(Nanowerk News) Applied Materials (Santa Clara, Calif.) concurrently held its 12th Annual Technology Forum with this week’s SPIE Advanced Lithography Conference in San Jose. Having “Reality Takes Shape: Patterning at 32 nm” as its theme, the wide-ranging event covered a number of subjects, not the least of which were the challenges faced by metrology.
Hans Stork, group vice president and CTO of Applied’s Silicon Systems Group, noted that metrology’s chief challenge lies in increasingly smaller feature sizes, whether produced by double patterning or not. “These features are far below the wavelength of light, so we cannot make them visible; we only have electron-beam tools and other indirect methods to see them. This only results in more complicated tooling, machinery, algorithms. It isn’t a fundamental issue in that we don’t know how to do it; however, it is hard to do it effectively with high productivity and ease of use.”
Some of the presenters viewed resist not only as the IC fundamental building block, but also as a challenging link in the whole process chain because it is an active polymer, and polymers have a relatively large size to the dimensions that the industry wants to pattern. It was noted that a side benefit that has resulted from self-aligned double patterning is that, with a combination of resist and some of the other carbon films, it becomes possible to smooth out line edge roughness (LER). While the principal photoresist will probably remain as it is, it most likely will have to be enhanced or modulated by other materials to obtain the desired dimensions and final features. Certainly, that is a promising direction, although it adds one more layer and one more set of activities.
In the areas of etch and gate, metrology must reckon with the 2-D nature of the new features. As Stork put it, “We know that, especially for high-performance devices, the angle of the gate stack is as critical as its final dimension. Angle differences of 89, 89.5 have become relevant — they can cause very observable differences in electrical performance.” For etch, it was observed that metrology must offer an inline, rapid feedback capability that can be used for automated process control (APC). This should include not just linewidth dimension but also line angle. Although scatterometry has been very effective, it heavily depends on models. The new stacks being designed require the production of new models and, although this is not a big concern in manufacturing, during development this can become a hurdle because of the complicated iterations needed to find the right models and correct feedback signatures.
Read the full article at Semiconductor International.