In this paper we will give an overview of the epitaxial lift-off (ELO) technique and its applications. The first part will describe the basic technology, which includes chemical lift-off, handling, bonding, stress, alignment, etc. The second part will give an overview of device results obtained with ELO (LEO and lasers on Si, MESFETS on InP, OEICS, etc).

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The interaction of 91.6eV EUV photons with photoresist is very different to that of optical lithography at DUV wavelength. The latter is understood quite well and it is known that photons interact with the resist in a molecular way through the photoacid generator (PAG) of the chemically amplified resist (CAR). In EUV however, the high energy photons interact with the matter on atomic scale, resulting in the generation of secondary electrons. It is believed that these secondary electrons in their turn are responsible in chemical modification and lead to switching reactions that enable resist local dissolution. However, details of the interaction are still unclear, e.g. which reaction an electron with a given energy can initiate.In this work we have introduced a method to measure the chemical interaction of the secondary electrons with the EUV resist. The method is based on electron gun exposures of low energy electrons (range ~1eV to ~80eV) in the photoresist. The chemical interaction is then measured by Residual Gas Analysis (RGA), which can analyze out of the outgassing which and how much reaction products are generated. In this way a 'chemical yield' can be quantified as function of electron energy. This method has been successfully applied to understand the interaction of secondary electrons on the traditional CAR materials. The understanding was facilitated by testing different compositions of an advanced EUV CAR, where resp. polymer only, polymer+PAG, and polymer+PAG+quencher are tested with the electron gun. It was found that lowenergy electrons down to ~3-4eV can activate PAG dissociation, which can lead to polymer deprotection. However it was observed too that energy electrons of ~12eV and higher can do direct deprotection even in absence of the PAG. In addition, testing suggests that electrons can generate also other chemical changes on the polymer chain that could lead to cross-linking.

Limitations on current performances of the chemically amplified resists (CAR), as well as the productivity driven low exposure dose requirements (below 20 mJ/cm 2 ), have brought the researchers to look at a novel class of materials as possible alternative to the CA resists to simultaneously achieve resolution, line-width roughness (LWR) and sensitivity. In 2014, imec has started a new project to look into novel materials for EUV lithography with particular attention to metal containing materials (MCR) to explore alternative approaches that can offer superior characteristics in photoresist imaging: improved LWR and line collapse, high sensitivity and high etch resistance. In this paper we report the first assessment on the enablers of the MCRs from a manufacturing compatibility prospective, as metal cross-contamination and outgassing, to a device integration prospective through the patterning on the ASML NXE:3300 full field scanner exposure tool, the etch performances and new litho-etch integration scheme for 1x nm technology and below. The results obtained are highly promising and give a clear indication that other chemical paths in novel resist formulations are possible in advanced EUV lithography.