High-resolution UV wavelength reticle contamination inspection

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A new reticle inspection system with laser UV imaging for contamination inspection has been developed to detect contamination defects on advanced reticles for DUV steppers and low k<SUB>l</SUB> lithography. The extension to UV wavelength improves the resolution of the imaging optics while maintaining compatibility with current STARlight inspection algorithms, thus improving both sensitivity and minimum linewidth capability. This enables inspection of reticles for 4X lithography design rules at 0.18 micrometer, 0.15 micrometer and 0.13 micrometer. The system also is capable of inspecting Tri-Tone PSM and reticles with OPC assist bars. Initial simulations were performed to optimize performance of optical components and defect detection algorithms of the UV system. The simulations identified that with no changes to optics and algorithms, UV wavelength contamination inspection was more sensitive to defects on clear and on chrome surfaces, however, showed different sensitivity to defects on a quartz/chrome edge. This UV edge effect (UEE) was investigated in depth. From these simulations additional defect detection algorithms have been implemented to optimize transmission defect and on edge defect detection. Using both PSL defect test masks and real production reticles, initial observations of the nature and the frequency of defects detected with this 180 nm contamination sensitivity instrument will be presented. Total number of defects captured on the UV system is shown to be as much as two times greater than non-UV systems. In one case 169 more defects were found on clear areas of the pattern using the UV system. The UV contamination inspection system has recently been evaluated with production reticles with dense geometry, OPC, and Tri-tone phase shift. A transmission defect causing a bridge on wafer in a very dense geometry, was detected with the UV contamination inspection system. This same defect was not found on a non-UV system. This micro- fissure defect causes more scattering UV wavelength compared to longer wavelength. The linewidth capability of the system was verified in part with OPC reticles. Scatter bars as small as 0.25 micrometer were inspected with the UV wavelength. Linewidth capability was also verified on a Tri-tone reticle using the smallest pixel available for inspection. With more defects to review, the UV system software estimates the printability of defects so defect disposition is faster and more accurate. Comparisons with non-UV systems illustrate the advantage of using shorter wavelengths for contamination inspection of DUV reticles. The quality of defect review images has a direct impact on the effectiveness and ease-of- use of reticle inspections systems. The smaller review pixel with the system yields high quality UV transmitted and reflected light defect images.