Doped oxides diffusion

Dielectric Film Deposition. Dielectric films are found in all VLSI circuits to provide insulation between conducting layers, as diffusion and ion implantation (qv) masks, for diffusion from doped oxides, to cap doped films to prevent outdiffusion, and for passivating devices as a measure of protection against external contamination, moisture, and scratches. Properties that define the nature and function of dielectric films are the dielectric constant, the process temperature, and specific fabrication characteristics such as step coverage, gap-filling capabihties, density stress, contamination, thickness uniformity, deposition rate, and moisture resistance (2). Several processes are used to deposit dielectric films including atmospheric pressure CVD (APCVD), low pressure CVD (LPCVD), or plasma-enhanced CVD (PECVD) (see Plasma technology). 

Diffusion. Another technique for modifying the electrical properties of siUcon and siUcon-based films involves introducing small amounts of elements having differing electrical compositions, dopants, into substrate layers. Diffusion is commonly used. There are three ways dopants can be diffused into a substrate film (/) the surface can be exposed to a chemical vapor of the dopant at high temperatures, or (2) a doped-oxide, or (J) an ion-implanted layer can be used. Ion implantation is increasingly becoming the method of choice as the miniaturization of ICs advances. However, diffusion is used in... 

The uses of CVD silicon dioxide films are numerous and include insulation between conductive layers, diffusion masks, and ion-implantation masks for the diffusion of doped oxides, passivation against abrasion, scratches, and the penetration of impurities and moisture. Indeed, Si02 has been called the pivotal material of IC s.1 1 Several CVD reactions are presently used in the production of Si02 films, each having somewhat different characteristics. These reactions are described in Ch. 11. 

Silicon Dioxide. Si02 layers produced by PECVD are useful for intermetal dielectric layers and mechanical or chemical protection and as diffusion masks and gate oxides on compound-semiconductor devices. The films are generally formed by the plasma-enhanced reaction of SiH4 at 200-300 °C with nitrous oxide (N20), but CO, C02, or 02 have also been used (238-241). Other silicon sources including tetramethoxysilane, methyl dimethoxysilane, and tetramethylsilane have also been investigated (202). Diborane or phosphine can be added to the deposition atmosphere to form doped oxide layers. 

In this chapter we will summarize our initial research efforts covering some key processing steps in device technology such as doping via diffusion, thermal oxidation and contact deposition with respect to porous SiC. In addition, working on preparation of porous SiC samples we found significant variations in pore morphology as a function of... 

Dielectric materials are used for isolating conducting layers, to facilitate the diffusion of dopants from doped oxides, as diffusion and ion implantation masks, capping doped films to prevent loss of dopant, for gettering impurities, for protection against mois-... 

When the potential scan was extended to a more anodic region, an oxidation peak was observed at about 4.7V [17,18]. This is considered to be irreversible oxidation caused by over-doping. The diffusion of dopants in polyacetylene has been studied by some researchers, but the coefficient diffusion values show large discrepancies. Using the current pulse method and assuming one-dimensional linear diffusion. Will estimated the diffusion coefficient of BF4 anions in polyacetylene to be 6 x 10 cm s [19]. Takehara et al. estimated the diffusion coefficients of BF4, CIOJ, and PF ... 

This can be accomplished by using materials between the metal lines that have a lower dielectric constant (also referred to as the k-value). Copper interconnect was first introduced with silicon oxide as the dielectric material, with a dielectric constant of about 4.0 (the value depends on the specifics of the deposition process, such as the precursor used, the temperature of deposition, plasma parameters, etc.). Substitution of some of oxygen atoms with fluorine in fluorinated silicon glass decreased the dielectric constant (with values about 3.7, depending on the fluorine content and process parameters). It should be noted that the incorporation of fluorine was not an unalloyed benefit, since the addition of greater amounts of fluorine can affect the moisture stability of the F-doped oxide films, and the F can attack Ta-based diffusion barriers. 

By using p-n junction and 4-point probe resistivity techniques, an investigation was made of the diffusion of B into n-type single crystals from a doped oxide layer which was produced by reactive sputtering. The diffusion profiles which were obtained corresponded closely to the complementary error function. At 1100 to 1270C, and for a concentration of about lOl /cm, the data could be described by ... 

The diffusion of Sn from a Sn-doped oxide was studied by means of back-scattering and channelling techniques. It was found that the depth distribution of Sn could be fitted by a complementary error function. It was deduced that the diffiisivity at 1100 to 1200C could be described by ... 

Kiingas, R., Bidrawn, F., Vohs, J.M. Gorte, R.J. Doped-ceria diffusion barriers prepared by infiltration for solid oxide fuel-cells. Electrochem. Solid-State Lett. 13 (2010), pp. B87-B90. 

The result is the formation of a dense and uniform metal oxide layer in which the deposition rate is controlled by the diffusion rate of ionic species and the concentration of electronic charge carriers. This procedure is used to fabricate the thin layer of soHd electrolyte (yttria-stabilized 2irconia) and the interconnection (Mg-doped lanthanum chromite). 

There are several approaches to the preparation of multicomponent materials, and the method utilized depends largely on the nature of the conductor used. In the case of polyacetylene blends, in situ polymerization of acetylene into a polymeric matrix has been a successful technique. A film of the matrix polymer is initially swelled in a solution of a typical Ziegler-Natta type initiator and, after washing, the impregnated swollen matrix is exposed to acetylene gas. Polymerization occurs as acetylene diffuses into the membrane. The composite material is then oxidatively doped to form a conductor. Low density polyethylene (136,137) and polybutadiene (138) have both been used in this manner. 

Chemical erosion can be suppressed by doping with substitutional elements such as boron. This is demonstrated in Fig. 14 [47] which shows data for undoped pyrolitic graphite and several grades of boron doped graphite. The mechanism responsible for this suppression may include the reduced chemical activity of the boronized material, as demonstrated by the increased oxidation resistance of B doped carbons [48] or the suppressed diffusion caused by the interstitial trapping at boron sites. 

The transition from non-protective internal oxidation to the formation of a protective external alumina layer on nickel aluminium alloys at 1 000-1 300°C was studied by Hindam and Smeltzer . Addition of 2% A1 led to an increase in the oxidation rate compared with pure nickel, and the development of a duplex scale of aluminium-doped nickel oxide and the nickel aluminate spinel with rod-like internal oxide of alumina. During the early stages of oxidation of a 6% A1 alloy somewhat irreproducible behaviour was observed while the a-alumina layer developed by the coalescence of the rodlike internal precipitates and lateral diffusion of aluminium. At a lower temperature (800°C) Stott and Wood observed that the rate of oxidation was reduced by the addition of 0-5-4% A1 which they attributed to the blocking action of internal precipitates accumulating at the scale/alloy interface. At higher temperatures up to 1 200°C, however, an increase in the oxidation rate was observed due to aluminium doping of the nickel oxide and the inability to establish a healing layer of alumina. 

CVD, the other major deposition process, is used on a large scale. A typical low-E glass is obtained by depositing a thin film of silicon dioxide followed by another thin film of fluorine-doped tin oxide. The Si02 acts as a diffusion barrier and the Sn02 reduces the emissivity. A typical CVD apparatus is shown in Fig. 

Nanoparticles of Mn and Pr-doped ZnS and CdS-ZnS were synthesized by wrt chemical method and inverse micelle method. Physical and fluorescent properties wra cbaractmzed by X-ray diffraction (XRD) and photoluminescence (PL). ZnS nanopatlicles aniKaled optically in air shows higher PL intensity than in vacuum. PL intensity of Mn and Pr-doped ZnS nanoparticles was enhanced by the photo-oxidation and the diffusion of luminescent ion. The prepared CdS nanoparticles show cubic or hexagonal phase, depending on synthesis conditions. Core-shell nanoparticles rahanced PL intensity by passivation. The interfacial state between CdS core and shell material was unchan d by different surface treatment. 

An example of a layer structure mixed conductor is provided by the cathode material L CoC used in lithium batteries. In this solid the ionic conductivity component is due to the migration of Li+ ions between sheets of electronically conducting C0O2. The production of a successful mixed conductor by doping can be illustrated by the oxide Cei-jPxx02- Reduction of this solid produces oxygen vacancies and Pr3+ ions. The electronic conductivity mechanism in these oxides is believed to be by way of electron hopping between Pr4+ and Pr3+, and the ionic conductivity is essentially vacancy diffusion of O2- ions. 

Franco T, HoshiarDin Z, Szabo P, Lang M, and Schiller G. Plasma sprayed diffusion barrier layers based on doped perovskite-type LaCr03 at substrate-anode interface in solid oxide fuel cells. J. Fuel Cell Sci. Technol. 2007 4 406-412. 

---