Materials

In the past decade or so, the semiconductor chemistry landscape has become ever more complicated. Before the 1990s, silicon CMOS transistor-level production (frontend of line) was generally based on a handful of elements, silicon (of course), oxygen, boron, phosphorous, arsenic and hydrogen. Nitrogen and fluorine were added during the 1990s. Since 2005, carbon and germanium have been introduced to create strain for high-mobility channels, and now high-k and metal gate insulator and electrode stacks have added some 40 extra elements to the mix (Fig 1). To successfully respond to this chemical explosion, integrated device manufacturers (IDMs) are hiring greater numbers of materials scientists and chemists.

Although there are a number of strong companies in the electronics chemicals market, SAFC Hitech doesn’t compete directly with them. “We’re a little bit different,” says Geoff Irvine, director of marketing and commercial development.

For starters, Hitech is just one division of the wide-ranging Sigma-Aldrich Fine Chemicals subsidiary. Other divisions cover pharmaceuticals (Pharma), supply chain services (Supply Solutions) and cell culture technologies (Biosciences). SAFC has been manufacturing highpurity organics and organometallics for over 20 years at its Sheboygan Falls facility in Wisconsin, but did not have a specifically named brand.

“We had a healthy business in the electronics sector but we were not exploiting our position with a formal brand in the marketplace,” comments Irvine. “In 2004, the SAFC Hitech segment was launched when SAFC rebranded and established the sector as a specific business focus area. Inside our sector, we identified the high tech (electronics) industry as one of our growth targets and investigated numerous strategies to develop our strength and presence in this area, and to move closer to our target customer groups.”

Build and acquire
SAFC operates a ‘build and acquire’ strategy to expand its business. One example of this is SAFC Hitech’s takeover of Epichem in the UK for US$60 million in February 2007. Hitech took on all of Epichem’s management and staff, including appointing the managing director, Barry Leese, as president of the business segment.

Irvine describes the process by which this took place. “We investigated both green-site building (organic growth) and/or acquiring an established leader to push us into this direction. Epichem seemed to be the perfect fit of technology and a market-leader, and combined with our chemistry expertise and manufacturing prowess provided us with a big step forward into the industry.”

The Epichem acquisition has extensive experience mainly in supplying the compound semiconductor and photovoltaics industries and some silane for the European silicon semiconductor industry. Epichem also brings expertise in producing materials such as trimethyl-aluminium (TMA) for metal-organic chemical vapour deposition (MOCVD), one of the leading techniques for precision deposition of materials.

The Hitech division contributed more than US$70 million to SAFC’s $500 millions sales in 2006, has seven manufacturing sites and has some 200 dedicated staff. In addition, it has access to SAFC’s global sales, manufacturing and technical support services. Epichem adds US$40 million to Hitech’s potential sales.

As an example of the ‘build’ side of the growth strategy, SAFC is planning a manufacturing complex in Wuxi, China. The site is to be developed in three phases. Sigma-Aldrich expects to initially invest US$25 million to acquire land rights and construct its first-phase that includes a large-scale multi-purpose organic manufacturing facility. The plant is due to be in place for 2009, not initially constrained by the current good manufacturing practices (cGMP) of the chemical, food and pharmaceutical industries but for these standards to follow on later. Construction of the new plant is due to begin by the end of 2007.

Hitech is among the segments planned to have manufacturing space at the facility when it is fully developed. The site, with manufacturing plant, and analytical, packaging and warehousing facilities, is expected to produce raw materials, key intermediates and final products also for the Pharma and Supply Solutions businesses.

The site was chosen on the basis of the area having the strongest infrastructure and customer base, along with low construction and staff costs.

The new facilities will be geared up to serve the Asia Pacific and local markets. As the site develops quality assurance, quality control and analytical services will be developed. Such concerns have been highlighted by the scandal where Mattel and its Fisher-Price subsidiary had to recall tens of millions of toys produced in China due to the possibility that they contained lead paint.

Surely, such product safety concerns will now be addressed or China could find itself locked out of advanced markets, particularly in the USA.

Another Asia-Pacific development is a Memorandum of Understanding (MoU) with the Gyeonggi Province of South Korea. Hitech is exploring investment in a facility in the province for the supply and manufacture of electronic materials.

Atomic-level manufacturing
Hitech believes that it has a wide opportunity to apply and develop the expertise on advanced deposition technologies acquired from Epichem as semiconductor manufacturing probes ever deeper towards the atomic level. Replacement of the traditional silicon dioxide/polysilicon gate insulator/electrode combination now demands atomic-level deposition capabilities. Scaling of CMOS device structures has reached the scale where silicon dioxide gate insulators would need to be less than 1nm, a few molecular layers, to deliver the speed and power performance expected from naive theory and demanded by industry expectations for high speed and low power drain.

Since the layers are becoming increasingly granular, it is not surprising that actual performance is not a simple extrapolation from continuum models. One of the leading problems is that the insulator thickness is not sufficient to block leakage between the gate electrode and the channel. Further, a change of one molecule becomes a more significant difference in layer thickness, so hot spots can develop.

The industry solution to this problem is to choose a different gate insulator material (often still called a ‘gate oxide’) so that thicker layers can be used once again. This requires the material to have a higher dielectric constant k. However, silicon CMOS structures are delicately balanced structures from the chemical and electrical perspectives. It was a fluke of nature that silicon dioxide deposited on silicon works so well with the ability to reduce interface states to acceptable levels that don’t impact performance and that the electronic levels are aligned suitably between the gate electrode and channel. In particular, moving to a high-k gate insulator requires a new gate electrode, a metal gate. SAFC Hitech sees the high-k/metal gate introduction as giving the Epichem acquisition ‘great timing’ given its wide experience in MOCVD chemical supply.

MOCVD has been extensively developed to produce the complex and difficult near-atomic layer structures of compound semiconductor material on mismatched substrates, junctions between different materials (heterojunctions), superlattices and quantum wells needed to produce incoherent and coherent (laser) light-emission, high-sensitivity light and other electromagnetic radiation detection and high-speed/high-power high-electron mobility transistor (HEMT) devices for radio signal amplification. MOCVD precursors have been among the main markets supplied by Epichem.

Laser diodes produced using such techniques are used in optical storage (CD, DVD, high definition DVD, BluRay), bar-code scanners and fibreoptic communication systems. High-brightness light-emitting diodes are increasingly used in the automotive and traffic control industries and new applications include more reliable, more efficient traffic lights and external car lights. High-sensitivity photodetection is widely used in infrared imaging as applied in night vision goggles and low-light cameras. Compound semiconductor radio frequency amplifiers are used in mobile phones, the mobilenetwork basestation connection, and in radar and electronic warfare.

Hitech offers a wide set of skills in development, integration and large-scale manufacture of chemical vapour deposition precursors for conductive films, barrier layers, high-k dielectrics for advanced gate stacks, low-k dielectrics for inter-level dielectric layers and speciality optical or surface coatings.

The company has a five-year chemical roadmap for MOCVD and atomic layer deposition (ALD) processes on silicon semiconductor substrates that adheres to the International Technology Roadmap for Semiconductors (ITRS) guidelines. The Hitech roadmap (Fig 2) puts in place an extensive programme of materials development across a number of semiconductor device layers.

These include materials for high-k dielectrics in logic and memory devices, additional functional memory architectures, electrodes in DRAM or gate stacks, barrier layers, wiring and low-k dielectrics. The company is seeking to support the silicon semiconductor industry from the 65nm node now in production through 45nm (now piloting at Intel), 32nm and beyond.

SAFC Hitech President, Barry Leese comments: “We believe the semiconductor market is entering an ‘age of chemistry’ where continual materials evolution will be vital to enable future technology nodes. As our roadmap indicates, SAFC Hitech is positioning itself at the forefront of this material development with a number of advanced materials in production.”

The leading material for high-k dielectric use has been hafnium dioxide, as used by Intel and by the IBM-led process development alliance that includes common platform partners Samsung and Chartered Semiconductor, and joint-development partners Freescale, Infineon and STMicroelectronics. Other high-k oxides and binary oxides and materials that have been tried include aluminium oxide, hafnium silicate, zirconium oxide and complex rare earth oxides.

Dr Peter Heys, R&D director at SAFC Hitech, reports: “Over the course of the new roadmap, SAFC Hitech will be introducing more complex high-k oxides for silicon semiconductor manufacturing, such as hafnium zirconium based layers, which offer greater flexibility as they can be doped with other materials like silicon, nitrogen, aluminium, lanthanum and yttrium to meet individual customer requirements in creating a layer that functions well for a particular device design.

Beyond that, the research and development of, for example, lanthanide and strontium chemistries, binary metals and complex metals oxides or iterations of oxides will facilitate the delivery of the 50+ k values needed for future technology nodes.”

From thimbles to high volume
In doing lab research on new materials and structures, it must always be remembered that what may be available in thimblefuls may not scale up or even be available in the quantities needed for volume production. Here, the expertise within SAFC, such as in its supply chain services division, is seen as giving the company an important edge in the contribution it can make to meeting the needs of the semiconductor industry.

Companies have a wide range of manufacturing styles in developing and applying advanced technologies. While some insist on extensive testing, others seem to put new process recipes straight into pilot production to see what happens rather than engaging in extensive research.

SAFC Hitech seeks to enter into collaborative partnerships to accelerate a customer’s research and development work through process development and scale-up to commercial manufacturing, speeding the time-to-market for advanced products. At the innovation stage, SAFC Hitech can provide technical evaluation, molecular design, sample preparation and material performance evaluation services.

During process development and scale-up, it offers help with technology transfer, hazardous materials evaluations & disposal and process window optimisation. Once ready for commercial manufacturing, packaging, delivery system design, supply chain management, consulting on statistical process control, and local support and servicing are available.

The company also funds university materials R&D and analysis. Collaborators include University of Liverpool, University of Bath, University College London, University of Southampton, in the UK, and, Helsinki University of Technology (HUT) and University of Helsinki in Finland. This global programme won the 2007 EuroAsia Semiconductor Education Initiative of the Year award.

The company is also collaborating with other process developer such as with Japan’s JSR Micro in looking beyond vacuum deposition to a potentially ‘disruptive technology’ (i.e. the company is not willing to give details).

The company has also made a strategic alliance made in 2007 with a micro-electromechanical tool supplier, MEMSSTAR. Hitech will supply standard precursor chemical materials for surface coatings on micro-devices produced on MEMSSTAR’s Surface Preparation and Deposition (SPD) systems.

Such processes are used in microfluidics to ensure hydrophobic or hydrophilic surface properties for devices such as inkjets or microneedles. In medical applications surface coatings can be used to provide essential biocompatibility. Moisture barriers or anti-stiction properties for moving micro-sensors can also be provided.

Further potential markets that the company is investigating include organic electronics and the company sees opportunities and challenges arising from the overlaps between a number of its segments such as electronics and biosciences.