German scientists determine source of contaminations in multicrystalline silicon

• Scientists from Fraunhofer IISB, Wacker Chemie and also Alzchem claim undesirable metals go into the silicon mostly with finish of the quartz crucible. The searching for can make it possible for manufacturers to make forecasts concerning the high quality of silicon blocks.

Why do metallic contaminations appear during the production of multicrystalline silicon blocks?

Researchers from research study body the Fraunhofer Institute for Integrated Systems and also Device Technology, polysilicon manufacturer Wacker Chemie and chemical company Alzchem are checking out the issue in the government-funded SYNERGIE study project. With the help of a numerical simulation design, the researchers determined impurities and also their resources and got insights right into the systems whereby steel atoms permeate crystals during production. The results of the project can make it possible for straight forecasts of the extent to which the purity of complementary products used in manufacturing-- the crucible and also its covering plus the silicon raw material-- will impact the electric quality of silicon wafers.

To create silicon crystals, the raw material is thawed in a quartz crucible and also cooled. Throughout solidification of the solution, a silicon crystal with defined electrical buildings is formed. The quartz crucible is coated with a high-purity silicon nitride powder-based product which works as a separation layer to prevent the silicon adhering to the crucible, which would cause cracking as it cools.

The scientists recognized the crucible and layer system as the largest source of metallic contaminations in the silicon crystals. Throughout condensation, steel atoms are continuously introduced into the fluid and also solid silicon. In the silicon crystal, they produce problems to the level crystal edges can be so heavily polluted they have to be removed.

To recognize extra precisely which metals existed in the silicon crystal, their concentration and also resource; scientists at the Fraunhofer-Institut für Integrierte Systeme und Bauelementetechnologie (IISB) established a testing method which entailed silicon cubes being placed on a base of crucible and also covering materials as well as being subjected to a temperature simply listed below the 1,412 levels Celsius melting point of silicon for a particular time. Succeeding chemical evaluation exposed which steels had actually penetrated the crystal.

The tests suggested focus of iron, chromium as well as cobalt enough to break down performance in solar cells made from the silicon crystal with the problematic steels not observable later on in the production process.

The Fraunhofer scientists established a mathematical simulation design for computing the distribution of undesired metals in silicon crystal. The version thinks about the level of contamination of the crucible, silicon nitride finish as well as silicon resources in addition to criteria for procedure control. The outcomes plainly showed boosted pureness in such supporting materials substantially reduced metal contamination. With such high-purity crucibles deemed unwise, it was suggested obstacle layers in between crucible and also covering could protect the crystals.

The SYNERGIE project findings could make it possible for suppliers to much more accurately forecast the purity of their silicon crystals, with top quality dependent on the supporting materials made use of, as well as would certainly supply the possibility of enhancing the item cost properly.

The 'synergetic further growth of vendor products to reduce production prices as well as raise the worldly high quality of crystalline silicon obstructs in photovoltaics' (SYNERGIE) project was funded by German business economics and also energy ministry the Bundesministerium für Wirtschaft und Energie.