The National Institute of Standards and Technology (NIST), Gaithersburg, Md., has earned a 2013 R&D 100 Award for its development of quantitative hybrid metrology (QHM). This method integrates statistical techniques and measurements made with two or more instruments to rigorously determine the sizes of nanoscale transistor features on semiconductor chips. The research team estimates that a three-fold decrease in measurement uncertainty achievable with this innovation could save manufacturers as much as $7 for each chip.
The NIST inventors of QHM include physicists Bryan Barnes and Richard Silver, and statistician Nien Fan Zhang. Hui Zhou, a NIST research associate, was a member of the development team. The public-domain invention does not replace chip makers’ standard measurement tools, such as scanning electron microscopes (SEMs) and optical devices known as scatterometers. Rather, the new method enhances these tools and ties them together in novel combinations. This flexibility in measurement strategies minimizes measurement uncertainties and optimizes throughput.
A key element of the NIST method is a model library-a collection of simulated data based on typical chip feature dimensions that are compared to actual measurements, made with an SEM, scatterometer, or by other means. Before making the comparison, however, the NIST team employs an elegant statistical treatment-called Bayesian analysis-to incorporate a few key additional measured values from other tools into the library model. This step reduces the uncertainty in the measurements, lowering them by more than a factor of three in some cases.
