Beyond Catalysis: Ruthenium’s Untapped Potential in Next-Gen Semiconductors

The relentless pursuit of smaller, faster, and more energy-efficient electronics has pushed the boundaries of traditional materials. While ruthenium has long been celebrated for its catalytic properties, a new frontier is emerging: its potential to revolutionize next-generation semiconductors. As copper interconnects reach their scaling limits, ruthenium is stepping up as a promising alternative, poised to reshape the future of chip design and performance. In fact, Applied Materials announced the use of ruthenium in equipment designed to enhance efficiency in advanced semiconductor processes. This initiative supports wafer foundries like TSMC and Samsung as they transition to more efficient processes.

The Limitations of Copper and the Rise of Ruthenium

For decades, copper has been the workhorse for interconnects – the tiny wires that connect transistors and other components on a chip. However, as devices shrink to nanometer scales, copper faces significant challenges:

Increased Resistance: As copper wires become thinner, their electrical resistance increases, hindering performance and generating heat. The 1nm node will have 20nm pitch and larger metal lines, but the interconnect stack already consumes a third of device power and accounts for 75% of the chip’s RC delay.
Electromigration: The “electron wind” caused by high current densities can dislodge copper atoms, leading to wire degradation and failure.
Barrier Layer Issues: Copper requires barrier layers to prevent it from diffusing into surrounding materials. These barrier layers take up valuable space, further reducing the effective size of the copper wire.
High resistivity: Copper’s severe resistivity size effect is attributed to the relatively long bulk electron mean free path (39 nm at 298 K), which is inherently determined by phonon scattering.

Ruthenium (Ru) offers a compelling solution to these problems, exhibiting properties that make it ideal for next-generation interconnects:

Lower Resistivity at Small Dimensions: Ruthenium maintains lower resistivity than copper at extremely small dimensions, crucial for advanced nodes. The wire resistivities of Ru and Co will cross below that of Cu at wire-widths of 10-15 nm.
Superior Reliability: Ruthenium is more resistant to electromigration and thermal degradation, enhancing the longevity of chips.
Barrierless Interconnects: Ruthenium has the potential to create barrierless interconnects, allowing for smaller device architectures and reducing the number of process steps.
High melting point: Ruthenium’s high melting point allows for heat prone applications.
Shorter electron mean free path: The significantly shorter electron mean free paths for Ru (6.6 nm) and Co (11.8 nm) have been predicted to lead to a dramatically reduced resistivity size effect, which may allow lower resistivity of these materials than Cu at sufficiently reduced interconnect dimensions despite their relatively high bulk resistivies.

Ruthenium’s Role in Semiconductor Manufacturing

Ruthenium’s unique properties make it suitable for various applications in semiconductor manufacturing:

Interconnects: Replacing copper with ruthenium in interconnects can significantly improve chip performance, reduce power consumption, and enhance reliability. A likely solution involves replacing copper with ruthenium (Ru) interconnects at the lowest, tightest levels, perhaps as soon as the 14 Å node.
Transistors: Ruthenium can be used as a gate metal for metal-oxide-semiconductor transistors, contributing to faster switching speeds and improved energy efficiency.
Memory Devices: Ruthenium is a promising material for electrodes in dynamic random access memory (DRAM) devices, enhancing their performance and storage capacity.
Contact Wiring: Ruthenium is being evaluated for use as the contact wiring that connects transistors to multilayer substrates.
Capping Material: The use of ruthenium as the capping material to be precipitated on the upper part of copper wiring is also gaining attention.
Extreme Ultraviolet Photomasks: A new application of ruthenium is as the capping layer for extreme ultraviolet photomasks.

Overcoming Challenges and Embracing Innovation

While ruthenium holds immense promise, its integration into semiconductor manufacturing is not without challenges. Fabricating ruthenium wires using traditional methods can be difficult due to the metal’s hardness. However, innovative techniques like atomic layer deposition (ALD) and chemical vapor deposition (CVD) are paving the way for successful ruthenium deposition.

ALD and CVD: These methods allow for the creation of ultra-thin, highly conformal ruthenium films with precise control over thickness and composition.
Subtractive Etch: A change to subtractive schemes is more than likely because it enables a more flexible, scalable path to connecting taller CFET devices and beyond.
Recycling Technologies: Recycling technologies are important for ensuring a stable supply of ruthenium.

The Future is Ruthenium

As the semiconductor industry continues to push the limits of miniaturization and performance, ruthenium is poised to play a central role. Its superior electrical properties, reliability, and potential for barrierless interconnects make it an indispensable material for next-generation chips.

The transition from copper to ruthenium may also bring about changes in semiconductor manufacturing processes. For example, subtractive deposition-etch flows are likely to replace damascene-based flows.

By embracing innovation and overcoming existing challenges, the industry can unlock the full potential of ruthenium and usher in a new era of high-performance, energy-efficient electronics.

Investment Considerations

Given the increasing demand for ruthenium in semiconductor manufacturing, investors may want to consider companies involved in:

Ruthenium production and refining: Companies that mine and process ruthenium ore.
Ruthenium precursors: Companies that manufacture volatile ruthenium precursors for ALD and CVD processes. Heraeus offers 8 different volatile ruthenium precursors and intermediates for application in atomic layer deposition and chemical vapor deposition processes.
Semiconductor equipment: Companies that develop and manufacture equipment for depositing and etching ruthenium films.

Open Questions

What are the long-term reliability characteristics of ruthenium interconnects in advanced semiconductor devices?
How will the cost of ruthenium affect its adoption in high-volume manufacturing?
What new applications for ruthenium will emerge as semiconductor technology continues to evolve?

Disclaimer: This blog post is for informational purposes only and does not constitute financial advice. Please consult with a qualified financial advisor before making any investment decisions.