### 6.1.4 Summary to: 6.1 Materials and Processes for Silicon Technology

| Making "metallurgical" (= "dirty") Simet is easy: Þ |  |
SiO2 + 2C Þ Simet + 2CO
Si + 3HCl Þ SiHCl3 + H2
SiHCl3 + H2 Þ Si + 3 HCl
|  | A large scale Simet production (> 1 Mio tons/a) exists for metallurgical ("alloying") and chemical ("silicones") uses |
| A small amount of Simet (some 20.000 to/a) is purified (factor 109 or so) to "semiconductor grade Si" Þ |
|  | Produce high-purity trichlorosilane (SiHCl3) gas in a reactor and distill. |
|  | Use SiHCl3 and H2 to deposit Si on some Si core by a CVD process |
| The final result is ultra-high purity (and expensive) poly Si (already doped if so desired) |
| Growing a "perfect" single crystal from this poly-Si is not easy - but possible. |  |
|  | The major crystal growth method is the CZ (= Czrochalski) method: "Pull" the crystal from a crucible full of molten Si. Þ |
|  | Some (ususally < 300 mm diameter) crystals are grown by the FZ (= float zone) method. Somewhat better perfection, but more expensive than CZ. |
| Major problem: Impurity segregation = general tendency for most impurities (including doping atoms) to remain (= enrich) in the melt. |
|  | Segregation coeffcient = ccryst/cmelt at interface, often << 1 and dependent on parameters like growth speed (usually a few mm/min). |
|  | + Crystal is purer than melt. – It is practically impossible to grow a crystal with a uniform impuritiy (including dopant!) concentration along its length. |
| Produce wafers by cutting, grinding and polishing |  |
|  | Extreme precision for a mass product is needed. |
|  | "Flats" or "notches" (for wafers > 200 mm) identify the crystallographic orientation and the doping type. |
|  | Beware! Flats are often custome specific and different from the norm. Þ |
Questionaire
Multiple Choice questions to all of 6.1

© H. Föll (Electronic Materials - Script)