Stress engineering related to the LSI process is required. With shallow trench isolation (STI) structures, a high stress field causes a variation in electrical characteristics. Although stress fields in a Si substrate can be detected by Raman spectroscopy, no effective technique has been reported for the measurement of nanoscale stress fields in a dielectric material used for STI filling. Recently, we have reported that ''cathodoluminescence (CL) spectroscopy'' enables us to detect nanometer-scale stress fields in LSI structures. In this study, we performed the first estimation of the stress fields with a STI structure by CL and Raman spectroscopy, as well as finite element method (FEM) calculation. We were able to repeatedly acquire clear stress distributions by CL and Raman spectroscopy. Moreover, CL, Raman, and FEM results showed excellent agreement with one another, revealing that a large variation in stresses along the AA/STI boundary was induced by the intrinsic tensile stress of the SiO 2 film.

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A new effect has been observed at low temperatures when conduction is restricted to two dimensions in an n-type GaAs impurity band. When the carrier concentration is less than 10" cm-2 the conductance is found to oscillate as a function of carrier concentration. The oscillations can be resolved into simple series with the minima periodic functions of the mean electron separation. Suppression of the main series and enhancement of a subsidiary series is achieved by increasing the electric field responsible for transport; this results in differential negative resistance at certain carrier concentrations. The effect may possibly arise from, an ordering of the electrons by Coulomb repulsion, although it is difficult to envisage how this can happen in a random array of donors and we have at present no model to explain the effect.