Single crystal growth → cutting → external diameter rolling → flat edge or V-groove treatment → slicing.
Chamfering → grinding
Corrosion-polishing → cleaning → packaging
Cutting: The purpose is to cut off the head and tail of the monocrystalline silicon rod and the part exceeding the customer's specifications, divide the monocrystalline silicon rod into lengths that can be processed by slicing equipment, and cut the specimen to measure the resistivity and oxygen content of the monocrystalline silicon rod.
Cutting equipment: internal cutting machine or external cutting machine.
Main imported materials for cutting: blades.
Outer diameter grinding: Because the outer diameter surface of monocrystalline silicon rod is uneven and the diameter is larger than the diameter specification specified by the final polished wafer, more accurate diameter can be obtained by outer diameter rolling.
Outside diameter rolling equipment: grinder.
Flat edge or V-groove treatment: refers to orientation and specified treatment, which is used for flat edge or V-shape of monocrystalline silicon in a specific crystallization direction.
Processing equipment: grinder and X-ray diffractometer.
Slicing: refers to cutting single crystal silicon rods into thin wafers with precise geometric dimensions.
Slicing equipment: internal cutting machine or wire cutting machine.
Chamfering: refers to trimming the tax edge of the cut wafer into an arc to prevent the wafer edge from cracking and lattice defects, and to increase the flatness of the epitaxial layer and photoresist layer.
The main equipment for chamfering: chamfering machine
Grinding: Grinding can remove the saw marks and surface damage layers caused by slicing and grinding wheel grinding, effectively improve the curvature, flatness and parallelism of monocrystalline silicon wafer, and reach the specifications that can be handled during polishing.
Grinding equipment: grinding machine (double-sided grinding)
Main raw materials: grinding slurry (mainly composed of alumina, chrome sand and water) and mud.
Corrosion: refers to the damage layer formed on the wafer surface by processing stress after slicing and grinding, and is usually removed by chemical etching.
Corrosion method: (a) Acid corrosion is the most commonly used. The acidic corrosion solution consists of nitric acid (HNO3), hydrofluoric acid (HF) and some buffer acids (CH3COCH, H3PO4).
(b) alkaline corrosion, wherein the alkaline corrosion solution consists of KOH or NaOH and pure water.
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Polishing: refers to polishing the wafer with high flatness by improving the micro-defects on the surface of monocrystalline silicon wafer.
Polishing equipment: multi-piece polisher, single-piece polisher.
Polishing method: rough polishing: it is mainly used to remove the damaged layer, and the general removal amount is about10-20um;
Fine polishing: it is mainly used to improve the micro-roughness of wafer surface, and the removal amount is generally below 1um.
Main raw materials: the polishing solution consists of micro-suspended silica gel containing SiO2 _ 2 _ 2 and NaOH (or KOH or NH _ 4OH), which can be divided into coarse polishing and fine polishing.
Cleaning: Many steps in the processing of monocrystalline silicon wafer need cleaning, and the cleaning here is mainly the final cleaning after polishing. The purpose of cleaning is to remove all pollution sources on the wafer surface.
Cleaning method: mainly the traditional RCA wet chemical cleaning technology.
Main raw materials: sulfuric acid, hydrogen peroxide, hydrofluoric acid, ammonia water and hydrochloric acid.
(3) Causes of loss
A. polysilicon-monocrystalline silicon rod
In the process of processing polycrystalline silicon into monocrystalline silicon rods, if the bottom material and head and tail material of the heavily doped crucible are lost, they cannot be reused and can only be used as additives in metallurgical industries such as ironmaking and aluminum smelting. If the loss of non-heavily doped crucible bottom material and head and tail material can be used to manufacture low-grade silicon products, this part should be taxed as scrap.
Heavy doping refers to mixing polycrystalline silicon raw materials with nearly saturated impurities (such as boron, phosphorus, antimony and arsenic). The type of impurity depends on the type of resistor (n or p), and the resistor is put into a crucible to be melted.
Heavy additives are mainly used to produce silicon wafers with low resistivity (resistivity < 0.0 1 1 ohm/cm).
Loss: The bottom material of crucible after single crystal drawing is about 15%.
The head and tail materials account for about 20% in the process of single crystal silicon rod forming.
In the single crystal forming process (outer diameter grinding process), because the outer diameter surface of single crystal silicon rod is uneven and the diameter is larger than the diameter specification specified by the final polished wafer, more accurate diameter can be obtained by outer diameter grinding. The loss is about 10%- 13%.
Example:
4 inches and 5 inches
Nominal diameter 100 mm 125 mm
Pulling diameter106 mm131mm.
Grinding loss 12.36% 9.83%
Drawing reference loss 0.70% 0.80%
Total loss 13.06%
In addition, the parameters such as resistivity range, resistivity uniformity, impurity type and defect state of monocrystalline silicon will have an impact on the yield of finished products under different customer requirements. Even products of the same specification produced by different manufacturers will have different yield. Generally speaking, the loss rate due to crystal quality is 7.5%.
From polysilicon to monocrystalline silicon rod: the total loss rate of 4 inches is about 45.3%
5 inches is about 43.8%
B, monocrystalline silicon rod-monocrystalline silicon polishing sheet
The loss in the process of processing monocrystalline silicon rod into monocrystalline silicon polishing sheet is mainly caused by slicing process, such as grinding of blade and swinging of blade in the cutting process using internal cutting machine. The loss here is about 34%-35%, so the blade quality is the key, and the thinner the blade, the smaller the loss.
Example:
4 inches and 5 inches
Thickness of slicing knife 3 10+-25 380+-25
Silicon wafer thickness 650 750
Loss rate 34% 35%
From slicing to final polishing, the net loss of other processes is about 16.67%- 19.23%.
Example:
4 inches and 5 inches
Slice thickness 650 750
Polishing thickness 525 625
Loss rate 19.23% 16.67%
The loss from single crystal silicon rod to polished wafer also includes edge collapse and crack in slicing process, chip and notch in grinding process, contamination and mottling in alkali corrosion process and chip scratch in polishing process, which are as follows: slicing 5%, chamfering 6+0%, grinding 5%, etching 2%, annealing 2%, polishing 5% and cleaning 2%.
Single crystal silicon rod-single crystal silicon polishing sheet: the total loss rate of 4 inches is about 57.4%
5 inches is about 56.7%