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In electronics, a self-aligned gate is a transistor manufacturing feature whereby a refractory gate electrode region of a MOSFET transistor is used as a mask for the doping of the source and drain regions. This technique ensures that the gate will slightly overlap the edges of the source and drain. The use of self-aligned gates is one of the many innovations that led to the large increase in computing power in the 1970s. Self-aligned gates are still used in most modern integrated circuit processes. ==Introduction== The self-aligned gate is used to eliminate the need to align the gate electrode to the source and drain regions of a MOS transistor during the fabrication process.〔 〕 With self-aligned gates the parasitic overlap capacitances between gate and source, and gate and drain are substantially reduced, leading to MOS transistors that are faster, smaller and more reliable than transistors made without them. After the early experimentation with different gate materials (aluminum, molybdenum, amorphous silicon) the industry almost universally adopted self-aligned gates made with polycrystalline silicon, the so-called Silicon Gate Technology (SGT), which had many additional benefits over the reduction of parasitic capacitances. One important feature of SGT was that the silicon gate was entirely buried under top quality thermal oxide (one of the best insulators known), making it possible to create new device types, not feasible with conventional technology or with self-aligned gates made with other materials. Particularly important are charge coupled devices (CCD), used for image sensors, and non-volatile memory devices using floating silicon-gate structures. These devices dramatically enlarged the range of functionality that could be achieved with solid state electronics. Innovations that made Self-Aligned Gate Technology possible Certain innovations were required in order to make self-aligned gates: # a new process that would create the gates; # a switch from amorphous silicon to polycrystalline silicon. This is because amorphous silicon would break where it passed over "steps" in the oxide surface; # a method for etching polycrystalline silicon (photolithography); # a method to reduce the impurities present in silicon. Prior to these innovations, self-aligned gates had been demonstrated on metal-gate devices, but their real impact was on silicon-gate devices. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Self-aligned gate」の詳細全文を読む スポンサード リンク
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