Physics of thin film and multilayers (TFM)

Research programme

The goal of the TFM group is to study the basic physics of thin single and multilayered films of nanometer thicknesses, including interface phenomena. Following the currently running projects, i.e. FOM Programme XMO and the SenterNovem funded ACHieVE project, the aim is to develop the physics required for the second generation of Extreme UV reflecting multilayer structures. These EUV optics represent fundamental challenges in thin-layer and surface physics as well as multilayer optics and plasma deposition. The multilayer systems are targeted to meet the requirements of Extreme UV Lithography, following the Zeiss-ASML industrial development road map. Simultaneously, the reflectivity and lifetime requirements on the multilayer systems create a unique opportunity to address the basic physics aspects. The XMO research programme is aimed to exploiting these fundamental aspects. Recent results are described in the annual report 2008.

Fig. 1 High resolution TEM micrograph of a Mo/Si multilayermirror for Extreme UV lithography. The picture shows nano-crystals and silicide interlayer formation, phenomena which have been successfully addressed in research on ultrathin diffusion barriers between the Mo and the Si layers.

Examples of physics phenomena typical for multilayered, XUV reflective systems include the formation and properties of interface layers, the growth and structuring of artificial diffusion barriers at the interfaces, and the study of diffusion processes under EUV radiation and at elevated temperatures. All these effects typically take place at thickness scales of single to several atoms. Mastering of these processes in the group has recently led to a world record of EUV reflectivity: a value of over 70% of 13.5 nm light was obtained. For this result a newly developed deposition process was used (Fig. 2).

Highlights

In the world-wide, highly competitive area of multilayer research for Extreme UV lithography, Rijnhuizen has managed to obtain another world record. A novel multilayer composition and layer design was developed to increase the optical contrast between the layers of the multilayer using so-called ‘compounded artificial interlayers’. Ultra-thin layers of materials, selected on favourable optical and diffusion properties, were incorporated in the multilayer stack. In the first pilot experiments a world record reflectivity of 70.15% at the EUV wavelength of 13.5 nm was shown. The structures were grown using a new, patented deposition method. The process makes use of combination of deposition with particles of different energies including so-called ‘thermalized particle magnetron’ (TPM) deposition, a novel method specially designed for coating of ultra-thin films. The demonstration of the new structures was a result of a fruitful collaboration with researchers at ASML, Carl Zeiss SMT, and the Physikalische Bundesanstalt PTB, and has been obtained within the FOM-Zeiss industrial partnership programme XMO (FOM Programme I10).

Fig 2 Standard deposition processes used in multilayer synthesis (left two pictures), and a new, FOM developed process allowing accurate adjustment of the energy of the deposited particles. The method has led to a world record in EUV reflectivity.

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