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Under exposure to oxygen, a silicon surface oxidizes to form silicon dioxide (SiO2). Native silicon dioxide is a high-quality electrical insulator and can be used as a barrier material during impurity implants or diffusion, for electrical isolation of semiconductor devices, as a component in MOS transistors, or as an interlayer dielectric in multilevel metallization structures such as multichip modules. The ability to form a native oxide was one of the primary processing considerations which led to silicon becoming the dominant semiconductor material used in integrated circuits today.

Thermal oxidation of silicon is easily achieved by heating the substrate to temperatures typically in the range of 900-1200 degrees C. The atmosphere in the furnace where oxidation takes place can either contain pure oxygen or water vapor. Both of these molecules diffuse easily through the growing silicon dioxide layer at these high temperatures. Oxygen arriving at the silicon surface can then combine with silicon to form silicon dioxide. The chemical reactions that take place are either for so-called "dry oxidation" or for "wet oxidation". Due to the stoichiometric relationships in these reactions and the difference between the densities of Si and SiO2, about 46% of the silicon surface is "consumed" during oxidation. That is, for every 1 um of SiO2 grown, about 0.46 um of silicon is consumed.

In most microelectronic process temperature range, the crystallization rate of the silicon dioxide can be ignored. Although fused silica is not long range order, but it showed a short ordered structure, its structure can be considered as four oxygen atoms located triangular polygon feet. Polyhedron center is a silicon atom. Thus, approximately every four oxygen atoms covalently bonded to a silicon atom, satisfy the valence shell of silicon. If each oxygen atom is part of two polyhedron, the valence of oxygen is also satisfied, the result became known as quartz crystal structure of rules. Therefore, it is believed, SiO2 so much atomic crystals, but more similar to the ionic crystals. The transition to the ionic bond oxygen atoms to silicon atoms.


 

 

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