Phase shift effects of radio-frequency bias on ion energy distribution in continuous wave and pulse modulated inductively coupled plasmas

A retarding field energy analyzer(RFEA) is used to measure the time-averaged ion energy distributions(IEDs) on the substrate in both continuous wave(CW) and synchronous pulse modulated radio-frequency(RF) inductively coupled Ar plasmas(ICPs).The effects of the phase shift θ between the RF bias voltage and the RF source on the IED is investigated under various discharge conditions.It is found that as θ increases from 0 to π,the IED moves towards the low-energy side,and its energy width becomes narrower.In order to figure out the physical mechanism,the voltage waveforms on the substrate are also measured.The results show that as θ increases from 0 to π,the amplitude of the voltage waveform decreases and,meanwhile,the average sheath potential decreases as well.Specifically,the potential drop in the sheath on the substrate exhibits a maximum value at the same phase(i.e.,θ = 0) and a minimum value at the opposite phase(i.e.,θ = π).Therefore,when ions traverse across the sheath region above the substrate,they obtain less energies at lower sheath potential drop,leading to lower ion energy.Besides,as θ increases from π to 2π,the IEDs and their energy widths change reversely.     

近代物理实验系列化教学模式探索

近代物理实验对培养学生动手能力和创新能力具有重要作用。如何才能更好地发挥近代物理实验课的作用,是值得从事该课程教学的教师深入思考的问题。本文针对系列化实验内容的设计,以及教学内容、教学方法和预习及考核机制进行改革探讨。在近代物理实验的教学中实施系列化实验教学模式,收到了较好的教学效果。     

双频容性耦合等离子体密度径向均匀性研究

利用自主研制的全悬浮双探针, 对影响双频容性耦合等离子体径向均匀性的因素进行了研究. 发现低频功率、放电气压和放电间距对径向均匀性有明显影响. 合适的低频功率、放电气压及较大的极板间距可以得到更均匀的等离子体. 采用与实验相同的放电参数, 利用改进的二维流体模型进行理论模拟, 得到了不同极板间距下径向离子密度分布, 并和实验测量结果进行了比较, 两者的变化趋势基本符合. 关键词： 双频容性耦合等离子体 径向均匀性 全悬浮双探针 二维流体模型     

加快成果交流为促进中国化学学科的发展与应用而拼博——办好学术期刊庆祝中国化学会成立六十周年

在全党和全国人民努力贯彻小平同志南巡讲话精神,加快改革开放步伐、集中精力把经济建设搞上去的热潮中,迎来了中国化学会成立六十周年。1982年9月中国化学会曾在其诞生地——南京举行了隆重的国际学术活动庆祝它的五十诞辰,至今已整10年了。10年来     

Fundamental study towards a better understanding of low pressure radio-frequency plasmas for industrial applications

Two classic radio-frequency (RF) plasmas, i.e., the capacitively and the inductively coupled plasmas (CCP and ICP), are widely employed in material processing, e.g., etching and thin film deposition, etc. Since RF plasmas are usually operated in particular circumstances, e.g., low pressures (mTorr-Torr), high-frequency electric field (13.56 MHz-200 MHz), reactive feedstock gases, diverse reactor configurations, etc., a variety of physical phenomena, e.g., electron resonance heating, discharge mode transitions, striated structures, standing wave effects, etc., arise. These physical effects could significantly influence plasma-based material processing. Therefore, understanding the fundamental processes of RF plasma is not only of fundamental interest, but also of practical significance for the improvement of the performance of the plasma sources. In this article, we review the major progresses that have been achieved in the fundamental study on the RF plasmas, and the topics include 1) electron heating mechanism, 2) plasma operation mode, 3) pulse modulated plasma, and 4) electromagnetic effects. These topics cover the typical issues in RF plasma field, ranging from fundamental to application.     

双频容性耦合等离子体相分辨发射光谱诊断

采用相分辨发射光谱法, 对双频容性耦合纯Ar和不同含O₂量的Ar-O₂混合气体放电等离子体的鞘层激发模式进行了探究. 在射频耦合电源上极板的鞘层区域处观察到两种电子激发模式: 鞘层扩张引起的电子碰撞激发模式和二次电子引起的电子碰撞激发模式; 并发现这两种激发模式均受到低频射频电源周期的调制. 在纯Ar放电等离子体中, 两种激发模式的激发轮廓相似; 而在Ar-O₂混合气放电等离子体中, 随着含O₂量的增加, 二次电子的激发轮廓变弱. 此外, 利用相分辨发射光谱法对不同含O₂量的Ar-O₂混合气放电下Ar的 750.4 nm谱线的平均低频电源周期轴向分布进行了研究, 得到了距耦合电源上极板约3.8 mm处为双频容性耦合射频等离子体的鞘层边界. 关键词： 双频容性耦合等离子体 等离子体鞘层 发射光谱     

Measurement of electronegativity during the E to H mode transition in a radio frequency inductively coupled Ar/O_2 plasma

This paper presents the evolution of the electronegativity with the applied power during the E to H mode transition in a radio frequency(rf)inductively coupled plasma(ICP)in a mixture of Ar and O2.The densities of the negative ion and the electron,as well as their ratio,i.e.,the electronegativity,are measured as a function of the applied power by laser photo-detachment combined with a microwave resonance probe,under different pressures and O2 contents.Meanwhile,the optical emission intensities at Ar 750.4 nm and O 844.6 nm are monitored via a spectrograph.It was found that by increasing the applied power,the electron density and the optical emission intensity show a similar trench,i.e.,they increase abruptly at a threshold power,suggesting that the E to H mode transition occurs.With the increase of the pressure,the negative ion density presents opposite trends in the E-mode and the H-mode,which is related to the difference of the electron density and energy for the two modes.The emission intensities of Ar 750.4 nm and O 844.6 nm monotonously decrease with increasing the pressure or the O2 content,indicating that the density of high-energy electrons,which can excite atoms,is monotonically decreased.This leads to an increase of the negative ion density in the H-mode with increasing the pressure.Besides,as the applied power is increased,the electronegativity shows an abrupt drop during the E-to H-mode transition.     

Measurements of argon metastable density using the tunable diode laser absorption spectroscopy in Ar and Ar/O_2

Densities of Ar metastable states 1s_5 and 1s_3 are measured by using the tunable diode laser absorption spectroscopy(TDLAS) in Ar and Ar/O2 mixture dual-frequency capacitively coupled plasma(DF-CCP). We investigate the effects of high-frequency(HF, 60 MHz) power, low-frequency(LF, 2 MHz) power, and working pressure on the density of Ar metastable states for three different gas components(0%, 5%, and 10% oxygen mixed in argon). The dependence of Ar metastable state density on the oxygen content is also studied at different working pressures. It is found that densities of Ar metastable states in discharges with different gas components exhibit different behaviors as HF power increases. With the increase of HF power, the metastable density increases rapidly at the initial stage, and then tends to be saturated at a higher HF power. With a small fraction(5% or 10%) of oxygen added in argon plasma, a similar change of the Ar metastable density with HF power can be observed, but the metastable density is saturated at a higher HF power than in the pure argon discharge. In the DF-CCP, the metastable density is found to be higher than in a single frequency discharge, and has weak dependence on LF power. As working pressure increases, the metastable state density first increases and then decreases,and the pressure value, at which the density maximum occurs, decreases with oxygen content increasing. Besides, adding a small fraction of oxygen into argon plasma will significantly dwindle the metastable state density as a result of quenching loss by oxygen molecules.     

教育家、科学家和科教事业领导之集大成者——唐敖庆

唐敖庆的一生同时集教书育人、科学研究和行政领导于一身,创造了3个方面都达到很高水平的“三肩挑”奇迹。在他光辉的一生中,始终以党、国家和人民的需要为己任,以严谨、求实、创新的科学态度,发扬甘当人梯和铺路石的精神,顽强地拼搏在我国科教战线上。他殚精竭虑,毕生无私奉献,为吉林大学创建了化学学科,并使其展翅腾飞进入国内前列,世界闻名;为新中国创建了理论化学学科,培养出一大批被国际同行誉为“中国学派”的从事理论化学研究的高级人才队伍,其中有12人当选为中国科学院或工程院院士;做出多项高水平的科研成果,荣获国家自然科学奖一等奖2次及二等奖2次,使我国的理论化学在国际前沿占有一席之地。他出任吉林大学校长,率先提出高等学校要办成“两个中心”,即教育中心和科研中心的办学思想并率先垂范、亲自实践,使吉林大学的办学水平迅速跻身于世界一流大学的行列。唐敖庆是我国学识渊博、业绩卓著、德厚流光、闻名遐迩的教育家、科学家和科教事业的组织领导者。我们后辈应牢记他的谆谆教导,继承他的遗志,为我国的科教事业赶超世界先进水平努力奋斗,为中华民族的伟大复兴贡献力量。