Profile measurements of dry etched structures

Dry etching is one of the most critical process steps in semiconductor fabrication, used to transfer circuit patterns from photoresist into the underlying material layers such as silicon dioxide, silicon nitride, or metal with nanometer-scale precision. Unlike wet chemical etching, dry etching uses plasma or reactive ion beams to remove material anisotropically, meaning it etches straight down rather than undercutting laterally, which is essential for defining the vertical sidewalls of transistor gates, contact vias, and interconnect trenches at advanced nodes.

lineWLI’s ability to measure the three-dimensional profile of etched structures — depth, sidewall angle, and floor roughness — in a single shot without mechanical scanning makes it a natural fit for inline etch process monitoring, where speed and vibration immunity are as important as measurement accuracy.

Today’s example comes from a structure that is used in the manufacturing and testing of this wafer. The structure itself is a via that exposes a underlying layer. Within the exposed layers, there’s actually an alignment mark used during production. The alignment mark is barely visible with a normal RGB camera:

The lineWLI sensor measures one line within 10 ms. Scanning the lineWLI sensor across the sample in the indicated direction creates a high resolution height map. The height profile clearly brings out the alignment mark. Unlike the camera picture, each line is resolved clearly

The measurement of each pixel is independent of each other without cross talk. Hence, lineWLI can measure large steps from one pixel to the next with a default spatial resolution of 1.8 µm per Pixel.