Predicting electron projection lithography mask membrane image placement errors.

Electron projection lithography (EPL) has been identified as a viable candidate of the next-generation lithography technologies for moderate-volume production of systems-on-a-chip for the sub-65 nm nodes. EPL is especially suited for the fabrication of contact structures. The development of a low-distortion mask is essential for meeting the stringent requirements at these lower nodes. This research focuses on quantifying in-plane distortions (IPDs) due to mask fabrication and the effects of different mounting schemes in the e-beam writer and exposure tools for a 200 mm EPL stencil mask. In order to quantify the IPD of the freestanding membranes, three-dimensional finite element (FE) models have been developed and benchmarked with experimentally measured data. Metrology measurements in both the membrane-side up and membrane-side down configurations can be used to correct for image placement errors (due to the fabrication and chucking of the mask) by compensating for IPD during the exposure process. To correct for higher order distortions associated with pattern specific errors, FE models were generated to simulate the entire process flow, including chucking. As a sample test case, a stencil pattern was replicated uniformly over the membrane arrays. The actual mask was fabricated and metrology measurements were taken. Selected membranes were experimentally measured to compare with FE results and the data correlated well in both direction and magnitude. Results illustrate that FE modeling and simulation can be used to predict mask distortions due to fabrication. Such techniques can be instrumental in meeting the stringent error budget required at the lower lithographic nodes. [ABSTRACT FROM AUTHOR]