The reactive ion etching of titanium is described using rf discharges of CCl4 and O2 with additions of fluorine containing gases. Because of these additions the titanium etch rate increases substantially in comparison with the pure CCl4/O2 plasma. This is presumably due to a shift of equilibrium reactions within the discharge towards the production of the volatile etch product. Process parameters are given for which the reactive ion etching of titanium with a photoresist mask is highly anisotropic and an etch end point control by optical emission spectroscopy is possible.
A new process to form shallow trench isolation for ultra-large-scale integrated devices is presented. This technique utilizes chemical mechanical polish steps to provide a virtual planar surface at the end of processing for isolations of various size, ranging from 0.5 μm to several hundred μm. Superior uniformity has been obtained on wafers of 8 in. diam processed in a productionlike environment. Good device isolation also has been found.
The net positive charge density QN/q and the interface state density D~T of MNOS structures on p-Si (100) with APCVD and plasma silicon nitride is studied as a function of the nitride deposition temperature and the postdeposition annealing temperature. For APCVD silicon nitride, a decrease of QN/q is accompanied by an increase of D~T with increasing deposition an d annealing temperature. Electron irradiation (30 keV and 5 • 10 -5 C/cm 2 dosage) did not affect QN/q, whereas D~T was increased for nitride films deposited below 800~ For plasma silicon nitride, both QN/q and D~T decreased with deposition and annealing temperature up to 450~ Very low interface state densities (8 • 109 cm -2 eV -~) could be achieved. These low D~T values are due to the influence of hydrogen incorporated in the PECVD silicon nitride films. Very high positive charge densities (>1013 cm -2) could be obtained by cesium contamination of the plasma nitride films.Pyrolytic chemical vapor deposited (CVD) silicon nitride films are widely used as active layers in microelectronics, e.g., as gate dielectric in nonvolatile memory elements. The performance of these metal-nitride-oxide-silicon (MNOS) devices is strongly dependent on the density of fast interface states and fixed insulator charges (1-3).Plasma enhanced CVD (PECVD) silicon nitride films are almost exclusively applied for final passivation of semiconductor devices. There is, however, growing interest in using plasma Si nitride as an electrically active layer. It appears to be promising as dielectric for high efficiency silicon inversion layer solar cells (4, 5), as well as for amorphous silicon thin film transistors for application as switching elements in large area displays and imaging arrays (6, 7). In both cases, the properties of the plasma Si nitride/silicon interface, such as the fixed nitride charges and the fast interface states, are of great importance. However, no data about these quantities are available in the literature up to now. For the case of inversion layer solar cells, a high density of fixed positive insulator charges in conjunction with a low interface state density is required in order to obtain a highly conductive inversion layer (8,9). In contrast to MOS devices, where a correlation between the fixed oxide charges and the interface states was found (10), for MNOS structures with atmospheric pressure CVD (APCVD) Si nitride, some data pointing to an inverse behavior were already reported by us (11,12).In the present work the grown-in fixed charges (density QJq) and the fast surface states (density D*~T at midgap) have been investigated as a function of the nitride deposition temperature and after postdeposition heat-treatment in nitrogen.The studies were performed on A1/Si nitride/thin Si oxide/p-Si (100) structures with APCVD as well as with PECVD Si nitride; the different behavior of these dielectric films will be outlined. Particularly for the case of plasma Si nitride on silicon, where very low interface state densities could be achieved, the crucial role of hy...
Two-dimensional microshutter arrays are being developed at NASA Goddard Space Flight Center (GSFC) for the Next Generation Space Telescope (NGST) for use in the near-infrared region. Functioning as focal plane object selection devices, the microshutter arrays are 2-D programmable masks with high efficiency and high contrast. The NGST environment requires cryogenic operation at 45 K. Arrays are close-packed silicon nitride membranes with a unit cell size of 100x100 micrometer. Individual shutters are patterned with a torsion flexure permitting shutters to open 90 degrees with minimized mechanical stress concentration. The mechanical shutter arrays are fabricated with MEMS technologies. The processing includes a RIE front-etch to form shutters out of the nitride membrane, an anisotropic back-etch for wafer thinning, and a deep RIE (DRIE) back-etch down to the nitride shutter membrane to form frames and to relieve the shutters from the silicon substrate. A layer of magnetic material is deposited onto each shutter. Onto the side-wall of the support structure a metal layer is deposited that acts as a vertical hold electrode. Shutters are rotated into the support structure by means of an external magnet that is swept across the shutter array for opening. Addressing is performed through a scheme using row and column address lines on each chip and external addressing electronics.
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