Having done interference lithography for more years than I'd like to admit,
I can offer some of these suggestions:

- what presents itself as sloped sidewalls, under-developed or underexposed
can often be entirely due to poor resist/substrate interface. Lines that
are fully developed with straight walls can often float away during
development, making diagnostics very difficult. I've had much better
success since switching to vapor priming the substrates (assuming silicon).

- I have had better success with i-line resists than with g-line, even as
far away as 488nm (Ar ion laser). The sensitivity will be low, so you have
to increase the dose.

- You can get even better sidewall results with an anhydrous ammonia image
reversal.

- as for resistance to fluorine plasma etching, it depends on what
substrate you are trying to etch. Most resists are more sensitive to ion
energy than to the fluorine radicals. Reducing the ion energy and
increasing the plasma density would give better results, although it will
produce some undercut.  An ICP would be useful here to control these
parameters.

- For even greater etch resistance, I have used negative-acting chemically
amplified resist in the deep-UV (266nm).

- As for dilution, I am surprised to hear the difficulty getting consistent
dilutions. I have found the variations due to spin & bake steps to be more
significant than the dilution step. If you use a sensitive weighing scale,
and make large batches, that should not be much different than the premixed
bottles.



On Tue, Jan 15, 2013 at 1:01 PM, Justin Hannigan
wrote:

> Hi,
>
> I am looking for a high-contrast, high-resolution photoresist to use for
> interference lithography.  Our source is a HeCd laser operating at the 442
> nm line.  Ultimately, we would like to use the resist as an etch mask, so
> resistance to fluorine-based chemistry would be beneficial but isn't
> strictly necessary.
>
> I have been working with ma-p 1205 but I have difficulty getting steep
> sidewalls.  I have gotten some good prints using a diluted SPR 220 in the
> past, but I have had difficulty getting consistent dilutions so I would
> prefer a commercial pre-mixed product.
>
> As I understand it, the high-resolution requirement requires a low
> viscosity resist that will produce a thin layer when spin coated. (Since we
> are doing an interference lithography we don't have depth of focus issues,
> but there's still a limit on the aspect ratio for the lines that limits the
> resist thickness to less than a micron.)
>
> To summarize, I'm looking for a photoresist that has the following
> properties:
> 1) Sensitive at 442 nm (g-line resists seem fine)
> 2) Low viscosity; film thickness less than 1 micron
> 3) High contrast (large change in development rate when exposed)
>
> Can anyone recommend a suitable product for this?
>
> Justin
>
> --
> Justin M. Hannigan, Ph.D.
> Process Development Engineer
> LightSmyth Technologies,Inc.
> 875 Wilson St, Unit C
> Eugene, OR 97402
> Tel: 541-431-0026
> www.lightsmyth.com
>
>
> !DSPAM:**50f5999e205381938014717!
>
>
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