Radio frequency (RF) generators are key components in semiconductor manufacturing units and therefore it is important to have a reliable methodology for monitoring and controlling RF power levels while at the same time not incurring losses in the transmission line and load. In general, we find that plasma chambers are lacking in diagnostics. Power measurements from the generator are not accurate as the power reaching to the plasma is less due to match box losses. Since plasma offers the dynamic load to the generator, it is also important to monitor plasma directly. To improve process productivity, process monitoring techniques based on ex-situ plasma diagnostic methods have garnered much attention since key process parameters such as etching and deposition rates are related to the plasma parameters.
The traditional non- invasive solution to monitor the plasma process is the use of directional couplers and VI probes, inserted in a transmission line. The measurements about impedance, phase, current and voltages waveform etc. enable the customer to appreciate many important characteristics about the process. To name a few, we will discuss briefly about fault detection, end point detection and matchbox characterization.
Radio-Frequency (RF) voltage-current (VI) probes mounted between the matching network and the plasma can detect plasma impedance changes at the fundamental and harmonic RF frequencies. The plasma impedance is very sensitive to any electrical, chemical, mechanical and/or geometrical changes that may occur in the reactor.
Find out more about Fault Detection here.
Endpoint detection is primarily performed to indicate the completion of a chamber cleaning process or to indicate when a wafer layer is etched through. Deposition chambers usually go through a cycle of chamber wall seasoning, wafer processing and chamber cleaning.
Find out more about End Point Detection here.
RF matching unit is a critical component of a radio frequency (RF) plasma processing equipment’s power delivery system. In general, the RF matching network consists of load and tune capacitors as well as an inductive coil. In the ideal world, the matching unit should not absorb any power.
Find out more about Matchbox Characterization here.
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