Fume is major pollution source which is occurred after etch process. [1] Fig. 1 is shown how fume is exhausted after etch process. And wafer stay in buffer during exhausting. At this time, this fume is absorbed with surface of wafer or remained on surface of wafer. Additionally, this fume combines with atmospheric moisture in air. And it is changed to particle the diameter of this particle is less than 1um. So, this fume often make serious wafer defect. For these reasons, if we cannot control this fume, product quality and wafer yield is seriously decreased. Moreover, it makes productivity issues because we spend a lot of time for fume removal process of defected equipments like fig 1. So, our paper proposes several optimization methods for ‘out buffer system’. Firstly, several gases stay in exhaust system like fig 2(a). This analysis is use aero-dynamics simulation for traditional exhaust systems. This result of simulation is shown some gas stay in system. This gas is normally changed to fume. For reducing this remained gas, we change diameter of vacuum line like fig 4. It shows our final optimized system. Major optimization of systems that the diameter of vacuum line is changed from 200 Ø to 100 Ø. To choose this optimized diameter, we use Bernoulli's theorem [2]. Fig 3 shows that two output vacuum lines are connected to same direct line. So there are different pressures in vacuum line. This is the reason why turbulence flow occurred. To find optimal diameter of this exhaust pipe line, we use Bernoulli's theorem simulation with various test design. Finally we found a optimal structure of vacuum line. REFERENCE 1. Effects of reactant rotational excitation on reactivity: Perspectives from the sudden limit B Jiang, J Li, H Guo - The Journal of chemical physics, 2014 - scitation.aip.org 2. Department of Mathematics, Hoseo University, Chungnam 336-795, Korea *School of Mechanical Engineering Figure 1