Topic/Type: 1.5 Low-temperature, dusty and nano-plasmas, Oral

Space- and time-varying velocity distribution of electrons in a 2-frequency capacitively coupled plasma for material processing

Toshiaki Makabe, Takashi Yagisawa

Faculty of Science and Technology, Keio University

During the last three decades, modeling of non-equilibrium collisional plasmas driven at radio frequency source has been developed in the region at pressure greater than ~Pa. The collisional plasma has distinct characteristics induced by a quantum property of each of feed gas molecules through collisions with electrons or heavy particles. That is, there exists a proper function caused by chemically active radicals, positive- and negative-ions, and radiations based on a molecular quantum structure through short-range interactions. This differs from high-density, collisionless plasmas controlled by the long-range Coulomb interaction. The quantum property in the form of the collision cross section is the first essential in order to investigate the collisional plasma structure and to predict the function. These structure and function, of course, appear under a self-organized spatiotemporal distribution of electrons and positive ions as a bulk-plasma and ion-sheath. Under these circumstances in real space, the velocity distribution of electrons will exhibit temporally interesting characteristics, essentially differing from Maxwellian form, in a time-varying field in a two-frequency capacitively coupled plasma (CCP).
In the present study, we will discuss space and time characteristics of electrons in phase space (i.e., the density and velocity distribution) in a two-frequency CCP in CF4(5%)/Ar, driven at VHF(100 MHz, amplitude 300 V) and biased at LF(1 MHz and 700 V) at each of parallel electrodes at 50 mTorr [1, 2].

[1]. T.Makabe and Y. Yagisawa, Nonequilibrium radio frequency plasma interacting with a surface, Plasma Sources Sci. Technol. 18, 014016 (2009).
[2]. T. Makabe and Z. Petrovic, Plasma Electronics: Applications in Microelectronic Device Fabrication Taylor and Francis (New York, 2006).