We present here a scanning tunneling microscope study of the initial bonding structure and subsequent reaction mechanism of C 2 H 2 with the Si͑001͒ surface. Upon exposure of the sample at room temperature to 0.2 L of C 2 H 2 ͑approximately 20% coverage͒ adsorption of the molecule on alternate dimer pairs is observed, leading to either a local 2ϫ2 or c(2ϫ4) structure. In the filled-state image, a local minimum is observed in the center of the reacted dimer pairs, while the unreacted dimer pairs maintain the normal bean-shaped contour of the clean surface. The molecule forms an overlayer with either local 2ϫ2 or c(4ϫ2) order, leading to a saturation coverage of 0.5 monolayers. Upon annealing the substrate at 775 K the surface becomes disordered and the steps are no longer visible. After further annealing at 875 K, SiC clusters are formed and the 2ϫ1 structure is again seen between the clusters. For a starting coverage of 20%, annealing to higher temperatures around 1100 K leads to pinning of the step movement by the SiC clusters. For a starting coverage of 0.5 monolayer, annealing at 1100 K results in faceting of the surface. Further annealing at 1275 K creates anisotropic facets that are oriented along the ͓110͔ direction with a typical aspect ratio of approximately 4 to 5. These facets act as nucleation sites for subsequent carbonization and SiC growth. ͓S0163-1829͑97͒05032-7͔
This report describes the characteristics for the development of a compound lens that consists of a single pole-piece objective lens and an electrostatic bipotential lens. By applying a relatively small voltage of around 1 kV to the specimen and the bipotential lens, the image quality for low acceleration voltage is improved to a condition better than with just a single pole-piece lens. Even if the wafer is tilted to a large angle, the electric field near the specimen does not become asymmetrical, and there is no occurrence of astigmatic aberration or a reduction of the secondary electron signal. Therefore, 300 mm diameter wafers can be tilted with large angles to observe patterns, particles and defects with high-resolution SEM. Lastly, when the specimen is not tilted, a topographic image of the specimen surface can be obtained by detecting the secondary electron with dual detectors.
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