Electron Beam Resist – Irresistible Materials

Electron-beam lithography is a mask-less lithographic technique that can be used to direct-write custom patterns with a sub-10 nm resolution (beam diameter). The technique offers high resolution, but its relatively low throughput primarily limits its exploitation to photomask fabrication, low-volume production of semiconductor devices, and research and development.

Even for these applications the choice of resist material is key to maximising the exploitation of the electron-beam technique. Due to the serial nature of the exposure process, high sensitivity resists are required to enhance the throughput. Thin resist layers are generally required to realise the high-resolution potential of the technique (electron beam diameters can be a few nm, but the feature resolution limit is determined by forward scattering (broadening) of the beam in the resist (together with secondary electron blur)). Additionally resist collapse upon development tends to limit resist film thicknesses to no more than three times the minimum feature size for a typical resist. In order to utilise such thin resists, a very high etch durability is required.

IM’s E-Beam Resist:

Irresistible Materials has developed a patented new category of fullerene based E-Beam resists. The IM E-Beam resists offer a range of benefits to electron beam lithography applications, including:

The small molecular size has been shown as a route to lower Resolution and LER. However, unlike other molecular resists, the fullerene is a spherical molecule which enhances its propensity to form highly (three dimensionally) crosslinked structures in negative tone, while minimizing the need for acid diffusion (as the reaction sites of the molecule ‘stick out’ in all directions) which is beneficial in both tones. It is also known to complex with a wide range of other molecules, which helps reduce the propensity to phase-separation seen in some thin film blended materials.

Furthermore, the fullerene core is an extremely good electron acceptor, which allows ready quenching of longer range low energy secondary electrons and thermalised electrons to reduce electron blur, while simultaneously having quite low ionisation potential (~7.5 eV) which has previously been shown in other systems to enhance sensitivity. We have also demonstrated that the negative tone variant of the resist has excellent thermal durability, allowing its use as a mask in aggressive situations, and high etch durability allowing successful transfer from extremely thin films.