Kaoru Fujihara

Study of ADI(after develop inspection) using electron beam

In this paper, we established a method to detect defects with a size of 40nm, which is required in the machine to inspect defects on the photo resist of hp65nm generation. First of all, we clarified the mechanism of nuisance generation by electron beam and established a method to control nuisances. Next, we examined the inspection conditions required for detection of minute defects. As a result, the relation between the landing energy, brightness, or contrast and the defect detection ratio were clarified. We successfully detected minute defects of 40nm in the inspection based on a strategies obtained from these examination results to confirm that we established a method to detect minute defects. In addition, we compared defects on photo resist in electron beam inspection and electric defects in the wiring resistance measurement. As a result, the defect distribution on photo resist was found identical to the electric defect distribution. Thus, we proved that the defect inspection on photo resist using electron beam was detecting the killer defects. Therefore, we showed that the resist defect inspection using electron beam is effective for the 65nm generation.

Electron beam charging of a SiO2 layer on Si: a comparison between Monte Carlo-simulated and experimental results

Recently, a unique capability in highly sensitive detection of residue defects in photoresist patterns on a metal hard mask has been verified experimentally [T. Hayashi et al., Proc. SPIE, 6922 (2008) 6922-129]. In order to reveal the mechanism for the new defect inspection technique, the charging up induced by 300 eV - 2000 eV electron bombardment of thin insulating layers (SiO2, ~tens of nm) on Si is studied by using a self-consistent Monte-Carlo simulation of the transport of a primary electron and secondary electrons (SE) and the generation of an electric field due to the charges in the layer. The calculation is compared with the contrast changes in the SEM images of thermally oxidized layers (20~100 nm) on a Si wafer. Low-energy EB (or thick SiO2 layer) causes the positive charging of the layer, whereas the high-energy EB, which penetrates under thin SiO2 layer, relaxes the charging of the layer due to electron-hole recombination in Si. The thickness dependence of the SE yield for low- and high-energies is investigated, which explains the observed changes in the SEM images of the insulating layers on Si.

Study of ADI (After Develop Inspection) on photo resist wafers using electron beam (III): novel method for ADI on metal hard mask by penetration contrast

We proposed a model for highly sensitive detection of residue defects in electron beam defect inspection of photo resist patterns on a metal hard mask and verified the principle of that model. When there are photo resist residue defects on the bottom anti-reflective coating (BARC), the thickness of total organic layer is thicker at the defect pattern than in areas where there is no residue. The model proposed here focuses on this increase in layer thickness. The landing energy of the primary electrons allows electron penetration to the under layer (TiN) in the patterns where there is no defect (thin layer), but does not allow such penetration in the defective patterns (thick layer). In that landing energy region, SEM image contrast differs according to the primary electron penetration or nonpenetration in the non-defective patterns and in the defective patterns. This method detects defects according to the contrast change (penetration contrast method). The principle of this model (i.e., the penetration contrast method) is verified in this report. The behavior of the defect that caused with the variation of an actual exposure condition was compared with this method and without this method. This method was also applied for quantitative detection of defects considered to be caused by dose amount of lithography process. This method was shown to be clearly effective in ADI for the metal hard mask.

Study of ADI (After Develop Inspection) on photo resist wafers using electron beam (II)

We have clarified that the low-damage, high-resolution defect inspection of the photo resist patterns is ensured by the electron-beam defect inspection equipment for 32-nm generation and beyond. It has first been confirmed that the CD variations on the 65-nm width line structure formed on an ArF resist under general inspection conditions are equal to or less than the CD variations due to a general CD-SEM. We have also succeeded in understanding the resist deterioration mechanism when the ArF resist is exposed to e-beams. This understanding has led us to learn that the layer that, located in the vicinity of the resist surface, is deteriorated by e-beams has its etching rate lowered to cause even improvement on the etching resistance. These findings have enabled us to use inspection conditions that cause lower damage to resists. By using those conditions, we have been able to inspect ArF resist line-space structure wafers with line width of 65nm and pitch width of 140nm. The inspection successfully detected 15 to 20nm programmed extrusion defects with a capture rate of at least 95% and a nuisance rate of 5% or less. It has thus been revealed that e-beam defect inspection equipment are useful for inspecting defects on resist wafers with 32-nm generation and beyond.