EUV 마스크 표면 손상 최소화를 위한 유기물 및 나노입자 세정공정에 관한 연구

Abstract

Extreme ultraviolet (EUV) lithography is one of the technologies of choice for below 22 nm half-pitch node among major semiconductor manufacturers. In contrast to conventional optical mask, an EUV patterned mask works in a reflective mode. The EUV mask introduces new materials and surfaces such as silicon/molybdenum (Si/Mo) multilayer to reflect EUV light, ruthenium (Ru) capping layer to protect multilayer and tantalum-based absorber patterns such as tantalum nitride (TaN) to absorb the EUV light. During the EUV mask manufacturing and EUV lithography process, various contaminants such as particulate and carbon contaminants can be attached on EUV mask surface. EUV mask does not have a pellicle which is protected EUV mask surface from contaminants. Therefore EUV mask cleaning process should be required. The adhesion and removal behavior between contaminants and surfaces must understand to perform the cleaning process effectively. The adhesion and removal behavior of particulate contaminants and carbon contaminants on EUV mask was investigated. To investigate the interaction force between various contaminants and EUV mask materials, we used silica (SiO2), tantalum (Ta), and polystyrene latex (PSL) particles as representative of inorganic, metallic, and organic contaminants. Particle contamination and removal behavior on Si, Mo, TaN, and Ru were investigated. To predict the adhesion force between particles and substrate, the van der Waals force was estimated depending on the particle and substrate type. Based on the theoretical calculation of adhesion force, the removal behavior of the contaminant particles was evaluated. The adhesion force between the particles and the substrate was found to have a large influence on the chemical bonding along with the van der Waals force. The removal of oxide particles such as silica particles on the surface of Si was found to be very difficult due to hydrogen bonding between the Si substrate surfaces and oxide particle. In the case of Ta particles, Ta is a metallic particle, but native oxide formed on its surface. Therefore, Ta particles also generated the hydrogen bonding with Si surface. The PSL contaminant particles were easily removed from Si surface because there is no hydrogen bonding interaction between surfaces and only van der Waals force attraction occurred. The removal tendency on TaN was observed, and it is similar to the result of particle removal on Si surface. The particle removal efficiency on the surface of TaN substrate was higher than that of Si substrate surface. The removal efficiency of oxide particles was increased from TaN surface is due to the weak hydrogen bonding between them compare to the surface of Si substrate. Further, the particle removal efficiency was analyzed on the surface of Mo and Ru substrates. The removal efficiency of particles from metal surfaces was higher than that of Si and TaN substrates because there is no hydrogen bonding between the particles and the Mo and Ru substrate. On the other hand, the removal efficiency of PSL particles was found to be decreased. This is due to the formation of chemical bonding between the surface of the metal substrate and the organic contaminants, thereby increasing the adhesion and reducing the particle removal efficiency. It was confirmed that the removal efficiency of PSL particles was increased when the cleaning process was conducted by using tetramethylammonium hydroxide (TMAH) cleaning solution, as compared with ammonium hydroxide (NH4OH) and deionized water (DIW). The TMAH chemical is commonly used by fab and researchers to remove organic contaminants such as photoresist materials. To improve the removal efficiency of contaminants, TMAH is used to weakening the chemical bonding between the PSL particles and the Ru surface. In EUV lithography process, the carbon contaminant generated on the Ru and TaN surface by the high-energy EUV light is reduced the pattering performance of the device. Therefore, carbon contaminant could be removed, and it was achieved by using organic solvents based cleaning solution. A hydrocarbon film similar to EUV carbon contaminant was deposited on the Ru surface and TaN surface using plasma enhanced chemical vapor deposition (PECVD) system. Then, it was removed using quaternary ammonium hydroxide (QAH) solutions on the TaN surface, but not on the Ru surface. The adhesion between the Ru surface and the hydrocarbon contaminants is higher like chemical bonding, which reduces the hydrocarbon film removal efficiency. To effectively remove hydrocarbons from Ru surface, the removal was carried out by using a cleaning solution containing QAH, and polar aprotic organic solvents. The removal efficiency of hydrocarbons was higher when QAH solution was mixed with tetrahydrofuran (THF) organic solvent. Among the QAH solutions, TBAH is effectively removing hydrocarbons from Ru surface. Since the hydrocarbon film deposited on the Ru surface is a nonpolar type contaminant, ant it can be removed very effectively from the low polarity of TBAH mixed with THF cleaning solution. The high polarity dimethyl sulfoxide (DMSO) an organic solvent, when mixed with the TBAH solution, was able to remove the hydrocarbon film at a high concentration of TBAH and long cleaning time than the cleaning solution using THF organic solvent. Therefore, to effectively remove the contaminants on the surface of the EUV mask, it is very important to accurately understand the interaction between the substrate and the contaminants and the characteristics of the contaminants.