ABSTRACT
The scanning electron microscope (SEM), the workhorse metrology tool in integrated circuit (IC) production, is used mostly for simple top-down measurements of line width, roughness, and contours. Nonetheless it is also capable of delivering excellent results beyond these applications by actually performing three-dimensional (3D)
measurements. Optical lithography is printing photoresist features that are much smaller than the wavelength of the light applied, and therefore it is indispensable to use optical proximity correction (OPC) methods. This includes modeling and compensation for the various errors in the lithography process down to subnanometer, essentially atomic level. The process has to rely on sophisticated and complex simulations and on accurate and highly repeatable dimensional metrology. The necessary dimensional metrology is beyond the conventional one-dimensional line width measurements, and must include two-and three-dimensional measurements of the contours and shapes of structures. Contour metrology needs accurate and highly repeatable measurements on sets and individual OPC structures, for which the critical-dimension measurement scanning electron microscope (CD-SEM) is the key metrology tool. Three-dimensional metrology is now indispensable for IC technology, but current metrology tools and methods cannot fulfill the requirements. We believe that with the implementation of several new methods described here briefly and others, it is feasible to develop 3D metrology that will well serve measurements of future nanometer-scale devices and IC development and production, even for structures only a few nanometers in size.
