# Numerical Simulation-Based Study of Controlled Particle Deposition Technology for Wafer Surfaces
## 2 Materials and Methods
### Experimental Materials and Methods  
Table 2 presents the primary materials and instrumentation parameters used in the experiments:  
Figure 2 illustrates the particle generation-deposition system. A diluted polystyrene latex (PSL) suspension was prepared by mixing a PSL standard suspension (1:2000 mass ratio) with deionized water. This mixture was used to generate monodisperse polystyrene aerosol particles. The suspension was atomized using a pneumatic atomization generator to produce droplets containing PSL particles. These droplets were subsequently dried using a heating and diffusion dryer to remove moisture, resulting in solid aerosol particles. The aerosol was then charge-neutralized and classified by a differential mobility classifier (DMC) to obtain a monodisperse sample with the desired particle size. The size distribution was measured by a scanning mobility particle sizer (SMPS), and a portion of the aerosol flow was directed into the deposition chamber, which was connected to a condensation particle counter (CPC) for real-time concentration monitoring. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Materials and** & **Parameters and Models** & **Manufacturer** & **Sourced** \\ \hline PSL standard suspension & 70–200 nm & \
\begin{tabular}{c} National Institute of \\ Metrology, China \\ \end{tabular} & Beijing, China \\ Clean wafers & 50 mm &
\begin{tabular}{c} Topvendor \\ \end{tabular} & Beijing, China \\ Atomization generator & ATM 220 & Topas GmbH & Dresden, Germany \\ Cold dryer & HLW-10 AC & Hailwang & Hangzhou, China \\ Neutralizer & 5.520 & Grimm & Anring, Germany \\ Differential mobility classifier & 55-U & Grimm & Anring, Germany \\ Condenser particle counter & 3775 & TSI Inc. & Shoreview, MN, USA \\ Scanning mobility particle sizer & S 82 & TSI Inc. & Shoreview, MN, USA \\ Scanning surface inspection & E3200 & AK OPTICS & Beijing, China \\ system & Ultra 55 & ZEISS & Oberkochen, Germany \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Primary materials and instrumentation. Figure 2: Schematic diagram of particle generation and deposition device. CPC (1) and CPC (2) are two separate units used for particle counting before and after deposition, respectively. To ensure the stability and cleanliness of the aerosol generation process, a three-stage purified air supply system was used. Compressed air was first provided by an air compressor with a discharge pressure of 0.5 MPa and a flow rate of 156 L/min. It was then cooled and dehumidified using a refrigerated dryer with a rated capacity of 1.5 Nm\({}^{3}\)/min. Finally, the air passed through a series of three precision filters with filtration ratings of 3 \(\upmu\)m, 1 \(\upmu\)m, and 0.01 \(\upmu\)m, respectively, effectively removing particulates, oil mist, and moisture. This purification system ensured a clean and stable carrier gas throughout the aerosol generation and deposition process. Figure 3 illustrates the schematic of the particle deposition chamber, a sealed unit composed of a high-efficiency fan filter unit (FFU), a stand, a platform, a wafer base, a nozzle, and an exhaust hole. The FFU ensures chamber cleanliness before and after deposition. The stand stabilizes the platform and allows deposition height adjustments with 1 mm accuracy. The platform provides controlled deposition conditions, including rotation and temperature variations. The wafer base prevents direct contact between the wafer and rough surfaces, maintaining its stability during rotation, translation, and changes in the deposition position. The chamber features a single inlet nozzle mounted on a horizontally movable baffle plate, enabling selective deposition area adjustments. Exhaust holes facilitate gas circulation within the FFU and particle detection in the CPC. During the deposition process, the optimal parameters were identified as follows: nozzle diameter of 4 mm, deposition height of 15 mm, chamber volume greater than 657 cm\({}^{3}\), rotation speed of 0.314 rad/s, and aerosol flow rate of 0.3 L/min.