FEI Helios NanoLab 600 TEM specimen prep recipe Nicholas G. Rudawski ngr@ufl.edu (352) 392 3077 (office) (805) 252-4916 (cell) Last updated: 01/19/17 This recipe is based on the methods of Schaffer et al. for preparing relatively soft semiconductor-based specimens for HR-S/TEM analysis as described in detail at: http://dx.doi.org/10.1016/j.ultramic.2012.01.005. However, depending on the nature of your particular specimens, substantial deviations from this recipe may be necessary including (but not limited to) changes to Pt strap thickness, pattern dimensions (Z in particular), and the method of attachment of the lamella to the grid. You should always consult the scientific literature to see if any FIB-based methods of specimen preparation have been reported for your specific materials and consult staff if you need any recommendations. 1. Grids for in-situ liftouts 1.1. Special grids are needed to perform liftouts. The most effective are made specifically by Omniprobe and are referred to as Omniprobe grids. The grids are made of Cu or Mo and have 3, 4, or 5 fingers with recessed edges to provide points of attachment for samples. In general, it is preferable to use Mo rather than Cu as a grid material. Mo is very stiff, will deform less easily than Cu, and will redeposit less material onto the lamella (though the Mo grids are more expensive with rougher surfaces). 1.2. When loading a grid into the TEM row holder, it should be loaded so that Omniprobe reads forwards as viewed from the top with the row holder inserted into the loading device (clips side facing up). After loading the grid into the row holder, it should be examined edge-on using the optical microscope to make sure it is basically straight. If it appears bent, it should be removed from the row holder and discarded and another (unbent) grid loaded. 1.3. When loading the TEM row holder into the TEM row holder module in the UMB, orient the row holder so the clips side of the holder faces towards the computer desk (this will properly orient the grid when it is time to attach the lamella, assuming you loaded it properly in the previous step). 2. Stage adjustments for specimen 2.1. When the vacuum is sufficient, turn on the beams; make sure the I-beam is initially set to 30 kv with a low beam current (10 or 30 pa); adjustments to the I-beam voltage and current for subsequent steps will be indicated. 1
2.2. If the lamella needs to be prepared so it is aligned with a particular sample direction (e.g. a cleaved edge of a single crystal), first navigate over to the feature to be used for alignment in the live E-beam image and focus the image. Then select Stage from the pull-down menu and then xt Align Feature and follow the instructions; when finished, the stage will rotate to align the feature as specified. 2.3. Navigate to a region of interest on the sample where the lamella is to be made; bring the region of interest to eucentic height, set the stage tilt to T = 52, link the beams (making sure the I-beam scan rotation = 180 ), and set the magnification to 8000 (usually sufficient for lamella preparation). 3. Pt strap deposition 3.1. Set the I-beam to, insert the Pt GIS, and take a snapshot. Draw a rectangle pattern with dimensions X = 8.0, Y = 1.0, and Z = 2.0 µm, respectively, and set the application to Pt dep. Position the pattern as desired (it should remain close to the center of the image) and execute pattern is finished, retract the Pt GIS.. When the 2
4. Milling trenches 4.1. Set the I-beam to, tilt the stage to T = 47, and take an I- beam snapshot ; draw a regular cross-section pattern with X = 12.0, Y = 4.0, and Z = 2.0 µm, respectively, and set the application to Si the Pt strap and execute.. Position the pattern so the thick line is just below 4.2. Tilt the stage to T = 57, take an I-beam snapshot, and set the pattern rotation to ; position the pattern so the thick line is just above the Pt strap and execute. 3
5. Rough cleaning cuts 5.1. Set the I-beam to, tilt the stage back to T = 47, and take an I-beam snapshot ; set the pattern rotation to and set the pattern dimension to X = 12.0, Y = 1.0, and Z = 1.0 µm, respectively. Position the pattern so the thick line is just below the Pt strap and execute 5.2.. Tilt the stage to T = 57 and taken an I-beam snapshot ; set the pattern rotation to and position so the thick line is just above the Pt strap and execute µm thick after finishing this step.. The lamella should be 0.5 1.0 4
6. Undercutting and post-undercut cleaning 6.1. Set the I-beam current to, tilt the stage to T = 7, and delete the regular cross-section pattern used up to this point. Take I- beam snapshots and adjust the Y beam shift until the specimen is back within the field of view. Draw three rectangle patterns as shown in the image below; the width (X or Y dimension) of each pattern should be >0.7 µm with Z = 1.0 µm; position the patterns to there is overlap between the corner regions. Make sure the patterns are set for parallel milling and execute. 5
6.2. Tilt the stage to T = 57 and delete the rectangle patterns used for the undercut; take snapshot I-beam snapshots and adjust the Y beam shift for the I-beam image until the specimen is back within the field of view. Draw a cleaning cross-section pattern with dimensions X = 12.0 and Z = 1.0 µm, respectively, and manually adjust the Y dimension so it covers the wings generated from the undercut; set the pattern rotation to the Pt strap and execute.. Position the pattern so the thick line is just above 6
7. Lifting out the sample 7.1. Set the I-beam current to, tilt the stage to T = 0, and delete the cleaning cross-section pattern just used. Start live I-beam imaging and adjust the Y beam shift until the lamella is back within the field of view. Insert the Omniprobe and use live E- beam and I-beam imaging to approach it to the lamella; when the Omniprobe is a few µm away from the lamella, insert the Pt GIS. Position the Omniprobe so it is over the free end of the lamella as shown below. Draw a rectangle pattern with X and Y dimensions sufficient to cover the point of contact between the Omniprobe and lamella and Z = 0.2 µm and set the application to Pt dep ; take an I-beam snapshot, position the pattern so it is centered over the point of contact, and execute. 7
7.2. Set the I-beam to and take an I-beam snapshot. Change the application of the rectangle pattern to Si and adjust the X and Y dimensions of the pattern so it covers the remaining point of attachment of the lamella to the sample (on the left in the I-beam image) and set Z = 1.0 µm. Position the pattern over the remaining point of attachment, and then execute it. Take E- beam snapshots stop the pattern frequently to observe the progress of the pattern and once the lamella is released. 8
7.3. Set the I-beam to and start live I-beam imaging. Slowly lower the Z stage control to pull the specimen away from the lamella. Once the specimen is sufficiently clear of the specimen surface (a few 10s of µm), retract the Pt GIS ; then place the Omniprobe into the Park position and retract the Omniprobe. 8. Aligning the grid prior to sample attachment 8.1. Navigate over to the position on the grid where the sample is intended to be attached and bring it to eucentric position. The grid may be rotated a few degrees off from being perfectly horizontal in the E-beam image (or more, depending on if the stage was rotated to align a feature on the sample). If that is the case, select Stage from the pull-down menu and then xt Align Feature and follow the instructions to align the grid. 9
8.2. The grid may also be tilted slightly away from being perfectly aligned with the E-beam. Adjust the stage tilt (usually T = 1 to 2 ) until the grid appears flat and not tilted; if you have to tilt to T < 2, leave the tilt at T = 2 (the Omniprobe cannot be inserted for T < 2 ). Keep in mind now that the stage tilt corresponding normal incidence for the I-beam will be differ by this amount (e.g. 2 + 52 = 50 is now the stage tilt for normal incidence for I-beam). Before After 10
9. Attaching the lamella to the grid 9.1. Start live I-beam imaging and adjust the Y beam shift until the desired point of attachment is within the field of view. Insert the Omniprobe and use live E-beam and I-beam imaging to approach the lamella; when the lamella is a few µm away from the grid, insert the Pt GIS. Position the lamella so the free end is barely separated from the edge of the grid. Set the I-beam to and draw a rectangle pattern with Z = 0.2 µm and X and Y dimensions sufficient to cover the point of contact between the lamella and grid; set the application to Pt dep. Take an I-beam snapshot contact, and execute., position the pattern so it is centered over the point of 11
9.2. Set the I-beam to and take an I-beam snapshot. Change the application of the pattern to Si, set Z = 1.0 µm, and adjust the X and Y dimensions of the pattern so it covers the weld between the lamella and Omniprobe and extends slightly beyond the top and bottom of the Omniprobe. Position the pattern over the weld and execute. Take E-beam snapshots frequently to observe the progress of the pattern and stop the pattern released from the lamella. once the Omniprobe is 9.3. Set the I-beam to and start live I-beam imaging. Move the Omniprobe so it is a few 10s of µm clear of the lamella and then retract the Pt GIS ; then place the Omniprobe in the Park position and retract the Omniprobe. 9.4. If you have additional lamellas to prepare, it is best to lift out and attach each lamella to the grid and then final thin all lamellas at once. 12
10. Lamella adjustments before final thinning 10.1. Set the I-beam to ; bring the lamella to eucentric height, then set the stage tilt to the appropriate value for normal I-beam incidence accounting for the pre-tilt to align the grid (e.g. 2 + 52 = 50 ), and link the beams. 10.2. Set the I-beam to and take a snapshot. If the lamella appears slightly rotated from horizontal in the I-beam image, select Stage from the pull-down menu and then Scan Rotation Align Feature and follow the instructions to horizontally align the lamella in the I-beam image (the scan rotation for the I-beam image should still be close to 180 ). If the lamella appears rotated during later steps, you can repeat this alignment process again as needed. 13
10.3. Draw a rectangle pattern, set Z = 1.0 µm, and adjust the X and Y dimensions of the pattern so it covers the end of the specimen where the Omniprobe was attached. Take an I-beam snapshot pattern over the end of the lamella and execute. and position the 14
11. Final thinning: 30 to 8 kv 11.1. Tilt the stage to +7 relative to normal incidence for the I-beam and take an I-beam snapshot. Delete the rectangle pattern just used and draw a cleaning cross-section pattern with X = 7.0 and Z = 1.0 µm with Y dimension sufficient to cover the upper side of the lamella; set the pattern rotation to. Position the pattern over the upper side of the lamella and execute. 15
11.2. Tilt the stage to 7 relative to normal incidence for the I-beam and take an I-beam snapshot. Decrease the X dimension of the pattern to X = 6.5 µm and set the pattern rotation to. Position the pattern over the bottom side of the lamella and execute. 16
11.3. Set the I-beam to. Tilt the stage to +4 relative to normal incidence for the I-beam and take an I-beam snapshot. Decrease the X dimension of the pattern to X = 6.0 µm, adjust the Y dimension of the pattern to cover the upper side of the lamella, and set the pattern rotation to upper side of the lamella and execute.. Position the pattern over the 17
11.4. Tilt the stage to 4 relative to normal incidence for the I-beam and take an I-beam snapshot. Decrease the X dimension of the pattern to X = 5.5 µm and set the pattern rotation to. Position the pattern over the bottom side of the lamella and execute. 18
11.5. Set the I-beam to. Tilt the stage to +2.5 relative to normal incidence for the I-beam and take an I-beam snapshot. Decrease the X dimension of the pattern to X = 5.0 µm, adjust the Y dimension of the pattern to cover the upper side of the lamella, and set the pattern rotation to upper side of the lamella and execute.. Position the pattern over the 19
11.6. Tilt the stage to 2.5 relative to normal incidence for the I-beam and take an I-beam snapshot. Decrease the X dimension of the pattern to X = 4.5 µm and set the pattern rotation to. Position the pattern over the bottom side of the lamella and execute. 20
12. Final thinning: 5 and 2 kv 12.1. Set the I-beam to. Tilt the stage to +2 relative to normal incidence for the I-beam and take an I-beam snapshot. Decrease the X dimension of the pattern to X = 4.0 µm, adjust the Y dimension of the pattern to cover the upper side of the lamella, and set the pattern rotation to lamella and execute milling is proceeding and stop the pattern reduced in thickness by ~33%.. Position the pattern over the upper side of the ; observe the lamella in the E-beam image while once the Pt strap has 21
12.2. Tilt the stage to 2 relative to normal incidence for the I-beam and take an I-beam snapshot. Decrease the X dimension of the pattern to X = 3.5 µm and set the pattern rotation to. Position the pattern over the bottom side of the lamella and execute ; observe the lamella in the E-beam image while milling is proceeding and stop the pattern once the Pt strap has reduced in thickness by ~50% (there should still be some Pt strap left after this step). 22
12.3. Set the I-beam to. Tilt the stage to +7 relative to normal incidence for the I-beam and take an I-beam snapshot. Delete the cleaning cross-section previously used and draw a rectangle pattern with X = 3.0 and Z = 1.0 µm, respectively, and Y dimension sufficient to cover the upper side of the lamella. Position the pattern over the upper side of the lamella and execute ; observe the lamella in the E-beam image while milling is proceeding and stop the pattern strap has reduced in thickness by ~50%. once the Pt 23
12.4. Tilt the stage to 7 relative to normal incidence for the I-beam and take an I-beam snapshot. Position the rectangle pattern used in the last step over the bottom side of the lamella and execute. As this is the last milling step, it is critical to monitor the lamella in the E-beam image during milling to safely stop the pattern before over-milling occurs. Ideally, this pattern should be stopped while there is still a very small amount of Pt strap left on the lamella (to ensure the surface is still intact and damage-free). However, if additional protective layers are present on the surface (evaporated C, for example), it may be possible (though not always necessary) to continue thinning beyond this point. 12.5. The sample is now finished; do not perform any further imaging of the specimen with the I-beam to prevent any additional specimen damage. Additionally, it is best to minimize E-beam imaging of the completed lamella to prevent the generation of a contamination layer prior to TEM analysis. 24