Effect of Addition of Nitrogen to a Capacitively Radio-Frequency Hydrogen Discharge

effect of Addition of Nitrogen to a Capacitively

Radio-Frequency Hydrogen Discharge?

ZHANG Lianzhu(张连珠),YAO Fubao(姚福宝),ZHAO Guoming(赵国明),HAO Yingying(郝莹莹),SUN Qian(孙倩)

【摘 要】AbstractA hybrid PIC/MC model is developed in this work for H2-xN2capacitively coupled radio–frequency(CCRF)discharges in which we take into account 43 kinds of collisions reaction processes between charged particlesand ground-state molecules(H2,N2).In addition,the mean energies and densities of electrons and ions,and electric field distributions in the H2-N2CCRF discharge are simulated by this model.Furthermore,the effects of addition of a variable percentage of nitrogen(0-30%)into the H2discharge on the plasma processes and discharge characteristics are studied.It is shown that by increasing the percentage of nitrogen added to the system,the RF sheath thickness will narrow,the sheath electric field will be enhanced,and the mean energy of hydrogen ions impacting the electrodes will be increased.Because the electron impact ionization and dissociative ionization rates increase when N2is added to the system,the electron mean density will increase while the electron mean energy and hydrogen ion density near the electrodes will decrease.This work aims to provide a theoretical basis for experimental studies and technological developments with regard to H2-N2CCRF plasmas.

【期刊名称】等离子体科学和技术（英文版） 【年(卷),期】2014(016)003 【总页数】8

【关键词】Keywords:H2-N2capacitively coupled radio-frequency discharge,H2plasma,PIC/MC simulation

1 Introduction

H2-N2capacitively coupled radio-frequency(CCRF)plasmas are widely used in hydrogenated microcrys-talline silicon film deposition,chemical synthesis of ammonia and nitridation of materials surface.In the synthesis of nitrogen-doped diamond-like carbon(DLC:N),the ratio of added N2to the hydrogen plasma is one of the important factors considered in this technology[1].Recently,H2-N2CCRF plasmas have been used to etch organic low dielectric constant(low-k) films.As the size of ultra-large scale integrated-devices becomes smaller,several interconnection layers can be used to highly integrate the devices.In order to meet the requirement for low capacitance,low-k materials are used as an interconnecting film.At present,there have been many efforts to establish an etching technology for low-k materials using different gas plasmas.Currently,an N2-H2 plasma is considered to be a promising candidate for etching low-k materials because it is nontoxic,easy to process,permits independent control over the partial pressure of each of the constituent gases and because H or N radicals play important

roles[2,3].Study on the characterization and microcosmic process mechanism of H2-N2CCRF plasmas is the basis for understanding the etching process of organic low-k films,for the control of N and H radicals,and for achieving an anisotropic etching pro file for low-k materials.

A variety of applied technologies for H2-N2plasma are required to study the generation and behavior of active particles as well as to understand the microscopic mechanism in the plasma process.In H2-N2plasma research,theoretical simulation has been less extensive than experimental studies[4?6].Gordiets’study group simulated the H2-N2DC glow discharge using a kinetic model and calculated relative densities of particles(N,H,NH3)that changed when the ratio of added H2[7,8]was adjusted.Tatarova et al.theoretically and experimentally studied the dissociation of H2and N2 molecules in H2-N2microwave discharges[6].We have previously studied the effects on electron behavior when H2was added to N2DC glow discharges using Monte Carlo(MC)modeling[9].Although theoretical simulations of RF plasmas have been reported for more than 20 years,these studies didn’t included numerical simulations of an H2-N2mixture gas in a capacitive RF plasma.Therefore,this paper presents an in-depth study to provide a more accurate quantitative description of the microscopic processes in H2-N2CCRF plasmas and the effect of adding N2to an H2discharge on