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17 December 2003 Bias optimization through simulation for contact array pattern
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A binary mask with a 2D contact array pattern was simulated for the purpose of determining optimum amounts of bias for various pitches. The objective was to center the elliptical process windows for a given set of pitches about a nominal dose. The nominal dose was set by the center of the process window for smallest pitch case with a fixed bias of 15nm. Calculating the optimal bias values required calculation of process windows, which in turn required the calculation of CD through defocus and dose (or threhsold). CDs for the procss windows were calculated in three ways: 1. From aerial image (simplest, fastest, no 3D resist simulation required). 2. From resist image (fast, no 3D resist simulation required). 3. From resist profile (slow, 3D resist simulation required). Straightforward, brute-force "batching" is employed in the first two methods. To minimize the number of 3D resist simulations in the 3rd method, special "scripted" algorithms were employed. The algorithm run times for each of the three methods were compared. The three methods are observe to yield different values of bias. It is shown that, under the assumption that the resist model is accurate, the resulting biases obtained from the faster (1st and 2nd) methods are incorrect, that relying on CD measurements from aerial or resist images is insufficient for the task at hand, and that 3D resist simulation is required.
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Thomas V. Pistor and Ksenia Berger "Bias optimization through simulation for contact array pattern", Proc. SPIE 5256, 23rd Annual BACUS Symposium on Photomask Technology, (17 December 2003);

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