In semiconductor manufacturing, new generations of devices have entered the nano-world, with critical dimensions of the order of 10 nm or less. Moreover, new transistor and memory geometries are vertical, with the generation of 1-D and 2-D nanoconfined spaces. While many process steps are performed using aqueous chemistries, e.g. wet etching of materials for patterning and wet cleaning of surfaces. The properties of nanoconfined solutions are different from bulk properties and frequently playing an adverse role in wet processing. Recent studies performed at imec have shown that nano-confinement is affecting all the steps in a wet process, from wetting to chemical reactions, rinsing and drying. The observed phenomena are of interest not only for nanoelectronic manufacturing but also for nanofluidics.
The goals of the proposed PhD are threefold. (1) understand better nanoconfinement effects through characterization, (2) propose solutions to counter-care the effects of nanoconfinement and validate these through characterization, (3) test the proposed solutions in real applications in semiconductor manufacturing.
- Characterization: understand the effects of nanoconfinement on the properties of solutions; develop the use of the methods needed. The characterization of nanoconfinement effects can rely on published progress, particularly in the field of nanofluidics. Also, the use of new methods should be explored. At imec, the methods developed to date make use of IR spectroscopy and X-ray diffraction. Evidence was found for water structuring, decreased permittivity, modified chemical equilibria and slower diffusivity in nanoconfined solutions. Methods not available at imec could be the object of collaborations.
- Propose new solutions to counter-care the effects of nanoconfinement and characterize the effect of proposed solutions using the methods identified in (1.). Propositions will rely on the creativity of the candidate and research available in the literature. Solutions considered at imec presently are twofold. First, the addition of ions to modify the structure of the solution, according to a classification proposed in the literature for bulk solutions. The validity of this classification was verified using IR spectroscopy on solutions confined in nanotrenches (i.e. between fins). It was then applied to select an additive to control the wet etching of an oxide between fins in the STI (shallow trench isolation) module of FinFETs. The selection of ions to control the etching of TiN in the RMG module of FinFETs is on-going. Second, the addition of small organic molecules to control the contact angle (read wetting) of exposed surfaces. Research on this topic has just been started, with the selection of molecules and the measurement of contact angle. The assessment of their effect on water structuring will be performed using the IR method developed at imec.
- Test the proposed solutions on applications. Applications will be selected from issues showing up in the development work performed in the pilot line of imec. Presently, we are looking at the wet etching of SiGe films in the making of Silicon nanosheets for advanced vertical cFET transistors. Other applications envisaged are cleaning after dry recess etching in nanocavities and rinsing in deep nanocontacts. As to rinsing, a preliminary test showed that rinsing in nanoholes was not efficient, taking too much time for an effective implementation in manufacturing. In this part, beaker tests on coupons are performed first, before going to full wafer testing of best candidates in the pilot line.
Required background: Engineering science, nanoelectronics manufacturing, chemistry, materials science, and physical-chemistry
Type of work: 50% experimental, 40% data interpretation, 10% literature
Supervisor: Stefan De Gendt
Daily advisor: Guy Vereecke
The reference code for this position is 2022-130. Mention this reference code on your application form.