Advances in micromachining (MEMS) applications such as optical components, inertial and pressure sensors, fluidic pumps and radio frequency (RF) devices are driving lithographic requirements for tighter registration, improved pattern resolution, and improved process control for pattern placement on both sides of the substrate. Consequently, there is a similar increase in demand for advanced metrology tools capable of measuring the Dual Side Alignment (DSA) performance of lithographic systems.
The requirements for an advanced DSA metrology tool include the capability of measuring points over the entire area of the substrate, and of measuring a variety of different substrates and film types and thicknesses. This paper discusses the precision and accuracy of an advanced DSA metrology system, the UltraMet 100. This system offers DSA registration measurement at greater than 90% of a wafer's surface area, providing a complete front to back side registration evaluation across a wafer. The system uses top and bottom cameras and a pattern recognition system that allow simultaneous target capture and measurement on both substrate surfaces.
Because no industry standard has been established to determine the accuracy of dual side pattern metrology, an accuracy gauge was designed for this study that allows both top and bottom cameras to simultaneously measure offsets between two targets on one substrate surface. In this paper, an accuracy gauge is measured on the UltraMet 100 and the results are compared to measurements taken on a reticle X/Y pattern placement metrology tool calibrated to a NIST traceable standard. In addition, tool performance is analyzed in terms of system repeatability and reproducibility.