Abstract:
A method and apparatus for in-situ lift-out rapid preparation of TEM samples. The invention uses adhesives and/or spring-loaded locking-clips in order to place multiple TEM-ready sample membranes on a single TEM support grid and eliminates the use of standard FIB-assisted metal deposition as a bonding scheme. Therefore, the invention circumvents the problem of sputtering from metal deposition steps and also increases overall productivity by allowing for multiple samples to be produced without opening the FIB/SEM vacuum chamber.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims one or more inventions which were disclosed in Provisional Application No. 61/413,083, filed Nov. 12, 2010, entitled “METHOD AND APPARATUS FOR RAPID PREPARATION OF MULTIPLE SPECIMENS FOR TRANSMISSION ELECTRON MICROSCOPY”. The benefit under 35 USC §119(e) of the United States provisional application is hereby claimed, and the aforementioned application is hereby incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention is in the technical field of methods of sample preparation and manipulation for preparing a specimen for transmission electron microscopy (TEM) examination. More particularly, the present invention is in the technical field of sample preparation and manipulation by methods of in-situ lift-out techniques. 
         [0004]    2. Description of Related Art 
         [0005]    The standard in-situ lift-out method involves moving a micromanipulator probe to a sample membrane that was previously milled from a wafer by use of a focused ion beam/scanning electron microscope (FIB/SEM) or similar machine. This leaves the sample membrane approximately 1-2 microns thick with varying length and height (typically 5-15 micron length and 5-15 micron height). The micromanipulator probe is then welded to the sample membrane by ion beam assisted metal deposition. When the weld is secured, the sample membrane is then cut from the wafer by a focused ion beam (FIB) and extracted from the wafer. 
         [0006]    The probe then moves the sample to a transmission electron microscope (TEM) grid where it is welded to the TEM grid by ion beam assisted metal deposition. When the sample membrane is secured to the TEM grid, the probe is cut from the sample by FIB. The sample membrane is then milled again by FIB until it is thin enough for use in a TEM, typically between 50-200 nanometers thick. The entire method is done within the FIB/SEM machine chamber while it is activated and under vacuum. 
         [0007]    The current method of in-situ lift-out has a low productivity, as the number of samples that are produced is relatively low in comparison to the total amount of time and effort that is used for this purpose. Features that shorten the time of preparing a sample and/or increase user productivity are highly desirable in this field. 
         [0008]    The current method also has problems in metal deposition steps where excess material may sputter on, and contaminate unintended objects. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides a method and apparatus for in-situ lift-out rapid preparation of samples for electron microscopy. The invention uses adhesives and/or spring-loaded locking-clips in order to place multiple sample membranes on a single support grid and eliminates the use of standard FIB-assisted metal deposition as a bonding scheme. Therefore, the invention circumvents the problem of sputtering from metal deposition steps and also increases overall productivity by allowing for multiple samples to be produced without opening the FIB/SEM vacuum chamber. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0010]      FIG. 1  is a flowchart demonstrating the method. 
           [0011]      FIG. 2  is a perspective view of a lift-out system. 
           [0012]      FIG. 3  is a perspective view of the continuation of a lift-out system from  FIG. 2 . 
           [0013]      FIG. 4  is a perspective view of the continuation of a lift-out system from  FIG. 3 . 
           [0014]      FIG. 5-A  is a perspective view of an alternate embodiment of a lift-out system. 
           [0015]      FIG. 5-B  is a perspective view of an alternate embodiment of a lift-out device. 
           [0016]      FIG. 5-C  is a side view of an alternate embodiment of a lift-out device of  FIG. 5-B . 
           [0017]      FIG. 6  is a wide perspective view of a continuation of a lift-out system from  FIG. 4 . 
           [0018]      FIG. 7  is a close up perspective view of  FIG. 6  and continuation of a lift-out system from  FIG. 6 . 
           [0019]      FIG. 8  is a close up perspective view of  FIG. 6  and continuation of a lift-out system from  FIG. 7 . 
           [0020]      FIG. 9-A  is a wide perspective view of a repetition of a lift-out system. 
           [0021]      FIG. 9-B  is a wide perspective view of an alternate embodiment of  FIG. 9-A . 
           [0022]      FIG. 9-C  is a wide perspective view of an alternate embodiment of  FIG. 9-A . 
           [0023]      FIG. 10-A  is a wide perspective view of an alternate embodiment of  FIG. 9-A . 
           [0024]      FIG. 10-B  is a close up cross sectional view of  FIG. 10-A . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The Method 
       [0025]    Referring now to  FIG. 1 , there is shown a flowchart  100  of the method. The method is comprised of the following steps shown in the flowchart
     101 : Place wafer, microprobe assemblies and TEM support grid into FIB/SEM chamber—Set up all the necessary parts in order to do an in-situ lift-out according to the method shown in the flowchart  100 . A wafer, microprobe assemblies, and TEM support grids are loaded into a FIB/SEM chamber, which is then activated, placing all its contents under vacuum.     102 : Place microprobe assembly in micro gripping and manipulation device—a micro gripping and manipulation device reaches and grasps a micromanipulator probe, which has an adhesive or a spring loaded locking clip at the end of it.     103 : Ion mill sample membrane from wafer—the FIB/SEM is used to create a sample membrane by etching out portions of the wafer using an ion beam. The sample membrane will be approximately 5-15 microns long, 5-15 microns deep, and less than 200 nanometers thick when the step is completed. The sample membrane will also be partially cut away from the wafer.     104 : Attach microprobe assembly to sample membrane—the micro gripping and manipulation device moves the micromanipulator probe so that the adhesive or spring loaded locking clip will touch and attach to the sample membrane. The sample membrane is attached to both the wafer and the microprobe assembly.     105 : Detach sample membrane from wafer—the sample membrane is completely severed from the wafer by the FIB/SEM ion beam. The sample membrane is now only attached to the microprobe assembly.     106 : Move microprobe assembly with attached sample membrane to a TEM support grid—the microprobe assembly is moved from the wafer to the TEM support grid so that the sample membrane is over a hollow viewing window.     107 : Secure microprobe assembly with attached sample membrane to a TEM support grid—the microprobe assembly is attached to the TEM support grid using an adhesive or a spring loaded locking clip so that it is secured to the TEM support grid.     108 : Release microprobe assembly from micro gripping and manipulation device—the micro gripping and manipulation device releases the microprobe assembly with sample membrane only attached to the TEM support grid.     109 : Repeat Process?—the process may be repeated to create and attach more sample membranes to the TEM support grid.   
 
         [0035]    If yes, return to step  102  and repeat the method; 
         [0036]    If no, go on to the last step.
     110 : Remove TEM support grid from FIB/SEM for examination—the TEM support grid has as many sample membranes attached to it as required by the user and the FIB/SEM is deactivated, releasing the vacuum chamber. The TEM support grid is removed so that it can by viewed by a TEM.   
 
       The Apparatus 
       [0038]    Referring now to  FIG. 2  to  FIG. 4 , there is shown a microprobe assembly  1  held by a micro gripping and manipulation device  2 , which is next to a wafer  6 . The microprobe assembly  1  consists of a micromanipulator probe  3  with a sample attachment element—in this embodiment shown as an adhesive  4 —at the end opposite the end held by device  2 . A sample membrane  5  is part of the wafer  6 . 
         [0039]    In more detail, still referring to  FIG. 2  to  FIG. 4 , the microprobe assembly  1  is moved by the micro gripping and manipulation device  2  to the sample membrane  5 . The sample membrane  5  was previously ion milled by FIB from the wafer  6 . The micromanipulator probe  3  is attached to the sample membrane  5  by the adhesive  4 . After the adhesive  4  bonds the sample membrane  5  to the micromanipulator probe  3 , the sample membrane  5  is detached from the wafer  6  and moved by the micro gripping and manipulation device  2  holding the microprobe assembly  1  with respect to the wafer  6 . 
         [0040]    In reference to the flowchart  100  shown in  FIG. 1 ,  FIG. 2  is shown after the following steps were previously completed; “Place wafer, microprobe assemblies and TEM support grid into FIB/SEM chamber”  101 ; “Place microprobe assembly in micro gripping and manipulation device”  102 ; “Ion mill sample membrane from wafer”  103 .  FIG. 3  is shown after the step, “Attach microprobe assembly to sample membrane”  104 .  FIG. 4  is shown after the step, “Detach the sample membrane from wafer”  105 . 
         [0041]    In further detail, still referring to  FIG. 2  to  FIG. 4 , the wafer  6  is loaded into a Focused Ion Beam/Scanning Electron Microscope (FIB/SEM) machine chamber along with the micromanipulator probe  3  and adhesive  4  before beginning the process. The micro gripping and manipulation device  2  is attached to the FIB/SEM machine so that it may manipulate the micromanipulator probe  3 . The microprobe assembly  2  must be sufficiently small to capture the sample membrane  5  typically in sizes of five to fifteen microns long, five to fifteen microns deep and approximately 200 nanometers thick or less, but not subject to these limits. The micromanipulator probe  3  may vary in size, length, or geometry, but must be usable with typical manipulating devices that are compatible with FIB/SEM machines. The adhesive  4  may either be preloaded on the micromanipulator probe  3  prior to insertion into a FIB/SEM machine or a small amount of the adhesive may be placed in the FIB/SEM machine where it is accessible to the micromanipulator probe  3 . 
         [0042]    The construction details of the invention as shown in  FIG. 2  to  FIG. 4  are that the micromanipulator probe  3  be made of a metal typically used in the art, such as tungsten, molybdenum, or others. The micromanipulator probe  3  is cylindrical and tapers to a point where the adhesive  4  is placed. The adhesive  4 , in its preferred embodiment would be usable in vacuum chamber environments of a FIB/SEM machine and would also be curable by exposing it to charged electron particles such as particles exerted from a FIB/SEM machine. 
         [0043]    Referring now to  FIG. 5-A  to  FIG. 5-C , there is shown a sample wafer  24  attached to a microprobe assembly  20 , which is held by a micro gripping and manipulation device  21 , which is near a wafer  25 . The microprobe assembly  20  consists of a micromanipulator probe  22  attached to a spring-loaded locking clip  23  at its end. 
         [0044]    In more detail, still referring to  FIG. 5-A  to  FIG. 5-C , the microprobe assembly  20  attaches the sample membrane  24  to the micromanipulator probe  22  using the spring loaded locking clip  23 . The sample membrane  24  is held in place by the force applied from the spring loaded locking clip  23 . The sample membrane  24  was previously ion milled by FIB from the wafer  25 . This is an alternate embodiment of the invention. 
         [0045]    In further detail, still referring to  FIG. 5-A  to  FIG. 5-C , the wafer  25  is loaded into a Focused Ion Beam/Scanning Electron Microscope (FIB/SEM) machine chamber along with a micromanipulator probe  22  and spring loaded locking clip  23  before beginning the process. The micro gripping and manipulation device  21  is attached to the FIB/SEM machine so that it may manipulate the micromanipulator probe  22 . The microprobe assembly  20  must be sufficiently small to capture the sample membrane  24  typically in sizes of five to fifteen microns long, five to fifteen microns deep, and approximately 200 nanometers thick or less, but not subject to these limits. 
         [0046]    The micromanipulator probe  22  may vary in size, length, or geometry, but must be usable with typical manipulating devices that are compatible with FIB/SEM machines. The spring loaded locking clip  23  is securely attached to the micromanipulator probe  22  and must apply sufficient force in order to latch and hold onto the sample membrane  24 . 
         [0047]    The construction details of the invention as shown in  FIG. 5-A  to  FIG. 5-C  are that the micromanipulator probe  22  be made of a metal typically used in the art, such as tungsten, molybdenum, or others. The spring loaded locking clip  23  is made of a metal typically used in the art, such that the metal is pliable as to exert a force suitable to hold the sample membrane  24  without inflicting damage to the sample membrane  24 . The spring loaded locking clip  23  may vary in shape, size, and geometry as long as it can deliver the same function. 
         [0048]    Referring now to  FIG. 6  to  FIG. 8 , there is shown a sample membrane  5  attached to a microprobe assembly  1  held by a micro gripping and manipulation device  2  and attached to a grid adhesive  7  which is attached to a modified TEM mesh support grid  8 . The microprobe assembly  1  consists of a micromanipulator probe  3  and an adhesive  4  at the end. 
         [0049]    In more detail, still referring to  FIG. 6  to  FIG. 8 , the microprobe assembly  1  with the sample membrane  5  attached by the adhesive  4  is moved by the micro gripping and manipulation device  2  to the modified TEM mesh support grid  8 . The microprobe assembly  1  is then bonded by the grid adhesive  7  to the TEM mesh support grid  8  in such a way that the attached sample membrane  5  will be in a hollow viewing window of the modified TEM mesh support grid  8 . When the grid adhesive  7  is sufficiently cured so that the microprobe assembly  1  is bonded to the modified TEM mesh support grid  8 , the micro gripping and manipulation device  2  releases the microprobe assembly  1 . In reference to the flowchart  100  shown in  FIG. 1 ,  FIG. 6  and  FIG. 7  is shown after the following steps; “Move microprobe assembly with attached sample membrane to a TEM support grid”  106 ; “Secure microprobe assembly with attached sample membrane to a TEM support grid”  107 .  FIG. 8  is shown after the step, “Release microprobe assembly from micro gripping and manipulation device”  108 . 
         [0050]    In further detail, still referring to  FIG. 6  to  FIG. 8 , the modified TEM mesh support grid is placed in a FIB/SEM chamber before beginning the process as shown in the flowchart of  FIG. 1 . The grid adhesive  7  would be preloaded onto the modified TEM mesh grid  8  or a small amount of the grid adhesive  7  may be placed in the FIB/SEM machine where it is accessible to the microprobe assembly  1 . The modified TEM mesh support grid  8  is built with hollow viewing windows where the sample membrane  5  may be viewed later by a TEM or similar machine. 
         [0051]    The construction details of the invention as shown in  FIG. 6  to  FIG. 8  are that the grid adhesive  7  would be curable either inside or outside the vacuum chamber of a FIB/SEM machine. The grid adhesive  7  must also be able to sufficiently secure the microprobe assembly  1  to the modified TEM mesh support grid  8 . A modified TEM mesh support grid  8  is a standard 3 millimeter mesh support grid, typically made of metals used in the art, such as copper, molybdenum or others with mesh of viewing windows incorporated into its structure. It would typically be approximately 20-50 microns thick and circular or semicircular with a typical diameter of 3 millimeters. It has been modified by cutting a portion of the mesh support grid off to expose the viewing windows at the edge of the cut. 
         [0052]    Referring now to  FIG. 9-A , there is shown a modified TEM mesh support grid  32  attached to a group of microprobe assemblies  30  which are each individually attached to a sample membrane  31 . 
         [0053]    In more detail, still referring to  FIG. 9-A , the modified TEM mesh support grid  32  has been processed with multiple sample membranes  31  from their attached microprobes assemblies  30 . The method in the flowchart shown in  FIG. 1  is repeated until the desired number of sample membranes  31  are placed onto the modified TEM mesh support grid  32 . In reference to the flowchart  100  shown in  FIG. 1 ,  FIG. 9-A  is shown after the following step, “Repeat Process?”  109 , has occurred multiple times. The step “Repeat Process?”  109 , repeats the method starting at the step, “Place microprobe assembly in micro gripping and manipulation device”  102 . When the process no longer needs to be repeated, then the last step, “Remove TEM support grid from FIB/SEM for examination”  110 , would follow. 
         [0054]    Referring now to the invention shown in  FIG. 9-B , there is shown a micro gripping and manipulation device  40  near a group of micromanipulator probes  41  that are attached to a temporary bonding agent  42 , which is attached to a modified TEM slotted support grid  43 . 
         [0055]    In more detail, still referring to  FIG. 9-B , the micro gripping and manipulation device  40  may detach the micromanipulator probe  41  and use the previously described method as shown in the flowchart in  FIG. 1 . After the method described is completed, the micromanipulator probe  41  may be returned to the modified TEM slotted support grid  43 . The temporary bonding agent  42  may allow for the micromanipulator probe  41  to detach and reattach to the modified TEM slotted grid  43 . This is an alternate embodiment of the invention. 
         [0056]    In further detail, still referring to  FIG. 9-B , the modified TEM slotted support grid  43  with the temporary bonding agent  42  is placed in a FIB/SEM machine chamber before beginning the process as shown in the flowchart of  FIG. 1 . The temporary bonding agent  42  allows the micromanipulator probe  41  to bond to the modified TEM slotted grid  43 . The micro gripping and manipulation device  40  may grab the micromanipulator probe  41  and pull it from the modified TEM slotted grid  43 . The micro gripping and manipulation device  40  may also move a micromanipulator probe  41  to the modified TEM slotted grid  43  where contact with the temporary bonding agent  42  will allow the pieces to bond. 
         [0057]    The construction details of the invention as shown in  FIG. 9-B  are that the temporary bonding agent  42  to be strong enough to securely hold a micromanipulator probe  41  but weak enough to detach the micromanipulator probe  41  from it without damage to the micromanipulator probe  41  when force is applied by the micro gripping and manipulation device  40 . The temporary bonding agent  42  may also be able to reattach a micromanipulator probe  41  to the modified TEM slotted support grid  43  by contact and force applied without damage to the micromanipulator probe  41 . 
         [0058]    The modified TEM slotted support grid  43  is a typical TEM slotted support grid used in the art. It is approximately 3 millimeters in diameter with a slotted hole in the middle. It is made of typical metals used in the art, such as copper, molybdenum or others. The TEM slotted support grid is modified by cutting a portion away from the grid so that the cut is roughly parallel with the long axis of the hollow slot. The extent of cut is variable, but leaves the hollow slot of the slotted TEM grid intact. 
         [0059]    Referring now to  9 -C, there is shown a micro gripping and manipulation device  50  near a micromanipulator probe  51  which is attached to a temporary bonding agent  52 , which is attached to a modified TEM slotted support grid  53 . 
         [0060]    In more detail, still referring to  FIG. 9-C , the micro gripping and manipulation device  50  may manipulate the micromanipulator probe  51  and use the previously described method shown in the flowchart of  FIG. 1 . After the method described is completed, the micromanipulator probe may be returned to the modified TEM slotted support grid  53 . The temporary bonding agent  52  may allow for the micromanipulator probe  51  to detach and reattach to the modified TEM slotted support grid  53 . This is an alternate embodiment of the invention. 
         [0061]    In further detail, still referring to  FIG. 9-C , the modified TEM slotted support grid  53  with the temporary bonding agent  52  is placed in a FIB/SEM machine chamber before beginning the process as shown in the flowchart of  FIG. 1 . The temporary bonding agent  52  allows a micromanipulator probe  51  to bond to the modified TEM slotted support grid  53 . The micro gripping and manipulation device  50  may grab the micromanipulator probe  51  and pull it from the modified TEM slotted support grid  53 . The micro gripping and manipulation device  50  may also move a micromanipulator probe  51  to the modified TEM slotted support grid  53  where contact with the temporary bonding agent  52  will allow the pieces to bond. 
         [0062]    The construction details of the invention as shown in  FIG. 9-C  are that the temporary bonding agent  52  be strong enough to securely attach a micromanipulator probe  51  but weak enough to be able to detach the micromanipulator probe  51  from it without damage to micromanipulator probe  51  when force is applied by the micro gripping and manipulation device  50 . The temporary bonding agent  52  will also be used to reattach the micromanipulator probe  51  to the modified TEM slotted support grid  53  by contact and force applied without damage to the micromanipulator probe  51 . The modified TEM slotted support grid  53  is based on a typical TEM slotted support grid used in the art or a close variation of it. It is approximately 3 millimeters in diameter with a slotted hole in the middle. It is made of typical metals used in the art, such as copper, molybdenum or others. A TEM slotted support grid is modified by cutting a portion away from the grid so that it is roughly parallel with the long axis of the slot. The extent of the cut is variable, but leaves the slotted portion of the grid intact. The micromanipulator probe  51  is flat and made of a metal typically used in the art, such as copper, molybdenum or others. 
         [0063]    Referring now to  FIGS. 10-A  and  10 -B, there is shown a micro gripping and manipulation device  63  near a micromanipulator probe  60  which is attached to a spring loaded locking clip  61 , which is attached to a modified TEM slotted support grid  62 . 
         [0064]    In more detail, still referring to  FIG. 10-A  and  FIG. 10-B , the micro gripping and manipulation device  63  may manipulate the micromanipulator probe  60  and use the previously described method shown in the flowchart of  FIG. 1 . After the method described is completed, the micromanipulator probe  60  may be returned to the modified TEM slotted support grid  62 . The spring loaded locking clip  61  may allow for the micromanipulator probe  60  to detach and reattach to the modified TEM slotted support grid  62 . This is an alternate embodiment of the invention. 
         [0065]    In further detail, still referring to  FIG. 10-A  and  FIG. 10-B , the modified TEM slotted support grid  62  with the spring loaded locking clip  61  is placed in a FIB/SEM machine chamber before the process begins as described in the flowchart of  FIG. 1 . The spring loaded locking clip  61  allows a micromanipulator probe  60  to attach to the modified TEM slotted support grid  62 . The micro gripping and manipulation device  63  may grab the micromanipulator probe  60  and pull it from the modified TEM slotted support grid  62 . The micro gripping and manipulation device  63  may also move a micromanipulator probe  60  to the modified TEM slotted support grid  62  where contact and applied force with the spring loaded locking clip  61  will allow the micromanipulator probe  60  to attach to the modified TEM slotted support grid  62 . 
         [0066]    The construction details of the invention as shown in  FIG. 10-A  and  FIG. 10-B  are that the spring loaded locking clip  61  is strong enough to hold a micromanipulator probe  60  but weak enough to be able to detach the micromanipulator probe  60  from it without damage to the micromanipulator probe  60  when force is applied by the micro gripping and manipulation device  63 . The spring loaded locking clip  61  must also be able to reattach a micromanipulator probe  60  to a modified TEM slotted support grid  62  by contact and force applied without damage to the micromanipulator probe  60 . The spring loaded locking clip  6  may vary in shape, size, and geometry as long as it can deliver the same function. 
         [0067]    The modified TEM slotted support grid  62  is a typical TEM support slotted grid used in the art or a close variation of it. It is typically approximately 3 millimeters in diameter with a slotted hole in the middle. It is made of typical metals used in the art, such as copper, molybdenum or others. The modified TEM slotted support grid  62  is modified by cutting a portion away from the grid so that it is roughly parallel with the long axis of the slot. The extent of cut is variable, but leaves the slotted portion of the support grid intact. 
         [0068]    The advantages include, without limitation, that it allows for multiple sample membranes to be placed on a single TEM support grid for viewing by a TEM or similar machine. The method further avoids the need for assisted metal weld deposition and its inherent metal sputtering on and around the area of interest for microscopy. The method further allows for SEM only type of machines to continue the lift-out process, thereby freeing the more expensive FIB/SEM machine from the downtime of the in-situ lift-out attachment process. 
         [0069]    While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The invention should therefore not be limited by the above described embodiment, method, and examples, but by all embodiments and methods within the scope and spirit of the invention. 
         [0070]    Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.