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Hollow Cathode Plasma Sources – a wider operating pressure range than you might think

We 20190422_143455want to correct some recent disinformation in a journal article, the review paper J. Vac. Sci. Technol. A 37 (2019) 030902, on plasma ALD, appears to have mistakenly reported a very narrow operating range for our hollow cathode plasma sources of only 0.3 to 2 Torr. It is unclear what this range was based on as none of the references cited actually provide a pressure range. Apparently it is a simple misconception of the authors, presumably due to their inexperience with hollow cathode plasma sources. However, all our designs have had larger pressure ranges than those given in the review, and in fact there have been some exciting recent advances in our designs that have extended operation down to tens of milliTorr and perhaps even lower.

For clarification, the operating pressure range of our earliest hollow cathode design is provided in Japanese Journal of Applied Physics 51 (2012) 01AF02. The optimum pressure for that cathode – used for CVD work – was 1 Torr, however measurements presented there clearly show an operating range of at least 0.23 to 6.6 Torr for that very early design, though in fact it was probably much broader.

When designing for ALD systems, lower optimum pressure ranges have been required, so from about 2014, our designs have been optimised for operation between 0.3 and 1 Torr, though the full operating range of our barrel design plasma sources – such as our series 50 source, commonly used as an ICP replacement – have  a lower  limit of approximately 100 mTorr and an upper limit of > 5 Torrs. The picture below shows one of these sources at 120 mTorr with nitrogen at 100 watts of RF power.

Our newer designs, based on our large area hollow cathode plasma sources, go to even lower pressures, which we’ve now run to the base pressure of our test systems, to as low as 35 mTorr. A measurement system upgrade will be required to see just how low these sources can go, an example at ~50 mTorr is shown top left.

Check out the Meaglow website at www.meaglow.com or contact us at info@meaglow.com or +1 807 252 4391, for more information on our plasma products.

 

120 mTorr nitrogen 100 watts 0.0005 sec exposure

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New Hollow Cathode Plasma Source Designs Provide Better Quality Films

0.125 sec exposure 278 watt 4130 mTorr

The University of Connecticut group of Dr. Necmi Biyikli, with others, have recently published a paper (J. Vac. Sci. and Technol. A 37 (2019) 020927) where they were able to achieve good quality, highly stoichiometric AlN using hollow cathode plasma assisted atomic layer deposition (HCPA-ALD) with film densities near bulk values. Because of the high radical flux from the source, significantly lower RF power was required to achieve this improvement in material quality compared to past experience, and shorter plasma on cycles could be used at these lower powers (20 seconds at 100 watts compared to 40 seconds at 300 watts).

Similar improvements in silicon nitride deposition were recently achieved by a team at the University of Texas, Dallas, where excellent quality, highly stoichiometric, high density PA-ALD grown material was achieved using one of our hollow cathode plasma sources (see, for instance, IEEE Electron Device Letters 39 (2018) 1195 ).

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Meaglow’s hollow cathode plasma sources are widely used by the ALD Research Community as replacements for inductively coupled plasma (ICP) sources because there is less oxygen contamination when depositing non-oxide materials. However, these recent papers, by the University of Connecticut and the University of Texas, Dallas, illustrate advantages that may be far more important for the industry moving forward. Those being an extremely high radical flux, to the point where the ion signal (ion densities are similar to ICP sources) is swamped by the signal of radicals during optical emission spectroscopy measurements, and relatively low plasma damage (see our company white paper on hollow cathode sources). These result in quicker deposition times with potentially more stoichiometric, better quality material.

The image to right shows the University of Connecticut plasma source with ellipsometer ports and sample entry door. The 4″ diameter source was custom made for use with an Okyay Tech ALD system.

 

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Ammonium Nitrate Sensor/ALD Paper From Oklahoma State University

IMG-3804Congratulations to Prof. Dave McIlroy’s group, at the Physics Department of Oklahoma State University, for their recent publication in ACS Sensors Vol. 3 (2018) pg. 2367. The paper, authored by Lyndon Bastatas, provides some of the first results from the Okyay Tech ALD system recently acquired by that group. The ALD system includes a 4″ diameter Meaglow hollow cathode plasma source that was used to pretreat silica nanowire mat samples prior to the thermal deposition of ZnO in the Okyay Tech system. The ALD steps were part of a process to make a collection of 1D structures for ammonium nitrate sensors.

The picture shows Aaron Austin, one of the Oklahoma team next to the Okyay Tech ALD system with Mealgow plasma source shown at the top. Apparently more papers are on the way, with another 2019 publication already available. Meaglow is pleased to be an enabler of this next generation of research, check our products at www.meaglow.com.

 

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Happy holidays from Meaglow

IMG_2125The Meaglow team wishes everyone a Joyous holiday season! And may 2019 bring you good health, prosperity and happiness.

Meaglow also thanks all our customers for their support. 2018 was our best year so far for plasma source sales, our hollow cathode product lines (see our homepage at www.meaglow.com) continue an upward trajectory, especially within the atomic layer deposition community where our plasma sources are providing some of the highest quality nitride materials grown by that technique. We were particularly pleased to see publications this year by the University of Texas, Dallas group of Prof. Jiyoung Kim which showed exceptional (possibly the best) quality PE-ALD silicon nitride – grown using one of our hollow cathode plasma sources (see our July 16th article). There have also been publications by Berkeley National Laboratories – one of those in Nature Communications – and by others (see publications here).

This year we had our first sales to Germany, Israel, South Korea and the United Kingdom, in addition to sales to Taiwan, Turkey and the United States. Our first orders for 2019 are already in hand, with one of our university customers ordering their fourth and fifth hollow cathode sources for conversion of their new and existing commercial PE-ALD deposition equipment.

Below are a few customer photos of systems converted in 2018 and now operating with Meaglow’s hollow cathode plasma sources. These are now taking advantage of the low oxygen contamination that allows higher quality nitride films using Meaglow’s patented technology (see related company white papers here).

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The University of Liverpool adds a Hollow Cathode Plasma Source

meaglow1Dr. Richard Potter of the University of Liverpool, in the UK, has upgraded his thermal ALD system for deposition with a Meaglow hollow cathode plasma source. This upgrade, which proceeded earlier this year, adds to the ever growing list of equipment that has been converted for use with this enabling technology.

Apart from being relatively inexpensive, the Meaglow plasma source has the advantages of low oxygen contamination and has generally shown higher growth per cycle than other plasma sources. See our website at www.meaglow.com for details, or our recent white paper on hollow cathode plasma sources.

 

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Dr. Potter used one of our very popular and versatile Series 50 plasma sources for this conversion. However, an ultrahigh-vacuum series is also available, as are custom plasma sources. Meaglow is happy to aid our customers. Congratulations to the University of Liverpool, we’re glad we could help with another successful adaptation.

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Meaglow and Okyay Tech Sponsoring Nano-Ontario Conference

At the invitation of Prof. Sean Barry of Carleton University, Meaglow Ltd, together with it’s industry partner Okyay Tech, will be sponsoring part of the 9th Annual Nano-Ontario Conference to be held in Ottawa on 22-23 Nov 2018 on the Carleton campus. We look forward to catching up with as many nano-experts as we can! Look for Dr. Scott Butcher to attend on behalf of Meaglow (pictured below).

Meaglow Ltd. produces a range of innovative hollow cathode plasma sources that have seen strong uptake for plasma enhanced ALD. See our website at www.meaglow.com. A company white paper on our hollow cathode plasma source technology can be found here. Okyay Tech produces low-cost custom ALD systems for the research community, see their website at http://www.okyaytech.com/

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Caltech Convert to Hollow Cathode for Better Quality Nitride Layers

IMG_2164Researchers at the California Institute of Technology (Caltech) have joined a growing number of institutes that have upgraded their plasma assisted ALD system with a hollow cathode plasma source. Meaglow’s plasma sources are well known for improving nitride layers by lowering oxygen content.

One such upgrade enabled low temperature GaN thin film transistors to be deposited at 200 degrees C (see the related Applied Physics Letter). While more recent work has allowed the demonstration of superior silicon nitride layers grown for device purposes (see our earlier article).

Meaglow is committed to enabling the next generation of materials development by providing deposition solutions that meet the stringent requirements of today’s researchers. See our product lines at www.meaglow.com.

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First Hollow Cathode Plasma Source in Israel

IMG_6838Dr Eran Edri of Ben-Gurion University of the Negev has the first Meaglow hollow cathode source in Israel. Eran was formally from Lawrence Berkeley National Laboratories in the US, where he used one of our plasma sources there for the near room temperature ALD of silicon oxide. Several of Eran’s papers are listed on our website at our journal publication page.

Initial tests with the plasma source have gone well. A commercial ALD system was converted to use with the hollow cathode, the second of this particular brand. Meaglow has converted many of the popular ALD brands to use with its sources, including thermal systems. Among other advantages, the Meaglow sources offer lower oxygen contamination for nitride films. See our brochures page here.

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Meaglow Introduces its Hollow Cathode Plasma Sources to Four New Countries

While ALD2018 was going on in Incheon, South Korea, the first Meaglow hollow cathode plasma source in South Korea was being installed at Hanyang University in Ansan.

This is one of a number of firsts for Meaglow this year, we’ve also had our first sale to Israel (to Ben-Gurion University of the Negev), our first sale to Gerrmany (to Otto-von-Guericke University, Magdeburg) and our first sale to the United Kingdom (to the University of Liverpool). All of these sales have been for Meaglow’s popular Series 50 Plasma Source, which is used by many of our customers to upgrade from ICP to hollow cathode plasma operation.

Contact us at info@meaglow.com to learn more about the benefits of Meaglow’s plasma technology.

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UT Dallas Lower Silicon Nitride Leakage Currents with Meaglow Hollow Cathode Plasma Source

In a recent IEEE advance publication, staff at UT Dallas have achieved high density (2.9 g/cubic cm) crystalline silicon nitride for SiN/GaN  devices using hollow cathode plasma enhanced ALD. These films were deposited at 300 degrees C, but have other features akin to silicon nitride grown at much higher temperatures using LPCVD, including a low etch rate in 100:1 HF solution of 0.8 nm/min and excellent electrical device properties.

In a related paper the same UT Dallas group were able to measure low oxygen content for their silicon nitride grown with a Meaglow hollow cathode plasma source, and exceptionally low leakage currents of 1-2 nA/cm square, at 2 MV/cm with a breakdown field of about 12 MV/cm.

Says Dr. Antonio Lucero of UT Dallas, “The Meaglow hollow cathode plasma system has allowed our group to deposit SiN films using a variety of precursors. We consistently obtain excellent film properties and have observed a number of unique characteristics due to the hollow cathode plasma source.

Meaglow’s hollow cathode plasma sources are well known for reducing the oxygen contamination known to occur with other plasma sources (see company white paper). Contact us at info@meaglow.com to talk about upgrading your plasma source to a hollow cathode.

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