Helium Ion Microscopy has been established as a powerful imaging technique offering unique contrast and high
resolution surface information. More recently, the helium ion beam has been used for nanostructuring applications
similar to a gallium focused ion beam. A key difference between helium and gallium induced sputtering is the less
intense damage cascade which lends this technique to precise and controlled milling of different materials enabling
applications. The helium ion beam has been used for drilling 5nm holes in a 100nm gold foil (20:1 aspect ratio) while
the gallium beam sputtered holes of a similar aspect ratio seem to be limited to a 50nm hole size. This paper explores
the drilling of nanopores in gold films and other materials and offers an explanation for the observed differences in
results between helium and gallium ions.
The effects on pattern fidelity of material deposition on photomasks due to interactions of the primary electrons with the organic molecules contained in the vacuum chamber while being analyzed in CD SEM were investigated. The photomasks experienced contamination in the area that was electron-irradiated by the SEM, but it was not detected with either a transmitted or reflected light inspection. Wafers were exposed at various illumination conditions and at multiple wavelengths, which produced no noticeable effects on the images as compared to unanalyzed locations.
An investigation was performed to determine the printability and defect detectability of reticle OPC defects for the 180 nm technology node. Two different OPC approaches were investigated, one based upon assist bar/serif features and the other based upon serif/jog features. Several critical defects were studied, including chrome extension defects on assist bars and pindots between assist bars and primary features. Wafers were printed using a 0.6 NA, DUV stepper and resulting wafer resist images measured by CD SEM. Edge defects as small as 200 nm cause greater than 10% change in local linewidth, 400 nm defects cause catastrophic wafer defects, and chrome spot with 260 nm diameter can shorten gap between two line ends by 10%. CD defects less than 75 nm on the reticle were found to have a significant impact on the process window. The programmed defect test reticles used to print the wafers were inspected on KLA-Tencor reticle inspection systems and the defect sensitivity capture curves plotted. Defect capture rates indicated that smaller than 200 nm edge defects and 125 nm CD defects are detected. Defect printability simulations were performed using database and aerial images gathered from an automated defect inspection system and compared to the experimental wafer results. The purpose of this test is to determine the feasibility of performing printability predictions in a mask production environment. A correlation between the simulations and the wafer results are shown.
As semiconductor processes have moved towards lower k1 and mask inspection equipment has moved into the UV range, more subtle reticle defects have been found to cause manufacturing problems. Lower k1 and new lithography processes and reticle technologies, such as OPC and PSM, have made it difficult to determine the significant and these defects. This paper reports on the development of a simulation tool that will improve the yield and productivity of photomask manufacturers and wafer manufacturers by improving reticle defect assessment. This study demonstrates the accuracy of simulation software that predicts resist patterns based on sophisticated modeling software that uses optical images obtained from a state-of-the-art UV optical inspection system. A DUV 4X reduction stepper was used to print a reticle with programmed defects across an exposure/focus matrix, with the minimum feature size being 200 nm. Quantitative comparisons between predicted and measured wafer CDs were made. In summary, it was found that the simulation software based solely on aerial images predicted absolute CDs with limited accuracy, but differential CDs with limited accuracy, but differential CDs, obtained by utilizing both the reference and defect images, were predicted accurately. Comparison of simulations using both reticle SEM images and optical reticle inspection images showed good agreement, demonstrating the accuracy and high resolution of the optical reticle inspection images. Application of differential aerial images to a simple test case showed that it was possible to identify and therefore eliminate a significant number of defects that did not print, thereby improving defect assessment.
This paper presents results obtained using a low-voltage critical dimension scanning electron microscope (CD SEM) for the imaging and measurement of features patterned on quartz photomasks. The SEM system used was designed for handling silicon wafer substrates and has been adapted to accommodate 6', 250 mil photomask substrates. The scope for this initial characterization is limited to the two most common reticle metrology applications on current technology photomasks; patterned PBS photoresist features on chrome, and patterned chrome features on quartz. Images, data, and analysis of the characterization results are presented, and the unique difficulties of imaging and measurement of each of these two types of samples is discussed.