Integrated circuits are very complex devices that include multiple layers. Each layer may include conductive material and/or isolating material while other layers may include semi-conductive materials. These various materials are arranged in patterns, usually in accordance with the expected functionality of the integrated circuit. The patterns also reflect the manufacturing process of the integrated circuits.
Integrated circuits are manufactured by complex multi-staged manufacturing processes. During these multi-staged processes, resistive material is (i) deposited on a substrate/layer, (ii) exposed by a photolithographic process, and (iii) developed to produce a pattern which defines some areas to be later etched.
Resistive materials are usually selected such as to be responsive to a light at a predefined narrow range of frequencies (wavelengths). A commonly utilized resistive material is responsive to 193 nm light emitted from ArF light sources. This resistive material is referred to as 193 nm resist.
Various inspection and failure analysis techniques evolved for inspecting integrated circuits both during the fabrication stages and between consecutive manufacturing stages, either in combination with the manufacturing process (also termed “in line” inspection techniques) or not (also termed “off line” inspection techniques). Various optical as well as charged particle beam inspection tools and review tools are known in the art, such as the VeraSEM™, Compluss™ and SEMVision™ tools of Applied Materials Inc. of Santa Clara, Calif.
Manufacturing failures may affect the electrical characteristics of the integrated circuits. Some of these failures result from unwanted deviations from the required dimensions of the patterns. A “critical dimension” is the width of a patterned line or the distance between two patterned lines.
One of the goals of the inspection process is to determine whether the inspected wafer includes deviations from these critical dimensions. This inspection is usually done by charged particles beam imaging that provides the high resolution required to measure said deviations.
Various resistive materials are also responsive to charged particle beams, such as electrical beams emitted during scanning electron microscope (SEM) imaging. For example, the 193 nm resist shrinks as result of an interaction with the electron beam. The shrinkage is due to both quantum effects (breaking of chemical bonds) and localized heating effects. Thus, SEM imaging causes an unwanted change in the pattern imprinted upon a semiconductor.