Cross-sectional atomic force microscopy of III-V semiconductor device structures

Atomic force microscopy (AFM) in air has been used to study various III-V semiconductor heterostructures. Topography of the (110) cleaved cross-sections has been examined where oxidation processes modify the surface and allow the structures to be investigated. This research aims to establish the potential of this technique as a metrology tool for use in an industrial environment. AlGas/GaAs was used as the prototypical system, and a test structure grown in order to establish how differences in oxidation rates between the different material compositions may be used to establish composition and layer thickness for heterostructure devices. The dependence of oxidation rate on layer composition and thickness has been confirmed. The mechanisms of field-aided and diffusion limited growth have been determined to be responsible for the oxidation of the AlGas layers within the test structure, with field aided being the dominant mode for materials x < 0.8 and diffusion limited dominating for layers x > 0.8 observed. In addition, a new effect of interface enhanced oxide growth have been observed and quantified in terms of layer composition. It is found to be most important for Al09Gao, As layers of 50--100 nm thickness during relatively early stages of oxidation. The use of phase detection microscopy has also been applied for the first time to determine the presence of layers where no measurable step heights are present. Unlike previous reports, there has been no observed difference in oxidation rate between p- and -type materials. These findings have been applied to real device structures, where the material composition of Al/JaAs can be determined to within x 0.02 and layer widths may be determined to within 3 nm at best. It has been shown that step height differences of as little as 0.1 A are sufficient to distinguish between layers, and that quantum wells of as little as 42 A in width are detectable