Afternoon Liuchang,

  This can be quite a common problem with AFM "scratching" lithography onto
polymers. Generally, after spin coating of the polymer film, a tensile strain is
created between the polymer chains in the film. When you cut the polymer using
an AFM probe, the strain is released, widening the trench to a distance greater
than the AFM tip diameter.

  You have a couple of alternatives to reduce line widths; add solvents to the
PR to dilute it, trying different lithography parameters. Try controlling the
way in which the polymer contracts after scracthing can help also.

  The depth-to-width ratio  10:1 is typical for AFM work; I’m not surprised you
can’t get higher. If you want high aspect ratios, you’re using the wrong
technology!

  Jeff Kettle




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            From:
    "Áõ³©" 
      To:
    mems-talk@memsnet.org
      Date:
    Mon, 2 Jun 2008 17:03:45 +0800
      Subject:
    [mems-talk] AFM scratch photoresist for nanograting

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Dear All,


Recently, I use AFM to fabricate micro-nano structure, along with other
methods such as wet etching, sputter and photolithography.

The first step is to fabricate nano-grating by AFM. I have used many
photoresists such as SU-8 and AZ1800. I find that SU-8 is too
sticky to form a groove. AZ1800 is better than SU-8, however,
 depth-to-width
ratio is too small(1:10). The height of the groove is about
100nm, the groove bottom is about 300 nm, and the dap is nearly 750nm.

Tip Radius (max.) is 20nm. What is the main reason that the dap comes
to 750nm?


I still can not find a suitable photoresist for AFM scratching.

If you have advice, please tell me in details.

Your help will be highly appreciated.