Semiconductor substrates

For films on non-metallic substrates (semiconductors, dielectrics) the situation is much more complex. In contrast with metallic surfaces both parallel and perpendicular vibrational components of the adsorbate can be detected. The sign and intensity of RAIRS-bands depend heavily on the angle of incidence, on the polarization of the radiation, and on the orientation of vibrational transition moments [4.267]. 

One of the simplest techniques used to electrodeposit semiconductors is cathodic deposition from nonaqueous solutions containing elemental chalcogen (S, Se) and a metal salt, first described by Baranski and Fawcett [17]. Two main mechanisms have been considered deposition of metal (e.g. Cd) followed by chemical reaction with elemental chalcogen in solution and reduction of chalcogen to (poly)chalcogenide followed by ionic reaction between chalco-genide and metal cations. Which mechanism will dominate depends on the specific system (substrate, semiconductor, deposition conditions) and may change in the same deposition. 

When dissimilar materials are joined and subsequently heated, the differential expansion introduces stresses and strains in the materials and joints. Examples of material pairs that may see differential expansions are semiconductors to substrates, semiconductors to packages, leadless packages to circuit cards, flip chips to substrates, substrates to packages, and packages to heat sinks. If the differential expansion is not accommodated, then a fracture will occur in one or more of the materials. 

The ability to tailor CTE is important in many applications. For example, titanium fittings are often used with carbon/epoxy (C/Ep) structures instead of aluminum, because the latter has a much larger CTE that can cause high thermal stresses under thermal cycling. Another application for which CTE is important is electronic packaging, because thermal stresses can cause failure of ceramic substrates, semiconductors, and solder joints. 

Plasmonic metamaterials can be utilized to match the impedance of environment (air) to the substrate (semiconductor material) in the optical range (or acmally any other range) directly by optimizing their particles design. Thus one can obtain perfect black surfaces denoted as superabsorbers [229, 230]. Such nanostructured surfaces are able to absorb light in a wide bandwidth regardless of its polarization and for literally any incident angle. 

In corrosion, adsorbates react directly with the substrate atoms to fomi new chemical species. The products may desorb from the surface (volatilization reaction) or may remain adsorbed in fonning a corrosion layer. Corrosion reactions have many industrial applications, such as dry etching of semiconductor surfaces. An example of a volatilization reaction is the etching of Si by fluorine [43]. In this case, fluorine reacts with the Si surface to fonn SiF gas. Note that the crystallinity of the remaining surface is also severely disrupted by this reaction. An example of corrosion layer fonnation is the oxidation of Fe metal to fonn mst. In this case, none of the products are volatile, but the crystallinity of the surface is dismpted as the bulk oxide fonns. Corrosion and etching reactions are discussed in more detail in section A3.10 and section C2.9. 

The growth of solid films onto solid substrates allows for the production of artificial stmctures that can be used for many purposes. For example, film growth is used to create pn junctions and metal-semiconductor contacts during semiconductor manufacture, and to produce catalytic surfaces with properties that are not found in any single material. Lubrication can be applied to solid surfaces by the appropriate growth of a solid lubricating film. Film growth is also... 

The molecules for SA monolayers are chosen or syntliesized according to tire substrate tliat should be coated. Thiol-tenninated entities have been mostly used in connection witli metal surfaces, but also on GaAs [126]. Chloro- and acid-tenninated molecules are most often employed on oxide surfaces of metals or semiconductors. However, tliey have also occasionally been used witli metal surfaces [127]. 

III-V compound semiconductors with precisely controlled compositions and gaps can be prepared from several material systems. Representative III-V compounds are shown in tire gap-lattice constant plots of figure C2.16.3. The points representing binary semiconductors such as GaAs or InP are joined by lines indicating ternary and quaternary alloys. The special nature of tire binary compounds arises from tlieir availability as tire substrate material needed for epitaxial growtli of device stmctures. 

CVD gaseous reactants (precursors) delivered to a heated substrate in a flow reactor undergo tliennal reaction to deposit solid films at atmospheric or reduced pressure, and volatile side products are pumped away. CVD is used for conductors, insulators and dielectrics, elemental semiconductors and compound semiconductors and is a workliorse in tire silicon microelectronics industry. 

Fig. 3. An overview of atomistic mechanisms involved in electroceramic components and the corresponding uses (a) ferroelectric domains capacitors and piezoelectrics, PTC thermistors (b) electronic conduction NTC thermistor (c) insulators and substrates (d) surface conduction humidity sensors (e) ferrimagnetic domains ferrite hard and soft magnets, magnetic tape (f) metal—semiconductor transition critical temperature NTC thermistor (g) ionic conduction gas sensors and batteries and (h) grain boundary phenomena varistors, boundary layer capacitors, PTC thermistors.

AppHcations for electroplated indium coatings include indium bump bonding for shicon semiconductor die attachment to packaging substrates and miscehaneous appHcations where the physical or chemical properties of indium metal are desired as a plated deposit. 

Polymers are only marginally important in main memories of semiconductor technology, except for polymeric resist films used for chip production. For optical mass memories, however, they are important or even indispensable, being used as substrate material (in WORM, EOD) or for both substrate material and the memory layer (in CD-ROM). Peripheral uses of polymers in the manufacturing process of optical storage media are, eg, as binder for dye-in-polymer layers or as surfacing layers, protective overcoatings, uv-resist films, photopolymerization lacquers for repHcation, etc. 

Gate oxide dielectrics are a cmcial element in the down-scaling of n- and -channel metal-oxide semiconductor field-effect transistors (MOSEETs) in CMOS technology. Ultrathin dielectric films are required, and the 12.0-nm thick layers are expected to shrink to 6.0 nm by the year 2000 (2). Gate dielectrics have been made by growing thermal oxides, whereas development has turned to the use of oxide/nitride/oxide (ONO) sandwich stmctures, or to oxynitrides, SiO N. Oxynitrides are formed by growing thermal oxides in the presence of a nitrogen source such as ammonia or nitrous oxide, N2O. Oxidation and nitridation are also performed in rapid thermal processors (RTP), which reduce the temperature exposure of a substrate. 

---