Semiconductor wafers are the basic material for manufacturing chips. The most important raw material for semiconductor integrated circuits is silicon, which is widely found in rocks and gravel in the form of silicate or silicon dioxide in nature. The manufacturing process of semiconductor wafers/silicon wafers can be divided into three basic steps: silicon purification, monocrystalline silicon growth, and wafer formation.
Silicon purification
The sandstone material is placed in a 2000 °C electric arc furnace which has a carbon source. At high temperatures, the silica in the carbon and in the sandstone undergoes a chemical reaction (carbon is combined with oxygen, leaving silicon) to obtain pure silicon having a purity of about 98%, also known as metallurgical grade silicon. This purity of silicon is not sufficiently pure for microelectronic devices because the electrical properties of the semiconductor material are very sensitive to the concentration of impurities and therefore require further purification of the metallurgical grade silicon. The pulverized metallurgical grade silicon is chlorinated with hydrogen chloride gas to form a liquid silane. Then, through distillation and chemical reduction processes, high-purity polycrystalline silicon is obtained, which has a purity of up to 99.999999999%, and is called electronic grade silicon. SAM Sputter Target offers electronic-grade silicon sputtering targets and silicon evaporation materials of high purity.
Monocrystalline silicon growth
The most commonly used method for the growth of single crystal silicon is called the Czochralski method, CZ method for short. High-purity polysilicon was placed in a quartz crucible and heated continuously with a graphite heater surrounded by the outside, maintaining the temperature at approximately 1400 °C. The air in the furnace is usually an inert gas that melts the polysilicon without unwanted chemical reactions. In order to form single crystal silicon, it is also necessary to control the direction of the crystal: the polysilicon melt is rotated in the crucible, at which point a seed crystal is immersed therein, and the rod is rotated in the opposite direction by the seed crystal while slowly and vertically pulled upward from the silicon melt. The molten polycrystalline silicon adheres to the bottom end of the seed crystal and grows continuously in the direction in which the seed crystal lattice is arranged. Therefore, the directionality of the crystal grown is determined by the seed crystal, and after it is pulled out and cooled, it grows into a single crystal silicon rod having the same crystal lattice direction as the inside of the seed crystal.
Wafer molding
After the single crystal silicon is grown by the Czochralski method, the single crystal rod is cut in an appropriate size, and then ground to grind the notch, and then at least one side is smoothed as a mirror by a chemical mechanical polishing process. The diameter of the single crystal silicon rod is determined by the speed at which the seed crystal is pulled out and the rotational speed. In general, the slower the pull-up rate is, the larger the diameter of the grown single crystal silicon rod is. The thickness of the wafer is related to the diameter. Although the semiconductor device is prepared only in the range of a few micrometers at the top of the wafer, the thickness of the wafer is generally 1 mm to ensure sufficient mechanical stress support. Therefore, the thickness of the wafer will increase as the diameter increases. The wafer manufacturer melts the polysilicon, implants the seed crystal in the melt, and then slowly pulls it out to form a cylindrical single crystal silicon ingot, which is determined by the orientation of the crystal ingot. The seed crystal is gradually formed in the molten silicon raw material, and this process is called “long crystal”. After the silicon ingot is cut, barreled, sliced, chamfered, polished, laser engraved, and packaged, it becomes the basic material of the integrated circuit factory – silicon wafer, also called semiconductor wafer.
Stanford Advanced Materials (SAM) Corporation is a global supplier of various sputtering targets such as metals, alloys, oxides, ceramic materials. If you are interested, please visit our website https://www.sputtertargets.net/ for more information.
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