US20160284913A1 - Solar cell emitter region fabrication using substrate-level ion implantation - Google Patents
Solar cell emitter region fabrication using substrate-level ion implantation Download PDFInfo
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- US20160284913A1 US20160284913A1 US14/672,071 US201514672071A US2016284913A1 US 20160284913 A1 US20160284913 A1 US 20160284913A1 US 201514672071 A US201514672071 A US 201514672071A US 2016284913 A1 US2016284913 A1 US 2016284913A1
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- H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
- H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by at least one potential-jump barrier or surface barrier
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- H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
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Definitions
- Embodiments of the present disclosure are in the field of renewable energy and, in particular, methods of fabricating solar cell emitter regions using substrate-level ion implantation, and the resulting solar cells.
- Photovoltaic cells are well known devices for direct conversion of solar radiation into electrical energy.
- solar cells are fabricated on a semiconductor wafer or substrate using semiconductor processing techniques to form a p-n junction near a surface of the substrate.
- Solar radiation impinging on the surface of, and entering into, the substrate creates electron and hole pairs in the bulk of the substrate.
- the electron and hole pairs migrate to p-doped and n-doped regions in the substrate, thereby generating a voltage differential between the doped regions.
- the doped regions are connected to conductive regions on the solar cell to direct an electrical current from the cell to an external circuit coupled thereto.
- Efficiency is an important characteristic of a solar cell as it is directly related to the capability of the solar cell to generate power. Likewise, efficiency in producing solar cells is directly related to the cost effectiveness of such solar cells. Accordingly, techniques for increasing the efficiency of solar cells, or techniques for increasing the efficiency in the manufacture of solar cells, are generally desirable. Some embodiments of the present disclosure allow for increased solar cell manufacture efficiency by providing novel processes for fabricating solar cell structures. Some embodiments of the present disclosure allow for increased solar cell efficiency by providing novel solar cell structures.
- FIGS. 1A-1F illustrate cross-sectional views of various stages in the fabrication of a solar cell, in accordance with an embodiment of the present disclosure, wherein:
- FIG. 1A illustrates a cross-sectional view following formation of a lightly doped region in a semiconductor substrate by ion implantation
- FIG. 1B illustrates a cross-sectional view of the structure of FIG. 1A following formation of a first plurality of dopant regions of the first conductivity type by ion implantation;
- FIG. 1C illustrates a cross-sectional view of the structure of FIG. 1B following formation of a second plurality of dopant regions by ion implantation
- FIG. 1D illustrates a cross-sectional view of the structure of FIG. 1C following formation of a doped amorphous silicon layer on the light-receiving surface of the semiconductor substrate;
- FIG. 1E illustrates a cross-sectional view of the structure of FIG. 1D following thermally annealing of the semiconductor substrate
- FIG. 1F illustrates a cross-sectional view of the structure of FIG. 1E following formation of a first plurality of contacts electrically connected to the first plurality of dopant regions, and formation of a second plurality of contacts electrically connected to the second plurality of dopant regions.
- FIG. 2 is a flowchart listing operations in a method of fabricating a solar cell as corresponding to FIGS. 1A-1F , in accordance with an embodiment of the present disclosure.
- FIG. 3A illustrates a plan view showing the implant regions of the structure of FIG. 1C , in accordance with an embodiment of the present disclosure.
- FIG. 3B illustrates a plan view of a mask pattern used to form the diffusion regions described in association with FIGS. 1A and 1B , in accordance with an embodiment of the present disclosure.
- FIGS. 4A-4C illustrate cross-sectional views of various stages in the fabrication of a solar cell, in accordance with an embodiment of the present disclosure, wherein:
- FIG. 4A illustrates a cross-sectional view of illustrates a cross-sectional view following formation of a patterned lightly doped region in a semiconductor substrate by ion implantation
- FIG. 4B illustrates a cross-sectional view of illustrates a cross-sectional view of the structure of FIG. 4A following formation of a first plurality of dopant regions of the first conductivity type by ion implantation, and following formation of a second plurality of dopant regions by ion implantation;
- FIG. 4C illustrates a cross-sectional view of the structure of FIG. 4A following formation of a polycrystalline silicon layer on the light-receiving surface of the substrate and following formation of a first plurality of contacts electrically connected to the first plurality of dopant regions, and formation of a second plurality of contacts electrically connected to the second plurality of dopant regions.
- FIG. 5A illustrates a plan view showing the implant regions of the structure of FIG. 4B , in accordance with an embodiment of the present disclosure.
- FIG. 5B illustrates a plan view of a mask pattern used to form the diffusion regions described in association with FIGS. 4A and 4B , in accordance with an embodiment of the present disclosure.
- FIGS. 6A and 6B illustrate plan views of a pair of mask patterns used to form the diffusion regions described in association with FIGS. 4A and 4B , in accordance with another embodiment of the present disclosure.
- FIG. 7 schematically illustrates a cross-sectional view of an inline platform for patterned implant involving a traveling wafer and stationary shadow mask, in accordance with an embodiment of the present disclosure.
- FIG. 8 is a flowchart listing operations in another method of fabricating a solar cell, in accordance with an embodiment of the present disclosure.
- first “First,” “Second,” etc. As used herein, these terms are used as labels for nouns that they precede, and do not imply any type of ordering (e.g., spatial, temporal, logical, etc.). For example, reference to a “first” solar cell does not necessarily imply that this solar cell is the first solar cell in a sequence; instead the term “first” is used to differentiate this solar cell from another solar cell (e.g., a “second” solar cell).
- Coupled means that one element/node/feature is directly or indirectly joined to (or directly or indirectly communicates with) another element/node/feature, and not necessarily mechanically.
- inhibit is used to describe a reducing or minimizing effect. When a component or feature is described as inhibiting an action, motion, or condition it may completely prevent the result or outcome or future state completely. Additionally, “inhibit” can also refer to a reduction or lessening of the outcome, performance, and/or effect which might otherwise occur. Accordingly, when a component, element, or feature is referred to as inhibiting a result or state, it need not completely prevent or eliminate the result or state.
- a method of fabricating a solar cell involves forming a lightly doped region in a semiconductor substrate by ion implantation, the lightly doped region of a first conductivity type of a first concentration. The method also involves forming a first plurality of dopant regions of the first conductivity type of a second, higher, concentration by ion implantation, the first plurality of dopant regions overlapping with a first portion of the lightly doped region.
- the method also involves forming a second plurality of dopant regions by ion implantation, the second plurality of dopant regions having a second conductivity type of a concentration higher than the first concentration, and the second plurality of dopant regions overlapping with a second portion of the lightly doped region and alternating with but not overlapping the first plurality of dopant regions.
- a solar cell includes a semiconductor substrate having a light-receiving surface and a back surface opposite the light-receiving surface.
- a blanket dopant region is disposed in the semiconductor substrate at the back surface of the semiconductor substrate.
- the blanket dopant region is of a first conductivity type of a first concentration.
- a first plurality of dopant regions is disposed in the semiconductor substrate and is overlapping with the blanket dopant region.
- the first plurality of dopant regions is of the first conductivity type and of a second, higher, concentration.
- a second plurality of dopant regions is disposed in the semiconductor substrate and is overlapping with the blanket dopant region but alternating with and not overlapping the first plurality of dopant regions.
- the second plurality of dopant regions is of a second conductivity type of a concentration higher than the first concentration.
- a first plurality of contacts is electrically connected to the first plurality of dopant regions at the back surface of the solar cell.
- a second plurality of contacts is electrically connected to the second plurality of dopant regions at the back surface of the solar cell.
- a solar cell in another embodiment, includes a semiconductor substrate having a light-receiving surface and a back surface opposite the light-receiving surface.
- a patterned dopant region is disposed in the semiconductor substrate at the back surface of the semiconductor substrate.
- the patterned dopant region is of a first conductivity type of a first concentration.
- a first plurality of dopant regions is disposed in the semiconductor substrate and is contacting at least a portion of the patterned dopant region.
- the first plurality of dopant regions is of the first conductivity type of a second, higher, concentration.
- a second plurality of dopant regions is disposed in the semiconductor substrate and is contacting at least a portion of the patterned dopant region.
- the second plurality of dopant regions is alternating with and not overlapping the first plurality of dopant regions.
- the second plurality of dopant regions is of a second conductivity type of a concentration higher than the first concentration.
- a first plurality of contacts is electrically connected to the first plurality of dopant regions at the back surface of the solar cell.
- a second plurality of contacts is electrically connected to the second plurality of dopant regions at the back surface of the solar cell.
- One or more embodiments described herein provides a simplified process flow for fabricating high efficiency, all back-contact solar cell devices involving the use of ion implant technology for generating one or both of N+(e.g., typically phosphorous or arsenic doped) and P+(e.g., typically boron doped) diffusion regions in a substrate.
- a fabrication approach involves the use of ion implantation to introduce atoms of the required dopant type.
- implant technologies for solar cell fabrication. If implant technologies can be incorporated in to a manufacturing scheme, cost savings may be realized as other more expensive processing approaches are replaced with such technologies. Addressing such issues, in accordance with an embodiment of the present disclosure, approaches for solar cell fabrication described herein involve implanting of a solar cell substrate directly.
- an implant and anneal process for back end emitter fabrication is combined with front surface layer fabrication to provide “hybrid” front surface solutions.
- a thin layer of N-type amorphous silicon (a-Si) deposited on a front or light-receiving surface of the solar cell using, e.g., plasma enhanced chemical vapor deposition (PECVD).
- PECVD plasma enhanced chemical vapor deposition
- the front surface a-Si layer is crystalized to form a polycrystalline silicon layer.
- the resulting front surface provides a large improvement over state of the art technologies that typically involve heavy front side doping.
- the resulting front surface may exhibit improved ultra-violet (UV) performance.
- direct substrate implantation for back side processing is implemented to provide one dimensional (1D) lines at varying dopant levels. That is, embodiments described herein involve the use of back side implantation, e.g., for 1D emitter fabrication based on implanted diffusion regions of a bulk semiconductor substrate.
- FIGS. 1A-1F illustrate cross-sectional views of various stages in the fabrication of a solar cell, in accordance with an embodiment of the present disclosure.
- FIG. 2 is a flowchart 200 listing operations in a method of fabricating a solar cell as corresponding to FIGS. 1A-1F , in accordance with an embodiment of the present disclosure.
- the method of fabricating a solar cell involves forming a lightly doped region 104 in a semiconductor substrate 100 by ion implantation.
- the lightly doped region is of a first conductivity type of a first concentration.
- the semiconductor substrate 100 is a monocrystalline silicon substrate, such as a bulk single crystalline N-type doped silicon substrate. It is to be appreciated, however, that semiconductor substrate 100 may be a layer, such as a multi-crystalline silicon layer, disposed on a global solar cell substrate. In an embodiment, semiconductor substrate 100 has light-receiving surface 101 opposite a back surface 102 , and may be used to ultimately fabricate a back contact solar cell.
- the lightly doped region 104 is a blanket (non-patterned) lightly doped region formed in the semiconductor substrate 100 , as is depicted in FIG. 1A .
- the lightly doped region 104 is formed by implanting dopants during a pass under a stationary mask in an implanter.
- the first concentration of the first conductivity type is approximately 1E18 atoms/cm 3 .
- the first conductivity type is P-type, and boron atoms are implanted to form the lightly doped region 104 .
- the first conductivity type is N-type, and phosphorous atoms are implanted to form the lightly doped region 104 .
- the implanting is performed by using ion beam implantation or plasma immersion implantation.
- the light receiving surface 101 of the substrate 100 is texturized.
- a texturized surface may be one which has a regular or an irregular shaped surface for scattering incoming light, decreasing the amount of light reflected off of the light-receiving surfaces of the solar cell.
- the light-receiving surface 101 is texturized using a hydroxide-based wet etchant.
- the method of fabricating a solar cell further involves forming a first plurality of dopant regions 106 of the first conductivity type by ion implantation.
- the first plurality of dopant regions 106 of the first conductivity type is of a second, higher, concentration than lightly doped region 104 .
- the first plurality of dopant regions 106 is overlapping with first portions of the lightly doped region 104 .
- the first plurality of dopant regions 106 is formed by implanting dopants during a pass under a stationary mask in an implanter.
- the second, higher, concentration of the first conductivity type is approximately 1E19 atoms/cm 3 .
- the first conductivity type is P-type, and boron atoms are implanted to form the first plurality of dopant regions 106 .
- the first conductivity type is N-type, and phosphorous atoms are implanted to form the first plurality of dopant regions 106 .
- the implanting is performed by using ion beam implantation or plasma immersion implantation.
- the lightly doped region 104 and the first plurality of dopant regions 106 are both formed by implanting dopants during a single pass under a stationary mask in an implanter, the single pass forming both the lightly doped region 104 and the first plurality of dopant regions 106 .
- implanting of the dopants of the first conductivity type during the single pass under the stationary mask is performed using a mask having a slit pattern for forming the first plurality of dopant regions 106 and a full opening for forming the lightly doped region 104 .
- An example of such a mask is described in greater detail below in association with FIG. 3B .
- the method of fabricating a solar cell further involves forming a second plurality of dopant regions 108 by ion implantation.
- the second plurality of dopant regions 108 is of a second, opposite, conductivity type as compared to the first conductivity type.
- the second plurality of dopant regions 108 is of a concentration higher than the concentration of the first plurality of dopant regions 106 .
- the second plurality of dopant regions 108 is overlapping with second portions of the lightly doped region 104 and is alternating with, but not overlapping, the first plurality of dopant regions 106 .
- the second plurality of dopant regions 108 is formed by implanting dopants during a pass under a stationary mask in an implanter.
- the concentration of the second conductivity type is approximately 1E19 atoms/cm 3 .
- the second conductivity type is N-type, and phosphorous atoms are implanted to form the second plurality of dopant regions 108 .
- the second conductivity type is P-type, and boron atoms are implanted to form the second plurality of dopant regions 108 .
- the concentration of second conductivity type dopants is sufficient to change the conductivity type from the first to the second conductivity type in the locations of the second plurality of dopant regions 108 .
- the implanting is performed by using ion beam implantation or plasma immersion implantation.
- the method of fabricating a solar cell further involves forming a doped amorphous silicon layer 110 on the light-receiving surface 101 of the semiconductor substrate 100 .
- the lightly doped region 104 , the first plurality of dopant regions 106 , and the second plurality of dopant regions 108 are formed in the back surface 102 of the semiconductor substrate 100 , the back surface opposite the light-receiving surface 101 of the semiconductor substrate 100 , as is depicted in FIG. 1D .
- the doped amorphous silicon layer 110 is formed using plasma enhanced chemical vapor deposition (PECVD) or low pressure chemical vapor deposition (LPCVD).
- the doped amorphous silicon layer 110 is an N-type doped amorphous silicon layer formed using PECVD. It is to be appreciated that, although represented as being formed following the above described implant processes (operations 202 , 204 , 206 ), the doped amorphous silicon layer 110 may be formed on the light-receiving prior to any or all of the implant operations.
- the doped amorphous silicon layer 110 is formed on a thin tunneling dielectric layer first formed on the light-receiving surface of the semiconductor substrate.
- the thin tunneling dielectric layer has a thickness approximately in the range of 10-150 Angstroms.
- the thin tunneling dielectric layer is a layer of silicon oxide having a thickness approximately in the range of 15-20 Angstroms.
- the method of fabricating a solar cell further involves thermally annealing the semiconductor substrate subsequent to the ion implantation operations described in association with FIGS. 1A-1C .
- the thermal anneal is performed in a substantially nitrogen (N 2 ) atmosphere.
- the annealing is performed at a temperature approximately in the range of 850-1100 degrees Celsius for a duration approximately in the range of 1-100 minutes.
- the thermal anneal crystallizes the doped amorphous silicon layer 110 to form a doped polycrystalline silicon layer 112 on the light-receiving surface 101 of the semiconductor substrate 100 , as is depicted in FIG. 1E .
- the resulting doped polycrystalline silicon layer 112 is an N-type doped polycrystalline silicon layer. It is to be appreciated that the annealing process implemented post implant for dopant activation can have the added benefit of enhancing front side passivation through the above described crystallization process. In such scenarios, there is likely no need for doping during the anneal and, accordingly, the anneal may be performed in an N 2 environment. This may allow for double slot loading in a furnace. It is also to be appreciated that, although not depicted, following crystallization to form the doped polycrystalline silicon layer 112 , other front side passivation or ARC layers may be formed on the doped polycrystalline silicon layer 112 .
- the method of fabricating a solar cell further involves forming a first plurality of contacts 116 electrically connected to the first plurality of dopant regions 106 , and forming a second plurality of contacts 118 electrically connected to the second plurality of dopant regions 106 .
- the contacts are fabricated by first depositing and patterning an insulating layer 114 to have openings and then forming one or more conductive layers in the openings.
- the conductive contacts 116 and 118 include metal and are formed by a deposition, lithographic, and etch approach or, alternatively, a printing process.
- a solar cell includes a semiconductor substrate 100 having a light-receiving surface 101 and a back surface 102 opposite the light-receiving surface 101 .
- a blanket dopant region 104 is disposed in the semiconductor substrate 100 at the back surface 102 of the semiconductor substrate 100 .
- the blanket dopant region 104 is of a first conductivity type of a first concentration.
- a first plurality of dopant regions 106 is disposed in the semiconductor substrate 100 and is overlapping with the blanket dopant region 104 .
- the first plurality of dopant regions 106 is of the first conductivity type and of a second, higher, concentration.
- a second plurality of dopant regions 108 is disposed in the semiconductor substrate 100 and is overlapping with the blanket dopant region 104 , but alternating with and not overlapping the first plurality of dopant regions 106 .
- the second plurality of dopant regions 108 is of a second conductivity type of a concentration higher than the first concentration.
- a first plurality of contacts 116 is electrically connected to the first plurality of dopant regions 106 at the back surface 102 of the solar cell.
- a second plurality of contacts 118 is electrically connected to the second plurality of dopant regions 108 at the back surface 102 of the solar cell.
- the first conductivity type is P-type (regions 104 and 106 ), and the second conductivity type is N-type (regions 108 ).
- the semiconductor substrate 100 is a monocrystalline semiconductor substrate.
- the first plurality of dopant regions 106 includes boron dopants, and the second plurality of dopant regions 108 includes phosphorous dopants.
- the first conductivity type is N-type (regions 104 and 106 ), and the second conductivity type is P-type (regions 108 ).
- the semiconductor substrate 100 is a monocrystalline semiconductor substrate.
- the first plurality of dopant regions 106 includes phosphorous dopants, and the second plurality of dopant regions 108 includes boron dopants.
- the first concentration of the first conductivity type is approximately 1E18 atoms/cm 3 .
- the second concentration of the first conductivity type is approximately 1E19 atoms/cm 3 .
- the concentration of the second conductivity type is approximately 1E19 atoms/cm 3 .
- FIG. 3A illustrates a plan view showing the implant regions of the structure of FIG. 1C .
- FIG. 3B illustrates a plan view of a mask pattern used to form the diffusion regions described in association with FIGS. 1A and 1B .
- the first plurality of dopant regions of the first conductivity type 106 described in association with FIG. 1B alternates with, but does overlap, the second plurality of dopant regions of the second conductivity type 108 described in association with FIG. 1C .
- Both the first plurality of dopant regions 106 and the second plurality of dopant regions 108 overlap with portions of the lightly doped region of the first conductivity type 104.
- the lightly doped region 104 and the first plurality of dopant regions 106 are both formed by implanting dopants during a single pass under a stationary mask in an implanter.
- implanting of the dopants of the first conductivity type to form regions 104 and 106 during the single pass under the stationary mask is performed using a mask 300 having a slit pattern 302 for forming the first plurality of dopant regions 106 .
- a full opening 304 in the mask 300 is for forming the lightly doped region 104 .
- the mask 300 is a graphite shadow mask for use positioned off of, but in close proximity to, a silicon substrate 100 during implantation.
- FIGS. 4A-4C illustrate cross-sectional views of various stages in the fabrication of a solar cell, in accordance with an embodiment of the present disclosure.
- a method of fabricating a solar cell involves forming a lightly doped region 404 in a semiconductor substrate 100 by ion implantation.
- the lightly doped region 404 is of a first conductivity type of a first concentration.
- the lightly doped region 404 is a pattern of lightly doped regions formed at the back surface 102 in the semiconductor substrate 100 , as is depicted in FIG. 4A .
- the method of fabricating a solar cell further involves forming a first plurality of dopant regions 106 of the first conductivity type by ion implantation.
- the first plurality of dopant regions 106 of the first conductivity type is of a second, higher, concentration than lightly doped region 404 .
- the first plurality of dopant regions 106 is overlapping with first portions of the lightly doped region 404 .
- a second plurality of dopant regions 108 is also formed by ion implantation.
- the second plurality of dopant regions 108 is of a second, opposite, conductivity type as compared to the first conductivity type.
- the second plurality of dopant regions 108 is of a concentration higher than the concentration of the first plurality of dopant regions 106 . Furthermore, the second plurality of dopant regions 108 is overlapping with second portions of the lightly doped region 404 and is alternating with, but not overlapping, the first plurality of dopant regions 106 .
- the method of fabricating a solar cell further involves forming a doped polycrystalline silicon layer 112 on a light-receiving surface 101 of the semiconductor substrate 100 , as was described in association with FIGS. 1D and 1E . Additionally, a first plurality of contacts 116 is electrically connected to the first plurality of dopant regions 106 . A second plurality of contacts 118 is electrically connected to the second plurality of dopant regions 106 .
- a solar cell includes a semiconductor substrate 100 having a light-receiving surface 101 and a back surface 102 opposite the light-receiving surface 101 .
- a patterned dopant region 404 is disposed in the semiconductor substrate 100 at the back surface 102 of the semiconductor substrate 100 .
- the patterned dopant region 404 is of a first conductivity type of a first concentration.
- a first plurality of dopant regions 106 is disposed in the semiconductor substrate 100 and is contacting at least a portion of the patterned dopant region 404 .
- the first plurality of dopant regions 106 is of the first conductivity type of a second, higher, concentration.
- a second plurality of dopant regions 108 is disposed in the semiconductor substrate 100 and is contacting at least a portion of the patterned dopant region 404 .
- the second plurality of dopant regions 108 is alternating with and not overlapping the first plurality of dopant regions 106 .
- the second plurality of dopant regions 108 is of a second conductivity type of a concentration higher than the first concentration.
- a first plurality of contacts 116 is electrically connected to the first plurality of dopant regions 106 at the back surface 102 of the solar cell.
- a second plurality of contacts 118 is electrically connected to the second plurality of dopant regions 108 at the back surface 102 of the solar cell.
- the first conductivity type is P-type (regions 404 and 106 ), and the second conductivity type is N-type (regions 108 ).
- the semiconductor substrate 100 is a monocrystalline semiconductor substrate.
- the first plurality of dopant regions 106 includes boron dopants, and the second plurality of dopant regions 108 includes phosphorous dopants.
- the first conductivity type is N-type (regions 404 and 106 ), and the second conductivity type is P-type (regions 108 ).
- the semiconductor substrate 100 is a monocrystalline semiconductor substrate.
- the first plurality of dopant regions 106 includes phosphorous dopants, and the second plurality of dopant regions 108 includes boron dopants.
- the first concentration of the first conductivity type is approximately 1E18 atoms/cm 3 .
- the second concentration of the first conductivity type is approximately 1E19 atoms/cm 3 .
- the concentration of the second conductivity type is approximately 1E19 atoms/cm 3 .
- FIG. 5A illustrates a plan view showing the implant regions of the structure of FIG. 4B .
- FIG. 5B illustrates a plan view of a mask pattern used to form the diffusion regions described in association with FIGS. 4A and 4B .
- the first plurality of dopant regions of the first conductivity type 106 described in association with FIG. 4B overlap with portions of the patterned lightly doped region of the first conductivity type 404.
- the lightly doped region 404 e.g., B ⁇ level doping
- the first plurality of dopant regions 106 e.g., B + level doping
- implanting of the dopants of the first conductivity type to form regions 404 and 106 during the single pass under the stationary mask is performed using a mask 500 having an opening 502 .
- the opening 502 has a wide region 504 for forming a region of the pattern of lightly doped regions 404 .
- the opening 502 also has a narrow region 506 for forming the first plurality of dopant regions 106 .
- the mask 500 is a graphite shadow mask for use positioned off of, but in close proximity to, a silicon substrate 100 during implantation.
- FIGS. 6A and 6B illustrate plan views of a pair of mask patterns used to form the diffusion regions described in association with FIGS. 4A and 4B , in accordance with another embodiment of the present disclosure.
- implanting of the dopants of the first conductivity type to form regions 404 and 106 of FIG. 4B during a single pass under a stationary mask is performed using a mask 600 having openings 602 .
- implanting of the dopants of the second conductivity type to form regions 108 of FIG. 4 b under a stationary mask is performed using a mask 650 having openings 652 .
- the openings 602 of the mask 600 are substantially wider than the openings 652 of the mask 650 .
- the masks 600 and 650 are graphite shadow masks for use positioned off of, but in close proximity to, a silicon substrate 100 during implantation.
- FIG. 7 schematically illustrates a cross-sectional view of an inline platform for patterned implant involving a traveling wafer and stationary shadow mask, in accordance with an embodiment of the present disclosure.
- an inline platform 700 includes a wafer input region for an input wafer.
- a first station 750 is configured to implant dopant impurity atoms of a first conductivity type through a first shadow mask and into a substrate.
- a second station 754 is configured to implant dopant impurity atoms of a second, different, conductivity type through a second shadow mask into the substrate.
- the first station 750 is configured to implant boron atoms or ions
- the second station 754 is configured to implant phosphorous atoms or ions.
- a stationary stencil mask 702 such as a stationary graphite mask, is held in proximity to, but not in contact with, the substrate during implantation.
- a stationary stencil mask 702 such as a stationary graphite mask
- the usable distance for spacing from the receiving substrate may be determined by the degree to which the ion beam can be collimated.
- a typical spacing may be between 50-250 microns which is roughly the same order of thickness as a Si solar wafer substrate.
- the spacing may be as high a 1000 microns (1 mm) under conditions which minimize the angle of divergence (from vertical) below the lower edge of the shadow mask.
- the resulting pattern of implanted regions is a one-dimensional interdigitated finger pattern.
- a stencil mask such as a stationary graphite shadow mask may be used for implantation.
- FIG. 7 schematically illustrates a possible inline platform for patterned implant involving stationary shadow masks, in accordance with an embodiment of the present disclosure.
- some deposition or residue accumulation may occur on the stencil masks. After numerous runs, such deposition or accumulation may require removal from the masks. It is to be appreciated that an optimal number of runs may be determined to balance throughput against an over-accumulation of material on the stencil mask that could in some way impact later implantation processes. In one such embodiment, after a certain number of runs, the accumulated material is removed by selective etching, and the stencil mask can then be reused.
- FIG. 8 is a flowchart 800 listing operations in another method of fabricating a solar cell, in accordance with an embodiment of the present disclosure.
- a pre-etched silicon wafer is received, or reduced step wet etch process is performed.
- Phosphorous silica glass (PSG) and undoped silica glass (USG) layers are then deposited on the device side (e.g., substrate back side) at operation 804 .
- a texturizing etch is performed for exposed light-receiving surfaces.
- the PSG/USG layers are then patterned at operation 808 .
- boron is implanted in a blanket (non-patterned) manner at the device side.
- Front side treatments such as oxidation (Ox), nitridation (N) and PECVD deposition of amorphous silicon (a-Si) are then performed at operation 812 .
- an anneal is performed.
- Anti-reflective coating (ARC) and bottom anti-reflective coating (BARC) layers are then formed on the device side at operation 816 .
- lower contact metallization is then performed.
- Backend process is then completed at operation 820 of flowchart 800 .
- the process does not require patterned ion implant capability. Instead, a patterned solid state N-type dopant (phosphorous) source is first formed. The patterned solid state N-type dopant source is then used as a mask for a blanket boron implant operation. Thus, a medium-low dose blanket boron implant operation can be implemented for P-type emitter region fabrication.
- a patterned solid state N-type dopant (phosphorous) source is first formed.
- the patterned solid state N-type dopant source is then used as a mask for a blanket boron implant operation.
- a medium-low dose blanket boron implant operation can be implemented for P-type emitter region fabrication.
- IBC interdigitated back contact
Abstract
Description
- Embodiments of the present disclosure are in the field of renewable energy and, in particular, methods of fabricating solar cell emitter regions using substrate-level ion implantation, and the resulting solar cells.
- Photovoltaic cells, commonly known as solar cells, are well known devices for direct conversion of solar radiation into electrical energy. Generally, solar cells are fabricated on a semiconductor wafer or substrate using semiconductor processing techniques to form a p-n junction near a surface of the substrate. Solar radiation impinging on the surface of, and entering into, the substrate creates electron and hole pairs in the bulk of the substrate. The electron and hole pairs migrate to p-doped and n-doped regions in the substrate, thereby generating a voltage differential between the doped regions. The doped regions are connected to conductive regions on the solar cell to direct an electrical current from the cell to an external circuit coupled thereto.
- Efficiency is an important characteristic of a solar cell as it is directly related to the capability of the solar cell to generate power. Likewise, efficiency in producing solar cells is directly related to the cost effectiveness of such solar cells. Accordingly, techniques for increasing the efficiency of solar cells, or techniques for increasing the efficiency in the manufacture of solar cells, are generally desirable. Some embodiments of the present disclosure allow for increased solar cell manufacture efficiency by providing novel processes for fabricating solar cell structures. Some embodiments of the present disclosure allow for increased solar cell efficiency by providing novel solar cell structures.
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FIGS. 1A-1F illustrate cross-sectional views of various stages in the fabrication of a solar cell, in accordance with an embodiment of the present disclosure, wherein: -
FIG. 1A illustrates a cross-sectional view following formation of a lightly doped region in a semiconductor substrate by ion implantation; -
FIG. 1B illustrates a cross-sectional view of the structure ofFIG. 1A following formation of a first plurality of dopant regions of the first conductivity type by ion implantation; -
FIG. 1C illustrates a cross-sectional view of the structure ofFIG. 1B following formation of a second plurality of dopant regions by ion implantation; -
FIG. 1D illustrates a cross-sectional view of the structure ofFIG. 1C following formation of a doped amorphous silicon layer on the light-receiving surface of the semiconductor substrate; -
FIG. 1E illustrates a cross-sectional view of the structure ofFIG. 1D following thermally annealing of the semiconductor substrate; and -
FIG. 1F illustrates a cross-sectional view of the structure ofFIG. 1E following formation of a first plurality of contacts electrically connected to the first plurality of dopant regions, and formation of a second plurality of contacts electrically connected to the second plurality of dopant regions. -
FIG. 2 is a flowchart listing operations in a method of fabricating a solar cell as corresponding toFIGS. 1A-1F , in accordance with an embodiment of the present disclosure. -
FIG. 3A illustrates a plan view showing the implant regions of the structure ofFIG. 1C , in accordance with an embodiment of the present disclosure. -
FIG. 3B illustrates a plan view of a mask pattern used to form the diffusion regions described in association withFIGS. 1A and 1B , in accordance with an embodiment of the present disclosure. -
FIGS. 4A-4C illustrate cross-sectional views of various stages in the fabrication of a solar cell, in accordance with an embodiment of the present disclosure, wherein: -
FIG. 4A illustrates a cross-sectional view of illustrates a cross-sectional view following formation of a patterned lightly doped region in a semiconductor substrate by ion implantation; -
FIG. 4B illustrates a cross-sectional view of illustrates a cross-sectional view of the structure ofFIG. 4A following formation of a first plurality of dopant regions of the first conductivity type by ion implantation, and following formation of a second plurality of dopant regions by ion implantation; and -
FIG. 4C illustrates a cross-sectional view of the structure ofFIG. 4A following formation of a polycrystalline silicon layer on the light-receiving surface of the substrate and following formation of a first plurality of contacts electrically connected to the first plurality of dopant regions, and formation of a second plurality of contacts electrically connected to the second plurality of dopant regions. -
FIG. 5A illustrates a plan view showing the implant regions of the structure ofFIG. 4B , in accordance with an embodiment of the present disclosure. -
FIG. 5B illustrates a plan view of a mask pattern used to form the diffusion regions described in association withFIGS. 4A and 4B , in accordance with an embodiment of the present disclosure. -
FIGS. 6A and 6B illustrate plan views of a pair of mask patterns used to form the diffusion regions described in association withFIGS. 4A and 4B , in accordance with another embodiment of the present disclosure. -
FIG. 7 schematically illustrates a cross-sectional view of an inline platform for patterned implant involving a traveling wafer and stationary shadow mask, in accordance with an embodiment of the present disclosure. -
FIG. 8 is a flowchart listing operations in another method of fabricating a solar cell, in accordance with an embodiment of the present disclosure. - The following detailed description is merely illustrative in nature and is not intended to limit the embodiments of the subject matter or the application and uses of such embodiments. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Any implementation described herein as exemplary is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description.
- This specification includes references to “one embodiment” or “an embodiment.” The appearances of the phrases “in one embodiment” or “in an embodiment” do not necessarily refer to the same embodiment. Particular features, structures, or characteristics may be combined in any suitable manner consistent with this disclosure.
- Terminology. The following paragraphs provide definitions and/or context for terms found in this disclosure (including the appended claims):
- “Comprising.” This term is open-ended. As used in the appended claims, this term does not foreclose additional structure or steps.
- “Configured To.” Various units or components may be described or claimed as “configured to” perform a task or tasks. In such contexts, “configured to” is used to connote structure by indicating that the units/components include structure that performs those task or tasks during operation. As such, the unit/component can be said to be configured to perform the task even when the specified unit/component is not currently operational (e.g., is not on/active). Reciting that a unit/circuit/component is “configured to” perform one or more tasks is expressly intended not to invoke 35 U.S.C. §112, sixth paragraph, for that unit/component.
- “First,” “Second,” etc. As used herein, these terms are used as labels for nouns that they precede, and do not imply any type of ordering (e.g., spatial, temporal, logical, etc.). For example, reference to a “first” solar cell does not necessarily imply that this solar cell is the first solar cell in a sequence; instead the term “first” is used to differentiate this solar cell from another solar cell (e.g., a “second” solar cell).
- “Coupled”—The following description refers to elements or nodes or features being “coupled” together. As used herein, unless expressly stated otherwise, “coupled” means that one element/node/feature is directly or indirectly joined to (or directly or indirectly communicates with) another element/node/feature, and not necessarily mechanically.
- “Inhibit”—As used herein, inhibit is used to describe a reducing or minimizing effect. When a component or feature is described as inhibiting an action, motion, or condition it may completely prevent the result or outcome or future state completely. Additionally, “inhibit” can also refer to a reduction or lessening of the outcome, performance, and/or effect which might otherwise occur. Accordingly, when a component, element, or feature is referred to as inhibiting a result or state, it need not completely prevent or eliminate the result or state.
- In addition, certain terminology may also be used in the following description for the purpose of reference only, and thus are not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, “side”, “outboard”, and “inboard” describe the orientation and/or location of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import.
- Methods of fabricating solar cell emitter regions using substrate-level ion implantation, and the resulting solar cells, are described herein. In the following description, numerous specific details are set forth, such as specific process flow operations, in order to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to one skilled in the art that embodiments of the present disclosure may be practiced without these specific details. In other instances, well-known fabrication techniques, such as lithography and patterning techniques, are not described in detail in order to not unnecessarily obscure embodiments of the present disclosure. Furthermore, it is to be understood that the various embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.
- Disclosed herein are methods of fabricating solar cells. In one embodiment, a method of fabricating a solar cell involves forming a lightly doped region in a semiconductor substrate by ion implantation, the lightly doped region of a first conductivity type of a first concentration. The method also involves forming a first plurality of dopant regions of the first conductivity type of a second, higher, concentration by ion implantation, the first plurality of dopant regions overlapping with a first portion of the lightly doped region. The method also involves forming a second plurality of dopant regions by ion implantation, the second plurality of dopant regions having a second conductivity type of a concentration higher than the first concentration, and the second plurality of dopant regions overlapping with a second portion of the lightly doped region and alternating with but not overlapping the first plurality of dopant regions.
- Also disclosed herein are solar cells. In one embodiment, a solar cell includes a semiconductor substrate having a light-receiving surface and a back surface opposite the light-receiving surface. A blanket dopant region is disposed in the semiconductor substrate at the back surface of the semiconductor substrate. The blanket dopant region is of a first conductivity type of a first concentration. A first plurality of dopant regions is disposed in the semiconductor substrate and is overlapping with the blanket dopant region. The first plurality of dopant regions is of the first conductivity type and of a second, higher, concentration. A second plurality of dopant regions is disposed in the semiconductor substrate and is overlapping with the blanket dopant region but alternating with and not overlapping the first plurality of dopant regions. The second plurality of dopant regions is of a second conductivity type of a concentration higher than the first concentration. A first plurality of contacts is electrically connected to the first plurality of dopant regions at the back surface of the solar cell. A second plurality of contacts is electrically connected to the second plurality of dopant regions at the back surface of the solar cell.
- In another embodiment, a solar cell includes a semiconductor substrate having a light-receiving surface and a back surface opposite the light-receiving surface. A patterned dopant region is disposed in the semiconductor substrate at the back surface of the semiconductor substrate. The patterned dopant region is of a first conductivity type of a first concentration. A first plurality of dopant regions is disposed in the semiconductor substrate and is contacting at least a portion of the patterned dopant region. The first plurality of dopant regions is of the first conductivity type of a second, higher, concentration. A second plurality of dopant regions is disposed in the semiconductor substrate and is contacting at least a portion of the patterned dopant region. The second plurality of dopant regions is alternating with and not overlapping the first plurality of dopant regions. The second plurality of dopant regions is of a second conductivity type of a concentration higher than the first concentration. A first plurality of contacts is electrically connected to the first plurality of dopant regions at the back surface of the solar cell. A second plurality of contacts is electrically connected to the second plurality of dopant regions at the back surface of the solar cell.
- One or more embodiments described herein provides a simplified process flow for fabricating high efficiency, all back-contact solar cell devices involving the use of ion implant technology for generating one or both of N+(e.g., typically phosphorous or arsenic doped) and P+(e.g., typically boron doped) diffusion regions in a substrate. In one embodiment, a fabrication approach involves the use of ion implantation to introduce atoms of the required dopant type.
- To provide context, it is advantageous to seek out applications for implant technologies for solar cell fabrication. If implant technologies can be incorporated in to a manufacturing scheme, cost savings may be realized as other more expensive processing approaches are replaced with such technologies. Addressing such issues, in accordance with an embodiment of the present disclosure, approaches for solar cell fabrication described herein involve implanting of a solar cell substrate directly.
- In some embodiments described herein, an implant and anneal process for back end emitter fabrication is combined with front surface layer fabrication to provide “hybrid” front surface solutions. In an exemplary embodiment, a thin layer of N-type amorphous silicon (a-Si) deposited on a front or light-receiving surface of the solar cell using, e.g., plasma enhanced chemical vapor deposition (PECVD). During the implant anneal used post implant processing on the back side of the solar cell (e.g., typically a so-called back end process), the front surface a-Si layer is crystalized to form a polycrystalline silicon layer. Other layers such as a silicon nitride (SiN) anti-reflective coating (ARC) layer or film stack may then be incorporated on the polycrystalline silicon layer on the front side of the cell. In one embodiment, the resulting front surface provides a large improvement over state of the art technologies that typically involve heavy front side doping. For example, the resulting front surface may exhibit improved ultra-violet (UV) performance.
- Perhaps more generally, although front side synergies may be achieved, it is to be appreciated that embodiments need not include such front side synergies. In an embodiment, direct substrate implantation for back side processing is implemented to provide one dimensional (1D) lines at varying dopant levels. That is, embodiments described herein involve the use of back side implantation, e.g., for 1D emitter fabrication based on implanted diffusion regions of a bulk semiconductor substrate.
- In an exemplary process flow using substrate-level ion implantation,
FIGS. 1A-1F illustrate cross-sectional views of various stages in the fabrication of a solar cell, in accordance with an embodiment of the present disclosure.FIG. 2 is aflowchart 200 listing operations in a method of fabricating a solar cell as corresponding toFIGS. 1A-1F , in accordance with an embodiment of the present disclosure. - Referring to
FIG. 1A andcorresponding operation 202 offlowchart 200, the method of fabricating a solar cell involves forming a lightly dopedregion 104 in asemiconductor substrate 100 by ion implantation. The lightly doped region is of a first conductivity type of a first concentration. - In an embodiment, the
semiconductor substrate 100 is a monocrystalline silicon substrate, such as a bulk single crystalline N-type doped silicon substrate. It is to be appreciated, however, thatsemiconductor substrate 100 may be a layer, such as a multi-crystalline silicon layer, disposed on a global solar cell substrate. In an embodiment,semiconductor substrate 100 has light-receivingsurface 101 opposite aback surface 102, and may be used to ultimately fabricate a back contact solar cell. - In an embodiment, the lightly doped
region 104 is a blanket (non-patterned) lightly doped region formed in thesemiconductor substrate 100, as is depicted inFIG. 1A . In an embodiment, the lightly dopedregion 104 is formed by implanting dopants during a pass under a stationary mask in an implanter. - In an embodiment, the first concentration of the first conductivity type is approximately 1E18 atoms/cm3. In one embodiment, the first conductivity type is P-type, and boron atoms are implanted to form the lightly doped
region 104. In another embodiment, the first conductivity type is N-type, and phosphorous atoms are implanted to form the lightly dopedregion 104. In an embodiment, the implanting is performed by using ion beam implantation or plasma immersion implantation. - Referring again to
FIG. 1A , in an embodiment, as shown, thelight receiving surface 101 of thesubstrate 100 is texturized. A texturized surface may be one which has a regular or an irregular shaped surface for scattering incoming light, decreasing the amount of light reflected off of the light-receiving surfaces of the solar cell. In one embodiment, the light-receivingsurface 101 is texturized using a hydroxide-based wet etchant. - Referring to
FIG. 1B andcorresponding operation 204 offlowchart 200, the method of fabricating a solar cell further involves forming a first plurality ofdopant regions 106 of the first conductivity type by ion implantation. The first plurality ofdopant regions 106 of the first conductivity type is of a second, higher, concentration than lightly dopedregion 104. The first plurality ofdopant regions 106 is overlapping with first portions of the lightly dopedregion 104. - In an embodiment, the first plurality of
dopant regions 106 is formed by implanting dopants during a pass under a stationary mask in an implanter. In an embodiment, the second, higher, concentration of the first conductivity type is approximately 1E19 atoms/cm3. In one embodiment, the first conductivity type is P-type, and boron atoms are implanted to form the first plurality ofdopant regions 106. In another embodiment, the first conductivity type is N-type, and phosphorous atoms are implanted to form the first plurality ofdopant regions 106. In an embodiment, the implanting is performed by using ion beam implantation or plasma immersion implantation. - In an embodiment, the lightly doped
region 104 and the first plurality ofdopant regions 106 are both formed by implanting dopants during a single pass under a stationary mask in an implanter, the single pass forming both the lightly dopedregion 104 and the first plurality ofdopant regions 106. In one such embodiment, implanting of the dopants of the first conductivity type during the single pass under the stationary mask is performed using a mask having a slit pattern for forming the first plurality ofdopant regions 106 and a full opening for forming the lightly dopedregion 104. An example of such a mask is described in greater detail below in association withFIG. 3B . - Referring to
FIG. 1C andcorresponding operation 206 offlowchart 200, the method of fabricating a solar cell further involves forming a second plurality ofdopant regions 108 by ion implantation. The second plurality ofdopant regions 108 is of a second, opposite, conductivity type as compared to the first conductivity type. Also, the second plurality ofdopant regions 108 is of a concentration higher than the concentration of the first plurality ofdopant regions 106. The second plurality ofdopant regions 108 is overlapping with second portions of the lightly dopedregion 104 and is alternating with, but not overlapping, the first plurality ofdopant regions 106. - In an embodiment, the second plurality of
dopant regions 108 is formed by implanting dopants during a pass under a stationary mask in an implanter. In an embodiment, the concentration of the second conductivity type is approximately 1E19 atoms/cm3. In one embodiment, the second conductivity type is N-type, and phosphorous atoms are implanted to form the second plurality ofdopant regions 108. In another embodiment, the second conductivity type is P-type, and boron atoms are implanted to form the second plurality ofdopant regions 108. - It is to be appreciated that since the second plurality of
dopant regions 108 is formed as overlapping the lightly dopedregion 104 of the first conductivity type, in an embodiment, the concentration of second conductivity type dopants is sufficient to change the conductivity type from the first to the second conductivity type in the locations of the second plurality ofdopant regions 108. In an embodiment, the implanting is performed by using ion beam implantation or plasma immersion implantation. - Referring to
FIG. 1D and correspondingoptional operation 208 offlowchart 200, the method of fabricating a solar cell further involves forming a dopedamorphous silicon layer 110 on the light-receivingsurface 101 of thesemiconductor substrate 100. In one such embodiment, the lightly dopedregion 104, the first plurality ofdopant regions 106, and the second plurality ofdopant regions 108 are formed in theback surface 102 of thesemiconductor substrate 100, the back surface opposite the light-receivingsurface 101 of thesemiconductor substrate 100, as is depicted inFIG. 1D . - In an embodiment, the doped
amorphous silicon layer 110 is formed using plasma enhanced chemical vapor deposition (PECVD) or low pressure chemical vapor deposition (LPCVD). In one such embodiment, the dopedamorphous silicon layer 110 is an N-type doped amorphous silicon layer formed using PECVD. It is to be appreciated that, although represented as being formed following the above described implant processes (operations amorphous silicon layer 110 may be formed on the light-receiving prior to any or all of the implant operations. It is also to be appreciated that although not depicted, in an embodiment, the dopedamorphous silicon layer 110 is formed on a thin tunneling dielectric layer first formed on the light-receiving surface of the semiconductor substrate. In one such embodiment, the thin tunneling dielectric layer has a thickness approximately in the range of 10-150 Angstroms. In a particular such embodiment, the thin tunneling dielectric layer is a layer of silicon oxide having a thickness approximately in the range of 15-20 Angstroms. - Referring to
FIG. 1E and corresponding optional operation 210 offlowchart 200, the method of fabricating a solar cell further involves thermally annealing the semiconductor substrate subsequent to the ion implantation operations described in association withFIGS. 1A-1C . - In an embodiment, the thermal anneal is performed in a substantially nitrogen (N2) atmosphere. In an embodiment, the annealing is performed at a temperature approximately in the range of 850-1100 degrees Celsius for a duration approximately in the range of 1-100 minutes.
- Referring again to
FIG. 1E , in an embodiment where a dopedamorphous silicon layer 110 is formed on the light-receivingsurface 101 of thesemiconductor substrate 100, the thermal anneal crystallizes the dopedamorphous silicon layer 110 to form a dopedpolycrystalline silicon layer 112 on the light-receivingsurface 101 of thesemiconductor substrate 100, as is depicted inFIG. 1E . - In an embodiment, the resulting doped
polycrystalline silicon layer 112 is an N-type doped polycrystalline silicon layer. It is to be appreciated that the annealing process implemented post implant for dopant activation can have the added benefit of enhancing front side passivation through the above described crystallization process. In such scenarios, there is likely no need for doping during the anneal and, accordingly, the anneal may be performed in an N2 environment. This may allow for double slot loading in a furnace. It is also to be appreciated that, although not depicted, following crystallization to form the dopedpolycrystalline silicon layer 112, other front side passivation or ARC layers may be formed on the dopedpolycrystalline silicon layer 112. - Referring to
FIG. 1F and corresponding optional operation 212 offlowchart 200, the method of fabricating a solar cell further involves forming a first plurality ofcontacts 116 electrically connected to the first plurality ofdopant regions 106, and forming a second plurality ofcontacts 118 electrically connected to the second plurality ofdopant regions 106. - In an embodiment, the contacts are fabricated by first depositing and patterning an insulating
layer 114 to have openings and then forming one or more conductive layers in the openings. In an embodiment, theconductive contacts - With respect to a completed or mostly completed solar cell, referring again to
FIG. 1F , in accordance with an embodiment of the present disclosure, a solar cell includes asemiconductor substrate 100 having a light-receivingsurface 101 and aback surface 102 opposite the light-receivingsurface 101. Ablanket dopant region 104 is disposed in thesemiconductor substrate 100 at theback surface 102 of thesemiconductor substrate 100. Theblanket dopant region 104 is of a first conductivity type of a first concentration. A first plurality ofdopant regions 106 is disposed in thesemiconductor substrate 100 and is overlapping with theblanket dopant region 104. The first plurality ofdopant regions 106 is of the first conductivity type and of a second, higher, concentration. A second plurality ofdopant regions 108 is disposed in thesemiconductor substrate 100 and is overlapping with theblanket dopant region 104, but alternating with and not overlapping the first plurality ofdopant regions 106. The second plurality ofdopant regions 108 is of a second conductivity type of a concentration higher than the first concentration. A first plurality ofcontacts 116 is electrically connected to the first plurality ofdopant regions 106 at theback surface 102 of the solar cell. A second plurality ofcontacts 118 is electrically connected to the second plurality ofdopant regions 108 at theback surface 102 of the solar cell. - In an embodiment, the first conductivity type is P-type (
regions 104 and 106), and the second conductivity type is N-type (regions 108). In one such embodiment, thesemiconductor substrate 100 is a monocrystalline semiconductor substrate. The first plurality ofdopant regions 106 includes boron dopants, and the second plurality ofdopant regions 108 includes phosphorous dopants. - In another embodiment, the first conductivity type is N-type (
regions 104 and 106), and the second conductivity type is P-type (regions 108). In one such embodiment, thesemiconductor substrate 100 is a monocrystalline semiconductor substrate. The first plurality ofdopant regions 106 includes phosphorous dopants, and the second plurality ofdopant regions 108 includes boron dopants. - In either case, in an embodiment, the first concentration of the first conductivity type is approximately 1E18 atoms/cm3. The second concentration of the first conductivity type is approximately 1E19 atoms/cm3. The concentration of the second conductivity type is approximately 1E19 atoms/cm3.
- To further exemplify embodiments of the present disclosure with respect to the process of
FIGS. 1A-1F ,FIG. 3A illustrates a plan view showing the implant regions of the structure ofFIG. 1C .FIG. 3B illustrates a plan view of a mask pattern used to form the diffusion regions described in association withFIGS. 1A and 1B . - Referring to
FIG. 3A , the first plurality of dopant regions of thefirst conductivity type 106 described in association withFIG. 1B alternates with, but does overlap, the second plurality of dopant regions of thesecond conductivity type 108 described in association withFIG. 1C . Both the first plurality ofdopant regions 106 and the second plurality ofdopant regions 108 overlap with portions of the lightly doped region of thefirst conductivity type 104. In an embodiment, the lightly dopedregion 104 and the first plurality ofdopant regions 106 are both formed by implanting dopants during a single pass under a stationary mask in an implanter. - Referring to
FIG. 3B , in an embodiment, implanting of the dopants of the first conductivity type to formregions mask 300 having aslit pattern 302 for forming the first plurality ofdopant regions 106. Afull opening 304 in themask 300 is for forming the lightly dopedregion 104. In an embodiment, themask 300 is a graphite shadow mask for use positioned off of, but in close proximity to, asilicon substrate 100 during implantation. - In another aspect, instead of a blanket pattern for the lightly doped region, a patterned lightly doped region is formed. In an example,
FIGS. 4A-4C illustrate cross-sectional views of various stages in the fabrication of a solar cell, in accordance with an embodiment of the present disclosure. - Referring to
FIG. 4A , a method of fabricating a solar cell involves forming a lightly dopedregion 404 in asemiconductor substrate 100 by ion implantation. The lightly dopedregion 404 is of a first conductivity type of a first concentration. In an embodiment, the lightly dopedregion 404 is a pattern of lightly doped regions formed at theback surface 102 in thesemiconductor substrate 100, as is depicted inFIG. 4A . - Referring to
FIG. 4B , the method of fabricating a solar cell further involves forming a first plurality ofdopant regions 106 of the first conductivity type by ion implantation. The first plurality ofdopant regions 106 of the first conductivity type is of a second, higher, concentration than lightly dopedregion 404. The first plurality ofdopant regions 106 is overlapping with first portions of the lightly dopedregion 404. A second plurality ofdopant regions 108 is also formed by ion implantation. The second plurality ofdopant regions 108 is of a second, opposite, conductivity type as compared to the first conductivity type. The second plurality ofdopant regions 108 is of a concentration higher than the concentration of the first plurality ofdopant regions 106. Furthermore, the second plurality ofdopant regions 108 is overlapping with second portions of the lightly dopedregion 404 and is alternating with, but not overlapping, the first plurality ofdopant regions 106. - Referring to
FIG. 4C , the method of fabricating a solar cell further involves forming a dopedpolycrystalline silicon layer 112 on a light-receivingsurface 101 of thesemiconductor substrate 100, as was described in association withFIGS. 1D and 1E . Additionally, a first plurality ofcontacts 116 is electrically connected to the first plurality ofdopant regions 106. A second plurality ofcontacts 118 is electrically connected to the second plurality ofdopant regions 106. - With respect to a completed or mostly completed solar cell, referring again to
FIG. 4C , in accordance with an embodiment of the present disclosure, a solar cell includes asemiconductor substrate 100 having a light-receivingsurface 101 and aback surface 102 opposite the light-receivingsurface 101. A patterneddopant region 404 is disposed in thesemiconductor substrate 100 at theback surface 102 of thesemiconductor substrate 100. The patterneddopant region 404 is of a first conductivity type of a first concentration. A first plurality ofdopant regions 106 is disposed in thesemiconductor substrate 100 and is contacting at least a portion of the patterneddopant region 404. The first plurality ofdopant regions 106 is of the first conductivity type of a second, higher, concentration. A second plurality ofdopant regions 108 is disposed in thesemiconductor substrate 100 and is contacting at least a portion of the patterneddopant region 404. The second plurality ofdopant regions 108 is alternating with and not overlapping the first plurality ofdopant regions 106. The second plurality ofdopant regions 108 is of a second conductivity type of a concentration higher than the first concentration. A first plurality ofcontacts 116 is electrically connected to the first plurality ofdopant regions 106 at theback surface 102 of the solar cell. A second plurality ofcontacts 118 is electrically connected to the second plurality ofdopant regions 108 at theback surface 102 of the solar cell. - In an embodiment, the first conductivity type is P-type (
regions 404 and 106), and the second conductivity type is N-type (regions 108). In one such embodiment, thesemiconductor substrate 100 is a monocrystalline semiconductor substrate. The first plurality ofdopant regions 106 includes boron dopants, and the second plurality ofdopant regions 108 includes phosphorous dopants. - In another embodiment, the first conductivity type is N-type (
regions 404 and 106), and the second conductivity type is P-type (regions 108). In one such embodiment, thesemiconductor substrate 100 is a monocrystalline semiconductor substrate. The first plurality ofdopant regions 106 includes phosphorous dopants, and the second plurality ofdopant regions 108 includes boron dopants. - In either case, in an embodiment, the first concentration of the first conductivity type is approximately 1E18 atoms/cm3. The second concentration of the first conductivity type is approximately 1E19 atoms/cm3. The concentration of the second conductivity type is approximately 1E19 atoms/cm3.
- To further exemplify embodiments of the present disclosure with respect to the process of
FIGS. 4A-4C ,FIG. 5A illustrates a plan view showing the implant regions of the structure ofFIG. 4B .FIG. 5B illustrates a plan view of a mask pattern used to form the diffusion regions described in association withFIGS. 4A and 4B . - Referring to
FIG. 5A , the first plurality of dopant regions of thefirst conductivity type 106 described in association withFIG. 4B overlap with portions of the patterned lightly doped region of thefirst conductivity type 404. In an embodiment, the lightly doped region 404 (e.g., B− level doping) and the first plurality of dopant regions 106 (e.g., B+ level doping) are both formed by implanting dopants during a single pass under a stationary mask in an implanter. - Referring to
FIG. 5B , in an embodiment, implanting of the dopants of the first conductivity type to formregions mask 500 having anopening 502. Theopening 502 has awide region 504 for forming a region of the pattern of lightly dopedregions 404. Theopening 502 also has anarrow region 506 for forming the first plurality ofdopant regions 106. In an embodiment, themask 500 is a graphite shadow mask for use positioned off of, but in close proximity to, asilicon substrate 100 during implantation. - In another aspect, with respect again to the process of
FIGS. 4A-4C ,FIGS. 6A and 6B illustrate plan views of a pair of mask patterns used to form the diffusion regions described in association withFIGS. 4A and 4B , in accordance with another embodiment of the present disclosure. - Referring to
FIG. 6A , in an embodiment, implanting of the dopants of the first conductivity type to formregions FIG. 4B during a single pass under a stationary mask is performed using amask 600 havingopenings 602. Referring toFIG. 6B , implanting of the dopants of the second conductivity type to formregions 108 ofFIG. 4b under a stationary mask is performed using amask 650 havingopenings 652. Theopenings 602 of themask 600 are substantially wider than theopenings 652 of themask 650. In an embodiment, themasks silicon substrate 100 during implantation. - In another aspect,
FIG. 7 schematically illustrates a cross-sectional view of an inline platform for patterned implant involving a traveling wafer and stationary shadow mask, in accordance with an embodiment of the present disclosure. - Referring to
FIG. 7 , aninline platform 700 includes a wafer input region for an input wafer. Afirst station 750 is configured to implant dopant impurity atoms of a first conductivity type through a first shadow mask and into a substrate. Asecond station 754 is configured to implant dopant impurity atoms of a second, different, conductivity type through a second shadow mask into the substrate. In a particular embodiment, thefirst station 750 is configured to implant boron atoms or ions, and thesecond station 754 is configured to implant phosphorous atoms or ions. - Referring again to
FIG. 7 , astationary stencil mask 702, such as a stationary graphite mask, is held in proximity to, but not in contact with, the substrate during implantation. Although shown as one mask with two corresponding slit patterns, it is to be appreciated that an individual shadow mask will typically be used for each of themodules - In an embodiment, as described above, a stencil mask such as a stationary graphite shadow mask may be used for implantation. As an example,
FIG. 7 schematically illustrates a possible inline platform for patterned implant involving stationary shadow masks, in accordance with an embodiment of the present disclosure. In either of the above described cases, in an embodiment, some deposition or residue accumulation may occur on the stencil masks. After numerous runs, such deposition or accumulation may require removal from the masks. It is to be appreciated that an optimal number of runs may be determined to balance throughput against an over-accumulation of material on the stencil mask that could in some way impact later implantation processes. In one such embodiment, after a certain number of runs, the accumulated material is removed by selective etching, and the stencil mask can then be reused. - Referring again to the process flows described in association with
FIGS. 1A-1F and 4A-4C , in an embodiment, two boron doses are performed in one pass using a stationary mask that has a full wafer opening to create a blanket lightly doped region followed by a slit pattern to provide selective emitter regions. It is to be appreciated that other processing schemes may benefit from direct implant of a back surface of a substrate of a solar cell. As an example,FIG. 8 is aflowchart 800 listing operations in another method of fabricating a solar cell, in accordance with an embodiment of the present disclosure. - Referring to
operation 802 offlowchart 800, a pre-etched silicon wafer is received, or reduced step wet etch process is performed. Phosphorous silica glass (PSG) and undoped silica glass (USG) layers are then deposited on the device side (e.g., substrate back side) atoperation 804. Referring tooperation 806, a texturizing etch is performed for exposed light-receiving surfaces. The PSG/USG layers are then patterned atoperation 808. Referring tooperation 810, boron is implanted in a blanket (non-patterned) manner at the device side. Front side treatments such as oxidation (Ox), nitridation (N) and PECVD deposition of amorphous silicon (a-Si) are then performed atoperation 812. Referring tooperation 814, an anneal is performed. Anti-reflective coating (ARC) and bottom anti-reflective coating (BARC) layers are then formed on the device side atoperation 816. Referring tooperation 818, lower contact metallization is then performed. Backend process is then completed atoperation 820 offlowchart 800. - With reference again to the process flow described in association with
flowchart 800, the process does not require patterned ion implant capability. Instead, a patterned solid state N-type dopant (phosphorous) source is first formed. The patterned solid state N-type dopant source is then used as a mask for a blanket boron implant operation. Thus, a medium-low dose blanket boron implant operation can be implemented for P-type emitter region fabrication. - Thus, the introduction of high throughput ion implant tools targeting high efficiency solar applications with patterning capabilities may be applicable to the fabrication of interdigitated back contact (IBC) solar cells. Overall, although certain materials are described specifically above, some materials may be readily substituted with others with other such embodiments remaining within the spirit and scope of embodiments of the present disclosure. For example, in an embodiment, a different material substrate, such as a group III-V material substrate, can be used instead of a silicon substrate. In another embodiment, a polycrystalline or multi-crystalline silicon substrate is used. Furthermore, it is to be understood that, where the ordering of N+ and then P+ type doping is described specifically for emitter regions on a back surface of a solar cell, other embodiments contemplated include the opposite ordering of conductivity type, e.g., P+ and then N+ type doping, respectively. Additionally, although reference is made significantly to back contact solar cell arrangements, it is to be appreciated that approaches described herein may have application to front contact solar cells as well. In general, embodiments described herein may be implemented to provide lower cost, high throughput ion implant platforms for the fabrication of high efficiency interdigitated back contact (IBC)-type solar cells.
- Thus, methods of fabricating solar cell emitter regions using substrate-level ion implantation, and the resulting solar cells, have been disclosed.
- Although specific embodiments have been described above, these embodiments are not intended to limit the scope of the present disclosure, even where only a single embodiment is described with respect to a particular feature. Examples of features provided in the disclosure are intended to be illustrative rather than restrictive unless stated otherwise. The above description is intended to cover such alternatives, modifications, and equivalents as would be apparent to a person skilled in the art having the benefit of this disclosure.
- The scope of the present disclosure includes any feature or combination of features disclosed herein (either explicitly or implicitly), or any generalization thereof, whether or not it mitigates any or all of the problems addressed herein. Accordingly, new claims may be formulated during prosecution of this application (or an application claiming priority thereto) to any such combination of features. In particular, with reference to the appended claims, features from dependent claims may be combined with those of the independent claims and features from respective independent claims may be combined in any appropriate manner and not merely in the specific combinations enumerated in the appended claims.
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US14/672,071 US20160284913A1 (en) | 2015-03-27 | 2015-03-27 | Solar cell emitter region fabrication using substrate-level ion implantation |
CN201680024747.8A CN107534070B (en) | 2015-03-27 | 2016-03-22 | Solar battery emitter region is manufactured using substrate grade ion implanting |
KR1020177031170A KR102570174B1 (en) | 2015-03-27 | 2016-03-22 | Solar Cell Emitter Area Fabrication Using Substrate-Level Ion Implantation |
TW105108843A TWI720974B (en) | 2015-03-27 | 2016-03-22 | Solar cell and manufacturing method thereof |
PCT/US2016/023640 WO2016160432A1 (en) | 2015-03-27 | 2016-03-22 | Solar cell emitter region fabrication using substrate-level ion implantation |
CN201911000522.0A CN110828601B (en) | 2015-03-27 | 2016-03-22 | Fabrication of solar cell emitter regions using substrate-level ion implantation |
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- 2016-03-22 WO PCT/US2016/023640 patent/WO2016160432A1/en active Application Filing
- 2016-03-22 CN CN201680024747.8A patent/CN107534070B/en active Active
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CN107534070A (en) | 2018-01-02 |
TWI720974B (en) | 2021-03-11 |
US20220020894A2 (en) | 2022-01-20 |
WO2016160432A1 (en) | 2016-10-06 |
KR20170132828A (en) | 2017-12-04 |
CN110828601A (en) | 2020-02-21 |
KR102570174B1 (en) | 2023-08-23 |
US20200411711A1 (en) | 2020-12-31 |
CN110828601B (en) | 2023-08-04 |
TW201707220A (en) | 2017-02-16 |
CN107534070B (en) | 2019-11-12 |
US11942565B2 (en) | 2024-03-26 |
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