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Three steps of silicon wafer fabrication purification, single crystal silicon growth, wafer forming


As we all know, silicon wafer is the basic material for manufacturing semiconductor devices and chips, and plays a pivotal role in the industry. It can be said that silicon is the most important and widely used semiconductor material today.


Silicon is widely found in rocks and gravels in the form of silicate or silica in nature, and the manufacture of silicon wafers has three major steps: silicon extraction and purification, single crystal silicon growth, and wafer forming. Next, let me take you to know about it.


1. Silicon extraction and purification


The purification of silicon is the first process. It is necessary to put the sand and gravel raw materials into an electric arc furnace with a carbon source with a temperature exceeding 2,000 degrees Celsius, and undergo a reduction reaction at a high temperature to obtain metallurgical grade silicon, and then crush the metallurgical grade silicon. It reacts with gaseous hydrogen chloride to generate liquid silane, and then through distillation and chemical reduction processes, high-purity polysilicon is obtained.


2. Monocrystalline silicon growth


The Czochralski method is commonly used in this process. High-purity polysilicon is placed in a quartz crucible and heated continuously by a graphite heater surrounded by the outside. The temperature is maintained at about one thousand degrees Celsius. The air in the furnace is usually an inert gas, so that the Polysilicon melts without unwanted chemical reactions.


In order to form single crystal silicon, it is also necessary to control the direction of the crystal. The crucible is rotated with the polysilicon melt, a seed crystal is immersed in it, and the seed crystal is rotated in the opposite direction by the draw rod, while slowly and vertically pulled up from the silicon melt.


The molten polysilicon sticks to the bottom of the seed crystal and grows continuously in the direction of the seed crystal lattice arrangement. After growing by Czochralski, the single-crystal rods are cut to the appropriate size, then ground, and chemical-mechanical polishing is used to make at least one side mirror-smooth, at which point the wafer is complete.


The wafer fabrication plant melts these polysilicon, seed crystals in the melt, and then slowly pull it out to form a cylindrical monocrystalline silicon ingot, because the silicon ingot is determined by the orientation of a crystal plane The seed crystal is gradually formed in the molten silicon raw material.


3. Wafer Forming


After completing the above two processes, the silicon ingot is then cut into sections, rolled, sliced, chamfered, polished, laser engraved, and packaged, and then becomes the basic raw material of the integrated circuit factory - silicon wafer, which is the so-called silicon wafer. "Wafer".


In real life, we often hear people talk about a few-inch fab, which actually refers to the size of a single wafer. In general, the larger the diameter of the silicon wafer, the stronger the technical strength of the fab. In order to reduce the size of transistors and wires, several wafers can be fabricated on the same wafer to produce more silicon die, but the most critical parameter for silicon wafer production is yield, which is the fab It is inseparable from the quality of silicon wafer production equipment.


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