Abstract:
A wafer level image module includes a photo sensor for outputting an electrical signal upon receiving light, a lens set for focusing incident light onto the photo sensor, and an adjustment member disposed between the photo sensor and the lens set for controlling the distance between the photo sensor and the lens set to compensate the focus offset of the photo sensor for enabling the lens set to accurately focus the incident light onto the photo sensor in an in-focus manner so as to provide a high image quality.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Divisional of application Ser. No. 11/528,461, filed on Sep. 28, 2006, which issued as U.S. Pat. No. 7,592,680 on Sep. 22, 2009, and for which priority is claimed under 35 U.S.C. §120; and this application claims priority of Application No. 094134100 filed in Taiwan, R.O.C. on Sep. 29, 2005 under 35 U.S.C. §119; the entire contents of all of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to image modules and more particularly, to a wafer level image module, the method for making the same and the apparatus for assembling and testing the same. 
     2. Description of the Related Art 
       FIG. 12  shows a conventional CMOS (Complementary Metal-Oxide Semiconductor) image module  80 . According to this design, the CMOS image module  80  comprises a sensor chip  82  and a lens holder  81  covering the sensor chip  82 . The lens holder  81  comprises a rotary lens barrel  83 , and a lens set  84  on the center of the rotary lens barrel  83 . When the lens set  84  is mapping an image onto the sensor chip  82 , the rotary lens barrel  83  is rotatable to change the distance between the lens set  84  and the sensor chip  82 , thereby focusing light rays on the sensor chip  82 . 
       FIG. 13  shows an image module according to WO2004/027880. This design of image module comprises an image pickup device  103  and a set of lenses  111  and  127 . The lenses  111  and  127  are arranged in a stack and closely attached to the image pickup device  103  to map the image of incident light rays onto the image pickup device  103 . The main feature of this patent is that the image pickup device  103  and the lenses  111  and  127  are made through an integrated circuit manufacturing process to minimize the size for use in a cell phone, PDA, or any of a variety of other consumer electronics. 
     However, during the fabrication of the image module according to WO2004/027880, the lenses  111  and  127  may deform by the manufacturing process and the manufacturing temperature. The focal distance of the finished product shows a 0-50 μm error when compared to the original theoretical design. In actual practice, the lenses  111  and  127  cannot accurately focus the image of incident light rays onto the image pickup device  103 , resulting in an out-of-focus problem (see the imaginary line A or B in  FIG. 13 ). Further, when mounting the lenses  111  and  127  on the image pickup device  103 , the respective size tolerance, for example, 0-20 μm thickness tolerance of each glass chip makes distance control between the lenses  111  and  127  and the image pickup device  103  difficult, resulting in inaccurate focusing of the lenses  111  and  127  on the image pickup device  103 . 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished under the circumstances in view. It is an objective of the present invention to provide a wafer level image sensor, which has adjustment means to compensate focus offset, thereby improving the image mapping quality. 
     It is another objective of the present invention to provide a wafer level image sensor assembly apparatus, which allows in-situ adjustment and test of each assembled wafer level image sensor, assuring a high quality of each assembled wafer level image sensor. 
     It is still another objective of the present invention to provide a wafer level image sensor assembly method, which is practical to assemble high quality wafer level image sensors. 
     To achieve these objectives of the present invention, the wafer level image module comprises a photo sensor, a lens set, and an adjustment member. The photo sensor outputs an electrical signal when induced by light. The lens set maps the image of incident light rays onto the photo sensor. The adjustment member is set between the photo sensor and the lens set to control the distance between the photo sensor and the lens sent, and to compensate the focus offset of the photo sensor, enabling the lens set to accurately focus the image of incident light rays onto the photo sensor. 
     The method for making a wafer level image module comprises the steps of a) providing a photo sensor, b) stacking a lens set on the photo sensor, c) measuring a focus offset of the lens set, and d) disposing an adjustment member between the lens set and the photo sensor to compensate the focus offset of the lens set so as to have the photo sensor be in an in-focus status. 
     The present invention also provides an apparatus for in-situ assembling and testing the aforesaid wafer level image module. The apparatus comprises a positioning unit for positioning the photo sensor on the lens set and for setting the adjustment member between the photo sensor on the lens set, a signal pickup device electrically connected to the photo sensor for picking up a signal from the photo sensor upon focusing of an image onto the photo sensor by the lens set, a signal processor electrically connected to the signal pickup device for determining in-focus or out-of-focus status of the image focusing on the photo sensor, and a bonding unit for bonding the photo sensor, the adjustment member and the lens set together. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1  is a schematic sectional view of a wafer level image module in accordance with a first preferred embodiment of the present invention; 
         FIG. 2  is a perspective view of a wafer level image module assembly apparatus according to the present invention; 
         FIG. 3  is a schematic view showing the clamping device clamped the stacked first water and the second wafer on the test table; 
         FIG. 4  is a schematic side view showing the first water and the second wafer stacked together and placed on the test table; 
         FIG. 5  is a schematic drawing showing an out-of-focus status of an image mapped on the photo sensor according to the present invention; 
         FIG. 6  is similar to  FIG. 4 , showing the adjustment member set in between the first wafer (photo sensors) and the second wafer (lens sets); 
         FIG. 7  is a schematic drawing showing an image mapped onto the photo sensor after installation of the adjustment member in the wafer level image module according to the present invention; 
         FIG. 8  is schematic drawing showing an in-focus status of an image mapped on the photo sensor according to the present invention; 
         FIG. 9  is a schematic sectional view of a wafer level image module in accordance with a second preferred embodiment of the present invention; 
         FIG. 10  is a schematic sectional view of a wafer level image module in accordance with a third preferred embodiment of the present invention; 
         FIG. 11  is a schematic sectional view of a wafer level image module in accordance with a fourth preferred embodiment of the present invention; 
         FIG. 12  is a schematic drawing showing an image module according to the prior art, and 
         FIG. 13  is a schematic drawing showing another design of image module according to the prior art. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in  FIG. 1 , a wafer level image module  10  in accordance with a first preferred embodiment of the present invention comprises a photo sensor  20 , an adjustment member  25 , and a lens set  30 . The photo sensor  20  can be a CMOS (Complementary Metal-Oxide Semiconductor) image sensor or CCD (Charge Coupled Device) image sensor adapted to output an electrical signal when induced by light. The photo sensor  20  is mounted on the top side thereof with a light transmissive spacer  22 . The light transmissive spacer  22  protects the photo sensor  20  against outside pollutants and moisture. The adjustment member  25  can be a glass ball spacer  25  or fiber spacer formed on the top surface of the transmissive spacer  22  by sputtering deposition, spot adhesive, or screen printing. The adjustment member  25  has a thickness about 1-50 μm. This thickness is determined subject to the depth of focus required and the focus offset. Further, the adjustment member  25  can be formed on the transmissive spacer by means of thick film photolithography technology, or directly made of a glass plate. Alternatively, the adjustment member  25  can be formed on the lens set  30 . 
     The lens set  30  can be molded from transparent ultraviolet polymers, or made by etching. The lens set  30  is covered on the top side of the adjustment member  25  such that the adjustment member  25  is sandwiched between the lens set  30  and the photo sensor  20  for controlling the distance between the lens set  30  and the photo sensor  20 . Incident light rays go through the lens set  30  to the photo sensor  20 , thereby mapping the image onto the photo sensor  30 . The focus offset in which the lens set  30  maps the image of incident light rays onto the photo sensor  20  is about 0-50 μm. When setting the adjustment member  25  in between the lens set  30  and the photo sensor  20 , the thickness of the adjustment member  25  compensates the focus offset, thereby controlling the precision of the focal distance of the lens set  30  within the desired depth of focus. For an image module of FNO equal to 2.8 and pixel size 3.6 μm, the focus precision is about 10 μm. By means of the adjustment member  25  to compensate light rays, incident light rays are accurately focused on the photo sensor  20 . 
     When making the aforesaid wafer level image module  10 , an assembly apparatus  40  is used for in-situ assembly and in-situ test of wafer level image modules  10 . The structure of this assembly apparatus  40  is outlined hereinafter with reference to  FIGS. 2 through 4 . 
     As illustrated in  FIGS. 2-4 , the assembly apparatus  40  comprises a positioning unit  42 , a signal pickup device  43 , a signal processor  46 , and a bonding unit  48 . The positioning unit  42  comprises a base  50  and a test table  51 . The base  50  supports a sliding carrier  52  and a clamping device  54 . The sliding carrier  52  is movable in and out of the base  50  to carry wafer level image modules  10 . The clamping device  54  is adapted to hold wafer level image modules  10  in position and to place wafer level image modules  10  on the test table  51 . The signal pickup device  43  comprises a probe card  44 . The signal pickup device  43  is mounted in the base  50  of the positioning unit  42 . The signal processor  46  is electrically connected to the signal pickup device  43 , and adapted to check in-focus or out-of-focus status of the image signal picked up from wafer level image modules  10 . The bonding unit  48  is adapted to bond the photo sensor  20 , adjustment member  25  and lens set  30  of wafer level image modules  10 . 
     The assembly process of the wafer level image module  10  by the assembly apparatus  40  includes the following steps. 
     Step I: Perform an integrated circuit manufacturing process to prepare a first wafer  56 . As shown in  FIG. 2 , the first wafer has a plurality of photo sensors  20  each carrying a first alignment mark (not shown). 
     Step II: Perform an integrated circuit manufacturing process to prepare a second wafer  58 , which has a plurality of lens sets  30  each carrying a second alignment mark (not shown). 
     Step III: Place the first water  56  in the sliding carrier  52  of the assembly apparatus  40  and then stack the second wafer  58  on the first wafer  56  to have the second alignment marks of the lens sets  30  in alignment with the first alignment marks of the photo sensors  20  respectively, and then, as shown in  FIG. 3 , use the clamping device  54  to pre-bond the first wafer  56  and the second wafer  58  and to place the stacked first water  56  and second wafer  58  on the test table  51  to have the photo sensors  20  correspond to the probe card  44 . 
     Step IV: Control the test table  51  to electrically connect the stacked first water  56  and second wafer  58  to the probe card  44 , as shown in  FIG. 4 . The test table  50  can move the stacked wafers  56  and  58  horizontally or tilt the stacked first water  56  and the second wafer  58  subject to test requirements. 
     Step V: Operate the signal processor  46  to receive electrical signal from the signal pickup device  43  so as to obtain the focus offset in which the respective lens sets  30  map the image of incident light rays onto the respective photo sensors  20  for determining in-focus or out-of-focus status of the photo sensors  20  (see  FIG. 5 ) and discriminating far coal or near focal status in case of out-of-focus status. 
     Step VI: Move the sliding carrier  52  out of the base  50 , and then apply the prepared adjustment member  25  to the first wafer  56  and the second wafer  58  to have the adjustment member  25  be sandwiched between the lens sets  30  and the photo sensors  20 , as shown in  FIG. 6 , and then electrically connect the integrated wafer level image modules of the stack of wafers  56  and  58  and adjustment member  25  to the probe card  44 . 
     Step VII: Repeat the aforesaid steps IV through VI if the improved image, as shown in  FIG. 7 , produced by the photo sensors  20  still lightly shows an out-of-focus status till the in-focus status shown in  FIG. 8  where the adjustment member  25  accurately compensates the focus offset. 
     Step VIII: Operate the clamping device  54  to hold tight the first wafer  56  and the second wafer  58 , and then operate the bonding unit  48  to bond the first wafer  56 , the adjustment member  25  and the second wafer  58  together. 
     Step IX: Cut the stacked wafers  56  and  58  and adjustment member  25  into single chips, i.e., individual wafer level image modules  10 . 
     When the lens sets  30  of the second wafer  58  are stacked on the photo sensors  20  of the first wafer  56  by means of the aforesaid assembly apparatus  40  and the aforesaid assembly process, the signal processor  46  is used to check in-focus or out-of-focus status of the electrical signal received from the signal pickup device through the photo sensors  20 . If the photo sensors  20  are at an out-of-focus status, the thickness of the adjustment member  25  is adjusted to correct the out-of-focus status of the photo sensors  20  to an in-focus status, assuring image quality of the assembled wafer level image modules  10 . Further, by means of changing the thickness of the adjustment member  25 , the distance between the respective lens sets  30  and the respective photo sensors  20  is relatively adjusted, thereby accurately compensating the focus offset between the respective lens sets  30  and the respective photo sensors  20  so that the respective lens sets  30  accurately focus light rays onto the respective photo sensors  20 . 
     As stated above, the invention uses the structure of the adjustment member to have the wafer level image module provide a better image quality. 
       FIG. 9  shows a wafer level image module  60  in accordance with a second embodiment of the present invention. Similar to the aforesaid first embodiment of the present invention, the wafer level image module  60  comprises a photo sensor  61 , a lens set  62 , and an adjustment member  63  sandwiched between the photo sensor  60  and the lens set  62 . The main feature of this second embodiment is that the lens set  62  comprises a first lens layer  64 , a second lens layer  65 , a first transmissive pad  66  sandwiched between the first lens layer  64  and the second lens layer  65 , and a second transmissive pad  67  bonded to the top surface of the second lens layer  65  opposite to the first transmissive pad  66 . The first lens layer  64  is bonded to the adjustment member  63  above the photo sensor  61 . The first lens layer  64  and the second lens layer  65  are transparent for mapping the image of incident light rays onto the photo sensor  61 . This lens set  62  enables the wafer level image module  60  to have more image characteristics. 
       FIG. 10  shows a wafer level image module  70  in accordance with a third embodiment of the present invention. This third embodiment is substantially similar to the aforesaid second embodiment with the exception that the transmissive spacer  72  on the photo sensor  71  has an opening  73  corresponding to the photo sensing area of the photo sensor  71 . This third embodiment achieves the same various effects as the aforesaid first and second embodiments of the present invention. 
       FIG. 11  shows a wafer level image module  75  in accordance with a fourth embodiment of the present invention. According to this fourth embodiment, the adjustment member  76  is directly bonded to the surface of the photo sensor  77 , and the first lens layer  79  of the lens set  78  is bonded to the adjustment member  76 . This fourth embodiment achieves the same various effects as the aforesaid various embodiments of the present invention. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.