Atomic Layer Deposited Tantalum Phosphide Achieves 227 Micro-ohm Cm Resistivity at 2.3nm on Amorphous Substrates

The demand for energy-efficient components drives innovation in materials for advanced computing systems, and researchers are now focusing on novel conductors to overcome limitations in traditional metals. Dong-Hyun Lim, Young-Min Song, and Yeji Kim, alongside colleagues at their institutions, present the first demonstration of tantalum phosphide, an amorphous semimetal, grown across entire wafers using a precise technique called atomic layer deposition. This achievement overcomes a significant challenge in materials science, producing a highly conductive material directly on a common substrate without the need for crystalline order or seed layers. The resulting films exhibit an unexpected property, resistivity actually decreases as the material becomes thinner, reaching exceptional levels of conductivity, and establishes this amorphous semimetal as a strong candidate for future, high-density, low-power electronic interconnects.

Atomic Layer Deposition Enables Robust TaP Films

This research details the successful development of an atomic layer deposition (ALD) process for creating thin films of tantalum phosphide (TaP), a topological semimetal. Scientists have demonstrated, for the first time, a controllable ALD route to synthesize stoichiometric TaP, offering precise thickness control and compatibility with nanoscale device fabrication. The synthesized TaP films exhibit robust electrical conductivity even in an amorphous state, suggesting that topological semimetal functionality can be retained without long-range crystallinity, and demonstrate excellent thermal and electrical stability up to 600°C, making them suitable for integration into advanced electronic devices. Stacking multiple layers of TaP with silicon nitride interfaces further enhances conductivity, indicating that the interfaces contribute to high-conductivity surface channels.

Analysis confirms a two-channel conduction mechanism with parallel contributions from bulk and surface channels, with surface conduction dominating in thinner films. This research demonstrates a pathway to create stable, conductive TaP films using ALD, opening up possibilities for integrating topological semimetals into future nanoscale electronic devices, even in amorphous forms. The ability to achieve robust surface conduction in amorphous TaP is a particularly noteworthy finding, suggesting that crystallinity may not be essential for realizing the benefits of topological semimetals.

Wafer-Scale Tantalum Phosphide Deposition via PE-ALD

Scientists achieved a breakthrough in interconnect technology by realizing wafer-scale amorphous tantalum phosphide (TaP) films directly on amorphous silicon dioxide substrates using low-temperature plasma-enhanced atomic layer deposition (PE-ALD). This innovative process, conducted at temperatures ranging from 150 to 300 degrees Celsius, enabled precise control over film growth, with 170 degrees Celsius identified as optimal for stoichiometric composition. Immediately following deposition, films underwent in-situ capping with a silicon nitride layer to prevent surface oxidation. Film thickness was meticulously measured, and composition was determined through detailed analysis, including depth profiling with ion beams.

Crystal structure was examined, and conformality was rigorously tested on silicon trench structures. High-resolution imaging and structural analysis confirmed the film’s properties. Electrical properties were characterized by measuring total sheet resistance and extracting intrinsic TaP sheet resistance, accounting for the silicon substrate. A parallel-resistance model was used for multilayer stacks, enabling accurate determination of material properties at the nanoscale. These advanced characterization techniques confirmed the exceptional properties of the deposited TaP films and validated their potential for future electronic applications.

Wafer-Scale Tantalum Phosphide Shows Unique Conduction

Scientists have achieved a breakthrough in materials science with the first wafer-scale realization of amorphous tantalum phosphide (TaP), grown directly on amorphous silicon dioxide substrates using low-temperature atomic layer deposition. This innovative process yields films exhibiting unconventional resistivity scaling, decreasing as film thickness decreases to a remarkable 227 micro-ohm cm at just 2. 3 nanometers. The team demonstrated that this behavior arises from dominant surface conduction, establishing ALD-TaP as a promising material for back-end-of-line integration in future electronic devices.

Experiments reveal excellent conformality and stoichiometry control in the deposited TaP films, alongside thermal stability up to 600 degrees Celsius. Detailed analysis using X-ray diffraction and cross-sectional imaging confirms the amorphous structure of the films, even after annealing up to 500 degrees Celsius, with only limited nanocrystallization observed at 600 degrees Celsius. Electrical measurements demonstrate that the resistivity of TaP films decreases by nearly an order of magnitude as thickness scales from 18 nanometers down to 2. 3 nanometers, a trend attributed to the progressive dominance of surface channels at reduced dimensions. Further investigation using a two-channel conduction model confirms surface-dominated transport in ultrathin regimes, and this is enhanced in multi-stacked configurations.

Ultrathin Tantalum Phosphide via Atomic Layer Deposition

This research demonstrates a new method for creating ultrathin films of tantalum phosphide, an amorphous semimetal, directly on silicon dioxide substrates using atomic layer deposition. Scientists achieved this without the need for seed layers, a significant advancement in materials science, and successfully produced films exhibiting exceptional conformality, stoichiometry control, and thermal stability up to 600 degrees Celsius. Crucially, the resulting films display an unusual resistivity scaling, where resistivity decreases as film thickness decreases, reaching 227 micro-ohm cm at approximately 2. 3 nanometers.

The team confirmed that this behavior arises from dominant surface conduction, particularly in ultrathin regimes, and further enhanced conductivity by stacking multiple layers of the material. This two-channel conduction model highlights the potential of this amorphous semimetal for future electronic interconnects requiring high density and low power consumption. The successful implementation of atomic layer deposition for phosphorus-based compounds expands the scope of this technique beyond traditional materials and offers a scalable route for integrating novel materials into nanoscale architectures. These findings represent a significant step towards realizing the potential of amorphous topological semimetals in advanced electronic applications.