In semiconductor wet etching processes, Within-Wafer Uniformity is a core metric for measuring equipment precision and process stability, and a key factor determining the performance consistency of individual chips. Unlike Wafer-to-Wafer Uniformity (WIL), which focuses on the replicability of multiple wafers, Within-Wafer Uniformity emphasizes the uniformity of etching effects from the center to the edge of a single wafer. It directly relates to the performance matching of billions of micro-devices on the wafer, serving as a core technical checkpoint in advanced semiconductor processes.
The core of Within-Wafer Uniformity lies in the deviation control of etching rates, depths, Critical Dimensions (CDs), and surface roughness at various points on the surface of a single wafer. The more advanced the process node, the stricter the control requirements: for mature processes, deviations need to be ≤±3%, while for advanced processes at 7nm and below, they must be controlled within ±1.5%. This precision enhancement directly tests the capabilities of wet etching technology.
Within-Wafer Uniformity is the "lifeline" of individual chip performance. Billions of devices in advanced chips need to work collaboratively, and their performance relies on the physical and electrical characteristics imparted by etching. Insufficient uniformity leads to issues such as threshold voltage shifts, response speed differences, and contact resistance fluctuations across devices in different regions. Mild cases reduce the chip's performance ceiling, while severe cases result in device mismatch failure and chip scrap.
The core sources of Within-Wafer deviations stem from the uneven superposition of mass transfer, heat transfer, and reaction kinetics during etching. Four key triggers dominate: First, uneven flow field distribution—abnormal tank design or spray/stirring anomalies create "dead zones," causing etching rate deviations. Second, etchant concentration gradients—insufficient stirring leads to attenuation of active components and accumulation of by-products. Third, uneven temperature distribution—minor temperature differences from inadequate precision in constant temperature systems significantly impact etching rates. Fourth, bubble adhesion and wafer placement deviations, which hinder reagent contact and exacerbate local deviations.
Achieving precise Within-Wafer Uniformity control requires synergistic efforts across three dimensions: equipment, process, and monitoring. At the equipment level, optimize tank flow field structures, upgrade constant temperature control systems, and refine wafer carriers to ensure precise positioning. At the process level, control etchant ratio concentrations via online detection, optimize stirring methods and etching parameters to prevent deviations. At the monitoring level, use high-precision equipment for real-time parameter detection and introduce digital closed-loop systems for timely deviation warnings and corrections.
As semiconductor processes advance to 5nm and 3nm, with wafer sizes upgrading to 300mm and above, requirements for Within-Wafer Uniformity grow increasingly stringent, driving continuous breakthroughs in wet etching equipment, processes, and detection technologies. From an industrial value perspective, improving Within-Wafer Uniformity enhances chip performance consistency, reduces defect rates, supports mass production of high-end chips, and serves as a key to boosting core competitiveness and promoting high-quality industrial development for semiconductor enterprises.
In summary, Within-Wafer Uniformity in wet etching directly relates to chip performance, reliability, and yield. Only by continuously deepening equipment and process optimization and refining the full-process control system can technical bottlenecks be broken, providing guarantees for the high performance and consistency of individual chips, and assisting the semiconductor industry in advancing to higher precision.
