Effect Of Gas Pressure On Discharge Characteristics In Low Pressure Radio Frequency Discharge

Due to the advancement of industry and improvement of living standards,people's demand for material diversity in their work life is increasing day by day.In order to meet various requirements such as wear resistance,heat resistance,high temperature,and high hardness,it is necessary to continuously develop various kinds of requirements that meet people's needs.The new materials,taking into account the cost and various aspects of people try to surface treatment on the general material to improve its application performance,avoid corrosion and wear and other common problems,greatly improve the material's use time.The material surface modification technology is a hot spot in the current material research.It can form an alloy layer on the surface of some common metal substrate materials instead of the expensive alloy material,which obviously reduces the cost used in the production.Plasma surface modification has become an important research direction in the field of scientific research because of its superior performance and low cost.It is widely used in the field of surface modification of metallic materials and semiconductor materials.The surface modification of materials mainly adopts low temperature plasma surface modification technology.Low-pressure radio-frequency glow discharges easily generate plasma and consume less energy.Therefore,many materials surface modification uses low-pressure RF glow discharge technology.In this gas discharge,the gas pressure has a crucial influence on the discharge characteristics.The system deeply studies the influence of gas pressure on the discharge characteristics and plays an important role in improving its application efficiency.Numerical simulation of the discharge characteristics of this gas discharge is a convenient and effective way.Based on plasma fluid theory and drift diffusion approximation,a one-dimensional fluid model was established for the plasma generated by low-pressure RF glow discharge.For the established model,the staggered uniform grids are adopted in space and the implicit finite difference scheme is adopted in time,which makes the initial value of the differential equations of the model become an algebraic equations.The corresponding equations are solved numerically and the corresponding numerical results are obtained.By analyzing the numerical results obtained,the influence of gas pressure on the discharge characteristics was studied.This article is divided into two parts to study the effect of gas pressure on the discharge characteristics in low pressure RF discharge.On the one hand,when the discharge reaches a steady state,the influence of gas pressure on the spatial distribution of physical quantities,such as ion density,electron density,electron temperature,potential,and electric field,is periodically averaged.The results show that in the plasma region,as the gas pressure increases from 0.1 Torr to 0.4 Torr,the ion density and electron density also increase,and the ion density and electron density are almost equal;in the sheath region,the ion density is greater than the electron density.In the entire discharge area,as the gas pressure increases from 0.1 Torr to 0.4 Torr,the electron temperature decreases,and the potential increases as the gas pressure increases.The electron temperature in the sheath region is higher than the electron temperature in the plasma region.On the other hand,the influence of gas pressure on the evolution of discharge was studied.In the study,one point was taken in each of the driving sheath region,the grounding sheath region,and the plasma region,and the physical density of the ion density,electron density,electron temperature,potential,and electric field at these three points were respectively given at the gas pressure.The numerical results evolved over time at 0.1?0.2?0.3 and 0.4 Torr.The effects of gas pressure on the evolution of discharge are analyzed and discussed in detail.The results show that the discharge process can be divided into three phases: In the first phase,the plasma density is small,but the growth rate is relatively fast and is called the rapid growth phase;in the second phase,the plasma density is larger but the growth rate is higher.Slower,it is called slow growth phase;in the third phase,plasma density oscillates within a certain fixed range and is called steady state phase.As the gas pressure increases from 0.1 Torr to 0.4 Torr,the rapid growth phase becomes longer.The time to reach the steady state stage of discharge becomes longer.In addition,in the driving sheath and the ground sheath,the plasma density oscillates.The frequency of the oscillation is the same as the frequency of the driving power.The oscillation amplitude increases with the gas pressure;the oscillation amplitude of the electron density is greater than the oscillation amplitude of the ion density.Big.At the center of the discharge region,the plasma density gradually increases during the discharge to finally reach a steady state with no oscillation.In the fast-growth phase and the steady-state phase,the characteristics of physical properties such as plasma density,electron temperature,and electrical potential,which evolved over time in different regions and pressures were analyzed.