Wet etching of thin films in nano-confinement for advanced transistors

In semiconductor manufacturing, new generations of devices have entered the nano-world, with critical dimensions of the order of 10 nm. Moreover, new transistor geometries are vertical, with the generation of 1-D and 2-D nano-confined spaces. While many process steps are still performed using aqueous chemistries, e.g. wet etching of materials for patterning and wet cleaning of surfaces. Recent studies have shown that nano-confinement is affecting all the steps in a wet process from wetting to chemical reactions, rinsing and drying [1-6]. Evidence was found for water structuring, decreased permittivity, modified chemical equilibria and slower diffusivity in nanoconfined solutions. The observed phenomena are of interest not only for nanoelectronic manufacturing but also for nanofluidics.

Current activities target the wet etching of nanoconfined films, such as TiN in the RMG module of FinFET. In the etching tests, the etch rates on planar films are determined typically by ellipsometry, while cross-section-SEM (scanning electron microscopy) and image analysis are used on structures. Here the composition of etch chemistries are modified with additives to suppress the confinement effects. The student typically performs the wet etching tests, the ellipsometry measurements, the data treatment of the SEM pictures generated by operators in the pilot-line, and a kinetic analysis comparing planar to patterned etch rates, leading to new chemistry proposals. ATR-FTIR (attenuated total reflection Fourier-transform IR spectroscopy) can be used to confirm the impact of additives on water structuring, or to pre-select additives for testing. ATR- FTIR  has become a major technique to characterize wetting and chemical reactions, as well as properties of aqueous solutions such as structuring, permittivity and diffusivity. Typically, the student prepares the ATR crystals (polishing), performs the FTIR tests using a home-build liquid cell, as well as the data treatment and interpretation. Progress in the understanding of phenomena are used to propose and test solutions to the confinement effects.

The content of the student project will be adapted depending on the progress of our research.

[1] K. Mawatari et al., Anal. Chem. 86 (2014) 4068-4077; [2] A. Okuyama et al., Solid State Phenom. 219 (2015) 115-118; [3] N. Vrancken et al., Langmuir 33 (2016) 3601-3609; [4] G. Vereecke et al., Solid State Phenom. 282 (2018) 182-189, [5] G. Vereecke et al., Microel. Eng. 239–240 (2021) 111515, [6] G. Vereecke et al., Microel. Eng. 279 (2023) 112058.