**1. Introduction**

A large-scale integrated circuit (LSI), various sensors, and other semiconductor devices are essential for various electrical and electronic devices and automobile [1, 2]. In general, these devices are fabricated by plasma-processing techniques such as dry etching and plasma deposition using low-pressure plasma. The plasma processing is the most usually utilized chemical and physical processes in microelectronics fabrication for functional thin film preparation and dry etching of silicon-based films.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

In the dry-etching processing, the silicon wafer patterned by the photoresist mask for LSI is exposed in plasma containing halogen molecules (e.g., CF<sup>4</sup> , CHF<sup>3</sup> , SF<sup>6</sup> ) [3–7]. In the case of these gases, the fluorine atoms dissociated by an electron impact collision with the molecules react with the silicon surface to generate a volatile etch product like SiF<sup>4</sup> so that the silicon wafer is etched with assistance of energetic ions produced in the plasma. For example, a high-density plasma sources have been developed to challenge patterning features less than 0.25 μm with high aspect ratios [8].

lost to the electrodes. *ε*<sup>c</sup>

, can be determined from Eq. (1)

When only thermal electrons are lost to the boundary surfaces [18], *ε*<sup>e</sup>

*ne* <sup>=</sup> *<sup>P</sup> \_\_*\_\_\_\_\_\_\_\_\_ *ab*

**capacitively coupled plasma production**

that of conventional metal electrodes such as aluminum [21].

a working gas, Ne or Ar gas was introduced in the vessel at 133 Pa.

plasma density, *n*<sup>e</sup>

increases, while *ε*<sup>i</sup>

less than 1010 cm−3.

denotes the collisional energy loss per electron-ion pair created. The

Physics of High-Density Radio Frequency Capacitively Coupled Plasma with Various Electrodes…

regularly decreases with increasing gas pressure, because the sheath is

. (2)

http://dx.doi.org/10.5772/intechopen.78387

will be negligible.

211

*ene S*(*ε<sup>e</sup>* + *ε<sup>i</sup>* + *εc*)

In general, the electron temperature decreases with increasing gas pressure [17]. Then, *ε*<sup>c</sup>

more collisional. For a fixed absorbed power, the increase in the plasma density is resulted with increasing gas pressure. Even for a relatively high-gas pressure of 50 Pa used in RF PECVD, however, the plasma density at a conventional driving frequency of 13.56 MHz is

In order to increase the plasma density at the typical frequency of 13.56 MHz, ingenious

In general, plasma is generated by electrons with an energy higher than an ionization potential of target neutral gas [19]. According to the ionization cross section [20] for noble gases of He, Ne, Ar, and Xe, their ionization energy ranges from 10 to 30 eV, while the energy is a few 100 electron volts when the ionization cross section becomes maximum. These electrons are effectively possible to ionize neutral gases through inelastic collisions. Then, it is expected to produce high-density plasma. In CCP discharge, it is also easy to generate a high voltage of a few hundred volts between the powered and grounded electrodes, that is, CCP can generate secondary electron emission (SEE) from the powered electrode. It was reported that magnesium oxide (MgO) electrodes have a high SEE coefficient which are a few 10 times higher than

In this section, the effect of SEE as the acceleration mechanism of electrons is proposed to solve the serious problem of CCP density. The RF breakdown voltage and plasma density are studied experimentally. As show in **Figure 1(a)**, an RF power of 13.56 MHz was supplied to generate CCP between two electrodes of 20-mm diameter with a gap *d*gap of 10 mm, which were mounted into the center of a cylindrical vessel of 160-mm diameter and 200-mm length. The back of the RF electrode is covered by a grounded metal enclosure to avoid additional discharge between the RF electrode and the grounded vessel. An MgO disk of 20-mm diameter and 2-mm thickness was connected to the Al metal electrode, as shown in **Figure 1(b)**. As

**Figure 2** shows RF breakdown voltage *V*Brf characteristics. *V*Brf is expressed as a peak-to-peak value measured by a high voltage probe and a digital oscilloscope. *V*Brf characteristics exhibit a roughly U-shaped distribution like Paschen's curve of Townsend discharge [22] for both Ne

device is required. In the next section, the various ingenuities will be introduced.

**3. Effect of high secondary electron emission oxide on high-density** 

The plasma deposition has a sputtering deposition and a plasma-enhanced chemical vapor deposition (PECVD) method. The sputtering deposition is to impinge ions to the material target biased by a negative potential so as to sputter atoms from the target. The functional thin films such as transparent conductive oxide used in tableted computer and smartphone are deposited by sputtering method [9]. The sputtering depositions are prepared by DC magnetron and radio frequency (RF) magnetron plasma sources [10]. Various typed sputtering sources have been developed for the synthesis of high-quality thin films [10]. Especially, RF magnetron plasma source has an advantage that the insulated films can be deposited on the various substrates compared with DC magnetron plasma source. The PECVD is to dissociate molecule by electron impact so as to deposit radicals [8].

In these plasma-processing techniques, capacitively coupled plasma (CCP) with parallel plates was widely utilized. The physics of CCP has been studied by many researchers [11–16]. The sustaining mechanism of CCP is the electron heating process that the oscillating radio frequency sheath near the powered electrode plays an important role in electron acceleration as well as the collisional heating in the presence of electric fields and the emission process of secondary electrons from the electrode [11–16]. However, the electron heating process cannot produce high-density plasma.

The requirement of these semiconductor devices with high-speed operation and high performance is increasing annually. In order to perform the demand, high-speed plasma processing, that is, a high-density plasma production, is important. However, CCP does not attain high-density plasma. Thus, the high-density CCP is required. In this chapter, the production principle of conventional CCP and the special CCP with various electrodes and magnets is reviewed.
