Tomoya Noda

A study of source and mask optimization for ArF scanners

The k1 factor continues to be driven downwards, in order to enable the 32 nm feature generation and beyond. Due to the extremely small process window that will be available for such demanding imaging challenges, it is necessary not only for each unit contributing to the imaging system to be driven to its ultimate performance capability, but also that active techniques that can expand the process window and robustness of the imaging against various kinds of imaging parameter be implemented. One such technique is a Source & Mask Optimization1 (SMO). In this paper we are going to study the effect of SMO and discuss its application to ArF exposure tools. Free form optimization example and constrained optimization will be compared with conventional illumination setting. Furthermore realization of the SMO with sPURE, which is optical element to generate customized illumination discussed.

Global source optimization for MEEF and OPE

This work describes freeform source optimization considering mask error enhancement factor (MEEF), optical proximity effect (OPE), process window, and hardware-specific constraints. Our algorithm allows users to define maximum allowed MEEF and OPE error as constraints without defining weights among the metrics. We also consider hardware specific constraints, so that the optimized source is suitable to be realized in Nikon’s Intelligent Illumination hardware. Our approach utilizes a global optimization procedure to arrive at a freeform source shape solution, and since each source grid-point is assigned as variable, the source solution encompasses the maximum amount of degrees of freedom.

Aberration averaging using point spread function for scanning projection systems

Scanning projection system plays a leading part in current DUV optical lithography. It is frequently pointed out that the mechanically induced distortion and field curvature degrade image quality after scanning. On the other hand, the aberration of the projection lens is averaged along the scanning direction. This averaging effect reduces the residual aberration significantly. The aberration averaging based on the point spread function and phase retrieval technique in order to estimate the effective wavefront aberration after scanning is described in this paper. Our averaging method is tested using specified wavefront aberration, and its accuracy is discussed based on the measured wavefront aberration of recent Nikon projection lens.

Finite Element Models of Lithographic Mask Topography

Photolithography simulations are widely used to predict, to analyze and to design imaging processes in scanners used for IC manufacture. The success of these efforts is strongly dependent on their ability to accurately capture the key drivers responsible for the image formation. Much effort has been devoted to understanding the impacts of illuminator and projection lens models on the accuracy of the lithography simulations [1-3]. However, of equal significance is the role of the mask models and their interactions with the illuminator models.