The recent ALDALE 2023 conference in Bellevue witnessed the growing use of PillarHall chips in thin film conformality research. It was remarkable to see PillarHall applied to answer fundamental research questions and aid in the development of new process technologies for high aspect ratio challenges and 3D nanodevice applications. Here, we summarize our key pick-ups from the ALDALE 2023 thin film conformality research.

FUNDAMENTAL CONFORMALITY RESEARCH

  • A joint presentation with Chipmetrics, TU-Eindhoven, and VTT revealed that the film penetration depth onto vertical and lateral high aspect ratio structures is similar in the ALD Al2O3 TMA/H2O process, provided the dimensional details are considered in data interpretation. However, given the existence of hundreds of ALD processes other than Al2O3, along with varying process conditions, more experiments and studies will be needed. The presented VHAR and LHAR test structure toolbox opens up opportunities for a more profound understanding of growing conformal films and accelerating their applications.
  • The same study demonstrated that pre-treatment procedures can significantly affect the film penetration depth in HAR structures, underlining the crucial role of substrate surface chemistry in conformal growth. This effect was observed to be more pronounced than that of surface roughness, a finding that might not be immediately apparent. Chipmetrics metrology chips, PillarHall, and VHAR1 can be effectively used to study the effects of surface treatments on conformal growth.
  • Riikka Puurunen and her team from Aalto University presented modelling results of film growth on PillarHall LHAR type structures. The interesting finding was the ballistic transport-reaction model supports the “ALD trunk” effect; this new term means the film growth can accumulate in the bottom of the HAR cavity under favourable conditions. We believe this effect will be experimentally confirmed. PillarHall LHAR4 chips will be invaluable tools to make these findings and improve our understanding of conformal thin film growth.

APPLICATIONS OF PILLARHALL

  • Meiden Nanoprocess Innovation Inc. presented their studies on the development process for a novel Pure Ozone Generator, using the PillarHall approach. The objective of this new ozone generator technology was to meet the demands of 3D NAND high aspect ratio challenges, where, for example, oxygen plasma is not well compatible for the deposition of high-k oxides, such as HfO2. The results showed that the film penetration depth could exceed a 1000 aspect ratio, indicating the desired high reactivity and long lifespan of the generated ozone.
  • A renowned Molecular Layer Deposition (MLD) expert team led by Prof. Maarit Karppinen from Aalto University, Finland, demonstrated that PillarHall serves as a proficient metrology tool for MLD films. This is particularly valuable when the materials are less known or have not been reported with any other synthetic route. The PillarHall method, paired with optical microscope image analysis of the film penetration depth, proved incredibly useful for demonstrating MLD growth. The effectiveness of using Raman spectroscopy for the analysis of material microstructure as a function of penetration depth was reported for the first time.
  • Mike Van De Poll from TU-Eindhoven competed for the ALD student award with his presentation titled: “Conformality of Atmospheric Pressure Plasma-Enhanced Spatial Atomic Layer Deposition of SiO2 and TiO2.” Mike delivered a remarkable presentation, and he emerged as one of the top candidates for the award. This marked the first use of PillarHall in spatial ALD conformality research. The study used TiO2 and SiO2, and similar to low-pressure ALD, SiO2 showed better conformality. Additionally, a clever physical model of the film growth was also developed.

The film penetration depth profile obtained from PillarHall LHAR4 test chip (right panel) and the optical microscope images (left panel). PD50% (penetration depth at 50% of initial thickness) is indicated as well as the slope (k) at PD50%.

           (a) ALD Al2O3 result without pre-treatment.

           (b) ALD Al2O3 results from 2 minutes O2 plasma treated PillarHall LHAR4 chips.

In both cases thermal ALD (420 cycles to yield ≈50 nm Al2O3 film) at 300 °C was performed using a pulse/purge sequence as follows; 0.15 s TMA / 1 s purge / 0.15 s H2O / 1 s purge.

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