Wafer production

The wafer is processed through a series of machines, where it is ground smooth and chemically polished to a mirrorlike finish (i.e., luster). The wafers are then ready to be sent to the wafer-fabrication area, where they are used as the starting material for manufacturing integrated circuits. The heart of semiconductor manufacturing is the wafer-fabrication facility where the integrated circuit is formed in and on the wafer. The fabrication process, which takes place in a clean room, involves a series of steps described below. Typically it takes from 10 to 30 d to complete the fabrication process. 

Thermal oxidation or deposition. The silicon polished wafers are heated in the diffusion furnaces at high temperature ranging between 700 and 1300°C and exposed to a reactive atmosphere of water and ultrapure oxygen under carefully controlled conditions forming an 

Etching. The wafer is then developed, i.e., the exposed photoresist is removed, and baked to harden the remaining photoresist pattern. It is then exposed to chemical solutions (e.g., hydrofluoric acid, HF, or ammonium dihydrogenofluoride, NH H Fj, solutions) or plasma so that areas not covered by the hardened photoresist are etched away. The photoresist is removed using additional chemicals or plasma, and the wafer is inspected to ensure that the image transferred from the mask to the top layer is correct. 

Doping. Electron-acceptor atoms such as boron or electron-donors such as phosphorus are introduced into the area exposed by the etch process to alter the electrical character of the pure silicon, which is an intrinsic semiconductor. These areas are called p-type (e.g., with boron) or n-type (e.g., with phosphorus) to reflect their particular charge carrier in the conduction process. Repeating the previous steps, i.e., thermal oxidation, masking, etching, and doping operations are repeated several times until the last front-end layer is completed, i.e., all active devices have been formed. 

Dielectric deposition and metallization. Following completion of the front end, the individual devices are interconnected using a series of metal depositions and patterning steps of dielectric films (i.e., electric insulators). Current semiconductor fabrication includes as many as three metal layers separated by dielectric layers. 

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If formation wafer production is expected, a chemical analysis of the water will also be required. It is good practice to record the details of the methods used for sampling and analysis in each case so that measurement uncertainties can be assessed. 

For epitaxial silicon wafers, product design focuses on optimizing the geometry of the plasma-enhanced, chemical-vapor-deposition (PECVD) reactor. To increase productivity, and maintain acceptable thickness uniformity, on the order of 5%, a simple optimization strategy locates a design that completes the deposition in 62 s. Then, for a standard manufacturing process, the economics are driven by the wafer costs, which are provided by a vendor at 206/wafer. At a sales price of 260/epitaxial wafer, the investor s rate of return is 18.3% and the return on investment is 25.3%. 

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Due to the large economical and technological potential of silicon ribbons, their application in solar wafer production will be a major milestone in PV cost reduction. Thus, it is very likely that silicon wafer based PV module manufacturing will maintain the cost advantage over other upcoming technologies and, therefore, the role as the major PV technology. 

Semiconductor wafer production also consumes a large quantity of fresh water. The Philips San Antonio facility was producing 150 mm wafers and planned to move into 200 mm wafer production in early 2000. One task it encountered was the need to increase its supply of high purity water. Its project team evaluated several options, including expanding the fresh water supply and recycling waste wafer rinse water. The team... 

The analysis of the evaluation duration provides complementary information. In particular, if TDS data are standardized (see Section 13.4.3), information about evaluation duration is lost, but this complementary analysis enables filling this gap. This is the case in the paper of Lenfant et al. (2009), for which the evaluation/mastication duration of the six wafer products were compared (Fig. 13.13) and evidenced long evaluation duration for product WF B (34.1 s) than for products WF C (29.9 s) and WF D (30.6 s). 

Cost often becomes an important driver since in-line instrumentation can be quite costly to install and maintain multiplied across many systems. The financial impact of how much wafer production can be affected if an excursion occurs must be compared with the overall cost of ownership for in-line monitoring. Sometimes, increasing measurement frequency with using manual sampling and bench-top analysis can be an economical balance to reduce the potential for excursion impact but not burden the chemical system with additional metrology hardware and the associated maintenance. 

Crystallization is mainly used for separation as an alternative to distillation, if the involved compounds are thermally unstable (e.g., acrylic acid), have a low or practically no vapor pressure (like salts), if the boiling points are similar, or if the system forms an azeotrope. Crystallization is used for the production and purification of various organic chemicals ranging from bulk chemicals (p-xylene and naphthalene) to fine chemicals like pharmaceuticals (e.g., proteins). Further examples of industrial crystallization processes are sugar refining, salt production for the food industry, and silicon crystal wafer production. 

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