Low Energy Electron Beam Lithography, Less than 100 eV

Looking for some ideas on very low energy electron beam lithography (like resist, process). Energy should be less than 100 eV. A high resolution low energy electron source is not the issue.

It can be done, but your energy range would depend on what your source is.

There is a lot of data over many resists which can even be noticeably thick (>100 nm). Lower energy generally better with STM or AFM; higher (approaching 100 eV) may be possible on these SPMs but you also can look at some experimental electron optical systems (SEMs) built for this energy range.

We have C-AFM and STM, and looking at Magellan (SEM). Yes, the C-AFM and STM we are afraid to break at high voltage so for >50 V we will probably start to switch to SEM. Of course some nitpick and say these are not really "high resolution" but it is good enough for us.

What resists can be used? How high is the required dose for say 100 nm thickness? Can 200 nm be possible?

STM has the most data, see for example USP6042993 describing 45 nm thick e-beam resist exposed with -35 to -55 V STM or SFM bias. Also APL 58, 2526 (1991) demonstrated 50 nm thick SAL-601 exposure for 15-50 V STM operation.

PMMA works too. It can actually be damaged in the range 10-50 eV (JVST B 17, 2512 (1999)).

The most relevant data for SEM would be from JJAP 29, 2212 (1990). They used a retarding field to slow down initially fast (keV) electrons.

For 40 eV and 100 eV electrons, the estimated E0 (minimum dose) for self-developing poly(2-methylpentene-1 sulfone) is 10 microC/cm^2 for 50 nm thick, 30 microC/cm^2 for 100 nm thick, and 50 microC/cm^2 for 150 nm thick.

A high keV electron is more likely to pass through the resist before giving up any energy, in contrast to the sub-keV electron. Somewhere in between, i.e., low keV electrons, the generation of secondary electrons is maximized. Hence, the resist is more sensitive to these low energy electrons and the dose can be lower.

But the slower electron is also more likely to change direction just by elastic scattering and is more sensitive to local charging potential.

Very good thanks.

BTW, the data would also prove the effect of photoelectrons (e.g., EUV, or soft or hard X-ray) and secondary electrons, right?

Yes it should, but then it would also show why electron beam resolution is never as reliable as thought.