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Chapter 3 is a tutorial on optical lithography which encompasses the physics and theory of operation including issues associated with advanced processes, and corresponding solutions. It begins with a brief historical perspective, an introduction and simple imaging theory. Then it takes the reader through the challenges for the 100 nm nodes and beyond. This is followed by an overview of the significant process variations, the impact of low‐κ imaging on process sensitivities. A detailed discussion of low‐κ imaging follows, including its effect on depth of focus; exposure tolerance; mask error factor; sensitivity to aberrations; CD variation as a function of pitch; and corner rounding radius. The next topic covered is the state of the art resolution enhancement techniques which will extend the resolution of the current lithography down to a quarter of the wave‐length of the illumination used. This is followed by a discussion of the Physical Design Style Impact on RET and OPC Complexity. The chapter concludes with a look ahead into the future Lithography Technologies—the evolutionary as well as the revolutionary road maps.

The geometry of weirs is a prime factor influencing hydraulic performance and accuracy. One of the geometric components of weirs, is the situation of its top corners, are they sharp or rounded, and what is the most suitable radius of such rounding curves? The present study was conducted to examine the effect of using five different radius of curvature for both the upstream and downstream top corners of a clear over-fall weir on its hydraulic performance and accuracy. Eleven models of wooden weirs were shaped and prepared with five different values of rounding curvature. The prepared weir models were located in a laboratory tilting flume of 13.50 m length, 0.30 m width, and 0.30 m depth. The study was carried out in the Irrigation and Hydraulic Laboratory of the Civil Department, Faculty of Engineering, Assiut University, Egypt. A discharge ranging from 2.0 to 22.0 dm[3] s[−1] was used, and through 66 experimental runs, all the necessary hydraulic parameters were measured, and recorded. The obtained data were tabulated, analyzed, plotted, and technically discussed. The main results and obtained conclusions proved that when the front weir top edge is curved the discharge coefficient increases up to 8%. Also, when both front, and behind weir top edges are curved the discharge coefficient increases up to 14%. At the same time the discharge coefficient has a maximum value when the radius of curvature in upstream and downstream top corners equals 20% of the height of the weir.