Silicon vapor phase, deposition

Organoindium substances are important, especially for the production of materials by metal-organic chemical vapor-phase deposition (MOCVD). This technique involves the thermal decomposition of mixtures of an organoindium compound and a compound such as phosphine (PH3), leading to the deposition of ordered layers of InP. The resulting compound can be used in the formation of semiconductors and solid-state optical devices (similar to silicon), see also Inorganic Chemistry. 

Derivation (1) Sintering mixtures of metal powder and boron at 2000C (2) reduction of mixture of the metal oxide and boric oxide with aluminum, silicon, or carbon (3) fused-salt electrolysis (4) vapor-phase deposition. 

The silicon wafers were placed above a previously de-aired solution consisting of a mixture of 100 pL organosilane and 3 mb paraffin. The vapor-phase deposition of the molecular film on the substrate was performed in a vacuum chamber (50 min at 5 x 10 Torr) at room temperature. 

Bhushan B, Hansford D, Lee KK (2006) Surface modification of silicon and polydimethylsiloxane surfaces with vapor-phase-deposited ultrathin fluorosilane films for biomedical nanodevices. J Vac Sci Technol A 24(4) 1197-1202... 

Surface modification using vapor-phase deposition is very promising for some biomedical nanodevices and has advantages over liquid-phase deposition, since the vapor phase has the ability to permeate more efficiently into silicon nanochannels. A vapor-phase deposition system described by Bhushan et al. [11] used... 

This reaction is carried out in tall fluidized beds of high L/dt ratio. Pressures up to 200 kPa are used at temperatures around 300°C. The copper catalyst is deposited onto the surface of the silicon metal particles. The product is a vapor-phase material and the particulate silicon is gradually consumed. As the particle diameter decreases the minimum fluidization velocity decreases also. While the linear velocity decreases, the mass velocity of the fluid increases with conversion. Therefore, the leftover small particles with the copper catalyst and some debris leave the reactor at the top exit. 

Epitaxial Layers. Epitaxial deposition produces a single crystal layer on a substrate for device fabrication or a layer for multilevel conductive interconnects which may be of much higher quality than the substrate. The epitaxial layer may have a different dopant concentration as a result of introducing the dopant during the epitaxial growth process or may have a different composition than the substrate as in silicon on sapphire. Methods used for epitaxial growth include chemical vapor deposition (CVD), vapor phase epitaxy (VPE), liquid phase epitaxy (LPE), molecular beam epitaxy (MBE) and solid phase epitaxy (SPE). 

Another approach in generating molecular insulating layers without the need of chemical conversion after deposition is the use of preliminarily modified molecules which can form dense self-assembled monolayers. To create dense self-assembled monolayers with sufficient robustness and insulating properties, a modified alkyltrichlorosilane with an aromatic end-group (18-phenoxyoctadecyl)tri-chlorosilane (PhO-OTS chemical structure Fig. 6.15a) was synthesized and tested [50]. The SAMs were created in a one-step process from vapor phase or solution. On self-assembly on a natively oxidized silicon surface the n-n interaction between the phenoxy end-groups of adjacent molecules creates an intermolecular top-link, leading to a more closely packed surface compared to monolayer than when linear end groups are used. 

Chemical vapor infiltration (CVI) is widely used in advanced composites manufacturing to deposit carbon, silicon carbide, boron nitride and other refractory materials within porous fiber preforms. " Because vapor phase reactants are deposited on solid fiber surfaces, CVI is clearly a special case of chemical vapor deposition (CVD). The distinguishing feature of CVI is that reactant gases are intended to infiltrate a permeable medium, in part at least, prior to... 

For silicon, the process can be used to grow films with thicknesses of 1 jtimto >100 nm. Some processes require high substrate temperature, whereas others do not require significant heating of the substrate. For photovoltaic applications, epitaxial silicon is usually grown using liquid-phase epitaxy (LPE) [1-3] and vapor-phase epitaxy (VPE) [4-6], which is a modification of chemical vapor deposition (CVD). 

When silicon is deposited from the vapor phase at ambient temperature, it solidifies as amorphous silicon. Vapor deposited bilayers and multilayers of silicon with metals thus consist of polycrystallinc metal and amorphous silicon. The earliest observations of amorphous silicide formation by SSAR were made on such diffusion couples [2.51, 54], Similar results were also obtained earlier by Hauser when Au was diffused into amorphous Tc [2.56], Figure 2.15 shows an example of an amorphous silicide formed by reaction of amorphous silicon with polycrystallinc Ni-metal at a temperature of 350"C for reaction times of 2 and 10 s [2.55,57], The reaction experiments were carried out by a flash-healing method (see [2.55] for details). In this example, the amorphous phase grows concurrently with a crystalline silicide. The amorphous phase is in contact with amorphous Si and the crystalline silicide in contact with the Ni layer. As in the case of typical mctal/metal systems, the amorphous interlayer is planar and uniform. It is also interesting that the interface between amorphous silicon and the amorphous silicide appears to be atomically sharp despite the fact that both phases are amorphous. This suggests that amorphous silicon (a covalently bonded non metallic amorphous phase with fourfold coordinated silicon atoms) is distinctly different from an amorphous silicide (a metallically bonded system with higher atomic coordination number). These two phases are apparently connected by a discontinuous phase transformation. 

Next, the sacrificial layer is patterned and holes are etched into the oxide using established lithography and etching processes. These holes will be filled and thus act as anchor points on the left end of the two cantilevers formed later (Fig. 5.3.1 e). In the next step, the functional polysilicon layer is deposited (Fig. 5.3.1b). The thickness of this layer determines the mechanical properties of the movable beam. The thicker it is, the stiffer the beam will be in the z axis, which is desirable for structures intended to move only in the xy direction. But its thickness is limited by the capabilities of the deposition process used. The functional layer is next patterned and etched (Fig. 5.3.1c). Depending on the thickness of the polysilicon layer, specific trench etch processes (as described later on) may be required, especially when this layer is rather thick. Finally, the sacrificial layer is removed (Fig. 5.3.1 d). This is typically done with wet or vapor phase etches to dissolve the silicon dioxide and leave parts of the functional structures free-standing and movable. When using wet etching, special care has to be taken to prevent Stic-... 

Clays are actually secondary minerals—meaning that they are formed chiefly by the weathering of primary minerals. Primary minerals are those that form directly by precipitation from solution or magma, or by deposition from the vapor phase. In the case of clays their primary or parent minerals are feldspars, the mineral group with the greatest abundance in Earth s crust. Feldspars and clays are actually aluminosilicates. The formation of an aluminosilicate involves the replacement of a significant portion of the silicon in the tetrahedral backbone by aluminum. 

---