1. CRYSTAL GROWTH, WAFER FABRICATION
 Crystal
Structure:
• Silicon has the basic diamond crystal structure – two merged FCC cells offset by
a/4 in x, y and z.
Crystal Growth:
Chemical reactions required are as follows;
STEP
PROCESS
REACTIONS
1
Produce metallurgical grade
silicon (MGS) by heating silica
with carbon.
C(s) + SiO2 (s) Si (l) + SiO
(g) + CO(g)
2
Purify MG silicon through a
chemical
reaction to produce a siliconbearing gas of trichlorosilane
(SiHCl3)
Si (s) + 3HCl (g) SiHCl3(g)
+ H2 (g) + heat
3
SiHCl3 and hydrogen reaction
a process called Siemens to obtain
pure semi conductor- grade silicon
(SGS)
2SiHCl3 (g ) + 2H2 (g) 
2Si (s) + 6HCl (g)

2. Czochralski (CZ) crystal growth
• Si used for crystal growth is purified from SiO2 (sand) through refining,
fractional distillation and CVD.
• The raw material contains < 1 ppb impurities. Pulled Crystals contain O (≈ 1018
cm-3) and C (≈ 1016 cm-3), Plus any added dopants placed in the melt.
• CZ is more common method to grow silicon crystal today because it is capable
of producing large diameter crystals, from which large diameter wafer can be cut.
• The raw Si used for crystal growth is purified from SiO2 (sand) through refining,
fractional distillation and CVD.
• The raw material contains < 1 ppb impurities except for O (» 1018 cm-3) and C
(» 1016 cm-3).
• Essentially all Si wafers used for ICs today come from Czochralski grown crystals.
Polysilicon material is melted, held at close to 1415 °C, and a single crystal seed is
used to start the crystal growth.
• Pull rate, melt temperature and rotation rate are all important control
parameter

3. • Sequence of photographs and drawings illustrating
CZ crystal growth. The charge is melted,
• the seed is inserted, the neck region is grown at a high rate to remove
dislocations and finally the growth is
• slowed down to produce a uniform crystal.
THANK YOU………FOR GIVING ME SUCH OPPURTUNITY
PROFESSOR: MR SANJEEV BRAHMA
(VLSI TECHNOLOGY)
BY: KALYANI GAYAKWAD
ROLL NO: U11EC109