DEFORMATION OF X-RAY-LITHOGRAPHY MASKS DURING TOOL CHUCKING

Finite element modeling is used in this article to describe the elastic deformation of x-ray lithography masks due to chucking in the electron-beam writer or the lithographic tool. The total overlay budget for the lithography of 0.25 mum ground rule devices is less than 0.1 mum (3 sigma) including all possible sources of error. Chuck induced random deformation of x-ray masks can contribute a significant amount to this overlay error [A. Chen et al., J. Vac. Sci. Technol. B 10, 2628 (1992)]. In addition, errors could arise also if different chucking techniques are used in the writing and exposure tools [A. Chen, S. Lalapet and J. R. Malonado, J. Vac. Technol. B 9, 3306 (1991)). Based on the state of the art of the precision and accuracy of mask aligners and e-beam writers, it is required that the mask deformation due to chucking should be kept below 10 nm (3 sigma). Several finite element models were constructed to simulate x-ray lithography masks under different chucking methods: (a) an idealized kinematic chucking, (b) full surface chucking, e.g., chucked by a vacuum ring, and (c) three point chucking. The maximum in-plane deformation of the x-ray mask membrane was normalized to the ratio of the modulus of elasticity of the mask support structure (Pyrex; trademark of Cornia Glass) and the chuck material. The calculated in-plane deformations of the x-ray mask membrane were compared among the various chucking techniques mentioned above. The results are helpful in the design of aligner and exposure tools from the point of view of selecting proper chuck materials and methods to minimize mask membrane deformations.