## 2 Materials and Methods  
### Test Process Equipment and Experimental Setup  
This study used a 300 mm ATM Si Epi-reactor of Applied Materials, Inc., of SK Siltron's silicon wafer manufacturing line located in Gumi, Gyeongsangbuk-do. Chemical reaction of the Si epitaxy process for production of single-crystal thin film on a wafer is shown as follows:  
\[\text{SiHCl}_{3}(\text{gas})+\text{H}_{2}(\text{gas})\rightarrow\text{Si}( \text{solid})+3\text{HCl}(\text{gas}) \tag{1}\]  
Figure 1 shows the setup schematic of residual particle measurement during N\({}_{2}\) gas purge. The exhaust of the scrubber in the process chamber was used as the particle sampling port. Due to extreme conditions of the in-process environment using toxic, ignitable, and high-temperature gas, there were difficulties in real-time measurement during the process. Therefore, residual particles were measured and collected for further analysis during chamber inactivation and N\({}_{2}\) gas purge before preventive maintenance. The purge flowrate of the N\({}_{2}\) gas inside the chamber was 25 LPM. The purge was performed every 1 min and 30 s at 20 s intervals. When using the ELPI, the flowrate incoming to the inlet of the cascade impactor should be fixed to be around 10 LPM for correct measurement and collection after separating particles by their sizes. The flowrate adjustment was performed using an orifice gasket for a 10 LPM flow when fastening the VCR fitting connection between the chamber exhaust and the ELPI inlet. When using an orifice, particles may inertially collide with the front surface, resulting in particle loss. Although this could not be prevented, all measurements were carried out by checking that the sampling was conducted under constant velocity conditions. Instrument for Concentration Measurement of Particles in the Process Chamber: Electrical Low Pressure Impactor (ELPI)  
Measurements of number concentration and mass concentration by particle size were carried out using an ELPI+ (Dekati Ltd., Tampere, Finland). The instrument is capable of real-time measurement of aerosol-phase particles with particle sizes of about 5 nm to 10 \(\upmu\)m [27]. Figure 2 shows a schematic and cut-off diameters (D50%) of the cascade impactor employed in ELPI. D50% was the collection efficiency of an impactor, meaning a particle diameter that resulted in 50% collection efficiency. Detailed principles of measurement and collection are as follows. First, particles introduced to the inlet were charged with a large number of cations generated in the corona glow region when high voltage was applied to the needle in the middle. These charged particles were then categorized and collected in 15 stages depending on the aerodynamic diameter. The topmost stage, with a D50% value of 10 \(\upmu\)m, simply acted as a pre-separator to prevent inflow of large particles. At this time, the generated current at the substrate was measured through electrodes connected to the impactor. The current value was then converted into a number concentration through formulas [28; 29]. If the principal component of the incoming particle is known, the number concentration can be converted to a mass concentration by entering the density value into the own program for data processing. Figure 1: Schematic of the residual particle measurement setup during N\({}_{2}\) gas purge. Even within a clean room, the leakage of particles from the chamber and instrument to the outside might affect the human body during measurement. Thus, prior to particle measurement in the epitaxial growth chamber, the ELPI was improved to check and prevent gas leakage to the outside during measurement. First, the inlet of the impactor was improved to use international organization for standardization (ISO) quick flanges (aka QF, KF, or NW) for vacuum fitting fastening. It was then confirmed that there was no gas leakage factor between the equipment and the outside using Heliot 900 model (ULVAC, Kanagawa, Japan), a pressurization-type vacuum leak tester.