Some nice Raman and other optical spectroscopy results for GaN films grown at only 200 C with a plasma assisted ALD system converted to use with one of our hollow cathode plasma sources. The results have recently been published in. J. Vac. Sci. Technol. A 37 (2019) 050901 by Nese Gungor and Mustafa Alevli of Marmara University in Turkey. There are some impressively narrow phonon line widths for GaN grown at that temperature. This is the 28th paper we are aware of on ALD using hollow cathode plasma sources, and this paper continues to demonstrate the dominance in the low temperature growth of GaN by the Turkish groups making use of hollow cathode technology.
The main advantage of the hollow cathode plasma sources has been the reduction of oxygen contamination from the source itself. The attached image shows a quartz ICP source etched through over a period of some years by plasma etching. This source of oxygen contamination has been known since at least 1989 and is discussed in our company white paper “Oxygen Contamination in PE-ALD“. However, the hollow cathode sources are also high radical density plasma sources with many other lesser known advantages (see “Hollow Cathode Plasma Sources for Plasma Enhanced ALD and PECVD“).
Meaglow Ltd has sent it’s second Series 50 hollow cathode plasma source to South Korea. A big thanks to our local agents Paultec Co. Ltd. for penetrating into this market, we couldn’t have done it without them. The Series 50 is our most popular source, so it’s been good to see it’s sales into Asia. Most of our plasma sources have gone to the US, but Asia is our second biggest market with multiple sales to Taiwan, Turkey, India, and now, South Korea. There has also been a single sale to Israel.
Says company President, Scott Butcher: “Our biggest customer to date is actually the National Taiwan University, who have five of our plasma sources on site for various ALD systems, though sales to South Korea seem to be picking up. Results for the first plasma source over there have been very good and word is getting around. We hope to see a third sale later in the year“.
Meaglow will be there next week!
Dr K. Scott Butcher (pictured below) will be attending ALD 2019, but to give him a bit of time to go to some of the talks Meaglow will have a literature table. You can catch up with Scott by texting him on +1 807 252 4391 during the conference, or you can email him at email@example.com Scott will be happy to talk about plasmas and hollow cathode sources with you.
One of the potential benefits of Meaglow’s hollow cathode plasma technology is scalability. In a recent news article from June 2019, we mentioned that Meaglow was breaking the old paradigm of high density but small area legacy plasma sources, for which delivery to larger areas dilutes the active plasma species. The question has to be asked, why can’t a high density plasma source be the same size as the substrate? And the answer is, with a hollow cathode source it can.
Meaglow had already developed designs for 4″ and 8″ diameter hollow cathode sources for high radical flux delivery over a similar area during plasma assisted atomic layer deposition. Now those designs have been refined in a 12″ plasma source, the first of which has now been shipped to a customer in the semiconductor deposition equipment market. The cathode, shown above before cleaning, was all aluminum for compatibility with silicon processing. The current design has been tested for operation over a pressure range from 80 mTorr to 8 Torr, though other pressure ranges can be achieved through custom design, and lower pressure operation with this current source may also be possible.
Shown below, left, is the plasma source in our test chamber with nitrogen at only 100 watts of RF power, though the source is designed for operation up to 3 kilowatts. On the right is the plasma source itself.
Inductively coupled plasma (ICP) sources were developed for use in the semiconductor industry decades ago, at a time when mainly silicon oxide and silicon nitride were being deposited by plasma sources. Today new materials have more exacting demands, especially for plasma assisted atomic layer deposition. The older sources have problems with oxygen contamination from sputtered dielectric windows (typically quartz or alumina). However, apart from that, the idea of using a high density power source generated in a small area tube and then diluting the activated species over a larger deposition area may be an idea that’s had its day. Small area sources are used so that back flow of metalorganic into the dielectric tube is minimised, since such deposition can block RF transmission to the plasma gas, and potentially cause damage to the dielectric liner.
Enter the hollow cathode plasma source, free of oxygen contamination problems (see our company white paper on this issue) and able to cope with both metallic and insulating deposition on the cathode. Now a high density plasma source can be made to the same dimensions as a substrate – there is no need to dilute the plasma species over a larger area. The plasma source can also be brought closer in. The OkyayTech P100 (shown above) utilizes Meaglow’s large area high density hollow cathode source. Below is a useful table showing some results from the University of Connecticut group of Dr. Necmi Biyikli (pictured above). These demonstrate the advantage of breaking away from the old ICP plasma delivery paradigm.
Check out the Meaglow website at www.meaglow.com or contact us at firstname.lastname@example.org or +1 807 252 4391, for more information on our plasma products. Meaglow and OkyayTech collaborate to build ALD tools with new generation plasma sources. You can check out the OkyayTech website at www.okyaytech.com or contact them at email@example.com or +1 818 318 9616, for more information on their ALD and ALE tools.
We want 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 firstname.lastname@example.org or +1 807 252 4391, for more information on our plasma products.
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 ).
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.
Congratulations 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.
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).