Align after bake

This is the procedure for a full "service" alignment, this is not for daily fine tuning alignment

Simplified Column Alignment instructions

1. Put large featureless sample, at least 3-4 mm, such as Si wafer in stage, no tilt
1. Get image at 8 kV, focus on sample
2. open "Aperture Calibration" and "Calibrate Stigmation" windows (these only work in service mode)
1. Select probe current max
2. zero gun align and aperture align in service window AND user aperture window
3. zero stig and beam offset
4. All electronic offsets should be neutral
3. Get emission image, uncheck Condenser Normal box
1. all apertures should be evenly illuminated, circles will overlap
1. If circles are clipped, distorted, partial, mechanical source align is required
2. if illumination is good, mechanical source alignment is OK,go to next step
3. loosen 4 6 mm screws at top of column. do push-pull adjustments in X and Y to try to get uniform illumination. 
4. to the extent possible, center illuminated aperture pattern, however uniform illumination is more important than centering.
5. recheck condenser normal. Now large diffuse aperture images will change to sharp smaller circles. These should also be uniform. Reduce SEM contrast since these will be saturated.
6. slowly tighten all four screws to lock source. This will cause shifts, correct as needed to get good illumination with source locked. 

Best align with current filament state, 200 pA mode (60 um aperture)
gun 44.5, 27.5 aperture -47.0 -22.9
user aperture -4.0, -6.0
stig 5.7 19.5 balance X 81.3, 95.9 Y 69.6, 94.7

Best max current
gun 44.5 27.5 aperture -47.0 -22.09
stig 24.7, 39.0 bal X 84.1, 93.0 Y 74.3, 94.7

Condenser lens needs mechanical alignment. Here is emission image for 1 nA, 600 pA, 400 pA all 90 um aperture

clear shift with condenser excitation















Align gun, aperture, stig, stig balance for 120, 90, 60, 30 um apertures

SEM Source Mechanical Align

Prior status

• just after bake, EHT off current up 246 vs 232
• Gun align near user software limit, stig balance off, time for full align

Align

8 kV aperture image condenser at "max"

aperture positions:

1. 60 um center
2. 20 um right
3. 30 um lower left
4. 75 um lower right
5. 90 um left
6. 120 um top right
7. blank top left

Procedure

First check mechanical alignment, use Si 10 um grid for test

Alignment, all offsets zero user and service. Cond normal

condenser off

Clear problems with mechanical alignment

Bring aperture to exact center, bad illumination

very poor aperture illumination on exact mechanical center

condenser on, illumination distorted here too

Procedure says illumination trumps centering

illumination better but is 120 better than 60??

best mechanical source alignment

after this use gun offset/align for center aperture

Gun Arc at 30 kV

• On Thursday 12/6/12 low-level radiation group requested SEM be operated at max voltage and current.
• I set the beam voltage to 30 kV. The system had not be operated above 10 kV for some time. Just as the voltage reached 30 kV I heard the "snap" of an arc. The gun went off, there were no error messages.
• I had trouble restarting the gun, I got "EHT Vac not ready" (see previous notes). Raising pressure, restarting PC no help. After putting electronics to standby and back to run, EHT Vac was good, gun started.
• Emission current almost doubled, from ~ 107 uA to ~ 170 uA. I was afraid filament had been damaged during arc, however the same feature was centered in the field of view, and it was possible to get similar image quality. 
• Robert Ribay from Zeiss happened to be working on the Supra, he looked at the image quality, did a quick alignment, and did not see serious problems.

Gun off for thanksgiving

• Extractor 5.02 kV current 107.2 uA fil 2.33 A 15 Nov 12
• Gun vac 2.72 e-10 system 1.2e-10 before gun off
• Gun vac drops slightly to 2.27 e-10 while gun runs down 

before restart on Mon 26 Oct 12

• Gun vac 1.1e-10, system 1.3e-10, gun vac fluctuates near zero
• have "column pumping" = pumping, "ready", occasionally off, EHT vac ready = no
• Throttle ion pump, open Ar leak valve to get system pressure 1e-8, try to get SEM ion pressure stable above 1e-10. Not enough, pressure (ion pump current monitor) fluctuates below 1e-10
• Have to open pump bypass, get ion pump pressure ~ 3 e-10 with no fluctuations below 1e-10, after ~ 100 sec stable pressure, EHT vac goes to ready, now start gun run up

Extractor reaches 5020 V at 9:50

9:50  78.4 uA

9:53  83.4

9.56  85.2  also close bypass, gun vac 8.8e-11

10:13  92.3

11:48 105.6 close to steady state

On Tuesday, gun 107.8 uA EHT off, 62 uA EHT on 3 kV, 42.5% extraction