North Seattle Community College
Nanotechnology Program
SEM
Process Outline
Rev.1.1
Date: June 12, 2006 Rev: April 29th, 2011
Author: Matt Martin-Vegue
The purpose of this document is to list all necessary materials and processes needed to
successfully conduct a photolithography process on a silicon wafer.
Materials and Equipment
Leica Stereoscan 430
Conductive Tape or Paint
Sample Stub
Precautions
Only trained users may operate the SEM!
Wear powder-free gloves when working with specimens and working inside the
chamber or column.
Always log into the log book before starting to use the instrument and log out
when you have completed your session.
Procedure
1. Startup from SEM shutdown mode
1.1. Turn on the SEM by pressing the green button above the disk drive with a picture
of a circle (middle), then pressing the other green button on the left.
1.2. After Windows loads, double click the LEO UIF icon.
1.3. Select directory for files by choosing [c:] then OK.
1.4. Go to ‘Stage/Vac’ on the toolbar.
1.4.1. Click ‘Vacuum Status’, which shows the chamber conditions.
1.4.2. Click ‘Pump’ to turn pump down the chamber. You must wait until the
Vacuum Status reads ‘Ready’ (P ~ 10-5 torr) before continuing.
1.5. After loading of UI, click the Run Up icon (traffic light icon). This will obtain
an image. The starting parameters should be:
Magnification: 35 X
WD: 25 mm
EHT: 20.00 kV
Fil I: 2.34 A
Focus: 25 mm
Beam Current: 400 uA
I Probe: 200 pA
1.6. Verify that an image is displayed on the monitor.
1.7. Move the desired sample into view by using the X and Y knobs or the rotate
knob on the microscope. Alternatively, click on ‘Stage/Vac’ and then ‘Stage
Move’ and use the joystick to move the sample into view.
2. Adjusting brightness, contrast, magnification and focus to sharpen an image
2.1. Adjust the brightness and contrast levels of the image by clicking with the left
mouse button the Brightness and Contrast icon (black and white circle with the
yellow sun).
2.1.1. Depress the left mouse button while sliding the mouse either left or right
to adjust brightness.
2.1.2. Depress the center mouse button while sliding the mouse either left or
right to adjust brightness.
2.2. Click the magnification/focus icon (magnifying glass) to allow for modification
of magnification and focus.
2.2.1. Depress and hold the left mouse button and slide the mouse the left to
lower the magnification. Start with a low magnification (~50X)
2.2.2. Depress and hold the center mouse button and move the mouse to either
the left or right until the image is clear and distinguishable.
3. Setting the kV and Probe Current
NOTE: The accelerating voltage will depend upon the sample. As a base line,
uncoated non-conductive samples should be examined using a kV between 1 and
3. Non-conductive but coated samples should be examined between 5 and 15 kV.
Conductive sample should be examined between 10 and 25 kV. Inexperienced
users should start with an accelerating voltage of 20 kV and a probe current of
200 pA.
3.1. To adjust the kV (EHT), click the left button on the kV and probe icon (lightning
bolt).
3.2. Depress and hold the center button and move the mouse to the left or right to
increase or decrease the kV. (See note above for values)
3.3. Depress and hold the left button and move the mouse to the left or right to adjust
the probe current. (See note above for values)
3.3.1. Note: A large probe current will produce noise free images but will
produce low resolution images at high magnifications.
3.4. It may be necessary to readjust the brightness and contrast levels. Repeat step 2
if necessary.
4. Setting the filament current
4.1. Select the filament current icon (looks like a light bulb).
4.2. The filament current may be set to either the first or second peak. Adjust the
current by sliding the mouse to the left and the right until the image appears
brightest. The first peak allows a longer filament life but lower resolution
images. The first peak is adequate for this class’s purpose. Image will appear
bright and dark as you slide the mouse and change the current values. Refer to
the Leica manual p1-20.
4.3. Use the Gun Alignment panel to VERY SLOWLY drag the slider bar in either
direction to adjust to the appropriate peak. Adjustments should not exceed 200.
5. Adjusting the Final Aperture
5.1. Testing if Final Aperture is misaligned
5.1.1. Center the image on the screen. Do this at high magnification. You can
also click on the icon which has a monitor with cross-hairs to center the
image (on the right).
5.1.2. Take the focus out and bring back into focus.
5.1.3. If the aperture is misaligned then the specimen will move in a slight arc or
shift.
5.2. To adjust the Final Aperture, use Focus Wobble (5th icon from the left).
5.2.1. Select Focus Wobble from the drop down menu under Beam or from the
Gun Align panel.
5.2.2. Go to ‘Image’ on the toolbar and select ‘Noise Reduction’. The speed and
amplitude of the sweep can be adjusted from the Wobble panel by using the
amplitude scroll bar. NOTE: Select a reduced raster and a fast scan speed.
5.2.3. Adjust the X and Y aperture micrometers located above the sample
chamber until the image ceases to shift laterally.
5.2.4. Close Focus Wobble panel.
6. Adjusting Beam Alignment
6.1. Beam alignment should be conducted in conjunction with filament current
adjustment for optimal resolution.
6.2. Adjust the black gun align screws on the outside of the column until the
brightness level of the signal cannot be increased (ensure the system is on manual
brightness).
7. Adjusting Stigmation
7.1. Click the Stigmation icon or go to ‘Beam’ on the toolbar and select ‘Stigmation’.
At this point, the stage should be set at a WD (working distance) of about 10mm.
Do not go below this depth. To set the stage height, turn the stage height
adjustment knob located to the side of the sample chamber.
7.1.1. Press Auto Stig in the stigmation panel
7.1.2. Press Dynamic Stig and using the mouse pointer, left click on the best
focused image.
7.1.3. Press Stigmation icon. Adjust the X and Y parameters as normal with the
mouse.
8. Obtaining a reduced noise image
8.1. The line average mode applies the same noise reduction to all active zones but
frame average allows for different frame counts for each zone.
8.2. Increasing the pixel averaging has an effect similar to a slow scan rate which
decreases noise but takes longer to scan. This is necessary for a final clear
image.
9. Measuring using Point to Point
9.1. Right click on the image.
9.2. Select Annotation.
9.3.
9.4.
9.5.
9.6.
9.7.
Close the window.
Right click the image again.
Click measurement.
Select Point to Point.
Two points appear on the image. Move the point to the desired starting and
ending points of the measurement.
9.8. To remove the points, Right click the image once more. Select mode and select
quit. Now click one of the points on the image. The points will then be
removed.
10. Capturing an Image
10.1.
Freeze the image by selecting ‘Image’ on toolbar, then ‘Freeze’.
10.2.
Save the image by selecting ‘File’, then ‘Export Photo’, then ‘OK’.
10.3.
When the ‘Replace?’ prompt appears, click ‘No’.
10.4.
Rename the image, and then click ‘OK’.
11. Shutdown of SEM
11.1. Go back to the copper grid sample and set parameters so as to get a clear image
before you begin the shutdown procedure.
11.2.
Click the traffic light button to restore the original state.
11.3.
Click ‘Beam’ on the toolbar, then click ‘Beam Off!’
11.4.
Click ‘Stage/Vac’ on the toolbar, then click ‘Vent’ in the Vac Status box
11.5.
Click SEM Shut Down
11.6.
If asked to save operating conditions, click ‘No’.
11.7.
Once the SEM program closes, the user is exited to Windows. Click the
File button in the Program Manager window. Select Exit Windows.
11.8.
Push the circle/line green button, then the red button.
Operating the EDS (Energy Dispersing Spectroscopy)
1. On the SEM screen click on the ‘Reduced screen mode’ (the monitor looking icon
with a square in the middle of it). This will select an area in the center of the
screen which will include the area of interest on the sample.
2. Turn I probe value to 80nA for best results.
3. Set WD (working distance) to 25mm (setting 5 on the knob) using the stage
adjustment knob located to the side of the sample chamber.
4. At this point, switch to EDS monitor.
5. Go to Program – Oxford Instruments – Link ISIS
6. Click on the graph (spectrum) icon.
7. Click on the magnification icon to zoom in and out of spectrum.
8. Click on the round blue button icon to start collecting data.
9. To identify peaks, click on the ? icon. You can search by element and the
selected element peaks will then be marked on the spectrum.
Glossary:
Accelerating Voltage – The difference in potential between the filament and the anode.
As the voltage is increased, the electrons travel with higher velocity. Typically, higher
accelerating voltages increases resolution, but may make it harder to see surface
roughness.
Final Aperture – This may be referred to as “focus wobble”, “image wobble”, or
“aperture align”. Aperture alignment should be used while focused on a small roundish
feature.
Probe Current – The total amount of current to be irradiated on the specimen. The
control is done by varying the excitation of the SEM’s condenser lens. A higher
condenser lens current means a smaller electron beam current, and a smaller electron
beam size where it hits the sample. Lower currents might need to be used to avoid
charging effects and sample damage.
SEM – Scanning Electron Microscope. An SEM is a type of electron microscope
capable of producing high resolution images of a sample surface.
Stigmation – Astigmatism is when a lens has different strengths as a function of the
rotation about the lens axis. This gives the lens two lines of foci instead of a single point
focus.
UI – User Interface. Referring to the interface a computer displays on the monitor.
References:
Scanning Electron Microscope (SEM) Operation [Electronic version]. (2006). Michigan
State University. Retrieved June 12, 2006, from
http://www.chems.msu.edu/curr.stud/mse.sops/sem.oper.htm
Stereoscan 430 Operator Manual (1994). Cambridge, England: Leica Cambridge Ltd