Frequency domain reflectometry of plasma chambers

Frequency domain reflectometry (FDR) is used to compare the electrical characteristics of five industrial plasma chambers, without the plasma present, used in the manufacture of semiconductors devices at Intel-Ireland. A scalar network analyzer (SNA), consisting of a tracking generator/spectrum analyzer and a radio frequency bridge was used to sweep the chambers from 1 MHz to 1 GHz. The non-invasive nature of the measurement interrogates the matching network, the wafer platen electrode fringing capacitance to ground, and radio frequency resistive loss. The resulting frequency response gives a unique fingerprint of the chamber, and is completely transferable between chambers for post-maintenance qualification and chamber comparison. The results from three electron cyclotron resonance (ECR) chambers are compared with the two single-frequency capacitively coupled plasma chambers and one dual-frequency inductively coupled plasma chamber. A comparative chamber survey of the three ECR chambers reveals a strong wafer electrode reflection in the 500 MHz frequency region. Whereas, for slab-like plasma chamber designs (such as the LRC Rainbow 4400 chamber) the wafer electrode response is at 14-15 MHz. It is found that the chamber design and individual components have a unique frequency response. A linear analogue circuit simulator was used to verify and characterize the measurements.