Binary thinning

Poocza (P2), 1958 Theoretical treatment of binary thin-film distillation,... 

There are two general types of CVD reactors, one is the chamber type and the other is the tube type. The tube type reactor is typically a hot wall reactor and has been used in the semiconductor industry for the deposition of simple binary thin films such as SijN. This type of deposition reactor usually has quite large throughput because a few hundred wafers can be loaded and processed. However, the CVD precursors should have large diffusivities in the gas phase and be stable over the homogeneous reactions to produce uniform deposition on a large number of wafers. For tube type reactors, as for all hot wall type reactors, the CVD reaction occurs on the wall of the reactor as well as on the wafers. This increases the consumption of the precursors. Therefore, CVD reactors for BST thin films are the other type, except for a very recent report from Toshiba of Japan. They reported CVD of BST thin films utilizing a tube type reactor which had a rotatory wafer holder to improve the uniformity of deposited films. Details of the CVD reactor have not been reported yet, thus, in this section only the details of chamber type reactors are discussed. 

Wise, S.M. (2003) Diffuse Interface Model for Microstructural Evolution of Stressed, Binary Thin Films on Patterned Substrates. PhD thesis, University of Vhginia. 

Wise, S.M. and Johnson, W.C. (2003) Numerical simulations of pattern-directed phase decomposition in a stressed, binary thin film./, Appl. Phys., 94 (2), 889-898. 

Johnson, W.C. and Wise, S.M. (2002) Phase decomposition of a binary thin film on a patterned substrate. Appi. Phys. Lett., 81 (5), 919-921. 

S. M. Wise and William C. Johnson, Numerical Simulation of Pattern-directed Phase Decomposition in a Stressed, Binary Thin Film, J. Appl. Phys. 94(2), 2003,889... 

Ott A W, Kiaus J W, Johnson J M and George S M 1997 Ai203 thin fiim growth on Si(IOO) using binary reaction sequence chemistry Thin Solid Films 292 135-44... 

In many cases, this binary material will not be homogeneous all the way up to the surface, because it is covered with a thin ovedayer of contamination. Therefore, for most real samples, the photoelectrons of interest from atoms A and B are coming from a depth equal to the thickness of the ovedayer, d. In this case. 

Go Binary and Ternary Alloyed Thin Films. Most of the thin-film media for longitudinal and perpendicular recording consist of Co—X—Y binary or ternary alloys. In most cases Co—Cr is used for perpendicular recording while for the high density longitudinal media Co—Cr—X is used X = Pt, Ta, Ni). For the latter it is essential to deposit this alloy on a Cr underlayer in order to obtain the necessary in-plane orientation. A second element combined with Co has important consequences for the Curie temperature (T ) of the alloy, at which the spontaneous magnetisation disappears. The for... 

It is believed that the thin TLCP-rich skin layer or interlayer may be responsible for a pluglike flow (i.e., a continuous velocity profile), due to a composition-dependent interfacial slippage [9], and, therefore, for the improved fluidity of this binary system. 

Dilute binary alloys of nickel with elements such as aluminium, beryllium and manganese which form more stable sulphides than does nickel, are more resistant to attack by sulphur than nickel itself. Pfeiffer measured the rate of attack in sulphur vapour (13 Pa) at 620°C. Values around 0- 15gm s were reported for Ni and Ni-0-5Fe, compared with about 0-07-0-1 gm s for dilute alloys with 0-05% Be, 0-5% Al or 1-5% Mn. In such alloys a parabolic rate law is obeyed the rate-determining factor is most probably the diffusion of nickel ions, which is impeded by the formation of very thin surface layers of the more stable sulphides of the solute elements. Iron additions have little effect on the resistance to attack of nickel as both metals have similar affinities for sulphur. Alloying with other elements, of which silver is an example, produced decreased resistance to sulphur attack. In the case of dilute chromium additions Mrowec reported that at low levels (<2%) rates of attack were increased, whereas at a level of 4% a reduction in the parabolic rate constant was observed. The increased rates were attributed to Wagner doping effects, while the reduction was believed to result from the... 

Fig. 8. The system CHCla-HaS-HaO. The univariant equilibria of the single-component systems have been indicated by dotted lines, those of the binary systems by thin lines, and those of the ternary system by heavy lines. The latter are approximate only, except for the lower half of the four-phase line HnLxL%G measured by von Stackelberg and Friihbuss.4 ...

Figure 8 represents the system CHC13-H2S-H20, where hydrates occur in the binary systems H2S-H20 and CHC13-H20, both of which are known.41 48 It is assumed that the binary system H2S-CHC13 does not show demixing in the liquid phase so that Lx represents a nonaqueous liquid which changes continuously from pure H2S to pure CHC13. All binary equilibria have been drawn with thin lines in Fig. 8. 

Later on, this concept was extended to precursors containing both elements of the desired material already connected by a chemical bond in a single molecule. Such precursors are mainly referred to as single source precursors. Their potential application for the deposition of thin films of the corresponding binary materials by MOCVD processes could be demonstrated. In particular Lewis acid-base adducts R3M—ER3 and four- and six-membered heterocycles [R2MER x (Fig- 1) have been in the focus of research groups both in industry and university. Consequently, the development of powerful synthetic pathways for the preparation of such precursors has been forced. 

A smaller class of type II alloys of II-VI binaries also exists, including the (CdS) ,(ZnSe)i (CdS) ,(ZnTe)i (CdSe) ,(ZnSe)i (CdS) ,(CdTe)i-. (CdSe)x(CdTe)i i , and (CdS) c(ZnS)i i systems, which transform at some critical composition from the W to the ZB structure. Importantly, the transition temperatures are usually well below those required to attain a thermodynamically stable wurtzite form for the binary constituents (e.g., 700-800 °C for pure CdS and > 1,020 "C for pure ZnS). The type 11 pseudobinary CdxZni jcSe is of considerable interest in thin film form for the development of tandem solar cells as well as for the fabrication of superlattices and phosphor materials for monitors. The CdSe Tei-x alloy is one of the most investigated semiconductors in photoelectrochemical applications. 

In the following, selected results will be presented on the conventional electrochemical synthesis of metal chalcogenide binary and ternary systems, conducted by employing variants of the methods outlined in the previous sections. A brief account of chemical bath deposition principles exemplified will be addressed at the end of this chapter, as being closely related to electrochemical deposition of thin films. 

A quantitative analysis of the kinetics of CdSe deposition from selenosulfate, Cd(II)-EDTA baths in terms of a mechanism involving nucleation and electrode kinetics has been given by Kutzmutz et al. [65], Note also that selenosulfate-containing baths have been used for the anodic selenization of vacuum-deposited metal films in order to synthesize CdSe and other binary selenide semiconductor thin films such as CuSe and InSe [66],... 

In a similar way, electrochemistry may provide an atomic level control over the deposit, using electric potential (rather than temperature) to restrict deposition of elements. A surface electrochemical reaction limited in this manner is merely underpotential deposition (UPD see Sect. 4.3 for a detailed discussion). In ECALE, thin films of chemical compounds are formed, an atomic layer at a time, by using UPD, in a cycle thus, the formation of a binary compound involves the oxidative UPD of one element and the reductive UPD of another. The potential for the former should be negative of that used for the latter in order for the deposit to remain stable while the other component elements are being deposited. Practically, this sequential deposition is implemented by using a dual bath system or a flow cell, so as to alternately expose an electrode surface to different electrolytes. When conditions are well defined, the electrolytic layers are prone to grow two dimensionally rather than three dimensionally. ECALE requires the definition of precise experimental conditions, such as potentials, reactants, concentration, pH, charge-time, which are strictly dependent on the particular compound one wants to form, and the substrate as well. The problems with this technique are that the electrode is required to be rinsed after each UPD deposition, which may result in loss of potential control, deposit reproducibility problems, and waste of time and solution. Automated deposition systems have been developed as an attempt to overcome these problems. 

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