Imaging and lithography on the Zeiss SEM at CAMCOR

Contact person at CAMCOR is Kurt Langworthy (office 541 346 3660, ebeam room 541 346 4778)

Basic parameters are:

  • PMMA (950k, 5% in Anisole) is spun at 3000 rpm for 60 seconds to get 175 nm. (At 400 rpm the thickness is 130 nm, spin curve is available from the Microchem website). Baked 10 minutes on a 165 deg hotplate.
  • 30kV accelerating voltage to minimize secondary electrons.
  • 10 micron aperture (beam current ~ 25 pA).
  • WD of 5 mm (Thumb on camera image is about 8 mm).
  • Focus, aperture position and stigmatism optimized using the gold nanoparticle standard.
Figure shows the qualitative difference in resolution between using 30 kV (left beam) and 5 kV (right beam)

Aperture optimization

At high mag (~ 100,000) find a small round object. Turn on wobble (adjust the extent of the wobble) and watch for lateral motion of the small round object as the focal plane is swept up and down. The aperture position is represented by the red dot on the computer screen. Move the position of the aperature one click at a time until lateral motion is stopped.

Stigmatism optimization

At high mag (~ 100,000) find a small round object. Change the focus manually. Look for evidence of two focal planes (seperated in height) at right angles to one another (not necessarily aligned with the x and y axis on the screen). If the two focal planes are separated, a round object will look stretched and blurry along one axis while it looks sharp/small along the perpendicular axis.

  1. Focus at the plane roughly in between the pair of focal planes (i.e. where the object looks round).
  2. Start adjusting x-stigmation and y-stigmation to optimize the image.

Repeat steps 1 and 2 several times.

Exposure parameters

After drawing a pattern in DesignCAD you make a job file in the Nabity software (different computer from the SEM imaging controls). Exposure parameters for the job file are typically

  • Line dose 1.2 nC/cm
  • Center-center distance 10 nm.

Notes

  • The largest aperture available has a 7 nA beam current.
  • Signal from inline detector increases when WD is decreased.
  • Signal from SE2 detector decreases when WD is decreased.

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