Overlay Analysis Of Step-And-Repeat Lithographic Systems For Mask Making

The demand for smaller device geometrics and larger wafer size has drastically increased the need for more accurate level-to-level registration. It is more important than ever before to understand and control the overlay parameter of a step-and-repeat mask-making system. Furthermore, such an understanding is necessary for evaluation of mask quality. This paper discusses some important aspects of mask-making systems and gives a mathematical description of the first order and higher-order parameters. Some measurement techniques for obtaining those parameters are presented. Data are presented for special test patterns and for product masks fabricated on both optical and e-beam systems. This paper also includes a discussion of measurement strategy and a scheme for data reduction which minimizes estimating errors.