ACS - Closing the Gap - Wafer Process Controll

The growing importance of micron-level control

In advanced semiconductor processes, precise wafer positioning across X, Y, and Z axes is critical. Even minor deviations, particularly in vertical gap, can influence uniformity, contribute to edge defects, or introduce backside contamination. In more severe cases, misalignment can lead to wafer handling issues or unexpected tool alarms. In multi-chamber tools, the challenge extends further. It is not enough for each chamber to be accurate in isolation; they must also be matched to one another to ensure consistent results across production lots. Without this level of consistency, subtle variations can accumulate, impacting yield and complicating process optimization.

The implications can also be significant during recipe development, where engineers need confidence that any observed variation is driven by process chemistry rather than mechanical inconsistency. Without reliable measurement, isolating these factors becomes increasingly complex.

Measurement versus interpretation

One of the more understated challenges in traditional approaches is the reliance on visual feedback. In many cases, inspection methods provide only an image or qualitative indication of alignment, leaving interpretation to the operator. While useful, this still introduces subjectivity. One engineer may judge a deviation differently from another, and even small differences can be critical in high-precision processes. As a result, visualization alone is often insufficient to ensure repeatable outcomes.

The shift toward quantitative, in-situ measurement addresses this gap. By providing precise, repeatable data on wafer position and gap conditions – alongside real-time visual feedback – modern sensing technologies remove ambiguity from the process, enabling adjustments to be based on accurate and objective measurement rather than judgement.

Bringing measurement inside the process

This need for greater precision and repeatability is driving adoption of advanced in-situ solutions. Nordson’s WaferSense® Auto Centering Sensor (ACS), for example, is designed to replicate the form of a production wafer and move through the tool path while capturing real-time X, and Y offset data for centre transfer positions without disassembly or requiring the equipment to be opened to ambient conditions.