Abstract:
Methods and apparatuses for forming optical packages, and intermediate structures resulting from the same are disclosed, which provide an optical element over a device. The optical element is formed by applying a force to lateral portions of a liquid material layer formed below an elastomeric material layer such that the liquid material layer has a radius of curvature sufficient to direct light to a light sensitive portion of the device, after which the liquid material layer is exposed to conditions which maintain the radius of curvature after the lateral force is removed.

Description:
FIELD OF THE INVENTION 
   The embodiments described herein relate to methods of fabricating optical packages and systems having the same and, more particularly, to an adaptive formation of optical elements, and uses thereof. 
   BACKGROUND OF THE INVENTION 
   Conventional optical packages, which comprise an optical element formed in association with a corresponding imager, are often made simultaneously such that hundreds or even thousands of optical packages are formed on a single wafer. The wafer is then diced to create individual optical packages that are subsequently incorporated into digital systems, such as, for example, digital cameras, digital displays, and other light receiving or light emitting devices. 
   One drawback of forming multiple optical packages on a single wafer is that optical precision across an entire wafer on which optical elements are typically formed is inconsistent. Each imager has its own optical variation due to slight misalignments during its fabrication. For example, a first imager may have an ideal focal depth at which light is absorbed that is different from a second imager formed on the same substrate, even one that may be adjacent to the first imager. Conventional methods of forming optical elements, however, do not account for the individual focal lengths for each imager. As a result, conventional methods of forming optical elements may not achieve the ideal focal properties required in high end digital systems, such as, for example, digital cameras, digital displays, and other light receiving or light emitting devices. 
   Accordingly, there is a desire and need for a method of fabricating multiple optical packages with optical elements that are tailored to each imager to mitigate against the shortcomings of conventional optical packages. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a partial cross-sectional view of an optical package constructed in accordance with an embodiment discussed herein. 
       FIGS. 2-5  illustrate partial cross-sectional views of an embodiment of fabricating the optical package illustrated in  FIG. 1 . 
       FIG. 6  illustrates a partial cross-sectional view of an optional step of fabricating the optical package illustrated in  FIG. 1 . 
       FIG. 7  illustrates a flow chart of optional steps of fabricating the  FIG. 1  optical package  100 . 
       FIG. 8  illustrates a partial cross-sectional view of an optional step of processing the  FIG. 4  structure in accordance with a second embodiment discussed herein. 
       FIG. 9  illustrates a partial cross-sectional view of an optical package constructed in accordance with a third embodiment discussed herein. 
       FIG. 10  illustrates a partial cross-sectional view of an embodiment of fabricating the optical package illustrated in  FIG. 9 . 
       FIG. 11  illustrates a partial cross-sectional view of an optical package constructed in accordance with a fourth embodiment discussed herein. 
       FIG. 12  illustrates a partial cross-sectional view of an optical package constructed in accordance with a fourth embodiment discussed herein. 
       FIG. 13  is a partial top-down block diagram view of the optical package illustrated in  FIG. 1 . 
       FIG. 14  is a partial top-down block diagram view of a plurality of  FIG. 13  optical packages. 
       FIG. 15  illustrates a system having the optical package illustrated in  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In the following detailed description, reference is made to various specific embodiments. These embodiments are described with sufficient detail to enable those skilled in the art to practice the embodiments, and it is to be understood that other embodiments may be employed, and that structural and electrical changes may be made. 
   The term “substrate” used in the following description may include any supporting structure including, but not limited to, a semiconductor substrate that has an exposed substrate surface. A semiconductor substrate should be understood to include silicon, silicon-on-insulator (SOI), silicon-on-sapphire (SOS), doped and undoped semiconductors, epitaxial layers of silicon supported by a base semiconductor foundation, and other semiconductor structures, including those made of semiconductors other than silicon. When reference is made to a semiconductor substrate or wafer in the following description, previous process steps may have been utilized to form regions or junctions in or over the base semiconductor or foundation. The substrate also need not be semiconductor-based, but may be any support structure suitable for supporting an integrated circuit, including, but not limited to, metals, alloys, glasses, polymers, ceramics, and any other supportive materials as is known in the art. 
   As used herein, the term “elastomeric material” and “flexible material” are to be understood to include any material, including, but not limited to, epoxy, polyimide, polyester, or any other material capable of withstanding a 180° angle bend at a radius of at least ⅛ inch or less. Similarly, an “elastomeric material” or “flexible material” may be any material having substantially the same or equivalent properties as DuPont Kapton® or Oasis®. Specifically, the material may have a tensile strength of about 10 kpsi or greater, a tensile modulus of about 200 kpsi or greater, and/or an elongation property of about 25% or more (values based on ASTM D-882-83 Method A). 
   Embodiments are now explained with reference to the figures, throughout which like reference numbers indicate like features.  FIG. 1  is a partial cross-sectional view of an optical package  100  having an optical element  10  capable of being adjusted such that the optical element  10  focuses light onto a light sensing region  12  of the optical package  100 . The adjustability of the focal depth associated with the optical element  10  allows for more efficient light capture by the light sensing region, and a clearer resulting picture (in the case the optical package  100  is included in a digital camera system, as discussed below with respect to  FIG. 13 ). 
   The  FIG. 1  optical package  100  includes a wafer  14  supporting the light sensing region  12 . The light sensing region  12  could comprise hundreds or even thousands of pixel cells, each having a photosensitive region; the photosensitive regions could be photodiodes, photogates, photosensors, or any combination thereof. The optical element  10  is formed over the light sensing region  12 . The optical element  10  comprises an elastomeric membrane  16  formed over a material layer  18 . The material layer  18  may comprise any transparent material that has an initially fluid state capable of being hardened upon exposure to appropriate conditions, such as, for example, ultraviolet radiation (e.g., UV light) or heat (in the case of, for example, thermally cured compounds). 
   Additional components of the  FIG. 1  optical package  100  include thru-wafer interconnects  20 , which may connect to solder balls  22  connected to probe contacts  24 . The solder balls  22  and probe contacts provide electrical connectivity from the light sensing region  12  of the optical package  100  to peripheral circuitry. 
   It should be noted that a plurality of optical packages (e.g., optical package  100 ) is typically formed on a single wafer that is subsequently diced to create individual optical packages. The illustrated wafer  14  provides scribes  26  (illustrated schematically) that are used to dice the wafer  14  to create individual optical packages  100  that are typically incorporated into digital systems, such as, for example, digital cameras, digital displays, and other light receiving or light emitting devices. 
   It should also be noted that although described as a light sensing region  12  capable of capturing light, the embodiments of the invention are not so limited. For example, the light sensing region  12  could instead be a light emitting region such as those used in Liquid Crystal Display (LCD) devices. For simplified description, region  12  is described as a light sensing region  12 , which may be used, for example, in CMOS, CCD or other solid state image capturing devices. 
     FIGS. 2-5  illustrate an embodiment of a method of forming the  FIG. 1  optical package  100 . Specifically,  FIG. 2  illustrates the light sensing region  12  formed in association with the wafer  14 . As illustrated, the light sensing region  12  is formed at a topmost surface  14   a  of the wafer  14 ; it should be noted, however, that the illustration is not intended to be limiting in any way. For example, the light sensing region  12  could be formed over the topmost surface  14   a  of the wafer  14  or at a predetermined depth below the topmost surface  14   a  of the wafer  14 . Indeed, the light sensing region  12  could be a backside illuminated region that is formed in association with a bottom most surface  14   b  of the wafer  14 . 
   The  FIG. 2  wafer  14  includes the thru-wafer interconnects  20  that may connect with solder balls  22  connected to probe contacts  24 . The solder balls  22  and probe contacts  24  may provide electrical connectivity from the light sensing region  12  of the optical package  100  to peripheral circuitry. The scribes  26  are also provided; it should be noted, however, that the scribes  26  can be formed subsequent to the formation of the material layer  18  ( FIG. 1 ), and need not be provided in the wafer  14  at this stage. 
     FIG. 2  also illustrates a drop of a material layer precursor  18   a  formed between the light sensing region  12  and the elastomeric membrane  16 . The illustrated material layer precursor  18   a  has a shapeable fluid form, and may be selected from any negative photoresist known in the art, such as, for example, SU-8 (IBM), or NR9-1500PY (Norland). Alternatively, the material layer precursor  18   a  may also be selected from any polymer capable of being hardened, such as, for example, polydimethylsiloxane (PDMS) polymer or polyethylene terephthalate (PET). 
   It should be noted that the listed compounds are merely examples of the classes of materials the material layer precursor  18   a  could comprise, and is not intended to be limiting in any way. For example, the material layer precursor  18   a  could be formed of any material that is capable of being deposited in an amorphous state and subsequently hardened to retain its hardened shape at room temperature. 
     FIG. 3  illustrates a shaping element  30  that includes vertical and horizontal structures  32 ,  34  provided over the elastomeric membrane  16 . The illustrated vertical structure  32  is adjustable in a vertical direction (i.e., in a direction substantially perpendicular to the topmost surface  14   a  of the wafer) as illustrated by arrows V. The illustrated horizontal structure  34  is adjustable in a horizontal direction (i.e., in a direction substantially parallel to the topmost surface  14   a  of the wafer) as illustrated by arrows H. 
   As illustrated in  FIG. 4 , the vertical and horizontal structures  32 ,  34  are used to exert pressure (at every angle) on the elastomeric membrane  16  to change the shape of the material layer precursor  18   a  in both height (x) and width (y); the changes in shape (e.g.,  18   b ,  18   c ) of the material layer precursor  18   a  allows for the adjustment of the focal depth of the resulting material layer  18  ( FIG. 1 ). The radius of curvature (as measured from the topmost surface  14   a  of the wafer  14 ) can be adjusted to achieve a desired focal depth of light passing through the resulting material layer  18  ( FIG. 1 ). 
   Once a desired focal depth has been achieved, the material layer precursor  18   a  is exposed to curable condition such as, for example, ultraviolet (UV) radiation emitted from a pair of UV sources  36 , as illustrated in  FIG. 5 , which is positioned over the material layer precursor  18   a . The exposure to UV radiation polymerizes the material layer precursor  18   a  to result in a hardened material layer  18  that serves as a lens. The shaping element  30  can be removed, and the optical package  100  can be separated from adjacent optical packages on the wafer  14 . 
   It should be noted that the material layer precursor  18   a  could be formed of a thermally cured compound in which case the UV sources  36  would be replaced by heating elements. The heating elements would expose the entire optical package  100  to heat, and cure (or harden) the material layer precursor  18   a  comprising a thermally curable compound. It should also be noted that other materials that are have an initially fluid state that can be hardened upon exposure to certain conditions could also be implemented in the embodiments illustrated in  FIGS. 1-5  discussed above, and  FIGS. 6-12  discussed herein. 
     FIG. 6  illustrates a partial cross-sectional view of an optional step performed between the steps illustrated in  FIGS. 4 and 5 . Specifically, during the adjustment of the material layer precursor  18   a  ( FIG. 4 ) and prior to curing the material layer precursor  18   a  ( FIG. 5 ), a probe fixture  40  is placed over the optical package  100  to test the resulting image taken and output by the optical package  100 . The illustrated probe fixture  40  includes a light source  42 , a first lens layer  44 , a test image  46 , and a second lens layer  48 . Generally speaking, the test image  46  is placed between the light source  42  and the optical package  100  such that the light sensing region  12  captures light  50  from the test image  46 , and displays the captured image  47  on a peripheral display device  49 , such as, for example, a computer screen or Liquid Crystal Display (LCD) monitor. 
   The height (x) and width (y) ( FIG. 4 ) of the material layer precursor  18   a  can be adjusted by the shaping element  30  if the displayed image  47  is out of focus. Once the material layer precursor  18   a  is adjusted by the shaping element  30  such that the displayed image  47  is in focus, the material layer precursor  18   a  is hardened (in this example, the material layer precursor  18   a  is exposed to UV radiation by the UV sources  36 , polymerizing the material layer precursor  18   a ). 
   The probe fixture  40  allows for probe-time testing of the image quality of the optical package  100  prior to fixing the shape of the material layer  18  ( FIG. 1 ). By having the capability of changing the shape of the material layer  18  ( FIG. 1 ), the focal length of the material layer  18  ( FIG. 1 ) can be varied for each particular optical package  100  on the wafer  14 . 
   The probe testing of the image quality of the optical package  100  can be performed automatically.  FIG. 7  illustrates a flow chart of automatic processing of the optical package  100  ( FIG. 6 ). Specifically, step  710  illustrates fabricating the optical package  100  ( FIG. 1 ) with the material layer precursor  18   a  ( FIG. 6 ) in a substantially fluid state. The probe fixture  40  ( FIG. 6 ) is provided over the optical package  100  ( FIG. 6 ) in step  720 . The light sensing region  12  of the optical package  100  ( FIG. 6 ) is subsequently exposed to light  50  ( FIG. 6 ) in step  730 , and an image is captured by the optical package  100  ( FIG. 6 ) in step  740 . The captured image  47  ( FIG. 6 ) is subsequently analyzed to determine whether it is in focus in step  750 ; if the captured image  47  ( FIG. 6 ) is not in focus (a “NO” response after step  750 ), the shaping element  30  ( FIG. 6 ) is adjusted to direct the shape of the material layer precursor  18   a  ( FIG. 6 ) in step  760 . 
   A processor  780  may determine whether the captured image  47  ( FIG. 6 ) is in focus, and whether an adjustment is required based on the determination that the captured is either in or out of focus. The processor  780  may have bi-directional communication capabilities with the optical package  100  ( FIG. 6 ) and the shaping element  30  ( FIG. 6 ). The processor  780  may drive the adjustments of the shaping element  30  ( FIG. 6 ). 
   Once the desired adjustments are made to the material layer precursor  18   a  ( FIG. 6 ), the material layer precursor  18   a  ( FIG. 6 ) may be exposed to curable conditions in step  790 . The curable conditions cure the material layer precursor  18   a  ( FIG. 6 ) such that it hardens, and maintains its shape. In an optional step, the optical package  100  ( FIG. 6 ) is retested by shining light onto the light sensing region  12  of the optical package  100  ( FIG. 6 ) in step  730 , and the process repeats itself (steps  740 ,  750 ,  760 ) until the captured image  47  ( FIG. 6 ) is in focus (a “YES” response after step  750 ), and the material layer precursor  18   a  ( FIG. 6 ) is exposed to curable conditions in step  790 . As discussed above, the curable conditions cure the material layer precursor  18   a  ( FIG. 6 ) such that it hardens, and maintains its shape. 
     FIG. 8  illustrates a partial cross-sectional view of another optional step performed after the formation of the  FIG. 5  structure. A second material layer precursor  19  is formed over the material layer  118 . The second material layer precursor  19  could have substantially similar properties as the material layer precursor  18  ( FIG. 4 ); for example, the second material layer precursor  19  could have a substantially fluid state. A second elastomeric membrane  17  is formed over the second material layer precursor  19 , and the shaping element  30  is used to shape the second material layer precursor in a substantially similar manner as that discussed above with respect to  FIG. 4 . Once the second material layer precursor  19  has achieved the desired shape, it can be cured in a substantially similar manner as the precursor material layer  18  ( FIG. 4 ), as discussed above with respect to  FIG. 5 . 
   Although illustrated as being formed over the cured material layer  118 , it should be noted that the precursor material layer  18  ( FIG. 4 ) and the second material layer precursor  19  could be shaped by the shaping element  30  simultaneously. It should also be noted that the optional steps discussed above with respect to  FIG. 7  could be performed on the  FIG. 8  structure (or any other structure discussed below) prior to exposing it to curable conditions. Additional precursor materials having substantially similar properties as the material layer precursor  18  and the second material layer precursor  19  could be formed as an optical stack element focusing light  50  ( FIG. 6 ) onto the light sensing region  12 . 
     FIG. 9  illustrates a partial cross-sectional view of a third embodiment of an optical package  200  formed in a substantially similar manner as the  FIG. 1  optical package  100 , discussed above with respect to the embodiments illustrated in  FIGS. 2-7 . The  FIG. 8  optical package  200  has an optical element  110  that includes a material layer  118  formed between an elastomeric material layer  116  and a planarizing layer  115 . 
   As illustrated in  FIG. 10 , the  FIG. 9  material layer  118  is formed by squeezing a material layer precursor  118   a , having a substantially fluid state, in a space  111  formed between the elastomeric material layer  116  and the planarizing layer  115 . The planarizing layer  115  could be formed of any substantially transparent material, including, but not limited to, a material forming the elastomeric material layer  116 . 
   Once the fluid material layer precursor  118   a  is inserted between the elastomeric material layer  116  and the planarizing layer  115 , the material layer precursor  118   a  can be positioned (indicated by the dashed line  118 ) over the light sensing region  12 . The shaping element  30  then exerts pressure on the elastomeric material layer  116  to direct the shape of the material layer precursor  118   a  formed below the elastomeric material layer  116 . Once the desired characteristics (or shape) of the material layer precursor  118   a  is achieved, the material layer precursor  118   a  is exposed to curable conditions; in this example, the curable condition includes UV radiation from the pair of UV sources  36 . 
   The optical package  200  of  FIGS. 9 and 10  allow blanket deposition of material layers (e.g., the elastomeric material layer  116  and the planarizing layer  115 ) prior to forming the material layer  118  ( FIG. 9 ). The insertion of the material layer precursor  118   a  through the space  111  ( FIG. 10 ) allows formation of the material layer  118  ( FIG. 9 ) over select light sensitive regions  12  in the array. This allows flexibility in the fabrication process. 
     FIG. 110  illustrates a partial cross-sectional view of a fourth embodiment in which an optical package  300  includes an optical element  210  comprising a shaping lens layer  215 , a material layer  218 , and an elastomeric material layer  216 . The shaping lens layer  215  reduces the amount of pressure required to shape the material layer  218  through use of the shaping element  30 . 
   Other components of the  FIG. 11  optical package  300  include a wafer  14  having thru-wafer interconnects  20  that may connect with solder balls  22  and probe contacts  24 . The solder balls  22  and probe contacts  24  provide electrical connectivity from the light sensing region  12  of the optical package  300  to peripheral circuitry. Scribes  26  are also provided for dicing the optical package  300  from adjacent optical packages on the wafer  14  (as discussed below with respect to  FIG. 14  in relation to optical package  100  of  FIG. 1 ). 
   The shaping lens layer  215  can be formed by any conventional method of forming lens layers, such as, for example, conventional pattern and reflow methods. The material layer  218  is formed over the shaping lens layer  215  after reflow, and the elastomeric material layer  216  is formed over the material layer  218 . Once the material layer  218  has been adjusted, the UV source  36  emits UV radiation that polymerizes the material layer  218  over the light sensing region  212 . The shaping lens layer  215  could be formed of any substantially transparent material including, but not limited to, the same material selected for the material layer  218 . If the shaping lens layer  215  is formed of a curable material, such as a photoresist, for example, the shaping lens layer  215  is exposed to curable conditions prior to formation of the material layer  218 . 
   In an alternative embodiment, illustrated in  FIG. 12 , the optical package  300 ′ shaping lens layer  215 ′ could be formed of a liquid, gas, gel, or any other non-solid material. The shaping lens layer  215 ′ could be formed by injecting the selected material (e.g., gas, liquid, gel, etc.) below the material layer  218  prior to polymerization. The injected material can form the lens shaping layer  215 ′ as a bubble below the surface of the material layer  218 . The injected lens shaping layer  215 ′ could also be suitably controlled such that the shaping element  30  ( FIG. 11 ) need not be used at all. Once the injected shaping layer  215 ′ is injected to a sufficient volume, and the material layer  218  has achieved a desired shape, the UV sources  36  can emit UV radiation to cure the material layer  218 . It should be noted, however, that the shaping element  30  ( FIG. 11 ) can also be used during the fabrication of the  FIG. 12  optical package  300 ′. 
     FIG. 13  illustrates a partial top-down block diagram view of the  FIG. 1  optical package  100  where a light sensing region  12  (shown as a pixel array) is covered with a lens formed in accordance with any of the embodiments described above.  FIG. 13  illustrates a CMOS imager and associated readout circuitry, but the embodiments may be used with any type of imager. In operation of the optical package  100 , i.e., light capture, pixel circuitry comprising photosensors  108  in each row in the light sensing region  12  are all turned on at the same time by a row select line, and the signals of the photosensors  108  of each column are selectively output onto output lines by respective column select lines. A plurality of row and column select lines are provided for the entire array. The row lines are selectively activated in sequence by the row driver  510  in response to row address decoder  520  and the column select lines are selectively activated in sequence for each row activation by the column driver  560  in response to column address decoder  570 . Thus, row and column addresses are provided for each pixel circuit comprising a photosensor  108 . The optical package  100  is operated by the control circuit  550 , which controls address decoders  520 ,  570  for selecting the appropriate row and column select lines for pixel readout, and row and column driver circuitry  510 ,  560 , which apply driving voltage to the drive transistors of the selected row and column lines. 
   In a CMOS imager, the pixel output signals typically include a pixel reset signal Vrst taken off of the floating diffusion region (via a source follower transistor) when it is reset and a pixel image signal Vsig, which is taken off the floating diffusion region (via a source follower transistor) after charges generated by an image are transferred to it. The Vrst and Vsig signals are read by a sample and hold circuit  561  and are subtracted by a differential amplifier  562  that produces a difference signal (Vrst−Vsig) for each photosensor  108 , which represents the amount of light impinging on the photosensor  108 . This signal difference is digitized by an analog-to-digital converter (ADC)  575 . The digitized pixel signals are then fed to an image processor  580  which processes the pixel signals and form a digital image output. In addition, as depicted in  FIG. 13 , the optical package  100  is formed on a single semiconductor chip. 
   It should be understood by those in the art that the optical packages fabricated in accordance with the embodiments discussed above (i.e., e.g.,  100 ,  200 ,  300 ,  300 ′ of  FIGS. 1-12 ) are formed on a wafer;  FIG. 14  illustrates a partial top-down, block diagram of a plurality of optical packages  100  formed on a single wafer  14 . Scribes  26  are illustrated on a topmost surface  14   a  of the wafer; it should be noted, however, that scribes  26  can be formed on a bottom surface  14   b  ( FIG. 1 ) of the wafer  14  as well. Scribes  26  are typically formed on both surfaces to assist in separating each optical package  100  from the array. 
     FIG. 15  shows a typical system  600 , such as, for example, a camera. The system  600  includes an imaging device  630  having an optical package  100 . The system  600  is an example of a system having digital circuits that could include image sensor devices. Without being limiting, such a system could include a computer system, camera system, scanner, machine vision, vehicle navigation system, video phone, surveillance system, auto focus system, star tracker system, motion detection system, image stabilization system, and other systems employing an imager. 
   System  600 , for example, a camera system, includes a lens  680  for focusing an image on the optical package  100  when a shutter release button  682  is pressed. System  600  generally comprises a central processing unit (CPU)  610 , such as a microprocessor that controls camera functions and image flow, and communicates with an input/output (I/O) device  640  over a bus  660 . The optical package of device  630  also communicates with the CPU  610  over the bus  660 . The processor-based system  600  also includes random access memory (RAM)  620 , and can include removable memory  650 , such as flash memory, which also communicates with the CPU  610  over the bus  660 . The imaging device  630  may be combined with the CPU  610 , with or without memory storage on a single integrated circuit or on a different chip than the CPU. 
   It should again be noted that although the embodiments have been described with specific references to optical packages (e.g.,  100 ,  200 ,  300 ,  300 ′ of  FIGS. 1-12 ) intended for light capture, the embodiments have broader applicability and may be used in any imaging apparatus, including those that require image display. For example, without limitation, embodiments may be used in conjunction with Liquid Crystal Display (LCD) technologies. In addition, although an example of use of the optical packages with CMOS image sensors have been given, the invention has applicability to other image sensors, as well as display devices. 
   The above description and drawings illustrate embodiments which achieve the objects, features, and advantages described. Although certain advantages and embodiments have been described above, those skilled in the art will recognize that substitutions, additions, deletions, modifications and/or other changes may be made.