Atmospheric downstream plasma etching of Si wafers

A dry etch technology for processing Si wafers using an atmospheric downstream plasma (ADP) source is described. Application of ADP etching for backside damage removal after grinding and wafer thinning is discussed. ADP is an inert gas thermal plasma generated by DC discharge at atmospheric pressure in the process chamber. The reactant (freon) is injected into the plasma stream outside the plasma source. Due to the high temperature of the plasma, the reactant is fully decomposed, resulting in high reactant usage efficiency and no freon emission from the tool. Plasma stream stability is maintained via a closed loop system, resulting in uniform removal of thin Si layers. By deploying the plasma in a downstream configuration, ADP prevents ion impact damage while keeping wafer temperatures below 200°C. This technique enables high rates of Si removal without generating Si crystal defects, surface contamination, or wafer stress. Wafer thinning results are reported. Critical success factors include thickness uniformity, surface roughness, Si crystal defects, and contamination levels. SEM, TEM, AFM and TXRF techniques were used for the study. In addition to ADP technology, this paper also describes ADP tool design