Ruthenium Is Replacing Copper in Advanced Semiconductor Interconnects and the Transition Has Already Started

The Metal That Copper Cannot Be at the Smallest Dimensions

Copper has been the preferred conductor material for on-chip electrical interconnects in integrated circuits since IBM introduced copper interconnect technology for its IBM PowerPC microprocessors in 1997, replacing the aluminium that had been the interconnect metal of choice since the semiconductor industry's early years. Copper's advantages over aluminium for interconnect applications are substantial: its lower electrical resistivity, approximately 1.67 microohm-centimetres compared with aluminium's 2.65 microohm-centimetres, allows the same electrical resistance to be achieved in a smaller cross-section wire that occupies less chip area and reduces the capacitive coupling between adjacent wires that limits signal transmission speed. The dual-damascene copper metallisation process, in which copper is electroplated into pre-etched trenches and vias in the dielectric layer and the excess copper is removed by chemical mechanical planarisation, creates the sub-micrometre copper wire structures that have been scaled across twenty-five years of semiconductor process node advancement from the 250-nanometre node at which copper was introduced through the current sub-five-nanometre nodes at which the most advanced logic chips are manufactured.

The physical limitation that copper interconnects encounter at the smallest wire dimensions in the most advanced semiconductor nodes is a fundamental material property rather than an engineering constraint that improved processing can overcome. As copper wire width decreases below approximately ten nanometres, the mean free path of electrons in copper, approximately thirty-nine nanometres at room temperature, becomes larger than the wire width, creating the surface scattering and grain boundary scattering mechanisms that increase the effective resistivity of the copper wire above the bulk copper value in a wire-width-dependent fashion that makes narrow copper wires substantially more resistive than bulk copper's resistivity would predict. A copper wire of two nanometre width has an effective resistivity four to five times higher than bulk copper, substantially degrading the performance advantage over the aluminium it replaced and creating the interconnect resistance and the associated power dissipation, signal delay, and electromigration reliability problems that motivate the search for alternative metallisation at advanced semiconductor nodes.

Ruthenium's Properties at the Nanoscale

Ruthenium, a platinum group metal whose bulk resistivity of approximately 7.6 microohm-centimetres is higher than copper's in bulk form, has a much shorter electron mean free path of approximately six nanometres that makes its effective resistivity in nanoscale wire geometries substantially lower than copper's at equivalent wire dimensions below approximately five nanometres. The direct consequence is that a ruthenium wire of two nanometre width has a lower effective resistivity than a copper wire of the same width, reversing the resistivity comparison that makes copper superior in bulk but makes ruthenium superior at the smallest dimensions that the most advanced semiconductor nodes are now manufacturing. Intel's disclosure of its Intel 20A and 18A process node details confirmed the use of ruthenium in its RibbonFET gate-all-around transistor contacts and in its PowerVia backside power delivery interconnects, while TSMC's N2 and beyond process node details similarly indicate ruthenium adoption in local interconnect layers whose finest wire dimensions are below the crossover point where ruthenium's effective resistivity advantage over copper materialises.

The deposition of ruthenium films for semiconductor interconnect applications requires either chemical vapour deposition from organometallic ruthenium precursor compounds or atomic layer deposition whose single-monolayer deposition precision enables the conformal ruthenium film thickness control that the most advanced device structures require. The ruthenium CVD and ALD precursor market, whose growth is directly driven by the semiconductor industry's adoption of ruthenium metallisation in advanced logic nodes, has created the commercial opportunity for specialty chemical companies including Entegris, Versum Materials, and Tanaka Precious Metals whose ruthenium precursor chemistry and semiconductor-grade purity create the materials supply chain that advanced node ruthenium deposition depends on. The ruthenium supply chain's dependence on South Africa and Zimbabwe for primary ruthenium production, where ruthenium is recovered as a byproduct of platinum group metal mining, creates the supply concentration risk that the semiconductor industry's ruthenium adoption must manage through strategic inventory, recycling programmes, and supply diversification.

Applications Beyond Logic Interconnects

Ruthenium's application in advanced semiconductor manufacturing extends beyond logic interconnect metallisation to DRAM storage capacitor electrodes, where ruthenium's high work function and chemical stability create the electrode material for the capacitors whose storage charge density is critical for DRAM performance at the cell dimensions that ten nanometre-class DRAM processes require. Samsung and SK Hynix's adoption of ruthenium in DRAM capacitor electrodes predates the logic interconnect application, providing the ruthenium precursor supply chain development and semiconductor-grade ruthenium material handling knowledge that logic interconnect adoption builds on. The magnetic tunnel junction applications in MRAM memory devices, where ruthenium's half-metallicity and spin transport properties create functional layers in the magnetic stack, represent the emerging next application of ruthenium in advanced semiconductor devices whose commercialisation will further expand ruthenium's role in semiconductor manufacturing.

Top 10 Companies in Ruthenium Semiconductor Materials and Interconnects Globally

1. Entegris (Versum Materials heritage): US semiconductor materials company with ruthenium CVD and ALD precursors for advanced logic node metallisation; its Versum Materials acquisition expanding its semiconductor specialty chemical portfolio and its ruthenium precursor product for Intel and TSMC advanced nodes create the dominant semiconductor ruthenium precursor supplier.
2. Tanaka Precious Metals: Japanese precious metal company with semiconductor-grade ruthenium targets, precursors, and process materials; its platinum group metal expertise and its semiconductor materials supply relationships create the Japanese precious metal company's ruthenium semiconductor commercial position for the logic and DRAM applications that are adopting ruthenium metallisation.
3. Intel: US semiconductor company with RibbonFET gate-all-around transistors and PowerVia backside power delivery using ruthenium in Intel 20A and 18A process nodes; its process node disclosure of ruthenium adoption and its advanced logic manufacturing create the semiconductor manufacturer whose process technology choices define the metallisation standards that the advanced logic industry follows.
4. TSMC: Taiwanese semiconductor foundry with N2 and beyond process node ruthenium local interconnect adoption; its foundry manufacturing for Apple, AMD, NVIDIA, and Qualcomm chips creates the most commercially significant advanced logic ruthenium application whose production volume drives ruthenium precursor demand at semiconductor manufacturing scale.
5. Samsung Electronics: South Korean semiconductor company with ruthenium DRAM capacitor electrode adoption predating logic interconnect use; its DRAM manufacturing scale and its leading-edge logic foundry process create the semiconductor manufacturer whose ruthenium adoption across both memory and logic applications makes it the largest single semiconductor ruthenium consumer.
6. Merck KGaA (EMD Electronics): German chemical company with semiconductor process materials including ruthenium precursors through its EMD Electronics division; its specialty semiconductor chemical portfolio and its global semiconductor customer relationships create the chemical company's ruthenium semiconductor material commercial position alongside Entegris and Tanaka.
7. Anglo American Platinum (Amplats): South African platinum group metals company with primary ruthenium production from platinum mining operations; its Bushveld Complex platinum group metal mining creates the largest primary ruthenium supply source whose production as a byproduct of platinum determines the available ruthenium supply that semiconductor and other industrial demand must be sourced from.
8. Umicore: Belgian materials technology company with ruthenium refining and precious metal materials for semiconductor and other applications; its precious metal refining expertise and its semiconductor catalyst and electrode materials create the European ruthenium material supplier whose refining capability converts primary ruthenium from platinum group metal mining into the semiconductor-grade material that advanced node deposition processes require.
9. Air Liquide: French industrial gas company with semiconductor specialty gas and precursor supply including ruthenium compounds for advanced CVD and ALD processes; its semiconductor specialty material supply infrastructure and its global semiconductor fab gas supply relationships create the industrial gas company's ruthenium precursor commercial position in the semiconductor manufacturing market.
10. SK Materials: South Korean specialty gas and semiconductor material company with ruthenium precursor development for Korean semiconductor manufacturers; its Samsung and SK Hynix supply relationships and its specialty semiconductor gas manufacturing create the Korean semiconductor material company's ruthenium commercial position serving the Korean semiconductor industry's domestic material sourcing preference.