In a collaborative project led by aBeam Technologies for developing a new class of ultra-minaturized spectrometers, researchers Christophe Peroz and Scott Dhuey of Lawrence Berkeley National Laboratory's Molecular Foundry have devised an imprint process to replicate photonic chips at low cost.

The fabrication of templates is reduced to one single step, by using electron beam lithography (EBL) to directly pattern spin-on-glass (HSQ), which gives high-resolution patterning and avoids extra etching steps. The pattern replication is performed with a stepper UV-NIL – Imprio 55 from Molecular Imprints. Resist films are first spin-coated and slightly baked on 6 inch wafers.

Imprinting is performed at low pressure and ambient temperature, taking less than two minutes to replicate a pattern requiring more than 12 hours using EBL. In addition, this pattern can then be replicated across the entire wafer.

This process allows imprinting feature sizes from 10 µm to 14 nm. The high fidelity between the template and imprinted structures is verified with a difference in line edge roughness of less than 0.5 nm (3σ deviation value). Having minimal residual layer thickness and maximum homogeneity below the pattern is key in transferring the patterns from resist into functional material. The residual layer thickness is easily tuned to a minimum of less than 5 nm and a variation of approximately 3 nm across the wafer. This result is demonstrated in the pattern transfer via plasma etching of the smallest features sizes (13 nm) reported in the literature.

Nano-spectrometers and more

The technique has been used to fabricate nano-spectrometers (presented at the MNE 2010 Conference) and is suitable more generally for fabricating photonics and nanofluidic chips at low cost and high throughput.

More information can be found in the journal Nanotechnology.