Design and application of Gray FieldTM technology for defect inspection systems

There has been increased interest in optical inspection tools that utilize UV illumination. This originates from the belief that diffraction limits will render tools employing longer wavelengths blind to many defects identified as being critical. In response to concerns over the applicability of UV illumination to rapid defect detection we performed a series of experiments to explore and develop new inspection techniques to provide the capability of detecting the dimensionally challenging defects associated with advanced technology nodes while maintaining high speeds needed for chipmakers´ volume production lines. Initial results indicated that by radically redesigning the collection optics to a multiple perspective configuration that compiles information from six different scattering and reflecting directions, improved sensitivity, noise rejection and wafer throughput could be realized while using laser scanning illumination in the visible region of the spectrum. Also, defects that traditionally could only be observed in “bright field” tools were now detectable with ease at production worthy throughputs. Results are presented that show the optical experimental design data and simulations, and are corroborated by examples of defects from the resulting production defect inspection system, Compass^TM. In addition, electron micrographs of a range of detected defects are presented that show the system versatility and the exact nature of the defects, thus allowing a clear understanding of the increase in sensitivity, speed and dimensional range these tools provide over traditional instrumentation to be made