| AVS 62nd International Symposium & Exhibition | |
| Plasma Science and Technology | Monday Sessions |
| Session PS-MoM |
| Session: | Advanced FEOL/Gate Etching |
| Presenter: | Miyako Matsui, Hitachi Ltd., Japan |
| Authors: | M. Matsui, Hitachi Ltd., Japan M. Morimoto, Hitachi High-Technologies Corp. N. Ikeda, Hitachi High-Technologies Corp. T. Ono, Hitachi High-Technologies Corp. |
| Correspondent: | Click to Email |
Three dimensional (3D) transistors, such as a Fin-FET, have increasingly necessitated etching processes with higher selectivity and greater anisotropy. For example, a Si3N4 spacer layer needs to be anisotropically etched with a vertical profile without leaving residue on the sidewalls of the fins while keeping high selectivity in regard to Si fins. To provide more highly selective and more anisotropic etching for fabricating next-generation 3D devices, an etching system combining a pulsed-microwave ECR plasma and time-modulated wafer bias was developed.
In this study, the mechanism of highly selective etching with a pulsed-microwave ECR plasma was investigated by analyzing surface-reaction layers formed on etched materials. To clarify the etching mechanisms of poly-Si, Si3N4, and SiO2, surface-reaction layers formed not only on unpatterned surfaces but also at the bottoms of line-and-space patterns were analyzed by XPS. Specimens were etched using an HBr/O2/Ar/CH4 gas chemistry for poly-Si etching and using a CH3F/O2/Ar gas chemistry for Si3N4 etching. The XPS results revealed that a modified layer formed on all etched materials and that a polymer layer formed on the modified layer. To determine the effects of the etching parameters on etching selectivity, the thickness and composition of the reaction layers, which were the polymer layer and the modified layer, were quantitatively analyzed. To examine the thermal reactivity between the reaction layers and the etched materials, etched surfaces were analyzed by TDS.
Highly selective etching mainly originated from the difference in the thickness of the polymer layers that formed on the etched materials under the pulsed plasma. The thickness of the polymer layer was controlled so that etching did not stop even at a low wafer bias voltage. Reactivity between the reaction layers and the etched material was controlled by adjusting the composition of the reaction layers. Especially in the case of Si3N4 etching, the N in the Si3N4 layer thermally reacted with the reaction layers, forming NH3 or HCN, and the Si in the Si3N4 layer had high reactivity with the F in the reaction layers. Due to the high reactivity between the F-rich reaction layers and the Si3N4 layer caused by the pulsed plasma, the polymer layer became thin even at a low wafer bias and thus promoted ion-assisted etching. As a result, wide process windows were provided by formation of the reaction layers under the pulsed plasma.