Applied unveils EUVL mask etch system

September 19, 2011 -- Applied Materials (Nasdaq: AMAT) unveiled its Centura Tetra EUV advanced reticle etch system at the SPIE BACUS conference (Monterey, CA) on Sept. 19. The system addresses the changing requirements as the industry goes from transmission photomasks used in optical lithography to reflection photomasks needed for EUV lithography (EUVL). [The much shorter EUV wavelength would be absorbed in a transmission photomask.]

Among the challenges to be addressed for the new etch system are: 1) being able to handle Ta-based 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. The Bragg mirror alone has 40 alternating layers of Mo and 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 the company 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. Multiple systems have already been shipped and the company says it is working with “virtually every leading mask maker.”