Patent Publication Number: US-2010109673-A1

Title: Heat-resistant lens kit

Description:
Cross Reference to Related Application 
     This application is a continuation application of, and claims a priority to the U.S. patent application Ser. No. 11/819,083 filed on Jun. 25, 2007, which claims a priority to the foreign patent application in Taiwan with a serial number TW96107169, filed on Mar. 2, 2007. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to a wafer tester for a photo sensor, and particularly to a wafer tester that includes a hear-resistant lens kit to form an enclosed room for isolating the surface of a device under test. 
     2. Description of the Related Art 
     It is necessary for a CMOS sensor to be tested under low-temperature environment for sure of practical work in the low-temperature environment. 
       FIG. 1  is a schematic diagram of a wafer tester  10  having a test base  11  as an upper portion and a chuck  13  for loading a device under test as a bottom portion. The test base  11  includes a pogo tower  13 , a probe card  14  and a test head  16 . The test head  16  is associated with a test probe  18  for touching a device under test, a room for light transmission and a probe card holder  17  for connecting the pogo tower  12  and the probe card  14  into a piece. Obviously, there is a hole individually in the pogo tower  12 , probe card  14  and a test head  16  for passing light onto the device under test. Shown in  FIG. 1 , in order to maintain a device in a low-temperature state, the device under test is necessarily attached to the chuck  13  through low-temperature treatment for sure of low temperature. Meanwhile, the probe card  14  of the wafer tester  10  is close to the device under test in low-temperature state. However, the device under test is in low-temperature state on one hand. On the other hand, the probe card  14  is in room-temperature or higher-temperature state. Thus, there is vapor, also called as saturated vapor, formed on the interface of the low-temperature surface and the high-temperature surface. When light is incident continuously, light though vapor may be reflected, refracted or scattered. Thus, light incident on the device under test may be disordered and further cause incorrect measurement and short to damage the apparatus. Thus, in order to correctly and rapidly test the device under test, the vapor generation should be overcome. 
     SUMMARY OF THE INVENTION 
     In order to test a photo sensor in low-temperature state, one object of the present invention is to provide a heat-resistant lens kit to prevent from vapor generation. 
     Another one object of the present invention provides a heat-resistant lens kit having a main body with a through hole and two parallel lenses to enclose a room. The main body is associated with a suction hole and an indicator to make the room vacuum. 
     The other object of the present invention provides a wafer tester of photo sensor. The wafer tester includes a heat-resistant lens kit to form a vacuum room for isolating the surface of a device under test from the incident surface of light and preventing from vapor formation. 
     Another object of the present invention provides a wafer tester of photo sensor which includes a pair of lenses directly attached to the two ends of an opening on a pogo tower to form an enclosed room. A vacuum pump maintains the enclosed room in vacuum state. The low-temperature surface and the room-temperature surface are isolated from each other to prevent vapor formation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a testing apparatus according to a prior art. 
         FIG. 2A  is a schematic diagram illustrating a heat-resistant lens kit according to the present invention. 
         FIG. 2B  is a schematic diagram illustrating a heat-resistant lens kit according to the present invention. 
         FIG. 3  is a schematic diagram illustrating an exemplary testing apparatus according to the present invention. 
         FIG. 4  is a schematic diagram illustrating an exemplary testing apparatus according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention provides a wafer tester. Following illustrations describe detailed components and steps for understanding the present invention. Obviously, the present invention is not limited to the embodiments of wafer tester, however, the preferable embodiments of the present invention are illustrated as followings. Besides, the present invention may be applied to other embodiments, not limited to ones mentioned. 
     In a known technology, the device under test would be maintained in a low-temperature state when attached to a low-temperature chuck  13 . However, the room-temperature probe card  14  causes vapor formation on the interface. The vapor film results in the reflection and fraction of lights and further in test error and apparatus damage. One best resolution to such a problem is to isolate the interface of objects in different temperature with a room in a vacuum state. 
     Accordingly, one exemplary embodiment of the present invention provides a heat-resistant lens kit  20  shown as  FIG. 2A  including a main body  22  and two lenses  24 . A through hole is set in the main body  22  and the two lenses  24  are parallel configured on the two ends of the through hole of the main body  22 . The main body  22  and the two lenses  24  enclose a vacuum room. The two lenses  24  are fixed on the main body  22  with built-in screws or adhesive, and so on. Furthermore, the main body  22  may be made of low thermo-conductivity and heat resistant materials to form a heat resistant element in good quality. 
     In a preferred embodiment, the enclosed room between the main body  22  and two lenses  24  is kept vacuum to be configured for blocking heat conduction. However, in another embodiment, the main body  22  and the two lenses  24  may enclose a non-vacuum room. Gas in the non-vacuum room may be exhaust out to meet vacuum requirement for blocking heat conduction. 
     The method for making vacuum is not limited to in the present invention. For example, in  FIG. 2A , the heat-resistant lens kit  20  includes a suction hole  26  and an indicator  28  to exhaust gas out of the heat-resistant lens kit  20  by an air extractor (not shown). When a vacuum degree is read out within the heat-resistant lens kit  20 , the indicator  28  may be sucked into the heat-resistant lens kit  20 . Reversely, the indicator  28  may float up to remind a user of extracting gas within the heat-resistant lens kit  20  when the vacuum degree is below a threshold in the heat-resistant lens kit  20 . Accordingly, the indicator  28  may be made of spring, elastic sheet, sponge or any suitable elastic element. When a low-temperature environment, for example, room temperature down to −100° C., is configured by a chuck  13 , vapor due to temperature difference does not result because the enclosed vacuum room by the heat-resistant lens kit  20  may isolate the contact surface of a device under test from incident surface of a probe card  14 . Moreover, in order to maintain identical phase of light when light reaches to the element in a test, it is necessary to make the two lenses  24  parallel for fear of interference on light source in the test. 
     Next, shown in  FIG. 3  is a schematic diagram illustrating the combination of the heat-resistant lens kit  20  and a wafer tester  10  in accordance with the present invention. The upper portion is a test plate  11  and the lower portion is the wafer tester  10  for loading a device under test. The test plate  11  includes a POGO Tower  12 , a probe card  14 , a chamber  15  and a test head  16 . There are a plurality of test probes  18  for contacting the device under test and a probe card holder  17  for combining the POGO Tower  12  and the probe card  14 . There is an opening within the POGO Tower  12  to load the heat-resistant lens kit  20 . The fixing of the heat-resistant lens kit  20  and POGO Tower  12  may be implemented with a screw  21 , shown in  FIG. 2A . Moreover, the heat-resistant lens kit  20  may be fixed on the POGO Tower  12  with at least one O-ring  23  on the main body  22  of the heat-resistant lens kit  20  to fix the POGO Tower  12  of the heat-resistant lens kit  20 , show in  FIG. 2B . Thus, when the light source emits light through the chamber  15  of the wafer tester  10 , the light is incident into the opening of the POGO Tower  12  and through the two lenses  24  of the heat-resistant lens kit  20  and the enclosed room, the probe card  14  and the aperture on the test head  16  in sequence, and then on the device under test. The low temperature conducted by the device under test may be isolated and prevent the probe card  14  from vapor. 
     In another embodiment of the present invention, the two lenses  25  are directly fixed on the through hole of the chuck  13 , shown as  FIG. 4 . The fixation of the two lenses  25  and the two ends of the POGO Tower  12  is not limited, such as screw fixation, O-ring fixation or direct attachment as long as the fixed two lenses  25  are parallel and in vacuum state. In the embodiment, the vacuum formation is implemented by the vacuum pump  40  on the wafer tester  10  that may associate with the usage condition to maintain vacuum between the two lenses  25  and the POGO Tower  12 . Thus, the low temperature conducted by the device under test may be isolated and prevent the probe card  14  from vapor. 
     Obviously, according to the illustration of embodiments aforementioned, there may be modification and differences in the present invention. Thus it is necessary to understand the addition of claims. In addition of detailed illustration aforementioned, the present invention may be broadly applied to other embodiments. Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that other modifications and variation can be made without departing the spirit and scope of the invention as hereafter claimed.