Photolithography is a process by which a reticle having a pattern is irradiated with light to transfer the pattern onto a photosensitive material overlying a semiconductor substrate. Over the history of the semiconductor industry, smaller integrated chip minimum features sizes have been achieved by reducing the exposure wavelength of optical lithography radiation sources to improve photolithography resolution. Extreme ultraviolet lithography (EUVL), which uses extreme ultraviolet (EUV) light having an exposure wavelength of between 10 nm and 130 nm, is a promising next-generation lithography solution for emerging technology nodes (e.g., 32 nm, 22 nm, etc.).
EUVL is performed using a reflective reticle that selectively reflects EUV radiation onto a light sensitive photoresist material. A mask substrate used to form an EUVL reflective reticle consists of a low thermal expansion material that is coated with a plurality of reflective layers (Mo/Si multi-layers) configured to reflect EUV radiation. A patterned absorber layer is disposed over the reflective layers. The patterned absorber layer is configured to selectively absorb EUV radiation, such that the reflected EUV radiation exposes the light sensitive photoresist material in a desired pattern.
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