Electronic processes in EUV lithography - photoelectron yield and photoemission

The photoelectron yield is a key parameter of a photoresist that quantifies the magnitude of electronic processes occurring during exposure to extreme ultraviolet (EUV) light. Contrary to previous technologies, EUV lithography is triggered by a large cascade of low energy electrons generated by few primary photoelectrons. It is believed that photoresists with high electron yield are more efficient in generating the secondary electron cascade, which could lead to higher sensitivity, lower dose and increased throughput. The adjacent layers, such as the underlayer hardmask, might also play a role and enhance the photoelectron generation and transfer from and toward the photoresist. However, there is not yet enough experimental evidence to confirm this hypothesis.

At imec we are exploring state-of-the-art materials for lithography using a dedicated tool for photoemission in the extreme ultraviolet wavelength (13.5 nm) of thin films of less than 30 nm thickness to enable the fabrication of next generation integrated circuits. The main challenge of photoelectron yield measurement lies in the undesired effects introduced by, for example, surface conditions and charging, in addition to the chemical modifications induced in the material during exposure to the beam itself. On the other hand, this latter feature opens new opportunities to track the chemical changes happening in the photoresist during exposure to the EUV beam “in situ”. The tool can also be used to evaluate photoemissivity and electronic processes during exposure.

In the framework of this project, the trainee will develop the instrumentation needed to measure electron yield and understand how secondary electron cascade evolves in photoresists of different composition and chemistry. Exposure of patterned resist will also be carried out as a complementary technique to assess dose and sensitivity and other lithographic figures of merit. The outcome of this work is relevant not only for EUV but for all next generation nano-fabrication methods which will be based on electron-mediated exposure, such as electron-beam lithography.

The availability of this position is subject to funding: priority will be given to self-supporting candidates. The internship is to be carried out during the second half of 2023 or later preferably. The ideal candidate has a background in physics, chemistry or materials science preferably with a good understanding of solid state physics, mathematics and statistical analysis. Previous training in cleanroom environment, programming skills in MATLAB or python are also additional assets.