Modal analysis of a hybrid grillage-plate-membrane structure

The semiconductor industry is faced with a major challenge of implementing a new technology to produce microchip features with ever decreasing dimensions. One of the leading candidates is the SCattering with Angular Limitation Projection Electron-beam Lithography (SCALPEL) system being developed at Bell Labs, Lucent Technologies, Inc. [1]. The system utilizes a lithographic mask, which contains the original integrated circuit pattern, as a means to reproduce the image onto multiple microchips. The mask consists of a silicon wafer with the central region etched to form a grillage structure that supports an extremely thin silicon nitride membrane on which the pattern lies. The in-plane and out-of-plane mode shapes and respective frequencies must be known accurately to ensure the effective use of the mask during both exposure processes and cleaning procedures. Finite element (FE) modeling, experimental procedures, and analytical methods have been used to investigate the characteristic behavior of this hybrid structure. FE models have predicted the modal response with various boundary conditions. These results have been verified and correlated with experiments conducted using a MTI Fotonic Sensor and a Polytec Scanning Laser Vibrometer. Analytical methods have also been developed to further benchmark the studies and a provide additional information, including the added mass effect of the surrounding fluid.