Fluid Simulation Of Radio Frequency Inductively Coupled CF₄ And CHF₃ Discharge At Low Pressure

Radio Frequency inductively coupled plasma (RF-ICP) is widely used in the fields of semiconductor fabrication and material surface treatment due to its advantages of easily producing large area, uniform, high plasma at low pressure, its simple equipment and easily adjustable working parameters. In practice, the plasma state is determined by external factors, such as parameters of plasma sources, properties of working gas, and chamber geometry. Because of the high etching rate, the high selectivity and anisotropy etc., fluorocarbon gas has been widely used in micro-electronics fabrication.A two-dimensional fluid model is used to investigate the discharge of CF4 and CHF3 in an ICP chamber respectively aiming to acquire the spatial distribution of the particle density and the electron temperature, further analyze the physical mechanism of the two kinds of gas discharge. Ignoring the interaction process within the study objects, fluid model is used to calculate the CF4 and CHF3 gas due to its fast computing speed, short simulating time. The general rules of CF4 and CHF3 discharge are acquired under certain discharge condition using fluid model. The maximum values of electron density and F- density appear in the center of the discharge chamber in CF4, while in CHF3 the maximum values of electron density and F" density deviate from the discharge chamber. The maximum value of electron temperature appears below the coils in both two gases and the electronegativity of CHF3 is less than CF4.The article also analyzes the variation trend of electron density, F- density and electron temperature with power and pressure in the two gases. It is found that the electron density and electron temperature both increase with power in the two gases, but the change rule of F- s density is different. In the CF4 discharge, the density of F- increases first and then decreases in the center of the chamber with the power. The density of F- always increases with increasing power in CHF3. And in the two gases, the maximum value of the F- deviates from the center of the chamber with increasing power. In the two gases, the electron density increases, and electron temperature decreases with the gas pressure in the two gases. The F- density in CF4 increases with gas pressure, while decreases in CHF3. Since active radicals in fluorocarbon gases play an important role in the etching process of semiconductor fabrication, in the end, we also focus on comparing the change of CF2 and F particles content in the discharge and find that F density is greater than the CF2 density in CF4 gas, while in CHF3 is opposite.