Electron Beam Lithography

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Apply Resist / Soft Bake / Measure Thickness

1. Use Spin Coater

2. Apply ~1mL of MicroChem 495 PMMA C4 with dropper

3. Example recipe:  Prespin at 500 RPM for 5 sec.  Spin at 3500 RPM for 45 sec.  This will yeild thickness of ~3000A (post-bake)

4. Soft bake on Hot Plate for 45 min at 180 degrees

5. Use the NanoSpec to measure thickness.  Chose index of refraction option and use Nf=1.486

Sample Preparation

1. Cleave samples into ~1X1cm pieces and blow off debris with air hose

2. Look at sample under optical scope and identify corner where resist looks good.  Make sure to identify this corner, perhaps by putting a sample ID in the opposing corner

Load Sample into SEM - Set SEM Parameters

1. Place sample on SEM holder with carbon tape and load into SEM

2. Typical SEM settings have been used to successfully print at BSU:  Working Distance (WD) = 7mm (adjust z-axis to achieve a focused image at the WD; SEM Measured beam current = 10-80uA with spot size 50-343; Collector Bias = 300V; Auto brightness/contrast.

3. Focus on the gold standard and make sure you get a good image at a magnification of 100kX.

4. It has been experimentally determined that it takes 20-30minutes for the beam to reach an equilbrium value, which may or may not effect your printing.  If possible (if picometer is available), measure beam current with Faraday cup.  When the "measured beam current" (in SEM control panel) is 80uA, the current hitting the sample, and thus that read with the picometer, is ~32-35pA.  This is a good current for features larger than ~0.5um.

Focusing on Sample (Via burning holes in the resist)

1. Focus on the edge of your sample at as high of a magnification as you can (80kX is good).  Remember that when you are looking at the resist, you are exposing it. 

2. Blank the beam and move away from the edge (into your sample) by a couple hundred microns.

3. Unblank the beam and quickly hit the "Spot" option in scanning.  This holds the beam in one location on the sample.  The objective here is to burn a hole in the resist that you will be able to focus on.  Let the beam sit in spot mode for about a minute, then turn "Spot" mode off.  You should see a little circle (about the size of a dime on the screen at 80kX) in the resist (if you don't see this, check brightness and contrast and remember than the SEM must be pretty well focused on this spot anyways, which is why you shouldn't move too far from the edge you focused on - move stage and try again until spot shows up).  Focus on this circle as best as you can.

Printing

1. Once you have focused on the mark, blank the beam again.

2. Move the stage by a couple hundred of microns from the burn mark you focused on

3. Set magnification to that required by your pattern (NPGS tells you what the magnification for your pattern needs to be set at).

4. Unblank the beam, quickly switch the green toggle box from "SEM" to "NPGS" and hit the space bar to start printing (assuming you have already selected the NPGS runfile)

5. When NPGS is done printing, quickly switch the green toggle from "NPGS" to "SEM" and then quickly blank the beam.

6. Unload your sample and properly shut SEM down.

 

Develop

1. Develop in MIBK:IPA 1:3 for ~60 seconds.  Rinse in DI water for 30 seconds.