МММ / 01_Layer_Deposition_Thermal_Oxidation_and_CVD

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Depletion Effects

Source gas depletion occurs down the length of susceptor as reactant gases are consumed.

Important in Reaction limited regime

Solution: 5-25° temperature gradient imposed along the chamber to compensate. Alternatively the gas can be injected straight down from above.

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Unintentional Doping

Common when depositing a lightly doped epitaxial Si film on a highly doped Si substrate.

1.Outdiffusion

•Solid State Diffusion

2.Autodoping

•Addition of dopant atoms to gas stream

•Evaporation from wafer frontside, backside, other wafers or susceptor

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Pressure

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LPCVD

Atmospheric pressure systems have some major drawbacks:

•If operated at high T (transfer controlled) the wafers must be placed horizontally

•If operated at low T (reaction controlled) the deposition rate is low. No restriction on wafers

Both result in low throughput

Solution: Operate at low pressure in reaction controlled limited regime

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Pressure Lowering

Diffusivity (no. of collisions experienced by gas species)1

Diffusivity 1

PTotal

P h (Diffusion Coeff .)

Total g

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Effect of Pressure Lowering

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LPCVD Reactor

P

Quartz tube

Pump

A ‘Hot Wall’ Reactor

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Plasma Enhanced CVD

There may be restrictions on temperatures the substrate can be exposed to

At low T, APCVD and LPCVD proceed at low deposition rates

Solution: Using plasma source in addition to thermal source

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PECVD Equipment

Inert Gas Process Gas

RF Power

Wafer

Heated Plate

By Products

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Mechanism