The CVD of Metals

This and the following chapters are areview of the materials that aredepositedby CVD, either onaproductionbasisor experimentally. The listing i s not all inclusive as the CVD of many elements and compounds has yetto be investigated or at least adequately reported in the literature. Each material is listed with its basic properties, its maj or CVD reactions and processes, and its present and potential applications. 

Large spreads in the reported values of properties are frequently found in the literature and the testing conditions are often poorly described. In addition to the testing conditions, many other factors may influence the results such as the following  

These factors should be described as much as possible for a test to be meaningful. 

The present chapter deals with the CVD of metals and some metal alloys and intermetallics. The metals are listed alphabetically. The range of applications is extensive as many of these materials play an important part in the fabrication of integrated circuits and other semiconductor devices in optoelectronic and optical applications, in corrosion protection, and in the design of structural parts. These applications are reviewed in greater depth in Chs. 13 to 19. 

Aluminumisalightmetal characterized by alowmeltingpointand high electrical conductivity. It has relatively low strength and is highly ductile. Its properties are summarized in Table 6.1. 

---

Gordon,R. G., Recent Advances in the CVD of Metal Nitrides and Oxides, Proc. of the Conf on MOCVD of Electronic Ceramics, Material Research Soc., Pittsburgh, PA (1994)... 

In view of the above applications and of the fact that extensive literature is actually available on the CVD of aluminum, copper, and tungsten, processing of nickel films has been chosen in this chapter as an introduction to the actual challenges in the CVD of metals. This field is large, especially if it is considered to include deposition on substrates such as preforms, membranes or, particles. Because of space limitations no attempt has been made to provide a comprehensive overview. Although the choice of materials to be discussed was of necessity subjective, it is expected that the present approach will be useful for the investigation of different cases of metal CVD. 

During the initial development period for most CVD processes, the selection of reactant species is quite simple Compounds commercially available for other purposes are considered. These include the traditional organometallic molecules MR, where M represents the metal of interest and R generally is restricted to methyl, ethyl, or other lower alkyl radicals. Several main group elements have volatile hydrides. Recently, unacceptable restrictions imposed on CVD processes by this limited range of precursors have reared their unsightly head, which has led to the development of a number of new source molecules. In this section, the structural motifs of some organometallic molecules are considered. A more detailed discussion of these concepts, as specifically applied to the CVD of metallic films, may be found in a VCH companion book, edited by Kodas and Hampden-Smith [2]. 

Although some of the more volatile metal iodides have been used as precursors in the CVD of metals and metal oxides [10], reports on the preparation of metal iodides by CVD are sparse. Copper iodide has been prepared by laser-assisted molecular beam deposition [11] and vapor phase electrolytic deposition has been used for the preparation of silver iodide [12]. 

---