The current state of the technologies of machining and processing of silicon wafers is described. The 8 inches diameter wafer process is just shifting to the process for 12 inches wafers. Actually, in wafer plants it is necessary to reconsider the wafer making methods which have been used so far. For instance, the method of wafer slicing is changing to multi-wire lapping from grinding with inner type thin diamond wheels, since the preparation of thinner and wider wheel metal plates becomes impossible for prospective large diameter silicon wafers. In wafer surface finishing, the present lapping and polishing methods will be replaced with a kind of grinding method using abrasive wheels as in glass lens manufacturing. However it might not become realistic soon, and, for the time being, the current conditions of lapping and chem-mechanical polishing will be utilized. The stock removing mechanism and the damaged layer in lapping or polishing are given an account.
The surface flatness of GaAs and InP mirror-polished wafers, which are typical III-V compound semiconductors substrates, is briefly reviewed with regard to the epitaxial-growth on them. The local thickness variation (LTV : 10 mm ?? ) of 3-inch (100) wafers is less than 1 μm, which is sufficient to fabricate the integrated circuits for the present. On the mirror-polished wafers with native oxide layers, no steps, estimated from the macroscopic surface unevenness and/or the inclination of the wafer orientation, are observed. There is only an atomic-scale roughness with four monolayers in depth. On the other hand, monolayer steps and terraces are formed by the epitaxial growth under appropriate growth conditions. The studies on the control of the shape and spacing of the steps ranging from 100 μm to 8 nm are continued.
An overview of the current attention to the oxide epitaxy is given to emphasize the importance of atomic scale control of oxide substrate surfaces. Examples of the ways to define the surfaces are presented. A detailed study on SrTiO3 substrate surfaces, including surface dynamics during wet etching and high temperature annealing is presented in real space in order to show the state of the arts for regulation of oxide substrate surface towards perfect epitaxy of oxide heterostructures.
Single crystal metal substrates have been used for the investigations of surfaces and adsorption kinetics of gas and many other kinds of materials. In order to people well-defined crystal surface, high accurate cutting from single crystal rods using X-ray technique, mechanical polishing and electrolytic polishing are necessary. In ultra high vacuum the single crystal surfaces are processed by use of several methods to obtain clean surfaces. In this paper, general metal surface processing techniques for obtaining clean surface are reviewed.
Layered materials, represented by graphite, mica, MoS2 or GaSe, have a lamellar structure consisting of two-dimensional unit layers. Each unit layer is formed via strong covalent or ionic type bonds, while there is no strong bond between two unit layers; they are bound together via van der Waals-type weak interaction. Then layered materials can be easily cleaved and the clean cleaved surface has a very wide and flat terrace without an active dangling bond. When the thin film growth is investigated on such an inactive surface of a layered material, only weak interaction works between the substrate and the grown material. This results in far small lattice-mismatch distortion in the grown film even if it has a different lattice constant or a crystal structure from the substrate. Consequently, single-crystalline heteroepitaxial growth of layered materials or organic molecular crystals can be achieved from the initial layer on the layered material substrate. In this paper we will explain structure, physical property and usage of some layered material substrates.
An experimental procedure for Au(111) single crystalline substrate fabrication on mica is described with its know-how from the preparation of cleaved mica and gold wires through annealing process in air. Relation between etch pit formation in a self-assembled monolayer (SAM) and 22 × √3 surface reconstruction is briefly overviewed. A new surface-reconstructed structure on Au(111) was confirmed and an etch-pit-free SAM was obtained on the surface for the first time. This new Au(111) surface will open a new field in fundamental surface studies and applications of SAM.
It is found that the secondary electron intensity from GaAs(001) surfaces, during molecular beam epitaxy (MBE) growth, relates to the work function (WF). Quantitative theoretical evaluation of the WF for the surface reconstructions was performed using the electron counting model. The relative and absolute values of WF agree well with the reported values. The WF for the other components, mixed compositions and surface reconstruction can be predicted.
We have studied the etching of Si(100)-2×1 by Cl and Br, using scanning tunneling microscopy to obtain morphological information that can be related to reaction and desorption pathways. Clean surfaces were exposed to molecular halogens at room temperature to produce well-defined chemisorption structures for coverages in the range 0.2-1.0 ML. Heating to 750-850 K induced etching by thermal desorption. Analysis of the halogen concentration before and after heating indicated that the rates of desorption for SiCl2 or SiBr2 were greatest for the intermediate coverage around 0.8 ML and were suppressed at the higher coverages. Hence, desorption is not simply proportional to the concentration of species that can form adsorbed precursors SiX2(a). We conclude that it is directly coupled to the creation of monomer vacancies adjacent to the SiX2(a) unit because this increases the lifetime of the excited state and increases the likelihood of its desorption. Increasing the surface concentration of halogens reduces the rate of vacancy formation. We show that these rates are also affected by a redimerization process in the high temperature Br-stabilized Si(100)-3×1 reconstruction that increases the likelihood of SiBr2(a) formation and enhances its desorption.