Stabilization of impedance matching system using RF transformer

We have investigated a new dry ashing system for manufacturing of semiconductor devices. For this purpose, we have proposed a plasma system using RF transformer, which is essential to dry ashing, in order to maintain the plasma excitation. This RF transformer can achieve a balanced connection of inductive coil. This system also can improve the ashing uniformity, resulting in high capability for various plasma processing. From the measurement of antenna potential, the deviation of etching rate for balanced connection was reduced to 35%, as compared to that for the unbalanced connection, resulting in improvement of uniformity. By employing an impedance conversion method using RF transformer, the incident signal power can be supplied even though the 25 times higher load impedance than conventional plasma systems. As for the T-type impedance matching using RF transformer, the matching time was reduced to 0.2 s from 8 s for conventional L-type impedance matching system. Wide range impedance matching can be achieved by using T-type impedance matching system. It was confirmed that this system can achieve a stable plasma processing and reduction of ashing process step number, as well as reduction of power consumption and environmental load.