【作者】 袁强华；

【导师】 宁兆元； 辛煜；

【作者基本信息】 苏州大学 ， 凝聚态物理， 2009， 博士

【摘要】 等离子体刻蚀是超大规模集成电路制造工艺中最为关键的工艺流程之一,是实现超大规模集成电路生产中的微细图形高保真地从光刻模板转移到硅片上不可替代的工艺。等离子体反应器和等离子体工艺是十分紧密地联系在一起的。随着集成电路特征尺寸不断地减小,器件线宽越来越窄,集成度越来越高,且膜层越来越薄,对等离子体加工处理及优化过程提出越来越高的要求,需要发展新的能满足特定要求的等离子体源和技术。在这样的背景之下,新型双频驱动的容性耦合等离子体源(双频CCP)被研究,并期望将其用到微电子工业当中。在这种使用两个不同频率电源驱动的双频CCP中,一方面可以通过调节高频电源的功率来控制等离子体密度,进而控制入射到鞘层上的离子通量,另一方面还可以通过调节低频电源的功率,对离子的能量进行控制。目前,对这种双频CCP放电的物理过程和相应的刻蚀机理,仍有很多问题需要研究。本文利用补偿朗缪尔探针诊断技术、光强标定的发射光谱技术和质谱技术,研究了双频CCP中的一些物理特性和对反应基团的调控行为。1、利用补偿朗缪尔探针技术和Druyvesteyn方法对60/13.56 MHz双频CCP氩气放电的研究表明,在约10 mTorr的低气压下,离子的通量和能量的独立调控有可能在60/13.56 MHz双频CCP中实现,即用60 MHz的高频源控制等离子体密度(离子通量),而用13.56 MHz的低频源来控制离子轰击基片的能量。在50 mTorr及更高的气压下,低频功率也对等离子体密度有明显的影响。在实验中我们发现,在50 mTorr及更高的气压下,随着低频功率的增加,电子能量概率分布函数EEPF由类Druyvesteyn分布的形式变为类麦克斯韦分布的形式。同时,电子密度则随低频功率的上升而增加,而电子温度则随低频功率的上升而降低。与数值模拟的结果比较可知,产生这种变化趋势的原因,除了有低频功率本身所导致的电离因素以外,还有二次电子发射导致的电离过程的影响。高低频功率之间耦合的存在,使得这种独立调控难以实现。EEPF随气压的演变表明,在较低的气压下以随机加热为主,在较高的气压下以碰撞加热为主。对射频感应电流的测量表明,在较低的气压下还有等离子体串联共振的加热机制存在。等离子体参数随径向位置的分布则表明,等离子体沿径向位置存在一定程度的不均匀性。2、利用光强标定的发射光谱技术,研究了27/2、60/2及60/13.56 MHz CHF3放电等离子体中,驱动频率及功率对反应基团的调控行为。研究显示,射频频率的选择对等离子体中反应基团的形成有重要影响。在双频CCP中,低频频率对反应基团的调控起着更加重要的作用。在我们的27/2和60/2 MHz放电研究中,改变2 MHz射频功率可以有效地调控CHF3等离子体中的活性基团F的相对密度及F/CF2相对密度之比。而这种对反应基团的调控行为在60/13.56 MHz双频CCP中则不能实现。形成这种现象的原因可能是因为,不同双频CCP中电子能量分布函数有差异,而等离子体中的化学反应过程对电子能量分布函数的变化非常敏感。研究显示,在27/2 MHz和60/2 MHz双频CCP中,可能具有相似的电子能量分布函数,而60/13.56 MHz双频CCP中的电子能量分布函数则有较大差别。3、利用质谱技术对CHF3放电等离子体的反应基团作了研究。质谱研究的结果显示,在射频驱动的CHF3放电等离子体中,存在着丰富的HF基团,而且,随着驱动频率和功率的升高这种基团更为丰富。更多还原

【Abstract】 Plasma etching is becoming an important part of the manufacturing process for ultra-large scale integrated circuits (ULSIs). Plasma processing is the only commercial technology that could make the mask pattern being faithfully transferred into the substrate. Plasma reactors are very important in plasma process. The reduction in ULSI feature size proposes higher and higher requirements on the plasma processing technology. There is a need to develop new type of plasma reactors. Thus, the dual-frequency capacitively coupled plasmas (DF-CCPs) driven with two different frequencies, were studied and hoped to be used in the microelectronic industry.In the DF-CCPs, it is expected that the ions energy is controlled by low frequency component while the ion flux by the high frequency. There are still a lot of problems need to be studied on the DF-CCPs, such as the mechanisms of discharge and etching. Using compensated Langmuir electrostatic probe, actinometrical optical emission spectroscopy and mass spectrometry, we investigated the characteristic and the control of discharge chemistry in DF-CCPs.(1) In Argon DF-CCPs driven with 60/13.56 MHz, the plasma characteristics was investigated using compensated Langmuir electrostatic probe. At the lower pressure (about 10 mTorr), it is possible to control the plasma density and the ion bombardment energy independently. That is, the high frequency (60 MHz) controls the plasma density and hence the ion flux while the low frequency component (13.56 MHz) controls the ions energy. At the pressure of 50 mTorr and higher, this independent control could not be achieved, because the low frequency power also affects the plasma characteristics, such as the electron energy probability functions (EEPFs), electron densities and electron temperatures. As the low-frequency power increases, the EEPF changes from Druyvesteyn-like to Maxwellian-like type at the pressure of 50 mTorr and higher, along with the drop in electron temperature and the rise in electron density. Compared with simulation results, this could be results of enhanced ionization by the low-frequency power and secondary electron emission.It can be seen from the variation of EEPF with the pressure that the stochastic heating is predominant in low pressure while the collision heating is predominant in high pressure. The distribution of plasma parameters showed that it was not uniform in radial position for some extent.(2) The discharge chemistry of CHF3 in 27/2, 60/2, 60/13.56 MHz DF-CCPs is studied with actinometrical optical emission spectroscopy. The effects of frequency and its power on the generation of reactive species were investigated. It is shown that the chosen of frequency is important in generation of reactive species. The reactive radicals and the density ratio of F/CF2 could be controlled by the 2 MHz rf power in 27/2 and 60/2 MHz DF-CCPs. This control could not be obtained in 60/13.56 MHz DF-CCP by adjusting the power of 13.56 MHz. This could be the result of the different EEPFs in different DF-CCPs. A change in EEPF could lead to radical changes in the plasma chemistry. The results show that the EEPFs in 27/2 MHz DF-CCP may be similar with that in 60/2 MHz DF-CCP, whereas may be quite different from that in 60/13.56 MHz DF-CCP.(3) The DF-CCPdischarge chemistry of CHF3 is also studied with mass spectrometry. It was shown that there are abundant HF radicals in CHF3 plasma. Moreover, the HF radicals are even more when the driven frequency and its power are higher.更多还原