Silicon substrate material

Fuel Cells Using Low-Cost Porous Silicon Substrate Materials... 

Semiconductor materials are special cases of ceramics. Single crystal silicon, for instance, is grown from a melt. To fabricate the silicon substrate material, the bulk single crystal material is sliced with a diamond saw and then polished into wafers which may be over eight inches in diameter and as thin as 0.5 micron. 

It is very clear that silicon is one of the most important materials in modern technologies, especially in electronics. Silicon is also one of most common element on the earth. Silicon surface is readily oxidized under ambient condition. A silicon substrate is covered by a silica (SiO c) layer. This silica layer can be controlled easily by chemical reagents, heating, electrochemical treatment, and so on. 

Progress in semiconductor processing has evolved in a number of substrate materials, pre-destined for the use in micro structured devices, such as Silicon, Silicon-on-Insulator (SOI), Silicon Carbide and Gallium Arsenide [1]. 

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. 

Figure 4.2 Schematic diagram of a charge-coupled device (CCD) imaging sensor. It consists of a semiconducting substrate (silicon), topped by a conducting material (doped polysilicon), separated by an insulating layer of silicon dioxide. By applying charge to the polysilicon electrodes, a localized potential well is formed, which traps the charge created by the incident light as it enters the silicon substrate.

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. 

Many theories on the formation mechanisms of PS emerged since then. Beale et al.12 proposed that the material in the PS is depleted of carriers and the presence of a depletion layer is responsible for current localization at pore tips where the field is intensified. Smith et al.13-15 described the morphology of PS based on the hypothesis that the rate of pore growth is limited by diffusion of holes to the growing pore tip. Unagami16 postulated that the formation of PS is promoted by the deposition of a passive silicic acid on the pore walls resulting in the preferential dissolution at the pore tips. Alternatively, Parkhutik et al.17 suggested that a passive film composed of silicon fluoride and silicon oxide is between PS and silicon substrate and that the formation of PS is similar to that of porous alumina. 

The figure on the inner front cover of this book can be used to convert between doping density, carrier mobility and resistivity p for p- or n-type doped silicon substrates. One of the major contaminants in silicon is oxygen. Its concentration depends on the crystal growth method. It is low in FZ material and high (about 1018 cm-3) in Czochralski (CZ) material. 

Figure 23. Processing flow for 3-D electrode array fabrication using silicon micromachining with colloidal filling of the electrode material. The six steps are identified as the following (i) patterned photoresist (PR) on silicon substrate, (ii) PR removal after DRIB micromachining, (iii) insulate silicon mold by oxidation, (iv) colloidal electrode filling material centrifuged into the mold, (v) silver epoxy added to provide mechanical stability and electrical contact, (vi) the electrode flipped over and released from the mold by immersion in a TEAOH solution.

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