20 years of supplying high-purity vacuum components to ASML

The quality of vacuum components and chambers hinges on the absence of leaks in connections and the prevention of outgassing from surfaces exposed to the vacuum. During the production of vacuum components, various substances are introduced, leading to surface contamination. These include cutting oils, cooling lubricants, marking dyes and even the touch of human hands. Components may also come into contact with vacuum greases, hydraulic fluids, alcohols or pump oils during quality tests. These substances are primarily composed of volatile elements, which can ultimately jeopardize the final pressure and pump-down time of the assembled vacuum chamber.

Today, the need for high-purity surfaces extends across a broad spectrum of industrial and scientific applications. Even the slightest particle intrusion can disrupt precision processes, leading to unforeseeable results and increased maintenance costs. The exacting purity requirements for component surfaces are intrinsically tied to the specific application. A prominent example lies within the semiconductor industry, where nanometer-scale structures are meticulously fabricated. With structures of such diminutive dimensions, sub-10 µm particles – ubiquitous in ambient air and invisible to the naked eye – present a formidable challenge.

Ultra-clean vacuum

Vacuum technology is very important to ASML as well. The latest lithography systems employ extreme ultraviolet (EUV) radiation with a wavelength of 13.5 nm, necessitating operation within a finely tuned vacuum environment. Furthermore, the lack of sufficiently low-loss transmission optics for EUV radiation requires the use of mirrors for guidance and focusing. To maintain the mirrors’ optimal reflectivity, stringent requirements govern the composition of the residual gas within the systems. This stringent control prevents certain residual gas components from adhering to the mirror surfaces, ensuring peak reflectivity.

In addition to achieving the lowest possible final pressure, vacuum cleanliness – specifically the composition of the residual gas – is paramount. Residual gas components with significant mass scatter accelerated particles, shortening beam lifetimes. Surface analysis, a critical function, is also conducted in a vacuum. To prevent sample contamination during analysis, exacting standards apply to the final pressure, residual gas composition and residual particle contamination in the system.

In 2006, Ton van de Kerkhof joined ASML, bringing his extensive experience to the table to address these challenges. His focus was having the best ultra-clean vacuum (UCV) solutions. This brought VACOM, a German specialist in the field of vacuum technology, and ASML together to make the manufacturing of UCV components suitable for serial production.

True cleanroom product

Essential to the manufacturing of vacuum components is the use of coolants, lubricants, oils and gases. However, once these components are integrated into a vacuum system, the contaminants can desorb from the surfaces in contact with the vacuum, limiting the achievable final pressure. Moreover, the impurities can disrupt highly sensitive processes, particularly in the semiconductor industry.

The seemingly straightforward solution to this challenge is to prevent contamination. This can be achieved by, for instance, exclusively using dedicated cooling lubricants during the production process and ensuring that all objects and media in contact with components are entirely free of contaminates. This applies notably to all media-carrying pipes and the cleaning agents used in wet cleaning. However, certain contaminants are unavoidable, such as moisture from ambient air condensing on component surfaces. In such instances, the second-best solution comes into play: post-production cleaning of vacuum components.

During the production of vacuum components, it’s virtually impossible to avoid contamination and particles on the component surfaces. Nonetheless, surface treatment and cleaning can significantly diminish contaminant concentrations on these surfaces. Potential remaining sources of particles during the final cleaning of components include ambient air, particles in the rinsing water, lint from wiping cloths, abrasions from gloves when handling cleaned components and, notably, human contact.

To ensure that the end product is largely free of contamination and particles, it’s crucial to consider potential particle generation and other contamination when selecting substances that come into contact with the products. For example, the water used for wet cleaning should be as pure as possible, necessitating the use of fully demineralized water. Cleaned components should be dried using air filtered for particles to prevent recontamination after cleaning. Following cleaning, components should be promptly packaged to minimize exposure to ambient air.

It’s paramount to emphasize that processing vacuum components in a cleanroom is the ultimate solution to preventing particle contamination. Recontamination of previously cleaned parts is highly improbable under cleanroom conditions. Therefore, the final treatment of vacuum components in a cleanroom is fundamental for maintaining part cleanliness. For assemblies and components with stringent requirements for low particle levels, it’s advisable to assemble them under cleanroom conditions. Competent personnel must handle sensitive components and assemblies. To maintain quality standards, it’s recommended to have workstations and cleanrooms regularly inspected by an independent quality assurance (QA) team to ensure compliance with the required cleanroom class and to document and archive measurement results.

Following cleaning and assembly, everything should be packaged in a manner that preserves the achieved cleanliness. This ensures that the product remains cleanroom-compatible – a true cleanroom product (CRP). Additionally, packaging under inert gas is advisable for some products. A cleanroom-compatible packaging typically consists of at least two layers: primary packaging (eg ESD protective film to prevent electrostatic discharge, moisture barrier bags, nylon bags or polythene film) to protect the component and preserve its cleanliness and secondary packaging to maintain the cleanroom compatibility of the primary packaging. Furthermore, transport packaging is essential to protect components from potential damage during transportation to their destination.

Vital role

For two decades, ASML has tackled the formidable challenge of EUV lithography, driving the evolution of Moore’s Law. This technology demands a vacuum environment with thousands of precision components, which in turn require ultra-pure treatment. Achieving and maintaining vacuum cleanliness is paramount, not only for the semiconductor industry but also for high-tech processes like particle accelerators. Cleanrooms and meticulous packaging to preserve product integrity play a vital role in this journey of producing high-purity vacuum components.

Main picture credit: VACOM