Metal carbides thin films

The number of oxides is large since most metallic elements form stable compounds with oxygen, either as single or mixed oxides. However, the CVD of many of these materials has yet to be investigated and generally this area of CVD has lagged behind the CVD of other ceramic materials, such as metals, carbides, or nitrides. The CVD of oxides has been slower to develop than other thin-film processes, particularly in optical applications where evaporation. 

Apart from the reactions described above for the formation of thin films of metals and compounds by the use of a solid source of the material, a very important industrial application of vapour phase transport involves the preparation of gas mixtures at room temperature which are then submitted to thermal decomposition in a high temperature furnace to produce a thin film at this temperature. Many of the molecular species and reactions which were considered earlier are used in this procedure, and so the conclusions which were drawn regarding choice and optimal performance apply again. For example, instead of using a solid source to prepare refractory compounds, as in the case of silicon carbide discussed above, a similar reaction has been used to prepare titanium boride coatings on silicon carbide and hafnium diboride coatings on carbon by means of a gaseous input to the deposition furnace (Choy and Derby, 1993) (Shinavski and Diefendorf, 1993). 

However, when heated with carbon monoxide at temperatures above 1,000°C, no carbonyl is obtained but a thin film of molybdenum carbide forms over the metal. 

Thin films of carbides and nitrides of Group 6 metals were synthesized by reaction of a metal film with a reactive gas at high temperature and by reactive sputtering. The phases obtained depended on the experimental conditions. High temperatures metastable phases (/i-WC, v and 6-MoC]. ) were obtained by reactive sputter deposition of films. The carbon concentration in such films depended on the temperature of the substrate and on the pressure. In some cases ordered sublattices of carbon and nitrogen were observed and epitaxial relationships between the deposit and the substrate were studied. 

During the last years, a great number of studies have focused on transition metal carbides and nitrides because of their numerous technological applications. Thin films are particularly interesting in integrated circuits,1 in decorative coatings,2 and as hard surface layers in cutting tools.3... 

Carbide or nitride films were also made by reacting metal films deposited by thermal evaporation or d.c. sputtering on MgO or Si02 with a flow of reactive gas at high temperature. The reactive gas was a CH4/H2 mixture or pure NH3. The reaction time was typically 2-4 h. As it is known that many phases of the metals can exist (bcc Cr, fee Cr, bee Mo, fee Mo, bcc W, fee W,. . . ), we will only present in this chapter the results where the precursor is the normal phase (the bcc metal). The conditions to prepare thin films of metals in this form have been described earlier.10... 

Arsenic Inorganic Chemistry Borides Solid-state Chemistry Carbides Transition Metal Solid-state Chemistry Chalcogenides Solid-state Chemistry Electronic Structure of Solids Mixed Valence Compounds Phosphoras Inorganic Chemistry Thin Film Synthesis of Solids Zintl Compounds. 

At high temperatures the metal will react slowly with certain gases. With carbon monoxide it produces a surface film of carbide, with nitrogen it produces a nitride film, and with hydrogen sulphide it reacts to form molybdenum disulphide. All of these films presumably interfere with the flow of gas to the metal surface, and in each case only a thin film of the product arises. Molybdenum is also very resistant to corrosive attack by mineral acids except for those such as nitric acid or chromic... 

Numerous ceramics are deposited via chemical vapor deposition. Oxide, carbide, nitride, and boride films can all be produced from gas phase precursors. This section gives details on the production-scale reactions for materials that are widely produced. In addition, a survey of the latest research including novel precursors and chemical reactions is provided. The discussion begins with the mature technologies of silicon dioxide, aluminum oxide, and silicon nitride CVD. Then the focus turns to the deposition of thin films having characteristics that are attractive for future applications in microelectronics, micromachinery, and hard coatings for tools and parts. These materials include aluminum nitride, boron nitride, titanium nitride, titanium dioxide, silicon carbide, and mixed-metal oxides such as those of the perovskite structure and those used as high To superconductors. 

In the case of glass, however, no great variations in behaviour between different types are expected because of their very similar structure and surface composition. Chemical vapour deposition reactions had already been tried by the last century, for instance in the refinement and deposition of silicon by reduction of SiF4 and SiCU with alkali metals [71] and in the refining of Ni using Ni-carbonyl in the Mond process [72,73]. The major impact of chemical vapour deposition on thin-film technology took place, starting some 60 years ago, when refractory compounds such as metal carbides, nitrides, silicides, borides and oxides as well as mixed phases of... 

---