- High brightness plasma ion source have been researched to be utilized in focused ion beam.
In focused ion beam (FIB) system, ion beam generated from ion source is accelerated up to 30 keV and focused in a few nanometer in diameter simultaneously. For many years, FIB system with high resolution has been a critical tool for nanofabrication in semiconductor industry. FIB is used in TEM specimen preparation, nano-machining, nano-measurement, nano-lithography, and so on.
In the performance of a FIB system, ion source plays an essential role because both achievable productivity and resolution of FIB system are determined by current density and emittance of the ion source respectively. Commercial FIB devices utilize a liquid ion metal source using Ga ion in favor of its high brightness (ability to deliver and focus a large current ion beam onto a small area at a small divergent angle) even though it has various drawbacks such as Ga-contaminations. For the research, there are numerous requirements to develop high brightness plasma ion source operating with various gases.
Plasma ion sources have larger emittance (lower brightness) due to a relatively large virtual diameter compared to the LMIS. While this feature is inherent in plasma ion source, reducing the size of extraction aperture is still considered as the most suitable method to overcome the high emittance of plasma ion source. However, as the diameter of aperture is getting smaller, the electric field for ion extraction is more difficult to penetrate into the extraction hole.
A novel high-brightness plasma ion source is developed by generating additional localized plasma with an extra electrode biased positively. The plasmas localized near the biased electrode provide high density ions to be extracted even through the micro-sized aperture.
- Negative hydrogen ion source for accelerator and fusion research is under development.
A transformer coupled plasma negative hydrogen ion source with an external rf antenna has been developed at SNU, which is capable of continuous operation with long lifetime. Using 13.56MHz RF wave, 1.6mA of H- beam has been extracted and accelerated up to ~20keV. H- ion source can be utilized for the ion injection into high energy particle accelerators (Storage rings, synchrotrons, tandems, cyclotrons, including RIB and AMS facilities), neutral beam heating of thermonuclear experimental devices (tokomaks, mirrors, stellarators) and low-energy accelerators (organic mass spectroscopy, ion implantation and etc).
TCP H- ion source in SNU uses external planar RF antenna installed at the opposite side of the extraction system, which is isolated by a quartz window. Since the antenna is located external to the plasma, it is immune to damage from the energetic particles in plasma. Therefore the TCP negative ion source is capable of continuous operation with long lifetime.
The enhancement of H- ion production is observed when Tantalum or Molybdenum plasma electrode was used at the bias voltage lower than the plasma electrode. To optimize the extration of H- ion which require higher bias potential than plasma potential and the enhancement of H- production related with electrode surface which require lower electrode bias potential simultaneously, additional electrode called secondary electrode has been introduced. Currently TCP negative ion source is under optimization using secondary electrode.
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