Dielectric substrate self-bias and plasma confinement in two-dimensional scanning radio frequency plasma-enhanced chemical vapour deposition
Introduction
Conventional large area plasma-enhanced chemical vapour deposition (PECVD) or reactive eching requires extensive and costly optimization of systems and processes in order to obtain a “uniform” effect. As required substrates become larger or a variety of dimensions of substrates are required, this approach becomes less feasible for both technical and cost reasons. Some difficulties in the large area plasmas were studied recently [1], [2], for example, non-uniform distribution of radio frequency (RF) current along the edges of electrodes can result in non-uniform plasma potential and power dissipation, and when plasma or substrate dimensions become very large compared to the wavelength standing waves can occur generating non-uniform plasmas. A desired profile often relies on many parameters including gas flow distribution, pressure, plasma power, and impedance matching, which depend on the dimensions and properties of the substrates.
Alternative approach for large area PECVD or reactive plasma was proposed by performing two-dimensional scanning over large substrates with a small reactive plasma source and a small biasing electrode. It showed that uniform and controlled “non-uniform” thickness profiles could be achieved [3]. However, It is known that parasitic discharge resulted from the small RF plasma sources can be significant. Parasitic plasma is undesirable in the scanning plasma system as it results in difficulties in controlling both thickness profiles and film properties. In the two-dimensional scanning system [3], the parasitic plasma mainly resulted from the biasing electrode at the backside of substrates. In this paper, we report our development of eliminating the parasitic plasmas and controlling self-bias on dielectric substrates using different electrode configurations.
Section snippets
Experimental details
The RF scanning plasma source consisted of a showerhead-type planar electrode and its counterpart biasing electrode at the backside of substrate, which both were connected to (13.56 MHz) RF source via a matching network and phase shift controller. The schematic diagram of the 2-dimensional scanning system is shown in Fig. 1. The diameter of the plasma source was 40 mm. The confinement of plasma was achieved using a grounded guardhouse for the electrode 1. The guardhouse and the electrode formed a
Results and discussion
Self-bias in RF plasma is developed on dielectric substrates to increase with RF power at the biasing electrode. Fig. 3 shows the dependence of self-bias on RF power of the biasing electrode for different electrode configurations. Gas pressure in this experiment was 30 Pa, and electrode 1 was not RF powered. In Fig. 3(a) for case A, it shows that the self-bias increased with increase of the biasing electrode RF power on both the biasing electrode (Ve) and the surface of the dielectric substrate (
Conclusions
A two-dimensional scanning RF plasma-enhanced chemical vapour deposition method was developed for large area deposition using a small and localized plasma source, which has advantages in precision control of plasma and uniformity of both thickness and microstructure, and in simplicity of system design. By introducing guarded electrode housing to form localized plasma, parasitic plasma or deposition was essentially eliminated. Self-bias on the dielectric substrate was studied for different
Acknowledgement
This work was supported by His Royal Highness Prince Nawaf bin Adul Aziz of the Kingdom of Saudi Arabia through the Science Foundation for Physics within the University of Sydney and USSS Pvt. Ltd.
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