E ditorial
The 32nm Node is Already Here Ben Tsai CTO, KLA-Tencor Corporation
To technologists at the leading edge of chip development, the 45nm node is almost a done deal. They are looking ahead already to the challenges of 32nm and beyond. Since the most advanced inspection and metrology technology must keep pace with the latest developments, I want to briefly mention some of the issues we see emerging at the 32nm node. Customers are well aware that new tools and inspection strategies are essential to overcome the blurring of defect categories in deep nanometer-scale device designs. With the extremely tight process windows of 45nm and below designs, a slight variation in the process can appear to be almost like a random defect because so many conditions are close to the process window margin. It can be very hard to distinguish systematic from random defects. Advanced metrology and inspection tools must produce not only accurate data and information, but enable users to take corrective actions that improve yield. Accurate defect classification and binning to distinguish systematic from random defects is one of the most critical areas of development. The patterning process is going to be a second challenge. Many experts believe that patterning will continue to use 193nm immersion lithography tools, but with double or even triple patterning methods. More patterning layers, plus more interactions between the patterning layers, will require much more control to stay within the process window. There will also be more reticles to inspect. All of this patterning complexity means that more overlay and CD measurement steps will be needed to ensure that the lithography process is under control. Between now and 2010, when 32nm is expected to be in production, the precision requirements of metrology tools are pushing beyond CD-SEM capability, making optical CD (OCD) scatterometry even more important. I expect the adoption of OCD technology to increase significantly because it provides more precise measurements for increasingly tight process windows. OCD throughput is much faster than CD-SEM, allowing chipmakers to do more measurements, a requirement for 32nm devices.
Ben Tsai ben.tsai@kla-tencor.com
Overlay metrology is also positioned for growth. With double patterning, the CD linewidth is closely linked to the interlayer overlay. Overlay precision requirements are much tighter, and customers will need to measure the overlay much more often. They may have to start measuring the overlay on every wafer. At the 32nm node, the industry is likely to introduce new materials, including more widespread adoption of high k materials and additional use of low k materials. Greater variety of materials requires inspection tools to have a higher level of sensitivity to find more defects, as well as greater wavelength flexibility to find the defect and measure it on a wider range of materials. The approach to 32nm is revealing many additional applications for e-beam inspection, in layers where it wasn’t necessary before. Customers are now developing combinations of optical and e-beam technologies to develop and qualify and monitor certain layers within a comprehensive inspection strategy. We are working closely with our customers to develop BKMs for different layers and materials, using the optimal sampling methodology and strategy between e-beam and optical technologies. Technologists at KLA-Tencor and our customers are already working at 32nm design rules. This kind of futuristic work is what keeps our industry vibrant and always moving forward at high speed. We hope that this issue of YMS magazine helps highlight interesting areas of technology that help our customers stay on the bullet train of Moore’s Law. Spring 2007 Yield Management Solutions