On a 300mm line, the lithography bay is the heartbeat. If the AHU heater drifts, the bake profile drifts with it—and you start bleeding yield long before the defect scanner flags anything. We built our Fab Air Conditioning Heater Module to keep the thermal field stable where it counts: right at the wafer. What matters under the hood We hold ±0.1°C thermal uniformity across the supply air stream, so the bake plate sees repeatable inlet conditions. It runs in Class 1–100 cleanrooms with zero particle generation, confirmed by in-situ particle monitoring. The heater uses low-outgassing materials and a sealed thermal path, so you don’t introduce contamination during soft bake and hard bake. The output is sized for 24/7 operation with controlled ramp rates, and it drops into existing AHU control loops through standard industrial interfaces. Here’s the thing: photoresist bake isn’t a coarse step—it’s a dimensional boundary. Even a small temperature ripple shows up as critical dimension variation and edge-bead non-uniformity. We hold room temperature at the wafer plane so the bake recipe behaves the same lot after lot. You get tighter CD control, fewer reworks, and a predictable thermal budget. Efficiency improves too, because you stop wasting energy on overshoot-and-correct cycles. Installation needs attention to airflow direction and static pressure tolerances of the AHU; mismatched ducting creates micro-turbulence that chews into uniformity. The module also needs a clean power feed—voltage ripple translates into short-term temperature jitter. Plan the commissioning window with your lithography bake tracks and validate the profile against your specific resist stack.