Papers by Author: Guy Vereecke

Abstract: The use of SiGe substrate as a semiconductor material is increasing because of its unique properties. In order to manufacture high-performance devices, it is necessary to develop SiGe selective etching technology. In this study, SiGe epi and oxide substrates with varying germanium percentages (15, 25, and 40 %) were used for the investigation of the selective etching process. As the etchant, APM (1:4:20) solutions were used, and added HF and HCl to confirm the pH effect. The evaluation was conducted while adjusting the pH level. In the case of the SiGe epi substrate, the etching rate was very low at high pH, but the etching rate rapidly increased at a specific pH. And then, the etch rate gradually decreased. On the other hand, the etch rates of the oxide substrate rapidly increased as the pH decreased. To explain the etch rate behavior due to the difference in Ge content and type of substrates, the surface chemistry was measured, and the speciation of the solution was analyzed.

Abstract: In advanced semiconductor manufacturing, deep hydrophilic nanoholes are found in various applications, which require a wet clean after patterning. In this work, we use an in-situ ATR-FTIR spectroscopy technique to characterize the wetting of nanoholes in a silica matrix by UPW and electrolyte solutions. Wetting was much slower than predicted by a numerical model, while temperature cycling evidenced the formation of unexpectedly stable gas pockets in the wetted nanoholes. Water structuring in the nanoholes was characterized by an analysis of the OH stretching peak. Besides, monitoring the dissolution of CO2 in the wetted nanoholes allowed to compare the diffusivity in the nano-confined solutions with that in bulk solutions. Our results strongly suggest that the gas pockets were stabilized by the decreased gas diffusivity resulting from water structuring.

Abstract: The continuous down scaling of the dimensions for the logic devices has imposed to carefully track the pattern collapse issue when cleaning after FIN etch. Showing the limitations of the hot IPA drying technique toward scaled FIN dimensions, a cleaning using a surface modification drying technique has been proposed and successfully implemented. It is also discussed the use of some post treatment solutions to remove the grafted layer used to modify the FIN surface while preserving the integrity of the FIN structures.

Abstract: In semiconductor manufacturing of 3-D nano-structures, modified kinetics have been encountered for the aqueous chemical etching of thin films in nano-confined spaces. A popular explanation relies on changes in reactant concentration from the overlap of electrostatic double layers (EDL) on opposite walls of the nano-structures. In this study, the cycloaddition of dibenzylcyclooctyne-PEG3-alcohol (DBCO) to a linear azide-terminated SAM was performed in nanochannels of width varying from 62 to 32 nm. ATR-FTIR was used to monitor the reaction kinetics, characterize water structuring and determine the pH in nanochannels. Reaction kinetics were slower in nanochannels as compared to a planar surface, while pH shifts were observed in absence of EDL overlap, with a significant influence of channel width. Actually only the overall decrease in reaction rate could be explained by EDL overlap. The discussion shows that the water structuring measured in nanochannels may play a significant role in the observed phenomena.

Abstract: A self-limiting wet etching of metal thin films has been developed for the replacement metal gate patterning in advanced logic devices, which will have aggressively scaled gate length and fin pitches. A uniform and highly selective wet etching of polycrystalline TiN films is demonstrated by a diffusion-limiting oxide growth on the metal surfaces as well as a subsequent highly selective oxide removal.

Abstract: Accurate characterization of the underwater stability of superhydrophobic surfaces is crucial for the design of durable anti-fouling materials and advanced microfluidic concepts. Although superhydrophobic breakdown is a major issue that hampers full exploitation of superhydrophobic functional materials, suitable characterization methods are lacking and relatively little is known about the wetting dynamics. In this work we explore a novel method based on attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) for large-area in-situ analysis of wetting states and wetting transitions on nanostructured surfaces. Spontaneous wetting is induced on superhydrophobic silicon nanopillars through in-situ modulation of the liquid composition and surface tension. The high surface sensitivity of ATR-FTIR enables quantitative evaluation of the instantaneous liquid composition and wetted area. Critical transition criteria for superhydrophobic breakdown are assessed using both ATR-FTIR and goniometric measurements. Significant deviations from classical wetting models are revealed, emphasizing the need for more accurate transition criteria and careful experimental validation. Breakdown kinetics near the critical transition are found to be significantly slowed down on nanostructured surfaces, which underlines the necessity for accurate characterization of wetting dynamics at the nanoscale. The proposed ATR-FTIR method can be promising for dynamic studies of wetting transitions on more advanced surfaces, as hierarchical structures or oleophobic designs.

Abstract: Over the past decade, many advanced drying techniques have been developed to reduce and prevent pattern collapse of high aspect ratio (HAR) structures after wet processing. However, different dimensions, profiles and materials of HAR structures used in literature make it difficult to compare the efficiency of different drying processes. In this work, standard 300 mm wafer test structures, characterization and analysis techniques have been developed for quantitative analysis of pattern collapse rate as a function of the intrinsic mechanical property of HAR structures. Such standardized single wafer evaluations are important for benchmarking different drying techniques.

Abstract: In semiconductor fabrication, pattern collapse of high aspect ratio structures after wet processing is a major problem that could reduce production yield. In this work, several critical issues which limit our understanding of pattern collapse phenomenon are discussed together with some recent results of experiment and modeling. Special efforts have been put to update some of the most recent developments in characterization techniques.

Abstract: This work focuses on capillary-induced collapse of high-aspect-ratio silicon nanopillars. Modification of the surface chemistry is demonstrated to be an efficient approach for reducing capillary forces and consequently reduce pattern collapse. Special effort is spent on determination of the wetting state of chemically modified surfaces as complete structure wetting is of utmost importance in wet processing. In light of this, an ATR-FTIR based method has been developed to unambiguously distinguish between wetting and non-wetting states.

Abstract: The introduction of 3-D nanostructures in semiconductor manufacturing may create wetting issues in aqueous processing. In this work we evaluated the use of a CO₂ gas atmosphere to promote the wetting of superhydrophobic nanopillars, relying on the high solubility of CO₂ in aqueous solutions. The patterned surface was first flushed with CO₂ gas, before dispensing the aqueous solution that was saturated with N₂ and switching the gas flow from CO₂ to N₂. The liquid penetration was characterized by monitoring the disappearance of CO₂ gas using ATR-FTIR. Results showed only a modest improvement in wetting, presumably due to a fast N₂-CO₂ gas exchange at the wetting front.