We have developed two multilayer based solutions that provide reflectivity of EUV radiation and suppression of IR radiation. The first solution is based on the B4C/Si periodical multilayer mirror deposited on a specially designed resonant absorbing structure. Substantial transparency of B4C and Si for IR radiation allowed us to integrate the periodical multilayer structure with a quarter-wavelength thin film absorber. The samples produced demonstrated suppression of the infrared radiation by about a factor of 300, with the EUV peak reflectance currently being achieved of about 45% at 13.5 nm. The FWHM of the B4C/Si multilayer mirror is about 0.284 nm that matches the 2% bandwidth of a typical EUV litho tool optical system. A second very viable solution is the application of a standard high reflectance EUV Mo/Si multilayer with a reflective grating. First experimental results on the optical response of lamellar quarter lambda reflectors have been obtained, where the filtering principle is based on suppression of the 0th diffracting order for 10.6 mm, with the energy being diffracted into higher orders, thus eliminating the specular reflection. At these not yet optimized optical elements, an EUV peak reflectance of 53% is currently obtained.
|Place of Publication||Veldhoven|
|Publication status||Published - 2011|