Si silicon substrates

Si Silicon substrate and processing technology and research has reached a level of perfection unmatched by any other material. Inherent material limitations are frequently overcome by continued optimisation and progress in processing technology. 

Two of the most important FET configurations make use of a-Si H as semiconductor material for the source - drain conduction channel. One uses a c-Si silicon substrate as gate material (Neudeck and Malhotra, 1975,1976 Matsumura and Nara, 1980 Thompson et al., 1982 Powell et al., 1981 Hayama and Matsumura, 1980 Matsumura et al., 1980 Abdulrida and Allison, 1983), the other uses glass only as a supporting substrate (Le-Comber et al., 1979, 1981 Tuan et al., 1982 Matsumura et al., 1981 Ishibashi and Matsumura, 1982 Lloyd et al., 1983 Nara and Matsumura, 1982 Matsumura and Hayama, 1980), and both employ the a-Si H technology for the semiconductor channel. Merely to give an idea of the differences, schematics of the two types of devices are shown in Fig. 15a,b. The transfer characteristics are reported and discussed in the previously mentioned literature. 

Several MCM designs have been developed MCM-C (ceramic substrate), MCM-L (laminate substrate), MCM-Si (silicon substrate), and MCM-D (deposited dielectric substrate). For MCMs, according to Feger and Feger [76], polymers are becoming the dielectric materials of choice because ... 

Figure 8. Atomic force microscopy cross-sectional scan of spun cast superlattice. Si silicon substrate PS polystyrene layer l ABD-grafied PMMA compound 1.

Figure 4.30 Schematic representation of a MOSFET transistor (S -source D - drain G - metallic gate Si - silicon substrate SiOj -insulating layer).

Figure 4.31 Schematic representation of a semiconductor enzyme sensor (ENFET), in which the enzyme is immobilized on the sensitive component of an ISFET (S - source D - drain Si - silicon substrate SiOt insulator).

As an example of the use of AES to obtain chemical, as well as elemental, information, the depth profiling of a nitrided silicon dioxide layer on a silicon substrate is shown in Figure 6. Using the linearized secondary electron cascade background subtraction technique and peak fitting of chemical line shape standards, the chemistry in the depth profile of the nitrided silicon dioxide layer was determined and is shown in Figure 6. This profile includes information on the percentage of the Si atoms that are bound in each of the chemistries present as a function of the depth in the film. 

Figure 7 SIMS depth profile of Si implanted into a 1- im layer of Al on a silicon substrate for 6-keV O2 bombardment The substrate is B doped.

Figure 3. Valence band spectra of Co/Si(100). Upper curve UPS spectra for 100 nm thick Co/Si(l 1 1) film middle curve thinned 4-5 nm Co/Si(l 1 1) film after ion etching (Co nanoparticles) lower curve clean silicon substrate after removing the Co layer by in situ sputtering. The photoemission data were obtained by He(I) excitation. (Reprinted from Ref [78], 1994, with permission from Springer.)...

Si-C formation technique with hydrogen-terminated silicon substrates can also be used as the covalent attachment of nanomaterials onto silicon surface. The possibility of assembling nanomaterials in order is strongly desired in order to enable efficient utilization of their unique nano-sized properties. Ordered arranging and position controlling of nanomaterials on solid substrates especially on silicon surface have been intensively studied [10]. In this manuscript, the nanoparticle immobilization by thermal Si-C formation will be discussed [11]. 

The time-of-flight secondary ion mass spectrum of a thick film prepared from Si(OEt)4 on a hydrophilic silicon substrate (Fig. 1) reveals a distribution of masses up to 1200 amu. The observed formation of cationized oligomers with a distribution shown in Fig. 1 can be explained by bond cleavage within the uppermost monolayer of the polycondensate of TEOS as a result of primary Ar+ ion impact. 

Fig. 2. Cross-section scanning electron micrographs of a-Si H deposited on etched crystalline silicon substrates under (a) CVD conditions, 2W, 300°C, 100% SiH4 and (b) PVD conditions, 25W, 300°C, 5% SiH4 in argon (Tsai et al., 1986).

The formation of etch pits and tunnels on n-Si during anodization in HF solutions was reported in the early 1970 s. It was found that the solid surface layer is the remaining substrate silicon left after anodic dissolution. The large current observed on n-Si at an anodic potential was postulated to be due to barrier breakdown.5,6 By early 80 s7"11 it was established that the brown films formed by anodization on silicon substrate of all types are a porous material with the same single crystalline structure as the substrate. 

It has been speculated that there is a common origin of the reduced chemical etch rate for (111) oriented silicon substrates and for highly p-type doped substrates. But the electrochemical investigations discussed above indicate that the passivation of highly doped p-type Si can be ascribed to an oxide film already present at OCP, while no such oxide film is observed on (111) silicon below PP. This supports models that ascribe the reduced chemical etch rate on (111) planes to a retarded kinetic for Si surface atoms with three backbonds, present at (111) interfaces [Gil, A12], as discussed in Section 4.1. 

A single layer of a micro PS film on a silicon substrate always reduces its reflectivity, because of its lower refractive index compared to bulk Si. Hence micro and meso PS films of a thickness around 100 nm have been proposed as anti-reflec-tive coatings for solar cells [Pr8, Gr9, Pol, Bi4, Scl8, StlO]. 

Therefore, surface modification strategies for the formation of direct silicon-carbon bonds require, first, a special pre-treatment of the silicon surface to prevent oxidation and, second, an activation of the silicon surface for subsequent reaction with organic moieties. This has been achieved by treatment of the silicon surface with hydrofluoric acid to generate a hydrogen-terminated Si(lll) surface, which can further react with unsaturated co-functionahzed alkenes in the presence of UV irradiation or by thermal activation [27,44,45]. Using this method, carboxylic acid modified silicon substrates have been successfully generated and coupled to thiol modified ONDs via a polylysine/sulfosuccinimidyl 4-(M-maleimidomethyl)-cyclohexane-l-carboxylate couphng (Fig. 12). 

In nonalkaline and nonfluoride aqueous solutions, silicon substrates behave as essentially inert electrodes due to the presence of a thin oxide film. Even in alkaline solutions, silicon is passivated by an oxide film at anodic potentials beyond the passivation peak. Very small current can pass through the passivated silicon surface of n- or p-type materials in the dark or under illumination. Depending on the pH of the electrolyte, oxidized surface sites Si—OH are more or less ionized into anionic species Si—0 owing to the acido-basic properties of such radicals so that the passivation current can vary in a wide range from a few... 

Organomagnesium alkoxides and aryloxides have been utilized in only a few applications. Methyhnagnesium f-butoxide 68 has been used in the chemical vapor deposition of MgO films onto silicon substrates . MgO films with good crystallinity were grown at 800 °C on Si(lll) surfaces, whereas polycrystalline films were formed at 400 °C. Intermediate temperatures produced multiple crystallite orientations. Similar results were obtained for deposition onto Si(lOO) surfaces over this range of temperatures. 

---