The Applicability of a Microwave Resonant Probe to the Plasma Processing of Silicon Oxide

Semiconductor plasma equipment manufacturers are met with consistently increasing demands from device manufacturers for increased process control, robustness, and system health checks. This appetite for data has soared in recent years since the application of machine learning techniques within the industry. Unfortunately, diagnostic access within processing chambers is a sizeable challenge. Laser based diagnostics are both too expensive and complex for mass production, most electrical probes are too invasive and disrupt process, and optical techniques face substantial difficulty in their analysis due to the complex chemistries and high powers that are characteristic of plasma processing. Microwave resonant probes present an interesting solution to this challenge.

This work presents the applicability of a spiral-shaped slot-type antenna known as the curling probe is used to measure the resonant frequency of the plasma within an Oxford Instruments Plasma Pro 100 - a commercially relevant plasma etching reactor. The probe was deployed in a SiO₂ etching process to ascertain the potential influence of the probe on the plasma process. Here, 150 mm silicon oxide wafer is clamped to a RF-biased table and is exposed to a CF4/O2 plasma acorss a range of plasma parameters. Clear dependencies on the resonance frequency can be seen across a plethora of operating conditions. Equally, spatially resolved etching rates were measured and no local variance of the etching rates near the curling probe was observed.