With an evident requirement for Gaussian electron beam direct write lithography for prototyping and development on
300mm substrates below the 32nm node Vistec Lithography began the development of a new tool. A key requirement of
this tool development was the integration and use of an interferometry solution for stage position measurement. Existing
products had shown limitations in their practical application and performance and a new solution sought by the design
team. Vistec entered into a development programme with Renishaw to utilise their newly developed interferometry
systems.
We describe a novel coolant suitable for high heat load optics called Binary-IceR. This coolant exploits the latent heat of microscopic ice particles in a water/antifreeze mixture, which confer an effective specific heat capacity up to eight times that of water. Binary-IceR has a film heat transfer coefficient several times that of water or brine which reduces the thermally induced strain in optical components compared to identical water-cooled configurations. Furthermore, the coolant temperature only increases by a few degrees under normal operating conditions, yielding uniform cooling. Finite element analysis has been used to model a thin silicon [111] crystal that is back-cooled by brine or Binary- IceR with an incident power density of 4 Wmm-2 commensurate with a modern bending magnet monochromator. Water cooling was found to be impracticable due to the thermal bump inducing a spread in the selected bandwidth which was greater than 50% worse than the intrinsic resolution of Si[111], and a downward shift in the energy by more than the intrinsic bandwidth. By comparison Binary-IceR yielded the intrinsic resolution at low energies and a shift in the energy by only 10% of the bandwidth. The application of Binary-IceR for cooling of diamonds in undulator monochromators, and for the cooling of x-ray mirrors and multilayers is also discussed.
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