UV nanosecond pulsed laser annealing (UV NLA) enables both surface-localized heating and short timescale high temperature processing, which can be advantageous to reduce metal line resistance by enlarging metal grains in lines or in thin films, while maintaining the integrity and performance of surrounding structures. In this work UV NLA is applied on a typical Cu thin film, demonstrating a mean grain size of over 1 μm and 400 nm in a melt and sub-melt regime, respectively. Along with such grain enlargement, film resistivity is also reduced.

pdf/copper-large-scale-grain-growth-by-uv-nanosecond-pulsed-2ecxpf1hjr.pdf

Copper Large-Scale Grain Growth by UV Nanosecond Pulsed Laser Annealing

Three-dimensional (3D) CMOS technology encourages the use of UV laser annealing (UV-LA) because the shallow absorption of UV light into materials and the process timescale typically from nanoseconds (ns) to microseconds (μs) strongly limit the vertical heat diffusion. In this work, μs UV-LA solid phase epitaxial regrowth demonstrated an active carrier concentration surpassing 1 × 1021 at cm−3 in an arsenic ion-implanted silicon-on-insulator substrate. After the subsequent ns UV-LA known for improving CMOS interconnect, only a slight (∼5%) sheet resistance increase was observed. The results open a possibility to integrate UV-LA at different stages of 3D-stacked CMOS.

Microsecond non-melt UV laser annealing for future 3D-stacked CMOS

Increasing structural complexity in both 2D and 3D architectures and implementation of new materials in electronic devices is bringing severe limitations of thermal budget. In this context, UV nanosecond laser annealing (UV-NLA) is supposed to be a key thermal process technology owing to its surface localized and very short timescale heating. On the other hand, extension of Cu-based BEOL interconnect technology becomes more and more challenging with very narrow interconnect lines beyond the 7 nm node era. New metals such as Ru start to be explored as an alternative of Cu because of a potential benefit on both line resistance and reliability. But temperatures much higher for these materials than for Cu may be required to improve the line resistance. UV-NLA is therefore a promising process for Ru interconnect performance enhancement. In this paper, benefits of UV-NLA on both Ru blanket and 21 nm half-pitch line structures is studied.

UV nanosecond laser annealing for Ru interconnects

A novel nanosecond (ns) laser anneal (multiple laser shots at sub-melting low laser energy) was employed to reduce the blanket sheet resistance of Ru thin films deposited by physical vapor deposition (PVD). The laser anneal was conducted after PVD Ru deposition and then followed up with a standard 400°C anneal in a forming gas environment. Blanket sheet R decreased by 30% for the laser + furnace annealed Ru films, whereas the drop for just 400°C furnace annealed Ru films was only 18%. Multiple laser exposures at an optimized laser fluence was identified as a key factor in enabling this benefit at BEOL compatible thermal budget suitable for scaled-down Ru interconnects.

Impact of Nanosecond Laser Anneal on PVD Ru Films

In the history of semiconductor device fabrication, annealing is one of the critical process steps used to achieve the targeted device performance. Thermal budget requirements in most semiconductor manufacturing process steps have always followed a downward trend through either a reduction of the time spent at high temperature or a lowering of the peak temperature. This was driven at first by the traditional shrinking of structure dimensions which naturally required reducing species diffusion. From the last decade, performance improvements started to be driven essentially by the introduction of new materials (e.g., SiGe alloy, high-k/metal gate stack) and device architecture changes (e.g., 2D planar to 3D FinFET). The current development trend is leading toward 3D integrated circuits to answer the growing demand for increased functionality and performance. Such new drivers impact the whole supply chain, and low thermal budget solutions are now key to manage local strain and stress; limit species diffusion and interdiffusion; and control layer deposition, etch, and quality. In this regard, for a wide variety of applications, laser exhibits superior performance and a more cost-effective solution than nonlaser technologies. Moreover, laser provides flexible, higher throughput to process various materials. Trends regarding laser annealing are expected to experience fast growth, driven by 3D integration applications. In this chapter, we will review the most promising applications for laser annealing from the recent published literature with a focus on realistic candidates for integration in a high-volume semiconductor manufacturing flow, based on electrically relevant results. The first section will be dedicated to power devices, the second section to CMOS logic and 3D integration, and the final section to memory.

Laser annealing applications for semiconductor devices manufacturing

Nanosecond laser-induced grain growth in Cu interconnects is demonstrated for the first time using 14nm FinFET technology. We achieved a 35% reduction in Cu interconnect resistance, which delivers a 15% improvement in RC and a gain of 2 – 5% in I Dsat . Additionally, reliability was enhanced with an improvement in dielectric VBD and Cu EM performance without impacting the ULK mechanical integrity. Our results demonstrate a path to extending Cu interconnects for performance boost in 14nm FinFETs and beyond.

Nanosecond Laser Anneal for BEOL Performance Boost in Advanced FinFETs

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Nanosecond Laser Anneal for BEOL Performance Boost in Advanced FinFETs