Polycrystalline silicon ingot annealing temperature and ingot handling

Polaris solar PV net news: (a) the annealing temperature

Provide an environmental temperature of the ingot annealing refers to converge at a slow pace, and remain so for some time. Annealing ingot internal stress can be eliminated also defects such as dislocations in the crystal growth process with some degree of elimination, so crystal is not easy to break. Even if growth really well, improper annealing can also cause a breakdown of silicon ingots. For the next step for the ingot to be sliced, cracked was equal to scrap. If only purified without ingot, a complete silicon ingots are easier to work with than broken, such as the tops and tails. Therefore, the annealing process, should not be overlooked, not because growth has been completed, to the effect that by this time.

Crystal growth is complete, due to the high temperatures at the top and, therefore, need to keep the temperature cool slowly. Typically, power from the Crystal of power according to a fixed rate, meanwhile, will drop insulation body and heat hit bottom when power drops below a minimum value.

There are different versions of the annealing temperature. At 1300 ° c for thermal insulation, it is called high temperature annealing; annealed at 1100 ℃, known as low-temperature annealing.

Optimum annealing temperature is controversial. Generally considered long Crystal should be completed, middle of top and bottom of ingot temperature value, this argument seems reasonable, but also consider Silicon annealing from cold to heat up to temperature and annealing temperature from cool to hot, are subject to thermal stress is different. Cold temperature, thermal stress seems to be bigger, from this perspective, the annealing temperature should be around 1100 ℃ appropriate.

The annealing time, based on theory and experience, in 3-4 hours, after which the annealing temperature, then heat for 3 hours or so, and then, you can supplement the natural heating and cooling.

Natural cooling stage of so-called supplementary heating, cooling the ingot insulation inside were slow, and the temperature of the heating element should also be given a small amount so that temperatures do not drop too fast. Since at temperature up to 900 ° c, you can turn off the power, so its completely natural cooling.

Often think of temperature below 400 ℃, can turn on the stove, and then in about 100 ℃ Crucible even trim out, but kept in a closed, airless room, wait until more than 12 hours, remove shielding and the crucible.

(B) ingots

Ingots from the furnace out, best even with boards and backplane removed, wait until the temperature slow cooling after removing the trim to avoid cooling ingot cracking caused by too fast. After removing trim, first production records of the ingot.

Ingots of data records

Each ingot to data records as follows:

Photographed and must complete the orientation marking indicating the direction for each silicon ingot furnace, furnace (SI ingot refers to a furnace stove, furnace without), batch number and practice, record name.

Measuring the size of silicon ingots, including 12 bian Bian Changhe of the four sides of the central height;

Weighing;

If the ingot exception, to record anomalies. Such as the length and orientation of the crack, bulge at the top, uplift area, size and location; if possible photographed.

Silicon ingot is an important basis for quality assessment of the data. In addition, the ingot of data analysis of production process, quality, process improvement has an important role and should therefore be properly archived.

Dispose of silicon ingots

Yiqian, casting ingot go straight to the root machine for the successful conclusion of evolution. But now, due to the cost of the request, each ingot manufacturers hope will prescribe after the side leather and leather for recycling. Edge recycling of leather and leather need to be cleaned, so that some work needs to be conducted before prescribing.

First of all, the ingots are sand blasted and six planes to spray the 1~5 mm thick. Especially the top surface to spray off the thicker. This is because the crucible of silicon nitride coating on internal surface, some of these coatings in the ingot process of silicon nitride powder will permeate the solidification of ingot surface, so you want to remove it. In the top of the ingot, often there is loss of silicon nitride coated, but throughout the casting process, due to the evaporation of graphite heating elements, carbon will be rendered into the Silicon surface, formation of Silicon Carbide. Whether it is silicon nitride and silicon carbide, hardness higher than silicon, thus forming a Silicon in the so-called “hard spots” and, therefore, before the ingot is not prescribing use of sandblasted on the surface removed, is a relatively simple way to eliminate these hard spots. Once after the radical, form tails, sandblasting process was cumbersome, and may only be able to use the wheel except to come and go. After sand blasting, the ingots at the time of prescribing, and less prone to breakage phenomenon.

If it is a metallurgical method, or recycled, because impurities may be thicker at the top, band saw can be used to very top of the ingot resection, excision of thickness approximately in about 15mm.

After the ingot after sandblasting can be sent to the root machine, after the root, after cleaning, for the small ingots according to measurement of resistivity and minority carrier lifetime, dashes, and according to data truncation. Silicon for grinding chamfers to the truncated, aimed at removal of Silicon surface damage layer formed at the time of prescribing.

Wash immediately after packaging, or send the slice shop.

Truncate the Silicon material washing down can be repeated after casting.

Leather and leather after cleaning, cannot directly ingots or admixture with the original raw ingots must be carried out again after melting and purification, or mixed with raw polysilicon materials of ingot casting ingots. This is because the skin due to excess material inside the silicon nitride and silicon carbide, they cannot be removed by pickling methods, only the melting process can remove.

Shanghai General RDS series purified ingot furnace can whether it tails, top or bottom leather, as well as radical formed in the process of recovery of silicon materials for purification. Due to the Silicon purification melting temperature is higher than the ingot, RDS series purified ingot furnace process is different from conventional ingot furnace process, also has a special design of furnace structure.

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