texture. The donor was implanted with a total ion dose of 8.0×10 ¹⁶ H atoms/cm ³ at 400 keV. The injection temperature is about 160°C. This implantation resulted in a cleavage plane 4.5 μm from the first surface of the donor body.

After implantation, the implanted surface of the donor wafer is contacted with the susceptor assembly. The susceptor assembly comprises a susceptor disk of porous graphite. Additionally, the porous graphite has been machine smoothed with a 1500 grit sandpaper to provide an evenly flat and smooth surface. The susceptor assembly further includes a thermally anisotropic second susceptor disk. The second susceptor disk contains pyrolytic graphite and provides a thermally anisotropic material to promote uniform heat treatment. The donor body was secured to the base assembly by applying a -13 psi vacuum to the first base plate.

A thermal exfoliation profile comprising a thermal ramp rate of 2.3°C/sec to a first exfoliation temperature of 440°C for 60 seconds followed by a duration of 500 seconds was applied after contacting the susceptor assembly to the donor body A thermal ramp rate of 0.2°C/sec at 490°C. After exfoliation, the thin free-standing laminate comprising a first surface which is the first surface of the donor and a second surface opposite the first surface was annealed at 950° C. for 3 minutes. Allow the wafer to cool to room temperature.

The donor body was detached from the laminate at room temperature while the first surface of the laminate (former donor body) remained secured to the base plate with an applied vacuum force of -13 psi. A portion of the second surface of the donor body opposite the first surface of the laminate contacts the porous disk of the separation fixture coupled to the vacuum line. The porous disk is coupled to a rigid arm containing a pivot point. When vacuum is applied to the porous disk, a portion of the disk against the donor body causes the rigid arm to rotate at a pivot point, lifting a portion of the donor body off the deck. The donor body is manually lifted from the donor body and returned to the process line. The laminates are further processed to form photovoltaic devices.

The various embodiments have been provided for clarity and completeness. Obviously it is not practical to enumerate all possible implementations. Other embodiments of the invention will be apparent to those skilled in the art from this specification. Detailed methods of fabrication have been described here, but any other method of forming the same structure may be used while the results fall within the scope of the invention. The foregoing detailed description has described only a few of the many forms that the invention can take. For this reason, this detailed description is intended to be illustrative and not limiting. It is only the following claims including all equivalents and are intended to define the scope of protection of this invention.

Claims (29)

1. method of producing laminate from executing body, described method comprises following steps:

Thereby a. inject at the first surface of executing body with ion dose and form cleavage surface;

B. in injection period the described body of executing is heated to implantation temperature;

C. the described described first surface of executing body is touched discretely the first surface of base assembly, wherein saidly execute the described first surface of body and the described first surface of described base assembly directly contacts;

Thereby d. apply exfoliation temperature and in described cleavage surface laminate is peeled off from the described body of executing to the described body of executing, the wherein said described first surface of executing body comprises the first surface of described laminate;

E. described laminate is separated from the described body of executing; And

F. the combination of adjusting dosage, implantation temperature, exfoliation temperature and peeling off pressure, thus in described laminate, will substantially there be the area of physical imperfection to maximize.

2. method according to claim 1, wherein said base assembly is positioned at described executing below the body, and the wherein said described first surface of executing body only comprises the power that is provided by the described weight of executing body to the described separable contact of the described first surface of described base assembly.

3. method according to claim 1, the wherein said described first surface of executing body comprise to described pedestal to the described separable contact of the described first surface of described base assembly and apply vacuum power.

4. it is basically even that method according to claim 1, wherein said exfoliation temperature section are striden the described described first surface of executing body.

5. method according to claim 1, wherein said exfoliation temperature section comprise with speed of 1 ℃ of per second etc. change to peak temperature between 600 and 1000 ℃ at least.

6. method according to claim 1, the wherein said step that applies exfoliation temperature comprise executes body moves to the second temperature from the zone of the first temperature zone with described, and wherein said the second temperature is higher than described the first temperature.

7. method according to claim 1, wherein said physical imperfection from by wavefront defective, radial streak, delaminate, tear, select hole or its any group who constitutes.

8. method according to claim 1, wherein said implantation temperature is between 80 and 250 ℃.

9. method according to claim 1, the thickness of wherein said laminate is approximately between 1 and 20 micron.

10. method according to claim 1, do not have described physical imperfection greater than 90% in the described surface area of the described first surface of wherein said laminate, and the described surface area of wherein said laminate is substantially equal to the described described surface area of executing the described first surface of body.

11. method according to claim 1, wherein said peeling off at ambient pressure occurs.

12. method according to claim 1 further is included in described laminate is executed the step that the body after separating is reused described pedestal from described.

Can execute the first dish that body contacts with described 13. method according to claim 1, the described first surface of wherein said base assembly comprise, wherein said the first dish comprises vacuum pressure and can permeate the porous material that passes through.

14. method according to claim 13, wherein said the first dish comprises porous graphite, porous boron nitride, porous silicon, porous silicon carbide, laser drill silicon, laser drill carborundum, aluminium oxide, aluminium nitride or silicon nitride or its any combination.

15. method according to claim 13, wherein said the first dish has the first thermal coefficient of expansion and the described body of executing has the second thermal coefficient of expansion, and wherein said the first and second thermal coefficient of expansions are substantially the same.

16. method according to claim 13, wherein said base assembly further comprise the second dish of contiguous described the first dish, and wherein said the second dish is the thermal anisotropy.

17. method according to claim 16, wherein said the second dish comprises pyrolytic graphite.

18. comprising to have, method according to claim 13, wherein said the first dish be lower than the described material of executing the thermal capacity of body.

19. method according to claim 1, wherein described laminate is separated to comprise power is applied to a described part of executing the second surface of body from the described body of executing, wherein said second surface is relative with the described first surface of described laminate, and the wherein said body deformability of executing leaves described laminate.

20. method according to claim 1 wherein described laminate is separated and to comprise a part that power is applied to the described first surface of described laminate from the described body of executing, and the described body of executing is left in the distortion of wherein said laminate.

21. method according to claim 1 further comprises following steps:

A. described laminate is separated from the described body of executing; And

B. make photovoltaic cell, wherein said photovoltaic cell has the first amorphous si-layer of directly contacting with the described first surface of described laminate and the second amorphous si-layer that directly contacts with the second surface of described laminate.

22. a method of producing laminate from executing body comprises:

Thereby a. inject the first surface of executing body with ion dose and form cleavage surface;

B. execute the first surface that body touches base assembly discretely with described, the wherein said described first surface of executing body and described base assembly directly contacts;

C. in described cleavage surface laminate is peeled off from the described body of executing, the wherein said described first surface of executing body comprises the first surface of described laminate; And

D. apply deformation force by described first surface or the described second surface of executing body to described laminate, thereby the described first surface of described laminate or the described described second surface distortion of executing body are separated described laminate from the described body of executing, the wherein said described second surface of executing body is relative with the described described first surface of executing body.

23. method according to claim 22 wherein comprises the described described second surface distortion of executing body:

A. the first chuck is coupled to the described described second surface of executing body, wherein said chuck is coupled to bending device; And

B. apply described deformation force to described bending device, wherein said deformation force leaves described laminate with described bending device and described the first chuck and the described body deformability of executing.

24. method according to claim 22, wherein the described first surface distortion with described laminate comprises:

A. the first chuck is coupled to the described first surface of described laminate, wherein said chuck is coupled to bending device; And

B. apply described deformation force to described bending device, wherein said deformation force leaves the described body of executing with described bending device and described the first chuck and the distortion of described laminate.

25. according to claim 23 with 24 described methods, wherein said the first chuck comprises vacuum pressure can permeate the porous material that passes through, and wherein said method further is included in described the first chuck and the described step that applies vacuum pressure between the body of executing, and wherein said vacuum pressure is so that the described body of executing can be coupled to described the first chuck.

26. method according to claim 25, wherein said porous material is selected from the group who is made of porous graphite, porous boron nitride, porous silicon, porous silicon carbide, laser drill silicon, laser drill carborundum, aluminium oxide, aluminium nitride and silicon nitride.

27. with 24 described methods, further comprise the back of the body dish that appends to described bending device periphery according to claim 23, and the step that wherein applies described deformation force is included in mineralization pressure volume between described bending device and the described back of the body dish.

28. method according to claim 22, wherein with described execute body deformability comprise with 1 and 3mm between a described part of executing body from the described first surface displacement of described laminate.

29. method according to claim 22, further comprise the step of described laminate being transferred to transferring clamp from described base assembly, wherein said transferring clamp comprises vacuum pressure can permeate the porous transfer table that passes through, and the second surface of wherein said laminate contacts discretely with the first surface of described porous transfer table.

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