Wireless Retarding Field Analyzer for Ion Energy Distribution Measurements in Plasma Processes

Retarding field analyzers (RFAs) have been used for decades to measure the ion energy distribution at surfaces during plasma processing. At first, RFAs were used mostly in grounded situations. In more recent times, RFAs suitable for radio-frequency (RF) biasing were developed. A typical design consists of the RFA grid stack embedded in a substrate-like carrier. The grid signals are supplied to the RFA (installed in the plasma chamber) from the airside through RF chokes and vacuum feedthrough located at a vacuum port. The RFA carrier is wired to the vacuum feedthrough on the vacuum side. While this type of solution works well for R&D applications, it is not ideal for a production environment (even for off-line maintenance work) due to the wiring and the need to open the chamber for installation.

There is an increasing demand for plasma measurement and control solutions to cope with the growing complexity of integrated circuit manufacture in the semiconductor industry. Production compatible plasma diagnostic instruments are highly desireable. Silicon wafer based wireless sensors, which measure temperature during the process, have gained the most traction with tool manufacturers and device makers. In this presentation we will present a novel wireless wafer probe with integrated RFAs, power supplies and measurement circuitry which can be loaded to the process chamber using the robotic transfer mechanism. RFA sensor data is gathered and stored in memory where it can be downloaded later for analysis. This technology has the potential for widespread use in the fab environment.