| AVS 61st International Symposium & Exhibition | |
| Plasma Science and Technology | Monday Sessions |
| Session PS-MoA |
| Session: | Advanced FEOL/Gate Etching |
| Presenter: | Tamotsu Morimoto, Tokyo Electron Limited, Japan |
| Authors: | T. Morimoto, Tokyo Electron Limited, Japan H. Ohtake, Tokyo Electron America, Inc. T. Wanifuchi, Tokyo Electron Miyagi Limited, Japan |
| Correspondent: | Click to Email |
In this study, we found that the degradation of a silicon active area during N2/H2 block etching strongly depends on ion energy and flux because ions generate significant damage on the silicon surface as compared with the damage to the active area due to hydrogen radicals.
Plasma-induced damage on Si substrates has become a serious concern in CMOS fabrication processes. In addition, the appearance of Fin-FETs have made it necessary for plasma etching processes to use masks made by the organic film opening process and block etching in order to implant the P- or N-type regions. In this study, part of the fin structure was exposed to plasma during organic block etching. It was found that the source and drain regions of the fin area were damaged. However, the impact of the generated damaged layer on the electrical properties has not been clarified, especially junction leakage of the source and drain. In this paper, effect of etching using N2/H2 gas combination on p–n junction leakage current at reverse bias was investigated. Parameters of the N2/H2 plasma like flow rate, etching time, peak-to-peak voltage of the RF bias (Vpp), and the micro wave power (MW) were varied. Si substrate with a p–n junction was exposed to the N2/H2 plasma, followed by nickel silicidation to enable electrical characterization.
Junction leakage current increased by increasing Vpp and reducing MW for fixed etching times and was independent of the hydrogen ratio in the N2/H2 gas. This indicates that ion has a stronger influence on Si damage than H2 radicals. With etching depth kept fixed, a high hydrogen ratio showed less damage because etching rate was higher. In addition, we obtained smaller damage for higher Vpp at constant MW because etching time was shorter owing to the high etching rate. Accordingly, we can infer that ion energy and cumulative ion flux have a significant impact on the degradation of the p–n junction. From the transmission electron microscopy analysis, the damaged layer, which degraded Si crystallinity, became thicker by increasing the exposure time of the Si substrate to the N2/H2 plasma. Most probably, the damaged layer has a lot of defect sites which act as trap sites beside the junction, which in turn causes the p–n junction leakage current to increase.
We found that the ratio of ion/radical in the plasma should be lower to reduce the damage of silicon active area by N2/H2 block etching. High etching rate and low Vpp, which correspond to high hydrogen ratio and low RF bias, is the best combination for low-damage organic block etching.