Full Wafer Thin Film Measurements

Thin film layers are the foundation of every modern semiconductor device. Controlling the thickness and uniformity of these films across the entire wafer is critical because even nanometre-scale variations translate directly into device-to-device performance spread, yield loss, and reliability risk at scale. A silicon nitride layer deposited 5 nm thicker at the wafer edge than at the centre changes the threshold voltage of every transistor in that zone. At advanced nodes where tolerances are measured in single-digit nanometres, this is the difference between a functional and a failed die.

Wafer-scale thin film metrology therefore sits at the heart of process control: deposition tools are tuned, qualified, and monitored using film thickness maps that reveal the characteristic signatures of each process — centre-thick, edge-thick, or rotationally symmetric non-uniformity patterns that point directly to the root cause when something drifts. As wafer diameters have grown to 300 mm and process complexity has increased with 3D architectures and multi-layer stacks, the demand for fast, high-density, full-wafer thickness mapping has intensified — making inline measurement capability not just a quality assurance tool but an active input to closed-loop process control.

The technology behind lineWLi is independent of scale. With the right optics, lineWLI can perform wafer scale thickness measurements. It covers a 300 mm wafer with up to 1 million measurement points with in less than 30s. Each exposure measures the thickness along a line. Moving the wafer perpendicular to the line builds up a 2D wafer map over time.

The first example are two unpatterned Si wafer with with 500 nm or 1500 nm of AlN. AlN’s strong piezoelectric response makes it the dominant material in bulk acoustic wave (BAW) resonators and film bulk acoustic resonators (FBARs) — the filters found in virtually every modern smartphone for 4G/5G band filtering. The thickness of the layer directly impacts the filter frequency so thickness needs to be tightly controlled either through process control or subsequent material removal.

lineWLI large number of measurement points allows the user to focus on specific structures. Here’s the patterned wafer from previous measurements again. This time, we’re focusing on membrane structures. They consist of a freestanding membrane covered with SiOx and finally a SiNx layer for passivation. LineWLI can measure and processes all layers simultaneously.