Challenges of Next-Generation Lithography
John Canning, International SEMATECH -- Semiconductor International, 9/1/2000
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At a Glance | | |
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 Click for full-size image 1. Many alternatives exist for 100 nm and below nodes, including 193 nm, 157 nm, Electron Projection (EPL), Proximity X-Ray (XRL), Ion Projection (IPL), Extreme Ultraviolet (EUV) and E-Beam Direct Write (EBDW). |
1999 ITRS Roadmap revision
The ITRS Lithography Technology Working Group (TWG) has revised the Roadmap for 1999 and has accelerated the requirements in several major areas. The key changes from the 1997 Roadmap are:
• The international process initiated by the Semiconductor Industry Association (SIA) in 1998 was implemented successfully by all five supporting regions: Europe, Japan, Korea, Taiwan and the United States.
• Timing for the DRAM half-pitch has been pulled in one year for the 130 nm technology node and below. Also, the chip size growth rate has been reduced from about 14% per year to about 5%.
• Optical lithography continues to extend its domain of application with the addition of 157 nm technology at the 100 nm to 70 nm nodes. The introduction of next-generation lithography (NGL) technologies has been moved out to 100 nm and below.
• Increased emphasis has been placed on mask technology to address mask error function (MEF) and PSM requirements. Also, the requirement for the 230 mm mask size has been dropped. An overview of specific requirements for the 180 nm to 35 nm nodes is shown in Table 1.
The Potential Solutions Roadmap (Fig. 1) shows the options at the 130 nm node have been narrowed to 248 nm + PSM and 193 nm. It is expected that both technologies will be used in production at that node. For 100 nm and below, there are many alternatives. They include 193 nm, 157 nm, Electron Projection (EPL), Proximity X-Ray (XRL), Ion Projection (IPL), Extreme Ultraviolet (EUV) and E-Beam Direct Write (EBDW). The options should be narrowed soon to have tools and the infrastructure ready by 2004 for the 100 nm node.
Further progress in accelerating the Roadmap is limited by the industry's mask capability. Mask writing and inspection equipment must be developed to handle the increased requirements for accuracy, feature size, critical dimension (CD) control, image placement, defect size and data volumes. In addition, both technical and business solutions must be found for repair technology. The mask industry needs major focus, paradigm shifts and worldwide collaboration to overcome these challenges along with the rapid escalation of mask costs.
A program for next-generation lithography
International SEMATECH established the next-generation lithography program in mid-1996 when it became clear the industry needed a coordinated process to narrow the options on the Roadmap. Today there are many worldwide efforts developing the NGL alternatives, as shown in Table 2.
The International SEMATECH next-generation lithography program is targeted to narrow the options by providing: 1) global industry coordination of the consensus-building process; and 2) short-term technical projects on critical issues. An overview of the program is shown in Figure 2.
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At the third NGL Workshop, held in December 1999, the industry recommended International SEMATECH continue its support in 2000 of two technologies: EUV and EPL. There also is a growing recognition that the industry may want and can support two NGL technologies for the diverging applications of DRAM/MPU and ASIC/SOC.
As a result of this workshop, International SEMATECH is organizing a program to introduce next-generation lithography technology at the 70 nm node, but on a schedule that anticipates future acceleration of the ITRS Roadmap. The program will address critical issues and the mask infrastructure such as mask substrates, mask processes and mask usage.
In 1999 International SEMATECH funded several short-term projects for both EPL and EUV. Key results from the EUV projects included a more than ten-fold reduction in the defect density on the mask blank by improvements in the deposition tool and mask handling (Fig. 3). Also, three blanks achieved <0.01 defects/cm2 at 100 nm defect size. For the EPL projects, key results included the development of models to predict and correct for image displacement resulting from wafer heating during exposure.
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Challenges for next-generation lithography
To succeed in replacing optical lithography, any next-generation lithography technology must address four major challenges:
• Keeping up with the Roadmap acceleration.
—Planning and executing aggressively.
— Demonstrating extendibility (below 50 nm).
• Solving the critical issues.
— Building confidence in end users.
— Lowering the risk of decision.
• Reducing cost-of-ownership.
— Tool throughput.
— Mask costs.
• Funding parallel development of two solutions (EPL and EUV).
— Can the industry afford it?
The enormity of this last challenge is shown in Figure 4. Based on industry workshops International SEMATECH has conducted, total R&D spending for one regional solution could approach $1B in 2002 alone. That's almost twice the previous spending rate! Finding both the funds and the necessary talented people may be the biggest challenge of all.
Conclusions
The 1999 ITRS Roadmap needs are accelerating, while optical lithography continues to extend capability. The International SEMATECH next-generation lithography program is targeted at:
• Building global consensus on the options.
• Funding critical issues and infrastructure for introduction at the 70 nm node in 2006.
The 1999 projects addressed several critical issues with substantial progress demonstrated at the December Workshop, especially in EUV mask blank defect density and EPL wafer heating.
Finally, to succeed NGL must demonstrate:
• Extendibility below 50 nm.
• Defect-free and stable mask technology.
• Funding for parallel solutions.
The author would like to thank NGL technology champions Lloyd Harriott, Akihiko Ishitani, Chuck Gwyn and Rainer Kaesmaier, who have guided and driven their technical teams to provide these results. Thanks also to the many people at International SEMATECH who have supported and managed this program, especially Judy Behr, Gerhard Gross, Scott Mackay, Phil Seidel, Mark Sheedy, Walt Trybula and Neil Wester.
