Control of radial density profile of nano-particles produced in reactive plasma by amplitude modulation of radio frequency discharge voltage
Introduction
Nano-particle technology, which can be regarded as the extension of the conventional fine particle and powder technology, is one of the core nano-technologies. This technology plays a vital role in the application of nano-technology in numerous industrial and engineering areas such as ultra-large-scale integrations [1], [2], [3], solar cells [4], [5], thin film transistor [6], hydrogen storage [7], and so on [8]. The highlight of this technology is the unique properties of nano-particles, which differ greatly from those of the bulk materials. One of the important applications of nano-particles is nano-particle composite film, properties of which can be improved significantly by incorporating nano-particles in the films. Such nano-particle composite films can be deposited using nano-particles formed in reactive plasmas [9], [10], [11]. Realization of large-area uniform density profile of nano-particles in reactive plasmas has been one of the concerns in nano-particle composite films [12]. Recently, we have developed a two-dimensional laser-light scattering (2DLLS) method to obtain information about the growth of nano-particles [13], [14], [15]. By applying the 2DLLS method, we obtain information about uniformity of density of nano-particles. Here we report uniformity control of density profile of nano-particles by amplitude modulation (AM) of radio frequency (rf) discharge voltage.
Section snippets
Experimental setup
Experiments were performed using a capacitively-coupled rf discharge reactor with a 2DLLS system as shown in Fig. 1 [15]. A powered disc electrode of 60 mm in diameter and 1 mm in thickness was set 20 mm below an upper grounded electrode of 60 mm in diameter. Gas of Si(CH3)2(OCH3)2 (dimethyldimethoxysilane: DM-DMOS) of 0.2 sccm in flow rate diluted with Ar of 40 sccm in flow rate was supplied to the reactor. The total gas pressure in reactor was 133 Pa. To generate nano-particles, we sustained a
Results and discussion
Plasma fluctuations can be synchronized with the AM of rf discharge voltage [15]. Fig. 4 shows that AM level dependence on LLS intensities at t = 8 s at plasma/sheath boundary region near the upper grounded electrode. The increase of LLS intensity without AM is faster than that with AM. The LLS intensity decreases by 60% with increasing the AM level up to 30%. This result shows AM of rf discharge voltage suppresses the growth of nano-particles.
When scatters (nano-particles) are much smaller than
Conclusions
Investigation of uniformity of nano-particle density plasma was studied in reactive CVD plasmas with AM method. The growth of nano-particles during rf discharge decelerates as AM level increases. The LLS intensity at t = 8 s decreases by 60% with the AM level of 30%. The uniformity of nano-particle density improves with increasing the AM level up to 30%. The densities at the center and that at the edge of electrode increase by 3 and 24 times as AM level increases from 0 to 30%. Radial
Acknowledgment
This work was partially supported by a Grant-in-Aid for Scientific Research on Innovative Areas (no. 2109) of MEXT, Japan.
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