摘要
在现代半导体行业中,低温等离子体常应用于薄膜生长、基片刻蚀和表面改性等。相比于感应耦合等离子体源而言,容性耦合等离子体源的结构简单,更容易形成大口径等离子体,因而被半导体工业广泛应用。最近兴起的双频激发容性耦合等离子体源进一步地拓展了容性耦合等离子体源的功能,其中的甚高频率用来激发产生等离子体,而较低的频率则用来诱导等离子体中的离子轰击基片表面,这一离子通量和离子能量独立可控的特性大大拓宽了容性耦合等离子体的工作窗口,为半导体工业超细线宽的沟槽刻蚀带来了新的希望。
本文中所提及的容性耦合等离子体源是在原有的感应耦合等离子体源基础上改进而来,激发等离子体所用射频频率主要由信号发生器所产生,射频信号经过射频功率放大器的放大后直接传输到射频匹配器,匹配器的功率输出极与功率电极相连,等离子体的激发频率从5MHz到150MHz的范围内连续可调。
利用电压探针、电流探针和Langmuir探针等诊断设备对射频激发等离子体电学参量进行了测量,主要是针对不同频率下射频电压与输入功率的关系,射频电流与Ar气压的关系,以及频率、气压对极板自偏压的影响等进行了研究。
使用60MHz和13.56MHz的双频激发产生容性耦合等离子体,从两者的射频输入功率对彼此自偏压的变化来说明两者之间的耦合。60MHz射频激发产生的容性耦合等离子体的放电特性及电子行为采用电流、电压探针以及朗缪尔探针诊断技术进行了研究。实验结果表明,等离子体的等效电阻或电容随着射频输入功率的增加而减小或增加;等离子体中电子行为不仅依赖于射频输入功率,还与放电气压密切相关;放电气压的增加导致电子能量几率分布函数(EEPF)从双温Maxwellian分布向Druyvesteyn分布转变,而且转变气压远低于文献所报道的数值,这主要是由于在60MHz容性耦合等离子体中电子反弹共振加热效率大为降低所致。
In the modern semiconductor industry, cold plasma is commonly used in thin film deposition, etching and surface modification. In comparison with the inductively coupled plasma, the capacitive coupled plasma has a simple structure, so it is easy to generate large area plasma which is widely used in the semiconductor industry. Recently, capacitive coupled plasma driven by dual-frequency further expands its function, where the higher frequency is used to generate the plasma, while the lower to induce ions from the plasma to bombard the wafer. The independent control of ion flux and energy power greatly broadens the process window of this kind capacitively coupled plasma, and thus takes on a new future for the trench etching with ultra-fine feature size in semiconductor fabrications.
In this thesis, the driving frequency in the concerned capacitively coupled plasma is generated from radio frequency signal generator, the desired radio frequency (RF) signal direct transmits to the RF match after magnified by RF power amplifier, the output of RF power from match box is connected to electrode, the driving frequency is ranged and adjusted continuously from 5MHz to 150MHz.
We use high voltage probe, current probe and Langmuir probe techniques to measure the characteristics of capacitively coupled plasma driven by RF. We mainly focus on the relation of RF voltage vs. RF input power under the different driving frequency, the relation of RF current and Ar pressure and the influences of frequency and pressure on self-bias of the powered electrode.
Frequencies of 60MHz and 13.56MHz are used to drive the capacitively coupled plasmas, the coupling between them are illustrated by the influences of their RF input powers on their self-bias of electrodes. The discharge characteristics driven by 60MHz and its electron behavior are investigated by using current and voltage probes and Langmuir probe diagnostics. The experimental results show that equivalent resistance increases while capacitance decreases with the increasing of input RF power. It is also shown that electron behavior in the plasma is not only related with RF input power but also with discharge pressure closely. Increasing pressure causes a transition of electron energy distribution function from Bi-Maxwellian type to Druyvesteyn type, with its transition pressure much less than that reported by others. This contributes to a great drop in efficiency of electron bounced resonance heating in CCP driven by 60MHz.
引文
1、《90年代物理学等离子体和流体》,[美]等离子体和流体物理学专门小组,霍裕平等译,“科学出版社”。
2、O. A. Popov and V. A. Godyak, J. Appl. Phys. 57(1), 1985
3、O. A. Popov and V. A. Godyak, J. Appl. Phys. 59(5), 1986
4、
, M. A. Lieberman and Allan. J. Lichtenberg
5、《等离子体电子工程学》,[日]菅井秀朗,“科学出版社”。
6、Dai Z L, Xu X, and Wang Y N 2007 Phys. Plasmas. 14 013507
7、G. Gozadinos, M. M. Turner and D. Vender, Phys Rev Lett. 87. 135004 (2001)
8、Boyle P C, Ellingboe A R, and Turner M M 2004 J. Phys. D. 37 697-701
9、Turner M M, and Chabert P 2007 Plasma. Sources. Sci. Technol. 16 364-371
10、Turner M M, and Chabert P 2006 Phys. Rev. Lett. 96 205001
11、Turner M M, and Chabert P 2006 Appl. Phys. Lett. 89 231502
12、Kim H C, Lee J K, and Shon J W 2003 Phys. Plasmas. 10 4545
13、Kim H C, and Lee J K, 2004 Phys. Rev. Lett. 93 085003
14、Boyle P C, Robiche J, and Turner M M, 2004 J. Phys. D. 37 1451
15、Guan Z Q, Dai Z L, and Wang Y N 2005 Phys. Plasmas. 12 123502
16、Godyak V A, and Piejak R B 1997 J. Appl. Phys. 82 5944
17、Godyak V A, and Piejak R B 1990 Phys. Rev. Lett. 65 996
18、Buddemeier U, Kortshagen U, and Pukropski I 1995 Appl. Phys. Lett. 67 191
19、Abdel- Fattah E, and Sugai H 2003 Appl. Phys. Lett. 83 1533
20、You S J, Ahn S K, and Chang H Y 2006 Appl. Phys. Lett. 89 171502
21、Sobolewski M A, 1992 J. Vac. Sci. Technol. A. 10 3550
22、Godyak V A, Piejak R B, Alexandrovich B M 1990 Rev. Sci. Instrum. 61 2401
23、Park G Y, You S J, Iza F, and Lee J K 2007 Phys. Rev. Lett. 98 085003
24、Godyak V A, Piejak R B, Alexandrovich B M 1992 Phys. Rev. Lett. 68 41
25、Godyak V A, Piejak R B, Alexandrovich B M 2002 Plasma Sources Sci. Technol. 11 525
26、Kaganovich I D, Kolobov V I, Tsendin L D 1996 Appl. Phys. Lett. 69 381
27、Igor. Odrobina and Masashi Kando, Plasma Sources Sci, Technol. 5, 1996
28、C. M. Deegan, J. P. Goss, D. Vender and M. B. Hopkins, Appl Phys Lett, Vol. 74,No.14,5, 1999
29、Dai Z L, Xu X, and Wang Y N 2007 Phys. Plasmas. 14 013507
30、Guan Z Q, Dai Z L, and Wang Y N 2005 Phys. Plasmas. 12 123502
31、池凌飞、林揆训、姚若河等2001物理学报50 1313 [Chi L F, Lin K X, Liu J Y, et al 2007 Acta Phys. Sin. 50 1313]
32、牛田野、曹金祥、刘磊等2007物理学报56 2330 [Niu T Y, Cao J X, Liu J Y, et.al 2007 Acta Phys.Sin. 56 2330]
33、Francis F. Chen "Langmuir Probe Diagnostics",Mini-Course on Plasma Diagnostics, IEEE-ICOPS meeting, Jeju, Korea, June 5, 2003
34、赵化侨,《等离子体化学与工艺》,中国科学技术大学出版社,合肥,1993
35、徐学基,诸定昌,《气体放电物理》,复旦大学出版社,上海,1999
36、许根慧,姜恩永,盛京,徐廷献,李振花,《等离子体技术与应用》,化学工业出版社,北京,2006
37、等离子体物理学科发展战略研究课题组,《核聚变与低温等离子体》,科学出版社,北京,2004
38、李定,《等离子体物理学》,高等教育出版社,北京,2006
39、甄汗生,《等离子体加工技术》,清华大学出版社,北京,1990
40、孙恺、辛煜、黄晓江、袁强华、宁兆元,《物理学报》,2008,57(10)