ASD 2026 Session ASD1-TuM: ASD: Plasma, Selective Etching and Sustainability

As the semiconductor industry advances toward extreme miniaturization and 3D integration, transistor architectures are progressively evolving toward gate-all-around devices based on stacked nanosheet channels. In parallel, emerging complementary field effect transistor (CFET) technologies further extend this concept by vertically stacking n- and p-type channels on top of each other within the same device footprint. The fabrication of such highly integrated architectures puts stringent demands on thin film deposition processes, making the development of innovative atomic layer deposition (ALD) approaches increasingly critical, owing to intrinsic advantages, such as high conformality, excellent uniformity over large surface areas and precise control of film composition at relatively low temperatures. ALD also provides numerous opportunities for the selective and precise placement of materials (semiconductors, dielectrics and metals) with nanoscale thickness control on horizontal and/or vertical surfaces, thereby enabling simplified integrated fabrication flows. This presentation will discuss various process routes based on ABC super-cycle strategies to achieve selective growth in semiconducting device fabrication. Tailoring precursor sequencing and surface chemistry through controlled adsorption, ligand exchange, and surface termination will be addressed, in the light of precise control of nucleation and selectivity required in complex 3D features in the context of extreme miniaturization.

Area-selective etching (ASE) of polymers is a novel self-aligned patterning technique.^1-3 Polymer patterning is achieved by catalytic decomposition of the polymer film only on top of catalytically active surfaces, whereas the polymer film stays intact on top of the noncatalytic surfaces. After the self-aligned patterning, area-selective deposition can be done using the patterned polymer as an inhibition layer.

Previously, we have demonstrated the feasibility of the ASE process with three polymers: MLD-polyimide¹, poly(methyl methacrylate) (PMMA)², and poly(lactic acid) (PLA)³ – using Pt as the catalytic surface and native SiO₂ as the noncatalytic surface. Additionally, we showed that by choosing the right polymer, ASE can be achieved both in oxidative and non-oxidative atmospheres, and over a wide temperature range. Furthermore, we showed that the catalytic effect can be achieved with a very small amount of catalytic material, even less than a monolayer.² We demonstrated this with two catalytic materials, Pt and CeO₂. This means that metal surfaces can be converted to catalytic by depositing a small amount of Pt and dielectric surfaces by a small amount of CeO₂.

Here, we show that most metal oxide and nitride surfaces are noncatalytic, or their usage as a catalytic surface is unclear. We demonstrate this by testing two polymers, PMMA and PLA, in three different atmospheres, O₂, H₂, and inert. However, we convert a noncatalytic dielectric surface, HfO₂, to catalytic by depositing 30 cycles of ALD-CeO₂ (< 1 nm). After this, we deposit a line pattern of another noncatalytic material, TiO₂, via direct atomic layer processing (DALP^®). We then spin-coat ~40 nm PMMA film on top and pattern the PMMA film by ASE in air. Finally, we deposit 50 cycles of ALD-ZrO₂ (~5 nm) area-selectively, using the ASE-patterned PMMA film as an inhibition layer. Furthermore, we show that only a thin layer of the noncatalytic TiO₂ (~3.5 nm) is enough to deactivate the catalytic effect of CeO₂. Additionally, we show that by increasing the molecular weight of the polymer, we can significantly decrease the polymer flow during the ASE process.

References

1. Zhang et al. Coatings. 2021, 11, 1124

2. Lasonen et al. Chem. Mater. 2023, 35, 6097

3. Lasonen et al. Chem. Mater. 2024, 36, 11645

Atomic layer deposition (ALD) has attracted significant attention for next-generation semiconductor manufacturing due to its precise thickness control and excellent step coverage. In addition, active research has been conducted on realizing sub-10-nm devices with extremely high aspect ratios through area selectivity using small-molecule inhibitors, as well as on the fabrication of vertical structures by controlling chemisorption behavior depending on the substrate.

In this presentation, we introduce the results of area-selective atomic layer deposition (AS-ALD) enabled by plasma treatments. First, we demonstrate an approach to improve gap-fill characteristics by exploiting the inherently poor step coverage of plasma processes. During SiO₂ ALD, NH₃ plasma (NH₃^*) treatment reduces the growth per cycle (GPC) due to inhibited chemisorption of the DIPAS precursor. By incorporating an NH₃^* treatment step into the SiO₂ ALD sequence for patterned structures, SiO₂ deposition is suppressed at the opening region, resulting in bottom-up gap-fill growth behavior.

We also present Co AS-ALD results on TiN and SiO₂ using NH₃^* treatment. The NH₃^* treatment simultaneously induces a decrease in GPC on SiO₂ and an increase in GPC on TiN. This behavior is attributed to suppressed chemisorption of the CpCo(CO)₂ Co precursor on SiO₂ due to surface NH_x termination, while on TiN, precursor chemisorption is enhanced by the removal of surface TiO_xN_y species.

These results indicate that NH₃^* treatment is a promising approach for enabling AS-ALD across a wide range of materials and device structures.