CRYSTAL GROWTH, WAFER FABRICATION
 Crystal

Structure:

• Silicon has the basic diamond crystal structure – two merged FC...
Czochralski (CZ) crystal growth
• Si used for crystal growth is purified from SiO2 (sand) through refining,
fractional dis...
• Sequence of photographs and drawings illustrating
CZ crystal growth. The charge is melted,
• the seed is inserted, the n...
Wafer formation
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Wafer formation

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Wafer formation

  1. 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. 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. 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

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