E-beam-induced distortions on SiN x-ray mask membrane

In this work we characterized (1) the resist stress dependence on exposure dose and (2) in-plane distortions of the mask caused by resist and substrate. A NIST standard ring with a SiN membrane window as used throughout this work. Resist stress was determined by measuring the resonant frequency of membrane coated with resist. Stress was measured at several doses for SAL605, APEX-E and PMMA resists. In-plane distortion was measured using in-situ measurement approach. An array of standard alignment fiducials for Leica-Cambridge EBMF10.5 e-beam system were placed directly on the membrane. Also, an array of fiducials was placed on the NIST ring to provide a reference point for measurements. The position of the fiducials on the membrane was measured before and after exposure, and compared to position of a common reference point. The magnitude of displacements agreed with theoretical values for measured stress coefficients. The accuracy and limitations of the methods used to obtain the distortion data, as well as possible strategies for reducing the in-plane distortions are also discussed here.