oxidation process

7/30/2019 oxidation process

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Oxidation Process

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What is oxidation?

The word oxidation originally implied reaction with oxygen toform an oxide.

N2 (g) + O2(g) 2NO(g)

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What is silicon dioxide?

Whenever a silicon surface is exposed to oxygen, it is

converted to silicon dioxide Silicon dioxide is composed of one

silicon atom and two oxygen atoms (SiO2)

Silicon dioxide layers are formed on bare silicon surfaces at

elevated temperatures in the presence of an oxidant. The

process is called thermal oxidation.

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Uses of SiO2 layer

Surface passivation

It protects the in two waysa)- Physical protection of the surface

Silicon dioxide layers formed on the surface are very dense

(nonporous) and very hard.

b)- Chemical protection of the surface Regardless of the cleanliness of the processing environment

some electrically active contaminants (mobile ionic

contaminants) end up in or on the wafer surface.

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Contd..

Doping barrier The silicon dioxide left on the wafer acts to block the dopant

from reaching the silicon surface

Surface dielectric Silicon dioxide is classified as a dielectric.

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Contd

Device dielectric grown oxides are also used as the dielectric layer in capacitors

formed between the silicon wafer and a surface conduction

layer.

Silicon

SiO2 layer

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Thermal Oxidation Mechanisms Thermal oxide growth is a simple chemical reaction. This

reaction takes place even at room temperature. However, an

elevated temperature is required to achieve quality oxides in

reasonable process times for practical use in circuits and

devices. Oxidation temperatures are between 900 and 1200C.

Si(solid)+ O2(gas) SiO2 (solid)

(heat)

Si(solid) + 2H2O(gas) SiO2(solid)+2H2(gas)

(heat)8


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Thermal Oxidation Methods

There are three methods for thermal oxidation

1- Horizontal Tube Method2- Vertical Tube Method

3- Rapid Thermal Processing

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Horizontal tube furnace1.Outer surface

2.Oxidation tube

3.Columns of movable modular

4.Muffle

5.Movable modular's head

6.Source zone, centre zone and

load zone7.Proportional band controller

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Fig. horizontal tube furnace


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Section of Horizontal Tube Furnace

1-Reaction chamber

2- Temperature control system 3- Furnace section

4- Source cabinet

5- Wafer cleaning station

6- Wafer load station 7- Process automation

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Drawback of Horizontal Tube Furnace

Difficult to produce larger wafer diameter

Less contamination control Less production

Gravity tends to separate mixed gases as they flow down the

tube

So a new technology came to avoid drawbacks of horizontalTube Furnace i.e. the vertical furnace tube

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Vertical Tube Furnace In vertical tube configuration, the tube is held in a vertical

position with loading taking place from the top or bottom.

Ease of rotating the wafers in the tube, which produces a moreuniform temperature acrosssource.

Tube materials and heating systems are the same as for

horizontal systems.

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Contd The gas moves parallel to

gravity minimizing the gas

separation problem and the boat

rotation minimizes gasturbulence.

More packaging density means

we placed more wafers in tube

for oxidation process.

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Fig. Vertical tube furnace


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Rapid Thermal Process(RTP)

RTP technology is based on the principle of radiation heating.

RTP technology is a natural choice for the growth of thinoxides used in MOS gates

Advantages of RTP Reduces the thermal budget required for a process.

Minimizing the total wafer process time.

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Conclusion

1- Uses of SiO2 layer

2- Mechanism of SiO2 formation

3- Methods

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References

Peter van Zant , Microchip Fabrication,, Tata McGraw Hill ,

2nd edition, 2012.

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Query

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THANK YOU19

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oxidation process