Chemical Reactions Used in Wafer Fab

    

Fab Area

Chemical Reaction

Reaction Equation(s)

Remarks

Epitaxy

Hydrogen reaction of SiCl4 to deposit a silicon epitaxial layer

SiCl4 + 2 H2 Si + 4 HCl

reversible process - Si may also be etched using HCl

Epitaxy

Silane (SiH4) reaction to deposit a silicon epitaxial layer

SiH4 Si + 2H2

can be done at a relatively lower temperature

SiO2 Thermal Oxidation

Silicon dioxide (SiO2) deposition through dry thermal oxidation

Si + O2 → SiO2

deposition temperature usually bet. 700-1300 deg C

SiO2 Thermal Oxidation

Silicon dioxide (SiO2) deposition through wet thermal oxidation

Si + H2O → SiO2 + 2H2

deposition temperature usually bet. 700-1300 deg C

SiO2 CVD

SiO2 deposition through CVD reaction between silane (SiH4) and O2

SiH4 + O2 → SiO2 + 2H2

low-temperature deposition process

SiO2 CVD

SiO2 deposition through PECVD reaction between silane (SiH4) and N2O

SiH4 + 2N2O → SiO2 + 2N2 + 2H2

deposition temperature usually bet. 200-400 deg C

SiO2 CVD

SiO2 deposition through LPCVD reaction between dichlorosilane (SiH2Cl2) and N2O

SiH2Cl2 + 2 N2O → SiO2 + 2N2 + 2HCl

high deposition temperature of almost 900 deg C

Si3N4 CVD

Silicon nitride (Si3N4) deposition through LPCVD reaction between dichlorosilane (SiCl2H2) and ammonia (NH3)

3 SiCl2H2 + 4 NH3 → Si3N4 + 6H2 + 6 HCl

deposition temperature usually bet. 700-800 deg C

Si3N4 CVD

Si3N4 deposition through PECVD reaction between silane (SiH4) and NH3

SiH4 +  NH3 → SixNyHz+ H2

deposition temperature usually bet. 200-350 deg C

Poly-Si CVD

Polysilicon deposition through LPCVD reactions of SiH4

SiH4 + surface site → SiH4 (adsorbed);

SiH4 (adsorbed) →  SiH2 +  H2; SiH2 → Si +H2

deposition temperature usually bet. 580-650 deg C;

over-all reaction:

SiH4 → Si +2H2

W CVD

Tungsten (W) deposition through CVD reaction between WF6 and Si

WF6 + 3 Si  → 2W + 3 SiF4

deposition done between 200-400 deg C

W CVD

Tungsten (W) deposition through CVD reaction between WF6 and H

WF6 + 3 H2  → W + 6HF

deposition done between 250-500 deg C

WSi2 CVD

Tungsten silicide (WSi2) deposition through CVD reaction between WF6 and SiH4

WF6 + 2 SiH4 +  → WSi2 + 6HF + H2

deposition must be done at an elevated temperature

TiSi2 CVD

Titanium silicide (TiSi2) deposition through CVD reaction between TiCl4 and SiH4

TiCl4 + 2 SiH4 +  → TiSi2 + 4HCl + 2H2

deposition must be done at an elevated temperature

Si Wet Etching

Removal of Si through wet etching with HNO3 and HF

Si +  HNO3 + 6 HF → H2SiF6 + HNO2 + H2 + H2O

acetic acid is preferred as a buffering agent

SiO2 Wet Etching

Removal of SiO2 through wet etching with HF

SiO2+  6 HF → SiF6 + H2 + 2H2O

use at room temp to prevent HF attack of Si

   

See Also:  Wafer Fabrication Thermal OxidationCVD;

Semiconductor Matls Hazardous Chemicals

   

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