| Popis: |
It is well‐known that many improvements concerning resolution and focus latitude can be obtained by the use of phase‐shifting masks. Different phase‐shifting mask designs are proposed already, and one of the most suitable designs for periodical structures is the alternated shifter design. If such phase‐shifting masks are investigated, it is assumed that all shifter parameters are ideal. A major problem, however, is the production of such an ideal phase‐shifting mask with perfect shifter parameters. In this work, the influence of shifter parameters such as transparency, thickness, and sidewall slope are studied for the alternated phase‐shifting design. The investigation is carried out by simulations and by experiments, and for various coherence factors. It is found that all shifter deviations cause linewidth differences between shifter and quartz lines, often resulting in a reduced depth‐of‐focus (DOF). Especially if various deviations occur simultaniously, the DOF reductions are important, putting stringent demands on mask processing in order to obtain tolerable shifter deviations. In order to print L/S down to 0.3 μm with reasonable DOF for production applications, the shifter transparency and thickness should not deviate more than 5% from their ideal values. |
