Development of the patch-type flat-cutoff sensor for real-time plasma density monitoring

In industrial plasma processing, monitoring electron density is significantly important because it is closely related to discharge characteristics that affect the processing yield. Among various methods for measuring plasma parameters in plasma processing, the flat-cutoff sensor^1,2 has gained attention because it allows non-intrusive and real-time electron density measurements. In this study, a patch-type flat cutoff sensor (P-FCS) with an antenna-dielectric-metal structure was introduced to simplify and thin the structure. The electromagnetic (EM) simulation was utilized to optimize the P-FCS compared to the previously researched flat-cutoff sensor. Moreover, it exhibits the characteristic of deeper penetration of EM waves into the plasma region. These results indicate that the P-FCS, with its improved directionality compared to the conventional flat-cutoff sensor, is capable of measuring electron density closer to the plasma bulk when compared to the conventional flat-cutoff sensor. Through experimental verification, it was confirmed that P-FCS measures plasma density adjacent to the plasma bulk compared to the conventional flat-cutoff sensor.