Phase change materials progress

SAFC Hitech Successfully Demonstrates Device-Quality GST 
September 4, 2008
St. Louis, MO - September 4, 2008 – SAFC Hitech ™, 
a focus area within SAFC®, a member of the Sigma-Aldrich Group
 (NASDAQ: SIAL), today announced that it has made significant 
progress in developing Germanium Antimony Telluride (GexSbyTez or GST) 
precursors for use in high volume manufacturing phase change memory 
(PCM) applications. Extensive development work has been conducted
 with both the precursors and with the use of conventional Metal-Organic 
Chemical Vapor Deposition (MOCVD) techniques to deposit them,
 resulting in the successful deposition of device-quality GST. 
These advances represent a major step towards achieving a commercially-viable 
solution to address the aggressive memory device scaling issues 
faced by the semiconductor industry to keep pace with Moore’s Law.

PCM, a non-volatile computer memory, takes advantage of the unique 
behavioral properties of chalcogenide compounds to enable scaling of 
ultimate feature size further than is possible with conventional Flash memories1. 
This translates to greater storage capacity and superior performance for memory
devices. Chalcogenide compounds, such as GST, are very 
attractive materials for PCM and have already been used as the basis for 
optical storage media and prototype PCM devices. 

“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,” commented SAFC Hitech Chief Technology Officer, 
Ravi Kanjolia. “Vapor phase deposition techniques, such as 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.” 

Since 2005, SAFC Hitech has been a participant in the European
Commission-supported CHEMAPH project, a consortium set up 
to look at deposition methods for GST films. Researchers at the 
company’s Bromborough facility in the UK have been actively
 investigating a variety of GST sources suitable for MOCVD, 
and have matched the physical properties of each metal precursor 
to enhance efficiencies at the desired growth parameters. 

“Variations in cracking efficiencies were one major hurdle that we had
 to overcome,” explained Kanjolia. “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.” 

The actual chemicals of choice were found to be Ge(NMe2)4, Sb(NMe2)3 and iPr2Te. With these identified, SAFC Hitech then developed synthesis protocols to allow the isolation of high purity product in both small and large laboratory scale equipment. These materials are now available to customers with guaranteed quality by state-of-the-art in-house analysis. Samples have been shipped to various centers, and collaborations with partners have taken place to test the different combinations. Recent growth trials have resulted in successful deposition of device-quality GST using nitrogen as a carrier gas.  

“While a full process to make MOCVD devices remains to be demonstrated on anything other than very small research structures, the quality of the films on flat substrates is improving, and the precursor chemistry is ideally-suited,” concluded Kanjolia. “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. The temperature window with this process remains critical, and highlights both the difficulties associated with this system and the need for advanced precursors to move forward with integration into future phase change memory applications. We are confident that our sources will allow the development of next-generation devices to maintain the speed of performance enhancement required to meet market targets.”

1 A. L. Lacaita, Solid-State Electron 50 (2006) page 24.

About SAFC Hitech: SAFC Hitech provides a unique chemistry service
 translating application understanding into performance materials worldwide. 
Through collaborative partnerships and an integrated approach from
 research and development, process development and scale up to 
commercial manufacturing, SAFC Hitech invests in innovation and 
manufacturing enabling current and future technology needs. 
Further information can be found at www.safchitech.com

About SAFC: SAFC® is the custom manufacturing and services group 
within Sigma-Aldrich that focuses on high-purity inorganics for high 
technology applications, cell culture products and services for 
bio-pharmaceutical manufacturing, biochemical production and the 
manufacturing of complex, multi-step organic synthesis of APIs and
 key intermediates. SAFC has manufacturing facilities around the
world dedicated to providing manufacturing services for companies 
requiring a reliable partner to produce their custom manufactured materials. 
SAFC has four focus areas – SAFC Pharma™, SAFC Supply Solutions®, 
SAFC Biosciences™, and SAFC Hitech™ – and had annual sales of nearly 
$600 million in 2007. SAFC is one of the world’s 10 largest fine chemical 
businesses. For more information about SAFC, visit www.safcglobal.com

About Sigma-Aldrich: Sigma-Aldrich: is a leading Life Science and 
High Technology company. Its biochemical and organic chemical 
products and kits are used in scientific and genomic research, 
biotechnology, pharmaceutical development, the diagnosis of 
disease and as key components in pharmaceutical and other high 
technology manufacturing. The Company has customers in life 
science companies, university and government institutions, hospitals, 
and in industry. Over one million scientists and technologists use its 
products. Sigma-Aldrich operates in 36 countries and has 8,000 
employees providing excellent service worldwide. Sigma-Aldrich
 is committed to Accelerating Customer Success through Leadership
 in Life Science, High Technology and Service. For more information 
about Sigma-Aldrich, please visit its award-winning Web site at
www.sigma-aldrich.com. 

SAFC®, SAFC Supply Solutions® and Sigma-Aldrich® are 
registered trademarks and SAFC Pharma™, SAFC Biosciences™ 
and SAFC Hitech™ are trademarks of Sigma-Aldrich 
Biotechnology L.P. and Sigma-Aldrich Co.
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