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Semiconductor chemistry comes to the fore

18 September 2008 | By Dr Mike Cooke | News > Materials and Gases

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Periodic Table Sigma-Aldrich Fine Chemicals (SAFC), recently gathered technology journalists from across Europe in Lyon, France, to report on its commercial progress. Among the pharmaceutical and bioscience reporters, there was a solitary semiconductor press representative, Dr Mike Cooke.

As the semiconductor industry increasingly comes to grips with changing device structures and compositions, the problems of chemical supply and cost come to the fore where before the focus was on engineering. Some of the increasing numbers of chemical elements coming into play in semiconductor devices are extremely rare, hence expensive.

chemical elements


Figure 1. The expanding use of chemical elements in semiconductor production based on [T.N. Theis, “Performance Improvement No Longer Possible by Scaling Alone,” SEMI Strategic Materials Conference, 2006.]

Further, these chemical recipes and designs are expected to have a shorter useful life in terms of application with less time to recoup moneys spent in research and development.

While some chemical companies are standing back from the problems of supplying such a complex market, Sigma-Aldrich’s Fine Chemicals (SAFC) business unit sees an opportunity to move out from its previous core activities in the pharmaceutical and bioscience sectors.

SAFC’s Hitech division was augmented last year by the $60 million acquisition of Epichem based in the United Kingdom. A ‘new’ SAFC Hitech was duly launched at Semicon West a few months later. Epichem specialized in supplying precursor materials (often consisting of organic combinations with metal atoms) for deposition of the complex heterostructures of the compound semiconductor industry and silane for photovoltaic production. Such complex chemical design capabilities are increasingly demanded for mainstream silicon semiconductor development and production. Hitech also sells a range of hardware devices for delivery of liquid and vapor precursors and monitoring of deposition processes.

SAFC Hitech’s EpiSensor metal-organic precursor level sensing device.

In 2007, SAFC Hitech made sales of more than $70 million while the whole SAFC business unit, consisting in addition of three other divisions (Pharma, Supply Solutions and Biosciences), brought in $591 million out of Sigma Aldrich’s $2.039 billion total. SAFC sales growth for 2007 over 2006 is 19.1%, but currency (4.4%) and Epichem acquisition (7.6%) adjustments reduce this to 7.1%. First and second quarter sales of $153.2 million (+18.8%, +11.7% adjusted) and $165.5 million (+14.6%, +8.1% adjusted), respectively, continue the growth trend. These figures suggest the Epichem acquisition makes up more than half of Hitech’s sales.

Geoff Irvine, director of commercial development and marketing at Hitech, comments that his division is ‘constantly on the scout for potential acquistions’ along with continuing investment in expanding manufacturing and services. Hitech will clearly be an important contributor to achieving Sigma-Aldrich’s objective of 25% of total revenue in CAPLA (Canada, Asia-Pacific, Latin America) markets by 2010.

Application sectors

Hitech is focusing on three sectors: next-generation silicon emerging materials with R&D/educational collaborations and joint development projects; strengthened service and support for compound semiconductor production; and, optoelectronics applications such as photovoltaics, organic light emission and sensors.

For the silicon semiconductor sector, Hitech has a precursor roadmap to meet the coming needs of the industry (Figure 3). In the immediate future, more DRAM manufacturers will be seeking to apply high-k capacitors for higher density memory in high volume processes. Irvine also sees high-k precursor materials being explored for application in Flash memory. Future Flash control and floating gates in silicon/oxide/nitride/oxide/silicon (SONOS), tantalum-nitride/aluminum-oxide/nitride/oxide/silicon (TANOS) and other formations could need Al2O3, HfOx and HfSiOx. Hitech is exploring advanced precursors for low-carbon Al2O3, Hf, Zr, Si and TaN with Flash memory producing customers.
And, of course, high-k gate insulation with metal gates is on the International Technology Roadmap (ITRS) for high-performance logic in 2010 and is being applied by Intel in its 45nm process.

Figure 3. SAFC Hitech’s roadmap for precursor development

Figure 3. SAFC Hitech’s roadmap for precursor development 

Hitech has recently completed extensive research and development for metal precursors for GST (GexSbyTez) aimed at development of phase-change memory (PCM) devices. The company collaborated on the EU CHEMAPH project designed to find better ways to deposit GST. Deposition tool companies Aixtron and Genus were also involved in CHEMAPH. One problem that had to be overcome for a vapor phase deposition/MOCVD solution was that the source materials tend to decompose (crack) into the deposited materials and reaction products at different rates.

“After extensive work to synthesize a number of different chemicals and characterize their physical properties, a combination of sources was found with a much improved match of thermal stability to allow decomposition to the same degree when simultaneously introduced to the deposition reactor chamber,” comments SAFC Hitech Chief Technology Officer, Ravi Kanjolia.

A combination of sources has now been found with an improved match of thermal stability allowing simultaneous introduction of materials into the deposition reactor chamber. Synthesis protocols have been developed for isolation of high purity product in small- and large-scale laboratory equipment. These materials – Ge(NMe2)4, Sb(NMe2)3 and iPr2Te (Me = methyl group CH3–; iPr = isopropyl group (CH3)2CH–) – are now available for customer sampling and analysis.
 
“Until now, PCM materials have generally been deposited by sputtering or other physical vapor deposition (PVD) techniques, which are line of sight methods and have inherent weaknesses relating to uniformity of deposition,” adds Kanjolia. “Vapor phase deposition techniques, such as metal-organic chemical vapor deposition (MOCVD), offer several advantages in relation to GST precursors, in particular, a better step coverage for deposition on patterned substrates, industrial scaling and high compositional control. Furthermore, we have achieved advances in precursor chemistries that allow similar layers to be deposited using conventional MOCVD, without the need for an activation process.”

To move from very small research structures to a full process to make MOCVD devices, the next challenge is to get the correct parameters in place to control the growth and lay down the correct layers in the correct structure, according to Kanjolia. “The quality of the films on flat substrates is improving, and the precursor chemistry is ideally-suited,” Kanjolia says.
An area that plays to Hitech/Epichem’s historical strengths is the application of III-V compound semiconductors on silicon substrates to boost channel performance. Proponents believe that such an option in a planar configuration could be competitive or better in performance/implementation compared with proposals for double-, triple- or FinFET wrap-around-gates.

Advanced lithography materials will also need to be produced to meet the challenges of ever higher resolution and new imaging technology (immersion, EUV, e-beam, etc.). Another important area for silicon semiconductor contributions is new processes and chemistries to enhance existing high-volume production at larger technology nodes away from the leading edge.

Irvine sees a need for greater collaboration through the supply chain both in terms of incorporating new molecules and in terms of hardware to deliver the chemicals effectively in equipment. Some materials with attractive technical properties such as ruthenium cost more than platinum. Irvine also believes that intellectual property rights (IPR) protection measures will have an increasing role in chemical designs. Irvine sees an increasing activity in IPR filings on precursor material compositions. Historically, IPRs were filed around application and process, not composition.
 
In the III-V market, the focus is on the rapidly growing lighting markets – both for replacement of general application and of backlights in LCDs. Light-emitting diodes offer 50,000 hours of life compared with 1000 hours for incandescent lights and are more environment-friendly in not involving highly toxic chemicals such as mercury in production. The LED market for these applications is showing a healthy annual compound growth rate of around 53% for backlighting and 37% for general lighting.

Hitech also sees its chemicals used in large area display (LCD, plasma, OLED) production for etch of aluminum interconnect and boron trichloride co-etchants.

In the rapidly expanding photovoltaic market, Hitech expects its silane deliveries to increase from 36 tonnes in 2007, to 53 tonnes this year and 70 tonnes next. This is a key material both for polycrystalline and thin-film silicon cells. These expectations are based on the compound growth rate of ~37% in the market. Other Hitech materials that find use in this market are dimethyl zinc, phosphorous oxychloride, and compounds of indium, cadmium, sulfur and selenium.

REACH out

Another aspect raised during the meeting was the European Union Registration, Evaluation, Authorisation and Restriction of Chemical substances (REACH) regulations that have been coming into force since 1 June 2007. This will affect not only chemical producers and handlers, but also importers of ‘articles’ containing substances of ‘high concern’, which according to an EU flyer includes electronic components along with construction materials, toys and vehicles. So even if articles are not produced in the EU, importers will need to know from their supply chain what goes into their merchandize. In the secretive high tech sector, this is surely not welcome. However, there are quantity thresholds for the regulation that are not likely to be breached for super-exotic/expensive concoctions.

The http://ec.europa.eu/environment/chemicals/reach/reach_intro.htm)">REACH web site  comments: “The aim of REACH is to improve the protection of human health and the environment through the better and earlier identification of the intrinsic properties of chemical substances. At the same time, innovative capability and competitiveness of the EU chemicals industry should be enhanced. The benefits of the REACH system will come gradually, as more and more substances are phased into REACH.”

Skeptics are not so clear that these effects, particularly that of competitiveness, will be the result. Although pre-registration is due in December 2008, the first full-registration phase of existing chemicals is up to 30 November 2010. This will involve the most toxic and highest quantity sectors: carcinogenic, mutagenic or toxic for reproduction (CMR) substances in quantities above 1tonne/year/legal entity; chemicals very toxic to the aquatic environment (>100tonnes/year); general chemicals in quantities above 1000tonnes/year. The next deadline is 31 May 2013 for general chemicals above 100tonnes/year and the final registration date, 31 May 2018, is for quantities greater than 1tonne/year. New chemicals will need to be registered and tested as applied in volume.
 
Dr Mike Cooke is a freelance technology journalist who has worked in the semiconductor and advanced technology sectors since 1997.

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