Crystal growth and wafer fabrication processes are described. Silicon has a diamond crystal structure. Metallurgical grade silicon is produced by heating silica with carbon, then purified through chemical reactions producing trichlorosilane gas. Czochralski crystal growth is the most common method, where silicon is melted and a seed crystal is used to start growth of a large, pure single crystal for wafer production. Important parameters like pull rate, temperature and rotation must be carefully controlled during crystal growth.

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