Apparatus and method for hard-docking a tester to a tiltable imager

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.

BACKGROUND OF THE INVENTION

1. Field of the Invention

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.

2. Description of the Related Art

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.

FIGS. 1A and 1Bare 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.

InFIGS. 1A and 1B, the ATE100is shown with its tester head110extended over the emission tester150, so as to connect to a device under test (DUT)130via flexible connector115. The tester head110is movable for docking using manipulation arm105. The ATE100generally comprises a controller, such as a pre-programmed computer105, that generates and delivers test signals to the DUT130in a manner well known in the art. Specifically, the ATE100is used to generate signals that stimulate the DUT130to perform various tasks, as designed by the chip designer to check and/or debug the DUT130. The various signals generated by the controller105are delivered to the DUT130via the connector115. As is well known in the art, as the DUT130reacts to the various test signals received from the ATE, the DUT's various active elements emit light. The light is then detected by the emission tester150and is used by the emission tester150to decipher the operation of the DUT130.

On the emission tester side, the DUT130is held on an adapter plate155, which is connected to a self-leveling, vibration-isolation bench160via tilting mechanism165. The tilting mechanism165can 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 bench160can 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 tabletop175riding on plungers170. Each plunger170is operable, pneumatically, for example, to rise or drop so as to level to tabletop175. A level control valve180is used to control the plunger so as to provide automatic leveling of the tabletop175. An x-y-z stage185is connected to the underside of the tabletop175. The stage185is used to support and navigate the collection optics190so as to collect light from the DUT130. 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 controller195via connector120, which may be a general purpose computer pre-programmed to perform specific tasks.

As can be understood, for maximum light collection efficiency, the inspected surface of the DUT130needs to be orthogonal to the optical axis of the collection optics190. To achieve that, the tilt mechanism165is operated so as to tilt the adapter plate155as shown by the double-headed arrow, so as to achieve the required alignment. InFIG. 1Athe adapter plate155is shown leveled with the tabletop175, while inFIG. 1Bthe adapter plate155is shown tilted with respect to the tabletop175. However, while the tilt mechanism165is operable to tilt the adapter plate155, as shown inFIG. 1Bthe tester head110is stationary and does not move with the adapter plate155. Therefore, in the prior art, a flexible connector115is used to maintain the connections between the tester head110and the DUT130. 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.

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

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.

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.

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.

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.

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.

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.

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

An embodiment of the invention will now be described in details with reference toFIGS. 2A and 2Band, for illustration purposes, it will be depicted as implemented in the system ofFIGS. 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 toFIGS. 2A and 2Buses 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.

InFIGS. 2A and 2B, elements that are the same or similar to those inFIGS. 1A and 1Bhave the same enumeration, except that it's in the two-hundreds rather than the one-hundred series. To illustrate the problem solved by the invention, the DUT230is depicted inFIGS. 2A and 2Bas having a slanted surface. Consequently, the surface of the DUT230is not perpendicular to the optical axis of the collection optics290. This is illustrated by dashed line “P”, which represents a line perpendicular to the surface of the DUT230, and dashed line “O”, which represents the optical axis of collection optics290. 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 optics290.

In the embodiment ofFIGS. 2A and 2B, a blocking valve225is inserted in each line of each level control valve280. Each of the blocking valve225may be manually or remotely controlled. If the blocking valve is remotely controlled, it can be connected to the controller295to be controlled according to the program run by the controller295. The function of the blocking valve225is to block the operation of the control valve280and decouple it from the plunger270. When the blocking valve225is in the open position, the level control valve280is coupled to the plunger270and operates to maintain leveling of the tabletop275. On the other hand, when the blocking valve is in the close position, the level control valve280cannot change the pressure applied to the plunger270and, consequently, the plunger270does not maintain the tabletop at a level position.

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'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 stage285is used to navigate the collection optics290so that the appropriate area of the DUT230can 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 optics290. Such a situation causes a reduction in the image quality as well as the collection efficiency of the collection optics290. To overcome this problem the angular orientation between the DUT230and the collection optics290needs to be changed.

In the prior art the angular orientation between the DUT and the collection optics is changed by tilting the adapter plate using the tilting mechanism, which, as explained before, required the use of a flexible adapter. According to this embodiment of the invention, on the other hand, no flexible adapter is used, but rather, the tester head210is hard-docked to the adapter plate255. 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 rigid215, rather than a flexible connector such as connector115.

According to an illustrative method of the invention, after the tester head210is hard-docked to the adapter plate255and the tabletop has been stabilized in the level position, the blocking valves225are actuated so as to assume to closed position. Under this condition, the tabletop275is counter-balanced by pressurized plungers270, which makes it very easy to tilt the tabletop275. However, if the tabletop275is tilted, the plungers270will not correct the tilt, since the conduits from the control valves280are blocked by the blocking valves225. Therefore, when the tilting mechanism265is actuated to change the angular orientation between the DUT230and the collection optics290, the tabletop275, rather than the adapter plate255is tilted. This is because the adapter plate255is held in its position by the hard-dock to the tester head210, while the tabletop275is easily moved since it is riding on pressurized plungers270. This tilt position is demonstrated inFIG. 2B.

As can be appreciated by comparingFIGS. 2A and 2B, inFIG. 2Athe tilting mechanism265is in a somewhat extended position. The tabletop is maintain level by the plungers270, two of which are shown in the Figures, and both of which are shown as extending to the same extent. On the other hand, inFIG. 2Bthe tilt mechanism265has been pulled to reduce its extension. Consequently, the tabletop275is tilted by the right plunger270R extending, while the left plunger270L compressing. The adapter plate255has not moved as it is hard docked to the tester head210. Accordingly, a change in the angular orientation between the DUT230and the collection optics290has been achieved as is illustrated by the two dashed lines “P” and “O” coinciding inFIG. 2B.

FIGS. 3A and 3Bdepict another embodiment of the invention. For illustration purposes, this embodiment is depicted as implemented in the system ofFIGS. 1A and 1B. Also, elements that are the same or similar to those inFIGS. 1A and 1Bhave the same enumeration, except that it's in the three-hundreds rather than the one-hundred series. In the embodiment ofFIGS. 3A and 3B, the adapter plate355is connected to the tabletop375via elastic connection302. By elastic it is meant that the connection allows for relative motion between the adapter plate355and the tabletop375. Such connection may be, for example, a bellow arrangement, a bearing arrangement, and the likes. Elevating mechanism362R and362L are provided on top of plungers370. 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 controller395.

In the embodiment ofFIGS. 3A and 3B, when a change in the angular orientation between the DUT and the collection optics is needed, the elevation mechanisms362are activated so as to tilt the tabletop375, while the adapter plate355remains connected to the tester head310in a hard-dock manner. This is shown inFIG. 3B, wherein elevating mechanism362R is extended while elevating mechanism362L is contracted, so that the tabletop375is tilted.

FIGS. 4A and 4Bdepict another embodiment of the invention. For illustration purposes, this embodiment is depicted as implemented in the system ofFIGS. 1A and 1B. Also, elements that are the same or similar to those inFIGS. 1A and 1Bhave the same enumeration, except that it's in the four-hundreds rather than the one-hundred series. In the embodiment ofFIGS. 4A and 4B, the adapter plate455is rigidly connected to the tabletop475, so that no relative motion is allowed. For example, the adapter plate455may be bolted to the tabletop475. As also shown, the x-y-z stage485is provided with an additional motion element468, such as, e.g., an R-Theta stage. The motion element468enables moving the collection optics490so as to change the angular orientation of the collection optics490with respect to the DUT430. This is depicted inFIG. 4B, wherein the motion element468is activated to move the collection optics490is exemplified by the double-headed arrow. As can be understood, due to the two-dimensional nature of the drawing, only one motion element468is 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.

FIGS. 5A and 5Bdepict another embodiment of the invention. For illustration purposes, this embodiment is depicted as implemented in the system ofFIGS. 1A and 1B. Also, elements that are the same or similar to those inFIGS. 1A and 1Bhave the same enumeration, except that it's in the five-hundreds rather than the one-hundred series. In the embodiment ofFIGS. 5A and 5B, the adapter plate555is rigidly connected to the tabletop575, so that no relative motion is allowed. For example, the adapter plate555may be bolted to the tabletop575. The embodiment ofFIGS. 5A and 5Bis similar to that ofFIGS. 4A and 4Bin that additional degrees of motion are provided to enable better manipulation of the collection optics590.

In the embodiment ofFIGS. 5A and 5Btwo rotational elements,564A and564B, are provided on the support of the collection optics590. The rotational elements564A and564B may be manually of remotely controlled. If remote control is desired, the rotational elements564A and564B may be stepper motors or servomotors connected to the controller595. Using the x-y-z stage585the collection optics590can be placed in the appropriate spatial position to enable investigation of a particular area of the DUT530. If the particular area of interest is not perpendicular to the optical axis of collection optics590, one of both of the rotational elements564A and/or564B can be used to tilt the collection optics590so as to provide correction to the angular orientation, as shown by the arrows.

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's spirit and scope, as defined by the appended claims. Additionally, all of the above-cited prior art references are incorporated herein by reference.