Abstract:
A method for irradiating a plate ( 104 ) using multiple co-located radiation sources ( 108 - 1,108 - 2,108 - 3,108 - 4 ) includes that each of the multiple co-located radiation sources ( 108 - 1,108 - 2,108 - 3,108 - 4 ) is responsible for irradiating one of a plurality of bounded sub-regions ( 110 - 1,110 - 2,110 - 3,110 - 4 ) in the plate ( 104 ). As a result, sub-regions of the plate ( 104 ) that are to be irradiated receive relatively even, relatively well-defined radiation from the multiple co-located radiation sources ( 108 - 1,108 - 2,108 - 3,108 - 4 ). An apparatus performs the method, and a solar cell is produced using the method. The method and the apparatus can be applied in laser doping and laser cutting.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to irradiating plates with multiple co-located radiation sources, and in particular, to laser scribing a semiconductor wafer or substrate using multiple co-located laser devices. 
       BACKGROUND 
       [0002]    Radiation from laser can be used in many applications. For example, a thin film of amorphous silicon may be cut in a laser cutting process to form a number of disjoint regions that can be serially connected as a solar electric power cell to provide a suitable voltage to run a hand-held calculator. 
         [0003]    In another application, laser radiation can be used to cause dopants to diffuse into a semiconductor wafer or substrate. Specifically, when radiation from a laser is directed at a spot (e.g., a surface spot) on a silicon wafer, an area around that spot warms up, allowing nearby dopants (which may be positioned on top of the silicon wafer as a thin film or in a gaseous state near the surface of the silicon wafer) to diffuse into vicinity of the area. Laser doping as described may be used to create a selective emitter structure on a solar cell. A selective emitter structure comprises selective areas that are relatively highly doped, for example, through a laser doping process previously mentioned. Subsequent metallization of these selective areas of the solar cell forms a low serial resistance contacts in these areas, while other areas that have not been selectively doped form high sheet resistance sunlight-receiving areas. As a result, charges generated in the sunlight-receiving areas can be efficiently collected through the metal in the highly doped areas. 
         [0004]    There are a number of disadvantages with laser scribing or doping under existing techniques. Under some of the existing techniques, an object to be irradiated by a laser is placed on a moving stage. To form a particular pattern of irradiation (e.g., parallel lines), the moving stage on which the object is mounted moves within a plane that is substantially vertical to the laser beam during irradiation. Thus, when the stage moves too fast (for example, over 1 meter per second), vibrations from the motion may cause imprecise scribing on the object. For example, where lines should be straight, parallel, and non-crossing, these lines may instead be zigzagged or cross one another inadvertently. 
         [0005]    Under some other existing techniques (including those similar to photolithography), an object may be placed in a fixed, stationary position relative to a platform during irradiation. A laser beam from a laser source may be shifted around (e.g., by moving mirrors within a laser device) to create a desired pattern of irradiation on a surface of the object. Typically, the laser beam is in focus only at certain spots on the surface of the object. When the beam moves to different spots, due to the different lengths of optical paths, different incident angles, and other factors involved in the propagation of the beam from the laser source to the object, the beam may be out of focus in these different spots. Consequently, a laser beam may produce uneven intensities of radiation on the object. This shortcoming is worsened if the surface to be irradiated is large. 
         [0006]    As applied to making selective emitters on solar cells, a common disadvantage of these existing techniques is uneven concentration of dopant in areas where selective emitters are to be formed. For example, certain areas may be overly doped while other areas may be under-doped. In the worst-case scenarios, undesirable warping, cracks and grooves may be developed on a surface of a semiconductor wafer or substrate, causing serious surface and/or structural damages. 
         [0007]    As clearly shown, techniques are needed to increase the speed and improve the quality of irradiation of an object, in particular, as related to irradiation of a semiconductor wafer or substrate by laser light. 
         [0008]    The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    In the drawings: 
           [0010]      FIG. 1A ,  FIG. 1B  and  FIG. 1C  illustrate example configurations of an example system that can be used for irradiating a plate using multiple co-located radiation sources; 
           [0011]      FIG. 2A ,  FIG. 2B , and  FIG. 2C  illustrate example configurations that can be used to perform laser-enabled selective irradiation; and 
           [0012]      FIG. 3  is an example processing flow for irradiating a plate using multiple co-located radiation sources. 
         SUMMARY 
         [0013]    In some embodiments, a method for irradiating plates comprises: using a first radiation obtained from a first co-located radiation source to irradiate within a first bounded region of a plate, wherein the plate is placed at a first position, wherein the first co-located radiation source is one of a plurality of co-located radiation sources, wherein the first bounded region is one of a plurality of bounded regions of the plate; moving the plate to a second position; and using a second radiation obtained from a second co-located radiation source to irradiate within a second bounded region of the plate, wherein the plate is fixed at the second position, wherein the second co-located radiation source is another one of the plurality of co-located radiation sources, wherein the second bounded region is another one of the plurality of bounded regions of the plate. 
           [0014]    In an embodiment, a first intensity of the first co-located radiation source is regulated. In an embodiment, at least one of the plurality of co-located radiation sources is a laser light source. In an embodiment, this laser light source operates at a first wavelength. In an embodiment, the first radiation is a light beam. In another embodiment, the first radiation is a light pattern. 
           [0015]    In various embodiments, the plate may be a substrate, a wafer, or generally a planar object (which may have a microscopically uneven surface, for example, one with random pyramids of dimensions of micrometers or fractions of a micrometer). The substrate or wafer may be intended for use in solar power cells or modules, or in semiconductor products. In an embodiment, a thin film of n-type dopants may be placed on top of a light-facing surface of the plate. The first bounded region of the plate may comprise a first layer, which is proximate to a light-facing surface of the plate, and which is lightly doped by n-type dopants. The first bounded region of the plate may further comprise a second layer that is doped by p-type dopants. 
           [0016]    In various embodiments, moving the plate to a second position may comprise translating the plate to the second position, rotating the plate to the second position, or a combination of the two. 
           [0017]    By logically dividing a substrate or wafer into a finite number of regions, which may be similar or dissimilar, and performing a corresponding number of movements (translation, rotation, or a combination of the two) to allow each of a plurality of co-located radiation sources such as a laser light source to irradiate in each of the regions, the techniques described herein can be easily scaled up to process plates of very large planar dimensions. In this context, “logically dividing” refers to dividing without physically breaking. Since a co-located radiation source only irradiates a particular region of much smaller planar dimensions, intensity of the co-located radiation source absorbed by substrates can be easily regulated for irradiating that particular region. Consequently, structural damages such as warping, cracks and grooves can be avoided or mitigated in this region. Smooth radiation results can be accomplished in this region since the region has much smaller dimensions than those of the plate and defocus of laser beam in this small area becomes less. 
           [0018]    In embodiments where a co-located radiation source is a laser light source, the laser light source can be adjusted (e.g., through automatic focusing capability of the optics that is a part of the laser light source) so that much, or all, of a region is within a depth of focus of the laser light source. Well-defined lines of radiation can be created on the region. As applied to creating selective emitter structures on a solar panel, relatively narrow, well-defined lines of metallization and relatively large sunlight receiving areas may be created on the solar cell or panel. 
           [0019]    Each co-located radiation source can be independent from others. As a result, the radiation from each such co-located radiation source independently may pass through a different mask pattern or traverse along a different planar trajectory. Since each co-located radiation source may be independent, any two or more co-located radiation sources can be spatially arranged so that a sufficiently large free space can be provided around any of these co-located radiation sources. This facilitates installation, alignment, calibration, maintenance, and operation of such a system. 
           [0020]    Various embodiments include a system or an apparatus that implements corresponding embodiments of the method as described above. Various embodiments also include products that are produced using corresponding embodiments of the method as described above. These products include solar cells and/or solar panels. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    Techniques for irradiating a plate using multiple co-located radiation sources are described. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the present invention. 
       A First Example System Configuration 
       [0022]    According to an embodiment, as illustrated in  FIG. 1A , a system  100  comprises a platform  102 - 1 , two or more co-located radiation sources (e.g.,  108 - 1  through  108 - 4  as shown). The system  100  may include a stage  220  as illustrated in  FIG. 2A  and  FIG. 2B . A plate  104  may be mounted on the stage. This plate  104  may be irradiated by radiations  112 - 1  through  112 - 4  emitted from the two or more co-located radiation sources  108 . In some embodiments, as shown in  FIG. 1A , the stage may be operable to move along axis  106 - 1 . 
         [0023]    As used herein, the term “co-located radiation source” may refer to any device that provides a form of radiation that may be directed at some points or areas of the plate  104 . Examples of a co-located radiation source include a laser device, an electron beam device, a particle beam device, an ink jet device, etc. The term “radiation” may refer to coherent light, non-coherent light, an electron beam, a particle beam, ink particles, etc. The term “directed at some points or areas of the plate” means that these points or areas of the plate are irradiated by a radiation (e.g., a laser beam) from a co-located radiation source  108 . 
         [0024]    In some embodiments, one or more of the co-located radiation sources  108  may be laser light sources. For example, the co-located radiation source  108 - 2  may be a galvanometer scan laser that provides a laser beam that may be directed at some points or areas of the plate  104 . 
         [0025]    The plate  104  comprises a surface that receives radiations  112  and into which radiations may penetrate or touch. Types of the plate  104  include, but are not limited to, a substrate, a wafer, and a planar object that is of a material, or of a composite of several materials. In some embodiments, the plate  104  is a thin planar object with a height, in a z dimension that is vertical to the surface of the plate much smaller than either of the plate&#39;s planar dimensions (x and y dimensions). For example, the plate  104  may be of a planar dimension of 125 millimeters (hereinafter mm) or 155 mm, while the height of the plate may be 200 micrometers (hereinafter μm). 
         [0026]    The plate  104  comprises two or more regions (e.g.,  110 - 1  through  110 - 4 ). In one embodiment, these regions  110  may be formed by logically dividing or separating the plate  104  vertically (i.e., in the z-direction) along certain lines, or segments of lines, or shapes such as circles and polygons, represented on the surface of the plate  104 . In some embodiments, each of these regions  110  comprises a contiguous, bounded area in the surface that is to receive a radiation  112  from one of the co-located radiation sources  108 . In some embodiments, these regions  110  are non-overlapping and may together cover a part, or all, of a surface of the plate  104 . In some other embodiments, these regions  110 , while each comprising a bounded area, may be partially overlapping with one another. 
         [0027]    For the purpose of illustration only, the plate  104  may be logically divided into four regions  110 - 1  through  110 - 4  as shown in  FIG. 1A . 
         [0028]    In some embodiments, system  100  is operable to place the plate  104  at a plurality of positions (e.g.,  114 - 1 - 1  through  114 - 1 - 4 ) on the platform  102 - 1 . Thus, the positions are stationary relative to the platform  102 . These positions  114 - 1  are aligned with the co-located radiation sources  108  such that one of the co-located radiation sources  108  may irradiate a particular region  110 , which is associated with a particular position  114 - 1  on the platform  102 - 1 , when the plate  104  is placed at the particular position  114 - 1  on the platform  102 - 1 . In some embodiments, each region (e.g.,  110 - 1 ) in a plurality of regions  110  of the plate  104  has a one-to-one correspondence to a different position (e.g.,  114 - 1 - 1 ) among the positions  114 . 
         [0029]    For instance, system  100  is operable to place the plate  104  initially at the position  114 - 1 - 1 . The region  110 - 1  is associated with this position  114 - 1 - 1 . When the plate  104  is at position  114 - 1 - 1 , the co-located radiation source  108 - 1  that is associated with this position  114 - 1 - 1  is operable to irradiate the region  110 - 1 . 
         [0030]    Similarly, the system  100  is operable to place the plate  104  at the position  114 - 1 - 2 . The region  110 - 2  is associated with that position  114 - 1 - 2 . When the plate  104  is at position  114 - 1 - 2 , the co-located radiation source  108 - 2  that is associated with position  114 - 1 - 2  is operable to irradiate the region  110 - 2 . The system may place the plate  104  at positions  114 - 1 - 3  and  114 - 1 - 4  and cause operation of co-located radiation sources  108 - 3 ,  108 - 4 , respectively, at successive times in a similar manner. 
         [0031]    In the embodiment of  FIG. 1A , regions  110 - 1  through  110 - 4  are non-overlapping. Moreover, each of the regions  110  comprises a bounded area on the surface receiving a radiation  112 . The term “bounded area” refers to an area that can be placed entirely inside a circle with a finite radius. In some embodiments, the finite radius is less than 75 percent of one of the planar dimensions of the plate  104 . In some embodiments, the finite radius is less than 50 percent of one of the planar dimensions of the plate  104 . In other embodiments, the finite radius may have other dimensions. 
         [0032]    In some embodiments in which at least one of the co-located radiation sources  108  is a laser device, radiation from such a laser device is coherent light. The coherent light may travel along an optical path from the laser source to points and/or areas on the plate  104 . Along the optical path, there may be lenses, mirrors, splitters, filters, apertures, masks, or other elements that may affect the optical and/or geometric properties of the light  112 . In a particular embodiment, the light  112  may be focused in certain spots (e.g., at a center, at a circle, or a distorted circle, etc) that are located on the plate  104 . Therefore, areas on the plate  104  that are irradiated by the light may take a form of fine lines with a finite width, as shown in  FIG. 1A . The width may have orders of magnitude of one nanometer, ten nanometers, hundred nanometers, one micrometer, ten micrometers, hundred micrometers, and/or one millimeter. In some embodiments, outside this finite width, any unintended light radiation can be safely ignored. 
         [0033]    Other forms of radiation and other types of optics may be provided in zero or more of the co-located radiation sources  108 . For example, in some embodiments, instead of using optics that focuses a coherent light into a narrow area, a non-coherent light co-located radiation source may be operable to create a light that is not narrowly focused. In a few of these embodiments, such a light may have a beam width of over 1 mm. 
         [0034]    In some embodiments, the positions  114 - 1  on the platform  102 - 1  are arranged to permit sufficient free space between the co-located radiation sources  108 . In a particular embodiment, neighboring positions  114 - 1  on the platform  102 - 1  are selected such that each co-located radiation source  108  is easily installed, operated, replaced, or maintained. 
         [0035]    In some embodiments, auxiliary points on the platform  102 - 1  may be defined. The system  100  may be operable to position, through one or more suitable motions, the plate  104  in one of the auxiliary points. When the plate  104  is positioned at an auxiliary point, the system  100  may be operable to perform one or more actions related to the plate  104 . For example, one auxiliary point on the platform  102 - 1  may be defined and used to load the plate, while another auxiliary point on the platform  102 - 1  may be defined and used to unload the plate. Yet another auxiliary point on the platform  102 - 1  may be defined and used to wash the plate. 
         [0036]    In some embodiments, while one of the co-located radiation source  108  irradiates the plate  104  at a particular position on the platform  102 , other co-located radiation sources  108  may irradiate other plates or planar objects in other positions on the platform  102  at the same time. Thus, multiple plates may be pipelined through a sequence of positions defined on the platform  102  so that various tasks can be performed on the multiple plates in parallel at these positions. 
       A Second Example System Configuration 
       [0037]    According to an embodiment of the present invention, the techniques may be performed by the system  100  in an alternative configuration as illustrated in  FIG. 1B . 
         [0038]    In  FIG. 1B  system  100  comprises a platform  102 - 2  and co-located radiation sources  108 - 1  through  108 - 4 . In an embodiment, system  100  comprises a stage  220  ( FIG. 2A ,  FIG. 2B ) on which the plate  104  may be mounted to be irradiated by radiations  112 - 1   112 - 4  from the co-located radiation sources. In some embodiments, as shown in  FIG. 1B , the stage may be operable to rotate the plate  104  through a plurality of positions  114 - 2 - 1  through  114 - 2 - 4  on the platform  102 - 2  in a rotational direction  106 - 2 . In some embodiments, if necessary, once the plate  104  is positioned at any of positions  114 - 2 , the stage may be operable to rotate (spin) around that position  114 - 2  to orient or align the plate  104  with a co-located radiation source that is to irradiate the plate  104  at that position  114 - 2 . 
         [0039]    In the embodiments of  FIG. 1B , system  100  is operable to place the plate  104  at positions  114 - 2 - 1  through  114 - 2 - 4  on the platform  102 - 2 . These positions  114 - 2  are aligned with the co-located radiation sources  108  in such a manner that one of the co-located radiation sources  108  may irradiate a particular region  110  (which is associated with a particular position  114 - 2  on the platform  102 - 2 ) on the plate  104 , when the plate is placed at the particular position on the platform. 
         [0040]    For instance, system  100  as shown in  FIG. 1B  is operable to place the plate  104  initially at position  114 - 2 - 1 . The region  110 - 1  is associated with this position  114 - 2 - 1 . When the plate  104  is at position  114 - 2 - 1 , the co-located radiation source  108 - 1  that is associated with the position  114 - 2 - 1  is operable to irradiate the region  110 - 1 . 
         [0041]    Similarly, system  100  as shown in  FIG. 1B  is operable to place the plate  104  at the position  114 - 2 - 2 . The region  110 - 2  is associated with that position  114 - 2 - 2 . When the plate  104  is at position  114 - 2 - 2 , co-located radiation source  108 - 2  that is associated with the position  114 - 2 - 2  is operable to irradiate the region  110 - 2 . Analogous operation may be used for the positions  114 - 2 - 3  and  114 - 2 - 4 . 
         [0042]    In some embodiments, positions  114 - 2  on platform  102 - 2  are arranged to permit sufficient free space between the co-located radiation sources  108 . In a particular embodiment, a distance between two neighboring points  114 - 2  on the platform  102 - 2  is selected to ensure that each co-located radiation source  108  is easily installed, operated, replaced, or maintained. 
         [0043]    As in  FIG. 1A , in some embodiments, auxiliary points on the platform  102 - 2  as illustrated in  FIG. 1B  may be defined. The system  100  may be operable to position through suitable motions the plate  104  in one of these auxiliary points. At that position, the system  100  may be operable to perform one or more actions related to the plate  104 . For example, an auxiliary point on the platform  102 - 2  may be defined for the purpose of loading the plate. Similarly, another auxiliary point on the platform  102 - 2  may be defined for the purpose of unloading the plate. Yet another auxiliary point on the platform  102 - 2  may be defined for the purpose of washing the plate. 
       Additional and/or Alternative Configurations 
       [0044]    At a position  114 , a region  110  on a plate  104  may be irradiated by a co-located radiation source  108 . Alternatively, depending on an application of the system  100 , at a position  114 , the plate  104  may not be irradiated. Furthermore, in some embodiments, at a position  114 , system  100  may perform one or more actions other than irradiation, and/or in addition to irradiation. These actions may include, but are not limited to, spinning the plate  104  to a desired orientation in the planar dimensions, aligning a co-located radiation source  108  with the plate, automatically focusing a radiation at a particular depth within, or at a distance away from, the plate, directing a radiation to different points or areas on the plate, and adjusting the intensity of the radiation. 
         [0045]    In some embodiments, the system  100  may be operable to step the plate  104  through the positions  114  in a manner such that distances between successive positions are minimized and/or that the number or types of motions involved between successive positions are minimized. For example, in the configuration of  FIG. 1A , system  100  may be operable to move the plate  114  in sequence to successive positions along the imaginary straight-line axis  106 - 1 . Each such movement may be denoted a step. Similarly, in the alternative configuration as illustrated in  FIG. 1B , the system  100  may be operable to move the plate  114  in sequence along the rotational direction  106 - 2  to different positions in different steps. 
         [0046]    In some embodiments, the co-located radiation sources  108  may be pre-positioned in the system  100  in such a way that spinning around any of the positions  114  is minimized or that the effort involved in aligning the co-located radiation sources  108  and the plate  104  is minimized. 
         [0047]    In some embodiments, the laser device may optionally and/or additionally comprise modulation devices, amplifiers, drivers, and control logic.  FIG. 1C  is a block diagram that illustrates an example configuration of system  100 , which comprises a system controller  140 . System controller  140  is operatively linked to other parts of system  100 , such as the radiation sources  108 , the stage  220 , and/or the platform  102  and controls and coordinates operations of various parts of system  100  for the purpose of obtaining status of and exercising control over these other parts of system  100 . In some embodiments, system controller  140  comprises plate positioning logic  142  that controls a conveyance mechanism to move the plate  104  to various positions  114  on the platform  102 , radiation source selection logic  144  that selects a radiation source  108  for a particular position  114 , bounded region selection logic  146  that determines which bounded region/area is to be radiated on, and radiation logic  148  that controls a radiation  112  by the selected radiation source over the selected bounded region at the particular position  114 . 
       Example Laser Scribing 
       [0048]    In some embodiments, the co-located radiation sources  108  of  FIG. 1A  and  FIG. 1B  are laser light sources. The plate  104  is a single semiconductor wafer that undergoes a manufacturing process to become a part of a solar panel product. As part of this manufacturing process, as shown in  FIG. 2A , a region  110  of the plate  104  (e.g.,  110 - 2  of  FIG. 1A  or  FIG. 1B ) may be placed in position for radiation from a laser light source  108  (in this example,  108 - 2  of  FIG. 1A  or  FIG. 1B ) when the plate  104  is placed at the position  114 - 1 - 2  of  FIG. 1A  or at the position  114 - 2 - 2 . In some embodiments, the plate  104  including the region  110  is mounted on a stage  220 , which may be fixed, or moved relative to, relative to a platform  102  (which may be  102 - 1  of  FIG. 1A  or  102 - 2  of  FIG. 1B ). 
         [0049]    Referring now to  FIG. 2A , the irradiation of the region  110  by the laser light source  108  is one of a plurality of phases in a manufacturing process to create one or more high doped areas in the region  110 , in order to enhance the solar panel product&#39;s ability to collect electric charges in the region when the product is deployed in the field. 
         [0050]    The region  110  or the semiconductor wafer may initially comprise two layers  204 ,  206  that form a photovoltaic p-n junction. A first layer is a p-type conductivity layer  206  and the second layer is an n-type conductivity layer  204 . In some embodiments, in order to increase the sheet resistance, the n-type conductivity layer  204  is relatively lightly doped with a suitable type of n-dopants and thus may be denoted as an n −  layer. However, variations of n-type of doping in the layer  204  at various concentration levels of n-type dopants may be used in different embodiments. 
         [0051]    As a part of creating the selective emitter structure, the system  100  may be operable to first create a structure  212  with a relatively high n-dopant concentration, denoted as an n +  structure. Thus, the system  100  may be used to perform laser doping in selected sub-regions of the region  110  of the semiconductor wafer  104 . 
         [0052]    In some embodiments, a thin film  208  containing n-dopants may first be formed on top of the n −  layer  204 . Subsequently, the laser light source  108  is operable to send radiation  112  in the form of a laser beam that focuses at a spot  210  of the semiconductor wafer  104 . As result of this radiation  112 , a sub-region of the wafer near the spot  210  receives a heat shock, in the form of a rapid raising and subsequent lowering of temperature, causing the n-dopants contained in the thin film  208  to diffuse inside the n −  layer  204  near the spot  210 , thereby creating the structure  212  with a relatively high concentration of n-dopants. 
         [0053]    In some embodiments, the laser light source  108  is a galvanometer scan laser. The laser light source  108  is operable to shift the incident direction of the laser beam  112  to various points in the x-y plane that is vertical to the z axis. In some embodiments, the structure  212  that has a relatively high concentration of n-dopants appears as interconnected parallel lines on the region  110 , as viewed from the vertical direction (along the −z axis) to the plate  104 . 
         [0054]    Metal lines may thereafter be deposited over the n +  structure  212 , as created by the laser doping described above. The deposition of metal over the n +  structure  212  may be done using a suitable metallization technique including but not limited to electroplating or electroless plating. In some embodiments, these metal lines form electrically interconnected connected lines. In various embodiments, various interconnection patterns may be used. As a result, selective emitter structures with a relatively low serial resistance may be created in the region  110  of the plate  104 . 
       Example Semiconductor Wafers 
       [0055]    In various embodiments, the semiconductor wafer  104  may be either mono-crystalline, polycrystalline, or amorphous silicon, or other materials such as TCO. In some embodiments, the height of the region  110  in the plate  104  is between 50 μm and 5 mm. In a particular embodiment, this height is 100-300 μm. 
         [0056]    In some embodiments, typical planar dimensions of the region  110  may be between 10 mm and 300 mm. In a particular embodiment, such a planar dimension is 100-200 mm. In some embodiments, the height of the n −  layer  204  is between 0.1 μm and 3 μm. In a particular embodiment, this height is 0.3 μm. 
         [0057]    In some embodiments, the thickness of the thin film  208  of dopants is between 1 nanometer (hereinafter nm) and 1000 nm. In a particular embodiment, this thickness is 100 nm. 
         [0058]    In some embodiments, the laser beam  112  from the laser light source  108  is non-pulsed. However, in some other embodiments, the laser beam  112  from the laser light source  108  is pulsed with a frequency that is suitable for a particular application of the system  100 . 
         [0059]    In various embodiments, the p layer  206  is doped with suitable p-type dopants at various levels of concentrations. In a particular embodiment, the p layer  206  is doped with boron ions B +  with a concentration level of 1*10 15˜1*10   16 . 
         [0060]    In various embodiments, the n −  layer  204  is doped with suitable n-type dopants. In a particular embodiment, then layer  204  is doped with 5*10 16˜5*10   20 . 
       Example Laser Light Sources 
       [0061]    In some embodiments, the laser beam  112  has an intensity that is regulated within a range of power values. As used herein, the term “intensity” means an average intensity used to irradiate a spot (which may be of a width of several mm, a fraction of mm, several nm, several tens or hundreds of nm, etc. depending on applications) for a duration (which may be a time period of several nanoseconds, several tens of nanoseconds, several hundreds of nanoseconds, etc. depending on applications). In an embodiment, the intensity is limited by an upper bound value. In another embodiment, the intensity is limited by a lower bound value. In some embodiments, this intensity may be of several hundred watts to several kilowatts. Depending on applications of new techniques as described herein, the intensity may be of other values (e.g., several tens of watts, several watts, several tens of kilowatts, etc.). In some embodiments, the laser beam  112  may, but is not limited to, be generated from a commercially available Nd:YAG laser system. 
         [0062]    In some embodiments, the laser beam  112  is polychromatic, comprising a plurality of wavelengths. In some other embodiments, the laser beam  112  is monochromatic and of a single wavelength whose value, for example, falls between 100 nm and 2200 nm. In a particular embodiment, this wavelength is within a range of wavelength such as between 500 nm and 1000 nm, inclusive. For some applications, this single wavelength is greater than a threshold wavelength. For some other applications, this single wavelength is lower than a threshold wavelength. 
         [0063]    It should be noted that values as described herein are for illustration purposes only. For example, other wavelengths and other power ratings of a laser light source may be also used, depending the types of applications that use new techniques as described herein. 
         [0064]    In some embodiments, the system  100  (or the laser light device  108  therein) is operable to focus the laser beam  112  at the center of the region  110 . In some other embodiments, the laser light device  108  is operable to focus the laser beam  112  at a spot that is different from the center of the region  110 . In these other embodiments, for example, the laser beam  112  may focus at the spot  210  as shown in  FIG. 2A . In example embodiments, the focus spot may be between 0 mm and 100 mm away from the center of the region  110 . In an example embodiment, the focus spot is 70 mm away from the center. 
         [0065]    In some embodiments, instead of focusing at a spot (e.g.,  210  of  FIG. 2A ) right on the upper surface of the plate  104 , the laser beam  112  may focus at a spot that is above or below the spot on the surface. In some embodiments of laser doping, the focus of the laser beam may be at a spot that is slightly above or below the surface through which the radiation enters. The distance between the focused spot and the surface may be between 0 nm and 1 mm. 
         [0066]    In some embodiments, the optics of the laser light source  108  is of a depth (of focus) within which the laser beam  112  is deemed as focused. As the laser beam  112  scans the region  110 , some sub-regions in the region  110  may or may not be located within the depth of focus of the laser light source. Thus, in some embodiments, the region  110  is entirely within the depth of focus, for example, when the region  110  is small enough so as to be within the capability of the optics of the laser light source  108 . 
         [0067]    In some other embodiments where the region  110  is large enough so that irradiating some sub-regions of the region  110  exceeds the capability of the optics of the laser light source  108 . In some embodiments, as only a portion of the region  110  lies within the depth of focus, irradiation of the laser beam on various spots of the region  110  may not be completely uniform. In some other embodiments, the system  100  is operable to restrict irradiating the plate  104  to sub-regions of the region  110  within its depth of focus. 
         [0068]    The techniques herein can be used to create selective high n-doped sub-regions in a region  110  of  FIG. 2A  of a semiconductor wafer that comprises an n layer and a p layer. In other embodiments, the techniques herein can be used to cut a contiguous thin film that has been formed on a glass substrate. Using multiple co-located radiation sources to radiate multiple regions of a plate that is movable to various positions may be applied for other purposes and products. 
         [0069]    For the purpose of illustrating a clear example, each radiation  112  at a particular position  114  has been described as using a separate co-located radiation source  108 . However, in other embodiments, a common co-located radiation source  108  may be used to provide two or more radiations  112 . For example, in an alternative embodiment where a co-located radiation source  108  is a laser light source, a light from such a laser light source may be split, additionally and/or alternatively redirected, to provide lights at two or more positions  114 . 
       Example Configuration Using a Stationary Laser 
       [0070]      FIG. 2B  illustrates irradiating a region  110  of the plate  104  for laser doping applications using a stationary laser. In  FIG. 2B , the laser beam  112  is stationary with respect to the laser light source  108  and to the platform  102 . Thus, the laser beam  112  does not shift its direction within the x-y plane that is vertical to the z-axis (which is normal to the light-facing surface of the region  110 ). For example, the laser beam  112  may maintain a direction that is vertical to the region  110 . 
         [0071]    In this alternative, the stage may make relative motions in the x-y plane relative to and about the position  114  to which the plate  104  is placed so that the region  110  (e.g.,  110 - 1 - 2  of  FIG. 1A ) as shown in  FIG. 2B  is irradiated by a corresponding laser light source  108  (i.e.,  108 - 2  of  FIG. 1A ) as shown in  FIG. 2B . These relative motions with reference to the position  114  may be made in a particular manner so that a desired radiation pattern is made on the region  110 . 
       Some Other Example Applications 
       [0072]    An application of creating a highly doped structure with n-type dopants on a plurality of regions of a single plate is just one example application. It should be noted, however, the present invention is not so limited. Techniques as described herein can be used in many other applications. For example, another application may be creating a highly doped area or region with p-dopants using techniques as described herein. Furthermore, other applications using techniques as described herein are within the scope of the present invention. 
         [0073]      FIG. 2C  illustrates another example application in which irradiation of a region  110  by a laser light source  108  is one of a plurality of phases in a manufacturing process to create laser fired contacts in the region  110  (as in other figures,  FIG. 2C  is provided for illustration purposes only; dimensions in  FIG. 2C  are not necessarily proportionally drawn from actual systems). 
         [0074]    The region  110  may be initially a semiconductor wafer comprising a p-type conductivity layer and an n-type conductivity layer. Although only the p-type conductivity layer is illustrated as  236  of  FIG. 2C , it may be understood that the n-type conductivity layer may be situated proximate to and right below the p-type conductivity layer in  FIG. 2C . In some embodiments, in order to reduce loss of solar energy and to create surface passivation, a dielectric reflective layer  234  with a suitable refractive index may be placed on top of the p-type conductivity layer  236  (the top surface of which is a rear surface of a solar cell when deployed in the field). This dielectric reflective layer  234  may be of a thickness of, for example, 5 nm to 300 nm (other thickness may also be used). In some embodiments, this dielectric reflective layer  234  may be made of sub-layers. In a particular embodiment, this dielectric reflective layer  234  may comprise a sub-layer of PECVD-SiN x  and another sub-layer of PECVD-SiO x , with various thickness dimensions of the sub-layers (not illustrated in  FIG. 2C ). 
         [0075]    In some embodiments, an aluminum layer  238  is pre-deposited on top of the dielectric reflective layer  234 . To provide an efficient positive electrode to the photovoltaic junction formed by the n-type conductivity layer and the p-type conductivity layer, a good metallic connection between the aluminum layer  238  and the p-type conductivity layer  236  (through the dielectric reflective layer) may be desired. In some embodiments, the system  100  may be operable to create laser fired contacts (LFCs) between the aluminum layer  238  and the p-type conductivity layer structure  236  through the dielectric reflective layer  234 . 
         [0076]    For example, with a radiation  112 , a sub-region of the wafer near the spot  230  receives a heat shock, causing metallic materials in the aluminum layer  238  to penetrate the dielectric reflective layer  234  near the spot  230  and to reach inside the p-type conductivity layer (silicon)  236 , thereby creating a laser fired contact  232  at the spot  230 . 
         [0077]    In some embodiments, the laser light source  108  may be a pulsed galvanometer scan laser. The laser light source  108  is operable to shift the incident direction of the laser beam  112  to various points in the x-y plane that is vertical to the z axis. In some embodiments, as the laser beam  112  moves, a plurality of laser fired contacts may be created in the region  110 . 
         [0078]    In some embodiments, instead of using a laser beam such as  112  illustrated in  FIG. 2C , a suitable optical mask may be used to create a pattern on the top surface of the aluminum layer/film  238 . For example, the pattern may be formed as a grid of points in the region  110 . Only these points are simultaneously irradiated with laser light. In these embodiments, a plurality of laser fired contacts may be created simultaneously. In various embodiments, various LFC patterns may be used and formed in the region  110 . As a result, an efficient positive electrode may be created in the region  110  of the plate  104  in the rear side (i.e., the top surface as shown in  FIG. 2C ) of a solar cell. 
       Example Process Flow 
       [0079]      FIG. 3  illustrates an example process of irradiating a plate (e.g.,  104 ) using a system such as  100  of  FIG. 1A  or  FIG. 2A . For the purpose of illustrating a clear example,  FIG. 3  is described with reference to  FIG. 1A ,  FIG. 1C , and  FIG. 2A . 
         [0080]    In block  320 , the system  100  is operable to invoke the plate positioning logic  142  to cause the plate  104  to be placed at a first position  114 - 1 - 1 . 
         [0081]    In block  320 , the system  100  is operable to cause a first radiation from a first co-located radiation source to irradiate within a first bounded region of a plate  104 . For example, in block  320 , the system  100  may invoke radiation selection logic  144  to select the first co-located radiation source in the plurality of co-located radiation sources. The system  100  may also invoke bounded region selection logic  146  to determine that the region to be irradiated on is the first bounded region of the plate  104 . The first bounded region  110 - 1  is one of a plurality of bounded regions of the plate  110 - 1  through  110 - 4 . 
         [0082]    In some embodiments, the system  100  may invoke radiation operation logic  148  to provide a radiation  112 - 1  in the form of a laser beam from a co-located radiation source  108  to irradiate within a first bounded region  110 - 1  of plate  104 . 
         [0083]    In the present example, irradiation of the first bounded region  110 - 1  by the first light source occurs before irradiation of other regions  110 - 2  through  110 - 4 . However, in other embodiments, one or more other regions  110  may have already been irradiated before the first bounded region  110 - 1  is irradiated in block  320 . 
         [0084]    In block  330 , the plate is moved to a second position. For example, the system  100  is operable to invoke the plate positioning logic  142  to cause the plate  104  to be placed at a second position  114 - 1 - 2 . This occurs, for example, in response to that the system  100  has finished irradiating the region  110 - 1  at the position  114 - 1 - 1 . In some embodiments, during moving the plate  104  from one position to another position, the system  100  is operable to avoid and/or prevent irradiating any spot of the plate  104  by any radiation source  108 . In a particular embodiment, when the plate  104  is being moved from one position to the next position, some or all of the radiation sources  108  may be in a state in which there is no radiation (e.g., laser light) being emitted by the radiation sources  108 . 
         [0085]    In some embodiments, the plate is mounted on and fixed relative to a stage. Moving the stage to the second position may include translating the stage to the second position, or rotating the stage to the second position, or moving the stage to the second position using both rotation and translation. In some other embodiments, other types of conveying mechanisms (e.g., a conveyor belt) other than a stage type may be used. In still other embodiments, one or more stages may be combined with one or more conveying mechanisms of one or more other types. For example, in some embodiments, a conveyor belt is used to move a stage from one position to another position while the stage is used to make planar motions relative to a position. 
         [0086]    In some embodiments where a light (e.g.,  112 - 2 ) from a laser light source (e.g.,  108 - 2 ) can shift its incident direction in the x-y plane during irradiating the plate  104 , as shown in  FIG. 2A , the system  100  is operable to cause the plate  104  to be fixed at a position (e.g.,  114 - 1 - 2 ) of, and stationary relative to, the platform  102  during irradiating by the laser (i.e.,  112 - 2 ) at the position (i.e.,  114 - 1 - 2 ). 
         [0087]    In block  340 , a second radiation from a second co-located radiation source is used to irradiate within a second bounded region of the plate. For example, regardless of whether the stage (or another mechanism) on which the plate  104  is mounted can move relative to the position  114 - 1 - 2  during irradiating the plate  104  at that position, the system  100  is operable to use a second light (which, for example, may be a laser beam  112 - 2 ) obtained from a second light source  108 - 2  (which, for example, may be a laser device) to irradiate within a second bounded region  110 - 2  of the plate  104 . As illustrated, the second light source  108 - 2  is different from the first light source  108 - 1  among the plurality of light sources  108 . The second bounded region  110 - 2  is different from the first bounded region  110 - 1  among the plurality of bounded regions  110  of the plate  104 . 
         [0088]    In the foregoing specification, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. Thus, the sole and exclusive indicator of what is the invention, and is intended by the applicants to be the invention, is the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction. Any definitions expressly set forth herein for terms contained in such claims shall govern the meaning of such terms as used in the claims. Hence, no limitation, element, property, feature, advantage or attribute that is not expressly recited in a claim should limit the scope of such claim in any way. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.