Haze formation on reticle continues to be a significant source of concern for the photolithography.
Possible sources and causes continue to be investigated. This paper provides a haze source evaluation result
under the sub-pellicle defect on the mask.
It is well known that there are several sources to produce the haze. One is inorganic molecules such as SOx, NH3,
H2O and CO2. The haze formation of inorganic sources is promoted for growing defect size by the exposure
energy in time. The other is organics that are prevalent Fab and storage environment.
In this paper, we deal with the haze that is immediately generating with a low energy exposure. Especially, this study
treats the haze source during the mask packaging method.
As the semiconductor industry requires lithography suitable for 32-nm node, extreme ultraviolet lithography (EUVL) has the potential to provide this capability for the mass fabrication of semiconductor devices. But because an extreme ultraviolet (EUV) lithography exposure system is operated in vacuum, during irradiation by EUV light, hydrocarbons are decomposed in vacuum1-3, for example, by the out-gassing from EUV mask, and contaminate the surface of imaging optics which is coated with Mo/Si multi-layers with carbon. Thus, this contamination not only reduces the reflectivity of the Mo/Si multi-layers of imaging optics and degrades the exposure uniformity, but also degrades the resolution of the imaging optics. In this study, as we examined the volume of the out-gassing and the species from EUV mask after every process for EUV mask production, we will control the carbon contamination of EUV mask.
Keywords: EUV, carbon contamination, reflectance, out-gassing
To countermeasure the haze problem on a reticle, we investigated the mask storage environment of wafer manufacturing Fab and mask manufacturing Fab. Through IC (Ion chromatography) and AIM system, we measured the outgas quantities of Fab environment, SMIF pod, mask carrier boxes and pellicle. With the evaluation result, the environmental factors around the production mask do not meet the level of its residual SO<sub>4</sub> ion. We suggested the imminent priority to improve the environment surrounding the production masks. Additionally, we adopted a new process to decrease the SO<sub>4</sub> outgas of pellicle frame up to 90%.
This is an experimental result for the inhibition of effects of the growing defect. Up to now, it has been considered and defined that the growing defect is an unexpected and unusual reaction by bonding impure ions existed on the mask each other. This study is not only to suppress the unexpected reaction when making the final mask but also to stabilize the surface of mask by controlling by-product occurred when stripping upper Cr layer and damaged layer from sputtering process. According to the analysis of the surface roughness stemming from each process (from wet etching to cleaning Process) of MoSi layer, the surface still comes to be rough when a mask is done through all process. So, heat treatment was performed and surface roughness was measured to figure out how much the surface condition would be improved and how many remaining SO4, NH4 Ions on the surface after cleaning process reduced. This study shows the major factor causing plasma damage is a dry etcher, a way to control the damaged layer of MoSi at PR strip process, the level of stabilization of mask surface through cleaning process and a clue to be able to prove the stabilization by adding specific process. Analysis tools for this study are as follows. AFM (for checking the roughness of surface), TEM (for checking cross-section) and IC (Ion chromatography)analysis equipment.
The critical source of haze contamination which mainly occurred on MoSiN surface and the interface of MoSiN and quartz is known as sulfuric ions remained after mask process. In this experiment, the UV treatment with oxygen gas was carried out before and after wet cleaning process for reducing residue ions from mask surface, and the effect with the sequence of UV treatment and wet cleaning was investigated. The composition of amorphous MoSiN layer was slightly modified by 172nm UV treatment with oxygen gas, and the amount of chemical residue ions after wet cleaning which use the piranha and SC-1 was reduced according to the transformation of surface composite. And also the relation of the surface transformation and the phase shift after SC-1 cleaning was evaluated.
In this study we investigated the defect due to pellicle frame materials for repeating exposure in months. Defects were found in the sub-pellicle and the defect density was high in the 4 corners compared to the center of the mask. The defects grew on MoSiON or the interface Quartz and MoSiON film, and the defect size was below 0.5 um. By analyzing with Raman Spectroscopy, defects consist of Ammonium Sulfates, Melamine Formaldade Resin and KClO<sub>3</sub>. The evaluation method for cleaning process and pellicles was Ion Chromatography. According to Ion Chromatography analysis, the main composition of defect was substances of pellicle frame materials. Also we confirmed the pellicle frame effect with the exposure test.
In this study, Cr defects resulted from high voltage E-beam writing in high Cr load Logic Mask were investigated. The Cr defect, which is a damage of anti-reflection layer on Cr, is mainly found in isolated Cr patterns of high Cr load Logic Mask. This defect appears under high voltage E-beam writing with high dose and dry etch process. High accelerating voltage and dose of E-beam writing decrease the thickness of remaining E-beam resist after developing. These phenomena are more significant in high Cr load Logic Mask consisted of isolated Cr patterns. Because the resist thickness of isolated Cr pattern is not enough for enduring dry etch process-induced damage, Cr surface is damaged during etching. Consequently, the Cr surface damage of high Cr load Logic Mask is related with voltage and dose of E-beam and dry etch process time. To prevent these defects, low accelerating voltage and dose of E-beam and low thickness of Cr layer to increase dry etch process margin are necessary.