Si Wafer 제조 공정 중 발생하는 금속오염물 및 오염입자 제거를 위한 세정 공정 연구

Abstract

The RCA cleaning process is a standard wet cleaning process which is used to remove particles and contaminants from silicon wafer surface. The standard cleaning 1(SC1) solution which is an efficient particle removal solution consists of a mixture of ammonium hydroxide (NH4OH), hydrogen peroxide (H2O2) and water. It was designed to remove the particles from silicon surface that lift off by both the etching action of NH4OH and the oxidizing action of H2O2. SC1 cleaning process may result in the removal of only a few atomic layers of silicon surface. However, contamination on the metal which has a high redox potential is critical when bare silicon is exposed. Metal deposition on Si surface is induced by both oxidation and reduction reaction between metal ions and Si surface. Metal ion can take electrons from Si surface and are reduced to become metal. The metal particles on the Si surface are oxidized to become SiO2 and etched away by OH- in SC1 solution. The metal pit is a form of localized etching that leads to the creation of small hole under the metal. Thus, the etching has a crucial effect on the formation of defects and removal of particles. The etching rate of Si increased with NH4OH concentration whereas it decreased with H2O2 concentration. This indicates that metal pitting increased with NH4OH concentration while H2O2 inhibits it. However, the particle removal efficiency decreased at high H2O2 concentration. Particle removal is affected by etching rate and pH of cleaning solution. For high pH value in the SC1 solution, particles take on a strongly negative charge. The particles are repelled from a Si surface. This electrostatic interaction prevents recontamination by particles. Therefore, the optimization of SC1 cleaning process is required to study. In this study, the metal pitting mechanism has investigated which is strongly related to the etching rate of Si surface. Etching rate was measured in various SC1 conditions with using patterned wafer. Also, Particle Removal Efficiency (PRE) has measured in various SC1 conditions by two different particle sizes (50 nm, 100 nm). This indicates that high PRE was measured by increasing time and temperature. PRE was low at higher H2O2 concentration. PRE also exhibits different trend with respect to the particle size. Large particle is removed easier than small particle. At same etching amount condition, etching time was more dominant than etching rate on removal efficiency while low etching rate condition has limitation to reach 100 % PRE although etching time was enough.