Charakterisierung der Ätzrückstände nach dem Plasmaätzverfahren in der Aluminium-Strukturierung

Heidenblut, Maria

The subject of this thesis is the characterization of post etch residues after a metal etch process with Cl2/BCl3 plasma etch gases. Plasma etching processes are important for the fabrication of integrated circuits because these processes have a great impact on the size and the quality of the semiconductors on the wafer. As the semiconductor industry con-tinues to scale down the dimensions of the structures, a more and more precise control of the line shape profile of the etched features is required. The post etch residues formed mainly, but not only, on the sidewalls of structures after the completed plasma etching are regarded as a reliability risk and, thus, have to be re-moved. The removal process can be run in many ways with different chemistries due to different characteristics of the post etch residues. One of the influence factors on the features of the post etch residues is the photo-resist removal process (DSQ). Depending on the DSQ process, the molecular structure of the residues will differ. The chemical characteristics and changes in the molecular structure of the post etch residues were investigated, also, the cause of different solubility in the hydroxylamine-based solutions was subjected to analyses. Following analytical methods were used to characterize the residues: EDX (Energy Dispersive X-Ray Spectrometry), AES (Auger Electron Spectroscopy), TEM (Transmission Electron Microscopy), XPS (X-Ray Photoelectron Spectroscopy), ToF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry), Raman-Spectroscopy and FT-IR-Spectroscopy. Different metallization systems and the two main photo-resist removal modes were used to find out about the relationship between the structures, concentration of the elements, cross-linking of the residues and the process flow in the metallization block. The application of AES and EDX methods allowed the characterization of the surface of the post etch residues; by using TEM, structural information was obtained and the mate-rial characterization carried out; and by applying XPS, data about the concentration as well as the chemical and oxidation states of elements was collected; and the ToF-SIMS method provided specific molecular information. The results of the analytical methods verified the known facts about post etch residues consisting of aluminum, hydrogen, chlorine, carbon, titanium and other elements used in metallization systems. The chemi-cal bonding of the elements was also investigated. Using FT-IR and Raman spectros-copy, organic and inorganic molecular groups of the photo-resist were characterized. The organic compounds of the post etch residues could be identified as the incompletely oxidized or decomposed photo-resist molecules. By applying the Raman spectroscopy, it became evident that, depending on the DSQ mode, the cross-linking of the carbon-containing molecules in the post etch residues changes. A big impact on this effect can be ascribed to water that may be used in the first step of the DSQ photo-resist removal process. In the case of its application the ten-dency towards stronger cross-linking during the DSQ-process could be observed already after the first step of the process. As to the possible mechanisms of the cross-linking, various suggestions have been made.

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Heidenblut, Maria: Charakterisierung der Ätzrückstände nach dem Plasmaätzverfahren in der Aluminium-Strukturierung.

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