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Measuring resist-induced contrast loss using EUV interference lithography

In this paper the contrast behavior of photoresists upon EUV exposure is addressed. During a lithographic exposure, the intended shape undergoes contrast loss which can be divided into two portions. One part is assigned to exposure tool induced contrast loss (e.g. aberrations of the exposure optics, mechanical stability of the system), while the other part is due to chemical processes in the resist during exposure and development. Both contributors have to be decoupled from each other in order to solely analyze the resist contrast loss. The method presented here is based on an experimental evaluation of dense line/space patterns obtained from EUV exposures. For decoupling of the resist induced contrast loss from the exposure tool contrast, the aerial image has to be determined. As an alternative EUV exposure tool the EUV interference lithography (EUV-IL) beamline at Paul Scherrer Institute is applied for resist qualification. The theoretical description of the sinusoidal aerial image of the EUV-IL tool is presented as well as the experimental method applied to analyze resist patterns in terms of resist contrast. Finally, the results are compared with data obtained from ASML's ADT EUV scanner.