Mass flow control using estimated output feedback in semiconductor processes

Abstract

In the semiconductor manufacturing, process gas switching during atomic layer deposition and etching is critical for improving throughput. Thermal mass flow controller (MFC) used in this process requires a fast flow response. However, the slow response of thermal flow sensor leads to issue under transient conditions. Specifically, the observable flow value and the actual flow deviate, resulting in overshoot in the flow supplied to the chamber. To mitigate this issue, thermal flow response lag can be compensated through deviation operation. However, this method amplifies sensor noise and degrades flow stability, creating a trade-off between response time and stability. To address these challenges, this study proposes a feedback control system that employs an estimated output instead of direct sensor measurements, enabling a fast response with reduced noise and eliminating steady-state errors. The effectiveness of the proposed control scheme is validated experimentally.