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Nucleation and growth of R.F. sputtered thin films / B. Belmekki 

Public ISBD Titre : Nucleation and growth of R.F. sputtered thin films Type de document : texte imprimé Auteurs : B. Belmekki, Auteur ; M. S. Raven, Directeur de thèse Editeur : Nottingham : [s.n.] Année de publication : 1983 Importance : 146 f. Présentation : ill. Format : 30 cm. Note générale : PhD Thesis : Electronics : University of Nottingham: 1983 Bibliogr. en fin de chapitre Langues : Anglais (eng) Mots-clés : ZnO  layers SiO₂  surface Single  crystal  layer rf  plasma Transmission  electron X-ray  diffraction Index. décimale : D003483 Résumé : An account is given of an investigation into the growth and microstructure of ZnO layers on SiO₂ surfaces by the rf sputtering process. The formation of single crystal layer-like structures of ZnO is reported for the first time. Such material has an important application for piezoelectric devices, and in particular surface acoustic wave devices. Also described is a study of the physical and elctrical properties of an rf plasma. A novel magnetron source has been developed which increases the sputtering rate by a factor of two, and simplifies the method of changing the target. The microstructure of ZnO layers was studied for different sputtering conditions using transmission electron microscopy (TEM) and X-ray diffraction. It is found that with increasing gas pressure in the range 15 - 50 m Torr at room temperature, the grain size increased and the density of c-axis orientated grains increased. Also with increasing substrate temperature at a pressure of 25 m Torr, the density of c-axis orientated grains increased. This is shown to be consistent with nucleation and growth theory. For higher substrate temperature, but below the recrystallisation temperature, ZnO layers were found to contain metal (Zn) precipitate which probably accounts for the high conductivity observed in ZnO layers produced under such conditions. Wich the application of a steady state electric field to the substrate, single crystal layers were produced. However, the crystals contained a large density of faults. With the aid of transmission electron microscopy, it aws possible to devise a structural model for the faults generated. These were observed as 1/3 and 2/3 (11.0) additional spots in the electron diffraction pattern. A model of the fault structure is proposed which is found to be consistent with the TEM observations using dark field imaging techniques. The results were interpreted as arising from low energy stacking fault formation which may begin either on a βb-layer (Zn excess) or on an αa-layer (O-vacancy). Such a movement of a single partial, leaves behind a stacking faut transforming a lamella of wurtzite into a lamella of sphalerite. The growth of such layers was found to be proceeded by a 2-dimensional sheet formation and plate-like features ware observed even at an early stage of film formation. A chemical analysis, using electron spectroscopy, was carried out on the ZnO layers in order to investigate the possible chemical effects resulting from the application of negative d.c. field to the substrate. Differences in the analysis of biased layers and non-biased layers were found. ESCA was also carried out on rf sputtered SiO₂ on Si. No interface layer was found, as is normally observed on thermally grown oxide SiO₂. Nucleation and growth of R.F. sputtered thin films [texte imprimé] / B. Belmekki, Auteur ; M. S. Raven, Directeur de thèse . - Nottingham : [s.n.], 1983 . - 146 f. : ill. ; 30 cm. PhD Thesis : Electronics : University of Nottingham: 1983 Bibliogr. en fin de chapitre Langues : Anglais (eng) Mots-clés : ZnO  layers SiO₂  surface Single  crystal  layer rf  plasma Transmission  electron X-ray  diffraction Index. décimale : D003483 Résumé : An account is given of an investigation into the growth and microstructure of ZnO layers on SiO₂ surfaces by the rf sputtering process. The formation of single crystal layer-like structures of ZnO is reported for the first time. Such material has an important application for piezoelectric devices, and in particular surface acoustic wave devices. Also described is a study of the physical and elctrical properties of an rf plasma. A novel magnetron source has been developed which increases the sputtering rate by a factor of two, and simplifies the method of changing the target. The microstructure of ZnO layers was studied for different sputtering conditions using transmission electron microscopy (TEM) and X-ray diffraction. It is found that with increasing gas pressure in the range 15 - 50 m Torr at room temperature, the grain size increased and the density of c-axis orientated grains increased. Also with increasing substrate temperature at a pressure of 25 m Torr, the density of c-axis orientated grains increased. This is shown to be consistent with nucleation and growth theory. For higher substrate temperature, but below the recrystallisation temperature, ZnO layers were found to contain metal (Zn) precipitate which probably accounts for the high conductivity observed in ZnO layers produced under such conditions. Wich the application of a steady state electric field to the substrate, single crystal layers were produced. However, the crystals contained a large density of faults. With the aid of transmission electron microscopy, it aws possible to devise a structural model for the faults generated. These were observed as 1/3 and 2/3 (11.0) additional spots in the electron diffraction pattern. A model of the fault structure is proposed which is found to be consistent with the TEM observations using dark field imaging techniques. The results were interpreted as arising from low energy stacking fault formation which may begin either on a βb-layer (Zn excess) or on an αa-layer (O-vacancy). Such a movement of a single partial, leaves behind a stacking faut transforming a lamella of wurtzite into a lamella of sphalerite. The growth of such layers was found to be proceeded by a 2-dimensional sheet formation and plate-like features ware observed even at an early stage of film formation. A chemical analysis, using electron spectroscopy, was carried out on the ZnO layers in order to investigate the possible chemical effects resulting from the application of negative d.c. field to the substrate. Differences in the analysis of biased layers and non-biased layers were found. ESCA was also carried out on rf sputtered SiO₂ on Si. No interface layer was found, as is normally observed on thermally grown oxide SiO₂.

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