SEMI New England Forum Highlights Trends in Emerging Technologies
Immersion Litho, Touchless Automation Cited as Tools to Improve Chip Yield
BOSTON, MASS., March 10, 2005 -- The potential of immersion lithography to extend the semiconductor roadmap and the application of “touchless” automation to improve fab productivity were topics of discussion at the SEMI New England Breakfast Forum held yesterday at the Renaissance Hotel in Bedford, Massachusetts.
Michael Passow, senior manager of technology development and deployment at IBM East Fishkill, said the challenge for any new fab was how to ramp up to high volume, high yield production “without breaking the bank”.
The approach taken by IBM at its 300-mm fab in East Fishkill, New York, was to introduce so-called touchless automation. Rather than trying to develop a fab that was “paperless” or devoid of people, IBM employs fully automated systems for manufacturing and relies on human intervention only to monitor error conditions and take corrective action.
Passow noted the importance of having fab development located close to manufacturing in order to facilitate innovation and ensure seamless technology transfer. To this end, IBM East Fishkill incorporates both operations in a single building. “We can address [technical] issues quickly and continue down the roadmap,” said Passow.
The East Fishkill fab, which cost $2.5 billion, relies upon sophisticated communications and control systems that consume 575 miles of Ethernet cable and utilize more than one and a half miles of automation system overhead track. The fab’s server room has more processing power than NASA uses to launch a space shuttle, according to Passow. The complexity of the operation also generates huge amounts of data, requiring 110 terabytes of storage and 1.5 terabytes of RAM.
Passow concluded by noting that operating a fab of this complexity would never be possible without the existence of technical standards and that standards were key to achieving future generation solutions.
Mordecai Rothschild from MIT’s Lincoln Labs told the New England Breakfast Forum delegates that the concept of using immersion to enhance resolution was not new, having been first applied in 1840 for microscopy. Although a patent for immersion lithography was issued to Hitachi in 1984, “in practice nothing much happened until four years ago,” Rothschild said.
At that time MIT Lincoln Labs demonstrated immersion interference at 157-nanometers with a 30-nm half pitch. “Immersion lithography has caught on very quickly,” he said. “Our first published results were in the summer of 2001. Prior to that there was almost no published work in a serious way.”
A SEMATECH workshop followed in 2002, and in 2004 the industry saw the first deliveries of pre-production immersion lithography tools.
Rothschild said the initial driver for immersion lithography was to reduce device feature sizes to meet the Moore’s Law roadmap. However, there was an added benefit. “Even if you don’t reduce your resolution [through immersion] we can improve the depth of focus of the whole process, and DOF is one of those parameters that is very important for yield purposes and for maintaining control of the process,” he said.
Although ultra-pure water was required as the immersion fluid, there were still technical concerns including purity control of the liquid, its interaction with photoresist, and defects caused by bubbles or chemical and particulate contamination. Yield studies were currently underway to quantify the impact of bubbles on yield in the manufacturing process, and to determine methods to improve fluid handling designs, according to Rothschild.
So far none of these concerns have turned into major barriers, but it was still early days because volume production using immersion techniques has only just begun, he added.
Looking ahead, Rothschild said the extension of immersion lithography beyond the 45-nm node will require the use of transparent fluids with a higher index of refraction than water, in addition to a redesign of the optics used in lithography systems.
“Nevertheless, all of the arrows point in the positive direction as far as immersion lithography is concerned,” he said. “I am fairly comfortable that optical lithography in one form or another will keep the roadmap alive and well for at least another decade.”
The next SEMI New England Breakfast Forum will be held June 1 at the same venue. The topic will be “A Market Trend Update,” featuring Bill McClean, president of IC Insights and Bob Johnson, analyst with Gartner Dataquest.
SEMI is a global industry association serving companies that develop and provide manufacturing technology, materials and services to make semiconductors, flat panel displays (FPDs), micro-electromechanical systems (MEMS) and related microelectronics. SEMI maintains offices in Austin, Beijing, Brussels, Hsinchu, Moscow, San Jose (Calif.), Seoul, Singapore, Tokyo, Shanghai and Washington, D.C. For more information, visit SEMI at www.semi.org.