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Lithography 공정에서 사용되는 Blank Mask 제작을 위한 Quartz 기판의 연마 및 세정공정에 관한 연구

Lithography 공정에서 사용되는 Blank Mask 제작을 위한 Quartz 기판의 연마 및 세정공정에 관한 연구
Other Titles
Development of Abrasion and Cleaning Process of Quartz Substrate for the Fabrication of Blank Mask in Lithography Process
Alternative Author(s)
Hyuk-Min Kim
Issue Date
The trends of high integration and miniaturization have been required for the advanced semiconductor electronic devices by designing feature sizes below 10 nm currently. The lithography has become an increasingly important technology for the formation of various structures. The photo-mask in lithography exposure step process plays an important role in the performance and yield of the devices. The photo-mask is produced from the blank mask which has the PR and metal film on the quartz surface. The preparation of quartz substrate is important for the fabrication of blank mask which is the foundation material of photo-mask. However, the literatures and researches about the fabrication of the blank mask using quartz substrate are rare yet because of the difficulty in handling of transparent material. Moreover, the production methods are restricted and monopolized by a few companies due to the nature of technology in lapping and polishing of quartz which are based on traditional know-hows. Since there are not much study and information in public domain on quartz lapping and polishing, the fundamental study was carried out to understand the previous traditional based unknown phenomena in the quartz substrate preparation which includes abrasion and cleaning process. The abrasion process is classified into lapping and polishing of quartz substrate. Lapping is necessary to control the thickness and flatness of substrate. In lapping part, eco-friendly and economical 2-body processes mode was investigated to compare with conventional 3-body mode. The high concentration of slurry which contains the micron size of high hardness abrasive particle has been supplied to the metal platen in conventional process. The pad that has the diamond abrasives on the surface was used to lap the quartz substrate with only DIW in 2-body process which has many advantages compared to the conventional process. The research of lapping was focused on the analysis of fixed diamond abrasive pad which is relatively new to lapping process. The experiment was performed as the function of pressure and platen speed. The removal of material showed a different behavior as compared to the polishing or CMP (Chemical Mechanical Planarization) process for the film. The chemical effect was negligible but the mechanical action became dominant due to the high pressure applied in the process. Not like other literatures on abrasion for SiO2 materials, there is no dependency on medium pH in removal rates of quartz during lapping. The removal rate of quartz (SiO2) substrate was the highest in DI water of neutral pH. The frictional behavior was observed as a function of medium pH in lapping based on the hypothesis that pH affects the mechanical action. The removal mode of quartz was proposed using theoretical calculation by analysis of quartz residues after lapping. It was found that the brittle fracture mode is dominant in the modified lapping process for quartz substrate using the fixed diamond abrasive based on DIW. CMP of quartz substrate is essential to make the smooth surface as the high quality of surface is required for the high transmission of various optical sources which determines the efficiency of lithography process and yield. Usually, 15~20 wt% of ceria slurry is used for the polishing of quartz surface. The dispersant is necessary in slurry due to its high concentration of ceria abrasive particles. The dispersion of ceria abrasives is the critical point otherwise it will cause the defect like scratch on the surface. The research was progressed based on the control and understanding of ceria dispersion using 2 kinds of dispersants. The fundamental study was conducted through the dispersion behavior of ceria particles
the adsorption of dispersant on the ceria particle surface and electrokinetic behavior for the stable dispersion of ceria abrasive particles. The stability of high concentration slurry was achieved and its mechanism was also proposed. There is an optimized concentration of additives for the stable dispersion of 20 wt% ceria particles. At the lower concentration of dispersants, the stability of ceria particles were poor as the steric hindrance and electrostatic repulsive force were not enough to overcome the van der Waals forces due to the lower adsorption amounts of polyelectrolyte on ceria particle surface. On the contrary to this, the number of free polymers increases as the increase of dispersants in slurry medium which causes the agglomeration of ceria particles because of the bridging flocculation. The adsorbed dispersants on the ceria particle surface provide sufficient steric hindrance along with the electrostatic repulsive forces which can maintain the stable dispersion even at the static state for 24 hr. Post CMP cleaning plays a vital role in removing the contaminants such as abrasive particles, organics and debris after abrasion process for the prevention of defect generation on the surface. H2-DIW with megasonic was tried in post CMP cleaning process for the removal of particles in the single wafer cleaning tool. The interaction forces between the ceria abrasive particles and quartz surface were calculated based on zeta potential as the function of medium pH. The surface particle scanner and optical microscopy were used for the inspection of target surface after cleaning process.
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