Abstract:
An apparatus, a method and a computer program product for inspecting at least side faces of a semiconductor device are disclosed. A frame construction is provided, which holds a camera, defining an imaging beam path. The semiconductor device is inserted into a mirror block. The mirror block has a first mirror, a second mirror, a third mirror and a fourth mirror, wherein the mirrors are arranged such that they surround a free space in the form of a rectangle. The opposing first mirror and third mirror are fixedly mounted and the opposing second mirror and fourth mirror movably mounted. A tilted mirror directs an image of the side faces of the semiconductor substrate generated by the mirror block to the camera.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is filed under 35 U.S.C. §120 and §365(c) as a continuation of International Patent Application Serial No. PCT/US2015/042194, filed on Jul. 27, 2015, which application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 62/171,906 filed on Jun. 5, 2015, which applications are incorporated herein by reference in their entireties. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention refers to an apparatus for the inspection of at least side faces of a semiconductor device. 
         [0003]    Furthermore, the present invention refers to a method for the inspection of at least side faces of a semiconductor device. 
         [0004]    Additionally, the present invention refers to a computer program product disposed on a non-transitory computer readable medium for the inspection of at least side faces of a semiconductor device, the product comprising computer executable process steps operable to control a computer. 
       BACKGROUND 
       [0005]    For example, U.S. Pat. No. 6,339,337 B1 discloses an infrared ray test for a semiconductor chip. The test is conducted by irradiating an infrared ray onto a bottom surface of a semiconductor chip, receiving the infrared ray reflected from a bonding pad and displaying the image of the bonding pad on a monitor. The image obtained from the infrared ray has information whether the bonding pad itself or a portion of the silicon substrate underlying the bonding pad has a defect or whether or not there is a deviation of the bonding pad with respect to the bump. 
         [0006]    Chinese utility model CN 2791639 (Y) discloses a detecting device, which is mainly used for detecting internal defects of semiconductor material of which the band gap is larger than 1.12 eV. The detecting device for detecting internal defects of semiconductor material is composed of an optical microscope, an infrared CCD camera, video cable, a simulation image monitor, a digital image collection card, a computer and analysis process and display software. 
         [0007]    Additionally, EP 2 699 071 A2 discloses an optoelectronic method for recording in heat diagram form the temperature distribution of land in which an infrared linescan system is used in an aircraft. The apparatus utilizes a rotary scanning mirror system receiving heat radiation through windows. The mirror system has four reflecting sides and is rotated about an axis by an electric motor. The radiation being directed by mirrors to an IR lens and thence to a row of optoelectronic receiver elements. The row of receiver elements is parallel to the axis of rotation of the mirror system, each receiver element being individually connected by a lead and an amplifying device to a corresponding one of a number of luminescent diodes. 
         [0008]    The traditional method for finding side defects  9  in a semiconductor device  2  is shown in  FIG. 1 . A four sided or a five sided inspection is carried out. The semiconductor device  2  has a first side face  31 , a second side face  32 , a third side face  33 , a fourth side face  34 , a top face  4  and a bottom face  5 . In the setup of  FIG. 1  a camera  6  with a lens  7  looks to the bottom face  5  of the semiconductor device  2 . A mirror  8  is arranged under 45 degrees with each of the first side face  31 , the second side face  32 , the third side face  33  and the fourth side face  34  of the semiconductor device  2 , respectively. In  FIG. 1  only the second mirror  82  arranged with respect to the second side face  32  and the fourth mirror  84  arranged with fourth side face  34  of the semiconductor device  2  are shown. 
         [0009]    The setup of  FIG. 1  is used obtain an image  10  (see  FIG. 2 ) the first side face  31 , the second side face  32 , the third side face  33 , the fourth side face  34  and the bottom face  5 , respectively. The setup of  FIG. 1  has significant drawbacks. The optical length  11  of the bottom face  5  view differs from the optical length  12  of the first side face  31  view, the second side face  32  view, the third side face  33  view and the fourth side face  34  view. Therefore, the focus is always a trade-off between focus on the bottom face  5  of the semiconductor device  2  and focus on the first side face  31 , the second side face  32 , the third side face  33  and the fourth side face  34 , respectively. In case an image showing both the four side faces  31 ,  32 ,  33 , 34  and the bottom face  5  is to be obtained, in a process often called 5S inspection, the optical system needs a very large depth-of-focus, in order to keep both the four side faces  31 ,  32 ,  33 , 34  and the bottom face  5  in focus. This becomes very challenging when magnification increases. 
         [0010]    According to a prior art method custom made mirror blocks are swapped. For a family of sizes of a semiconductor device, a custom mirror block (block with four 40-48 degree mirrors) is used. When another family of semiconductor devices needs to be inspected, the complete mirror block must be exchanged. The drawbacks are that one needs to keep expensive conversion parts and the lead time. Main disadvantages are: cost, flexibility, manual conversion, and risk of mistake. Conversion parts are needed for every family of semiconductor device sizes. These parts are custom so must be designed and manufactured when they are not yet available. 
         [0011]    This results in loss of flexibility as design must be started prior to having the family of semiconductor devices coming on-line. When the tool is converted, a line-technician or operator needs to manually change the mirror blocks. When the wrong type is mounted, damage to the tool or semiconductor device can result. 
         [0012]    Another prior art solution is a motorization of the mirrors of the mirror block which is divided over two individual inspection stations: The front and rear images of the side faces of the semiconductor device are taken by one optical set-up that is automated. The left and right images of the side faces of the semiconductor device are taken by another optical set-up that is automated as well. So when the semiconductor device size changes, the mirrors are automatically adjusted on two inspection stations. The drawbacks are: the semiconductor devices need to pass by two inspection stations, two inspection stations increase costs and two inspection stations consume more space. 
         [0013]    A further prior art method is that the unit or the mirror block is moved. In this concept the front/left side faces of the semiconductor device are inspected which is followed by a move of the unit or the mirror block, and then the rear/right side faces of the semiconductor device are inspected (other permutations are possible where always 2 adjacent sides are inspected). The major drawback is that the inspection is slow, which reduces throughput. 
         [0014]    A motorization of all four mirrors  81 ,  82 ,  83  and  84  according to a prior art design is shown in  FIGS. 3A to 3C . Here the set of the first mirror  81  and the third mirror  83 , and the set and of the second mirror  82  and the fourth mirror  84  are moved and adapted to the size of the semiconductor device  2 . The drawbacks of this arrangement are that it is very complicated and is only applicable for a limited range of sizes of the semiconductor devices. 
       SUMMARY 
       [0015]    It is an object of the invention to provide an apparatus for inspecting at least side faces of a semiconductor device, which is cost effective, flexible, reliable, save and easy to use in a variety of applications. 
         [0016]    The above object is achieved by an apparatus for inspecting at least side faces of a semiconductor device. The apparatus includes a camera, defining an imaging beam path, a mirror block, having a first mirror, a second mirror, a third mirror, and a fourth mirror, the mirrors being arranged such that they surround a free space in the form of a rectangle and that the opposing first mirror and third mirror are fixedly mounted and the opposing second mirror and fourth mirror are movably mounted, and a tilted mirror, for directing to an image of the side faces from the mirror block to the camera. 
         [0017]    The advantage of the inventive apparatus is the flexibility. Once the inventive apparatus (inventive optical module) is installed, a whole range of semiconductor device sizes (square and rectangular) can be handled without the need of new parts. Optical resolution stays equal for the complete range of types of semiconductor devices. So no recalibration or resolution modeling is required. Additionally, the compactness of the inventive apparatus allows that the whole assembly can be mounted in a single slot of a turret based machine. 
         [0018]    It is a further object of the invention to provide a method for inspecting at least side faces of a semiconductor device, wherein the method is easy to apply, works for a plurality of various types of semiconductor devices, is cost effective, flexible, reliable, save and easy to use in a variety of applications. 
         [0019]    This object is achieved by a method for inspecting at least side faces of a semiconductor device, the method including placing the semiconductor device centrally into a free space defined by a mirror block, having a first fixed mirror and a third fixed mirror, and a second movable mirror and a fourth movable mirror, providing information about a type of the semiconductor device to a control unit, moving the second mirror and the fourth mirror such that a first distance between a respective side face of the semiconductor device and the second mirror and the fourth mirror, respectively, is equal to a second distance between a respective side face of the semiconductor device and the first fixed mirror and the third fixed mirror, respectively, and adjusting a focus position of the camera along an imaging beam path to compensate for a change in a focal distance. 
         [0020]    The advantage of the inventive method is the flexibility because a whole range of semiconductor device sizes (square and rectangular) can be handled without the need to exchange parts for the ongoing inspection process. With the inventive method the semiconductor devices can be inspected in a reliable, fast and uncomplicated manner. 
         [0021]    An object of the invention is as well to provide a computer program product disposed on a non-transitory computer readable medium for inspecting at least side faces of a semiconductor device which allows the inspection of a plurality of various types of semiconductor devices, is flexible to use and avoids damage of semiconductor devices under inspection. 
         [0022]    The above object is achieved by a computer program product disposed on a non-transitory computer readable medium for inspection of at least side faces of a semiconductor device, the product including computer executable process steps operable to control a computer to place the semiconductor device with a placing mechanism into a free space of a mirror block; determine a type to the semiconductor device, move, according to the type to the semiconductor device, a second mirror and a fourth mirror of the mirror block such that a first distance between a respective side face of the semiconductor device and the second mirror and the fourth mirror is equal to a second distance between a respective side face of the semiconductor device and a first fixed mirror and a third fixed mirror of the mirror block, and adjusting a focus position of a camera along an imaging beam path in order to obtain a focused image of the at least four side faces of the semiconductor device. 
         [0023]    Typical defects to be detected by the present invention are side cracks created by the dicing process of the semiconductor devices or embedded cracks created by internal stress in the work piece. In case the work piece is a semiconductor device, the internal stress can exist for example between the dielectric layer and the silicon structure. It is noted, that the invention (apparatus, method and computer program) is not restricted to semiconductor devices and is applicable for side and internal defects in general. 
         [0024]    The main innovation of the apparatus is that two mirrors are fixed in combination with two symmetrically moving mirrors. When the semiconductor device is replaced with a semiconductor device of different size, the moving mirrors are repositioned, so that the distance between the side faces of the semiconductor device and the fixed mirrors equals the distance between the side daces of the semiconductor device and the moving mirrors. To compensate for the change in focal distance, the camera moves linearly. This could also be accomplished by using a zoom-lens set-up with auto-focus. 
         [0025]    Due to the compactness of the inventive apparatus, which is an elongated module, the described invention is a key building block in a turret-based wafer-to-tape inspection machine. In this tool, a compact auto conversion optical set-up is needed. 
         [0026]    According to an embodiment of the invention an apparatus for inspection of at least side faces of a semiconductor device has a housing, which defines a compact module. Inside the housing a camera, defining an imaging beam path, is linearly movable along the imaging beam path. The at least four side faces of the semiconductor device are imaged with a mirror block. The mirror block carries a first mirror, a second mirror, a third mirror and a fourth mirror. The mirrors are arranged such that they surround a free space in the form of a rectangle. The free space of the mirror block is accessible from the outside of the housing. The opposing first mirror and third mirror are fixedly mounted and the opposing second mirror and fourth mirror are movably mounted, which allows an adjustment of the inventive apparatus to the various types of semiconductor device. A tilted mirror is arranged in the housing with respect to the camera and the mirror block, such that an image of at least the side faces of the semiconductor device in the mirror block is directed to the camera. 
         [0027]    A first motor, which is arranged in the housing, is used to move the camera in a linear motion in the direction of the image beam path. A second motor, which is arranged inside the housing, is assigned to the opposing second mirror and fourth mirror for positing them in such a way that a first distance between a side face of the semiconductor device and the respective first and third fixed mirrors equals a second distance between a side face of the semiconductor device and the respective second and fourth mirrors. The tilted mirror is arranged in the housing with respect to the camera and the mirror block such that an image of at least the side faces of the semiconductor device in the mirror block is directed to the camera. The moving mirrors in combination with zoom-lens/autofocus allow for an adjustment of the focus position, so that all types of semiconductor devices are imaged with the correct focus position. 
         [0028]    With the invention swapping custom made mirror blocks is no longer necessary. For a family of sizes of a semiconductor device, a mirror block with two opposing movable mirrors is used. There is no longer the need to exchange the complete mirror block. This saves costs, since no expensive conversion parts are needed and the lead time is reduced. 
         [0029]    Another embodiment relates to an apparatus including in the housing a light source for generating light in order to illuminate the side faces of the semiconductor device. 
         [0030]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the present disclosure. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate subject matter of the disclosure. Together, the descriptions and the drawings serve to explain the principles of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    Below, the invention and its advantages will be further described with reference to the accompanying figures in which: 
           [0032]      FIG. 1  is a prior art set-up for detecting interior defects by looking at the sides of a semiconductor device; 
           [0033]      FIG. 2  is a schematic representation of an image obtained by the set-up shown in  FIG. 1 ; 
           [0034]      FIG. 3A  is a schematic representation of a traditional arrangement of four motorized mirrors in order to adapt to the various sizes of the semiconductor device; 
           [0035]      FIG. 3B  is a schematic representation of a traditional arrangement of four motorized mirrors in order to adapt to the various sizes of the semiconductor device; 
           [0036]      FIG. 3C  is a schematic representation of a traditional arrangement of four motorized mirrors in order to adapt to the various sizes of the semiconductor device; 
           [0037]      FIG. 4  is a schematic representation of a semiconductor device to be inspected; 
           [0038]      FIG. 5  is a schematic top view of the apparatus for carrying out the inspection of four side faces of a first type of a semiconductor device; 
           [0039]      FIG. 6  is a schematic top view of the apparatus for carrying out the inspection of four side faces of a second type of a semiconductor device; 
           [0040]      FIG. 7  is a schematic top view of the apparatus for carrying out the inspection of four side faces of a third type of a semiconductor device; 
           [0041]      FIG. 8  is a schematic top view of the apparatus for carrying out the inspection of four side faces of a fourth type of a semiconductor device; 
           [0042]      FIG. 9  is a schematic side view of the apparatus for carrying out the inspection of four side faces of a semiconductor device as shown in  FIG. 5 ; 
           [0043]      FIG. 10  is a perspective view of an embodiment of the inventive apparatus for the inspection of side faces of semiconductor devices; 
           [0044]      FIG. 11  is a perspective view of the embodiment of the inventive apparatus for the inspection of side faces of semiconductor devices as shown in  FIG. 10 , wherein housing parts are removed; 
           [0045]      FIG. 12  is a top view of the embodiment of the inventive apparatus for the inspection of side faces of semiconductor devices as shown in  FIG. 10 , wherein housing parts are removed; 
           [0046]      FIG. 13  is an enlarged perspective view of the mirror block of the embodiments shown in  FIG. 10, 11 or 12 ; and, 
           [0047]      FIG. 14  is a schematic view of the turret for feeding semiconductor substrates to the mirror block. 
       
    
    
     DETAILED DESCRIPTION 
       [0048]    In the figures like reference numerals are used for like elements or elements of like function. Furthermore, for the sake of clarity, only those reference numerals are shown in the figures which are necessary for discussing the respective figure. 
         [0049]      FIG. 4  is a schematic representation of a semiconductor device  2  which is inspected by an apparatus or method of the present invention. The semiconductor device  2  has the form of a cuboid with a first side face  31 , a second side face  32 , a third side face  33 , a fourth side face  34 , a top face  4 , and a bottom face  5 . There are different types of semiconductor devices which differ in the outer dimensions. 
         [0050]      FIG. 5  is a schematic top view of the apparatus  20  for carrying out the inspection of the first side face  31 , the second side face  32 , the third side face  33 , and the fourth side face  34  of a first type of the semiconductor device  2 . According to the top view shown in  FIG. 5 , the various types of the semiconductor devices  2  can have the form of a rectangle or a square. A mirror block  18  defines a free space  16 , into which the semiconductor device  2  to be inspected is positioned. The free space  16  of the mirror block  18  is defined by a first mirror  81 , a second mirror  82 , a third mirror  83 , and a fourth mirror  84 . The free space  16  has the form of a rectangle  17  (see dashed lines in  FIG. 5 ). The first mirror  81 , the second mirror  82 , the third mirror  83 , and the fourth mirror  84  are arranged parallel to the sides of the rectangle  17 . 
         [0051]    The opposing first mirror  81  and third mirror  83  are fixedly mounted. The opposing second mirror  82  and fourth mirror  84  are movably mounted. The second mirror  82  and the fourth mirror  84  are coupled with a second motor  14 . With the second motor  14  a symmetric position change of the second mirror  82  and the fourth mirror  84  can be effected. By the position change a second distance  22  between second mirror  82  and a corresponding side face of the semiconductor device  2 , as well as a second distance  22  between fourth mirror  84  and a corresponding side face of the semiconductor device  2  can be made equal to a first distance  21  between first mirror  81  and a corresponding side face of the semiconductor device  2 , as well as equal to a first distance  21  between a third mirror  83  and a corresponding side face of the semiconductor device  2 . 
         [0052]    The camera  6  captures with its lens  7  an image of the four side faces  31 ,  32 ,  33  and  34  (see  FIG. 4 ) of the semiconductor device  2 . The camera  6  defines an imaging beam path  24  and can be moved linearly by a first motor  13  along the imaging beam path  24 . The movement of the camera  6  is necessary to compensate for the change in focal distance of the apparatus  20 . According to another embodiment of the invention, the linear movement of the camera  6  can be substituted by a zoom-lens set-up with auto-focus. 
         [0053]      FIG. 6 ,  FIG. 7  and  FIG. 8  show the inventive apparatus  20  wherein different types of the semiconductor device  2  are inspected. Once the mirror block  18  is installed in the inventive apparatus  20 , the apparatus  20  achieves full flexibility to inspect a whole range of sizes (square and rectangular) of semiconductor devices  2 . The semiconductor devices  2  can be handled without the need for new parts. 
         [0054]      FIG. 6  shows the situation that a large, square semiconductor device  2  is inspected. The second motor  14  carries out a symmetric position change of the second mirror  82  and the fourth mirror  84 . By the position change a second distance  22  between second mirror  82  and a corresponding side face of the semiconductor device  2 , as well as a second distance  22  between fourth mirror  84  and a corresponding side face of the semiconductor device  2  can be made equal to a first distance  21  between first mirror  81  and a corresponding side face of the semiconductor device  2 , as well as equal to a first distance  21  between a third mirror  83  and a corresponding side face of the semiconductor device  2 . The camera adjusts a focus position along the imaging beam path  24 . According to a preferred embodiment the first motor  13  moves the camera  6  along the imaging beam path  24 . The movement of the camera  6  is necessary to compensate for the change in focal distance of the apparatus  20 . 
         [0055]      FIG. 7  shows the situation that a rectangular semiconductor device  2  is inspected. The second motor  14  carries out a symmetric position change of the second mirror  82  and the fourth mirror  84 . By the position change a second distance  22  between second mirror  82  and a corresponding side face of the semiconductor device  2 , as well as a second distance  22  between fourth mirror  84  and a corresponding side face of the semiconductor device  2  can be made equal to a first distance  21  between first mirror  81  and a corresponding side face of the semiconductor device  2 , as well as equal to a first distance  21  between a third mirror  83  and a corresponding side face of the semiconductor device  2 . The focus position of the camera is adjusted according to the processes described in  FIGS. 5 and 6 . 
         [0056]      FIG. 8  shows the situation that a rectangular semiconductor device  2  is inspected, wherein the semiconductor device  2  is rotated by 90° compared with the situation shown in  FIG. 7 . The second motor  14  carries out a symmetric position change of the second mirror  82  and the fourth mirror  84 . By the position change a second distance  22  between second mirror  82  and a corresponding side face of the semiconductor device  2 , as well as a second distance  22  between fourth mirror  84  and a corresponding side face of the semiconductor device  2  can be made equal to a first distance  21  between first mirror  81  and a corresponding side face of the semiconductor device  2 , as well as equal to a first distance  21  between a third mirror  83  and a corresponding side face of the semiconductor device  2 . 
         [0057]      FIG. 9  is a is a schematic side view of the inventive apparatus  20  for carrying out the inspection of at least four side faces  31 ,  32 ,  33  and  34  of a semiconductor device  2  as shown in  FIG. 5 . The mirror block  18 , having the first mirror  81 , the second mirror  82 , the third mirror  83 , and the fourth mirror  84 , surrounds the semiconductor device  2  for inspection. Each of the four mirrors  81 ,  82 ,  83  and  84  has a mirror surface  25  which is tilted by 40 to 48 degrees with respect to the side faces  31 ,  32 ,  33  and  34  of the semiconductor device  2 . An image of the side faces  31 ,  32 ,  33  and  34  is reflected down to a tilted mirror  27 . The tilted mirror  27  directs to the image of the side faces  31 ,  32 ,  33  and  34  from the mirror block  18  along the image beam path  24  to the camera  6 . 
         [0058]      FIG. 10  is a perspective view of an embodiment of the inventive apparatus  20  for the inspection of side faces of semiconductor devices  2  (not shown here). There are several wall panels  31  which together define a housing  30  of the apparatus  20 . The housing  30  surrounds at least the camera  6  and the mirror block  18 . The mirror block  18  is arranged at a first end  33  of the housing  30 . As mentioned above, the mirror block  18  carries the first mirror  81 , the second mirror  82 , the third mirror  83 , and the fourth mirror  84  (see  FIGS. 5 to 8 ). The mirror block  18  defines the free space  16  (see  FIG. 5 ) which is accessible from the outside the housing  30 . 
         [0059]      FIG. 11  is a perspective view of the inventive apparatus  20  for the inspection of side faces of semiconductor devices, wherein the wall panels  31  of the housing  30  have been removed. The apparatus  20  has a frame construction  40  which carries the camera  6  with the lens  7  and an electronic back  32 ; the mirror block  18 , a tilted mirror  27  and at least one illumination device (see  FIG. 13 ). According to the embodiment as described in  FIGS. 10 to 13 , the apparatus  20  forms a single module. Once this optical module is installed, a whole range of semiconductor device sizes (square and rectangular) can be handled without the need to install new parts. The module allows easy motorization. The first motor  13  is assigned to the camera  6  for an adjustment of a focus position of the camera  6 . The second motor  14  is assigned to the opposing second mirror  82  and fourth mirror  84  (see  FIGS. 5 to 8 ) for adjusting their position with respect to the semiconductor device. The first motor  13  and the second motor  14  are not coupled. 
         [0060]    The first motor  13  can be part of the camera  6  with a zoom-lens  7  set-up with auto-focus as well. For the adjustment of the focus of the camera  6  the first motor  13  is coupled to a slide  15  by a leadscrew in order to carry out a linear movement  35  of the camera  6  and/or the lens  7  along the imaging beam path  24 . 
         [0061]    The second motor  14  drives a leadscrew  34 , and via a cam mechanism  36  the second mirror  82  and the fourth mirror  84  are moved simultaneously. 
         [0062]    The tilted mirror  27  directs an image of the mirror block  18  along the image beam path to the camera  6 . 
         [0063]      FIG. 12  is a top view of the inventive apparatus  20  for the inspection of side faces of semiconductor devices. As already mentioned in the description of  FIG. 11  the housing parts have been removed. The free space  16  of the mirror block  18  can accommodate a whole range of semiconductor device sizes to be inspected, without the need of new parts. The whole apparatus  20  has a compact and elongated design. The apparatus  20  stretches from the first end  33  to the electronic back  32  of the camera. The first motor  13  and the second motor  14  fit into the compact and elongated design as well. 
         [0064]      FIG. 13  is an enlarged perspective view of the mirror block  18  at the first end  33  of the embodiments shown in  FIGS. 10 and 11 . Each of the first mirror  81 , the second mirror  82 , the third mirror  83 , and the fourth mirror  84  has the mirror surface  25  tilted by 40 to 48 degrees. Under the mirror block  18  an illumination device is provided, in order to illuminate the semiconductor device which is positioned for inspection in the free space  16  defined by the first mirror  81 , the second mirror  82 , the third mirror  83 , and the fourth mirror  84  of the mirror block  18 . The images of the side faces of the semiconductor device are reflected by the tilted mirror  27  to the camera. Although not shown in the embodiment described above, one could also use a view of the bottom face of the semiconductor device, which allows bottom face inspection. In order to carry out the so called five sided-inspection (5S-inspection), a very large depth-of-focus is required, in order to keep both the side faces and the bottom face in focus. 
         [0065]    Due to the compactness of the apparatus  20  (see  FIG. 10 ) the whole assembly can be mounted in a single slot of turret based machine  41 .  FIG. 14  is a schematic view of a turret  42  of the turret based machine  41  for feeding semiconductor substrates  2  to the mirror block  18 . The turret  42  has a plurality of holding arms  43 . By a control  23  the turret  42  is rotated in order to position the holding arms  43  with respect to the mirror block  18 . Each holding arm  43  is configured to place the semiconductor device in the free space of the mirror block  18 . Images from at least the four side faces are sent to a computer  26  for data processing. With the turret  42  a series of semiconductor devices  2  can be positioned automatically in the mirror block  18  for inspection. 
         [0066]    In the above description, numerous specific details are given to provide a thorough understanding of embodiments of the invention. However, the above description of illustrated embodiments of the invention is not intended to be exhaustive or to limit the invention to the precise forms disclosed. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific details, or with other methods, components, etc. In other instances, well-known structures or operations are not shown or described in detail to avoid obscuring aspects of the invention. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. 
         [0067]    These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims. Rather, the scope of the invention is to be determined by the following claims, which are to be construed in accordance with established doctrines of claim interpretation. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           2  semiconductor device 
           31  first side face 
           32  second side face 
           33  third side face 
           34  fourth side face 
           4  top face 
           5  bottom face 
           6  camera 
           7  lens 
           81  first mirror 
           82  second mirror 
           83  third mirror 
           84  fourth mirror 
           9  defect, interior defect 
           10  image 
           11  optical length 
           12  optical length 
           13  first motor 
           14  second motor 
           15  slide 
           16  free space 
           17  rectangle 
           18  mirror block 
           20  apparatus 
           21  first distance 
           22  second distance 
           23  control 
           24  imaging beam path 
           25  mirror surface 
           26  computer 
           27  tilted mirror 
           30  housing 
           31  wall panels 
           32  electronic back 
           33  first end 
           34  leadscrew 
           35  linear movement 
           36  cam mechanism 
           38  illumination device 
           40  frame construction 
           41  turret based machine 
           42  turret 
           43  holding arm