New negative-tone EBL resist in stock: AQM SiOx


Hydrogen silsesquioxane (HSQ) is a negative-tone electron-beam lithography (EBL) resist with good dry etch resistance, high resolution (~10 nm features), and excellent line-edge roughness. These characteristics have made Dow Corning HSQ the traditional EBL resist of choice for applications which require dry-etching of very fine features, such as in silicon-based photonics.

One challenge with using HSQ in MIBK, however, is that it has a relatively short shelf life of six months from date of manufacture, after which there may be changes in resist sensitivity, precipitation of particles, or both. Contamination of the HSQ:MIBK solution with water—which can easily occur when a refrigerated vial of HSQ is opened before reaching room temperature—can also cause the mixture to solidify into a gel.

To help overcome these challenges, the nanoFAB now stocks a made-in-Alberta alternative to Dow Corning HSQ: AQM SiOx, manufactured by Applied Quantum Materials Inc. AQM SiOx is also a silsesquioxane-based, negative-tone EBL resist, with characteristics very similar to the Dow Corning product in terms of resist sensitivity and achievable resolution. A side-by-side EBL comparison of the two resists yielded comparable results for single-pixel line and dot arrays:

Comparison of single-pixel dots of Dow Corning HSQ and AQM SiOx patterned on Si substrates. Process details may be found here.

The nanoFAB now stocks AQM SiOx as a resist kit, which includes 0.2556 g of AQM SiOx powder and 30 mL MIBK, each in its own 30 mL Nalgene bottle (see image to right). When stored in dry form, AQM SiOx has a very long shelf life, and can be mixed with anhydrous MIBK in small quantities shortly before processing, to avoid risks associated with aging. By adding 5 mL of MIBK to the pre-measured 0.2556 g of AQM SiOx, a standard 6% w/w solution is obtained; addition of 30 mL MIBK will yield a ~1% w/w solution. Syringes with 0.1 µm filters are also now available for dispensing the resist during spin-coating, as a recommended added measure to achieve a uniform, particle-free film.

For more information about using this resist, please contact Aaron Hryciw.

Documentation

  • MSDS [.pdf]
  • EBL exposure comparison between AQM SiOx and Dow-Corning HSQ [.pdf]


† This is in stark contrast to positive-tone EBL resists such as PMMA and ZEP-520A, which can be used for years after their “expiry date” with little change in their behaviour, except for a gradual increase in viscosity due to the slow evaporation of the solvent (anisole), which can be corrected via dilution.


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