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.  
CZ crystal growth
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
Flats on wafers
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  
Multiple Choice questions to all of 6.1

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© H. Föll (Electronic Materials - Script)