Abstract:
An apparatus and method are disclosed for hard-docking of a tester head to a DUT, while permitting the angular alignment of a specimen to be inspected to the optical axis of an optical testing tool. In one example, a system for orthogonal alignment of a specimen to an optical axis of a collection optics is provided. The system comprises a self-leveling tabletop; a specimen holder coupled to the tabletop and held at a fix orientation; collection optics coupled to the tabletop; a plunger coupled to the tabletop and operable to maintain the leveling orientation of the tabletop; a control valve sensing the leveling orientation of the tabletop and coupled to the plunger to control the operation of the plunger; and an aligner coupled to the tabletop and operable to change the alignment of the optical axis of the collection optics with respect to the specimen without changing the fixed orientation of the specimen holder.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an apparatus and method for controlling the tilt of an imager to allow alignment to a specimen, while permitting a hard-dock to a tester connected to the specimen.  
         [0003]     2. Description of the Related Art  
         [0004]     Many optical systems for inspection of specimen, such as substrates, exist in the prior art. One such system is described in U.S. Pat. No. 6,621,275, which is assigned to the current assignee and which is incorporated herein by reference in its entirety. Such systems can be used for inspection or testing and debug of semiconductor substrates or integrated circuits. Examples of systems for imaging flip-chip type integrated circuits through the silicon substrate are described in U.S. Pat. Nos. 5,208,648, 5,220,403 and 5,940,545, which are incorporated herein by reference in their entirety.  
         [0005]      FIGS. 1A and 1B  are general schematics depicting major components of an arrangement of an Automated Testing System (ATE) connected to an emission testing and debug system (Such as the Sapphire™ and the EmiScope™, respectively, available from Credence Systems, Inc. of Milpitas, Calif.) that is helpful for the understanding of the present invention. A system that is similar to the EmiScope is described in co-assigned U.S. patent application Ser. No. 10/912,896 which is incorporated herein by reference in its entirety. As will become apparent from the description, this arrangement is used to illustrate the features of the invention; however, the invention is not limited in its applicability to such an arrangement and is rather useful in various other systems and arrangements.  
         [0006]     In  FIGS. 1A and 1B , the ATE  100  is shown with its tester head  110  extended over the emission tester  150 , so as to connect to a device under test (DUT)  130  via flexible connector  115 . The tester head  110  is movable for docking using manipulation arm  105 . The ATE  100  generally comprises a controller, such as a pre-programmed computer  105 , that generates and delivers test signals to the DUT  130  in a manner well known in the art. Specifically, the ATE  100  is used to generate signals that stimulate the DUT  130  to perform various tasks, as designed by the chip designer to check and/or debug the DUT  130 . The various signals generated by the controller  105  are delivered to the DUT  130  via the connector  115 . As is well known in the art, as the DUT  130  reacts to the various test signals received from the ATE, the DUT&#39;s various active elements emit light. The light is then detected by the emission tester  150  and is used by the emission tester  150  to decipher the operation of the DUT  130 .  
         [0007]     On the emission tester side, the DUT  130  is held on an adapter plate  155 , which is connected to a self-leveling, vibration-isolation bench  160  via tilting mechanism  165 . The tilting mechanism  165  can be implemented using servomotors, or in other manners as described more fully in the above-cited co-assigned patent application. While only one tilting mechanism is shown, it should be appreciated that several can be used so as to obtain the appropriate degrees of freedom for the required tilting. The bench  160  can be any commercially available self-leveling vibration-isolation bench (e.g., the Precision-Aire™available from Fabreeka™ of Boston, Mass. or an Optical Table 5000 series, available from Kinetic Systems, Inc. of Boston Mass.). Such a bench generally includes a tabletop  175  riding on plungers  170 . Each plunger  170  is operable, pneumatically, for example, to rise or drop so as to level to tabletop  175 . A level control valve  180  is used to control the plunger so as to provide automatic leveling of the tabletop  175 . An x-y-z stage  185  is connected to the underside of the tabletop  175 . The stage  185  is used to support and navigate the collection optics  190  so as to collect light from the DUT  130 . The collection optics may include an objective lens and a solid immersion lens (SIL), in a manner known in the art. The various elements of the emission tester are controlled by a controller  195  via connector  120 , which may be a general purpose computer pre-programmed to perform specific tasks.  
         [0008]     As can be understood, for maximum light collection efficiency, the inspected surface of the DUT  130  needs to be orthogonal to the optical axis of the collection optics  190 . To achieve that, the tilt mechanism  165  is operated so as to tilt the adapter plate  155  as shown by the double-headed arrow, so as to achieve the required alignment. In  FIG. 1A  the adapter plate  155  is shown leveled with the tabletop  175 , while in  FIG. 1B  the adapter plate  155  is shown tilted with respect to the tabletop  175 . However, while the tilt mechanism  165  is operable to tilt the adapter plate  155 , as shown in  FIG. 1B  the tester head  110  is stationary and does not move with the adapter plate  155 . Therefore, in the prior art, a flexible connector  115  is used to maintain the connections between the tester head  110  and the DUT  130 . However, the use of such a flexible adapter introduces several drawbacks to such an arrangement. Such flexible adapters are complex and expensive. Additionally, in order to obtain accurate testing, each such flexible adapter needs to be accurately characterized, which adds to the cost of the arrangement. Regardless of characterization, the flexible adapter may introduce inaccuracies into the testing. Moreover, the adapter may be exposed to repeated stresses due to repeated tilting and may fail prematurely.  
         [0009]     Accordingly, there is a need in the art for a system that will allow docking of the tester head to the DUT without a flexible adapter, i.e., hard docking, while still maintain the ability to align the DUT to the optical axis of the collection optics.  
       SUMMARY OF THE INVENTION  
       [0010]     The present inventors provide an apparatus and method for hard-docking of a tester head to a DUT, while permitting the angular alignment of a specimen to be inspected to the optical axis of an optical testing tool.  
         [0011]     In one aspect of the invention, a system for orthogonal alignment of a specimen to an optical axis of a collection optics is provided. The system comprises a self-leveling tabletop; a specimen holder coupled to the tabletop and held at a fix orientation; collection optics coupled to the tabletop; a plunger coupled to the tabletop and operable to maintain the leveling orientation of the tabletop; a control valve sensing the leveling orientation of the tabletop and coupled to the plunger to control the operation of the plunger; and an aligner coupled to the tabletop and operable to change the alignment of the optical axis of the collection optics with respect to the specimen without changing the fixed orientation of the specimen holder.  
         [0012]     In various illustrative implementations the aligner is structured as a blocking valve operable to block the operation of the control valve, and a tilting mechanism coupled between the tabletop and the specimen holder. The tilting mechanism can be implemented as a plurality of electrical motors. According to another implementation the aligner is structured as several lifters, each coupled to the plungers and the tabletop. According to yet another implementation, the aligner is structured as a tilt stage supporting the collection optics. By “tilt stage” what is meant is a stage that allows changing the angular alignment of the optical axis with respect to the specimen, in contrast with a stage that allows navigation in the plane of the specimen and distance therefrom. According to another implementation the collection optics is coupled to a holder and the holder comprises rotation mechanism that allows changing the angular alignment of the optical axis with respect to the specimen.  
         [0013]     Various embodiments of the invention also provide for a method for orienting an optical system with respect to a specimen. The method is particularly useful for an optical system having a tabletop, collection optics coupled to the tabletop, and a specimen holder coupled to the tabletop. The method proceeds by placing the specimen in the specimen holder; fixing said specimen holder at a fixed orientation; and controlling the optical system so as to place the collection optics in an orientation such that the optical axis of the collection optics is perpendicular to an area of interest on the specimen without disturbing the fixed orientation of the specimen holder. In one example, the process of controlling the optical system is implemented by tilting the tabletop. According to another example the process of controlling the optical system is implemented by tilting the collection optics. When a solid immersion lens is used, once the appropriate tilting has been achieved, the SIL is made to contact the specimen.  
         [0014]     In a more specific implementation, a system for testing an integrated circuit (IC) stimulated to simulate operating conditions is provided. The system includes a tabletop; a specimen holder coupled to the tabletop. The IC is mounted onto the specimen holder; a collection optics arrangement is coupled to the tabletop; an adapter is provided for hard-docking a tester head to the IC and thereby hold the specimen holder in a fixed orientation; an aligner is coupled to the tabletop and is operable to change the alignment of the optical axis of the collection optics with respect to the IC without changing the fixed orientation of the specimen holder.  
         [0015]     In various implementations the system may further include a plurality of plungers coupled to the tabletop and operable to maintain the leveling orientation of the tabletop, and a plurality of control valves each sensing the leveling orientation of the tabletop and coupled to respective one of the plungers to control the operation of the plunger. The system may also include blocking valves, each operable to block the operation of a respective control valve, and a tilting mechanism coupled between the tabletop and the specimen holder. The tilting mechanism may be implemented as a plurality of electrical motors, such as stepper motors or servomotors. The tiltable holder can be implemented as a test bench having lifter system operable to adjust the tilt of the test bench, and the lifter system may be implemented as a plurality of lifters and a plurality of motors, each of the motors coupled to a respective lifter. The aligner may further be implemented as a plurality of lifters coupled to respective plungers, or as a tilt stage supporting the collection optics. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIGS. 1A and 1B  are general schematics depicting the major components of the testing and debug system according to the prior art.  
         [0017]      FIGS. 2A and 2B  depict an embodiment of the invention as implemented in the system of  FIGS. 1A and 1B .  
         [0018]      FIGS. 3A and 3B  depict another embodiment of the invention as implemented in the system of  FIGS. 1A and 1B .  
         [0019]      FIGS. 4A and 4B  depict another embodiment of the invention as implemented in the system of  FIGS. 1A and 1B .  
         [0020]      FIGS. 5A and 5B  depict another embodiment of the invention as implemented in the system of  FIGS. 1A and 1B .  
     
    
       [0021]     The invention is described herein with reference to particular embodiments thereof, which are exemplified in the drawings. It should be understood, however, that the various embodiments depicted in the drawings are only exemplary and may not limit the invention as defined in the appended claims.  
       DETAILED DESCRIPTION  
       [0022]     An embodiment of the invention will now be described in details with reference to  FIGS. 2A and 2B  and, for illustration purposes, it will be depicted as implemented in the system of  FIGS. 1A and 1B . Such a system is particularly useful for photon emission testing of integrated circuits. Since photon emission from integrated circuits is very faint, the system described with respect to  FIGS. 2A and 2B  uses a SIL. However, those skilled in the art can readily observe that the invention can be easily implemented in other optical systems that may or may not use a SIL.  
         [0023]     In  FIGS. 2A and 2B , elements that are the same or similar to those in  FIGS. 1A and 1B  have the same enumeration, except that it&#39;s in the two-hundreds rather than the one-hundred series. To illustrate the problem solved by the invention, the DUT  230  is depicted in  FIGS. 2A and 2B  as having a slanted surface. Consequently, the surface of the DUT  230  is not perpendicular to the optical axis of the collection optics  290 . This is illustrated by dashed line “P”, which represents a line perpendicular to the surface of the DUT  230 , and dashed line “O”, which represents the optical axis of collection optics  290 . Of course, the invention is also helpful in other circumstances, such as when the surface of the DUT is irregular and a localized area to be investigated is not perpendicular to the optical axis of the collection optics  290 .  
         [0024]     In the embodiment of  FIGS. 2A and 2B , a blocking valve  225  is inserted in each line of each level control valve  280 . Each of the blocking valve  225  may be manually or remotely controlled. If the blocking valve is remotely controlled, it can be connected to the controller  295  to be controlled according to the program run by the controller  295 . The function of the blocking valve  225  is to block the operation of the control valve  280  and decouple it from the plunger  270 . When the blocking valve  225  is in the open position, the level control valve  280  is coupled to the plunger  270  and operates to maintain leveling of the tabletop  275 . On the other hand, when the blocking valve is in the close position, the level control valve  280  cannot change the pressure applied to the plunger  275  and, consequently, the plunger  275  does not maintain the tabletop at a level position.  
         [0025]     More specifically, as is known in the prior art, a self-leveling pneumatic tabletop uses air pressure to maintain the tabletop at a level position. For example, the tabletop may rest on four plungers, each of which may be connected to a control valve. When a weight is placed on one side of the table and disturbs the tabletop&#39;s equilibrium, the disturbance is sensed by the control valves, which then change the pressure inside the plunger so as to return the tabletop to a level position. In normal operation, the tabletop is allowed to automatically maintain its level position and the stage  285  is used to navigate the collection optics  290  so that the appropriate area of the DUT  230  can be inspected. However, as explained previously, sometimes the area to be inspected is not level or not aligned perpendicularly to the optical axis of the collection optics  290 . Such a situation causes a reduction in the image quality as well as the collection efficiency of the collection optics  290 . To overcome this problem the angular orientation between the DUT  230  and the collection optics  290  needs to be changed.  
         [0026]     In the prior art the angular orientation between the DUT  230  and the collection optics  290  is changed by tilting the adapter plate  255  using the tilting mechanism  265 , which, as explained before, required the use of a flexible adapter  215 . According to this embodiment of the invention, on the other hand, no flexible adapter is used, but rather, the tester head  210  is hard-docked to the adapter plate  255 . By hard-dock it is meant that once the tester head is docked to the DUT, no relative motion is allowed between the DUT and the tester head. Therefore, for hard-docking the tester head to the DUT the user may use a rigid, rather than a flexible connector such as connector  115 .  
         [0027]     According to an illustrative method of the invention, after the tester head  210  is hard-docked to the adapter plate  255  and the tabletop has been stabilized in the level position, the blocking valves  225  are actuated so as to assume to closed position. Under this condition, the tabletop  275  is counter-balanced by pressurized plungers  270 , which makes it very easy to tilt the tabletop  275 . However, if the tabletop  275  is tilted, the plungers  270  will not correct the tilt, since the conduits from the control valves  280  are blocked by the blocking valves  225 . Therefore, when the tilting mechanism  265  is actuated to change the angular orientation between the DUT  230  and the collection optics  290 , the tabletop  275 , rather than the adapter plate  255  is tilted. This is because the adapter plate  255  is held in its position by the hard-dock to the tester head  210 , while the tabletop  275  is easily moved since it is riding on pressurized plungers  270 . This tilt position is demonstrated in  FIG. 2B .  
         [0028]     As can be appreciated by comparing  FIGS. 2A and 2B , in  FIG. 2A  the tilting mechanism  265  is in a somewhat extended position. The tabletop is maintain level by the plungers  270 , two of which are shown in the Figures, and both of which are shown as extending to the same extent. On the other hand, in  FIG. 2B  the tilt mechanism  265  has been pulled to reduce its extension. Consequently, the tabletop  275  is tilted by the right plunger  270 R extending, while the left plunger  270 L compressing. The adapter plate  255  has not moved as it is hard docked to the tester head  210 . Accordingly, a change in the angular orientation between the DUT  230  and the collection optics  290  has been achieved as is illustrated by the two dashed lines “P” and “O” coinciding in  FIG. 2B .  
         [0029]      FIGS. 3A and 3B  depict another embodiment of the invention. For illustration purposes, this embodiment is depicted as implemented in the system of  FIGS. 1A and 1B . Also, elements that are the same or similar to those in  FIGS. 1A and 1B  have the same enumeration, except that it&#39;s in the three-hundreds rather than the one-hundred series. In the embodiment of  FIGS. 3A and 3B , the adapter plate  355  is connected to the tabletop  375  via elastic connection  302 . By elastic it is meant that the connection allows for relative motion between the adapter plate  355  and the tabletop  375 . Such connection may be, for example, a bellow arrangement, a bearing arrangement, and the likes. Elevating mechanism  362 R and  362 L are provided on top of plungers  370 . While only two elevating mechanisms are shown, it would be appreciated that a different number may be used. For example, one elevating mechanism can be provided on each plunger so that if four plungers are used, four elevating mechanisms are used. The elevating mechanism may be manually of remotely controlled. If remote control is desired, the elevating mechanism may be a servomotor connected to the controller  395 .  
         [0030]     In the embodiment of  FIGS. 3A and 3B , when a change in the angular orientation between the DUT and the collection optics is needed, the elevation mechanisms  362  are activated so as to tilt the tabletop  375 , while the adapter plate  355  remains connected to the tester head  310  in a hard-dock manner. This is shown in  FIG. 3B , wherein elevating mechanism  362 R is extended while elevating mechanism  362 L is contracted, so that the tabletop  375  is tilted.  
         [0031]      FIGS. 4A and 4B  depict another embodiment of the invention. For illustration purposes, this embodiment is depicted as implemented in the system of  FIGS. 1A and 1B . Also, elements that are the same or similar to those in  FIGS. 1A and 1B  have the same enumeration, except that it&#39;s in the four-hundreds rather than the one-hundred series. In the embodiment of  FIGS. 4A and 4B , the adapter plate  455  is rigidly connected to the tabletop  475 , so that no relative motion is allowed. For example, the adapter plate  455  may be bolted to the tabletop  475 . As also shown, the x-y-z stage  485  is provided with an additional motion element  468 , such as, e.g., an R-Theta stage. The motion element  468  enables moving the collection optics  490  so as to change the angular orientation of the collection optics  490  with respect to the DUT  430 . This is depicted in  FIG. 4B , wherein the motion element  468  is activated to move the collection optics  490  is exemplified by the double-headed arrow. As can be understood, due to the two-dimensional nature of the drawing, only one motion element  468  is shown, providing angular motion in the plane of the page. However, a second element may be provided in order to allow for angular motion in the plane perpendicular to the page, i.e., in and out of the page.  
         [0032]      FIGS. 5A and 5B  depict another embodiment of the invention. For illustration purposes, this embodiment is depicted as implemented in the system of  FIGS. 1A and 1B . Also, elements that are the same or similar to those in  FIGS. 1A and 1B  have the same enumeration, except that it&#39;s in the five-hundreds rather than the one-hundred series. In the embodiment of  FIGS. 5A and 5B , the adapter plate  555  is rigidly connected to the tabletop  575 , so that no relative motion is allowed. For example, the adapter plate  555  may be bolted to the tabletop  575 . The embodiment of  FIGS. 5A and 5B  is similar to that of  FIGS. 4A and 4B  in that additional degrees of motion are provided to enable better manipulation of the collection optics  590 .  
         [0033]     In the embodiment of  FIGS. 5A and 5B  two rotational elements,  564 A and  564 B, are provided on the support of the collection optics  590 . The rotational elements  564 A and  564 B may be manually of remotely controlled. If remote control is desired, the rotational elements  564 A and  564 B may be stepper motors or servomotors connected to the controller  595 . Using the x-y-z stage  585  the collection optics  590  can be placed in the appropriate spatial position to enable investigation of a particular area of the DUT  530 . If the particular area of interest is not perpendicular to the optical axis of collection optics  590 , one of both of the rotational elements  564 A and/or  564 B can be used to tilt the collection optics  590  so as to provide correction to the angular orientation, as shown by the arrows.  
         [0034]     While the invention has been described with reference to particular embodiments thereof, it is not limited to those embodiments. Specifically, various variations and modifications may be implemented by those of ordinary skill in the art without departing from the invention&#39;s spirit and scope, as defined by the appended claims. Additionally, all of the above-cited prior art references are incorporated herein by reference.