Thermally grown oxide films

The oxide film formed in dry air at room temperature consists of a spinel phase, probably a solid solution of magnetite and maghemite. Such films form on magnetic tapes. They are around 1.5-2.0 nm thick, and in a dry atmosphere, can provide indefinite protection (e.g. the Delhi pillar). Ali and Wood (1969) found that with time and at a relative humidity of 46%, some hematite developed as well. At higher temperatures (200-300 °C) well defined duplex films with an inner layer of magnetite 

1) Note that these passive layers v hich contained hematite w ere formed at room temperature. 

Iron plane/direction Oxide Oxide plane/direction 

Burnishing is the formation of black-brown oxide films on iron and its alloys by controlled oxidation of cleaned metal surfaces. These films are extremely complex and contain, in addition to maghemite and magnetite (or a substituted magnetite for Ni, Mo or Co alloys), various nitride phases - Fe4N, FeaN and FeN. The nitride phases are adjacent to the metal and the iron oxides are in the outer layers of the film (Gebhardt, 1973). 

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It is recognized that transmission IR only presents an integrated picture of the silicon conversion throughout the whole thickness of the resist. However, the bulk of the oxidation occurs at the surface, and the equivalent oxide thickness obtained from the calibration curve for thermally grown oxide films can be taken to represent the approximate thickness of the plasma-treated films. The thickness of the oxide film formed by the various pretreatments is summarized in Table II. 

The etch rate of thermally grown oxide may be altered by postoxidation treatments. Ion implantation at a certain level, depending on the nature of damage and distribution, has been found to increase the etch rate. Also, an electric field, by applying an anodic potential onto a thermally grown oxide film, is able to inject hydroxyls into the oxide. The etch rate of the hydroxyl penetrated region, depending on the hydroxyl concentration, is much faster than the unaffected thermal oxide... 

In the commercial semiconductor world of silicon (Si) devices, great importance is attached to diffusion and ion implantation. These processes play a key role in the local doping performance through windows in a thermally grown oxide film. Because the diffusion coefficients for most dopants in silicon carbide (SiC) are negligible, at temperatures below 1800°C, the development of ion implantation into SiC for microelectronic technology is of major importance. 

Akimichi et al. [79] used as a device substrate an n-type silicon wafer covered with a thermally grown oxide film (270 nm thick) which functions as a gate insulator. Two finger-shaped metal electrodes (Au... 

Some of the most significant developments in the CVD of Si02 include experiments in plasma CVD at 350°C via electron cyclotron resonance (ECR) to gain improved control of the deposition rate and obtain a quality equivalent to that of the thermally grown oxide (see Ch. 5). Deposition from diacetoxyditertiarybutoxy silane at 450°C has also been shown to significantly improve the Si02 film properties. " ]... 

The two most common substrates for thin film electrodes are various types of glass—soda-lime, Pyrex, and various forms of quartz or fused silica—and silicon wafers that have been treated to produce an insulating surface layer (typically a thermally grown oxide or nitride). Other possible substrates include mica, which can be readily cleaved to produce an ordered surface, and various ceramic materials. All of these materials can be produced in very flat, smooth... 

Si/SiOi Interface. There is little information on the interface of silicon and an anodic oxide film. For thermally grown oxides, a transition region exists at the Si/Si02 interface where there is an excess of unoxidized Si bonds with a density on the order of the surface atom density. The interface structurally consists of two distinct regions. A few atomic layers near the interface contain Si atoms in intermediate oxidation states, i.e., Sf (Si20), Si (SiO), and Si (Si203). The S atoms are located farther out than... 

The correlation between the midgap interfacial state density Du and the thickness strain in thermally grown Si02 films has been studied [110]. The At decreases with the oxidation temperature and with the oxide film thickness. The frequency of the Si—O stretching vibrations increases with increasing oxidation temperature and film thickness. The peak position v is expressed as a function of the average Si—O—Si bond angle as... 

The relative sensitivity factor (RSF) of LW spectra of the silicon were obtained for the calculation of the thickness estimation of the ultra thin native oxide film. Although the characteristics nature of the thermal silicon oxide film on the silicon wafers might be different from that of the ultra thin native oxide film, RSF of LVV spectra for the silicon were obtained by the measurement of Auger signal intensity using thermally grown silicon oxide film of 100 nm thickness as a reference sample... 

Vernon et al The cell construction is shown in Figure 15 it has a barrier consisting of an initial 40-50 A cromium film covered by a similar thickness of either copper or silver to enhance film conductivity. The contact grid is ly t ick aluminium and the insulator a thermally grown oxide 15 A. A typical V-I curve for a 1.75 cm cell is shown in Figure 16. 

Fig. 5.1. A cross-sectional micrograph of an electron-beam physical vapor deposited yttria-stablized zirconia film which is partially delaminated from the nickel-base superalloy substrate. This ceramic layer and the interlayers comprising the bond-coat and thermally grown oxide serve as the thermal-barrier coating system in gas turbine engines, as described in Section 1.2.4. Reproduced with permission from Padture et al. (2002).

A new two-step method, partial reactive sputtering deposition-wet oxidation, has been developed by the present authors. They found that modulation of precursors in the sputtering step can provide more opportunities for control of the structural and functional properties of the thermally grown oxides. This technique may also open a new way to fabricate porous ZnO films [205,218]. The innovative part of this processing is that a partial reactive deposition is introduced. 

Conventional electronic devices are made on silicon wafers. The fabrication of a silicon MISFET starts with the diffusion (or implantation) of the source and drain, followed by the growing of the insulating layer, usually thermally grown silicon oxide, and ends with the deposition of the metal electrodes. In TFTs, the semiconductor is not a bulk material, but a thin film, so that the device presents an inverted architecture. It is built on an appropriate substrate and the deposition of the semiconductor constitutes the last step of the process. TFT structures can be divided into two families (Fig. 14-12). In coplanar devices, all layers are on the same side of the semiconductor. Conversely, in staggered structures gate and source-drain stand on opposing sides of the semiconductor layer. 

As an example of the latter technique, Volkman et al. demonstrated the feasibility of using spin-cast zinc oxide nanoparticles encapsulated in 1-dodecanethiol to fabricate a functional transistor.44 The zinc oxide was deposited on a thermally grown silicon dioxide layer on a conventional silicon wafer, with thermally evaporated gold source and drain electrodes. As reported, the process requires very small particles (3nm or less) and a 400 °C forming gas anneal. A similar approach was also reported by Petrat, demonstrating n-channel thin-film transistor operation using a nanoparticle solution of zinc oxide dispersed onto a thermally grown silicon dioxide layer on a conventional... 

Electron injection has been observed during the chemical dissolution of an oxide film in HF [Mai, Ozl, Bi5]. The injected electrons are easily detected if the anodized electrode is n-type and kept in the dark. Independently of oxide thickness and whether the oxide is thermally grown or formed by anodization, injected electrons are only observed during the dissolution of the last few monolayers adjacent to the silicon interface. The electron injection current transient depends on dissolution rate respectively HF concentration, however, the exchanged charge per area is always in the order of 0.6 mC cm-2. This is shown in Fig. 4.14 for an n-type silicon electrode illuminated with chopped light. The transient injection current is clearly visible in the dark phases. 

The only other plasma-enhanced CVD film that has seen wide use in integrated circuit manufacture is the plasma oxide film. We say "so-called" because it is not truly Si02, but rather SiOxNyHz. In fact, it is just this ability to modify the film stoichiometry that makes these films so valuable. Many of the film characteristics change depending on this stoichiometry, so it allows a freedom to alter film characteristics that is not possible with thermally-grown films. 

As an example of the use of this technique, a silicon wafer lightly doped with phosphorus is doped with additional phosphorus by ion implantation (dose of 3.5 x 10ncm"2). A thermal oxide film of 857 A thickness was initially grown on the wafer. The variation of dopant concentration with depth from the oxide-silicon interface is shown in Figure 16. The rise in dopant close... 

The dual-channel reactor is a silicon chip device and was manufactured by photolithography and potassium hydroxide etching [274]. Silicon oxide was thermally grown on silicon and thin films of nickel were evaporated for passivation because direct fluorination was carried out in this device. Pyrex was bonded anodically to the modified microstructured silicon wafer (see Figure 4.34, top). 

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