DEFECT FORMATION IN EPITAXIAL OXIDE DIELECTRIC LAYERS DUE TO SUBSTRATE SURFACE-RELIEF

Defects were characterized in epitaxial (001) CeO2 films deposited and planarized in situ on patterned (001) LaAlO3 substrates by ion beam a ssisted deposition (IBAD). A hill and valley structure with steps runn ing parallel to the [100] LaAlO3 axis was produced on the surface of t he substrate by photolithography and ion beam etching prior to film de position. A conformal epitaxial CeO2 layer of similar to 100 nm thickn ess was deposited on the heated substrate by e-beam evaporation. Latti ce-matching between the e-beam film and the substrate was of the type: (001) CeO2\\(001) LaAlO3 and [110] CeO2\\[100] LaAlO3. Evaporative de position of additional film onto the conformal layer was accompanied b y bombardment with a 500 eV argon/oxygen ion beam to promote in situ p lanarization. Extreme lattice misfit for the orientation (001) CeO2\\( 001) LaAlO2 and [001] CeO2\\[001] LaAlO3 caused formation of dislocati ons in the e-beam CeO2 film in the vicinity of individual ledges in th e substrate surface. Coherence of the CeO2 film was locally lost in th e step regions of the hill and valley structure. The large patterned s teps, which are composed of numerous adjacent ledges in the LaAlO3 sur face, caused nucleation of CeO2 with a tilt misalignment of up to simi lar to 5 degrees about the substrate [100]. Nucleation and growth of n onepitaxial CeO2 crystallites was observed along the step regions of t he film during the IBAD portion of deposition. Defect formation in the e-beam ceria layer due to substrate surface relief indicates that ''l attice engineering'' of multilayer epitaxial structures may not be pos sible when nonplanar surfaces are created during device fabrication. T he IBAD CeO2 layer was more defective than the conformal layer deposit ed without the impinging ion beam, even in the portions of the film wh ere epitaxy was maintained throughout both layers.