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SEM4160 Operating Instructions

Hitachi S-4160 Field Emission Scanning Electron Microscope for in-process inspection and metrology of photoresist, e-beam resist and nanolithographic structures with on-board CD measurement and metrology funstions.

Contact List

Contact List

The following people make up the Tool Quality Circle:

  • Process Staff: Swaroop Kommera
  • Maintenance: Ted Berg
  • Super-Users:

 

Operating Procedures

 

SNF guidelines for the Hitachi 4160 SEM:

•    Any acceleration voltage may be chosen in the range from 0.5 to 30 kV.

•    Carbon dots are the only allowed adhesive to a fix specimens to the holder.

•    As with all SNF tools, please respect the reservation system:

-    Do not run your session into the next lab member's time.

-    As a courtesy to other users, post reservation cancellations to sem4160@snf.stanford.edu.

-    Show up promptly for your session. If you do not arrive within 16 minutes of your reservation start time, other labmembers are permitted to take your session.

•   Specimens may be of sizes ranging from small pieces to 6" wafers. Vertical chip-holding stubs are available at the worktable.

If any problems are encountered, contact Swaroop Kommera (skommera@stanford.edu) or Ted Berg (tberg@snf.stanford.edu).

 

1       Preliminaries

1.   Ensure that the vacuum system display is in the following standby state:

•   S.C. Vacuum: HIGH

•   S.E.C. Vacuum: HIGH

•   SEC Valve and S.C. Air Lock Valve: green blinking LED on OPEN, red solid LED on CLOSE, toggle switches set to CLOSE

•   S.C./S.E.C. toggle switch (below EVAC and AIR buttons) should always be set to S.E.C.

2.   Tum up brightness of SEM screens (1BRIGHT and 2BRIGHT dials under screens).

3.   If not already on, turn on Compaq computer (User: hitachi, Password: Hitachi) and start Horus Tech (Pyramid Icon).

4.  Enable sem4160 tool on Badger.

 

2       Sample loading

1.   Push AIR button to evacuate specimen exchange chamber (S.E.C.). The door should pop open ~1/8" after approximately 45s.

2.   Load specimens onto specimen holder using carbon dots or vertical chip-holding stubs. If using the vertical holders, ensure that the specimen height does not impede closing the door.

3.   Hold the S.E.C. door closed gently and push EVAC button. S.E.C. pumpdown takes approx­imately 90 s, after which the S.E.C. Vacuum display will again read HIGH and the S.E.C. Valve OPEN LED will blink. Allow the vacuum to reach base pressure by pumping for an additional 2 minutes. If the S.E.C. Vacuum does not reach HIGH after several minutes, press AIR and check the chamber door 0-ring for particles which may cause a leak, or contact SNF staff.

4.   Move SEC Valve toggle switch to OPEN; the switch is spring-loaded and must be pulled out gently before moving. The stage must be in the exchange position for the SEC valve to open, which is indicated by the letters "LCK" shown in the upper-right comer of the Stage Controller display. If this is not the case, move the stage to the exchange position (push "MODE" to switch to "COMMAND" mode, enter "01", and push "ENTER") and retry the SEC Valve toggle.

5.   Slowly slide the specimen holder into the chamber: gently overcome the initial resistance, which is due to a detent, and slide the transfer rod to the end. Unscrew the transfer rod (CCW) and retract it, restoring it to its initial position in the detent.

6.   Move the SEC Valve toggle switch to CLOSE. If the valve does not close, ensure that the transfer rod is fully back in the detent.

7.   Move the S.C. Air Lock Valve to OPEN. The green LED above the HV OFF READY button should light. If not, contact SNF staff.

 

3       Making a beam

The "PFX" keys are located in a row above the display console  keyboard.  PF1 and PF2 are  most often used to adjust the accelerating voltage (Vacc) and flash intensity, respectively. PF12 (measure mode) and PF15 (screen text) may also be useful; see §B for instructions on how to  use  these  functions.

1.   Press PF1 to check set Vacc· Enter the desired value using the keyboard or numerical keypad and press "Enter" or "Return".  The "Erase" key may be used  to clear text from the screen.  A good starting value for Vacc is 5kV (good resolution, less charging or specimen damage). Increases in resolution for higher values of Vacc will only be noticeable for magnifications above ~50kX.

2.   Press PF2 and ensure that FLASH INT is set to 2. This determines the "flash intensity" used to clean the filament. A setting of 1 is mostly ineffectual and a setting of 3 risks damaging  the tip. Press EXIT to return to the normal display screen.

3.   Press the HV ON button. The Vacc and V ext (extraction voltage) displays will ramp up, followed  by  the  "Emission"  display.

•   The normal emission current is ~10 µA; if the current drops to a low value, the image becomes dim and/or noisy and the HV ON LED will blink, indicating that Vext should be reset by pressing the HV ON button. When Vext reaches its maximum of 6.5 kV, the filament must be flashed: press HV OFF, press FLASH STANDBY until the HV ON LED blinks, press HV ON, wait for the flash to finish (a few seconds), and press HV ON again to tum on the beam.

 

4       Making an image

1.   Using the MAGNIFICATION dial, reduce the magnification to a low value (on the order   of 100x), and select the fast TV scan speed (press the TV button to light the "F" LED). The normal standby condition for the sem4160 is to have a magnification over 5kX and a slow scan speed because this results in less wear and tear on the beam deflection system; for initial focus, however, these settings are impractical.

2.   Drive the stage to find your specimen. It is usually easiest to drive the stage to the approxi­mate position of your specimen using the Stage Controller, then to use the joystick for more precise adjustments.

(a)    Press MODE on the Stage Controller to switch to COMMAND mode.

(b)    Input "02" (the code for the DRIVE X,Y command) using the keypad, then ENTER.

(c)    Enter the desired stage position using the keypad and the arrow buttons. The center of the stage is at (75, 75) mm.

(d)    Use the joystick to find an appropriate location on your specimen (e.g., edge, position of known features, etc.). The stage speed may be selected with the arrows above the joystick.

3.   Adjust the working distance (WD) to ~10 mm. The current value of the WD is displayed in the top-left corner of the left monitor, but this reading is only accurate when the image is focussed. The height (Z) of the stage in the exchange position is 30 mm, measured from the lens to the surface of the stage. Use command "04" (DRIVE Z) to adjust the stage height, then focus on your specimen using the coarse and fine FOCUS knobs. For a standard Si wafer, driving the stage to Z = 8 mm yields a WD of 10 mm.

4.   Adjust the aperture centering. It is also prudent to recheck the aperture alignment after changing the WD by more than a few mm.

(a)        Focus on a feature at a magnification of ~1000X.

(b)        Run the focus up and down repeatedly. If the feature moves back and forth in any direction, the aperture is out of alignment; if not, go on to the stigmation adjustment.

(c)        Adjust the aperture position using the two dials directly above the chamber until the image no longer undergoes any linear movement when the focus is rocked. A slight rotation of the image, however, is normal.

5.   Adjust the stigmation. Use the X and Y STIGMA/ ALIGNMENT knobs to achieve the best image. For a properly stigmated beam, features should go isotropically in and out of focus when the focus is rocked, without any distortion in the X and/or Y directions.

6.   Acquire images, saving them when you are satisfied with their appearance (see §5). Adjust­ments which can be made include:

-    Adjust the brightness and contrast to obtain a good image using the arrow buttons to the left of the magnification dial. A high-brightness, low-contrast setting can be used to yield a smooth grayscale image without graininess.

-    Six scan speeds are possible: fast and slow TV scan, and four slow scan speeds. Better­ quality images are possible with slower scan speeds, at the expense of longer acqui­sitions. The scan speed may be changed by pressing the appropriate buttons under SCAN SPEEDS.

-    Two reduced-raster settings are also available, which may be used during focussing to limit the spatial extent of charging and contamination. Pressing the reduced-raster button once yields the smallest image; a second press provides a larger area.

-   The rotation of the image may be changed by switching on the RASTER ROTATION toggle and adjusting the angle using the dial.

5       Saving images

Images are acquired and saved using the Horus Tech software.

1.  logon password is: Hitachi

2.  Click on Pyramid icon: Horus Tech

3.  In the top menu, select View, then Device

4.  Highlight Port 3

5.  To have constant image, select far left Icon: continuous grab

6.  Select camera icon to capture image

7.  Select file-save, select type of file and location to save  


6       Shutting down

1.   Tum off the beam by pressing the HV OFF button.

2.   Set the magnification to a high value, over 5kX.

3.   Set the scan speed to 4 (the slowest speed).

4.   Close the S.C. airlock valve.

5.   Drive the stage to the exchange position (Stage Controller command "01"). Wait until "LCK" is shown in the top-right comer of the Stage Controller display.

6.   Open the S.E.C. valve.

7.  Slowly insert the transfer rod, screw it clockwise into the sample holder, and slowly with­ draw the rod fully, ensuring that it is in the detent at the end of its range of    motion.

8.  Close the S.E.C. valve.

9.   Vent the sample exchange chamber by pressing the AIR button.

10.  When the door opens, remove your specimen(s).

11.  Holding the S.E.C. door closed, pump down th  chamber by pressing the EVAC button.

12.  Turn down the brightness of the SEM screens (1BRIGHT and 2BRIGHT dials).

13.  Return any "unusual" system settings you may have made to their normal state.

14.  Remove your images from the computer, via USB memory stick.

15.  Clean up the area around the tool, removing anything (gloves, wafers, boxes, pens, etc.) you may have brought with you.

16.  Disable sem4160 on Badger.

 

A       Stage Controller commands

PLEASE DO NOT USE COMMAND “07” “Home Position”. IT IS NOT WORKING AND WILL PUT THE TOOL IN A DIFFICULT POSITION TO RECOVER.

To enter a command on the Stage Controller, first press the MODE button to switch from LOCA­TION to COMMAND mode (indicated by a lit LED). The desired two-digit command may then be entered using the keypad, followed by the ENTER button. Input additional parameters using the keypad, if necessary, followed by ENTER. A command may be aborted by pressing the CANCEL button.

When in LOCATION mode, the current stage location is displayed, and is updated in real time as you drive the stage with the joystick.

The most useful commands are listed below. Speak to Swaroop Kommera for information on how to use any functions which are not in this list.

01: EXCHANGE POSITION

Drive the stage to the position aligned with the transfer rod. This command must be en­tered before unloading specimens, since the S.E.C. valve will not open unless the stage is in the exchange position (indicated by "LCK" shown in the upper-right comer of the Stage Controller display).

02: DRIVE X,Y

Drive the stage to an absolute location specified by its X and Y coordinates, which may range from 0 to 150 mm. Note that there is a little backlash on the stage motion motor. The center of the stage is located at (75, 75)mm.

04: DRIVE Z

Drive the stage in the vertical (Z) direction. This is most often used to make adjustments to working distance. Be careful when adjusting Z, since it is possible to crash the specimen into the lens (visible as a conical object at the top of the right monitor). There is a sensor which will stop motion if electrical contact is made between the stage and the lens, but non­ conductive specimens such as ceramics, resist, and polymers (including Kapton and Teflon) may not trigger the sensor, resulting in lens damage.

05: DRIVE TILT

Adjust the tilt of the stage. A non-zero tilt angle (specified in degrees) is useful for obtaining images of the sidewalls of structures with an appreciable height. The Stage Controller is also equipped with a sensor to prevent contact between the stage and the lens when tilting, but it is &dvisable to make tilt adjustments in small increments. Note that, in general, changing the tilt also adjusts the WD, so refocussing will be required.


06: DRIVE ROTATION

Rotate the stage, given an angle in degrees. The default position is 0°. This command is use­ ful to align the horizontal and vertical axes on a specimen to the stage's X and Y directions.

09: RELATIVE DRIVE

Drive the stage to a location relative to its current position, given in X and Y coordinates, in

mm. This is particularly useful for samples with repeating patterns.                                                                                            

B  Programmed functions

The row of PFX keys along the top of the keyboard are used to change many of the microscope functions, some of which should not be changed, as this could adversely affect the operation of the tool. If you change any of the "non-forbidden" values to achieve special imaging effects, be sure to change them back to their default values as a courtesy to the next user.

PF1

Used to adjust Vacc· Acceptable values range from 0.5 to 30 kV. Press ENTER after inputting anew  value.

PF2

Used to adjust the condenser lens strength, working distance, emission, flash intensity, pre­ set magnification and auto-start status. The normal settings for these functions are:

-    Condenser lens: 10 or 12

-    Working distance: this is read out from the objective lens, and is accurate  only when  the image is in focus.

-    Emission: 10 µA. Do not change this value!

-    Flash intensity: 2

-    Preset mag: any convenient value, to which the magnification will be adjusted when the "preset mag" button is pushed.

-    Autostart: OFF

PF3

Column adjust. This enables critical adjustments to the column. Do not change any of these settings!

PF4

Signal select: not in use.

PF5

Monitor assign: not in  use.

PF6

Signal processing. May be of use when trying to image difficult specimens. See Swaroop Kommera or read the manual for instructions, and be sure to change back any settings to their normal values when your session is over.

PF7

Auto data display. Select which data will appear onscreen (and therefore in images acquired via Quartz PCI), such as the magnification, the scale bar, etc.

PF8

Photo conditions. This is a vestigial, from when images were captured using photographic film; it is not particularly useful with the digital image acquisition now in use.

PF9 

System adjust. Enables other critical adjustments to the system. Do not change any of these settings!

PF10

Critical dimensions. This function adjusts how the signal is processed for detection of linewidths.

PF11

Calibration settings. Enables adjustments  to the calibration  of  the  measurement  cursors.  Do not change any of these settings!

PF12

Measure mode. Vertical and horizontal cursors are overlaid on the image, allowing for direct measure of feature sizes. The distance between the cursors is displayed on the screen. Cursor positions may be adjusted using the CURSOR dials and the X/Y toggle button. Push PF12 again to remove the cursors.

PF13

Image storage: no longer operative.

PF14

Oblique image. Changes the scan direction from horizontal to "oblique." Of limited use.

PF15

Screen text. Allows a label of your choice to be printed on the screen and positioned, using the arrow keys. Pressing ERASE clears the text buffer and removes the text from the screen. Pressing PF15 again will remove the text from the screen, but keep it in the buffer, such that it will appear again with the next press of PF15.

EXIT

Exits out of most PFX functions (with the exception of the "Measure" function), clearing the associated screen text.

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