High Reflectivity Mo/Be and Ru/Be Mirrors for X-ray Projection Lithography

LIGHT METAL TECHNOLOGIES, INC. proposes to develop beryllium-based multilayer mirros for soft X-rays that have high reflectivity at near normal incidence to advance the development of x-ray projection lithography. Multilayer mirrors will be frabricated for two specific wavelengths - 11.4 nm and 8 nm. Other wavelengths may be investigated if time permits. Beryllium has the lowest absorption (< 4x10(4)/cm) for these two wavelength regimes of any stable metal. To date there is no published data on Be-based multilayer mirrors for near normal incidence. Preliminary first order calculations show a number of metals with high atomic numbers, Mo and Ru, in combination with Be can be used to fabricate multilayer mirrors with high reflectivities: e.g., Mo/Be, 75% at 11.4 nm. The multilayer mirrors will be fabricated using two magnetron sources mounted within a state-of-the-art custom designed coating chamber. Preliminary multilayer mirrors of W/Be show a interlayer roughness of 3-5 A [rms]. Innovative approaches will be taken to reduce layer roughness or interdiffusion to a minimum, inlcuding the use of Ne as a sputter gas. MIrror substrates will be well polished Si wagers (<5A[rms]) and super smoothe sapphire substrates (<1A[rms]). Process parameters will be optimized to lay down smooth and continguous layers of each metal. Soft x-ray reflectivity measurements and modelling analysis will be carried out at the design wavelengths and over a variety of incident angles. A variety of analytic test procedures will be used to assess the coatings: x-ray reflectivity measurements, Cu Ka x-ray diffraction, SEM, and TEM analysis. Anticipated Benefits: The Phase-I effort will demonstrate that high reflectivity Be-based multilayer mirrors can be fabricated at a variety of wavelengths at and below 11.4 nm. Commercial applications will include providing superior multilayer mirrors for soft x-ray projection lithography and the water window microscope.