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Semiconductor silicon wafer refers to the silicon single crystal ingot cut from the sheet, also known as silicon wafer, is the semiconductor, photovoltaic and other industries widely used substrate materials. Silicon in the earth's crust accounted for about 27% of the rich reserves and low prices, so it has become the world's most widely used and largest production of semiconductor base materials, more than 90% of semiconductor products are manufactured using silicon-based materials.
Silicon wafers can be fabricated into integrated circuits and various semiconductor devices by means of photolithography and ion implantation. Semiconductor wafers for the integrated circuit industry have extremely high product quality requirements, the purity must reach 99.999999999% (9 9) or more, the most advanced process needs to reach 99.99999999999% (11 9), the photovoltaic industry on the demand for monocrystalline silicon wafers is 99.9999% (6 9), the difficulty of preparation is far less than the semiconductor silicon wafers.
Classified according to the size of silicon wafers, the general diameter to distinguish between specifications, usually 6 inches, 8 inches, 12 inches and so on. From the first production of 2-inch wafers in 1965 to the realization of mass production of 12-inch wafers in 2000, semiconductor silicon wafers are constantly developing in the direction of large size.
Semiconductor production costs and efficiency and wafer size is directly related to the enhancement of the diameter of the wafer can reduce the average production cost per unit of chip, which in turn provides higher economies of scale. However, large-size wafers due to higher purity, technology development and scale production is difficult, the need to improve the production process and equipment performance enhancement, will also bring higher costs to producers. In the 1980s, 4-inch wafers were the mainstream, in the 1990s the mainstream 6-inch wafers, and in the 2000s the mainstream 8-inch wafers. Currently the most mainstream products in the global wafer market is 8-inch wafers and 12-inch wafers.
In 2020, 8-inch and 12-inch silicon wafers accounted for 23.94% and 69.15% of the overall market share of silicon wafers, accounting for a total of more than 90%.
According to the classification of silicon wafer application scenarios, silicon wafers can be divided into positive wafers, companion wafers and etched electrodes. Accompanying wafers are further categorized into test wafers, blocking wafers, and control wafers according to their functions. Positive wafers can be used directly in wafer manufacturing; test wafers are used to experiment and check the status of manufacturing equipment at the initial stage of operation, in order to improve its stability; blocking wafers are used for debugging new production lines and protecting positive wafers in the wafer production process; control wafers are used to test the new process and monitor yields before formal production. Blocking and controlling pieces are cut from the poor quality parts on both sides of the wafer bars, which are used for warming up, filling vacancies, testing the process status of the production equipment or the quality status of a certain process.
In order to improve product quality and monitor process accuracy and yield in the formal production process, it is necessary to increase the monitoring frequency by inserting control pads into the wafer positive production process. 6 pads are required for every 10 positive wafers in the 65nm process, and 15-20 pads are required for every 10 positive wafers in the 28nm process and below. Because of the huge consumption of the blocking control sheet as an auxiliary production material, the wafer fab will be reused after polishing and grinding processes. There is an upper limit to the number of times a block can be reused, and once the threshold is exceeded, it can only be used as a photovoltaic-grade silicon wafer. The situation is more special, used in some special processes in the control sheet directly scrapped, can not be reused. The blocking control wafers that can be recycled are also known as renewable wafers.
According to the manufacturing process classification, semiconductor wafers can be divided into polished wafers, epitaxial wafers and SOI wafers. Monocrystalline silicon ingots are cut, ground and polished to obtain polished wafers. Polished wafers undergo epitaxial growth to form epitaxial wafers, and polished wafers undergo oxidization, bonding or ion implantation processes to form SOI wafers. Polished wafers are manufactured on the basis of ground wafers through double-sided polishing, edge polishing, surface polishing and other processes, the polishing process can remove residual damage layer on the processed surface, realize the semiconductor wafer surface flattening, and further reduce the surface roughness of the wafer in order to meet the chip manufacturing process on the wafer flatness and the surface granularity of the requirements of the silicon wafer; epitaxial growth by chemical vapor deposition in the polished surface of one or more layers, doping type, doping type, doping type, doping type, doping type, doping type, doping type, doping type, doping type, and doping type. Epitaxy is the growth of one or more layers on the polished surface by chemical vapor deposition, and the doping type, resistivity, thickness, and lattice structure are in line with the requirements of the specific device of the new silicon single-crystal layer; annealed wafers refers to the polished wafers placed in an annealing furnace, through the annealing thermal treatment of silicon annealed wafers; SOI wafers, i.e., silicon-on-insulator, is one of the common silicon-based materials, and the core feature of which is the introduction of a layer of oxide insulating buried layer between the top layer of silicon and the supporting substrate.
Silicon wafer preparation process a wide range of semiconductor wafer manufacturing process is complex, mainly divided into deoxygenation and purification, refining polycrystalline silicon, monocrystalline silicon rod preparation, tumbling, slicing, grinding, polishing, cleaning, testing, packaging and so on.
Silicon element in the form of silicon dioxide and silicone hydrochloric acid exists in large quantities in sand, rocks, minerals, sand, ore in the silicon dioxide can be obtained after high-temperature purification of metallurgical-grade silicon with a purity of more than 98%.
The crushed metallurgical-grade silicon is chemically reacted with gaseous hydrogen chloride to produce liquid silane, and then through distillation and chemical reduction processes, electronic-grade polysilicon with a purity of 99.999999999% (9 out of 9) or more is finally obtained. Silicon wafer manufacturers and then electronic grade polysilicon processing into silicon wafers, mainly including pulling a single crystal and wafer cutting and grinding throwing epitaxial and other processes.
Slicing: Using advanced wire cutting machines and processes, single crystal wafers are cut to the appropriate thickness.
Rough grinding: the two sides of the wafer will be adjusted to parallel, while using alumina grinding material will be sliced and polished to the required thickness, the purpose of grinding is to remove in the slicing process due to the cutting of the surface of the mechanical stress produced by the damage to the layer and the surface of the surface of a variety of metal ions and other impurities such as contamination, so as to form a flat surface on the silicon wafer.
Etching: After the wafer has been sliced and milled, due to process pressure, a layer of damage will be formed on the surface of the wafer, chemical etching is the use of mixed acid to eliminate the damage caused by mechanical processing attached to the surface of the wafer before the previous process, so that the entire wafer to maintain high-quality single-crystal characteristics.
Polishing: The wafer is polished and cleaned to obtain a finished polished wafer that meets customer specifications for resistivity, geometric parameters and particle data.
Cleaning and inspection: The purpose of cleaning is to remove the organic matter, particles, metals, etc. left on the surface of the wafer after polishing, to ensure the cleanliness of the wafer surface, so that it can meet the quality requirements of the subsequent processes.
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