Deposition thin films

Thin film deposition for producing dense membranes has been presented in Sections 3.1.1 and 3.1.2. The processes can also be used to prepare porous membranes by adjusting the operating conditions. For example, transition metals and their alloys can be deposited on a porous ceramic, glass, or stainless steel support by the thin-film deposition process to produce porous metal membranes with small pore sizes [Teijin, 1984]. 

In order to study the diffusion of metal atoms in the organic films, Ag containing radioactive Ag tracer atoms was evaporated at a crucible temperature of 680 °C at a base chamber pressure of 1.8 x 10 mbar. During evaporation the pressure increased to 10 mbar. The Au tracers were evaporated at 860 °C at a base pressure of 1.8 x 10 mbar. 

The source and drain contacts of the examined OFETs were deposited by thermal evaporation of Au as described above for deposition of the radiotracers. Deposition of the contacts was not performed in the same chamber as the radio-tracer deposition in order to avoid contamination of the sample with radioactive isotopes. Patterning of the contact stractures was obtained using a stainless steel shadow mask. By deposition of Au an array of nine contacts was formed. The contact area of the Au was 50 x 50 pm and the distance between the contacts varied from 300 pm to 3290 pm. Three Au contact arrays with a thickness of 50 nm were deposited onto a 40 nm Pc film at a substrate temperature of 75 °C. The first contact array (Array 1 in the following) was deposited at a rate of 0.8 nm/min. For the second set of contacts (Array 2 in the following) first a submonolayer of Au was deposited very slowly ( 1 ML/h) on top of the Pc film in order to allow strong diffusion. Afterwards, the contacts were deposited at the same rate of 0.8 nm/min as the first set. The third array (Array 3 in the following) was deposited at 0.8 nm/min with the substrate at room temperature. 

In this section we will discuss three basic steps in microfabrication thin film deposition, photolithography, and etching. The whole fabrication process usually involves iterations of these steps so the device structure is built layer by layer until it is completed. 

The first step to build the devices is depositing materials onto the substrates. This is usually performed by deposition of thin films. 

The first method is physical vapor deposition (PVD) divided into subcategories of evaporation and sputtering. Evaporation is used primarily for deposition of metals. A metal sample is held in a container (crucible) and heated by a resistive coil made of a refractory metal, an inductive coil, or an electron (e-) beam. The metal sample is heated and evaporated as a result. A flux of the metal vapor thus reaches the substrate, where it cools and deposits a thin film of the metal onto the substrate. 

The second method is chemical vapor deposition (CVD). As suggested by the name, unlike PVD, chemical reactions are involved in CVD. Precursor materials in gas phases are introduced into heated furnaces and react at the substrate surface to deposit the desired thin film. For example, CVD is typically performed in low pressure conditions ( 1 Torr) this technique is called LPCVD and usually requires an inert diluent gas such as nitrogen. CVD processes typically involve high temperatures (above 500°C). This is a very important factor to consider in a designing a fabrication process. For example, no metal except tungsten (W) is allowed into CVD furnaces. LPCVD usually has very slow deposition rate. Plasma-enhanced CVD (PECVD) can deposit dielectric films much faster. It also allows deposition at lower temperatures ( 400°C). This is very useful when a substrate has already been metalized. 

A final remark concerns the oxidation of silicon by reacting oxygen with silicon or polycrystalline silicon to form Si02—also performed in a furnace. Although technically the Si02 is directly thermally grown from the Si, this process is similar to LPCVD in many aspects. 

The synthesized diblock copolymers were dried in a vacuum oven at 60 °C overnight. Then 10 %wt stock solutions were prepared in anhydrous toluene and filtered with 0.45 xm Teflon (PTFE) Alters. Micrometer thick copolymer Aims were spun, drop-or blade-coated, typically using 3.5 xl of copolymer solution per square centimeter. Films prepared by spin coating were spun at 200-700rpm for 45 s. 

One method of overcoming the detrimental solvent dewetting effects is to use liquid C02 as the solvent for nanoparticle dispersions [52], since C02 does not experience the dewetting instabilities due to its extremely low surface tension [53]. In this case, nanoparticles must be stabilized with fluorinated ligands [30, 33, 54—65] or other C02-philic ligands [60,66-76], such that they will disperse in the C02 prior to dropcasting. These fluorinated ligands tend be toxic and environmentally persistent and, typically, only very small nanoparticles can be dispersed at low concentrations. 

CXLs can be used to provide improved solubilities compared with neat C02 while still providing the desirable low interfacial properties. The controlled reduction in 

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The following two sections will focus on epitaxial growth from a surface science perspective with the aim of revealing the fundamentals of tliin-film growth. As will be discussed below, surface science studies of thin-film deposition have contributed greatly to an atomic-level understanding of nucleation and growth. 

Figure C2.13.6. Schematic illustrations of plasma - assisted thin - film deposition.

Smith D L 1997 Thin-Film Deposition Principles and Practice (New York McGraw-Hill)... 

Finishes for aluminum products can be both decorative and useful. Processes in use include anodic oxidation, chemical conversion coating, electrochemical graining, electroplating (qv), thin film deposition, porcelain enameling, and painting. Some alloys respond better than others to such treatments. 

The thermal decomposition of silanes in the presence of hydrogen into siUcon for production of ultrapure, semiconductor-grade siUcon has become an important art, known as the Siemens process (13). A variety of process parameters, which usually include the introduction of hydrogen, have been studied. Silane can be used to deposit siUcon at temperatures below 1000°C (14). Dichlorosilane deposits siUcon at 1000—1150°C (15,16). Ttichlorosilane has been reported as a source for siUcon deposition at >1150° C (17). Tribromosilane is ordinarily a source for siUcon deposition at 600—800°C (18). Thin-film deposition of siUcon metal from silane and disilane takes place at temperatures as low as 640°C, but results in amorphous hydrogenated siUcon (19). 

Surface Coverage. The surface-covering abiHty of deposition techniques is best when the materials are deposited from a vapor or from a fluid having no need for an appHed voltage. The macroscopic and microscopic surface coverage of a thin film deposited by PVD techniques on a substrate surface may be improved by the use of gas scattering and concurrent bombardment during film deposition. 

Figure 1 The FTIR spectrum of the oxide of siiicon (thin film deposited by CVD). Primery...

Fig. 4.10. Fluorescence signal from small particles or thin films deposited on a silicon substrate used as sample carrier. The intensity was calculated for particles, thin films, or sections ofdiffe-rent thickness but equal mass of analyte, and plotted against the glancing angle f. A Mo-Ka beam was assumed for excitation. Particles or films more than 100 nm thick show double intensity below the critical angle of0.1° [4.21].

Epitaxy. There is often a sharp orientation relationship between a singlecrystal substrate and a thin-film deposit, depending on the crystal structures and lattice parameters of the two substances. When such a relationship exists, the deposit is said to be in epitaxy with the substrate. The simplest relationship is parallel orientation, and this is common in semiconductor heterostructures, but more complex relationships are often encountered. 

R. W. Smith. A kinetic Monte Carlo simulation of fiber texture formation during thin-film deposition. J Appl Physics 57 1196, 1997. 

Zilko, J. L., Metallo-Organic CVD Technology and Equipment, in Handbook of Thin-Film Deposition Processes and Techniques, (K. K. Shuegraf, ed.), Noyes Publications, Park Ridge, NJ (1988)... 

Interconnect. Three-dimensional structures require interconnections between the various levels. This is achieved by small, high aspect-ratio holes that provide electrical contact. These holes include the contact fills which connect the semiconductor silicon area of the device to the first-level metal, and the via holes which connect the first level metal to the second and subsequent metal levels (see Fig. 13.1). The interconnect presents a major fabrication challenge since these high-aspect holes, which may be as small as 0.25 im across, must be completely filled with a diffusion barrier material (such as CVD titanium nitride) and a conductor metal such as CVD tungsten. The ability to fill the interconnects is a major factor in selecting a thin-film deposition process. 

Conversely, in the summer, it would still have a high transparency for the visible, but a high reflectivity for the near infrared and a high emissivity for the far infrared. The present state of the art of thin-films deposition still falls short of this goal which may have to wait for the development of suitable photochromic coating materials. 

Appendix Alternative Processes for Thin-Film Deposition and Surface Modification... 

Fig. 46—XPS spectrum of [emim][Tf2N] thin film deposited on a polycrystalline Au substrate.

Yamaguchi K, Yoshida T, Sugiura T, Minoura H (1998) A Novel approach for CdS thin-film deposition electrochemically induced atom-by-atom growth of CdS thin films from acidic chemical bath. J Phys Chem B 102 9677-9686... 

Nicolau YF, Dupuy M, Brunei M (1990) ZnS, CdS, and Zni j Cdj S thin films deposited by the successive ionic layer adsorption and reaction process. J Electrochem Soc 137 2915-2924... 

Venkatasamy V, Mathe MK, Cox SM, Happek U, Stickney JL (2006) Optimization studies of HgSe thin film deposition by electrochemical atomic layer epitaxy (EC-ALE). Electrochim Acta 51 4347-4351... 

Laser ablation of polymer films has been extensively investigated, both for application to their surface modification and thin-film deposition and for elucidation of the mechanism [15]. Dopant-induced laser ablation of polymer films has also been investigated [16]. In this technique ablation is induced by excitation not of the target polymer film itself but of a small amount of the photosensitizer doped in the polymer film. When dye molecules are doped site-selectively into the nanoscale microdomain structures of diblock copolymer films, dopant-induced laser ablation is expected to create a change in the morphology of nanoscale structures on the polymer surface. 

Figure 5. Morphology and particle size distribution of an island silver thin film deposited on native oxide covered silicon (a) before ion bombardment and after (b) 0.5 keV Ar sputtering with 1.1 X 10, (c) 2.5 X 10, and (d) 3.9 x 10 ion/cm dose. Sputtering speed for silver was around 3-4ML/min. Total elapsed sputtering time is indicated on each size distribution graphs. (Reprinted from Ref [123], 2003, with permission from Springer.)...

Maurice H. Francombe and John L. Vossen, Physics of Thin Films, Advances in Research and Development, Plasma Sources for Thin Film Deposition and Etching,yo ivat 18, 1994. 

Nanoparticle Thin-Film Deposition on MEMS Devices... 

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