Sequential purification and crystal growth
US4200621A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jul 18, 1978 |
| Grant date | Apr 29, 1980 |
| Priority date | — |
| Expiry date | Jul 18, 1998 |
Classification
- Technology area (CPC C)Chemistry; Metallurgy
- CPC primaryC30B15/00
- WIPO fieldSurface technology, coating
- WIPO sectorChemistry
Abstract
A combined method for purifying silicon and growing single crystals. A multiple step process is disclosed by which metallurgical grade silicon is purified and converted into a high quality monocrystalline silicon ingot. Each of the steps in the process is designed to remove specific impurities and thus improve the electrical quality of the silicon material. First, the insoluble slag and high segregation coefficient impurities are removed. Soluble impurities are then removed by a reactive gas step, and by a liquid-liquid extraction step using reactive metallic oxides or an oxide solvent. The remaining impurities are removed by segregation during freezing by pulling an ingot from a portion of the molten metallurgical grade silicon. The ingot so formed is then used to charge a second crystal puller. One or more of the previous purifying steps can then be repeated for the charge of the second crystal puller and an ingot of improved purity can be pulled from the melt of the second puller. In like manner, third and successive reiterations of the process can be used to obtain silicon of the desired purity and crystal quality.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.