September 19, 2011 -- Applied Materials (Nasdaq:AMAT) unveiled its Centura Tetra EUV advanced reticle etch system at the SPIE BACUS conference (Monterey, CA). The system addresses changing requirements from transmission photomasks used in optical lithography to reflection photomasks needed for extreme ultraviolet lithography (EUVL).
The much shorter EUV wavelength would be absorbed in a transmission photomask. The EUV light source wavelength is approximately 15x shorter than that of deep ultraviolet lithography. The figure shows a comparison between a conventional photomask and an EUV photomask.
|Figure. Photomask sees paradigm change with EUVL. Short EUV wavelength would be absorbed in a transmission mask. SOURCE: Applied Materials.
Applied Materials' new etch system addresses: 1) being able to handle tantalum (Ta) materials used in EUV masks, 2) using optical emission spectroscopy to determine when to stop the etch process, and 3) minimizing damage to the ruthenium (Ru) surface, which is the stopping layer underneath the absorber.
According to Amitabh Sabharwal, GM, mask etch products, at Applied Materials, end users are experimenting with Ta-based materials and the complex structure required for an EUV mask. Listen to Sabharwal's interview below. The Bragg mirror alone has 40 alternating layers of molybdenum (Mo) and silicon (Si). When using Ta-based materials, “the chemistry must be compatible with the chamber walls, cathodes and anodes,” said Sabharwal, “It’s quite different from designing a reactor to etch chrome or Mo.”
The etch endpoint in the new system is determined using optical emission spectroscopy. “On an EUV mask, you cannot endpoint from the backside as you would on a conventional mask,” said Sabharwal. “We had to come up with a new methodology so we can endpoint the mask from the top.” The other challenge Applied had to tackle involves the etch process for the Bragg mirror, specifically, how the endpoint is determined under several layers of Mo and Ru. In addition to using chemistries that are highly selective to Ru, the company was able to minimize damage to the Ru surface by making several modifications to the RF design of the tool.
Applied says the new tool is able to achieve nanometer-level accuracy and near-zero defect performance. The Centura Tetra EUV system meets stringent pattern accuracy, surface finish, and defectivity specifications required to achieve high lithography yields when operating in this reflected mode. The chamber and power-delivery designs complement specialized process chemistries and etch technology, delivering virtually damage-free etch with best-in-class CD uniformity and world-class defectivity control. Multiple systems have already been shipped and the company says it is working with "virtually every leading mask maker."
Learn more at http://www.appliedmaterials.com/
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