Strata DB235 FESEM FIB

Transcription

1 Strata DB235 FESEM FIB Standard Operating Procedure Revision: 5.0 Last Updated: August 16/2016, revised by Li Yang Overview This document will provide a detailed operation procedure of the Focused Ion Beam (FIB), and a guideline of FIB applications on Strata DB235 FESEM FIB. Formal Training is required for all users prior to using FIB of the system. A trainee must be a qualified Phase 3 or after hour DB235 user. Revision History # Revised by: Date Modification 1 Li Yang 2 Li Yang Aug rd 3 Li Yang August 14 4th 4 Li Yang August 16 5th 5 Document No. 4DSOP000X

2 Table of Contents Overview... 1 Revision History... 1 Table of Contents... 2 General Information... 3 I. FIB Basics Check System Console and confirm the system at working state Access Ion column controls in User start up page Set up focused ion beam Set sample for dual beam imaging Get dual beam aligned to the sample feature Optimize the ion beam... 8 II. Introduction of FIB applications on DB GISs on DB Files for FIB nanofabrication III. FIB applications Use FIB to sharpen GIS2 W probe Pt deposition Pattern milling View SEM sample in a cross section way Preparation of TEM sample IV. Finish operations References and Files Contact Information

3 General Information Fig. 1 The DualBeam TM Strata 235 systems FEI s DualBeam TM Strata 235 systems integrate a field emission scanning electron microscope (FE-SEM), with focused ion beam (FIB) technology; provide automated navigation, FIB fabrication and SEM imaging, ranging from micrometers to nanometers. The control computer and software were upgraded in May The User Interface (UI) software is FEI xp 3.80, operated by Windows xp. This version of Standard Operation Procedure provides a guideline to work with the FIB, aims to inform users of the tool s basic controls, in an effective and safe way. Some FIB applications are also briefly listed in the SOP. A Trainee of FIB must be a qualified Phase 3 or after hour DB235 user, who is good at setting his sample to the best SEM imaging conditions and eucentric height rapidly. The default equipment related to FIB applications is featured in Fig. 1. They are all located in the left side of sample chamber. The Gallium Ion column is in the middle, while 2 Gas Injection Systems (GIS) are to its right side: Name Location Function GIS 1 In the up right corner of the A crucible filled with Trimethyl Platinum may provide Pt-C compound left side of the chamber deposition by Ga ion beam or electron beam through a GIS 2 In the down right corner of the left side of the chamber tube needle. A W needle probe installed in it may be used to lift-out FIB TEM cross section sample, or to do electrical measurement to fibers in nanometers. 3

4 Fig. 2 Parameter settings of Electron column, Ga ion column and stage The FIB works normally with stage tilting 52 to have the sample top surface faced to the ion column. Conductive, smaller and flat sample will work more effectively. I. FIB Basics 1. Check System Console and confirm the system at working state. Fig. 3 Normal FESEM/FIB work state indication The System Console is located to the left side of the monitor. The buttons on it must be illuminated the same as in Fig.3, and identical to the descriptions in the table below. If not, ask Li for help. Button Label ON OFF STAB Vacuum High Tension Illuminated State Not lit, green color Lit, red color Lit, white color Lit, white color Lit, white color 4

5 2. Access Ion column controls in User start up page a. Off state of dual beams b. E-beam is turned on c. Dual beams on Fig. 4 User startup page contains all systems controls of DB235 FIB Gallium is used as ion source in the FIB of DB235 TM Dual Beam systems. The FIB controls are in the space labelled as Ion Column in user startup page, which is on the top of Electron Column. The HV is preset only at 30 kv. FIB working conditions on DB 235 is shown in below table: Items Display in User start up page: Ion Emission current (ua) 2.2 Extractor Voltage (kv) 12.0 Suppressor Voltage (V) Any data between to High Voltage (kv) 30 (preset set for ion source), HV key is yellow Ion column HV (kv) 1 (the condition to get HV on) 5

6 Note: a. The ion source should be off (Key grey) with Ion column HV displays 1kV if user only works with SEM imaging, as shown in Fig. 4b b. While the electron source must display a data of E-Emission Current even its HV is not applied as 0.0 kv, as shown in Fig. 4a. 3. Set up focused ion beam There are two ways to turn on the ion beam: a. Turn on both ion beam and electron beam by clicking on Beams on in System space which is exactly on the top of Ion Column space. Note: This set up is recommended for using dual beam. b. The ion source can be turned on separately by clicking on HV in Ion Column. Note: This is recommended for using the FIB in a part of user s test It takes a little while for the FIB to stabilize. Better to start the source at the beginning of the test. FIB works well if the ion source was heat in last 3 days, and it works continuously. It will help users to use the FIB more effectively in after hours and weekend if Li is informed by of their FIB plan 2 days in advance. If the ion beam does not start well, users are possible to fix it, or report to Li. Trouble Reason Solution The Extractor Voltage simply goes to 14.0kV with warning messages pop-up Computer is impossible to regulate the ion beam Turn the Apply key to grey, increase the Suppressor Voltage gradually by The Ion Emission Current <2.0µA, or simply 0.0, even the Suppressor voltage is increased to 2150V for more than 3 min. 4. Set sample for dual beam imaging The ion source needs to be heat click the of Suppressor to increase the Ion Emission Current to 2.2µA Report to Li a. Get the same magnification for both pictures of electron beam and ion beam: Check Mags Coupled in either E-mag menu or Ion-mag menu. Fig. 5 Part of E-Mag menu 6

7 b. SEM imaging: confirm the electron beam as primary beam for image either by click or check Primary Beam E, as shown in Fig. 6. Get a feature on the sample, in SRH mode at magnification 1000x (4 frames on monitor); set the feature to eucentric height with zero beam shift. Tune the SEM images well, and take a picture. Fig. 6 Menu below DB Control c. FIB imaging: choose the ion beam as primary beam for image, either by click or check Primary Beam I. Tilt the feature to 52 and take a picture. Note: Refer to SOP of SEM 1 - DB235 to do the above a and b operations. The stage tilt range is -15 to +60 for 0.5 inch stub holder. Oversized sample, or sample with many bump surface may restrict the tilt range, and challenge the setting up of eccentric height. 5. Get dual beam aligned to the sample feature Click scan/freeze to display live ion image, tune the SHIFT knobs on the MUI, as shown in Fig. 7 to get the ion beam image of 52 tile sample feature identical to the electron beam one of 0 tilt, as shown in Fig. 8 Fig. 7 MUI of DB235 Dual Beam Systems Fig. 8 Good alignments of dual beam reveal the feature at the same position in the frame 7

8 6. Optimize the ion beam a. Figure out suitable ion beam current for users samples in their Phase 3 supervised practice by selecting the apertures from the I-beam menu for imaging and / or for fabrication, as shown in Fig. 9 Fig. 9 Aperture settings of Magnum ion column on the DB235 Note: The FIB of the DB235 uses fixed setting of column aperture to regulate the ion beam current. Higher dose ion bump on the sample when larger hole aperture applies, which milling larger volume material away faster. Suggestions in the table below are based on tests of Si wafer. Aperture Use 1pA High resolution imaging 10pA High resolution imaging 30pA High resolution imaging, small cross-section cleaning 50pA High resolution imaging, small cross-section cleaning 100pA General imaging, cross-section cleaning 300pA Imaging, cross-section cleaning 500pA Cross-section cleaning 1000pA Medium bulk mill or large cross-section cleaning 3000pA Large cross-section bulk milling 5000pA Rough bulk milling 7000pA Rough bulk milling for large cross-sections 20000pA Extremely rough bulk milling for large cross-sections b. Optimize the ion beam to get a sharpen picture of the feature: 8

9 1) Choose the ion beam as primary beam for image. 2) With the similar approaching of optimizing electron beam, tune the ion beam with imaging the sample feature by adjusting FOCUS and STIGMATOR knobs on the MUI. The optimized image should be sharp with good balance of contrast and brightness, revealing the sample s fine details. Fig. 10 Scan menu c. Prove the excellent state of the selected ion beam by punching a round hole with spot scanning: 1) Check spot in Scan menu, as shown in Fig.10. The beam will do the spot scan. Keep it scanned at 1 point for 6s, may shorter or longer depends on sample. 2) Freeze the spot scan by clicking. The Full Frame scan will automatically re-check. 3) Grab 1I to take an ion beam image of the hole. 4) The hole may be examined in more details with electron beam with 0 tilt. Fig 11 displays a good case. Fig. 11 a hole punched on Si wafer with 100 pa reveals well-tuned ion beam Note: The hole is round when the sample is at eccentric height, tilted to 52, and the ion beam stigmatism is corrected. 9

10 II. Introduction of FIB applications on DB GISs on DB235 Two Gas Injection Systems (GISs) are equipped to the DB235 for FIB applications: Name Location Function GIS 1 In the up right corner of the A crucible filled with Trimethyl Platinum may provide Pt-C compound left side of the chamber deposition by Ga ion beam or electron beam through a GIS 2 In the down right corner of the left side of the chamber tube needle. A W needle probe installed in it may be used to lift-out FIB TEM cross section sample, or to do electrical measurement of fibers in nanometers. a) It is necessary to heat the crucible in GIS 1 before depositing Pt-C compound. The heat control is in the User startup page below the control of the electron column, as shown in Fig. 12. Activate on by clicking on it, it will turn from grey to yellow. Following it, the status LED will turn on with color changing, indicating heating status. For the proper heating distribution, wait 15 min. to use the GIS1. Color Heat status GIS 1 status Status text Blue Off Room temperature Heat off Yellow on Not at usable temperature Heating Orange Off Not at usable temperature Cooling Red On At operating temperature Hot enough to deposit Pt-C 10

11 Fig. 12 GIS heating Control in user start page b) Insertion and retraction of the needle of GISs: The in / out controls are in the work page, as shown in Fig. 13, both GIS1 and GIS2 are driven pneumatically. The open / close of valve of GIS1 are in control of GIS Injection, controlled pneumatically. Fig. 13 The needle inserts and retracts control of GISs The GIS1 tube needle must be inserted for Pt deposition by click on In. It must be extracted during any stage moving (x, y, z, and tilt) for protection of both the needle and sample. 11

12 2. Files for FIB nanofabrication The FEI-xp interface software works with loading files to digitally vector the scan of the focus ion beam during the FIB nanofabrication. 1. Pattern file Fig. 14 Pattern tool bar The pattern files can be generated by selecting and editing pattern from pattern tool, and the file can be saved by using File > Save as, and is reloadable. 2. Material file Material file contains 3 components: the beam Overlap percentage, Dwell time and Deposition or Sputter rate. There are default material files listed in the interface software dedicated to the GIS chemistry and FIB applications. Two common using material files are shown in the table below, User may chose and try out the most suitable one for his work from the default ones list in Patterning. File Name Application Overlap (%) Dwell time (µs) pt_mag.mtr Standard Pt deposition si.mtr General purpose milling file Deposition or Sputter Rate (µm 3 /nc) 3. Stream file A stream file is a ASCII text or binary file that addresses the patterning DAC directly, it produces custom pattern. Stream files contain information of number of loops the pattern mills, total number of X, Y coordinates. The stream file cannot be created from the interface software. They are prepared and tested by users before access the DB235 FIB. 12

13 Fig. 15 Select Material File and edit pattern parameters in Patterning on work page III. FIB applications The Focused Ion Beam on DB235 is used for fabrication after it is optimized dedicatedly to users FIB plan. Guidelines below show several applications available. 1. Use FIB to sharpen GIS2 W probe a. Image the tip of the probe with both electron beam and ion beam. b. Shape the mill pattern on the ion beam image with control icons in pattern tool bar, such as Polygon, as shown in Fig. 16, c. Select material file as Si.mtr in Patterning, d. Click to start the mill. e. Check the progress by Grab 1I after milling f. Confirm good sharpening with electron beam image. Fig 16 W probe is sharpen by FIB 13

14 2. Pt deposition It is necessary to heat the crucible in GIS 1 before depositing Pt-C compound. The heat control is in the User startup page below the control of the electron column, as shown in Fig. 12. Activate on by clicking on it, it will turn to yellow. The status LED will turn on with color changing, indicating heating status. For the proper heating distribution, wait 15 min. to use the GIS1. Color Heat status GIS 1 status Status text Blue Off Room temperature Heat off Yellow on Not at usable temperature Heating Orange Off Not at usable temperature Cooling Red On At operating temperature Hot enough to deposit Pt-C Pt deposition is carried out with GIS1. It can be done with either electron beam or ion beam. Ion beam way works faster, while electron beam way protects the sample surface better. Carbon is richer in the electron beam deposited one. I. Pt deposition with electron beam: a. Choose the appropriate electron beam condition, such as 2kV, spot size 5, 50um AVA using SRH mode. b. Set sample to eucentric height, then lower it 500um c. Insert GIS1 needle by click in in GIS Injection as shown in Fig.13 d. Adjust sample position on the stage to confirm the feature is not blocked by the needle. e. Select Serial as the Pattern Order, as shown in Fig.13. f. Check the electron beam as primary beam, and choose E-beam in Patterning. g. Draw a pattern, such as a fill box on the feature. Its shape can be modified with Edit in Patterning. h. Load material file, as suggested in Fig. 15 i. Begin the deposition by click. The sound of GIS valve opening and closing signals the process. j. Extract the GIS1 by clicking out in GIS Injection in the work page, as shown in Fig. 13. k. Check the deposition with tilting sample. II Pt deposition with ion beam: a. With electron beam, set sample to eucentric height. Tilt to 52, then lower it 500um. b. Insert GIS1 needle by click in in GIS Injection as shown in Fig.13 c. Adjust sample position on the stage to confirm the feature is not blocked by the needle. d. Chose ion beam as primary beam, and choose I-beam in Patterning. e. Select and try out proper ion beam current depends on the size of the deposition area, 100pA is suggested good for depositing of a strap with 1um wide and 20 um long. f. Load material file, as suggested in Fig. 15. g. Draw a pattern, with the fill box, and edit it to the size, such as 20um 2 h. Begin the deposition by click. i. Extract the GIS1 by clicking out in GIS Injection in the work page, as shown in Fig. 13. j. Check the deposition with electron beam image. 14

15 For the safely using of the GIS, it must be cooled down before open the chamber to switch sample. Click on in GIS Heating to grey and wait till the LED turns Blue. Pt deposition finds it application in DB235 FIB: a. Protect sample surface during ion milling. b. It is used as an image feature for process controlling during XTEM sample preparation. c. It is used to edit device. Such as, build up electronic connection, as shown in Fig. 17a. d. It is used as glue to fix XTEM sample for further thinning, as shown in Fig. 17b. 3. Pattern milling a. Build electronic connection b. Fix Cross-section TEM sample Fig.17 Pt deposition applications a. DB235 FIB realizes the pattern milling with Pattern File, or Stream File. In both cases, the sample must be imaged well with both electron beam and ion beam, set to eucentric height, tilted to 52 and aligned to the dual beam. Pattern file may be generated with the interface software or load the one saved before by open Pattern data, File > Pattern Data > *.pat. Stream Files are for users who write their own programes for specific applications, such as Nanohole arrays milling. A stream file created as an ASCII text or binary file that addresses the patterning of DAC diectly, produces custom pattern. It can not created directly from the interface software FEI xp. Note: The ion column of the DB235 is a Magnum type. The stream file need to be prepared elsewhere, with its feasibility tested in advance of access the DB235 15

16 Fig. 18. Load pattern or stream file b. Load the workable stream file to the ion beam image: File > Pattern Data > *.str. The yellow dots in Fig. 18 reveal the feasibility of the stream file, not the real pattern. c. Select proper ion beam current, depends on the materila of sample. d. Select proper material file from Patterning. e. Click Patterning icon to start the milling, or run the script. f. Tilt the sample back to 0 when the milling finishes, and check the effect with SEM. A good case is shown in Fig.19. FIG. 19 SEM image of FIB Nanohole arrays on Au film 16

17 4. View SEM sample in a cross section way a. Image the sample well with both electron beam and ion beam, set it to eucentric height, tilt it to 52, and aligned the dual beam to it. b. Select proper material file, such as Si.mtr. c. Mill a regular cross section with 5 superimposed box patterns sharing three common edges with larger ion beam current. Try out and select the ion beam current depends on sample material and size of interested area, and confirm the good ion beams state. For the Step1 milling, click regular cross section icon in Pattern tool bar to put the box on the ion beam image of interested area. And edit the size with Patterning. Remember to fill in the depth of your cross section in the Z edit box in the Patterning group on the work page. Then click to start the milling. A typical pattern milling process for cross section view of the sample is shown in Fig. 20 Fig. 20 A typical Cross section procedure. Fig. 21 Perspective view of the cross section on the edge of a sample d. Mill a Filled box to approach to the interested area, remember to fill in the depth of your cross section in the Z edit box in the Patterning group on the work page. 17

18 e. Click to do the Cleaning cross section with lower ion beam current. Also need to fill in the depth of your cross section in the Z edit box in the Patterning group on the work page. f. The cross section can be checked with electron beam for each milling, as shown in Fig. 22. The SEM cross section may be speed up with proper parameter settings built up during trials. Fig. 22 SEM imaging of sample s cross section during FIB 5. Preparation of TEM sample There are generally two ways in the DB235 to prepare cross section sample for TEM observation: Pre-thin and Lift-out. Going through below guidelines well to adapt the machine to the sample will enable a user to speed up the preparations by running script of AutoTEM (A software, available on the DB235) smoothly. Preparation Pre-thin Lift out Request of sample Fixed to specific sample holder, a strip ~3mmx100um with the interested area up. Sample fixed to normal SEM stub with top surface as the interested area Below steps are necessary in both Pre-thin and Lift-out: a. Image the interested area of sample well with both electron beam and ion beam. Set it to eucentric height, tilt it to 52, and aligned the dual beam to it. b. Select proper material file, such as Si.mtr. c. Deposit Pt-C to the top surface for protection from ion beam damage, and for milling position locating. For very fragile surface, deposit Pt-C with electron beam before deposit Pt-C in ion beam. 18

19 a. Pre-Thin Preparation of TEM sample: With FIB, thin the sample chunk to electron transmision ~150nm, the sample with the 3mm stripe can be examined in TEM. Fig. 23 A Pre-thin TEM cross section sample b. Lift out preparation of TEM sample 1. Confirm that both GIS1 and GIS2 are centered and functioned well before milling. 2. Deposit a Pt-C chunk (2µm x 2 µm x 15um is appropriate) on to the interested area. a. Pt-C bar on sample b. Mill boxes parallel to the bar c. Mill to shape the lamella Fig.24. Generate the lamella 19

20 3. Mill material from both sides of metal line with (10 µm x 10 µm x 10 µm is an approximate size of each box). The boxes should be milled in parallel, and the top box rotated 180 degrees, as shown in Fig. 24b 4. Clean up the edges of the lamella with a lower beam current (~150pA) to get the lamella about 500nm thick. 5. Tilt stage to 0 degrees so that the broad side of the lamella is visible with the Ion Beam view. Create three rectangular milling patterns along the perimeter of the lamella, set to mill in parallel. Mill through the perimeter of the lamella with filled box, and leaving only a 2um tag holding the lamella to the sample. You can tell the milling is complete by viewing the Electron Beam image and watching for the projection of the milling pattern on the inside of the milled trench, as shown in Fig. 24c 6. Work with GIS2: Lower the sample 100um microns in Z (to avoid interference) and insert the Probe. The probe tip should be visible in both the ion beam image and the Electron Beam image. Begin imaging with the ion beam with low current and move the X and Y axis of the stage to orient the Lamella with the probe tip. Raise the sample with the Z axis (be extremely careful) and view the Electron Beam image to watch as the lamella approaches the probe tip. Alternate viewing between the Ion Beam image (to adjust X and Y axis ) and the Electron Beam image (to adjust Z axis) until the probe tip is barely in contact with the lamellas top edge (actual contact is not necessary but it must be within 1um). The result is shown in Fig. 25a. a. Get the probe close to the lamella b. Fix the probe to the lamella with Pt-C Fig. 25 Work with GIS 2 and GIS1 7. Work with GIS1: The probe must now be welded to the lamella. View the lamella with the Ion Beam at a low current. Insert the GIS1 needle for Pt-C deposition, open the GIS valve, and grab a single frame image with the Ion Beam. Put the Ion Beam in Spot Mode and place the spot on top of the lamella about 100nm from the tip of the probe. Grab images with the Electron Beam to see the progress of the metal deposition. When a noticeable accumulation of metal appears to connect the lamella to the probe tip you may return the ion beam to normal imaging mode, close the GIS valve and retract the GIS needle (do not move the stage). The result is shown in Fig. 25b. 20

21 8. Clipping the tag by doing another small filled box. The sample lamella is now disconnected from the substrate. 9. View with the Ion Beam the top of the lamella and create a small rectangular milling pattern over the area of the lamella. Start the milling and monitor progress by viewing with the Electron Beam, as shown in Fig. 26. A 10. Extract the lamella by carefully lowering the stage (Z axis), as shown in Fig. 26b. 11. Further thin the lamella with the Ion Beam at a low beam current and mill along the edges of the lamella. 12. Rotate the lamella 2 degrees and repeat the above thinning process until the thinned area appears evenly bright when viewed with the Electron Beam, this indicates that the lamella is producing secondary electrons from the back side and the sides are parallel, as shown in Fig. 26d. 13 The lamella sample is now ready for placement on a TEM grid. Fig. 17b shows a lamella was fixed to the grid with Pt-C deposition, with the probe was cut off with FIB. a. Clip the tag with FIB b. Lower Z to extract the lamella c. Further thinning the lamella d. Lamella of electron transmission Fig. 26 Further thinning of the Lamella 21

22 IV. Finish operations 4.1 Click Beams off in system to turn off both HV of electron column and ion column, as well ion source. 4.2: Users are requested to set the instrument to its common initial states before finishing their sessions: a. E-column displays: Spot size 3; HV 5kV. b. I-column displays: Ion Column Aperture: 10pA if FIB is used. c. Extract the all the GISs if they were used. d. Stage position: x and y to zero. If you observe very thin or thick samples, after take off your sample, readjust the stub holder thread back to the height you found it. Tilt degree to 0, Rotation with Absolute selected. 4.3 Vent the chamber, take out your sample, and make sure to pump the chamber down to higher vacuum. Note: If GIS 1 is used, wait 5 min. after it cooled completely, then vent the chamber. 4.4 Transfer your data in your slot by loading them to 2 USBs. Note: Users are responsible for the security of their data. The data should be transferred to 2 USBs, which can be tested with the lab computer in booked slots. User data should be removed from the SEM PC after the files are confirmed to be successfully copied onto the user s USB. 4.5 Log out your user account, and sign off in the lab logbook Note: please also fill-in and do the 4D labs ticket as soon as the slot ends. 4.6 Tidy up the desktop you used, pack up and take all your stuffs. Note: Note: a. Do not turn the SEM and the computers off when you finish your test. b. Make sure that the chamber door is closed properly and that the chamber is pumped well before logging out your user account. c. If you are the last user of the day, make sure that the lab door is closed. References and Files xp DualBeam System User s Guide (Versions 3.80 and Higher), and training notes. Contact Information Questions or comments in regard to this document should be directed towards Li Yang (yang@4dlabs.ca) in 4D LABS at Simon Fraser University, Burnaby, BC, Canada. 22