Nondestructive SAWs Measure High-Aspect-Ratio Features

摘要

Not surprisingly, structures with height-to-depth ratios ranging from 20:1 to as much as 60:1 pose metrology problems. Traditionally, the depth of high-aspect-ratio (HAR) structures has been measured with an ellipsometer or reflectometer illuminating the structure's bottom to obtain a reflection, or by cross-sectioning. However, cross-sectioning can become an issue when even focused ion beams (FIBs) might produce artifacts that complicate the measuring process. HARs are needed in trench-capacitor style DRAMs because, as the device shrinks, designers want to avoid being limited by the capacitor's spatial width or size - area is needed in a capacitor to hold a charge. A solution is to make the capacitor deeper, requiring a submicron-sized cross-sectional area etched into the silicon, with holes 4-8 μm deep.