Misako Saito

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.

Modelling and observations of electron beam charging of an insulator/metal bilayer and its impact on secondary electron images in defect inspection equipment

A self-consistent simulation of secondary electron (SE) emission and charging of a SiO(2) layer with the thickness of several tens of nanometres on Si is incorporated into a trajectory simulation of emitted SEs above the surface, the centre area of which is charged by electron beams (EBs) at the energy range from 300 to 2000 eV. In order to study the influence of the charging of an insulating layer on defect inspection, a pseudo-image is reconstructed from net SE yields calculated at each point of the SiO(2) surface locally applied the positive voltage. The image contrast between charged and uncharged areas is compared with the observation of thermally oxidized layer with the thickness of 24-106 nm on a Si wafer. The image contrast is very sensitive to the thickness of the SiO(2) layer, which is verified by both observed and calculated images. The calculated changes of the images with the layer thickness and the primary electron energy reproduce the experimental observations fairly well. This confirms a highly sensitive detection mechanism for tiny defects in insulating patterns on a metal hard mask for an EB defect inspection equipment.

Ultrafine Particle Removal Using Gas Cluster Ion Beam Technology

In this paper, the ultrafine particle removal using CO2 gas cluster ion beam (GCIB) technology is investigated. The CO2 GCIB is irradiated the sample at an angle of 0 ° with respect to the surface normal. The higher particle removal efficiency can be achieved at the higher kinetic energy of the gas cluster, and the inside space of line and space pattern particles can be removed. We also suggested that the CO2 GCIB process has the high particle removal uniformity without redeposition of the removed particles. It is possible to remove the ultrafine particle as small as 12 nm in diameter (which is required for 2014 by ITRS 2011). The pattern damage is not observed for 45 nm poly-Si pattern. Moreover, the molecular dynamics simulation is performed to investigate the mechanisms of the particle removal by GCIB irradiation.

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.

Organic outgassing behavior of plastic material and reduction of organic contamination in semiconductor equipment

We developed a low organic contamination (LOC ) electric cable as part of efforts to reduce organic contamination in semiconductor equipment. Our development strategies for LOC cables were obtained from the study of the behavior of outgassing from electric cables and the behavior of adsorption on silicon wafers. Strategy I: Reduce low boiling point organic contaminants from electric cables. Strategy II: Reduce organic contaminants with high adsorption rates on silicon wafers. Developing LOC cable under these two strategies, consequently, the amount of organic contaminants that are outgassed from the developed LOC cable was 1/10 or less of the level that is achieved by conventional cables. When compared with conventional cables, the flame-retardancy and flexibility are comparable. Then, we installed LOC cables in actual semiconductor equipment. The amount of organic contaminants adsorbed on the silicon wafer exposed in the equipment that was installed LOC cable and other low outgas parts were 1/6 lower than the conventional equipment. By using this low-outgassing cable in semiconductor equipment, we succeeded in reducing organic contamination in the equipment.

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.

Analysis method of metal contamination for the isopropyl alcohol (IPA)

Isopropyl alcohol (IPA) has been commonly used for drying wafers at a final step of cleaning process. As a result, the demand for higher purity IPA has been increasing, and the quality control of metallic impurities in IPA using the reliable analytical method is required. In this study, issues on the analysis of metallic impurities in IPA at ultra-trace level were investigated, and some accurate analysis methods were successfully developed. Furthermore, Fe (iron) impurities in IPA were studied and we indicated that Fe impurities in IPA were smaller than 15 nm and have a positive charge.