JP2014506008A - Method and apparatus for forming thin films - Google Patents

Abstract

  A method for producing a thin film from a donor body includes implanting an ion dose into the donor body and heating the donor body to an implantation temperature during implantation. The donor body is in detachable contact with the susceptor assembly, and the donor body and susceptor assembly are in direct contact. The thin film is peeled from the donor body by applying a thermal profile to the donor body. Implantation and stripping conditions may be adjusted to maximize areas free of thin film defects.

Description

RELATED APPLICATIONS This application is a U.S. patent application Ser. No. 12 / 980,424 filed Dec. 29, 2010, “A Method to Form a Device by Support Element on” filed December 29, 2010, owned by the assignee of the present application. a partial continuation to "Thin Semiconductor Lamina", which is hereby incorporated by reference. This application is subject to US Provisional Application No. 61 / 510,477 “Detection Methods in Exfoliation of Lamina”, filed July 21, 2011, as required by US Patent Act 119 (e). U.S. Provisional Application No. 61 / 510,476 "Support Apparatus and Methods for Production of Silicon Lamina", U.S. Provisional Application No. 61 / 510,478, filed July 21, 2011 Methods ", US Provisional Patent Application No. 61 / 510,475, filed July 21, 2011," Apparatus and Methods for Production of S ". Claims priority to LiCoN Lamina ", the entire disclosure of which is incorporated herein by reference.

  A conventional prior art photovoltaic cell includes a pn diode, an example of which is shown in FIG. A depletion zone is formed at the pn junction, creating an electric field. Incident photons (incident light is indicated by arrows) will hit electrons from the valence band to the conduction band, creating free electron-hole pairs. Within the electric field of the pn junction, electrons tend to migrate towards the n region of the diode, while the holes migrate towards the p region, resulting in a current called photocurrent. Typically, the junction is either a p + / n− junction (as shown in FIG. 1) or an n + / p− junction because the dopant concentration in one region will be higher than the other dopant concentration. The lighter doped region is known as the base of the photovoltaic cell, while the more heavily doped region of the opposite conductivity type is known as the emitter. Most carriers are generated in the base and are usually the thickest part of the battery. Together the base and emitter form the active area of the battery.

  Ion implantation is a known method for forming cleaved surfaces with semiconductor materials for forming thin films used in photovoltaic cells. The ion implantation and stripping steps of this method can have a significant effect on the quality of the thin film produced. It would be desirable to improve the methods and apparatus for producing thin films.

  A method of manufacturing a thin film from a donor body includes implanting an ion dose into the donor body and heating the donor body to an implantation temperature during implantation. The donor body detachably contacts the susceptor assembly, where the donor body and susceptor assembly are in direct contact. The thin film is peeled from the donor body by applying a thermal profile to the donor body. Implantation and stripping conditions can be adjusted to maximize areas free of thin film defects.

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

It is sectional drawing of the photovoltaic cell of a prior art. FIG. 6 is a cross-sectional view showing the steps in the formation of the photovoltaic device of US patent application Ser. No. 12 / 026,530 to Sivaram et al. FIG. 6 is a cross-sectional view showing the steps in the formation of the photovoltaic device of US patent application Ser. No. 12 / 026,530 to Sivaram et al. FIG. 6 is a cross-sectional view showing the steps in the formation of the photovoltaic device of US patent application Ser. No. 12 / 026,530 to Sivaram et al. FIG. 6 is a cross-sectional view showing the steps in the formation of the photovoltaic device of US patent application Ser. Figure 3 is a flow chart showing the steps of an exemplary method according to an aspect of the present invention. FIG. 6 is a cross-sectional view showing a stage in the formation of a thin film according to an embodiment of the present invention. FIG. 6 is a cross-sectional view showing a stage in the formation of a thin film according to an embodiment of the present invention. FIG. 4 is a cross-sectional view illustrating thin film separation according to an embodiment of the present invention. FIG. 4 is a cross-sectional view illustrating thin film separation according to an embodiment of the present invention. FIG. 4 is a cross-sectional view illustrating thin film separation according to an embodiment of the present invention. FIG. 4 is a cross-sectional view illustrating thin film separation according to an embodiment of the present invention. FIG. 4 shows a cross-sectional view of a stage in the formation of a photovoltaic device having a constructed metal support element according to an alternative embodiment of the present invention. FIG. 4 shows a cross-sectional view of a stage in the formation of a photovoltaic device having a constructed metal support element according to an alternative embodiment of the present invention. FIG. 4 shows a cross-sectional view of a stage in the formation of a photovoltaic device having a constructed metal support element according to an alternative embodiment of the present invention. 2 is a cross-sectional and perspective top view of an exemplary susceptor assembly of the present invention. FIG. 2 is a cross-sectional and perspective top view of an exemplary susceptor assembly of the present invention. FIG. It is a top view which shows embodiment of the susceptor plate of this invention. It is a top view which shows embodiment of the susceptor plate of this invention. It is a perspective sectional view showing a separation chuck of an embodiment of the present invention. It is a perspective sectional view showing a separation chuck of an embodiment of the present invention.

  A method and apparatus is described in which a free-standing film is formed and separated from the donor body without adhesive or permanent bonding to the support element. The method and apparatus of the present invention includes implanting an ion dose into the first surface of the donor body and heating the donor body to the implantation temperature during implantation. The first surface of the donor body is in detachable contact with the first surface of the susceptor assembly, and the thin film is peeled from the donor body by applying a thermal profile to the donor body. The thin film can then be separated from the donor body. In some embodiments, the separation method includes applying a deformation force to the surface of the membrane or donor body. The conditions for implantation and stripping can be adjusted according to the members of the donor body to maximize the area free of defects in the thin free-standing film.

  A conventional photovoltaic cell formed from a silicon body includes a pn diode in which the degradation zone forms a pn junction as shown in FIG. The silicon donor body used to form the photovoltaic cell is typically about 200-250 microns thick. The thinner film formed from the silicon donor body is permanently attached to the support element of the film via epitaxial growth, adhesive material, or other method that results in a bonded film prior to cleavage or separation from the donor body. By fixing, it can be used to form photovoltaic cells. Typically, a thin film formed in this manner must engage in a debonding step to incorporate or remove the support element from any final photovoltaic cell. In the present invention, a thin, self-supporting thin film is formed and separated from the donor body without the need for debonding or cleaning steps prior to photovoltaic fabrication, without an adhesive or permanent bond to the support element. Methods and apparatus are also described, which are possible. In the present invention, the donor body is injected through the first surface to form a cleaved surface. The first surface of the donor body can then be placed in the vicinity of the support element. A heating step is performed to peel the thin film from the donor body on the first surface, producing a second surface. This process occurs in the absence of support elements bonded on the membrane. Ion implantation and stripping conditions can have a significant effect on the quality of thin films produced by this method and are optimized to reduce the amount of physical defects that may be formed in free-standing thin films Can be done. A method for the separation of a peeled thin free-standing film is also described.

  Sivaram et al., US patent application Ser. No. 12 / 026,530, “Method to Form a Photovoltaic, filed Feb. 5, 2008, owned by the assignee of the present invention and incorporated herein by reference. "Cell Compiling a Thin Lamina" describes the fabrication of a photovoltaic cell comprising a thin semiconductor thin film formed from a non-deposited semiconductor material. Referring to FIG. 2A, in the embodiment of Sivaram et al., The semiconductor donor body 20 is implanted with one or more types of gas ions, such as hydrogen and / or helium ions, through the first surface 10. . The implanted ions define a cleaved surface 30 within the semiconductor donor body. As shown in FIG. 2B, the donor body 20 is attached to the receiver 60 at the first surface 10. Referring to FIG. 2C, annealing causes the thin film 40 to be cleaved from the donor body 20 at the cleaved surface 30 to produce a second surface 62. In the embodiment of Sivaram et al., Any thickness within the specified range is possible with additional processing before and after the cleaving step, but for example between about 0.2 and about 50 microns, for example about 1 to about 20 Thickness between 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 Etc. to form a photovoltaic cell comprising a semiconductor thin film 40 that is between about 0.2 and about 100 microns thick. FIG. 2D shows an inverted structure with a receiver 60 at the bottom, such as in operation in some embodiments. Receiver 60 is owned by the assignee of the present application and is filed Mar. 27, 2008, Herner, US patent application Ser. No. 12 / 057,265, “Method to”, which is incorporated herein by reference. It may be an individual receiver element with a maximum width that is 50 percent or less greater than the donor body 10 as described in “Form a Photovoltaic Cell Compiling a Thin Lamina Bonded to a Discrete Receiver Element”. Alternatively, multiple donor bodies may be added to a single larger receiver and a thin film cleaved from each donor body.

  Rather than being formed from sliced wafers using the method of Sivaram et al., Photovoltaic cells are formed from thin semiconductor thin films without wasting silicon, through cut losses or by unnecessarily thick cell fabrication, Costs are therefore reduced. The same donor wafer can be reused to form multiple thin films, which further reduces costs and can be re-sold after stripping multiple thin films for some other use.

  In the present invention, the self-supporting thin film is formed by implanting ions into the semiconductor donor body so as to define a cleavage plane and peeling the semiconductor thin film from the donor body at the cleavage plane. The thin film has an unbonded first surface and an unbonded second surface opposite the first. After the stripping step, the thin film is separated from the donor body, and the thin film is fabricated into a photovoltaic cell comprising the photovoltaic cell base region. The thickness of the thin film may be from about 4 microns to about 20 microns. One or more layers can also be formed on the first surface of the thin film prior to incorporating the thin film into the photovoltaic cell. One or more layers can also be formed on the second surface of the free-standing film. The thickness of the thin film is determined by the depth of the cleavage plane. In many embodiments, the thickness of the thin film is from about 1 to about 10 microns, such as from about 2 to about 5 microns, such as about 4.5 microns. In other embodiments, the thickness of the thin film is about 4 to about 20 microns, such as about 10 to about 15 microns, such as about 11 microns. The second surface is created by cleaving. Although different flows are possible, generally a thin film is provided without permanent or adhesive fixation to the support element. In most embodiments, the thin film is stripped and separated from a larger donor body, such as a wafer or boule.

  Turning to FIG. 3, which outlines the method of the present invention, the donor body is first implanted with ions through the first surface so as to form a cleavage plane (step 1, FIG. 3). . Implant conditions are adjusted to mitigate physical defects (eg, lacerations, cracks, lips, wavefront defects, radial streaks, flaking, or any combination thereof) within the final thin film. It is also possible. In one embodiment, the physical defect comprises a crack and the method of the present invention provides a self-supporting thin film with an overall crack length of less than 100 mm. Physical defects include any defects that can cause a short circuit or degraded performance in the finished battery. The area of the thin film with physical defects may be equivalent to the area that is disabled in the photovoltaic cell. Injection conditions that can also maximize areas that are substantially defect-free within the conditioned and cleaved film include the temperature and / or pressure applied to the donor body during injection. In some embodiments, the implantation temperature can be maintained at 25-300 ° C, 100-200 ° C, 120-180 ° C, or the like. One aspect of the present invention is that the implantation temperature can be adjusted depending on the material and the orientation of the donor body. In some embodiments, the material is {111} oriented silicon and the implantation temperature may be 150-200 ° C. In other embodiments, the material is {100} oriented silicon and the implantation temperature may be 25-150 ° C. The methods disclosed herein apply to any other oriented semiconductor donor body and oriented silicon, such as {110} or {001}. The implantation temperature can be optimized for any silicon orientation and implantation energy. Other implantation conditions that can also be adjusted may include initial process parameters such as implantation dose and implanted ion ratio (eg, H: He ratio). In some embodiments, the implantation conditions may include stripping temperatures, stripping susceptor vacuum levels, heating rates, and / or stripping pressures, etc. to maximize areas that are substantially free of physical defects present in the film. It is also possible to optimize in combination with conditions. In some embodiments, greater than 90% of the surface area of the thin film produced by the method of the present invention is free of physical defects.

  After implantation to form the cleaved surface, the donor body can contact a temporary support element (FIG. 3, step 2), such as a susceptor assembly for further processing. Typically, the donor body, thin film or photovoltaic cell at various stages of manufacture can be affixed to a temporary carrier containing an adhesive or by chemical bonding. If an adhesive is used, additional steps are required to initiate thin film debonding and / or clean the surface of the photovoltaic cell and temporary carrier after desorption. Alternatively, the support element can be dissolved or removed and disabled for further support steps. In one aspect of the invention, the donor body is in detachable contact with a support element, such as a susceptor assembly, without an adhesive or permanent bond to stabilize the film being peeled. The contact may be a direct contact between the donor body and the support element, and requires a chemical or physical step that interrupts the contact beyond just lifting the donor body or film from the susceptor. It does not have to include steps. The susceptor can then be reused as a support element without further processing. In some embodiments of the method of the present invention, the injected donor body has a force that interacts between the donor body and the susceptor during delamination, so that only the weight of the donor body on the susceptor or the susceptor on the donor body. It is also possible to detachably contact a support element such as a susceptor assembly that is only the weight of the assembly. If contact is established only by the weight of the donor body, the donor body can also be oriented with the injected side facing down and in contact with the susceptor. Alternatively, the donor body can be oriented with the injected side facing up and without contacting the susceptor. In this case, the cover plate can also be used to stabilize the film before and after peeling. In other embodiments, the contact further includes a vacuum force between the susceptor and the donor body. A vacuum force can also be applied to the donor body to temporarily secure the donor body to the susceptor assembly without the use of adhesives, chemical reactions, electrostatic voltages, or the like.

  Contacting the thin film to the unbonded support element during the peeling and damage annealing steps provides several significant advantages as in the present invention. The stripping and annealing steps occur at relatively high temperatures. The pre-formed support element is necessarily exposed to high temperatures with the thin film, such as any intervening layer, when applied to the donor body, such as with an adhesive or chemical agent, prior to these high temperature steps. Will. Many materials cannot easily tolerate high temperatures, and heating and cooling can damage thin membranes when the coefficient of thermal expansion (CTE) of the support element and thin film is mismatched, Will cause distortion. Thus, the unbonded support element provides a surface optimized for thin film manufacture that is independent of bonding and debonding protocols that would potentially inhibit the formation of defect free thin films. Annealing may occur before or after the film is separated from the donor body.

  After contact of the donor body to the susceptor assembly, heat may be applied to the donor body such that the film is cleaved from the donor body at the cleavage plane. The stripping conditions should be optimized to cleave the membrane from the donor body (FIG. 3, step 3) to minimize physical defects in the stripped membrane in the absence of sticky support elements. Is also possible. Exfoliation parameters can be optimized for a particular donor body. Delamination can occur at atmospheric pressure. An exfoliation thermal profile having one or more thermal gradients can also be applied. In some embodiments, the stripping conditions may include a single rapid thermal ramp to a peak stripping temperature above 600 ° C. The thermal ramp rate may exceed 100 ° C./min or 200 ° C./min. The material of the susceptor may have a lower heat capacity than that of the donor body and may be resistant to thermal degradation at the final stripping temperature to facilitate stripping by this method. In other embodiments, the final strip temperature at which the ramp rate is any rate may be 400-600 ° C., but the temperature is applied substantially uniformly in the surface area of the film. The susceptor assembly may include a thermally anisotropic material to facilitate a uniform thermal profile in the surface of the donor body during stripping. In some embodiments, the donor body can be transferred to a higher temperature zone so that heating of the donor body proceeds from one end 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 motion can also provide a rapid change in donor temperature, such as 60 ° C./min, over 200 ° C./min.

  The peeled thin film is separated by any means (FIG. 3, step 4), such as by applying a deformation force to the first surface of the donor body away from the opposite surface of the newly formed thin film. It can also be separated from the donor body. In some embodiments, the donor body can be deformed away from the peeled film. In other embodiments, the peeled film can be deformed away from the donor body. After peeling, the surface of the self-supporting thin film that was the first surface of the donor body can be detachably contacted with a support device such as a susceptor assembly. In some embodiments, the contact force may include a vacuum force between the membrane and the susceptor plate. In some embodiments, the contact force may be only the weight of the donor body on the membrane. The chuck plate may adhere to the donor body on the surface opposite the thin film. In some embodiments, the tack may be a vacuum force applied to the donor body through the porous chuck plate. Vacuum pressure may be applied through the chuck plate, thus sticking the donor body to the chuck plate. The chuck plate can also be coupled to a bending device such as a bending arm or a deformable plate. The force applied to the bending device can also deform the donor body away from the membrane. The force can also deform any part of the donor body, such as an edge or other site, away from the membrane. The deformation can also separate the donor body at a distance greater than 1 mm away from a portion of the thin film surface, removing the edge of the donor body for complete separation of the thin film from the next donor body. . The separated membrane can remain on the susceptor plate or be transferred to a different temporary or permanent support element for further processing. In some embodiments, the permanent support can be built on a free-standing membrane.

Aspects of the invention include a process for manufacturing a photovoltaic cell from a free-standing film, starting with a donor body of a suitable semiconductor material. A suitable donor body may be a single crystal silicon wafer of actual thickness, for example, about 200 to about 1000 microns thick. Typically, the wafer has a Miller index of {100} or {111}, although other orientation wafers may be used. In an alternative embodiment, the donor wafer may be thicker and the maximum thickness is limited only by the practicality of the wafer handling. Alternatively, polycrystalline silicon, such as germanium, silicon germanium, or microcrystalline silicon of other semiconductor materials, including III-V or II-VI semiconductor compounds such as GaAs, InP, or wafers or ingots (Polycrystalline or multicrystalline) silicon may be used. Other materials such as SiC, LiNbO ₃ , SrTiO ₃ , sapphire, etc. may be used. In such a context, the term multicrystalline line usually refers to a semiconductor material having particles that are approximately 1 millimeter or larger in size, while a polycrystalline semiconductor material refers to smaller particles of approximately 1000 angstroms. Have. The particles of the microcrystalline semiconductor material are very small, for example, about 100 angstroms. For example, the microcrystalline silicon may be completely crystalline or may include these microcrystals in an amorphous matrix. Polycrystalline or multicrystalline semiconductor is understood to be fully or substantially crystalline. It will be appreciated by those skilled in the art that the term “single crystal silicon” as customarily used will not exclude silicon with occasional defects or impurities, such as dopants that increase conductivity. .

  The process of forming single crystal silicon generally results in a circular wafer, but the donor body may have other shapes. For photovoltaic applications, cylindrical single crystal ingots are often machined into octagonal cross sections before cutting the wafer. The wafer may also have other shapes, such as a square. Square wafers, unlike circular or hexagonal wafers, have the advantage that they can be aligned end to end on the photovoltaic module with minimal unused air gaps between the wafers. The diameter or width of the wafer may be any standard or custom size. For convenience, the present disclosure will describe the use of a single crystal silicon wafer as a semiconductor donor body, but it will be understood that other types or materials of donor bodies can be used.

  Preferably, ions that are hydrogen or a combination of hydrogen and helium are implanted into the body through the first surface to define a cleavage plane as previously described. The overall depth of the cleavage plane is determined by several factors, including implantation energy. The depth of the cleaved surface is between about 0.2 and about 100 microns from the first surface, such as between about 0.5 and about 20 or about 50 microns, such as between about 1 and about 10 microns. It can be between 1 or 2 microns and about 5 or 6 microns, or between about 4 and about 8 microns. Alternatively, the depth of the cleavage plane can be between about 5 and about 15 microns, such as about 11 or 12 microns.

The temperature and dose of ion implantation can also be adjusted depending on the material to be implanted and the desired depth of the cleavage plane to provide a free-standing film that is substantially free of physical defects. The ion dose may be any dose such as 1.0 × 10 ^{14 to} 1.0 × 10 ¹⁸ H / cm ² . The injection temperature may be any temperature exceeding 140 ° C. (for example, 150 to 250 ° C.). The implantation conditions can be adjusted based on the Miller index of the donor body and the energy of the implanted ions. For example, single crystal silicon having a Miller index {111} may require a different set of implantation conditions than a single crystal silicon donor wafer having a Miller index {100}. One aspect of the present invention includes adjusting the implantation conditions to maximize the area of the thin film that is substantially free of defects. In some embodiments, the implantation dose may be less than 1.3 × 10 ¹⁷ H / cm ² in combination with an implantation temperature that is greater than 25 ° C., such as 80 ° C. to 250 ° C. In some embodiments, a single crystal silicon donor body having a Miller index {111} can be implanted at a temperature of 150-200 ° C. In some embodiments, a single crystal silicon donor body having a Miller index {100} can be implanted at a temperature of 100-150 ° C. In some embodiments, a higher injection temperature may result in a more uniform debonding.

  With reference to FIG. 4A, the infused surface 10 of the donor body 20 can be in detachable contact with a support element, such as the susceptor assembly 400. The susceptor assembly can be in contact with the donor body while remaining uncoupled to the donor body. The contact force between the donor body and the susceptor assembly during stripping may be only the weight of the donor body. Alternatively, the entire assembly and donor body can be reversed, and the contact force can be the weight of the susceptor assembly on the donor body. In some embodiments, the contact force between the donor body and the susceptor can be increased by the vacuum force between the susceptor and the donor body. The material properties of the susceptor assembly can also facilitate the stripping of a thin film that is substantially free from the donor body. The susceptor assembly 400 may include a single susceptor plate that is flat as in FIG. 4A. In some embodiments, the surface of the susceptor assembly may include a material that has a coefficient of thermal expansion (CTE) that is approximately equivalent to that of the donor body over a wide range of temperatures (eg, 0-1000 ° C.). The susceptor assembly may include a material having a heat capacity that is approximately the same as or less than the heat capacity of the donor body to support a rapid thermal ramp to a stripping temperature greater than 400 ° C.

  In other embodiments, such as shown in FIG. 4B, the susceptor assembly 401 may include a plurality of plates to provide appropriate conditions for processing of the thin film from the donor body 20. In some embodiments, contact force between the susceptor assembly 401 and the donor body is applied via the vacuum channel 410 to the porous susceptor plate 405 of the susceptor assembly (as illustrated in FIG. 4B). It may be a vacuum force. When vacuum force is utilized to hold the donor body, the susceptor plate 405 may be any material that is porous graphite or permeable to vacuum pressure. For example, the material of the porous plate 405 is porous graphite, porous boron nitride, porous silicon, porous silicon carbide, laser drilled silicon, laser drilled silicon carbide, aluminum oxide, aluminum nitride, silicon nitride, or the like. Any combination of the above may be included. A vacuum pressure in the range of about 0 to about −100 psi (eg, 0 psi to −15 psi) may be applied. The susceptor assembly 401 may include a first plate 405 having a coefficient of thermal expansion that is similar or substantially the same as the coefficient of thermal expansion (CTE) of the donor body 20. In some embodiments, the thermal profile applied during stripping must be approximately uniform across the surface of the donor body to facilitate successful stripping of the free-standing film. In order to obtain a uniform thermal profile across the surface of the donor body, the susceptor assembly is preferentially higher in the plane parallel to the donor body compared to the donor body in the normal direction, and the thermal conductivity of the second plate 415. A second plate 415 in the vicinity of the first plate 405 may be included. Thermally anisotropic materials such as pyrolytic graphite are well adapted to facilitate the application of a substantially uniform thermal profile to the donor body in this manner. The susceptor assembly can be used to facilitate the maintenance of the thermal profile required for delamination by thermally isolating the donor body from potentially cooling forces such as an operating vacuum manifold. Some of them may include a thermally insulating plate 425 such as a quartz plate disposed under the thermally anisotropic plate 415.

  A thermal stripping protocol may be applied that results in a free-standing film that is substantially free of physical defects cleaved from the donor body 20 at the cleaved surface 30 after contact of the donor body with the susceptor assembly. The exfoliation protocol is one or more thermal ramps to one or more peak exfoliation temperatures followed by thermal immersion for periods such as 1, 2, 3, 4, 5, or less than 6 minutes. May be included. The peak peel temperature may be 350-900 ° C, such as 350-500 ° C or 500-900 ° C. The slope rate in the thermal delamination profile can also be optimized. The thermal ramp rate may range from 0.1 ° C./second to 20 ° C./second, for example. The peel pressure may be atmospheric pressure or higher. The thermal delamination profile can also be optimized depending on the donor body material and orientation to form a free-standing film that is substantially free of physical defects.

  In some embodiments, the single crystal silicon thin film can be obtained by applying a delamination thermal profile that includes a single thermal ramp rate that is greater than 15 ° C./sec. } Can also be peeled from the donor body oriented. The peak peel temperature can also be held for 100, 50, 25 seconds or less. In other embodiments, the thermal profile may include a ramp rate of 0.1-5 ° C./sec for a peak strip temperature of 400-600 ° C., where the thermal ramp rate is approximately the same in the surface area of the film. The peak peel temperature can also be held for less than 3 minutes, 1 minute, or less than 30 seconds. The susceptor may include a thermally anisotropic material, such as the second plate 415 of FIG. 4B, to facilitate application of a uniform thermal profile across the surface of the donor body during stripping.

  Alternatively, stripping may include two or more thermal ramps that provide a more controlled stripping process. Multiple thermal gradients can accommodate donor bodies having Miller indices {111}, {100}, or other orientations. For example, the thermal profile is a first thermal ramp rate that is 10-20 ° C./second up to a peak temperature of 350-500 ° C., followed by 5-20 ° C./second up to a peak temperature of 600-800 ° C. The second thermal gradient rate may be included. The peak stripping temperature after each thermal ramp can also be maintained for less than 60 seconds following cooling or further processing to anneal or separate the stripped film. In some embodiments, the stripping protocol may include two or more thermal gradients under thermally anisotropic conditions that provide a more controlled stripping process. Another example of a plurality of thermal ramp rates is a first thermal ramp of 0.5-10 ° C./sec to a peak temperature of 350-450 ° C., followed by a peak temperature of 450-700 ° C. A second thermal ramp of about 0.1-5 ° C./second. The peak peel temperature after each thermal ramp can also be maintained for less than 10 seconds following cooling or further processing to anneal the peeled film. The thermal profile is applied by moving the susceptor assembly / cleaved donor body from a first zone at one temperature to a second zone at a different temperature. The first temperature may be lower than the second temperature. This process can also be accomplished by a belt furnace or other transport device.

  It has been discovered that the implantation step to define the cleavage plane can cause damage to the crystal lattice of the single crystal donor wafer. This damage, if not repaired, can impair the efficiency of the battery. In the present disclosure, annealing can also remove residual physical defects in the peeled film. For example, relatively high temperature annealing above 800, 850, 900, or 950 ° C. will repair most implantation damage in the thin film body. After exfoliation, the free-standing film can contact the susceptor while the donor body remains on the top surface. The donor body can be deformed away from the peeled thin film by applying a deformation force to the surface of the donor body opposite the thin film. This method can also apply a sufficiently gentle force to separate the donor from the thin film that is less than 50 μm thick and does not damage the thin film. The vacuum chuck device is then placed on the upper surface of the donor body for contact with the surface of the donor body opposite the membrane. The first chuck plate of the vacuum chuck device has a whole surface opposite to the thin film as shown in FIG. 5 (chuck plate 515) or a part of the surface opposite to the thin film as shown in FIG. 6 (chuck plate 615). It is also possible to cover. The first chuck plate is a porous plate (for example, 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) or may include a vacuum channel. A vacuum is applied through the first chuck plate, and the vacuum chucks the donor body. Next, the first chuck plate is deflected. The pressure can also be applied to the back of the bending device, causing a slight deflection of the bending device and bringing the plate and vacuum chucked donor body into contact. An aspect of these vacuum chucking methods is that the edge of the donor body is first retracted from the film, allowing air to enter between the donor and the film surface. This action removes inspiration on the surface of the newly formed film that may lead to the appearance of physical defects.

  Referring now to FIGS. 5A and 5B, in some embodiments, separation of the thin film from the donor body occurs by using a bending plate to deform the donor body away from the thin film. The deformation can also facilitate the separation of the donor body from the free-standing film in a manner that minimizes defect formation in the free-standing film. FIG. 5A illustrates a first step of an embodiment of the method in which the donor body 20 is coupled to a separation chuck 500 such as a vacuum chuck. The chuck 500 can also be held against the surface 520 of the donor body 20 opposite the thin film 40 by vacuum pressure or other adhesive force applied through the vacuum channel 525. May be included. The first chuck plate 515 can also be coupled to a bending device such as a compliant arm, a bending arm, a bending plate 535, and the like. The bending device can also be coupled to the reinforcing plate 545 or the support arm, the pivot point and the like. The peeled thin film 40 can also detachably contact the susceptor plate 405 in the susceptor assembly 402. The additional contact force can also be applied to the susceptor plate 405 by a vacuum pressure applied through the vacuum channel 410. Separation is achieved by applying a force to a bending device that bends the surface of the donor body opposite the membrane. This separation embodiment is illustrated in FIG. 5B and shows the bending of the bending plate 535 and the final deformation of the donor body 20 away from the membrane 40. In this embodiment, a positive pressure that causes a slight deflection of the bending plate 535, the first chuck plate 515 and the chucked donor body 20 is applied to the back surface of the bending plate 535 via the channel 555. The positive pressure can be applied between the bending plate 535 and the reinforcing plate 545 by any means such as gas flow. A portion of the donor body 20 can also be deformed from 1 to 3 mm or more from the membrane to initiate separation of the donor body away from the cleaved membrane 40 that remains stationary on the susceptor plate 405. is there. In an alternative embodiment, the donor body may remain secured to the susceptor plate, but the cleaved membrane is attached to the chuck plate and separated from the donor body as described above.

  6A and 6B include a first chuck plate 615 in which the separation chuck adheres to only a portion of the surface of the donor body 20 opposite the membrane 40 and is coupled to a bending device that is a rigid arm 635. Figure 3 illustrates an embodiment of a separation process. The adhesion between the first chuck plate 615 and the donor body 20 may utilize a vacuum force transmitted through the vacuum channel 625. The first chuck plate 615 may be porous. Rigid arm 635 can also be coupled to pivot point 645 or other device designed to move the rigid arm away from the donor body. The thin film 40 may be fixed or only in contact with the susceptor plate 405. Bending the rigid arm 635 away from the membrane 40 as shown in FIG. 6B results in some deformation of the donor body 20 away from the membrane 40 that remains stationary on the susceptor plate 405. In an alternative embodiment, the donor body may remain fixed to the susceptor plate, but the cleaved membrane is attached to the chuck plate 615 and separated from the donor body as described above. An annealing step is performed at any stage of the process, such as after free-standing thin film separation, to repair damage caused to the crystal lattice in the body of the thin film during the implantation, delamination step, or separation step. Also good. Annealing is in place on the susceptor assembly for any time, for example, at temperatures above 500 degrees, for example, 550, 600, 650, 700, 800, 850 degrees or more, about 950 degrees or more. It may be done while remaining. The structure may be annealed, for example, at about 650 degrees for about 45 minutes, or at about 800 degrees for about 10 minutes, or at about 950 degrees for 120 seconds or less. In many embodiments, the temperature can exceed 850 degrees for at least 60 seconds. In some embodiments, it is advantageous to remove the donor body before annealing the thin film to a temperature of 700 ° C. or higher so that the donor's structural and electronic properties are preserved for subsequent iterations of the implant-peel process. It is.

  The photovoltaic device can also be fabricated from a free-standing thin film after the film is annealed. The thin film is described in U.S. Patent Application No. 12 / 980,424, filed December 29, 2010, "A Method to Form a Device by Support Element on a Thin Semiconductor," the present specification. It may be moved to temporary or permanent support for further processing for this purpose, which is incorporated into the document. This may be done, for example, using a vacuum paddle (not shown). To affect this movement, a vacuum paddle is placed on the second surface while the vacuum on the first surface is released. Following movement to the vacuum paddle, the second surface is carried by the vacuum while the first surface is exposed. Referring to FIG. 7A, the thin film 40 is applied to the temporary carrier 50 using, for example, an adhesive. The adhesive must tolerate moderate temperatures (up to about 200 degrees) and must be easily releasable. Suitable adhesives include, for example, hydrocarbon soluble polyesters with maleic anhydride and rosin, or surfactant soluble polyisobutylene and rosin. The temporary carrier 50 may be any suitable material such as glass, metal, polymer, silicon, and the like. Following movement, the first surface 10 will be carried on the temporary carrier 50 by the adhesive while the second surface 62 is exposed.

  Further processing to form the photovoltaic device may be followed, as illustrated in FIG. 7B. An etch step to remove damage caused by exfoliation may be performed, for example, by applying a mixture of hydrofluoric (HF) acid and nitric acid, or using KOH. Annealing is sufficient to remove all or nearly all damage, and this etch may prove unnecessary. The surface may be removed from the organic material and residual oxide using a thin HF solution, for example at 10: 1 HF for 2 minutes. Following this wet process, an amorphous silicon layer 72 is deposited on the second surface 62. This layer 72 is heavily doped silicon and may, for example, have a thickness between about 50 and about 350 angstroms. FIG. 7B illustrates an embodiment that includes a native or near native amorphous silicon layer 74 between the second surface 62 and the doped layer 72 that is in direct contact with both. In other embodiments, layer 74 may be omitted. In the present embodiment, the heavily doped silicon layer 72 has the same conductivity type as the heavily doped n-type, that is, the lightly doped n-type thin film 40. The lightly doped n-type thin film 40 comprises 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 thin enough that it does not interfere with electrical contact between thin film 40 and heavily doped silicon layer 72.

  A transparent conductive oxide (TCO) layer 110 is formed on the amorphous silicon layer 74 and is in direct contact with the amorphous silicon layer 74. Suitable materials for TCO 110 include indium tin oxide and zinc oxide doped with aluminum. This layer may be, for example, approximately between about 500 and about 1500 angstroms thick, for example, about 750 angstroms thick. This thickness will enhance the reflection from the deposited reflective layer. In some embodiments, this layer may be substantially thinner, for example, from about 100 to about 200 angstroms. The amorphous silicon layer 76 may also be applied to the second surface for thin film annealing.

  Incident light will enter the thin film 40 at the first surface 10 as found in the completed device shown in FIG. 7C. After passing through the thin film 40, unabsorbed light will exit the thin film 40 at the second surface 62 and then pass through the TCO layer 110. The reflective layer 12 formed on the TCO layer 110 will reflect this light back into the cell so as to be absorbed at the second opportunity, improving efficiency. A conductive reflective metal may be used for the reflective layer 12. Various layers or laminates may be used. In one embodiment, the reflective layer 12 follows a very thin layer of, for example, about 30 or 50 angstroms to about 100 angstroms of chromium, and about 1,000 to about 3,000 angstroms of silver on the TCO layer 110. It is formed by vapor deposition. Although not depicted, in an alternative embodiment, the reflective layer 12 may be aluminum having a thickness of about 1000 to about 3000 angstroms. In the next step, the layer will be formed by plating. Since conventional plating cannot be performed on an aluminum layer, when aluminum is used for the reflective layer 12, no additional layer or layers are added to provide a seed layer for plating. must not. In one embodiment, for example, following a layer of titanium, for example, between about 200 and about 300 angstroms thick, may have any suitable thickness, for example, about 500 angstroms, for example, Cobalt seed layer.

  The metal support element 60 is formed on the reflective layer 12 (in this embodiment, a chromium / silver stack). In some embodiments, the metal support element 60 is formed by electroplating. Temporary carrier 50 and thin film 40, and associated layers are immersed in an electrolyte bath. An electrode was attached to the reflective layer 12 and current passed through the electrolyte. Ions from the electrolyte bath accumulate on the reflective layer 12 and form a continuous metal support element 60. The metal support element 60 may be, for example, an alloy of nickel and iron. While iron is less expensive, the coefficient of thermal expansion of nickel better matches that of silicon, reducing stress during later steps. The thickness of the metal support element 60 may be as desired. The metal support element 60 should be thick enough to provide structural support so as to form a photovoltaic cell. Thicker support elements 60 are less prone to varus. In contrast, cost is reduced by minimizing the thickness. Those skilled in the art will select a suitable thickness and iron to nickel ratio to balance these concerns. The thickness of the metal support element 60 may be, for example, approximately from about 25 to about 100 microns, such as about 50 microns. In some embodiments, the iron-nickel alloy is between about 55 and about 65 percent iron, such as 60 percent iron.

  The lightly doped n-type thin film 40 includes the base of the photovoltaic cell, and the lightly doped p-type amorphous silicon layer 76 serves as the emitter of the cell. The heavily doped n-type amorphous silicon layer 72 will provide excellent electrical contact to the base region of the battery. Electrical contact must be made on both sides of the battery. Contact to the amorphous silicon layer 76 is made by grid lines 57 via the TCO layer 112. Metal support element 60 is electrically conductive and makes electrical contact with base contact 72 via conductive layer 12 and TCO layer 110.

  FIG. 7C shows a completed photovoltaic assembly 80 that includes a photovoltaic cell and a metal support element 60. In an alternative embodiment, by changing the dopant used, the heavily doped amorphous silicon layer 72 may serve as an emitter, while the heavily doped silicon layer 76 is a contact to the base region. As a function. Amorphous silicon layers 72 and 76 may be in direct contact with the first and second surfaces of the free-standing thin film, respectively. Incident light (indicated by an arrow) strikes the TCO 112 and enters the cell with the heavily doped p-type amorphous silicon layer 76, enters the thin film 40 at the first surface 10, and passes through the thin film 40. Move. The reflective layer 12 will help reflect light back into the battery. In this embodiment, the receiver element 60 functions as a substrate. The receiver element 60 and the thin film 40 and associated layers form a photovoltaic assembly 80. A plurality of photovoltaic assemblies 80 can be formed and attached to the support substrate 90, or alternatively to a support top plate (not shown). Each photovoltaic assembly 80 includes a photovoltaic cell. The photovoltaic cells of the modules are generally in electrical contact in series.

Susceptor Apparatus Referring now to FIGS. 8A and 8B, a susceptor assembly as previously described in FIGS. 4A and 4B may also include one or more susceptor plates. The susceptor assembly 400 may be located at the bottom of the susceptor chamber 800 shown in FIG. 8B and may be designed to support appropriate conditions for peeling, annealing, or separating the free-standing film. In FIG. 8A, the first plate 405 may be used to contact the first surface of the donor body and separate for the thin film during peeling, separation, annealing, or any combination thereof. Possible support may be provided. The first susceptor plate 405 may be used throughout the thin film manufacturing process, or a separate plate having distinct properties optimized for a particular step may be used. For example, the donor body may contact a first susceptor plate assembly during infusion, a second susceptor plate during stripping, and a third susceptor plate during separation. An optional top surface (eg, chuck, not shown) may be utilized for contact with the second surface of the donor body opposite the first surface. The susceptor assembly 400 can provide physical support for the thin film after stripping and provide conductive thermal properties for the stripping and annealing protocols utilized. In some embodiments, the first susceptor plate 405 may be an inert solid such as graphite. In some embodiments of the present invention, the donor body or membrane is releasably contacted with a susceptor assembly that is vacuum permeable. A porous material may be used for the first susceptor plate 405 to allow vacuum pressure to hold the donor body or film against the susceptor during stripping. The porous material may be 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. May be included.

  A vacuum can also be obtained by applying a negative gauge pressure of the surrounding environment (eg air or nitrogen) or by a directional vacuum pressure through a series of vacuum channels 410. The selection of a porous susceptor plate material that is conductive to the process flow is important for the stripping process. Material properties that are conductive to the exfoliation process include low coefficient of static friction (CSF with value, eg, 0.1-0.5), low hardness (<10 on a Mohs hardness scale), average less than approximately 15 micrometers Pore diameter, ability to flatten the machine (ie conventional mechanical techniques / materials can be used on these susceptors), low roughness (<1 μm roughness), flatness (<10 μm on the body) Swell) and sufficient electrical conductivity to prevent the generation of electrostatic charges between the thin film and the susceptor. In one embodiment, the first susceptor plate 405 may have a CTE that is approximately the same as the coefficient of thermal expansion (CTE) of the donor body. In another embodiment, the susceptor plate may have a heat capacity that is the same as or lower than the heat capacity of the donor body. In some embodiments, the donor body is single crystal silicon and the heat capacity of the susceptor is approximately the same as that of silicon (about 19.8 J / mol- ° K).

  With these constraints, many engineering ceramics and other materials may be selected to provide these properties for the first susceptor plate 405. 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 film during the heat treatment associated with exfoliation or annealing. For graphite where the CTE is not similar to that of silicon, these temperature changes may result in thin film wrinkles or lacerations. With CTE-matched graphite, the thin film may remain in a light holding vacuum or not hold at all during these temperature changes. Bulk etching may be applied to the graphite to improve purity. A typical bulk etching process consists of high temperature bakeout for 24 hours in a vacuum chamber introduced with chlorinated gas.

  In other embodiments of the stripping process, a rapid high temperature thermal profile is applied. In these embodiments, a susceptor plate that is resistant to off-gas or decomposes at temperatures as high as 800, 900, or 1000 ° C. is desirable. The susceptor material may have properties that prevent contamination of the donor body to withstand temperature and atmospheric exposure of the process without undergoing material degradation. The material may be inherently resistant to degradation or may be coated with a material that acts as a barrier to donor body contamination at elevated temperatures. For example, porous silicon carbide is hard, durable, has good CTE match, but may be coated with boron nitride that is soft and has low CSF and high purity. In other embodiments, an optimized porous / laser drilling material may be utilized. Laser drilling materials should be differentiated between chuck bulk needs (porosity, CTE, flatness / machinability) and surface material needs (low CSF, softness, high purity, etc.) Hesitate. For example, a material that provides an interface with the desired properties listed above can be coated on a stock material that has the desired properties for the base bulk. In other embodiments, metal oxides, carbides, nitrides, ceramics, and high temperature alloys that meet the previously mentioned specifications are candidates for use. The properties of the susceptor material described above beneficially improve the quality of the manufactured thin film, including mechanical properties, uniformity, and thin film purity.

  In another embodiment of the invention, a uniform temperature profile may be applied to the donor body during stripping. In FIG. 8A, a thermally anisotropic second susceptor plate 415 is parallel to the donor body compared to the normal orientation to the donor body to facilitate application of a uniform thermal profile. It may be placed near the first plate 405 that provides preferentially higher thermal conductivity in a flat plane. The uniformity of the delamination temperature profile is enhanced by the presence of pyrolytic carbon, a graphite material that is highly conductive in the cleavage plane compared to the normal to the cleavage plane, and is therefore an ideal planar thermal conductor. . The thermally anisotropic second plate may include a vacuum channel 410 to facilitate the distribution of vacuum pressure to the bottom surface of the first susceptor plate 405. Another feature may include a vacuum channel 455 machined to the surface of the susceptor plate that improves the distribution of vacuum pressure. In the embodiment shown in FIG. 9A, a second susceptor plate 915 having a set of vacuum channels 955, shown as concentric rings connected by radial paths, distributes the vacuum pressure and separates the porous susceptor plate. May be used to The vacuum channel around 925 of the second susceptor plate 915 is used to distribute the vacuum pressure around the periphery of the susceptor plate to secure one susceptor plate to another device or plate.

  In some embodiments, a heating source for the susceptor device can be provided, such as by embedding a heating lamp in the susceptor chamber. The heating source may be any source capable of providing the temperature required for implantation, stripping, or annealing, such as up to 1000 ° C. In other embodiments, the heating source is separated from the susceptor chamber, including but not limited to quartz heating or an inductive heating element disposed within the susceptor chamber to heat the susceptor assembly and / or the donor body. May be arranged.

  In a further embodiment, the differentiation vacuum channel can be used on the susceptor plate, with the vacuum securing the plates 405 and 415 together separated from the vacuum holding the donor body against the susceptor assembly 400. It is. FIG. 8A illustrates an exemplary susceptor assembly having a differentiated vacuum channel. In order to vary the holding force, the vacuum being pulled through the susceptor may need to be throttled. Differentiated vacuum channels may also be used for these two to block the effect of traction through the porous material (eg, graphite) to the thin film against the effect of traction on the first susceptor plate itself. Is possible. The first set of channels 410 is centrally located and these control the inspiration in the membrane itself. A second set of vacuum channels 460 and annulus 470 are located around the edges of the first and second susceptors and place the first susceptor in place regardless of the chuck on the central donor body. Hold. By utilizing this scheme, it is possible to remove the thin film and still hold the susceptor assembly together.

  In some embodiments, a vacuum force is applied to secure the thin film to the susceptor assembly during an annealing or stripping process that can also contribute to cooling the susceptor assembly. In order to obtain the high temperatures required for the annealing or stripping process, the susceptor assembly may include a plate that provides a thermal interruption between the donor body and the lower vacuum manifold. A third susceptor plate 475 serving as a thermal interruption is added to the susceptor assembly 400 of FIG. 8A between a vacuum manifold (not shown) and the first susceptor plate 405 or the second susceptor plate 415. May be. In an alternative embodiment, the first or second susceptor plate can also serve as a thermal interruption between the vacuum manifold and the membrane. In some embodiments of the invention, thermal interruption in annealing and / or delamination can be achieved by a quartz disk, such as disk 975 shown in FIG. 9B. The number of disks may be one or two depending on the desired temperature range and uniformity. Instead of quartz, other thermally insulating materials that can withstand the annealing temperature, such as high temperature ceramics, can be used. The quartz disk is machined to allow vacuum to pass through, but still isolates the inner and outer annular portions of the differentiated vacuum channel. This thermal interruption disk can be dangerous when using a vacuum manifold under a water cooled susceptor assembly. The thermal interruption can also prevent heat loss from the first susceptor plate 405, potentially making it easier to obtain the temperature required to achieve annealing and / or delamination. Is possible. Thermally interrupted susceptor plate 475 characteristics that can also facilitate the annealing process include a low content of highly diffusible foreign matter (impurities less than 20 PPM), a thermal expansion coefficient similar to silicon (eg, 20% of silicon CTE). %), And high temperature compatibility (eg, 1,000 ° C.), as well as low electrical resistance.

  Although the susceptor assembly with differentiated channels illustrated in FIG. 8A is shown in connection with thermal lamination, it should be noted that the functions of differentiation channels 460/470 and thermal lamination 475 may be used independently of each other. I want to be. Similarly, thermal lamination can be utilized in any situation where the top surface that supports the thin film operates at a different temperature than the component under the thermal interruption element. Furthermore, the individual elements of thermal lamination (quartz as a thermal break separating the upper surface from the lower surface at different temperatures) may be used individually, in different orders, or in different configurations.

Separation Apparatus FIGS. 10A and 10B show an embodiment of a separation chuck 100 for separating the donor body from the thin film in the manner of FIG. 5B. In operation, the surface of the donor body opposite the membrane is placed against the separation chuck and the peeled (but not yet separated) membrane body will be placed on the susceptor assembly. Alternatively, the donor body / thin film may be inverted with this device. 10A and 10B includes a stack of plates including a porous plate 115 (eg, graphite), a bending device (eg, aluminum or PEEK) such as a flexible plate 135, and a rigid support plate 145 (eg, aluminum). ) Is accompanied. The porous plate 115 shall be referred to as graphite in this disclosure, but other materials are also possible as will be described later. The rigid plate 145 has a distribution channel 150 in it and applies positive pressure to the back of the flexible plate 135. The distribution channel may be configured, for example, as concentric rings connected by radial channels, or as a linear grid. The flexible plate 135 may be fixed to a rigid plate 145 around the circumference. When positive pressure is applied, the central portion of the flexible plate 135 will deflect convexly as shown in FIG. 10B, causing the porous plate 115 to take that shape. The flexible plate can also be deflected, for example, on the order of 1 or 2 millimeters. The operating pressure of this device may be, for example, any pressure from 0.1 to 5 bar. This pressure depends on the thickness of the material in the device. The requirements of the flexible plate are mechanical strength under applied pressure, adherence to elastic bending (as against brakes), impervious to pressurized air . In one embodiment, the porous layer 115 is approximately 3 mm thick and the impermeable flexible plate 135 is approximately 5 mm thick. Other material choices for flexible layer 135 include supple metals such as aluminum, thin gauge steel, or polymer, elastomer or rubber-based materials. In some embodiments, the donor body (not shown) can be held against the porous plate 115 by applying a vacuum between the flexible plate and the porous plate. . Since the graphite plate is porous, a vacuum is applied to the distribution channel 160 behind the plate 115 via a vacuum inlet to the vacuum volume to provide even air intake through the porous plate 115. Is also possible.

Example Thin Film Formation from {111} Single Crystal Donor Wafer The process begins with a donor wafer having a Miller index of {111}. A first surface is provided that is substantially planar, but may have some pre-existing structure. The donor body was implanted with a total ion dose of 4.0 × 10 ¹⁶ H atoms / cm ³ at 400 keV. The injection temperature was approximately ° C. The implantation resulted in a cleaved surface of 4.5 μm from the first surface of the donor body. The donor body was doped with an n-type dopant such as boron with a resistance ratio of 1 to 3 ohm-cm.

  After implantation, the implanted surface of the donor wafer was in contact with the susceptor assembly. The susceptor assembly included a porous graphite susceptor plate. Additionally, the porous graphite was mechanically smoothed with 1500 grit sandpaper to provide a uniformly flat and smooth surface. No vacuum pressure was applied to the wafer. Once in contact with the susceptor assembly, a thermal debond profile including two thermal gradients was applied. Starting at room temperature, the following ramping sequence was applied: 15 ° C./s ramp to 400 ° C., hold at 400 ° C. for 60 seconds, followed by 10 ° C./s ramp to 700 ° C. At this point, the thin film was annealed by peeling from the donor wafer, ramping to 950 ° C. at 10 ° C./s and holding for 1 minute. The wafer was then allowed to cool to room temperature.

  The donor body was separated from the film at room temperature, but the first surface of the film (former donor body) remained fixed to the susceptor plate. A vacuum force of -13 psi was applied to the porous plate in the susceptor assembly to secure the membrane to the susceptor assembly. A portion of the second surface of the donor body opposite the first surface contacted the porous plate of the separation chuck that was coupled to the vacuum line. The porous plate of the separation chuck was coupled to a rigid arm that included a pivot point. When vacuum was applied to the porous plate of the separation chuck, a portion of the plate was compressed against the donor body that caused the rigid arm to pivot on a pivot point, lifting the portion of the donor body away from the membrane. After initial separation from the thin film, the donor body was manually lifted from the thin film and returned to the process line. The thin film was further processed to form a photovoltaic device. The separation process occurred at ambient temperature and atmospheric pressure.

Thin film processes from {100} single crystal donor wafers begin with a donor wafer having a Miller index of {100}. A first surface is provided that is substantially planar but may have several pre-existing structures. The donor body was implanted with a total ion dose of 8.0 × 10 ¹⁶ H atoms / cm ³ at 400 keV. The injection temperature was approximately 160 ° C. The implantation resulted in a cleaved surface of 4.5 μm from the first surface of the donor body.

  After implantation, the implanted surface of the donor wafer was in contact with the susceptor assembly. The susceptor assembly included a porous graphite susceptor plate. The porous graphite was mechanically smoothed with 1500 grit sandpaper to provide a uniformly flat and smooth surface. The susceptor assembly further included a second susceptor plate that was thermally anisotropic. The second susceptor plate included pyrolytic graphite and provided a thermally anisotropic material to facilitate uniform heat treatment. The donor body was secured to the susceptor assembly by applying a -13 psi vacuum to the first susceptor plate.

  After contacting the susceptor assembly to the donor body, a thermal ramp rate of 2.3 ° C./s to a first strip temperature of 440 ° C. held for 60 seconds, followed by 0.2 to 490 ° C. held for 500 seconds. A thermal delamination profile was applied, including a thermal ramp rate of ° C / s. After exfoliation, a thin self-supporting thin film including a first surface that was the first surface of the donor body and a second surface opposite the first surface was annealed at 950 ° C. for 3 minutes. The wafer was cooled.

  The donor body was separated from the thin film at room temperature, but the first surface of the thin film (former donor body) remained fixed to the susceptor plate with an applied -13 psi vacuum force. A portion of the second surface of the donor body opposite the first surface of the thin film contacted a porous plate of a separation chuck that was coupled to a vacuum line. The porous plate was also connected to a rigid arm that contained a pivot point. When a vacuum was applied to the porous plate, the portion of the porous plate compressed against the donor body that caused the rigid arm to pivot on the pivot point, lifting the portion of the donor body away from the membrane. The donor body was manually lifted from the donor body and returned to the process line. The thin film was further processed to form a photovoltaic device.

  Various embodiments have been provided for clarity and completeness. Obviously, it is not practical to list all possible embodiments. Other embodiments of the invention will be apparent to those skilled in the art when given the information herein. Although detailed methods of fabrication have been described herein, the results fall within the scope of the present invention, although any other method that forms the same structure can be used. The foregoing detailed description has described only a few of the many forms that this invention can take. For this reason, the form for carrying out the invention is not intended to be limiting, but is intended to be illustrative. It is only the following claims, including all equivalents, that are intended to define the scope of this invention.

Claims (29)

A method for producing a thin film from a donor body,
a. Implanting an ion dose into the first surface of the donor body to form a cleavage plane;
b. Heating the donor body to an injection temperature during injection;
c. Detachably contacting the first surface of the donor body with a first surface of a susceptor assembly, wherein the first surface of the donor body and the first surface of the susceptor assembly are in direct contact Step, and
d. Applying a stripping temperature to the donor body to strip the thin film from the donor body at the cleaved surface, wherein the first surface of the donor body includes a first surface of the thin film. When,
e. Separating the thin film from the donor body;
f. Adjusting the combination of dose, implantation temperature, stripping temperature, and stripping pressure to maximize areas of the thin film that are substantially free of physical defects.   The susceptor assembly is positioned under the donor body, and the separable contact of the first surface of the donor body to the first surface of the susceptor assembly is only a force provided by the weight of the donor body The method of claim 1, comprising:   The method of claim 1, wherein the separable contact of the first surface of the donor body to the first surface of the susceptor assembly includes applying a vacuum force to the susceptor.   The method of claim 1, wherein the stripping temperature profile is substantially uniform in the first surface of the donor body.   The method of claim 1, wherein the stripping temperature profile comprises ramping to a peak temperature of 600-1000 ° C. at a rate of 1 ° C. at least every second.   The step of applying a stripping temperature comprises moving the donor body from a first temperature zone to a second temperature zone, wherein the second temperature is higher than the first temperature. The method described.   The method of claim 1, wherein the physical defect is selected from the group consisting of wavefront defects, radial streaks, flaking, lacerations, holes, or any combination thereof.   The method of claim 1, wherein the injection temperature is 80-250 ° C.   The method of claim 1, wherein the thickness of the thin film is 1 to 20 microns.   The surface area of more than 90% of the first surface of the thin film is free of physical defects and the surface area of the thin film is approximately equal to the surface area of the first surface of the donor body. the method of.   The method of claim 1, wherein the peeling occurs at atmospheric pressure.   The method of claim 1, further comprising reusing the susceptor after separating the thin film from the donor body.   The first surface of the susceptor assembly includes a first plate that can contact the donor body, and the first plate includes a porous material through which a vacuum pressure is passed. The method described in 1.   The first plate is porous graphite, porous boron nitride, porous silicon, porous silicon carbide, laser drilled silicon, laser drilled silicon carbide, aluminum oxide, aluminum nitride, or silicon nitride, or any of them 14. The method of claim 13, comprising a combination of:   14. The first plate has a first coefficient of thermal expansion, the donor body has a second coefficient of thermal expansion, and the first and second coefficients of thermal expansion are substantially the same. The method described in 1.   The method of claim 13, wherein the susceptor assembly further comprises a second plate near the first plate, wherein the second plate is thermally anisotropic.   The method of claim 16, wherein the second plate is pyrolytic graphite.   14. The method of claim 13, wherein the first plate comprises a material having a heat capacity that is lower than the heat capacity of the donor body.   Separating the thin film from the donor body includes applying a force to a portion of the second surface of the donor body, the second surface being opposite the first surface of the thin film. The method of claim 1, wherein the donor body is deformed away from the thin film.   The method of claim 1, wherein separating the thin film from the donor body includes applying a force to a portion of the first surface of the thin film, the thin film being deformed away from the donor body. Method. a. Separating the thin film from the susceptor assembly;
b. A first amorphous silicon layer in direct contact with the first surface of the thin film; and a second amorphous silicon layer in direct contact with the second surface of the thin film. Manufacturing a photovoltaic cell; and
The method of claim 1, further comprising: A method for producing a thin film from a donor body,
a. Implanting an ion dose into the first surface of the donor body to form a cleavage plane;
b. Detachably contacting the donor body with a first surface of a susceptor assembly, wherein the donor body and the first surface of the susceptor assembly are in direct contact;
c. Peeling the thin film from the donor body at the cleaved surface, wherein the first surface of the donor body comprises the first surface of the thin film;
d. Deforming the first surface of the thin film or the second surface of the donor body by applying a deformation force to the first surface of the thin film or the second surface of the donor body; Separating from the donor body, and wherein the second surface of the donor body is opposite the first surface of the donor body. Deforming the second surface of the donor body;
a. Coupling a first chuck plate coupled to a bending device to the second surface of the donor body;
b. 23. The method of claim 22, comprising applying the deforming force to the bending device that deforms the bending device, the first chuck plate, and the donor body away from the thin film. Deforming the first surface of the thin film;
a. Coupling a first chuck plate coupled to a bending device to the first surface of the thin film;
b. Applying the deformation force to the bending device to deform the bending device, the first chuck plate and the thin film away from the donor body;
23. The method of claim 22, comprising:   The first chuck plate includes a porous material, and a vacuum pressure is applied throughout, and the method further includes applying a vacuum pressure between the first chuck plate and the donor body; 25. The method of claims 23 and 24, wherein vacuum pressure allows the donor body to be coupled to the chuck plate.   The porous material is selected from the group consisting of porous graphite, porous boron nitride, porous silicon, porous silicon carbide, laser drilled silicon, laser drilled silicon carbide, aluminum oxide, aluminum nitride, or silicon nitride 26. The method of claim 25.   25. The method according to claim 23 and 24, further comprising a backing plate attached to the periphery of the bending device, wherein the step of applying the deforming force comprises forming a pressure capacity between the bending device and the backing plate. The method described.   23. The method of claim 22, wherein deforming the donor body comprises moving a portion of the donor body from 1 to 3 mm from the first surface of the thin film.   Moving the thin film from the susceptor assembly to a moving chuck, the moving chuck including a porous transfer plate, through which a vacuum pressure travels, and the second surface of the thin film is the porous transfer plate 23. The method of claim 22, wherein the method is in detachable contact with the first surface of the substrate.