DLI processes

Vaporization technologies

Direct Liquid Injection

In the direct liquid injection the precursor container and the vaporizer are two separated parts. The precursor container always remains at room temperature. The vaporizer is heated and the carrier gas flow is delivered in the vaporizer with the liquid or solution flow.

The quantity of liquid or solution injected/delivered per unit time in the vaporizer is only what is required per unit time for the process. The chemical precursor remains at room temperature as long as it is not required to be vaporized for the process.

DLI vaporizers can handle both liquid and solid ALD and CVD precursors. Solid precursors need to be dissolved in an organic solvent. The technology is a particularly well suited method for low vapor pressure and poorly thermally stable liquid or solid ALD and CVD precursors.

Advantages of DLI:
  • Precise measurement and control of the precursor quantity injected in the vaporizer per unit time and by consequence precise control of the vapor flow that is generated
  • Fast vapor flow ON and vapor flow OFF
  • Capability to operate under vacuum or at atmospheric pressure
  • Precursor container remains at room temperature: no precursor thermal decomposition overtime, no safety issue, easy and quick container refill/replacement
  • Best approach to generate stable vapors flow when solid precursor is used
  • Best approach to vaporize low vapor precursors and thermally sensitive precursor while minimizing precursor thermal decomposition
  • Accurate control of doping levels
  • Capability to vaporize high flows of liquid precursors (organometallic and organic ones) that are significantly volatile such as for instance TMA (trimethyl aluminum), DEZ (diethyl zinc)…

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

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

Bubbler

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.