We have analyzed the interfacial structure of selectively deposited LPCVD tungsten on monocrystalline silicon, polycrystalline silicon, and polycrystalline aluminum substrates. Cross‐sectional specimens were examined by transmission electron microscopy to determine the amount of substrate consumed by the selective deposition process and to assess the degree of lateral encroachment under masking SiO2 layers for different conditions of deposition and surface preparation. The tungsten‐silicon interfacial structure was found to depend strongly on the initial surface preparation. Immersion in a dilute HF solution resulted in a smooth interface, while a glow‐discharge treatment false(CF4+O2false) led to highly irregular interfaces, which, in extreme cases, contained tunnels extending 1 μm or more into the silicon substrate. Layers formed in WF6 plus H2 were found to consist of two layers, of which the lower layer is formed by the substrate reduction of WF6 .

The influence of p- and n-type doping on microdefect formation in macroscopically dislocation-free as-grown Czochralski silicon crystals has been studied using copper decoration, x-ray transmission topography, preferential etching, and high-voltage transmission electron microscopy. B-doped crystals are found to contain undecorated perfect dislocation loops of an interstitial nature. In Sb-doped crystals two other types of microdefects are present, one of which consists of a precipitate particle exhibiting a vacancy type of strain field. All defects are distributed in a striated pattern.

A qualitative model to explain the influence of processing parameters on the shape of the "bird's beak" structure, the transition region from field oxide to pad oxide, has been developed. The parameters included are (i) pad oxide thickness, (ii) field oxidation temperature, (iii) wafer orientation, (iv) thickness of the field oxide grown, and (v) field oxidation pressure. The strength of the influence of each parameter is also discussed. Experimental results are also presented that Verify the model.The local oxidation process (LOCOS) has been widely applied as a device isolation technique to improve the performance and to increase the packing density of integrated circuits (1). In a typical LOCOS process, there is a layer of SiO2 (the pad oxide layer) under the SisN4 oxidation mask. The pad oxide layer serves two major purposes: (i) as a buffer layer to reduce the stress from Si3N4 which causes defects in silicon during the LOCOS step, and (ii) as an etch step layer during the nitride etching step. Lateral diffusion of the oxidant through the pad oxide layer during the LOCOS step creates a region which is called the bird's beak (BB) near the edge of the masking nitride layer.The length of the BB (Lbb) is comparable to the thickness of the field oxide which is typically of the order of 1 #m. Therefore, the magnitude of Lbb makes it an important factor in VLSI technology. Not only does the BB region reduce the area of the active devices, but also the edge effect due to the BB has to be taken into account for small geometry devices. For two-dimensional device modeling, it is important to know the shape of the BB in detail. Furthermore, it is desirable to use the oxide wall as a self-aligned edge for the contact opening to improve the density of the circuit. The contact etching step then is critical so that a good contact can be made without exposing the p-n junction under the BB region. All of these require an understanding of the influence of the LOCOS processing parameters on the shape of the BB.In this paper, a qualitative model is presented to describe the relationship between the processing conditions and the shape of the BB. The processing parameters included in this paper are (i) pad oxide thickness (ii) oxidation temperature, (iii) wafer orientation, (iv) thickness of the field oxide grown, and (v) oxidation pressure. The shape of the BB is obtained by transmission electron microscope (TEM) or scanning electron microscope (SEM) cross-sectional techniques. The data agree very well with the proposed model. The Mechanism of the Bird's Beak FormationThe growth mechanism of the BB can be illustrated by the schematic drawing of Fig. la. At a particular time during the LOCOS process, the point S (t), y ___ 0, is the end of the BB. At the same time, some amount of the field oxide, Tox(t), has grown in areas without SisN4. As the oxidation reaction continues, the oxidant diffuses through Tox(t) to increase the thickness of the field oxide and through the existing BB region to extend the length of the BB. By comparing...

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