The direct liquid injection technology was developed to overcome the limitation of conventional vaporization technologies like bubblers of vapor draw.

In vapor draw the precursor container is the vaporizer and can be heated. There is no carrier gas flow inside the canister. Vapors can be mixed with carrier gas at container outlet.

This is the classical solution used for ALD machines.

Advantages:

• Simple hardware

• Cheap hardware

Drawbacks:

• No or poor control of the vapor flow

• In case of low vapor pressure precursor, heating is required and precursor can decompose (thermal decomposition) overtime inside the container

• Small exchange surface between the condensed precursor (liquid or solid) and the gas phase in the container limits the vaporization kinetic

• For solid precursor (not melted) total vaporization surface (exchange surface between solid and vapor) changes overtime leading to unstable and not reproducible vapor flow

• This solution cannot be used for process requiring continuous vapor flow or high vapor flow such as CVD process

• When container is heated, refilling or replacement of container takes a long time because container has to be cooled down and then heated up again

• When heating is needed, all the precursor is heated leading to potential safety issue

The bubbler is the precursor container and the vaporizer. The container can be heated and a carrier gas flow is delivered through the liquid to extract some precursor vapor.

This is the classical solution used for III-V MOCVD machines and ALD machines with fast ALD valves.

Advantages:

• Simple hardware

Drawbacks:

• Poor control of the vapor flow

• In case of low vapor pressure precursor, heating is required and precursor can decompose (thermal decomposition) overtime inside the container

• Small exchange surface between the condensed precursor (liquid or solid) and the gas phase in the container limits the vaporization kinetic

• For solid precursor (not melted) total vaporization surface (exchange surface between solid and vapor) changes overtime leading to unstable and not reproducible vapor flow

• This solution cannot be used for process requiring continuous vapor flow or high vapor flow such as CVD process

• When container is heated, refilling or replacement of container takes a long time because container has to be cooled down and then heated up again

• When heating is needed, all the precursor is heated leading to potential safety issue.