The relief structure (RS) with vertical sidewalls (SW) is promising as the linewidth measure for low-voltage (LV)SEM due to similarity of its profile to the one of the SCCDRM linewidth standards. So it can be used as the terminal link in the metrological traceability chain beginning from this standard. But there is an obstacle for its calibration: RS image are changing over time during continuous scanning the measure by electron beam that is natural for measure usage. Changes arise from the variation of the emission of slow secondary electrons (SSE) forming the image of the RS surface. This emission variation appears in turn due to the change of induced charge on the RS surface. Changes of the charge disposed near RS edges have critical influence on RS linewidth that leads to its value uncertainty. It is revealed that the degree of the influence depends on the layout of emitting site on RS sidewall (SW). Emission variations from its lower sites have a less induction on the RS image. So if one uses a regime of SSE extraction from these lower SW sites then the linewidth uncertainty is bound to decrease. Internal parts of the vertical SW are preferred not only due to its higher degree of its surface smoothness compared to its upper parts but also due to its SSE emission stability during scanning.
A scan of trapezoidal protrusions by an electron beam was carried out in a SEM during an hour. This allows detecting some laws of a profile change due to contamination. The detection is based on analysis of distorted protrusion images obtained by the SEM. The greatest distortion of protrusion images was discovered around a scanned area. This distortion is not uniformed in the area (and associated with a non-uniform profile change in that area) that leads to a pitch change of a periodic structure. The protrusion image change in the scanned area is minimal, contrary to perceptible structure profile changes in that area. The latest circumstance allows defining geometrical parameters of a protrusion using a model developed for measurement of these parameters for a non-distorted structure. It was discovered that contamination process of periodic linear structures beyond the scanned area differs from the corresponding process for a flat surface. The difference firstly is due to dissimilar contribution of a volume and surface diffusion of hydrocarbon particles (HCP) that induce the contamination into various structure areas. Secondly it is due to different diffusion velocity of surface HCPs that are moving along and across of stripes with trapezoidal profile and over surfaces with different crystallographic indexes.
KEYWORDS: Scanning electron microscopy, Monte Carlo methods, Electron microscopes, Calibration, Instrument modeling, Software, Clocks, Image acquisition, Device simulation, Nanotechnology
Application of virtual instruments to a process of measurements of geometrical characteristics of investigated objects is considered. Methods of construction of virtual instruments on a base of imitators and simulators are discussed. It is demonstrated, that a virtual scanning electron microscope (SEM) can be constructed only on the base of simulator. Examples of work of the virtual SEM in a low-voltage mode and in modes of registration of back scattered electrons (BSE) and slow secondary of electrons (SSE) are given.
Traditional insight of effective probe of scanning electron microscope (SEM) is considered. A contradiction of this insight with experimental results registered at scanning of test objects with the trapezoidal profile and large slope angles by SEM probe is detected. A new insight of effective probe based on analyzes of the experimental results registered by SEM working in a back scattered electron (BSE) mode is proposed.
Semi empirical model of image formation is proposed for scanning electron microscope (SEM) working in low and high voltage modes with registration of back scattered (BSE) and slow secondary (SSE) electrons. The model is based on analysis of experiments executed with a test object with trapezoidal profile and with large slope angles scanned in a SEM. The model is designated for application in virtual SEM.
An unusual phenomenon of non-monotone change of phosphosilicate glass network, including its structural elements (i.e. inter-atomic bonds, phosphorous and siliceous point defects, ring structures of SiO4 tetrahedra) under laser irradiation at 193 nm is discovered. The phenomenon is explained by applying
conceptions of the rigidity percolation theory, which describes connectivity of atoms in network, for the phosphosilicate glass under UV-exposure. Presence of phosphorous atoms in silica glass decreases the rigidity of the network in comparison with silica. Generation of point defects in the phosphosilicate network due to the two-photon light absorption decreases of the rigidity in addition and finally leads to achievement of the network rigidity threshold. This results in a transformation of the network from the rigid to a floppy mode where switches of bonds between atoms are possible. But later under exposure the network switches back into the rigid mode and the cycle of rigidity change can be repeated several times. This quasi-periodical transformation of phosphosilicate glass network leads to the corresponding change of inter-atomic bonds, point defects concentration and reconstruction of ring structures during an exposure. The presence off the network in the floppy mode affords one to explain a change off phosphosilicate glass density and induced index in a new manner.
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