Optimum dose for shot noise limited CD uniformity in electron-beam lithography

To maximize the performance of an electron-beam lithography system the resist sensitivity must be chosen carefully. Very sensitive resists require only a low illumination dose, thus increasing the throughput. However, shot noise effects may give rise to unacceptable line edge roughness and variations in critical dimension (CD). In this study, the physical parameters which influence the effect of shot noise statistics on CD uniformity (CD-u) and linewidth roughness (LWR) are determined and an analytical model for CD-u and LWR is derived. It is found that the CD-u and LWR depend on the dose, the Gaussian beam probe size, the diffusion length dr of secondary electrons and acids in resist. The influence of background dose and non-shot-noise dose variations must also be taken into account. Monte Carlo simulations are performed to obtain the statistical variation of the two-dimensional solubility distribution of illuminated resist in a developer. The results of this simulation are used to validate the model. Fo...

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