Scanning Electron Microscope

      ESEM Operation Manual

Last update: March 29, 2012 by Prashant Patil

You should be trained before you use this machine. Please email prashant.patil@cba.mit.edu for training information

Machine name : Environmental Scanning Electron Microscope                    
Model : Phillips XL-30 (S/N D1513)
Contact: Prashant Patil         prashant.patil@cba.mit.edu         617-758-9402



Note - 
- Always vent chamber with nitrogen. If vented with air, overtime chamber will get really dirty. If the chamber is really dirty then during high resolution imaging say for gold nanopaticles, at higher resolution there will be carbon deposition and the image will blur out so you will never be able to image at higher resolution
- IMPORTANT : Keep venting pressure at 5psi. Because its such a low pressure, its ideal to have a separate nitrogen cylinder for SEM.
- The idea pressure inside the chamber is in 10^-6 to 10^-5 range. In my system, may be because of leak the pressure is just about 3.2x10^-5, this creates problem during high-resolution imaging.

Machine Overview

This machine is equipped with electron beam column. This allows electron microscope imaging. As an additional function, ESEM mode can be selected which injects water molecule into the chamber for low vacuum(compared to conventional high vacuum environment) observation.
A separate patterning system is available.(NPGS, Nano Pattern Generation System) This function overrides beam position control, so draws predefined patterns for e-beam lithography.

Emergency Action

- Turn off the beam
- Vent the chamber

Note

The red ‘OFF’ button on the front panel shuts down all machine parts, requiring days of re-alignment and, possibly, lot's of service charge. Refrain from operating the front panel buttons(ON, OFF, STBY) unless you are in maintenance position.

Quick manual

1. Turn off the beam.
2. Vent the chamber.
3. Load your sample.
4. Pump the chamber.
5. Turn on the beam.
6. Do your process.
7. Turn off the beam.
8. Vent the chamber.
9. Remove your sample.
10. Pump the chamber.

Details

On the control software, there are four boxes on the right side. From the top, vacuum control box, beam control box, video control box and stage control box.(The official name can be different. However, these would be the names in this manual.) By default, each box shows minimal controls. On the top right of each box, there is an expansion button which shows all detailed controls. After completion, contract the detailed box by selecting the expansion button again.

1. Sign Instrument Log Sheet

Before using the instrument, please sign the log sheet. Also please don't forget to report any error if observed at the end of the session.

2. Turn off the beam

- Turn off high tension button.(it is numeric(e.g. 10kV) button in beam control box, not the hardware button on the front control panel) Yellow fill is on, and gray is off.
- In the ‘Detectors’ menu, choose ‘CCD’. Chamber will be shown.
 

3. Vent the chamber

- Open nitrogen cylinder (~40psi)
- Open the purging valve located near the water pipe line
- Click ‘Vent’ button in vacuum control box.
- Click ‘OK’ at the confirmation dialog box.
- Wait 3~5min and gently pull the chamber handle.
- Close the purging valve and nitrogen cylender

4. Load your sample

- Place proper stub and carbon tape on it.
- Attach your sample.
- Place height standard beside the stub.
- Raise the Z height to 10mm point.
- Option1: Rotate Z dial to desired point manually.
- Option2: Put desired number in the ‘Z’ value of stage control box.

  (Note : Pay special attention when your sample is not planar, or too large. Above 10mm point, it may touch or break machine parts.)

- Make a rough sketch of the sample location w.r.t. the stub center.
- Close the chamber and make sure it doesn't collide with e-beam column.

5. Pump the chamber

- Click ‘Pump’ button in vacuum control box. Push and hold the chamber handle for about 5 seconds.
- Wait until chamber pressure drops below 1.3e-4 mbar showing ‘Vac OK’. (The indicator changes ‘pumping’ à ‘pre vac’ à ‘vac ok’)

Note - Some times following error will appear "Leakage in chamber", just click ok in error box and press 'Pump' button again.

6. Center the stage

This feature is currently disabled, proceed to step 7
- Maximize the stage sub-menu in the left of the screen. You will see the box with a x sign. The x sign indicate the position of the center of the sample stage and the center of the box is the e-beam position.
- Change the detector to ‘CCD’ and double click at the center of the box. This will move the center of the stage just below the e-beam. The motion of the stage can be seen in the monitor screen.

7. Turn on the beam

- Change the detector(in the menu) to ‘SE’
-Select the beam acceleration voltage, click the beam control expansion button. For normal imaging, start from 10kV and spot 3, and adjust if necessary. Lower voltage is used for fragile samples like biological samples and Higher voltage is used for better resolution. The max resolution can be achieved by selecting 30kV and 1 spot size. At lower spot size, there is low current and its less damaging. However it has low signal to noise ration.
- Field emission gun is always on. So you only have to click high tension(the numeric button) in beam control box.
- A message window will appear “Microscope confirm Focus Box with text “For safety reason …...”. Do NOT click OK. First, focus the image to get the sharp image and then click OK.

7. Do your process

- Imaging

1) Select ‘TV' fro Scan menu
2) Focus your image by mouse left-right motion while holding right mouse button down.
3) If necessary, adjust astigmatism by mouse motion while holding SHIFT + right mouse button.
4) Change contrast and brightness in the video control box.
5) Change magnification by “+” and “-“ keys in keyboard.
6) To move stage, choose proper method in the toolbar. Crossmark(+) allows center position movement by double click. Drag(O-) function allows drag-movement toward mouse pointer position. Or, you can directly insert numeric coordinate value in the stage control box and press enter.
7) To save an image, do either of these actions first

 - Freeze current live image by deselecting ‘live’ button, or
 - Press ‘F2’ button to make a single grab
- Go to In/Out menu -> Image

 Then, go to ‘XL docu’ program window.(if not activated, launch the icon in the desktop.) In the toolbar, click grab button(camera icon), and save the image to the desired folder.

- Patterning

1) Move to the desired position
2) Change beam conditions(acceleration voltage, spot size, focus, magnification…), then blank the beam.
3) In the ‘scan’ menu, choose ‘”External XY”.
4) Go to NPGS pc, and choose your desired RF6 file in the NPGS software.

- Note: you must prepare dc2 and corresponding rf6 files in advance.

5) Click “Run process”.
6) As instructed in the command line, press any key to proceed.

8. Turn off the beam

- Select lowes magnification by going to Magn. menu -> 200
- Turn off high tension in beam control box.
- Change the detector to CCD.

9. Vent the chamber

- The same as instruction 3.

10. Remove your sample

- Carefully remove your sample. Usually, new carbon tape is very sticky. Be careful not to break your substrate.

11. Pump the chamber

- Click ‘Pump’ button in the vacuum control box.
- Leave the machine pumped down.

Additional references

Patterning

 NPGS system uses propriety Design Cad 2000 file for patterning. This is compatible with vector based graphic files like “.DXF”. In convention, 1 unit corresponds to 1 um.

1. Import “.dxf” file in Design Cad

- To launch Design Cad, go to NPGS software. Choose any *.DC2 file and click ‘Design Cad LT’ button on the left.

2. Edit the entities

- Line type change
- Select the entity to modify
- Change line type
- Dashed line(filled entity): line 1(serpentine) or line 5(one direction)
- Solid line(outline): line 0
- Click “apply to selection” button
- Drawing order change
- Go to menu, NPGS
- ‘Order check’ – shows the drawing order information
- ‘Order entity’ – changes the order of drawings
- Sometimes, features like circle may not be reproduced well. In this case,
- Select the entity to modify
- Go to menu, Edit
- ‘modify selection’ – ‘vector convert’
- Click “apply to selection” button

3. Save the file into DC2 format by “NPGS-SAVE-SAVE TO CURRENT NPGS PROJECT”.

4. Make a new RF6 file(or copy old one, rename and edit it.)

-  Insert necessary number of entity(normally 3)                                              
- right side window : Y/N/Y/Y/N                       
- 1st entity(batch process for unblanking the beam)                                      
- type : command                                  
- mode : batch(dos)                              
- pause : before only                            
- command name : unblank                              
- right side data : \NPGS\Projects\pg_fei 63il, 0, 0.2               
- 2nd eneity(drawing pattern)                                                 
- type : pattern or array                      
- name : assign DC2 file name                           
-  in case of array                     
    -  # of rows and columns :                   
    - initial XY move to pattern center : assign pattern center. This point is center for overall array.          
    -  array spacing : spacing(there is no clear rule. It is recommended to assign (+,-)  

- Right window layer data                                  
    - layer : assign activity(normal writing or skip)           
    - magnification : synchronize with SEM mag.(normally, 1000x)          
    - center to center distance / line spacing: you can assign or use default        
    - measured beam current : using picoammeter, read the current value(spot 1) and write down. 
    - dwell : choose line or area dose and fill the value.                
    - For PMMA, areadose ~100uC/cm2 and linedose 0.3-0.5nC/cm

- 3rd entity (blanking)                                                   

    - type : command                                  
    - mode : batch(dos)                              
    - pause : never                       
    - command name : blank                    
    - right side data : \NPGS\Projects\pg_fei 63il, 1, 0.2               
    - in the manual, you can find all kinds of command names.                  

5. Run “.RF6” as instructed in process 6

ESEM mode

For ESEM mode, make it sure water bottle contains enough water and auxiliary pump is connected to the power securely. The pump is normally off, and starts to operate when ESEM mode is engaged.

1) Prepare wet body insert, insertion/removal tool and GSED. They are stored in the black case named ‘spares kit esem’ in the shelf.

2) Open the chamber and remove previously installed high vacuum insert using insertion/removal tool.

3) Install wet body insert. DO NOT TIGHTEN TOO MUCH.

4) Install GSED.

5) Place your sample and vacuum the chamber.

6) Expand vacuum control box.

Select H2O in ‘mode’ selection. Click ‘ok’ in the dialog box.
Adjust the ‘pressure’ slide bar to about 2.5 Torr.(or your own value)

7) Click “Pump” button.

8) Do your process when ‘vac ok’ appears.

9) After process, remove ESEM accessories and replace with the original configurations.

 

Notes and maintenance

1. System shut-down

Sometimes, system shut-down or reboot is a good solution for electronic malfunction. There are three different types of them.

a. PC reboot

This only reboots PC, not the physical system. Therefore, it is a safe. When you face a malfunction, try this first.

- Turn off high tension.
- Close all the programs.
- Reboot PC.
- After booting, operate ‘Microscope Control’ in the desktop.
- Initialize the stage.
- Depending on diffusion pump condition, you may need to go through regular pump procedure, cooling-disabled-heating-idle-pumping.

b. Standby

This shuts down PC and peripheral electronic controls of ESEM. Essential electronics like beam control are still on. If ‘a’ does not heal the problem, standby is a doable option.

- Turn off high tension.
- Click ‘filament off’ button in beam control box.
- Vent the chamber.
- Close all the programs.
- Shut down Windows.
- When “Now it is safe to turn PC off” message appears, press ‘Standby’ button once. It takes about 5~10 seconds before the system turns off. Wait! Don’t press the button twice.
- To restart the system, press ‘ON’ button once.
- After booting, operate ‘Microscope Control’ in the desktop.
- Initialize the stage.
- Start regular pumping procedure.
- Click ‘start gun’ button in beam control box.

c. Complete shut-down

This shuts down all the systems including beam control. Not recommended. You may need to start from bake-out process.

 

2. Vacuum level

Due to unknown reason, ESEM vacuum is not great. It typically reaches around 3*10^-5 mbar, but no below this level. For normal operation, this is fine. However, for column vacuuming(like FEG replacement), this is problem since IGP only works below certain pressure. To tweak IGP, use metallic wrench and attach it to the magnetic pressure gauge. Then, the bake-out works. FEI engineers already know this. Typically, you may not face this situation.

3. Pump maintenance

There are two rotary pumps and one diffusion pump.

1) Rotary pump

Following is rotary pump oil change procedure.

- Place the pump on a raised surface. This is because drain plug is located near the bottom.

- Using empty bottle and funnel(stored near the cuby hole entrance), drain the old oil. After drain, fasten the drain plug again.

- Open the top plug, and fill up flushing oil. Close the plug.
- Operate the pump for about 15 minutes.
- Drain the flushing oil in the same way.
- Fill up the oil chamber with high vacuum oil

è We typically use Edwards, ultra grade 19 oil.

- Close the plug, and re-install the pump.

a. Auxiliary pump is only used for ESEM mode. Since the usage is very minimal, pumping oil may not need to be replaced frequently. However, oil degrades as time. At least, change it every 2~3 years.

b. Main roughing pump is always on, so must be replaced at least once a year. Before removing roughing pump, vent ESEM chamber to deactivate diffusion pump.

2) Diffusion pump

It is unclear what the lifetime of diffusion pump oil is. We only refills the pumping oil once it is not enough. The procedure is:

- For safety, turn the system into standby.
- Wait until heating plate of diffusion pump cools down. It will take about 30~60 minutes.
- The pumping oil(Santovac 5, Monsanto) is very viscous, so hard to pour. Therefore, in the mean time, heat the oil.

- Open the refill cover.

- Using the attached gauge(a stick), check the oil level.
- If oil is not enough, pour proper amount of oil into the refill hole. FYI, oil capacity is 60cc.
- Close the cover firmly, and start the system.

3. Image fade

This tool has chronic symptom of image fading. The reason is unknown.

Description: Screen suddenly fades during imaging or blank. You can see only gray screen with almost zero contrast. If you see carefully, the feature outline is shown, but it is impossible to get a meaningful image.

Effect: This is believed to coming from image processing flow. Except imaging, all other functions including vacuum and beam control are fine. For example, even though the screen fades, ebeam writing works just ok.

Solution: There is no fundamental solution. However, we found that, when this happens, unplugging and plugging X6 coaxial cable generally solves the problem.

4. Stage tilt

ESEM has motorized stage for X,Y,Z,R direction. However, tilt must be done manually.

Before tilt, change the detector to CCD to see the physical condition to prevent accidental touch. While holding tilt handle, loosen tilt lock. Tile the stage as you desire, then lock the stage again.

5. Pico ampere meter

Pico ampere meter is connected to the stage to read incoming current.

6. Field emission gun, ion source replacement

Electron beam sources must be replaced by FEI engineers.

Field emission gun(FEG) is always on. So, its lifetime is somewhat predictable. Typically it lasts 2~3 years. When FEG is first installed, emission current is typically less than 200 uA. If you don’t adjust extractor voltage, end-of-life FEG shows about 330~360 uA. Since this emission can be adjusted by extractor to some extent, this numbers are not very precise. However, it gives rough idea.

Supplies

1) Carbon tape to mount sample into stub (product# 16084-1) can be bought from here 

2) Special high purity tape for EDAX (product# 16084-4) can be bought from here

System Maintenance Log

1) Date - 02/09/12

    Problem - Vacuum Error

Description - The machine was not able to create vacuum in the sample chamber. There was repeated cycle of cooling, heating and electron gun turned off after some time

Remedy - I suspected its due to low level of vacuum oil in the diffusion pump and the problem was fixed.

2) Date - 02/10/12

Problem - Monitor was not able to turn on (no power supply)

Description - When the system was turned on after the ‘system Ideal state’. The computer of the PC turned on but not monitor. I changed the monitor and new monitor worked. I took some images with the system.

3) Date - 02/11/12

Problem - The following error was in the screen when I came to the lab

I tried to restart the software, but I didn’t because during the software start, it checks for all the error and It got stuck at ‘PLCB’ checking.